目录

1 前言. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( 3 )

2 页岩气藏及其开采方式. . . . . . . . . . ( 7 )

2.1 引言

2.2 页岩气藏的地质及开采特征

2.3 页岩气藏开采方式

2.4 本节小结

3 页岩力学行为与基本表征方法

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( 28 )

3.1 引言

3.2 页岩天然裂缝的分布

3.3 页岩的脆性

3.4 页岩的弹性

3.5 页岩的断裂强度

3.6 页岩弹性性能的统计描述

3.7 页岩的I 型断裂

3.8 页岩天然弱面对裂纹路径的影响

3.9 岩体材料的本构关系

3.10 本节小结

4 页岩气藏实验模拟技术. . . . . . . . . . ( 56 )

4.1 引言

4.2 页岩储层评价技术

4.3 开发模拟实验技术

4.4 含气量计算方法

4.5 本节小结

5 页岩气微观流动机制及流固耦合特征

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( 78 )

5.1 引言

5.2 页岩气微观流动机制

5.3 解吸附条件下的渗流力学规律

5.4 人工压裂过程裂缝起裂及流固耦合

机理

5.5 页岩复杂介质的非均质特征

5.6 本节小结

6 页岩气水力压裂数值模拟方法. . . (107)

6.1 前言

6.2 理论计算模型

6.3 水力压裂数值计算

6.4 页岩裂缝网扩展的数值模拟研究

6.5 本节小结

7 水力压裂过程微地震监测技术. . . (132)

7.1 引言

7.2 微地震监测技术的发展现状

7.3 微地震监测中的关键问题

7.4 本节小结

8 无水压裂技术. . . . . . . . . . . . . . . . . . . . (173)

8.1 前言

8.2 二氧化碳压裂技术

8.3 氮气压裂技术

8.4 液化石油气(LPG) 无水压裂技术

8.5 爆炸压裂技术

8.6 高能气体压裂(HEGF)

8.7 本节小结

9 结束语. . . . . . . . . . . . . . . . . . . . . . . . . . . . (196)

参考文献. . . . . . . . . . . . . . . . . . . . . . . . . . . (197)

1 前言^*(本节撰稿人: 魏宇杰¹(E-mail: yujie wei@lnm.imech.ac.cn))

页岩气的开采已经有近200年的历史,其在近20年的井喷式发展主要依赖于水力压裂、水平钻井等关键技术的突破.

自1997年Mitchell能源公司首次成功利用水力压裂开发Barnett页岩气藏以来,水力压裂技术在页岩气开发中的应用开始迅猛发展.

随后研究人员发现通过滑溜水压裂液可以显著提高页岩气的采收率,因此滑溜水压裂技术得到了广泛应用并成为目前页岩气开采主要的技术之一.

水平井开发技术尤其是"水平井,$+$,多级压裂技术"的成功应用,使得页岩气藏的开采体积从以直井为中心的有限半径内的径向流动状态扩展到以水平井为中心的类椭球流动状态,显著地增加了页岩气井所在区域内渗流波及体积;采用网状水平井组的"井工厂"高效开发模式,将页岩气的三维开采区域空间进行了立体化扩展,其对页岩气开采效率的提高及成本的降低十分明显,目前已成为世界范围内页岩气开发的主流模式.无论是利用直井还是水平井进行页岩气开发,其开采过程都主要包含4个关键步骤: 井、压裂完井、采气和对外集输,国内外页岩气开采的基本流程如 图1.1所示.

技术上的快速发展和地质储量迅速增加,使得页岩气的开采获得了全球推广并成为改变全球能源供给和价格的杠杆之一.目前整个北美地区, 欧洲的德国、法国、波兰,拉美的阿根廷、墨西哥、巴西,亚太的澳大利亚、中国、印度、印尼等多个国家纷纷积极开展页岩气技术研究和试验开发,在全球掀起了"页岩气革命"的浪潮.

从美国页岩气开采的发展来看, 2007年美国成为天然气生产第一大国,目前页岩气产量已占其天然气总产量的40%左右.预计到2035年,页岩气产量将占其天然气总产量的46%.页岩气生产已在一定程度上改变了世界能源格局, 甚至影响到政治格局.美国页岩气的成功开采使得越来越多的国家都将目光聚焦到页岩气的开发,由于有丰富的资源和良好的开发潜力, 页岩气已成为世界能源的新领域(邹才能等 2010). 目前全球页岩气资源量为4.562,4,$\times$,10$^{14}$,m$^{3}$,主要分布在北美、中亚、中国、拉美、中东、北非和前苏联,中国拥有丰富的页岩气资源, 初步计算页岩气资源量约为(1.5,$\sim$,3.0),$\times $,10$^{13}$,m$^{3}$ (耿龙祥等 2015,邹才能等 2010). 近年来, 中国页岩气勘探开发工作获得重要突破,先后设立了涪陵、长宁--威远和昭通等国家级页岩气示范区,提交探明地质储量5.441,29,$\times $,10$^{11}$,m$^{3}$,2016年页岩气产量为 7.8,$\times $,10$^{9}$,m$^{3}$,实现了工业化生产 (邹才能等 2011).

页岩气开采过程中的水平钻井和水力压裂两项核心技术的发展历程, 是工程实践先于理论研究的典型案例. 对于这样的工程现象的出现, 我们并不能因此而低估理论研究的重要性. 事实上, 后续的页岩气采收率的提高、不同环境的工程方案优化、致裂过程的实时监控等等重要工程技术问题都需要开展基础研究, 需要通过页岩气采出机理研究来进一步提升其开发技术, 从而形成工程-理论交替发展, 相互促进的局面.

为更好地提升页岩气层的致裂效果, 提高页岩气的开采效率, 需要从页岩性质、破裂过程、微纳尺度孔隙中流体的输运、压裂过程的实时监控及内部裂纹网络信息反演、全过程数值模拟方法、环保高效的压裂技术等方面开展结合工程实践的深入系统研究. 这篇文章正是基于这一出发点, 召集了部分和页岩开采工程技术相关的力学领域的学者针对其中的问题和目前的研究进展展开论述. 页岩气开采过程中涉及的力学问题较多, 关于其中的一些基础力学问题, 可见最近非常好的总结文章(陈勉等 2015, 庄茁等 2015, 柳占立等 2017). 根据页岩气开采的过程, 对页岩气开采不同阶段所涉及的关键力学问题进行全面深入的分析归纳, 总结过程按照开采中的关键环节来展示, 各环节的主要内容示意图参见图1.2.

按照页岩气开发过程中所涉及的各方面的问题, 除去集输阶段的多相管流问题,从以下8 个方面来阐述页岩气开采过程中的相关力学前沿问题.

页岩气藏及其开采方式: 以页岩气藏的基本特征为基础, 以开采方法的发展为主线, 介绍直井及直井压裂开发、水平井及水平井压裂开发、同步压裂开发方式、工厂化水平井压裂开发等的发展历程以及我国在水平井及水平井压裂开发方面的最新工程实践情况.

页岩材料本构关系及力学行为表征: 岩体在细(微) 观上存在大量的微裂隙、孔洞、矿物夹杂和层面等缺陷, 在宏观上存在节理、断层和各向异性等特征. 这些宏微观结构使得岩体呈现不连续性、不均匀性和各向异性等特征, 并极大地影响着岩体的力学行为, 例如塑性变形、损伤及破坏、各向异性、渗透性、多场耦合等. 为了更真实地描述、解释和预测岩体材料的力学行为, 解决复杂的工程实际岩体力学问题, 构建合理的岩体本构关系是岩体力学一直以来的重要研究方向. 这一部分介绍岩体本构关系的发展和研究现状, 并对主要本构理论的优缺点和适用性进行简要评述. 水力压裂的关键是在含天然裂隙的页岩中获得三维裂纹网络. 这一部分还从天然裂缝分布、页岩脆性、弹性、断裂强度等方面对现有页岩研究成果进行介绍, 并就页岩天然裂缝方向的分布、页岩脆性及其断裂韧性等方面的研究提供了前瞻性观点.

页岩气藏实验模拟技术: 页岩储层具有低孔低渗、微纳米孔隙发育、富含有机质等非常规特征, 其实验研究需要采用\非常规" 的测试技术和实验方法. 在大量调研国内外页岩实验方法和测试技术的基础上, 总结了页岩储层评价技术、开发模拟实验技术和含气量计算方法等方面的研究进展, 结合渗流所非常规实验室的研究成果, 探讨了页岩的孔隙结构特征、气体赋存与扩散机理、储层吸水特征、耦合流动规律和含气量计算方法.

页岩气宏微观输运机理: 页岩气等非常规油气藏储层的孔隙结构尺度极低, 页岩喉道大小在0~1000nm 之间. 这样微小尺度的孔隙喉道难以形成有效的页岩气渗流通道. 页岩气的渗流主要依赖于储层中天然发育的微裂隙以及开采时的人工压裂裂隙. 微裂隙是页岩气储层中天然发育裂隙的主要存在形式, 同时它们对页岩气的开采起到了至关重要的作用: 微裂隙作为页岩的主要储集空间, 影响着气藏的富集程度, 页岩孔隙与微裂隙越发育, 气藏富集度越高; 其次微裂隙能够在很大程度上提高泥页岩的渗流能力, 为页岩气从基岩孔隙进入井孔提供必要的运移通道. 该部分深入讨论了有机质丰度、孔隙度、渗透率、储层的可压裂性、地应力、含气性及吸游比等因素对页岩油气开发后期产油效率的影响, 同时从基础研究方面讨论了现阶段理解负责裂缝网络渗流规律的理论模型.

页岩气水力压裂计算和数值模拟: 通过理论计算来再现压裂过程, 评估压裂效果,针对不同地质环境探索最优压裂方案一直是水力压裂技术发展的一个热点问题. 这一部分详细介绍了水力压裂的理论计算模型的发展以及各类模型的优缺点.

水力压裂的微地震监测技术: 水力压裂过程的一个重点和难点是如何评估压裂效果. 通过对页岩气开采水力压裂期间岩体破裂过程中, 所发生的微地震的数据采集、记录、实时分析, 不仅可以确定微地震事件的具体位置分布, 实现裂纹及裂纹网络实时成像, 还可以优化压裂过程设计, 从而增加岩体的有效压裂体积提高页岩气开采的经济效益. 虽然微地震监测技术已经在美国的页岩气开采中被广泛使用, 并且在页岩气的前期勘探、中期开采和后期的经验总结等各个阶段都起到了关键作用, 但是目前微地震监测技术仍然面临一些挑战存在难点问题, 需要在水力压裂过程中微地震事件的有效识别(包括初至时间的拾取、多震源的定位、复杂环境干扰信号的滤波)、微地震波的全波形分析和时频域瞬时谱分解、震源机制的合理反演以及监测数据的分析结果与实际情况不自洽、大数据的采集和处理等方面加强基础理论和工程应用的研究. 这一部分对微地震监测技术及其面临的机遇和挑战做了一个全面介绍.

页岩气开采的无水压裂技术: 成熟的页岩气开采技术一般采用水力压裂, 该技术需要数万立方米的淡水资源, 且目前淡水资源可重复利用率较低, 消耗量大. 考虑到我国目前页岩气所在区域有时淡水资源短缺, 难以远距离输送, 限制了水力压裂技术的应用, 因此有必要对其他新型环保的压裂技术开展探索. 这一部分就目前采用超临界CO₂ 压裂技术、N₂ 压裂技术、石油液化气压裂技术、爆炸压裂技术以及高能气体压裂技术等研究热点进行了探讨, 综述了相关的研究进展, 以及其中可能需要关注的重点问题.

2 页岩气藏及其开采方式^*(*本节撰稿人: 刘曰武¹(1 E-mail: lywu@imech.ac.cn), 高大鹏, 李奇, 万义钊, 段文杰)

2.1 引言

页岩气藏是一种非常规气藏, 储层物性极差, 多数页岩气藏需要人工改造后才能获得经济开采效益. 其非常规特征主要表现在5 个方面: (1) 成藏的非常规性, 不同于常规气藏需要经过二次运移成藏, 页岩气藏是自生自储; (2) 储层构造的非常规性, 相比于常规油气藏, 具有大范围、无构造等特性; (3) 赋存方式的非常规性, 常规气藏内只存在游离气, 而页岩气藏内还赋存了大量的吸附气, 不同区域的吸附气含量为20%~85%; (4) 开采技术的非常规性, 由于储层的分层及低渗透特征, 页岩气的开发需要特殊的压裂工艺和技术, 如滑溜水压裂液、多级分段同步压裂、工厂化压裂等技术; (5) 气藏的人工特性, 常规气藏连通范围是天然形成的, 而页岩气藏的连通范围是需要人工进行扩大的, 气藏的大小往往决定于压裂裂缝的沟通范围.

全球第一口商业页岩气井于1821年完钻于纽约州的Fredonia小镇,完井深度8.23,m, 但由于该气井产量极低, 一直被认为不具有开采价值.随后在1914年, 密歇根盆地发现第一个页岩气田. 1926年,阿帕拉契亚盆地成功实现了页岩气的商业开发.技术进步是页岩气藏实现高效开发的催化剂,随着新钻井以及储层改造技术的运用和推广,页岩气单井产量得到了显著增长,页岩气藏的开发开始表现出巨大的经济效益. 20世纪70年代初,美国在东部泥盆纪页岩气开发中,采用裸眼完井、硝化甘油爆炸增产技术以及高能气体压裂技术来提高气藏的采收率.到了70年代后期,CO$_{2}$或N$_{2}$泡沫压裂技术迅猛的势头在北美得到广泛运用,该技术使得页岩气产量提高了3,$\sim $,4倍, 但产量仍然较低.20世纪90年代,Mitchell能源公司首次将清水压裂应用在Barnett页岩气田的开发中,滑溜水压裂液在Barnett页岩地区的成功应用很快扩展到美国Haynesville,Marcellus, Woodruff和Fayetteville等地区.页岩气的压裂方式变为以大规模滑溜水压裂为主,页岩气产量再次增大25%左右. 进入21世纪以来, 美国Barnett,Fayetteville等页岩油气区以水平井开发为主,美国完钻非常规水平井钻井数量大幅度增加,形成了比较成熟的"水平井,$+$,多级压裂"的非常规油气开发模式.2007年, Marcellus页岩气开发开始应用"井工厂"高效开发模式,逐步成为世界范围内页岩气开发的主流模式.

除美国外, 加拿大是第2个实现页岩气规模化开发的国家.受北美成功开发页岩气的影响, 页岩气成为全球能源热点, 欧洲的德国、法国、波兰,拉美的阿根廷、墨西哥、巴西,亚太的澳大利亚、中国、印度、印尼等30多个国家纷纷积极开展页岩气开采技术研究和试验开发,在全球掀起了"页岩气革命"的浪潮.页岩气从资源发现到大规模开发的漫长历程表明,技术进步是推动页岩气成功开发的关键,水平井钻完井和水力压裂是页岩气开发的核心技术.

中国页岩气开发起步较晚, 虽然在20世纪60年代四川威远钻开了一部分页岩气层,但主要作为常规气井进行开发. 中国页岩气开发的标志是:中国国家政府2011年将页岩气确定为特殊矿种并制定了许多相关的优惠政策. 目前,中国的页岩气主要由中石化、中石油、中海油、延长石油四大国有石油公司进行开发,商业性开发的最大页岩气区块是重庆的涪陵焦石坝区块.焦石坝区块一期工程计划建设63个开发平台, 钻井253口,目前已成为世界第2大页岩气整装气田.该气田主要采用双钻机批量式钻井"井工厂"模式,这大大加快涪陵页岩气的商业开发步伐, 其中焦页50号平台共部署8口水平井,是涪陵页岩气田目前布井最多、最密集的一个平台.

2.2 页岩气藏的地质及开采特征

2.2.1 页岩气藏的地质特征

页岩是由粒径小于3.9,$\mu$m的细粒碎屑、黏土、有机质等组成,具页状或薄片状层理、易碎裂的一类沉积岩,亦即美国所称的粒径小于3.9,$\mu$m的细粒沉积岩.页岩气是指从富有机质黑色页岩中开采的天然气,或自生自储在页岩纳米级孔隙中连续聚集的天然气.页岩气在世界范围内分布广泛、储量巨大,是目前最具开发潜力的非常规天然气资源.

美国海相页岩分布广, 包括古生界--中生界大部分富有机质页岩地层,其中Fort Worth盆地Barnett页岩勘探较早, NewarkEast气田为德克萨斯州最大气田,东部Haynesville页岩气2007年进行商业性开采, 近年发展速度很快,阿巴拉契亚盆地Marcellus页岩是目前美国最大的页岩气储层.

中国四川盆地海相页岩气勘探开发和理论研究取得重要进展,目前已累计完钻页岩气井近200口, 压裂获工业气流近100口,2014年实现页岩气年产量12$\times $10$^{8}$,m$^{3}$,五峰组--龙马溪组页岩气已形成长宁--威远、富顺--永川、焦石坝及昭通四大工业化生产示范区,筇竹寺组页岩气仅在威远、犍为地区发现工业气流井,仍存在诸多问题与挑战.本文系统开展了我国页岩气藏的沉积背景、岩性、烃源性、储集性、含气性、脆性和保存条件等地质特征研究,并与美国Barnett, Marcellus和Haynesville三大页岩气区带进行对比,明确中国四川盆地海相页岩气地质特征与美国的相似性和特殊性,为我国复杂构造和高演化程度背景下的海相页岩气开发提供有益的参考.

2.2.1.1 构造地质背景

中国四川盆地是位于上扬子地台西部的大型叠合盆地,下部为古生代克拉通盆地, 上部为中新生代前陆盆地,产气页岩层为上奥陶统--下志留统五峰组--龙马溪组和下寒武统筇竹寺组,经历了多期构造运动和长期隆升剥蚀.

美国三大页岩气盆地主要为前陆盆地和克拉通盆地, 其中FortWorth盆地位于德克萨斯中北部, 产气页岩为Barnett,是由Ouachita造山运动形成的前陆盆地. Appala-chian盆地位于美国东部,产气页岩为Marcellus, 是Acadian造山运动形成的前陆盆地. North LorthLouisiana Salt位于德克萨斯和路易斯安那之间, 产气页岩为Haynesville,是一个拉张形成的克拉通盆地.

2.2.1.2 沉积环境

盆地类型、沉积物供应、水体结构、气候条件以及海平面变化会形成不同沉积环境.中国四川盆地海相优质页岩总体为缺氧环境沉积,其中筇竹寺组页岩主要沿成都--泸州"裂陷槽"大面积分布(如图2.1所示), 五峰组--龙马溪组页岩发育于半闭塞滞留海盆,除川中古隆起遭受剥蚀外, 其他地区均有沉积,发育川北、川东--鄂西和川南3个深水沉积区(如图2.1所示).根据岩相组合、沉积构造等特征,筇竹寺期和龙马溪期陆棚相可分为深水和浅水陆棚亚相(如图2.1所示), 深水陆棚亚相为静水强还原沉积, 水动力条件弱,底部静水环境适合有机质保存, 有利于形成富有机质页岩.浅水陆棚亚相处于弱氧化--弱还原环境, 水动力条件变强,有机质含量较低, 形成互层黏土质页岩, 是下伏产层的良好盖层.

美国Barnett页岩、Marcellus页岩和Haynesville页岩也沉积于深水陆棚闭塞环境,形成优质页岩的缺氧环境总体受海平面上升控制. 因此,中国与美国海相页岩沉积环境相似, 同为深水陆棚相、海侵体系域产物.

2.2.1.3 页岩类型

页岩岩石类型可依据矿物学、结构、构造、颜色、粒度分布等划分.四川盆地海相页岩发育4种类型:硅质页岩、钙质页岩、黏土质页岩和混合页岩.四川盆地五峰组--龙马溪组页岩和筇竹寺组页岩以硅质页岩和混合页岩为主(如图2.2所示), 硅质页岩富含放射虫、海绵骨针等微体化石(如图2.3所示), 为生物成因, 指示沉积环境为富硅深水陆棚相带,有利于富有机质页岩形成, 且高硅质含量有利于页岩储层压力改造,是主要产气层, 与Barnett页岩硅质生物成因相同(如图2.3所示).纵向上五峰组--龙马溪组表现为向上石英和长石含量逐渐减少,碳酸盐矿物增加, 由硅质页岩变为钙质页岩,且硅质富有机质页岩具有高伽马特征.总体上四川盆地2套海相页岩岩石类型纵向变化快, 非均质性强.筇竹寺组产层主要发育硅质页岩,龙马溪组产层主要发育硅质页岩、钙质硅质混合页岩、黏土质硅质混合页岩,寒武系筇竹寺组与Barnett页岩和Marcellus页岩类似,志留系龙马溪组与Haynesville页岩相似, 为深水海湾沉积.

2.2.1.4 总有机碳含量

页岩有机碳含量、有机质类型和成熟度对优质页岩气储层的形成、高含气性具有重要作用.四川盆地2套页岩与美国3套页岩在烃源特性上的主要差别在于热成熟度不同,美国3套页岩的热成熟度非常适中, 为成熟生气阶段.四川盆地2套页岩热成熟度均较高, 普遍为高成熟或过成熟.

总有机碳含量(TOC)是评价页岩气的关键地质要素之一,高有机碳含量为页岩气形成与富集提供良好生烃能力,同时也是有机质孔隙发育的基础, 且有机碳含量越高, 页岩吸附能力越强.

美国Barnett页岩和Marcellus页岩TOC含量高,Haynesville页岩和中国2套海相页岩TOC含量相似(如图2.4(a)所示).Barnett页岩有机碳含量为3%~13%, 平均为4.5%,Marcellus页岩有机碳含量较高, 为3%~12%,平均为4.0%, TOC含量自西向东增大.Haynesville页岩有机碳含量为0.5%~4.0%.四川盆地2套海相页岩TOC含量测试与统计表明五峰组--龙马溪组TOC含量为1.5%$\sim$6.0%, 平均为4%, TOC含量$>2%$的集中段分布于底部,筇竹寺组页岩TOC含量为0.8%~6.0%,TOC含量$>2%$的集中段分布于底部和中部2段.

2.2.1.5 热成熟度

成熟度是评价页岩气的另一关键地球化学参数,控制有机质生烃、有机质孔隙发育和甲烷稳定性. 随着成熟度增加,页岩气生成量增加, 页岩微孔隙增多, 吸附能力增强, 页岩含气量相应增加,因此高成熟度并不完全制约页岩气成藏, 但若页岩过成熟时,生气潜力、微孔隙量、吸附能力等不仅不会进一步增大, 相反会逐渐降低,因此适中的热演化程度是页岩气成藏的必要条件.

四川盆地2套页岩时代老, 距今分别为530Ma和430Ma,在地质历史中一般经过6000~10000m深埋,热演化程度普遍很高,其中筇竹寺组在川南--昭通、川东、中扬子等地区出现大面积炭化,基本处于生气衰竭阶段. 四川盆地筇竹寺组页岩$R_{\rm O}$值一般为2.5%~4.5%, 平均为3.5%,局部高达5.0%以上, 整体处于高--过成熟阶段.五峰组--龙马溪组页岩$R_{\rm O}$值为1.5%~3.5%,平均为2.5%, 整体处于高成熟阶段.

Barnett页岩热演化程度较低, $R_{\rm O}$值为0.5%$\sim$2.1%, 从盆地东部向西降低. Marcellus页岩$R_{\rm O}$值为1.2%~3.5%, 自西向东增大,其中宾夕法尼亚州和纽约州成熟度最高, 有机质处于高成熟和过成熟阶段,天然气为热成因. Haynesville页岩$R_{\rm O}$值为1.2%$\sim$3%. 3套页岩的主力产气区, 即核心区, 热演化程度$R_{\rm O}$值为1.1%~3.5%, 处于有利成气热成熟阶段.

对比发现,四川盆地五峰组--龙马溪组页岩与美国Marcellus岩页和Haynesville页岩相似,热演化程度适中, 为成气有利阶段, 而筇竹寺组页岩的热成熟度已过高(如图2.4(b)所示), 成气潜力较低. 实验发现当页岩成熟度不断增加到一定程度后,不仅导致有机质生烃衰竭, 而且会导致岩石中有机碳石墨化趋势,从而使有机质微孔隙发育程度降低甚至消失,这也可能是筇竹寺组页岩储层较差原因之一.

2.2.1.6 有机质类型

有机质类型影响页岩的生气能力和含气量, 是重要的参数之一,可通过氯仿沥青"A"组分、热解、碳同位素组成和干酪根显微组成等确定.四川盆地五峰组--龙马溪组和筇竹寺组有机质类型为典型的腐泥型,呈无定形状, 含少量腐殖型.与美国三大盆地产气页岩的有机质干酪根类型基本一致,主要为I型和II$_{1}$型.

2.2.2 页岩气藏的储层特征

2.2.2.1 储层厚度

中国与美国海相页岩厚度差别不大.Barnett页岩在整个盆地厚度从小于15m到超过305m,核心区厚度为30~180m, 平均为107m,总体从北东方向向西南方向厚度逐渐减少. Marcellus页岩厚度为15$\sim$60m, 自西向东厚度增大, 宾夕法尼亚州东北部厚度最大.与其他页岩气藏相比, Marcellus页岩厚度不占优势,但参照其他页岩气藏评价参数如有机碳含量、有机质成熟度和吸附气含量等,Marcellus页岩气地质资源量巨大. Haynesville页岩厚度一般为70$\sim$100m, 呈现东厚西薄的特征, 东部沉积中心最厚可达120$\sim$130m, 西部则小于30m.四川盆地五峰组--龙马溪组页岩厚度为25~120m,川南--川东地区厚度较大, 川南最厚可达130m;筇竹寺组页岩厚度为40~100m,川东--鄂西、川南2个地区厚度较大, 超过160m (如图2.1所示).

2.2.2.2 储层物性

页岩储层总体具有超低孔、渗特征,孔隙发育且具有高孔、渗是优质页岩气储层的重要条件.美国3套页岩储层孔隙度普遍较高,Barnett页岩和Marcellus页岩孔隙度分别为4%$\sim$5%和10%, 渗透率小于1.0$\times $10$^{-6}\mu$m$^{2}$, Haynesville页岩孔隙度为8.0%~9.0%,渗透率小于5.0$\times $10$^{ - 3}\mu $m$^{2}$.

中国2套页岩孔隙度变化范围大且比美国的低(如图2.5(c)所示).五峰组--龙马溪组页岩孔隙度为3%~10%,平均为4.75%, 比表面积为6~32m$^{2}$/g,平均为15m$^{2}$/g; 筇竹寺组页岩孔隙度为0.4%~3%,平均为1.7%, 为五峰组--龙马溪组的1/3, 比表面积为210$\sim$10m$^{2}$/g, 平均为5m$^{2}$/g; 两者的渗透率为(1$\sim$90)$\times $10$^{ - 8}\mu $m$^{2}$.

研究发现五峰组--龙马溪组和筇竹寺组2套页岩的孔隙度大小与TOC含量正相关性好,因为干酪根生烃会形成大量有机质孔,这与观察到的储集空间以有机质孔为主相吻合,有机质孔占比为10%~36%, 平均为25%,五峰组--龙马溪组储集空间还包括粒间孔、溶蚀孔、层间缝等, 如图2.6所示. 筇竹寺组孔隙度较低与其过高热演化程度密切相关,主要表现为受有机质炭化影响,页岩中有机质孔隙出现明显的塌陷和充填现象, 孔径变小,孔隙体积和比表面积大幅度减小(小于五峰组--龙马溪组的1/2).

2.2.2.3 页岩脆性

页岩脆性好坏直接影响页岩储层压裂改造诱导裂缝的形成. 脆性越好,改造中越易形成诱导裂缝. 页岩脆性程度可以用岩石力学参数表征,也可以用脆性矿物含量表征.页岩脆性矿物含量是影响页岩基质孔隙度、微裂缝发育和可压性的重要因素,石英或长石等脆性矿物含量丰富有利于压裂改造产生诱导裂缝.

中美海相页岩脆性矿物含量相似(如图2.5(d)所示), Barnett,Marcellus和Haynesville等页岩脆性矿物含量分别为40%$\sim$79.7%, 30%~60%和35%~65%.五峰组--龙马溪组脆性矿物含量为44.5%~82%(石英和长石含量为16.8%~63.2%),筇竹寺组脆性矿物含量为32%~80%(石英和长石含量为13.4%~73.6%).与其他页岩略有不同的是筇竹寺组页岩的石英以陆源碎屑来源为主,硬而不脆, 其他页岩的以生物成因为主. 因此,优质页岩储层段的脆性矿物含量高且以生物成因为主.

2.2.2.4 裂缝系统

页岩气初期高产与天然裂缝发育程度有关, 高产页岩气层段一般微裂缝发育.页岩裂缝发育程度与岩石矿物组成和后期构造活动有关.但裂缝系统对页岩气形成、富集的作用具有两面性: 一方面提供运移通道和储存空间;另一方面大规模裂缝可导致页岩气散失, 不利于保存.

中美海相页岩气储层普遍发育天然裂缝.四川盆地海相富有机质页岩在区域应力场作用下,通常发育页理缝、构造缝、节理缝等丰富的天然裂缝,在局部构造褶皱区可形成复杂网状裂缝体系. 在威远气区,龙马溪组上部页岩段为灰绿色富黏土(泥土矿物含量为68%$\sim$71%)、贫有机质$({TOC}<0.5%)$的黏土质页岩段,电阻率曲线平滑, 一般为6~10$\Omega \cdot $m,显示裂缝不发育;下部页岩段为硅质页岩、钙质硅质页岩和硅质黏土质页岩组合,有机质丰度一般在1%以上, 发育大量层间缝, 单条缝宽可达5$\sim$25mm, 且多为黄铁矿充填, 电阻率测井曲线显示锯齿状异常响应特征,裂缝密度达1.1~4.4条/m, 裂缝段厚46m,其中底部17m富有机质页岩段$( TOC >2%)$为大中型裂缝集中发育段,裂缝密度达2.5~4.4条/m.涪陵焦石坝梳状背斜核部为网状裂缝发育区,五峰组--龙马溪组下部出现电阻率曲线密集性锯齿状响应,显示裂缝段厚度超过80m、裂缝密度为1~20条/m,中上部为天然裂缝不发育的黏土质页岩段,电阻率曲线响应特征与威远相似.

总体上, 筇竹寺组整套页岩天然裂缝发育,五峰组--龙马溪组页岩天然裂缝主要发育在下部优质页岩储层段.

2.2.2.5 含气量 页岩含气量是评价页岩气资源潜力、储量规模和衡量页岩气目标区是否具有商业开采价值的关键指标.页岩含气量与TOC含量密切相关.一般认为具商业性开发的页岩含气量下限为2.0m$^{3}$/t.中美海相页岩含气量差别不大(如图2.5(e) 所示),Barnett页岩、Marcellus页岩和Haynesville页岩含气量分别为4.2$\sim$9.9m$^{3}$/t、1.7~2.8m$^{3}$/t和2.5$\sim$9.0m$^{3}$/t, 五峰组--龙马溪组页岩含气量为1.7$\sim$4.5m$^{3}$/t, 筇竹寺组页岩含气量较差,仅为五峰组--龙马溪组页岩的1/3, 为0.55~1.2m$^{3}$/t,造成含气量偏低的原因在于其成熟度过高导致有机质产气能力降低.

吸附气含量是评价页岩气藏产能的关键参数之一,也是其长期稳产的重要保障. 页岩吸附气含量大小主要受有机碳含量影响,有机碳含量越高, 吸附能力就越大, 这是因为干酪根中微孔隙发育,对天然气具有较强的吸附能力.Barnett页岩、Marcellus页岩和Haynesville页岩吸附气含量分别占到页岩总含气量的20%,20%和10%, 五峰组--龙马溪组页岩吸附气量占20%$\sim$40%, 筇竹寺组页岩吸附气含量占40%~50%.

2.2.3 页岩气藏的开采特征

从20世纪80年代初Barnett第一口页岩气井的发现至今,美国近代的页岩气勘探开发已经历了30余年的发展历程.从早期的直井泡沫压裂到目前的水平井多段滑溜水压裂,从早期东部页岩气的开采逐步向中西部扩展, 其发展过程是循序渐进的. 目前,中国已在四川盆地及其周缘的下古生界龙马溪组和筇竹寺组获得重大突破,并于涪陵、长宁--威远、富顺--永川、昭通等地启动页岩气产能建设,初步进入规模开发阶段.

综合对比分析, 中美页岩气藏勘探开发的发展历程具有以下几点特征.

2.2.3.1 优惠政策的扶持

早在20世纪70年代末, 美国政府制定了非常规能源开发税收的补贴政策,而德克萨斯州自20世纪90年代初开始对页岩气的开发不征收生产税. 此外,美国还专门设立了非常规油气资源研究基金,有利的政策支持为页岩气的快速发展提供了强劲的动力. 同时,能源紧缺也迫使美国开发非常规页岩气资源.

页岩气的开发具有高投入、高风险、回收期长等特点, 特别需要协调一致的政策环境.自2000年起, 美国天然气价格连年飙升, 使页岩气的开采有利可图.虽然2008年以来天然气价格受金融危机的影响一路走低,但页岩气的大规模开发依然可以获得可观的利润.

2.2.3.2 体积压裂

与常规油气藏的水平井压裂方式不同, 页岩气藏主要是进行体积压裂,压裂的目的除了形成作为气体高速流动通道的大型人工裂缝外,主要是沟通和扩展储层中的天然裂缝,从而在页岩储层区域创造最大化的立体缝网体系,充分发挥出压裂裂缝和天然裂缝的增产优势, 大幅提高气井产量和最终采收率.

Fisher等(2002)通过分析微地震裂缝监测结果, 首次提出页岩气藏的体积压裂理念:在压裂过程中, 随着缝内净压力的逐渐增大,页岩储层会发生相应的拉伸破裂和剪切滑移,此时在平面和纵向上形成的不再是单一对称的双翼拉伸简单裂缝,而是会形成拉伸裂缝、剪切裂缝以及天然裂缝相互沟通连接的复杂裂缝体系(如图2.7所示).

2.2.3.3 勘探开发关键技术不断发展进步

20世纪80—90年代初期, 美国天然气研究所和美国能源部资助了大量的油气研发项目.20世纪90年代中期, 北美非常规天然气初步实现了商业化生产. 目前,美国非常规天然气的勘探开发仍在享受20世纪80—90年代的研发硕果,如美国在页岩气勘探开发方面形成的以水平井、分段压裂、微地震裂缝监测为代表的特色技术,不断实现了页岩气的高效、低成本开发,已将以往不能经济开采的非常规天然气资源转化为今日天然气供应的重要来源.

近年来, 水平井和多级压裂技术的提高使成本不断降低. 2000—2016年,水平井的钻井深度从2078m增至3785m,是当年美国的井深平均值的2.1倍, 平均钻井周期从28.2d缩短到24.5d.同时,多级压裂技术也从2008年压开11个水平段油层发展到2010年压开32个水平段油层,单级压裂作业成本也呈现明显的下降趋势.

以美国西南能源公司费耶特维尔页岩气产区的水平钻井为例,2007—2010年间水平段的平均长度从701m增至1496m,平均钻井周期从17d缩减到8d, 单位进尺钻井成本下降30%以上.在此期间, 新投产水平井的初始产量平均增长1倍以上,页岩气产量从15$\times $10$^{8}$m$^{3}$增至99$\times$10$^{8}$m$^{3}$,平均的勘探、开发成本从0.44元/m$^{3}$降至0.18元/m$^{3}$,公司净利润从2.22$\times $10$^{8}$美元增至6.04$\times$10$^{8}$美元.

2.2.3.4 产量递减率较高

多个气田的实际生产数据证实, 10年内将采出页岩气单井可采量的80%,剩余的产量很小但会保持稳定开采. 为了保证页岩气的产量,美国应用将井口集中在富气区域的技术,并且通过持续钻井保证新开采的气能不断弥补旧气井产量的不足.以Barnett页岩气田为例, 该页岩气田第2年的产气量比第1年下降39%,在第3年又比第1年下降50%. 数年之后, 产量递减率放缓,仍有很大部分的可采气不断被采出.

2.2.3.5 环保问题面临挑战

水力压裂技术使页岩气得以快速发展,但页岩气开采所用的水力压裂技术不仅消耗大量水资源,而且向地下注入压裂液可能污染地下水. 有专家指出,向页岩层大量注水可能促使深层岩石滑动而引发地震, 也会威胁饮用水,大批量的钻、完井还会破坏地表植被. 因此,页岩气的开发已经遭到美国环保主义者的抵制.

2.3 页岩气藏开采方式

从页岩气的开采发展历程上看, 主要有5种开采方式:直井开发方式、直井压裂开发方式、水平井及水平井压裂开发方式、同步压裂开发方式和"工厂化"水平井压裂开发方式.

2.3.1 直井及直井压裂开发方式

无论是国外还是国内, 页岩气藏开发都是从垂直井开发方式开始,这种开发方式与常规油气藏的直井开发方式并无任何区别,采用直井开发方式的主要原因是投入成本低、多为实验性开发.但由于页岩气储层的渗透率较低, 直井开发的产气量一般达不到经济开发产量,因此页岩气藏的开采开始尝试利用水力压裂进行储层改造. 20世纪80年代, FortWorth盆地的Barnett页岩气田开始采用大型水力压裂技术; 1992年,Barnett页岩气田试钻了水平井, 但当时并没有取得成功; 1998年,清水压裂取代了凝胶压裂, 完井技术也取得了突破; 1999年,二次压裂增产技术获得成功应用.

2.3.2 水平井及水平井压裂开发方式

2002年以后, 水平井钻井技术取得了巨大成功并成为主流钻井方式. 此后,水平井钻完井以及压裂技术仍然在不断进步并逐步得到推广应用,使得美国的页岩气开发成本在近15年间持续降低了85%,促进了页岩气产量的快速增长, 在2006年以后更是呈现出爆发式的增长态势.

水平井及水平井压裂技术主要是利用了常规油气井中的钻井及压裂技术,在水平井压裂技术中最主要的2个技术关键点是滑溜水压裂技术和多级分段水力压裂技术.

2.3.2.1 滑溜水压裂技术

滑溜水压裂技术(slickwater fracturing)即通常所说的清水压裂、减阻水压裂,是页岩气开发的关键技术之一. 相对于传统的凝胶压裂液体系,滑溜水压裂液体系以其高效、低成本的特点在页岩气开发中广泛应用.

White和Mungal(2008)提出滑溜水的降阻机理: 滑溜水压裂液的黏度较低,它的加入改变了平均速度剖面, 使边界层中的剪切力重新进行分布.上述效应使湍流边界层近壁结构发生明显改善, 可以更有效地开启储层中的天然裂缝,体现出滑溜水压裂液的降阻效果.

与黏度较大的传统压裂液相比, 滑溜水压裂的主要优点是:(1)滑溜水压裂液的黏度较低, 更容易开启天然裂缝, 从而产生较大面积的缝网;(2)配合加入少量的支撑剂,可以支撑开启的天然裂缝从而形成具有一定导流能力的网状缝; (3)开发成本大幅降低,相对于传统压裂液, 滑溜水压裂可以在不减产的前提下节约30%的开发成本; (4)是一种清洁压裂技术, 所用压裂液的主要成分是清水, 具有很好的环保功效(文霞等 2011).

1997年,Mitchell能源公司首次将滑溜水压裂应用在Barnett页岩气田的开发中.Cipolla(2009)对比了Barnett气藏传统冻胶和滑溜水压裂后形成的裂缝体积:应用传统冻胶进行压裂, 储层改造体积为1.2$\times$10$^{7}$m$^{3}$; 而应用相同体积的滑溜水进行重复压裂,储层改造体积增大到4.1$\times $10$^{7}$m$^{3}$,改造体积增大了2.42倍(如图2.8所示). 因此,滑溜水压裂在Barnett页岩气田的成功应用很快扩展到美国Haynesville,Marcellus, Woodruff和Fayetteville等地区,滑溜水已经成为目前页岩气储层改造过程中应用效果最好、相关技术最为成熟的压裂液.

但是, 滑溜水压裂技术存在两个主要缺点: (1)需要充足的水资源供应,美国国家环保护局(EPA)统计,2010年单口页岩气井平均用水量在7.6~23.9t,其中20%~85%的用水滞留于井下无法返还;(2)受到页岩储层特征的限制, 如果储层的石英含量较低、黏土含量较高,会导致支撑剂嵌入后蠕变明显, 裂缝容易重新闭合,造成压裂裂缝的导流能力不足.

2.3.2.2 多级分段压裂技术

随着页岩气开发的深入,常规的直井压裂和水平井单段压裂已经无法满足工业生产的要求. 自2002年以来,美国开始尝试多级分段压裂技术, 多级压裂(multi-stagefracturing)是利用封堵技术或限流技术分隔储层不同层位,然后进行多段一起压裂的压裂技术.

最初水平井的压裂阶段一般仅采用单段或2段的压裂方式,但多级分段压裂技术使原本低产或无气流的页岩气井重新获得工业价值成为可能,极大地延伸了页岩气在横向与纵向的开采范围,是目前美国页岩气藏实现工业化生产的关键技术之一, 水平井多级分段压裂技术如图2.9所示.

Kettel等(2006)分析了多级分段压裂技术的增产原理:(1)多级分段压裂先后形成的裂缝之间存在着应力干扰,前期的裂缝会在后续裂缝面上产生诱导应力,诱导应力的干扰有利于提高页岩水平井的改造体积;(2)应力干扰还可以使后续裂缝壁面的压应力增加,从而阻止距初次裂缝距离较近的平行裂缝起裂,增加了后续裂缝与初次裂缝的起裂间距; (3) 应力干扰迫使裂缝在长度延伸方向上发生弯曲,形成天然裂缝与人工裂缝相互交错的裂缝网络.

因此, 与常规气藏的水平井分段压裂技术不同,页岩气藏多级分段压裂技术的主要优点是:(1)针对页岩储层天然裂缝较发育的特点,在压裂改造过程中采用分段多簇射孔、多段一起压裂的施工方式,能够充分利用缝间干扰, 促使多级裂缝产生,最终形成复杂的裂缝网络体系; (2)通过射孔实现上层定点启裂,压裂层位会比较精准; (3)压裂段数不受限制,水平井段最多可形成8~15段的裂缝簇,使压裂裂缝与天然裂缝的沟通效果更好, 如 图2.10所示.

目前, 水平井多级分段技术应用成熟并且适用于页岩的地质特征,被广泛应用于北美Barnett, Marcellus等页岩气田的压裂作业中,该技术已经成为北美页岩气藏压裂改造的主体技术. 目前,在美国页岩气生产井中,有约85%的井应用水平井和多级压裂技术结合的方式进行开发. 其中,2006年美国Newfield公司在阿科马盆地Woodford页岩气聚集带的Tipton-1H-23井开展了7段压裂改造,气井增产效果显著, 压裂后页岩气的产量高达1.416$\times$10$^{5}$m$^{3}$/d (唐颖等 2011).

2.3.3 同步压裂开发方式

以上技术除了滑溜水压裂技术更适合于页岩储层外,其他各项技术都在常规油气藏的开采中成功应用. 因此,页岩气藏的实用开发技术是同步压裂技术和"工厂化"水平井压裂技术. 其中,同步压裂技术包括两种方式: 同步压裂技术和拉链式压裂技术.

2.3.3.1 同步压裂技术

同步压裂技术(simultaneousfracturing)是近几年在美国Barnett页岩气田开发中成功应用的最新压裂技术.该项技术的特点是: 在一口水平井进行压裂改造的同时,应用两口以上的配对井进行同步压裂,促使压裂裂缝在扩展过程中相互作用, 使压裂裂缝受到更大的压力作用,从而增加裂缝的延伸距离, 沟通更多的储层天然裂缝, 相对于单井压裂,可以形成一个复杂的裂缝网络体系, 如图2.11所示.

Stefanski(2012)提出了多个水平井同步压裂与单井压裂对储层的作用机理有着本质的不同,集中体现在以下几个方面: (1)应力状态.从单井产生的应力场转变为多口井压裂产生的应力场叠加,一个区块相邻的几口井同层位进行同步压裂过程中,压裂泵入的流体将促使人工流体产生应力场的叠加和干扰. (2)裂缝与层理.从单井形成的复杂裂缝转变为多井同步压裂后产生的复杂裂缝,裂缝延伸不再只受注入井产生的应力控制,相邻的同步压裂井在注入过程中也将影响注入井的裂缝延伸. 因此,单井形成的裂缝通过同步压裂后,进一步发展为多井压裂产生的更为复杂的裂缝网络体系. 同步压裂技术的主要优点是: (1)多口井同时作业,节省开采时间且压裂效果好于单井依次压裂;(2)利用井间应力干扰增大裂缝的延伸距离, 从而沟通更多的储层天然裂缝,形成复杂的裂缝网络体系.

同步压裂技术虽然有一些优点, 但其缺点同样明显:(1)对场地条件要求较高; (2)入地液量大, 并且返排较为困难.

2006年, 同步压裂技术首先在美国的Barnett页岩气田中实施.施工者在水平井段相隔152$\sim$305m的2口大致平行的水平井之间进行同步压裂,两井均得到了高速生产. 其中一口井以25.5$\times$10$^{4}$m$^{3}$/d的速度持续生产30d,而其他未同步压裂的气井只有(5.7~14.2)$\times$10$^{4}$m$^{3}$/d,统计结果显示同步压裂井比单独压裂井的平均产量高21%$\sim$55%, 说明同步压裂可以更好地沟通储层中的天然裂缝,形成一个复杂的裂缝网络体系.

2.3.3.2 拉链式压裂技术

当受场地条件所限, 无法对多口井开展同步压裂时,可以采用拉链式压裂的施工方式对页岩气藏进行开发.

拉链式压裂(zipper fracturing)的技术特点是: 应用1口水平井进行压裂,另1口井进行电缆桥塞射孔联作, 两项作业交替进行并无缝衔接.拉链式压裂可以产生不同方向的段间应力干扰, 促使压裂裂缝不断转向, 如图2.12所示.

相比于同步压裂, 拉链式压裂的优点有以下几点:(1)可以形成更为复杂的裂缝网络体系.同步压裂产生的应力干扰仅局限于裂缝尖端附近区域,而拉链式压裂利用第1压裂段与第2、第3压裂段之间产生的不同应力扰动关系,不断促使压裂裂缝的延伸方向发生改变,进而形成更大范围、相互交错的复杂裂缝网络体系;(2)拉链式压裂由于两井延伸裂缝的相交叠部分与井筒有一定距离,降低了井筒附近应力反转的可能性, 避免了在井筒附近形成纵向裂缝,增加了裂缝网络方向上的复杂性, 如 图2.13所示.

拉链式压裂技术在北美页岩气藏取得了很好的应用效果,East等(2011)的微地震监测结果表明:2口典型页岩气井拉链式压裂的改造体积达到了3.0$\times$10$^{8}$m$^{3}$, 远远超过了直井压裂的改造体积,相对于水平井多级压裂的改造体积也增加了50%以上.

与拉链式压裂技术相似的页岩气藏开发技术,还有交替压裂技术与改进拉链式压裂技术.

交替压裂技术, 也称作"德州两步跳"压裂, 其技术特点是:在水平井多段压裂过程中, 利用水力压裂产生的裂缝对储层应力场的改变,将压裂主缝和分支缝与诱导应力松弛缝相连通, 实现储层体积缝网压裂改造.在无分支水平井段中, 该技术利用常规压裂技术对单个射孔簇实施水力压裂,与常规压裂技术不同的是, 需要改变各压裂段的施工顺序, 如 图2.14所示. 交替压裂技术原理是利用第1压裂段与第2压裂段之间产生的应力扰动,当在前两个压裂段之间某一合理位置进行第3次压裂时,容易形成与主裂缝相互连通的应力松弛缝,有效沟通第1段与第2段压裂之间页岩储层,从而进一步增大页岩储层的改造体积, 提高页岩气井产气量.

改进拉链式压裂技术是Rafiee等(2012)在研究了拉链式压裂和交替压裂技术的优缺点后,创造性地将拉链式压裂和交替压裂相结合, 并且规避了它们的不足,提出的页岩气藏先进开发方式.

改进拉链式压裂作业过程与交替压裂相类似: 首先,在第1口水平井趾端进行第1次压裂, 如图2.15中序号①;该段压裂结束后将压裂工具向水平井跟端移动至预定位置进行第2次压裂如图2.15中序号②; 再仿照交替压裂第3段压裂的做法,在第2口水平井井筒上与第1口水平井已形成的两条裂缝之间合理位置进行第③次压裂,压裂顺序在两口井之间如此交替直至完成两口井整段水平井的压裂.

相比于拉链式压裂和交替压裂, 改进拉链式压裂的优点如下:(1)传统的拉链式压裂产生的应力干扰仅局限于裂缝尖端附近区域,而改进拉链式压裂由于第2口井中产生的裂缝处于第1口井产生的两条裂缝之间,具有更大的应力干扰作用范围, 进而容易形成更大范围的复杂裂缝网络,储层改造体积更大; (2)传统的交替压裂中间主裂缝宽度和长度受应力干扰影响较大,存在砂堵风险高和导流能力不足等缺点,而改进拉链式压裂中间主裂缝宽度受应力干扰影响小, 导流能力高, 砂堵几率小;(3)改进拉链式压裂由于两井延伸裂缝相交叠部分与井筒有一定的距离,降低了井筒附近应力反转可能性, 避免了在井筒附近形成纵向裂缝,增加了远场裂缝网络复杂性. 但是,拉链式压裂、交替压裂、改进拉链式压裂的主要缺点与同步压裂基本一致:(1)压裂施工的规模较大, 所需压裂设备更为复杂、要求更高;(2)入地液量大, 且返排困难; (3)增产效果在初期十分明显,但后期下降较快.

2.3.4 工厂化水平井压裂开发方式

为了进一步降低开发成本, 北美地区把工厂的概念应用到页岩气开发中,促进了工厂化压裂模式的形成.工厂化水平井压裂的理念是由加拿大能源公司(EnCana)最先提出的,工厂化压裂就是要像普通工厂一样, 在一个固定场所,连续不断的泵注压裂液和支撑剂.工厂化压裂可以大幅提高压裂设备的利用率, 减少设备动迁和安装,减少压裂罐拉运, 降低工人劳动强度. 北美地区的开发实践证明,在页岩气开发中应用工厂化压裂技术可以大幅提高压裂施工速度、缩短投产周期、降低采气成本(王林等 2012). 工厂化水平井压裂技术作业流程图如 图2.16所示.

工厂化压裂技术的主要优点为:(1)工厂化丛式井压裂通过井间应力和段间应力的同时干扰,不仅具有更大的应力干扰作用,还利用不同压裂井之间不同方向的应力扰动关系, 促使裂缝不断发生转向,最后能最大范围地沟通储层天然裂缝, 形成最大范围的立体裂缝网络体系,如 图2.18所示; (2)减少作业时间、设备动迁次数,降低施工成本; (3)提高气井初始产量和最终采收率,平均产量比单独压裂可类比井提高21%~55%.

但工厂化水平井压裂的施工技术尚处于起步阶段, 在今后的工厂化压裂过程中,涉及大量的交叉作业内容,如何控制其中的各种安全风险和优化作业流程是目前现场最需要解决的迫切问题,有待相关操作程序和安全规范的制定和完善.

通过几年的探索和实践, 北美地区在页岩气田通过开展工厂化水平井压裂技术,进一步探索页岩气藏的高效开发模式. 丛式水平井组工厂化压裂的成功,标志着页岩气初步实现了从直井到水平井再到工厂化压裂的跨越,页岩气改造趋势已从单一水平井分段改造趋于井组化的工厂化压裂改造. 可以预见,丛式水平井组结合工厂化压裂将逐渐成为页岩气规模效益开发的主流技术(钱斌等 2015).

2.4 本节小结

本章在分析岩气藏的地质特征与开采特征的基础上,综合阐述了页岩气的主要开发方式, 得到如下结论:

(1)通过对页岩气藏的压裂技术发展的分析,厘清了页岩气藏水平井压裂技术的主要发展历程大致可以分为3个阶段:第1阶段, 页岩气藏压裂技术以尝试不同的压裂液工艺为主,明确滑溜水是页岩气藏储层压裂改造效果最佳的压裂液; 第2阶段,以水平井多级分段压裂技术为主,旨在通过压裂让主裂缝与多级次生裂缝交织形成复杂裂缝网络; 第3阶段,开始应用同步压裂、工厂化压裂等技术,旨在通过井间、段间应力干扰形成最大范围的立体裂缝网络体系.

(2)同时研究结果表明, 页岩气藏与常规气藏的水平井压裂目的不同,常规气藏水平井压裂的主要目的是建立连通井筒与储层的流动通道,而页岩气藏水平井压裂的主要目的除了建立连通井筒与储层的流动通道之外,更重要的是沟通和扩展储层中的天然裂缝,形成立体缝网体系从而达到提高页岩气井产量的目的.

(3)页岩气藏与常规气藏的水平井压裂方式不同,常规气藏水平井压裂的主要方式是单段和分段压裂,而页岩气藏水平井压裂方式除此之外,还发展了同步压裂、拉链式压裂以及工厂化压裂等方式,主要目的在于沟通井间的天然裂缝. (4)通过分析各种水平井压裂技术的实际应用情况,明确了各种压裂技术的优缺点与适用性, 指明了页岩气藏水平井压裂技术的趋势是:发展能在整个页岩气藏中更大范围、更有效地沟通天然裂缝网络的环保型水平井压裂技术.

(5)由于我国实际地质条件与北美地区有一定差异,不同区域页岩气藏必须结合实际地质状况选取最为适宜的水平井压裂方式,文中研究成果可以为实现我国页岩气藏的高效开发提供理论依据.

3 页岩力学行为与基本表征方法^*(*本节撰稿人: 曾霞光, 李晓雁, 李明耀, 苏业旺, 范永波, 李世海, 魏宇杰¹(1 E-mail: yujie wei@lnm.imech.ac.cn))

3.1 引言

页岩是一种成分复杂的沉积岩, 非均质性强, 而且在不同尺度下具有不同结构, 如图3.1所示(Li et al. 2017). 在图示微观尺度6,页岩是由多孔黏土、夹砂、有机物等组成的复合材料; 在更小尺度7,页岩是多孔的黏土/有机物复合材料. 在纳米尺度8,可以看到干酪根包裹着基本的黏土矿物. 在上述小尺度,扫描电镜、原子力显微镜、纳米压痕等方法广泛用于表征页岩的形态、拓扑和力学性质.在更大尺度上, 比如宏观尺度4和细观尺度5, 页岩是层状沉积岩,通常可视为横观各向同性层状材料,其中的沉积面、层理等对页岩的断裂行为具有重要影响. 另外, 在矿层尺度2或者3,断层和天然裂缝对水力压裂裂缝扩展也有很大影响.

当有机质含量较高时, 页岩成为一种重要的非常规油气资源.页岩储层的一个重要特点是基岩非常致密, 孔隙尺寸非常小, 渗透率极低.Javadpour对北美9个油藏152块岩芯进行实验分析,发现90%试样的渗透率小于1.5$\times $10$^{ - 4 }$D;Loucks等研究北美页岩气藏的孔隙结构和存储空间,发现页岩气藏的孔隙主要是微米孔隙和纳米孔隙, 大部分为纳米孔隙,纳米孔隙直径尺寸在5~800nm之间,大部分分布在100nm左右, 孔喉直径一般在10~20nm(姚军等 2013). 由此可见, 页岩基岩是超低孔和超低渗的致密多孔介质,这为页岩油气开采带来了巨大挑战. 为开发页岩储层中的油气资源,人们通常采用水平井水力压裂法在页岩储层中形成复杂的裂缝网络,这是目前实现页岩油气规模化高效开采的唯一手段.为进一步提高页岩储层水力压裂效果,研究人员对页岩的水力压裂力学行为展开了广泛研究.姚军等(2013)总结了北美和我国几个典型页岩气藏的矿物组成和其常见力学性质,如表3.1所示. 可以看到, 由于组分差异, 页岩力学性质变化很大.除组分的影响, 页岩力学性质的影响因素还有很多,比如温度、压力、天然裂缝分布等,本文将对这些方面的研究进行系统梳理,展现关于页岩弹性、断裂、本构模型发展方面的研究现状,以期对页岩开展中面临的力学问题提供相应的力学背景和基础.

3.2 页岩天然裂缝的分布

天然裂缝普遍存在于页岩储层中, 它们对页岩宏观力学性能具有巨大影响,因此首先需对其分布特征进行研究. Gale等(2007,2014)对北美地区几种典型页岩进行了系统全面的裂缝形态表征,发现该地区的页岩普遍含有天然裂缝. 这些裂缝形态各异,一般都被方解石等矿物完全填充或者部分填充.他们观测到所有试件都含有几乎竖直分布的裂缝,大部分含有近似水平分布的裂缝, 还有一部分含有团状分布的裂缝.裂缝密度是页岩储层中裂缝含量的一个重要表征参数,统计数据显示页岩的竖向裂缝密度分布在7$\sim$160条每100英尺岩芯之间.另外, 露头也显示竖向裂缝的间距在0.5$\sim$10m之间.根据岩芯观测结果, 他们给出了不同裂缝宽度和裂缝高度对应的裂缝数目,如图3.2所示. 从图中可以看出, 页岩裂缝的长度和宽度变化很大,而且不同地区页岩裂缝的宽度和长度分布差别很大.这种分布随机性给页岩裂缝形态的准确统计带来了困难,人们难以建立一个通用的模型去描述不同地区页岩裂缝的形态分布.

国内,久凯等(2012)对黔北地区寒武统牛蹄塘组黑色页岩岩芯的裂缝进行特征统计,认为该储层主要含构造裂缝, 裂缝倾角总体平缓地围绕水平分布,其中64%为水平裂缝, 22%为竖直裂缝.这些裂缝多为完全充填或者半充填裂缝, 充填物有方解石、黄铁矿等,其中方解石充填占79%, 这与野外露头观测结果一致. Zeng等(2013)对重庆地区龙马溪组页岩和牛蹄塘组页岩的裂缝进行了表征,指出这两个区块具有较好的裂缝发育,其中龙马溪组天然裂缝类型59\%为泥页岩韧性剪切破裂形成的斜交剪切缝,且按雁列式排列, 这些裂缝之间的距离一般在2$\sim$40mm;其次为高角度张剪性裂缝和垂直张性缝, 约占总数的36\%.所有裂缝的宽度在0.1$\sim$36mm之间, 完全填充裂缝占53%,部分填充裂缝占6%, 其余裂缝是张开的,而且充填物质主要为方解石(87%);牛泥塘组裂缝的宽度和长度分布特征与龙马溪组的相似,方解石也是绝对主要的填充材料(95%),不同的是他们的张开裂缝占54%, 完全填充裂缝占41%,部分填充裂缝占5%.何龙(2014)对四川盆地涪陵地区页岩储层的裂缝形态进行了统计,发现其裂缝包括水平裂缝、低角度斜裂缝、高角度斜裂缝和竖直裂缝等,以低角度斜裂缝和水平裂缝为主, 裂缝宽度集中分布在1mm以内,裂缝线密度在2.3$\sim$3.5条/米之间,其中完全充填裂缝占裂缝总数的65%, 半充填裂缝占26%,张开裂缝仅为9%. 根据上述三地页岩裂缝的统计情况可见,国内页岩储层中天然裂缝的分布方向有一定规律,长度和角度分布特征有较大地区差异,因此仍然需要对更多地区页岩储层的裂缝分布形态进行详细统计和总结,其中裂缝分布方向应为重点.

3.3 页岩的脆性

从天然裂缝分布这个单一因素来看就能判断页岩的力学性质必定具有很大随机性.水力压裂时需要综合考虑多个随机因素对页岩力学行为的影响,这是页岩油气开发技术的核心问题之一.

在20世纪中期,研究人员已经发现岩石在不同受限环境下的显著韧脆性差异(Paterson 1958, Baud et al. 2000, Paterson & Wong 2005, Wei & Anand 2008).例如Paterson(1958)针对Wombeyan 大理石的系列围压实验,很好地展示了该类材料随着围压增大变形能力逐步增强的现象, 如图3.3所示.

通过细观层次的计算, Wei和Anand(2008)阐明围压作用下的变形能力逐步增强现象源自非常弱的岩石晶界破坏和岩石晶粒塑性变形之间的竞争,如图3.4和图3.5所示.

Amann等(2011, 2012)对泥页岩岩芯进行了单轴和三轴压缩实验,发现这些岩芯的最终断裂形态与围压有密切关系, 当围压小于0.5MPa时,试件发生轴向劈裂; 当围压大于2MPa时, 试件发生剪切破坏.类似压缩实验表明页岩是否形成复杂断裂形态与载荷和页岩层理方向的夹角也有关系(Islam& Skalle 2013).这些室内压缩实验为页岩矿区复杂水力裂缝网络的形成机制和控制因素提供了研究线索.赵金洲等(2013)总结了室内实验、矿场压裂实践、理论分析和数值模拟等方面的成果,指出页岩储层的裂缝延伸形态受地质因素和工程因素双重影响,其中地质因素包括岩矿成分、岩石力学性质、水平应力场、天然裂缝分布等.综合众多影响因素, 页岩的脆性被认为与复杂缝网的形成直接相关(Holt et al. 2011), 因此脆性评价是一个具有重要应用价值的研究课题.

材料脆性有不同定义, Morley将脆性定义为材料塑性的缺失,Ramsey认为岩石内聚力被破坏时, 材料即发生脆性破坏,Obert和Duvall以铸铁和岩石为研究对象,认为试样达到或稍超过屈服强度即破坏的性质为脆性,地质学及相关学科学者认为材料断裂或破坏前表现出极少或没有塑性形变的特征为脆性(李庆辉等 2012a).关于页岩脆性一个直观想法是脆性矿物越多页岩脆性越高,据此观点并结合Barnett页岩矿区的成功开采经验, Jarvie等(2007)提出了一个简单的脆性评价公式$ B = \dfrac{c_{\rm qtz}}{c_{\rm qtz} + c_{\rm cl} + c_{\rm carb} } $ (字母说明见表3.2). 随后, Rickman等(2008)认为泊松比反映了岩石在应力作用下的破裂能力,而杨氏模量反映了岩石破裂后的支撑能力,并提出一个采用杨氏模量和泊松比计算岩石脆性的数学公式.% $B =%\dfrac{1}{2}\left( {\dfrac{E - 1}{8 - 1} + \dfrac{v - 0.4}{0.15 -%0.4}} \right) \times 100$, 根据该公式脆性参数越高, 当脆性参数大于%0.5后将形成复杂缝网.这两个脆性参数一个只考虑矿物组成,另一个只考虑弹性力学常数杨氏模量和泊松比. 之后, Waters等(2011)提出一个新的考虑杨氏模量和泊松比的页岩脆性评价 指数 $ {B} = \dfrac12 \left[ {\dfrac{100(E_3 - E_{3\min } )}{E_{3\max } -E_{3\min } } + \dfrac{100(v_3 - v_{3\max } )}{v_{3\min } -v_{3\max } }} \right] $ (脚标数字请参考图3.18),对后者进行了修正.

从矿物组成和弹性常数两个方面评价页岩储层的脆性在矿场实践中都有成功经验,但不能相互取代. 陈勉等(2012a,2012b)对不同页岩试样进行室内三轴压缩实验,指出脆性应当是一个综合评价指标,受自身非均质性和外在测试环境共同影响,于是提出综合利用岩石弹性参数和矿物组成来评价页岩脆性.这种方法的本质是利用Jarvie等(2007)、Rickman等(2008)给出的两个脆性指标进行某种组合来评价页岩脆性.类似地, 唐颖等(2012)、刁海燕(2013)、Liu和Sun(2015)指出页岩脆性与其弹性参数和矿物组成关系密切,也提出了几种综合利用弹性参数与矿物成分的方法来修正页岩的脆性评价.

最近, Holt等(2015)回顾岩石力学中关于脆性的基本概念,选出了几种可能作为页岩脆性指标的定义式, 如 表3.2所示.

Holt等(2015)对Mancos页岩进行单轴、三轴压缩实验和巴西劈裂实验后认为对脆性进行准确定量是困难的,不同脆性指标得到不同的结果, 即使使用某一个脆性指标, 比如$B_1 $,也难以得到一致结果; 但是定性地看, 页岩脆性具有各向异性,且一般随着围压增大而减小, 如图3.6所示. Rybacki等(2015)研究了欧洲某地的黑色页岩, 得到了类似的结论: 围压越大,脆性越小, 延展性越好.

工业界仍在寻找一个能准确评价页岩可压裂性能的简单指标,脆性概念是根据室内实验和矿场实践经验给出的一个描述性说法,还没有统一和准确定义及对应的标准测量方法. 根据断裂力学基本理论,页岩脆性应与其有效断裂韧性有关,而页岩的有效断裂韧性又与更多因素相关(Holt et al. 2015),目前尚难确定. 因此,脆性概念底层的科学问题及其与断裂力学常用断裂参数(例如断裂韧性)的关系仍是一个亟待研究的课题.

3.4 页岩的弹性

3.4.1 杨氏模量

页岩脆性与其弹性参数有关,因此页岩的弹性力学性能是相关研究的重要组成部分. Lo等(1986)用页岩超声波测量实验证实平行层理方向的动态杨氏模量大于垂直方向的动态杨氏模量,确定其弹性力学性能具有很强的各向异性特征.层理和页岩孔隙和矿物颗粒取向是产生各向异性特征的主要原因,而且各向异性特征随围压增大而减小.利用超声波测量页岩弹性参数是一种间接方法,为直接测量弹性模量和其他力学性能参数,人们对页岩岩芯进行了室内力学实验. Ibanez和Kronenberg(1993)利用三轴压缩实验研究了富含伊利石页岩的力学行为,发现页岩的压缩力学性能受围压影响很大, 当围压小于100MPa时,页岩发生脆性断裂, 当围压在100MPa到400MPa之间增大时,页岩逐步变成延性断裂. 断裂过程中, 页岩中产生了微裂缝和剪切断裂带,其典型应力应变曲线如图3.7所示.

图 3.7显示平行层理方向的静态杨氏模量$E_{1}$一般大于垂直方向的静态杨氏模量$E_{3}$. 由于围压很大, 页岩在3个方向上都未发生脆性断裂,而是表现出较好的延展性, 由此可见围压对页岩力学行为具有重要影响.Niandou等(1997)详细研究了围压对页岩静态杨氏模量的影响, 发现:围压越大, 杨氏模量越大, 但不同层理方向受影响程度不同,平行层理方向受影响最小, 垂直层理方向受影响最大. Niandou等(1997)进一步给出了不同等效剪应力(第二偏应力不变量乘以3再开根)时平均应力(第一应力不变量除以3)对垂直和平行层理方向杨氏模量的影响曲线,结果表明主要影响由平均应力产生, 等效剪应力对杨氏模量影响不大,如图3.8所示.

页岩的杨氏模量随载荷与层理的夹角变化而变化(Niandou et al. 1997,王倩等 2012), 一般情况下平行层理方向的杨氏模量最大,垂直层理方向的杨氏模量最小, 具体变化趋势与围压有关, 如图3.9所示.

Valès等(2004)研究了含水饱和度对页岩杨氏模量的影响, 发现:平行层理方向的静态杨氏模量随饱和度增大而减小,当饱和度大于0.6时又开始缓慢增大,而垂直层理方向的静态杨氏模量随着饱和度增大而增大,当饱和度大于0.6时开始减小,而且饱和度对平行方向杨氏模量的影响程度大于对垂直方向杨氏模量的影响,如图3.10所示.

有机物含量对页岩杨氏模量影响很大, Agapito和Hardy(1982)的研究表明油页岩有机质含量越高, 其杨氏模量越小;温度对页岩的杨氏模量有较大影响,在一定温度范围内温度越高杨氏模量越小(Eseme et al. 2007);矿物组成显然也对页岩的杨氏模量有很大影响, 例如, Sone和Zoback(2013a, 2013b)的研究了表明黏土和干洛根体积含量之和增大,页岩杨氏模量 $E_{1}$和 $E_{3}$都将减小,而且其实验测量结果基本被Voigt-Reuss边界曲线包络,刁海燕(2013)发现页岩杨氏模量随石英含量增大线性增大,随方解石含量增大线性减小. 总之, 页岩杨氏模量的影响因素多而复杂,这使得页岩的弹性模量分布在一个很大范围内, 大约在5$\sim$200GPa之间(姚军等 2013), 因此要想获得比较准确的结果,通常需要对多个岩芯进行力学实验测量.

3.4.2 泊松比

Lo等(1986)的超声波测量实验表明页岩在不同方向上有不同动态泊松比,随着围压增大这些泊松比有所增大, 但总体变化不大. 然而, Niandou等(1997)的岩芯力学试验结果表明围压对泊松比的影响是比较显著的,如图3.11所示.

图3.11表明同一围压下页岩横观各向同性层理面内的泊松比比各向异性面的泊松比小,而且各向异性面内平行层理方向的泊松比 $ \upsilon _{\rm {13}}$比垂直层理方向的泊松比 $\upsilon _{\rm {31}} $大. 然而,唐杰(2014)研究发现: 围压增大, 静态泊松比 $ v_{31}$增大,而静态泊松比 $ v_{12} $和 $v_{13} $减小, 这与Niandou等(1997)的研究结论有很大差异. 因此,围压对泊松比的影响仍是一个没有一致结论的问题.

王倩等(2012)的试验给出了无围压情况下页岩层理倾角对动态和静态泊松比的影响,结果显示各向异性面平行层理方向的泊松比最大,泊松比随角度增大几乎线性减小, 但在垂直层理方向处却增大了,据分析这可能是一个不准确的测量结果, 如图3.12所示.

与杨氏模量类似, 页岩泊松比的影响因素很多, 例如, Agapito和Hardy(1982)证实油页岩的泊松比随着有机质含量增大而增大;刁海燕(2013)发现泊松比随石英含量增大而显著减小,随方解石含量增大而显著增大; Valès等(2004)表明饱和度对泊松比的影响很大, 而且饱和度越高泊松比越大,如 图3.13所示.

综上所述, 页岩杨氏模量和泊松比等弹性参数的影响因素众多,主要包括矿物组成、有机质含量、裂隙含量、围压、温度等.这些因素通常混合在一起,从岩芯实验中定量研究单个因素的影响是极其困难的,因此通常需借助理论和数值模拟等方法来厘清每个因素的影响.

3.5 页岩的断裂强度

3.5.1 压缩断裂强度

页岩力学行为研究中还有一个重要关注点: 断裂强度. 如图3.14所示, 在不同围压情况下压缩,页岩岩芯最后的断裂形态有不同模式(Amann et al. 2012).

围压对页岩的断裂强度有显著影响: 高围压情况下,页岩的延展性有很大提高(Amann et al. 2012, 李庆辉等 2012b),破坏时不再表现为脆性断裂. 将Ibanez和Kronenberg(1993)和Niandou等(1997)的三轴压缩实验结果整理到一起可以发现围压越大,页岩同一方向上的压缩断裂强度越大, 如 图3.15 所示. Valès等(2004)对法国Tournemire页岩进行压缩实验也得到了类似的结果. Amann等(2012)的研究进一步表明围压增大, 页岩压缩断裂强度线性增大; 然而,Rybacki等(2015)的研究表明围压增大, 页岩压缩断裂强度非线性增大.

从 图3.15 可以看到, 页岩的压缩断裂强度随方向变化, 具体趋势是:以平行层理方向的断裂强度为起点,断裂强度随载荷与层理夹角的增大先减小再增大, 经历一个U形变化过程,在约45$^\circ$角时断裂强度最小, 这说明剪切时页岩最容易破坏.

国内, 刁海燕(2013)对大庆地区页岩进行了三轴压缩实验,发现压缩强度随围压增大而线性增大;压缩强度也随杨氏模量增大线性显著增大; 另外,陈天宇等(2014)对寒武统牛泥塘组黑色页岩进行了三轴压缩实验,发现页岩压缩强度随着围压增大几乎线性显著增大,且随着层理与轴向载荷角度的增大先减小再增大, 经历一个U形变化过程.

页岩的压缩断裂强度还受其他因素影响, 例如, Agapito和Hardy(1982)指出油页岩无围压情况下, 有机质含量越高, 压缩断裂强度越低; Eseme等(2007)、Rybacki等(2015)发现页岩压缩断裂强度随温度升高按对数曲线规律非线性下降,而且在100MPa围压以内, 压缩断裂强度与静态杨氏模量线性相关;Horsrud(2001)的研究表明,页岩压缩断裂强度随孔隙率增大经历一个类似指数衰减规律的急剧减小过程;Ibanez和Kronenberg(1993)的研究表明温度和含水量对页岩压缩断裂强度也有较大影响,特别是含水量, 当含水量从原始重量分数2.1%增大到4.3%时,页岩强度下降比例为79MPa每体重百分点,当含水量从原始重量分数2.1%减少到0时,页岩强度下降比例是45MPa每体重百分点.

3.5.2 拉伸断裂强度

对页岩拉伸断裂强度的研究主要采用巴西劈裂实验. Mokhtari等(2014)对Eagle Ford油页岩试件进行巴西劈裂实验, 典型实验结果如图3.16所示.

Mokhtari等(2014)的实验结果表明页岩在垂直层理方向拉伸强度最小,在平行层理方向最大, 后者约为前者的1.6至1.9倍.实验中当层理与载荷方向的夹角在15$^\circ$到30$^\circ$之间时,裂缝可能沿层理面扩展或者穿越层理面, 据此他们指出存在一个临界角度,且这个角度是判断裂缝是否沿层理扩展的判据.

Chong等(1982)对Colarado和Utah两地的油页岩进行巴西劈裂实验,研究有机质含量对层理方向拉伸断裂强度的影响,发现有机质体积含量越大, 强度越小, 它们之间的关系可用线性式拟合.Eseme等(2007)和 Mokhtari等(2014)的实验结果也证实页岩拉伸强度随着有机质含量增大线性减小.

Closmann 和Bradley(1979)和 Eseme等(2007)的研究表明温度越高,页岩拉伸断裂强度越低, 而且下降趋势可用对数曲线拟合.比较页岩的压缩和拉伸断裂强度,可以发现页岩的压缩断裂强度比拉伸断裂强度大得多,而且平行层理方向的压缩或拉伸断裂强度也分别大于垂直方向的压缩或拉伸断裂强度.

3.6 页岩弹性性能的统计描述

建立页岩这种复杂各向异性复合材料的本构模型是一项极具挑战的工作,因为这个模型不仅需考虑页岩多种组分各自的物性,而且需考虑这些组分的空间分布情况, 还要考虑外部载荷条件等. 目前,页岩本构关系研究集中在相对简单的弹性阶段,下面首先对现有宏观弹性模量模型进行梳理,然后再探讨这些模型在页岩宏观力学性能描述中的应用情况.

考虑各向同性弹性基质包含完全随机分布直裂缝的情况,研究者们发展了一些等效弹性模量的理论近似计算方法.Budiansky和O'Connell(1976)通过自洽法研究了裂缝密度对杨氏模量、剪切模量、体积模量和泊松比等弹性参数的影响,给出了它们的计算表达式. Huang等(1994) 采用广义自洽法, Kachanov(1987)采用非相互作用解法, 和Zimmerman(1985)Hashin(1988)采用微分法也给出了一些等效弹性参数的近似计算公式.这些公式由不同的简化和假设得到,因此由这些公式计算得到的弹性模量存在较大差异. 以杨氏模量为例,这些近似公式之间的差异随着裂缝密度增大而增大, 如图3.17所示.

上述研究中裂缝描述参数只有裂缝密度,因此这些模型不能考虑裂缝角度分布的影响. Hoenig(1979)发展自洽模型研究了平行裂缝的情况. 随后, Thomsen(1995)、Huang等(1996)、Zhan等(1999)、Wang等(2000)、Feng等(2003)发展微分法来考虑平行裂缝的情况. 除平行裂缝这种特殊情况外,裂缝角度按某种规律分布是更一般的问题. Sevostianov(2001,2004)、Giordano和Colombo(2007a, 2007b)、 Kushch(2009)研究了这种情况, 给出了一些近似计算公式.

当各向同性基质包含完全随机分布的孔洞时, Mackenzie(1950)、Eshelby(1957)、Zimmerman(1986)、Zhao等(1989)、Kachanov等(1994)针对这种情况发展了一些等效弹性模量的近似计算方法.这些研究采用的基本方法仍然是裂缝问题中常用的自洽法、广义自洽法或者Mori-Tanaka方法.对于多相复合材料, Hashin等(1962,1963)基于同心球模型和弹性变分原理得到了其有效体积模量和剪切模量上下边界的近似计算公式,在准各向同性和准均质情况下,这些理论结果与两相合金实验测量结果吻合很好; Hill(1963)发展了Hashin的方法, 给出了改进的弹性模量计算公式; Budiansky(1965)也给出了一套非均质复合材料弹性模量的估算方法.这些方法均要求材料的各个组分是连续分布的各向同性弹性体.随后几十年,研究者们在上述方法的框架下给出很多计算复合材料等效模量的方法,常用的有稀疏方法、Mari-Tanaka方法、自洽方法、广义自洽方法和微分法等. 随着计算机的发展,数值方法被广泛用于计算含裂缝、孔洞或夹杂材料的宏观弹性力学性能参数,例如有限元法(Makarynska et al. 2008, Shen & Li 2004)、边界元法(Huang et al. 1996, Renaud et al.1996)、扩展有限元法(Zeng & Wei 2016). 对裂缝问题,数值模拟研究表明微分法在低裂缝密度时通常能给出最准确的估计值,而高裂缝密度时广义自洽法一般比其他方法更准确. 与理论近似方法相比,数值方法更容易考虑更加复杂的情况,比如三相介质、复杂几何微观结构等,而且通过增强计算机硬件可以不断提高计算效率,但是数值计算结果的通用性显然低于近似方法.

根据页岩的结构观测和力学行为实验结果,人们普遍将其视为横观各向同性复合材料.在沉积平面(通常为近似水平面)页岩是各向同性的,在垂直于沉积平面的剖面(通常为近似竖直面)页岩是各向异性的, 如图3.18所示.

根据横观各向同性假设,可用5个独立弹性刚度常数来描述页岩的弹性行为(Sayers 2013),即$C_{{11}} $, $C_{{12}} $, $C_{{13}} $, $C_{{33}} $, ${C}_{44} $, 且有 $ {C}_{11} = C_{22} $, $ C_{12} = C_{21} $, $C_{13} = C_{31} = C_{23} = C_{32} $, $ C_{44} = C_{55} $, $C_{66} = (C_{11} - C_{12} ) / 2 $.这些弹性常数与弹性柔度系数的关系是: $ S_{11} + S_{12} = C_{33} /C$, $ S_{11} - S_{12} = 1 / (C_{11} - C_{12} )$, $ S_{13} = -C_{13} / C$, $ S_{33} = (C_{11} + C_{12} ) / C$, $ S_{55} = 1 /C_{55}$, $ S_{66} = 1 / C_{66} $, 其中 $ C = C_{33} (C_{11} +C_{12} ) - 2C_{13}^2 $. 另外, 常用弹性常数杨氏模量 $ E$、剪切模量$ G$和泊松比 $ v$与这些柔度常数的关系是: $ S_{11} = 1 / E_1$, $S_{12} = - v_{21} / E_1$, $ S_{13} = - v_{31} / E_3$, $ S_{33} = 1/ E_3$, $ S_{55} = 1 / G_{13} $, $ S_{66} = 1 / G_{12} $.

为表征横观各向同性材料的各向异性程度, Thomsen(1986)定义了3个各向异性参数, 即 $ \varepsilon = \dfrac{C_{11} -C_{33} }{2C_{33} }$, $ \gamma = \dfrac{C_{66} - C_{55} }{2C_{55}}$, $\delta = \dfrac{(C_{13} + C_{55} )^2 - (C_{33} - C_{55})^2}{2C_{33} (C_{33} - C_{55} )}$. 利用弹性横观各向同性假设,Hornby等(1994)基于自洽法和微分有效介质法构建了一个页岩的固液两相弹性本构模型,其先建立一个黏土--液体椭球混合体,这个混合体的5个弹性常数是含液量和长细比的函数,然后根据实际情况给出一个合适的混合体分布,并根据这个分布构建一个含多个混合体的大体系,最后向这个体系加入其他球状粉土矿物颗粒并计算这个大体系的弹性常数.这个模型与实际页岩结果比较吻合, 可用于油页岩本构关系模拟,但是计算量巨大.

Sayers(2013)利用横观各项同性模型研究了页岩的黏土颗粒取向、沙土体积含量、干洛根体积含量和天然裂隙对杨氏模量和泊松比的影响,发现: 这两种弹性参数对黏土颗粒取向敏感,弹性模量随沙土含量增大而增大, 泊松比随之减小,干洛根含量或孔隙增大杨氏模量和泊松比都随之减小.

Vasin等(2013)基于Eshelby模型,利用自洽法解释了Kimmeridge页岩的弹性常数变化规律,但与试验结果存在较大差异, 于是采用微分有效介质法,得到了与实验数据吻合较好的结果, 但这种方法的物理基础是有疑问的.

Zeng和Wei(2016)利用扩展有限元法研究了裂缝角度分布对页岩杨氏模量、剪切模量和泊松比的影响,并给出了这些弹性参数的拟合公式,但仍需进一步考虑夹杂、黏接天然裂缝等的影响才能更好预测天然页岩的弹性参数. Jin等(2016)拓展了弹性微平面法来研究横观各向同性材料的弹性性能.他们提出两种办法:利用刚度张量的频谱分解法定义微平面本构关系或采用方向相关微平面弹性模量.之后, Li等(2017)提出一种离散跨尺度数值框架来模拟各向异性页岩的力学行为,比如断裂.他们着重考虑了弱面层对材料宏观弹性性质和断裂强度等的影响, 如图3.19所示.结果显示该方法能成功捕获弹性刚度、强度和断裂模式等对载荷方向的依赖性.

关于页岩的断裂强度, 研究者们总结了实验结果, 给出了一些经验模型,例如, Eseme等(2007)发现页岩断裂强度随温度按对数规律下降,Gale和Holder(2008)的实验证实随着天然裂缝密度增大,页岩断裂强度非线性急剧减小, 并给出了拟合曲线, Zeng和Wei(2016)通过数值模拟也给出了类似的拉伸强度拟合曲线.

页岩基质本身成分复杂, 其空间分布具有很强的各向异性特征,且随外部载荷变化发生变化. 页岩的本构模型构建尚处于起步阶段,已有的宏观弹性模量理论成果还不能直接用于表征天然页岩的弹性力学性能,因此构建页岩的本构模型仍是一个具有重要意义的待解问题.

3.7 页岩的I型断裂

考虑到真实地层应力和孔隙压裂环境的各向异性, 天然裂纹的大量存在,使得裂纹扩展不再是能提前知晓的, 研究者因此采用扩展有限元法.采用孔隙黏结单元模拟水力压裂,一般适用于均质环境下的可预见裂纹扩展方向上的研究. 考虑流固耦合,水力压裂模拟仍然是一件十分具有挑战性的工作. 表3.3中列出了目前的一些典型数值工作.

为研究工程中复杂条件下的压裂问题,一般将水力压裂的裂纹扩展理论作出较大简化,主要是在断裂准则的表达式上, 常常假设为I型裂纹,此时对应的裂纹扩展准则即可写为${K}_{\rm I} = {K}_{\rm {IC}}$.针对不同的裂纹面载荷作用的假设, 研究者们给出了 ${K}_{\rm I}$与裂纹作用面载荷$ P$, 裂纹高度$ w$, 以及裂纹位置/长度 $a$之间的关系, 总结在表3.4中.

通过将裂纹的高度、断裂因子及裂纹内壁流体作用相互联系,这些作者基于不同的假设来获取对问题的深刻理解. 单从尺度上来看,水力压裂一般发生在地下2$\sim$4km, 可以视为无限大基体,裂纹的长度一般在数百米, 裂纹的高度则可能是毫米量级,如此大的几何尺度跨越下,裂缝里的流体压力是否均匀分布、裂纹高度是否一致等细节等都无法一一考虑到.

与理论对应的实验也不断涌现. 目前, 实验观察一般分为室内和室外两类,室内实验的研究尺度较小,同时缺乏相应的观测工具对试样内部的流体流动、裂纹扩展等信息进行实时跟踪.现有方法主要有3种: 声发射、核磁以及高速摄像机, 在表3.5总结了目前的相关实验研究报告. 由于上述监测设备的各种特点, 造成现有的试验很难全面反映水力压裂的真实物理背景.

从20世纪90年代开始, 国内的研究者也开展了一系列的水力压裂试验,主要研究了三轴压力边界条件对裂纹形态的影响(如 表3.6 中归纳).考虑到所使用的试样均为岩石或者石膏等非透明材料,所采用的声发射设备并没有获得较为细观的信息.他们一般是将试验后岩样割开, 肉眼观察裂纹形态. 所以在这种情况下,研究者们获得的试验结论基本上是定性的.

对比国内与国外研究者的水力压裂试验,容易发现国内的研究者注重应力条件对压裂的裂纹扩展的影响,虽然从工程中可知地应力是压裂效果评估的最主要因素,但缺乏相应的先进设备, 很难获得较详细的裂纹扩展信息,这将影响试验效果的评估. 国外的研究者更加重视裂纹扩展信息的获取,他们一般通过高速摄像机或者声发射监测裂纹扩展. 考虑到设备的局限性,试验所采用的一般是均质透明材料代替岩石以及较为简单的应力边界条件,这样设计试验将更加有效获取边界条件与裂纹扩展关系,但是这就忽略了真实岩石所带来的力学效应.

需要提及的是, 这些实验中, 非常具有代表性的工作是Bunger 和Detournay(2008)的试验, 他认为前人的理论研究获得了两个重要的渐进表达式:${K}_{\rm I} > 0$, $\mu = 0$时, $ w \approx \alpha x^{1/2}$, 这里$ x$表示裂纹位置; 当 ${K}_{\rm I} = 0$, $\mu > 0$时, $ w \approx\beta x^{2 / 3}$. 通过采用试样尺寸为 200mm$\times$200mm$\times $150mm的PMMA材料,作者验证了两种极端条件下的渐进表达式, 有兴趣的读者可仔细阅读原文.

3.8 页岩天然弱面对裂纹路径的影响

尽管关于页岩断裂的研究中, I型裂纹的分析最为基础全面,但通常大部分的裂纹都可能不是沿直线扩展.页岩含有大量平行沉积平面的层理面,这些层理面一般具有比页岩基质小很多的断裂韧性,将对水力裂缝的扩展行为产生重要影响. 由于页岩材料性质高度各向异性, 页岩水力裂缝与层理弱面扩展相遇后的行为变得异常复杂.目前, 研究人员通常利用各种数值模拟技术来研究水力裂缝的扩展行为,例如: Zhang等(2007), Taleghani和Olson(2011, 2014), Weng等(2011), Kresse等(2013), Guo等(2015)和>Zou等(2016)模拟了水力裂缝与带摩擦裂缝或与黏结裂缝的相互作用;Lecampion和Desroches(2015)和Grassl等(2015)发展了一些新数值模型来分析水力裂缝的起裂和扩展过程.从数值模拟研究中,可定性了解弹性性质的各向异性、页岩基质的强度和断裂韧性、页岩中弱面的强度和断裂韧性、裂缝面的摩擦力、水力裂缝入射角等都将影响水力裂缝的扩展行为.

Zeng和Wei(2017)最近从理论上研究了与弱面相遇时水力裂缝的扩展路径问题.他们将沉积界面和天然黏结裂缝面等弱面都视为厚度为零的材料断裂韧性不连续面,基于线弹性断裂力学原理和若干假设等给出页岩水力裂缝--弱面扩展问题的理论解,即

当 $ \bar{s}_q > 0$和 $ \bar{s}_\tau > f\bar{s}_q$ 时,水力裂缝的转向扩展条件是

$$ G_{dc} = G_\alpha = \left\{ \begin{array}{ll} \dfrac{\pi {\rm ccos}^{2}\left(\dfrac{\alpha }{2}\right)\left( {1 - 3\cos \alpha }\right)^2(\bar{s}_\tau - f\bar{s}_q )^2} {4E'},&\quad \sin \alpha> 0 \\ \dfrac{\pi {\rm ccos}^{2}\left(\dfrac{\alpha }{2}\right)\left( {5 - 3\cos \alpha }\right)(\bar{s}_\tau - f\bar{s}_q )^2}{2E'},&\quad \sin \alpha \leq 0 \\ \end{array} \right.{ (3.1a)} $$

且

$$ \dfrac{G_{dc} }{G_{mc} } < \dfrac{G_\alpha}{G_{\theta \max } } = \left\{ \begin{array}{ll} 3\cos ^2\left(\dfrac{\alpha }{2}\right)\left( {1 - 3\cos \alpha } \right)^2 /16, &\quad \sin \alpha > 0 \\ 3\cos ^2\left(\dfrac{\alpha }{2}\right)\left( {5 - 3\cos \alpha } \right) /8,&\quad \sin \alpha \leq 0 \\ \end{array} \right. {\rm (3.1b)}$$

当$\bar{s}_{q}$< 0 时, 水力裂缝的转向扩展条件为

$$ G_{dc} = G_\alpha = \left\{ \begin{array}{l} \dfrac{\pi c\cos ^2\left(\dfrac{\alpha }{2}\right)\left[\left( 6\cos \alpha - 2\right) \bar{s}_\tau - 2\bar{s}_q \sin \alpha \right]^2 }{16E'},\\ \qquad (1 + \cos \alpha )\bar{s}_q + 3\sin \alpha \bar{s}_\tau >0 \\ \dfrac{\pi c\cos ^2\left(\dfrac{\alpha }{2}\right)\left[4\sin \alpha \bar{s}_\tau \bar{s}_q + (1 + \cos\alpha )\bar{s}_q^2 + (5 - 3\cos \alpha )\bar{s}_\tau ^2 \right]} {2E'}, \\ \qquad (1 + \cos\alpha )\bar{s}_q + 3\sin \alpha \bar{s}_\tau \leq 0 \\ \end{array} \right. {\rm (3.2a)} $$

且

$$ \dfrac{G_{dc} }{G_{mc} } < \dfrac{G_\alpha}{G_{\theta \max } } = \dfrac{{\rm sec} ^2\left(\dfrac{\theta _0}{2}\right)\cos ^2\left(\dfrac{\alpha }{2}\right)\left[(6\cos\alpha - 2)\bar{s}_\tau - 2\sin \alpha \bar{s}_q\right]^2}{8[4\sin \theta _0 \bar{s}_\tau \bar{s}_q + (1 + \cos\theta _0 )\bar{s}_q^2 + (5 - 3\cos \theta _0 )\bar{s}_\tau ^2 ]} {\rm (3.2b)} $$

如果 $ (1 + \cos (\alpha ))\bar{s}_q + 3\sin (\alpha )\bar{s}_\tau> 0$; 或者

$$\dfrac{G_{dc} }{G_{mc} } < \dfrac{G_\alpha }{G_{\theta \max } } =\dfrac{{\rm sec} ^2\left(\dfrac{\theta _0 }{2}\right)\cos^2\left(\dfrac{\alpha }{2}\right)[4\sin \alpha \bar{s}_\tau\bar{s}_q + (\cos \alpha + 1)\bar{s}_q^2 + (5 - 3\cos \alpha)\bar{s}_\tau ^2 ]}{4\bar{s}_\tau \bar{s}_q \sin \theta _0 + (\cos\theta _0 + 1)\bar{s}_q^2 + (5 - 3\cos \theta _0 )\bar{s}_\tau ^2} {\rm (3.2c)}$$

如果 $ (1 + \cos \alpha )\bar{s}_q + 3\sin \alpha \bar{s}_\tau\leq 0$; 其中, $ \bar{s}_{\rm q} = \sigma _n \sin ^2\beta + \sigma_v \cos ^2\beta - p$, $ \bar{s}_\tau = (\sigma _n - \sigma _v)\sin \beta \cos \beta $, $c$为裂缝半长, $\beta$为裂缝与坐标系$x$轴的夹角$( 0 \leq \beta \leq \pi / 2)$, $ P$为裂缝面作用水压力, $ q$为接触压力, $ \tau $为摩擦力, $\sigma _n$为水平地应力, $ \sigma _v $为垂直地应力, $ E$为页岩基质的杨氏模量,$ v$为泊松比, $ G_{mc} $为基质的断裂韧性, $ G_{dc}$为弱面的断裂韧性,最大应变能释放率对应角度由下式确定

$$ \theta _0 = \pm a\cos \left( {\dfrac{3\bar{s}_\tau ^2+ \sqrt {\bar{s}_q^2 (\bar{s}_q^2 + 8\bar{s}_\tau ^2 )}}{\bar{s}_q^2 + 9\bar{s}_\tau ^2 }} \right) (3.3)$$

利用上述理论结果, Zeng和Wei(2017)从理论上揭示了三条重要工程规律(如图3.20所示):

(1)随着水压力增大,页岩储层将可能依次经历摩擦锁定阶段、II型(剪切)断裂阶段和混合断裂阶段,而沿弱面II型(剪切)断裂是页岩水力压裂时的主要断裂模式;

(2)裂缝面摩擦系数越小,水力裂缝沿页岩弱面或基质扩展所需的压裂压力越小, 类似地,地应力差越大, 页岩储层也越容易被压裂;

(3)在II型(剪切)断裂阶段,裂缝面摩擦力和地应力之差不影响裂缝扩展方向,而裂缝与弱面之间的入射角是裂缝转向行为的决定因素. 这些理论结果和实验与现场监测反映的情况一致:水力压裂过程中伴随剪切滑移破裂. Zoback等(2012), Hossain等(2000)通过现场监测和室内试验表明水力压裂过程中剪切滑移可能是压裂过程中重要因素.Zoback等(2011)还认定剪切滑移是控制水力压裂的主要因素,这一方面的研究和观察还有待进一步加强,尤其是理论分析、边界条件、破裂形式的现场实验的结合需要更为紧密.

3.9 岩体材料的本构关系

考虑到岩体材料广泛存在页岩油气等非常规能源开采等工程问题(Atkinson 1987, Zhang & Wong 2014, Hoek & Bieniawski 1965)中,涉及塑性变形、损伤及破坏、各向异性、渗透性、多场耦合等(Jaeger et al. 1979, Goodman 1989, Shen et al. 2014).为了更真实地描述、解释和预测岩体材料的力学行为,解决复杂的工程实际岩体力学问题,构建合理的岩体本构关系是岩体力学一直以来的重要研究课题.我们在这一部分介绍目前典型且受到广泛应用的几类页岩本构关系.

3.9.1 脆性破坏理论

岩体的结构复杂, 在岩体基体中存在缺陷、微裂缝及孔隙等微结构,这使得岩体在微观结构上是不连续的. 为了描述材料的固有特性,建立应力应变之间的关系, 在宏观尺度上岩体可认为是连续介质.在工程应用中, 岩体的本构理论最早是从脆性破坏准则的研究开始.库仑最早通过岩土力学实验研究提出了岩体脆性剪切破坏准则,认为岩体抗剪强度由岩体本身的内聚力和剪切面上法向力产生的内摩擦力组成,其形式可表示为$$ \tau = \sigma \tan (\varphi ) + c (3.4) $$式中, $\tau $表示材料的抗剪强度, $\sigma $为剪切面上的正应力,$\varphi $为材料内摩擦角, $c$是材料的内聚力. 库仑强度准则形式简单,不仅适用于岩体压剪破坏, 也适用于结构面压剪破坏,但不适用于受拉破坏.

莫尔通过实验数据的统计分析提出材料在复杂受力状态下的破坏取决于材料的最大主应力和最小主应力.摩尔强度准则的一般形式可表示为$$ \tau = f(\sigma ) (3.5) $$式中, $\tau $表示破坏面上的剪切应力, $\sigma$表示破坏面上的法向应力.摩尔强度准则通过一系列破坏应力极限状态的极限应力圆(莫尔圆)及其包络线(莫尔强度包络线),表示材料受到不同应力作用达到极限状态时,破坏面上法向应力和剪切应力的关系.运用莫尔强度包络线即可判断岩体是否发生破坏.当包络线为直线型时其表达式和库仑准则(式(3.4))一致(见 图3.21),因此由库仑公式表示的摩尔包络线强度准则也称为莫尔--库仑强度准则.莫尔--库仑强度准则是目前岩体力学中应用最广泛的一种理论.

格里菲斯强度理论认为脆性材料的破坏是由内部存在的裂缝在外力作用下扩展、连接和贯通最终形成宏观裂缝所致.通过对初始长度为$2a$的椭圆形裂缝扩展研究,格里菲斯发现裂缝尖端处的有效拉应力$\sigma _t$大于新裂缝形成所需的能量时裂缝开始扩展, 其形式可表达为

$$ \sigma _t \geq \sqrt {\dfrac{2E\gamma }{\pi a}} (3.6)$$

式中, $E$为非破裂材料的弹性模量, $\gamma $为裂缝单位面积的表面能.格里菲斯强度准则的解析形式如下

$$ \left. \begin{array}{ll} (\sigma _1 - \sigma _3 )^2 / (\sigma _1 + \sigma _3 ) = 8\sigma _t, &\quad \sigma _1 + 3\sigma _3 \geq 0\\ \sigma _3 = - \sigma _t, &\quad \sigma _1 + 3\sigma _3 \leq 0 \\ \end{array} \right\} (3.7) $$

格里菲斯强度理论很好地解释了脆性岩体被拉伸破坏的结果,在任何应力状态下, 裂缝尖端产生拉应力集中从而导致裂缝扩展.格里菲斯强度理论只能考虑主要裂缝的张开扩展,忽略了压应力作用下裂缝闭合和缝面上的摩擦力,且不能考虑多裂缝扩展及其相互影响, 不适用于实际工程应用.在此基础上, 还发展出修正格里菲斯理论.

此外,基于大量岩土实验统计分析提出的霍克--布朗准则被广泛采用为岩石强度准则.脆性破坏理论在一定程度上能够合理地解释和预测岩体材料破坏的原因、破坏的形态,确定岩体破坏时的应力状态等宏观力学行为.

3.9.2 弹塑性理论

在工程条件下, 岩体材料常常表现为脆性, 承受很小的应变就发生破坏.随着围压、含水量和温度等因素的变化, 岩体能承受的应变量逐渐增大,在破坏前常常会产生不可逆的非线性变形特征, 在宏观上表现出塑性行为.区别于传统弹塑性理论,岩体材料的塑性理论需要考虑屈服对静水压力的敏感性、减胀和扩容、应变软化和弹塑性耦合等现象(王仁和殷有泉 1981). 岩体材料屈服函数的一般形式可表示为

$ f(\sigma,\gamma ) = 0 (3.8) $

式中, $\sigma $表示应力, $\gamma $为描述塑性的内部变量.Drucker-Prager屈服准则考虑了静水压力的影响被广泛用于岩土材料,其表示式为

$$ f = \alpha I_1 + \sqrt {J_2 } - k = 0 (3.9) $$

式中, $\varphi $为应力第一不变量, $J_2 = S_{ij} S_{ij} / 2$(其中$S_{ij} = \sigma _{ij} - \sigma _{kk} \delta _{ij} /3)$为应力偏量第二不变量, $\alpha$和$k$为和岩体内聚力$c$及内摩擦角$\varphi $相关的系数.当参数$\alpha = 0$时, Drucker-Prager准则退化为Von-Mises屈服准则.

岩体材料的体积在塑性变形过程中存在减胀和扩容现象,非关联性流动准则通过增大相应的塑性势函数来描述塑性体积变形. 例如,Drucker-Prager屈服准则相应的塑性势函数$G$可表示为

$$ G = \theta \alpha I_1 + \sqrt {J_2 } - k (3.10) $$

式中, $\theta $是材料常数, 通常有$\theta \in \left[ {0,1}\right]$, 其中$\theta = 1$时表示是关联流动.

弹塑性本构理论能够简单直接地描述准脆性岩体材料的基本力学行为,被广泛应用于岩体力学研究和工程应用.许多学者在弹塑性理论的基础上引入新的理论来不断完善和补充岩体的本构理论.例如通过引入强化函数、损伤参数、温度参数、水含量参数、时间参数等,进一步研究了岩体材料的硬化和软化现象、温度、水力耦合行为以及时效性变形等长短期力学行为(Adachi& Oka 1995; Lomov et al. 2002; Shao et al. 2006, 2003).

3.9.3 损伤力学理论

岩体在细(微)观上存在大量的微裂隙、孔洞、矿物夹杂和层面等微结构,这些微结构在外力作用下不断产生、发展形成不可逆变形,累积到一定程度后使材料产生宏观裂纹导致破坏.在热力学理论和弹塑性理论的框架内,通过引入损伤变量和损伤演化方程建立损伤本构方程,能更有效地描述岩体材料由内部损伤演化引起的宏观渐进式破坏过程(陈良森和李长春1992).

对于准脆性岩体材料,微裂缝引起的材料劣化可通过引入各向同性损伤变量$d$来描述材料损伤的程度.$d = 0$表示材料无损伤, $d = 1$表示完全损伤(破坏),介于两者之间的状态表示损伤过程区.岩体材料发生损伤后的有效弹性刚度矩阵$D$可表示为损伤参数$d$的函数

$$ D(d) = 2\mu (d)K + 3k(d)J (3.11) $$

式中, $\mu \left( d \right)$和$k\left( d\right)$分别表示损伤材料的剪切模量和体积模量, $K = \delta \otimes\delta - J$和$J = \delta \otimes \delta /3$分别代表材料的体积四阶张量和偏四阶张量, $\delta $是二阶单位张量.损伤的演化方程可由热力学损伤应变能释放率表示为(Krajcinovic &Fonseka 1981; Chaboche 1988a, 1988b)

$$\dot{d} = \dfrac{\partial \psi }{\partial Y} (3.12)$$

式中, $\psi $是耗散势能, $Y$是广义热力学力.Kachanov和Lemaitre利用有效应力概念和应变等效假设定义了二阶损伤张量,更有效地描述了变形的特征(Lemaitre 1985).Dragon和Morz以及Kachanov等定义了裂缝密度张量作为损伤变量,有效地反映了损伤的程度, 但不能区分损伤演化和损伤本身(Lubarda &Krajcinovic 1993). 在连续损伤力学理论的基础上,许多学者在热力学框架下建立弹塑性--损伤耦合模型,研究了岩体材料矿物成分及水含量等因素对岩体材料力学性能的影响(Lemaitre 1985).

在宏观损伤理论的基础上, 细观损伤模型考虑了损伤的具体形式,例如微裂纹、微孔洞等,损伤变量不再是宏观唯象参数而是具有真实物理意义的参数.Hori和Nemat-Nasser通过实验和理论研究了微裂隙的闭合、摩擦滑移、晶界扩展等现象对岩体材料有效模量的影响(Nemat-Nasser & Hori 1993).Bazant等提出的分布断裂力学理论充分考虑了微裂隙群的演化特征及其对宏观力学行为的影响(Bazant 1986).

3.9.4 微平面模型本构理论

微平面模型本构理论的思想由Taylor在处理晶体塑性时提出,经过Batdorf和Budiansky、Zienkiewicz和Pande和Bazant等的发展和改进被广泛应用于岩土材料(Bazant& Planas 1997).微平面模型从微观结构入手研究岩体的微平面非弹性变形行为、强度特性、微结构(微裂隙等)特征及其演化机理,通过建立微平面上的微观力学本构关系,从而推导出合理的宏观本构模型来描述岩体的弹塑性变形行为、损伤演化及各向异性等力学行为(Bazant& Oh 1985; Bazant & Prat 1987, 1988).

微平面模型的示意图和流程图如 图3.22和 图3.23所示,微平面的方向由单位法向量$n$来定义( 图3.22(a)),通过几何关系将微元体上的宏观应变张量$E_{ij} $投影到相应微平面上,然后在各微平面上建立微观应变和微观应力的关系,通过虚功原理建立这些微观应力分量和宏观应力张量之间的关系,从而得到宏观应力张量$\sum_{ij} $.在建立微平面非线性应力应变关系时,微平面模型引入了应力应变边界的概念. 基于一些合理的假设,微平面模型经过几代的发展(从模型M0到M7)建立了一套针对于具有复杂微观结构的混凝土材料的本构模型,来描述、模拟和预测材料的非线性、破坏和各向异性等力学行为,并成功应用到岩土材料, 例如黏土岩及其各向异性特征等 (Bazant & Prat 1987).

3.10 本节小结

目前全世界范围内掀起了页岩油气开采技术研究的热潮,其中一个重要组成部分就是页岩的力学行为表征研究. 总体来看,页岩的力学行为主要受层理、矿物组分、有机质含量、含水饱和度、天然裂隙、围压、温度等因素的影响.页岩组分种类多样, 含量变化大,且其天然缝隙等微观结构的形态具有很大随机性,因此不同地区页岩的力学性能差异很大. 通过回顾以往研究成果,有以下基本结论:

(1)不同地区页岩的裂缝宽度和长度分布差别很大,人们难以建立一个通用模型去描述不同地区页岩裂缝的形态分布,但天然裂缝分布方向的规律比较明显,因此需对更多地区页岩储层的裂缝分布形态进行统计和总结,其中裂缝分布方向应为重点.

(2)从矿物组成和弹性模量两方面评价页岩储层的脆性在矿场实践中都有成功经验,脆性是一个综合评价指标, 受自身非均质性和外在测试环境共同影响,但脆性概念底层的科学问题及其与断裂韧性等断裂参数的关系仍是一个亟待研究的课题.

(3)页岩具有显著的各向异性特征, 可视为横观各向同性复合材料,其杨氏模量、泊松比、断裂强度等在不同方向上差异较大,且与组分、围压、温度等因素有关.通过实验分析各个因素对页岩某个力学性能参数的影响是困难的,可通过数值方法对各因素的影响进行单独分析,然后根据各结果来组合构建页岩的本构模型.

(4)页岩中弱面的强度和断裂韧性对水力裂缝的扩展行为具有重要影响,另外页岩宏观弹性性质的各向异性、页岩基质的强度和断裂韧性、裂缝面的摩擦力、水力裂缝入射角等都将影响水力裂缝的扩展行为.

(5)岩体材料在微观结构上的不均匀性、不连续性和各向异性等特征使得岩体的力学行为非常复杂,单一的本构理论很难全面的反映岩体材料的力学行为.

(6)温度影响是另一个值得深入的方向.尽管研究者在模拟中将水力压裂过程中温度因素忽略,但是在高温油气藏或者干热岩是应该考虑的(彪仿骏等 2011).

尽管岩体脆性破坏理论在工程应用中能有效地解释和预测岩体破坏等现象,但忽略了材料内部特征及其物理机理.目前的微观损伤力学理论、分布式断裂力学理论能充分考虑微观结构对宏观力学行为的影响;而微平面模型通过结合材料微观特征建立最优化的微观本构模型,可有效描述岩体材料非线性、破坏、各向异性和时效变形等力学行为.如何进一步完善从岩体材料微观特性、变形物理机理出发的宏观本构理论,使其能准确、真实地反映岩体在不同载荷历程和不同观察窗口下的力学行为,为水力压裂设计方案提供充分的理论依据,可能是页岩本构模型发展的方向所在.

4 页岩气藏实验模拟技术^*(*本节撰稿人:胡志明¹ (1 E-mail: Huzhiming69@petrochina.com.cn), 端祥刚, 高树生, 沈瑞, 常进)

4.1 引言

页岩气藏为自生自储的非常规气藏, 具有独特的储层特征,基质孔隙度低、发育多类型微纳米级孔隙; 页岩基质渗透率极低,主要靠扩散和裂缝渗流形成有效导流能力(杨峰等 2013, Gensterblum et al. 2015).因此需要针对页岩储层特征和渗流特征进行一些特殊的实验和理论研究,目前室内实验能够得到孔隙大小分布、渗透率以及扩散系数等特征系数,但是对页岩纳微米级孔隙的研究深入程度以及气体在页岩中的流动能力研究较少,本文在大量调研国内外页岩实验方法和测试技术的基础上,总结了页岩储层评价技术、开发模拟实验技术和含气量计算方法等方面的研究进展,结合中国科学院渗流研究所非常规实验室的研究成果,探讨了页岩的孔隙结构特征、气体赋存与扩散机理、储层吸水特征、耦合流动规律和含气量计算方法.研究结果表明, 页岩储层渗透率和孔隙度极低, 大量发育纳米级有机质孔,以介孔$(2\sim 50$nm)和微孔$(<2$nm)为主,为吸附气赋存的主要空间;目前常规测试的低压吸附等温实验难以完全表征储层条件下的页岩气等温吸附过程,需要针对性研究高压等温吸附实验和模型.针对性设计的页岩流动与开发模拟实验有效揭示了页岩传质输运和衰竭开发规律,建立的流态辨识图版、基质压力传播规律图版和解吸区域分析方法,为明确压力传播规律及建立数学模型奠定基础.建立的3种计算页岩含气量方法能够充分利用孔径分布、等温吸附曲线及测井数据等基础资料表征含气特征,还原页岩气的原始赋存状态, 从而更为准确的计算含气量.论文对于全面认识页岩气储层特征、开发机理、开发动态及储量评价具有重要的指导与实践意义,是页岩气有效开发的重要基础理论之一.

4.2 页岩储层评价技术

页岩的孔隙结构特征是影响气体在页岩中流动能力的主要因素之一,孔隙结构研究与页岩气的赋存状态以及资源量的评价密切相关(张琴等 2015). 由于页岩孔隙结构复杂, 孔隙非常微小,常规的孔隙结构研究方法不再适用,超高压压汞、BET比表面法、核磁共振法、超高倍电子显微镜、氩离子抛光电子显微镜、CT扫描等方法被运用到页岩孔隙结构研究(Wang et al. 2009).美国和加拿大等国家通过这些手段对页岩气藏的孔隙结构进行了研究,发现页岩中各种不同的孔隙主要分布在$0.38 \sim 150$nm之间(Josh et al. 2012).

4.2.1 微观结构测试技术

页岩的矿物组成和孔隙结构复杂, 在研究页岩的微孔结构时,用常规扫描电子显微镜分析孔隙、裂缝、有机质等结构时,往往会出现相同的图像效果, 不能反映页岩的微观结构.目前使用的射线探测法包括光学显微镜、扫描电子显微镜、透射电子显微镜、小角度X射线和中子散射(Josh et al. 2012). 光学显微镜仅仅能够观察到非常规储层的最大孔隙,对于了解埋藏条件和孔隙度类型(如粒间空隙、粒内孔隙、裂隙)效果不大(Perdomo et al. 2010). 样品表面经氩离子抛光处理后,场发射扫描电镜照片能较好地观察样品的形貌、孔隙率、有机质等矿物晶体,甚至填充形貌.一些研究人员运用3D技术建立孔隙体积的立体结构(Sondergeld et al.2010), 但是这些孔隙体积都是微米级的, 在工程实际中很难增大.扫描透射电子显微镜(STEM)最近也用于泥页岩的研究,能够观察到更小的孔隙结构, 但是随着样品体积的增大,这种方法不再适用(Passey et al. 2010).

聚焦离子束扫描电镜(FIB-SEM)用聚焦离子束代替扫描电镜及透射电镜中所用的质量很小的电子对样品进行连续切割,同时在电子束下成像, 不仅具有较高的分辨率,还避免了制样过程中产生的人造孔隙,能够真实地还原页岩中孔隙的三维结构特征,提供了一种研究页岩纳米级孔隙结构的新方法(Curtis et al. 2010,Holzer et al. 2004). 成像扫描技术(CT)也是一种很好的无损检测方法,通过X 射线获得样品的密度, 同时对基质和孔隙流体进行成像,根据成像材料的密度在三维空间中可以清楚地分辨出页岩孔隙空间的连通性、流体分布.而高分辨率的Micro-CT技术则可以观察更小的岩样并且可以得到更高分辨率的成像(Elgmati et al. 2011, Grochau et al. 2010). Josh et al.(2012)使用Micro-CT扫描和FIB-SEM方法对页岩进行了三维重构(图4.1), 图4.1(a)可以清晰地看出岩样裂缝的几何形状,即使在很小的体积就可以很清楚的辨别出有几个较窄且细长的裂纹,这些裂纹几乎是相互平行的.页岩内部三维结构是通过许多单个的图像堆砌而成的(图4.1(b)),其中蓝色的表面代表低长宽比的裂纹, 红色的部分是黄铁矿颗粒.在三维空间中对裂隙几何形态和分布的构建对解释储层的各向异性和预测页岩的力学性质及压裂情况具有非常重要的意义.

本研究室采用聚焦离子束扫描电镜(FIB-SEM)对四川盆地龙马溪组的页岩样品进行了大量的分析,部分扫描结果如图4.2. 图中可以清晰看出页岩岩心的孔隙结构特征,页岩内部普遍发育有机质孔隙、粒间孔、粒内孔等孔隙,有机质中发育大量孔隙, 因此比较集中;有机质孔隙大小往往与有机质成熟度相关,成熟度较低的有机质的孔径较大, 而成熟度较高的有机质的孔径较小(Kuila et al. 2011). 有机质孔发育程度差异性较大,有机质孔与非有机质孔隙的相对比例也存在较大差异.基质储集空间主要为有机质孔隙、无机粒内孔隙(黄铁矿、黏土)、粒间孔隙及微裂缝.孔隙尺度分布广泛, 主要分布在$0.5\sim 500$nm之间;通过扫描图片不难发现页岩中存在很多微孔(孔隙直径小于2nm),这正是页岩具有吸附特性的一个决定性因素.

4.2.2 孔径分布测试技术

页岩储层的孔隙尺寸分布从纳米到微米尺度,常规的单一孔隙结构研究方法难以获取页岩的全尺度孔隙尺度分布,目前常采用超高压压汞法、气体吸附法、NMR弛豫谱方法和小角度中子探测方法来获取页岩的孔径分布(蒲泊伶等 2010). 高压压汞的压力可以达到418MPa,最高压力下对应的孔隙半径大约为4nm (谢晓永等 2006),低温吸附法测定固体比表面和孔径分布是依据气体在固体表面的吸附规律,氮气等温吸(脱)附线按照毛细凝聚理论,利用BJH法可测定的孔径范围是$2\sim 50$nm.而对于孔隙小于2nm的微孔隙,比表面法采用CO$_{2}$气体在0${^\circ}$C (冰水浴)等温吸附法测定,这是因为CO$_{2}$气体可以进入0.35nm的孔隙,进而通过D-R理论模型可以计算微孔分布(杨峰等 2013).

NMR弛豫谱方法是一种非直接、宏观测量孔隙大小分布的方法(李军等 2016), Sondergeld等(2010)测量了Barnett页岩的NMR弛豫谱图,通过T2弛豫时间, 算的孔隙半径在$5\sim 150$nm的范围.NMR方法的T2谱分布能够将自由水(FFI)和束缚水(BVI)的体积分开,还可以用来测量页岩中的可动流体饱和度.小角度中子探测(SANS)和超小角度中子探测(USANS)已经用于测定煤层气储层样品的基质孔隙大小分布(夏庆中等 2005).这种方法的独特之处在于可在高温和高压条件(模拟地层条件)下开展实验,能够观察到孔隙度作为压力的函数随压力变化的过程,确定孔隙连通和闭合的临界条件(Ross et al. 2009).

高压压汞法、液氮吸附法以及低温CO$_{2}$吸附法是目前最常用的测试方法,其所测量的范围不同, 因此在页岩孔隙大小分布测量中,将这3种方法有机结合起来可以得到完整的孔隙分布.采用Poremaster高压压汞仪器研究龙马溪组页岩样品的微观孔隙结构分析(图4.3(a)), 可以看出孔径分布差异较明显, 孔径分布呈双峰形态,最大峰值出现在6nm左右, 第二峰值出现在$700\sim 1000$nm左右.采用Autosorb-6B液氮吸附仪测试同一组页岩样品, 测量结果(图4.3(b))发现直径为10nm及以下的孔隙的总体积占总孔隙体积的$30%\sim50%$, 而且平均孔隙半径越小,10nm及以下的孔隙所占的孔隙体积越大,说明小孔及微孔对孔隙体积贡献较大.采用CO$_{2}$吸附法测试的更小范围的孔隙半径如图4.3(c),由于二氧化碳分子的平均动能比液氮分子的平均动能大,可以进入孔径小于2nm的孔隙, 测量的孔隙尺寸也更精确.

根据各种方法的最佳测量范围, 大于50nm孔径选择高压压汞的测量结果,液氮吸附的适用范围为$2\sim 50$nm,低于2nm选择CO$_{2}$吸附的测试结果,将不同尺度范围的测试结果通过有效拼接的方式可获取页岩全尺度孔径分布曲线(图4.4), 从所获取的全尺度孔径分布曲线可以看出,该方法充分利用了不同仪器的最佳测试范围,获取了从纳米到微米级的孔径分布特征. 可以看出,该样品的微孔和介孔占有比例孔隙的最高, 其中介孔$(2\sim50$nm)所占比例高达60%以上, 微孔的比例约为30%, 宏孔最少.

4.2.3 物性测试技术

页岩孔隙度是游离气储集空间及含气量最主要的控制因素,由于页岩具有一定量的微孔和大量中孔,故常规的充气式测定方法难以测到全部孔隙空间,因此需要更高充气压力的氦孔隙度仪,或者在原有测试压力条件下延长测试时间(Ross et al. 2009).采用气体膨胀方法测量页岩孔隙度时, 由于页岩的渗透率极低,气体流动缓慢, 需要准确测量孔隙度所需要的时间长, 为此Soeder等(1988)提出利用气体膨胀法测量压碎后的页岩样品孔隙度的方法,该方法的问题在于页岩被压碎后使得原本不连通的死孔隙变得连通,因此压碎后测量得到的孔隙度属于绝对孔隙度,而用岩心柱测量得到的孔隙度为有效孔隙度, 柱体内部颗粒完整,气体不能充入岩样内的死孔隙.采用不同方法测量的孔隙度值对比结果如图4.5(a), 可以看出,采用柱体测得的孔隙度介于吸附法和密度法中间,采用低温氮气吸附法测定的孔体积和颗粒密度计算的孔隙度值不确定性较大,颗粒密度法由于对样品的微孔和大孔体积的测定存在偏差,偏差大小与样品中发育的孔隙情况和样品粉碎程度有关.吸附法同样测试的是粉碎样品, 测试原始孔隙度的结果略高.本研究室通过大量实验,建立了通过合理延长测试时间获取有效孔隙度的方法,使用氦气膨胀法测量了龙马溪组页岩岩心柱的孔隙度(图4.5(b)),实验结果表明该地区样品的孔隙度较小, 基本上在2%$\sim$ 4%的范围.

页岩的渗透率极低, 目前测试渗透率的方法一般为稳态法和非稳态法,采用稳态法测试渗透率时, 由于页岩流体流动速率很小,通过岩样的微小流量难以直接测量, 而且达到稳态流动需要时间很长,测试难度大(Wang et al. 2009). Rushing等(2004)研究表明采用非稳态法测量的气测渗透率值(考虑滑移修正)要高于稳态法测量的渗透率值.Freeman和Bush(1983)的研究表明稳态法和非稳态法测量的渗透率值误差小于5%,渗透率越低, 这种差异越明显.

压力剖面衰减法、脉冲衰减法、压力衰减-破碎法和孔隙压力震荡法(流动)是实验室常用的非稳态测量岩石渗透率的方法.Brace等(1968)提出利用岩心柱脉冲衰减渗透率测试法测量页岩渗透率,缺点是如果页岩样品存在天然裂缝或者人工诱导裂缝,测试渗透率为样品基质和裂缝渗透率的合成, 难以区分基质和裂缝的性质.岩屑脉冲衰减法通过测量岩心切片或钻井岩屑在原始含水饱和度条件下的渗透率可以准确获得页岩基质渗透率,但是这种方法的弊端在于该方法只能在没有围压的条件下进行测试,不能反映地层条件下基质渗透率情况,其次页岩中本来发育的天然裂缝的渗透率也无法获得(Loucks et al.2012). Ghanizadeh等(2014)研究Duvernay地层的岩样发现,干燥岩样剖面衰减法测量的渗透率高于脉冲衰减法渗透率和破碎法测量渗透率.脉冲渗透率可能高于或者等于破碎渗透率,这取决于脉冲法的岩性和有效应力状态,脉冲渗透率更多测量的是流动方向上的渗透率,而破碎渗透率则是测量多个方向上的渗透率(Clarkson et al. 2012,卓仁燕等 2016). 采用PoroPerm-200型孔渗仪和流动法测得岩心柱脉冲渗透率如图4.6. 可以看出,该地区的渗透率大部分在$0.001\sim 0.1$mD的渗透率范围,脉冲渗透率稍高于克氏渗透率, 二者具有较好的相关性(图4.6(b)),由于氦气脉冲渗透率测试速度较快,经过脉冲渗透率测试后可利用其与克式渗透率之间的关系得出相应的克氏(绝对)渗透率.

4.2.4 吸附气测量技术

据统计, 吸附态页岩气含量占页岩气总含量的$20%\sim 85%$,美国沃思堡盆地Barnett页岩气吸附量在$38%\sim 72%$ (Curtis et al. 2011), 当油藏压力很高时, 吸附气对气体的采收率影响不大(Jarvie et al. 2007), 然而在油田生产的后期,吸附气的解吸对产量和储量产生非常重要的影响.测量吸附气的等温吸附曲线可分为静态法和动态法两种.静态法测试精度较高, 包括经典的容积法(volumetricmethod)和重量法(gravimetric method)(Zuo et al. 2014),其实验方法和实验设备已经非常成熟,目前大部分研究都是基于这两种方法.近年来开发的电磁法(electro-magneticmethod)和振荡法(oscillometricmethod)虽然测试精度较高, 但由于价格昂贵, 尚未得到普遍的应用(Keller et al. 2011). 动态法中包括穿透法和色谱法,穿透法是在进口浓度保持一定的条件下,同时测量出口气体浓度来计算吸附量, 色谱法是通过注入一个脉冲气体量,测量其保留时间. 动态法获得数据较快, 但其测试精度没有静态法好,实验过程中影响因素较多, 对仪器的依赖性较强(Zuo et al. 2015). 目前页岩气的吸附规律通常沿用煤层气的测试方法和理论,等温吸附曲线的测试温度、压力偏低(15MPa),远远低于目前开发储层的温度和压力(长宁--威远: $30\sim 60$MPa),不能真实反映储层气体的吸附和解吸规律. 为获取储层的吸附气量,通常的做法是采用低压的测试结果,然后利用Langmuir模型获得高压等温吸附曲线,近几年的研究表明(Gasparik et al. 2015, Alexej et al. 2016),高压下页岩的等温吸附曲线与低压规律具有不同的趋势, 采用常规的Langmuir模型也无法描述高压下的等温吸附曲线, 如图4.7(b).

为研究储层压力的等温吸附规律,采用美国CORELAB公司的GAI-100高压气体等温吸附仪(图4.8(a))最大工作压力为69MPa,其压力传感器精度达到最大量程的0.05%,恒温油浴最高可达177${^\circ}$C, 控制精度为0.1${^\circ}$;整个仪器有3个独立的测试单元, 可以单独或同时进行测试.

威远地区测试最大过剩吸附量为$1\sim 2$m$^{3}$/t,样品的吸附量存在一定的差异性, 虽然取样样品都来自于龙马溪组,但是样品的TOC、黏土矿物、温度等因素都会对吸附气量产生影响.从页岩等温吸附曲线可以看出, 随着压力的增大,吸附量曲线先上升后下降,等温吸附曲线具有超临界高压等温吸附曲线的典型特征,这与低压下页岩等温吸附曲线单调递增的形态不同,说明实验室直接测得的吸附量是过剩吸附量而不是绝对吸附量(真实吸附量),Gibbs所定义的过剩吸附量为

$n_{\rm exc}=n_{\rm abs}-V_{\rm a}\rho_{\rm g}=V_{\rm a}(\rho_{\rm a}-\rho_{\rm g}) (4.1)$

式中, $n_{\rm exc}$为过剩吸附量, $n_{\rm abs}$为绝对吸附量,$V_{\rm a}$为吸附相的体积, $\rho _{\rm a}$与$\rho _{\rm g}$分别为吸附相与体相气体的密度.超临界条件下的吸附量不再随着压力的增大单调递增,当游离相密度和吸附相密度的增大速率相同时, 会出现一个最大值,之后随着压力继续升高, 吸附量反而下降,这是由于吸附相密度与体相密度之差导致的.事实上页岩的绝对吸附量会随着压力的增加而增加直到饱和,即绝对等温吸附曲线是压力的单调递增函数,所以即使实验的温度、压力达到储层条件直接测出的吸附量也无法作为储层条件下页岩的真实吸附量.选取吸附曲线的最大值所对应的压力为页岩的临界解吸压力,因为当系统压力大于这个压力值时过剩吸附量随压力增加而降低.当系统压力小于这个压力时页岩会发生大量的解吸,所以当页岩气藏压力高于临界解吸压力时, 页岩气井基本不会产出吸附气.

目前普遍利用亚临界吸附模型及其改进形式来描述页岩超临界等温吸附数据,但这些模型与页岩超临界吸附背景相悖, 缺乏明确的物理意义,如采用常规的Langmuir理论来拟合往往出现偏差, Rexer等(2013)用修正的DR方程和Langmuir方程模拟了超临界吸附. Clarkson等(2013)讨论了扩展的Langmuir方程及DR方程模拟超临界单组分吸附, Heller等(2014)研究Langmuir模型拟合所获取的等温吸附曲线,侯晓伟等(2015)结合D-A和Langmuir-Freundlich模型建立了一个可以描述$0\sim20$MPa下页岩超临界等温吸附曲线的模型. Chareonsuppanimit等(2012)用简化局部函数理论对页岩的吸附等温曲线进行了模拟,认为该方法可以用来模拟高压条件下页岩等温吸附曲线.不同模型在不同程度上都可以对页岩等温吸附曲线有一定的拟合精度,但是都有一定的局限性.

4.2.5 扩散能力测试技术

气藏中平流是气体运移的主要模式, 它是由压力梯度引起的,由于气体的压缩性, 气体的压力梯度直接导致了气体浓度梯度,所以扩散和平流运移两者共同存在.在常规气藏中由于浓度差异造成的扩散运移不是很重要,但是页岩的基质渗透率低到只有数纳达西, 在如此低的渗透率下,气体扩散对运移能力的贡献就显得尤为重要(王瑞等 2013).

页岩气体的扩散包括Fick扩散、Knudsen扩散、过渡型扩散和表面扩散(Keller et al. 1995).表面扩散与体相气体的黏性流动和努森扩散共存,在页岩微孔$(<2$nm)和强吸附的条件下,气体传输以表面扩散为主(Harpalani et al. 1996), Shi等(2013)通过实验和理论模型研究表明,纳米孔气体传输机理主要包括体相传输和表面扩散.表面扩散是吸附气分子的活化过程, 在低温或者低压条件下,表面扩散甚至更为重要, 表面扩散量是体相传输量的 $20\sim 30 $倍.李武广等(2016)认为基质岩块中不存在达西渗流,渗透率和扩散系数的意义一致,因此采用压力脉冲测渗透率的方法测量扩散系数.

采用游离烃浓度法(黄志龙等 1996)测试页岩有效扩散系数时,首先需要在岩心两端的扩散室中充入不同类型的气体(甲烷和氮气),并保持两端的气体总压相等(无压差). 在浓度梯度作用下,组分气体将逐渐从岩心一端扩散到另一端.通过监测不同时间段两扩散室中气体组分的浓度变化,代入计算模型即可得到相应的有效扩散系数. Harpalani等(1995)研究了煤层甲烷气体扩散系数(图4.9),首先装有煤层岩心样本的容器(SC)中充入高压甲烷浸入岩心,然后氦气以同样的压力注入到样本容器中,同时周期性将混合气体排入固定容器(FV)中, 保持样本容器压力不变,因此建立样品内外的甲烷气浓度差,因此得到甲烷的分压差随着时间的变化关系.该方法的优点是岩心内外无压力差, 流动为纯扩散,但是无法估算氦气的存在对甲烷流动产生的影响.

时滞法要求将天然气由入口端不断注入,让其从很薄的岩样(厚约2mm)经扩散后进入出口端,用氮气或空气不断地将其扩散过来的天然气带走, 使此端烃浓度保持为零.用色谱仪测定扩散的烃物质总量, 并记下相应的时间. 重复多次记录后,可得到时间与烃总量曲线图, 将曲线后半部(近似直线部分)延长,交于时间轴上一点$t_{o}$, 称为滞迟时间,然后通过公式计算扩散系数(Krooss et al. 1988).

为研究页岩中甲烷的扩散能力,本研究室建立了近平衡态扩散流量实验装置(图4.10(a))采用微压差的方法降低总流量中的达西流量,在岩心两侧分别接上充满甲烷的中间容器,然后在初始时刻两侧中间容器保持微小压差,随着甲烷在流过岩心的过程中, 两侧中间容器的压差逐渐减小,直至压差趋于零.在近平衡条件下采用了体相相减法和达西公式计算了总流量和达西流量,获得的黏性流量和扩散流量结果如图4.10(b).

近平衡态实验结果(图4.10(b))可以看出, 随着时间的延长,入口和出口的岩心压差越小, 达西流量所占的比重越小,扩散流量比重越大. 微压差条件下实验流量远大于达西理论流量,压差越小扩散比重越大, 可以达到50%以上,因此扩散是页岩开发主要的传质机理,以常规测试方法获得的渗透率不足以表达储层流动能力,储层真实流动能力被严重低估.

4.2.6 储层吸水特征测试技术

页岩储层开发时必须依靠大规模压裂来获得可观的工业气流,但是与致密砂岩气藏相比, 页岩储层普遍存在压裂液返排率低的现象.国外页岩气井生产一年后压裂液返排率平均仅为$35%\sim 62%$(高树生等 2013), 这说明有大量的压裂液依旧残留在地层中.残留的压裂液去向是大家非常关注的一个问题,由于页岩压裂的压裂液中水含量一般都大于90%,水的存在对于页岩气的流动以及页岩气的解吸都会有影响,因此从机理上认识水在页岩中的存在方式对提高压裂液返排率以及提高页岩气的产气能力提供理论依据(Willberg et al. 1998).

Chenevert等(1970)利用Mancos页岩、Willington页岩及Pierre页岩岩心,对泥页岩在不同水活动度溶液中的膨胀动力学过程进行了全面深入的研究.实验证明, 泥页岩的膨胀百分比与其所吸的水分重量百分比成正比.页岩膨胀是水化的结果, 故可以用膨胀的程度来说明水化程度.先测干页岩的体积, 再测页岩与试液接触一定时间后的体积,膨胀率的大小表征页岩水化的强弱, 膨胀率愈大说明水化愈严重,因此通过页岩膨胀性实验可以定性研究页岩在不同液体中的吸水能力.

实验使用瓦氏WZ-1型膨胀仪(图4.11(a)),由于该仪器在径向上受到刚性约束, 那么体积的变化只呈现在轴线方向.因此用它可以测得一定精度的轴向线膨胀量和线膨胀百分数(即膨胀率,膨胀高度与原始样品高度之比).测得QJ某井段岩心粉碎后的实验结果可以看出(图4.11(b)),页岩在蒸馏水中的膨胀率最高, 接近20%;而压裂液中页岩的膨胀率比地层水和蒸馏水的明显低很多,说明了压裂液在抑制页岩吸水膨胀方面有不错的效果.

由于页岩的吸水膨胀实验是在页岩粉末压实后的样品上进行的,因此它反映的是页岩在不同液体中整体吸水的能力. 而在实际地层情况下,页岩是以致密岩石的形状存在的,因此进行页岩储层岩心吸水能力实验是研究页岩储层吸水能力的必要条件.

因此改进的实验方法如下: 为了统一实验标准, 将页岩磨成如图4.12(a)所示的大小均匀的薄片, 薄片的厚度为3.45mm;然后将小薄片烘干$(100{^\circ}{\rm C})$ 48h后冷却,将页岩块悬挂在天平上, 沉入需要测试的液体中,记录页岩吸水后质量随时间的变化.

实验过程中使用的液体分别为蒸馏水、地层水、压裂液A和压裂液B.实验结果如图4.12(b)所示, 页岩在蒸馏水中的吸水能力最大,最大单位面积吸液量为0.0158cm$^{3}$/cm$^{2}$;在地层水中的吸水能力次之,最大单位面积吸液量为0.0114cm$^{3}$/cm$^{2}$;在压裂液B中的吸水能力最弱,最大单位面积吸液量为0.009cm$^{3}$/cm$^{2}$.这与页岩粉末样品吸水膨胀能力测试的结果一致,说明所用压裂液能够有效抑制页岩的吸水. 从页岩吸水的力学机制来看,由氢键力、范德华力、渗透水化力以及表面水化力作用的页岩吸水很难返排,而在本实验中, 综合考虑了氢键力、范德华力以及表面水化力的作用影响,实验结果可以定量反映由于这几个因素所造成不能返排的液量.

4.3 开发模拟实验技术

页岩气藏开采中, 气体在页岩中的渗流机理是非常重要的一部分,直接影响着页岩气开采方式的制定以及页岩产气量的预测.气体在孔隙中的渗流过程包括吸附气的解吸、微孔表面至基质孔隙中的扩散、基质孔隙中游离气的扩散和滑脱渗流,以及天然裂缝中的达西渗流.研究页岩中气体生产的物理过程对页岩气藏的评价以及产量优化是非常重要的,建立的物理模型可对其运移机理进行模拟,并为建立数学模型提供有效参数(郭为等 2015).

与常规流动相比, 页岩孔隙中的微纳米尺度流动具有其独特的方面,首先由于纳米流动的临界尺度与流体的分子尺度相当,流体与固体表面之间的相互作用对流体流动影响很大, 不能忽略,因而连续性假设理论在微纳尺度能否适用也值得商榷.目前页岩的流动模型大多基于纳米孔隙的流动规律, 如Javadpour等(2009)提出了一个基于努森扩散和滑移流动叠加来描述页岩纳米孔隙气体流动的公式,并且给出表观渗透率的表达式,指出表观渗透率和达西渗透率的比值在孔隙小于100nm时随着孔隙的减小迅速增加.

Swami等(2012)为模拟真实的气流,用纳米圆管建立了纳米级孔隙流动实验模型(图4.13),模型中有一个被干酪根包围的纳米孔,纳米孔中存在自由(压缩)气体、吸附在孔隙壁面的气体分子及干酪根中的溶解气.初始时整个系统在原始气藏压力下.孔隙的左边界是一个开放的定压边界(井底或者裂缝),右边界是无渗透边界. 生产时最开始是自由气的流动. 随着压力的下降,气体分子从孔隙壁面解吸并从干酪根开始扩散,并通过实验建立了考虑真实气体努森扩散、滑脱效应、解吸及干酪根扩散下的微分方程.

4.3.1 流态实验

页岩微纳米级孔隙发育, 当解吸到基质孔隙中的气体流动时,由于尺度远小于常规的空间尺度, 流动机理也发生了变化.通常依据努森数划分流动形态,对于孔隙半径小于10nm的页岩气流动基本上为滑脱流和过渡流(Wu et al.2014).单相气体滑脱效应主要受到压力、温度、岩石孔隙结构及气体种类等因素的影响(姚约东等 2004). 温度越高, 平均压力越小, 滑脱效应就越明显, 而岩心致密,气体相对分子量小, 也会使滑脱效应显著(Turgay et al. 1986).高树生等(2011)通过实验研究提出孔隙压力较低(小于10MPa)时存在滑脱效应,且浅层储层中滑脱效应显著, 对气井产能的影响很大.杨正明等(2006)认为产生滑脱效应的必要条件是低孔压而非低流速.王勇杰等(2006)提出随着岩心渗透率降低, 滑脱因子增大,滑脱现象更明显.

由于页岩渗透率低, 物理模拟实验难度非常大,因此本研究室建立了流态测试系统(图4.14)来获取流态曲线,用来评价页岩气在真实储层条件下的流动状态. 由于实验压差范围很大,实验系统需要使用不同压力测量仪器来实现精准地压力控制.较低压力条件下(如1MPa以下),高压气瓶通过精密气压控制调节阀与岩心夹持器相连.实验气体经过调压阀, 保持在所需压力范围内流向岩心.较高压力条件下(如1MPa以上), 由ISCO泵提供稳定压力,实验气体从中间容器流向岩心. 当流动稳定后, 通过排水法多次测量流量.由于页岩样品中有大量微纳米孔隙,因此气体流动出现滑脱效应或过渡流、努森扩散等流态.计算不同进口表压下岩心的表观渗透率, 得到氮气流态曲线, 如图4.15所示.

图4.15(a)可以看出, 当平均压力高于2MPa时,气体流动均为滑移流, 表观渗透率随压力降低近似线性缓慢增大,滑移区表观渗透率总体增幅小于1个量级. 平均压力小于0.5MPa时,流态为过渡流, 在极小的压力变幅内, 表观渗透率迅速增大,渗透率较低的岩心表观渗透率可增大1个量级以上. 岩心渗透率越低,滑移流过程表观渗透率也越低, 在产生过渡流后,低渗岩心的表观渗透率增幅更大. 这是由于过渡流存在努森扩散,气体流动不再符合连续介质假设, 低渗岩心的流动通道尺度较小,努森扩散作用相应地更强. 当使用表观渗透率反映岩心流动能力时,由于低压条件下扩散作用的影响, 低渗岩心的流动能力增大更明显.由于努森数由压力和孔径共同决定,除上述的压力界限可以判断岩心样品的气体流态, 当压力水平相同时,孔隙特征尺度成为划分流态的关键参数(Wu et al. 2015).

平均压力倒数曲线(图4.15(b))可以看出,渗透率随着平均压力的不同呈现三段式,在低压段、高压段均会出现非达西渗流, 低压段滑脱效应明显.与致密砂岩相比, 致密砂岩的平均压力倒数与渗透率为直线关系,符合气体滑脱流动规律, 而页岩的平均压力倒数与渗透率出现了弯曲段,可能为吸附/解吸作用引起的.

4.3.2 多测压点耦合传质实验

为模拟甲烷在页岩中的流动状态,自主研发了解吸--扩散--渗流耦合流动实验装置(图4.16),该装置主要包括ISCO泵、高压中间容器、高压甲烷体积流量计、高压氦气体积流量计、高精度压力传感器、岩心夹持器、环压泵、计算机、恒温箱、甲烷监测防爆装置等.实验采用同一块页岩样品, 等距切三段, 中间布测压点,进行流态曲线测试实验.

由于这3个样品的渗透率较低, 气体在岩心中的流动相对缓慢,实验时间更久, 在时间尺度上与开发实际更为类似,更有利于获取长时间下的压力剖面,有助于分析吸附解吸对页岩气在基质中流动的影响规律,测得不同段的渗透率值如图4.17.

从图4.17(a)可以看出, 同样物性的岩心在不同的压力水平下,呈现出不同的渗透率, 越靠近出口段, 压力越低, 岩心的渗透率越高,但是其压力降落也越快, 由于压力水平低, 分子自由程越大,扩散越强导致. 说明平均压力不能完美表征岩心内部压力水平,在高压段岩心流态表明储层压力条件下, 扩散仍是传质的重要机制,可能数倍于渗流.

选取相同时间下各测压点的压力, 作出了相应的压力剖面图(图4.17(b)),从剖面图上可明显看出同一时刻甲烷组实验的压力剖面比氦气组实验的压力剖面陡峭,越到实验后期两压降漏斗相差也越大,说明越到实验后期吸附解吸作用对压降的延缓作用越大.在此类实验的基础上,可以通过建立数值模型计算页岩基质压力传播规律、基质供气能力,形成了页岩气压力传播的部分图版.

4.3.3 全直径岩心地层模拟开发实验

为真实模拟页岩气在地层中的流动, 采用现场取心的全直径岩心,实验岩心长度40cm, 直径10cm,孔隙度低于2.5%、渗透率低于1mD(图4.18(a)).在密闭取心之后在实验室补充甲烷至储层压力,恢复吸附气原始赋存状态至200d,然后采用与现场相同的衰竭开发模式开始放压生产, 实验持续1100多天,目前仍有少量气体产出.

从产出曲线可以看出(见 图4.18(b)), 初期产气量大, 递减速度快,后迅速进入稳产期, 产量递减曲线与单井产量递减曲线相似度很高,成典型L形递减, 前期产量高是由于游离气动用, 随后吸附气动用,实验进入稳产期, 长达1000d,实验产气量变化曲线和实际产气量曲线的变化规律一致,物理模拟很好反映了页岩气初期产气量大、递减速度快、后期稳产期长的特点(李立 2010).

通过实验数据建立数值模型可计算耦合传质实验岩心的压力传播距离,如图4.19所示, 可以看出, 基质的压力传播距离很慢,根据等温吸附曲线可以确定临界解吸压力, 再结合基质压力传播距离模型,就可以研究发生解吸附的区域, 进而计算基质压降漏斗图版.

4.4 含气量计算方法

由于页岩生成与赋存状态的复杂性,导致其含气量预测存在着很大的不确定性,准确估算页岩储层的含气量是页岩气藏合理有效开发的基础与前提,但是如何获取合理有效的含气量, 选择正确的计算方法与评价参数是关键.由于在页岩气藏中溶解气所占比例非常小,一般忽略溶解气对页岩含气量的贡献, 只考虑吸附气和游离气.页岩含气量可以通过分析实验(取心现场解吸和实验室等温吸附实验)和测井解释等两种方法获得.现场解吸法通过取心后解吸罐现场解吸的数据来反求页岩的含气量,但岩心在放入解吸罐之前气体会有所损失, 并且无法确认这种损失规律.此外,取心方式、测定方法及估算方法等诸多因素都会影响损失气量的大小及损失规律,因此该方法的工作量较大、成本较高而且得出的含气量与真实含气量存在较大差异(刘洪林等 2010).等温吸附实验和测井解释计算吸附气量目前大多数采用Langmuir模型计算,无法反应储层条件下的真实吸附气量,目前实验室获取页岩含气量的方法有很多,如董谦等(2012)提出的直接法和间接法、左罗等(2015)提出的利用绝对吸附量计算含气量的可行方法、李武广等(2015)提出的考虑地层温压的吸附气含量计算新模型,还有很多学者都从不同角度提出了储层条件下页岩含气量获取的新方法,其实每种方法都存在各自的优缺点.下面结合本研究室的研究工作提出了3种计算含气量的方法.

4.4.1 等温吸附法

页岩气的储量来自于游离气与吸附气两部分,且二者都随孔隙压力增大而增大.由于页岩孔隙表面的吸附气体积测试的不确定性,因此很难准确获取特定地层压力下的吸附相体积,当然也就难以确定游离相体积,因此直接用游离相体积气量加上吸附相体积气量来获得页岩气储量就变得不再可行.根据页岩孔隙中游离相与吸附相模型(图4.20),页岩含气量的计算方法为

$n = \left( {\rho _{\rm a} V_{\rm a} + \rho _{\rm f} V_{\rm f} }\right)\dfrac{RT_{\rm {sc}} Z_{\rm {sc}} }{M_{\rm r} m_{\rm c}p_{\rm {sc}} } (4.2)$

式中, $n$为页岩含气量, m$^{3}$/t; $\rho _{\rm a}$为吸附相平均密度,g/mL; $\rho _{\rm f}$为游离相密度, g/ml; $V_{\rm a}$为吸附相体积,mL; $V_{\rm f}$为游离相体积, mL; $R$为通用气体常数,$R=8.314$J/(mol$\cdot $K); $T_{\rm sc}$为标准状况下温度, K;$Z_{\rm sc}$为标况下甲烷压缩因子; $M_{\rm r}$为页岩质量, t;$m_{\rm c}$为甲烷分子质量, g/mol; $p_{\rm sc}$为标准状况下压力,Pa.

因为在实验中获取的吸附量是Gibbs过剩吸附量, 可知过剩吸附量计算式为

$n_{\rm {ex}} = \dfrac{\int_{V_{\rm a} } {\left[ {\rho \left( r\right) - \rho _{\rm f} } \right]}{\rm d}r}{M_{\rm r} } =\dfrac{0.0224\left( {\rho _{\rm a} - \rho _{\rm f} }\right)V_{\rm a} }{m_{\rm c} M_{\rm r} } (4.3)$

式中 $n_{\rm ex}$为过剩吸附量, m$^{3}$/t;$\rho(r)$为页岩孔隙中甲烷密度分布, g/mL; $r$为坐标, m,则含气量可以通过过剩吸附量获得

$n = \left[ {n_{\rm {ex}} M_{\rm r} + \rho _{\rm f} \left( {V_{\rm a} + V_{\rm f} } \right)} \right]\dfrac{RT_{\rm {sc}} Z_{\rm {sc}}}{M_{\rm r} m_{\rm c} p_{\rm {sc}} } (4.4)$

从上式可看出, 绝对吸附量的获取通常需要知道吸附相体积,由于其不确定性, 实验中很难准确测试吸附相体积.而本文运用的高温高压等温吸附仪可以方便、准确测试到地层压力温度下页岩的过剩吸附量,再运用室内实验技术可以准确测到页岩样品不含吸附气时的孔隙度$(V_{\rm a} + V_{\rm f})$,此时孔隙度内的游离气加上测试的过剩吸附气即可得到页岩样品的准确含气量.

4.4.2 微观孔隙结构法

该方法采用孔径测试方法,利用高压压汞、氮气吸附和CO$_{2}$吸附获得页岩的全尺度孔径分布,然后结合分子动力学模拟, 根据简化局部函数理论,假设页岩中的孔隙为狭缝型孔隙,根据模型可以计算出不同温度下特定大小孔隙中壁面分子对其中甲烷分子的作用势能在孔道中的分布,进而得到甲烷在孔径中的密度分布, 如图4.21(a)所示. 可以看出,壁面甲烷的密度远高于体相密度, 随着压力升高, 吸附的厚度增大,从而使得吸附体积增大.通过气体在孔径中的密度分布可以计算得到等温吸附曲线(图4.21(b)), 从而计算得到该孔径对应的含气量.

根据黔江1井的全尺度孔径分布特征和分子动力学模拟计算不同孔隙中的含气量(图4.22), 通过耦合叠加可以获得页岩样品的总含气量.

4.4.3 测井资料法

目前测井含气量的计算方法通过获得页岩孔隙度、渗透率、含气饱和度和矿物组成,利用含气饱和度和孔隙度计算游离气量,利用等温吸附模型来计算吸附气量,经过修正相加后得到地层总含气量(郑伟等 2013).但是目前各方法还是采用Langmuir模型来模拟和预测吸附等温线,与前文提到一样, 采用Langmuir等温吸附模型,在高压和地层条件下Langmuir拟合的精度并不准确,因此这些方法都具有一定的局限性(左罗等 2015).

本文提供一种利用高压吸附等温模型结合测井资料的含气量计算方法,首先根据测井曲线获取的全岩及黏土组成及含量与孔隙度,再结合SLD模型预测高压吸附等温线来获取井剖面的含气量,进而获取页岩气开发区块内各井剖面的含气量, 结果如图4.23所示.该方法优点在于利用分子动力学的高压等温吸附模型拟合,能够获取地层条件下的较为准确的吸附气量.

现场含气量测试时取心方式、测定方法及估算方法等诸多因素都会影响损失气量的大小及损失规律,而且工作量大、成本较高;该方法的优势在于可以使用常规方法获取的孔隙度、TOC含量、矿物组分等参数来计算含气量,而且基本能还原页岩气的原始赋存状态, 以此得出的含气量更为准确;其结果还可以与页岩等温曲线预测方法、测井曲线结合快速计算页岩气井剖面上的含气量分布,在时间及财力消耗方面远低于现场测试.

5 本节小结

(1)采用超高压压汞、气体吸附法、核磁共振法、聚焦离子束扫描电镜、CT扫描等方法研究页岩孔隙结构,能够清楚表征页岩的储层特征. 页岩储层渗透率和孔隙度极低,大量发育纳米级有机质孔, 以中孔$(2\sim50$nm)和微孔$(<2$nm)为主, 为吸附气赋存的主要场所.

(2)等温吸附曲线测试存在测试温度、压力偏低(15MPa),高压段吸附规律依靠Langmuir理论拟合不准等问题,高压下的页岩气的过剩吸附量并不是单调递增的关系,因此需要针对高压、超临界条件下的页岩气吸附等温展开实验和模型研究.近平衡态扩散实验表明扩散是页岩开发主要的传质机理,以常规测试方法获得的渗透率不足以表达储层流动能力,储层真实流动能力被低估.

(3)开发模拟实验从宏观上得到了页岩气的流动规律,通过实验数据建立宏观的流态图版、基质压力传播规律图版和解吸区域分析方法,可以实现页岩岩心生产过程的全真模拟,进而反演到单井的流动规律和产量分析, 为页岩气藏的研究提供关键参数.

(4)等温吸附法、孔隙结构法和测井资料法来计算页岩含气量的优点在于充分利用孔径分布、等温吸附曲线及测井数据等基础资料来计算含气量,能还原页岩气的原始赋存状态, 以此得出的含气量更为准确,在时间及财力消耗方面远低于现场测试.

5 页岩气微观流动机制及流固耦合特征^*(*本节撰稿人:刘曰武¹(1 E-mail:lywu@imech.ac.cn), 鲁晓兵, 高大鹏, 李奇, 万义钊)

5.1 引言

页岩气藏是特低孔、特低渗且存在吸附解吸特性的非常规气藏,其储渗空间介于纳微米数量级之间并具有很强的多尺度性,页岩气渗流涵盖了分子尺度、微观尺度及宏观尺度等范围.气体在纳米孔隙中的流动不同于在常规孔隙中的流动, 其存在微尺度效应,因此基于连续介质假设的达西方程不再适用.由于页岩气藏一般处于高压环境, 气体比较稠密,理想气体状态方程也不再适用. 在页岩气微观运移过程中,页岩气解吸与扩散、渗流为一个整体过程, 相互影响, 相互制约.页岩气的产出过程是在微观孔喉、微裂缝、宏观裂缝以及水力裂缝等孔渗空间中多场耦合作用的结果.首先是裂缝中的自由气在压力差作用下流入井筒; 而后随着压力波的传播,吸附在基质表面的吸附气在压降作用、浓度差作用的综合作用下发生解吸,并与原有的自由气体混合后一起运移至裂缝, 最后由裂缝流到井筒.开展页岩气微观渗流机理研究, 有助于揭示页岩气藏中流体运移机制,为后期开展产能评价与预测奠定理论基础.

5.2 页岩气微观流动机制

5.2.1 微观尺度渗流机理研究

5.2.1.1 流动的分区

为了科学区分稀薄气体动力学和经典气体动力学各自研究的区域,定义了一个努森数 $(Kn)$的无量纲参数来加以区分, 努森数的定义为

$ Kn = \dfrac{\lambda }{d} (5.1)$

其中, $\lambda $ 表示气体分子平均自由程, m.对于气体来说平均分子自由程表示的是分子两次碰撞之间通过的平均距离;$d$表示流场的特征长度, m.

根据气体流动和换热机理的不同, 可将流动与传热划分为几个区域 (如图5.1), 在不同区域采用不同的研究方法. 按照$Kn$的大小,可将气体的流动区域划分如下:

(1) $Kn<0.001$, 为连续介质区.此时气体分子之间的碰撞概率远比气体分子与物体之间的碰撞概率高得多,N-S方程和傅里叶导热定律适用,并且在气体与固体的交界处不存在速度滑移和温度跳跃.通常的传热学和流体力学研究的正是这种情形.

(2) $0.001<Kn<0.1$, 为滑移区.此时气体分子之间的碰撞频率仍然比气体分子与物体表面之间的碰撞概率高很多,但是稀薄气体效应已不能忽略.通常采用以下方法处理该区域的流动与传热问题:在广大的气体区域仍采用N-S方程和傅里叶导热定律,而边界条件需考虑气体与固体交界处的速度滑移和温度跳跃.

(3) $0.1<Kn<10$, 为过渡区.此时气体分子之间的碰撞概率与气体分子同物体表面之间的碰撞概率大致相当,都不能认为小到可以忽略,从而不能应用以气体分子之间的碰撞占支配地位为前提的连续介质的处理方法,也不能沿用以气体分子之间碰撞可以忽略为前提的自由分子流区的处理方法.

(4) $Kn>10$, 为自由分子区.此时气体分子之间的碰撞概率比气体分子与物体表面之间的碰撞概率小的多,可以忽略不计, 问题的处理较过渡区大为简化,该区域内流动与传热问题的求解需依靠动理论方法.

5.2.1.2 微观流动过程

页岩基质中含有大量有机质, 而且页岩孔隙大多以纳米孔存在于有机质中(Javadpour 2009). 国际理论与应用化学联合会按纳米孔尺度,将纳米孔分为微孔 (孔隙直径$<2$nm)、介孔 (2$\sim$50nm)和宏孔 $(>50$nm). 在页岩气开发降压过程中,吸附气部分解吸, 有效水动力传输通道增大,同时气体分子平均自由程增加, 气体在孔隙壁面滑脱更加明显,页岩体相气体传输能力大幅度提高. 吸附气除了解吸附,在浓度梯度作用下还发生表面扩散, 其对纳米孔气体传输也起着重要作用.与气体分子之间碰撞相比, 气体分子和纳米孔隙壁面碰撞不可忽略,当努森数较大时, 努森扩散是纳米孔气体的主要传输机理.页岩纳米孔气体传输机制依次如图5.2(a)~图5.2(d)所示.

(1)连续流动

当页岩纳米孔为宏孔, 或气相压力大, 气体平均分子自由程小, 努森数$Kn<10 ^{ - 3}$时, 气体分子间碰撞占主导地位, 气体流动满足连续性条件,为连续流动, 可用Hagen-Poiseuille 方程表达如下

$ J_{\rm V} = - \zeta _{\rm {mb}} \dfrac{r^2}{8\mu _{\rm g}}\dfrac{p}{RT}\dfrac{{\rm d}p}{{\rm d}l} (5.2)$

其中,$J_{\rm V}$ 为气体连续流流量, mol/(m$^{2}\cdot $s);$r$为孔隙半径, m; $\mu _{\rm g}$为气体黏度, Pa$\cdot $s;$R$为气体常数, J/(mol$\cdot $K); $T$为地层温度, K;$p$为地层压力, Pa; $l$为气体传输方向的距离, m; $\zeta _{\rm mb}$为气体在多孔介质中流动时的修正系数.

当气体为连续流动时, 纳米孔隙结构特征对气体传输能力具有显著影响,气体传输能力与孔隙半径平方成正比, 随孔隙度增大而增大, 随迂曲度增大而降低;气体传输能力还与压力成正比, 当压力降低, 气体连续流动逐渐过渡到努森扩散,气体连续流量很低; 由于气体黏度是温度$T^{0.5}$的函数,因此气体传输能力与温度$T^{1.5}$成反比, 说明其对温度很敏感.

(2)滑脱流动

当努森数$10^{ - 3} < Kn< 10^{ - 1}$,气体分子间碰撞和气体与微裂缝壁面的碰撞均不可忽略,气体分子在壁面发生滑脱, 通过修正滑脱边界条件,则气体滑脱流动可表达为

$ J_{\rm {VS}} = - \zeta _{\rm {mb}} \dfrac{r^2p}{8\eta RT\mu _{\rm g} }\left( {1 + \alpha Kn } \right)\left( {1 +\dfrac{4Kn }{1 - bKn }} \right)\dfrac{{\rm d}p}{{\rm d}l} (5.3)$

其中, $J_{\rm VS}$为气体滑脱流动流量, mol/(m$^{2}\cdot$s); $b$为气体滑脱常数, 无因次. 边界为一阶滑脱条件则$b=0$;边界为二阶滑脱条件, 则$b=-1$; $Kn$为努森数,是气体平均分子自由程与孔隙半径之比, 无因次. $\alpha $为稀薄效应系数, 无因次.

随着努森数的增大, 滑脱效应更加明显, 气体传输量持续增大;但即使努森数很大, 式(5.3)也无法退化成努森扩散方程,无法描述气体的努森扩散过程.

(3)努森扩散

当页岩纳米孔为介--微孔、或气相压力小、气体平均分子自由程大以致努森数$Kn\gg1$时, 气体分子运动过程中, 与孔隙壁面碰撞占主导地位, 为努森扩散,可用努森方程表达

$ J_{\rm K} = - \dfrac{2}{3}\zeta _{\rm {mb}} r\left({\dfrac{8}{\pi RTM}} \right)^{0.5}\dfrac{{\rm d}p}{{\rm d}l} (5.4)$

其中, $J_{\rm K}$为气体努森扩散量, mol/(m$^{2}\cdot$s); $M$为气体摩尔质量, kg/mol.

努森扩散量随着气体分子量减小而增大, 即同样的压力梯度下,分子量越小的气体传输速度更快. 与连续流动和滑脱流动相比,努森扩散能力与气体压力和黏度无关, 与温度$T^{0.5}$成反比,因此其对温度相对不敏感.

5.2.1.3 微纳尺度流动特点

微纳尺度中的流动由于空间的细化而有其独特的性质, 其中最重要的有两个方面:稀薄气体效应和低马赫数下的可压缩效应, 除此之外还有两个重要的因素:黏性加热效应和热蠕变效应. 微纳尺度流动由于有较大的努森数,连续性假设不再成立而具有气体稀薄效应是很容易理解的. 但对于可压缩效应,则完全不同于宏观流动. 有观点认为微流动中较小的横向尺度导致了较高的黏性耗散,压降很大而且不同于典型流动的线性分布, 气体密度的变化相当剧烈,引起了低马赫数流动的可压缩效应.

在微纳尺度流动中, 当特征尺度还远大于流体分子的平均自由程时,连续介质假设仍能成立, 但由于特征尺度的变小,使得各种影响因素的相对重要性发生了变化, 从而导致流动规律的变化;而当特征尺度小到与流体分子的平均自由程在同一量级时,基于连续介质的一些宏观概念和规律就不再适用, 黏性系数等概念也需重新讨论.微纳系统里的小尺度可能引起连续性假设的失败,滑移现象、热蠕动效应、稀薄效应、黏性加热效应、可压缩性、分子间作用力和一些其他的非常规效应可能要考虑进来.

(1)尺度效应

在流体运动中, 作用于流体上的力主要为体积力和表面力.长度尺度是表征作用力的基本特征量, 体积力以特征长度的三次幂标度,而表面力则依赖于特征尺度的一次幂或二次幂. 随着流动尺度的减小,表面积与体积之比值增大, 可达百万倍之巨,这更强化了表面力和其他表面效应的作用, 表面力的作用不断加强.

在微纳尺度流动中, 表面力和其他表面效应将起主要作用.表面积体积比的增大影响到通过表面的质量、动量和能量的传输.

(2)表面力

微纳系统中的流动因一些表面力的作用而出现了一些新现象,这些表面力在宏观尺度流动中通常可以忽略. 在讨论不同的表面力之前,重要的是应清楚这些力都来源于分子间的相互作用力.分子间基本作用力本质上是短程力 $(<1$nm),但累积效果可导致大于0.1$\mu$m的长程作用,如液体的表面张力效应等. 另外, 所有分子间相互作用力基本上都是静电力(库仑力), 一旦薛定愕方程确定了空间电子分布,所有分子间相互作用力就能从经典静电理论算出,而实际上通常利用作用力的经验或半经验定律.

(3)相对表面粗糙度

在常规流动中, 管壁的表面形状对层流流动无影响,仅对湍流流动及由层流向湍流的过渡区有一定的影响. 而在微纳流动中,虽然管内流动几乎为层流, 但由于尺寸微小, 使得相对表面粗糙度(管壁粗糙度与管径之比)增大, 从而对微流动产生不可忽视的影响. 在微小管道内,即使粗糙度较小, 但由此引起的微小扰动也能渗入主流区而影响整个通道内的流动,而且表面粗糙度还可使流体的流动阻力增大. 在微流动中,不仅粗糙度单元的大小对流动有影响, 单元的分布情况也对流动有一定的影响.

(4)流体极性

流体在总体上虽不呈现极性, 但流体中是否含有极性离子,对流动特性有显著影响. 对于极性流体, 由于极性离子的吸附作用,其流动阻力将大于非极性流体. 即使对非极性流体,其流动阻力也各不相同. 例如, 在0.2$\mu$m管道内蒸馏水的流动阻力仅是酒精的1/3.虽然关于极性流体与非极性流体对流动的影响还没有令人满意的解释,但流体的极性对其流动的影响非常明显.

5.2.2 微观流动的研究方法

经典的流体力学控制方程 (N-S方程和傅里叶传热定理)只适用于小 $Kn$数的流场, 当气体的流动进入滑移区开始, 采用 N-S方程进行求解将与实验结果或实际情况出现偏差.微纳系统中的气体流动一般处于滑移过渡区,如果按照连续介质流动处理会导致较大的误差,所以需要寻找新的研究方法.

流体运动可以从宏观或者微观尺度来模拟.宏观尺度的模拟认为流体介质连续地无间隙地分布于物质所占有的整个空间,流体宏观物理量 (比如速度、密度、压力和温度等)是空间点和时间的连续函数,而通过质量、动量和能量守恒, 可以推导出一组非线性偏微分方程.微观尺度的模拟把流体看成是分子的集合, 在这个基础上产生了许多基于分子的模型,这些模型可以分为确定性方法和统计性方法两大类. 流体的模拟可以通过图5.3来表示.

5.2.2.1 分子动力学方法

分子动力学 (molecular dynamics,MD)方法是用于计算经典的多体系统平衡及传递的模拟方法,基本原理是首先通过分子系统 (或粒子系统)的势能求解作用在分子上的力,然后根据牛顿运动定律求解分子的运动参数如速度和加速度等,最后由统计得到分子系统的相关性质. 系统的势能为分子中各个原子所处位置的函数(Alder & Wainwright 1957).

一般地, 势能可分为分子或原子间的非键势能与分子内部势能两大部分,非键作用一般可近似为是各原子对间的非键作用的合成. 根据经典力学原理,系统内任一分子受力为势能的梯度, 由此可求得任意分子受到的力.求得分子受力之后, 根据牛顿第二定律, 可以求得分子的加速度、速度和位置.通过重复以上过程,可以求得不同时刻作用在各分子上的势能、作用力、加速度、速度等,即分子系统随时间的演化过程. 由统计力学相关原可以得到所需的物理量 (林缅等 2015).

通过MD方法可以获得许多实验中无法获得的微观细节, 解释疑难实验现象,揭示发生机制. 因此半个多世纪以来MD方法在物理、化学、材料科学等领域中发挥着显著的作用.在认识微纳米孔隙中油气分子的运动细节、吸附机理、流动特性修正等方面,近几年人们逐渐开始利用分子动力学方法开展相关的研究.如隋宏光和姚军(2016)和郑莲慧等(2014)利用分子动力学方法模拟了压力、温度、狭缝宽度和形态等因素对甲烷和二氧化碳在页岩孔隙中的吸附行为.欧志鹏(2014)利用分子动力学模拟方法研究了甲烷在页岩储层纳米孔隙中的赋存状态和扩散规律.Ambrose等(2012)利用分子动力学方法分析了干酪根中甲烷气体的吸附及密度分布特点,表明大多数干酪根中解吸附满足Langmuir等温吸附理论, 只有孔径足够小时不适用.

分子动力学模型是一种较为流行的微观动力学模型,对于页岩储层的微纳米级孔隙系统及其复杂的天然赋存状态和渗流扩散行为的研究,具有明显的优势. 但是,在利用该模型来研究微孔隙流体运动时,需要跟踪系统当中的每个粒子的运动,确定每个粒子在各个时刻的速度和位置,因此该模型所需的计算量以及所需的计算资源都非常巨大.尽管该模型在原则上可以用来模拟任意的流体系统,但巨大的计算量使得该方法目前只能用来研究微米或纳米尺度下的一些流动问题.

5.2.2.2 直接蒙特卡洛模拟方法

直接蒙特卡洛模拟(direct simulation of Monte Carlo,DSMC)方法是由Graeme在计算单一气体的松弛问题时最先采用的.其实质就是用适当数目的模拟分子代表大量真实气体分子,用计算机模拟气体分子运动、碰撞引起的动量和能量的输运、交换,产生气动力和气动热这一宏观物理过程.

在DSMC方法中, 宏观速度从热速度统计平均得到,热运动速度由平衡态Maxwell 速度分布函数如下

$ f^{(0)} = f_0 = n\left( {\dfrac{m}{2\pi k_{\rm B} T}}\right)^{3 / 2}\exp \left( {\dfrac{mV^2}{2k_{\rm B} T}} \right) (5.5)$

其中, $R$是气体常数,$T$为温度.从而分子热运动速率为$V$的几率$\psi (V)=4\pi V^{2}f_{0}$, 热运动的最大速率为$V_{\rm m} = \sqrt {2RT} $.

由此可知对于一般气体, $V$ 略大于声速$C = \sqrt {\gamma RT} $.因此对于亚声速流动, 特别是在马赫数小于0.1的微系统中, DSMC要得到收敛解比较困难, 需要计算的宏观速度很容易被背景噪声淹没.这种方法被广泛应用于如稀薄气体动力学问题、空间平台的污染等研究中.

DSMC方法主要用于高速稀薄气体流动的研究, 对于低流速的气体运动,由于统计噪声的原因, 需要大量的计算时间和空间. 近年来,DSMC方法也被用来模拟微纳尺度里的低速气体流动. 但是,Karniadakis等指出DSMC方法用于微纳尺度低速气体流动还有一些缺点:

(1) 收敛慢. DSMC方法的误差与模拟分子数目的平方根成反比,误差降低二分之一需要模拟分子数增大4倍.与使用二阶或更高阶空间精度的连续介质模型相比, 这是一个很低的收敛速度. 因此,如果连续介质方程有效, 使用连续介质模型比使用DSMC方法的计算效率更高.

(2) 统计噪声大. 微纳尺度流动是低速流的,宏观流体速度通过长时间平均分子速度得到.分子速度与平均速度值之间5到2个数量级的差异导致大的统计噪声,且需要对气体微流动模拟结果进行长时间的平均.

(3) 需很长时间达到稳定状态. 对低速微纳尺度流动,达到稳定状态所需的时间通常由对流时间尺度而不是扩散时间尺度确定,在DSMC方法中时间步长一般小于10$^{ - 10}$s,因此在微通道达到稳态之前, 至少需要运行10$^{10}$步. 事实上,对于简单的几何形状, 稳定状态可能发生早得多. 然而, 在MEMS装置中,外形复杂的几何形状非常普遍, 上述量级分析是有效的.

(4)缺少确定的表面效应.分子--壁面相互作用由切向速度和温度协调系数$K$确定. 如果存在漫反射,$K=1$, 被反射的分子失去其入射切向速度, 以壁面的切向速度被反射.对于$K=0$的情况, 入射分子的切向速度没有改变.对$K$取其他任何值的情况, 可以结合使用上面两种情况.这个壁面和边界相互作用的处理方法比滑移条件更基本, 然而,仍然缺乏最基本的, 包括壁面分子结构的方法来模拟分子壁面相互作用.

5.2.2.3 格子玻尔兹曼方法

格子玻尔兹曼方法(LBM)也可看作是从统计物理的Boltzmann方程发展而来的一种介观模拟方法,该方法一方面没有连续介质假设的要求使其可模拟微尺度问题,一方面不关心单分子运动细节而可模拟较大尺度的宏观问题.这个特性使其在页岩气赋存和开采模拟中能发挥特别的作用 (MeNamara & Zannetti 1988). 一般认为,流体的宏观运动是流体分子微观热运动的统计平均结果,因而宏观流体的运动对单个分子的运动的具体细节是不敏感的.宏观层次的N-S方程所描述的守恒定律与微观分子所遵循的运动规律是一致的,流体分子内部相互作用的差别仅仅反映在N-S方程中的一些输运系数上.因此, 从这个角度来讲, 人们可以设想构造一个微观模型或介观模型,使其在遵循宏观的一些基本守恒律的前提下尽可能地简洁,这也正是LBM的构造原理. 流体的微观动力学模型是LBM诞生的理论基础,并进一步指导着LBM的发展与完善.LBM同时也为理解宏观现象和揭示物理机理提供了一种新的途径.以常用的BGK模型为例, LBM的演化方程一般可写为

$ f_i \left( {r + e_i \Delta t,t + \Delta t} \right) =f_i \left( {r,t} \right) - \dfrac{1}{\tau _0 }\left( {f_i \left({r,t} \right) - f_i^{\rm eq} \left( {r,t} \right)} \right) (5.6)$

其中, $f_i $为实变量, $i$指对应的某个节点号, $\tau _0$为松弛时间, $f_i^{\rm eq} $随时间和空间变化,称为局部平衡态分布函数.

在利用LBM进行多孔介质渗流模拟时,提出了多种LBM模型以模拟不同的情况.一般根据模拟尺度的不同可分为孔隙尺度LBM模型和表征体元(REV)尺度LBM模型. 孔隙尺度LBM模型就是通常LBM模型,可模拟孔隙中流体流动.REV尺度LBM模型不考察孔隙内流体流动的详细信息,只关注体积平均后的宏观物理参数,该模型主要优点是可以模拟比孔隙尺度LBM模型范围大的情况.

Dardis 和McCloskey(1998)率先在LBM中考虑了流固之间的相互作用,从而能有效模拟多孔介质中流体的流动. Chen等(2015)利用考虑Klinkenberg效应的LBM模型分析了页岩中气体的流动,其中气体被视为理想气体.他们研究得到了在非均匀含不同尺度孔隙条件下,Klinkenberg效应在致密页岩介质中起非常重要的作用,裂隙的存在将强化渗流等结论. 任俊杰(2015)利用非理想气体条件下LBM研究了页岩中不同尺度孔隙中的气体流动,重点分析了干酪根中纳米尺度孔隙中的流动, 考虑不同格子形状、努森数,以及表面扩散和滑移的影响. 王华龙等(2009)利用二维格式模型,分析了气体在致密孔隙介质中渗流的滑脱效应,同时分析了渗透率、努森数及平均压力这些渗流参数之间的关系; 孙海等(2014)利用三维格子模型计算了三维页岩岩心的孔隙度及固有渗透率,分析了表观渗透率、固有渗透率和努森数之间的关系.

总的来说, LBM具有如下优点: LBM是一种具有二阶精度的显式差分格式,并且该方法中的对流项是线性的, 而宏观N-S方程中的对流项却是非线性的.在宏观的流体力学方程中,压力作为速度的源项用运动方程式来表示,因此在用有限差分方法求解N-S方程时,必需采用反复计算. LBM方程中压力则是用状态方程式来表示的,无需反复计算; 边界条件易于处理. LBM的上述特点,使得该方法在流体动力学、燃烧、渗流力学、磁流体力学、多相多组分系统、界面动力学、化学反应、微尺度流动与传热、血液流动以及颗粒悬浮流等众多领域中都得到了广泛应用,在页岩气的流动分析中也将发挥重要的作用.

5.2.2.4 Burnett 方程

Burnett 方程是采用 Chapman-Enskog 展开对 Boltzmann方程取二阶近似所得到,能够描述气体在轻微偏离平衡态时应力和应变之间非线性的本构关系,适合于描述 $Kn<1 $时的稀薄气体运动,但是由于其对小扰动反应的不稳定性, 在最初并没有得到广泛的应用.直到20世纪90年代初, Zhong 为了增大方程的稳定性,在应力张量和热通量上增大了部分 Chapman-Enskog 展开的线性三阶项,得到增广 Burnett 方程. 自20世纪90年代初以来,许多学者采用Burnett方程来研究超音速稀薄气体流动. 研究发现,采用Burnett 方程的结果与 DSMC 方法的结果符合得较好, 并且要优于 N-S方程的结果.

直到近几年, Burnett 方程才被用来模拟微通道里的流动, 平板间的Couette流最开始被关注, 有研究采用 Burnett 方程研究了 Couette流的流动和传热特性, 并与 DSMC 方法的结果作了比较, 由于稳定性问题,他们只能在粗糙的网格上获得收敛解, 计算不能应用到过渡区.通过在边界上引入松弛技术, Lockerby 和 Reese成功的获得了 $Kn<1$ 时Couette 流的收敛解, 在计算中他们采用一阶滑移边界条件, 得到的结果在$Kn <0.1$时与 DSMC 结果符合得较好, 但是在 $Kn>0.1$ 时, Burnett 方程的结果开始偏离 DSMC 的结果, 只能定性的符合.平板间压力驱动的 Poiseuille 流是另一种基本流动,最近也有不少人采用Burnett 方程来模拟. 同样的由于稳定性的问题,Poiseuille 流的最大收敛解只能达到 $Kn =0.2$, 后来通过在 Burnett方程源项的处理中添加松弛因子的方法, 成功的把解题范围扩展到 $Kn<0.4$. 也有人采用Burnett方程来模拟Poiseuilie流的流动和传热问题.Uribe等模拟得到的速度剖面等计算结果与DSMC结果符合得很好. 但是,由于Burnett方程的稳定性问题,Poiseuille流动的收敛解只有在小$Kn$数才能得到.Fang采用增广Burnett方程模拟了微通道里的气体流动,在他的计算中能获得收敛解.Burnett方程的稳定性问题成了该方程在微纳尺度流动中应用的瓶颈,寻找导致Burnett方程稳定性问题的根源,拓宽Burnett方程的使用范围至关重要.

5.2.2.5 逾渗理论

逾渗 (percolation)理论最早由Broadbent和Hammersley于1957年提出,用以研究无序孔隙介质中流体的流动等随机物理过程,这种随机性不是源于流体流动本身, 而是源于介质结构的随机性.其基本思想是: 介质内部有许多"节点", 节点称为"座",节点之间通过所谓的"键相连",这样整个介质的流通通道可视为一种由"座"和"键"构成的网络结构.任意两个座之间的连通概率设为$p$, 则不连通的概率为$1-p$.当$p$较小时, 只有座之间经由许多"路径"连接在一起,形成多个尺度较小的独立的连接集团, 称为"节点集团",不能贯通整个网络. 当$p$增大到某一值时,则会演化出贯通整个孔隙介质的"节点集团",这种发生连通性的突然转变称为逾渗的临界现象,对应的概率$p$称为逾渗阈值.

逾渗理论从本质上讲是属于概率论的一个分支,其所研究的模型不仅限于渗流的模拟,也是处理强无序随机几何结构的重要模型. 在逾渗理论中,流体可以是电流、热流、蒸汽流甚至可以是传染性的病毒,而随机介质也可以是岩体、煤体、复合材料、树林、社会群体、交通网络等等.逾渗理论的突出特点是能够用来研究事物从量变向质变的转换过程,模拟相变现象如: 孔隙介质由不渗透变为可渗透,由导体和绝缘体所构成的复合材料由绝缘体转变为导体等.在这些相变的过程中存在一个临界点, 即逾渗阈值. 在构成"节点集团"的过程中,根据各个"座"和"键"形成连通的方式不同,形成了逾渗理论中两种最基本的逾渗形式——键逾渗和座逾渗.键逾渗是指模型中所有的"座"都是连通的,而"键"则有些连通有些不连通,"座"通过连通的"键"联系在一起构成"连通集团",进而构成贯穿整个区域的"逾渗集团"; 座逾渗正好相反,模型中所有的"键"都是连通的, 而"座"则有些连通有些不连通,"键"通过连通的"座"联系在一起构成"连通集团",进而构成贯穿整个区域的"逾渗集团". 在实际应用中,网络结构是多种多样的, 比如在二维情况下,就有正方形、三角形、蜂窝形等, 对应地, 就有各种各样的逾渗模型.在不同类型的网格模型中, 逾渗阈值是不同的. 在相同构型下,键的逾渗阈值要小于座的逾渗阈值.三维模型的逾渗阈值小于二维模型的逾渗阈值,这是因为三维网络中的座和键比二维网络的连接多, 键比座有更多的连接.通过理论计算可得到各种逾渗模型的逾渗阈值,比如正方形网格的键逾渗阈值为0.5, 座逾渗阈值为0.5937,三角形网络的键逾渗阈值为0.3473, 座逾渗阈值为0.5.键逾渗和座逾渗两种模型通过变化、组合生成很多更加复杂模型.

孔隙介质与逾渗模型具有很强的相似性:多孔介质中的孔隙和孔道、裂隙和裂隙交点可以直接映射到逾渗模型中的"座"和"键",从而构成逾渗模型. 在岩土力学领域,逾渗模型有可分为孔隙逾渗模型、裂隙逾渗模型和孔隙--裂隙逾渗模型,前两种模型分别认为岩土介质中只存在孔隙或只存在裂隙,第3种模型则认为介质中同时存在孔隙和裂隙, 且需同时考虑,因此又称为孔隙裂隙双重逾渗模型.

Torelli等(1971)根据逾渗理论建立了一套等径管道网络系统,通过该系统模拟了多孔介质中的扩散问题. Simon等(1971)利用逾渗网络管道模型研究了石油开采中的注水采油过程. Robinson(1983) 结合逾渗理论计算了简单二维裂隙网络的连通性. Stephan等(1985)研究了法国Auriat地区花岗岩地层中的两口异常水井,它们位置临近而水位的变化却完全相互独立,Stephan等(1985)认为这种现象可以用逾渗理论中不同连通集团相互独立来解释,他们还建立了三维的逾渗网格, 计算了逾渗阈值与网格密度的关联,证实了逾渗理论可以用于实际地层中研究区域的连通性.

裂隙逾渗网络的构成有很多种构型, 每条裂隙延伸出多条"键",连接相邻裂隙. 这些"键"的连通与否由一个概率$P$随机给定;同时还需要考察任意两条裂隙之间是否存在相互搭接的情况.只要存在上述两种连通情况中的任意一种, 则认为两条裂隙是相互贯通的.然后推广至整个区域, 考察整个区域内是否会形成贯通性的裂隙系统.对于裂隙网络, 只考虑细小裂隙间的直接相互搭接,不考虑裂隙的发展和裂隙间潜在的连接通道. 因此,关注点在于区域内的裂隙是否会形成经由几何搭接而形成的贯穿性裂缝系统,以及在何种参数组合下出现这种贯穿性裂缝系统.裂隙模型规模在处理问题时变化可以很大,即单位区域内裂隙的条数变化很大. 而当裂隙条数变动时,其对裂隙系统是否出现贯通还需要考虑引入裂隙长度,因此需要引入一个参量, 能够同时考虑裂隙条数和裂隙长度的影响.

孔隙裂隙双重逾渗模型是由裂隙网络与基质孔隙逾渗网络相互映射而得到,裂隙中心点与基质逾渗网络"点座"之间相互映射,裂隙间潜在联系与基质逾渗网络"键"之间相互映射.裂隙网络用以模拟岩石中存在的大量的微小裂隙,而基质逾渗网络则用以模拟岩石中除去微小裂隙以外,还存在的较大孔隙以及在一定应力应变状态下潜在的缺陷.两种网络的相互映射与相互关联,则模拟了岩石中的小裂隙通过裂隙间直接连接作用和基质孔道的潜在连接作用形成窜通通道情况.

冯增朝等(2005)建立了孔隙裂隙双重逾渗模型,采用座逾渗原理模拟孔隙介质, 并在此基础上叠加随机裂隙,对这种裂隙--孔隙二元多孔介质的渗流连通性进行了研究. 郑委(2010)使用双重逾渗模型展开了网络连通性和渗透性的研究.首先构建裂隙逾渗网络, 设裂隙长度服从正态分布,裂隙中心点的位置和裂隙倾角服从均匀分布,根据实际情况将分析区域划分为一定数目的裂隙网格;然后在裂隙逾渗网络基础上构建孔隙逾渗网络,将整条裂隙抽象为键逾渗中的"点座",裂隙之间潜在连通的孔隙通道对应为键逾渗中的"键".连键表示两条裂隙之间发生了通过孔隙通道连通的情况; 反之,断键表示两条裂隙之间的孔隙通道是堵塞的. 通过分析,找到了能够量化反映裂隙多孔介质连通性的参数.

页岩是典型的孔隙裂隙双重网络结构,其连通程度决定了页岩气的赋存状态、含气性以及采收率.在这方面需要针对页岩储层的孔隙裂隙特点,如层厚、有机质含量、埋深等因素与裂隙长度、宽度等的关系,孔喉分布等,利用逾渗理论分析页岩的连通性、以及达到可生产必须的人工压裂程度等问题.

5.2.2.6 孔隙网络模型

孔隙网络模型 (pore-scale network model)属于逾渗模型的一种,其优点是: 模型理论相对简单,空间孔隙分布、微观流动机制易于理解和引入.当前对孔隙网络模型的大概定义是: 孔隙网络模型将多孔介质(通过压汞实验或者微观三维成像技术获得真实孔隙结构的数据表述)抽象为理想的几何形状,模型中相互连通的喉道和孔隙组成了复杂的孔隙空间,模型中的孔隙代表真实多孔介质中较大的孔隙空间,模型中的喉道代表真实多孔介质中相对狭长的孔隙空间.这样模型可在一定程度上反映真实岩心的孔隙特征,然后基于统计物理中逾渗理论的基本思路以及孔隙介质中的微观渗流物理机制赋予模型以流动机制,最后通过微观水平的具有蒙特卡罗性质的随机模拟来研究孔隙介质中的渗流及驱替规律,从而定量预测一些渗流参数、模拟渗流过程,不同尺度的孔隙网络模型如图5.4所示.

孔隙网络模型作为研究渗流的有效工具,近年来在石油工业中当任了越来越重要的角色.孔隙网络模型由Fatt在1956年首先提出,他用一些二维网络系统研究了多孔介质的动静态性质;该系统以圆柱形毛管为模型单元,毛管通过相互联结形成正方形、六边形、双重六边形甚至三重六边形等;同时认为毛管与毛管的接合点或节点是没有大小的数学意义上的点;将毛管依次编号,毛管半径以及任意半径的毛管数目均按随机数表以随机方式分布;假设驱替开始时网络完全被湿相流体所饱和, 网络周围是非湿相;当驱替压力增全网络中最大管径所对应的入口压力时,非湿相就进入网络边界上的最大毛管, 而该毛管内的润湿相则逸出. Koplik(1981)利用孔隙网络模型对多元球填充层的毛管压力曲线进行预测.该网络模型用一个规则的二维毛管组来表示孔隙结构,毛管和毛管间的接合点处假设为球形空穴;毛管和球形空穴的尺寸按提出的堆积不等径球的四面体模型来计算;模拟结果在经过水力半径模型校正后,和实测毛管压力曲线有非常高的一致性. 20世纪七、八十年代,滑铁卢大学的 Chatzis和Dullien(1983)对前人关于孔隙网络模型的研究作了系统化的梳理,整理出了毛管压力、饱和度等宏观参数的计算公式.他们的工作对孔隙网络模型的推广起了很大的推进作用. 自此,从事油层物理研究的人员开始逐渐接受孔隙网络模型作为一种模拟工具.近年来对孔隙网络模型研究较为活跃的小组之一就是Heriot-Watt大学的Dixit等(1997).他们主要应用孔隙网络模型对具有不均匀润湿性的孔隙介质中的驱替特征进行了模拟研究,同时在模拟的基础上还提出了采收率与不均匀润湿性的关系.英国帝国理工的Blunt(1997)主要对非均匀性孔隙网络模型开展了研究,分析了相渗曲线等渗流参数 (如图5.5).同时对于孔隙网络模型吸入过程中孔穴的不同充填机制,也做过详细的论述.

国内近几年也开展了相关的研究工作.中国石油勘探开发研究院的刘庆杰和王金勋(2001)提出了一种新的孔隙网络模型相对渗透率计算方法,针对砂岩得到了很好的模拟结果. 他同时考虑滑脱效应,对致密岩石中的气体渗流进行了模拟.

中国科学院力学研究所的张旭辉等(2011)利用编制的三维动态孔隙网络模型研究了微小喉道对岩心驱油特征的影响,得到了与实验结果相符的模拟结果 (如图5.6), 即大庆岩心峰值半径小, 峰值半径含量高, 喉道的分布比较集中均匀,而长庆峰值半径含量显著较小, 喉道半径分布范围宽.随着微小喉道份额的增多, 水相相对渗透率减小, 交点饱和度增大,共流区减小. 中国石油大学 (华东)的汲广胜(2013)对重建真实孔隙结构有系统性的研究.

孔隙网络模型的特点在于其可以在微观和宏观之间建立桥梁,由微观结构高效地模拟宏观的特性.同时孔隙网络模型模拟和微观物理模拟一样,也能够提供较为直观的微观驱替过程的静态或动态显示. 因为这些特点,孔隙网络模型作为联系微观与宏观的重要桥梁在不均匀湿润性、非达西渗流、三相渗流、泡沫在孔隙介质中流动、地层伤害等问题中有重要应用.但孔隙网络模型也存在运算量较大、在模拟复杂渗流时缺乏有效机制等缺点.

目前孔隙网络模型大多只考虑了孔隙级别尺度这一单一尺度.孔隙级网络模型针对均质性较强的岩心, 例如砂岩,能够取得比较好的模拟预测效果; 但对于双重介质, 例如砾岩、碳酸盐岩,孔隙级网络模型并不能进行准确的模拟. 这就需要拓宽研究工具,编制考虑多种尺度的网络模型.

近年来, 国内外的学者在多尺度网络模型上已有一些研究成果. Pillai等(2009)利用网络模型展开了关于双重介质中液体蒸发研究,该研究建立了二维网络模型, 将网络模型划分为大孔区域和小孔区域.研究大孔区域在上小孔区域在下,小孔区域在上大孔区域在下时的液体蒸发异同. Noetinger等(2013)建立了一种多尺度离散裂隙网络模型. 基于一系列假设,该模型在几何上忽略了基质网络, 并将裂隙进行最简管网化;同时在渗流理论上将Barenblatt的经典公式进行了简化.该研究者使用该模型进行了一系列的算例计算,结果表明该模型计算结果与理论结果拟合情况好,并具有尺度灵活性强、计算速度快等特点. 姚军、王晨晨等(2013)使用两种方法建立了双重尺度数字岩心,同时研究了不同类型孔隙的拓扑结构和渗流特征,用建立的网络模型研究了不同网络结构和润湿性参数对水驱油过程相对渗透率曲线的影响.

可以看到现有的双重介质网络模型研究中建立的多为考虑双孔隙度的网络模型,或者直接忽略基质仅考虑多尺度裂隙的网络模型.针对裂隙和基质相互作用比较强的介质,此类网络模型不能进行很好的模拟.需要建立新型的网络模型来拓宽研究手段.

5.2.3 微观尺度向宏观尺度过渡问题

页岩气藏中的流体流动是一个多尺度流动问题,主要包含了5个不同尺度的状况, 如图5.7所示.其尺度的跨越在12个量级, 具体尺度及用途如下:

(1)宏观尺度: 尺度的量级为米至千米,主要用于实际工程中页岩气储层评价、数值模拟、储量计算和产能预算等.

(2)介观尺度: 尺度的量级为毫米至米,主要用于页岩气裂缝描述和压裂机理研究.

(3)微观尺度: 尺度的量级为微米至毫米,主要用于页岩气微观渗流机理研究和渗流规律的实验模拟.

(4)纳米尺度: 尺度的量级为纳米至微米,主要用于页岩气流动机理研究和分析.

(5)分子尺度/纳米以下尺度: 尺度的量级为纳米级以下,主要用页岩气流动机理研究和分析.

根据Javadpour(2009)相关研究结果,页岩气纳米孔气体传输机理包括连续流动、滑脱流动和努森扩散,可通过2类概念模型描述纳米孔气体传输机理: (1)考虑气体分子属性的分子模型; (2) 考虑气体宏观属性的宏观模型.描述页岩气纳米孔气体传输机理的分子模拟, 其考虑了气体分子属性,能够准确地描述各种物理机制. 然而, 分子模拟技术应用于页岩气模拟,需要巨大的计算机资源和计算时间, 其应用性受限.常规水动力连续性模型达西定律无法合理描述页岩气纳米孔中的气体传输机理.目前, 描述页岩气纳米孔气体传输机理宏观模型有2类: (1)基于水动力连续性模型, 修正边界滑脱条件来考虑多种传输机理; (2)基于多种传输机理, 按一定的贡献权重系数进行叠加.

结合气体通量守恒原理, 纳米级基质孔隙表观渗透率表达式为

$ K_{\rm m} = \left( {1 - \alpha } \right)K_\infty + \alpha D_{\rm k} \mu c_{\rm g} (5.7)$

Wu等(2015, 2016, 2017)基于滑脱流动与努森扩散两种传输机理,分别以分子之间的碰撞频率和分子与壁面的碰撞频率占碰撞总频率的比值作为滑脱流动和努森扩散的权重系数,建立纳米孔综合气体传输数学模型.气体滑脱流动和努森扩散占总传输的份额,分别根据气体分子之间的碰撞频率和气体分子与壁面的碰撞频率占碰撞总频率的比值来确定,则纳米孔综合气体总传输量为

$ J_{\rm b} = \dfrac{\lambda _{\rm r} }{\lambda }J_{\rm {VS}} + \dfrac{\lambda _{\rm T} }{2r}J_{\rm K} (5.8)$

其中,$J_{\rm b}$为纳米孔气体总传输量, mol/(m$^{2}\cdot $s); $J_{\rm VS}$为气体滑脱流动流量, mol/(m$^{2}\cdot $s); $J_{\rm K}$为气体努森扩散量, mol/(m$^{2}\cdot $s); $\lambda _{\rm T}$为整体气体分子平均自由程, m; $\lambda $ 为气体平均分子自由程,m.

根据滑脱流动、努森扩散等流动机制的表达式,可进一步推导出纳米孔气体表观渗透率为

$ K_{\rm b} = \dfrac{1}{1 + Kn }\zeta _{\rm {mb}} \dfrac{r^2\left( {1+ \alpha Kn } \right)\left( {1 + \dfrac{4Kn }{1 - bKn }}\right)}{8} +$$ \dfrac{1}{\left( {1 + 1/{Kn }}\right)}\dfrac{2}{3}\zeta _{\rm mb} r\delta ^{D_{\rm f} - 2}\left({\dfrac{8RT}{\pi M}} \right)^{0.5}\dfrac{\eta }{p} (5.9)$

式中, $r$为孔隙半径, m; $\mu _{\rm g}$为气体黏度, Pa$\cdot $s;$R$为气体常数, J/(mol$\cdot $K); $T$为地层温度, K;$p$为地层压力, Pa; $l$为气体传输方向的距离, m; $\zeta _{\rm mb}$为气体在多孔介质中流动时的修正系数; $b$为气体滑脱常数, 无因次.边界为一阶滑脱条件则$b=0$; 边界为二阶滑脱条件, 则$b=-1$;$Kn$为努森数, 是气体平均分子自由程与孔隙半径之比, 无因次; $\alpha$为稀薄效应系数, 无因次; $M$为气体摩尔质量, kg/mol.

综合以上模型建立考虑应力敏感和非达西效应、页岩气吸附和解吸的产能模型,进而从微观运移机制出发认识宏观流动规律. 运用数值方法绘制典型曲线,并对其产能影响因素进行了分析发现: 页岩气流动共分为4个阶段:人工裂缝中的线性流阶段、人工裂缝和天然裂缝中的双线性流阶段、基质向天然裂缝中的窜流阶段和气藏边界控制流动阶段.考虑天然裂缝中的应力敏感效应后, 由于页岩气解吸,窜流以及边界控制的影响, 天然裂缝中发生应力敏感效应,其中在天然裂缝双线性阶段, 窜流前期阶段以及后期边界控制流阶段,应力敏感影响显著发生, 并且应力敏感系数越大,无因次产量导数曲线下移量越多, 产能降低越显著.

目前, 对于微观向宏观过渡的研究仅是探索性的工作,有许多影响因素没有得到考虑,这是在实际工程中要做出努力的主要方向之一.

5.3 解吸附条件下的渗流力学规律

5.3.1 吸附动力学问题

美国在页岩气勘探和开发取得成功很大程度上得益于成藏理论的进步和勘探技术的迅速发展,其中最主要的是认识到吸附气的赋存特点.页岩气的吸附作用又分为物理吸附和化学吸附, 以物理吸附为主.物理吸附是由范德华力引起的可逆反应, 需要消耗的吸附热量较少.当被吸附时, 气体失去3个自由度中的一个,运动能量的损失转换成与吸附作用有关的热量. 而化学吸附作用更强,主要以离子键吸附, 反应更慢且不可逆, 一般只限在单层,需要很大的能量才能把离子键打开而使甲烷解吸.

5.3.1.1 页岩吸附特征的影响因素

关于页岩气吸附特征的实例研究较多,页岩的吸附能力与总有机碳含量、矿物成分、储层温度、地层压力、页岩含水量、天然气组分和孔隙结构等因素有关.有机质越多吸附气含量越高, 图5.8描述了干酪根中的页岩气的吸附和流动状态.

Lu等(1993)利用Langmuir等温吸附模型通过实验研究了美国多个盆地泥盆系页岩的吸附作用和温度压力之间的关系,证实吸附能力随着压力增高而增高, 随着温度升高而降低. 在低压情况下,吸附气含量随压力升高迅速增大, 而达到一定压力后增大缓慢. Raut等(2007)指出在压力较低的情况下, 气体吸附需达到较高的结合能,当压力不断增大, 所需结合能不断减少, 气体的吸附量增大速度随之降低.

Martini等通过实验研究发现,乙烷、丙烷等碳氢化合物对活性炭吸附存储甲烷能力有显著的影响,当混合气体中含有乙烷 (4.1%)和丙烷 (2%)时,甲烷的吸附能力分别下降了25%和27%. 在页岩层中, 含水量越高,水占据的孔隙空间就越大,从而减少了游离态烃类气体的容留体积和矿物表面吸附气体的表面位置,因此含水量相对较高的页岩, 其气体吸附能力较小. Ross和Bustin(2007,2008)发现仅在含水量较大 (大于4%)时,页岩对气体的吸附能力才有显著的降低,饱和水的样品的气体吸附量比干燥样品低40%. 此外,页岩层中含水量的增大, 可能会导致天然气相态的改变,因为当页岩层中孔隙水增大时, 天然气溶解于孔隙水中的量就会增大,从而使一定数量的游离态和吸附态页岩气溶于水, 呈溶解态存在.

5.3.1.2 吸附理论及模型

目前主要吸附理论有分子层吸附、吸附势及格子理论等,吸附理论模型主要包括: 亚临界吸附模型(如Langmuir模型)及超临界吸附模型(如吸附势理论模型、格子理论模型及密度泛函等分子模型).这些方法一般都具有特定假设, 如Langmuir的4个特定假设为:单分子层吸附; 固体表面均一, 吸附热不变; 吸附质分子间无横向力作用;动态吸附平衡. 一般认为超临界态吸附质为多分子层吸附,分子间具有一定作用势, 吸附使固体表面维持能量最低,因此与以上假设多有不符.多分子层吸附方程其假设表面均一、忽视分子间作用力及第1吸附层吸附热为常数也与实际不符.吸附势理论假设分子吸附服从高斯分布, 同时其参数定义不甚明确.

(1)分子层吸附Langmuir模型

目前Langmuir模型(式(5.10))在表征较低平衡压力条件下甲烷--页岩的气--固吸附方面具有较多应用.但当测试温压超过临界条件之后,一般认为吸附原理及吸附线型式会发生一定变化,分子吸附状态也会从简单单层吸附逐渐变得复杂.此时该模型假设的吸附分子呈单层吸附、吸附热不变、吸附分子间无横向作用及吸附满足动态平衡等假设与实际情况往往不符

$q_{\rm ads} = \dfrac{\rho _{\rm s} M_{\rm g} }{V_{\rm std} }q_{\rm std} = \dfrac{\rho _{\rm s} M_{\rm g} }{V_{\rm td} }\dfrac{V_{\rm L} p_{\rm m} }{p_{\rm L} + p_{\rm m} } (5.10)$

式中,$q_{\rm ads}$为页岩单位面积的吸附量, kg/m$^{3}$; $V_{\rm std}$为标准状况下的摩尔体积, m$^{3}$/mol; $q_{\rm std}$为标准状况下页岩单位质量的吸附体积, m$^{3}$/kg; $V_{\rm L}$为Langmuir体积, m$^{3}$/kg; $p_{\rm L}$为Langmuir压力, Pa;$\rho _{\rm s}$为页岩岩心密度, kg/m$^{3}$.

Langmuir 方程适用于埋藏浅 (小于1000m)的煤层,可能在本质上还是不适用于页岩气, 因为页岩气藏的深度一般高于3000m,随着地层深度的增大地层温度也在增大,而有机质的吸附量是会随温度增高而降低. 已有实验结果显示出, 1500m以下页岩气的存在状态有以游离气为主的趋势. Hildenbrand等(2006)提出了煤的吸附量随温度压力变化的模型,国内有学者根据它建立了地质条件温度和压力协同变化下的有机质吸附甲烷气模型,并且研究发现温度与压力对气体吸附量的控制存在竞争关系,在埋深约1000m 处出现甲烷的最大吸附量, 而后开始降低, 这与Langmuir方程所获的单调结果是不相符的.同时因为甲烷在真实页岩储层中是超临界状态的, 特性异常, Langmuir方程完全没有考虑这一点, 崔永君等(2005)就认为因甲烷在储层中是处于超临界状态的,其体积不能简单使用状态方程来求取.

(2)吸附势理论模型

吸附势理论又称微孔填充理论, 通过Ruthven, Dubinin 等学者 (Ruthven 1984, Dubinin 1966)的深入研究, 逐步发展成为一门热力学理论,通过不断发展最终扩展应用到超临界领域,在确定吸附剂微观结构及孔隙等级划分等方面起到了重大作用.一般认为在相对较大的孔隙中,孔隙尺寸及曲率等对气体分子的吸附特征影响不大; 而在纳微级孔隙中,存在巨大势能, 距离吸附剂表面越近势能越大,如仅能容纳单分子的孔壁之间吸附势约为距离单孔壁2个分子直径时吸附势的3.5倍.因此在较高平衡压力及超过临界值点条件下,气体分子会发生"毛细凝聚",显然若此时假设气体分子在吸附剂表面呈单层或多层分布则与实际不符.微孔填充理论在一定程度上更能代表吸附质分子真实存在状态 (Jaycock & Parfit 1981), 相比Langmuir模型来说该模型具有重要发展,其重要意义主要体现在可以帮助人们进行吸附机理正确推断及吸附性能合理评价,进一步了解吸附分子真实赋存状态及气-固作用机理.

Dubinin和Astakhov(1971) 等对该理论概念的发展奠定了基础;周理和周亚平(1996)利用吸附势理论探讨了超临界条件下氢在富含纳微孔活性炭中的吸附行为;李明等(2003)对甲烷在微孔活性炭中吸附行为进行了吸附势理论分析,重点对吸附相密度和虚拟饱和蒸汽压进行了讨论; Kaneko和Murata(1997)对超临界条件下不同气体分子 (如N$_{2}$, CH$_{4}$,CO及H$_{2}$O)在石墨微晶狭缝型孔隙中势能计算方法进行了研究,发现纳米空间特异分子场可使吸附气体分子呈高压态.通过以上研究可以看出,吸附势理论能确定不同类型吸附剂--吸附质分子间吸附能力,在纳微孔吸附剂及超临界条件下具有特殊优势, 但该模型仍存在一些不足:即假设分子吸附服从高斯分布, 同时部分参数的指示意义不够明确.

(3)格子理论模型

Ono-Kondo格子理论(1960)根据吸附位的格子模型对分子吸附进行表征,Aranovich等(1995)最先将该理论应用到气体在富含纳米级微孔的多孔炭中的吸附,并发现该理论在表征超临界态气体分子吸附及以平板狭缝类型为主的纳米级微孔时优势较大.

利用格子理论模型探讨甲烷在页岩中的吸附特征,该模型基于不同假设可发生一定转变,利用该理论预测甲烷吸附量的精度较高, 预测精度随着温度的升高而略升;模型中确定的理论单层饱和吸附密度及吸附质分子与微孔表面之间的接触势能等参数可用来指示温压对甲烷吸附特征的影响及页岩中纳米级微孔发育程度.随着温度的升高吸附质分子与微孔表面之间的接触势能减小,吸附质分子与微孔表面之间的接触势能与温度间的变化近乎线性;理论单层饱和吸附密度可以大体表征分子吸附状态,甲烷在页岩中吸附的理论单层饱和吸附密度和吸附质分子与微孔表面之间的接触势能比富含纳米级微孔的多孔活性炭小得多.利用该理论对不同地区及不同类型页岩在更宽尺度温压范围内对页岩微观结构表征或真实含气量关系研究具参考价值.

5.3.2 解吸附与流动耦合问题

在页岩气含气量分析和渗流机理研究中都涉及页岩气的吸附和解吸附,只不过前者是求静态吸附气量, 后者分析的是动态气体解吸过程.页岩气开采中, 气体产出过程一般认为要经历3个阶段: (1)在钻井、完井降压的作用下, 裂缝系统中的页岩气流向生产井筒,基质系统中的页岩气在基质表面进行解吸; (2) 在浓度差的作用下,页岩气由基质系统向裂缝系统进行扩散; (3) 在流动势的作用下,页岩气通过裂缝系统流向生产井筒. Javadpour(2007)还认为,在气体从干酪根 (或黏土)表面的解吸完成后,这种不平衡状态还会驱动气体分子从干酪根主体到干酪根表面的扩散,然后才是气体跨过吸附界面到孔隙网络的扩散. 页岩气的解吸,也就是页岩气开采后气体由吸附态向游离态的转化.解吸是指吸附质离开界面使吸附量减少的现象, 为吸附的逆过程,所以可通过先分析吸附, 一定程度上来研究气体解吸过程.

由于吸附状态和机理并不完全清楚,目前解吸附与页岩气流动的耦合多采用Langmuir等温吸附来描述,包括目前使用的商业化软件如CMG, Eclips,Saphir等都采用Langmuir等温吸附进行数值模拟和页岩气储层评价. Wan等(2015)提出了源汇项理论来进行解吸附与页岩气流动的耦合分析,主要理论公式如下

$ \dfrac{\partial ^2p_D }{\partial x_D ^2} +\dfrac{\partial ^2p_D }{\partial y_D ^2} + \dfrac{k_z }{k_r}\dfrac{\partial ^2p_D }{\partial z_D ^2} + \alpha _{1D} + \alpha_{2D} \left( {p_D - p_{sD} } \right) = \dfrac{1}{C_De^{2S}}\dfrac{\partial p_D }{\partial T_D } (5.11)$

对于页岩气的解吸过程, 页岩气与煤层气的解吸过程存有差异,对比观察煤样和页岩岩样在水中气体的解吸过程发现,煤样中仅仅是单纯的气泡放出,页岩岩样中气体的析出则有由气相转化为气-固两相的趋势,这可能因为岩样是放在水中解吸,页岩矿物成份、气、水相互间做用的缘故.他还认为页岩气解吸模型中高斯分布模型优于常用于煤层气脱气的球形扩散模型.在同一温度压力条件下, 页岩气体解吸过程相对吸附过程有滞后现象,且解吸不够彻底. 页岩气解吸时间和解吸速度不是一个均质过程,需要使用高精度传感器再进行测量分析.页岩岩心解吸附实验有一个从地下取芯到地面岩心放入解吸筒的不可测阶段,等温吸附实验使用的是取出相当时间并粉碎后的页岩样品,这两者从对象到环境条件与真实地下页岩气的吸附与解吸附过程有本质的区别,早已不是地层原始状态, 所以这两种研究手段都有一定局限性.值得关注的是类似于煤层气的成藏模拟,国内已有将页岩气成藏模拟与解吸相结合起来进行研究的报道.

经典模型如BET模型、D-R模型在拟合超临界状态的页岩气以及对多组分的拟合下都有各自的优越之处,同时在这些模型的实际拟合中也存在一些不足之处,例如有些模型计算过程复杂以及不适应某些状态下的拟合等.还有一些认识不清或未解决的问题, 值得深入研究, 总结如下:

(1)页岩气的主体赋存状态存有争议, 对固溶态的页岩气的研究还很少. (2)页岩气含气量测试中损失气量的准确获得, 从实测到模型估算都有问题.页岩气等温吸附实验和其数学解释模型可靠程度有待提高, 如:实验中使用气体的类型、地层温度和压力下的校正、实验样品的种类等诸多测试对象和环境与页岩气地层原始状态的差异.

(3)页岩气在超临界状态下的吸附规律研究较少,相关吸附模型对此鲜有涉及.

(4)单一矿物和有机质的吸附特性关注较少,多组分气体中各气体间竞吸机理还未有详细研究.

5.4 人工压裂过程裂缝起裂及流固耦合机理

页岩气井水力压裂过程中, 通过高压压裂液的压裂,使页岩储层产生新的裂缝, 连通原有的天然裂缝,进而形成复杂的裂缝网络.页岩储层中人工裂缝与天然裂缝、以及天然裂缝相互之间的连通性对于储层产能有着重大影响.

常规油气藏压裂假设形成平面对称双翼裂缝,而页岩气藏压裂页岩储层改造一般采用大量低黏度压裂液和低浓度小颗粒支撑剂,往往形成非平面、非对称、多分支的复杂裂缝网络,即非常规油气藏的体积压裂,储层改造体积的大小直接关乎页岩气产量的高低.体积压裂裂缝几何形态主要由岩石力学性质、地应力、压裂液的流变性质和局部非均质性(天然裂缝和软弱层面)决定,有必要对页岩体积压裂如何形成以及形成怎样的裂缝形态进行研究,这归结于页岩人工压裂裂缝的扩展力学问题,涉及岩石力学、断裂力学和流体力学等多学科的综合.

5.4.1 页岩裂缝起裂及扩展机理

页岩人工压裂裂缝扩展力学耦合了地层岩石力学变形、裂缝网络流体流动以及断裂扩展等过程,国外学者根据不同的假设使用不同的理论对这些过程进行了分析,典型研究包括:使用线弹性理论、弹塑性理论和多孔弹性理论来描述岩石变形;使用Reynolds润滑理论和Carter滤失模型来模拟裂缝流体流动;使用线弹性断裂力学理论和内聚区模型来描述断裂扩展过程.中国页岩储层破裂具有许多新的特性: (1) 页岩储层为层叠沉积岩,每一叠层属性各不相同, 具有明显的各向异性,如水平面内弹性模量和渗透系数与竖直方向有很大差别,是典型的横观各向同性材料; (2) 受层间界面阻碍,裂缝很难沿竖直方向扩展, 造成油气沿竖直方向渗透困难; (3)由于层间黏接弱面、节理及天然裂缝的存在,页岩断裂后具有复杂的几何形态,大量裂缝分支的存在给压裂液的设计及对裂缝网渗透性及连通性的评估带来了困难.由于页岩是多孔、各向异性缝、节理等弱面的非均质材料,建立合适的页岩本构模型及其起裂、扩展准则是进行裂缝扩展研究的基础.

5.4.1.1 页岩各向异性多孔本构

现有理论和数值软件中多把页岩简化成无孔、各向同性材料处理.而在开采页岩气时, 由于油气流动改变页岩气储层的应力分布,导致页岩储层变形, 使其孔隙体积发生变化,进一步影响孔隙气体的压力变化. 当页岩气的压力分布发生变化时,会反过来影响页岩储层基体的应力分布. 因此研究页岩储层的力学特性时,不能忽略页岩孔隙压力变化的影响. Terzaghi(1925)最早开始研究多孔介质的变形与流体流动的耦合作用,提出了有效应力公式并建立了一维固结模型. 后来Biot(1941)将固结模型推广到三维空间, 提出了相应的本构模型,首次在岩土研究中引入达西定律,考虑了多孔介质孔隙气体压力与介质变形互相影响,从此Biot本构模型便成为岩土流固耦合研究的常用本构模型.Detournay和Cheng(1993)从等效应力本构出发,基于弹性力学系统推导了多孔介质流固耦合的理论基础,并给出了几种问题的解析解. Zhang等(2008)在Biot本构模型中增大了考虑解吸附过程引起的体积应变项.Dmitry等(2011)又基于Biot本构导出了在压裂液黏性和岩石断裂韧性主导下的裂尖应力场奇异性,对理解页岩起裂具有重要意义. Thompson和Willis(1991)使用增量形式重新考察了Biot所描述的各向异性多孔介质本构,它用张量形式重写了Biot的方程,并将Biot的系数表达为实验更容易测量的系数 (全渗、无渗),相当于使用了Rice与Cleary(1976)参数定义方法.同时还给出了各向异性下的Biot等效应力的定义,总结了横向各向同性时的应变--应力关系; Abousleiman和Cui(1998)进一步将Thompson和Wills在横观各向同性下的结果,转写为应力--应变关系, 至此将Biot本构推广到各向异性.

5.4.1.2 页岩各向异性强度和断裂准则

由于层理和天然裂缝等弱面的存在,使得页岩不仅在弹性和渗流参数上具有各向异性和随机性,在断裂和强度上也具有明显的各向异性和随机性.因此需要充分结合含损伤本构理论和断裂理论的优势才能描述裂缝在页岩这种复杂介质中的扩展问题.在分析水力压裂造成的岩石断裂时, 最常见的判断准则是最大拉应力准则.实验研究表明在页岩水力压裂中应考虑页岩中孔隙压力对岩石开裂准则的影响.Terzaghi认为应将岩石中的应力与孔隙压力求和, 称为Terzaghi等效应力,再与岩石的抗拉强度比较作为岩石的断裂准则. 另一方面,当页岩的抗拉强度和断裂韧性具有各向异性特征时,最大拉应力准则显然不再适用,需要引入新的准则判断起裂应力及裂缝扩展方向. 在剪切破坏时,各向异性岩石应当同时校核弱面准则与Mohr-Coulomb准则,在弱面附近方向上破坏所需的应力更小,因而强度的各向异性导致岩石更易破坏.

岩石沿某个方向因弱面或天然裂缝存在而具有较低临界能量释放率时,会形成应力驱动和弱面驱动的竞争,裂缝最终在弱面方向和最大压应力方向之间选择扩展路径 (Jaeger 2009),如图5.9所示. Erdogan和Sih(1963)提出基于最大能量释放率或局部最大能量释放率准则判断各向异性材料中的裂纹扩展路径,Hakim和Karma等(2005)在此基础上提出力平衡原则作为扩展方向判断准则.

5.4.1.3 水压裂缝和天然裂缝相互作用规律

当水压裂缝与天然裂缝、断层等弱面相遇时会出现多种情况: (1)压裂裂缝终止, 天然裂缝扩展; (2) 压裂裂缝穿过天然裂纹扩展,天然裂缝保持静止; (3) 压裂裂缝和天然裂缝同时扩展等,其中天然裂缝的扩展路径选择对复杂裂缝网的形成非常重要．国内外学者对穿越界面的裂纹扩展问题进行了大量研究,Renshaw和Pollard(1995)利用线弹性断裂力学分析水力裂缝垂直逼近天然裂缝时的力学作用,提出了水力裂缝贯穿天然裂缝的准则; Gu(2010)将其扩展到任意角度,得到贯穿天然裂缝的解析隐式解; Taleghani(2009)提出了比较水力裂缝贯穿天然裂缝与开启天然裂缝所需要的能量释放率来确定水力裂缝的走向的方法,如图5.10所示.

页岩储层水平井压裂主要采用数十米至百米量级的间隔区域微爆致裂、然后注入高压水力产生裂缝网络.这里有两点需重点考虑: (1)微爆形成的主裂缝在水力压裂过程中不断形成多尺度或多层次裂纹,为难以解吸附的页岩气提供更多的自由表面积,即产生具有损伤意义的弥散裂缝网; (2) 各层次的裂纹均能够稳定性扩展,尽量平行扩展致远, 而非长裂纹对短裂纹形成屏蔽效应,这种裂纹扩展的局部化称其为失去稳定性,如何创造这种多尺度稳定裂缝网体系是页岩水力压裂的重要研究内容之一.

5.4.2 页岩裂缝扩展数值模拟方法

针对页岩压裂的复杂特点,在页岩压裂领域急需发展符合真实物理状况的水力压裂数值模拟工具.这里的关键问题是要发展复杂裂缝网扩展的数值模拟方法,同时还要考虑裂缝扩展和气体渗流及裂缝内流体流动的耦合作用.

针对页岩水力压裂过程的多物理场耦合特征,一般的耦合计算流程是首先通过求解固体平衡方程得到岩石变形和裂缝几何信息,然后把位移场和裂缝张开宽度等信息传递给流体求解器, 求出全场流场压力(包括页岩基质孔隙压力和缝内压力)分布,再返回给固体求解器用于更新当前压力载荷下的位移和裂缝信息,如此循环下去实现流体驱动下的多孔介质中裂缝扩展的模拟.目前主要基于润滑理论和Poiseuille's Law来求解缝内的流动,得到裂缝内的流体压力分布,然后将求得的压力作用在裂缝面上驱动裂缝张开、扩展.缝内流动的控制方程主要有缝内流动的连续方程、润滑方程以及滤失方程.国内外对裂缝扩展的数值模拟方法大致可以分为两类:一类是通过网格对裂缝几何进行描述,典型的有网格重剖分方法、边界元法、内聚力单元法等;一类是不需要通过网格对裂缝几何进行描述,而是通过增大单元自由度或引入独立损伤变量对断裂过程进行描述,典型代表为扩展有限元方法和相场法.

下面对几种代表性方法予以介绍: 基于边界元的位移间断方法 (DDM),当裂纹扩展时需要重新剖分网格,以求解裂纹面处位移间断在岩体内部产生的变形场;基于有限元和非连续变形分析的流形元方法 (NMM),该方法很容易处理岩体内断层、节理、裂纹等不连续面,但扩展到三维有一定困难; 基于单位分解的扩展有限单元法 (XFEM),在传统有限单元法的基础上进行了重要的改进,无需重划网格即可实现裂纹在规则网格中的任意扩展;基于解析或半解析裂缝模型的离散裂缝网方法 (DFN), 该方法求解效率高,在商业软件中广泛采用, 但其基于简单的平面裂缝模型,难以考虑天然裂纹、材料各向异性、孔隙压力等对裂缝网形貌的影响.这些方法各有千秋,目前在岩体压裂裂缝扩展数值模拟研究中都已经得到有效应用,取得了丰硕的成果.

5.5 页岩复杂介质的非均质特征

由于不同类型富有机质页岩形成环境的差异性,页岩储层在纵向上具有多重非均质性,包括岩性的纵向非均质性、储层物性的纵向非均质性、岩石力学参数的纵向非均质性、地应力的纵向非均质性以及含气性特征的纵向非均质性等,这造成了页岩油气储层的纵向非均质性明显强于横向非均质性,有机质丰度、孔隙度、渗透率、储层的可压裂性、地应力、含气性及吸游比等参数在纵向上的变化均较大,并且直接影响了后期页岩油气开发过程中的渗流规律.

5.5.1 横纵向各向异性

页岩储层的横向渗透率与纵向渗透率的差异巨大,必须考虑横纵向各向异性对渗流规律的影响. 针对页岩气渗流的各向异性,可对比研究储层各向同性和局部异性基质内页岩气的渗流规律,并给出了精确描述渗透率变化的数学模型,充分考虑了局部孔隙结构多样化分布和基质组份含量,采用小扰动理论研究储层内页岩气的吸附和运移,研究发现与各向同性的基质相比,孔隙系统局部渗透率变化将影响页岩气的运移效率.通过研究异质性岩层中井筒周围基质对二氧化碳的束缚和控制,也证明了异质性岩层对储层气体渗流效率的明显影响.页岩气基质的各向异性对页岩气渗流控制的机理尚未研究清楚,这也是以后重点研究的内容之一.

5.5.2 基质本身的非均质性

陆相页岩气储层岩石组成相对复杂, 除泥粒级岩石矿物组分外,还有粉砂质、细砂质等粒级较粗的岩石矿物, 以及灰质等;岩性组合在纵向上的变化相对海相页岩更为迅速且复杂.海相页岩岩性组合以厚层泥页岩夹海相砂质岩、碳酸盐岩等为主要特征,而陆相泥页岩岩性组合以大套巨厚泥页岩夹薄层砂质岩或多层厚层泥页岩夹薄层砂质岩组合为主要特征.含油气页岩层段的矿物成分在剖面上的变化也较明显.

含油气页岩储层的非均页岩储层基质孔隙度一般小于10%;孔隙空间类型多样, 包括粒间孔、粒内孔、有机质孔隙和裂隙质性强,纵向非均质性明显, 这点与致密油气储层有明显的差异.上扬子地区龙马溪组的基质孔隙主要有黄铁矿粒内孔、黏土矿物层间孔隙、残余原生孔隙、不稳定矿物溶蚀孔及有机质微孔隙等.龙马溪组页岩中较为常见的是莓状黄铁矿粒内孔, 孔隙形状常不规则,大小在50~300nm, 孔隙之间的连通性较差,这种孔隙类型对页岩气储集与渗流意义不大 (图5.11(a)),而残余原生孔隙、不稳定矿物溶蚀孔在页岩中有少量发育,有机质在生烃过程中常会产生一部分有机酸,这些有机酸会对邻近的不稳定矿物 (如方解石与长石矿物)产生局部溶蚀,形成溶蚀孔, 形状常不规则, 有时可见溶蚀港湾或锯齿状,大小在1$\mu$m左右 (图5.11(b)), 另外,龙马溪组页岩有机质内普遍发育有蜂窝状、线状、串珠状孔、复杂网状等多种形态孔隙,该类孔隙的形成常与有机质的生烃作用有关,通常在低成熟度页岩样品中缺乏该类纳米级孔隙,而在较高成熟度页岩样品中普遍发育这类孔隙, 孔径大小一般在0.1$\sim$1$\mu$m.

由于岩性的纵向变化, 页岩气储层的岩石力学参数也发生变化.其中岩石弹性模量和泊松比的大小与岩石的脆性直接相关,是岩石脆性的直接反映. 同时, 由于不同岩性层的强度不同,其应力特征在剖面上的分布也不同.黏土矿物和有机碳含量较高的岩性层泊松比相对较大、最小主应力相对较小,黏土矿物和有机质含量较低岩性层泊松比相对较小, 最小主应力相对较大.如果在页岩气储层中部为低应力, 上、下部为高应力时,上、下部的高应力层可以起到屏蔽作用, 控制缝高,这对体积压裂缝网的形成十分有利.

5.5.3 天然裂缝引发的非均质性

地应力状态、地层力学性质、层理和裂缝等控制了压裂裂缝的形态和空间展布.随着埋深的增大, 垂向应力逐步增大,由近地表和浅部的最小主应力、逐步过渡到中间主应力、最大主应力.由于岩石的抗张强度一般较小, 当应力差达到一定值时,压裂裂缝总体上会沿最大主应力和中间主应力平面形成, 随着埋深的增大,压裂裂缝的总体形态也从近水平变为近垂直; 随着应力差的增大,压裂裂缝的形态也越来越平直. 因此, 在应力差较大的地区,需要采用相关技术, 对压裂裂缝的延伸方向进行干预,并缩短压裂段的长度和射孔间距, 尽量增大压裂裂缝的影响范围.可见页岩储层水平方向上的层理性结构导致了页岩较强的非均质性和各向异性.采用常规的弹性各向同性地层的裂缝起裂预测模型已不能满足页岩气井水力压裂工程实际需求,需要考虑层理性页岩的横向各向异性特性,开展页岩弹性各向异性以及地应力各向异性对水平井裂缝起裂的敏感性研究,根据岩石横向各向异性本构关系,最终建立渗流与变形的耦合数值模拟方法.为层理性页岩气井水力压裂优化设计提供指导意见.

5.5.4 页岩储层的变形规律

页岩气藏开发过程中, 压力不断降低, 应力敏感增强, 导致孔隙减小,从而降低绝对渗透率, 但同时滑脱效应和自由分子流动效应会增强.随着压力进一步降低, 吸附气解吸, 基质产生收缩, 导致孔隙增大,绝对渗透率升高, 但同时滑脱效应和自由分子流动效应会减弱;应力敏感和基质收缩共同影响着绝对渗透率.页岩基质渗透率变化是一个多因素影响的复杂过程.页岩气藏孔渗结构具有强烈的多尺度性, 渗流机理复杂,纳米级基质孔隙克努森扩散效应、裂缝应力敏感效应,以及气体解吸收缩效应等多重机制对页岩气多尺度流动特征及页岩气产能模型都有一定影响.建立考虑纳米级基质孔隙努森扩散流、裂缝应力敏感变形、基质解吸收缩效应协同作用的非线性渗流数学模型.

页岩气生产过程中随着孔隙压力的下降, 天然裂缝可能逐渐闭合,天然裂缝表现出较强的应力敏感特征, 基于Ozkan和Raghavan(2009,2011)的研究成果得到天然裂缝随孔隙压力变化的渗透率方程如下

$ K_{\rm f} = K_{\rm {fi}} \exp \left[ { - d_{\rm f}\left( {p_{\rm {fi}} - p_{\rm f} } \right)} \right] (5.12)$

式中, $K_{\rm f}$为考虑应力敏感的天然裂缝渗透率, mD; $K_{\rm fi}$为原始天然裂缝渗透率, mD; $d_{\rm f}$为天然裂缝应力敏感系数,MPa$^{ - 1}$.

随着地层压力下降, 页岩储层中的吸附气体开始解吸,页岩基质收缩引起渗流通道的增大对渗透率有重要影响.采用Bangham固体变形理论描述压力下降时吸附气解吸对页岩气渗透率影响,页岩收缩程度采用式(5.13)计算

$ K_{\rm f} = K_{\rm {fi}} \exp \left[ { - d_{\rm f}\left( {p_{\rm {fi}} - p_{\rm f} } \right)} \right] (5.12)$

$ \Delta \varepsilon = \rho _{\rm s} \dfrac{RT}{EV_{\rm b}}\int_{\psi _i }^{\psi _{\rm m} } {\dfrac{V}{\psi }}{\rm d}\psi (5.13)$

式中, $\Delta \varepsilon$为有效应力下的页岩收缩程度, 无量纲; $\rho _{\rm s} $为岩石密度,kg/m$^{3}$; $R$为气体常数, MPa$\cdot $L/(mol$\cdot $k);$T$为绝对温度, K; $E$为杨氏模量, MPa; $V_{\rm b} $为气体摩尔体积,10$^{ - 3}$m$^{3}$/mol; $\psi $为地层拟压力,MPa$^{2}$/(mPa$\cdot $s); $\psi _{\rm m} $为基质孔隙拟压力,MPa$^{2}$/ (mPa$\cdot $s); $V$为吸附气含量, m$^{3}$/t.

结合兰格缪尔方程, 将式(5.8)积分得到基质收缩量百分数.随着储层压力的降低, 吸附气体开始解吸导致基质收缩,同时裂隙内的有效应力增大, 岩体也产生膨胀变形, 得到岩体的总变形量.进一步根据理想毛管束模型, 得到基质直径.

为了准确刻画储层改造体积对页岩气藏渗流规律的影响,可针对页岩气藏中水平井结合体积压裂开采、吸附气和游离气共存的方式,建立考虑储层改造体积的页岩气藏复合模型.将储层分为人工主裂缝区域、储层改造区域和未改造区域,其中人工主裂缝基于离散裂缝模型降维处理,储层改造区域为双孔双渗模型, 未改造区域为单孔隙介质模型;模型采用有限元方法进行求解. 姚军等(2013)研究结果表明:页岩气藏水平井体积压裂复合模型主要存在主裂缝周围线性流、过渡区域拟稳态、窜流阶段、未改造区域的拟径向流动和到达边界后的拟稳态等5个主要流动阶段,且考虑吸附解吸后, 定产量生产所需压差小, 压力波传播到边界时间长,压力导数曲线凹槽更加明显, 定井底流压生产时压裂水平井产量更大,稳产时间更长; 储层改造体积越大, 到达区域拟稳态流越晚,可判定储层改造体积; 吸附体积越大, 压力波传播越慢, 所需压差越小,压力导数曲线凹槽越深, 页岩气藏稳产时间越长, 产量越大,但产量的增幅越来越小.

5.6 本节小结

(1)微观流动机理需要更多手段进行分析验证,重要的发展方向是微观机理向宏观流动规律的过渡方法的研究,实现多尺度的跨越.

(2)页岩气的吸附及解吸附机理研究结果较少,如何寻求微观解吸机理与宏观流动的耦合应是发展的重要方向.

(3)页岩气藏人工压裂后形成复杂的裂缝网络,通过建立页岩各向异性的多孔本构, 形成页岩各向异性强度和断裂准则,进而分析水压裂缝和天然裂缝之间的相互作用规律,深入探究页岩裂缝的扩展理论.利用双重介质模型、离散裂缝模型和嵌入裂缝模型表征复杂裂缝网络,耦合天然、人工裂缝和页岩基质内的流体流动, 分析页岩气井的生产规律.

(4)由于不同类型富有机质页岩形成环境的差异性,页岩储层在纵向上具有多重非均质性,表现为孔喉结构类型丰富、岩性差异大、地应力各向异性.由于地应力状态、地层力学性质、层理和裂缝等控制了压裂裂缝的形态和空间展布,需要开展页岩弹性各向异性以及地应力各向异性对水平井裂缝起裂的敏感性研究.

(5)页岩气藏孔渗结构具有强烈的多尺度性, 渗流机理复杂,纳米级基质孔隙努森扩散效应、裂缝应力敏感效应以及气体解吸收缩效应等多重机制对页岩气多尺度流动特征及页岩气产能模型都有一定影响.

6 页岩气水力压裂数值模拟方法^*(*本节撰稿人: 周东¹(1E-mail: zhoudong@imech.ac.cn), 李世海, 柳占立)

6.1 前言

目前页岩储层压裂主要是以水力压裂为主.水力压裂研究和设计中所涉及的现场和物模实验成本高昂,能捕获的信息也相对有限, 因此随着计算技术的发展,数值模拟逐渐成为研究压裂过程的重要手段.目前国际上已形成了一些水力压裂的软件体系, 从整体区块的压裂设计,到单井压裂设计和实时监测分析等方面, 都有相应的软件,代表性的主要有FracpropPT, Meyer, TerraFrac, E-StimPlan等,这些软件的开发和使用大大促进了水力压裂技术的发展. 但总体而言,目前的商用软件大多采用简化的力学模型, 采用解析或半解析的裂缝模型,把裂缝简化成对称平面裂纹,忽略了裂缝复杂的几何形态及多个裂缝之间的相互作用,很难处理裂纹交汇、分叉和裂纹网络等问题.而压裂数值模拟技术本身经过多年发展已经日趋成熟,可以较好的分析压裂过程中的复杂裂缝扩展问题.本章将对页岩压裂中可能用到的水力压裂计算模型和数值模拟方法作简单介绍.

6.2 理论计算模型

水力压裂的理论计算模型最早可追溯到20世纪中期. 1946年, Sneddon(1946)率先研究了圆形裂纹(penny-shaped fracture)的扩展问题,给出了圆形裂纹在静压作用下的开度公式. 到20世纪70年代,关于水力压裂计算的研究大多是二维理论模型方面的研究.这个阶段发展了几个著名的理论计算模型, 包括PK模型(Perkins & Kern 1961)、PKN模型(Nordgren 1972)、KGD模型(Khristianovich & Zheltov 1955, Geertsma & de Klerk 1969)等.这类模型可通过加入滤失系数(Carter 1957)来考虑滤失效应,但均是二维(2D)模型, 无法同时模拟裂缝高度和长度两个方向上的扩展.20世纪80年代, 发展出了拟三维(pseudo 3D, P3D)模型(Settari &Cleary 1986). 拟三维模型可以模拟裂缝高度和长度方向上的共同扩展,但是裂缝的形状和方位是固定的. 为了解决这个问题,有学者发展出三维模型, 但这些模型大多数是平面三维(planar 3D,PL3D)模型(Siebrits & Peirce 2002).PL3D模型中的裂缝宽度和长度是可以任意扩展的,并且裂缝可以沿任意方位扩展, 但裂缝只能是平面的.上述模型通常被称为常规计算模型, Rahman(2010)和Adachi等(2007)的文章对这些模型作了综述, 它们的特点是:计算量小、计算效率高, 但受假设条件限制导致计算精度不足. 21世纪,非常规计算模型得到了发展, 如线网模型(Xu et al.2010)、非常规裂缝模型(Weng et al. 2011)等.这些模型的特点是将理论模型与现场监测数据有机结合起来,模型做了一定简化, 计算量小, 跟实际结合也更紧密.现对几类经典的水力压裂计算模型进行简单介绍.

6.2.1 传统水力压裂模型

6.2.1.1 PKN模型

Perkins和Kern(1961)根据图6.1所示模型通过做出以下假设,建立了二维水力压裂模型:

(1) 裂缝高度$h_{\rm f}$固定, 与缝长无关.

(2) 与裂缝扩展方向垂直的横截面中的液体压力$p$为常数.

(3) 每一个垂直截面独立变形, 不受邻近截面影响.

(4) 横截面形状为椭圆形, 模型中心截面的宽度为

$ w(x,t) = \dfrac{(1 - \nu )h_{\rm f} (p - \sigma _{\rm h} )}{G} (6.1) $

(5)流体在椭圆形通道中符合牛顿流动

$ \dfrac{\partial (p - \sigma _{\rm h} )}{\partial x} =- \dfrac{64}{\pi }\dfrac{q\mu }{w^3h_{\rm f} } (6.2) $

(6) 缝内流体在缝端逐步下降, 在缝长$L$处, 压力$p = \sigma _{\rm h}$.

在最初始的理论中, 忽略裂缝宽度增长对流量的影响. 后来,Nordgren(1972)考虑了裂缝宽度增长的影响, 连续性方程为

$ \dfrac{\partial q}{\partial x} = - \dfrac{\pi h_{\rm f} }{4}\dfrac{\partial w}{\partial t} (6.3) $

通过引入初始条件和边界条件

$ w(x,t) = 0; \quad w(x,t) = 0\quad {\rm for}\quad x > L(t),\quad (0,t)= q_0 (6.4) $

可解得PKN模型裂缝长度与宽度的解为

$ \left.\begin{array}{l} L(t) = 0.605\left[ {\dfrac{Gq_0^3 }{(1 - \nu )\mu h_{\rm f}^3 }} \right]^{1/ 5}t^{4 / 5} \\ w(0,t) = 2.104\left[ {\dfrac{(1 - \nu )q_0^2 \mu }{Gh_{\rm f} }} \right]^{1/ 5}t^{1 / 5} \\ \end{array} \right\} (6.5) $

6.2.1.2 KGD模型

Khristianovich和Zheltov(1955), 以及Geertsma和deKlerk(1969)推导了KGD模型, 如图6.2所示, 其假设为:

(1) 假设缝高固定.

(2) 仅在水平面考虑岩石刚度.

(3) 裂缝截面为矩形, 裂缝中流体的流动满足立方定律

$ p_{{\rm net}} = p(0,t) - p(x,t) = \dfrac{12\mu q_0}{h_{\rm f} }\int_0^x {\dfrac{{\rm d}x}{w^3(x,t)}} (6.6) $

应用Barenblatt缝端条件

$ \int_0^L {\dfrac{p_{{\rm net}} (x,t)}{\sqrt {L^2 -x^2} }} {\rm d}x = 0 (6.7) $

式(6.1)中令$h_{\rm f} = L/2$,得到缝宽为

$ w(x,t) = \dfrac{2(1 - \nu )Lp_{{\rm net}} }{G} (6.8) $

根据式(6.6)~式(6.8)得出缝长和缝宽的理论解为

$ \left.\begin{array}{l} L(t) = 0.68\left[ {\dfrac{Gq_0^3 }{\mu (1 - \nu )h_{\rm f}^3 }} \right]^{1/ 6}t^{2 / 3} \\ w(0,t) = 1.87\left[ {\dfrac{(1 - \nu )\mu q_0^3 }{Gh_{\rm f}^3 }}\right]^{1 / 6}t^{1 / 3} \\ \end{array}\right\} (6.9) $

6.2.1.3 P3D模型

图6.3所示为一种P3D模型, 该模型把储层分为多层,裂缝在不同层中长度存在分布, 裂缝所在层的位置即表示裂缝高度.该模型可分别计算裂缝长度、高度和宽度的分布.流体在每一层中均服从一维裂隙渗流,裂缝尖端流体压力与地应力的差的大小决定裂缝的开裂.与PKN模型的假设相似的是, 垂直于裂缝平面的各层位移是相互独立的.

从以上3个模型的假设可以看出, 上述水力压裂模型局限性在于: (1)模型仅限于单裂缝的扩展, 无法模拟复杂裂缝网络的交叉问题; (2)裂缝在某一假定的空间域内进行扩展, 无法真实模拟裂缝的开裂; (3)不考虑滤失或者是凭借经验以滤失系数的形式来考虑.

6.2.2 非常规水力压裂模型

6.2.2.1 线网模型(wire-mesh model)

Xu(2010)以及Meyer和Bazan(2011)提出了线网模型(wire-mesh model),该模型中水力裂缝网络用一个由预设的两组正交均匀分布的垂直裂缝构成的椭圆体代表.

线网模型固体计算应用岩石力学方法考虑了压裂过程中裂缝椭球体的实时扩展,考虑了施工参数的影响, 并计算了支撑剂在页岩裂缝中的分布情况(Xu et al. 2010, Meyer & Bazan 2011).线网模型流体计算基于常规的拟三维模型的裂缝高度延伸方程和整体的质量守恒. 线网模型分析水力压裂的过程如图6.4所示,该模型通过与微震监测数据进行对比以修正模型预测的裂缝网络.

线网模型的局限在于:(1)必须将储层改造区域近似为沿井筒注入点对称分布的椭球体,不能模拟不规则的裂缝形态, 限制了与微地震数据的拟合;(2)裂缝间距和改造体积由微地震监测结果确定, 仅限于本段压裂施工模拟,计算结果不具有普遍适用性; (3)没有建立判断准则,直接认为天然裂缝与人工裂缝相连接;(4)没有考虑人工裂缝之间相互干扰对裂缝形态的影响.

6.2.2.2 非常规裂缝模型

Weng(2011)和Kresse等(2013)提出了非常规裂缝模型(unconventionalfracture model, UFM), 该模型做了很多同常规拟三维模型相似的假设,但考虑了复杂裂缝网络扩展及水力裂缝尖端与天然裂缝相交时的相互作用,考虑了压裂液的一维流动、支撑剂的输送和裂缝宽度的弹性变形,通过计算应力阴影考虑相邻人工裂缝间的相互作用.该模型采用三层模型模拟支撑剂输送, 分别为支撑剂、混砂液和压裂液.

非常规裂缝模型比线网模型提供了一种更为精确预测裂缝分布、几何形态和支撑剂分布的方法,综合考虑了地层天然裂缝、应力分布和力学性质的非均质性,能够模拟裂缝网络的非对称和不规则形态,计算结果可以很好的与微地震数据拟合和校正.非常规裂缝模型分析水力压裂的过程, 如图6.5所示,可看出其裂缝网络更加复杂化,而不是像线网模型中使用一个椭圆代替整个压裂区域.

非常规模型的不足之处是：做了同常规拟三维模型相似的假设,单条水力裂缝仍为平面缝, 扩展路径受限, 不能模拟裂缝的随机弯曲转向;裂缝的分布依赖于离散裂缝地质建模的结果;人工裂缝的模型依赖于计算参数的精确性.

6.3 水力压裂数值计算

为了克服水力压裂模型中的不足,各国学者纷纷开始研究使用数值计算方法模拟水力压裂问题.使用数值方法的优势是, 可以考虑任意情况下的压裂过程,包括任意路径的裂缝扩展、真实的流体流动过程、各种复杂模型条件等.

6.3.1 数值计算模型

6.3.1.1 固体破裂计算模型

(1) 线弹性断裂力学模型

线弹性断裂力学认为, 裂纹扩展前裂纹尖端无塑性区,或塑性区尺寸远远小于裂纹长度(Broek 1982).研究裂纹扩展包括两种观点: 一种是能量平衡观点, 如Griffith理论(Griffith 1921), 认为当应变能大于断裂能时发生断裂;另一种是应力场强度的观点, 如Irwin理论(Irwin 1968),该理论认为应力强度因子大于临界值时发生断裂.

(2)损伤模型

根据不同的力学行为, 很多学者发展出不同的损伤模型,如Lubliner等(1989)的塑性损伤模型, Simo(1987)的黏弹性损伤模型,Meschke等(1998)的各向异性弹塑性损伤模型等. Li和Zhou(2013)发展出一种新型损伤模型, 称为应变强度分布模型.该模型认为材料的强度在代表性体积元(RVE)上存在一定分布,材料微观发生拉伸、剪切以及拉剪三种破坏行为.RVE的宏观强度由材料的三种微观破坏行为所体现.该模型建立了材料微观破坏到宏观损伤的对应,可以刻画材料的渐进破坏过程.

(3)强度模型

最经典的强度模型即四大强度理论(刘鸿文 1997),包括最大拉应力准则、最大伸长线应变理论、最大剪应力理论、形状改变比能理论.此外, 还包括内聚力模型(Nguyen et al. 2001)、Mohr-Coulomb模型(Hoek 1990)等.

6.3.1.2 渗流计算模型

压裂改造的油气藏储层是一种节理化孔隙介质,针对这种介质发展的渗流计算模型主要包括3个:双重孔隙介质模型、等效连续介质模型和离散裂隙网络模型.这3种模型的对比, 如图6.6所示.

Barenblatt等(1960)于1960年率先提出均质、各向同性的双重孔隙介质模型;Warren和Root在1963年也独立提出该模型.该模型假定节理化孔隙介质是一种包含两种物性的连续介质,其几何区域是交叠的. 两种介质之间的物质交换, 以窜流项表示.1982年Long等(1982)把强节理化孔隙介质, 等效为一种连续介质来处理,提出等效连续介质模型. 该模型中介质的渗透率和孔隙度通过平均化获得,这种简化使得等效连续介质模型中不包含裂隙, 因此计算精度较低.1992年, Dverstorp等(1992)通过提取介质中的主导裂隙,建立了离散裂隙网络模型. 由于该模型的简化条件较少,因此该模型最为精确, 但使用该模型将导致计算量巨大.

6.3.2 数值计算方法

6.3.2.1 有限单元法

早在1982年, Advani和Lee(1982)就使用有限单元法(finite elementmethod, FEM)模拟水力压裂过程, 开启了水力压裂数值模拟的时代.该模型考虑岩体压裂后的响应,提供了一个用于评价裂缝扩展范围的统一框架. 在此框架下,可分别求解层状储层、不同地应力、相交化节理、裂纹分叉等工况. 后来,Lee(1990)专门研究了层状储层的水力压裂问题. Boone和Ingraffea(1990)开发了一个二维水力压裂程序,用于模拟弹性多孔介质的水力压裂问题.该程序使用有限元法计算固体应力场,使用有限差分法计算裂缝中水的流动. 有限元求解中使用矩阵分解法,进行了并行化.Sousa等(1993)分别研究了牛顿流体和幂律流体对水力压裂效果的影响.为了描述水力裂缝中支撑剂的分布,Ouyang等(1997)发展了一种自适应的二维有限元模型.模型中考虑水力压裂过程中, 非牛顿流体对支撑剂浓度影响.通过增加网格点或改变网格点的分布,实现求解支撑剂浓度过程中的网格自适应.

到了2000年以后, 三维有限元水力压裂程序开始发展.Carter等(2000)发展了全耦合的三维有限元水力压裂求解器.该求解器中固体计算和裂隙流体渗流均采用有限元法,可以模拟多裂缝、任意裂缝、非平面裂缝等情况.固体采用线弹性断裂力学模型, 裂隙渗流采用立方定律模型,滤失采用Carter滤失系数模型. 通过与理论解对比, 验证了算法的有效性.Devloo等(2006)也发展了一个三维有限元水力压裂求解器.该求解器考虑裂隙渗流、滤失效应以及周围孔隙介质的弹性响应.使用有限元法,求解流体流量守恒方程、边界力--裂隙开度耦合奇异积分方程(singularintegral equation). 该奇异积分方程是一个非线性方程,通过牛顿法进行求解. Pak和Chan(2008)使用隐式有限元法,模拟了砂岩的三维水力压裂耦合过程, 并与现场数据进行对比.通常模拟水力压裂的模型, 并不适用于砂岩的模拟,这是由于砂岩的渗透率高, 滤失效应显著. Pak和Chan(2008)所发展的热--流--固全耦合三维隐式有限元方法,适用于砂岩水力压裂模拟, 并且通过与试验数据进行对比,验证了模型的可靠性.

2008年以后, 各种新的有限元模型开始发展.Chen等(2009)发展了一种三维全耦合内聚力有限元模型(其示意图如图6.7所示), 通过与Penny-shaped理论模型进行对比,验证了该模型的有效性. Chen(2012)将验证过的三维有限元内聚力模型,用于研究黏性主导的水力压裂问题. 研究中,Chen还推导了基于内聚力模型的KGD理论模型, 并将数值模型与之对比,结果符合较好. Carrier和Granet(2012)同样使用内聚力模型,研究了可渗透的水力压裂问题.他们发展一种零厚度的有限单元来模拟裂隙单元,裂缝扩展由内聚力模型和光滑平板流方程控制. 模型求解为全耦合形式,通过与渐进理论解对比, 验证模型的正确性.

Wangen(2011)应用有限元法, 使用裂缝化单元模型(fractured elementmodel), 模拟了二维水力压裂过程.Wangen(2013)又将该模型推广到三维情况. 该模型示意图如图6.8所示. 该模型中, 通过强度准则判断裂缝的扩展:如果一个孔隙单元达到强度准则, 那么该单元将变成裂隙单元,通过裂隙孔隙度(fracture porosity)表征裂隙单元的流量守恒, 即

$ \phi _{\rm F} = \phi + \dfrac{V_{\rm F} }{V_{\rm E} } (6.10) $

裂缝化单元模型得到的裂纹如图6.9所示,从中可看出裂缝呈现网状分布, 但是裂缝宽度较宽, 显得不够真实.

此外, Zhang和Ghassemi(2011)以及Huang等(2013)使用多维度内部虚连接模型(virtualmultidimensional internal bond, VMIB),应用有限元法求解天然裂缝附近的水力压裂问题. VMIB模型中,单元内部通过虚拟的连杆连接, 通过断裂力学准则判断连杆是否进行断裂,从而实现水力裂缝的扩展.

Li等(2012)提出一种渗流--应力--损伤模型(flow-stress-damage model,FSDM), 用于有限元求解水力压裂过程, 通过与试验进行对比验证了该模型.FSDM模型中, 对岩体弹性模量进行损伤演化, 求解弹性模量的损伤系数$D$.如果$D = 0$, 那么认为单元即发生断裂, 从而进行渗流计算,以此实现水力压裂过程. 使用损伤模型得到的水力压裂效果图, 如图6.10所示. 从图中可看出, 该模型与微震监测得到的结果具有相似性.Shojaei等(2014)使用基于连续介质损伤模型(continuum damage model,CDM)的有限元法分析了孔隙介质的水力压裂问题,并与试验结果进行了对比, 验证了该模型分析的可靠性.CDM模型中考虑了塑性损伤对孔隙介质的裂缝扩展影响.

Hunsweck等(2012)考虑了流体在裂缝中流动的滞后特性,使用有限元分析了平面应变情况下单条直裂缝在不透水弹性介质中的扩展问题(如图6.11). 考虑流体压力与裂纹开度之间的非线性耦合关系,并且追踪了裂纹尖端和流体锋面, 因此该算法允许流体流动中存在滞后.流体锋面由显式算法求得, 但对于裂纹尖端需要使用隐式算法,确保满足Griffith裂纹扩展条件. 通过与相似解进行对比,验证了算法的正确性.

Fu等(2013)使用显式有限元求解了二维水力压裂问题.求解中有限元求解器调用网格划分程序,并使用断裂力学强度因子进行裂纹扩展判断.该方法实现了任意路径的裂纹扩展, 但计算量非常大,即使一个简单的算例也要计算很长时间. 通过与KGD理论解进行对比,验证显式有限元算法的正确性. 此外, 还推导了应力强度占主导的KGD模型,并进行了数值验证.

有限元法模拟水力压裂的主要特点是: 相比较水力模型来讲,计算更加精细化, 可考虑复杂条件下的计算工况, 因此计算精度高;多数是隐式求解压力和裂缝开度之间的耦合方程,也有少数学者使用显式迭代求解算法; 裂纹扩展大多假定扩展路径,并且裂缝扩展多为简单缝, 很少考虑复杂裂缝网络的情况,也有学者通过调用网格程序进行网格重划分的;边界条件是定压边界或固定流量边界; 判断准则多是断裂力学准则,也有通过强度准则或损伤准则进行开裂判断;滤失效应多数是以滤失系数的形式考虑,很少有学者考虑裂隙与孔隙基质之间的渗流效应;有限元数值算法通常与KGD解、Penny-shaped解、相似解等理论解进行对比,或者与简单缝水力压裂试验数据进行对比.

6.3.2.2 有限差分法

使用有限差分法(finite differencemethod,FDM)模拟水力压裂问题的文章相对较少,最早可查到的是20世纪80年代中期.Chouet(1986)使用有限差分法研究三维注水裂纹的动力响应问题.Groenenboom和Falk(2000)通过有限差分法计算裂缝产生的波动效应,并与现场微震监测数据进行对比, 从而反分析裂缝形态.Zhou和Hou(2013)使用基于有限差分的数值计算软件FLAC3D,加入裂隙--孔隙耦合渗流模型, 模拟了三维水力压裂问题. 为验证该模型,将数值解与试验解(试样来自Northern German Basin砂岩区)进行了对比,如图6.12所示.

6.3.2.3 边界单元法

边界单元法(boundary element method, BEM)适合求解裂纹扩展问题,在断裂力学中经常用到(Crouch & Starfield 1990, Aliabadi 1997).20世纪80年代末, 开始有学者用边界元法研究水力压裂问题.Vandamme和Curran(1989)使用边界元法研究了非平面水力裂缝的扩展问题,阐述了数值方法中所使用的各个模型构件(应力位移、渗流以及裂缝扩展准则),并且计算了几个非平面裂缝的算例.

Dong和de Pater(2001)应用位移不连续法(displacement discontinuitymethod, DDM)研究水力裂缝的扩展问题.DDM是早期模拟水力压裂流行的方法, 它属于边界元法的一种.Hossain和Rahman(2008)使用边界元法研究了致密储层的复杂裂缝扩展问题.

Olson(2008)以及Olson和 Taleghani(2009,2010)基于边界元法提出了一个拟三维复杂裂缝网络模型(如图6.13),多裂缝延伸遵守亚临界幂律扩展定律,同时考虑了裂缝的张性破裂和剪切破裂, 但是模型假设缝内压力恒定,没有考虑压裂液的流体耦合效应. Olson和Wu(2012)对模型进行了改进,加入了非牛顿流体注入、卡特滤失、随机非平面扩展和三层介质中缝高延伸模型.

Behnia等(2012)基于位移不连续法, 提出一种新的边界元求解模型.该模型使用高阶边界位移拼接技术(boundary displacement collocationtechnique)以及裂纹尖端单元进行裂缝扩展计算.分别使用最大剪应力准则和应变能密度准则作为裂缝扩展准则,并进行了对比研究. 边界元法模拟水力压裂的主要特点是: (1) 将体运算转化为边界运算,计算效率较高; (2) 裂缝扩展路径受到限制,难以做到任意路径下水力压裂模拟; (3)不能在缝面上施加变化的水力压力; (4) 难以考虑孔隙基质渗流.

6.3.2.4 扩展有限元法

扩展有限元法(extended finite element method,XFEM)是1999年提出的一种求解不连续力学问题的数值方法,在模拟裂纹扩展等不连续问题时特别有效,它所使用的网格与结构内部的几何或物理界面无关,从而克服了在诸如裂纹尖端等高应力和变形集中区进行高密度网格剖分所带来的困难,模拟裂纹扩展时无需对网格进行重新剖分(李录贤等 2005).

Lecampion(2009)率先使用扩展有限元法模拟水力压裂问题,考虑裂纹内部水压力的影响.模型分别计算断裂强度、流体黏度主导机制下的裂纹扩展,与这两者的渐进理论解进行了对比, 数值解符合渐进解$t^{2 /3}$幂次的扩展规律. 对单位分解法中缺乏转变区进行了修正,并说明这一项的重要性.Ren等(2009)也使用扩展有限元法研究水力压裂问题,同样考虑裂纹内部水压力的影响, 并对算法进行了验证.

Dahi-Taleghani(2009, 2010)以及Dahi-Taleghani和Olson(2011)基于二维平面应变弹性理论,应用扩展有限元法模拟了复杂裂缝问题,考虑人工裂缝与天然裂缝的相交问题(如图6.14所示).该模型的缺点是: 水力裂缝面上施加均匀、恒定的净压力,不考虑流体滤失或渗流作用.

Khoei和Haghighat(2011)使用扩展有限元法模拟了具有任意破裂面的孔隙介质的水力裂纹扩展问题.Khoei等(2012)又模拟了孔隙介质在热--流--固耦合作用下的裂纹扩展问题.通过给出裂缝扩展的实际案例, 说明了扩展有限元法的效率.

Shakib等(2012)以及Shakib(2013)使用扩展有限元法研究了储层中含有天然裂缝的水力压裂问题.计算结果表明,裂缝形态的复杂性受控于应力各向异性、天然裂缝的胶结强度、天然裂缝与人工裂缝之间的方位.人工裂缝的发展会导致天然裂缝开启,原岩应力的各向异性会增加这一开启的可能性, 并降低裂缝闭合的可能性.

Gholami等(2013)基于扩展有限元法, 考虑流--固全耦合过程,模拟了孔隙介质的水力压裂问题. 使用内聚力裂缝概念,用于描述准脆性材料的非线性裂纹扩展过程. Mohammadnejad和Khoei(2013)同样使用内聚力裂缝模型,用扩展有限元模拟了孔隙介质的水力压裂问题.

Weber等(2013)及Weber和Fries(2013)把显式--隐式裂缝描述方式引入到扩展有限元中,用于模拟水力压裂过程. Gordeliy和Peirce(2013)提出一种耦合扩展有限元算法.Fries等(2014)考虑了应力强度因子对水力压裂的影响.

庄茁等(2012, 2015)以及王涛等(2014)发展了一系列新的模型,用以研究人工裂缝与天然裂缝的复杂相互作用规律及多孔岩石中的水力压裂过程等,包括利用新的水平集理论描述裂缝的交汇、分叉等拓扑,同时具备扩展有限元单元和内聚力单元特点的混合单元,耦合变形--流动--扩散的断裂模拟程序等.这些模型实现了固体场和流体场的完全耦合,可以很好的捕捉裂缝的扩展路径,可以方便的描述水压裂缝穿过层理弱面扩展的行为.

扩展有限元法模拟水力压裂的特点是: (1) 可以考虑任意路径的裂缝扩展;(2) 裂纹扩展需要隐式迭代, 很难计算大规模问题; (3)裂缝中的压力常为静态压力; (4) 算法条件数高, 容易导致发散; (5)由于增加了节点自由度, 导致计算量很大; (6) 三维裂纹扩展难以实现.

6.3.2.5 离散单元法

离散单元法(discrete element method, DEM)由Cundall(1971)在1971年提出, 1979年经Cundall和Strack(1979)发展,适用于计算离散类物质, 如块体和颗粒等.

Al-Busaidi和Hazzard(2005)率先使用二维离散元法模拟Lac duBonnet花岗岩试样的水力压裂问题.将不连续介质当作一堆带有连接的颗粒物质来处理,通过断开颗粒物质的连接, 实现裂缝扩展.该模型与实验室所做试验进行了对比验证,试验获得的声发射数据佐证了该模型. Torres和Castañ;o(2007)也使用二维离散元法模拟了水力压裂过程,不过他们用的离散元几何模型是Voronoi多边形.通过Mohr-Coulomb准则判断多边形之间的断裂问题, 实现裂缝扩展. Wang(2008)使用颗粒离散元法模拟了二维水力压裂问题.Damjanac等(2010)使用颗粒离散元结合离散裂隙网络模型模拟了二维水力压裂问题.

Zhao(2009)应用二维颗粒离散元法(PFC2D) (图6.15)模拟水力裂缝与天然裂缝的相遇行为,模型由黏结颗粒和粒间孔隙空间构成,流体注入提高孔隙压力使得颗粒间黏结破裂, 天然裂缝没有黏结或弱黏结,其他黏结颗粒的破裂可以形成新的水力裂缝. Nagel(2011)应用三维离散元法(3DEC) (如图6.16)研究了裂缝性储层中排量和压裂液黏度对破裂类型的影响.模型中储层由离散的刚性或可变形块体构成,块体大小、形状、方向可由真实统计的三维离散裂缝网络(DFN)确定. Zangeneh等(2012)应用二维离散元法(UDEC) (如图6.17)模拟了水力裂缝网络. 模型中岩体被多组节理所分割,节理之间为可变形的岩块,压裂液流动和裂缝破裂仅能沿着预设的节理网络,除了初始天然裂缝外不能有新的裂缝扩展. Hamidi和Mortazavi(2014)使用3DEC, 模拟了有天然节理情况下的水力压裂过程,分析了各个影响因素的敏感性.

Shimizu等(2011)考虑流体黏度和颗粒尺寸的影响,使用离散元模拟了井筒附近区域的水力压裂问题.Deng等(2014)使用离散元法模拟了水力压裂过程中支撑剂和裂缝之间的相互影响.Wang等(2014)结合颗粒流与离散元法, 模拟水力压裂问题,用于煤矿中的水力压裂.

离散元法模拟裂缝网络的特点是: (1)一定程度上可以通过随机网格实现水力裂缝任意路径扩展; (2)计算精度不如有限元精度高; (3) 由于模拟非连续物质时比较灵活,更适用于模拟非连续介质.

6.3.2.6 连续非连续单元法

连续非连续单元法(continuum-discontinuum element method,CDEM)是由Li等(2008)提出一种连续--非连续耦合计算方法,结合水力压裂问题, 在原有算法框架下形成了的大量新计算模型,包括单元破裂模型(王杰等 2015)、基于中心型有限体积的三维孔隙--裂隙耦合渗流模型以及渗流--应力--破裂耦合计算模型(王理想等 2015). 该方法结合了有限元、离散元和有限体积法的优势,可有效的解决在缝面上施加变化压力、孔隙渗流与裂隙渗流的耦合、裂缝沿任意路径扩展等难题,适合页岩等非常规储层压裂中的复杂缝网动态扩展问题模拟.

王理想(2015)利用该算法对页岩水力压裂的裂缝扩展规律开展了大量模拟,分析了页岩储层压裂人工缝网形成的主控因素及水力裂缝扩展的力学机理. 连续非连续单元法模拟水力压裂的主要特点是: (1)可以考虑孔隙--裂隙--应力 场--破裂场的耦合; (2)裂缝可沿任意路径扩展, 可模拟多缝同时扩展问题; (3) 显式求解,集成了有限元、离散元和有限体积在精度和功能上的优势,但计算效率有待进一步提高.

6.4 页岩裂缝网扩展的数值模拟研究

大物模实验研究能获得重要的页岩裂缝扩展数据,如岩石本构参数、3个主应力与水力致裂的关系、裂纹扩展形貌,但其成本高昂, 一次实验动辄几万至几十万元, 需耗费大量的人力、物力;另外, 再大的物模也是从页岩露头样品采集的,不能完全表现地下几千米的地层形态和状态,只能对理论模型和数值模拟技术给予参数标定和方法验证.近年来随着数值模拟技术的发展,水力压裂的数值模拟已成为研究压裂过程的有效手段,对理解页岩复杂裂缝网形成机理、指导改进压裂技术具有重要意义.

针对页岩压裂的复杂特点,在页岩压裂领域急需发展符合真实物理状况的水力压裂数值模拟工具.这里的关键问题是一方面要发展复杂裂缝网扩展的数值模拟方法,一方面更要考虑裂缝扩展和气体渗流及裂缝内流体流动的耦合作用.

6.4.1 页岩压裂数值模拟研究现状

针对页岩水力压裂过程的多物理场耦合特征,一般的耦合计算流程是首先通过求解固体平衡方程得到岩石变形和裂缝几何信息,然后把位移场和裂缝张开宽度等信息传递给流体求解器,求出全场流场压力（包括页岩基质孔隙压力和缝内压力）分布,再返回给固体求解器用于更新当前压力载荷下的位移和裂缝信息,如此循环下去实现流体驱动下的多孔介质中裂缝扩展的模拟.其中固体和流体的求解可以是强耦合也可以是松耦合,下面将分别介绍流体和固体求解方法.

目前主要基于润滑理论和Poiseuille's Law来求解缝内的流动,得到裂缝内的流体压力分布,然后将求得的压力作用在裂缝面上驱动裂缝张开、扩展.缝内流动的控制方程主要有以下几个, 分别是缝内流动的连续方程

$ \dfrac{\partial w}{\partial t} + \nabla \cdot \pmb q + g = 0 (6.11) $

润滑方程

$ \pmb q = - \dfrac{w^3}{12\mu }\nabla p_f (6.12)$

以及滤失模型

$ g\left( {x,t} \right) = \dfrac{2C_l }{\sqrt {t - t_0\left( x \right)} } (6.13) $

页岩基质内的渗流可以近似为达西流动, 分别满足达西定律

$ q_i = - \kappa \left( {p_{,i} - f_i } \right) (6.14) $ 和连续方程

$ \dfrac{\partial \zeta }{\partial t} + q_{i,i} = \gamma (6.15) $

目前大多采用有限体积方法求解润滑方程和连续方程,这里不再详细介绍. 国内外对裂缝扩展的数值模拟方法大致可以分为两类：一类是通过网格对裂缝几何进行描述,典型的有网格重剖分方法, 边界元法, 内聚力单元法等;一类是不需要通过网格对裂缝几何进行描述,而是通过增加单元自由度或引入独立损伤变量对断裂过程进行描述,典型代表为扩展有限元方法和相场法.下面对两类描述中的几种代表性方法分别予以介绍：基于边界元的位移间断方法DDM(Crouch et al. 1990), 当裂纹扩展时需要重新剖分网格,以求解裂纹面处位移间断在岩体内部产生的变形场;基于有限元和非连续变形分析的流行元方法NMM (石根华 1997),该方法很容易处理岩体内断层、节理、裂纹等不连续面,但扩展到三维有一定困难; 基于单位分解的扩展有限单元法XFEM (Moes et al. 1999), 在传统有限单元法的基础上进行了重要的改进,无需重划网格即可实现裂纹在规则网格中的任意扩展;基于解析或半解析裂缝模型的离散裂缝网方法DFN (Dverstorp &Andersson 1989), 该方法求解效率高, 在商业软件中广泛采用,但其基于简单的平面裂缝模型,难以考虑天然裂纹、材料各向异性、孔隙压力等对裂缝网形貌的影响.这些方法各有千秋,目前在岩体压裂裂缝扩展数值模拟研究中都已经得到有效应用,取得了丰硕的成果.

Chen等(2009)使用内聚力模型求解了无限大不可渗弹性介质中的含液钱币型裂纹扩展问题,其计算结果与的断裂韧性主导的理论解$K$-顶点解吻合得很好.作者重点分析了内聚力模型中不同的参数对于计算结果的影响,指出内聚力模型中分离比$\alpha$影响较大. 该工作没有考虑流体的泄露,也只假设了裂纹中流体为轴对称一维流动. Gordeliy和Detournay(2011)使用位移不连续法(DDM)求解了轴对称的钱币型裂缝中的压裂问题.他们跟踪了全过程的lag区域变化, 指出早期裂缝内大部分区域都为lag,只有靠近注入点的部分含有液体, 裂缝形貌为中部鼓起; 在时间较长后,裂缝大部分区域都有液体, 裂纹形貌较为圆润;这分别对应两种不同的能量耗散模式.Garagash等(2011)也采用位移不连续法(DDM)模拟水力压裂中的多场耦合问题,他在缝内采用Poiseuille流动假设, 通过滤失模型来模拟基质渗流.Weng等(2011)基于DFN模型提出了非常规裂缝扩展模型(UFM),该模型能够模拟天然裂缝和人工裂缝之间的相互作用,建立了裂缝端部扩展准则,考虑了压裂液的一维流动、支撑剂的输送和裂缝宽度的弹性变形. 孙海成(2011)使用DFN数值方法模拟了页岩气储层的基质渗透率、裂缝连通性、裂缝密度(改造体积)、页岩气储层主裂缝与次裂缝对产量的影响,指出只有相互连通的有效裂缝对页岩气产出有贡献,并分析了页岩气压后产量递减的规律.

潘鹏志等(2011)将XFEM和流体模拟软件TOUGH结合,实现了固体变形和裂缝内流体流动的耦合分析.Watanabe等(2012)在XFEM框架下发展了界面单元来表示岩石中如节理、天然裂缝等已经存在的不连续弱面,该方法可以模拟多个交叉的裂缝, 但目前还只能处理二维问题,并且不能模拟非连续面的扩展.Chen等(2013)在把压力自由度引入到XFEM单元中模拟水力压裂,既利用了XFEM模拟任意裂纹扩展的优点,又引入了压力自由度模拟裂缝中的压裂液, 实现了二者的耦合,但目前只研究了单裂纹扩展问题.Elizaveta等耦合扩展有限元(XFEM)与润滑方程分析水力裂缝的扩展,指出断裂韧性主导时, 都可以用1/2奇异性, 但对于无lag的黏性主导时,应当使用2/3奇异性.Miehe等(2015)在JMPS的一篇文章中采用相场法来模拟裂缝演化,他将裂缝看做是一种含损伤的连续介质,可以很容易的捕捉到复杂裂缝的演化过程, 另外,他将基质内的渗流和缝内流动统一求解, 实现了完全的耦合过程,但是由于网格精度要求导致相场法计算裂缝的演化需要很大的计算量.

目前多场耦合水力压裂模拟的主要问题有:(1)相关研究大多集中于二维问题, 难以处理复杂的三维裂缝网络;(2)大多数研究忽略基质内渗流,缝内流动--基质渗流--裂缝扩展的耦合求解在求解效率及稳定性上都还面临问题.

6.4.2 基于XFEM的耦合变形--扩散--流动的水力压裂数值模拟研究

近十年来, XFEM被不断完善并发展,逐渐成为了一种处理非连续场、局部变形和断裂等复杂力学问题的功能强大、极具应用前景的新方法(庄茁等 2012, 2014), 在岩土工程领域得到了广泛应用.国内外课题组近年来基于扩展有限元发展多物理场耦合断裂模拟方法,对页岩水力压裂中的一些关键问题进行了初步研究(王涛等 2014).

(1)发展新的水平集理论描述裂缝的交汇、分叉等拓扑,研究人工裂缝与天然裂缝的复杂相互作用规律.

于每个裂缝面, 分别有裂缝面水平集函数和裂前水平集函数来描述,如图6.19所示.

对于每一个裂缝面, 有

$ \{\pmb X :\phi _i (\pmb X ) = 0\quad {\rm and} \quad \psi _i (\pmb X ) \leq 0,\quad i =1,2,\cdots,n\} (6.16) $

对于每一个裂缝前端, 有

$ \{\pmb X :\phi _i (\pmb X ) = 0\quad {\rm and} \quad \psi _i (\pmb X ) = 0,\quad i =1,2,\cdots, n\} (6.17) $

上面两个公式结合可以准确的捕捉裂缝面的位置. 在裂缝扩展的过程中,水平集函数会实时更新, 从而捕捉裂缝的扩展路径.

通过该方法研究了水压裂缝和天然裂缝间夹角、地应力、天然裂缝摩擦力及水压分布等因素对水压裂缝和天然裂缝相互作用结果的影响,模拟结果如图6.20所示.

(2)发展同时具备扩展有限元单元和内聚力单元特点的混合单元研究水压裂缝和岩石节理、层理等弱面的相互作用.

内聚力单元适合模拟粘接的节理、层理弱面的力学行为,扩展有限元单元适合模拟裂缝扩展,我们将内聚力单元和扩展有限元单元通过共节点法结合起来,两个单元占据相同的位置, 共享相同的节点, 如图6.21所示,使得混合单元同时具备扩展有限元和内聚力单元优势,便于描述水压裂缝穿过层理弱面扩展的行为.

应用该混合单元我们研究了如图6.22所示的水力裂缝与节理弱面的相互作用.水力裂缝在扩展的过程中会遇到3个胶结强度不同的节理弱面,其中中间的弱面胶结强度最强. 模拟结果如图6.23所示,分别是不同时刻水压裂缝扩展的示意图. 可以发现,水力裂缝穿过了胶结较强的弱面, 而沿着胶结较弱的面扩展,形成了工字形裂缝.

(3)发展耦合变形--流动--扩散的断裂模拟程序,研究多孔岩石中的水力压裂过程.

利用扩展有限元模拟裂缝的任意扩展, 在裂缝面上显式施加流体压力,同时应用Biot本构模型模拟多孔岩石的力学行为,另外将裂缝看做一种多孔介质,在有限元格式上将介质渗流和缝内流动统一起来进行求解,耦合框架如图6.24所示.该方法的优势是将固体场与流体场同时求解, 实现完全的耦合过程,又便于考虑压裂液在复杂缝网内的流量分配.

为了验证耦合方法的正确性, 模拟了基本的水力压裂平面应变KGD模型,并将数值结果和解析解进行了比较. 模拟的结果见图6.25所示.在该模型中, KGD模型的控制参数$M=0.0845$, 远小于1,可近似认为是断裂韧性控制的解.将数值模拟结果和解析解中的K解进行比较,可以发现数值模拟结果和解析解吻合较好.

通过耦合程序又进一步研究了水力压裂中流体黏性和岩石断裂韧性分别主导压裂过程时的裂尖lag区长度.图6.26给出了黏性主导时的裂缝尖端lag区及裂缝压力分布,可以发现压裂液黏性偏高时, 流体无法到达裂尖区域.

如前面介绍, 页岩水力压裂中缝网的形成对提高页岩气产量至关重要,而通过水压裂缝沟通天然裂缝被认为是形成缝网的主要因素之一.应用耦合方法, 模拟了压裂液由水压裂缝进入天然裂缝后,裂缝网系统的流量分配和裂缝扩展过程, 如图6.27所示,模拟结果表明地应力、天然裂缝间距、流量分配等都对裂缝网络系统的稳定扩展有重要影响.

6.5 本节小结

传统水力压裂模型通常仅限于单裂缝的扩展,无法计算多缝或复杂缝网问题,渗流滤失系数等也基本是通过经验公式确定,因此不适于页岩等非常规储层的压裂分析. 非常规模型可以刻画复杂裂缝,克服了传统模型只能计算单缝扩展的局限, 但扩展路径依赖于地质建模,其精度有待提高.数值计算可以考虑任意路径的裂缝扩展、真实的流体流动过程以及各种复杂模型条件等,但不同的数值方法存在各自的不足:现有的有限元法、扩展有限元法和边界元法不能在缝面上施加变化的水力压力,很少考虑孔隙基质渗流; 离散元法模拟裂缝网络时,一定程度上限定了水力裂缝扩展路径, 并不是完全随机的;连续非连续单元法可以有效模拟水力压裂缝网扩展的全过程,但适用于工程尺度模拟的计算效率还需进一步提高.

7 水力压裂过程微地震监测技术^*(*本节撰稿人:陈伟民¹(1 E-mail: wmchen@imech.ac.cn), 傅一钦, 姜春晖)

7.1 引言

随着世界天然气资源利用和开采的发展,产量有限的常规天然气开始无法满足生产建设的大量需求,人们开始开发和开采非常规天然气. 通常,非常规天然气一般指不能用传统石油地质理论来解释,地下赋存状态和聚集方式与常规天然气藏具有明显差异的天然气聚集,非常规气藏包括致密气、煤层气、页岩气等.其中页岩气储存于富含有机质的泥页岩中,以吸附和游离状态为主要赋存方式, 具有自生自储、高伽马射线(80$\sim$140单位)、黏土含量低$(25%\sim 40%)$、低孔隙率、高TOC(total organic carbon)含量等特点,因为其优异的气质条件(甲烷含量高达98%, 且不含硫化氢),被认为是与常规天然气同等质量、甚至更优的清洁高效能源(Arogundade et al. 2012).

由于页岩气储层比一般致密油气储层更致密, 实现对其有效开发难度很大.尽管页岩气开采在北美(主要是美国)已经有几十年历史,并且取得了相当大的成功, 被称为"game changer", 但是在其他国家,相关基础设施尚未成熟, 钻完井的成本仍然较高.中国的页岩气可采储量丰富,自2005年以来开始地质条件评价和勘探开发的先导性试验,中石化和中石油等已经在西南地区的长宁--威远、涪陵等地取得了突破,2014年中石化宣布涪陵页岩气田进入商业开发阶段,累计产量11.4亿立方米. 但是总体而言, 我国页岩气开采仍为起步阶段,还没有形成适合我国国情的完备自主技术体系,不具备大规模商业化生产能力. 此外,中国地质条件复杂(尤其是构造演变、沉积环境、热演化过程等),不同区域的页岩气形成和富集存在较大差异. 加强对页岩气开采的关键科学问题, 例如, 页岩储层的产能预测,页岩气的解吸附和流体在低渗透率介质中的非达西流动,水力压裂的岩石破坏机理和预测模型(高围压和压裂液作用下页岩的裂纹网络模型、天然裂纹和新生裂纹的相互作用),水力压裂过程的微地震实时监测和震源解释等的研究,需要建立页岩气开采的详尽标准化规范(郑哲敏 2016, 张东晓等 2013,谢和平等 2016, 刘振武等 2011, 庄茁等 2016, 卢德唐等 2016).

页岩气得以成功开采的关键为水平钻井和水力压裂技术的应用,其中水平钻井技术已经应用于海洋油气开发,而水力压裂技术却与常规油气开发中的有很大不同, 有"万吨水,千方砂"之说, 即使用大量滑溜水(或清水)并携带细砂(或陶瓷)支撑剂,在页岩中形成"为数众多的、相对密集的、网络状的开放型裂纹,从而有效克服页岩渗透率低的核心困难"(郑哲敏 2016).诸多因素例如地层应力状态、岩石力学性质、天然裂缝等都会影响水力压裂的裂缝发展,进而影响油气产量, 为了能实时而确定地了解水力压裂过程中的裂缝发展,给出裂纹位置、尺度、网络联通情况、甚至震源的破坏机理,需要引入微地震监测技术(Arogundade et al. 2012).

微地震事件普遍发生在裂隙断面上,通常情况下这些断裂面是稳定的(赵博雄等 2014), 然而,当原来的应力受到大量液体泵入干扰时,岩石中原来存在的或新产生的裂缝周围地区出现应力集中;当外力增加到一定程度时, 原有裂缝的缺陷地区发生微观屈服或变形,裂缝扩展使应力松弛,储藏能量的一部分以弹性波(声波)的形式释放出来产生小的地震,即微地震. 微地震监测(micro-seismic monitoring)通过观测和分析微弱地震事件来监测地下岩层的活动状态,涉及声发射学、地震学、信号处理、岩石力学等学科(吴有亮 2007).微地震监测技术能较完整地呈现裂缝的位置、几何尺寸以及裂缝类型,利用测井中或地表的检波器接收到微地震信号,通过数据处理对微地震事件进行定位或进一步分析(见图7.1),一般在垂直测井排列多个(通常多于8个, 每个垂直间距在91.4$\sim$304.8m之间)检波器, 微地震事件由于信号微弱在地面不容易监测,而在地下测井(通常距离压裂井304.8$\sim$914.4m)中可以收集到较好的信号(Cipolla et al. 2010).

事实上, 微地震监测的作用除了实时描绘水力压裂过程中的地下裂纹网络,还有很多其他方面的作用(Warpinski et al. 2012, Bonnet et al. 2001,Blackwood et al. 2008, Cipolla et al. 2010, Grieser et al. 2008,李君辉 2015, 伍藏原等 2005, 张山等 2002, Warpinski 2009), 例如,对于裂缝为主的储层,微地震事件可以作为位于储层内部的有效纵波和横波震源,用于速度成像和横波各向异性分析,对裂缝性储层有关的流动各向异性进行成像; 根据储层微地震资料,反演分析岩石物理参数, 预测油气"甜点"指导钻井部署;通过对压裂过程和后期产量数据的总结分析,可以得到非常规气藏钻井和开采经验. 研究表明(Warpinski et al. 2012,伍藏原等 2005, 张山等 2002, Warpinski 2009)对微地震波形和震源机制的分析,可提供有关油藏内部变形机制、传导性裂缝和再活动断裂构造形态的信息,以及流体流动的分布和压力前缘的移动情况.对微地震信号的合理分析和震源解释是微地震监测技术的关键问题之一,涉及声发射学、弹性波传播和散射理论、地震学、非平稳信号分析、岩石力学等多学科(Sicking et al. 2013, 余同希等 1992, Achenbach et al. 1973, Hudson 1981),尽管在美国的页岩气开采中微地震监测已经普遍使用,但是我国使用还不够普遍, 目前主要还是依靠引进国外技术和设备,微地震监测中的先进技术和相关基础理论的研究有待加强.

7.2 微地震监测技术的发展现状

7.2.1 微地震监测的国内外研究进展

7.2.1.1 国外微地震监测技术的开发和应用

20世纪40年代微地震监测首次使用,用于勘探危害严重的地下矿井冲击地压,但由于所需仪器价格昂贵且精度不够高、监测结果不明显而未能引起人们的足够重视和推广.1956年, 德国学者J. Kaiser发现,材料在受到极限载荷时会出现微小的声发射活动, 又称为Kaiser效应,证明了微地震监测的合理性. 1962年, 微地震监测技术被正式提出,以Kaiser效应为基础, 利用岩石破裂的声学传播进行监测,估算地下岩层地应力状态,应用在油气藏动态、地热状态、煤田动态和工程动态等监测.

1973年, 美国AMOCO (现为英国BP, BritishPetroleum)对科罗拉多州的Wattenberg油气田进行致密气开采,试图记录和分析水力压裂的裂缝,但是由于地面噪声太高、记录仪器及数据处理水平不高, 试验没有成功.1976年, 美国橡树岭国家实验室(Oak Ridge NationalLaboratory)在Wattenberg油田进行试验,考察了水力压裂诱发的微地震幅值和频率以及水力裂缝的定位; 之后,微地震监测成功的例子越来越多,主要用于油气开发井的目标确认、辅助断层描述.

20世纪80年代随着计算机的广泛使用,基于挪威AMOCO公司、Phillips公司、美国能源部Sandia国家实验室、日本Japex研究中心等发展的相关理论和实验基础(张山等 2002), 微地震监测技术有了实质性的进步. 1997年,在美国德州东部的棉花谷(CottonValley)成功进行了水力压裂微地震成像现场试验,验证了微地震成像技术的工程价值, 相比其他技术,其具有分辨率高、覆盖范围广、经济实用、可操作性强等优势.1999—2000年, 澳大利亚在Alpin对由采矿引起的微地震进行布网监测,效果显著, 为其后工作提供了丰富指导信息.

20世纪90年代之后, 世界几大石油公司, 其中包括加拿大ESG,美国Microseismic、Spectraseis、Schlumberger和Pinnacle(已被Halliburton收购),法国Magnitude等公司都相继提供了专业的微地震监测服务; 英国AppliedSeismology Consultants(ASC)公司开发了微地震、声发射、声波测试数据的专用软件(徐刚 2013);美国Tranform公司提供了多学科联合协同可视化工作平台.

7.2.1.2 国内微地震监测技术的发展现状

国内的微地震监测技术发展起步晚, 目前大部分研究集中于基础理论研究,尚需开发具有自主产权的仪器设备和成熟定型的微地震监测系统. 2004年,国内首次在大庆油田和南泥湾油田使用微地震监测技术进行裂缝监测;2005年, 伍藏原等在轧哈凝析气田利用气驱前缘技术直观反应气驱状态,为挖潜及注采井网的调整提供了科学依据 (伍藏原等 2014).

北京科技大学姜福兴等与澳大利亚联邦科学院采矿局合作研究开发了微地震监测系统;中国石油大学王爱国等研发了有自主产权的三份量检波器;北京京援伟达公司进行了微破裂地面监测及处理技术、相关软件开发、三分量采集仪器制造以及油气田裂缝监测、构造解释和储层分布等工作;南京捷诺科技有限公司开展了工程勘探、微地震监测、VSP (verticalseismic profiling)数据处理分析等项目研究. 另外,国内两大石油公司中石化和中石油也在发展微地震监测技术,微地震监测技术将为未来国内油气尤其是页岩气开采提供有益帮助(徐刚 2013).

由于微地震监测技术涉及不同的研究领域,需要声发射学、地震学、信号分析、岩石力学、测井等多学科的专家共同参与,也需要政府有关部门给予长期资助.美国的微地震监测已经在页岩气开发中起到了重要作用,美国最大的陆地天然气生产气田的德州Barnett ShalePlay的成功经验告诉我们,他们的水力压裂微地震监测技术发展先后经历了20多年,期间美国能源部在相关技术研究给予的必要资助起到了关键作用.英国的能源部与欧洲经济共同体也曾长期补贴地热项目的微地震的裂缝监测测试等,日本的政府部门亦补贴了储层描述的微地震裂缝监测方法测试(Daniels et al. 2007, Rutledge et al. 2004).

7.2.2 微地震监测在低渗透率气藏开发中的应用

微地震监测在前期的油气藏勘探/产量估测、中期的开采和后期的经验总结等多方面都有应用,尤其在近年来的非常规、低渗透率气藏的勘探和压裂开采的各个阶段中发挥了重要作用.利用微地震监测可以得到水力压裂过程中产生的裂缝的具体位置、尺寸和走向,通过后期的数据进一步分析可以得到裂纹类型(拉张型或剪切型)和震源发生机理(天然裂纹张开、新裂纹萌生、局部断层滑移)等,从而对水力压裂过程进行设计和优化、防范裂纹发展到附近的断层或含水层;最后, 通过对压裂过程和后期产量数据的总结分析,得到非常规气藏的钻井、开采、生产的经验、理论和数据,从而指导今后的工作. 归纳起来, 微地震监测有以下作用：

(1) 实时识别水力压裂裂缝几何特性, 监测并控制水力压裂发展过程 一方面,通过微地震监测可以识别水力压裂生成的裂缝几何特性(位置、尺寸和方向).微地震事件的距离可以通过P波与S波的到达时差计算,方向通过P波与S波能量的极化(矢量图)确定,深度通过不同检波器的时差计算. 图7.2为我国西南某页岩气田利用微地震成像观察到的微地震事件在压裂井周围的分布,图中的黑线是压裂井的方向, 在井的两侧进行水力压裂,红色和绿色的圆点是不同压裂阶段的微地震事件(共监测到272起事件),该水平井的西侧主裂缝长231m、东侧主裂缝长142m,裂缝网络的高度(井轨迹上5m,井轨迹下42m)和宽度分别为57m和66m,裂缝方向为北偏东71$^\circ$.

另一方面, 通过实时监测水力压裂的发展情况,可以确定裂缝网络的覆盖面积, 针对没有被(充分)压裂的区域,及时修改压裂方案,例如进行重复压裂或者采用纤维转移技术等引导裂缝的发展方向和位置, 图7.3 左上图为最初水力压裂的微地震事件分布,黑色和红色框内的区域分别为压裂不充分和尚未压裂的部分,在进行了重复水力压裂(图7.3中的第一级至第三级)并引入分步纤维转移技术后,增大了有效压裂面积(左上角图为压裂面积),微地震事件的数量也相应增加(右上角图) (Cipolla et al. 2010).

从优化压裂之后的产量曲线(图 7.4)可以看出,多次重复水力压裂之后的产量提高了一倍,其中一段时间内产量提高了60%. 这表明微地震监测可以为水力压裂提供实时监测,通过控制水力压裂裂缝发展, 优化水力压裂设计可以提高产量.

另外, 这种实时监控能帮助识别断层、防范灾害(断层滑移、泛水等)(Cipolla et al. 2010),通过对微地震事件的数量、发生的位置、时间及其变化趋势的监测和实时控制,可以防止裂纹延伸至断层或含水层造成破坏或灾害.

Wrpinski(2009)通过确定微地震事件的位置和等级判断出断层, 图7.5为美国不同页岩气田的微地震事件量级, 其中Barnett和WestTexas页岩在压裂过程中产生了高量级微地震事件(力矩的量级达到$-1.0\sim -1.5$, 高于常规的$-3.0 \sim -4.0$量级), 其附近有断层.图 7.6(a)表明某水平井的四级水力压裂过程,前两次(红色和浅蓝色的点)受气藏区域结构约束,后两次受到了断层的影响(深蓝色和黄色的点) (Cipolla et al. 2010),通常微地震事件数量和事件等级成正比,如果在水力压裂主要深度以下有密集的高强度事件,则表明那里可能有断层(图7.6(a)中红色框内); 类似地,在我国中石油西南页岩气开采中,通过微地震监测发现在两口水平井中间有大量高量级的微地震事件(图7.6(b)红框内), 表明有可能存在天然裂缝或者断层,后来的地质勘探证明了该地区确实存在断层.水力压裂的设计需要避开断层, 以免影响压裂效果.

(2) 给出地层的地球物理参数, 包括岩层的矿物组份、地应力状态等 根据地震波信号到达时刻可以推算波在地层介质中的传播速度,进而得到地层的地球物理特性,包括质量密度、矿物组成、含砂量、孔隙度等参数.页岩储层以小粒径物质为主,一般以黏土(粒径$<5\mu$m)和泥质(粒径$5 \sim 63\mu$m)为主要组分, 而砂(粒径$>63\mu$m)所占组分相对较小;页岩气储层孔隙率低(一般为4%$\sim$6%)、渗透率极低(低至10mD); 而且, 页岩成分不仅有无机矿物,还有有机质, 并且页岩气储层中存在大量吸附气;裂缝或裂隙是页岩气重要的储集空间和渗流通道,对页岩有效矿物组分评估很重要(Liu et al. 2011).通过微地震监测分析主裂缝走向, 判断储层最大/最小主应力方向,为储层后续水平井的造斜点、射孔位置以及压裂过程优化设计给出依据,如图7.7、图7.8所示.

(3) 优化配置钻井数量和位置

钻井阶段如果能够优化配置钻井数量和位置, 可以显著降低开采成本,使用微地震监测可以为非常规油气开采的经验累积提供更加完善的数据,经验表明尽管整个微地震监测系统的建立和实施需要前期投入,但是引入微地震监测后, 通过优化钻完井和水力压裂过程,前期成本较容易收回并较快实现盈利.

通常, 两个相近测井之间的数据具有一定相关性,通过微地震监测数据得到的非常规、低渗透率和常规气藏中两井间距相关性见图7.9 (Cipolla 2010), 与常规气藏不同,由于低渗透率或非常规气藏的沉积环境复杂、世代交替、天然裂缝分布等因素,当井间距大于一定距离之后, 其相关性快速下降接近零. Grieser(2006)和Blackwood(2008)的测井结果表明两个相近的测井数据有时候会有较大差异.图7.10为Barnett页岩气田测井得到的产量数据(Cipolla et al.2010), 虽然大多数情况下相近区域的井产量相近,但是有些区域(图中黑圈内)相邻两井之间却存在较大差异. 因此,需要通过微地震监测标定裂缝计算模型, 估计高产井的具体位置,再根据油气藏模型选择钻井数量和位置,因为井距太远可能会错过有利资源,而井距太近会增加井密度导致成本增加且由于邻井排采重叠区域的井间干扰导致减产.

(4)优化水力压裂和完井方式, 提高页岩气产量

气藏质量的多样性、不易预测性和水利压裂裂缝发展的复杂性导致了页岩气开采中较难总结规律、累积经验、制定统一的规则.图 7.11为近年来北美页岩气的产量数据(Arogundade et al.2012), 图中纵坐标表示6个月的累计产量, 横坐标表示井的数量,斜率为单井产量. Operator1是第一次钻井950口,其中初期阶段有垂直和水平井两种钻井方式,后续阶段借助微地震监测进行了完井优化和压裂优化设计,可见第四阶段优化完井后的单井产量明显比第一阶段增高.Operator2和Operator3&4是利用微地震监测对第一次水力压裂(Operator1)进行了优化设计,改进后的的曲线斜率都比初始曲线斜率大,说明微地震监测优化了水力压裂使单井产量明显提高.

当然, 目前还很难量化微地震监测对于产量到底有多大影响,但很多工程实例都证明了微地震监测可以提高完井技术和水力压裂设计.图 7.12为基于微地震监测的产量数据和分析,最初的100口井增加产量9BCF、经济收益4500万;利用经验累积加速后开展的勘探和测井,前20口井提高产量50%$\sim$100%,并且为接下来的完井和水力压裂方式的选取提供帮助.

总之, 微地震监测虽然前期投入较大, 尤其在起步阶段,没有现成的测井可以利用需要较高的成本,但是微地震监测减少了工程风险加速了经验累积,总体和长期收益远大于前期投入.

7.3 微地震监测中的关键问题

常规气藏可以通过井产量来估测水力压裂效果,而页岩气等非常规气藏还需要了解完井有效性和水力压裂的裂缝生成情况,以便于后续优化, 并且校正裂缝计算模型. 换句话说,了解水力压裂裂缝分布和完井方式是经济、成功地开发页岩气的关键.在页岩气藏开采中,微地震监测可以帮助判断完井质量、找出影响水力压裂和完井方式的因素,在北美的页岩气开采中,微地震监测技术已经被广泛用于水力压裂的裂缝监测,了解裂缝几何性和提高气藏导气能力, 从而提高了产量, 取得了很大成功.

然而, 由于水力压裂期间生成的微地震波其波形种类繁多,而且不同的波形对应的地层、岩石的活动机理各有不同,有天然裂纹延伸、新裂纹生成、断层滑移等各种活动产生的弹性波在地层中传播和反射;水力压裂过程中会产生多种干扰噪声,例如大型液压机等仪器设备的操作运转带来的背景噪声、临近井眼的异常地震波的衰减、附近地层反射波的混入等因素,因此微地震监测依然面临着一些挑战, 例如：

(1) 微地震事件的有效识别, 包括初至时间拾取、多震源定位等.微地震本身的信号幅值低而且事件发生密集,而水力压裂过程中机组操作等环境噪声大,因此这种低信噪比信号的有效识别和多震源事件的定位比较困难. (2) 岩层中的三维裂纹网络的准确反演.水力压裂生成的裂缝并不是单条大裂纹,而是不同尺寸、纵横交错的复杂裂纹网络, 根据微地震记录数据,准确地反演出岩层中的三维裂纹网络非常困难.

(3) 微地震信号的全波形记录以及震源解释.水力压裂期间生成的微地震波形种类繁多, 机理各有不同而且错综复杂,不容易区分和识别出不同活动事件; 微地震信号频谱是随着时间变化的,用常规的傅里叶变换不能得到每一时刻的频谱,需要其他频谱分析方法(如小波变换、匹配追踪瞬时谱分解等),而且要保证分析结果的稳定性和合理性;由于目前对震源机制的了解不够充分,震源类型和破坏机理还不能被准确反演和解释. (4)微地震监测数据的分析结果与实际情况尚存在不自洽、不能合理解释的现象.例如泵入流动液体携带的能量、岩层破裂的释放能量、检波器监测到的能量之间的关系不匹配;水力压裂的致裂面积与产量之间的关系并不确定,有时候即致裂面积大而产量未必高(有可能存在其他的未被识别出的裂缝);理论上预计不会发生微地震的时间(例如停止泵压或者完井之后),却也会监测到微地震; 从破坏机理上看水力压裂过程是拉伸破坏,但是微地震监测到的多数是剪切破坏等(Daniels et al. 2007).

7.3.1 事件有效识别

起初微地震信号分析主要借鉴地震波分析方法,后来针对微地震的发生及其信号特点, 发展了有针对性的方法.微地震监测主要是利用收集到的微地震波信号进行分析,判断事件发生的位置和时间, 事件识别的核心问题主要有:(1)初至时间的拾取. 这是地震信号拾取常见的问题,由于微地震事件信噪比太低, 使很多微地震事件淹没在噪声中,很难被分离出来; (2)震源定位. 这是水力压裂中的特殊问题,由于整个过程收集的数据量大且水力压裂期间是多震源,目前多震源定位还缺乏通用方法.在以往的地震定位方法(纵横波时差法、三圆相交定位法、偏振分析定位法等(Jurkevics 1988)基础上,针对水力压裂微地震的震源能量微弱、多震源同时发生、信噪比低的特点,发展了新的定位方法如三分量空间点集法、交叉相关台阵法和震源扫描法等(Kao & Shan 2004, Kummerow 2010),这些方法不需要提前收集噪声样本、初至波绝对时刻,而是通过找出最高亮度(或相关系数)或者根据多地震道的波形来识别出分散震源的位置和发生时刻,以减少人为因素引入的误差.

7.3.1.1 初至时间拾取

微地震能量微弱,找出微地震直达波初至时间并拾取有一定难度.对微地震信号的自动拾取技术主要借鉴了天然地震的自动拾取方法,初至拾取是地震勘探中的一个基础问题,对地震初至拾取有帮助的主要是瞬时属性和时窗属性,由于噪声对瞬时属性特征拾取的干扰, 目前多使用地震时窗属性特征,例如振幅比法、曲线长度法和能量比法等,当对同一地震记录进行初至拾取时,时窗内后、前能量比法在处理低信噪比的地震记录时有较大优势,并能快速和有效地提高计算效率和计算精度.目前地震信号自动拾取或震相识别方法有：能量比法、AIC算法、神经网络法、分形维法、极化分析法以及卡尔曼估计等方法(周基阳 2011, 王建华 2007).

(1) 能量比法.能量比法是最为快捷、最为广泛应用的一种自动拾取方法,为了更好地适用于地震数据, 先后有多种改进的能量比算法. Kannasewich(1981)提出将地震数据的绝对值、能量以及包络面的长时窗(LTA)与短时窗(STA)作为识别有效事件的特征参数,这种方法通过计算长短时窗的比值,默认发生地震时这个比值会大于预先设定的阈值.目前这种方法已成为微地震监测的常用方法,不过该方法受短时窗的影响不能准确拾取初至, 当信号的信噪比较高时,不容易分辨出地震信号.

能量比法主要运用地震波初至信号波形能量信息完成初至拾取.地震记录上的初至点是一个十分特殊的点,在初至点之前不存在有效地震信号只有噪声,在初至点之后开始有地震信号, 故初至点前后的波形能量会有较大差别,因此一般认定初至点为能量的突变点, 也就是说,能够用某点前后时窗的能量比值来判定该点是否为初至点.时窗能量比法的步骤是沿时间轴得到两个不同的滑动时窗,分别计算两个时窗内的能量值, 二者的比值存在一个极值,根据这个极值能够确定微地震的初至时间点,具体时窗的取法可以是前、后两个时窗, 或者长、短两个时窗.

(1)前后时窗能量比

$ A = \left( {{\int_{T_0 }^{T_2 } {x^2(t){\rm d}t} }\bigg/{\int_{T_1 }^{T_0 } {x^2(t){\rm d}t}}} \right)^{{1}/{2}} (7.1) $

式中, $x(t)$为地震记录的振幅值, $T_1 $为时窗起点,$T_{0}$为时窗中点, $T_{2}$为时窗终点. 图7.13为能量比法示意图, 从图中可看出,在初至点前只有噪声、信号能量较弱,而在初至点后突然有地震信号、能量突然增强, 能量比达到最大.在实际问题中只要求得前后能量比最大的时刻即为地震信号的初时刻.

(2)长短时窗能量比

$ STA / LTA(i) = N_{LTA} \int_{i - N_{STA} }^i{X(t){\rm d}t} \bigg / N_{STA} \int_{i - N_{LTA} }^i {Y(t){\rm d}t} (7.2)$

其中长时窗大小为$N_{LTA} $, 短时窗大小为$N_{STA} $,$i$为时间轴上的第$i$个采样点$X(t)$, $Y(t)$为地震记录的振幅绝对值.长短时窗能量比法(STA/LTA)所取的时窗位置和大小如图7.14所示.在初至时间点之后, 长时窗内能量缓慢变化, 而短时窗内的能量突然变大,二者比值瞬间变大, 通过给定一个阈值,当二者比值的突变点大于该阈值时, 就可以得到微地震事件的波至时间.

(2) 基于小波分析的AIC方法.自回归(AR)方法假设微地震初至前后的地震记录是两个不同的稳态过程,Sleeman(1999)提出了自回归模型下的 Akaike 信息准则(autoregressiveakaike in-formation criteria, AR--AIC),该方法将地震波形数据分成依据自回归过程确定的两个局部统计时段,检测震相前的时段(噪声模型)和被检测震相到达后的时段(信号模型)(段建华 2014, 刘劲松等 2013, 周银兴 2009), 在微地震事件的初至时间位置,因为噪声信号和微地震信号统计性质会有较大差别,故在最小平方统计下这两种信号的拟合度最差, 对应的AIC值最小,由此确定初至时刻.

若存在时间序列$x_t = \{x_1 ,x_2 ,\cdots ,x_{\rm N} \}$,其中包括噪声和地震信号, 对检测震相的初始到时估计,那么以检测震相到时为界, 将地震记录分为两个时段:检测震相前的时段(噪声模型)和被检测震相到达后的时段(信号模型).对每一个时段内的数据$x_t $分别用$M$阶的系数为$a_m^i$ $(m =1,2,\cdots ,M)$自回归模型来匹配

$ X_t = \sum\limits_{m = 1}^M {a_m^i X_{t - m} + e_t^i } (7.3) $

式中, 被检测震相前的$t = 1,2,\cdots ,M$,被检测震相后的$t = N - M + 1,2,\cdots ,N$.将位于模型窗口内的时间序列分为确定性部分和非确定性部分,非确定性的时间序列$e_t^i $ 看作噪声, 若均值$E[e_t^i ] = 0$且有方差$E[e_t^i ]^2 = \sigma _i^2 $,它与确定性的部分可看作是不相关的, 即$E[e^ix_{t - m}^i ]^2 = 0$.

若把$K$作为分割点, 使用AR系数$a_m^i $提取时间序列$[M+1,K]$和$[K+1, N-M]$中非确定性部分. 假设非确定性部分是高斯型的,对这两个时段的非确定性部分用似然函数表示

$ L(X;K,M,\theta _1 ,\theta _2 ) = \prod\limits_{i =1}^2 {\left(\dfrac{1}{\sigma _i 2\pi }\right)} ^{ {n_i}/{2}}\cdot \exp \left( - \dfrac{1}{2\sigma _i^2 }\sum\limits_{j =p_i }^{q_i } {X_j - \sum\limits_{m = 1}^M {a_m^i X_{j - m} } }\right) (7.4) $

式中, $\theta _i$代表了时段$i$的模型参数, $p_1=M+1$, $p_2=k+1$, $q_1=k$,$q_2=N-M$, $n_1=K-M$, $n_2=N-M-K$ 对上式取对数及偏导数

$ \dfrac{\partial \lg (L(X;K,M,\theta _1 ,\theta _2))}{\partial \theta _i } = 0 (7.5) $

可得到求模型参数的最大似然估计的解为

$ \sigma _{i\max }^2 =\dfrac{1}{n}\sum\limits_{j= p_i }^{q_i } {\left(X_j - \sum\limits_{m - 1}^M {a_m^i X_{j - m}} \right)^2} (7.6) $

模型对于$K$的对数似然函数的最大值为

$AIC(K) = (K - M)\lg (\sigma _{1,\max }^2 ) + (L - M - K)\lg(\sigma _{2,\max }^2 ) + C_2 (7.7) $

式中 $M$是AR过程的阶数; $L$是地震记录的长度; $\sigma _{1,\max }^2 $和$\sigma_{2,\max }^2 $是两个时段中 AR 过程的拟合误差; $C_{2}$是一个常数.

在微地震事件波至时间处, 由于噪声信号和微地震信号统计性质差别较大,因此在最小平方意义下这两种信号的拟合度最差, 对应的 $AIC$ 值最小.基于这点, 很多研究者通过计算 $AIC$ 并选择最小 $AIC$值对应的点作为两种不同平稳序列的分界点.

每一个微地震事件对应的 $AIC$ 位置处均会出现一个局部极小值,通过拾取这些局部极小值对应的时间, 即可得到微地震事件的波至时间.需要注意的是, $AIC$ 值出现局部极小值的位置却不一定就是微地震事件,比如在不含微地震事件的纯噪声记录中也总会出现一个最小的 $AIC$ 值,因此 AIC 方法不适用于微地震事件的识别,仅适用于微地震事件波至时间的拾取.

新提出的方法是将小波变换和AIC方法结合使用,即在运用AIC法来拾取微地震事件的波至时间时,首先用小波变换对微地震数据进行多尺度分解,然后分别对各尺度分解后的数据计算 $AIC$ 函数, 并记录 $AIC$函数的最小值, 最后对各尺度对应的最小 $AIC$ 值计算中值,就得到拾取时间. 左边是某个尺度下分解后的微地震数据, 右边是对应的AIC 曲线. AIC方法的主要缺陷在于无论所选的数据段中是否存在地震事件,总会在数据段中找到一个 $AIC$ 的最小值, 这使得无法单一利用 AIC算法进行有效事件的自动识别(如图7.15).

(3) 分形维法及其他方法.分形维数法(fractal-dimension,FD)判断初至时刻的原理是,在初至波到来前、后地震道上的分形维数值的改变(段建华 2014).初至波到达之前, 地震记录的主要成分是随机噪声,其能量较弱幅值也较小; 当初至到达时, 地震记录是噪声和初至波的叠加,能量较强幅值也较大; 基于对比初至到达前、后分形维的改变,能够定量地描述时间序列的变化,此时分形维的突变表示了地震波初至的时刻.

对于地震道的抽样序列,将其作无量纲图形化处理能够得到一条自仿射曲线.故地震信号能够用分形维来描绘其不规则程度. 在地震波初至波前后时刻,分形维发生了改变, 可以用分形维的这种改变来拾取地震波的初至.分形维的基本过程是用边长为$\varepsilon $, 分形维数等于分形体拓扑分形维的超立体对分形体进行覆盖(覆盖单元可有多种,这里统一称为超立方体), 分形维

$D_H = \mathop {\lim }\limits_{\varepsilon \to 0} ( - {\ln N(\varepsilon )} / {\ln \varepsilon }) (7.8) $

其中$N(\varepsilon )$ 为包覆边长$\varepsilon $的超立方体数.测量平面曲线时可以单元盒作为超立方体, 公式形式同于盒分形维数.

先选定一个具有一定长度工作窗,计算该工作窗内地震道采样序列的分形维,并将该值标记在此工作窗的右边界采样点上.把该工作窗在地震道上从道头到道尾以一个采样间隔向前移动,直到覆盖整个地震道, 计算每个工作窗的分形维,从而可以得到一个分形维的变化曲线. 分析轨线的总体形状,随着初至逐渐进入工作窗, 局部曲线呈现清晰的"V"字形状.把此"V"字形状的区域部分扩大,第一个突降点就是初至开始进入工作窗的标志, 亦即对应的初至到达.上述基于"初至的到达会引起分形维突变"原则的初至拾取方法,在"V"字形状的区域部分扩大的情况下, 自动拾取第一个突降点.该方法计算工作量较大, 需要依靠计算机编程实现.

弹性波初至时间拾取其他方法还有波形互相关、人工神经网络等多种方法.微地震射孔信号是震源已知的稳定的信号,各道地震信号之间存在很强的相关性,特别在初至信号附近主要为透射直达波, 因此更具相关性(吕鹏等 2011,黄媛 2008). 基于此特征,可以利用互相关算法来对微地震射孔信号的初至进行拾取.波形相关法初至拾取的结果只为各道初至时差, 并不能确定初至具体时间,所以要想得到各道初至波的时间就必须已知某一道的初至时间.

人工神经网络法作为一种应用于各个领域的方法, 被Wang等(2005)引入地震研究进行实时地震监测,他将时间序列的长短时窗能量与滑动时窗谱比作为系统的输入进行系统的训练,将这个系统应用于其他地震数据进行地震信号的检测.张范民等(1998)根据地震信号的初动特征与震源位置和地震波传播方向有关的性质,将瞬时矢量模作为系统的输入来进行地震信号的拾取,对确定地震震相和到时比较有效.

比较各种初至时间拾取方法可以看出,能量比法、AIC法、分形维(图7.16)等, 通过拾取地震波形特征,来识别初至时刻, 对于振幅和信噪比较高的地震波形, 能量比法比较适用,但是当信噪比很低, 需要做一些预处理例如降噪等.能量比算法基于地震时窗属性特征,初至到达时刻前地震波的有效信号为零只有噪声,之后才有我们关注的地震信号, 由于窗长度设定后, 不可以随意改变,这样就可能出现较大的误差,会出现第1个时窗内的能量和与它前一个时窗内的能量和的比值,小于第2个时窗内的能量和与第1个时窗的能量和比值,从而误认为地震波的初至在第2个时窗内, 出现错误判断, 因此,时窗选取非常重要, 如果选取不当很可能造成较大的误差.分形维法能够较稳定地拾取地震波的初至到达时刻,但是原理复杂、计算量比较大,而且对工作窗口宽度、度量(覆盖)尺度、地震道时间序列图形沿两个坐标方向变化的协调性等较敏感.AIC方法的缺陷是AIC值出现局部极小值的位置不一定对应微地震事件,比如在不含微地震事件的纯噪声记录中也总会出现一个最小的 $AIC$ 值,因此 AIC 方法不适于微地震事件识别, 可用于波至时间拾取.

针对于水力压裂的微地震问题, 由于信噪比较低,建议的拾取方法是先进行降噪等预处理,然后利用能量比法初步确定大概位置, 再利用AIC法进行自动拾取,从而得到较为精确的结果.

7.3.1.2 震源定位

震源定位问题的实质即求观测到时和理论到时之差所构造的以假想位置为函数的目标函数的极小值,不同定位方法在于对目标函数的构造、处理、求极小值方法的不同.微地震监测的最终目的是对震源的反演,通过采集和处理纵、横波地震记录,来确定由水力压裂所导致的岩石破裂位置, 从而描绘裂缝延伸方位和长度.目前震源位置确定方法主要沿用天然地震的反演方法,常用的有P波定位法、射线法等,以及近几年发展起来的针对水力压裂微地震的三分量定位法、震源扫描法、交叉相关法等(黄今,采动过程中微地震方位方法研究).

(1) P波定位法

由于地震波中P波传播速度最快, 可对P波到达事件进行拾取,因而在一般情况下宜于采用P波定位(赵博雄等 2014).假设已知P波在岩层传播的均匀速度模型,在4个以上不同地点布置监测台站(如图7.17). $P_{1}$, $P_{2}$, $P_{3}$, $P_{4}$为4个监测点, $Q$点为震源位置, $S_{1}$, $S_{2}$, $S_{3}$, $S_{4}$为震源点和监测点之间的距离.建立4个距离和速度方程, 可解4个未知数

$ S_i = V(t_i - t_0 ) (7.9)$

$S_i = \sqrt {(Z_i - Z_0 )^2 + (Y_i - Y_0 )^2 + (X_i - X_0 )^2},\quad i = 1,2,3,4 (7.10)$

方程中已知接收时间和传播速度$V$, 求出震源、起震时刻和震源坐标$(x_0 ,y_0 ,z_0 )$. 实际应用中, 通常有多个地震观测站,传感器的个数通常大于4个, 为了得到更加精确的定位值,可通过最小二乘法求最优解.

(2)射线法

如果微地震事件的监测台站只有1台,可通过地震波射线法得到震源位置(赵博雄等 2014). 首先,根据P波和S波的走时差和速度差求出监测台站与震源之间的距离,设震源发震时刻为$t_0$, 震源至台站距离为$L$,P波到达台站时刻为$T_{\rm P}$、传播速度为$V_{\rm P}$、传播时间为$t_{\rm P}$, S波到达时间为$T_{\rm S}$、传播速度为$V_{\rm S}$、传播时间为$t_{\rm S}$,P波和S波时差为$\Delta t$, 则得到

$V_{\rm P} \cdot t_{\rm P} = V_{\rm S} \cdot t_{\rm S} = L (7.11)$

$ t_{\rm S} = t_{\rm P} + V_t,\quad t_{\rm P} = T_{\rm P} - T_0, \quad t _{\rm S} = T_{\rm S} - T_0 (7.12) $

已知$V_{\rm P}$, $V_{\rm S}$, $T_{\rm P}$, $T_{\rm S}$, 则 $L = V_{\rm P} \cdot t_{\rm P} = V_{\rm P} \dfrac{V_{\rm S} \Delta t}{V_{\rm P} - V_{\rm S} } = \dfrac{V_{\rm P} V_{\rm S} }{V_{\rm P} - V_{\rm S} }(T_{\rm S} - T_{\rm P} ) (7.13)$

从而求出震源至监测台站的距离.然后根据台站接受的地震波测出东西、南北、垂直方向P波初动振幅,再根据公式求出震源方位角$\alpha _{0}$, $A_{\mu {\rm E}}$为东西方向P波位移, $A_{\mu {\rm N}}$为南北方向P波位移, $\alpha_{\mu {\rm E}}$为初至p波东西方向振幅, $\alpha _{\mu {\rm N}}$为初至P波南北方向振幅, $V_{{\rm E}}$和$V_{\rm N}$分别为东西方向和南北方向的放大倍数, 则P波传播(震源)方向满足

$ \tan \alpha = \dfrac{A_{\mu {\rm E}} }{A_{\mu {\rm N}} } = \dfrac{\alpha _{\mu {\rm E}} / V_E }{\alpha _{\mu {\rm N}}/ V_{\rm N} } (7.14) $

就可以得到震源的方位角和距离.

(3) P波射线交汇点法

当微地震监测台超过2个而少于4个时,可用P波射线交汇点法进行定位,该方法可对震源做出快速评估具有较好的时效性(赵博雄等 2014).根据式(14)求出每个监测台站的震源方位角,从而作出每个台站的P波射线传播方向.两个监测台站的P波射线相交点即为震源位置(图7.18).

精确定位地震发生时刻和震源一直是地震学的基本难题,通常情况下用P波和S波的到达时差定位,尽管计算机技术和地震学一直在发展,但是以上3种传统地震定位方法停留在利用时段拾取定位震源, 其缺点是:(1)时间拾取困难, 特别在信噪比低的情况; (2)实际情况复杂,当多震源在同一地区发生且时刻相近,同一震源在不同地区收集的信号不同. 因此,传统方法适用于单震源且信噪比高的情况,近年来相继发展了新的地震定位方法如三分量空间法、台阵法、扫描法等.

(4) 基于三分量的空间点集法

基于三分量的空间点集法(何惺华 2013)的出现主要是由于水力压裂造成的岩石破裂的微地震通常能量微弱,要找到震源直达波初至时间并加以拾取具有一定的难度,且反演误差大且多解. 因此,基于三分量的微地震反演法被经常用在水力压裂的微地震定位. 首先,利用定点射孔资料中三分量的水平分量的直达纵波来标定水平检波器的方位角(如图7.19(a))

$\varPsi = \dfrac{1}{2}\tan ^{ - 1}\dfrac{2{x'}{y'}}{{x'}^2 -{y'}^2} (7.15) $

对于三维空间的每个格点, 逐点计算直达纵波时距方程,再根据某一时刻沿直达纵波初至后给定时窗内3个分量能量叠加的极大值

$ Es = \sum\limits_{i = 1}^N {\sum\limits_{j = 0}^w{\left(Ax_{i,j}^2 + Ay_{i,j}^2 + Az_{i,j}^2 \right)} } (7.16)$

其中, $N$为检波器道数, $Ax$, $Ay$,$Az$分别为3个分量上的样点振幅值, 确定震源距离,避免了因能量微弱而不易拾取初至时间的问题.

再利用微地震直达纵波水平分量的坐标变换得到微地震纵波矢量方位角(如图7.19(b)), 结合震--检震源和检波器地震方位角, 当$\beta$和$\psi $差值最小时, 限定方位角, 确定震源的位置,最后采取能量重心法和平均点距法等空间点集统计方法,确定震源的精确位置.

基于三分量的空间点集法解决了传统方法反演误差大且存在多解的问题;但是适用范围较窄, 相对误差受介质反演速度影响较大,一旦反演速度脱离阈值, 相对误差会增加.

(5)交叉相关台阵法

相比于传统的初至时间拾取只能识别出少量到时,该方法利用不同事件的波形相关性定位震源,适用于信号微弱、密集发生的微地震事件.

传统的地震定位理论中,相关系数被用来衡量地震事件是否是密集发生或是重复的地震,交叉相关法的基础是相关系数和事件间距存在一定的关系, 例如,指数衰减关系, 那么就可以用这个关系反推事件的间距. La Rocca等(2005)首先通过已知的微地震事件,建立相关系数和震源之间距离的经验公式(指数衰减); 然后,通过在整个事件可能发生区域的网格点的逐点搜索,找出P波和S波的走时时差,以及参考事件和需要定位的微弱事件的距离(相关系数--间距的指数关系),满足误差最小(经验模型预测值与现场实测值之间的误差)的空间点即为震源点.交叉相关法最大的优势是能够在微地震密度大的区域,精确定位较小的微地震事件, 提高事件分辨率. 但是,其受限制于参考事件(reference events)的标定和列阵中检波器的数量.

Kummerow(2010)利用在一个区域内分布三组以上列阵,在每组列阵的150$\sim$300m附近配置6$\sim$7个检波器,采用小范围排列能收集到信号的细节,再分析各检波器上地震波到达的细节, 区分波形和方向,在时间领域利用零滞后互相关法(zero lag cross correlation, ZLCC),(Del Pezzo et al. 1997, Frankel et al. 1991)和极化分析(Jurkevics 1988)求解波形的反位角、慢值、颤动波局部特性.

首先, 利用已知地点和发生时刻的射孔事件来标定速度模型.通过对射孔事件的到达时刻拾取和相关性分析标定速度模型,应用各站台空间关系精确定位射孔事件(图7.20)标定检波器以及定位参考事件(referenceevents, 即传统方法定位的能量比较大的微地震事件).

然后,进行不同通道地震波信号的交叉相关性(cross-correlation)分析(如图7.21),$i$, $j$通道的信号相关性为

$ (u_i * u_j )(\tau ) = \frac{\sum\limits_{n = 1}^N{u_i (n)u_j (n + \tau )} }{\sqrt {\sum\limits_{n = 1}^N {u_i^2(n)} } \sqrt {\sum\limits_{n = 1}^N {u_j^2 (n)} } } (7.17)$

$u_i (n)$, $u_j (n)$代表两个离散的信号波时间历程, $n$表示时间,$N$是时窗长度, $*$代表卷积.进行相关性最大值正则化并考虑噪声后的交叉相关系数$cc$(cross-correlation coefficient)为 (Snieder et al. 2005)

$cc_{ij} = \dfrac{ncc_{ij} }{\sqrt {\left(1 - \dfrac{ \langle n_i^2\rangle }{ \langle u_i^2\rangle }\right)} \sqrt {\left( 1 -\dfrac{ \langle n_j^2\rangle }{ \langle u_j^2\rangle }\right) }} (7.18) $

$ \langle n_i^2\rangle $, $ \langle n_j^2\rangle$表噪声平均能量(在P波拾取之前计算得到), $ \langle u_i^2\rangle $, $\langle u_j^2\rangle$ 代表信号平均能量, 使用条件:$\dfrac{ \langle n_j^2\rangle }{ \langle u_j^2\rangle } < 1$, $\dfrac{ \langle n_i^2\rangle }{ \langle u_i^2\rangle } < 1$.

根据相关系数的分布$(cc, \Delta r)$, $\Delta r$表示事件的间隔距离,得到最佳拟合的指数函数$cc = {\rm e}^{ - \sqrt {\Delta r / s} }$,其中$s$是相关长度.再利用已知的参考事件$i$定位信号微弱的微地震事$j$件(图7.21(c)),即在一定范围内进行逐点网格搜索, 寻找P波和S波的走时差$ T_{ij}^{\rm obs} = (V_{\rm S}^{ - 1} - V_{\rm P}^{ - 1} ) \cdot s \cdot [{\rm In}(cc_{ij} )]^2$, 使下式最小值的网格点, 从而定位出事件$j$.

$ \left(\sum\limits_{i = 1}^{N + j - 1} {wcc_{ij} \cdot\left| \Delta T_{ij}^{\rm obs} - \Delta T_{ij}^{\rm cal} \right|}\right ) + wtt_j \cdot \left| \Delta T_j^{\rm obs} - \Delta T_j^{\rm cal} \right| (7.19)$

上式中$N$代表定位事件的数量, $wcc_{ij} $代表$cc$权重因子,$\Delta T_{ij}^{\rm cal}$ 理论上事件$i$, $j$之间的P波和S波走时差,$ \Delta T_j^{\rm obs} $是实际上从检波器上得到的, $\Delta T_j^{\rm cal} $是从检波器位置和事件$j$的位置计算得到的.权重因子反映了$\Delta r$和$cc$非线性增长的关系, 一般取0.3.

(5) 震源扫描法(Kao 和 Shan 2004)

源点扫描计算法(source scanning algorithm, SSA),(见图7.22)通过统计所有检波器观测到的到达时间和振幅,利用"亮度"描绘时间--空间场中分散的地震震源. 某一空间点 $ \eta$的亮度表达式为

$br(\eta,\tau)=\dfrac1N\sum_{n=1}^N\left|u_n(\tau+t_{\eta n})\right| (7.20)$

通过正则化之后各站台信号计算亮度点其对应时刻和预测到达时刻$(\tau+t_{\eta n})$. 通过计算每个站台到达最大振幅得到亮点$\eta$的位置(白色星星位置), 同样的方法计算非震源点$\eta'$ (黑色星星), 其亮度低

$u_n $ 是正则化之后监测站台$n$的地震图,$t_{\eta n} $是预测从点到达监测站台$n$的预测到达时间, $\tau$是点对应的发生时刻.

修正后的亮度方程

$br(\eta,\tau)=\dfrac1N\sum_{n=1}^N\left[\dfrac{\sum^M_{m=-M}W_m\left|u_n(\tau+t_{\eta n}+m\delta t)\right|}{\sum^M_{m=-M}W_m}\right] (7.21)$

$\delta t$ 表示附近时窗, $ W_m $是权重因子, $t_{\eta n}$表示能量到达时刻和预测到达时刻的距离,$2M$表示预测到达时刻附近时窗的点. 通过在整个空间上逐点扫描,找出最高亮度来识别出分散震源的位置和发生时刻.该方法不需要提前知道震源的几何性, 也不需要提前收集噪声样本.只需要研究波形(振幅和到达时刻)以确认某一时刻的震源位置,减少人为因素引入的误差. 通过系统扫描走时,确定震源位置和发生时刻而不需要拾取到达时间和计算震动曲线,还充分利用了已知3D速度模型, 减少了横向速度不均匀的影响. 但是,虽然SSA可以在监测范围内成功定位震源位置和发生时刻,但是如果震源位置与监测站点相距太远或不在网格划分范围内则无法定位;而且需要精确的3D速度模型. SSA基于走时去定位亮度,如果没有精确速度模型, 会产生较大误差.

总结上述几种震源定位方法,传统的地震定位方法适用于单震源且信噪比高的情况,主要通过P波和S波的走时差和速度差、初至时间的拾取, 来确定震源位置,当信噪比低而且多震源在同一地区且发生时刻相近时,传统方法对微地震的识别就变得困难了.

针对水力压裂的微地震信号微弱, 事件分布密集的特点,后来相继发展的三分量微地震反演法、地震台阵法、震源扫描法等,通过在整个事件可能发生区域的格网点的逐点搜索,或者是找出满足某一判定准则的空间点源, 例如,P波和S波的走时时差以及参考事件和需要定位的微弱事件的距离,满足误差最小的空间点;或找出最高亮度来识别出分散震源的位置和发生时刻.这类方法不需要精确的初至时间拾取或者提前收集噪声样本,只需要研究波形(振幅和到达时刻)以确认震源位置,可以减少人为因素引入的误差;当然如果震源位置与监测站点相距太远或不在网格划分范围内,或者地层的3D速度模型不够准确, 会产生较大误差.

7.3.2 水力压裂微地震发生及其信号特点

7.3.2.1 水力压裂"慢"过程伴随岩石破裂声发射的"快"过程

水力压裂是在低渗透率油气藏开发中,利用高压泵机组将大量压裂液泵入井内, 泵压可达几十、一百兆帕,液体泵入率可达10m$^3/$min, 随着大量高压液体持续进入地下岩层,当外力增加到一定程度时,页岩中原有的天然裂缝的缺陷地区就会发生微观屈服或变形,裂缝重新挤开或发展; 或者由于外力超过最小地应力和岩石抗拉应力之和,在结构的薄弱缺陷处就会产生新的裂纹. 随着压裂时间的持续延长,通常为几个小时, 和压裂液的注入以及支撑剂的到位,在页岩储层中造成了大范围的体积破坏, 最后液体反排,支撑剂在裂缝中留下, 形成通道扩大渗流面积(见图7.23).通常水平主裂缝半展长可达$150\sim 250$m,缝高几十米(接近页岩储层的厚度),众多的微裂纹尺度范围从微米至厘米量级(Maxwell & Cipolla 2011,White et al. 1975),许多实践结果证明水力压裂的微地震事件是大批生成的,一般能造成每个小时有数百次事件(赵博雄等 2014, Maxwell et al. 2011,Maxwell 2010).

如果观察压裂液的频谱, 图7.24为某一现场操作过程中的注入液体平均压力的时间历程,及其对应的时间平均能量频谱,可见压裂液的注入能量随着频率的增大而减小,如果考虑实际地震的频率范围(通常高于1Hz), 相比最低频率处的能量,能量已经衰减了8个量级, 也就是说, 水力压裂是一个低频率过程(长时间),大多数压力的频率远低于1Hz, 在$10^{ - 4}\sim 10^{ - 2}$Hz 范围(Maxwell & Cipolla 2011).

图7.25为实际观测到的微地震频谱,其微地震信号频率基本都大于100Hz,考虑实际检波器的频带范围(通常为$1\sim 1000$Hz),可以说微地震的频率范围(高频)远高于水力压裂的注入能量的频带范围(低频).大多数微地震事件频率范围为100~1500Hz,持续时间小于1s, 能量介于里氏$-3\sim +1$ (Cai et al. 2007).在地震记录仪上的微地震事件, 理想情况下一般表现为清晰的脉冲,微地震事件越弱,其频率越高、持续时间越短、能量越小、破裂长度也就越短. 因此,从水力压裂致使岩石破裂, 并且产生微地震的整个过程看,水力压裂本身是一个慢过程, 注入压裂液携带的能量在低频范围较大,微地震是发生在这样一个慢过程中的一系列不同裂纹尺度量级岩石断裂而释放微地震波的"快"过程.

7.3.2.2 岩石破坏机理复杂, 微地震的波形多样

页岩储层在高压液体的作用下的破坏机理和类型复杂多样,破坏包括天然裂纹被激活、重新张开和发展,非均匀岩石的应力集中(或薄弱)处的新裂纹的萌生和发展,诱发的井筒周围地层的局部活动(如断层缓慢滑移)等(谢和平等 2016,庄茁等 2016, White et al. 1975, Das & Zoback 2013a, 赵博雄等 2014); 从岩石断裂的破坏类型看,目前的微地震记录表明有拉伸、剪切以及拉剪混合破坏等(Maxwell et al.2011), 如图7.26中可以看出在同一口井中,震源发生破坏的方式不同, 有拉伸剪切破坏(tensile crackclosure)、剪切破坏(compensated linear vector dipole, CLVD, lineardipole)等多种形式. 另外, 从近几年对地震记录数据的深入分析看,整个水力压裂过程中的微地震信号不但包括一系列短时脉冲信号、还有一些长周期的持续一段时间的子波信号,这些子波信号的频率、幅值存在差异, 而且波形也不尽相同(Das & Zoback 2013a, Maxwell et al. 2011).

如果进一步分析微地震记录过程的波形特点, 可以看出,除了常规的脉冲信号, 还有一些其他形状的子波. 例如,图7.27为Barnett页岩开采过程中的微地震记录,可以看出微地震信号会夹杂其他事件,比如断层滑移引起的长时长周期事件(Long-period long-duration event,LPLD事件);图7.28为Barnett页岩的水力压裂过程中的微地震记录(经过滤波),也可以清楚看到微地震脉冲波形和LPLD波形并存.图7.29为一段持续的微地震波形(频率范围$40\sim 80$Hz),LPLD事件前期有一段$10\sim 15$s的小振幅的波动;接着因为S波的到达有大幅度的波动, 也持续了$10\sim 15$s;随后又削减到之前的低振幅波动, 这些变化在对应的频谱图中也可观察到.地震学家对这种波形的解释是,水力压裂过程中出了常规的裂纹萌生和发展造成的微地震,还有断层发生缓慢滑移--快速断裂等其他复杂地层活动释放能量,产生的复杂波形. 从频谱范围看(图7.30),整个水力压裂过程中的各种微地震事件的频率范围跨越了至少两个量级,从10Hz到100Hz甚至更高.

另外, 不同的微地震事件本身,或者微地震与其他事件(例如断层滑移)之间存在相互干涉.在Barnett数据的收集过程中发现有些微地震事件(低振幅脉冲信号)和LPLD事件(图7.31)同时出现;同时, 在一些LPLD事件内几乎没有微地震事件(图7.31).微地震和LPLD有可能同源, 但是微地震事件量级小, 容易被忽略.

7.3.2.3 水力压裂过程的信号干扰

一方面我国页岩目的层埋深差异较大,构造形态多变(褶皱多、隔槽式构造), 地震波场复杂成像难度大;另一方面, 由于水力压裂微地震监测期间, 为了保证油气田持续的生产,往往邻井生产设备没有关闭, 因此微地震信号常常淹没在机械噪声中,利用常规处理解释方法很难见到明显的微地震事件.微地震信号收集的干扰因素还有临近井眼地震波的异常衰减、附近地层反射波的混入和多相位等.液压机组运行和操作的背景噪声、临近井眼的异常、地震波的衰减、附近地层反射波的混入等给微地震事件的识别带来困难.

井中能观测的微地震波型主要有体波(包括纵波和横波两种)和导波,体波包含反射波、直达波、折射波及沿套管滑行的套管折射波等.微地震记录的主要是直达波, 即从震源出发,透过一些地层的分界面后传播至检波器,这在记录的微地震事件总数中占了绝大部分,直达波的三分量检波器上记载的所有波的波至时间都是一致的; 同时,微地震的反射波从震源出发先传播至地层分界面上,再经反射传递到井中也会被检波器被记录, 反射波也能用于微地震的定位,有助于进一步研究水力压裂的裂缝;折射波是由于地层中出现地震折射界面,震源所产生的波由临界角入射至其折射界面, 最终被井中检波器记录;套管的折射波是由于套管中的波速明显地高于地层中的波速,从微地震源发出的波以临界角入射至套管上时, 产生了沿套管的滑行的波,也称为套管的折射波.

由于水力压裂整个过程中微地震产生和波传播的上述特点, 可以看出微地震信号是一种特殊的非平稳过程(Maxwell et al. 2011, 陆基孟 1993,White et al. 1975, Das & Zoback 2013a),包含多种不同频率、幅值和波形的子波,而且各个子波的发生时刻不尽相同但是又存在一定的关联,信号的频谱在不同的时刻是不一样的,仅仅进行初至时刻拾取来定位震源还不够, 需要描述微地震信号在不同的时间和频率位置处的能量密度和强度,还需要分析信号的波形特征,区分和识别出水力压裂过程中不同破坏机理造成的微地震事件, 也就是说,需要在频域--时域二维空间中进行震源信号的全波形分析.

7.3.3 水力压裂微地震信号的时域--频域二维全波形分析

由于水力压裂工程中微地震监测的数据量大、波形种类繁多、环境噪声复杂,信号的频谱具有时变特性, 所以微地震波的全波形分析难度大.用常规的傅里叶变换(Fourier transform)不能得到每一时刻的频谱,需要引入其他频谱分析方法,地震波的时频分析是近十几年发展起来的新技术,在地震学里又称之为地震子波分解,其主要思想借鉴了信号分析中短时傅里叶变换(short time Fouriertransform, STFT)、小波变换(waveletstransform)、S变换以及近年来引起人们关注的匹配追踪法(matchingpursuit, MP)等(Hunt et al. 1993; Stockwell et al. 1996; Mallat et al. 1993; Liu et al. 2004, 2005; Wang 2007; Neff 1997; 陈发宇等 2007; 张海燕等 2007),这些时频分解方法已被广泛应用于无损探伤、医学超声扫描、地球物理的储层预测和流体识别等领域.

常规傅里叶变换只能对地震波动图做简单的一维变化(时间域变换到频率域),只能分析整个时间段里信号的平均频谱, 没有办法分析信号细节变化.短时傅里叶变换虽然受限制于时间--频率的分辨率,但是已经可以做到基本的二维变换. 之后小波分析的出现,打破出了常规方法分辨率的限制, 提供了高精度的频谱分解法, 因此,小波变换(wavelettransform)和能够进行基函数优化的匹配追踪法(matchingpursuit)成为将地震波动图转化到时间--频率二维空间再进行全波形分析的有利工具.

短时傅里叶变换 假设信号在足够小的窗内是准平稳的,利用移动时窗在短时段内进行傅里叶变换,该方法实现了把一维信号转变成二维空间的时间-频率域信号.但是窗函数时频窗宽度决定了时频分辨率, 由测不准原理可知,不可能同时得到任意小的时间窗和频率窗,也就是说要想得到较高时间分辨率必然要牺牲频率分辨率,要想得到较高的频率分辨率就必然要牺牲时间分辨率, 二者不可兼得.

虽然, Okaya等 (Okaya et al. 1992, Okaya 1995)在时频域内通过抑制能量,分离不相关波动数据在时--频图中来分辨低频率表面波和高频率反射波,基波和谐波的到达时刻以及人为因素产生的能量,但是微地震信号一般不稳定, 没有标准化的分解方法,短时傅里叶变换定位时--频精确度不高, 且受时间带宽的分辨率限制,当时间窗窄时, 只对高频信号有较好的分辨率, 对低频信号分辨率较差,反之亦然.

小波变换是一种分解信号识别其"频率分布$\sim$时间"的方法. 该方法继承了STFT的时频局部分析的思想,通过改变伸缩因子变更小波基函数时频窗口,实现了窗口性质随着信号特征的变化而变化,在信号低频处有较高的频率分辨率, 在信号高频处有较高的时间分辨率,小波变换具有"变焦"功能, 因此小波变换具有多尺度多分辨率的特性.该方法与短时傅里叶变换最大的不同是后者选用固定的时窗而小波变换的时窗是随尺度(频率)变化.目前, 小波分析已经在多个领域应用,如一维信号分析、时间尺度重现、滤波频带理论、数码成像边缘处理、数值分析和地震波数据分析. Hunt等(1993)指出小波分析就像数学显微镜,当窗函数是具有一定宽度的时, 就可以得到全部的信号结构,随着时窗宽度的变化, 用于分析的基函数越来越窄,细节特征就越来越明显. 连续小波变换(continuous wavelets transform,CWT)首先被Morlet等(1982)和Goupillaud等(1984)提出,真正开始受到关注是在Daubechies(1988)和Mallat(1989)利用小波分析分解信号过程. 分析小波函数$\varPsi(t)$方程定义如下

$ W(a,b) = \dfrac{1}{\sqrt a }\int {\varPsi ^\ast }\left( {\dfrac{t - b}{a}} \right)f ( t){\rm d}t (7.22) $

窗函数$\varPsi (t)$为基本小波,参数$a$和$b$分别表示尺度因子和平移因子.在每个时窗内(每个$a$值)基本小波伸缩变换$1/a$或平移$b$后得到新的小波函数系列.一般情况下, $a$取$2^j$是尺度因子.

虽然小波变换的窗函数的时间窗和频率窗均可改变,但是这种时频分析方法将伸缩因子和频率直接对应起来, 尺度代替了频率,小波变换对高频成分的频率估计不精确,对低频信号的时间分辨率不够精确. 因为一旦小波基函数确定,其时间窗口宽度与频率窗口宽度的面积即为定值,在低频区域时间窗口宽度大, 窗口读取的信号时间范围长,换句话说远离窗口中心时刻的信号也被包含进来,即使时间窗口中心无信号, 由于滑动窗口边缘也可能包含信号成份,就会在该时间中心点产生不期望的信号谱, 从而造成较大的时间误差,反之亦然.

匹配追踪(Chakraborty et al. 1995)在近年来引起了人们关注,该方法最早由Mallat(1993)等提出,其原始算法是基于Gabor函数组成的超完备子波库的"贪婪"寻优匹配算法,并以子波库中各匹配子波的Wigner-Ville分布之和对原信号进行时频表征.通过投影最大把信号分解成与其局部层次结构尽可能一致的时频原子的组合,求取这些原子的时频分布的线性组合就可得到信号的时频表达,每次迭代都是选取子波库中与信号最大相关的子波(原子),从信号中减去此匹配子波在信号上的投影,再对残余信号递推迭代直至残余能量满足收敛要求.由于匹配原子不要求互相正交, 可灵活地从过完备库上进行选取,这样选取的原子与信号更能趋近最佳匹配(Mallat et al. 1993; Liu et al. 2004, 2005; Wang 2007; Neff 1997),信号(尤其是对频谱随时间变化的非平稳信号)的时间和频率分辨率有明显提高.

匹配追踪分解通过调制和平移控制窗函数

$ \varPsi _{(s,\xi ,\tau )} (t) = \dfrac{1}{\sqrt s }\varPsi\left( {\dfrac{t - \tau }{s}} \right){\rm e}^{ -{\rm i}\xi t} (7.23) $

$s$是尺度因子, $\tau $是平移因子, $\xi$是频率调制因子. 正如 Mallat 和Zhang(1993)所说的,该方法提供率极佳的时频分辨率, 是一个迭代过程,基本方程包含了所有可能的时频宽度, 所有构造波的子集

$ f(t) = \sum\limits_{j = 0}^{N - 1} {a_j g_j } +R^{(N)}f (7.24) $

其中, $f(t)$是地震记录信号,$g_{j}$为自适应寻找的原子核, $R^{(N)}f$为拟合后的残差.一旦基本方程(时频原)被确定,则信号和这些原之间最好的匹配可以通过把该原带入信号,计算最大值找到.残差是原始信号减去原的乘积和被选择的原和信号的叉积.继续上述的分解过程, 直到剩余能量低于阈值.

事实上, 该思想方法已经在地质勘探领域地球物理信号处理方面得到应用,被用于分辨空间预测目的层段的储层,给出含油气性展布规律识别薄互层储层, 检测油气储层的低频阴影,刻画油气储层的岩性边界和空间展布(Liu et al. 2006, 周忠根 2006,张繁昌等 2010, 何胡军等 2010). 但是,目前该思想方法用于页岩气开采水力压裂的微地震数据解释的还不多见,针水力压裂中对微地震信号的频谱随时间变化、信号发生不连续且持续时间长、包含有多种不同频率/幅值和波形的子波的特点,结合岩石破坏的力学分析和弹性波传播规律分析,我们应该发展专门的基于时域--频域二维优化谱分解的全波形分析方法,在此基础上进一步对震源机制进行合理的解释.

对比连续小波变换、短时傅里叶变换匹配追踪法,可以看出这3种变换都能把一维空间(时间历程)的信号转化成二维空间(时间--频率域)信号,而常规傅里叶变换只能把一维信号转化成一维频谱.连续小波变换相比于短时傅里叶变化最大的优点是,其在低频区域信号对于频率分辨率高, 在高频区域事件分辨率高,但是小波变换在低频率时间分辨率不足, 在高频率区频率分辨率不足.匹配追踪法正好解决了小波分析这一缺点. 如图7.32同样的信号,分别进行短时傅里叶变换, 小波变换和匹配追踪法,匹配追踪法有最好的频率和时间分辨率,而小波分析在低频率段时间分辨率不足(图7.32(a)中D段),短时傅里叶变换在时间分辨率不足(图7.32(a)中A段).不同时频瞬时谱分析法的比较见表7.1.

7.3.4 微地震的数据解释

尽管近年来相关理论技术的提高已经为上述很多问题提供了有效解决方案,但是微地震监测技术仍然存在一些局限性(Daniels et al.2007)和尚未完全解决的问题,微地震监测数据的分析结果与实际情况不自洽或者尚无公认的合理解释.例如泵入流动液体携带的能量、岩层破裂的释放能量、检波器监测到的能量之间的关系尚存在不匹配;水力压裂的致裂面积与产量之间的关系并不确定,有时候即致裂面积大而产量未必高(有可能存在其他的未被识别出的裂缝);理论上预计不会发生微地震的时间(例如停止泵压或者完井之后),却也会监测到微地震; 从破坏机理上看水力压裂过程是拉伸破坏,但是微地震监测到的多数是剪切破坏;水力压裂过程是慢过程而微地震发生是快过程.

7.3.4.1 能量的匹配

具体指微地震和水力压裂能量不匹配;泵入的能量、裂纹的能量、岩石储存的能量不匹配;岩石的应变能、检波器接收到的能量、微地震的能量和泵入总能量不匹配.Kanamori 和Rivera(2006)列举了水力压裂过程中的3种能量分配模型(图7.33).$E_{\rm F}$是界面摩擦能量(interface frictionalenergy)等价于转换的热量; $E_{\rm G}$是断裂能量,它是除了界面摩擦之外, 所有和断层作用相关的能量总和,包括了裂缝能量、由弹塑性消耗的能量、产生断层裂缝的能量和流体增压的热量;$E_{\rm R}$是地震辐射的能量.

地震力矩$M_{o}$(断层的平均位移、断层面积、剪切模量的乘积)是一种表征微地震量级的方法(静态地、有绝对值的),不管微地震发生快或者慢,地震力矩是唯一能从低频率振幅谱中得到的参数, Kanamori和Rivera(2006)给出了弹性能和力矩的关系为$\Delta W = \dfrac{M_o \bar{\sigma }}{\mu }$, 其中, $\Delta W$是微地震释放的弹性能, $M_o $是地震力矩, $\bar {\sigma }$是主应力(3个主应力), $\mu $是岩石材料的弹性模量. 如果在相同的气藏中, $\bar {\sigma }$和 $\mu$的值在相同范围.图7.34为Barnett页岩水力压裂微地震的记录时间历程和频谱.

可以看出其中的LPLD事件(水力压裂过程中振幅量级较大的地震事件)对应的力矩小于$2.5\times10^8$N$ \cdot $m/s (图7.34(d)),取1s时窗内计算频谱得到累计力矩. 如果震级的定义使用Hanks(1979)公式$(M_w = 2 / 3(\lg M_o - 9.1)$,可以得到LPLD事件的量级约等于$+0.3$的微地震.在Barnett页岩的例子中(Das & Zoback 2013a), $\bar {\sigma }$和$\mu$ 的量级分别是兆帕和GPa量级,则弹性能量级大约是地震力矩的千分之一.

Maxwell等(Maxwell et al. 2008, Maxwell 2010)、Cipolla等(2012)、Warpinski等(2012)均指出微地震的累计能量仅占压裂液注入能量的一小部分,水力压裂缓慢的拉伸开裂和扩张仅占约15%$\sim$20%的注入能量. 那么,水力压裂期间发生的各种微地震占到总弹性能能量的多少呢?如果岩石中水力压裂激发的弹性能的总量通过偏应力计算, 即$E_d =\dfrac{1}{4G}(s_1^2 + s_2^3 + s_3^2 )$, 其中 $E_d$ 表示偏应变能,$G$是岩石剪切模量, $s_{1}$, $s_{2}$, $s_{3}$是偏应力.

表7.2给出了微地震能量、LPLD事件能量和总弹性能量的量级估算结果,可见不管是普通的微地震能量或是量级较大的LPLD事件,其能量都仅占总能量的不到千分之一, 那么大部分能量到哪里去了呢?摩擦消耗、继续储存在岩层中还是渗透和反排的液体携带走了?有待进一步考证.

7.3.4.2 致裂面积与产量之间的关系

虽然钻井和水力压裂技术已经成功用于低渗透率气藏的勘探和开采,但是我们对低渗透岩石的变形机理还不完全清楚. 此外,虽然多次水力压裂之后,地震记录图显示在水力压裂之后出现了新的裂缝和天然裂缝发生了滑移,但是微地震显示的致裂面积与产量之间的关系并未被证实,即致裂面积大的岩层, 其产量不一定高(Moos et al. 2011, Sicking et al. 2013).

7.3.4.3 微地震事件的发生时间

结合微地震记录和井压记录, 会发现原本预计不会发生微地震的时间,如停止泵压的时候或完井之后, 却出现微地震事件(Dos & Zoback 2013). 图 7.35给出了水力压裂过程中的井底压力和微地震频谱,图中黑色线代表井底压力, 细长条带状信号表示微地震事件,低频宽带信号表示LPLD事件, 可以看出在第7段水力压裂和第8段水力压裂之间, 尽管已经停止泵压, 却出现了微地震事件.

7.3.4.4 水力压裂的岩石破坏机理

从水力压裂的岩石变形机理看,岩石因为注入液体压力提高到结构的破坏压力而开裂,因为裂隙网络压力和流体的不断注入, 岩石体积持续被压裂,裂缝持续增长, 因此, 有人认为岩石开裂属于拉伸破坏(Fredd et al.2001, Maxwell & Cipolla 2011). 然而,根据微地震信号反演出的岩石变形却不尽相同,往往观测到的S波具有较大振幅(Warpinski 2004),明显的S波是剪切变形震源的特征.Rutledge等(2004)分析了不同地区水力压裂中微地震的数据(图7.36), 发现只有剪切变形具有高SH/P波振幅比,而拉伸开裂变形对应较低的SH/P振幅比,所以他认为水力压裂中微地震一般是剪切变形.水力压裂中导致微地震的岩石破坏机理目前尚未有统一定论,理论上认为剪切变形、拉伸开裂变形、亦或是两种方式同时存在(Baig & Urbancic 2010)均有可能,而对于大多数气藏岩石是否具有足够强大拉伸力和内聚力足够强,以至于可以产生足够的地震能量, 使得观测到的微地震是拉伸破坏模式,目前还不能完全确定.

7.4 本节小结

随着页岩气开采技术的进步,微地震监测在页岩气开采的各个阶段都发挥了重要的作用,例如前期的油气藏勘探、地层的地球物理参数判断(矿物含量、地应力状态等)、钻井数量和位置的优化配置等,中期的水力压裂的裂缝监测、控制压裂范围(避开含水层、断层滑移带),后期的产量总结、经验积累等多方面都有应用.尤其是在水力压裂过程监测中的应用非常突出,它能给出裂缝的具体位置、尺寸和走向,通过后期的进一步数据分析可以得到裂纹类型(拉张型或剪切型)、震源发生机理(天然裂纹张开、新裂纹萌生、地层中断层的微小滑移)等更深刻的信息,从而对水力压裂过程进行设计和优化,通过对压裂过程和后期产量数据的总结分析,得到非常规气藏的钻井、开采、生产的宝贵经验.

然而, 微地震监测技术仍然存在一些局限性(Daniels et al.2007)和尚未完全解决的问题,尽管近年来相关理论技术的提高已经为一些问题提供了解决方案. 近年来,水力压裂微地震监测的研究主要集中在裂缝成像的数据处理方法,资料解释方法以及相关理论上(Cipolla et al. 2012, Maxwell & Cipolla 2011, 刘振武等 2013, Warpinski et al. 2001, 李君辉 2015, Sicking et al. 2013), 从而使利用诱发微地震裂缝成像技术有了不少重要进展,这不仅能让我们听到压裂的声音, 更能准确地判断裂缝的方位与形态,提供水力压裂的裂缝发育过程等更加详细的资料,还可以提供在储层中流体的通道图像、渗透率参数、地层应力等等.从发展趋势来看:

(1)微地震监测正在从早期借鉴传统大范围地震监测方法向局部小范围微地震监测过度,从地面设站或者地下测井设站,到现在以地下测井设站为主、地面设站为辅, 两者结合共同监测.

(2) 微地震的信号处理由单纯的微地震序列的实时辨识,向全波形记录、自动分析并对事件进行预测、震源机制进行反演等方向发展.水力压裂期间生成的微地震波的波形种类繁多、机理错综复杂,不容易区分和识别出各种活动事件; 而且环境噪声大而且干扰因素多,微地震信号的频谱随着时间变化,而常规傅里叶变换不能得到每一时刻的频谱,需要更新的频谱分析手段如小波变换、匹配追踪等优化分解方法.水力压裂生成的裂缝网格复杂,准确地反演出岩层中的三维裂纹网络非常困难,对震源机制的了解尚不充分,震源类型和破坏机理还不能被精确反演和解释.

(3) 后期的微地震数据分析更注重对实测数据的理论分析,以得到适用于具体地质环境的可靠监测结论. 目前,微地震监测数据的分析结果与实际情况仍然存在一些不易解释的问题,例如泵入流动液体携带的能量、岩层破裂的释放能量、检波器监测到的能量之间的关系尚不匹配,水力压裂的致裂面积与产量之间的关系还并不确定,有时候致裂面积大而产量未必高(有可能存在其他的未被识别出的裂缝),理论上预计不会发生微地震的时间(例如停止泵压或者完井之后),却也会监测到微地震, 从破坏机理上看水力压裂过程是拉伸破坏,但是微地震监测到的多数是剪切破坏.

(4) 微地震监测基于的理论和方法,从沿用以往的地震理论和信号处理技术,向关注水力压裂微地震的发生和信号特点的针对性方法发展.从震源定位方法看,在以往的地震定位方法(纵横波时差法、三圆相交定位法、偏振分析定位法等(Jurkevics 1988)基础上,针对水力压裂微地震的震源能量微弱、多震源同时发生、信噪比低的特点,新的微地震定位方法如三分量空间点集法、交叉相关台阵法和震源扫描法等(Kao et al. 2004, Kummerow 2010)等正在发展.这些新方法不需要提前收集噪声样本、初至时刻,而是通过找出最高亮度、相关系数或研究多地震道的波形来识别出分散震源的位置和发生时刻,以减少人为因素引起的误差.

另外, 由于页岩气开采水力压裂过程中的岩石破坏机理复杂多样,包含天然裂纹张开、新裂纹生成/发展以及周围地层的断层局部滑移等多种活动;而且微地震波在含裂缝缺陷的地下介质传播时受到地层反射、散射和吸收衰减等因素影响,频率成分随着时间变化; 与常规的短时地震不同,整个水力压裂过程持续时间长, 微地震事件发生密集、振幅量级低,而且信号受到邻井生产以及液压操作设备等的机械噪声的干扰, 因此,微地震信号是一种特殊的非平稳信号, 其频谱随时间变化,信号发生不连续且持续时间长,包含有多种不同频率/幅值和波形的子波且信噪比低.

针水力压裂中微地震的发生环境、机理和其信号的特点,需要发展针高时频分辨率的瞬时谱分析方法,以描述微地震信号在不同时间和频率位置处的能量密度和强度,对微地震全波形进行合理的子波分解和事件识别;并结合岩石破坏的力学机理,对水力压裂的致裂和震源特征给予合理的解释.微地震监测作为近年来被广泛研究和应用的一种地球物理技术,尽管起步晚但是发展迅速,其前缘技术包括全波形记录和分析、优化子波分解和重构、低信噪比滤波、微地震震源机制反演、基于微震信息的压裂优化设计等,尚处于探索应用中需要进一步加强基础理论和工程应用研究.

8 无水压裂技术^*(*本节撰稿人:侯绍继, 潘利生, 刘曰武¹(1E-mail:lywu@imech.ac.cn), 魏小林, 高大鹏)

8.1 前言

自1935年水力压裂作为常用油气田增产措施以来,水力压裂技术已在油气开发工程上获得巨大成功, 但是水力压裂会引发许多环境问题.Darrah等(2014)认为为了减少水资源的使用和降低环境风险,有必要探索无水压裂技术来替代水力压裂技术.

纵观无水压裂技术的发展, 无水压裂技术与水力压裂技术相比,它是一种采用非水基液作为压裂介质进行岩石压裂、实现油气开发或者增产的技术.总体来说,无水压裂技术具有缓解水资源压力、环境风险小、储层伤害小、地面风险低等特点.根据压裂液类型的不同,无水压裂技术可分为二氧化碳(CO$_{2}$)压裂、氮气压裂、爆炸压裂、液化石油气压裂、高能气体压裂等.

下面将主要分析这些无水压裂技术的特征、优势与不足以及目前的研发进展,并且探讨了无水压裂技术的发展方向,为我国研发页岩气无水压裂技术提供建议和对策.

8.2 二氧化碳压裂技术

CO$_{2}$压裂技术是指在油气开采中,将液态CO$_{2}$作为压裂介质注入储层, 形成裂缝, 增加溶解气的能量,从而达到开发或增产的目的. CO$_{2}$压裂包含CO$_{2}$泡沫压裂和CO$_{2}$干法压裂2种.CO$_{2}$压裂技术主要适用于水敏感地层的干性压裂,主要是将天然砂粒、树脂涂敷砂或高强度陶瓷材料等支撑剂和液态CO$_{2}$一同注入储层,同时CO$_{2}$需要增加黏度来携带支撑剂的方法. 20世纪80年代,加拿大和前苏联的CO$_{2}$压裂技术取得巨大成功(Luk & Grisdale 1996), 仅加拿大就已有超过1200次成功的CO$_{2}$压裂.这项技术也被用于美国东肯塔基、西宾夕法尼亚州、德克赛斯和科罗拉多的泥盆纪页岩(Arnold 1998).

CO$_{2}$压裂技术的优点在于:

(1)对地层伤害小(Arnold 1998). CO$_{2}$压裂液不含水,压裂过程中受热膨胀, 全部气化并回流到井筒,对裂缝周围的相对渗透率和毛细管压力伤害最小;

(2)减少流体阻塞, 对地下环境污染少.CO$_{2}$压裂液在井筒和储层中压裂后气化膨胀, 洗井排液,对地下水和地表水的污染较少; (3)能提高压裂和裂缝扩展的效率(Meng et al. 2016).美国东肯塔基、宾夕法尼亚州等地泥盆纪页岩的压裂结果表明,CO$_{2}$压裂井的平均产气量是传统水力压裂方法的5倍;

(4)能增加页岩中吸附甲烷气的解吸. 使用CO$_{2}$压裂技术,污染问题和微地震问题将减少.

CO$_{2}$无水压裂的施工工艺设计按施工顺序排列,主要由系统增压、循环预冷、施工作业和系统放空4个子流程组成(Meng et al. 2016).

(1)系统增压:系统增压流程主要是通过液态CO$_{2}$储罐中的气相CO$_{2}$(2.00MPa左右)在全部地面管汇和设备通道内建立0.52MPa以上的基本压力.

(2)循环预冷: 当系统增压流程结束后, 需要开启循环预冷流程.该过程是通过储罐中的液态CO$_{2}$对所有的地面管汇和专用设备进行循环预冷,与此同时将液态CO$_{2}$注入到支撑剂低温储罐中, 对支撑剂进行预冷,可以将管线和设备的温度降低到$-20.0^\circ$C左右.循环预冷流程的重点是专用带压混砂设备储罐中的支撑剂和压裂泵液力端的预冷.

(3)施工作业: 循环预冷流程结束后进入施工作业流程.CO$_{2}$无水压裂施工流程与常规压裂流程一致,包括地面管线试压、泵送前置液、泵送携砂液和泵送顶替液4个过程.

(4)系统放空: 施工作业完成以后依次关井口并开启高压放空端口,全部地面设备内剩余的液态CO$_{2}$全部从高压放空端口统一放空.

8.2.1 二氧化碳干法压裂

CO$_{2}$干法压裂技术使用100%液态CO$_{2}$作为压裂介质,首先将支撑剂加压降温到液态CO$_{2}$的储罐压力和温度,在专用混砂机内与液态CO$_{2}$混合,然后用高压压裂泵泵入井筒进行压裂(才博等 2007).

CO$_{2}$干法压裂工艺按如下步骤进行(刘合等 2014, 宋振云等 2014): (1)将若干CO$_{2}$储罐并联,并依次与CO$_{2}$增压泵车、密闭混砂车、压裂泵车、井口装置连通,将仪表车与上述各车辆连通并监控工作状态;(2)将支撑剂装入密闭混砂罐中, 并注入液态CO$_{2}$预冷;(3)对高压管线、井口试泵, 对低压供液管线试压,若试压结果符合要求则继续进行后续步骤;(4)液态CO$_{2}$以$-25^\circ{\rm C}\sim - 15^\circ$C温度注入地层,压开地层并使裂缝延伸, 然后打开密闭混砂设备注入支撑剂,支撑剂注完后进行顶替, 直到支撑剂刚好完全进入地层, 停泵;(5)压裂施工结束后, 关井$1.5\sim 2.5$h; (6)压后放喷返排,既要控制返排速度以防吐砂, 又要最大限度地利用CO$_{2}$能量快速返排,可以先使用小口径油嘴控制放喷速度, 随后逐渐加大油嘴口径,并使用CO$_{2}$检测仪监测出口CO$_{2}$浓度变化.

CO$_{2}$干法压裂是以CO$_{2}$代替常规水力压裂液的一种新型无水压裂技术.其诸多优点主要体现在: (1)无水相, 完全消除水敏、水锁伤害;(2)压裂液具有极低的界面张力, 受热气化后能够从储层中完全、迅速返出;(3)压裂液无残渣, 对支撑裂缝导流床具有较好的清洁作用,保持了较高的裂缝导流能力和较长的有效裂缝长度; (4)CO$_{2}$在地层原油中具有较高的溶解度, 能够降低地层原油黏度,改善原油流动性; (5)超临界CO$_{2}$ 具有极低的界面张力, 理论上,对非常规天然气储层中吸附气的解吸具有促进作用.

二氧化碳干法压裂存在的问题:

(1)携砂及降滤失性能

液态二氧化碳本身黏度较低, 通常只有0.02~0.17mPa$\cdot$s, 携砂能力弱, 只能使用低密度支撑剂; 滤失量较大,不适合高渗透油藏. 在液态二氧化碳中添加增稠剂可以大幅度提高黏度,通常能够达到百倍以上,是增强二氧化碳携砂能力及降滤失能力的有效方法.

(2)摩擦阻力

液态二氧化碳是一种牛顿流体, 在管柱中有较高的流动摩擦阻力.目前国内外对液态二氧化碳减阻剂的研究较少,而在水溶液中适用的常规聚合物减阻剂则不适于液态二氧化碳,因而必须开发出一种能大幅降低液态二氧化碳在管柱中流动阻力的高效减阻剂.

(3)压裂施工设备

二氧化碳压裂技术的主要设备包括增压泵、混砂设备和压裂车组等,其中混砂设备是制约该技术发展的主要因素. 液态二氧化碳黏度低,携砂性能差, 这就要求混砂设备能够高效混砂;液态二氧化碳若接触空气一部分气化吸收大量热, 一部分会冻结为干冰,造成管线堵塞, 这就要求混砂设备有较高的密闭性与防冻性,同时能够排出气态二氧化碳; 混砂设备需要对支撑剂进行预冷却,若支撑剂含有水分会冻结成块, 造成混砂不均甚至砂堵;混砂设备还必须预留增稠剂接口.

CO$_{2}$干法压裂目前仅适用于低渗气井(Gupta & Bobier 1998).若开展相关研究,该技术将是适用于低渗、低压、高水敏油层的最经济有效的改造方法.例如:

(1)将CO$_{2}$干法压裂与CO$_{2}$吞吐、CO$_{2}$驱替结合起来,形成压裂--吞吐--驱替一体化工艺. 可在压裂前注入液态CO$_{2}$,焖井憋压一段时间, 待充分汽化和混相后, 再实施压裂改造;也可以延长压裂操作后的焖井时间,充分发挥CO$_{2}$补充低压油层能量、降低原油黏度的作用.CO$_{2}$压裂施工地面流程图见图8.1;

(2)开展碳酸盐岩储集层的盐酸--液态CO$_{2}$混合液酸化工艺试验,并在更加广阔的领域内推广应用.

8.2.2 二氧化碳泡沫压裂技术

CO$_{2}$泡沫压裂就是把液态CO$_{2}$与常规水基压裂液按照一定的比例混合后形成以气相为内相、液相为外相的稳定泡沫体系从而用于压裂施工的一种压裂方式.CO$_{2}$干法压裂是以液态CO$_{2}$代替常规水力压裂液的一种无水压裂体系.CO$_{2}$压裂的使用可以大大降低或者消除压裂施工中水与地层的接触机会,从而大大降低了水锁和水敏造成的地层伤害.对于广大低渗、低压、强水敏和水锁性油气藏的压裂改造展示出巨大的技术优势,具有良好的应用前景.

CO$_{2}$ 泡沫压裂的关键技术包括起泡、酸性交联和提高砂液比三方面.压裂前需针对储层埋深、地温梯度、裂缝温度场和地层压力的动态变化,分析CO$_{2}$起泡时间和深度范围, 保证正常起泡.液化CO$_{2}$呈弱酸性, 只适合选用酸性羟丙基瓜胶类作增黏剂,酸性条件下的有效交联是CO$_{2}$泡沫压裂设计、施工的核心.国外研究发现, 采用恒定内相技术可提高砂液比,保证压裂液黏度(郑新权和靳志霞 2003). 作业时,先将加压泵、管线、阀门、接头等组成的压裂系统用低温气态CO$_{2}$冷却至相态变化,防止管材热损(以系统表面凝霜为标志),然后开始泵入预先汽化、混配好的CO$_{2}$, 井下起泡,也可直接注入汽化好的CO$_{2}$泡沫 (谢平等 2005).

CO$_{2}$ 泡沫压裂的优点是清水用量少, 抗滤失和携砂能力强,泡沫黏度高, 储层伤害和返排问题少. 但由于水基压裂液用量少,难以实现高砂比, 施工压力对设备有较高要求.

二氧化碳泡沫压裂液体系的增产效果好, 其机理如下:

(1)黏度高: 二氧化碳泡沫压裂液体系中通常要加入适当的稠化剂,加上二氧化碳本身的结构特点, 其黏度较高.高黏度使得二氧化碳泡沫压裂液的造缝能力强, 能产生更宽更长的裂缝.

(2)滤失低: 泡沫的独特结构使得体系的滤失量较低.在体系中通常加有增稠剂, 增加了体系的造壁性能,使得滤失更容易得到控制. 所以二氧化碳泡沫压裂液体系的滤失系数很低,滤失量很小, 液体几乎都用于造缝上, 效率很高.

(3)悬砂性好: 在没有加二氧化碳的普通压裂液中,悬砂能力主要靠体系的黏度大小决定. 而在二氧化碳泡沫压裂液体系中,由于泡沫的独特结构使得高砂比的情况下, 砂在体系中的沉降速度非常小.在室内实验中发现, 10$\sim$20目大小的砂在二氧化碳泡沫压裂液体系中沉降速度几乎为0.这种好的悬砂能力使得形成的裂缝中的支撑层十分均匀,大大提高了裂缝的导流能力.

(4)摩阻小: 由于泡沫结构的存在, 二氧化碳泡沫压裂液体系的摩阻小,使得井口施工压力较低, 给大排量施工提供了良好的先决条件,以便产生较大的裂缝面积. 其摩阻仅仅相当于清水摩阻的一半左右.

(5)返排能力强: 返排是压裂过程中非常重要的环节.特别是在含气致密砂岩压裂时, 返排的好坏相当关键. 如果返排不彻底,会降低气体的相对渗透率, 降低产量. 因为二氧化碳具有较大的压缩性,所以其具有较强的储能能力.

压裂改造是通过在近井地带形成压裂裂缝, 沟通更多的油气层,提高压裂层的导流能力, 恢复并提高油井产量, 提高油气藏的开发效果.为了确保压裂施工的有效性, 选井选层是关键.二氧化碳泡沫压裂选井选层中, 应重点研究3个方面的问题,一般原则概括如下:

(1)构造优越. ①压力较高; ②油层均质情况相对较好, 隔层发育;③所选措施层位与周围水井连通, 确保后续能量充足; ④井况良好,能分层有针对性的进行施工; ⑤剩余油分布较高的地区.

(2)储层条件好. 二氧化碳压裂适用范围很广, 不存在严格的限制条件,既可适用于高渗透率的油气藏,更适用于低渗透率的油藏(小于1.0$\times $10$^{4}\mu$m$^{2})$, 既可用于稀油, 也可用于稠油的油藏. ①低含水井;②所选措施层段油层发育好, 厚度大, 剩余油饱和度高, 最好是新层;③产液量相对较好的地区; ④选择地层能量充足井.

(3)油气井井况好. ①对于新投产层,应选在主力区块的主力油层或非主力区块的主力油层; ②对于已开发区块,在主力油层已动用的情况下, 应选择主力区块的接替层, 即厚度大,砂体发育连片的地区;

8.2.3 超临界二氧化碳压裂

目前, 成熟的页岩气开采技术一般采用水力压裂,该技术动辄需要数万立方米的淡水资源, 并且淡水资源可重复利用率较低,消耗量大. 同时, 页岩气所在区域有时淡水资源短缺, 难以远距离输送,限制了水力压裂技术的应用. 采用超临界CO$_{2}$替代水应用于压裂技术,是目前页岩气开采的研究热点之一.页岩气开采地区可以采用燃烧、空气分离或工业废气提纯等办法获得CO$_{2}$.

超临界CO$_{2}$是一种介于气体和液体之间的流体, 它的密度接近液体,而黏度约为水的5%, 接近于气体; 它的表面张力很低,扩散系数较液体高, 将CO$_{2}$加温加压至临界点以上时,称为超临CO$_{2}$流体. 超临界CO$_{2}$流体既不同于气体,也不同于液体, 但有着比水力压裂更高的效率,中国石油大学沈忠厚院士已经开始着手研究如何将其应用到页岩气压裂中.研究表明, 在储层原有的微裂缝中, 高黏压裂液无法进入,而超临界CO$_{2}$流体却可以随意流动, 使得储层产生更多的微裂缝.由于裂缝的多少直接决定了产量的大小,所以超临界CO$_{2}$压裂技术的应用可以提高单井产量和采收率.更为重要的是, 超临CO$_{2}$压裂是一种更清洁的压裂技术,在压裂过程中不需要水的介入, 也无需添加其他化学物质,对储层没有污染, 也无需处理返排液, 压裂完毕后可直接投产.

超临界CO$_{2}$压裂是重要的无水压裂技术之一, 在压裂改造中,使用超临界CO$_{2}$作为压裂介质进行施工, 其增产机理主要为:

(1)由于超临界CO$_{2}$压裂流体黏度低、扩散性能强、表面张力接近零.因此, 容易渗入较小的孔隙和微裂缝中, 有利于微裂缝网络的形成,较大程度地增大渗流面积, 有效地驱替储层中的油气,进而提高油气藏采收率 (刘合等 2014).

(2)对于气井, CO$_{2}$和天然气主要成份CH$_{4}$一样,能够被页岩层以及煤层等储层吸附.但CO$_{2}$分子与储层的吸附能力比CH$_{4}$分子与储层的吸附能力强,再加上超临界CO$_{2}$在储层孔隙裂缝中非常容易流动,它能够置换出被吸附CH$_{4}$分子, 使吸附态的CH$_{4}$变为游离态,从而使气井投产后在较长时间内保持较高的产量 (Gupta et al. 2005). 对于油井, 压裂使CO$_{2}$进入储层后, 在地层温度下快速汽化,溶于原油中而大幅度降低其黏度, 并且增加了溶解气驱的能量. 同时,CO$_{2}$与储层中的水生成碳酸, 饱和CO$_{2}$水溶液的pH值为3.3$\sim$3.7, 腐蚀性小; 当pH值为4.5以上时, 能够降低黏土矿物水化膨胀,保持储层的渗透性, 有利于解除裂缝内的堵塞.

超临界二氧化碳压裂也存在一些不利因素, 主要表现在以下几个方面(Wang et al. 2012, 孙张涛等 2014,Gupta et al. 2005): (1)在压裂施工时,CO$_{2}$在井筒中随温度和压力的改变存在相态变化, 压裂设计复杂;(2)对于浅井, 地面需要安装加热设备, 并且存在不均匀加热的问题;(3)由于CO$_{2}$的穿透性强, 对压裂设备的密封性与防穿刺性能要求高;(4)超临界CO$_{2}$的黏度低, 导致其携砂能力差, 同时,超临界CO$_{2}$流动性能好, 在地层中的滤失速度快,因此需要较多的压裂设备进行大排量泵入.

目前, 纯液态CO$_{2}$压裂已在长庆油田有了成功案例,超临界CO$_{2}$压裂正是在这个基础上所做的创新.超临界CO$_{2}$压裂技术还处在试验阶段, 还有一些技术难点有待克服,进入现场应用尚需时日.

8.2.3.1 CO$_2$物性

CO$_{2}$临界温度为31$^\circ$C, 临界压力为7.38MPa.当CO$_{2}$的压力和温度同时超过它的临界压力和临界温度时,CO$_{2}$达到超临界状态. 表8.1给出了CO$_{2}$气体、超临界流体和液体的物理性能.CO$_{2}$相图如图8.2所示.

超临界状态是一种特殊的流体, 图8.3给出了超临界CO$_{2}$物性随压力和温度的变化规律(Cheng et al.2008). 在临界点附近, 它有很大的可压缩性, 适当增大压力,可使其密度接近一般液体的密度, 而且具有很好的溶解能力.超临界CO$_{2}$具有低黏度、高扩散系数、零表面张力的特性.超临界CO$_{2}$的黏度在10$^{ - 4 }$Pa$ \cdot $s量级,比液体黏度10$^{ - 3}$Pa$ \cdot $s 低一个数量级,扩散系数为10$^{ - 4}$cm$^{2}$/s, 比一般液体的扩散系数10$^{ -5}$cm$^{2}$/s高一个数量级.超临界CO$_{2}$的这些性质使其非常容易进入任何大于其分子的空间.

超临界CO$_{2}$在岩石缝隙中的吸附能力比CH$_{4}$气体更强,从而进入岩石缝隙的超临界CO$_{2}$有助于CH$_{4}$气体的置换,从而进一步提高页岩气的采收率和单井产量(贾虎等 2010, 蔚宝华等 2010).

另一方面, 采用超临界CO$_{2}$压裂技术也存在难点:(1)当有水存在的环境时, CO$_{2}$对钢材具有极强的腐蚀性,为防止CO$_{2}$腐蚀, 延长设备使用寿命,整套压裂工具需选用防CO$_{2}$腐蚀的材料(杨涛等 2007, 李淑华等 2008); (2)超临界CO$_{2}$黏度远低于水的黏度, 因此压裂设备密封较难,工具连接需采用可靠的密封办法.

前人已对较低参数CO$_{2}$热物理性质开展了大量的实验研究,Dordain等(1995)报导了温度在323~423K范围,压强达25MPa时CO$_{2}$的定压比热(如图8.4所示),根据实验数据、经验公式和热力学理论建立了热物理性质计算软件,如REFPROP. 然而, 由于现有实验数据工况范围的限制(一般在30MPa以下,523K以下), REFPROP仅在30MPa以下, 523K (约250${^\circ}{\rm C})$以下保持较高的计算精度 (密度: 0.03%~0.05%;定压比热: 0.15% (气态)~1.5% (液态))(Lemmon et al.2010, Span & Wagner 1996). 若超出上述范围,虽然可以采用软件计算得到相应物性, 但由于实验数据匮乏,并不能判断其精度, 或者说不能得到足够精确的数据.

8.2.3.2 超临界$CO_2$在微细流道中的流动与换热

采用超临界CO$_{2}$进行页岩压裂和CH$_{4}$驱替时,CO$_{2}$在微细页岩裂缝中流动并与页岩进行了热量交换,影响着CO$_{2}$流动阻力和CO$_{2}$物性参数.流体在微细流道中的流动及换热特性显著区别于常规尺度流道,尤其是处于超临界状态的流体.

在CO$_{2}$微细流道对流流动及换热特性方面,已有的研究主要着眼于CO$_{2}$制冷循环,大多聚焦在亚临界CO$_{2}$的蒸发与冷凝,少数研究超临界CO$_{2}$的流动及对流换热特性. 淮秀兰等(2004)指出,当远离临界温度时, 超临界CO$_{2}$温度越高, 流动产生的压降越大,对流换热系数与所处压力成正相关关系, 与所处温度成负相关关系(如图8.5所示). 这些研究中, 考察压力范围均在12MPa以下,并且流道尺寸均在0.5mm以上(Yoon et al. 2003, Dang & Hihara 2004, Son & Park 2006, Pettersen et al. 2000, Kuang et al.2004, Huai et al. 2005, Huai et al. 2007, Liao & Zhao 2002)(如表8.2所示). 然而,压裂工艺一般要求超临界CO$_{2}$达到50MPa以上的压力,并且页岩裂缝宽度尺寸一般非常低 (陈叶等 2015) (如表8.3所示),因此需要开展高压超临界CO$_{2}$在微细流道中的流动及对流换热特性研究.

8.2.3.3 CO$_2$射流破岩研究

与水射流破岩相比,采用超临界CO$_{2}$射流对页岩、花岗岩及大理石进行破碎时,需要的门限压力更低, 但达到的钻井速度更高.这两个特点可以显著缩短钻井周期, 降低设备系统工作压力,降低钻井设备功率, 减少能源消耗, 最终降低钻井成本. 例如,对大理石样品进行射流破岩实验,采用超临界CO$_{2}$时的门限压力仅为水射流破岩门限压力的2/3,在页岩中为1/2或更小. 图8.6为超临界CO$_{2}$射流破岩钻井速度与水射流破岩钻井速度的对比,钻井设备功率为100kW, 直径为50mm, 岩石样品为曼柯斯页岩,可以看出超临界CO$_{2}$射流破岩速度优势非常明显,同时还可以看出超临界CO$_{2}$射流破岩的有效压力为55MPa,远低于水射流破岩的124MPa (Kolle 2000).

两种破岩后的岩石断面形式也存在差异, 如图8.7所示,采用花岗岩和曼柯斯页岩为岩石样品, 对比两种破岩方式造成的断面形式.采用水射流破岩形成的断面, 射流流经区域留下轮廓清晰的小沟槽,岩石破碎程度较小, 而采用超临界CO$_{2}$喷射破岩形成的断面,射流流经区域留下轮廓不明显的大面积崩裂坑道, 岩石破碎程度大(Kolle& Marvin 2000). 此外, 由于不含水,采用超临界CO$_{2}$射流破岩技术, 还具有降低缩径、卡钻等风险的优点.

由于目前CO$_{2}$压裂还主要处于研究的初级阶段, 为了早日实现应用,还需要进一步开展较大规模的压裂中试研究以及现场示范,解决CO$_{2}$压裂大型化的关键科学问题与共性技术.

8.2.3.4 CO$_2$压裂后的地下封存

采用超临界CO$_{2}$对页岩气进行强化开采,不仅可以达到很好的开采效果,而且还可以将大量CO$_{2}$永久封存在地质结构当中,实现大气中温室气体的减少, 并可获取碳收益.

CO$_{2}$在地下含盐蓄水层的封存主要受地质结构、毛细力作用、溶解度和矿物质等因素影响,但在页岩气田中的封存机理完全不同,有机物和黏土矿物质的吸附作用非常关键(Liu et al. 2013). Godec等(2013)采用理论方法分析了美国东部马塞卢斯页岩, 915m以下,每平方千米的页岩可封存112万吨CO$_{2}$, 其中被吸附了72万吨,处于岩石缝隙中的游离CO$_{2}$为40万吨.全球页岩气田封存CO$_{2}$潜力可达740Gt (Godec M L et al. 2013).图8.8给出了CO$_{2}$封存与CH$_{4}$开采效果随CO$_{2}$注入压力和时间的变化规律(Sun et al. 2013). 在页岩中封存CO$_{2}$的成本中,CO$_{2}$的运输与注入是主要因素, 而CO$_{2}$分离,孔隙的获得和后期监测则对总成本影响不大.运输并将CO$_{2}$封存在马塞卢斯页岩中的成本大概在40$\sim$80美元/吨(Tayari et al. 2015).

从发展与环保的双重观点看:如果将页岩气的压裂开采与CO$_{2}$的地下封存相结合,可能会获得更好的经济与环境效益,但是封存在地下的CO$_{2}$是否能够稳定存在,是否污染地下水以及地质特征, 都是需要开展研究的课题.

8.2.4 小结

国内外的成功应用表明, 二氧化碳干法压裂技术是可行的,二氧化碳压裂技术使用无水的液态二氧化碳作为压裂介质,相比水基压裂体系具有优势. 目前干法二氧化碳压力技术也存在一些问题,包括携砂及降滤失性能差, 需要研制高效增稠剂、减阻剂等;该技术对混砂设备要求较高, 是制约技术发展的问题之一.

二氧化碳泡沫压裂液由于具有滤失量低,返排能力强、与地层流体配伍性良好等优点, 减小了压裂液对地层的伤害,比普通压裂液更适合于低渗低压、水敏性地层的压裂改造.目前已经得到普遍应用.压裂工艺技术和选井选层技术是取得良好增产效果的保证,所以合适的选井选层和正确的压裂工艺十分重要.以后应该更进一步优化二氧化碳泡沫压裂设计,提高压裂液体系和压裂对不同储层特征的针对性和适应性,进一步提高单井产量, 改善压裂增产效果.

超临界CO$_{2}$黏度低, 扩散系数高, 流动性能强,用其作为压裂液进行压裂改造具有对储层伤害小, 返排快等特点;超临界CO$_{2}$在储层中不仅能大幅度降低原油黏度,而且能置换出被吸附的CH$_{4}$分子, 有利于提高产量.但由于携砂能力差, 对压裂设备要求高, 在应用上受到了一定限制.

超临界CO$_{2}$压裂开采页岩气的研究现状表明,超高压状态下超临界CO$_{2}$的热物理性质研究、微细流道中的流动及换热特性研究非常匮乏.并且由于压裂过程中系统会混入空气、水等成分,实际工作介质将是一种成分复杂的混合工质,其性质与纯质CO$_{2}$有较大差别, 需要进一步开展研究.从应用角度出发,还需开展较大规模的压裂中试以及CH$_{4}$开采与CO$_{2}$地下封存结合的相关研究.

8.3 氮气压裂技术

8.3.1 氮气干压裂技术

氮气干压裂技术是指将氮气作为主要的压裂液体, 携带支撑剂注入井下,形成裂缝, 开发油气资源的技术. 氮气压裂技术的发展分为3个阶段:第1阶段是在1960年, 氮气作为辅助流体注入; 第2阶段是20世纪70年代末,将氮气和CO$_{2}$加入水力压裂中, 形成泡沫压裂;第3个阶段是90年代以后,采用高浓度氮气(体积浓度可达60%)携带支撑剂作为压裂液用于石油天然气增采.第3个阶段才真正属于无水压裂的范畴.

氮气干压裂技术具有经济和环保的优点(Tanmay 2014):(1)氮气作为可广泛获取的气体, 价格相对较低, 能减少地层开发的成本;(2)氮气是惰性气体, 不会对岩层造成伤害; (3)整个系统不使用水,排除了岩石膨胀的可能性; (4)不使用水还可以消除地层油水(w/o)乳状液,否则需要使用额外的化学剂; (5)清除气体过程简单, 气体能轻易移除,清理过程快速.

氮气压裂技术也存在一些问题,如高速率气流中如何置放支撑剂、如何避免侵蚀、如何避免首次压裂产生的裂隙的大小和几何形状会导致支撑剂沉淀问题、氮气运输费用高昂.

氮气压裂施工流程图见图8.9.

8.3.2 氮气泡沫压裂技术

氮气泡沫压裂技术是采用氮气为内相, 压裂基液(水)为外相,加入增稠剂及多种化学添加剂形成泡沫液体, 结合压裂工艺,达到改造油气层的目的.页岩储层使用泡沫(foams)压裂已超过30年的时间(Harris et al. 1983).该方法是水力压裂的修正, 是通过氮气分散以制造不同速率的泡沫.

氮气泡沫压裂施工一般由两组设备进行, 一组负责泵注压裂液和支撑剂,另一组泵注氮气, 在井口前端的高压管线汇合, 通过压裂井口进入井筒.地面氮气以液态存储在罐内,压裂施工时通过液氮泵车将氮气打入高压管汇与压裂液混合进入井内.这时氮气通过了泵车的高压泵和蒸发器,变成了温度为15$^\circ$C以上的氮气气体, 即在地面就已形成了泡沫.因为液柱压力低, 造成对井底的回压低, 导致地面施工压力相对较高,为有效地降低管柱摩阻, 通常采用光套管注入方式.

泡沫压裂施工有三种施工控制技术:恒定内相、恒定泡沫质量和恒定井底总排量. 泡沫液加入支撑剂后,泡沫压裂液的外相仍为液相, 内相变为支撑剂和气相.采用恒定内相和恒定泡沫质量的控制方式, 在操作上较为困难,氮气泵车挡位的排量变化难以达到设计要求的变化值,因此常采用恒定井底总排量方式进行施工.

与水力压裂相比, 泡沫压裂技术的优点是(Wamock et al. 1985):(1)降低蒙脱石扩大和伊利石膨胀的程度, 但不能完全消除黏土胀大现象;(2)黏度较高; (3)返排效果好; (4)使用较少的水,对岩石伤害较低; (5)泡沫压裂液可在裂缝壁面形成阻挡层,极大降低了压裂液向地层内的滤失速度和滤失量.

泡沫压裂技术的缺点主要有: (1)流体中支撑剂浓度低;(2)泡沫系统成本较高, 与水基和油基压裂液相比, 经济性较低;(3)泡沫流变性较难; (4)需要在地表提供较高的泵注压力.

8.3.3 小结

氮气压裂使用液体氮气作为携砂载体, 最大限度地降低了储层伤害.氮气泡沫压裂液携砂能力强, 实现了支撑剂远端有效铺置,提高了裂缝导流能力, 解决了高排量带来的控缝高难以及近井脱砂的问题.总之, 我国氮气泡沫压裂方面的研究和应用还在起步阶段,从压裂液体系到工艺技术目前还存在不足.但对于我国煤层气储层低压、易伤害、应力敏感强等特征,泡沫压裂具有广阔的应用前景.

8.4 液化石油气(LPG)无水压裂技术

液化石油气压裂技术也称丙烷/丁烷压裂, 由加拿大Gasfrac EnergyService研发, 荣获第一、二届世界页岩气技术创新奖.该技术采用液化丙烷、丁烷二者混合液进行储层压裂.液化石油气压裂相对清水压裂的突破在于使用液态烃类(丙烷和丁烷等)作为压裂介质而非清水基液,液态烃纯度常高于90%,若压裂成功液态烃低密、低黏和可溶的优势将非常突出,洗井迅速且100%返排, 可消除多相流问题, 压后获得更长的裂缝,从而大幅提高产量.

LPG原料气体积组成如 表8.4所示, 其混合物成分是可控的. 目前,HD-5丙烷是最常用的LPG原材料,100%HD-5丙烷制备的LPG压裂液可应用到96$^\circ$C的储层;当储层温度超过96$^\circ$C后, 需要与商业丁烷混合使用;100%商业丁烷制备的LPG压裂液可应用到150$^\circ$C的储层 (见图8.10) (刘鹏 2015)).

度超过96$^\circ$C后, 需要与商业丁烷混合使用;100%商业丁烷制备的LPG压裂液可应用到150$^\circ$C的储层 (见图8.10) (刘鹏 2015)).

液化石油气压裂系统由气体凝胶系统、氮气密闭系统、混配系统(凝胶与支撑剂)、压裂注入系统、远程监控系统(风险控制)、气体回收系统组成.施工时全程封闭, 先将气体液化,加入支撑剂完成混配后以远程红外监控压裂(图8.11).

低碳烃压裂液的优点是: (1)表面张力低、低黏度和密度,与储层流体的配伍性好, 不会造成水相圈闭伤害和黏土膨胀效应,对储层几乎无伤害等多项优良属性,从而获得更多的有效裂缝、更大的初始产量、更优的环保效果和更长的油气生产寿命(表8.5); (2)压裂液在压裂施工后由于高温、高压而汽化,在形成的缝隙中只留下支撑剂, 无压裂液残留,使裂缝长期具有良好的导流能力, 而且压裂后的有效裂缝面积更大(Freeman 1983); (3)压裂后可与天然气一同被抽回地面,其返排率、回收率可达100%, 且经过简单的分离处理后即可循环再利用;(4)低碳烃压裂液几乎不需要用水,能尽可能地缓解对环境和水资源造成的压力,同时也省去了压裂液废液处理的成本. 其缺点包括:(1)其短期成本比水基压裂液高; (2)目前低碳烃压裂技术还不够成熟,存在一定的安全隐患; (3)LPG压裂过程中的物理特性决定它与水的破岩机理存在着明显差异, 因而,需开展高温高压条件下LPG相态变化的研究工作;(4)对压裂设备的要求较高.

作为一项发展中的新技术,LPG无水压裂技术的推广应用正在逐渐由部分单井向大盆地或区块发展,并有可能成为众多石油公司的优选方案. 即便不能完全主导压裂开发市场,它也将在有特定需求的油气区块发挥重要作用.虽然油基压裂液成本高出水基压裂液20倍, 但一直持续应用至今,该技术对特殊地层的应用效果是不可替代的.两种压裂方式的有效裂缝长度对比图见图8.12.

8.5 爆炸压裂技术

爆炸压裂包括井内爆炸法、核爆炸法、层内爆炸法. 该类技术施工简单,不受水敏和酸敏地层的限制. 此外, 即使在压裂过程中不加入支撑剂,压裂裂缝在高闭合应力下仍保持张开.这主要是爆炸的压力在微秒级迅速上升,上升速度要比水力压裂的压力上升速度快得多,致使所产生的多条径向裂缝的方位偏离最小主应力方向, 产生偏轴效应,使剪切应力作用于偏轴裂缝, 发生剪切错动, 形成不闭合的裂缝.爆炸动载压裂试验系统见图8.13.

8.5.1 井内爆炸

井内爆炸包括固态、液态和气态炸药在井筒内的爆轰和爆燃,目的是使井筒周围地层产生多条裂缝,既消除在钻井过程中造成的表皮损害, 又使天然裂缝体系与井筒连通.美国Dennis(1860)首先在油井中使用黑火药爆炸方法激励了油井;美国Robert(1864)申请了以枪用火药使油井增产的专利,1867年用效果更好的液态硝化甘油取代了黑火药; 后来,杜邦公司研制了低感度的硝化甘油炸药、固态硝化甘油炸药、凝胶炸药和油井特种炸药等(朱华良 1997). 在19世纪60年代到20世纪50年代, 井内爆炸法被广泛应用.爆炸压裂物理模型示意图见图8.14.

20世纪40—50年代, 水力压裂兴起, 逐渐取代了古老的爆炸法.其主要原因是井内爆炸造成的压缩应力波使井周岩石发生不可恢复的塑性变形,爆炸初期形成的大量裂缝或因残余应力场(称为应力笼)的作用而重新闭合,或被爆炸残余物堵塞, 有时反而使岩层渗透率下降,只有在某些情况下才可能提高产量. 另外, 井内爆炸易损毁井筒,硝化甘油类药剂过于敏感, 这也是古老的爆炸法压裂失败的原因.我国在20世纪50—70年代多次试验井内爆炸法, 未获成功,由于人身及井身安全等原因停止试验.要将井内爆炸法再应用于油气田开采,就必须解决爆炸增产效果不稳定和井筒损害. 该方法存在的问题是裂缝区域半径小, 一般只有井筒半径的10倍左右;另外, 压力过高, 会造成永久性压实. 该法在前苏联应用较多,我国长庆油田也曾采用.

8.5.2 核爆法

美国和前苏联在20世纪60—70年代进行过用核装置激励油气层的地下试验,未获商业化应用;我国在20世纪80—90年代也曾进行核爆炸采油的规划和现场试验设计,由于多方面原因未付诸实施.

井筒核爆炸会造成并沟通各种空洞, 从而增加井筒周围岩石渗透率.美国和前苏联的试验结果显示, 用核爆炸来提高采收率是可行的.美国在1967年12月施爆的Gasbuggy项目的核装置TNT当量为3$\times$10$^{4}$t, 产生的爆穴半径约27m,由岩石崩落而形成的筒状囱道(本身就是导流能力极好的区域)高约100m,极高温和极高压以及极强大的压缩激波,使囱道周围大范围岩石产生复杂的裂缝网络.一般认为油层渗透率低于0.1$\times $10$^{ - 3}\mu$m$^{2}$的超低渗透油田不再有商业价值,但Gasbgugy项目储集层地下渗透率小于0.01$\times $10$^{ -3}\mu $m$^{2}$, 仍获得一定天然气流. 所以,用核爆促产的优势使可开发油气田的范围大大加宽.

核爆能量巨大,储集层要有一定厚度才能实施核爆而形成一定格局和规模的裂缝, 同时,核装置既要有足够的埋深以防止发生放射性泄漏, 又不能太深,以防岩石静压使产生的裂缝重新闭合. Atkinson和Jhoansen建议,产层净厚度至少要60m, 安全的最小深度为300m,最大深度约为2500m, 他们还指出, 从较长时间尺度来看,在破裂半径内平均升温不到1$^\circ $C, 破碎带升温仅5$^\circ$C,温度对提高采收率的作用不大.

核爆法产生的地震危害和核污染可以控制在可接受的程度. Rdoaen认为,地下核爆炸释放的巨大能量中一般只有0.01\%到1\%转化为地震能.如果3$\times $10$^{4}$TNT当量的核爆炸有0.1%的能量转化为地震能, 只相当于大约3.7级地震.放射性是人们十分关注的问题. 据有关资料显示, 在一次封闭的核爆之后,所有的在熔岩温度(1500$^\circ$C~2000${^\circ}{\rm C})$下不是气体的放射性元素都会被封存在空穴"锅底"熔体中,几乎完全不会泄漏. Rulison项目中所用的弹体,在裂变装置周围用碳化硼屏蔽, 可使氖减少为原来的1/3~1/4.如果把实施核爆井产出气和普通气井产出气均匀混合构成可控的稀释系统,人们遭受辐射的增量只不过是天然背景下放射性的1%. 从经济方面考虑,可以通过稀释或送往远处的发电站将其转化为另一种形式的能源.

丁雁生等(2001)利用Gasbuggy项目的数据,取6倍囱道半径为核爆沿横向的影响范围,估算核爆破碎每立方米岩石消耗约4kg的TNT (当量).这比一般岩土爆破单位体积岩石所需药量大得多, 因此核爆效率较低.

核爆法是否经济还在争论. 也许有一天,技术进步和大量作业能使其成本下降到商业化应用的水平.

8.5.3 层内爆炸

层内爆炸压裂是在水力压裂在油气层中形成一定长度的人工裂缝的基础上,通过压裂车把液体炸药泵送到人工裂缝中的预定位置,随后引爆人工裂缝内的液体炸药,利用爆炸破碎裂缝壁面岩石产生的岩石碎屑支撑水力裂缝,产生的爆生气体在水力裂缝附近产生多条微裂缝,在油气层内形成一个高渗透带,从而改进储层渗流条件的一种新型油气藏改造技术.

丁雁生等(2001)研究了层内爆炸压裂的可行性, 林英松等(2006)研究了爆炸载荷对水泥式样的损伤破坏规律,通过实验分析了爆炸对岩石的破坏作用.20世纪40—70年代进行的类似爆炸压裂现场应用,取得了一定的增产效果(李传乐等 2001).潘兆科等(2004)对地面爆破形成的岩石破碎块度分布预测进行了大量的研究.为了加深对层内爆炸压裂改造储层效果的认识, 赵志红等(2011)深入研究爆炸对地层岩石的破坏作用和对储层改造的影响,建立爆炸后岩石颗粒粒径的预测模型.

层内爆炸增产技术是一项具有战略性、前瞻性的创新技术,要将该技术实际应用于低渗透油气田,今后主要有以下四方面的工作需要开展:(1)实验室放大试验与相关理论研究; (2)安全技术研究;(3)现场试验用工艺设备研制; (4)现场井下试验.

8.5.3 小结

爆炸压裂技术作为一种潜在的开发低渗低丰度油气田的新方法,是一项具有巨大增产潜力的油藏改造技术.对该技术的研究涉及到岩石爆破、现代石油钻采技术、岩石力学等多门学科,必须将这些学科紧密结合起来, 才有可能获得具有突破性的研究成果.鉴于目前低渗透油田在石油工业发展中的重要地位,建议对该技术展开更为全面、深入的研究.

8.6 高能气体压裂(HEGF)

高能气体压裂又称可控脉冲压裂是20世纪70年代兴起、80年代迅速发展的一种增产、增注技术.它利用火药或火箭推进剂快速燃烧, 产生的大量高温、高压气体,在机械、热化学和振动脉冲等综合作用下,在井壁附近产生不受地应力约束的多条径向垂直裂缝,改善导流能力、增加沟通天然裂缝的机会, 从而达到增产、增注的目的.它具有工艺简单、不依赖水源、成本低廉、增产效果显著等特点.

目前高能气体压裂在长庆油田应用较多, 效果也比较明显,但是由于该技术所产生的裂缝较短、对油井状况的要求较高,应用不是很好. 最近,西安石油大学实现了使用液体炸药对低渗油藏进行压裂改造,该技术具有成本低、原料广、药量大和燃时长等优点,且该炸药在冲击摩擦感度、静电和压力感度等方面均比固体炸药安全.缝长可达到25~30m, 增产比为2.55,该技术是唯一可以和水力压裂相媲美的高能压裂增产技术. 2000年以来,研究人员又对高能气体压裂进行了全面的改进,开发了双级高能气体压裂技术,该技术使得高能气体压裂既可以在浅井中应用也可以在深井中应用,既可以用油管方式作业也可以用电缆作业,对于重堵塞井的解堵也具有较好的效果.3种压裂技术$P$-$t$曲线和主要参数分别见图8.15和表8.6.

目前国内外基本认为, 高能气体压裂过程中包括以下几个方面的作用: (1)机械作用(生成裂缝): 高能气体压裂一般能形成3~5条裂缝.据报道, 加载速率为10$^{2}\sim 10^{4}$MPa/s时, 可形成3$\sim$8条径向裂缝(王安仕等 1998)、径向长3$\sim$5m、高度为装药段长的1.2$\sim$1.4倍、不受地应力控制的多裂缝体系, 裂缝可自行支撑.由于裂缝的随机性, 一方面增大了与天然裂缝连通的可能性;另一方面能有效地穿透污染带,提高近井地带油层导流能力,可解除钻井、完井、作业及正常生产过程中造成的近井地带的污染和堵塞,对中低渗透油层亦能起到一定的改造作用.

(2)脉冲冲击波作用: 在高能气体压裂的动态过程中,压力的变化是脉冲式的逐渐衰减过程,形成的高压把井筒内液柱举升10~25m;压力降低后回落,在井筒附近形成较强的水力冲击波,对油层的机械杂质堵塞起到一定的解堵作用.

(3)热效应: 爆压时火药燃烧时释放出大量热量,一般能达到600$^\circ$C~800$^\circ$C,在绝热条件下使气体温度达千摄氏度以上, 而且相对集中,这些热量可溶解近井地带的蜡质和沥青质, 解除油层孔道的堵塞,改善地层流体的物性和流态, 加快原油向井底的流动速度,提高储层的驱油效率.

(4)化学作用: 火药燃烧后产生一定量的CO$_{2}$, CO, N$_{2}$,NO及HCl气体. NO及HCl溶于水生成腐蚀性较强的酸液,对油层能起到一定程度的酸化解堵作用.

高能气体压裂工艺优点(薄其众等 2003):

(1)地面无承受高压部分, 设备投入少, 施工简单, 不必加砂支撑,不受场地限制, 作业时间短、费用低, 经济效益高.

(2)增产机理独特, 可形成3$\sim$5条不受地应力限制、以井筒为中心的径向裂缝, 纵向上延伸小.

(3)适用范围广, 既可用来解除油层近井带的污染,又可在一定程度上改造中低渗透层,而且能适应层多且较分散井的多层压裂.

(4)生成物对油层无污染, 且有助于解除油层污染.

以上优点, 还使得高能气体压裂在胜利油田滚动勘探开发中,在交通运输条件不方便地区, 以及环境保护敏感地区的油田开发中,具有极大的吸引力.高能气体压裂对于那些使用昂贵的水力压裂没有多大意义的接近枯竭的油、气井也更为适宜.

高能气体压裂工艺缺点(薄其众等 2003):

(1)固井质量差, 尤其是射孔井段的固井质量差的下套管井不能采用.

(2)裂缝延伸长度比水力压裂裂缝短得多, 一般只有3~8m.

(3)不能加支撑剂, 因此压裂形成的裂缝有效作用期较短.

(4)试验井深虽曾达到4000m, 但一般仅适用于2000m以内的储层.

(5)井斜角度不能太大, 一般井斜角度控制在40$^\circ$以内.

高能气体压裂的发展方向:

HEGF作为油气井增产改造的一项有效措施, 为了收到更大的经济效益,今后必将沿着与其他技术相结合的方向发展.高能气体压裂技术与其他油气井增产技术结合, 可以实现优势互补,进而达到更好的增产效果.

(1)与射孔技术相结合

HEGF与射孔技术相结合称为复合射孔或增效射孔, 有时也叫延时射孔.与HEGF相比, 复合射孔可大大提高火药燃气能量的利用率,并减少了射孔后可能造成的对射孔孔眼及近井带的污染. 两项技术结合,综合效果明显高于单纯射孔或单纯的高能气体压裂,已在国内许多油田广泛应用.

(2)与水力压裂相结合

水力压裂前, 先用HEGF进行处理, 形成多条不受地应力控制的径向裂缝.一方面, 降低了水力压裂的破裂压力, 提高了成功率; 另一方面,可形成多条较长的裂缝, 提高了水力压裂的效果.

(3)与酸化相结合

HEGF造缝后, 再向油层挤入酸液, 酸液与裂缝壁发生化学反应,腐蚀并加宽裂缝表面, 从而提高裂缝的导流能力, 提高压裂效果.

(4)与化学解堵剂相结合

HEGF后, 向地层挤入化学解堵剂, 比如, ClO$_{2}$含水剂和酸液的混合液.目前, ClO$_{2}$解堵液与酸液相结合的新型化学解堵工艺逐渐成熟.早在20世纪90年代初期, 美国已使用该技术成功的处理了300多口井.

高能气体压裂技术虽有其显著的优越性, 但就目前国内外的研究水平来看,高能气体压裂的燃气能量及所形成的裂缝规模还远不及水力压裂,加之该技术在应用中的许多方面还处在工业性试验研究阶段,为了提高其成功率和压裂效果,因此必须根据本地区的实际情况对选井选层提出要求.高能气体压裂技术适用于以下情况的油水井的增产增注:(1)钻井过程中受到钻井液伤害的井; (2)水敏酸敏地层;(3)天然裂缝较发育,担心水力压裂压窜的井.

8.7 本节小结

(1)无水压裂技术能够解决中国水资源匮乏、大型压裂设备运输困难、压裂液处理技术繁琐等问题,施工时能减少清水压裂铺砂不到位、强滤失、易脱砂等技术问题,并能显著提高产量.

(2)每一类无水压裂技术要考虑多个学科的系统性技术, 需要系统性研究,才能较为全面地认识各类无水压裂技术带来的工程效果、环境影响和社会风险.

(3)需要针对我国地貌地层特点,遴选兼具工业化潜力、规模化潜力、经济性的无水压裂技术,在重视应用研究的同时, 有效地评价技术的实用性和可行性,为培养新的增长点提供技术储备.

(4)无水压裂技术在作用时基本不需用水, 对地层伤害小,有望成为非常规油气资源开发的先进技术.为了其能更好地在现场得到使用该技术还应向以下几个方面进行发展:

① 由于LPG是利用液化石油气和易挥发的烃类液体混合而成的压裂液体,如果发生泄露, 易发生火灾等事故, 因此有必要研究比较配套的压裂设备; ② 目前仍然对无水形成的裂缝机理没有成熟的认识,因此应从数值模拟及物理实验来认识无水压裂的工作机理;

③ 由于CO$_{2}$的摩阻较大而且黏度较低, 从而限制了其应用,因此应该从减阻和增稠两个方面来提高CO$_{2}$压裂液的性能.

(5) 利用超临界CO$_{2}$工艺开发非常规及低渗透油气资源,可能是一种符合我国地质条件的具有潜力的技术路径.但该技术目前尚处于室内实验阶段, 还需加强相关配套设备的研发,加快实施现场试验的步伐.要积极开展超临界CO$_{2}$钻井、压裂理论研究,并加快研制与其相配套的工具,对CO$_{2}$与页岩的吸附能力进行室内试验研究,深入了解影响其吸附能力的各种因素及吸附规律.

9 结束语^*(*本节撰稿人: 魏宇杰¹(1 E-mail: yujie_wei@lnm.imech.ac.cn), 郑哲敏²(2 E-mail:zhengzm@lnm.imech.ac.cn)

根据《页岩气发展规划(2011—2015年)》,我国陆域页岩气地质资源潜力预估在100万亿立方米量级,页岩气可采资源量为25万亿立方米, 与常规天然气资源相当.通过发展新型节能环保开采技术,页岩气将成为中国未来能源结构中的重要组成部分.随着水平钻和水力压裂技术的发展,我国的油气开采行业也一定程度上借鉴了国外的先进技术和经验,并在国内的页岩气开采中获得了一定范围的成功实践.考虑到中国的特殊环境和条件, 需要新的技术,而新技术的发展则需要基础理论的支撑. 具体表现在:

(1) 页岩气开采属于非常规资源开发,其经济可行性完全依赖于页岩层所在环境, 以及开采技术发展的成熟度.我国地质构造复杂, 如何确定优质页岩区将是关键点之一;致密岩体高地应力下的破裂及微观尺度的渗流规律是基础研究的重点内容的组成部分.

(2) 由于地质成因及构造特征的差异,我国的地应力状态与美国有很多差异, 钻井的成本高, 压裂的效果差,适合中国地质环境的、可大批量采用的压裂、钻井技术的发展;

(3) 水资源是国家持续发展的命脉所在, 水力压裂需要使用大量水资源,如何发展用水少甚至是无水的压裂技术是迫在眉睫的技术需求.形成高效且环保的初始致裂技术是页岩气作为清洁过渡能源的关键组成部分,如探索采用爆炸及高能气体压裂等方式.

从工程实现的角度而言,有效实现2000m以下的页岩层大面积形成网状裂纹,从而对孔、洞、缝中的游离气和吸附进行高效开采涉及到诸多核心力学问题:要研究地质体的渐进破坏必须考虑断裂力学、地质体力学、计算力学、波在地层的传播以及爆炸力学等多学科的交叉;压裂过程中, 需要对监测信息发展内部破坏状态的反演.这些过程都涉及到关键力学问题, 同时由于边界条件的不确定性,也是工程力学研究的难点. 为促进我国能源开采的可持续发展,需要相关的科研人员和工程实践结合,集中优势力量开展基础理论和工程规律研究:(1)掌握水力压裂、水平钻井基本规律和原理;(2)探索用水少甚至是无水的压裂技术, 如爆炸及气体压裂等方式;(3)将基本理论应用于工程实践, 获得工程规律.

魏宇杰, 研究员, 1997年从北京大学力学系获学士学位, 2000从中国科学院获硕士, 2006年获麻省理工学院博士; 之后在布朗大学开展博士后研究, 2008年加入阿拉巴马大学担任助理教授, 2010年加入中国科学院力学研究所. 主要从事固体力学中材料强度与塑性变形机理的研究,重点在于理解材料中典型微结构与宏观力 学性能这两个跨越多个空间与时间尺度的物理对象之间的关联; 同时关注力学在国家重大工程中的应用. 曾获2013年中国力学学会"青年科技奖", 2013年中国科学院"优秀导师奖", 获自然科学基金委杰出青年基金资助(2015--2020).
刘曰武, 博士, 中国科学院力学研究所研究员, 博士生导师.1997年中科院渗流所获流体力学博士学位. 1997年~1999年,在中国科学院力学研究所做一般力学博士后研究工作.主要研究方向是渗流力学基础理论研究及相关的地面渗流、工程渗流以及地下油气水渗流应用技术开发工作.目前主要从事非常规天然气渗流理论研究及工程技术开发工作.担任中国力学学会流体力学专业委员会渗流力学专业组副组长、科普工作委员会委员、《力学与实践》《油气油测试》编委.曾负责国家重大专项课题2项,参加国家973项目2项、中国科学院创新项目1项, 承担矿场项目20余项,发表论文40余篇, 授权发明专利7项, 软件著作权5项.获省部级科技进步1等奖2项.
高大鹏, 1989年出生, 山东东营人, 高级工程师,主要从事油气田开发工程方面的研究工作.2016年在北京大学获得地质学博士学位,2016年进入中国科学院力学研究所工作, 先后参与国家重大专项课题2项,承担国家自然科学基金1项、中国科技创新基金1项,发表论文30余篇（SCI/EI检索20余篇）, 授权发明专利7项.
曾霞光, 博士, 硕士生导师.2014年毕业于中国石油大学(北京), 获博士学位,2014年—2017年在中科院力学所从事博士后研究工作,现在佛山科技学院工作.主要从事海洋石油管道、页岩气开发等领域断裂力学问题的研究.在国内外学术期刊上发表论文10余篇, 获专利2项.
李晓雁, 清华大学工程力学系长聘副教授博导.2012年9月—2017年11月任副教授, 2017年12月至今任长聘副教授. 目前,应邀担任《中国科学: 技术科学》中英文版青年编委、iMechanica(全球最大的力学专业网站)的Journal ClubEditor、第14届纳米材料国际大会的国内和国际委员会委员 (National andInternational Committee Members).主要从事新型微纳米结构材料的力学性能和力学行为研究,主要采用宏微观力学理论、多尺度模拟和原位电镜实验相结合的方法探索多种新型微纳米结构材料的变形和断裂行为,同时从事力学超材料和高熵合金的制备、微结构表征以及力学性能测试.在Nature, Nature Nanotechnology, NatureMaterials, Nature Communications, Science Advances,PNAS, PRL, Nano Letters, AdvancedMaterials, JMPS等国际期刊上发表SCI论文48篇,撰写3篇英文书章. 这些成果先后被Nature子刊、ScienceDaily, PhysOrg,R&D Mag, Nanotimes, Nanowerk、中国科学网等国内外媒体所报道.目前主持和参与多项国家自然科学基金和国家重点研发计划.
胡志明, 高级工程师. 2006年毕业于中国科学院研究生院,流体力学硕士.在中石油勘探开发研究院渗流流体力学研究所从事低渗透油气藏及非常规气藏渗流机理研究工作, 主持科研项目30余项, 参与项目60余项, 目前主要负责"十三五"国家重大专项"页岩气渗流规律与气藏工程方法"(2017ZX05037-001), 任课题长. 发表文章60余篇, 获得发明专利3项.
鲁晓兵, 研究员. 1999于中国科学院力学研究所获博士学位.1999年以来一直在力学研究所从事岩土力学和油气开发领域的研究工作.在低渗油藏物理、水合物开采、页岩气支撑剂输运和力学性质方面开展了系列的工作.作为负责人和主要参与人承担了国家重大专项子课题:"致密油流体赋存状态及开采过程中应力效应分析";中石油重大科技攻关计划课题: "孔隙--裂隙网络模型与微观渗流研究",国家重大科技专项子课题"水合物沉积物渗流力学及离心机模拟研究";国家127专项子课题: "水合物分解的土力学响应及土层稳定性评价"等.相关研究成果在国内外重要期刊发表论文60余篇, 授权发明专利10余项.
李世海, 中国科学院力学研究所研究员, 博士生导师,非连续介质力学与工程灾害中英联合实验室主任, 973项目首席科学家,中国岩石力学与工程学会理事, 中国爆破工程协会理事,中国力学学会爆破专业委员会委员.主要从事非连续介质力学及工程地质体渐进破坏过程的理论与数值分析方法研究.发展了基于广义拉格朗日方程的连续非连续单元法,实现连续和非连续问题在同一框架下表述;提出了考虑泊松和纯剪效应的弹簧元模型,实现在局部坐标系下利用2到3组正交的基本弹簧直接描述连续介质力学行为;建立了基于应变强度分布准则的统计损伤本构模型,利用弹性微元和破裂微元的渐进演化刻画代表体积元的复杂力学行为.曾主持参与完成多项与滑坡灾害相关的国家重大基础研究项目、院西部计划项目、院方向性项目、国家自然科学基金项目、横向协作项目等,发表学术论文200余篇, 其中SCI/EI收录60余篇,授权发明专利及软件著作权30余项.
陈伟民, 中国科学院力学研究所研究员.2000年北京航空航天大学获工学博士学位,2002年北京大学力学系博士后出站进入中科院力学所,2012年曾于美国德州大学奥斯汀分校做高级访问学者.主要从事海洋/航空/土木工程中的流固耦合和结构动力学研究,涉及弹性波传播和缺陷/震源反演、复杂波信号时频谱全波形分析、水弹性/气动弹性动力学和主动反馈控制等.先后在Ocean Engineering 和Materials Science andEngineering A等海洋工程和结构材料期刊上发表论文50余篇.
侯绍继, 中国科学院工程力学硕士,现在苏州工业园区规划建设委员会工作, 曾经发表4篇论文,参与国家科技重大专项(2011ZX05004-004)中石油塔里木油田配套项目"哈拉哈塘碳酸盐岩典型缝洞系统数值试井与储层动态研究"和国家科技重大专项(2011ZX05038003)子课题 "煤层气生产测试技术".
潘利生, 中国科学院力学研究所,高温气体动力学国家重点实验室, 工学博士, 副研究员, 硕士研究生导师.长期从事热能的高效转化利用研究,主要包括非常规工质循环研究和高效强化传热技术研究.
郑哲敏, 著名力学家、爆炸力学专家.早期在水弹性力学研究中取得成就. 长期从事固体力学研究,开拓和发展了我国的爆炸力学事业. 擅长运用力学理论解决工程实际问题,提出了流体弹塑性体模型和理论,并在爆炸加工、岩土爆破、核爆炸效应、穿甲破甲、材料动态破坏、瓦斯突出等方面取得重要成果.倡导海洋工程力学、材料力学性能、环境灾害力学的研究,创建了中国科学院力学研究所非线性 连续介质力学实验室,为推动我国力学事业的发展作出了贡献. 1980年当选为中科院院士,1993年被选为美国国家工程科学院外籍院士. 2013年获2012年度国家最高科学技术奖.

The authors have declared that no competing interests exist.

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[1]	彪仿俊, 刘合, 张劲, 张士诚, 王秀喜. 2011. 螺旋射孔条件下地层破裂压力的数值模拟研究 . 中国科学技术大学学报, 41: 219-226 DOI      URL      [本文引用: 2]      摘要 水力压裂技术已经在低渗地层的 石油天然气开采中得到广泛的应用,螺旋射孔是该技术中的常用措施,在此条件下地层的破裂压力是影响施工成功率和效果的重要因素之一.采用三维有限元方法对 螺旋射孔条件下地层的破裂压力进行了研究,建立了套管完井(考虑水泥环及套管的存在)情况下井筒及地层的三维计算模型,首先计算和分析了定向射孔时不同的 射孔密度和射孔方向角对地层的破裂压力的影响,与前人的实验结论进行了比较,在此基础上,进行了螺旋射孔条件下不同射孔方位角、相位角以及射孔密度对地层 破裂压力的影响的研究,通过数值模拟的结果,给出了螺旋射孔对地层破裂压力的影响规律,可作为进一步研究螺旋射孔条件下的裂缝扩展规律的基础,同时对压裂 设计和实际压裂施工中螺旋射孔参数的选取给出了具体的建议. (Biao F J, Liu H, Zhang J, Zhang S C, Wang X X.2011. Numerical simulation of fracture pressure of formation under helix perforation conditions . Journal of University of Science and Technology of China, 41: 219-226). DOI      URL      [本文引用: 2]      摘要 水力压裂技术已经在低渗地层的 石油天然气开采中得到广泛的应用,螺旋射孔是该技术中的常用措施,在此条件下地层的破裂压力是影响施工成功率和效果的重要因素之一.采用三维有限元方法对 螺旋射孔条件下地层的破裂压力进行了研究,建立了套管完井(考虑水泥环及套管的存在)情况下井筒及地层的三维计算模型,首先计算和分析了定向射孔时不同的 射孔密度和射孔方向角对地层的破裂压力的影响,与前人的实验结论进行了比较,在此基础上,进行了螺旋射孔条件下不同射孔方位角、相位角以及射孔密度对地层 破裂压力的影响的研究,通过数值模拟的结果,给出了螺旋射孔对地层破裂压力的影响规律,可作为进一步研究螺旋射孔条件下的裂缝扩展规律的基础,同时对压裂 设计和实际压裂施工中螺旋射孔参数的选取给出了具体的建议.
[2]	彪仿俊, 刘合, 张士诚, 张劲, 王秀喜. 2011. 水力压裂水平裂缝影响参数的数值模拟研究 . 工程力学, 28: 228-235 URL      摘要 Horizontal fracture is the most common fracture configuration during hydraulic fracturing treatments in reservoirs at shallow depth. The practical exploitations in a main producing area of Daqing oilfield demonstrate that the majority of the hydraulic fractures is horizontal. The reservoir around a well in the area is simplified as a layered porous medium. The corresponding 3D finite element model is set up with the ABAQUS software and related user subroutines. The tube, cement sheath, perforation, pay zone and barrier layer are included in the model. Fluid-solid coupling solid elements are used to describe the mechanical behavior of rock and cohesive elements are employed to simulate the process of fracture initiation and propagation. The fracturing treatment of the well is simulated with the model. The formation parameters and physical property parameters in simulation are adopted from Daqing oilfield. The time history curves of the pressure at the fracture mouth from numerical simulation are in good coincidence with those obtained from the field measurements. The correctness of the proposed model is validated. The influences of major geological parameters and treatment parameters on horizontal fracturing are studied. The concerned parameters include in-situ horizontal stress contrast, permeability, elastic modulus, injection rate and viscosity. (Biao F J, Liu H, Zhang S C, Zhang J, Wang X X.2011. Numerical simulation study on influence parameters of hydraulic fracturing horizontal crack . Engineering Mechanics, 28: 228-235). URL      摘要 Horizontal fracture is the most common fracture configuration during hydraulic fracturing treatments in reservoirs at shallow depth. The practical exploitations in a main producing area of Daqing oilfield demonstrate that the majority of the hydraulic fractures is horizontal. The reservoir around a well in the area is simplified as a layered porous medium. The corresponding 3D finite element model is set up with the ABAQUS software and related user subroutines. The tube, cement sheath, perforation, pay zone and barrier layer are included in the model. Fluid-solid coupling solid elements are used to describe the mechanical behavior of rock and cohesive elements are employed to simulate the process of fracture initiation and propagation. The fracturing treatment of the well is simulated with the model. The formation parameters and physical property parameters in simulation are adopted from Daqing oilfield. The time history curves of the pressure at the fracture mouth from numerical simulation are in good coincidence with those obtained from the field measurements. The correctness of the proposed model is validated. The influences of major geological parameters and treatment parameters on horizontal fracturing are studied. The concerned parameters include in-situ horizontal stress contrast, permeability, elastic modulus, injection rate and viscosity.
[3]	薄其众, 葛刚, 马功联. 2003. 高能气体压裂技术与应用 . 海洋石油, 23: 69-71 DOI      URL      [本文引用: 2]      摘要 文章介绍了高能气体压裂的增产增注机理,高能气体在压裂过程中的机械作用、脉冲冲击波作用、热效应和化学作用以及高能气体压裂的优缺点。对高能气体压裂在胜利油田部分采油厂的应用效果进行了对比和分析。认为高能气体压裂是油田的生产开发中一个有效的增产增注手段,能获得良好的经济效益。 (Bo Q Z, Gang G E, Ma G L.2003. High energy gas fracture technology and application . Offshore Oil, 23: 69-71). DOI      URL      [本文引用: 2]      摘要 文章介绍了高能气体压裂的增产增注机理,高能气体在压裂过程中的机械作用、脉冲冲击波作用、热效应和化学作用以及高能气体压裂的优缺点。对高能气体压裂在胜利油田部分采油厂的应用效果进行了对比和分析。认为高能气体压裂是油田的生产开发中一个有效的增产增注手段,能获得良好的经济效益。
[4]	才博, 王欣, 蒋廷学, 吕雪晴. 2007. 液态CO$_{2}$压裂技术在煤层气压裂中的应用 . 天然气技术, 1: 40-42 URL      [本文引用: 2]      摘要 煤层气是一种非常规天然气资源。煤层气储层与常规天然气储层相比具有很大的差异。煤层通常以多个煤层组形式存在，各组之间相距的距离不等，这一特征加上煤岩本身的一些特性，使得煤层压裂与常规储层压裂之间存在一些差异。文章介绍了液态CO2压裂技术的原理、优缺点以及工艺技术特点。对利用液态CO2施工的步骤及效果进行了对比分析，建议在煤层气压裂中有针对性地利用谊项技术； (Cai B, Wang X, Jiang T X, Lü X Q.2007. Application of hydraulic CO$_{2}$ fracturing technique in coalbed gas fracturing . Natural Gas Technology, 1: 40-42). URL      [本文引用: 2]      摘要 煤层气是一种非常规天然气资源。煤层气储层与常规天然气储层相比具有很大的差异。煤层通常以多个煤层组形式存在，各组之间相距的距离不等，这一特征加上煤岩本身的一些特性，使得煤层压裂与常规储层压裂之间存在一些差异。文章介绍了液态CO2压裂技术的原理、优缺点以及工艺技术特点。对利用液态CO2施工的步骤及效果进行了对比分析，建议在煤层气压裂中有针对性地利用谊项技术；
[5]	陈发宇, 尚永生, 杨长春. 2007. Matching Pursuits方法综述 . 地震物理学进展, 22: 1466-1473 [本文引用: 1]      (Chen F Y, Shang Y S, Yang C C.2007. A general description of matching pursuits decomposition method . Progress in Geophysics, 22: 1466-1473). [本文引用: 1]
[6]	陈良森, 李长春. 1992. 关于岩体的本构关系 . 力学进展, 22: 173-182 DOI      URL      [本文引用: 1]      摘要 本文综述了近10年中有关岩石本构关系方面的主要研究成果,包括:岩石的强度理论;损伤理论;塑性理论及分布断裂力学理论。 (Chen L S, Li C C.1992. On the constitutive relations of rocks . Advances in Mechanics, 22: 173-182). DOI      URL      [本文引用: 1]      摘要 本文综述了近10年中有关岩石本构关系方面的主要研究成果,包括:岩石的强度理论;损伤理论;塑性理论及分布断裂力学理论。
[7]	陈勉, 葛洪魁, 赵金洲, 姚军. 2015. 页岩油气高效开发的关键基础理论与挑战 . 石油钻探技术, 43, 7-14. DOI      URL      [本文引用: 1]      摘要 为更好地指导我国页岩气资源高效开发,在概述我国页岩气资源和开采现状的基础上,从地质特征预测、安全快速钻井、环保高效开采等方面系统总结了我国页岩气开采面临的工程地质难题,指出页岩非线性工程地质力学特征与预测理论、多重耦合下的页岩油气安全优质钻井理论、页岩地层动态随机裂缝控制机理与无水压裂技术、页岩油气多尺度渗流特征与开采理论等是需要重点解决的关键理论问题,钻采过程中页岩储层物理力学化学特征演化规律与数学表征,多场耦合条件下非连续页岩与钻井完井流体作用机理,页岩地层动态随机裂缝控制、长效导流机制与无水压裂技术,页岩微纳尺度吸附/解吸机制、尺度升级及多场耦合的多相渗流理论等是亟需解决的关键前沿理论问题,并针对各前沿关键力学问题综述了研究进展和发展趋势,对促进我国页岩油气的科学、有效开发具有一定的借鉴作用。
[8]	陈勉, 庞飞, 金衍. 2000. 大尺寸真三轴水力压裂模拟与分析 . 岩石力学与工程学报, 19: 868-872 DOI      URL      [本文引用: 1]      摘要 采用大尺寸真三轴模拟试验系统模拟地层条件 ,对天然岩样和人造岩样进行水力压裂裂缝扩展机理模拟实验 ,并实现对裂缝扩展的实际物理过程进行监测。讨论了地应力、断裂韧性、节理和天然裂缝等因素对水压裂缝扩展的影响。 (Chen M, Pang F, Jin Y.2000. Simulation and analysis of dimensions of true three axis hydraulic fracturing . Chinese Journal of Rock Mechanics and Engineering, 19: 868-872). DOI      URL      [本文引用: 1]      摘要 采用大尺寸真三轴模拟试验系统模拟地层条件 ,对天然岩样和人造岩样进行水力压裂裂缝扩展机理模拟实验 ,并实现对裂缝扩展的实际物理过程进行监测。讨论了地应力、断裂韧性、节理和天然裂缝等因素对水压裂缝扩展的影响。
[9]	陈鹏飞, 刘友权, 邓素芬, 吴文刚, 雷英全, 张亚东, 黄晨直. 2013. 页岩气体积压裂滑溜水的研究及应用 . 石油与天然气化工, 42: 270-273 DOI      URL      摘要 页岩储层需要采用大排量、大液量体积压裂才能获得工业气流,体积压裂要求压裂液具有可连续混配、低摩阻和高返排率性能。根据四川页岩储层特征和实验结果,研制了降阻性能高的聚丙烯酰胺降阻剂、高效复合防膨剂及微乳助排剂,研制了适于四川页岩气体积压裂的滑溜水。该配方在四川W、C区块直井8井次现场试验表明,降阻率为65.5%～68.3%;W区块平均返排率为46.19%,C区块返排率27.93%;累计增加井口测试产量6.24×104～11.35×104 m3/d。 (Chen P F, Liu Y Q, Deng S F, Wu W G, Lei Y Q, Zhang Y D, Huang C Z.2013. Research and application of slick water for shale volume fracturing . Chemical Engineering of Oil & Gas, 42: 270-273). DOI      URL      摘要 页岩储层需要采用大排量、大液量体积压裂才能获得工业气流,体积压裂要求压裂液具有可连续混配、低摩阻和高返排率性能。根据四川页岩储层特征和实验结果,研制了降阻性能高的聚丙烯酰胺降阻剂、高效复合防膨剂及微乳助排剂,研制了适于四川页岩气体积压裂的滑溜水。该配方在四川W、C区块直井8井次现场试验表明,降阻率为65.5%～68.3%;W区块平均返排率为46.19%,C区块返排率27.93%;累计增加井口测试产量6.24×104～11.35×104 m3/d。
[10]	陈守雨, 杜林麟, 贾碧霞, 修书志. 2011. 多井同步体积压裂技术研究 . 石油钻采工艺, 33: 59-65 DOI      URL      摘要 多井同步体积压裂是对两口或两口以上的配对井同时进行体积压裂,以增加水力压裂裂缝网络的密度及表面积,达到初期高产和长期稳产的目的。探讨了多井同步压裂井间裂缝网络连通机理,对井间变应力压裂原理进行了分析,并从实例角度给出了多井同步体积压裂的实现方法。现场应用表明,同步压裂能够大幅度提高配对井初始产量和最终采收率。 (Chen S Y, Du L Q, Jia B X, Xiu S Z.2011. Research on the simultaneous volume fracturing of multiple wells . Oil Drilling & Production Technology, 33: 59-65). DOI      URL      摘要 多井同步体积压裂是对两口或两口以上的配对井同时进行体积压裂,以增加水力压裂裂缝网络的密度及表面积,达到初期高产和长期稳产的目的。探讨了多井同步压裂井间裂缝网络连通机理,对井间变应力压裂原理进行了分析,并从实例角度给出了多井同步体积压裂的实现方法。现场应用表明,同步压裂能够大幅度提高配对井初始产量和最终采收率。
[11]	陈天宇, 冯夏庭, 张希巍, 曹卫东, 付长剑. 2014. 黑色页岩力学特性及各向异性特性试验研究 . 岩石力学与工程学报, 33: 1772-1779 DOI      URL      [本文引用: 1]      摘要 Geochemical parameters of lower Cambrian black shale at Niutitang were measured in order to study the mechanical and anisotropic properties of black shale. The brittle mineral content of the lower Cambrian black shale at Niutitang was found to be as high as 79.01%. The scanning electron microscopy was used to obtain the microscopic structure of the black shale. The layered sedimentary characteristics and the lamellar structure of alternating plates were observed to exist in the black shale. Series of triaxial compression experiments on the black shale samples with different angles of bedding were carried out with the testing system ROCKMAN207，which was developed by Northeastern University and Chaoyang testing instrument company at Changchun. The whole stress-strain curves and failure modes were obtained. The effects of confining pressure and the angle of bedding on the mechanical behavior and failure modes of shale were analyzed. The stress-strain curves of the black shale exhibited no obvious stage of compaction of fissures and pores，and were largely straight lines ahead of the peak point. The failure modes of the black shale were related to the confining pressure and the angle of bedding. Under the condition of low confining pressure，complex networks of fractures were formed easily after the failure of the rock sample. When the axial loading direction was parallel to the shale?s bedding，the complex fracture networks were formed more easily. The wave velocity of the black shale samples decreases with the increase of the bedding angle. The anisotropic strength curve of the shale is U-shaped. The anisotropic coefficient of the black shale decreases with the increase of confining pressure. (Chen T Y, Feng X T, Zhang X W, Cao W D, Fu C J.2014. Experimental study on mechanical and anisotropic properties of black shale . Chinese Journal of Rock Mechanics and Engineering, 33: 1772-1779). DOI      URL      [本文引用: 1]      摘要 Geochemical parameters of lower Cambrian black shale at Niutitang were measured in order to study the mechanical and anisotropic properties of black shale. The brittle mineral content of the lower Cambrian black shale at Niutitang was found to be as high as 79.01%. The scanning electron microscopy was used to obtain the microscopic structure of the black shale. The layered sedimentary characteristics and the lamellar structure of alternating plates were observed to exist in the black shale. Series of triaxial compression experiments on the black shale samples with different angles of bedding were carried out with the testing system ROCKMAN207，which was developed by Northeastern University and Chaoyang testing instrument company at Changchun. The whole stress-strain curves and failure modes were obtained. The effects of confining pressure and the angle of bedding on the mechanical behavior and failure modes of shale were analyzed. The stress-strain curves of the black shale exhibited no obvious stage of compaction of fissures and pores，and were largely straight lines ahead of the peak point. The failure modes of the black shale were related to the confining pressure and the angle of bedding. Under the condition of low confining pressure，complex networks of fractures were formed easily after the failure of the rock sample. When the axial loading direction was parallel to the shale?s bedding，the complex fracture networks were formed more easily. The wave velocity of the black shale samples decreases with the increase of the bedding angle. The anisotropic strength curve of the shale is U-shaped. The anisotropic coefficient of the black shale decreases with the increase of confining pressure.
[12]	陈叶, 高向东, 韩文龙, 李媛媛, 周晓得. 2015. 页岩储层天然裂缝发育特征概述 . 西部探矿工程, 2: 73-78 DOI      URL      [本文引用: 3]      摘要 页岩储层中的裂缝既可以为页岩气提供聚集空间,也可以为页岩气的生产提供运移通道。页岩中存在的裂缝主要可以分为5类:构造缝(张裂缝和剪裂缝)、层间页理缝、低角度滑脱缝、成岩收缩微裂缝和有机质演化异常压力缝,可根据裂缝形成原因划分为原生裂缝和后生裂缝。裂缝的成因类型和分布规律各不相同,裂缝的发育与页岩气储藏密切相关。对页岩储层中裂缝的成因类型、识别特征、识别方法、基本参数(宽度、长度、密度、间距、产状、充填情况、溶蚀改造情况)、分布规律等进行了分析研究,为页岩气的资源评价和勘探开发提供储层裂缝地质信息。 (Chen Y, Gao X D, Han W L, Li Y Y, Zhou X D.2015. Development characteristics of natural fractures in shale reservoirs . West-China Exploration Engineering, 2: 73-78). DOI      URL      [本文引用: 3]      摘要 页岩储层中的裂缝既可以为页岩气提供聚集空间,也可以为页岩气的生产提供运移通道。页岩中存在的裂缝主要可以分为5类:构造缝(张裂缝和剪裂缝)、层间页理缝、低角度滑脱缝、成岩收缩微裂缝和有机质演化异常压力缝,可根据裂缝形成原因划分为原生裂缝和后生裂缝。裂缝的成因类型和分布规律各不相同,裂缝的发育与页岩气储藏密切相关。对页岩储层中裂缝的成因类型、识别特征、识别方法、基本参数(宽度、长度、密度、间距、产状、充填情况、溶蚀改造情况)、分布规律等进行了分析研究,为页岩气的资源评价和勘探开发提供储层裂缝地质信息。
[13]	陈作, 王振铎, 曾华国. 2007. 水平井分段压裂工艺技术现状及展望 . 天然气工业, 27: 78-80 DOI      URL      摘要 水平井目前已成为提高油田勘探开发综合效益的重要途径,其技术已在中国石油塔里木、辽河、冀东、大庆、新疆、吉林等13个油田得到了广泛的应用。对于钻遇在低渗透油气藏的水平井和产量达不到经济开发要求的其他水平井,必然要面临增产改造的问题。水平井水平段压裂与直井压裂改造的工作重点有所不同,为此,就国内外化学隔离分段压裂、机械封隔分段压裂、限流分段压裂、水力喷射分段压裂等水平井分段压裂改造工艺技术进行了论述,展望了水平井分段压裂改造技术的发展趋势,以期为国内水平井分段压裂改造技术攻关方向提供参考。 (Chen Z, Wang Z D, Zeng H G.2007. Status quo and prospect of staged fracturing technique in horizontal wells . Natural Gas Industry, 27: 78-80). DOI      URL      摘要 水平井目前已成为提高油田勘探开发综合效益的重要途径,其技术已在中国石油塔里木、辽河、冀东、大庆、新疆、吉林等13个油田得到了广泛的应用。对于钻遇在低渗透油气藏的水平井和产量达不到经济开发要求的其他水平井,必然要面临增产改造的问题。水平井水平段压裂与直井压裂改造的工作重点有所不同,为此,就国内外化学隔离分段压裂、机械封隔分段压裂、限流分段压裂、水力喷射分段压裂等水平井分段压裂改造工艺技术进行了论述,展望了水平井分段压裂改造技术的发展趋势,以期为国内水平井分段压裂改造技术攻关方向提供参考。
[14]	崔永君, 李育辉, 张群, 降文萍. 2005. 煤吸附甲烷的特征曲线及其在煤层气储集研究中的作用 . 科学通报, 50: 76-81 DOI      URL      [本文引用: 1]      摘要 以吸附势理论为基础,对4种不同煤级煤在不同温度下的等温吸附数 据进行了处理分析,研究结果表明:各煤样吸附甲烷的特征曲线是惟一的,并由特征曲线获得了甲烷吸附量和温度、压力之间的关系表达式.根据提出的思路和计算 方法,只需凭借一个温度下的吸附数据就可以获得其他平衡条件下的吸附量,研究成果对研究煤层气的储集机理等内容具有重要意义. (Cui Y J, Li Y H, Zhang Q, Jiang W P.2005. Characteristic curve of coal adsorption of methane and its role in coalbed gas reservoir . Chinese Science Bulletin, 50: 76-81). DOI      URL      [本文引用: 1]      摘要 以吸附势理论为基础,对4种不同煤级煤在不同温度下的等温吸附数 据进行了处理分析,研究结果表明:各煤样吸附甲烷的特征曲线是惟一的,并由特征曲线获得了甲烷吸附量和温度、压力之间的关系表达式.根据提出的思路和计算 方法,只需凭借一个温度下的吸附数据就可以获得其他平衡条件下的吸附量,研究成果对研究煤层气的储集机理等内容具有重要意义.
[15]	刁海燕. 2013. 泥页岩储层岩石力学特性及脆性评价 . 岩石学报, 29: 3300-3306 URL      [本文引用: 4]      摘要 泥页岩储层的岩石力学特性对油气开发影响极大,进行泥页岩力学特性和脆性评价方面的研究,可以为泥页岩油钻井和压裂设计工作提供技术支撑。实验研究表明,泥页岩抗压强度与围压、杨氏模量成正相关;体积应变量随杨氏模量减小而增大,随泊松比增加而增加;泥页岩破坏在低围压下以劈裂式破坏为主,高围压时多出现剪切式破坏。泥页岩的脆性与其弹性参数和矿物组成关系密切,通过数值模拟和实验测量,综合弹性参数和矿物组分两种方法提出了一种新的脆性评价方法-弹性参数与矿物成分组合法(EPMC Method),并实现了单井脆性评价,效果较好。脆性评价既是储层岩石力学特性分析的重要内容,也是压裂选层的重要依据。 (Diao H Y.2013. Rock mechanical properties and brittleness evaluation of shale reservoir . Acta Petrologica Sinica, 29: 3300-3306). URL      [本文引用: 4]      摘要 泥页岩储层的岩石力学特性对油气开发影响极大,进行泥页岩力学特性和脆性评价方面的研究,可以为泥页岩油钻井和压裂设计工作提供技术支撑。实验研究表明,泥页岩抗压强度与围压、杨氏模量成正相关;体积应变量随杨氏模量减小而增大,随泊松比增加而增加;泥页岩破坏在低围压下以劈裂式破坏为主,高围压时多出现剪切式破坏。泥页岩的脆性与其弹性参数和矿物组成关系密切,通过数值模拟和实验测量,综合弹性参数和矿物组分两种方法提出了一种新的脆性评价方法-弹性参数与矿物成分组合法(EPMC Method),并实现了单井脆性评价,效果较好。脆性评价既是储层岩石力学特性分析的重要内容,也是压裂选层的重要依据。
[16]	丁雁生, 陈力, 谢燮, 张盛宗, 刘先贵, 刘小. 2001. 低渗透油气田"层内爆炸"增产技术研究 . 石油勘探与开发, 28: 90-96 DOI      URL      [本文引用: 2]      摘要 回顾爆炸法（井内爆炸法、核爆炸法和高能气体压裂）增产油气的历史，提出低渗透油气田“层内爆炸”增产技术的基本思路：利用水力压裂技术将乳胶状爆燃药压入油层裂缝，并采取不损毁井筒的技术措施点燃该爆燃药，从而在水力压裂主裂缝邻域造成碎裂带，达到提高采收率、增产原油的目的。至少已找到一组特种火炸药基本配方，在２００ｍｍ小尺度模拟实验中实现了“层内爆炸”挤注、点火和爆燃的过程，证实技术原理基本可行。考虑流体内部的热传导、边界的热损失和阻尼，提出了有化学反应的薄层药爆燃一维可压缩流体力学模型，并对此模型进行恒稳推进和不可压缩简化，计算结果的物理图象符合常理，从理论上证实了薄层药爆燃可行。“层内爆炸”油井产出液的后处理，原则上是安全的：残留在岩缝的未爆炸炸药颗粒在生产阶段难以流出地层；进入集输系统的残药颗粒浓度低于１％，原则上能用离心法分离；残留在分离后原油中的的微量炸药在４００℃加热炉已完全热分解，热分解不可能导致爆炸。“层内爆炸”增产技术的研究是具有战略性、前瞻性的科技创新课题，预期增产效益显著高于水力压裂，有可能形成低渗透油气田开采的新局面，还可能使一些目前不可采的低渗透油气资源成为可采资源。今后工作主要有四方面：室 (Ding Y S, Chen L, Xie X, Zhang S Z, Liu X G, Liu X.2001. Low-permeability oil and gas fields layer in-fracture explosive fracturing Technology . Petroleum Exploration and Development, 28: 90-96). DOI      URL      [本文引用: 2]      摘要 回顾爆炸法（井内爆炸法、核爆炸法和高能气体压裂）增产油气的历史，提出低渗透油气田“层内爆炸”增产技术的基本思路：利用水力压裂技术将乳胶状爆燃药压入油层裂缝，并采取不损毁井筒的技术措施点燃该爆燃药，从而在水力压裂主裂缝邻域造成碎裂带，达到提高采收率、增产原油的目的。至少已找到一组特种火炸药基本配方，在２００ｍｍ小尺度模拟实验中实现了“层内爆炸”挤注、点火和爆燃的过程，证实技术原理基本可行。考虑流体内部的热传导、边界的热损失和阻尼，提出了有化学反应的薄层药爆燃一维可压缩流体力学模型，并对此模型进行恒稳推进和不可压缩简化，计算结果的物理图象符合常理，从理论上证实了薄层药爆燃可行。“层内爆炸”油井产出液的后处理，原则上是安全的：残留在岩缝的未爆炸炸药颗粒在生产阶段难以流出地层；进入集输系统的残药颗粒浓度低于１％，原则上能用离心法分离；残留在分离后原油中的的微量炸药在４００℃加热炉已完全热分解，热分解不可能导致爆炸。“层内爆炸”增产技术的研究是具有战略性、前瞻性的科技创新课题，预期增产效益显著高于水力压裂，有可能形成低渗透油气田开采的新局面，还可能使一些目前不可采的低渗透油气资源成为可采资源。今后工作主要有四方面：室
[17]	丁云宏, 丛连铸, 卢拥军, 雷群, 管保山, 慕立俊. 2002. CO$_{2}$泡沫压裂液的研究与应用 . 石油勘探与开发, 29: 103-105 DOI      URL      摘要 泡沫压裂液适用于低压、水敏性储集层。通过室内试验及研究 ,优选出CO2 泡沫压裂液配方 ,得出对其性能测试的结果 :起泡、稳泡能力强 ,流变性能、携砂能力好 ,低滤失 ,破胶快等 ,岩心实验证实具有低膨胀及低伤害特性 ,可以满足压裂工艺设计的要求。CO2 泡沫压裂施工中 ,如要提高施工规模、增大砂量及砂液比 ,使用酸性交联压裂液体系可确保施工的顺利进行。在长庆油田等现场实施的CO2 泡沫压裂液增产效果良好。图 2表 5参 3 (丁云宏摘 ) (Ding Y H, Cong L Z, Lu Y J, Lei Q, Guan B S, Mu L J.2002. Study and application of CO$_{2}$ foam fracturing fluids . Petroleum Exploration and Development, 29: 103-105). DOI      URL      摘要 泡沫压裂液适用于低压、水敏性储集层。通过室内试验及研究 ,优选出CO2 泡沫压裂液配方 ,得出对其性能测试的结果 :起泡、稳泡能力强 ,流变性能、携砂能力好 ,低滤失 ,破胶快等 ,岩心实验证实具有低膨胀及低伤害特性 ,可以满足压裂工艺设计的要求。CO2 泡沫压裂施工中 ,如要提高施工规模、增大砂量及砂液比 ,使用酸性交联压裂液体系可确保施工的顺利进行。在长庆油田等现场实施的CO2 泡沫压裂液增产效果良好。图 2表 5参 3 (丁云宏摘 )
[18]	董大忠, 邹才能, 李建忠, 王社教, 李新景, 王玉满, 李登华, 黄金亮. 2011. 页岩气资源潜力与勘探开发前景 . 地质通报, 30: 324-336 DOI      URL      摘要 页岩气为近年来在北美地区广泛勘探开发的天然气新目标，在全球非常规油气勘探开发中异军突起，成为突破最晚、近期发展最快的非常规天然气资源。依据北关地区页岩气勘探开发的历程和全球页岩气勘探开发的进展，阐述了全球页岩气勘探开发的基本态势和页岩气5个方面的典型特征，分析了全球页岩气的资源潜力与分布特征，预测中国页岩气资源潜力约100×10^12m^3，指出页岩气的成功勘探开发是近10年来油气地质理论与工程技术取得的最激动人心的重大成就，页岩气资源潜力丰富，实现全面开发将带来一场全球的能源革命。最后，提出了4点加快中国页岩气发展的建议。 (Dong D Z, Zou C N, Li J Z, Wang S J, Li X J, Wang Y M, Li D H, Li J L.2011. Resource potential, exploration and development prospect of shale gas in the whole world . Geological Bulletin of China, 30: 324-336). DOI      URL      摘要 页岩气为近年来在北美地区广泛勘探开发的天然气新目标，在全球非常规油气勘探开发中异军突起，成为突破最晚、近期发展最快的非常规天然气资源。依据北关地区页岩气勘探开发的历程和全球页岩气勘探开发的进展，阐述了全球页岩气勘探开发的基本态势和页岩气5个方面的典型特征，分析了全球页岩气的资源潜力与分布特征，预测中国页岩气资源潜力约100×10^12m^3，指出页岩气的成功勘探开发是近10年来油气地质理论与工程技术取得的最激动人心的重大成就，页岩气资源潜力丰富，实现全面开发将带来一场全球的能源革命。最后，提出了4点加快中国页岩气发展的建议。
[19]	董谦, 刘小平, 李武广, 董清源. 2012. 关于页岩含气量确定方法的探讨 . 天然气与石油, 30: 34-37 URL      [本文引用: 1]      摘要 页岩含气量是页岩气资源评价和有利区优选的关键性参数，也是评价页岩是否具有开采价值的一个重要标准。对页岩含气量的获取方法进行了介绍，其一是通过解吸法分别测量解吸气、残余气和损失气；其二是利用等温吸附实验、测井解释等方法分别计算页岩中的吸附气、游离气含量。分析认为：解吸法测量结果容易受到取心方式、测定方法、损失气量计算方法、气体解吸温度等因素的影响，所测得的总含气量比间接法更接近于真实值；吸附气量的估算需要综合考虑有机碳含量、粘土矿物组分、成熟度、温度和压力等因素对页岩吸附能力的影响，建立适当的吸附气含量计算模型，游离气量估算的关键是确定页岩的有效孔隙度和含气饱和度。建立针对页岩含气量测试技术和等温吸附实验技术标准，量化各种控制因素对页岩含气量的影响，对准确评价页岩含气量具有重要意义。 (Dong Q, Liu X P, Li W G, Dong Q Y.2012. Determination of gas content in shale . Natural Gas and Oil, 30: 34-37). URL      [本文引用: 1]      摘要 页岩含气量是页岩气资源评价和有利区优选的关键性参数，也是评价页岩是否具有开采价值的一个重要标准。对页岩含气量的获取方法进行了介绍，其一是通过解吸法分别测量解吸气、残余气和损失气；其二是利用等温吸附实验、测井解释等方法分别计算页岩中的吸附气、游离气含量。分析认为：解吸法测量结果容易受到取心方式、测定方法、损失气量计算方法、气体解吸温度等因素的影响，所测得的总含气量比间接法更接近于真实值；吸附气量的估算需要综合考虑有机碳含量、粘土矿物组分、成熟度、温度和压力等因素对页岩吸附能力的影响，建立适当的吸附气含量计算模型，游离气量估算的关键是确定页岩的有效孔隙度和含气饱和度。建立针对页岩含气量测试技术和等温吸附实验技术标准，量化各种控制因素对页岩含气量的影响，对准确评价页岩含气量具有重要意义。
[20]	段建华. 2014. 微地震事件不同初至拾取方法的对比分析 . 煤田地质与勘探, 3: 82-86 DOI      URL      [本文引用: 2]      摘要 微地震事件初至的精确拾取是微震时空定位的关键技术之一。简述了 STA/LTA（Short-Term to Long-Term Average）、AIC（Akaike Information Criteria）、分形维数3种微地震初至拾取方法的基本原理；采用理论模型数据对不同初至拾取方法进行了方法测试效果分析；并选取不同信噪比的实际数据对初至拾取精度、算法效率两个方面进行了比较。结果显示：高信噪比时，3种方法初至拾取的精度都比较高；在信噪比降低时，分形维数法初至拾取的精度仍然较高，具有较好的抗噪性；但是，分形维数法的效率较低，且受算法原理限制，并且与AIC法很难单独拾取事件初至。因此，采用STA/LTA识别微地震事件，初步确定初至范围，然后再使用AIC方法精确拾取初至，是微地震事件初至拾取的较好方法。 (Duan J H.2014. Comparison of picking method of microseismic first-break . Coal Geology & Exploration, 3: 82-86). DOI      URL      [本文引用: 2]      摘要 微地震事件初至的精确拾取是微震时空定位的关键技术之一。简述了 STA/LTA（Short-Term to Long-Term Average）、AIC（Akaike Information Criteria）、分形维数3种微地震初至拾取方法的基本原理；采用理论模型数据对不同初至拾取方法进行了方法测试效果分析；并选取不同信噪比的实际数据对初至拾取精度、算法效率两个方面进行了比较。结果显示：高信噪比时，3种方法初至拾取的精度都比较高；在信噪比降低时，分形维数法初至拾取的精度仍然较高，具有较好的抗噪性；但是，分形维数法的效率较低，且受算法原理限制，并且与AIC法很难单独拾取事件初至。因此，采用STA/LTA识别微地震事件，初步确定初至范围，然后再使用AIC方法精确拾取初至，是微地震事件初至拾取的较好方法。
[21]	冯增朝, 赵阳升, 文再明. 2005. 煤岩体孔隙裂隙双重介质逾渗机理研究, 岩石力学与工程学报, 24: 236-240 DOI      URL      [本文引用: 1]      摘要 介绍了孔隙裂隙双重介质逾渗概率的研究方法,在此基础上研究了煤岩体的逾渗概率与渗透系数的关系,分析了裂隙、孔隙及二者共同作用对煤岩体逾渗概率的影响。结果表明:煤岩体这类孔隙裂隙双重介质的逾渗概率与其渗透系数呈指数规律;煤岩体的裂纹孔隙率决定孔洞孔隙率对其渗透性的影响程度;同时,裂隙还决定了孔隙裂隙介质的逾渗规律,使其与多孔介质的逾渗规律具有完全不同的形式。 (Feng Z C, Zhao Y S, Wen Z M.2005. Percolation mechanism of fractured coal rocks as dual-continua . Chinese Journal of Rock Mechanics and Engineering, 24: 236-240). DOI      URL      [本文引用: 1]      摘要 介绍了孔隙裂隙双重介质逾渗概率的研究方法,在此基础上研究了煤岩体的逾渗概率与渗透系数的关系,分析了裂隙、孔隙及二者共同作用对煤岩体逾渗概率的影响。结果表明:煤岩体这类孔隙裂隙双重介质的逾渗概率与其渗透系数呈指数规律;煤岩体的裂纹孔隙率决定孔洞孔隙率对其渗透性的影响程度;同时,裂隙还决定了孔隙裂隙介质的逾渗规律,使其与多孔介质的逾渗规律具有完全不同的形式。
[22]	高树生, 胡志明, 郭为, 左罗, 沈瑞. 2013. 页岩储层吸水特征与返排能力 . 天然气工业, 33: 71-76 DOI      摘要 中国页岩气资源量巨大,但页岩储层渗透率极低,为了有效开发页岩气藏,通常采用体积压裂技术以增大渗流面积,但页岩储层压裂后普遍存在着压裂液返排率低的问题。针对该问题,全面分析了页岩的组分及其与水的力学作用机理;设计了页岩粉末膨胀和岩心吸水实验,分别研究了页岩对蒸馏水、地层水、压裂液A和压裂液B的吸水能力;同时运用缝网渗流能力等效原理,推导了页岩吸水强度的计算公式,概算了页岩气井体积压裂后的吸水百分比。研究结果表明:页岩受表面水化力、渗透水化力、氢键力及范德华力作用的水分子难以返排,而受重力和毛细管压力作用的水分子在一定条件下可以返排;压裂液能够有效抑制页岩的吸水能力,有助于压裂液的返排;通过改变压裂液组分提高压裂液返排率是可行的。该研究成果为认识页岩储层体积压裂液返排的内在机理以及压裂规模与返排率的关系,提供了较为翔实的理论依据。 (Gao S S, Hu Z M, Guo W, Zuo L, Shen R.2013. Water absorption characteristics and flowback ability of shale reservoir . Natural Gas Industry, 33: 71-76). DOI      摘要 中国页岩气资源量巨大,但页岩储层渗透率极低,为了有效开发页岩气藏,通常采用体积压裂技术以增大渗流面积,但页岩储层压裂后普遍存在着压裂液返排率低的问题。针对该问题,全面分析了页岩的组分及其与水的力学作用机理;设计了页岩粉末膨胀和岩心吸水实验,分别研究了页岩对蒸馏水、地层水、压裂液A和压裂液B的吸水能力;同时运用缝网渗流能力等效原理,推导了页岩吸水强度的计算公式,概算了页岩气井体积压裂后的吸水百分比。研究结果表明:页岩受表面水化力、渗透水化力、氢键力及范德华力作用的水分子难以返排,而受重力和毛细管压力作用的水分子在一定条件下可以返排;压裂液能够有效抑制页岩的吸水能力,有助于压裂液的返排;通过改变压裂液组分提高压裂液返排率是可行的。该研究成果为认识页岩储层体积压裂液返排的内在机理以及压裂规模与返排率的关系,提供了较为翔实的理论依据。
[23]	高树生, 于兴河, 刘华勋. 2011. 滑脱效应对页岩气产能影响的分析 . 天然气工业, 31: 55-58 DOI      URL      [本文引用: 1]      摘要 页岩气具有极低的渗透率且气井产能小,搞清滑脱效应存在条件及滑脱效应对气井产能的影响大小尤为重要。在物理模拟研究滑脱效应的基础上,根据页岩气开发特征,建立了考虑人工压裂和气体滑脱效应的气井产能公式,研究了不同储层压力条件下滑脱系数对于气井产能和生产压差的影响程度。结果表明:页岩储层在孔隙压力较低(小于10 MPa)的情况下,气体渗流存在较强的滑脱效应,而在孔隙压力较高的情况下气体滑脱效应不明显;浅层页岩气储层滑脱效应对气井产能和生产压差影响很大;中深层页岩气储层滑脱效应对于气井产能和生产压差存在一定程度的影响;深层页岩气储层滑脱效应对于气井产能和生产压差的影响可以忽略不计;压裂井无阻流量约是直井无阻流量的5.5倍。该研究成果对于页岩气储层的合理、有效开发具有一定的指导意义。 (Gao S S, Yu X H, Liu H X.2011. Impact of slippage effect on shale gas well productivity . Natural Gas Industry, 31: 55-58). DOI      URL      [本文引用: 1]      摘要 页岩气具有极低的渗透率且气井产能小,搞清滑脱效应存在条件及滑脱效应对气井产能的影响大小尤为重要。在物理模拟研究滑脱效应的基础上,根据页岩气开发特征,建立了考虑人工压裂和气体滑脱效应的气井产能公式,研究了不同储层压力条件下滑脱系数对于气井产能和生产压差的影响程度。结果表明:页岩储层在孔隙压力较低(小于10 MPa)的情况下,气体渗流存在较强的滑脱效应,而在孔隙压力较高的情况下气体滑脱效应不明显;浅层页岩气储层滑脱效应对气井产能和生产压差影响很大;中深层页岩气储层滑脱效应对于气井产能和生产压差存在一定程度的影响;深层页岩气储层滑脱效应对于气井产能和生产压差的影响可以忽略不计;压裂井无阻流量约是直井无阻流量的5.5倍。该研究成果对于页岩气储层的合理、有效开发具有一定的指导意义。
[24]	耿龙祥, 曹玉珊. 2015. 页岩气资源/储量计算与评价技术规范解读 . 非常规油气, 2: 10-14 URL      [本文引用: 1]      摘要 我国去年颁布的第一个页岩气行业标准——《页岩气资源/储量计算与评价技术规范》,是规范页岩气资源/储量分类、计算和管理,指导我国页岩气勘探开发的重要技术指南。由于我国页岩气处于起步阶段,对一些规定和要求还存在不同看法和争论。从页岩层段的定义、页岩气储集体的特殊性、页岩气储量分类方案、储量计算方法选择、储量起算标准、储量的经济性评价等方面对页岩气资源/储量的计算与评价进行阐述和剖析,加深了对页岩气资源/储量计算与评价的理解和认识,从而更好地开展页岩气资源/储量的计算、评价、勘探开发等工作。 (Geng L X, Cao Y S. Interpretation of the calculation and evaluation of shale gas resources/reserves . Unconventional Oil & Gas, 2015, 2: 10-14). URL      [本文引用: 1]      摘要 我国去年颁布的第一个页岩气行业标准——《页岩气资源/储量计算与评价技术规范》,是规范页岩气资源/储量分类、计算和管理,指导我国页岩气勘探开发的重要技术指南。由于我国页岩气处于起步阶段,对一些规定和要求还存在不同看法和争论。从页岩层段的定义、页岩气储集体的特殊性、页岩气储量分类方案、储量计算方法选择、储量起算标准、储量的经济性评价等方面对页岩气资源/储量的计算与评价进行阐述和剖析,加深了对页岩气资源/储量计算与评价的理解和认识,从而更好地开展页岩气资源/储量的计算、评价、勘探开发等工作。
[25]	郭建春, 周鑫浩, 邓燕. 2015. 页岩气水平井组拉链压裂过程中地应力的分布规律 . 天然气工业, 35: 44-48 DOI      URL      [本文引用: 1]      摘要 页岩储层具有低孔隙度、超低渗透率的特征,往往需要通过水力压裂才能使气井具备一定的生产能力。拉链压裂是近年来针对页岩气藏缝网压裂的一项新兴工艺,为了认清压裂过程中裂缝应力干扰后地应力场的分布规律并给页岩压裂设计提供参考,首先假设地层为均质、各向同性弹性体,然后通过位移不连续法,建立起地层应力场分布数学模型,并利用线性叠加原理,得到人工裂缝周围水平应力场的分布情况。研究发现:①裂缝周围的地应力随着与裂缝距离的远近有不同程度的增加;②裂缝尖端处存在应力集中现象,且在裂缝尖端附近产生的拉应力使得水平应力有所减小;③裂缝对水平最小主应力的影响程度大于对最大主应力的影响;④随着裂缝条数的增加,诱导应力的叠加干扰对水平主应力的影响不断增强,且水平应力差异性逐渐减小;⑤在裂缝交错排列的区域内,应力干扰较强,应力场分布较复杂。上述研究成果对页岩气水平井组拉链压裂的优化设计具有指导意义。 (Guo J C, Zhou X H, Deng Y.2015. Distribution rules of earth stress during zipper fracturing of shale gas horizontal cluster wells . Natural Gas Industry, 35: 44-48). DOI      URL      [本文引用: 1]      摘要 页岩储层具有低孔隙度、超低渗透率的特征,往往需要通过水力压裂才能使气井具备一定的生产能力。拉链压裂是近年来针对页岩气藏缝网压裂的一项新兴工艺,为了认清压裂过程中裂缝应力干扰后地应力场的分布规律并给页岩压裂设计提供参考,首先假设地层为均质、各向同性弹性体,然后通过位移不连续法,建立起地层应力场分布数学模型,并利用线性叠加原理,得到人工裂缝周围水平应力场的分布情况。研究发现:①裂缝周围的地应力随着与裂缝距离的远近有不同程度的增加;②裂缝尖端处存在应力集中现象,且在裂缝尖端附近产生的拉应力使得水平应力有所减小;③裂缝对水平最小主应力的影响程度大于对最大主应力的影响;④随着裂缝条数的增加,诱导应力的叠加干扰对水平主应力的影响不断增强,且水平应力差异性逐渐减小;⑤在裂缝交错排列的区域内,应力干扰较强,应力场分布较复杂。上述研究成果对页岩气水平井组拉链压裂的优化设计具有指导意义。
[26]	郭为, 胡志明, 左罗, 高树生,于荣泽, 曾博. 2015. 页岩基质解吸-扩散-渗流耦合实验及数学模型 . 力学学报, 47: 916-922 DOI      URL      [本文引用: 1]      摘要 Gas desorption-di usion-seepage coupled experiment was designed and carried out with Longmaxi shale samples collected from South of Sichuan, and both the gas flow characteristics and pressure propagation were then obtained. Shale gas desorption-di usion-seepage coupling mathematical model was derived and numerical solution of the mathematical model using finite difference method was obtained. Numerical simulation results compared with the experimental results show that the model can well describe the gas transport in the shale matrix. And shale matrix permeability, di usion coe cient, desorption constants and other factors can a ect the gas flow through shale matrix as well as pressure propagation, which should be taken into consideration in the development of shale gas reservoir. The presented mathematical model provides a new method to calculate the production capability of shale gas well. (Guo W, Hu Z M, Zuo L, Gao S S, Yu R Z, Zeng B.2015. Gas desorption-diffusion-seepage coupled experiment of shale matrix and mathematic model . Chinese Journal of Theoretical and Applied Mechanics, 47: 916-922). DOI      URL      [本文引用: 1]      摘要 Gas desorption-di usion-seepage coupled experiment was designed and carried out with Longmaxi shale samples collected from South of Sichuan, and both the gas flow characteristics and pressure propagation were then obtained. Shale gas desorption-di usion-seepage coupling mathematical model was derived and numerical solution of the mathematical model using finite difference method was obtained. Numerical simulation results compared with the experimental results show that the model can well describe the gas transport in the shale matrix. And shale matrix permeability, di usion coe cient, desorption constants and other factors can a ect the gas flow through shale matrix as well as pressure propagation, which should be taken into consideration in the development of shale gas reservoir. The presented mathematical model provides a new method to calculate the production capability of shale gas well.
[27]	韩烈祥, 朱丽华, 孙海芳, 谯抗逆. 2014. 无水压裂技术 . 天然气工业, 34: 48-54 [本文引用: 1]      (Han L X, Zhu L H, Sun H F, Qiao K N.2014. LPG waterless fracturing technology . Natural Gas Technology, 34: 48-54). [本文引用: 1]
[28]	何胡军, 王秋语, 程会明. 2010. 基于匹配追踪算法子波分解技术在薄互层储层预测中的应用 . 物探化探计算技术, 32: 641-644 DOI      URL      [本文引用: 1]      摘要 薄互层储层砂体预测技术的研究已成为国内、外各油田的重要研究课题,并已取得较多研究成果。但多数利用地震资料进行薄互层预测技术,均基于单一地震子波与地震反射系数函数的褶积假设,实际上地震子波在穿过不同物理特性地层时,其形状会发生不同变化,导致该假设与实际情况尚有一定距离,致使薄互层储层预测的精度降低。这里主要论述的是基于匹配追踪算法子波分解技术识别薄互层储层。通过研究表明,该技术能较好地分辨出储层在空间的展布规律,识别薄互层储层,为油藏的地质及地球物理解释提供有力的支持。 (He H J, Wang Q Y, Cheng H M.2010. The application of wavelet decomposition technique based on matching pursuit algorithm in thin interbedded reservoir prediction . Computing Techniques for Geophysical and Geochemical exploration, 32: 641-644). DOI      URL      [本文引用: 1]      摘要 薄互层储层砂体预测技术的研究已成为国内、外各油田的重要研究课题,并已取得较多研究成果。但多数利用地震资料进行薄互层预测技术,均基于单一地震子波与地震反射系数函数的褶积假设,实际上地震子波在穿过不同物理特性地层时,其形状会发生不同变化,导致该假设与实际情况尚有一定距离,致使薄互层储层预测的精度降低。这里主要论述的是基于匹配追踪算法子波分解技术识别薄互层储层。通过研究表明,该技术能较好地分辨出储层在空间的展布规律,识别薄互层储层,为油藏的地质及地球物理解释提供有力的支持。
[29]	何龙. 2014. 涪陵地区大安寨段页岩气裂缝特征及分布规律 . [硕士论文]. 成都: 成都理工大学 URL      [本文引用: 1]      摘要 四川盆地涪陵地区下侏罗统大安寨段属于超低孔低渗储层，岩性以介 壳灰岩和页岩为主，可分为三个亚段:大一亚段，大二亚段和大三亚段。其中大一亚段和大三亚段主要岩性为介壳灰岩，厚度分布稳定;大二亚段以黑色页岩为主， 夹薄层灰岩条带。总体上大安寨段的储层物性差，非均质性强，并以裂缝作为主要的储集空间和渗流通道。　　本文收集了工区内的钻井、测 井、地震及岩心分析等基础地质资料，应用了沉积学、测井地质学以及地球化学等方法，对裂缝的特征、成因期次和分布进行详细研究。取得的主要成果包 括:　　1、通过野外以及岩心裂缝观察，得到裂缝的产状、长度... (He L.2014. The development of characteristic and distribution of fracture of Da'anzhai member in Fuling area, eastern Sichuan Basin . [Master Thesis]. Chengdu: Chengdu Univeristy of Technology). URL      [本文引用: 1]      摘要 四川盆地涪陵地区下侏罗统大安寨段属于超低孔低渗储层，岩性以介 壳灰岩和页岩为主，可分为三个亚段:大一亚段，大二亚段和大三亚段。其中大一亚段和大三亚段主要岩性为介壳灰岩，厚度分布稳定;大二亚段以黑色页岩为主， 夹薄层灰岩条带。总体上大安寨段的储层物性差，非均质性强，并以裂缝作为主要的储集空间和渗流通道。　　本文收集了工区内的钻井、测 井、地震及岩心分析等基础地质资料，应用了沉积学、测井地质学以及地球化学等方法，对裂缝的特征、成因期次和分布进行详细研究。取得的主要成果包 括:　　1、通过野外以及岩心裂缝观察，得到裂缝的产状、长度...
[30]	何惺华. 2013. 基于三分量的微地震震源反演方法与效果 . 石油地球物理勘探, 48: 71-76 URL      [本文引用: 1]      摘要 微地震检测的关键是确定微震源的位置。本文讨论了利用井下多级三分量检波器资料反演微震源位 置的新方法。首先用射孔直达纵波水平分量确定检波器的方位角;再在三维空间逐点对检波器组计算直达波旅行时并通过沿直达纵波时距曲线进行能量叠加,反演得 到微地震震源位置的分布范围;针对微震源反演存在的多解性问题,利用微地震直达纵波水平检波器分量变换和震—检地理方位角的关系确定微震源的方位角;最后 采用两种空间点集的统计方法确定微震源点的位置坐标。在均匀介质、斜井直线观测系统的三分量微地震正演模拟记录上所作的微震源反演试验表明,在信噪比较低 的情况下,利用这些方法可以有效与稳定地反演微震源的位置。 (He X H.2013. Seismic source inversion method based on three component and its effect . Oil Geophysical Prospecting, 48: 71-76). URL      [本文引用: 1]      摘要 微地震检测的关键是确定微震源的位置。本文讨论了利用井下多级三分量检波器资料反演微震源位 置的新方法。首先用射孔直达纵波水平分量确定检波器的方位角;再在三维空间逐点对检波器组计算直达波旅行时并通过沿直达纵波时距曲线进行能量叠加,反演得 到微地震震源位置的分布范围;针对微震源反演存在的多解性问题,利用微地震直达纵波水平检波器分量变换和震—检地理方位角的关系确定微震源的方位角;最后 采用两种空间点集的统计方法确定微震源点的位置坐标。在均匀介质、斜井直线观测系统的三分量微地震正演模拟记录上所作的微震源反演试验表明,在信噪比较低 的情况下,利用这些方法可以有效与稳定地反演微震源的位置。
[31]	侯晓伟, 王猛, 刘宇, 刘娇男, 宋昱. 2016. 页岩气超临界状态吸附模型及其地质意义 . 中国矿业大学学报, 45: 111-118 URL      [本文引用: 1]      摘要 为了表征各类型页岩孔隙吸附机理,合理解释页岩气超临界吸附特征,建立了DubininAstakhov和Langmuir-Freundlich(简称D-A和L-F)超临界吸附模型.采用等温吸附实验、低温液氮吸附实验和压汞实验进行模型验证和页岩孔隙分布特征研究,进而依据D-A和L-F模型阐明页岩气超临界吸附特征及意义.结果表明:D-A和L-F模型能够同时表征超临界下微孔充填式吸附和中、大孔单层吸附机理,合理解释页岩气高压负吸附现象;基于吸附速率压力敏感性可将页岩吸附分为4个阶段,各阶段具有不同的地质意义;过剩吸附量与绝对吸附量差异随埋深增大愈为显著,绝对吸附量评价吸附气含量更符合实际;微孔吸附能力约为中、大孔的2倍;灰分和水分对吸附起负作用,且对各类型孔隙的影响程度相当. (Hou X W, Wang M, Liu Y, Liu J N, Song Y.2016. Supercritical adsorption model of shale gas and its geological significance . Journal of China University of Mining & Technology, 45: 111-118). URL      [本文引用: 1]      摘要 为了表征各类型页岩孔隙吸附机理,合理解释页岩气超临界吸附特征,建立了DubininAstakhov和Langmuir-Freundlich(简称D-A和L-F)超临界吸附模型.采用等温吸附实验、低温液氮吸附实验和压汞实验进行模型验证和页岩孔隙分布特征研究,进而依据D-A和L-F模型阐明页岩气超临界吸附特征及意义.结果表明:D-A和L-F模型能够同时表征超临界下微孔充填式吸附和中、大孔单层吸附机理,合理解释页岩气高压负吸附现象;基于吸附速率压力敏感性可将页岩吸附分为4个阶段,各阶段具有不同的地质意义;过剩吸附量与绝对吸附量差异随埋深增大愈为显著,绝对吸附量评价吸附气含量更符合实际;微孔吸附能力约为中、大孔的2倍;灰分和水分对吸附起负作用,且对各类型孔隙的影响程度相当.
[32]	淮秀兰, Shigeru K.2004. 微通道内超临界二氧化碳的压降与传热特性 . 工程热物理学报, 25: 843-845 DOI      URL      [本文引用: 1]      摘要 进行了微通道内超临界CO2的 局部和平均传热与压降特性实验研究。结果表明,临界点附近物性参数的剧烈变 化使压降增大,但传热被大大强化。同时也发现,系统压力、质量流速及CO2温度对流动与传热特性有重要影响。在大 量实验数据的基础上,得出了冷却条件下水平微通道内超临界CO2强制对流换热关联式。 (Huai X L, Shigeru K.2004. Heat transfer and pressure drop of supercritical carbon dioxide in multi-port channels . Journal of Engineering Thermophysics, 25: 843-845). DOI      URL      [本文引用: 1]      摘要 进行了微通道内超临界CO2的 局部和平均传热与压降特性实验研究。结果表明,临界点附近物性参数的剧烈变 化使压降增大,但传热被大大强化。同时也发现,系统压力、质量流速及CO2温度对流动与传热特性有重要影响。在大 量实验数据的基础上,得出了冷却条件下水平微通道内超临界CO2强制对流换热关联式。
[33]	黄媛. 2008. 结合波形互相关技术的双差算法在地震定位中的应用探讨 . 国际地震动态, 4: 29-34 DOI      URL      [本文引用: 1]      摘要 本文致力于探讨在数字化地震监测大规模发展后,如何更好地将大量丰富的数字化波形信息应用到地震定位领域,从而更大程度地提高地震定位精度问题。笔者认为"结合波形互相关技术的双差定位算法"是一种比较有发展前景的方法,因此分别从基本理论、发展历程、台网实用化过程以及推广使用中可能存在的问题等角度进行分析,探讨该技术在地震定位领域中的发展方向及推广使用的可能性。 (Huang Y.2008. Study on the application and development of the DD algorithm with cross crosslation of waveform data in the earthquake location . Recent Developments in World Seismology, 4: 29-34). DOI      URL      [本文引用: 1]      摘要 本文致力于探讨在数字化地震监测大规模发展后,如何更好地将大量丰富的数字化波形信息应用到地震定位领域,从而更大程度地提高地震定位精度问题。笔者认为"结合波形互相关技术的双差定位算法"是一种比较有发展前景的方法,因此分别从基本理论、发展历程、台网实用化过程以及推广使用中可能存在的问题等角度进行分析,探讨该技术在地震定位领域中的发展方向及推广使用的可能性。
[34]	黄志龙, 郝石生. 1996. 天然气扩散与浓度封闭作用的研究 . 石油学报, 17: 36-41 DOI      URL      [本文引用: 1]      摘要 盖层是天然气聚集的必要条件，盖层封闭作用除物性封闭、压力封闭之外，还有一种重要的封闭机理，即浓度封闭。本文在研究盖层浓度封闭机理的基础上，建立了天然气通过盖层的扩散模型，提出烃浓度封闭的定量研究方法，并以川西平落坝构造为例，分析了几个气藏的浓度封闭特征，说明浓度封闭对气藏的保存起重要作用。 (Huang Z L, Hao S S.1996. Study on sealing of gas concentration and difussion in overlying gas reservoirs . Acta Petrolei Sinica, 17: 36-41). DOI      URL      [本文引用: 1]      摘要 盖层是天然气聚集的必要条件，盖层封闭作用除物性封闭、压力封闭之外，还有一种重要的封闭机理，即浓度封闭。本文在研究盖层浓度封闭机理的基础上，建立了天然气通过盖层的扩散模型，提出烃浓度封闭的定量研究方法，并以川西平落坝构造为例，分析了几个气藏的浓度封闭特征，说明浓度封闭对气藏的保存起重要作用。
[35]	汲广胜, 姚军. 2013. 孔隙网络模型的可视化方法及应用 . 科学技术与工程, 13: 3073-3077 DOI      URL      [本文引用: 1]      摘要 在微观渗流领域,孔隙网络模型的应用日渐广泛;但可视化成像方面研究的不足,使其应用受到极大的限制。基于四个基本假设,利用立体几何知识得到了喉道和孔隙体的确定方法。以孔隙网络模型数据文件为研究对象,将其应用于Berea砂岩的孔隙网络模型、复杂孔隙网络模型及孔隙网络模型中含油饱和度分布的可视化;由此将孔隙网络模型立体地呈现在人们面前。这样既可以展现同一个孔隙网络模型的孔隙体和喉道分布,又可以展现复杂孔隙网络模型的孔隙体和喉道分布,甚至还可以展现含油饱和度的分布状况,便于进行流动机理分析和微观剩余油分布分析,从而拓展了孔隙网络模型的应用范围。 (Ji G S, Yao J.2013. Visualization and applications of pore network models . Science Technology and Engineering, 13: 3073-3077). DOI      URL      [本文引用: 1]      摘要 在微观渗流领域,孔隙网络模型的应用日渐广泛;但可视化成像方面研究的不足,使其应用受到极大的限制。基于四个基本假设,利用立体几何知识得到了喉道和孔隙体的确定方法。以孔隙网络模型数据文件为研究对象,将其应用于Berea砂岩的孔隙网络模型、复杂孔隙网络模型及孔隙网络模型中含油饱和度分布的可视化;由此将孔隙网络模型立体地呈现在人们面前。这样既可以展现同一个孔隙网络模型的孔隙体和喉道分布,又可以展现复杂孔隙网络模型的孔隙体和喉道分布,甚至还可以展现含油饱和度的分布状况,便于进行流动机理分析和微观剩余油分布分析,从而拓展了孔隙网络模型的应用范围。
[36]	贾承造, 郑民, 张永峰. 2012. 中国非常规油气资源与勘探开发前景 . 石油勘探与开发, 39: 129-136 URL      摘要 By analysis of the characteristics of unconventional hydrocarbon resources, this paper assesses the potential for unconventional hydrocarbons in China, summarizes the key technical progress in exploration and development, and discusses the prospects and developing strategies of unconventional hydrocarbons. The resources of unconventional oil and gas in China are abundant. The recoverable tight gas is 8.8×1012-12.1×1012 m3, the recoverable shale gas is 15×1012-25×1012 m3, the recoverable coalbed methane is 10.9×1012 m3, the recoverable tight oil is 13×108-14×108 t, and the recoverable shale oil is 160×108 t. There is also some resource potential for oil sand. Such key techniques as the full-digital seismic exploration technique, low permeability and low resistivity reservoir identification technique have been developed and their applications in oil and gas fields obtained good results. Tight gas and tight oil are the most realistic to develop in China, and the development and utilization of coalbed methane and shale gas just begins. In the next ten or twenty years, the production of unconventional hydrocarbons in China will increase remarkably and play an important role in national hydrocarbon resources. (Jia C Z, Zheng M, Z Y F.2012. Influencing factors for the development of shale gas industry . Petroleum Exploration and Development, 39: 129-136). URL      摘要 By analysis of the characteristics of unconventional hydrocarbon resources, this paper assesses the potential for unconventional hydrocarbons in China, summarizes the key technical progress in exploration and development, and discusses the prospects and developing strategies of unconventional hydrocarbons. The resources of unconventional oil and gas in China are abundant. The recoverable tight gas is 8.8×1012-12.1×1012 m3, the recoverable shale gas is 15×1012-25×1012 m3, the recoverable coalbed methane is 10.9×1012 m3, the recoverable tight oil is 13×108-14×108 t, and the recoverable shale oil is 160×108 t. There is also some resource potential for oil sand. Such key techniques as the full-digital seismic exploration technique, low permeability and low resistivity reservoir identification technique have been developed and their applications in oil and gas fields obtained good results. Tight gas and tight oil are the most realistic to develop in China, and the development and utilization of coalbed methane and shale gas just begins. In the next ten or twenty years, the production of unconventional hydrocarbons in China will increase remarkably and play an important role in national hydrocarbon resources.
[37]	贾虎, 王瑞英, 杨洪波, 王锐, 张凡, 宋孝丹. 2010. 低渗砂岩储层正压射孔中水锁损害试验研究 . 石油钻探技术, 38: 76-79 DOI      URL      [本文引用: 1]      摘要 低渗砂岩水锁损害已成为高效开发低渗透油气藏的一大技术瓶颈,因 此,如何通过室内试验评价水锁损害显得尤为重要.国内外许多学者大都研究钻完井中"相对稳定"正压差或欠平衡钻井自吸作用造成的损害,忽视了正压射孔完井 中瞬时附加压力对孔道水锁损害的影响.通过试验研究了在瞬时附加压力下东海地区低渗砂岩的水锁损害,结果表明,瞬时正压差可增加损害程度25%左右.根据 低孔低渗透岩心水锁损害试验结果,提出了低孔低渗透气藏降低水锁损害的措施和建议. (Jia H, Wang R Y, Yang H B, Wang R, Zhang F, Song X D.2010. Experimental study of water-block from overbalance perforation in low-permeable sandstone . Petroleum Drilling Techniques, 38: 76-79). DOI      URL      [本文引用: 1]      摘要 低渗砂岩水锁损害已成为高效开发低渗透油气藏的一大技术瓶颈,因 此,如何通过室内试验评价水锁损害显得尤为重要.国内外许多学者大都研究钻完井中"相对稳定"正压差或欠平衡钻井自吸作用造成的损害,忽视了正压射孔完井 中瞬时附加压力对孔道水锁损害的影响.通过试验研究了在瞬时附加压力下东海地区低渗砂岩的水锁损害,结果表明,瞬时正压差可增加损害程度25%左右.根据 低孔低渗透岩心水锁损害试验结果,提出了低孔低渗透气藏降低水锁损害的措施和建议.
[38]	蒋裕强, 董大忠, 漆麟, 沈妍斐, 蒋婵, 何溥为. 2010. 页岩气储层的基本特征及其评价 . 天然气工业, 30: 7-12 DOI      URL      摘要 页岩气独特的赋存状态,"连续成藏"的聚集模式,区别于常规天然气储层的特征以及评价内容等决定了页岩气储层研究的特殊性。目前,国内针对页岩气储层特征及评价的工作开展得相对较少,需要建立相应的评价标准。在大量调研国外文献的基础上,综合利用四川盆地最新的浅井钻探和野外露头取样资料,从常规储层研究思路入手,详细分析了页岩气储层的基本特征(有机质特征、矿物组成、物性特征、储渗空间特征),进而总结了页岩气储层评价的主要内容;同时,借鉴美国页岩气勘探成功经验,从实际资料出发,筛选出有机质丰度、热成熟度、含气性等8大关键地质因素,进而提出了一套较为适用的储层评价标准。据该标准评价后认为,四川盆地下古生界筇竹寺组和龙马溪组2套海相黑色页岩具有良好的勘探开发前景。 (Jiang Y Q, Dong D Z, Qi L, Shen Y F, Jiang C, He F W.2010. Basic features and evaluation of shale gas reservoirs . Natural Gas Industry, 30: 7-12). DOI      URL      摘要 页岩气独特的赋存状态,"连续成藏"的聚集模式,区别于常规天然气储层的特征以及评价内容等决定了页岩气储层研究的特殊性。目前,国内针对页岩气储层特征及评价的工作开展得相对较少,需要建立相应的评价标准。在大量调研国外文献的基础上,综合利用四川盆地最新的浅井钻探和野外露头取样资料,从常规储层研究思路入手,详细分析了页岩气储层的基本特征(有机质特征、矿物组成、物性特征、储渗空间特征),进而总结了页岩气储层评价的主要内容;同时,借鉴美国页岩气勘探成功经验,从实际资料出发,筛选出有机质丰度、热成熟度、含气性等8大关键地质因素,进而提出了一套较为适用的储层评价标准。据该标准评价后认为,四川盆地下古生界筇竹寺组和龙马溪组2套海相黑色页岩具有良好的勘探开发前景。
[39]	久凯, 丁文龙, 李玉喜, 张金川, 曾维特. 2012. 黔北地区构造特征与下寒武统页岩气储层裂缝研究 . 天然气地球科学, 23: 797-803 URL      [本文引用: 1]      摘要 裂缝发育程度是页岩气储层的主控因素之一,而裂缝的形成与构造特征密切相关。在对黔北地区构造特征分析的基础上,对该区下寒武统牛蹄塘组黑色页岩地层的裂缝特征及分布进行了研究。认为黔北地区褶皱、断裂发育复杂,褶皱整体以隔槽式为主,断裂是在多个走向断裂体系相互切割、联合下形成的,各断裂体系的主形成期具有差异性;构造裂缝是下寒武统黑色页岩层段的主要裂缝类型,而且以水平缝与低角度缝所占比例大。裂缝发育区的分布主要受到断裂带的控制,其中以北东向和北北东向断裂体系的控制作用最为显著,裂缝发育区多位于断裂带的末端、拐点处、不同走向断裂带相交处和相同走向的断层夹持带等应力集中部位。其次,在背斜的高陡部位,也有利于裂缝的形成。 (Jiu K, Ding W L, Li Y X, Zhang J C, Zeng W T.2012. Structural features in Northern Guizhou area and reservoir fracture of lower Cambrian shale gas . Natural Gas Geoscience, 23: 797-803). URL      [本文引用: 1]      摘要 裂缝发育程度是页岩气储层的主控因素之一,而裂缝的形成与构造特征密切相关。在对黔北地区构造特征分析的基础上,对该区下寒武统牛蹄塘组黑色页岩地层的裂缝特征及分布进行了研究。认为黔北地区褶皱、断裂发育复杂,褶皱整体以隔槽式为主,断裂是在多个走向断裂体系相互切割、联合下形成的,各断裂体系的主形成期具有差异性;构造裂缝是下寒武统黑色页岩层段的主要裂缝类型,而且以水平缝与低角度缝所占比例大。裂缝发育区的分布主要受到断裂带的控制,其中以北东向和北北东向断裂体系的控制作用最为显著,裂缝发育区多位于断裂带的末端、拐点处、不同走向断裂带相交处和相同走向的断层夹持带等应力集中部位。其次,在背斜的高陡部位,也有利于裂缝的形成。
[40]	李传乐, 王安仕, 李文魁. 2001. 国外油气井"层内爆炸"增产技术概述及分析 . 石油钻采工艺, 5: 77-78 DOI      URL      [本文引用: 1]      摘要 液体药用油气井增产技术时，其组分是NH4NO3（氧化剂），甘油（燃烧剂），水（溶剂），由于其自身燃烧特性，如果先经雾化过程后再燃烧，相对于固体药燃烧缓慢，燃烧过程持续时间长，可以加大药量，提高压裂效果，固体发射药，国内一次施工最多装填100kg，需采用分段延迟燃烧，最高压力100MPa，压力持续时间最长只能达1s，裂缝长度为2－8m，而液体药却能装填500－1000kg，最高压力60MPa，压力持续时间可达40s左右；液体药压裂的裂缝长度可达25－50m，由于液体药压裂裂缝长度大，油气增产效果显著。 (Li C L, Wang A S, Li W K.2001. Foreign oil and gas well "layer explosion" technical overview and analysis of yield . Oil Drilling & Production Technology, 5: 77-78). DOI      URL      [本文引用: 1]      摘要 液体药用油气井增产技术时，其组分是NH4NO3（氧化剂），甘油（燃烧剂），水（溶剂），由于其自身燃烧特性，如果先经雾化过程后再燃烧，相对于固体药燃烧缓慢，燃烧过程持续时间长，可以加大药量，提高压裂效果，固体发射药，国内一次施工最多装填100kg，需采用分段延迟燃烧，最高压力100MPa，压力持续时间最长只能达1s，裂缝长度为2－8m，而液体药却能装填500－1000kg，最高压力60MPa，压力持续时间可达40s左右；液体药压裂的裂缝长度可达25－50m，由于液体药压裂裂缝长度大，油气增产效果显著。
[41]	李建忠, 李登华, 董大忠, 王社教. 2012. 中美页岩气成藏条件、分布特征差异研究与启示 . 中国工程科学, 14: 56-63 DOI      URL      [本文引用: 2]      摘要 美国页岩气大多为海相热成因型,产气页岩主要分布在前陆和克拉通盆地的泥盆—石炭系,埋藏深度一般为1 500～3 500 m。我国页岩分为海相、海陆过渡相与煤系、湖相三类,其中海相页岩主要发育在坳拉槽和克拉通盆地的下古生界,富有机质集中段分布稳定,热成熟度偏高,有较高的含气量,勘探前景最好;海陆过渡相与煤系页岩主要发育在大型坳陷和前陆盆地,层系以石炭系—侏罗系为主,没有明显的富有机质集中段,含气量差别较大,勘探潜力有待落实;湖相页岩主要发育在中、新生代陆相盆地,富有机质集中段厚度大,成熟度较高的凹陷中心区可能具有一定资源前景。预测我国页岩气勘探将经历较长的探索期,未来年产量可达500亿～600亿m3规模。 (Li J Z, Li D H, Dong D Z, Wang S J.2012. Comparison and enlightenment on formation condition and distribution characteristics of shale gas between China and U.S. Engineering Sciences, 14: 56-63). DOI      URL      [本文引用: 2]      摘要 美国页岩气大多为海相热成因型,产气页岩主要分布在前陆和克拉通盆地的泥盆—石炭系,埋藏深度一般为1 500～3 500 m。我国页岩分为海相、海陆过渡相与煤系、湖相三类,其中海相页岩主要发育在坳拉槽和克拉通盆地的下古生界,富有机质集中段分布稳定,热成熟度偏高,有较高的含气量,勘探前景最好;海陆过渡相与煤系页岩主要发育在大型坳陷和前陆盆地,层系以石炭系—侏罗系为主,没有明显的富有机质集中段,含气量差别较大,勘探潜力有待落实;湖相页岩主要发育在中、新生代陆相盆地,富有机质集中段厚度大,成熟度较高的凹陷中心区可能具有一定资源前景。预测我国页岩气勘探将经历较长的探索期,未来年产量可达500亿～600亿m3规模。
[42]	李君辉. 2015. 基于微震监测与地应力分析的低渗油藏压裂致缝解释研究 . [硕士论文]. 长春: 吉林大学 URL      [本文引用: 2]      摘要 近年来，低渗透储层油气藏逐渐成为世界石油产量增加的重要组成部分。由于低渗透油气储层具有“三低”（低丰度、低压、低产）的特点，其开发难度大，水力压裂微震监测技术是目前国内外比较流行的一种改造低渗透油气田的有效方法。准确地获取压裂过程中产生的裂缝方位和几何形状等信息可以优化井网布置、优化注水方案、对油气产量进行评估等，有效地指导油气田勘探开发。现场油气田压裂过程中，准确地掌握水力裂缝的形态至关重要。目前，国内在水力裂缝监测方面开展了很多工作，但在裂缝解释方面的研究较少。本文基于水力压裂微震监测裂缝技术，以准确解释水力压裂中裂缝的方位、几何参数信息为研究目标，结合压裂现场地应力分析对微震监测反演出的震源点进行裂缝轮廓描绘，确定出裂缝的延伸方向，并对其做出合理的解释。本文提出的裂缝解释方法在现场压裂实验裂缝解释中取得了理想的效果。 本文围绕选题的依据和意义分别分析了水力压裂裂缝监测技术和微地震裂缝监测技术在国内外的研究现状。比较直接近井筒裂缝监测、分布式声传感裂缝监测和微震裂缝监测等方法的裂缝监测能力后，选择微震监测作为本文获取裂缝信息的方法。 为实现课题的研究目标，本文首先进行了微震裂缝监测技术的研究，分别对微震监测的理论基础、微震监测方法选择及微震监测系统进行了详细叙述，对微震裂缝监测系统进行了总体设计。由于水力压裂裂缝的形态和方位与地应力分布密切相关，本文对地应力相关技术进行了研究。从地应力的基本概念入手，总结了其分布规律、影响因素及获取方法。本文重点分析了压裂裂缝产生机理和其形态的影响因素。从力学的角度研究了压裂裂缝的造缝机理，在理论上给出产生垂直裂缝与水平裂缝的条件。在裂缝形态的众多影响因素中，系统地分析了地应力、断层、天然裂缝以及井底压力曲线对水力裂缝形态的影响。最后，针对山西省娄烦县开展的现场水力压裂微震监测裂缝实验，对压裂区域现场地应力进行了详细分析，通过实验区域的现场地应力状态与微震监测结果相结合确定出了裂缝的延伸方向和轮廓，计算出裂缝几何参数。现场压裂实验中，通过地应力状态分析出的裂缝延伸方向与微震监测获取的裂缝方向是相符的。 (Li J H.2015. Research on hydraulic farcture interpretation in low permeability reservoirs based on micro-seismic monitoring and in-situ stress analyzing . [Master Thesis]. Changchun: Jilin University). URL      [本文引用: 2]      摘要 近年来，低渗透储层油气藏逐渐成为世界石油产量增加的重要组成部分。由于低渗透油气储层具有“三低”（低丰度、低压、低产）的特点，其开发难度大，水力压裂微震监测技术是目前国内外比较流行的一种改造低渗透油气田的有效方法。准确地获取压裂过程中产生的裂缝方位和几何形状等信息可以优化井网布置、优化注水方案、对油气产量进行评估等，有效地指导油气田勘探开发。现场油气田压裂过程中，准确地掌握水力裂缝的形态至关重要。目前，国内在水力裂缝监测方面开展了很多工作，但在裂缝解释方面的研究较少。本文基于水力压裂微震监测裂缝技术，以准确解释水力压裂中裂缝的方位、几何参数信息为研究目标，结合压裂现场地应力分析对微震监测反演出的震源点进行裂缝轮廓描绘，确定出裂缝的延伸方向，并对其做出合理的解释。本文提出的裂缝解释方法在现场压裂实验裂缝解释中取得了理想的效果。 本文围绕选题的依据和意义分别分析了水力压裂裂缝监测技术和微地震裂缝监测技术在国内外的研究现状。比较直接近井筒裂缝监测、分布式声传感裂缝监测和微震裂缝监测等方法的裂缝监测能力后，选择微震监测作为本文获取裂缝信息的方法。 为实现课题的研究目标，本文首先进行了微震裂缝监测技术的研究，分别对微震监测的理论基础、微震监测方法选择及微震监测系统进行了详细叙述，对微震裂缝监测系统进行了总体设计。由于水力压裂裂缝的形态和方位与地应力分布密切相关，本文对地应力相关技术进行了研究。从地应力的基本概念入手，总结了其分布规律、影响因素及获取方法。本文重点分析了压裂裂缝产生机理和其形态的影响因素。从力学的角度研究了压裂裂缝的造缝机理，在理论上给出产生垂直裂缝与水平裂缝的条件。在裂缝形态的众多影响因素中，系统地分析了地应力、断层、天然裂缝以及井底压力曲线对水力裂缝形态的影响。最后，针对山西省娄烦县开展的现场水力压裂微震监测裂缝实验，对压裂区域现场地应力进行了详细分析，通过实验区域的现场地应力状态与微震监测结果相结合确定出了裂缝的延伸方向和轮廓，计算出裂缝几何参数。现场压裂实验中，通过地应力状态分析出的裂缝延伸方向与微震监测获取的裂缝方向是相符的。
[43]	李立. 2010. 国内第一口页岩气井"吐气" . 石油钻采工艺, 89-89 URL      [本文引用: 1]      摘要 正9月10日,四川盆地威201井在下古生界寒武系黑色页岩段喜获日产1.08×104m3工业气流。威201井是西南油气田分公司于2009年12月部署的国内第一口页岩气评价井,钻探目的是获取下古 (Li L.2010. The first domestic shale gas wells "out " . Oil Drilling & Production Technology, 89-89). URL      [本文引用: 1]      摘要 正9月10日,四川盆地威201井在下古生界寒武系黑色页岩段喜获日产1.08×104m3工业气流。威201井是西南油气田分公司于2009年12月部署的国内第一口页岩气评价井,钻探目的是获取下古
[44]	李录贤, 王铁军. 2005. 扩展有限元法(XFEM)及其应用 . 力学进展, 35: 5-20 DOI      URL      [本文引用: 1]      摘要 扩展有限元法(extendedfiniteelementmethod,XFEM)是1999年提出的一种求解不连续力学问题的数值方法,它继承了常规有限元法(CFEM)的所有优点,在模拟界面、裂纹生长、复杂流体等不连续问题时特别有效,短短几年间得到了快速发展与应用.XFEM与CFEM的最根本区别在于,它所使用的网格与结构内部的几何或物理界面无关,从而克服了在诸如裂纹尖端等高应力和变形集中区进行高密度网格剖分所带来的困难,模拟裂纹生长时也无需对网格进行重新剖分.重点介绍XFEM的基本原理、实施步骤及应用实例等,并进行必要的评述.单位分解概念保证了XFEM的收敛,基于此,XFEM通过改进单元的形状函数使之包含问题不连续性的基本成分,从而放松对网格密度的过分要求.水平集法是XFEM中常用的确定内部界面位置和跟踪其生长的数值技术,任何内部界面可用它的零水平集函数表示.第2和第3节分别简要介绍单位分解法和水平集法;第4节和第5节介绍XFEM的基本思想、详细实施步骤和若干应用实例,同时修正了以往文献中的一些不妥之处;最后,初步展望了该领域尚需进一步研究的课题. (Li L X, Wang T J.2005. The extended finite element method and its applications . Advances in Mechanics, 35: 5-20). DOI      URL      [本文引用: 1]      摘要 扩展有限元法(extendedfiniteelementmethod,XFEM)是1999年提出的一种求解不连续力学问题的数值方法,它继承了常规有限元法(CFEM)的所有优点,在模拟界面、裂纹生长、复杂流体等不连续问题时特别有效,短短几年间得到了快速发展与应用.XFEM与CFEM的最根本区别在于,它所使用的网格与结构内部的几何或物理界面无关,从而克服了在诸如裂纹尖端等高应力和变形集中区进行高密度网格剖分所带来的困难,模拟裂纹生长时也无需对网格进行重新剖分.重点介绍XFEM的基本原理、实施步骤及应用实例等,并进行必要的评述.单位分解概念保证了XFEM的收敛,基于此,XFEM通过改进单元的形状函数使之包含问题不连续性的基本成分,从而放松对网格密度的过分要求.水平集法是XFEM中常用的确定内部界面位置和跟踪其生长的数值技术,任何内部界面可用它的零水平集函数表示.第2和第3节分别简要介绍单位分解法和水平集法;第4节和第5节介绍XFEM的基本思想、详细实施步骤和若干应用实例,同时修正了以往文献中的一些不妥之处;最后,初步展望了该领域尚需进一步研究的课题.
[45]	李鹭光. 2004. 四川盆地低渗透气藏开发技术研究 . [博士论文]. 成都: 西南石油大学 URL      摘要 随着全世界对天然气能源需求量的不断增大，常规天然气藏的产量和储采比都显示出日益降低的趋势，非常规天然气资源被认为是最有希望的能源补充，因此加快低渗气藏的勘探开发是本世纪能源工业发展的必然趋势。 经过四十余年的勘探开发，四川已经成为了我国重要的天然气工业基地之一。随着四川和西南地区经济的不断发展，对天然气的需求量越来越大，但是，四川盆地气藏储层具有低渗、致密的大背景，低渗、特低渗储层在四川盆地气藏中占有相当比例，在现有剩余可采储量中，有1／3以上属于低渗、特低渗储量。这类气藏开发工艺复杂、储量动用难度高、稳产条件差、单井产能低、开采综合效益差。为了从根本上解决四川盆地低渗气藏开发这一难题，本文运用地震、测井、油藏工程、渗流力学、数值计算和实验研究等技术和理论开展四川盆地低渗透气藏储层特征、低渗透储层气体渗流机理、低渗透气藏试井分析方法、低渗透气藏储层改造技术、低渗透气藏储层保护技术及水平井、欠平衡钻井等方面的理论、实验和应用研究，并结合四川盆地低渗气藏已有开发技术和应用成果，进行了系统分析和总结，形成了一套适合四川碳酸盐岩和砂岩低渗透气藏的开发技术体系，为四川盆地低渗透气藏的高效开发打下了必要的基础。本文取得的主要研究成果如下： (1)在对四川典型低渗透气藏储层岩性、孔隙结构特征、裂缝类型和分布特征等研究的基础上，以岩石物性参数、孔隙类型和孔隙结构参数为主要定量依据，并综合考虑裂缝发育程度及其对储层渗透能力的改善作用，提出了将四川盆地低渗透储层划分为低渗、特低渗两大类，该划分既符合四川盆地低渗透气藏的实际情况，又能较好地指导四川盆地低渗透气藏的合理开发。 (2)首次建立了由宏观裂缝、微细裂缝和显微裂缝及孔隙喉道共同组成低渗储层四级渗滤通道的渗流模式，基质孔隙喉道和显微裂缝是储层储渗的基础，储层产能及渗流特征决定于四级渗流通道的搭配关系。该模式对低渗气藏的开发具有重要的指导意义。 (3)针对四川低渗储层特点，充分利用构造分析、地震反演、模式识别等储层预测技术，提出了裂缝发育综合强度指数评价等一整套裂缝和储层横向预测方法和技术，进一步完善和发展了低渗透储层评价和有利区块预测技术。这些技术在平落坝须二、白马～松花蓬莱镇和五百梯石炭系气藏裂缝～孔隙发育区预测工作中取得了较显著的效果。 (4)对低渗储层单相和残余水条件下气体低速非达西渗流机理进行了较为全面和深入的实验研究，掌握了低渗储层单相气体和残余水条件下气体的低速非达西渗流特征。该 四川盆地低渗透气藏开发技术研究 项成果对低渗气藏开发技术的研究具有重要的指导意义。 (5)在低渗储层低速非达西渗流机理研究的基础上，引入启动压差和临界压力梯度 两个特征参数，建立了描述低渗介质低速非达西渗流的数学模型，并成功实现了求解，在 此基础上，建立了低渗透气藏的试井分析方法，从而为低渗透气藏开发的动态监测和储层 改造的评层选井提供了技术保证。 (6)通过对不同类型低渗透储层酸化的机理研究，提出了低渗透储层“通缝扩喉” 改造的新思路，即针对孔隙胶结物和裂缝充填物矿物成分的特点，合理选择不同酸液配方 和施工参数进行微观基质酸化，从而提高基质酸化的效果。 (7)针对四川盆地低渗白云岩储层的地质特点，开发了三套新型的深穿透酸压裂工 作液体系(新型胶凝酸、助排剂和降滤失酸)。并研究配套了以交替泵注为主的深穿透酸 压工艺技术。该项成果为四川盆地低渗透碳酸盐岩储层的增产改造提供了新的工艺技术手 段。 (8)针对八角场气田香四气藏、平落坝须二气藏和白马一松华地区的蓬莱镇气藏以 砂泥岩薄互层为主的厚层碎屑岩储层，从施工设计、泵注技术和全缝支撑等方面进行了研 究，形成了一套在这类储层中有较好效果的高缝压裂和全缝支撑技术。现场应用效果显著。 (9)针对四川低渗气田纵向上具有多产层的特点，研制成功并配套试验完善了两套 适合不同井况的分层改造、分(合)层开采的增产措施及其施工技术，取得了良好的工艺 效果。 (10)在储层潜在损害因素研究的基础上，对钻井完井液、储层改造工作液损害储层 机理进行了全面评价，为钻井及储层改造过程中四川盆地低渗储层保护技术路线的制定和 保护措施的优化奠定了坚实的基础。 (11)针对四川盆地碳酸盐岩和碎屑岩低渗气藏的地质特征，筛选和研制出了有利于 储层保护的钻井液和储层改造工作液配方，形成了适合四川盆地特点的低渗气藏储层保护 特色技术，在应用中已经取得了较明显的效果. (12)欠平衡钻井技术在邓西3井、渔南1井及井浅2井取得重大勘探突破表明，在 四川盆地低渗气藏勘探开发过程中，欠平衡钻井配套技术对于发现和保护油气层具有十分 显著的效果，从而为四川盆地低渗透气藏的勘探和开发取得全面突破开辟了一条新的、具 有重要指导意义的途径。 (13)水平井技术是四川盆地低渗气藏实现高效开发的必需技术。磨75一H水平井的 成功完成，并获得显著的技术经济效益，必将推动水平井技术在四川盆地低渗气藏开发中 四川盆地低渗透气藏开发技术研究 的? (Li L G.2004. Research for the development technique of low permeability gas reservoirs in Sichuan basin . [PhD Thesis]. Chengdu: Southwest Petroleum University). URL      摘要 随着全世界对天然气能源需求量的不断增大，常规天然气藏的产量和储采比都显示出日益降低的趋势，非常规天然气资源被认为是最有希望的能源补充，因此加快低渗气藏的勘探开发是本世纪能源工业发展的必然趋势。 经过四十余年的勘探开发，四川已经成为了我国重要的天然气工业基地之一。随着四川和西南地区经济的不断发展，对天然气的需求量越来越大，但是，四川盆地气藏储层具有低渗、致密的大背景，低渗、特低渗储层在四川盆地气藏中占有相当比例，在现有剩余可采储量中，有1／3以上属于低渗、特低渗储量。这类气藏开发工艺复杂、储量动用难度高、稳产条件差、单井产能低、开采综合效益差。为了从根本上解决四川盆地低渗气藏开发这一难题，本文运用地震、测井、油藏工程、渗流力学、数值计算和实验研究等技术和理论开展四川盆地低渗透气藏储层特征、低渗透储层气体渗流机理、低渗透气藏试井分析方法、低渗透气藏储层改造技术、低渗透气藏储层保护技术及水平井、欠平衡钻井等方面的理论、实验和应用研究，并结合四川盆地低渗气藏已有开发技术和应用成果，进行了系统分析和总结，形成了一套适合四川碳酸盐岩和砂岩低渗透气藏的开发技术体系，为四川盆地低渗透气藏的高效开发打下了必要的基础。本文取得的主要研究成果如下： (1)在对四川典型低渗透气藏储层岩性、孔隙结构特征、裂缝类型和分布特征等研究的基础上，以岩石物性参数、孔隙类型和孔隙结构参数为主要定量依据，并综合考虑裂缝发育程度及其对储层渗透能力的改善作用，提出了将四川盆地低渗透储层划分为低渗、特低渗两大类，该划分既符合四川盆地低渗透气藏的实际情况，又能较好地指导四川盆地低渗透气藏的合理开发。 (2)首次建立了由宏观裂缝、微细裂缝和显微裂缝及孔隙喉道共同组成低渗储层四级渗滤通道的渗流模式，基质孔隙喉道和显微裂缝是储层储渗的基础，储层产能及渗流特征决定于四级渗流通道的搭配关系。该模式对低渗气藏的开发具有重要的指导意义。 (3)针对四川低渗储层特点，充分利用构造分析、地震反演、模式识别等储层预测技术，提出了裂缝发育综合强度指数评价等一整套裂缝和储层横向预测方法和技术，进一步完善和发展了低渗透储层评价和有利区块预测技术。这些技术在平落坝须二、白马～松花蓬莱镇和五百梯石炭系气藏裂缝～孔隙发育区预测工作中取得了较显著的效果。 (4)对低渗储层单相和残余水条件下气体低速非达西渗流机理进行了较为全面和深入的实验研究，掌握了低渗储层单相气体和残余水条件下气体的低速非达西渗流特征。该 四川盆地低渗透气藏开发技术研究 项成果对低渗气藏开发技术的研究具有重要的指导意义。 (5)在低渗储层低速非达西渗流机理研究的基础上，引入启动压差和临界压力梯度 两个特征参数，建立了描述低渗介质低速非达西渗流的数学模型，并成功实现了求解，在 此基础上，建立了低渗透气藏的试井分析方法，从而为低渗透气藏开发的动态监测和储层 改造的评层选井提供了技术保证。 (6)通过对不同类型低渗透储层酸化的机理研究，提出了低渗透储层“通缝扩喉” 改造的新思路，即针对孔隙胶结物和裂缝充填物矿物成分的特点，合理选择不同酸液配方 和施工参数进行微观基质酸化，从而提高基质酸化的效果。 (7)针对四川盆地低渗白云岩储层的地质特点，开发了三套新型的深穿透酸压裂工 作液体系(新型胶凝酸、助排剂和降滤失酸)。并研究配套了以交替泵注为主的深穿透酸 压工艺技术。该项成果为四川盆地低渗透碳酸盐岩储层的增产改造提供了新的工艺技术手 段。 (8)针对八角场气田香四气藏、平落坝须二气藏和白马一松华地区的蓬莱镇气藏以 砂泥岩薄互层为主的厚层碎屑岩储层，从施工设计、泵注技术和全缝支撑等方面进行了研 究，形成了一套在这类储层中有较好效果的高缝压裂和全缝支撑技术。现场应用效果显著。 (9)针对四川低渗气田纵向上具有多产层的特点，研制成功并配套试验完善了两套 适合不同井况的分层改造、分(合)层开采的增产措施及其施工技术，取得了良好的工艺 效果。 (10)在储层潜在损害因素研究的基础上，对钻井完井液、储层改造工作液损害储层 机理进行了全面评价，为钻井及储层改造过程中四川盆地低渗储层保护技术路线的制定和 保护措施的优化奠定了坚实的基础。 (11)针对四川盆地碳酸盐岩和碎屑岩低渗气藏的地质特征，筛选和研制出了有利于 储层保护的钻井液和储层改造工作液配方，形成了适合四川盆地特点的低渗气藏储层保护 特色技术，在应用中已经取得了较明显的效果. (12)欠平衡钻井技术在邓西3井、渔南1井及井浅2井取得重大勘探突破表明，在 四川盆地低渗气藏勘探开发过程中，欠平衡钻井配套技术对于发现和保护油气层具有十分 显著的效果，从而为四川盆地低渗透气藏的勘探和开发取得全面突破开辟了一条新的、具 有重要指导意义的途径。 (13)水平井技术是四川盆地低渗气藏实现高效开发的必需技术。磨75一H水平井的 成功完成，并获得显著的技术经济效益，必将推动水平井技术在四川盆地低渗气藏开发中 四川盆地低渗透气藏开发技术研究 的?
[46]	李明, 顾安忠, 鲁雪生, 汪荣顺. 2003. 吸附势理论在甲烷临界温度以上吸附中的应用 . 天然气化工, 28: 28-31 DOI      URL      [本文引用: 1]      摘要 使用吸附势理论对甲烷临界温度以上在微孔活性炭上的吸附平衡进行了研究。针对吸附势理论描述气体临界温度以上吸附所面临的问题,深入考察了各种计算吸附相密度和虚拟饱和蒸汽压的方法对吸附平衡预测结果的影响。研究表明,吸附势理论可以在较宽的范围内描述甲烷临界温度以上的吸附平衡,模型预测结果受吸附相密度计算方法的影响较小,但对于虚拟饱和蒸汽压的计算方法较敏感,其中Reich等采用的经验式更为准确。 (Li M, Gu A Z, Lu X S, Wang R S.2003. Study on methane adsorption above critical temperature by adsorption potential theory , Natural Gas Chemical Industry, 28: 28-31). DOI      URL      [本文引用: 1]      摘要 使用吸附势理论对甲烷临界温度以上在微孔活性炭上的吸附平衡进行了研究。针对吸附势理论描述气体临界温度以上吸附所面临的问题,深入考察了各种计算吸附相密度和虚拟饱和蒸汽压的方法对吸附平衡预测结果的影响。研究表明,吸附势理论可以在较宽的范围内描述甲烷临界温度以上的吸附平衡,模型预测结果受吸附相密度计算方法的影响较小,但对于虚拟饱和蒸汽压的计算方法较敏感,其中Reich等采用的经验式更为准确。
[47]	李庆辉, 陈勉, 金衍, 侯冰, 张保卫. 2012. 页岩脆性的室内评价方法及改进 . 岩石力学与工程学报, 31: 1680-1685 URL      [本文引用: 1]      摘要 Brittleness of gas shale reservoir is of vital significance to testing and evaluating the brittleness of shale. In view of this，through literature investigation and lab tests，20 kinds of basic methods for testing brittleness，including methods based on strength，hardness and ruggedness are summarized，focusing on discussing testing theory and lab method for shale brittleness based on complete stress-strain characteristics. Considering brittleness fracture mechanism and fracture feature，brittleness of shale is defined as a synthetic characteristic of material，affected by its heterogeneity and external testing environment. To identify brittleness of shale，complete stress-strain curve consisted of pre-peak and post-peak parts should both be considered. To improve the accuracy of brittleness evaluation，complete stress-strain testing in underground environment should be simulated. Capacity for resisting inelastic deformation before rupture and losing rate of bearing capacity after rupture are the main mechanical performance of brittleness. To improve the evaluation accuracy，existing mechanical testing schemes are also modified. Meanwhile，brittleness characteristics of black shale from South China is tested through true triaxial rock mechanics tests and then evaluated using improved methods. (Li Q H, Chen M, Jin Y, Hou B, Zhang B W. Indoor evaluation method for shale brittleness and improvement . Chinese Journal of Rock Mechanics and Engineering, 31: 1680-1685). URL      [本文引用: 1]      摘要 Brittleness of gas shale reservoir is of vital significance to testing and evaluating the brittleness of shale. In view of this，through literature investigation and lab tests，20 kinds of basic methods for testing brittleness，including methods based on strength，hardness and ruggedness are summarized，focusing on discussing testing theory and lab method for shale brittleness based on complete stress-strain characteristics. Considering brittleness fracture mechanism and fracture feature，brittleness of shale is defined as a synthetic characteristic of material，affected by its heterogeneity and external testing environment. To identify brittleness of shale，complete stress-strain curve consisted of pre-peak and post-peak parts should both be considered. To improve the accuracy of brittleness evaluation，complete stress-strain testing in underground environment should be simulated. Capacity for resisting inelastic deformation before rupture and losing rate of bearing capacity after rupture are the main mechanical performance of brittleness. To improve the evaluation accuracy，existing mechanical testing schemes are also modified. Meanwhile，brittleness characteristics of black shale from South China is tested through true triaxial rock mechanics tests and then evaluated using improved methods.
[48]	李庆辉, 陈勉, 金衍, 侯冰, 张家振. 2012. 页岩气储层岩石力学特性及脆性评价 . 石油钻探技术, 40: 17-22 DOI      URL      [本文引用: 2]      摘要 页岩气储层的岩石力学特性对开发影响极大,进行页岩破坏机理、力学特性和脆性评价方面的研究,可以为页岩气钻井和压裂设计工作提供技术支撑。采用室内试验和测井分析相结合的方法,在黑色页岩力学特性研究的基础上,分析了其脆性破坏特征及影响因素,提出了一种利用岩石弹性参数和矿物组成综合评价页岩脆性的方法,并介绍了利用测井资料计算单井脆性剖面的流程。研究表明,页岩普遍具有脆性破坏的特征,破坏类型与页岩种类、取心深度、取心方位和加载条件相关,低围压下标准试样以劈裂式破坏为主,全应力应变曲线经历极短的塑性屈服阶段即发生破坏,高围压时多出现双剪式和单剪式破坏,页岩的脆性与试样的弹性参数和矿物组成关系密切。实例分析表明,脆性特征影响压裂效果,与压裂造缝能力和产气情况吻合良好。综合脆性评价既是储层岩石力学特性分析的重要内容,也是压裂选层的重要依据。 (Li Q H, Chen M, Jin Y, Hou B, Zhang J Z.2012. Rock mechanical properties and brittleness evaluation of shale gas reservoir . Petroleum Drilling Techniques, 40: 17-22). DOI      URL      [本文引用: 2]      摘要 页岩气储层的岩石力学特性对开发影响极大,进行页岩破坏机理、力学特性和脆性评价方面的研究,可以为页岩气钻井和压裂设计工作提供技术支撑。采用室内试验和测井分析相结合的方法,在黑色页岩力学特性研究的基础上,分析了其脆性破坏特征及影响因素,提出了一种利用岩石弹性参数和矿物组成综合评价页岩脆性的方法,并介绍了利用测井资料计算单井脆性剖面的流程。研究表明,页岩普遍具有脆性破坏的特征,破坏类型与页岩种类、取心深度、取心方位和加载条件相关,低围压下标准试样以劈裂式破坏为主,全应力应变曲线经历极短的塑性屈服阶段即发生破坏,高围压时多出现双剪式和单剪式破坏,页岩的脆性与试样的弹性参数和矿物组成关系密切。实例分析表明,脆性特征影响压裂效果,与压裂造缝能力和产气情况吻合良好。综合脆性评价既是储层岩石力学特性分析的重要内容,也是压裂选层的重要依据。
[49]	李淑华, 朱晏萱, 毕启玲. 2008. H$_{2}$S和CO$_{2}$对油管的腐蚀机理及现有防腐技术的特点 . 石油矿场机械, 37: 90-93 DOI      URL      [本文引用: 1]      摘要 阐述了当前油气田井下油管的腐蚀现状、腐蚀机理及不同防腐措施的特点,详细介绍H2S和CO2对油管的腐蚀机理以及各种防腐措施的采用对油管起到的防护作用. (Li S, Zhu Y, Bi Q.2008. The corrosion and corrosion protection of the tubing in gas wells . Oil Field Equipment, 37: 90-93). DOI      URL      [本文引用: 1]      摘要 阐述了当前油气田井下油管的腐蚀现状、腐蚀机理及不同防腐措施的特点,详细介绍H2S和CO2对油管的腐蚀机理以及各种防腐措施的采用对油管起到的防护作用.
[50]	李武广, 钟兵, 杨洪志, 杨学锋, 胡志明, 陈满. 2016. 页岩储层基质气体扩散能力评价新方法 . 石油学报, 37: 88-96. DOI      URL      [本文引用: 2]      摘要 为了更好地评价页岩气在储层基质岩块中的流动能力,以便准确地预测页岩气水平井产量变化规律,以Fick第一定律为基础,依据物质平衡方程,建立了考虑在压差引起浓度差的作用下气体广义扩散能力评价模型,并提出了页岩气体扩散速率系数和扩散效率计算方法。在此基础上,设计了相应的页岩气体扩散能力评价实验装置和实验流程,通过在不同实验条件下的气体扩散实验,获得了随时间变化的气体累积扩散量,利用实验数据计算获得了页岩气体扩散系数、扩散速率系数、扩散效率及流动系数,进而对页岩扩散能力的影响因素进行分析。研究结果表明,页岩基质中的气体主要以广义扩散的方式为压裂裂缝中气体流动提供重要补充;页岩渗透率决定着页岩气体扩散能力大小,渗透率越大,扩散能力越强,而孔隙度与页岩扩散能力相关性小。 (Li W G, Zhong B, Yang H Z, Yang X F, Hu Z M, Chen M.2016. A new method for gas diffusivity evaluation in matrix rocks of shale reservoir . Acta Petrolei Sinica, 37: 88-96). DOI      URL      [本文引用: 2]      摘要 为了更好地评价页岩气在储层基质岩块中的流动能力,以便准确地预测页岩气水平井产量变化规律,以Fick第一定律为基础,依据物质平衡方程,建立了考虑在压差引起浓度差的作用下气体广义扩散能力评价模型,并提出了页岩气体扩散速率系数和扩散效率计算方法。在此基础上,设计了相应的页岩气体扩散能力评价实验装置和实验流程,通过在不同实验条件下的气体扩散实验,获得了随时间变化的气体累积扩散量,利用实验数据计算获得了页岩气体扩散系数、扩散速率系数、扩散效率及流动系数,进而对页岩扩散能力的影响因素进行分析。研究结果表明,页岩基质中的气体主要以广义扩散的方式为压裂裂缝中气体流动提供重要补充;页岩渗透率决定着页岩气体扩散能力大小,渗透率越大,扩散能力越强,而孔隙度与页岩扩散能力相关性小。
[51]	李小刚, 罗丹, 李宇, 张亚明. 2013. 同步压裂缝网形成机理研究进展 . 新疆石油地质, 34: 228-231 URL      摘要 同步压裂技术是实现页岩气、煤层气等非常规天然气储集层改造的新兴技术,揭示裂缝延伸的力学机理是进行施工参数优化的基础。研究表明,多裂缝同步延伸诱导应力场及其天然裂缝作用机制共同确定了同步压裂裂缝展布情况;裂缝网络工程方法是目前研究同步压裂裂缝延伸模型最好的手段;优化施工参数主要在于优化裂缝条数、裂缝间距、净压力和水力裂缝几何尺寸,以实现最大程度诱导应力场形成复杂裂缝网络。 (Li X G, Luo D, Li Y, Zhang Y M.2013. Advances of mechanism study of fracture networks formed by simultaneous fracturing process . Xinjiang Petroleum Geology, 34: 228-231). URL      摘要 同步压裂技术是实现页岩气、煤层气等非常规天然气储集层改造的新兴技术,揭示裂缝延伸的力学机理是进行施工参数优化的基础。研究表明,多裂缝同步延伸诱导应力场及其天然裂缝作用机制共同确定了同步压裂裂缝展布情况;裂缝网络工程方法是目前研究同步压裂裂缝延伸模型最好的手段;优化施工参数主要在于优化裂缝条数、裂缝间距、净压力和水力裂缝几何尺寸,以实现最大程度诱导应力场形成复杂裂缝网络。
[52]	林缅, 江文滨, 李勇, 易智星, 张召彬. 2015. 页岩油(气)微尺度流动中的若干问题 . 矿物岩石地球化学通报, 34: 18-28 DOI      URL      摘要 The recent researches on the micro-scale flow of shale oil (gas) worldwide were summarized and reviewed in this paper. On the basis of three models, the molecular dynamics model (MD), the lattice Boltzmann method (LBM) and the pore network model (PNM), the key factors of the oil and gas transport, the limitation of the three models and the existing problems were discussed. Finally, we suggested that the PNM should be used as the primary model for the micro-scale flow studying. This work pointed out the research direction for the shale oil (gas) micro-scale flow. (Lin M, Jiang W B, Li Y, Yi Z X, Zhang Z B.2015. Several questions in the micro-scale flow of shale oil/gas . Bulletin of Mineralogy Petrology and Geochemistry, 34: 18-28). DOI      URL      摘要 The recent researches on the micro-scale flow of shale oil (gas) worldwide were summarized and reviewed in this paper. On the basis of three models, the molecular dynamics model (MD), the lattice Boltzmann method (LBM) and the pore network model (PNM), the key factors of the oil and gas transport, the limitation of the three models and the existing problems were discussed. Finally, we suggested that the PNM should be used as the primary model for the micro-scale flow studying. This work pointed out the research direction for the shale oil (gas) micro-scale flow.
[53]	林英松, 蒋金宝, 朱天玉, 阮新芳, 丁雁生, 付英军, 张丰成, 王莉. 2006. 爆炸载荷对水泥试样损伤破坏规律研究 . 中国石油大学学报(自然科学版), 30: 55-58 DOI      URL      [本文引用: 1]      摘要 从实验和数值模拟两方面对爆炸载荷对水泥试样的损伤破坏进行了研究。首先,在水中利用爆炸产生的爆炸冲击波对水泥试样进行损伤破坏,模拟“层内爆炸”采油技术中激波使岩石损伤开裂的现象;然后,利用波动力学理论,对激波在实验条件下对水泥试样的损伤破坏进行了数值模拟。结果表明,在冲击载荷作用下,水泥试样的损伤破坏可分为压实破坏、压实损伤、拉伸损伤、拉伸破坏4个区域,在压实损伤区水泥试样也具有较好的渗透性。数值模拟可以用来确定各种裂纹形成的应力条件,并可通过预制剖面上的裂纹分布来预测水泥试样内部裂纹分布的基本规律。 (Lin Y S, Jiang J B, Zhu T Y, Ruan X F, Ding Y S, Fu Y J, Zhang F C, Wang L.2006. Reserch of cement samples damage and fracture by exploding load . Journal of China University of Petroleum (Edition of Natural Science), 30: 55-58). DOI      URL      [本文引用: 1]      摘要 从实验和数值模拟两方面对爆炸载荷对水泥试样的损伤破坏进行了研究。首先,在水中利用爆炸产生的爆炸冲击波对水泥试样进行损伤破坏,模拟“层内爆炸”采油技术中激波使岩石损伤开裂的现象;然后,利用波动力学理论,对激波在实验条件下对水泥试样的损伤破坏进行了数值模拟。结果表明,在冲击载荷作用下,水泥试样的损伤破坏可分为压实破坏、压实损伤、拉伸损伤、拉伸破坏4个区域,在压实损伤区水泥试样也具有较好的渗透性。数值模拟可以用来确定各种裂纹形成的应力条件,并可通过预制剖面上的裂纹分布来预测水泥试样内部裂纹分布的基本规律。
[54]	蔺海晓, 杜春志. 2011. 煤岩拟三轴水力压裂实验研究 . 煤炭学报, 36: 1801-1805 URL      [本文引用: 1]      摘要 为了更深入地研究煤岩水压致裂机理,首先对MTS815.02电 液伺服岩石力学实验系统进行改造;利用煤粉、水泥和石膏不同的配比制作相似材料,对型煤试件和原煤试件进行了拟三轴水压致裂实验,并与现场压裂数据进行了 比较分析。结果表明：合理的材料配比为煤∶水泥∶石膏=1.5∶1∶1;裂缝总是沿地应力最大的方向扩展,且裂缝表面特征对缝内压裂液的流动具有重要影 响;泵注流量越大,起裂压力也越大。 (Lin H X, Du C Z.2011. Experimental study on three axis hydraulic fracturing of coal and rock . Journal of Coal Science, 36: 1801-1805). URL      [本文引用: 1]      摘要 为了更深入地研究煤岩水压致裂机理,首先对MTS815.02电 液伺服岩石力学实验系统进行改造;利用煤粉、水泥和石膏不同的配比制作相似材料,对型煤试件和原煤试件进行了拟三轴水压致裂实验,并与现场压裂数据进行了 比较分析。结果表明：合理的材料配比为煤∶水泥∶石膏=1.5∶1∶1;裂缝总是沿地应力最大的方向扩展,且裂缝表面特征对缝内压裂液的流动具有重要影 响;泵注流量越大,起裂压力也越大。
[55]	刘合, 王峰, 张劲, 孟思炜,段永伟. 2014. 二氧化碳干法压裂技术--应用现状与发展趋势 . 石油勘探与开发, 41: 466-471 DOI      URL      [本文引用: 2]      摘要 总结了CO2干法压裂技术的原理、施工工艺、设备要求及技术特点等,并分析了该技术存在的问题和发展趋势。与常规水力压裂技术相比,CO2干法压裂技术具有高返排、对储集层伤害小、增产幅度大等优点。该技术存在的问题包括:液态CO2摩阻高;液态CO2黏度低,悬砂能力和降滤失性能差,不利于压裂造缝;压裂过程中CO2相态变化复杂,难以实现精确的相变预测和控制;压裂设备有待完善,关键设备密闭混砂车存在明显缺陷;缺乏适用于CO2干法压裂的施工参数计算方法。超临界CO2压裂技术具备传统CO2干法压裂技术的全部优点,且增产效果更佳、施工压力小、对混砂车要求更低,是CO2干法压裂技术的发展趋势。 (Liu H, Wang F, Zhang J, Meng S W, Duan Y W.2014. Fracturing with carbon dioxide: Application status and development trend . Petroleum Exploration & Development, 41: 513-519). DOI      URL      [本文引用: 2]      摘要 总结了CO2干法压裂技术的原理、施工工艺、设备要求及技术特点等,并分析了该技术存在的问题和发展趋势。与常规水力压裂技术相比,CO2干法压裂技术具有高返排、对储集层伤害小、增产幅度大等优点。该技术存在的问题包括:液态CO2摩阻高;液态CO2黏度低,悬砂能力和降滤失性能差,不利于压裂造缝;压裂过程中CO2相态变化复杂,难以实现精确的相变预测和控制;压裂设备有待完善,关键设备密闭混砂车存在明显缺陷;缺乏适用于CO2干法压裂的施工参数计算方法。超临界CO2压裂技术具备传统CO2干法压裂技术的全部优点,且增产效果更佳、施工压力小、对混砂车要求更低,是CO2干法压裂技术的发展趋势。
[56]	刘洪林, 邓泽, 刘德勋, 赵群, 康永尚, 赵宏新. 2010. 页岩含气量测试中有关损失气量估算方法 . 石油钻采工艺, 32: 156-158 DOI      URL      [本文引用: 1]      摘要 页岩含气量是页岩勘探开发、选区评价和储层研究必不可少的重要资料,而准确求取损失气量又是决定页岩含气量可靠性的关键。着重论述了页岩含气量测定过程中解吸温度、损失时间以及计算方法等因素对准确求取损失气量的影响,认为温度对页岩测试的影响尤为显著,应快速使岩样稳定到储层温度,解吸过程应严格控制解吸罐温度;对于USBM直线回归,应避免或少用不稳定数据点进行计算,从而求得较准确的页岩含气量。 (Liu H L, Deng Z, Liu D X, Zhao Q, Kang Y S, Zhao H X.2010. Discussion on lost gas calculating methods in shale gas content testing . Oil Drilling & Production Technology, 32: 156-158). DOI      URL      [本文引用: 1]      摘要 页岩含气量是页岩勘探开发、选区评价和储层研究必不可少的重要资料,而准确求取损失气量又是决定页岩含气量可靠性的关键。着重论述了页岩含气量测定过程中解吸温度、损失时间以及计算方法等因素对准确求取损失气量的影响,认为温度对页岩测试的影响尤为显著,应快速使岩样稳定到储层温度,解吸过程应严格控制解吸罐温度;对于USBM直线回归,应避免或少用不稳定数据点进行计算,从而求得较准确的页岩含气量。
[57]	刘鸿文. 1997 . 简明材料力学. 北京: 高等教育出版社 [本文引用: 1]      (Liu H W.1997.Concise Mechanics of Materials. Beijing: Higher Education Press). [本文引用: 1]
[58]	刘建中, 刘翔鹗, 张雪, 刘新美, 王连捷, 沈政亮, 彭华. 1994. 大尺度水压致裂模拟实验 . 地球物理学报, 37: 161-169 URL      [本文引用: 1]      摘要 This paper present the results of great scale hydraulic fracturing simulant experiment to be made in the large-scale two-way compressor.The scale of rock samples is 40 cm 40 cm 20 cm.The samples of gabbro and marble is four piece respectively.The results of experiment show that: We can measurement stable first fracturing pressure,again open pressure,and close pressure.The close pressure and again open pressure are not only relative with stress condition,and are relative with elastic recover ability of corresponding crack geometry shape.The beginning of crack is vertical along the orientation of maximum horizontal principal stress.The maximum injecting pressure isn't the open pressure of hole wall,the open pressure of hole wall is usually small than the maximum injecting pressure. (Liu J Z, Liu X E, Zhang X, Liu X M, Wang L J, Shen Z L, Peng H.1994. Large-scale hydraulic fracturing simulation experiments . Chinese Journal of Geophysics, 37: 161-169). URL      [本文引用: 1]      摘要 This paper present the results of great scale hydraulic fracturing simulant experiment to be made in the large-scale two-way compressor.The scale of rock samples is 40 cm 40 cm 20 cm.The samples of gabbro and marble is four piece respectively.The results of experiment show that: We can measurement stable first fracturing pressure,again open pressure,and close pressure.The close pressure and again open pressure are not only relative with stress condition,and are relative with elastic recover ability of corresponding crack geometry shape.The beginning of crack is vertical along the orientation of maximum horizontal principal stress.The maximum injecting pressure isn't the open pressure of hole wall,the open pressure of hole wall is usually small than the maximum injecting pressure.
[59]	刘劲松, 王赟, 姚振兴. 2013. 微地震信号到时自动拾取方法 . 地球物理学报, 5: 1660-1666 DOI      URL      [本文引用: 2]      摘要 本文讨论了用于微地震信号到时自动拾取的几种方法的原理及特点,包括长短时均值比(STA/LTA)方法、AIC方法、基于高阶统计量偏斜度和峰度的PAI-S/K方法等,提出了移动时窗峰度的快速算法和改进的峰度拾取初至方法.对我国西部某地观测到的13359个微地震记录,采用两种时窗进行了初至到时拾取,并与人工拾取的结果进行了对比.为使所研究的方法达到最佳效果,采用DE全局搜索方法,以人工拾取的初至作为参照,以时差在0.3s以内的记录所占百分比作为目标函数,自动搜索最佳的拾取参数.结果显示,在拾取时窗选为P波初至前3 s至S波初至位置时,AIC方法的结果最佳,时差在0.3s以内的记录占比达到93.6％；在拾取时窗选为包含S波到时的时窗时,改进的峰度法效果最佳,时差在0.3s以内的记录占比83.8％. (Liu J S, Wang Y, Yao Z X.2013. On micro-seismic first arrival identification: A case study . Chinese Journal of Ceophysics, 5: 1660-1666). DOI      URL      [本文引用: 2]      摘要 本文讨论了用于微地震信号到时自动拾取的几种方法的原理及特点,包括长短时均值比(STA/LTA)方法、AIC方法、基于高阶统计量偏斜度和峰度的PAI-S/K方法等,提出了移动时窗峰度的快速算法和改进的峰度拾取初至方法.对我国西部某地观测到的13359个微地震记录,采用两种时窗进行了初至到时拾取,并与人工拾取的结果进行了对比.为使所研究的方法达到最佳效果,采用DE全局搜索方法,以人工拾取的初至作为参照,以时差在0.3s以内的记录所占百分比作为目标函数,自动搜索最佳的拾取参数.结果显示,在拾取时窗选为P波初至前3 s至S波初至位置时,AIC方法的结果最佳,时差在0.3s以内的记录占比达到93.6％；在拾取时窗选为包含S波到时的时窗时,改进的峰度法效果最佳,时差在0.3s以内的记录占比83.8％.
[60]	刘鹏, 赵金洲, 李勇明, 陈鹏飞. 2015. 碳烃无水压裂液研究进展 . 断块油气田, 22: 254-257 DOI      URL      [本文引用: 1]      摘要 为解决页岩气等非常规油气藏压裂改造中耗水量巨大、返排废液处理困难以及储层伤害等问题,探索适宜的新型无水压裂技术,实现页岩气绿色、高效开发,显得十分重要而紧迫。通过系统调研发现,作为当前先进科技的石油液化气(LPG)无水压裂液,实际上是在汽油凝胶压裂液基础上发展起来的低碳烃无水压裂液。文中先后分析了这2种碳烃无水压裂液技术的现状,重点探讨了目前LPG压裂液的形成机理和增产特色,指出了该技术存在的问题;同时认为,LPG凝胶压裂液技术是一种绿色环保型页岩储层改造技术,具有广阔的应用前景。 (Liu P, Zhao J Z, Li Y M, Chen P F.2015. Study advance in hydrocarbon waterless fracturing fluid . Drilling & Production Technology, 22: 254-257). DOI      URL      [本文引用: 1]      摘要 为解决页岩气等非常规油气藏压裂改造中耗水量巨大、返排废液处理困难以及储层伤害等问题,探索适宜的新型无水压裂技术,实现页岩气绿色、高效开发,显得十分重要而紧迫。通过系统调研发现,作为当前先进科技的石油液化气(LPG)无水压裂液,实际上是在汽油凝胶压裂液基础上发展起来的低碳烃无水压裂液。文中先后分析了这2种碳烃无水压裂液技术的现状,重点探讨了目前LPG压裂液的形成机理和增产特色,指出了该技术存在的问题;同时认为,LPG凝胶压裂液技术是一种绿色环保型页岩储层改造技术,具有广阔的应用前景。
[61]	刘庆杰, 王金勋. 2001. 应用孔隙网络模型研究致密介质中气体渗流的滑脱效应//第六届全国流体力学会议文集, 北京: 气象出版社, 314-317 [本文引用: 1]      (Liu Q J, Wang J X.2001, Study on the slippage effects of gas seepage in compact medium//Proceedings of the 6th National Conference on Fluid Mechanics, Beijing: China Meteorological Press, 314-317). [本文引用: 1]
[62]	刘迎香, 赵宇新, 杨永平, 李凤霞, 苗宏. 2004. 重复压裂裂缝延伸模拟实验研究 . 江汉石油学院学报, 26: 92-93 DOI      URL      [本文引用: 1]      摘要 利用人工岩心,采用室内重复压裂模拟实验的方法,研究重复压裂的造缝机理,量化造新缝的可能性及条件,为现场预测裂缝转向或创造产生新缝的条件.对于选择重复压裂时机,优化压裂设计,改善重复压裂效果具有重要的指导意义. (Liu Y X, Zhao Y X, Yang Y P, Li F X, Miao H.2004. Simulation study on fracture extension of repeated fracturing . Journal of Jianghan Petroleum Institute, 26: 92-93). DOI      URL      [本文引用: 1]      摘要 利用人工岩心,采用室内重复压裂模拟实验的方法,研究重复压裂的造缝机理,量化造新缝的可能性及条件,为现场预测裂缝转向或创造产生新缝的条件.对于选择重复压裂时机,优化压裂设计,改善重复压裂效果具有重要的指导意义.
[63]	刘振武, 撒利明, 杨晓, 李向阳. 2011. 页岩气勘探开发对地球物理技术的需求 . 石油地球物理勘探, 46: 810-818 URL      [本文引用: 2]      摘要 近几年来,伴随着建设低碳经济的需要和对清洁能源需求的增长,页岩气产业发展迅速升温,特别是北美页岩气的发展已经改变了现今能源供应格局。我国页岩气资源潜力巨大,开发前景广阔,已经引起人们的高度重视。我国页岩气勘探开发仍处于起步阶段,特别是地球物理技术在页岩气勘探开发中究竟具有什么样的作用,还存在一些困惑。本文通过页岩气地球物理技术的需求分析和对未来发展的展望,明确指出地球物理技术作为页岩气储层评价和增产改造的关键技术,将在页岩气勘探开发中发挥重要的作用。 (Liu Z W, Sa L M, Yang X, Li X Y.2011. Needs of geophysical technologies for shale gas exploration . Oil Geophysical Prospecting, 46: 810-818). URL      [本文引用: 2]      摘要 近几年来,伴随着建设低碳经济的需要和对清洁能源需求的增长,页岩气产业发展迅速升温,特别是北美页岩气的发展已经改变了现今能源供应格局。我国页岩气资源潜力巨大,开发前景广阔,已经引起人们的高度重视。我国页岩气勘探开发仍处于起步阶段,特别是地球物理技术在页岩气勘探开发中究竟具有什么样的作用,还存在一些困惑。本文通过页岩气地球物理技术的需求分析和对未来发展的展望,明确指出地球物理技术作为页岩气储层评价和增产改造的关键技术,将在页岩气勘探开发中发挥重要的作用。
[64]	柳贡慧, 庞飞, 陈治喜. 2000. 水力压裂模拟实验中的相似准则 . 石油大学学报 (自然科学版), 24: 45-48 DOI      URL      [本文引用: 1]      摘要 目前预测裂缝的几何形态多采用数值模拟方法，所应用的模型是比较简单的二维或拟三维模型，无论是从研究裂缝扩展机理的角度，还是从发展，验证新模型的角度来讲，模拟实验都是最基本的环节。相似理论可用来指导实验的根本布局。文章通过相似理论中的方程分析法将压裂控制方程无因次比，并导出对水力压裂模拟实验具有指导意义的相似准则与相似比例系数。该相似准则与de.Pater基于二维模型所得结果大体吻合。 (Liu G H, Pang F, Chen Z X.2000. Similarity criterion in hydraulic fracturing simulation experiment . Journal of China University of Petroleum ( Natrual Science Edition), 24: 45-48). DOI      URL      [本文引用: 1]      摘要 目前预测裂缝的几何形态多采用数值模拟方法，所应用的模型是比较简单的二维或拟三维模型，无论是从研究裂缝扩展机理的角度，还是从发展，验证新模型的角度来讲，模拟实验都是最基本的环节。相似理论可用来指导实验的根本布局。文章通过相似理论中的方程分析法将压裂控制方程无因次比，并导出对水力压裂模拟实验具有指导意义的相似准则与相似比例系数。该相似准则与de.Pater基于二维模型所得结果大体吻合。
[65]	柳占立, 庄茁, 孟庆国, 詹世革, 黄克智. 2017. 页岩气高效开采的力学问题与挑战 . 力学学报, 49, 507-516 DOI      URL      [本文引用: 1]      摘要 页岩气是指赋存于富含有机质泥页岩中以吸附和游离状态为主要存在方式的天然气,中国资源量丰富,地域分布广泛.页岩气开采能缓解我国常规油气产量不足、煤化石燃料引起环境污染等问题,已成为中国绿色能源开发的重要领域.尽管北美页岩气"革命"取得了成功,目前也仅有预期产量5%～15%的采收率.与北美地区相比,中国页岩气埋藏深,赋存条件差,自然丰度低,因此,高效开采面临更多的困难和挑战.近年来,围绕国家重大能源战略需求,瞄准技术发展前沿,学术界和工业界联合对页岩气高效开采的关键科学和技术问题展开研究.本文结合近三年四川、重庆地区的页岩气试验区块遇到的新问题,针对中国未来3500 m以下深部开采的新挑战,如地质沉积、裂缝发育构造不同、上覆压力增加、水平应力场变化等新问题,介绍和总结了目前中国页岩气高效开采面临的力学科学问题,主要包括多重耦合下的安全优质钻完井力学理论和方法、水力压裂体积改造和多尺度缝网形成机制、多尺度渗流力学特性与解吸附机理等."深部页岩气高效开采"的研究面向国家重大能源需求,科学意义重大,工程背景明确,需要工程力学、石油工程、地球物理、化学工程和环境工程等多学科专家合作,开展理论研究、物理模拟、数值模拟及现场试验等综合应用基础研究,取得高效开采页岩油气理论与技术的突破.学科交叉是研究页岩气高效开采问题、突破技术瓶颈的桥梁,只有力学与石油工程、地球科学等学科实现深度交叉融合,才能更加有效地推动页岩油气等非常规油气资源的开发. (Liu Z L, Zhuang Z, Meng Q G, Zhan S G, Huang K Z.2017. Problems and challenges of mechanics in shale gas efficient exploitation . Chinese Journal of Theoretical and Applied Mechanics, 49: 507-516). DOI      URL      [本文引用: 1]      摘要 页岩气是指赋存于富含有机质泥页岩中以吸附和游离状态为主要存在方式的天然气,中国资源量丰富,地域分布广泛.页岩气开采能缓解我国常规油气产量不足、煤化石燃料引起环境污染等问题,已成为中国绿色能源开发的重要领域.尽管北美页岩气"革命"取得了成功,目前也仅有预期产量5%～15%的采收率.与北美地区相比,中国页岩气埋藏深,赋存条件差,自然丰度低,因此,高效开采面临更多的困难和挑战.近年来,围绕国家重大能源战略需求,瞄准技术发展前沿,学术界和工业界联合对页岩气高效开采的关键科学和技术问题展开研究.本文结合近三年四川、重庆地区的页岩气试验区块遇到的新问题,针对中国未来3500 m以下深部开采的新挑战,如地质沉积、裂缝发育构造不同、上覆压力增加、水平应力场变化等新问题,介绍和总结了目前中国页岩气高效开采面临的力学科学问题,主要包括多重耦合下的安全优质钻完井力学理论和方法、水力压裂体积改造和多尺度缝网形成机制、多尺度渗流力学特性与解吸附机理等."深部页岩气高效开采"的研究面向国家重大能源需求,科学意义重大,工程背景明确,需要工程力学、石油工程、地球物理、化学工程和环境工程等多学科专家合作,开展理论研究、物理模拟、数值模拟及现场试验等综合应用基础研究,取得高效开采页岩油气理论与技术的突破.学科交叉是研究页岩气高效开采问题、突破技术瓶颈的桥梁,只有力学与石油工程、地球科学等学科实现深度交叉融合,才能更加有效地推动页岩油气等非常规油气资源的开发.
[66]	卢德唐, 张龙军, 郑德温, 毕全福, 王磊, 杨景海. 2016. 页岩气组份模型产能预测及压裂优化 . 科学通报, 61: 94-101 URL      摘要 我国页岩、致密油气等非常规油气的储量极大,非常规油气的开发对保障国家能源安全有重要的意义.准确模拟预测非常规油气的流动行为是经济高效开采的关键.不同于常规油气,页岩气在地层中存在滑脱效应以及吸附现象,为准确描述此类机理和现象,本文在以非结构PEBI网格为主的混合网格的基础上建立了组分数值模型,并对气体组分比例、吸附作用以及滑脱效应对产能的影响进行了分析.同时,对国内某页岩气藏水平井的压裂进行了优化.结果表明,页岩气产量随裂缝数量的增多以及裂缝半长的增长而增加,但当裂缝数量达到一定数量,裂缝半长达到一定长度时,产量的增加不再明显.因此,为使页岩气的经济效益达到最大化,应合理布置裂缝数量及裂缝半长. (Lu D T, Zhang L J, Zheng D W, Bi Q F, Wang L, Yang J H.2016. Shale productivity prediction and fracturing optimization based on compositional simulation . Science China Press,61: 94-101). URL      摘要 我国页岩、致密油气等非常规油气的储量极大,非常规油气的开发对保障国家能源安全有重要的意义.准确模拟预测非常规油气的流动行为是经济高效开采的关键.不同于常规油气,页岩气在地层中存在滑脱效应以及吸附现象,为准确描述此类机理和现象,本文在以非结构PEBI网格为主的混合网格的基础上建立了组分数值模型,并对气体组分比例、吸附作用以及滑脱效应对产能的影响进行了分析.同时,对国内某页岩气藏水平井的压裂进行了优化.结果表明,页岩气产量随裂缝数量的增多以及裂缝半长的增长而增加,但当裂缝数量达到一定数量,裂缝半长达到一定长度时,产量的增加不再明显.因此,为使页岩气的经济效益达到最大化,应合理布置裂缝数量及裂缝半长.
[67]	陆基孟. 1993 . 地震勘探原理. 北京: 石油工业出版社 [本文引用: 1]      (Lu J M.1993.The Principle of Seismic Exploration. Beijing: Petroleum Industry Press). [本文引用: 1]
[68]	吕鹏, 丁志峰, 朱露培. 2011. 结合波形互相关的双差定位方法在2008年汶川地震余震序列中的应用 . 地震学报, 33: 407-419, 557 DOI      URL      [本文引用: 1]      摘要 选取了汶川地震主震后的2008年5月12日—2009年8月31日,震级为3.0≤MS≤5.0的余震4 240次.利用波形互相关方法得到其P波到时,用双差定位方法对其进行定位,最终得到了2 441次重新定位的结果.统计定位误差(两倍标准偏差)在E--W方向为0.4 km,N--S方向为0.4 km,垂直方向为0.7 km.定位结果表明,汶川地震的余震深度集中在10—20 km,震中分布与龙门山中央断裂带的走向关系密切.沿龙门山断裂的地震分布具有明显的分段性,西南段呈水平带状分布,东北段接近垂直分布,且在北川附近存在深度突变.这与龙门山断裂的地震在西南段多表现为逆冲,东北段多表现为走滑的现象相吻合.在深度剖面上地震的空间分布存在分立的特征,通过对比前人在此地区浅层的地震剖面资料,发现地震空间分布与已探知的浅部断层有较好的对应关系. (Lü P, Ding Z F, Zhu L P.2011. Application of double-difference relocation technique to aftershocks of 2008 Wenchuan earthquake using waveform cross-correlation . Acta Seismologica Sinica, 33: 407-419). DOI      URL      [本文引用: 1]      摘要 选取了汶川地震主震后的2008年5月12日—2009年8月31日,震级为3.0≤MS≤5.0的余震4 240次.利用波形互相关方法得到其P波到时,用双差定位方法对其进行定位,最终得到了2 441次重新定位的结果.统计定位误差(两倍标准偏差)在E--W方向为0.4 km,N--S方向为0.4 km,垂直方向为0.7 km.定位结果表明,汶川地震的余震深度集中在10—20 km,震中分布与龙门山中央断裂带的走向关系密切.沿龙门山断裂的地震分布具有明显的分段性,西南段呈水平带状分布,东北段接近垂直分布,且在北川附近存在深度突变.这与龙门山断裂的地震在西南段多表现为逆冲,东北段多表现为走滑的现象相吻合.在深度剖面上地震的空间分布存在分立的特征,通过对比前人在此地区浅层的地震剖面资料,发现地震空间分布与已探知的浅部断层有较好的对应关系.
[69]	欧志鹏. 2014. 纳米孔隙中甲烷扩散的分子动力学研究 . [硕士论文]. 成都: 西南石油大学 URL      [本文引用: 1]      摘要 页岩气是一种重要的非常规天然气资源,其成功开发对于保障能源安全具有重要战略意义。在页岩气开发领域,尚存在许多科学问题和技术难题,其中天然气在页岩储层纳米孔隙中的赋存状态和扩散规律是体现页岩气特点,控制页岩气生产的关键问题。目前对于页岩气赋存状态和扩散规律多采用传统实验方法和吸附扩散理论进行研究,对于描述纳米孔隙的微尺度效应存在一定的局限性,且对于微观机理的解释能力有限。引入新的微观或介观尺度研究方法成为该领域重要的发展趋势和方向。 为此,本文利用分子模拟方法研究了甲烷在页岩储层纳米孔隙中的赋存状态和扩散规律。根据页岩储层特征,选取在页岩气赋存及扩散过程中起重要作用的有机碳成分,以及在页岩储层矿物组成中占据较大比例的石英和伊利石作为孔隙骨架材料,分别建立不同孔径和不同形状的纳米孔隙模型,并结合甲烷联合原子模型及相应势能模型,建立分子模拟模型。在此基础上,通过巨正则系综Monte Carlo方法获取了页岩气藏温度压力下甲烷在纳米孔隙中的分布构型,并进一步利用正则系综分子动力学方法研究了甲烷的扩散规律。 研究结果表明,在页岩气藏典型温度压力条件下,吸附态与游离态甲烷的相对比例和性质变化的差异,是造成不同孔隙含气性不同的根本原因。相同条件下,孔径较小的孔隙中吸附态甲烷比例高于孔径较大的孔隙中吸附态甲烷比例,管状孔隙中吸附态甲烷比例高于层状孔隙中吸附态甲烷比例,有机碳孔隙中吸附态甲烷平均密度高于石英孔隙和伊利石孔隙中吸附态甲烷平均密度。吸附态甲烷密度和游离态甲烷密度随压力变化的趋势不同,造成不同孔隙的含气性差异在压力较低时较为明显。随着压力的升高,纳米孔隙内有出现双层吸附的趋势。在页岩气藏温度压力变化范围内,压力变化比温度变化对扩散系数的影响更为显著。压力较低时,甲烷分子扩散受到壁面作用势影响更为明显；压力较高时,甲烷分子扩散受其他甲烷分子作用势的影响更为显著。平行于孔隙壁面方向是扩散的主方向,该方向上的扩散系数对压力变化更为敏感。相同条件下,甲烷扩散系数随着孔径的增加而增加,层状孔隙中甲烷扩散系数大于管状孔隙中甲烷扩散系数,压力较低时石英孔隙和伊利石孔隙中主方向上甲烷扩散系数大于有机碳孔隙中主方向上甲烷扩散系数。 (Ou Z P.2014. Molecular simulation on the CH$_{4}$ diffusion in nano-pores . [Master Thesis]. Chengdu: Southwest Petroleum University). URL      [本文引用: 1]      摘要 页岩气是一种重要的非常规天然气资源,其成功开发对于保障能源安全具有重要战略意义。在页岩气开发领域,尚存在许多科学问题和技术难题,其中天然气在页岩储层纳米孔隙中的赋存状态和扩散规律是体现页岩气特点,控制页岩气生产的关键问题。目前对于页岩气赋存状态和扩散规律多采用传统实验方法和吸附扩散理论进行研究,对于描述纳米孔隙的微尺度效应存在一定的局限性,且对于微观机理的解释能力有限。引入新的微观或介观尺度研究方法成为该领域重要的发展趋势和方向。 为此,本文利用分子模拟方法研究了甲烷在页岩储层纳米孔隙中的赋存状态和扩散规律。根据页岩储层特征,选取在页岩气赋存及扩散过程中起重要作用的有机碳成分,以及在页岩储层矿物组成中占据较大比例的石英和伊利石作为孔隙骨架材料,分别建立不同孔径和不同形状的纳米孔隙模型,并结合甲烷联合原子模型及相应势能模型,建立分子模拟模型。在此基础上,通过巨正则系综Monte Carlo方法获取了页岩气藏温度压力下甲烷在纳米孔隙中的分布构型,并进一步利用正则系综分子动力学方法研究了甲烷的扩散规律。 研究结果表明,在页岩气藏典型温度压力条件下,吸附态与游离态甲烷的相对比例和性质变化的差异,是造成不同孔隙含气性不同的根本原因。相同条件下,孔径较小的孔隙中吸附态甲烷比例高于孔径较大的孔隙中吸附态甲烷比例,管状孔隙中吸附态甲烷比例高于层状孔隙中吸附态甲烷比例,有机碳孔隙中吸附态甲烷平均密度高于石英孔隙和伊利石孔隙中吸附态甲烷平均密度。吸附态甲烷密度和游离态甲烷密度随压力变化的趋势不同,造成不同孔隙的含气性差异在压力较低时较为明显。随着压力的升高,纳米孔隙内有出现双层吸附的趋势。在页岩气藏温度压力变化范围内,压力变化比温度变化对扩散系数的影响更为显著。压力较低时,甲烷分子扩散受到壁面作用势影响更为明显；压力较高时,甲烷分子扩散受其他甲烷分子作用势的影响更为显著。平行于孔隙壁面方向是扩散的主方向,该方向上的扩散系数对压力变化更为敏感。相同条件下,甲烷扩散系数随着孔径的增加而增加,层状孔隙中甲烷扩散系数大于管状孔隙中甲烷扩散系数,压力较低时石英孔隙和伊利石孔隙中主方向上甲烷扩散系数大于有机碳孔隙中主方向上甲烷扩散系数。
[70]	潘林华, 程礼军, 张士诚, 郭天魁, 柳凯誉. 2015. 页岩储层体积压裂裂缝扩展机制研究 . 岩土力学, 36: 205-211 DOI      URL      摘要 页岩储层天然裂缝、水平层理发育,水力压裂过程中可能形成复杂的体积裂缝。针对页岩储层体积裂缝扩展问题,基于流-固耦合基本方程和损伤力学原理,建立了页岩储层水力压裂体积裂缝扩展的三维有限元模型。将数值模型的模拟结果与页岩储层裂缝扩展室内试验结果进行对比,二者吻合较好,从而证明了数值模型的可靠性。通过一系列数值模拟发现:(1)水力压裂过程中水平层理可能张开,形成水平缝,水平与垂直缝相互交错,形成复杂的体积裂缝网络;(2)水平主应力差增大,体积裂缝的分布长度(水平最大主应力方向压裂裂缝的展布距离)增加、分布宽度(水平最小主应力方向压裂裂缝的展布距离)减小,体积裂缝的长宽比增加;(3)压裂施工排量增大,体积裂缝的分布长度减小、宽度增加,压裂裂缝的长宽比降低;(4)天然裂缝的残余抗张强度增大,体积裂缝分布宽度减小、分布长度增加,体积裂缝的长宽比增加。研究成果可以为国内的页岩气的压裂设计和施工提供一定的参考和借鉴。 (Pan L h, Cheng L J, Zhang S C, Guo T K, Liu K Y.2010. Mechanism of fracture propagation via numerical stimulation of reservoir volume fracture in shale reservoirs . Rock and Soil Mechanics, 36: 205-211). DOI      URL      摘要 页岩储层天然裂缝、水平层理发育,水力压裂过程中可能形成复杂的体积裂缝。针对页岩储层体积裂缝扩展问题,基于流-固耦合基本方程和损伤力学原理,建立了页岩储层水力压裂体积裂缝扩展的三维有限元模型。将数值模型的模拟结果与页岩储层裂缝扩展室内试验结果进行对比,二者吻合较好,从而证明了数值模型的可靠性。通过一系列数值模拟发现:(1)水力压裂过程中水平层理可能张开,形成水平缝,水平与垂直缝相互交错,形成复杂的体积裂缝网络;(2)水平主应力差增大,体积裂缝的分布长度(水平最大主应力方向压裂裂缝的展布距离)增加、分布宽度(水平最小主应力方向压裂裂缝的展布距离)减小,体积裂缝的长宽比增加;(3)压裂施工排量增大,体积裂缝的分布长度减小、宽度增加,压裂裂缝的长宽比降低;(4)天然裂缝的残余抗张强度增大,体积裂缝分布宽度减小、分布长度增加,体积裂缝的长宽比增加。研究成果可以为国内的页岩气的压裂设计和施工提供一定的参考和借鉴。
[71]	潘兆科, 刘志河. 2004. 矸石破碎块度的分形性质及计算方法 . 太原理工大学学报, 35: 115-117 DOI      URL      [本文引用: 1]      摘要 用分形几何方法对破碎矸石块度进行了统计分析，结果表明，分形维数D是反映矸石破碎程度恰当的统计特征量，同时，分析了两种破碎块度分布函数，并基于幂率关系建立了一种新的块度表达式。 (Pan Z K, Liu Z H.2004. Fractal properties of size distribution of gangue augmentation and routine calculation . Journal of Taiyuan University of Technology, 31: 669-672). DOI      URL      [本文引用: 1]      摘要 用分形几何方法对破碎矸石块度进行了统计分析，结果表明，分形维数D是反映矸石破碎程度恰当的统计特征量，同时，分析了两种破碎块度分布函数，并基于幂率关系建立了一种新的块度表达式。
[72]	蒲泊伶, 蒋有录, 王毅, 包书景, 刘鑫金. 2010. 四川盆地下志留统龙马溪组页岩气成藏条件及有利地区分析 . 石油学报, 31: 225-230 DOI      URL      摘要 四川盆地下志留统龙马溪组发育富含有机质页岩。作为页岩气的源岩,该套页岩在盆地内分布广泛,厚度大,有机质含量高,有机质类型好,热演化程度高,生气潜力大;作为储层,页岩中孔隙和裂缝发育,为页岩气提供了充足的储集空间,并且等温吸附实验也表明,页岩具有较强的气体吸附能力;由于页岩的致密性及抗构造破坏性,本地区构造条件满足页岩气成藏要求。多口井下志留统页岩的气测显示也为页岩气的存在提供了有利证据。根据页岩厚度、有机碳含量、热演化程度和生烃强度等信息,预测宜宾—自贡—泸州一带及达州—万县一带为页岩气的有利勘探区域。 (Pu B L, Jiang Y L, Wang Y, Bao S J.2010. Reservoir-forming conditions and favorable exploration zones of shale gas in Lower Silurian Longmaxi Formation of Sichuan Basin . Acta Petrolei Sinica, 31: 225-230). DOI      URL      摘要 四川盆地下志留统龙马溪组发育富含有机质页岩。作为页岩气的源岩,该套页岩在盆地内分布广泛,厚度大,有机质含量高,有机质类型好,热演化程度高,生气潜力大;作为储层,页岩中孔隙和裂缝发育,为页岩气提供了充足的储集空间,并且等温吸附实验也表明,页岩具有较强的气体吸附能力;由于页岩的致密性及抗构造破坏性,本地区构造条件满足页岩气成藏要求。多口井下志留统页岩的气测显示也为页岩气的存在提供了有利证据。根据页岩厚度、有机碳含量、热演化程度和生烃强度等信息,预测宜宾—自贡—泸州一带及达州—万县一带为页岩气的有利勘探区域。
[73]	钱斌, 张俊成, 朱炬辉, 方泽本, 寇双峰, 陈锐. 2015. 四川盆地长宁地区页岩气水平井组"拉链式"压裂实践 . 天然气工业, 35: 81-84 DOI      URL      [本文引用: 1]      摘要 经过几年的探索和实践,在四川长宁—威远国家级页岩气示范区内相继完成一批直井和水平井体积压裂改造并获得工业产能,初步形成了自主页岩气储层改造技术,下一步需要探索解决的就是如何通过"工厂化"模式来提高压裂作业效率的问题。为此,介绍了我国第一个页岩气丛式水平井井组长宁A平台的部署情况,针对该平台压裂改造工艺要求和四川盆地山地地形特点,对该平台"工厂化"作业模式进行了优化设计,在国内首次采用"拉链式"压裂作业模式对该平台开展了"工厂化"压裂。通过地面标准化流程、拉链式施工、流水线作业和井下交错布缝、微地震实时监测,实现了每天平均压裂3.16段,最大限度增加储层改造体积,充分体现了"工厂化"压裂对页岩气丛式水平井平台大规模体积压裂改造的提速、提效作用。同时还针对该井组"拉链式"压裂的施工工艺、作业模式、地面配套以及压后初步评价进行了综合研究分析,"拉链式"压裂实践表明:2口井的"拉链式"压裂相对于该地区前期水平井单井压裂作业而言,效率提高78%、增产改造体积增加了50%。 (Qian B, Zhang J C, Zhu J H, Fang Z B, Kou S F, Chen R.2015. Application of zipper fracturing of horizontal cluster wells in the changing shale gas pilot zone, Sichuan basin . Natural Gas Industry, 35: 81-84). DOI      URL      [本文引用: 1]      摘要 经过几年的探索和实践,在四川长宁—威远国家级页岩气示范区内相继完成一批直井和水平井体积压裂改造并获得工业产能,初步形成了自主页岩气储层改造技术,下一步需要探索解决的就是如何通过"工厂化"模式来提高压裂作业效率的问题。为此,介绍了我国第一个页岩气丛式水平井井组长宁A平台的部署情况,针对该平台压裂改造工艺要求和四川盆地山地地形特点,对该平台"工厂化"作业模式进行了优化设计,在国内首次采用"拉链式"压裂作业模式对该平台开展了"工厂化"压裂。通过地面标准化流程、拉链式施工、流水线作业和井下交错布缝、微地震实时监测,实现了每天平均压裂3.16段,最大限度增加储层改造体积,充分体现了"工厂化"压裂对页岩气丛式水平井平台大规模体积压裂改造的提速、提效作用。同时还针对该井组"拉链式"压裂的施工工艺、作业模式、地面配套以及压后初步评价进行了综合研究分析,"拉链式"压裂实践表明:2口井的"拉链式"压裂相对于该地区前期水平井单井压裂作业而言,效率提高78%、增产改造体积增加了50%。
[74]	任俊杰. 2015. 基于格子Boltzmann方法的页岩气微观流动机理研究 . [博士论文] . 成都: 西南石油大学 URL      [本文引用: 1]      摘要 页岩气在世界范围内储量巨大,初步探明全球页岩气储量接近致密砂岩气和煤层气已探明的总储量,而中国页岩气储量丰富,开发潜力巨大。页岩中的纳米级孔隙决定了页岩气在储层中的赋存状态和流动特征,进而决定了页岩气藏的开发特征。目前,在页岩气藏的开发过程中产生了很多科学和技术问题。这一系列的问题导致传统的宏观渗流理论在描述页岩气流动时存在一定的局限性,从而难以准确描述页岩气的流动规律。运用微观或介观方法在不同尺度上模拟页岩气在页岩中的流动,进而从不同角度全面认识页岩气的流动机理,已成为该领域未来的发展方向。目前,针对页岩气流动机理的研究方法主要表现为如下三种：一是基于连续介质假设的宏观方法；二是微观分子动力学方法；三是介观模拟方法,如：直接模拟Monte-Carlo方法(DSMC),格子Boltzmann方法(LBM)。与其他方法相比,格子Boltzmann方法没有连续介质假设条件且具有较高的计算效率和较低的统计噪声,因此格子Boltzmann方法在模拟多尺度、多物理场的复杂流动问题上具有较大的优势。为此,本文将运用格子Boltzmann方法研究页岩气微观流动机理,分别从孔隙尺度和表征体元(REV)尺度研究了页岩气在页岩中的流动规律,具体研究内容和主要成果如下：(1)对国内外文献进行了大量调研,介绍了格子Boltzmann方法的介观特点,总结了页岩气流动机理的研究方法及研究现状。(2)从Boltzmann方程出发对格子Boltzmann方法原理进行了系统的论述,介绍了常用的边界格式和格子Boltzmann方法的程序结构。(3)研究了长方形格子Boltzmann模型,通过Chapman-Enskog多尺度展开,发现长方形格子Boltzmann模型恢复的宏观方程含有误差项,并建立了微尺度流动的长方形格子Boltzmann模型,对长方形格子Boltzmann模型的微尺度边界条件进行了详细的分析,提出了通过调节组合系数r(或离散调节系数σ)和松弛参数s4来消除数值离散效应的方法,并在计算效率和计算精度方面对长方形格子Boltzmamn模型和正方形格子Boltzmann模型进行了对比。(4)建立了理想气体条件和非理想气体条件下的格子Boltzmann模型。针对页岩气藏高压的特点,运用非理想气体的格子Boltzmann模型研究了气藏条件下页岩气在干酪根孔中的流动机理,进而总结出了页岩气在干酪根孔中流动的一些物理规律。(5)针对非理想气体,分析了用于处理曲线边界的反弹与完全漫反射边界条件,提出了该边界条件中组合系数的确定方法,并运用孔隙尺度格子Boltzmann模型模拟了人工构造多孔介质中页岩气的流动,分析页岩气在干酪根多孔介质中特殊流动规律对表观渗透率的影响。(6)建立了非理想气体条件下页岩气的REV尺度格子Boltzmann模型,在REV尺度上研究了含有天然裂缝的页岩中页岩气的流动规律,分析了天然裂缝对页岩气流动的影响。(7)由于纳米级干酪根孔中表面扩散的存在,尤其是页岩中天然裂缝的存在,使得页岩的整体渗透能力大幅度的增加,这也使得页岩气藏的经济开发变成了现实。 (Ren J J.2015. Study of microscopic transport mechanisms of shale gas using the lattice Boltzmann method . [PhD Thesis]. Chengdu: Southwest Petroleum University). URL      [本文引用: 1]      摘要 页岩气在世界范围内储量巨大,初步探明全球页岩气储量接近致密砂岩气和煤层气已探明的总储量,而中国页岩气储量丰富,开发潜力巨大。页岩中的纳米级孔隙决定了页岩气在储层中的赋存状态和流动特征,进而决定了页岩气藏的开发特征。目前,在页岩气藏的开发过程中产生了很多科学和技术问题。这一系列的问题导致传统的宏观渗流理论在描述页岩气流动时存在一定的局限性,从而难以准确描述页岩气的流动规律。运用微观或介观方法在不同尺度上模拟页岩气在页岩中的流动,进而从不同角度全面认识页岩气的流动机理,已成为该领域未来的发展方向。目前,针对页岩气流动机理的研究方法主要表现为如下三种：一是基于连续介质假设的宏观方法；二是微观分子动力学方法；三是介观模拟方法,如：直接模拟Monte-Carlo方法(DSMC),格子Boltzmann方法(LBM)。与其他方法相比,格子Boltzmann方法没有连续介质假设条件且具有较高的计算效率和较低的统计噪声,因此格子Boltzmann方法在模拟多尺度、多物理场的复杂流动问题上具有较大的优势。为此,本文将运用格子Boltzmann方法研究页岩气微观流动机理,分别从孔隙尺度和表征体元(REV)尺度研究了页岩气在页岩中的流动规律,具体研究内容和主要成果如下：(1)对国内外文献进行了大量调研,介绍了格子Boltzmann方法的介观特点,总结了页岩气流动机理的研究方法及研究现状。(2)从Boltzmann方程出发对格子Boltzmann方法原理进行了系统的论述,介绍了常用的边界格式和格子Boltzmann方法的程序结构。(3)研究了长方形格子Boltzmann模型,通过Chapman-Enskog多尺度展开,发现长方形格子Boltzmann模型恢复的宏观方程含有误差项,并建立了微尺度流动的长方形格子Boltzmann模型,对长方形格子Boltzmann模型的微尺度边界条件进行了详细的分析,提出了通过调节组合系数r(或离散调节系数σ)和松弛参数s4来消除数值离散效应的方法,并在计算效率和计算精度方面对长方形格子Boltzmamn模型和正方形格子Boltzmann模型进行了对比。(4)建立了理想气体条件和非理想气体条件下的格子Boltzmann模型。针对页岩气藏高压的特点,运用非理想气体的格子Boltzmann模型研究了气藏条件下页岩气在干酪根孔中的流动机理,进而总结出了页岩气在干酪根孔中流动的一些物理规律。(5)针对非理想气体,分析了用于处理曲线边界的反弹与完全漫反射边界条件,提出了该边界条件中组合系数的确定方法,并运用孔隙尺度格子Boltzmann模型模拟了人工构造多孔介质中页岩气的流动,分析页岩气在干酪根多孔介质中特殊流动规律对表观渗透率的影响。(6)建立了非理想气体条件下页岩气的REV尺度格子Boltzmann模型,在REV尺度上研究了含有天然裂缝的页岩中页岩气的流动规律,分析了天然裂缝对页岩气流动的影响。(7)由于纳米级干酪根孔中表面扩散的存在,尤其是页岩中天然裂缝的存在,使得页岩的整体渗透能力大幅度的增加,这也使得页岩气藏的经济开发变成了现实。
[75]	石根华. 1997 . 数值流形方法与非连续变形分析. 北京: 淸华大学出版社 [本文引用: 1]      (Shi G H.1997.Numerical Manifold Method and Discontinuous Deformation Analysis. Beijing: Tsinghua University Press). [本文引用: 1]
[76]	宋振云, 陈建刚, 王兴建, 王玲, 王惠生. 2007. 水平井筒机械隔离分段压裂技术 . 钻采工艺, 30: 75-77 DOI      URL      摘要 低渗透油田水平井分段压裂是提高单井产量最有效的手段之一,其关 键在于水平井筒的隔离技术;采用机械工具隔离井筒必须安全、可靠,以保证分段压裂施工的顺利进行.针对水平井井身结构特点,采用可捞式桥塞隔离井筒,对塞 平5井等两口井进行了水平井机械隔离分段压裂试验.现场应用表明,桥塞对水平井筒的封隔有效、可靠,能够保证形成相互独立的裂缝系统;封隔工具性能良好、 操作简单,桥塞坐封、释放、打捞、解封均一次成功,填补了国内水平井筒机械隔离分段压裂技术的空白. (Song Z Y, Chen J G, Wang X J, Wang L, Wang H S.2007. Mechanical isolation and staged fracturing techniques in horizontal well bore . Drilling & Production Technology, 30: 75-77). DOI      URL      摘要 低渗透油田水平井分段压裂是提高单井产量最有效的手段之一,其关 键在于水平井筒的隔离技术;采用机械工具隔离井筒必须安全、可靠,以保证分段压裂施工的顺利进行.针对水平井井身结构特点,采用可捞式桥塞隔离井筒,对塞 平5井等两口井进行了水平井机械隔离分段压裂试验.现场应用表明,桥塞对水平井筒的封隔有效、可靠,能够保证形成相互独立的裂缝系统;封隔工具性能良好、 操作简单,桥塞坐封、释放、打捞、解封均一次成功,填补了国内水平井筒机械隔离分段压裂技术的空白.
[77]	宋振云, 苏伟东, 杨延增, 李勇, 李志航, 汪小宇, 李前春, 章东哲, 王玉. 2014. CO$_{2}$干法加砂压裂技术研究与实践 . 天然气工业, 34: 55-59 DOI      URL      [本文引用: 1]      摘要 CO2干法加砂压裂是以CO2代替常规水力压裂液的一种无水压裂技术,国外(美国和加拿大)的实践成果表明:该方法对低压、低渗透、强水锁/水敏储层的压裂改造效果十分明显。为此,就其增产机理、压裂液体系、密封混砂装置及压裂工艺开展了一系列的试验研究,获得了一系列成果:①CO2提黏技术使超临界CO2黏度提高了240~490倍,改善了CO2压裂液的携砂性和造缝性,是实现CO2干法加砂压裂的一项关键技术;②CO2密闭混砂装置的研制实现了对CO2干法加砂压裂关键装置的配套,能够满足CO2干法加砂压裂作业的施工需要;③CO2干法加砂压裂实现了完全自主返排;④CO2干法加砂压裂利用CO2代替水基压裂液,能够大量节约压裂作业的耗水量,实现循环经济;⑤CO2干法加砂压裂工艺是可行的,对低压、低渗透、强水锁伤害储层具有较好针对性,表现出了良好的增产效果。 (Song Z Y, Su W D, Yang Y Z, Li Y, Li Z H, Wang X Y, Li Q C, Zhang D Z, Wang Y.2014. Experimental studies of CO$_{2}$/sand dry-frac process . Natural Gas Technology, 34: 55-59). DOI      URL      [本文引用: 1]      摘要 CO2干法加砂压裂是以CO2代替常规水力压裂液的一种无水压裂技术,国外(美国和加拿大)的实践成果表明:该方法对低压、低渗透、强水锁/水敏储层的压裂改造效果十分明显。为此,就其增产机理、压裂液体系、密封混砂装置及压裂工艺开展了一系列的试验研究,获得了一系列成果:①CO2提黏技术使超临界CO2黏度提高了240~490倍,改善了CO2压裂液的携砂性和造缝性,是实现CO2干法加砂压裂的一项关键技术;②CO2密闭混砂装置的研制实现了对CO2干法加砂压裂关键装置的配套,能够满足CO2干法加砂压裂作业的施工需要;③CO2干法加砂压裂实现了完全自主返排;④CO2干法加砂压裂利用CO2代替水基压裂液,能够大量节约压裂作业的耗水量,实现循环经济;⑤CO2干法加砂压裂工艺是可行的,对低压、低渗透、强水锁伤害储层具有较好针对性,表现出了良好的增产效果。
[78]	隋宏光, 姚军. 2016. 页岩黏土矿物CH$_{4}$/CO$_{2}$吸附规律的分子模拟 . 东北石油大学学报. 40: 90-99 DOI      URL      [本文引用: 1]      摘要 CH4和CO2在页岩黏土矿物中的吸附行为对页岩气的开采和CO2的封存具有重要意义。选取黏土矿物的主要成分蒙脱石为研究对象,构建层状裂缝型孔隙的分子模型,采用巨正则系综蒙特卡洛（GCMC）方法和分子动力学（MD）方法,在不同压力、不同温度条件下,研究不同狭缝孔隙宽度CH4和CO2气体的吸附行为,同时分析离子交换结构对吸附的影响。结果表明：CH4吸附符合Langmuir吸附规律,可以采用Langmuir方程进行拟合。随着温度的升高两种气体吸附量减小,随着压力的增大而增大;蒙脱石的离子交换结构对CH4的吸附影响较小,但促进对CO2的吸附;不同的狭缝孔隙宽度对应CH4和CO2的赋存状态不同,蒙脱石的离子交换结构影响CO2的赋存状态;平均作用势说明吸附层中分子间结合能力大于游离层,吸附态是CH4和CO2在蒙脱石狭缝中的主要赋存形式之一。基于CH4和CO2在页岩黏土矿物中的吸附规律,可为页岩气的勘探开发提供依据。 (Sui H G, Yao J.2016. Molecular simulation of CH$_{4}$/CO$_{2}$ adsorption in clay minarals . Journal of Northeast Petroleum University, 40: 90-99). DOI      URL      [本文引用: 1]      摘要 CH4和CO2在页岩黏土矿物中的吸附行为对页岩气的开采和CO2的封存具有重要意义。选取黏土矿物的主要成分蒙脱石为研究对象,构建层状裂缝型孔隙的分子模型,采用巨正则系综蒙特卡洛（GCMC）方法和分子动力学（MD）方法,在不同压力、不同温度条件下,研究不同狭缝孔隙宽度CH4和CO2气体的吸附行为,同时分析离子交换结构对吸附的影响。结果表明：CH4吸附符合Langmuir吸附规律,可以采用Langmuir方程进行拟合。随着温度的升高两种气体吸附量减小,随着压力的增大而增大;蒙脱石的离子交换结构对CH4的吸附影响较小,但促进对CO2的吸附;不同的狭缝孔隙宽度对应CH4和CO2的赋存状态不同,蒙脱石的离子交换结构影响CO2的赋存状态;平均作用势说明吸附层中分子间结合能力大于游离层,吸附态是CH4和CO2在蒙脱石狭缝中的主要赋存形式之一。基于CH4和CO2在页岩黏土矿物中的吸附规律,可为页岩气的勘探开发提供依据。
[79]	孙海, 姚军, 张磊, 王晨晨, 孙致学, 闫永平, 庞鹏. 2014. 基于孔隙结构的页岩渗透率计算方法 . 中国石油大学学报(自然科学版), 38: 92-98 DOI      URL      [本文引用: 1]      摘要 采用修正表观渗透率的达西定律可描述气体在致密页岩中的运移机制。表观渗透率可用固有渗透率和孔隙度表示,而常规的试验方法无法准确测量页岩气藏的固有渗透率和孔隙度。提出一种基于孔隙结构图像的页岩固有渗透率、孔隙度和表观渗透率计算方法,首先基于X射线衍射和扫描电镜分析页岩岩心的矿物组成和孔隙结构,采用马尔科夫链蒙特卡洛方法构建页岩三维数字岩心,并应用格子Boltzmann方法计算数字岩心的孔隙度和固有渗透率,得到固有渗透率和孔隙度的关系式并计算页岩的表观渗透率。结果表明:页岩中孔隙主要为纳米级孔隙和微米级孔隙;努森数小于0.01时表观渗透率等于固有渗透率,此时达西定律仍然适用;努森数大于0.01时,数值越大,表观渗透率系数越大,此时达西定律不再适用;固有渗透率越小,压力越小,表观渗透率系数越大。 (Sun H, Yao J, Zhang L, Wang C C, Sun Z X, Yan Y P, Pang P.2014. A computing method of shale permeability based on pore structures . Journal of China University of Petroleum, 38: 92-98). DOI      URL      [本文引用: 1]      摘要 采用修正表观渗透率的达西定律可描述气体在致密页岩中的运移机制。表观渗透率可用固有渗透率和孔隙度表示,而常规的试验方法无法准确测量页岩气藏的固有渗透率和孔隙度。提出一种基于孔隙结构图像的页岩固有渗透率、孔隙度和表观渗透率计算方法,首先基于X射线衍射和扫描电镜分析页岩岩心的矿物组成和孔隙结构,采用马尔科夫链蒙特卡洛方法构建页岩三维数字岩心,并应用格子Boltzmann方法计算数字岩心的孔隙度和固有渗透率,得到固有渗透率和孔隙度的关系式并计算页岩的表观渗透率。结果表明:页岩中孔隙主要为纳米级孔隙和微米级孔隙;努森数小于0.01时表观渗透率等于固有渗透率,此时达西定律仍然适用;努森数大于0.01时,数值越大,表观渗透率系数越大,此时达西定律不再适用;固有渗透率越小,压力越小,表观渗透率系数越大。
[80]	孙海成, 汤达祯, 蒋廷学. 页岩气储层裂缝系统影响产量的数值模拟研究 . 石油钻探技术, 2011, 39: 63-67 DOI      URL      [本文引用: 1]      摘要 页岩气储层中的裂缝系统对页岩气产量有着重要的影响。以四川盆地志留系含气页岩气层为基础,利用数值模拟手段分析了页岩气储层的基质渗透率、裂缝连通性、裂缝密度(改造体积)、页岩气储层主裂缝与次裂缝对产量的影响,并对页岩气井的压后产量递减规律进行了分析。结果表明:基质渗透率越低,对完井方式和改造规模要求越高;在超低渗透页岩气储层中,只有相互连通的有效裂缝对产量有贡献;改造体积越大,压后产量和最终的采收率越高;相同改造体积下,主裂缝的发育程度对于初期产量的影响较大,但对最终采收率影响较小;页岩气井生产过程中的递减主要发生在投产初期的1.0～1.5a,其递减率60%～70%。 (Sun H C, Tang D Z, Jiang T X.2011. Numerical simulation of the impact of fracture system on well production in shale formation . Petroleum Drilling Techniques, 39: 63-67). DOI      URL      [本文引用: 1]      摘要 页岩气储层中的裂缝系统对页岩气产量有着重要的影响。以四川盆地志留系含气页岩气层为基础,利用数值模拟手段分析了页岩气储层的基质渗透率、裂缝连通性、裂缝密度(改造体积)、页岩气储层主裂缝与次裂缝对产量的影响,并对页岩气井的压后产量递减规律进行了分析。结果表明:基质渗透率越低,对完井方式和改造规模要求越高;在超低渗透页岩气储层中,只有相互连通的有效裂缝对产量有贡献;改造体积越大,压后产量和最终的采收率越高;相同改造体积下,主裂缝的发育程度对于初期产量的影响较大,但对最终采收率影响较小;页岩气井生产过程中的递减主要发生在投产初期的1.0～1.5a,其递减率60%～70%。
[81]	孙张涛, 吴西顺. 2014. 页岩气开采中的水力压裂与无水压裂技术 . 国土资源情报, 5: 51-55 DOI      URL      [本文引用: 1]      摘要 随着＂十二五＂规划的发布,页岩气的大规模勘探开发在我国被提上议事日程。对于我国目前的页岩气勘探开发而言,技术配套和攻关是首要任务,还需处理好相关的环境问题。然而,页岩气开采中常用的水力压裂技术始终面临着两大难题：水资源的大量消耗和压裂导致的相关污染等。因此,出于环保和节约水资源的考虑,国外许多公司都加大了对氮气泡沫压裂、CO2压裂和液化油气压裂等无水压裂技术的研发投入。无水压裂技术不仅可以解决缺水难题,还能减少页岩气开发对环境造成的污染,可谓一举两得。目前我国尚未完全掌握相关核心技术,水资源又相对缺乏,基于这样的现实考虑,无水压裂技术或许能够解决我国页岩气开发中的水资源难题。 (Sun Z, Wu X S.2014. Review on Hydraulic fracturing and non-aqueous fracturing in shale gas development . Land & Resources Information, 5: 51-55). DOI      URL      [本文引用: 1]      摘要 随着＂十二五＂规划的发布,页岩气的大规模勘探开发在我国被提上议事日程。对于我国目前的页岩气勘探开发而言,技术配套和攻关是首要任务,还需处理好相关的环境问题。然而,页岩气开采中常用的水力压裂技术始终面临着两大难题：水资源的大量消耗和压裂导致的相关污染等。因此,出于环保和节约水资源的考虑,国外许多公司都加大了对氮气泡沫压裂、CO2压裂和液化油气压裂等无水压裂技术的研发投入。无水压裂技术不仅可以解决缺水难题,还能减少页岩气开发对环境造成的污染,可谓一举两得。目前我国尚未完全掌握相关核心技术,水资源又相对缺乏,基于这样的现实考虑,无水压裂技术或许能够解决我国页岩气开发中的水资源难题。
[82]	唐杰. 2014. 各向异性岩石的静态模量与动态模量实验研究 . 岩石力学与工程学报, 1: 3185-3191 URL      [本文引用: 1]      摘要 Shales are important source rocks and sealing rocks with intrinsic anisotropy. The character of stress-strain response and ultrasonic speed response for shales are obtained by experimental measurement，and the features of static and dynamic moduli on anisotropic rock are studied. The dynamic modulus of anisotropic rock is gained by measuring vertical and horizontal wave velocities of core under different directions，and the static modulus is obtained through the measurement of stress-strain characteristics in loading process. Characteristics of wave velocity and elasticity modulus of anisotropic rock under quasi-static and dynamic conditions are analyzed. Except the difference of loading frequency，the strain amplitude difference are obtained respectively under static and dynamic measurements. Study of geophysical response characteristics for anisotropic rocks is of great significance. (Tang J.2014. Experimental study of static and dynamic moduli for anisotropic rock . Chinese Journal of Rock Mechanics and Engineering, 1: 3185-3191). URL      [本文引用: 1]      摘要 Shales are important source rocks and sealing rocks with intrinsic anisotropy. The character of stress-strain response and ultrasonic speed response for shales are obtained by experimental measurement，and the features of static and dynamic moduli on anisotropic rock are studied. The dynamic modulus of anisotropic rock is gained by measuring vertical and horizontal wave velocities of core under different directions，and the static modulus is obtained through the measurement of stress-strain characteristics in loading process. Characteristics of wave velocity and elasticity modulus of anisotropic rock under quasi-static and dynamic conditions are analyzed. Except the difference of loading frequency，the strain amplitude difference are obtained respectively under static and dynamic measurements. Study of geophysical response characteristics for anisotropic rocks is of great significance.
[83]	唐颖, 唐玄, 王广源, 张琴. 2011. 页岩气开发水力压裂技术综述 . 地质通报, 30: 393-399 DOI      URL      [本文引用: 1]      摘要 世界页岩气资源丰富,但由于页岩地层渗透率很低,目前还没有广泛开发。水力压裂技术是页岩气开发的核心技术之一,广泛用于页岩储层的改造。介绍了水力压裂作业的压裂设计、裂缝监测、压裂液配制和添加剂选择,以及常用的压裂技术,包括多级压裂、清水压裂、同步压裂、水力喷射压裂和重复压裂。结合国外页岩气开发的实例和国内压裂技术的应用情况,分析了各种压裂技术的适用性。研究认为,清水压裂是现阶段中国页岩气开发储层改造的适用技术,开采长度(厚度)大的页岩气井,可以使用多级分段清水压裂技术。同步压裂技术是规模化的页岩气开发的客观需要。 (Tang Y, Tang X, Wang G Y, Zhang Q.2011. Summary of hydraulic fracturing technology in shale gas development . Geological Bulletin of China, 30: 393-399). DOI      URL      [本文引用: 1]      摘要 世界页岩气资源丰富,但由于页岩地层渗透率很低,目前还没有广泛开发。水力压裂技术是页岩气开发的核心技术之一,广泛用于页岩储层的改造。介绍了水力压裂作业的压裂设计、裂缝监测、压裂液配制和添加剂选择,以及常用的压裂技术,包括多级压裂、清水压裂、同步压裂、水力喷射压裂和重复压裂。结合国外页岩气开发的实例和国内压裂技术的应用情况,分析了各种压裂技术的适用性。研究认为,清水压裂是现阶段中国页岩气开发储层改造的适用技术,开采长度(厚度)大的页岩气井,可以使用多级分段清水压裂技术。同步压裂技术是规模化的页岩气开发的客观需要。
[84]	唐颖, 邢云, 李乐忠, 张滨海, 蒋时馨. 2012. 页岩储层可压裂性影响因素及评价方法 . 地学前缘, 19: 356-363 URL      [本文引用: 1]      摘要 可压裂性是页岩在水力压裂中具有能够被有效压裂的能力的性质,是页岩开发中最关键的评价参数,影响因素包括页岩脆性、天然裂缝、石英含量、成岩作用及其他因素,目前常利用页岩矿物组成或岩石力学参数来表征,难以全面反映页岩在水力压裂过程中的综合性质。采用极差变换和经验赋值方法将参数标准化,使用层次分析法确定不同因数对可压裂性影响的权重,使用标准化值与权重系数加权得到可压裂系数的数学模型可对页岩可压裂性进行定量评价。可压裂系数越大,页岩可压裂性越强。采用该模型计算渝东南地区渝页1井龙马溪组页岩可压裂系数为0.485 5,Barnett页岩可压裂系数为0.484 4,总体处于同一水平;同时,使用该模型将页岩可压裂性分为3个级别,可压裂系数在0.132 0～0.282 0的页岩可压裂性低,水力压裂效果不佳;可压裂系数在0.282 0～0.456 7的页岩可压裂性中等,水力压裂能够取得较好的效果;可压裂系数在0.456 7～0.784 0的页岩可压裂性高,是优质的可压裂层。水力压裂应选择可压裂系数大于0.360 7的页岩。 (Tang Y, Xing Y, Li L Z, Zhang B H, Jiang S X.2012. Influence factors and evaluation methods of the gas shale fracability . Earth Science Frontiers, 19: 356-363). URL      [本文引用: 1]      摘要 可压裂性是页岩在水力压裂中具有能够被有效压裂的能力的性质,是页岩开发中最关键的评价参数,影响因素包括页岩脆性、天然裂缝、石英含量、成岩作用及其他因素,目前常利用页岩矿物组成或岩石力学参数来表征,难以全面反映页岩在水力压裂过程中的综合性质。采用极差变换和经验赋值方法将参数标准化,使用层次分析法确定不同因数对可压裂性影响的权重,使用标准化值与权重系数加权得到可压裂系数的数学模型可对页岩可压裂性进行定量评价。可压裂系数越大,页岩可压裂性越强。采用该模型计算渝东南地区渝页1井龙马溪组页岩可压裂系数为0.485 5,Barnett页岩可压裂系数为0.484 4,总体处于同一水平;同时,使用该模型将页岩可压裂性分为3个级别,可压裂系数在0.132 0～0.282 0的页岩可压裂性低,水力压裂效果不佳;可压裂系数在0.282 0～0.456 7的页岩可压裂性中等,水力压裂能够取得较好的效果;可压裂系数在0.456 7～0.784 0的页岩可压裂性高,是优质的可压裂层。水力压裂应选择可压裂系数大于0.360 7的页岩。
[85]	王爱国. 2008. 微地震监测与模拟技术在裂缝研究中的应用 . [博士论文]. 北京:中国石油大学 URL      摘要 油田注水和压裂微地震实时监测是目前国内外方兴未艾的研究热点课题,在油田的推广应用中主要面临着如何实现自动化监测、提高系统灵敏度和实时精确定位的难题。为此研制了一套以三分量MEMS检波器为核心硬件的微地震监测系统,并结合GPS系统对监测过程进行精确授时。同时编制数据化记录和处理软件,实现网络化自动监测功能,通过开发计算机判别标准和实时定位理论系统,对数据和微震源进行自动化处理和计算。 利用本系统对花岗岩单轴压裂过程的声发射事件进行了研究。由于当岩石受力变形和断裂时会产生声发射现象(弹性波),因此对其声发射事件的分析可用来研究岩石裂纹形成机制和断裂过程。研究发现岩石试样破裂失稳可划分为四个过程。在整个应力加载过程中,发现声发射事件次数随岩石应变呈增长趋势,后在岩石发生宏观断裂前呈减少趋势;声发射能量一直呈增长趋势,在岩石宏观断裂时达到最大;其声发射信号的频率一般为:0-800Hz;研究同时也表明可通过统计声发射事件数量来判断现场实际应用中岩石断裂发生几率,也可通过对事件本身的定位(微震源定位)来研究岩石断裂位置,因此这套系统可应用于煤矿、水库、和油田压裂等微地震的监测。 利用该系统对东辛油田营11进行了六个月现场注水微震监测,对监测数据的处理表明营11注水区域裂缝发育方向基本上为NE90°-NE125°;同时营11地区油藏地应力数值模拟结果分析表明其水平最大主应力的方向主要分布在NE90°-NE130°的范围内,研究范围中西北区块的水平最大主应力方向近似为东西向,研究区块的东部边界的水平最大主应力方向近似为NE130°左右,模拟结果与裂缝监测方位相符较好,两者结合给出了这个地区合理开发部署建议。裂缝误差分析表明监测结果可以控制在一个合理的范围内,监测结果表明系统还应该进一步提高监测灵敏度和完善算法功能,以符合在低渗透油田开发管理中的推广应用。 油田水力压裂是改造低渗透油气藏的重要手段,并且水力压裂的破裂能量更高,更有利于监测。在油田生产过程中,水力压裂产生裂缝有多长,裂缝朝哪个方向延伸,压裂井是否和周围的水井连通等问题在以前都无法即时直接地解决。因此利用微地震监测系统对西南油气分公司新场和马井地区进行了水力压裂监测试验,水力压裂微地震试验研究结果给出了可靠的裂缝三维图像,揭示了裂缝发育状况。同时发现水力压裂裂缝生长速率是不均匀的,在水力压裂的不同时间段,裂缝生长速率差别很大,在开始断裂的一段时间内,裂缝生长的最为迅速,而后裂缝生长速度减慢;通常裂缝两翼常常是不对称的;裂缝面基本上是垂直的。 研究发现岩石破裂与晶体结构有重要关系,而储层岩石的矿物成分及晶体结构也影响了岩石的破裂,宏观及微观上岩石的裂缝都是呈Z字型发展,具体的发展模式还要看储层的岩石性质。并且水饱和对岩石的波速具有影响,一般水饱和的岩石比干燥岩石波速要大,而与油气饱和的关系有待进一步进行实验研究。水-岩化学作用对岩石的断裂也有重要的影响,一方面可以增强岩石的破裂强度,另一方面也可能降低岩石的破裂强度,具体的影响还要看岩石的结构和成分,以及地层水的化学性质。另外,地温场也能够对岩石的破裂起到一定的辅助作用,其主要表现为高温增加岩石的裂缝孔隙度,从而加剧水-岩作用。 总之,本文利用自行研制的微地震监测系统对油田生产中的注水和水力压裂诱生微地震进行了监测,监测结果可以合理的解释出裂缝的发育规律,这一技术在未来油田的生产中具有重大的应用价值。 (Wang A G. 2008. Application of micro-seismic monitoring and simulation technology in the research of fracture. [PhD Thesis]. Beijing: China University of Petroleum). URL      摘要 油田注水和压裂微地震实时监测是目前国内外方兴未艾的研究热点课题,在油田的推广应用中主要面临着如何实现自动化监测、提高系统灵敏度和实时精确定位的难题。为此研制了一套以三分量MEMS检波器为核心硬件的微地震监测系统,并结合GPS系统对监测过程进行精确授时。同时编制数据化记录和处理软件,实现网络化自动监测功能,通过开发计算机判别标准和实时定位理论系统,对数据和微震源进行自动化处理和计算。 利用本系统对花岗岩单轴压裂过程的声发射事件进行了研究。由于当岩石受力变形和断裂时会产生声发射现象(弹性波),因此对其声发射事件的分析可用来研究岩石裂纹形成机制和断裂过程。研究发现岩石试样破裂失稳可划分为四个过程。在整个应力加载过程中,发现声发射事件次数随岩石应变呈增长趋势,后在岩石发生宏观断裂前呈减少趋势;声发射能量一直呈增长趋势,在岩石宏观断裂时达到最大;其声发射信号的频率一般为:0-800Hz;研究同时也表明可通过统计声发射事件数量来判断现场实际应用中岩石断裂发生几率,也可通过对事件本身的定位(微震源定位)来研究岩石断裂位置,因此这套系统可应用于煤矿、水库、和油田压裂等微地震的监测。 利用该系统对东辛油田营11进行了六个月现场注水微震监测,对监测数据的处理表明营11注水区域裂缝发育方向基本上为NE90°-NE125°;同时营11地区油藏地应力数值模拟结果分析表明其水平最大主应力的方向主要分布在NE90°-NE130°的范围内,研究范围中西北区块的水平最大主应力方向近似为东西向,研究区块的东部边界的水平最大主应力方向近似为NE130°左右,模拟结果与裂缝监测方位相符较好,两者结合给出了这个地区合理开发部署建议。裂缝误差分析表明监测结果可以控制在一个合理的范围内,监测结果表明系统还应该进一步提高监测灵敏度和完善算法功能,以符合在低渗透油田开发管理中的推广应用。 油田水力压裂是改造低渗透油气藏的重要手段,并且水力压裂的破裂能量更高,更有利于监测。在油田生产过程中,水力压裂产生裂缝有多长,裂缝朝哪个方向延伸,压裂井是否和周围的水井连通等问题在以前都无法即时直接地解决。因此利用微地震监测系统对西南油气分公司新场和马井地区进行了水力压裂监测试验,水力压裂微地震试验研究结果给出了可靠的裂缝三维图像,揭示了裂缝发育状况。同时发现水力压裂裂缝生长速率是不均匀的,在水力压裂的不同时间段,裂缝生长速率差别很大,在开始断裂的一段时间内,裂缝生长的最为迅速,而后裂缝生长速度减慢;通常裂缝两翼常常是不对称的;裂缝面基本上是垂直的。 研究发现岩石破裂与晶体结构有重要关系,而储层岩石的矿物成分及晶体结构也影响了岩石的破裂,宏观及微观上岩石的裂缝都是呈Z字型发展,具体的发展模式还要看储层的岩石性质。并且水饱和对岩石的波速具有影响,一般水饱和的岩石比干燥岩石波速要大,而与油气饱和的关系有待进一步进行实验研究。水-岩化学作用对岩石的断裂也有重要的影响,一方面可以增强岩石的破裂强度,另一方面也可能降低岩石的破裂强度,具体的影响还要看岩石的结构和成分,以及地层水的化学性质。另外,地温场也能够对岩石的破裂起到一定的辅助作用,其主要表现为高温增加岩石的裂缝孔隙度,从而加剧水-岩作用。 总之,本文利用自行研制的微地震监测系统对油田生产中的注水和水力压裂诱生微地震进行了监测,监测结果可以合理的解释出裂缝的发育规律,这一技术在未来油田的生产中具有重大的应用价值。
[86]	王安仕, 秦发动. 1998. 高能气体压裂技术. 西安:西北大学出版社 [本文引用: 1]      (Wang A S, Qin F D.1998. High Energy Gas Fracturing Technology. Xi'an: Northwestern University Press). [本文引用: 1]
[87]	王华龙, 柴振华, 郭照立. 2009. 致密多孔介质中气体渗流的格子Boltzmann模拟 . 计算物理, 26: 389-395 DOI      URL      [本文引用: 2]      摘要 为了能用格子Boltzmann方法来正确地刻画致密多孔介质中微尺度流动问题,对单通道模型进行推广,并将其应用于孔隙群里气体渗流的数值模拟.通过对部分具有代表性的多孔介质中的实际流动问题进行模拟,研究渗透率与平均压力和Knudsen数之间的相互关系.基于理论分析及相关文献中的试验结果,验证模拟结果,为用格子Boltzmann方法深入研究气体渗流问题奠定基础. (Wang H L, Cha Z H, Guo Z L.2009. Lattice Boltzmann simulation of gas transfusion in compact porous media , Chinese Journal of Computational Physics, 26: 389-395). DOI      URL      [本文引用: 2]      摘要 为了能用格子Boltzmann方法来正确地刻画致密多孔介质中微尺度流动问题,对单通道模型进行推广,并将其应用于孔隙群里气体渗流的数值模拟.通过对部分具有代表性的多孔介质中的实际流动问题进行模拟,研究渗透率与平均压力和Knudsen数之间的相互关系.基于理论分析及相关文献中的试验结果,验证模拟结果,为用格子Boltzmann方法深入研究气体渗流问题奠定基础.
[88]	王建华. 2007. 地震波初至自动拾取算法研究及三分量测井系统软件设计 . [博士论文]. 长沙: 中南大学 DOI      [本文引用: 3]      摘要 地震波初至时间的自动拾取一直是地震勘探中的一个基础问题。它在折射波静校正、VSP资料处理及解释、浅层折射波勘探和层析成像等地震勘探中起着关键的作用，因为在这些勘探方法的解释中初至时间直接关系地下地层结构速度或慢度的反演结果。 本文首先简述了各时期地震数据采集系统的特点和地震波初至拾取方法的基本原理，着重研究了能量比、分形维、人工神经网络和边缘检测这几种初至算法。在对这几种初至自动拾取方法理论研究的基础上，基于地震道的时窗属性特征和初至自动拾取的能量比方法，本文给出了一种改进的能量比初至拾取算法。该算法从二个方面对能量比方法进行了改进：第一，用波形的包络能量代替振幅能量，从而在弱初至时，可以较好拾取初至时间；第二，用滚动时窗法取代传统的静态时窗划分，实现快速拾取地震道的初至。本文从理论上论证了该方法的可行性，并且将该方法用于实际地震数据初至拾取，与常用初至自动拾取方法加以对比，验证了该方法的有效性。 基于该初至拾取算法，根据实际检层法测井的需要，结合物探所现有“震(振)动综合测试系统”硬件设备，利用Visual C++6.0开发工具，设计了相应的系统数据采集及解释软件——三分量检层法测井软件，其主要功能有：文件管理、数据的采集及实时显示、波形的操作、数据的处理、资料的解释及成果输出等，论文给出了主要源程序代码。笔者在软件系统的设计中，嵌入了模块化思想，为今后完善和移植三分量检层法测井软件奠定了基础。最后，通过模拟三分量检层法测井实验全面验证了软件的可操作性及实用性。 (Wang J H.2007. The automatic pick of seismic first arrivals and the design of the simulation of three-component logging . [PhD Thesis]. Changsha: Central South University). DOI      [本文引用: 3]      摘要 地震波初至时间的自动拾取一直是地震勘探中的一个基础问题。它在折射波静校正、VSP资料处理及解释、浅层折射波勘探和层析成像等地震勘探中起着关键的作用，因为在这些勘探方法的解释中初至时间直接关系地下地层结构速度或慢度的反演结果。 本文首先简述了各时期地震数据采集系统的特点和地震波初至拾取方法的基本原理，着重研究了能量比、分形维、人工神经网络和边缘检测这几种初至算法。在对这几种初至自动拾取方法理论研究的基础上，基于地震道的时窗属性特征和初至自动拾取的能量比方法，本文给出了一种改进的能量比初至拾取算法。该算法从二个方面对能量比方法进行了改进：第一，用波形的包络能量代替振幅能量，从而在弱初至时，可以较好拾取初至时间；第二，用滚动时窗法取代传统的静态时窗划分，实现快速拾取地震道的初至。本文从理论上论证了该方法的可行性，并且将该方法用于实际地震数据初至拾取，与常用初至自动拾取方法加以对比，验证了该方法的有效性。 基于该初至拾取算法，根据实际检层法测井的需要，结合物探所现有“震(振)动综合测试系统”硬件设备，利用Visual C++6.0开发工具，设计了相应的系统数据采集及解释软件——三分量检层法测井软件，其主要功能有：文件管理、数据的采集及实时显示、波形的操作、数据的处理、资料的解释及成果输出等，论文给出了主要源程序代码。笔者在软件系统的设计中，嵌入了模块化思想，为今后完善和移植三分量检层法测井软件奠定了基础。最后，通过模拟三分量检层法测井实验全面验证了软件的可操作性及实用性。
[89]	王杰, 李世海, 张青波. 2015. 基于单元破裂的岩石裂纹扩展模拟方法 . 力学学报, 47: 105-118 DOI      URL      摘要 In conventional discrete element methods, fracture is judged by criterion of interface and cracks can only propagate along the boundary of elements. However, criterion of interface can only be used rationally on the condition that macro or micro fractures exist in physical problems. The path and direction of crack will be limited severely by the initial mesh when crack propagates along the boundary. Given these two limitations, a continuous-discontinuous element method is proposed and applied to simulate the progressing cracking problem of rocks. Specifically, criterion is applied on element and intra-element fracture will form. In continuous calculation, element is denoted by a discrete spring system which has specific physical meaning and its deformation and stress are calculated by the characteristic length and area of springs in local coordinate system. The continuous calculation results demonstrate a satisfactory agreement with the traditional finite element method. By updating spring information and local coordinate system, large displacement and rotation of elements can be calculated directly. In addition, Mohr-Coulomb criterion is implemented into the new model to specify the failure state and fracture direction, and intact element will be divided into two elements by means of cutting block. In this way, fracture may be inserted along the boundary of elements or within intact element. A cohesive zone model is employed to simulate the fracture and the elements on two sides of the crack are set to two different nodes at the same time, causing the displacement to be discontinuous. Finally, from numerical results of several intense examples with crack propagation, this method can satisfactorily simulate the progressing cracking problems under tensile, compressive and shear conditions, and its rationality is approved. The continuous-discontinuous element method has been shown to be insensitive to quality of mesh and thus has the potential to simulate crack initiation and propagation. (Wang J, Li S H, Zhang Q B.2015. Simulation of crack propagation of rock based on splitting elements . Chinese Journal of Theoretical and Applied Mechanics, 47: 105-118). DOI      URL      摘要 In conventional discrete element methods, fracture is judged by criterion of interface and cracks can only propagate along the boundary of elements. However, criterion of interface can only be used rationally on the condition that macro or micro fractures exist in physical problems. The path and direction of crack will be limited severely by the initial mesh when crack propagates along the boundary. Given these two limitations, a continuous-discontinuous element method is proposed and applied to simulate the progressing cracking problem of rocks. Specifically, criterion is applied on element and intra-element fracture will form. In continuous calculation, element is denoted by a discrete spring system which has specific physical meaning and its deformation and stress are calculated by the characteristic length and area of springs in local coordinate system. The continuous calculation results demonstrate a satisfactory agreement with the traditional finite element method. By updating spring information and local coordinate system, large displacement and rotation of elements can be calculated directly. In addition, Mohr-Coulomb criterion is implemented into the new model to specify the failure state and fracture direction, and intact element will be divided into two elements by means of cutting block. In this way, fracture may be inserted along the boundary of elements or within intact element. A cohesive zone model is employed to simulate the fracture and the elements on two sides of the crack are set to two different nodes at the same time, causing the displacement to be discontinuous. Finally, from numerical results of several intense examples with crack propagation, this method can satisfactorily simulate the progressing cracking problems under tensile, compressive and shear conditions, and its rationality is approved. The continuous-discontinuous element method has been shown to be insensitive to quality of mesh and thus has the potential to simulate crack initiation and propagation.
[90]	王理想, 李世海, 马照松, 冯春. 2015. 一种中心型有限体积孔隙-裂隙渗流求解方法及其OpenMP并行化 . 岩石力学与工程学报, 34: 865-875 DOI      URL      [本文引用: 2]      摘要 An efficient three-dimensional cell-centered Finite Volume Method(ccFVM) is developed for single- phase fluid flow in fractured porous media. It works on arbitrary grids and is parallelized through OpenMP. With pressure centered in the cell，the ccFVM employs spring-in-series model for space discretization and explicit difference scheme for time discretization. It uses dynamic relaxation technique for element-by-element iteration. Numerical tests indicate that the ccFVM is as accurate as FEM，but more efficient. The parallel procedure obtains a speedup of 4.0 on CPU i7-3770 and a speedup of 4.2 on CPU i7-4770. High parallel efficiency of over 50% is achieved on both machines. (Wang L X, Li S H, Ma Z S, Feng C.2015. A cell-centered finite volume method for fluid flow in fractured porous media and its parallelization with OpenMP . Chinese Journal of Rock Mechanics and Engineering, 34: 865-875). DOI      URL      [本文引用: 2]      摘要 An efficient three-dimensional cell-centered Finite Volume Method(ccFVM) is developed for single- phase fluid flow in fractured porous media. It works on arbitrary grids and is parallelized through OpenMP. With pressure centered in the cell，the ccFVM employs spring-in-series model for space discretization and explicit difference scheme for time discretization. It uses dynamic relaxation technique for element-by-element iteration. Numerical tests indicate that the ccFVM is as accurate as FEM，but more efficient. The parallel procedure obtains a speedup of 4.0 on CPU i7-3770 and a speedup of 4.2 on CPU i7-4770. High parallel efficiency of over 50% is achieved on both machines.
[91]	王理想, 唐德泓, 李世海, 王杰, 冯春. 2015. 基于混合方法的二维水力压裂数值模拟 . 力学学报, 47: 973-983 DOI      URL      [本文引用: 1]      摘要 Hydraulic fracturing is widely used in exploitation of shale gas nowadays. It is of great significance to study the mechanism of fracturing process by numerical simulations. We present a mixed numerical model to solve hydraulic fracturing problems based on Continuous-Discontinuous Element Method (CDEM) and Finite Volume Method (FVM). In the mixed model, the CDEM is used for analysis of stress field and fracture propagation, and the FVM is used for analysis of pressure field in fracture. The three fields are all solved by explicit schemes and the coupling of them is implemented through data exchange. The model is verified against the classic KGD analytical solutions. Thereafter, it is validated by the results from a distinct element simulation. Finally, a hydraulic fracturing example related to complex fracture network is studied on the mechanism of fracturing process. The example shows bright future of the mixed numerical model for simulation and mechanism study of hydrauling fracturing. (Wang L X, Tang D H, Li S H, Wang J, Feng C.2015. Numerical simulation of hydraulic fracturing by a mixed method in two dimensions . Chinese Journal of Theoretical and Applied Mechanics, 47: 973-983). DOI      URL      [本文引用: 1]      摘要 Hydraulic fracturing is widely used in exploitation of shale gas nowadays. It is of great significance to study the mechanism of fracturing process by numerical simulations. We present a mixed numerical model to solve hydraulic fracturing problems based on Continuous-Discontinuous Element Method (CDEM) and Finite Volume Method (FVM). In the mixed model, the CDEM is used for analysis of stress field and fracture propagation, and the FVM is used for analysis of pressure field in fracture. The three fields are all solved by explicit schemes and the coupling of them is implemented through data exchange. The model is verified against the classic KGD analytical solutions. Thereafter, it is validated by the results from a distinct element simulation. Finally, a hydraulic fracturing example related to complex fracture network is studied on the mechanism of fracturing process. The example shows bright future of the mixed numerical model for simulation and mechanism study of hydrauling fracturing.
[92]	王理想. 2015. 页岩体水力压裂数值模拟方法及机理研究 . [博士论文]. 北京: 中国科学院大学 URL      摘要 美国页岩气开采取得巨大成功，掀起“页岩气革命”。虽然中国页岩气储量丰富，但受客观因素影响，开采难度极大且开采成本高。页岩气开采的关键技术之一是水力压裂技术。中国需要研究新的水力压裂技术，以节约开采成本。数值模拟为我们提供一种研究手段，可再现水力压裂过程，从而研究新压裂技术可行性。 使用水力压裂技术开发页岩气是否可行，关键是能否提高裂缝网络的复杂程度。该问题的本质是，如何通过人工裂缝诱导天然裂缝，从而使得天然裂缝激活并形成大规模连通性裂缝网络。天然裂缝的激活和裂缝网络的形成受诸多因素影响，如地应力的大小和方向、压裂液的黏度、压裂液注入流速等。采用数值模拟方法可研究上述压裂过程，并用于评价裂缝网络复杂程度。 当前最重要的是缺少高效的、准确的、能够模拟大规模多尺度的水力裂缝扩展模拟方法。当前数值模型和方法存在一些缺陷，如模型无法考虑页岩体水力压裂过程中可能存在的非线性流动，不考虑孔隙基质与裂隙之间的耦合流动，渗流-应力-破裂耦合无法做到真实大尺度模拟，裂缝扩展路径受到限制，隐式算法较难了解裂缝的动态扩展机理等等。 本文旨在解决上述问题，提出水力压裂裂缝网络扩展新数值模拟方法，包括： (1)实现三维孔隙-裂隙耦合渗流算法：该方法将压力节点置于中心处，提高计算效率，真实模拟孔隙基质-裂隙之间的耦合物理流动过程。 (2)一种新的渗流计算理论——LE渗流理论：该理论使用第二类Lagrange方程导出流体在多孔介质中的能量泛函，进而使用基于Euler描述下的Lagrange方程导出渗流积分方程，最后通过渗流面预估，使用中心型有限体积法进行数值离散求解。 (3)一种新的二维/三维水力压裂数值模拟方法——FE-DE-FV耦合数值方法：该方法将FEM、DEM、FVM进行耦合，求解多场问题，尤其是水力压裂问题；充分利用FEM的精度、DEM求解破裂问题的便捷性以及FVM高效性；该算法同时满足BB约束条件，保证了算法稳定性。 (4)GPU高性能并行算法研究：针对当前缺少快速求解大规模水力裂缝扩展模拟程序的状况，开发一种基于GPU的并行算法，用于高效求解水力裂缝扩展问题。 (5)水力压裂机理研究：通过计算不同水力压裂工况，研究压裂过程中的现象，了解其中的力学机理与规律。 (Wang L X.2015. Numerical simulation and mechanism analysis for hydraulic fracturing of shale . [PhD Thesis]. Beijing: University of Chinese Academy of sciences). URL      摘要 美国页岩气开采取得巨大成功，掀起“页岩气革命”。虽然中国页岩气储量丰富，但受客观因素影响，开采难度极大且开采成本高。页岩气开采的关键技术之一是水力压裂技术。中国需要研究新的水力压裂技术，以节约开采成本。数值模拟为我们提供一种研究手段，可再现水力压裂过程，从而研究新压裂技术可行性。 使用水力压裂技术开发页岩气是否可行，关键是能否提高裂缝网络的复杂程度。该问题的本质是，如何通过人工裂缝诱导天然裂缝，从而使得天然裂缝激活并形成大规模连通性裂缝网络。天然裂缝的激活和裂缝网络的形成受诸多因素影响，如地应力的大小和方向、压裂液的黏度、压裂液注入流速等。采用数值模拟方法可研究上述压裂过程，并用于评价裂缝网络复杂程度。 当前最重要的是缺少高效的、准确的、能够模拟大规模多尺度的水力裂缝扩展模拟方法。当前数值模型和方法存在一些缺陷，如模型无法考虑页岩体水力压裂过程中可能存在的非线性流动，不考虑孔隙基质与裂隙之间的耦合流动，渗流-应力-破裂耦合无法做到真实大尺度模拟，裂缝扩展路径受到限制，隐式算法较难了解裂缝的动态扩展机理等等。 本文旨在解决上述问题，提出水力压裂裂缝网络扩展新数值模拟方法，包括： (1)实现三维孔隙-裂隙耦合渗流算法：该方法将压力节点置于中心处，提高计算效率，真实模拟孔隙基质-裂隙之间的耦合物理流动过程。 (2)一种新的渗流计算理论——LE渗流理论：该理论使用第二类Lagrange方程导出流体在多孔介质中的能量泛函，进而使用基于Euler描述下的Lagrange方程导出渗流积分方程，最后通过渗流面预估，使用中心型有限体积法进行数值离散求解。 (3)一种新的二维/三维水力压裂数值模拟方法——FE-DE-FV耦合数值方法：该方法将FEM、DEM、FVM进行耦合，求解多场问题，尤其是水力压裂问题；充分利用FEM的精度、DEM求解破裂问题的便捷性以及FVM高效性；该算法同时满足BB约束条件，保证了算法稳定性。 (4)GPU高性能并行算法研究：针对当前缺少快速求解大规模水力裂缝扩展模拟程序的状况，开发一种基于GPU的并行算法，用于高效求解水力裂缝扩展问题。 (5)水力压裂机理研究：通过计算不同水力压裂工况，研究压裂过程中的现象，了解其中的力学机理与规律。
[93]	王林, 马金良, 苏凤瑞, 王大利. 2012. 北美页岩气工厂化压裂技术 . 钻采工艺, 35: 48-50 DOI      URL      摘要 北美地区页岩气开发的成功,在全球范围内掀起一股页岩气勘探的热潮,北美从上世纪80年代开始页岩气的开发,积累了丰富的经验,进入21世纪,随着水平井钻井和大型多段压裂技术的进步,使页岩气获得商业价值。为了进一步降低开发成本,开发者把工厂的概念应用到页岩气的开发中,促进了工厂化压裂模式的形成。北美开发实践表明,工厂化压裂可以缩短投产周期、降低采气成本、大幅提高压裂设备的利用率,减少设备动迁和安装,降低工人劳动强度。文章介绍了页岩气工厂化压裂的流程、组成部分和主要装备情况,并为国内开展此项技术提出了建议。 (Wang L, Ma J L, Su F R, Wang D L.2012. Shale gas factory fracturing technology North America . Drilling & Production Technology, 35: 48-50). DOI      URL      摘要 北美地区页岩气开发的成功,在全球范围内掀起一股页岩气勘探的热潮,北美从上世纪80年代开始页岩气的开发,积累了丰富的经验,进入21世纪,随着水平井钻井和大型多段压裂技术的进步,使页岩气获得商业价值。为了进一步降低开发成本,开发者把工厂的概念应用到页岩气的开发中,促进了工厂化压裂模式的形成。北美开发实践表明,工厂化压裂可以缩短投产周期、降低采气成本、大幅提高压裂设备的利用率,减少设备动迁和安装,降低工人劳动强度。文章介绍了页岩气工厂化压裂的流程、组成部分和主要装备情况,并为国内开展此项技术提出了建议。
[94]	王倩, 王鹏, 项德贵, 冯宇思. 2012. 页岩力学参数各向异性研究 . 天然气工业, 32: 62-65 DOI      URL      [本文引用: 4]      摘要 页岩气开发过程中钻遇的页岩储层,由于其层理构造具有明显的各向异性,开展相关研究对钻井和储层改造是十分重要的。分析认为,可以假设页岩为横观各向同性介质,并从横观各向同性应力应变关系的坐标变换出发,能够推导出层理性页岩方向性的弹性模量、泊松比与垂直层理、平行层理方向弹性常数的关系。通过不同层理倾角页岩岩样的单轴压缩实验和超声波实验测量岩样的抗压强度、动静态弹性模量和动静态泊松比,研究了页岩层理对其力学参数的影响。实验和理论计算结果均表明:将层理页岩看做横观各向同性介质在力学上是相对准确的;垂直层理方向的弹性模量和泊松比小于平行层理方向的弹性模量和泊松比;动态弹性参数的各向异性程度强于静态弹性参数的各向异性程度;层理岩石弹性模量、泊松比随层理倾角有规律变化;根据垂直和平行层理面的弹性常数可以确定任意方向上的弹性模量和泊松比。 (Wang Q, Wang P, Xiang D G, Feng Y S.2012. Anisotropic property of mechanical parameters of shales . Natural Gas Industry, 32: 62-65). DOI      URL      [本文引用: 4]      摘要 页岩气开发过程中钻遇的页岩储层,由于其层理构造具有明显的各向异性,开展相关研究对钻井和储层改造是十分重要的。分析认为,可以假设页岩为横观各向同性介质,并从横观各向同性应力应变关系的坐标变换出发,能够推导出层理性页岩方向性的弹性模量、泊松比与垂直层理、平行层理方向弹性常数的关系。通过不同层理倾角页岩岩样的单轴压缩实验和超声波实验测量岩样的抗压强度、动静态弹性模量和动静态泊松比,研究了页岩层理对其力学参数的影响。实验和理论计算结果均表明:将层理页岩看做横观各向同性介质在力学上是相对准确的;垂直层理方向的弹性模量和泊松比小于平行层理方向的弹性模量和泊松比;动态弹性参数的各向异性程度强于静态弹性参数的各向异性程度;层理岩石弹性模量、泊松比随层理倾角有规律变化;根据垂直和平行层理面的弹性常数可以确定任意方向上的弹性模量和泊松比。
[95]	王仁, 殷有泉. 1981. 工程岩体类介质的弹塑性本构关系 . 力学学报, 4: 317-325 DOI      URL      [本文引用: 1]      摘要 正 本文所讨论的岩石类介质是指岩石、土等地质材料以及混凝土一类的工程材料,而不讨论与地质构造运动有关的那些处在地壳深部以至地幔中的岩石。在工程条件下,岩石一般表现为脆性的,它只能承受很小的应变就行破坏。随着围压和温度的增加,它能承受的应变量逐渐增大,在宏观上表现出塑性的性质,而且蠕变、松弛等与时间因素有关的 (Wang R, Yin Y.1981. On the elastoplastic constitutive equation of engineering rock-like materials . Chinese Journal of Theoretical and Applied Mechanics, 4: 317-325). DOI      URL      [本文引用: 1]      摘要 正 本文所讨论的岩石类介质是指岩石、土等地质材料以及混凝土一类的工程材料,而不讨论与地质构造运动有关的那些处在地壳深部以至地幔中的岩石。在工程条件下,岩石一般表现为脆性的,它只能承受很小的应变就行破坏。随着围压和温度的增加,它能承受的应变量逐渐增大,在宏观上表现出塑性的性质,而且蠕变、松弛等与时间因素有关的
[96]	王瑞, 张宁生, 刘晓娟, 吴新民, 闫健. 2013. 页岩气扩散系数和视渗透率的计算与分析 . 西北大学学报: 自然科学版, 43: 75-80 DOI      URL      [本文引用: 1]      摘要 目的探究页岩低至纳米级孔隙中气体渗流能力以及分析扩散对总质量通量的贡献。方法先由Kn数划分流动区域，求得各区域对应扩散系数作为系统的扩散系数，然后将其代入气体在纳米孔隙介质中的扩散和渗流方程，最终求出相应的质量通量和视渗透率并分析孔隙半径大小和气体种类对它们的影响。结果页岩储层中气体扩散主要处在过渡扩散和Fick扩散区域；视渗透率与达西渗透率的比值以及扩散质量通量占总质量通量百分比都随孔隙半径的减小而增加；甲烷的扩散能力强于乙烷。结论页岩扩散系数的计算，如果只用Knudsen扩散系数模型会使计算结果偏大；考虑了扩散和滑脱效应后，在储层一般的温压条件下，甲烷在页岩纳米级孔隙中的视渗透率值为10^-6μm2级，而非10^-9μm2级。 (Wang R, Zhang N S, Liu X J, Wu X M, Yan J.2013. The Calculation and Analysis of Diffusion Coefficient and Apparent Permeability of Shale Gas . Journal of Northwest University (Natural Science Edition), 43: 75-80). DOI      URL      [本文引用: 1]      摘要 目的探究页岩低至纳米级孔隙中气体渗流能力以及分析扩散对总质量通量的贡献。方法先由Kn数划分流动区域，求得各区域对应扩散系数作为系统的扩散系数，然后将其代入气体在纳米孔隙介质中的扩散和渗流方程，最终求出相应的质量通量和视渗透率并分析孔隙半径大小和气体种类对它们的影响。结果页岩储层中气体扩散主要处在过渡扩散和Fick扩散区域；视渗透率与达西渗透率的比值以及扩散质量通量占总质量通量百分比都随孔隙半径的减小而增加；甲烷的扩散能力强于乙烷。结论页岩扩散系数的计算，如果只用Knudsen扩散系数模型会使计算结果偏大；考虑了扩散和滑脱效应后，在储层一般的温压条件下，甲烷在页岩纳米级孔隙中的视渗透率值为10^-6μm2级，而非10^-9μm2级。
[97]	王涛, 高岳, 柳占立, 王永辉, 杨立峰, 庄茁. 2014. 基于扩展有限元法的水力压裂大物模实验的数值模拟 . 清华大学学报(自然科学版), 54: 1304-1309 URL      [本文引用: 3]      摘要 该文在页岩水力压裂实验的基础上,采用扩展有限元方法(XFEM),发展了ABAQUS软件的显式用户单元子程序,实现了页岩水力压裂过程的初步数值模拟。通过在常规3维实体8节点单元中引入扩充自由度,实现在单元内引入不连续位移场,模拟了水力压裂的裂纹,且无需在裂纹扩展过程中重画网格。采用有限差分法(FDM)离散流体的连续方程,实现对裂缝内流体流动的模拟。对一般扩展有限元方法进行改进,引入虚拟节点,在显式方法中可以简化处理单元内的裂纹,同时在扩充8节点六面体单元中使用一点积分和沙漏控制,大大提高了计算效率。数值模拟结果与实验吻合得较好。 (Wang T, Gao Y, Liu Z L, Wang Y H, Yang L F, Zhuang Z.2014. Numerical simulations of hydraulic fracturing in large objects using an extended finite element method . J. Tsinghua Univ (Sci & Technol), 54: 1304-1309). URL      [本文引用: 3]      摘要 该文在页岩水力压裂实验的基础上,采用扩展有限元方法(XFEM),发展了ABAQUS软件的显式用户单元子程序,实现了页岩水力压裂过程的初步数值模拟。通过在常规3维实体8节点单元中引入扩充自由度,实现在单元内引入不连续位移场,模拟了水力压裂的裂纹,且无需在裂纹扩展过程中重画网格。采用有限差分法(FDM)离散流体的连续方程,实现对裂缝内流体流动的模拟。对一般扩展有限元方法进行改进,引入虚拟节点,在显式方法中可以简化处理单元内的裂纹,同时在扩充8节点六面体单元中使用一点积分和沙漏控制,大大提高了计算效率。数值模拟结果与实验吻合得较好。
[98]	王勇杰, 王昌杰, 高家碧. 1995. 低渗透多孔介质中气体滑脱行为研究 . 石油学报, 16: 101-105 DOI      URL      [本文引用: 1]      摘要 研究和讨论了气体滑脱的物理机制，推导了气体在多孔介质中流动包括滑脱速度在内的新方程，并且从实验得到了和理论分析一致的结果。 (Wang Y J, Wang C J, Gao J B.1995. A research of gas slip in low permeability porous media . Acta Petrolei Sinica, 16: 101-105). DOI      URL      [本文引用: 1]      摘要 研究和讨论了气体滑脱的物理机制，推导了气体在多孔介质中流动包括滑脱速度在内的新方程，并且从实验得到了和理论分析一致的结果。
[99]	王玉普, 左罗, 胡志明, 沈瑞, 熊伟, 高树生. 2015. 页岩高温高压吸附实验及吸附模型研究 . 中南大学学报(自然科学版), 46: 4129-4135 URL      摘要 基于对现有页岩吸附、超临界吸附的认识通过基本假设和统计热力学基本原理推导出一个高温高压等温吸附新模型,并用GAI-100高压等温吸附仪获取95.6℃下页岩及活性炭在0~50 MPa压力范围内的等温吸附曲线,研究结果表明:页岩及活性炭的高温高压等温吸附曲线具有超临界高压等温吸附曲线的典型特征即随着压力的增大过剩吸附量先增大后减小;该新模型能很好地描述页岩及活性炭的高温高压等温吸附曲线,说明此模型在很大程度上反映出超临界高压吸附的特性而且可用来描述页岩及活性炭的高温高压等温吸附曲线。 (Wang Y P, Zuo L, Hu Z M, Shen R, Xiong W, Gao S S.2015. Experiment of supercritical methane adsorption on shale and adsorption modelling . Journal of Central South University (Science and Technology), 46: 4129-4135). URL      摘要 基于对现有页岩吸附、超临界吸附的认识通过基本假设和统计热力学基本原理推导出一个高温高压等温吸附新模型,并用GAI-100高压等温吸附仪获取95.6℃下页岩及活性炭在0~50 MPa压力范围内的等温吸附曲线,研究结果表明:页岩及活性炭的高温高压等温吸附曲线具有超临界高压等温吸附曲线的典型特征即随着压力的增大过剩吸附量先增大后减小;该新模型能很好地描述页岩及活性炭的高温高压等温吸附曲线,说明此模型在很大程度上反映出超临界高压吸附的特性而且可用来描述页岩及活性炭的高温高压等温吸附曲线。
[100]	王祖文, 郭大立, 邓金根, 赵金洲, 曾晓慧. 2005. 射孔方式对压裂压力及裂缝形态的影响 . 西南石油学院学报, 27: 47-50 DOI      URL      [本文引用: 1]      摘要 利用大型真三轴压裂模拟试验系 统,通过模拟地层条件,监测压裂过程及其压力情况,观察裂缝的起裂及其延伸形态,进行射孔方式对压裂压力及裂缝形态的影响研究。研究结果表明,在地应力的 大小和分布确定的情况下,破裂压力随着射孔角度的增大而升高,随着射孔排数的增加而降低。为有效降低地层破裂压力、提高压裂成功率及效果,射孔方位应选择 0°方向,射孔密度在套管强度容许的前提下越大越好;单排射孔形成的裂缝形态较为简单,多排射孔形成的裂缝形态较为复杂,裂缝条数增加且形态各异。 (Wang Z W, Guo D L, Deng J G, Zhao J Z, Zeng X H.2005. The effect of perforation on fracturing pressure and fracture morphology . Journal of Southwest Petroleum Institute, 27: 47-50). DOI      URL      [本文引用: 1]      摘要 利用大型真三轴压裂模拟试验系 统,通过模拟地层条件,监测压裂过程及其压力情况,观察裂缝的起裂及其延伸形态,进行射孔方式对压裂压力及裂缝形态的影响研究。研究结果表明,在地应力的 大小和分布确定的情况下,破裂压力随着射孔角度的增大而升高,随着射孔排数的增加而降低。为有效降低地层破裂压力、提高压裂成功率及效果,射孔方位应选择 0°方向,射孔密度在套管强度容许的前提下越大越好;单排射孔形成的裂缝形态较为简单,多排射孔形成的裂缝形态较为复杂,裂缝条数增加且形态各异。
[101]	蔚宝华, 邓金根, 闫伟. 2010. 层理性泥页岩地层井壁坍塌控制方法研究 . 石油钻探技术, 38: 56-59 DOI      URL      [本文引用: 1]      摘要 涠州12-1北油田涠二段泥页岩地层层理发育、水敏性强,虽然采用了油基钻井液钻进,但井壁垮塌等井下复杂情况仍频繁发生.该油田涠二段地层岩石力学试验结果表明,涠二段泥页岩强度具有显著的各向异性,其受到的最大主应力方向与层理面法向之间的夹角为30°～70°,岩心易发生沿层理面的剪切滑移破坏,强度远低于最大主应力方向与层理面法向平行时的最大强度,这是造成定向井井壁失稳的主要原因.结合岩石力学试验结果,将层理性泥页岩视为横观各向同性材料,建立了合理钻井液密度的确定方法,确定了定向井坍塌压力随井眼轨迹的分布规律.利用定向井坍塌压力随井眼轨迹的分布规律,对该油田的定向井钻井液密度和井眼轨迹进行了优化,成功解决了涠二段地层的井壁失稳问题. (Wei B, Deng J, Yan W.2010. Borehole sloughing control in shale formations . Petroleum Drilling Techniques, 38: 56-59). DOI      URL      [本文引用: 1]      摘要 涠州12-1北油田涠二段泥页岩地层层理发育、水敏性强,虽然采用了油基钻井液钻进,但井壁垮塌等井下复杂情况仍频繁发生.该油田涠二段地层岩石力学试验结果表明,涠二段泥页岩强度具有显著的各向异性,其受到的最大主应力方向与层理面法向之间的夹角为30°～70°,岩心易发生沿层理面的剪切滑移破坏,强度远低于最大主应力方向与层理面法向平行时的最大强度,这是造成定向井井壁失稳的主要原因.结合岩石力学试验结果,将层理性泥页岩视为横观各向同性材料,建立了合理钻井液密度的确定方法,确定了定向井坍塌压力随井眼轨迹的分布规律.利用定向井坍塌压力随井眼轨迹的分布规律,对该油田的定向井钻井液密度和井眼轨迹进行了优化,成功解决了涠二段地层的井壁失稳问题.
[102]	吴奇, 胥云, 刘玉章, 丁云宏, 王晓泉, 王腾飞. 2011. 美国页岩气体积改造技术现状及对我国的启示 . 石油钻采工艺, 33: 1-7 DOI      URL      摘要 概述了美国页岩气改造技术发展历程,对微地震技术推动页岩气改造技术的进步进行了综述,对国 外提出的油藏改造体积概念进行了技术定义,分析了体积改造技术的内涵及作用。对实现体积改造的储层条件、天然裂缝的影响及起裂特征等进行了分析,总结出实 现体积改造的关键技术以及对我国页岩气改造技术发展的启示。对比了火山岩、碳酸盐岩等天然裂缝发育储层的常规改造与体积改造的不同理念,并提出了页岩气储 层改造技术未来发展方向。 (Wu Q, Xu Y, Liu Y Z, Ding Y H, Wang X Q, Wang T F.2011. The current situation of stimulated reservoir volume for shale in U.S. and its inspiration to China . Oil Drilling & Production Technology, 33: 1-7). DOI      URL      摘要 概述了美国页岩气改造技术发展历程,对微地震技术推动页岩气改造技术的进步进行了综述,对国 外提出的油藏改造体积概念进行了技术定义,分析了体积改造技术的内涵及作用。对实现体积改造的储层条件、天然裂缝的影响及起裂特征等进行了分析,总结出实 现体积改造的关键技术以及对我国页岩气改造技术发展的启示。对比了火山岩、碳酸盐岩等天然裂缝发育储层的常规改造与体积改造的不同理念,并提出了页岩气储 层改造技术未来发展方向。
[103]	吴有亮. 2007. 复杂构造地区三维微地震监测技术研究及在工程中应用 . [博士论文]. 成都: 成都理工大学 URL      [本文引用: 2]      摘要 微地震监测技术是一门新的地球物理技术，它是通过监测微震事件产生的地震波，确定微震坐标、发震时刻及烈度的技术。在国外，这方面研究起步较早，技术也相对成熟，多用于矿山安全监测、油气藏开发监测、火山活动性监测和天然地震监测等方面，但是由于探测精度、计算机处理能力的局限性，阻碍了其发展。近些年来，随着计算机技术的飞跃发展，微地震监测技术取得了长足进步，不仅可以实现微震的定位，还通过对震源机制的研究，对破裂性质进行更加细致的描述；监测还由一维、二维发展到三维、四维；精度也较以前有大幅度提高。而在国内，吸收了国外较多的成功经验，加上国内出现一些矿难教训，微地震监测技术也越来越受到重视，但总体水平还处在起步阶段。 本文以国家级锦屏一级水电站左岸微地震监测工程为依托，对微震监测的理论进行深入研究并根据实际存在的问题，对微地震监测的算法作以改进，建立切实可行的三维地质模型，提出更高效率的射线追踪和定位方法，从理论和实际方面阐述微地震监测的效果，并最终用于锦屏一级水电站左岸微地震监测工程中。 本篇论文首次将三维微地震监测技术用于大型水电工程，解决三维微地震监测的几个主要难点：首先，模型的建立。通常人们研究所采用的模型或为均匀或为层状地质模型，速度均匀或者层内均匀。但是对复杂构造地区来说，没有实际意义；其次，算法效率问题。三维微地震监测随地质体的增大，数据量以级数增长，应该设计高效的射线追踪算法解决传统算法在处理海量数据效率不高的问题。解决好上述问题，直接决定三维微地震在锦屏一级水电站微地震监测研究的现实性、可行性。 (Wu Y L.2007. Research on three dimensional microseismic monitoring technology in hydropower station and its application in Engineering . [PhD Thesis]. Chengdu University of Technology). URL      [本文引用: 2]      摘要 微地震监测技术是一门新的地球物理技术，它是通过监测微震事件产生的地震波，确定微震坐标、发震时刻及烈度的技术。在国外，这方面研究起步较早，技术也相对成熟，多用于矿山安全监测、油气藏开发监测、火山活动性监测和天然地震监测等方面，但是由于探测精度、计算机处理能力的局限性，阻碍了其发展。近些年来，随着计算机技术的飞跃发展，微地震监测技术取得了长足进步，不仅可以实现微震的定位，还通过对震源机制的研究，对破裂性质进行更加细致的描述；监测还由一维、二维发展到三维、四维；精度也较以前有大幅度提高。而在国内，吸收了国外较多的成功经验，加上国内出现一些矿难教训，微地震监测技术也越来越受到重视，但总体水平还处在起步阶段。 本文以国家级锦屏一级水电站左岸微地震监测工程为依托，对微震监测的理论进行深入研究并根据实际存在的问题，对微地震监测的算法作以改进，建立切实可行的三维地质模型，提出更高效率的射线追踪和定位方法，从理论和实际方面阐述微地震监测的效果，并最终用于锦屏一级水电站左岸微地震监测工程中。 本篇论文首次将三维微地震监测技术用于大型水电工程，解决三维微地震监测的几个主要难点：首先，模型的建立。通常人们研究所采用的模型或为均匀或为层状地质模型，速度均匀或者层内均匀。但是对复杂构造地区来说，没有实际意义；其次，算法效率问题。三维微地震监测随地质体的增大，数据量以级数增长，应该设计高效的射线追踪算法解决传统算法在处理海量数据效率不高的问题。解决好上述问题，直接决定三维微地震在锦屏一级水电站微地震监测研究的现实性、可行性。
[104]	伍藏原, 李汝勇, 张明益, 张明亮, 翟姝玲, 罗敏. 2005. 微地震监测气驱前缘技术在牙哈凝析气田的应用 . 天然气地球科学, 16: 390-393 DOI      URL      [本文引用: 3]      摘要 牙哈凝析气田采用"循环注气、保压开采"的开发方式4年多以来,已从油藏工程和数值模拟两方面证实了已有2口注气井组发生气窜,但是注入介质朝哪个方向推进、主力驱替方位如何、注入介质前缘波及何处都难以判断。用示踪剂方法存在人为因素很多、精度不够、施工复杂、周期长,而且只能粗略判断。利用注气井气驱前缘监测技术——微地震法对注气井进行监测,可得到该井的气驱前缘、注入气的波及范围、优势注气方向和区块的气体波及区。 (Wu Z Y, Li N Y, Zhang M Y, Zhai S L, Luo M.2005. The application of micro earthquake monitoring the gas injection advancing edge in the YAHA condensate gas reservoir . Natural Gas Geoscience, 16: 390-393). DOI      URL      [本文引用: 3]      摘要 牙哈凝析气田采用"循环注气、保压开采"的开发方式4年多以来,已从油藏工程和数值模拟两方面证实了已有2口注气井组发生气窜,但是注入介质朝哪个方向推进、主力驱替方位如何、注入介质前缘波及何处都难以判断。用示踪剂方法存在人为因素很多、精度不够、施工复杂、周期长,而且只能粗略判断。利用注气井气驱前缘监测技术——微地震法对注气井进行监测,可得到该井的气驱前缘、注入气的波及范围、优势注气方向和区块的气体波及区。
[105]	夏克文, 李民乐, 王建国, 侯爱萍, 谢雯晴, 李景卫, 王恩锡. 2012. 水力喷砂射孔分段压裂技术在水平井中的应用 . 油气井测试, 21: 38-39 DOI      URL      摘要 水力喷砂射孔分段压裂技术是将射孔、分层压裂融为一体的新型增产措施,无需下封隔器,一趟管柱即可完成多层段射孔压裂,提高了措施的有效性和安全性。通过实施该技术,可以避免常规射孔作业对地层的伤害,在一定程度上控制井筒附近裂缝起裂和延伸,与常规压裂技术相比有明显的优势。该技术成功应用于华北地区的水平井中,对提高油井的采收率有重大意义。 (Xia K W, Li M Y, Wang J G, Hou A P, Xie W Q, Li J W, Wang E X.2012. Application of the technique of hydraulic jet perforation and staged fracturing to horizontal well . Well Testing, 21: 38-39). DOI      URL      摘要 水力喷砂射孔分段压裂技术是将射孔、分层压裂融为一体的新型增产措施,无需下封隔器,一趟管柱即可完成多层段射孔压裂,提高了措施的有效性和安全性。通过实施该技术,可以避免常规射孔作业对地层的伤害,在一定程度上控制井筒附近裂缝起裂和延伸,与常规压裂技术相比有明显的优势。该技术成功应用于华北地区的水平井中,对提高油井的采收率有重大意义。
[106]	夏庆中, 陈波. 2005. 中子小角散射实验技术 . 中国核科技报告 URL      [本文引用: 1]      摘要 从实验技术角度出发,介绍了中子小角散射谱仪中各主要部件及其相应功能和参数,“Membrana-2”中子小角散射实验装置及详细技术特点。并以实际工作过程为主要内容,介绍了中子小角散射实验测量过程中所需要满足的基本要求和条件,分别详细阐述了实验样品选择方法、中子探测器效率刻度技术、标准样品选择技术、绝对散射强度标定技术和实验数据的初步处理过程,提出了中子小角散射实验中各参数优化与基本实验方法。可为今后国内开展中子小角散射实验提供主要的实验技术信息。 (Xia Q Z, Chen B.2005. Experimental technique of small angle neutron scattering . China Nuclear Science and Technology Report). URL      [本文引用: 1]      摘要 从实验技术角度出发,介绍了中子小角散射谱仪中各主要部件及其相应功能和参数,“Membrana-2”中子小角散射实验装置及详细技术特点。并以实际工作过程为主要内容,介绍了中子小角散射实验测量过程中所需要满足的基本要求和条件,分别详细阐述了实验样品选择方法、中子探测器效率刻度技术、标准样品选择技术、绝对散射强度标定技术和实验数据的初步处理过程,提出了中子小角散射实验中各参数优化与基本实验方法。可为今后国内开展中子小角散射实验提供主要的实验技术信息。
[107]	谢和平, 高峰, 鞠杨, 谢凌志, 杨永明, 王俊. 2016. 页岩气储层改造的体破裂理论和技术构思 . 科学通报 , 61: 36-46 URL      [本文引用: 2]      摘要 中国页岩气可采储量居世界第一位,但是中国页岩气开发面临气藏赋存条件复杂、地质构造运动剧烈、储层渗透性极低、气藏富集区水资源匮乏等一系列难题,迫切需要创新页岩储层改造的理论和方法,探索适合中国页岩气高效开发的非常规理论与技术.本文简要分析了目前储层压裂改造的主要方法、原理及面临的难题和挑战,提出了储层改造的体破裂理论及技术构想.定义体破裂是三维岩体在载荷作用下,内部孔隙、层理裂隙及人工裂隙互相作用、充分发展和贯穿、并形成新的三维裂隙网络系统这一完整力学过程,是岩体大尺度、多裂隙、高强度的破坏和能量释放的过程.指出页岩三维断裂形态和扩展机理、人工裂隙与结构裂隙相互作用、缝网形态和演化、实现高度体破裂的载荷类型、方式与介质以及真实三维断裂过程的可视化与计算模拟新技术等构建了体破裂力学理论的研究框架.基于早期实验室以及现场实验的探索,提出和分析了实现体破裂的新技术及有待研究的关键科学问题和技术难点. (Xie H P, Gao F, Ju Y, Xie L Z, Yang Y M, Wang J.2016. Novel idea of the theory and application of 3D volume fracturing for stimulation of shale gas reservoirs . Science China Press, 61: 36-46). URL      [本文引用: 2]      摘要 中国页岩气可采储量居世界第一位,但是中国页岩气开发面临气藏赋存条件复杂、地质构造运动剧烈、储层渗透性极低、气藏富集区水资源匮乏等一系列难题,迫切需要创新页岩储层改造的理论和方法,探索适合中国页岩气高效开发的非常规理论与技术.本文简要分析了目前储层压裂改造的主要方法、原理及面临的难题和挑战,提出了储层改造的体破裂理论及技术构想.定义体破裂是三维岩体在载荷作用下,内部孔隙、层理裂隙及人工裂隙互相作用、充分发展和贯穿、并形成新的三维裂隙网络系统这一完整力学过程,是岩体大尺度、多裂隙、高强度的破坏和能量释放的过程.指出页岩三维断裂形态和扩展机理、人工裂隙与结构裂隙相互作用、缝网形态和演化、实现高度体破裂的载荷类型、方式与介质以及真实三维断裂过程的可视化与计算模拟新技术等构建了体破裂力学理论的研究框架.基于早期实验室以及现场实验的探索,提出和分析了实现体破裂的新技术及有待研究的关键科学问题和技术难点.
[108]	谢平, 侯光东, 韩静静. 2009. CO$_{2}$压裂技术在苏里格气田的应用 . 断块油气田, 16: 104-106 URL      [本文引用: 1]      摘要 针对苏里格气田低压、低渗气藏的特点,以及常规压裂压后液体返排困难,储层水伤害严重的问题,研究利用CO2压裂技术提高压裂液返排效果,减少储层伤害。有针对性地研究了CO2压裂工艺的原理、压裂优化设计技术及压裂配套工艺等。该技术在长庆油田苏里格气田的现场应用表明,应用CO2压裂技术降低了压裂液对气层的伤害,提高了气井单井产量和压裂效果。 (Xie P, Hou G D, Han J J.2009. Application of CO$_{2}$ fracturing technology in Sulige Gas Field . Drilling & Production Technology, 16: 104-106). URL      [本文引用: 1]      摘要 针对苏里格气田低压、低渗气藏的特点,以及常规压裂压后液体返排困难,储层水伤害严重的问题,研究利用CO2压裂技术提高压裂液返排效果,减少储层伤害。有针对性地研究了CO2压裂工艺的原理、压裂优化设计技术及压裂配套工艺等。该技术在长庆油田苏里格气田的现场应用表明,应用CO2压裂技术降低了压裂液对气层的伤害,提高了气井单井产量和压裂效果。
[109]	谢晓永, 唐洪明, 王春华, 白蓉, 王自力. 2006. 氮气吸附法和压汞法在测试泥页岩孔径分布中的对比 . 天然气工业, 26: 100-102 DOI      URL      [本文引用: 1]      摘要 泥页岩比表面大,孔隙小,结构复杂,易吸水膨胀,一般方法很难准确描述其孔径分布情况。对泥页岩孔径分布的研究在石油钻井,完井,储层描述,泥页岩盖层封闭性等方面有着重要的意义。实验分别使用氮气吸附法和压汞法对同一泥页岩进行孔径分析。氮气吸附法中使用BJH原理分析泥页岩的中孔径,使用DA原理分析泥页岩的微孔径;压汞法中使用Wasburn公式分析泥页岩整体孔隙,对两种方法实验结果进行对比。氮气吸附法在泥页岩微孔和中孔分析方面有优势,能分别对泥页岩的微孔和中孔进行详细的描述;而压汞法受泥页岩孔径分布不均一性影响相对较小,能弥补氮气吸附法在大孔分析方面的不足。把氮气吸附法和压汞法测得的孔径分布结果结合使用,可以得到泥页岩从微孔到大孔的孔径分布情况。 (Xie X Y, Tang H M, Wang C H, Bai R, Wang Z L.2006. Contrast of nitrogen adsorption method and mercury porosimetry method in analysis of shale pore size distribution . Natural Gas Industry, 26: 100-102). DOI      URL      [本文引用: 1]      摘要 泥页岩比表面大,孔隙小,结构复杂,易吸水膨胀,一般方法很难准确描述其孔径分布情况。对泥页岩孔径分布的研究在石油钻井,完井,储层描述,泥页岩盖层封闭性等方面有着重要的意义。实验分别使用氮气吸附法和压汞法对同一泥页岩进行孔径分析。氮气吸附法中使用BJH原理分析泥页岩的中孔径,使用DA原理分析泥页岩的微孔径;压汞法中使用Wasburn公式分析泥页岩整体孔隙,对两种方法实验结果进行对比。氮气吸附法在泥页岩微孔和中孔分析方面有优势,能分别对泥页岩的微孔和中孔进行详细的描述;而压汞法受泥页岩孔径分布不均一性影响相对较小,能弥补氮气吸附法在大孔分析方面的不足。把氮气吸附法和压汞法测得的孔径分布结果结合使用,可以得到泥页岩从微孔到大孔的孔径分布情况。
[110]	邢庆河, 张士诚. 2010. 水平井限流法压裂技术的发展与应用 . 天然气工业, 30: 52-54 DOI      URL      摘要 水平井限流法压裂采用套管压裂,具有井下工具少、一次施工完成多条裂缝改造、压后增产效果好等优点,是低渗透油气藏水平井增产改造的很好选择,大庆油田已应用该方法压裂完成了20多口水平井的改造,取得了很好的经济效益。根据南214—平324井的主压裂施工曲线分析了水平井限流法压裂的特点,介绍了"有效孔数法"、G函数法、连续油管井温测井、大地电位和井下微地震等配套技术。从压裂液流动的角度提出了水平井限流法压裂存在径向流区的观点,对压裂液在径向流区流动的正确认识是水平井限流法压裂设计和施工控制的关键。最后总结了目前水平井限流法压裂在施工过程及压后裂缝诊断方面所存在的问题,并提出了相应的解决办法及技术发展思路。 (Xing Q H, Zhang S C.2010. Development progress and application of the limited-entry fracturing in horizontal wells . Natural Gas Industry, 30: 52-54). DOI      URL      摘要 水平井限流法压裂采用套管压裂,具有井下工具少、一次施工完成多条裂缝改造、压后增产效果好等优点,是低渗透油气藏水平井增产改造的很好选择,大庆油田已应用该方法压裂完成了20多口水平井的改造,取得了很好的经济效益。根据南214—平324井的主压裂施工曲线分析了水平井限流法压裂的特点,介绍了"有效孔数法"、G函数法、连续油管井温测井、大地电位和井下微地震等配套技术。从压裂液流动的角度提出了水平井限流法压裂存在径向流区的观点,对压裂液在径向流区流动的正确认识是水平井限流法压裂设计和施工控制的关键。最后总结了目前水平井限流法压裂在施工过程及压后裂缝诊断方面所存在的问题,并提出了相应的解决办法及技术发展思路。
[111]	熊伟, 郭为, 刘洪林, 高树生, 胡志明, 杨发荣. 2012. 页岩的储层特征以及等温吸附特征 . 天然气工业, 32: 113-116 DOI      URL      摘要 页岩的储层特征以及吸附特征是评价页岩气是否具有开采价值的一个重要标准,为此,以某页岩气藏为例,测量其岩心的孔隙度与渗透率,并进行X射线衍射全岩分析和黏土矿物测定,以分析其储层特征。结果表明:该页岩的孔隙度主要分布在0.01%～5%,渗透率主要分布在0.000 01～10mD,孔隙直径主要分布在4～6nm;页岩的孔隙度与渗透率没有明显的相关关系,黏土矿物主要为绿泥石、伊利石、蒙皂石以及伊蒙混层。挑选了6块岩心进行等温吸附试验,以确定TOC以及Ro对页岩吸附能力的影响,结果表明:①页岩的气体吸附遵循Langmuir等温吸附曲线,其总解析气量与页岩的TOC成正相关,但与孔隙度没有明显的关系;②不同成熟度、不同TOC页岩的吸附特征研究表明,页岩的吸附能力与页岩的TOC和Ro密切相关,随着页岩TOC以及Ro的提高,页岩的吸附能力增加;当页岩的TOC相近时,页岩的Ro越高,吸附能力越强;当页岩的Ro相近时,页岩的TOC越高,页岩的吸附能力越强。 (Xiong W, Guo W, Liu H L, Gao S S, Hu Z M, Yang F R. Shale reservoir characteristics and isothermal adsorption properties. Natural Gas Industry , 2012,32: 113-116). DOI      URL      摘要 页岩的储层特征以及吸附特征是评价页岩气是否具有开采价值的一个重要标准,为此,以某页岩气藏为例,测量其岩心的孔隙度与渗透率,并进行X射线衍射全岩分析和黏土矿物测定,以分析其储层特征。结果表明:该页岩的孔隙度主要分布在0.01%～5%,渗透率主要分布在0.000 01～10mD,孔隙直径主要分布在4～6nm;页岩的孔隙度与渗透率没有明显的相关关系,黏土矿物主要为绿泥石、伊利石、蒙皂石以及伊蒙混层。挑选了6块岩心进行等温吸附试验,以确定TOC以及Ro对页岩吸附能力的影响,结果表明:①页岩的气体吸附遵循Langmuir等温吸附曲线,其总解析气量与页岩的TOC成正相关,但与孔隙度没有明显的关系;②不同成熟度、不同TOC页岩的吸附特征研究表明,页岩的吸附能力与页岩的TOC和Ro密切相关,随着页岩TOC以及Ro的提高,页岩的吸附能力增加;当页岩的TOC相近时,页岩的Ro越高,吸附能力越强;当页岩的Ro相近时,页岩的TOC越高,页岩的吸附能力越强。
[112]	徐刚. 2013. 井中压裂微地震监测技术方法研究 . [硕士论文]. 青岛: 中国石油大学(华东) [本文引用: 2]      (Xu G.2013. Borehole fracturing microseismic monitoring technology and method research . [Master Thesis]. Qingdao: China University of Petroleum). [本文引用: 2]
[113]	杨峰, 宁正福, 胡昌蓬, 王波, 彭凯, 刘慧卿. 2013. 页岩储层微观孔隙结构特征 .石油学报$,$34: 301-311 DOI      [本文引用: 2]      摘要 为了研究页岩储层的微观孔隙结构特征,应用场发射环境扫描电子显微镜观察了页岩表面纳米级孔隙微观形态,并通过低温氮吸附法测定了页岩的氮气吸附等温线,同时结合高压压汞实验对页岩储层孔隙结构进行了深入研究。研究结果表明:页岩储层孔隙处于纳米量级,孔隙类型可分为有机质纳米孔、黏土矿物粒间孔、岩石骨架矿物孔、古生物化石孔和微裂缝5种类型,其中有机质纳米孔和黏土矿物粒间孔发育最为广泛;页岩孔径分布复杂,既含有大量的中孔(2～50nm),又含有一定量的微孔(2nm)和大孔(50nm);孔径小于50nm的微孔和中孔提供了大部分比表面积和孔体积,是气体吸附和存储的主要场所;页岩阈压非常高,孔喉分选性好,连通性差,退汞效率低,中孔对气体渗流起明显贡献作用,微孔则主要起储集作用。 (Yang F, Ning Z F, Hu C P, Wang B, Peng K, Liu H Q.2013. Characterization of microscopic pore structures in shale reservoirs . Acta Petrolei Sinica, 34: 301-311). DOI      [本文引用: 2]      摘要 为了研究页岩储层的微观孔隙结构特征,应用场发射环境扫描电子显微镜观察了页岩表面纳米级孔隙微观形态,并通过低温氮吸附法测定了页岩的氮气吸附等温线,同时结合高压压汞实验对页岩储层孔隙结构进行了深入研究。研究结果表明:页岩储层孔隙处于纳米量级,孔隙类型可分为有机质纳米孔、黏土矿物粒间孔、岩石骨架矿物孔、古生物化石孔和微裂缝5种类型,其中有机质纳米孔和黏土矿物粒间孔发育最为广泛;页岩孔径分布复杂,既含有大量的中孔(2～50nm),又含有一定量的微孔(2nm)和大孔(50nm);孔径小于50nm的微孔和中孔提供了大部分比表面积和孔体积,是气体吸附和存储的主要场所;页岩阈压非常高,孔喉分选性好,连通性差,退汞效率低,中孔对气体渗流起明显贡献作用,微孔则主要起储集作用。
[114]	杨涛, 杨桦, 王凤江, 谈锦锋, 黎洪珍. 2007. 含CO$_{2}$气井防腐工艺技术 . 天然气工业, 27: 116-120 DOI      URL      摘要 CO2腐蚀是世界石油天然气工业中常见的一种腐蚀类型，含CO2气井的相关工艺技术直接关系着气井的质量与寿命，是气井安全、高效生产的基础。为此，对我国几个不同类型含CO2油气田的现场的CO2腐蚀资料进行了调查、研究，分析了CO2腐蚀给天然气生产带来的严重危害性，总结出在不同类型油气田中CO2腐蚀的一般规律和不同区域CO2腐蚀的特殊性；在对CO2腐蚀的现象、特点、类型、机理以及腐蚀的影响因素研究的基础上，提出了含CO2气井防腐工艺技术应着重解决好含CO2气井的完井、生产管柱采用不锈钢或双金属复合油管、加注缓蚀剂等几种有效的防腐蚀措施。 (Yang T, Yang H, Wang F J, Tan J F, Li H Z.2007. Anti-corrosion technology in gas wells with CO$_{2}$ . Natural Gas Industry, 27: 116-120). DOI      URL      摘要 CO2腐蚀是世界石油天然气工业中常见的一种腐蚀类型，含CO2气井的相关工艺技术直接关系着气井的质量与寿命，是气井安全、高效生产的基础。为此，对我国几个不同类型含CO2油气田的现场的CO2腐蚀资料进行了调查、研究，分析了CO2腐蚀给天然气生产带来的严重危害性，总结出在不同类型油气田中CO2腐蚀的一般规律和不同区域CO2腐蚀的特殊性；在对CO2腐蚀的现象、特点、类型、机理以及腐蚀的影响因素研究的基础上，提出了含CO2气井防腐工艺技术应着重解决好含CO2气井的完井、生产管柱采用不锈钢或双金属复合油管、加注缓蚀剂等几种有效的防腐蚀措施。
[115]	杨正明, 张英芝, 郝明强, 刘先贵, 单文文. 2006. 低渗透油田储层综合评价方法 . 石油学报, 27: 64-67 DOI      URL      [本文引用: 1]      摘要 根据低渗透储层特点,利用恒速压汞、核磁共振、低渗透渗流理论和物理模拟实验研究手段,将喉道半径、可动流体百分数、启动压力梯度、有效驱动因子4个参数作为低渗透油储量的评价指标,建立了与之对应的分级评价方法和分级界限。同时以丰度、有效厚度、喉道半径、可动流体比率、启动压力梯度和有效驱动因子6个参数作为低渗透油田储量综合评价指标建立了评价新方法。该方法成功地应用于大庆油田外围低渗透储层评价,为低渗透储层的合理开发提供了理论依据。 (Yang Z M, Zhang Y Z, Hao M Q, Liu X G, Shan W W.2006. Comprehensive evaluation of reservoir in low-permeability oil fields . Acta Petrolei Sinica, 27: 64-67). DOI      URL      [本文引用: 1]      摘要 根据低渗透储层特点,利用恒速压汞、核磁共振、低渗透渗流理论和物理模拟实验研究手段,将喉道半径、可动流体百分数、启动压力梯度、有效驱动因子4个参数作为低渗透油储量的评价指标,建立了与之对应的分级评价方法和分级界限。同时以丰度、有效厚度、喉道半径、可动流体比率、启动压力梯度和有效驱动因子6个参数作为低渗透油田储量综合评价指标建立了评价新方法。该方法成功地应用于大庆油田外围低渗透储层评价,为低渗透储层的合理开发提供了理论依据。
[116]	姚军, 孙海, 樊冬艳, 黄朝琴, 孙致学, 张国浩. 2013. 页岩气藏运移机制及数值模拟 . 中国石油大学学报(自然科学版), 1: 91-98 DOI      URL      [本文引用: 3]      摘要 基于双重连续介质,采用尘气模型（DGM）建立基岩和裂缝运动方程,基岩中考虑气体在基岩孔隙中黏性流、Knudsen扩散、分子扩散以及气体在基岩孔隙表面的吸附解吸,吸附采用Langmuir等温吸附方程;裂缝中考虑黏性流、Knudesen扩散和分子扩散机制,在此基础上建立基岩-裂缝双重介质数值模型并采用有限元方法对模型进行求解。根据数值模拟结果对影响页岩气藏产能的因素进行分析。结果表明：页岩气产出气是游离气和吸附气解吸共同采出的结果,在给定的页岩气藏条件下,游离气影响更大,吸附对页岩气产能有较大影响,忽略吸附会导致预测产能偏低;Knudsen扩散（或Klinkenberg效应）对基岩视渗透率影响较大,越靠近生产井,Knudsen扩散和Klinkenberg效应的影响越大,基岩视渗透率随生产时间延长变大;裂缝渗透率越大,页岩气产量越大,基岩渗透率对页岩气产能影响不大。 (Yao J, Sun H, Fan D Y, Huang Z Q, Sun Z X, Zhang G H.2013. Transport mechanisms and numerical simulation of shale gas reservoirs . J China Univ Petroleum (Ed Nat Sci), 1: 91-98). DOI      URL      [本文引用: 3]      摘要 基于双重连续介质,采用尘气模型（DGM）建立基岩和裂缝运动方程,基岩中考虑气体在基岩孔隙中黏性流、Knudsen扩散、分子扩散以及气体在基岩孔隙表面的吸附解吸,吸附采用Langmuir等温吸附方程;裂缝中考虑黏性流、Knudesen扩散和分子扩散机制,在此基础上建立基岩-裂缝双重介质数值模型并采用有限元方法对模型进行求解。根据数值模拟结果对影响页岩气藏产能的因素进行分析。结果表明：页岩气产出气是游离气和吸附气解吸共同采出的结果,在给定的页岩气藏条件下,游离气影响更大,吸附对页岩气产能有较大影响,忽略吸附会导致预测产能偏低;Knudsen扩散（或Klinkenberg效应）对基岩视渗透率影响较大,越靠近生产井,Knudsen扩散和Klinkenberg效应的影响越大,基岩视渗透率随生产时间延长变大;裂缝渗透率越大,页岩气产量越大,基岩渗透率对页岩气产能影响不大。
[117]	姚军, 孙海, 黄朝琴, 张磊, 曾青冬, 隋宏光, 樊冬艳. 2013. 页岩气藏开发中的关键力学问题 . 中国科学: 物理学力学天文学, 43: 1527-1547 DOI      URL      摘要 简要概述了页岩气资源和开发现状,基于页岩储层的微纳尺度孔隙结构特征、力学特点以及开采方式,系统论述了页岩气开发中的多尺度、多物理场流动动力学的过程与机制,归纳凝练出页岩气微纳尺度流动、页岩人工压裂的裂缝扩展以及分段压裂水平井缝网宏观流动等方面是亟需解决的关键前沿力学问题,并针对各前沿关键力学问题综述了研究进展和发展趋势,为促进我国能源发展尤其是页岩气的科学、有效开发具有重要的意义. (Yao J, Sun H, Huang C Q, Zhang L, Zeng Q D, Sui H G, Fan D Y.2013. Key mechanical problems in the developmentof shale gas reservoirs . Sci Sin-Phys Mech Astron, 43: 1527-1547). DOI      URL      摘要 简要概述了页岩气资源和开发现状,基于页岩储层的微纳尺度孔隙结构特征、力学特点以及开采方式,系统论述了页岩气开发中的多尺度、多物理场流动动力学的过程与机制,归纳凝练出页岩气微纳尺度流动、页岩人工压裂的裂缝扩展以及分段压裂水平井缝网宏观流动等方面是亟需解决的关键前沿力学问题,并针对各前沿关键力学问题综述了研究进展和发展趋势,为促进我国能源发展尤其是页岩气的科学、有效开发具有重要的意义.
[118]	姚军, 王晨晨, 杨永飞, 黄朝琴, 樊冬艳, 孙海. 2013. 碳酸盐岩双孔隙网络模型的构建方法和微观渗流模拟研究 . 中国科学: 物理学力学天文学, 43: 896-909 DOI      URL      [本文引用: 1]      摘要 碳酸盐岩油藏作为全球的主力油气储集层,在微观尺度上分布有大量发育的大孔隙和微孔隙,研究不同孔隙对其微观渗流特征的影响具有重要意义.本文基于碳酸盐岩中分别描述大孔隙和微孔隙特征的单一尺度孔隙网络模型,利用整合法构建出能够同时描述大孔隙和微孔隙特征的双孔隙网络模型,最后模拟各网络模型的渗流过程,计算相应的渗流特征参数并同岩心实验室渗透率进行了对比.结果表明,基于整合法构建的双孔隙网络模型可根据区间域随机产生任意大小的网络尺寸,不仅同时包含大孔隙和微孔隙的几何拓扑结构信息,而且可同时描述大孔隙和微孔隙的渗流特征,能够较好描述真实碳酸盐岩油藏中多尺度孔隙特征.双孔隙网络模型的绝对渗透率和实验室岩心结果基本一致,水湿油藏条件下对比各网络模型的相对渗透率曲线发现,双孔隙网络模型的等渗点含水饱和度均大于大孔隙和微孔隙网络,其残余油饱和度明显减少,这是由于大孔隙和微孔隙的整合极大地提高了双孔隙网络的连通性,进而大幅度提高网络的渗流能力,本研究为碳酸盐岩微观渗流研究提供了重要的理论基础. (Yao J, Wang C C, Yang Y F, Huang C Q, Fan D Y, Sun H.2013. The construction method and microscopic flow simulation of carbonate dual pore network model . Scientia Sinica Physica Mechanica & Astronomica, 43: 896-909). DOI      URL      [本文引用: 1]      摘要 碳酸盐岩油藏作为全球的主力油气储集层,在微观尺度上分布有大量发育的大孔隙和微孔隙,研究不同孔隙对其微观渗流特征的影响具有重要意义.本文基于碳酸盐岩中分别描述大孔隙和微孔隙特征的单一尺度孔隙网络模型,利用整合法构建出能够同时描述大孔隙和微孔隙特征的双孔隙网络模型,最后模拟各网络模型的渗流过程,计算相应的渗流特征参数并同岩心实验室渗透率进行了对比.结果表明,基于整合法构建的双孔隙网络模型可根据区间域随机产生任意大小的网络尺寸,不仅同时包含大孔隙和微孔隙的几何拓扑结构信息,而且可同时描述大孔隙和微孔隙的渗流特征,能够较好描述真实碳酸盐岩油藏中多尺度孔隙特征.双孔隙网络模型的绝对渗透率和实验室岩心结果基本一致,水湿油藏条件下对比各网络模型的相对渗透率曲线发现,双孔隙网络模型的等渗点含水饱和度均大于大孔隙和微孔隙网络,其残余油饱和度明显减少,这是由于大孔隙和微孔隙的整合极大地提高了双孔隙网络的连通性,进而大幅度提高网络的渗流能力,本研究为碳酸盐岩微观渗流研究提供了重要的理论基础.
[119]	姚约东, 李相方, 葛家理, 宁正福. 2004. 低渗气层中气体渗流克林贝尔效应的实验研究 . 天然气工业, 24: 100-102 DOI      URL      [本文引用: 1]      摘要 低渗气田的开发在我国油气田开发中起着越来越重要的作用,故研究低渗气层中气体的基本渗流规律有着理论和应用价值.文章通过实验方案的设计和优化,选取典型的岩心,记录了CO2、N2和He等气体在不同岩心中渗流时的进出口压力和流量值.对以上实验数据进行分析,其结果为:气体在低渗透岩心中的渗流不遵循达西渗流规律,表现为视渗透率在渗流过程中随气体性质、外界温度和压力等因素的变化而变化.从岩心、气体的物理性质以及力学角度分析认为,低渗透岩心中的气体非达西渗流是由克林贝尔效应引起.文章还从岩心和气体的特性,以及温度、压力等因素系统地研究了气体渗流克林贝尔效应的影响因素,确定出克林贝尔效应常数的变化规律为:克林贝尔效应常数(b)与岩心综合参数成正比,与绝对温度(T)成正比,与气体的黏度成正比,与气体分子量的平方根成反比.所建立的低渗气层中气体的渗流规律为低渗透气田开发方案的制定奠定了理论基础. (Yao Y D, Li X F, Ge J L, Ning Z F.2004. Experimental study on klingberg effect of gas seepage in low permeability gas reservoir . Natrual Gas Industry, 24: 100-102). DOI      URL      [本文引用: 1]      摘要 低渗气田的开发在我国油气田开发中起着越来越重要的作用,故研究低渗气层中气体的基本渗流规律有着理论和应用价值.文章通过实验方案的设计和优化,选取典型的岩心,记录了CO2、N2和He等气体在不同岩心中渗流时的进出口压力和流量值.对以上实验数据进行分析,其结果为:气体在低渗透岩心中的渗流不遵循达西渗流规律,表现为视渗透率在渗流过程中随气体性质、外界温度和压力等因素的变化而变化.从岩心、气体的物理性质以及力学角度分析认为,低渗透岩心中的气体非达西渗流是由克林贝尔效应引起.文章还从岩心和气体的特性,以及温度、压力等因素系统地研究了气体渗流克林贝尔效应的影响因素,确定出克林贝尔效应常数的变化规律为:克林贝尔效应常数(b)与岩心综合参数成正比,与绝对温度(T)成正比,与气体的黏度成正比,与气体分子量的平方根成反比.所建立的低渗气层中气体的渗流规律为低渗透气田开发方案的制定奠定了理论基础.
[120]	殷诚, 高世葵, 董大忠, 朱文丽, 王欣蕊. 2015. 页岩气产业发展的影响因素 . 天然气工业, 35: 117-125 DOI      URL      摘要 美国页岩气开发全面进入了产业化发展阶段.作为页岩气资源蕴藏量同样极其丰富的中国,推动开发页岩气有利于改善能源结构、保障能源安全。以美国5个典型页岩气区带解剖为依据,对页岩气产业发展影响因素进行定量分析,提出了影响页岩气产业发展因素的分类方案;采用主成分分析法.分析了影响页岩气产业化各指标的影响程度;通过对比,总结了美国页岩气产业发展历程对中国页岩气产业发展的启示。结果表明:①影响页岩气产业发展的4个主要因素为资源基础、技术支持、产业政策和投入产出.由此构建了页岩气产业发展影响因素指标体系,包含11项具体指标;②对美国页岩气产业发展因素进行分析可知,埋深是最为重要的主控因素;③根据因素的重要程度和对比中美页岩气产业发展状况可知,中国要想页岩气产业化顺利发展,必须跨越地质条件复杂、单井投资高、油气开采公司数量少等3个方面的障碍。 (Yin C, Gao S K, Dong D Z, Zhu W L, Wang X R.2015. Influencing factors for the development of shale gas industry . Natural Gas Industry, 35: 117-125). DOI      URL      摘要 美国页岩气开发全面进入了产业化发展阶段.作为页岩气资源蕴藏量同样极其丰富的中国,推动开发页岩气有利于改善能源结构、保障能源安全。以美国5个典型页岩气区带解剖为依据,对页岩气产业发展影响因素进行定量分析,提出了影响页岩气产业发展因素的分类方案;采用主成分分析法.分析了影响页岩气产业化各指标的影响程度;通过对比,总结了美国页岩气产业发展历程对中国页岩气产业发展的启示。结果表明:①影响页岩气产业发展的4个主要因素为资源基础、技术支持、产业政策和投入产出.由此构建了页岩气产业发展影响因素指标体系,包含11项具体指标;②对美国页岩气产业发展因素进行分析可知,埋深是最为重要的主控因素;③根据因素的重要程度和对比中美页岩气产业发展状况可知,中国要想页岩气产业化顺利发展,必须跨越地质条件复杂、单井投资高、油气开采公司数量少等3个方面的障碍。
[121]	余同希, 苏先樾, 王晓东. 1992. 弹塑性波的研究现状与趋势 . 力学进展, 22: 347-357 DOI      URL      [本文引用: 1]      摘要 本文系统总结了弹塑性波理论的研究现状,并介绍了当前在弹塑性波理论和相关的工程领域中的重要课题。分析并指出了今后弹塑性波问题的研究趋势。 (Yu T X, Shu X Y, Wang X D.1992. Present situation and trend of the research on elastic plastic wave . Advances in Mechanics, 22: 347-357). DOI      URL      [本文引用: 1]      摘要 本文系统总结了弹塑性波理论的研究现状,并介绍了当前在弹塑性波理论和相关的工程领域中的重要课题。分析并指出了今后弹塑性波问题的研究趋势。
[122]	张东晓, 杨婷云. 2013. 页岩气开发综述 . 石油学报, 34: 792-801 [本文引用: 1]      (Zhang D X, Yang T Y.2013. An overview of shale-gas production . Acta Petrolei Sinica. 34: 792-801). [本文引用: 1]
[123]	张繁昌, 李传辉, 印兴耀. 2010. 基于动态匹配子波库的地震数据快速匹配追踪 . 石油地球物理勘探, 45: 667-673 URL      [本文引用: 1]      摘要 本文基于Liu等的改进算法,以Morlet小波作为基本匹配子波,在控制参数的确定过程中,充分利用地震信号的瞬时特征确定动态扫描范围,并根据地震信号本身的特点创建动态子波库;通过一次迭代同时确定多个匹配子波,再利用匹配子波控制参数之间的关系,提出了双参数快速匹配追踪算法,进一步减少了扫描参数的个数,使计算效率得到了质的提高.为了使算法更快收敛,利用残差信号的能量对双参数快速匹配追踪算法的迭代次数进行有效控制,不仅避免了毫无意义的计算,而且可在一定程度上去除随机噪声.最后,本文利用各匹配子波的独立性,提出了一种变窗口短时傅里叶变换方法,得到了高精度时频分布图. (Zhang F C, Li C H, Yin X Y.2010. Seismic data fast matching pursuit based on dynamicmatching wavelet library . Oil Geophysical Prospecting, 45: 667-673). URL      [本文引用: 1]      摘要 本文基于Liu等的改进算法,以Morlet小波作为基本匹配子波,在控制参数的确定过程中,充分利用地震信号的瞬时特征确定动态扫描范围,并根据地震信号本身的特点创建动态子波库;通过一次迭代同时确定多个匹配子波,再利用匹配子波控制参数之间的关系,提出了双参数快速匹配追踪算法,进一步减少了扫描参数的个数,使计算效率得到了质的提高.为了使算法更快收敛,利用残差信号的能量对双参数快速匹配追踪算法的迭代次数进行有效控制,不仅避免了毫无意义的计算,而且可在一定程度上去除随机噪声.最后,本文利用各匹配子波的独立性,提出了一种变窗口短时傅里叶变换方法,得到了高精度时频分布图.
[124]	张海燕, 李庆忠.2007. 几种常用解析子波的特性分析 .石油地球物理勘探, 42: 651-657 DOI      URL      [本文引用: 2]      摘要 本文通过对几种常见解析子波的数学表达式及相应波形和振幅谱的分析,阐述了它们的主要特点和适用范围,并首次介绍了最适于表达实际爆炸地震子波的阻尼拉伸正弦子波——李子波。文中着重强调了在选用带通子波进行带通滤波时,应采用频域归一化的滤波算子才能获得较好的振幅保持特性。比较宽带雷克子波和雷克子波的不同特征可知,子波分辨率的高低主要取决于主瓣的宽度和主瓣范围内的瞬时频率的高低,而与峰值频率没有关系。近似为最小相位的阻尼拉伸正弦子波——李子波,可应用于满足最小相位假设的反褶积等处理运算。 (Zhang H Y, Li Q Z.2007. Analysis on feature of common analytic wavelets . Oil Geophysical Prospecting, 42: 651-657). DOI      URL      [本文引用: 2]      摘要 本文通过对几种常见解析子波的数学表达式及相应波形和振幅谱的分析,阐述了它们的主要特点和适用范围,并首次介绍了最适于表达实际爆炸地震子波的阻尼拉伸正弦子波——李子波。文中着重强调了在选用带通子波进行带通滤波时,应采用频域归一化的滤波算子才能获得较好的振幅保持特性。比较宽带雷克子波和雷克子波的不同特征可知,子波分辨率的高低主要取决于主瓣的宽度和主瓣范围内的瞬时频率的高低,而与峰值频率没有关系。近似为最小相位的阻尼拉伸正弦子波——李子波,可应用于满足最小相位假设的反褶积等处理运算。
[125]	张唤兰, 朱光明, 王云宏. 2013. 基于时窗能量比和AIC的两步法微震初至自动拾取 . 物探与化探, 45: 667-673 DOI      URL      摘要 传统的微地震数据震源定位算法依赖于波至时间的拾取.由于微地震数据量较大且信噪比较低,手动拾取纵波和横波的波至时间很耗时,且引入的人为误差不易控制.笔者在分析已有方法特点的基础上,给出一种较快捷、准确的两步法微地震初至自动拾取方法.该方法首先使用时窗能量比法识别微震事件并大致确定波至时间,然后使用局部AIC精确拾取波至时间.与常规时窗能量比法相比,该方法减弱了时窗大小对拾取精度的影响；与常规的AIC法相比,由于只在局部使用AIC,避免了在低信噪比情况下AIC会出现多个局部极小从而难以准确拾取的问题,同时也提高了拾取效率.最后通过野外实际微地震数据进行了测试,分析了该方法的性能,验证了该方法的有效性和实用性. (Zhang H L, Zhu G M, Wang Y H. 2013. Automatic microseismic event detection and picking method . Geophysical & Geochemical Exploration, 45: 667-673). DOI      URL      摘要 传统的微地震数据震源定位算法依赖于波至时间的拾取.由于微地震数据量较大且信噪比较低,手动拾取纵波和横波的波至时间很耗时,且引入的人为误差不易控制.笔者在分析已有方法特点的基础上,给出一种较快捷、准确的两步法微地震初至自动拾取方法.该方法首先使用时窗能量比法识别微震事件并大致确定波至时间,然后使用局部AIC精确拾取波至时间.与常规时窗能量比法相比,该方法减弱了时窗大小对拾取精度的影响；与常规的AIC法相比,由于只在局部使用AIC,避免了在低信噪比情况下AIC会出现多个局部极小从而难以准确拾取的问题,同时也提高了拾取效率.最后通过野外实际微地震数据进行了测试,分析了该方法的性能,验证了该方法的有效性和实用性.
[126]	张琴, 刘畅, 梅啸寒, 乔李井宇. 2015. 页岩气储层微观储集空间研究现状及展望 . 石油与天然气地质, 36: 146-154 DOI      URL      摘要 从页岩气微观储层研究历程入手,总结页岩气微观储集空间的研究现状及进展,并探讨研究的不足和缺陷,提出科学展望,以期完善页岩气微观储层分类体系和理论。页岩气微观储集空间研究经历了随机观察和探索阶段及概念体系建立和实际应用阶段。页岩气微观储集空间分类方案繁多,代表性方案主要有基于孔隙尺寸、基于孔隙产状-结构和基于孔隙成因三大综合分类,各种分类标准和术语尚不统一。页岩微观储层孔隙演化研究逐步趋于定量化,微观孔隙发育控制因素复杂,沉积环境、构造背景、岩性及矿物组分控制了微观孔隙的类型及发育程度,有机碳含量(TOC)和干酪根类型影响有机质孔的发育,成岩演化直接控制着不同类型微观孔隙的发育和演化。针对页岩气微观储层研究现状,提出应进一步完善页岩气微观孔隙分类标准及划分方案,形成科学、客观、全面、系统的页岩气微观储层分类评价体系,加强微观孔隙发育控制因素定量研究,定量分析各种控制因素与各类孔隙的相关性,并不断改善测试手段,提高测量范围和精度,使页岩气微观储集空间直观、准确、全方位地展现和表征出来。 (Zhang Q, Liu CH, Mei X H, Qiao L J Y.2015. Status and prospect of research on microscopic shale gas reservoir space . Oil & Gas Geology, 36: 146-154). DOI      URL      摘要 从页岩气微观储层研究历程入手,总结页岩气微观储集空间的研究现状及进展,并探讨研究的不足和缺陷,提出科学展望,以期完善页岩气微观储层分类体系和理论。页岩气微观储集空间研究经历了随机观察和探索阶段及概念体系建立和实际应用阶段。页岩气微观储集空间分类方案繁多,代表性方案主要有基于孔隙尺寸、基于孔隙产状-结构和基于孔隙成因三大综合分类,各种分类标准和术语尚不统一。页岩微观储层孔隙演化研究逐步趋于定量化,微观孔隙发育控制因素复杂,沉积环境、构造背景、岩性及矿物组分控制了微观孔隙的类型及发育程度,有机碳含量(TOC)和干酪根类型影响有机质孔的发育,成岩演化直接控制着不同类型微观孔隙的发育和演化。针对页岩气微观储层研究现状,提出应进一步完善页岩气微观孔隙分类标准及划分方案,形成科学、客观、全面、系统的页岩气微观储层分类评价体系,加强微观孔隙发育控制因素定量研究,定量分析各种控制因素与各类孔隙的相关性,并不断改善测试手段,提高测量范围和精度,使页岩气微观储集空间直观、准确、全方位地展现和表征出来。
[127]	张山, 刘清林, 赵群, 姜宇东. 2002. 微地震监测技术在油田开发中的应用 . 石油物探, 41: 226-231 DOI      URL      [本文引用: 2]      摘要 微地震监测技术是近 2 0年才出现的地球物理新技术 ,其基本做法是通过在井中或地面布置检波器排列接收生产活动所产生或诱导的微小地震事件 ,并通过对这些事件的反演求取微地震震源位置等参数 ,然后 ,应用这些参数对生产活动进行监控或指导。在油气开发领域 ,该方法主要用于油田低渗透储层压裂的裂缝动态成像和油田开发过程的动态监测 ,主要是流体驱动监测。介绍了微地震监测方法的基本原理、数据采集方法和数据处理方法及应用实例 ,并对其应用效果和发展前景进行了分析 (Zhang S, Liu Q L, Zhao Q, Jiang Y D.2002. Application of microseismic monitoring technology in development of oil field . Gepphysical Prospecting for Petroleum, 41: 226-231). DOI      URL      [本文引用: 2]      摘要 微地震监测技术是近 2 0年才出现的地球物理新技术 ,其基本做法是通过在井中或地面布置检波器排列接收生产活动所产生或诱导的微小地震事件 ,并通过对这些事件的反演求取微地震震源位置等参数 ,然后 ,应用这些参数对生产活动进行监控或指导。在油气开发领域 ,该方法主要用于油田低渗透储层压裂的裂缝动态成像和油田开发过程的动态监测 ,主要是流体驱动监测。介绍了微地震监测方法的基本原理、数据采集方法和数据处理方法及应用实例 ,并对其应用效果和发展前景进行了分析
[128]	张太春. 2013. 人工微地震技术对压裂井实时监测应用研究 . [硕士论文]. 长春: 吉林大学 URL      摘要 微地震事件的实质是一个围岩应力应变、变形、开裂、失稳，破坏等一系列动态演变过程的一种表现形式。微地震监测的主要依据就是各传感器记录下的微地震事件信号波形。该波形含有最新的事件发生时震源及其附近的岩石状态信息。微地震研究的主要内容就是从信号波形中尽可能多地把有用的信息提取出来，并用一些定量的参数(主要用于表征岩石应力、应变的动态演变和围岩的最终破坏)来表示，以提供给工程应用。微地震研究必须与岩石(断裂)力学等相关专业理论知识有机地结合，并在实践中不断地积累经验。才能更有效地发挥其潜在优势，形成一套可供实践应用的微震监测系统。 微弱的地震波结合水力压裂作业，可用于监测从致密层中实施的油气增产措施。地震监测技术获取的微地震波可用来绘制裂缝的变化。 压裂井人工微地震实时监测评价技术是建立在微地震监测技术基础上的一项油田生产动态监测技术。微地震监测技术自上世纪七十年代来，已在国内外进行了广泛的研究和实践，应用该项技术，已在油田生产工作中取得了很多实际效果，诸如可利用该项技术监测压裂井的裂缝空间形态、有效缝长、缝高及地应力分布情况，为完善压裂工艺、评价压裂效果、对压裂井进行压后产能分析和井网布置提供有力的依据。压裂井人工微地震实时监测也是在这一已有的技术基础上，利用压裂时产生的微地震，使用现场监测系统，及计算机和其相应的专家解释系统，解释、分析现场监测实时数据。储层压裂是低渗透率储层实现高产稳产的重要手段。微地震监测是目前储层压裂中最精确、最及时、信息最丰富的监测手段。实时微地震成像可以及时指导压裂工程，适时调整压裂参数；压裂参数与震源参数的综合分析可以确定储层最大、最小水平地应力的主方向以及地应力的历史最大值；对压裂的范围、裂缝发育的方向、大小进行追踪、定位,客观评价压裂工程的效果，对下一步的生产开发提供有效的指导，降低开发成本。 (Zhang T C.2013. Application of artificial micro seismic technology on fracturing well real-time monitoring . [Master Thesis]. Changchun: Jilin University). URL      摘要 微地震事件的实质是一个围岩应力应变、变形、开裂、失稳，破坏等一系列动态演变过程的一种表现形式。微地震监测的主要依据就是各传感器记录下的微地震事件信号波形。该波形含有最新的事件发生时震源及其附近的岩石状态信息。微地震研究的主要内容就是从信号波形中尽可能多地把有用的信息提取出来，并用一些定量的参数(主要用于表征岩石应力、应变的动态演变和围岩的最终破坏)来表示，以提供给工程应用。微地震研究必须与岩石(断裂)力学等相关专业理论知识有机地结合，并在实践中不断地积累经验。才能更有效地发挥其潜在优势，形成一套可供实践应用的微震监测系统。 微弱的地震波结合水力压裂作业，可用于监测从致密层中实施的油气增产措施。地震监测技术获取的微地震波可用来绘制裂缝的变化。 压裂井人工微地震实时监测评价技术是建立在微地震监测技术基础上的一项油田生产动态监测技术。微地震监测技术自上世纪七十年代来，已在国内外进行了广泛的研究和实践，应用该项技术，已在油田生产工作中取得了很多实际效果，诸如可利用该项技术监测压裂井的裂缝空间形态、有效缝长、缝高及地应力分布情况，为完善压裂工艺、评价压裂效果、对压裂井进行压后产能分析和井网布置提供有力的依据。压裂井人工微地震实时监测也是在这一已有的技术基础上，利用压裂时产生的微地震，使用现场监测系统，及计算机和其相应的专家解释系统，解释、分析现场监测实时数据。储层压裂是低渗透率储层实现高产稳产的重要手段。微地震监测是目前储层压裂中最精确、最及时、信息最丰富的监测手段。实时微地震成像可以及时指导压裂工程，适时调整压裂参数；压裂参数与震源参数的综合分析可以确定储层最大、最小水平地应力的主方向以及地应力的历史最大值；对压裂的范围、裂缝发育的方向、大小进行追踪、定位,客观评价压裂工程的效果，对下一步的生产开发提供有效的指导，降低开发成本。
[129]	张晓春, 徐鹏, 程远方. 2009. 爆炸动载压裂模拟试验装置 . 中国专利:200910230809,2 [本文引用: 1]      (Zhang X C, Xu P, Cheng Y F.2009. Explosive dynamic load fracturing simulation test device . CN: 200910230809,2). [本文引用: 1]
[130]	张旭辉, 鲁晓兵. 2011. 基于孔隙网络模型的微小喉道对岩芯驱油特征的影响分析 . 兰州大学学报(自然科学版), 47: 207-213 URL      [本文引用: 1]      摘要 喉道半径微小与分布非均匀性是低渗透油藏岩石孔隙结构的特征,微小喉道孔隙是低渗透油藏岩芯驱油的关键控制因素之一。利用三维准静态孔隙网络模型模拟了按照Thamama油田岩石分类的五种喉道半径分布孔隙结构特征,考察了微小喉道孔隙份额大小对低渗透油藏驱油的相对渗透率以及共流区影响。结果表明:对于非均匀喉道孔隙结构,微小喉道占的份额越大,毛管压力逐渐控制流动,水相对渗透率越小,驱油效率越低。通过与实验结果对比验证了三维准静态模型模拟低渗透油藏驱油的有效性。 (Zhang X H, Lu X B.2011. Numerical simulation on influences micro pore throats to oil displacement for low permeable reservoirs based on pore-scale network models . Journal of Lanzhou University (Natural Sciences), 47: 207-213). URL      [本文引用: 1]      摘要 喉道半径微小与分布非均匀性是低渗透油藏岩石孔隙结构的特征,微小喉道孔隙是低渗透油藏岩芯驱油的关键控制因素之一。利用三维准静态孔隙网络模型模拟了按照Thamama油田岩石分类的五种喉道半径分布孔隙结构特征,考察了微小喉道孔隙份额大小对低渗透油藏驱油的相对渗透率以及共流区影响。结果表明:对于非均匀喉道孔隙结构,微小喉道占的份额越大,毛管压力逐渐控制流动,水相对渗透率越小,驱油效率越低。通过与实验结果对比验证了三维准静态模型模拟低渗透油藏驱油的有效性。
[131]	赵宝虎, 杨栋, 赵阳升, 胡耀青. 1999. 岩石三维应力控制压裂实验研究 . 太原理工大学学报, 30: 571-574 DOI      URL      [本文引用: 1]      摘要 通过对岩石三维应力控制压裂实验结果的分析，得出了裂缝的条数、长度、方向与应力场、装药量、孔径的关系。表明岩石三维应力控制压裂法能够产生随机的、两条以上的裂缝，有效提高岩体的渗透率。在用水压裂时各方向的裂缝都得到扩展，爆后炮孔壁基本保持完好。 (Zhao B H, Yang D, Zhao Y S, Hu Y Q.1999. Experimental study on three dimensional stress controlled fracturing of rocks . Journal of Taiyuan University of Technology, 30: 571-574). DOI      URL      [本文引用: 1]      摘要 通过对岩石三维应力控制压裂实验结果的分析，得出了裂缝的条数、长度、方向与应力场、装药量、孔径的关系。表明岩石三维应力控制压裂法能够产生随机的、两条以上的裂缝，有效提高岩体的渗透率。在用水压裂时各方向的裂缝都得到扩展，爆后炮孔壁基本保持完好。
[132]	赵博雄,王忠仁,刘瑞,雷立群. 2014. 国内外微地震监测技术综述 . 地球物理学进展, 4: 1882-1888 DOI      URL      [本文引用: 6]      摘要 微地震监测技术是以声发射学和地震学为基础的一种通过观测、分析生产活动中产生的微小地震事件来监测生产活动的影响、效果及储层状态的地球物理技术.与传统地震勘探不同,微地震监测中震源的位置、震源的强度和地震发生时刻都是未知的,确定这些未知因素正是微地震监测的首要任务.作为基于地球物理发展起来的一种可以对岩石微断裂发生位置进行有效监测的技术,微地震监测技术已经被广泛应用于矿山动力灾害监测、水力压裂等领域.本文概述了微地震技术的国内外研究历史及研究进展. (Zhao B X, Wang Z R, Liu R, Lie L Q.2014. Review of microseismic monitoring technology research . Progress in Geophysics, 4: 1882-1888). DOI      URL      [本文引用: 6]      摘要 微地震监测技术是以声发射学和地震学为基础的一种通过观测、分析生产活动中产生的微小地震事件来监测生产活动的影响、效果及储层状态的地球物理技术.与传统地震勘探不同,微地震监测中震源的位置、震源的强度和地震发生时刻都是未知的,确定这些未知因素正是微地震监测的首要任务.作为基于地球物理发展起来的一种可以对岩石微断裂发生位置进行有效监测的技术,微地震监测技术已经被广泛应用于矿山动力灾害监测、水力压裂等领域.本文概述了微地震技术的国内外研究历史及研究进展.
[133]	赵金洲, 任岚, 胡永全. 2013. 页岩储层压裂缝成网延伸的受控因素分析 . 西南石油大学学报(自然科学版), 35: 1-9 DOI      URL      [本文引用: 1]      摘要 压裂实践表明，页岩储层的水力裂缝呈现出非平面、多分支的复杂延伸模式，这与传统压裂理论认为的对称平面双翼裂缝从形成机理上存在本质的区别。基于室内实验、矿场压裂实践、理论分析和数值模拟等研究成果，系统分析了页岩储层压裂缝成网延伸的受控因素。研究表明：页岩储层的裂缝延伸形态受到地质因素和工程因素的双重作用，从储层地质属性上看，岩石的脆性矿物含量越高、岩石的力学弹性特征越强、水平应力差越小以及天然裂缝越发育，越有利于压裂缝的成网延伸与扩展；从压裂作业的工程条件上来说，施工净压力越高、压裂液流体黏度越低以及压裂规模越大，越有利于形成充分扩展的缝网。该研究对认识页岩储层缝网扩展机理以及提高页岩储层压裂设计的科学性具有重要的理论价值和现实意义。 (Zhao J Z, Ren L, Hu Y Q.2013. Controlling factors of hydraulic fractures extending into network in shale formations .Journal of Southwest Petroleum University: Science & Technology Edition, 35: 1-9). DOI      URL      [本文引用: 1]      摘要 压裂实践表明，页岩储层的水力裂缝呈现出非平面、多分支的复杂延伸模式，这与传统压裂理论认为的对称平面双翼裂缝从形成机理上存在本质的区别。基于室内实验、矿场压裂实践、理论分析和数值模拟等研究成果，系统分析了页岩储层压裂缝成网延伸的受控因素。研究表明：页岩储层的裂缝延伸形态受到地质因素和工程因素的双重作用，从储层地质属性上看，岩石的脆性矿物含量越高、岩石的力学弹性特征越强、水平应力差越小以及天然裂缝越发育，越有利于压裂缝的成网延伸与扩展；从压裂作业的工程条件上来说，施工净压力越高、压裂液流体黏度越低以及压裂规模越大，越有利于形成充分扩展的缝网。该研究对认识页岩储层缝网扩展机理以及提高页岩储层压裂设计的科学性具有重要的理论价值和现实意义。
[134]	赵益忠, 曲连忠, 王幸尊, 程远方, 沈海超. 2007. 不同岩性地层水力压裂裂缝扩展规律的模拟实验 . 中国石油大学学报(自然科学版), 31: 63-66 DOI      URL      [本文引用: 1]      摘要 利用真三轴模拟压裂实验系统对玄武岩、巨砾岩、泥灰岩岩心进行了水力压裂裂缝起裂及裂缝扩展模拟实验,得到了压后裂缝几何形态和压裂过程中压力随时间的变化规律。研究结果表明,玄武岩中天然裂缝发育程度较低,抗拉强度较高,裂缝起裂会导致明显的压降,压后能够形成比较理想的双翼缝;巨砾岩中天然裂缝较为发育,裂缝起裂不会导致明显的压降,高排量压裂后形成的裂缝为多组复杂裂缝,裂缝扩展摩阻很大,裂缝延伸压力几乎与破裂压力相当;泥灰岩抗拉强度较低,部分发育有天然裂缝,破裂压力较低,裂缝起裂后延伸压力与最小水平地应力相当。 (Zhao Y Z, Qu L Z, Wang X Z, Cheng Y F, Shen H C.2007. Simulation experiments of fracture propagation law of hydraulic fracturing in different lithostratigraphy . Journal of China University of Petrolium (Natrual Science Edition), 31: 63-66). DOI      URL      [本文引用: 1]      摘要 利用真三轴模拟压裂实验系统对玄武岩、巨砾岩、泥灰岩岩心进行了水力压裂裂缝起裂及裂缝扩展模拟实验,得到了压后裂缝几何形态和压裂过程中压力随时间的变化规律。研究结果表明,玄武岩中天然裂缝发育程度较低,抗拉强度较高,裂缝起裂会导致明显的压降,压后能够形成比较理想的双翼缝;巨砾岩中天然裂缝较为发育,裂缝起裂不会导致明显的压降,高排量压裂后形成的裂缝为多组复杂裂缝,裂缝扩展摩阻很大,裂缝延伸压力几乎与破裂压力相当;泥灰岩抗拉强度较低,部分发育有天然裂缝,破裂压力较低,裂缝起裂后延伸压力与最小水平地应力相当。
[135]	赵志红, 郭建春. 2011. 层内爆炸压裂岩石破碎颗粒尺寸的预测模型 . 爆炸与冲击, 31: 669-672 DOI      URL      [本文引用: 1]      摘要 借鉴爆破工程经验,结合层内爆炸压裂实际,应用能量守恒原理,将 液体炸药爆炸形成的冲击波能量分为岩石破碎的表面能和岩石内部的应变能,结合岩石断裂理论建立了粉碎区内岩石破碎粒径的预测模型.实例计算层内爆炸压裂形 成的岩石颗粒直径为1.43 mm.计算结果表明:液体炸药层内爆炸后形成的岩石破碎颗粒与石油工业中水力压裂使用的支撑剂粒径相当,能够支撑形成具有一定导流能力的裂缝. (Zhao Z H, Guo J C.2011. A size prediction model for rock particles generated by an explosion in fractured rock . Explosion and Shock Waves, 31: 669-672). DOI      URL      [本文引用: 1]      摘要 借鉴爆破工程经验,结合层内爆炸压裂实际,应用能量守恒原理,将 液体炸药爆炸形成的冲击波能量分为岩石破碎的表面能和岩石内部的应变能,结合岩石断裂理论建立了粉碎区内岩石破碎粒径的预测模型.实例计算层内爆炸压裂形 成的岩石颗粒直径为1.43 mm.计算结果表明:液体炸药层内爆炸后形成的岩石破碎颗粒与石油工业中水力压裂使用的支撑剂粒径相当,能够支撑形成具有一定导流能力的裂缝.
[136]	郑莲慧, 单钰铭, 钟敬敏. 2014. 页岩气等温吸附分子动力学特征研究 . 科学技术与工程, 14: 1-6 DOI      URL      [本文引用: 1]      摘要 页岩气等温吸附研究对了解页岩孔隙表面结构特征及认识气体分子在固体表面活动及吸附状态具有重要意义。利用基于狭缝假设的晶格理论方法,对甲烷在页岩中的吸附特征进行研究,对所定义的Y与X之间的线性关系进行了讨论,表明微孔中分子间平均势能Ea小于第1吸附层分子与固体间势能EA,EA/Ea在3.21~7.05之间,随温度升高该值保持在3.4左右。将利用晶格理论预测的Г与xb的关系与实测值进行了对比,结果表明晶格理论预测精度较高,表明该理论的假设合理,具有一定应用价值;但在平衡压力较高条件下尚需进一步研究。 (Zheng L H, Shan Y M, Zhong J M, Yin S.2014. Research of shale gas isotherm adsorption molecular dynamic characteristics . Science Technology and Engineering, 14: 1-6). DOI      URL      [本文引用: 1]      摘要 页岩气等温吸附研究对了解页岩孔隙表面结构特征及认识气体分子在固体表面活动及吸附状态具有重要意义。利用基于狭缝假设的晶格理论方法,对甲烷在页岩中的吸附特征进行研究,对所定义的Y与X之间的线性关系进行了讨论,表明微孔中分子间平均势能Ea小于第1吸附层分子与固体间势能EA,EA/Ea在3.21~7.05之间,随温度升高该值保持在3.4左右。将利用晶格理论预测的Г与xb的关系与实测值进行了对比,结果表明晶格理论预测精度较高,表明该理论的假设合理,具有一定应用价值;但在平衡压力较高条件下尚需进一步研究。
[137]	郑伟, 莫修文. 2013. 利用测井资料评价页岩气层含气量的方法//中国地球物理2013––第十九分会场论文集 [本文引用: 1]      (Zheng W, Mo X W.2013. Method for evaluating gas content of shale gas reservoir by using logging data//Chinese Geophysics 2013 -- Nineteenth) . [本文引用: 1]
[138]	郑委. 2010. CO$_{2}$地质埋存中的逃逸问题研究 . [硕士论文]. 北京: 中国科学院力学研究所 URL      [本文引用: 1]      摘要 中国科学院力学研究所机构知识库(IMECH-IR)以发展机构知识能力和知识管理能力为目标，快速实现对本机构知识资产的收集、长期保存、合理传播利用，积极建设对知识内容进行捕获、转化、传播、利用和审计的能力，逐步建设包括知识内容分析、关系分析和能力审计在内的知识服务能力，开展综合知识管理。 (Zheng W.2010. The leakage of after CO$_{2}$ geological sequestration . [Master Thesis]. Beijing: Institute of Mechanics. Chinese Academy of Sciences). URL      [本文引用: 1]      摘要 中国科学院力学研究所机构知识库(IMECH-IR)以发展机构知识能力和知识管理能力为目标，快速实现对本机构知识资产的收集、长期保存、合理传播利用，积极建设对知识内容进行捕获、转化、传播、利用和审计的能力，逐步建设包括知识内容分析、关系分析和能力审计在内的知识服务能力，开展综合知识管理。
[139]	郑新权, 靳志霞. 2003. CO$_{2}$泡沫压裂优化设计技术及应用 . 石油钻采工艺, 25: 53-56 DOI      URL      [本文引用: 1]      摘要 针对苏里格低压、低渗透气藏常规水基压裂液压后返排困难,导致储层水锁伤害的问题,研究利用CO泡沫压裂来降低压裂液滤失,提高压裂液返排率,降低对储层的伤害。有针对性地研究了CO泡沫压裂优化设计技术,包括:CO泡沫压裂起泡技术、酸性交联技术、变泡沫质量和恒定内相设计技术等。现场应用表明,长庆苏里格气田气藏应用CO泡沫压裂技术,可大大提高返排率,缩短压裂液返排时间,降低压裂液对气层的伤害,提高压裂效果。 (Zheng X Q, Jin Z X.2003. Optimizing design technology and application of CO$_{2}$ form fracturing . Land & Resources Information, 25: 53-56). DOI      URL      [本文引用: 1]      摘要 针对苏里格低压、低渗透气藏常规水基压裂液压后返排困难,导致储层水锁伤害的问题,研究利用CO泡沫压裂来降低压裂液滤失,提高压裂液返排率,降低对储层的伤害。有针对性地研究了CO泡沫压裂优化设计技术,包括:CO泡沫压裂起泡技术、酸性交联技术、变泡沫质量和恒定内相设计技术等。现场应用表明,长庆苏里格气田气藏应用CO泡沫压裂技术,可大大提高返排率,缩短压裂液返排时间,降低压裂液对气层的伤害,提高压裂效果。
[140]	郑哲敏. 2016. 关于中国页岩气持续开发工程科学研究的一点认识. 科学通报, 61: 34-35 [本文引用: 2]      (Zheng Z M.2016.A little understanding of the scientific research on the sustainable development of shale gas in China. Science China Press, 61: 34-35). [本文引用: 2]
[141]	周基阳. 2011. 基于信息量的地震波动初至拾取 . [博士论文]. 北京: 华北电力大学 DOI      [本文引用: 1]      摘要 能源问题是关系国计民生的大事,石油在我们的日常生活中起着越来越重要的作用,石油的准确勘探对我们有着重要的意义。要实现精确的石油勘探,首先就要处理大量的地震波信号,而地震波初至到达的时间检测,是处理地震波信号的一个基础又很重要的问题。 地震波初至的拾取广泛应用在表层调查方法和地质构造的探测中,初至的拾取对矿物资源和石油资源的开发,都起着重要的作用,本文研究的是地震波初至拾取的方法。目前有许多初至拾取的方法,例如能量比法,最大振幅法,分形维法及神经网络法等。但是这些方法有着自身的缺点。本文研究的是基于互信息量的地震波动初至拾取,互信息量的概念来源于信息论,用来度量两个随机变量之间的相似性。因此本文把信息论中的互信息量引入到地震信号的分析和处理中去,提出了一种互信息量检测地震信号并进行初至提取的方法,并且给出了该方法的基本原理和具体算法,然后把传统的能量比算法和这种互信息量的算法相结合,提出了一种新型的改进算法。然后把提出的互信息量的算法,改进的算法,各种算法如能量比法,振幅比法和曲线长度法进行了比较,互信息量的算法及其改进的算法大大减少了计算量,能够较好的检测地震波的初至到来时刻。 (Zhou J Y.2011. First arrical pickup of seismic waves based on mutual information . [PhD Thesis]. Beijing: North China Electric Power University). DOI      [本文引用: 1]      摘要 能源问题是关系国计民生的大事,石油在我们的日常生活中起着越来越重要的作用,石油的准确勘探对我们有着重要的意义。要实现精确的石油勘探,首先就要处理大量的地震波信号,而地震波初至到达的时间检测,是处理地震波信号的一个基础又很重要的问题。 地震波初至的拾取广泛应用在表层调查方法和地质构造的探测中,初至的拾取对矿物资源和石油资源的开发,都起着重要的作用,本文研究的是地震波初至拾取的方法。目前有许多初至拾取的方法,例如能量比法,最大振幅法,分形维法及神经网络法等。但是这些方法有着自身的缺点。本文研究的是基于互信息量的地震波动初至拾取,互信息量的概念来源于信息论,用来度量两个随机变量之间的相似性。因此本文把信息论中的互信息量引入到地震信号的分析和处理中去,提出了一种互信息量检测地震信号并进行初至提取的方法,并且给出了该方法的基本原理和具体算法,然后把传统的能量比算法和这种互信息量的算法相结合,提出了一种新型的改进算法。然后把提出的互信息量的算法,改进的算法,各种算法如能量比法,振幅比法和曲线长度法进行了比较,互信息量的算法及其改进的算法大大减少了计算量,能够较好的检测地震波的初至到来时刻。
[142]	周理, 李明, 周亚平. 2000. 超临界甲烷在高表面活性炭上的吸附测量及其理论分析 . 中国科学(B 辑), 30: 49-56 DOI      URL      摘要 实验测定了０￣１０ＭＰａ，２２３￣３３３ｋ（２０ｋ间隔）范围内超临界甲烷在高表面活性炭上的吸／脱附等温线，确定了此物理吸附过程的可逆性，并从实验数据计算出吸附热为１６．５ｋＪ／ｍｏｌ，建立了描述具有最大点的吸附等温线，其总体偏差为±２％，模型保持了特征吸附能恒定的性质，方程指数亦反映了吸附剂的微孔分布特征，模型参数给出了超临界甲烷的吸附相密度，将超临界吸附极限态引入了等温线模型中，经典的吸附理论亦 (Zhou L, Li M, Zhou Y P.2000. Adsorption measurement and theoretical analysis of supercritical methane on high surface activated carbon . Science in China(Series B), 30: 49-56). DOI      URL      摘要 实验测定了０￣１０ＭＰａ，２２３￣３３３ｋ（２０ｋ间隔）范围内超临界甲烷在高表面活性炭上的吸／脱附等温线，确定了此物理吸附过程的可逆性，并从实验数据计算出吸附热为１６．５ｋＪ／ｍｏｌ，建立了描述具有最大点的吸附等温线，其总体偏差为±２％，模型保持了特征吸附能恒定的性质，方程指数亦反映了吸附剂的微孔分布特征，模型参数给出了超临界甲烷的吸附相密度，将超临界吸附极限态引入了等温线模型中，经典的吸附理论亦
[143]	周理, 周亚平. 1996. 关于氢在活性炭上高压吸附特性的实验研究 . 中国科学(B辑), 26: 473-479 DOI      URL      [本文引用: 1]      摘要 利用研制的大容量超级低温恒温槽,以20K为步长,首次在298K至77K,0到7MPa的大范围内系统地研究了氢在活性炭上的吸附特性。采用容积法测定了氢在AX-21活性炭上的一组吸/脱附等温线。通过将该组数据拟合到描述I-型等温线的诸理论模型,发现Dubinin-Astakhov方程在整个实验范围内与实验数据较好地吻合。由非线性回归定出的参数值,使该方程可以±4％的误差预测吸附量。根据该模型作出了三维吸附面,并解析地计算出等量吸附热。除低压部分外,计算值与实验值符合良好。最后讨论了D-A方程在超临界领域遇到的问题。 (Zhou L, Zhou Y P.1996. Experimental study on high pressure adsorption characteristics of Hydrogen on activated carbon , Science in China(Series B), 26: 473-479). DOI      URL      [本文引用: 1]      摘要 利用研制的大容量超级低温恒温槽,以20K为步长,首次在298K至77K,0到7MPa的大范围内系统地研究了氢在活性炭上的吸附特性。采用容积法测定了氢在AX-21活性炭上的一组吸/脱附等温线。通过将该组数据拟合到描述I-型等温线的诸理论模型,发现Dubinin-Astakhov方程在整个实验范围内与实验数据较好地吻合。由非线性回归定出的参数值,使该方程可以±4％的误差预测吸附量。根据该模型作出了三维吸附面,并解析地计算出等量吸附热。除低压部分外,计算值与实验值符合良好。最后讨论了D-A方程在超临界领域遇到的问题。
[144]	周银兴. 2009. 微震事件检测及震相自动识别研究 . [博士论文]. 北京: 中国地震局地震预测研究所 URL      [本文引用: 1]      摘要 近30年我国数字地震观测台网迅速发展,特别是随着“十五”项目“中国数字地震观测网络项目”的完成,以及近年来经济发展迅猛,国家对于大型可能诱发水库地震的水库、受地震后可能引发次生灾害的油田、矿山、石油化工及大型煤矿等重要设施要求必须建设专用地震监测台网,地震台网规模越来越大,地震观测台站越来越多,数据每年以海量产出,人们对实时地震数据自动处理系统的要求越来越迫切,同时由于地震是自然灾害中破坏性最强的,近年来人们对于建立地震预警系统的呼声也越来越高,这些都是建立在深入研究地震事件和地震震相的自动识别基础之上。 微小地震虽然破坏性不大,但却是研究大地震和整个地震带应力场的基础,本世纪初在经历了印尼大地震引发的海啸和“5.12”汶川大地震以后,我们清楚认识到当前对于地震预报这一世界性科学难题仍然没有更好的办法,但对于减轻地震灾害的渴望越来越大,因此国家努力加大台网观测密度,丰富了观测资料,提供了我们进一步认识地下精细结构的可能,小地震震相简单,在目前的技术前提下,比较容易实现自动识别,震相的自动识别处理不但能减轻人们处理资料的负担,而且能快速的获得更多的震相识别结果、便于人们了解地震时空发展动态过程具有深远的意义。 地震的自动处理过程包括事件自动检测和震相自动识别两部分,目前没有一种方法可以把这两件事情做得很好,基于目前的情况,我们深入的研究了目前常用的SLT/LSA等检测算法。总结了人们对于地震事件的研究和震相识别的各种方法,国内的应用情况,具有征对性的进行了以下几方面的详细研究: 1.对区域地震事件检测方法进行了总结,详细研究了STA/LTA这一应用最广泛的检测方法和偏振(极化)检测法,编写程序验证地震波的偏振对于检测微震事件和判断震相的可行性。基于协方差矩阵的特征值法和奇异值分解的方法可较清晰的反映宽频带记录中的小地震事件,而且是基于三分向记录进行的检测方法,实践表明,该方法可增强识别率降低误检率,可用该方法构造特征函数与别的方法综合进行微震事件检测。 2.总结了震相自动识别的方法,以Akaike信息准则(AIC)为基础,用基于自回归的AR-AIC、基于样本方差的VAR-AIC、基于高阶统计量的TOC-AIC、和基于记录振幅(能量)的AOC-AIC方法对比进行自动检测了小地震中的PG、SG震相,自动识别的结果表明,较高的信噪比有较高的识别精度,低信噪比事件数据需要经过滤波处理后方能得到可靠的自动识别精度。各种AIC方法中,VAR-AIC、AOC-AIC方法计算量小,速度快,应用AIC方法识别震相到时必须保证计算的数据段便能保证识别的可靠性,AIC方法是基于单分向数据进行检测的。偏振特征法是基于三分向数据进行检测和震相分析的,具有较好的可信度,但是因检测识别计算过程中要取一定长的时间窗口构造协方差矩阵,因此在进行震相识别的时候所取数据长度窗口越小,震相起始点的精度越高。 3.我们应用P波与S波的质点运动特征,以乌江水库地震台网的资料分析了P波段、S波段质点偏振主轴方向Z与其它两个正交方向Y与X的特征关系进行了分析统计,结果表明以P波段为偏振模型进行坐标旋转以后与S波三分向特征值特点差异明显,P波质点运动主轴方向Z与另两正交方向上的特征值的幅值比2×Z / ( X + Y)、Y与X的幅值比、Y与主轴方向Z的幅值比均有不同的分布特征,P波与S波主轴方向与两正交方向特征值的比值2×Z / ( X +Y)差异最大,P波主轴方向的方位角入射角信息与S波也有明确的分界,这些偏振特征可作为自动检测结果的判定标准模型。 (Zhou Y X.2009. Research on the micro-earthquake detection and seismic phase automatic identification . [PhD Thesis]. Beijing: China Earthquake Administration: Institute of Earthquake Prediction). URL      [本文引用: 1]      摘要 近30年我国数字地震观测台网迅速发展,特别是随着“十五”项目“中国数字地震观测网络项目”的完成,以及近年来经济发展迅猛,国家对于大型可能诱发水库地震的水库、受地震后可能引发次生灾害的油田、矿山、石油化工及大型煤矿等重要设施要求必须建设专用地震监测台网,地震台网规模越来越大,地震观测台站越来越多,数据每年以海量产出,人们对实时地震数据自动处理系统的要求越来越迫切,同时由于地震是自然灾害中破坏性最强的,近年来人们对于建立地震预警系统的呼声也越来越高,这些都是建立在深入研究地震事件和地震震相的自动识别基础之上。 微小地震虽然破坏性不大,但却是研究大地震和整个地震带应力场的基础,本世纪初在经历了印尼大地震引发的海啸和“5.12”汶川大地震以后,我们清楚认识到当前对于地震预报这一世界性科学难题仍然没有更好的办法,但对于减轻地震灾害的渴望越来越大,因此国家努力加大台网观测密度,丰富了观测资料,提供了我们进一步认识地下精细结构的可能,小地震震相简单,在目前的技术前提下,比较容易实现自动识别,震相的自动识别处理不但能减轻人们处理资料的负担,而且能快速的获得更多的震相识别结果、便于人们了解地震时空发展动态过程具有深远的意义。 地震的自动处理过程包括事件自动检测和震相自动识别两部分,目前没有一种方法可以把这两件事情做得很好,基于目前的情况,我们深入的研究了目前常用的SLT/LSA等检测算法。总结了人们对于地震事件的研究和震相识别的各种方法,国内的应用情况,具有征对性的进行了以下几方面的详细研究: 1.对区域地震事件检测方法进行了总结,详细研究了STA/LTA这一应用最广泛的检测方法和偏振(极化)检测法,编写程序验证地震波的偏振对于检测微震事件和判断震相的可行性。基于协方差矩阵的特征值法和奇异值分解的方法可较清晰的反映宽频带记录中的小地震事件,而且是基于三分向记录进行的检测方法,实践表明,该方法可增强识别率降低误检率,可用该方法构造特征函数与别的方法综合进行微震事件检测。 2.总结了震相自动识别的方法,以Akaike信息准则(AIC)为基础,用基于自回归的AR-AIC、基于样本方差的VAR-AIC、基于高阶统计量的TOC-AIC、和基于记录振幅(能量)的AOC-AIC方法对比进行自动检测了小地震中的PG、SG震相,自动识别的结果表明,较高的信噪比有较高的识别精度,低信噪比事件数据需要经过滤波处理后方能得到可靠的自动识别精度。各种AIC方法中,VAR-AIC、AOC-AIC方法计算量小,速度快,应用AIC方法识别震相到时必须保证计算的数据段便能保证识别的可靠性,AIC方法是基于单分向数据进行检测的。偏振特征法是基于三分向数据进行检测和震相分析的,具有较好的可信度,但是因检测识别计算过程中要取一定长的时间窗口构造协方差矩阵,因此在进行震相识别的时候所取数据长度窗口越小,震相起始点的精度越高。 3.我们应用P波与S波的质点运动特征,以乌江水库地震台网的资料分析了P波段、S波段质点偏振主轴方向Z与其它两个正交方向Y与X的特征关系进行了分析统计,结果表明以P波段为偏振模型进行坐标旋转以后与S波三分向特征值特点差异明显,P波质点运动主轴方向Z与另两正交方向上的特征值的幅值比2×Z / ( X + Y)、Y与X的幅值比、Y与主轴方向Z的幅值比均有不同的分布特征,P波与S波主轴方向与两正交方向特征值的比值2×Z / ( X +Y)差异最大,P波主轴方向的方位角入射角信息与S波也有明确的分界,这些偏振特征可作为自动检测结果的判定标准模型。
[145]	周忠根. 2006. 由时频分布引导的四参数子空间匹配追踪算法 . [硕士论文]. 西安: 西安电子科技大学 DOI      URL      [本文引用: 1]      摘要 为了克服四参数匹配追踪计算量巨大的缺点,本文提出了一种由时频分布引导的四参数子空间匹配 追踪算法。该算法由引导时频分布确定chirp原子的时频中心,然后用模板匹配方法搜索原子的尺度和调频率（chirp rate）。这样,一个高计算复杂度的四维搜索问题被转化为两个相对简单的二维搜索问题。为有效利用时频分布,每次搜索多个时频原子,这些原子不再相互正 交。为此,我们利用最小二乘方法计算信号（或残差信号）在相应子空间上的正交投影。同快速脊追踪算法相比,四参数子空间匹配追踪需要更少的原子逼近信号, 对实测语音信号的数值计算也证实了这点。 (Zhou Z G.2006. Four-parameter subspace matching pursuit algorithm with the help of time-frequency distribution . [Master Thesis]. Xi'an: Xidian University). DOI      URL      [本文引用: 1]      摘要 为了克服四参数匹配追踪计算量巨大的缺点,本文提出了一种由时频分布引导的四参数子空间匹配 追踪算法。该算法由引导时频分布确定chirp原子的时频中心,然后用模板匹配方法搜索原子的尺度和调频率（chirp rate）。这样,一个高计算复杂度的四维搜索问题被转化为两个相对简单的二维搜索问题。为有效利用时频分布,每次搜索多个时频原子,这些原子不再相互正 交。为此,我们利用最小二乘方法计算信号（或残差信号）在相应子空间上的正交投影。同快速脊追踪算法相比,四参数子空间匹配追踪需要更少的原子逼近信号, 对实测语音信号的数值计算也证实了这点。
[146]	朱华良. 1997. 世界地理概览. 北京: 东方出版中心 (Zhu H L.1997. World Geographic Survey. Beijing: Oriental Publishing Center).
[147]	庄茁, 刘占立, 王涛, 高岳, 王永辉, 付海峰. 2016. 页岩水力压裂的关键力学问题. 科学通报, 61: 72-81 [本文引用: 2]      (Zhuang Z, Liu Z L, Wang T, Gao Y, Wang Y H, Fu H F.The key mechanical problems on hydraulic fracture in shale. Science China Press, 61: 72-81). [本文引用: 2]
[148]	庄茁, 柳占立, 成斌斌, 廖剑辉. 2012 . 扩展有限单元法. 北京: 清华大学出版社 [本文引用: 2]      (Zhuang Z, Liu Z L, Cheng B B, Liao J H.2012.The Extended Finite Element Method. Beijing: Tsinghua University Press). [本文引用: 2]
[149]	庄茁, 柳占立, 王永亮. 2015. 页岩油气高效开发中的基础理论与关键力学问题 . 力学季刊, 36: 11-25 URL      [本文引用: 3]      摘要 我国页岩油气开发刚刚起步,许多基础理论和关键科学(力学)问题亟需明确和解决.本文按页岩油气开发的全过程自然地将其分为四个相互关联的科学问题展开介绍和讨论,包括:页岩工程地质力学特征与预测理论,地质力学找到气;多重耦合下的页岩油气安全钻井完井理论,钻井完井够到气;页岩地层动态随机裂缝控制机理与新概念压裂理论,体积压裂释放气;页岩油气多尺度渗流特征与开采理论,解吸运移产出气.本文提出用水力压裂创造页岩传气能力,用气体二次压裂页岩基质来解决气源问题,实现水力压裂创造的页岩传气能力与页岩基质气体供应能力相匹配,避免"断气"现象发生,最终达到页岩气可持续性开采.解决这些关键科学(力学)问题可以为页岩油气高效开发奠定可靠的基础,具有重要的理论意义和应用前景. (Zhuang Z, Liu Z L, Wang Y L.2015. Fundamental theory and key mechanical problems of shale oil gas effective extraction . Chinese Quarterly of Mechanics, 36: 11-25). URL      [本文引用: 3]      摘要 我国页岩油气开发刚刚起步,许多基础理论和关键科学(力学)问题亟需明确和解决.本文按页岩油气开发的全过程自然地将其分为四个相互关联的科学问题展开介绍和讨论,包括:页岩工程地质力学特征与预测理论,地质力学找到气;多重耦合下的页岩油气安全钻井完井理论,钻井完井够到气;页岩地层动态随机裂缝控制机理与新概念压裂理论,体积压裂释放气;页岩油气多尺度渗流特征与开采理论,解吸运移产出气.本文提出用水力压裂创造页岩传气能力,用气体二次压裂页岩基质来解决气源问题,实现水力压裂创造的页岩传气能力与页岩基质气体供应能力相匹配,避免"断气"现象发生,最终达到页岩气可持续性开采.解决这些关键科学(力学)问题可以为页岩油气高效开发奠定可靠的基础,具有重要的理论意义和应用前景.
[150]	卓仁燕, 张烈辉, 郭晶晶, 马俊修. 2016. 含气页岩渗透率实验 . 大庆石油地质与开发, 35: 155-157 DOI      URL      [本文引用: 1]      摘要 采用压力脉冲衰减法测量了岩心柱的渗透率，讨论了内压和有效应力对渗透率的影响。同时，采用岩屑压力衰减法测量了页岩基质渗透率，并基于控制变量法优选出页岩基质渗透率实验参数。研究表明：在低内压的条件下，由于滑脱效应使渗透率增加；页岩渗透率随有效应力的升高呈非线性降低，孔隙压力越低，应力敏感性越强，有效应力在升高、降低过程中存在应力一应变滞后回线。岩屑压力衰减法测量基质渗透率实验的初始压力为1．3～1．38MPa，岩屑平均粒径为0．7～1mm，岩屑样品质量为25～30g。 (Zhuo R Y, Zhang L H, Guo J J, Ma J X.2016. Experiment on Gas-bearing Shale Permeability . Petroleum Geology and Oilfield Development in Daqing, 35: 155-157). DOI      URL      [本文引用: 1]      摘要 采用压力脉冲衰减法测量了岩心柱的渗透率，讨论了内压和有效应力对渗透率的影响。同时，采用岩屑压力衰减法测量了页岩基质渗透率，并基于控制变量法优选出页岩基质渗透率实验参数。研究表明：在低内压的条件下，由于滑脱效应使渗透率增加；页岩渗透率随有效应力的升高呈非线性降低，孔隙压力越低，应力敏感性越强，有效应力在升高、降低过程中存在应力一应变滞后回线。岩屑压力衰减法测量基质渗透率实验的初始压力为1．3～1．38MPa，岩屑平均粒径为0．7～1mm，岩屑样品质量为25～30g。
[151]	邹才能, 董大忠, 王社教, 李建忠, 李新景, 王玉满, 李登华, 程克明. 2010. 中国页岩气形成机理、地质特征及资源潜力 . 石油勘探与开发, 37: 6-18 URL      [本文引用: 2]      摘要 以四川盆地为重点,介绍中国海相、海陆过渡相、陆相三大类型页岩形成的沉积环境、地球化学与储集层特征、含气量与远景资源量。中国海相页岩是一套高有机质丰度(TOC为1.0%~5.5%)、高—过成熟(Ro值为2.0%~5.0%)、富含页岩气(含气量1.17~6.02 m3/t)、以陆棚相为主的沉积,主要分布在华南扬子地区古生界、华北地台古生界和塔里木盆地寒武系—奥陶系;海陆过渡相煤系炭质页岩有机质丰度高(TOC为2.6%~5.4%)、成熟度适中(Ro值为1.1%~2.5%);中新生界陆相页岩有机质丰度高(TOC为0.5%~22.0%)、低熟—成熟(Ro值为0.6%~1.5%)。在对四川盆地下古生界页岩储集层研究中首次发现,寒武系和志留系海相页岩发育大量与北美地区相似的微米—纳米级孔隙。综合评价认为四川盆地发育的多套页岩气层系是勘探开发的现实领域,四川盆地中南部威远—长宁等地区的寒武系和志留系是页岩气勘探开发的核心区与层系,其特点是:热演化程度较高(Ro值为2.0%~4.0%)、孔隙度较高(3.0%~4.8%),含气量较高(2.82~3.28 m3/t)、脆性矿物含量较高(40%~80%)、埋深适中(1 500~4 500 m),有利于开采。图7表7参38 ( Zou C N, Dong D Z, Wang S J, Li J Z, Li X J, Wang Y M, Li D H, Cheng K M.2010. Geological charactics, formation mechanism and resource potential of shale gas in China . Petroleum exploration and development, 37: 641-653). URL      [本文引用: 2]      摘要 以四川盆地为重点,介绍中国海相、海陆过渡相、陆相三大类型页岩形成的沉积环境、地球化学与储集层特征、含气量与远景资源量。中国海相页岩是一套高有机质丰度(TOC为1.0%~5.5%)、高—过成熟(Ro值为2.0%~5.0%)、富含页岩气(含气量1.17~6.02 m3/t)、以陆棚相为主的沉积,主要分布在华南扬子地区古生界、华北地台古生界和塔里木盆地寒武系—奥陶系;海陆过渡相煤系炭质页岩有机质丰度高(TOC为2.6%~5.4%)、成熟度适中(Ro值为1.1%~2.5%);中新生界陆相页岩有机质丰度高(TOC为0.5%~22.0%)、低熟—成熟(Ro值为0.6%~1.5%)。在对四川盆地下古生界页岩储集层研究中首次发现,寒武系和志留系海相页岩发育大量与北美地区相似的微米—纳米级孔隙。综合评价认为四川盆地发育的多套页岩气层系是勘探开发的现实领域,四川盆地中南部威远—长宁等地区的寒武系和志留系是页岩气勘探开发的核心区与层系,其特点是:热演化程度较高(Ro值为2.0%~4.0%)、孔隙度较高(3.0%~4.8%),含气量较高(2.82~3.28 m3/t)、脆性矿物含量较高(40%~80%)、埋深适中(1 500~4 500 m),有利于开采。图7表7参38
[152]	邹才能, 陶士振, 侯连华. 2011. 非常规油气地质. 北京: 地质出版社 [本文引用: 1]      (Zou C N, Tao S Z, Hou L H. 2011. Unconventional Petroleum Geology. Beijing: Geological Publishing House). [本文引用: 1]
[153]	邹才能, 张光亚, 陶士振, 胡素云, 李小地, 李建忠, 董大忠, 朱如凯, 袁选俊, 侯连华, 瞿辉, 赵霞, 贾进华, 高晓辉, 郭秋麟, 王岚, 李新景. 2010. 全球油气勘探领域地质特征, 重大发现及非常规石油地质 . 石油勘探与开发, 37: 129-145 URL      摘要 全球常规类大型、特大型油气田主要分布在特提斯域、被动陆缘、前陆冲断带和克拉通等盆地中。非常规类油气田主要分布于前渊斜坡、盆地（坳陷）中心、克拉通向斜区和冻土带等。21世纪以来全球油气勘探重大发现主要集中在被动陆缘深水区、碳酸盐岩、岩性-地层、前陆冲断带、成熟探区、新地区新盆地及非常规油气藏（场）等7大领域。这些重大发现涉及油气勘探中的常规与非常规2类油气资源。常规石油地质强调在单一明确圈闭中的油气运聚和成藏规律;非常规石油地质重点研究非常规资源、非常规储集层、非常规成藏与非常规技术等。非常规油气藏（场）在地质特征、分类方案、研究内容、评价方法和勘探阶段等方面与常规油气藏有明显不同,需要加强非常规石油地质研究,发展非常规石油地质理论。图8表7参63 (Zou C N, Zhang G Y, Tao S Z, Hu S Y, Li X D, Li J Z, Dong D Z, Zhu R K, Yuan X J, Hou L H, Zhai H, Zhao X, Jia J H, Gao X H, Guo Q L, Wang L, Li X J.2010. Geological features, major discoveries and unconventional petroleum geology in the global petroleum exploration . Petroleum Exploration and Development, 37: 129-145). URL      摘要 全球常规类大型、特大型油气田主要分布在特提斯域、被动陆缘、前陆冲断带和克拉通等盆地中。非常规类油气田主要分布于前渊斜坡、盆地（坳陷）中心、克拉通向斜区和冻土带等。21世纪以来全球油气勘探重大发现主要集中在被动陆缘深水区、碳酸盐岩、岩性-地层、前陆冲断带、成熟探区、新地区新盆地及非常规油气藏（场）等7大领域。这些重大发现涉及油气勘探中的常规与非常规2类油气资源。常规石油地质强调在单一明确圈闭中的油气运聚和成藏规律;非常规石油地质重点研究非常规资源、非常规储集层、非常规成藏与非常规技术等。非常规油气藏（场）在地质特征、分类方案、研究内容、评价方法和勘探阶段等方面与常规油气藏有明显不同,需要加强非常规石油地质研究,发展非常规石油地质理论。图8表7参63
[154]	左罗, 王玉普, 郭为, 熊伟, 高树生, 胡志明, 沈瑞. 2015. 简化局部密度理论预测页岩等温吸附曲线 . 天然气地球科学, 26: 592-598 DOI      URL      [本文引用: 1]      摘要 changes when temperature varies.We also predicted the sorption isotherm of methane on chlorite,illite,illite/smectite mixed layer and type Ⅱ kerogen at given temperature by SLD model with the known relation between ε and temperature of each material,and all the sorption isotherms of shale sample originated from prediction are close to experimental results. (Zuo L, Wang Y P, Guo W, Xiong W, Gao S S, Hu Z M, Shen R.2015. Predicting the sorption isotherm of methane on shale with simplified local-density model . Natural Gas Geoscience, 26: 592-598). DOI      URL      [本文引用: 1]      摘要 changes when temperature varies.We also predicted the sorption isotherm of methane on chlorite,illite,illite/smectite mixed layer and type Ⅱ kerogen at given temperature by SLD model with the known relation between ε and temperature of each material,and all the sorption isotherms of shale sample originated from prediction are close to experimental results.
[155]	左罗, 王玉普, 熊伟, 郭为, 高树生, 胡志明, . 2015. 页岩含气量计算新方法 . 石油学报, 36: 469-474 DOI      URL      [本文引用: 1]      摘要 通过分析常规页岩含气量测试所面临的问题,从页岩含气量本质入手,提出了利用绝对吸附量计算含气量的可行性方法。通过假设吸附相体积与比表面积间的关系及孔隙中密度分布最小值与体相密度之间随着压力的变化关系,提出了页岩含气量计算的新方法,并借助简化局部密度函数理论和页岩实测等温吸附曲线实现了页岩含气量的计算。研究发现:简化局部密度函数理论可以精确拟合页岩等温吸附曲线,说明该理论可以有效地描述页岩的吸附特性;利用简化局部密度函数理论及页岩等温吸附曲线可实现页岩含气量的计算,该方法的优势在于基本上能够还原储层温度、压力下气体在页岩中的原始赋存状态。 (Zuo L, Wang Y P, Xiong W, Guo W, Gao S S, Hu Z M, Shen R.2015. A new method to calculate the shale gas content . Acta Petrolei Sinica, 36: 469-474). DOI      URL      [本文引用: 1]      摘要 通过分析常规页岩含气量测试所面临的问题,从页岩含气量本质入手,提出了利用绝对吸附量计算含气量的可行性方法。通过假设吸附相体积与比表面积间的关系及孔隙中密度分布最小值与体相密度之间随着压力的变化关系,提出了页岩含气量计算的新方法,并借助简化局部密度函数理论和页岩实测等温吸附曲线实现了页岩含气量的计算。研究发现:简化局部密度函数理论可以精确拟合页岩等温吸附曲线,说明该理论可以有效地描述页岩的吸附特性;利用简化局部密度函数理论及页岩等温吸附曲线可实现页岩含气量的计算,该方法的优势在于基本上能够还原储层温度、压力下气体在页岩中的原始赋存状态。
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[165]	Amann F, Button E A, Evans K F, Gischig V S, Blümel M.2011. Experimental study of the brittle behavior of clay shale in rapid unconfined compression . Rock Mechanics and Rock Engineering, 44: 415-430. DOI      URL      [本文引用: 1]      摘要 The mechanical behavior of clay shales is of great interest in many branches of geo-engineering, including nuclear waste disposal, underground excavations, and deep well drilling. Observations from test galleries (Mont Terri, Switzerland and Bure, France) in these materials have shown that the rock mass response near the excavation is associated with brittle failure processes combined with bedding parallel shearing. To investigate the brittle failure characteristics of the Opalinus Clay recovered from the Mont Terri Underground Research Laboratory, a series of 19 unconfined uniaxial compression tests were performed utilizing servo-controlled testing procedures. All specimens were tested at their natural water content with loading approximately normal to the bedding. Acoustic emission (AE) measurements were utilized to help quantify stress levels associated with crack initiation and propagation. The unconfined compression strength of the tested specimens averaged 6.9 MPa. The crack initiation threshold occurred at approximately 30% of the rupture stress based on analyzing both the acoustic emission measurements and the stress train behavior. The crack damage threshold showed large variability and occurred at approximately 70% of the rupture stress.
[166]	Amann F, Kaiser P, Button E A.2012. Experimental study of brittle behavior of clay shale in rapid triaxial compression . Rock Mechanics and Rock Engineering, 45: 21-33. DOI      URL      [本文引用: 5]      摘要 AbstractThe brittle failure behavior of an over-consolidated clay shale (Opalinus Clay) in undrained rapid triaxial compression was studied. The confining stress levels were chosen to simulate the range of confining stresses relevant for underground excavations at the Mont Terri Underground Research Laboratory, and to investigate the transition from axial splitting failure to macroscopic shear failure. Micro-crack initiation was observed throughout the confining stress range utilized in this study at a differential stress of 2.102MPa on average, which indicates that friction was not mobilized at this stage of brittle failure. The rupture stress was dependent on confinement indicating friction mobilization during the brittle failure process. With increasing confinement net volumetric strain decreased suggesting that dilation was suppressed, which is possibly related to a change in the failure mode. At confining stress levels ≤0.5 MPa specimen rupture was associated with axial splitting. With increasing confinement, transition to a macroscopic shearing mode was observed. Multi-stage triaxial tests consistently showed lower strengths than single-stage tests, demonstrating cumulative damage in the specimens. Both the Mohr–Coulomb and Hoek–Brown failure criteria could not satisfactorily fit the data over the entire confining stress range. A bi-linear or S-shaped failure criterion was found to satisfactorily fit the test data over the entire confinement range studied.
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[189]	Boone T J, Ingraffea A R.1990. A numerical procedure for simulation of hydraulically-driven fracture propagation in poroelastic media . International Journal for Numerical and Analytical Methods in Geomechanics, 14: 27-47. DOI      URL      [本文引用: 1]      摘要 A procedure for numerical approximation to two-dimensional, hydraulically-driven fracture propagation in a poroelastic material is described. The method uses a partitioned solution procedur to solve a finite element approximation to problems described by the theory of poroelasticity, in conjunction with a finite difference approximation for modelling fluid flow along the fracture. An equilibrium fracture model based on a generalized, Dugdale-Barenblatt concept is used to determine the fracture dimensions. An important feature is that the fracture length is a natural product of the solution algorithm. Two example problems verify the accuracy of the numerical procedure and a third example illustrates a fully-coupled simulation of fracture propagation. Photographs taken from a high-performance engineering workstation provide insight into the nature of the coupling among the physical phenomena.
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[198]	Bunger A P, Detournay E.2008. Experimental validation of the tip asymptotics for a fluid-driven crack . Journal of the Mechanics and Physics of Solids, 56: 3101-3115. DOI      URL      [本文引用: 3]      摘要 This paper provides experimental confirmation of the opening asymptotes that have been predicted to develop at the tip of fluid-driven cracks propagating in impermeable brittle elastic media. During propagation of such cracks, energy is dissipated not only by breaking of material bonds ahead of the tip but also by flow of viscous fluid. Theoretical analysis based on linear elastic fracture mechanics and lubrication theory predicts a complex multiscale asymptotic behavior of the opening in the tip region, which simplifies either as 1 2 or as 2 3 power law of the distance from the tip depending on whether the dominant mechanism of energy dissipation is bond breaking or viscous flow. The laboratory experiments entail the propagation of penny-shaped cracks by injection of glycerin or glucose based solutions in polymethyl methacrylate (PMMA) and glass specimens subjected to confining stresses. The full-field opening is measured from analysis of the loss of intensity as light passes through the dye-laden fluid that fills the crack. The experimental near-tip opening gives excellent agreement with theory and therefore confirms the predicted multi-scale tip asymptotics.
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[201]	Carrier B, Granet S.2012. Numerical modeling of hydraulic fracture problem in permeable medium using cohesive zone model . Engineering Fracture Mechanics, 79: 312-328. DOI      URL      [本文引用: 2]      摘要 This paper considers the problem of a fluid-driven fracture propagating in a permeable poroelastic medium. We develop a zero-thickness finite element to model the fracture. The fracture propagation is governed by a cohesive zone model and the flow within the fracture by the lubrication equation. The hydro-mechanical equations are solved with a fully coupled approach, using the developed zero-thickness element for the propagating fracture and conventional bulk finite elements for the surrounding medium. The numerical results are compared to analytical asymptotic solutions under zero fluid lag assumption in the four following limiting propagation regimes: toughness-fracture storage, toughness-leak-off, viscosity-fracture storage and viscosity-leak-off dominated. We demonstrate the ability of our cohesive zone model in simulating the hydraulic fracture in all these propagation regimes.
[202]	Carrier B, Granet S.2012. Numerical modeling of hydraulic fracture problem in permeable medium using cohesive zone model . Engineering Fracture Mechanics, 79: 312-328. DOI      URL      摘要 This paper considers the problem of a fluid-driven fracture propagating in a permeable poroelastic medium. We develop a zero-thickness finite element to model the fracture. The fracture propagation is governed by a cohesive zone model and the flow within the fracture by the lubrication equation. The hydro-mechanical equations are solved with a fully coupled approach, using the developed zero-thickness element for the propagating fracture and conventional bulk finite elements for the surrounding medium. The numerical results are compared to analytical asymptotic solutions under zero fluid lag assumption in the four following limiting propagation regimes: toughness-fracture storage, toughness-leak-off, viscosity-fracture storage and viscosity-leak-off dominated. We demonstrate the ability of our cohesive zone model in simulating the hydraulic fracture in all these propagation regimes.
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[237]	%Dahi-Taleghani A, Olson J E.2011. Numerical modeling of %multistranded-hydraulic-fracture propagation: Accounting for the %interaction between induced and natural fractures. SPE % Journal, 16: 575-581. [本文引用: 1]
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[239]	Dahi-Taleghani A.2009. Analysis of Hydraulic Fracture Propagation in Fractured Reservoirs: an Improved Model for the Interaction between Induced and Natural Fractures. Austin: University of Texas. DOI      URL      [本文引用: 1]      摘要 Large volumes of natural gas exist in tight fissured reservoirs. Hydraulic fracturing is one of the main stimulating techniques to enhance recovery from these fractured reservoirs. Although hydraulic fracturing has been used for decades for the stimulation of tight gas reservoirs, a thorough understanding of the interaction between induced hydraulic fractures and natural fractures is still lacking. Recent examples of hydraulic fracture diagnostic data suggest complex, multi-stranded hydraulic fracture geometry is a common occurrence. The interaction between pre-existing natural fractures and the advancing hydraulic fracture is a key condition leading to complex fracture patterns. Large populations of natural fractures that exist in formations such as the Barnett shale are sealed by precipitated cements which could be quartz, calcite, etc. Even though there is no porosity in the sealed fractures, they may still serve as weak paths for fracture initiation and/or for diverting the path of the growing hydraulic fractures. Performing hydraulic fracture design calculations under these complex conditions requires modeling of fracture intersections and tracking fluid fronts in the network of reactivated fissures. In this dissertation, the effect of the cohesiveness of the sealed natural fractures and the intact rock toughness in hydraulic fracturing are studied. Accordingly, the role of the pre-existing fracture geometry is also investigated. The results provide some explanations for significant differences in hydraulic fracturing in naturally fractured reservoirs from non-fractured reservoirs. For the purpose of this research, an extended finite element method (XFEM) code is developed to simulate fracture propagation, initiation and intersection. The motivation behind applying XFEM are the desire to avoid remeshing in each step of the fracture propagation, being able to consider arbitrary varying geometry of natural fractures and the insensitivity of fracture propagation to mesh geometry. New modifications are introduced into XFEM to improve stress intensity factor calculations, including fracture intersection criteria into the model and improving accuracy of the solution in near crack tip regions.
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[243]	Daniels J L, Waters G A, Le Calvez J H, Bentley D, Lassek J T.2007. Contacting more of the barnett shale through an integration of real-time microseismic monitoring, petrophysics, and hydraulic fracture design//SPE Annual Technical Conference and Exhibition. Society of Petroleum Engineers. [本文引用: 4]
[244]	Dardis O, McClosekey J.1998. Lattice Boltzmann scheme with real numbered solid density for the simulation of flow in porous media . Physical Review E, 57: 4834-4837. DOI      URL      [本文引用: 1]      摘要 A modified lattice Boltzmann scheme for the simulation of flow in porous media is introduced, where momentum loss due to the presence of solid obstacles to flow is incorporated into the evolution equation. A real numbered parameter specified at each lattice node is related to the density of solid scatterers and represents the effect of porous medium solid structure on hydrodynamics. This scheme removes both the need for spatial and temporal averaging and the microscopic length scales associated with important classes of porous media. A numerical study demonstrates the adherence of the approach to the Navier-Stokes equation with an effective damping term. The potential use of the scheme to aid permeability predictions in realistic geological materials is discussed.
[245]	Darrah T H, Vengosh A, Jackson R B, Warner N R, Poreda R J.2014. Noble gases identify the mechanisms of fugitive gas contamination in drinking-water wells overlying the Marcellus and Barnett Shales//Proceedings of the National Academy of Sciences of the United States of America , 111: 14076-81. DOI      URL      [本文引用: 1]      摘要 Horizontal drilling and hydraulic fracturing have enhanced energy production but raised concerns about drinking-water contamination and other environmental impacts. Identifying the sources and mechanisms of contamination can help improve the environmental and economic sustainability of shale-gas extraction. We analyzed 113 and 20 samples from drinking-water wells overlying the Marcellus and Barnett Shales, respectively, examining hydrocarbon abundance and isotopic compositions (e.g., C2H6/CH4, (13)C-CH4) and providing, to our knowledge, the first comprehensive analyses of noble gases and their isotopes (e.g., (4)He, (20)Ne, (36)Ar) in groundwater near shale-gas wells. We addressed two questions. (i) Are elevated levels of hydrocarbon gases in drinking-water aquifers near gas wells natural or anthropogenic? (ii) If fugitive gas contamination exists, what mechanisms cause it? Against a backdrop of naturally occurring salt- and gas-rich groundwater, we identified eight discrete clusters of fugitive gas contamination, seven in Pennsylvania and one in Texas that showed increased contamination through time. Where fugitive gas contamination occurred, the relative proportions of thermogenic hydrocarbon gas (e.g., CH4, (4)He) were significantly higher (P < 0.01) and the proportions of atmospheric gases (air-saturated water; e.g., N2, (36)Ar) were significantly lower (P < 0.01) relative to background groundwater. Noble gas isotope and hydrocarbon data link four contamination clusters to gas leakage from intermediate-depth strata through failures of annulus cement, three to target production gases that seem to implicate faulty production casings, and one to an underground gas well failure. Noble gas data appear to rule out gas contamination by upward migration from depth through overlying geological strata triggered by horizontal drilling or hydraulic fracturing.
[246]	Das I, Zoback M D.2011. Long-period, long-duration seismic events during hydraulic fracture stimulation of a shale gas reservoir . The Leading Edge, 30: 778-786. DOI      URL      [本文引用: 1]      摘要 We report a series of long period and long duration (LPLD) seismic events observed during hydraulic fracturing in a gas shale reservoir located in West Texas. These unusual events, 10-100 seconds in duration, are observed most clearly in the frequency band of 10-80 Hz and are similar in appearance to tectonic tremor sequences which have been observed at depth in several subduction zones and continental strike slip faults. These complex but coherent wave trains have finite move-outs obtained from waveform cross-correlation. The move-out direction of the events confirms that they originate in the reservoir from the area where the fracturing is going on. Clear P- and S-wave arrivals cannot be resolved within the LPLD episodes, but in some cases, small micro-earthquakes occur in the sequences. Whether these micro-earthquakes are causal or coincidental is being studied. It has also been observed that in three contiguous frac-stages, all LPLD events appear to come from two distinct places along one of two hypothetical fracture planes. Interestingly, the stages which have the largest number of LPLD events also have the highest observed pumping pressures during fracturing, the highest density of natural fractures and the greatest number of microearthquakes. One possible explanation of these LPLD events is that the high pore fluid pressure during hydraulic fracturing stimulates slow slip on pre-existing fault planes that are poorly-oriented for slip in the ambient stress field. In the absence of elevated pressure, slip would not be expected on these planes. Slip on these fault planes appears to be occurring because the fluid pressure is close to the magnitude of the least principal stress. We observe a few events between pumping cycles perhaps indicating that once triggered, these planes continue to slip due to the high transient pressure within the fault planes after pumping has stopped.
[247]	Das I, Zoback M D.2013a. Long-period, long-duration seismic events during hydraulic stimulation of shale and tight-gas reservoirs – Part 1: Waveform characteristics . Geophysics, 78, KS107-KS118. DOI      [本文引用: 9]      摘要 ABSTRACTLong-period long-duration (LPLD) seismic events are relatively low-amplitude signals that have been observed during hydraulic fracturing in several shale-gas and tight-gas reservoirs. These events are similar in appearance to tectonic tremor sequences observed in subduction zones and transform fault boundaries. LPLD events are predominantly composed of S-waves, but weaker P-waves have also been identified. In some cases, microearthquakes are observed during the events. Based on the similarity with tectonic tremors and our observations of several impulsive S-wave arrivals within the LPLD events, we interpret the LPLD events as resulting from the superposition of slow shear-slip events on relatively large faults. Most large LPLD waveforms appear to start as a relatively slower, low-amplitude precursor, lacking clear impulsive arrivals. We estimate the energy carried by the larger LPLD events to be 651000 times greater than a 65MW612 microseismic event that is typical of the events that occur during hyd...
[248]	Das I, Zoback M D.2013b. Long-period long-duration seismic events during hydraulic stimulation of shale and tight-gas reservoirs – Part 2: Location and mechanisms . Geophysics, 78, KS97-KS105. DOI      [本文引用: 3]      摘要 ABSTRACTLong-period long-duration (LPLD) seismic events are relatively low-amplitude signals that have been observed during hydraulic fracturing in several shale-gas and tight-gas reservoirs. These events are similar in appearance to tectonic tremor sequences observed in subduction zones and transform fault boundaries. LPLD events are predominantly composed of S-waves, but weaker P-waves have also been identified. In some cases, microearthquakes are observed during the events. Based on the similarity with tectonic tremors and our observations of several impulsive S-wave arrivals within the LPLD events, we interpret the LPLD events as resulting from the superposition of slow shear-slip events on relatively large faults. Most large LPLD waveforms appear to start as a relatively slower, low-amplitude precursor, lacking clear impulsive arrivals. We estimate the energy carried by the larger LPLD events to be 651000 times greater than a 65MW612 microseismic event that is typical of the events that occur during hyd...
[249]	Daubechies I.1988. Orthonormal bases of compactly supported wavelets . Communications on Pure and Applied Mathematics, 41: 909-996. DOI      URL      [本文引用: 1]      摘要 Orthonormal bases of compactly supported wavelet bases correspond to subband coding schemes with exact reconstruction in which the analysis and synthesis filters coincide. We show here that under fairly general conditions, exact reconstruction schemes with synthesis filters different from the analysis filters give rise to two dual Riesz bases of compactly supported wavelets. We give necessary and sufficient conditions for biorthogonality of the corresponding scaling functions, and we present a sufficient conditions for the decay of their Fourier transforms. We study the regularity of these biorthogonal bases. We provide several families of examples, all symmetric (corresponding to linear phase filters). In particular we can construct symmetric biorthogonal wavelet bases with arbitraily high preassigned regularity; we also show how to construct symmetric biorthogonal wavelet bases close to a (nonsymmetric) orthonormal basis.
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[252]	Deng S, Li H, Ma G, Huang H, Li X.2014. Simulation of shale-proppant interaction in hydraulic fracturing by the discrete element method . International Journal of Rock Mechanics and Mining Sciences, 70: 219-228. DOI      URL      摘要 61We investigated shale–proppant07s interaction by our proposed DEM method.61Results reveal the more soft the shale is, it has a smaller aperture and larger plasticity.61Results reveal that higher pressure has a smaller aperture and larger plasticity.61Results reveal the larger proppant has a smaller aperture and larger plasticity.61The DEM and results can be used to guide hydraulic fracturing operation.
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[254]	Devloo P R B, Fernandes P D, Gomes S, Nia M, Damas R G.2006. A finite element model for three dimensional hydraulic fracturing . Mathematics and Computers in Simulation, 73: 142-155. DOI      URL      [本文引用: 1]      摘要 This paper is devoted to the development of a model for the numerical simulation of hydraulic fracturing processes with 3d fracture propagation. It takes into account the efects of fluid flow inside the fracture, fluid leak-off through fracture walls and elastic response of the surrounding porous media. Finite element techniques are adopted for the discretization of the conservation law of fluid flow and the singular integral equation relating the traction and the fracture opening. The discrete model for the singular integral equation is implemented using a stencil matrix structure allowing an efficient implementation of the fluid–structure interaction problem. Newton’s method combined with GMRES linear solver are used to solve the resulting nonlinear set of equations. An algorithm for fracture propagation is proposed which is based on the balance of the amount of fluid transported to a certain point with the amount of fluid that could be lost by leak-off. To illustrate the feasibility of the model, we present simulation results for typical operational parameters.
[255]	Dixit A B, McDougall S R, Sorbie K S.1998. A pore-level investigation of relative permeability hysteresis in water-wet systems . SPE Journal, 3:115-123. DOI      URL      [本文引用: 1]      摘要 Oil-recovery efficiency is known to depend crucially upon the surface chemistry of the particular crude-oil/brine/rock system under investigation. Mineralogy, brine chemistry/pH, crude-oil composition and ageing conditions all serve to modify the effective contact angles operating within a mixed-wet porous medium. Recent network modelling studies have helped to clarify the important role played by wettability during multiphase flow in non-uniformly wet systems and the consequences of modified contact angles during waterflooding have been described in terms of various "Regimes". These have subsequently been used to classify a wide range of apparently contradictory wettability experiments. The purpose of the present paper is to apply these ideas to the study of hysteresis phenomena in both strongly and weakly water-wet drainage/imbibition relative permeability curves. Such hysteresis effects have long been recognised by the industry but the precise direction of hysteresis appears to vary from study to study. Indeed, in water-wet media, even the degree of sample consolidation appears to play an important role. A 3-D network model is reported which takes into account a great deal of the underlying pore-scale physics. Initial water saturation, wettability alterations, film flow, phase trapping and realistic variations in advancing and receding contact angles are all incorporated into the simulations. More specifically, this study examines relative permeability hysteresis in systems from "Regime IA" which corresponds to strongly and weakly water-wet porous media i.e. media where some degree of modification in the distribution of effective contact angles has occurred. The consequences of different combinations of pore scale displacement mechanisms (viz. snap-off and piston-like displacement) for relative permeability hysteresis has been calculated using the pore-scale simulator. The effects of combining these mixed mechanisms with other network properties such as co-ordination number (z) and certain volume and conductivity exponents (v and ) are also reported. The nature of hysteresis is found to change quite dramatically as these parameters are varied and all experimentally-observed trends in relative permeability hysteresis are reproduced under suitable conditions. This appears to be the first time that a pore-scale model has been used to provide a clear interpretation of all experimentally observed hysteresis trends during primary drainage, secondary imbibition and secondary drainage displacements in both strongly and weakly water-wet systems. Introduction Relative permeability curves provide the reservoir engineer with a macroscopic description of the way in which two (or three) phases flow together locally in a porous medium. However, these functions tend to be history-dependent and often exhibit hysteresis when phase saturation reversals occur. The theoretical and experimental aspects of the hysteresis between primary drainage (PD) and secondary imbibition (SI) relative permeability curves have been discussed by many authors, although most of these studies have focused upon strongly water-wet porous media. It is now widely accepted, however, that an appreciable number of reservoirs are either mixed-wet or oil-wet in nature and it is the secondary drainage (SD) process (i.e. the displacement of water by oil from the residual oil saturation, Sor) which actually reveals a great amount of information about the wettability of the sample. Indeed, a number of wettability measurement techniques are based on the data obtained from the secondary drainage capillary pressure curves. The main difference between the primary and secondary drainage processes is the presence of trapped residual oil during secondary drainage and this is found to play a pivotal role during the subsequent displacement. The distribution of residual oil after waterflooding greatly depends upon the pore geometry, the pore network topology and the wettability of the s
[256]	Dong C Y, de Pater C J.2001. Numerical implementation of displacement discontinuity method and its application in hydraulic fracturing . Computer Methods in Applied Mechanics and Engineering, 191: 745-760. DOI      URL      [本文引用: 1]      摘要 A formulation of the quadratic displacement discontinuity method is presented to model two-dimensional elastic fracture problems. The new formulation is found by analytical integration of the fundamental solution along a straight-line crack within which three collocation points are taken. Each element has a quadratic distribution of displacement discontinuity values. For a curved crack, a general formulation of the displacement discontinuity method is proposed, based on the boundary integral equation. This formulation contains strongly singular and hypersingular integrals which can be evaluated in the sense of Cauchy principal value and Hadamard principal value, respectively. Special crack tip elements are adopted to show the r variation of displacements near the crack tips. Some examples are used to illustrate the accuracy of two formulations. General formulation is also used to simulate hydraulic fracturing propagation and interaction between a crack and a fault. The fracture propagation path is obtained by using the maximum tensile stress criterion.
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[258]	Douma H, Snieder R.2006. Correcting for bias due to noise in coda wave interferometry . Geophysical Journal International, 164: 99-108. DOI      URL      摘要 Coda wave interferometry (CWI) utilizes multiply scattered waves to diagnose small changes in a medium by using the scattering medium as an interferometer. Since the medium is usually stationary over the duration of a seismic experiment, different (non-overlapping) time windows in the coda allow for independent estimates of the medium perturbation. If the seismograms are contaminated with noise, only those time windows can be used for which the amplitude of the coda is significantly above the ambient noise level. This limits the usable number of independent time windows. Here, we show how bias due to noise in CWI can be accounted for, by deriving a correction factor for the cross-correlation coefficient, under the assumptions that the stochastic processes underlying the noise realizations in both signals are mutually uncorrelated and stationary with zero mean. This correction factor allows more time windows further into the decaying coda to be used, and hence allows for a reduction of the error bars on the medium perturbation estimates. We demonstrate the validity of this correction factor by using data from a numerical experiment and field measurements. These experiments involve the displacement of point scatterers and a change in the source location, respectively. The application of our correction factor is not limited to CWI, but can be used to correct for bias induced by noise in any application that uses cross-correlation between different signals that are contaminated with noise.
[259]	Dresen G, Stanchits S, Rybacki E.2010. Borehole breakout evolution through acoustic emission location analysis . International Journal of Rock Mechanics and Mining Sciences, 47: 426-435. DOI      URL      [本文引用: 1]      摘要 A series of thick-wall cylinder tests were performed on Bentheim sandstone to investigate the nucleation and propagation of borehole breakouts. Isotropic compression tests showed a significant decrease of the critical pressure required to nucleate breakouts with increasing borehole diameter. Advanced analysis of acoustic emission radiation and optical microstructures indicate a three stage process of breakout nucleation and growth. Relatively few acoustic emissions are observed during the elastic loading stage of the specimens. Once breakout nucleation has occurred at the borehole wall a drastic increase of acoustic emission activity is observed. A close spatial correspondence between located acoustic events and the breakout indicates formation of two symmetric cusp-shaped breakouts on opposite sides of the borehole. With increasing isotropic pressure the breakouts grow forming parallel-sided slots that are surrounded by a process zone revealing grain crushing and pore collapse as typically observed in experimentally produced compaction bands. We apply a simple fracture mechanics approach to predict the observed size effect of the critical pressure required to initiate breakouts.
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[262]	Dubinin M M.1968. Porous structure of adsorbents and catalysts . Advances in Colloid and Interface Science, 2: 218-234. DOI      URL      摘要 On the basis of analysis of adsorption and capillary phenomena occurring in adsorbent pores, a rational classification of pore varieties is given (macro-, transitional and micropores) and, as a consequence of its development, a classification of porous adsorbents and catalysts into basic structural types (macroporous, transitional-pore, and microporous). For the macro- and transitional-pore types of adsorbents, the basic parameters of the porous structures are: the pore volume, the specific surface area and the pore volume distribution according to the effective radii, corresponding to an equivalent model porous body with an assumed geometrical pore shape. The conventional nature of the distribution curves as characteristics of the porous structure is shown. For microporous adsorbents, in accordance with the theory of micropore filling, the basic parameters of the porous structure are: the micropore volume and the constant of the distribution function, B, expressed by the characteristic adsorption equation. The value of the constant B depends on the micropore sizes predominant in the structure. Examples of the presence of two microporous structures in a number of actual microporous adsorbents are quoted. An analysis of the specific features of adsorbents of mixed structural types is given, and rational methodical ways for determining the parameters of the porous structure for all the pore varieties in actual adsorbents are formulated.
[263]	Dverstorp B, Andersson J, Nordqvist W.1992. Discrete fracture network interpretation of field tracer migration in sparsely fractured rock . Water Resources Research, 28: 2327-2343. DOI      URL      [本文引用: 1]      摘要 Field tracer migration in sparsely fractured rock is analyzed with a discrete fracture network model that has been calibrated on fracture and flow data from the Stripa-3D experiment in Sweden. Comparison between transport simulations in the flow-calibrated discrete model and tracer tests of the field experiment confirms the fracture network parameters obtained from the flow analysis except for the variance of the fracture conductivities which had to be increased. The discrete model reproduces the uneven spatial distribution of flow and tracers, the complex dispersive behavior, and channeling effects that have been observed in the field experiment. As a result of flow channeling, transport occurs along preferential paths whose transport properties may substantially deviate from the medium average properties. For example, porosity and wetted fracture surface area available to sorption may be reduced by almost 2 orders of magnitude compared to the medium average values.
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[272]	Feng X Q, Li J Y, Yu S W.2003. A simple method for calculating interaction of numerous microcracks and its applications . International Journal of Solids and Structures, 40: 447-464. DOI      URL      [本文引用: 1]      摘要 The effects of microcrack interaction on the failure behavior of materials present one problem of considerable interest in micromechanics, which has been extensively argued but has not been resolved as yet. In the present paper, a simple and effective method is presented based on the concept of the effective field to analyze the interaction of microcracks of a large number or of a high density. To determine the stress intensity factors of a microcrack embedded in a solid containing numerous or even countless microcracks, the solid is divided into two regions. The interaction of microcracks in a circular or elliptical region around the considered microcrack is calculated directly by using Kachanov micromechanics method, while the influence of all other microcracks is reflected by modifying the stress applied in the far field. Both the cases of tensile and compressive loading are considered. This simplified scheme may yield an estimate for stress intensity factors of satisfactory accuracy, and therefore provide a potential tool for elucidating some phenomena of material failure associated with microcracking. As two of its various promising applications, the above scheme is employed to investigate the size effects of material strength due to stochastic distribution of interacting microcracks and to calculate the effective elastic moduli of elastic solids containing distributed microcracks. Some conventional micromechanics methods for estimating the effective moduli of microcracked materials are evaluated by comparing with the numerical results. Only two-dimensional problems have been considered here, though the three-dimensional extension of the present method is of greater interest.
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[279]	Fu P, Johnson S M, Carrigan C R.2013. An explicitly coupled hydro-geomechanical model for simulating hydraulic fracturing in arbitrary discrete fracture networks . International Journal for Numerical and Analytical Methods in Geomechanics, 37: 2278-2300. DOI      URL      [本文引用: 1]      摘要 SUMMARYModeling hydraulic fracturing in the presence of a natural fracture network is a challenging task, owing to the complex interactions between fluid, rock matrix, and rock interfaces, as well as the interactions between propagating fractures and existing natural interfaces. Understanding these complex interactions through numerical modeling is critical to the design of optimum stimulation strategies. In this paper, we present an explicitly integrated, fully coupled discrete-finite element approach for the simulation of hydraulic fracturing in arbitrary fracture networks. The individual physical processes involved in hydraulic fracturing are identified and addressed as separate modules: a finite element approach for geomechanics in the rock matrix, a finite volume approach for resolving hydrodynamics, a geomechanical joint model for interfacial resolution, and an adaptive remeshing module. The model is verified against the Khristianovich–Geertsma–DeKlerk closed-form solution for the propagation of a single hydraulic fracture and validated against laboratory testing results on the interaction between a propagating hydraulic fracture and an existing fracture. Preliminary results of simulating hydraulic fracturing in a natural fracture system consisting of multiple fractures are also presented. Copyright 08 2012 John Wiley & Sons, Ltd.
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[286]	Gensterblum Y, Ghanizadeh A, Robert C J, et al.2015. Gas transport and storage capacity in shale gas reservoirs - A review. Part A: Transport processes . Journal of Unconventional Oil and Gas Resources, 12: 87-122. DOI      URL      [本文引用: 1]      摘要 For decades, scientists and engineers have been investigating and describing storage and transport mechanisms in geological porous media such as reservoir rocks. This effort has resulted in the development of concepts such as single-phase and multi-phase flow, which describe the storage and transport of fluids in conventional reservoir rock types such as sandstones and carbonates. However, many of these concepts are not directly applicable to unconventional reservoirs. For example, shale gas reservoirs consist of organic-rich lithotypes, which have high compressibility, very small pore throats, low porosities and extremely low and anisotropic permeabilities, and relatively low gas storage capacities. The models developed to describe conventional reservoirs do not accurately describe the hydrocarbon transport processes involved in these rocks. In this part A of the review paper, we aim to provide a concise and complete review on characterizing the fluid transport processes in unconventional reservoirs. We will examine processes occurring at various spatial scales, ranging from fracture flow on the centimeter scale down to slip-flow on the nanometer scale. Due to the softer nature of tight shales, many processes, such as slip-flow and the pore-throat compressibility, will have to be considered as coupled. We also develop a detailed description of the coupling between slip-flow, which is a fluid dynamic effect, and the pore-throat compressibility, which is a poroelastic effect, in unconventional reservoirs, and interpret experimental observations in light of this description. Furthermore, we discuss in detail how these transport properties depend on organic content, clay content and type, amount of pre-adsorbed water and pore compressibility.
[287]	Ghanizadeh A.2014. A systematic review of reboxetine for treating patients with attention deficit hyperactivity disorder . Nordic Journal of Psychiatry, 75: 1-8. DOI      URL      [本文引用: 1]      摘要 Background: No published systematic review has ever assessed the efficacy and safety of reboxetine for treating of patients with attention deficit hyperactivity disorder (ADHD). Aim: This systematic review aimed to review the available evidence regarding the efficacy of reboxetine for treating ADHD. Method: The databases of Pubmed/Medline, Google scholar, SCOPUS and Web of Science were searched using the Keywords: “reboxetine”, “ADHD” and “attention deficit hyperactivity disorder”. The reference lists of the included studies were screened to find any possible other relevant articles. All the non-controlled and controlled clinical trials were included. Results: The current evidence mainly consists of un-controlled studies, such as case series. Only three of 33 studies were controlled clinical trials. They are from single sites and included a sub-sample of patients with ADHD. Conclusion: Non-controlled studies and controlled trials support the promising effect of reboxetine for treating ADHD in a sub-sample of patients that are without co-morbid psychiatric disorder and mental retardation. Reboxetine is tolerated well. However, more controlled trials are needed to reach any firm conclusion.
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[291]	Giordano S, Colombo L.2007. Effects of the orientational distribution of cracks in isotropic solids . Engineering Fracture Mechanics, 74: 1983-2003. DOI      URL      PMID      [本文引用: 1]      摘要 The paper deals with the elastic characterisation of microcracked solids: we analyse dispersions of cracks with arbitrary non-random orientational distributions. Particular cases of angular distributions are given by cracks all oriented in a given direction or cracks uniformly random oriented in the space. A unified theory covers all the orientational distributions between the random and the parallel ones. The micromechanical averaging inside the composite material is carried out by means of explicit results which allows us to obtain closed-form expressions for the macroscopic or equivalent elastic moduli of the overall material. The analysis has been performed in two-dimensional (2D) elasticity (plane stress and plane strain) with slit like cracks and in three-dimensional (3D) elasticity with planar circular cracks. The elastic behaviour of the microcracked solid depends upon the density of cracks and upon their orientational distribution. In particular, this study allows us to state that in two-dimensions the elastic behaviour of such a microcracked material is completely defined by one order parameter, which depends on the given angular distribution while the elastic characterisation in three-dimensions depends on two order parameters. The particular cases of isotropic orientations of cracks (both in 2D and in 3D) have been generalised to higher values of the cracks density by means of the method of the iterated homogenisation, which leads to some differential equations. Their solutions show that the equivalent elastic moduli depend exponentially on the cracks density.
[292]	Giordano S, Colombo L.2007. Effects of the orientational distribution of cracks in solids . Physical Review Letters, 98: 055503. DOI      URL      PMID      [本文引用: 1]      摘要 The paper deals with the elastic characterisation of microcracked solids: we analyse dispersions of cracks with arbitrary non-random orientational distributions. Particular cases of angular distributions are given by cracks all oriented in a given direction or cracks uniformly random oriented in the space. A unified theory covers all the orientational distributions between the random and the parallel ones. The micromechanical averaging inside the composite material is carried out by means of explicit results which allows us to obtain closed-form expressions for the macroscopic or equivalent elastic moduli of the overall material. The analysis has been performed in two-dimensional (2D) elasticity (plane stress and plane strain) with slit like cracks and in three-dimensional (3D) elasticity with planar circular cracks. The elastic behaviour of the microcracked solid depends upon the density of cracks and upon their orientational distribution. In particular, this study allows us to state that in two-dimensions the elastic behaviour of such a microcracked material is completely defined by one order parameter, which depends on the given angular distribution while the elastic characterisation in three-dimensions depends on two order parameters. The particular cases of isotropic orientations of cracks (both in 2D and in 3D) have been generalised to higher values of the cracks density by means of the method of the iterated homogenisation, which leads to some differential equations. Their solutions show that the equivalent elastic moduli depend exponentially on the cracks density.
[293]	Godec M L, Jonsson H, Basava-Reddi L.2013. Potential global implications of gas production from shales and coal for geological CO$_{2}$ storage . Energy Procedia, 37: 6656-6666. DOI      URL      [本文引用: 1]      摘要 Production of natural gas from shale formations and coal deposits is increasing, and new potential productive horizons are being identified. Producers are using horizontal drilling and hydraulic fracturing technologies to economically produce oil and gas from shales and coal seams. These technologies open up the possibility of using shales and coals as actual storage media for carbon dioxide (CO2) by increasing permeability and injectivity; though some worry that the same technology may compromise the integrity of shale cap rocks in some basins. This paper builds upon previous work to assess the global potential for geological storage of CO2 in shale and coal formations. This includes assessment and characterization of: (1) the global status of hydrocarbon production from shales and coal seams; (2) the potential theoretical capacities for CO2 storage in shales and coals; and (3) containment issues arising from shale fracturing, both for shales as a storage medium, and in terms of cap rock integrity for underlying storage units, particularly deep saline formations. Technical recovery potential for methane from the world's coal seams is estimated to be 79 trillion cubic meters (Tcm) globally, which could facilitate the potential storage of nearly 488 billion metric tons, or Gigatonnes (Gt), of CO2 in unmineable coal seams. In gas shales, an estimated 188Tcm of shale gas resources are potentially technically recoverable globally, and could facilitate the potential storage of 740 Gt of CO2 in gas shales. Concerns about the potential adverse impacts of the use of saline aquifers underlying gas shale formations for CO2 storage overlook the critical third dimension depth. Sedimentary basins consist of thousands of meters of multiple layers of shale, sandstones, limestones, etc. (that may also be ight or largely impermeable). If one shale formation layer directly above a storage zone is fractured; additional layers of impermeable rock overlying the fractured area could block upward migration of the CO2. Moreover, in many cases, even the targeted shale will not be fractured throughout its entire thickness, which could be hundreds of meters. With sensible safeguards, CO2 storage reservoirs can, in most areas, coexist with conventional and unconventional oil and gas operations, including shale gas production and hydraulic fracturing.
[294]	Godec M, Koperna G, Petrusak R, Oudinot A.2013. Assessment of factors influencing CO$_{2}$ storage capacity and injectivity in Eastern U.S. gas shales . Energy Procedia, 37: 6644-6655. DOI      URL      摘要 Organic-rich gas shales appear to behave similarly to coal and desorb methane while preferentially adsorbing CO2. In addition, the pore volume containing “free” (non-adsorbed) methane is expected to be available for CO2 storage, especially where previous hydraulic fracturing has enhanced injectivity. In theory, CO2 injection into organic-rich gas shale could provide dual benefits of incremental recovery of methane and secure CO2 storage. This paper will report on research to date, sponsored by the U.S. Department of Energy, to assess factors influencing effective CO2 storage capacity and injectivity in the Marcellus Shale in the Eastern United States. Geological characterization was conducted that estimated total gas in-place and theoretical maximum CO2 storage capacity within the Marcellus Shale. Theoretical maximum CO2 storage capacity assumes 100% of methane in-place, either as adsorbed or “free” gas, is replaced by injected CO2. Detailed reservoir characterization was conducted to determine depth, thickness, total organic carbon, effective porosity, apparent gas saturation, CO2 and methane adsorption isotherms, and permeability. Total gas in-place and maximum CO2 storage capacity are extrapolated for the study area where depth to the Marcellus exceeds 915 meters (3,000 feet). Estimated total theoretical maximum CO2 storage capacity is 1.12 million metric tonnes per square kilometer (MMt/km2), of which adsorbed CO2 storage capacity is estimated to be 0.72 MMt/km2. Detailed reservoir simulation was performed to develop a better understanding of the shale characteristics influencing storage capacity and injectivity. The work focuses on areas that may be optimal for CO2 storage due to over- pressured reservoir conditions, attractive shale thickness, and current gas production. A reservoir model was developed based on these data, and reservoir simulation was performed using Advanced Resources International's proprietary reservoir simulator COMET3. Simulated production results were compared to available data within the study area to demonstrate that the reservoir models are representative of existing field conditions. CO2 injection rates are estimated via simulation to predict the incremental volume of methane produced, the total volume of CO2 to be potentially stored, CO2 plume dimensions, and the disposition of CO2 in the reservoir over time.
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[296]	Gordeliy E, Detournay E.2011. A fixed grid algorithm for simulating the propagation of a shallow hydraulic fracture with a fluid lag . International Journal for Numerical and Analytical Methods in Geomechanics, 35: 602-629. DOI      URL      [本文引用: 1]      摘要 This paper describes a fixed grid algorithm to simulate the propagation of shallow hydraulic fractures, under plane strain or axisymmetric conditions. Because of the low stress environment that exists near a free surface, these fractures are generally characterized by a fluid front that lags behind the fracture edge. The simulation of shallow hydraulic fractures requires therefore the tracking of two distinct fronts. The proposed algorithm, which traces its roots to the one described by Zhang et al. (Int. J. Numer. Anal. Methods Geomech. 2005; 29:1317 1340), advances the fracture by a constant step and computes the corresponding time required to reach this new fracture configuration as well as the matching location of the fluid front within the fixed grid. For any trial value of the time and of the front position, a non-linear system of algebraic equations is solved using either Newton's method or a fixed point iteration scheme, with preconditioning. The non-linear system is formulated by combining an implicit finite volume method for solving the lubrication equation and the displacement discontinuity method for solving the elasticity equation. The critical difference with the algorithm of Zhang et al. lays in the approach chosen to update the fluid front position. Rather than using a filling fraction method, the new algorithm adopts a velocity treatment of the fluid-front location that is akin to a one-dimensional implementation of a level set algorithm for front tracking. This conversion from a fluid volume to a fluid velocity-based approach to update the front position increases the degree of implicitness of the algorithm, which is responsible for a significant reduction of the CPU time by about two orders of magnitude. Copyright 2010 John Wiley & Sons, Ltd.
[297]	Gordeliy E, Peirce A.2013. Coupling schemes for modeling hydraulic fracture propagation using the XFEM . Computer Methods in Applied Mechanics and Engineering, 253: 305-322. DOI      URL      [本文引用: 1]      摘要 We describe coupled algorithms that use the Extended Finite Element Method (XFEM) to solve the elastic crack component of the elasto-hydrodynamic equations that govern the propagation of hydraulic fractures in an elastic medium. With appropriate enrichment, the XFEM resolves the Neumann to Dirichlet (ND) map for crack problems with O(h(2)) accuracy and the Dirichlet to Neumann (DN) map with O(h) accuracy. For hydraulic fracture problems with a lag separating the fluid front from the fracture front, we demonstrate that the finite pressure field makes it possible to use a scheme based on the O(h(2)) XFEM solution to the ND map. To treat problems in which there is a coalescence of the fluid and fracture fronts, resulting in singular tip pressures, we developed a novel mixed algorithm that combines the tip width asymptotic solution with the O(h(2)) XFEM solution of the ND map away from the tips. Enrichment basis functions required for these singular pressure fields correspond to width power law indices lambda > 1/2, which are different from the index lambda = 1/2 of linear elastic fracture mechanics. The solutions obtained from the new coupled XFEM schemes agree extremely well with those of published reference solutions. (C) 2012 Elsevier B.V. All rights reserved.
[298]	Goupillaud P, Grossmann A, Morlet J.1984. Cycle-octave and related transforms in seismic signal analysis . Geoexploration, 23: 85-102. DOI      URL      摘要 High-resolution seismic methods are needed especially in oil and gas field development. They involve the use of backscattered energy rather than that of reflected signals, and make it interesting to look for representations of seismic traces in the time-frequency domain. One such representation was introduced by D. Gabor in 1946 into signal analysis; it is based on the consideration of a family of “elementary wavelets” that can be obtained from one “basic wavelet” by shifts in time and in frequency. We present here a different representation, in which frequency shifts are replaced by dilations. The resulting “voice transform” and “cycle-octave transform” are briefly described from the mathematical point of view and illustrated by numerical examples.
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[309]	Hamidi F, Mortazavi A.2014. A new three dimensional approach to numerically model hydraulic fracturing process . Journal of Petroleum Science and Engineering, 124: 451-467. DOI      URL      [本文引用: 1]      摘要 In this paper, a Three-dimensional Distinct Element Code (3DEC) was used and developed for simulating the initiation and propagation of hydraulically induced fractures in a typical reservoir hosted by a rock mass. Due to the fact that the modeling of the initiation of fracturing through intact rock within the Discrete Element Method (DEM) is not possible, a fictitious joint technique was introduced in order to simulate the process. The analysis results substantiate the previous understanding that the success of the hydraulic fracturing process not only depends on controllable parameters such as fracture fluid properties and injection rate, but also relies on the uncontrollable parameters such as ground in-situ stress regime, orientation of principal stresses, and in-situ rock mass properties. Moreover, a sensitivity study of input variables was carried out to examine the effect of different field conditions which involved the orientation and magnitude of principal stress components, fracture fluid properties, injection rate and rock parameters. Comparing the results with analytical solution indicated that the model provides a reasonable approximation for computing fluid injection pressure. Thus, the proposed modeling procedure can be employed in more complicated cases for further studies, such as interaction between induced hydraulic fractures and natural fractures. (C) 2013 Elsevier B.V. All rights reserved.
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[316]	Heller R, Zoback M.2014. Adsorption of methane and carbon dioxide on gas shale and pure mineral samples . Journal of Unconventional Oil and Gas Resources, 8: 14-24. DOI      URL      [本文引用: 1]      摘要 We have measured methane and carbon dioxide adsorption isotherms at 40 C on gas shale samples from the Barnett, Eagle Ford, Marcellus and Montney reservoirs. Carbon dioxide isotherms were included to assess its potential for preferential adsorption, with implications for its use as a fracturing fluid and/or storage in depleted shale reservoirs. To better understand how the individual mineral constituents that comprise shales contribute to adsorption, measurements were made on samples of pure carbon, illite and kaolinite as well. We were able to successfully fit all adsorption data for both gases in accordance with a Langmuir isotherm model. Our results show carbon dioxide to have approximately 2 3 times the adsorptive capacity of methane in both the pure mineral constituents and actual shale samples. In addition to obvious microstructural and compositional differences between real rocks and pure minerals, we hypothesize that water adsorption plays an important role in regulating surface area availability for other molecules to adsorb. The resultant volumetric swelling strain was also measured as a function of pressure/adsorption. We observe both clay and pure carbon to swell an amount that is approximately linearly proportional to the amount of adsorption.
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[318]	Hill R.1963. Elastic properties of reinforced solids: some theoretical principles . Journal of the Mechanics and Physics of Solids, 11: 357-372. DOI      URL      [本文引用: 1]      摘要 The title problem concerns two isotropic phases firmly bonded together to form a mixture with any concentrations. An elementary account of several theoretical methods of attack is given, among them the derivation of inequalities between various moduli. The approach is completely general and exact. Additionally, the problem is fully solved when the phases have equal rigidities but different compressibilities, the geometry being entirely arbitrary.
[319]	Hoek E, Bieniawski Z T.1965. Brittle fracture propagation in rock under compression . International Journal of Fracture Mechanics, 1: 137-155. DOI      URL      [本文引用: 1]      摘要 The results of studies of the initiation and propagation of fracture from a single Griffith crack in a biaxial compressive stress field are reported. It is concluded that Griffith's theory of brittle...
[320]	Hoek E.1990. Estimating Mohr-Coulomb friction and cohesion values from the Hoek-Brown failure criterion . International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts, 27: 227-229. DOI      URL      [本文引用: 1]      摘要 Ferrimolybdate (Fe2(MoO4)3) was prepared by precipitation from aqueous solutions. The reduction-carburization of ferrimolybdate with graphite was investigated by thermogravimetry and X-ray diffraction of the reaction products obtained in the temperature range 900-1100-degrees-C. Reduction-carburization with carbon monoxide in the temperature range 700-800-degrees-C was also studied. Reduction with graphite was found to proceed via the production of iron and Magneli phases, which are then reduced to MoO2 and Fe3Mo3C. Finally, Fe2MoC is formed after consumption of Fe3Mo3C. Reduction-carburization with CO, on the other hand, proceeds with carburization direct to Mo2C and Fe2MoC after the formation of MoO2 with no formation of the intermediate phase Fe3Mo3C.
[321]	Hoenig A.1979. Elastic moduli of a non-randomly cracked body . International Journal of Solids and Structures, 15: 137-154. DOI      URL      [本文引用: 1]      摘要 Calculations on the basis of the self-consistent approximation are used to study the effects of non-random distributions of dry and saturated circular cracks on the effective elastic stiffnesses of a cracked body. Analytic and numerical results are given for two special distributions. In the first, the cracks are assumed randomly distributed in planes parallel to a given plane. In the second instance, the crack normals are randomly distributed in parallel planes. In all cases, the magnitude of the crack induced variations depend upon a crack density parameter which, for circular cracks of radius a is given by = N<a 3>, where N is the number of cracks per unit volume, and upon an additional saturation parameter.
[322]	Holt R M, Fjaer E, Nes O M, Alassi H T.2011. A Shaly Look At Brittleness//45th U.S. Rock Mechanics/Geomechanics Symposium, 26-29 June, San Francisco , California. American Rock Mechanics Association. [本文引用: 1]
[323]	Holt R M, Fj&#x00026;r E, Stenebraten J F, Nes O M.2015. Brittleness of shales: Relevance to borehole collapse and hydraulic fracturing . Journal of Petroleum Science and Engineering, 131: 200-209. DOI      URL      [本文引用: 5]      摘要 61Use of the term “brittleness” requires a scientifically based definition.61Rock mechanics laboratory experiments quantify brittleness in various shales.61Experiments demonstrate anisotropy of brittleness/plasticity in Mancos shale.61Brittle failure is often linked to splitting or shear failure on weak planes.61Plasticity (lack of brittleness) increases borehole strength.
[324]	Holzer L, Indutnyi F, Gasser PH, Munch B,Wegman M.2004. Three-dimensional analysis of porous BaTiO$_{3}$ ceramics using FIB nanotomography . Journal of Microscopy,216: 84-95. DOI      URL      [本文引用: 1]
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[326]	Horsrud P.2001. Estimating mechanical properties of shale from empirical correlations . SPE Drilling & Completion, 16: 68-73. DOI      URL      [本文引用: 1]      摘要 http://www.onepetro.org/mslib/servlet/onepetropreview?id=00056017&amp;soc=SPE
[327]	Hossain M M, Rahman M K, Rahman S S.2000. Hydraulic fracture initiation and propagation: Roles of wellbore trajectory, perforation and stress regimes . Journal of Petroleum Science and Engineering, 27: 129-149. DOI      URL      [本文引用: 1]      摘要 This paper develops a generic model for predicting hydraulic fracture initiation from arbitrarily oriented wellbores. For a given in-situ stress condition and wellbore orientation parameters, the model predicts the fracture initiation pressure and the orientation and location of fractures on the wellbore wall. The model has been applied in a series of in-situ stress conditions to study the effect of wellbore orientation on fracture initiation using non-dimensional parameters, which have enhanced the applicability of presented results for any stress condition. Closed-form analytical solutions are also obtained for initiation of longitudinal, transverse and complex multiple fractures from vertical and horizontal wellbores with and without perforation. A numerical model is then incorporated in the study to analyze the propagation behavior of initiated fractures. Causes of fracture initiation at non-preferred locations and its effects on fracture propagation pressure and fracture volume due to twist of these initiated fractures during propagation are studied and discussed. Results from the analytical and numerical models used in this study are interpreted with a particular effort to enlighten the causes of abnormally high treating pressures during hydraulic fracture treatments.
[328]	Hossain M M, Rahman M K.2008. Numerical simulation of complex fracture growth during tight reservoir stimulation by hydraulic fracturing . Journal of Petroleum Science and Engineering, 60: 86-104. DOI      URL      [本文引用: 1]      摘要 The success or failure of hydraulic fracturing technology is largely dependent on the design of fracture configurations and optimization of treatments compatible with the in-situ conditions in a given reservoir. The petroleum industry continues to face challenges with this technology in the field, such as premature screen-outs, high treating pressures, complexities with multiple fractures propagation, complex fracture propagation from the deviated wellbore, etc. As these challenges persist better understanding of hydraulic fracture behavior for various reservoir conditions is still an important topic for research. Since the mechanism of hydraulic fracture growth involves the rock stress field and fluid flow field, the modeling work of fracture growth requires the treatment of coupled fluid flow and structural deformation phenomena. In this context, this paper briefly, summarizes an existing numerical tool for fracture growth analysis based on coupled fluid flow and structural deformation phenomena. Solid models have been developed to simulate different field conditions and then solved by using this numerical tool. The field conditions include different stress regimes, fracture geometry and fracture and well orientations. Results for different conditions have been presented and discussed to provide guide lines for better planning and design of hydraulic fracturing. The key finding is that if the well orientation and fracture configuration are not compatible with the in-situ stresses, complex fracture growth diminishes the likelihood of success and exhibits some of the above mentioned symptoms during treatments in the field.
[329]	Huai X L, Koyama S, Zhao T S.2005. An experimental study of flow and heat transfer of supercritical carbon dioxide in multi-port mini channels under cooling conditions . Chemical Engineering Science, 60: 3337-3345. DOI      URL      [本文引用: 2]      摘要 This paper presents the fluid flow and heat transfer characteristics of supercritical CO 2 in a horizontal multi-port extruded aluminum test section consisting of 10 circular channels with an inner diameter of 1.31 mm. Both local and average pressure drop and heat transfer coefficients were measured as CO 2 was cooled in the multi-port circular channels with pressures ranging from 7.4 to 8.5 MPa, inlet fluid temperatures ranging from 22 to 53 C, and mass velocity ranging from 113.7 to 418.6 kg/m 2 s. The results indicate that the operating pressure, the mass velocity and the temperature of CO 2 had significant effects on fluid flow and heat transfer characteristics. The pressure drop and the average heat transfer coefficient increased greatly with increasing the average temperatures of CO 2 in the near-critical region; the average heat transfer coefficient attained a peak value near the corresponding pseudocritical temperature; and the maximum heat transfer coefficient decreased as the pressure increased. Both the pressure drop and the heat transfer coefficient increased with the mass velocity, but decreased with the operating pressure. The measured average heat transfer coefficients were compared with the experimental data reported in the literatures and a large discrepancy was observed. Based on the experimental data collected in the present work, a new correlation was developed for forced convection of supercritical CO 2 in horizontal multi-port mini channels under cooling conditions.
[330]	Huai X, Koyama S.2007. Heat transfer characteristics of supercritical CO$_{2}$ flow in small-channeled structures . Experimental Heat Transfer, 20: 19-33. DOI      URL      [本文引用: 2]
[331]	Huang K, Zhang Z, Ghassemi A.2013. Modeling three-dimensional hydraulic fracture propagation using virtual multidimensional internal bonds . International Journal for Numerical and Analytical Methods in Geomechanics, 37: 2021-2038. DOI      URL      摘要 Propagation of fractures, especially those emanating from wellbores and closed natural fractures, often involves Mode I and Mode II, and at times Mode III, posing significant challenges to its numerical simulation. When an embedded inclined fracture is subjected to compression, the fracture edge is constrained by the surrounding materials so that its true propagation pattern cannot be simulated by 2D models. In this article, a virtual multidimensional internal bond (VMIB) model is presented to simulate three-dimensional (3D) fracture propagation. The VMIB model bridges the processes of macro fracture and micro bond rupture. The macro 3D constitutive relation in VMIB is derived from the 1D bond in the micro scale and is implemented in a 3D finite element method. To represent the contact and friction between fracture surfaces, a 3D element partition method is employed. The model is applied to simulate fracture propagation and coalescence in typical laboratory experiments and is used to analyze the propagation of an embedded fracture. Simulation results for single and multiple fractures illustrate 3D features of the tensile and compressive fracture propagation, especially the propagation of a Mode III fracture. The results match well with the experimental observation, suggesting that the presented method can capture the main features of 3D fracture propagation and coalescence. Moreover, by developing an algorithm for applying pressure on the fracture surfaces, propagation of a natural fracture is also simulated. The result illustrates an interesting and important phenomenon of Mode III fracture propagation, namely the fracture front segmentation. Copyright 2012 John Wiley & Sons, Ltd.
[332]	Huang M, del Castillo P E R D, Li Z.2006. Edge dislocation dipole emission from a blunt crack tip and its morphological effects . Scripta Materialia, 54: 649-653. DOI      URL      摘要 Expressions for describing the critical stress intensity factor for edge dislocation dipoles emission under mode I and II loads are presented. The conditions for the crack tip radius increase in finite and semi-infinite cracks are examined.
[333]	Huang Y, Chandra A, Jiang Z Q, Wei X, Hu K X.1996. The numerical calculation of two-dimensional effective moduli for microcracked solids . International Journal of Solids and Structures, 33: 1575-1586. DOI      URL      [本文引用: 2]      摘要 There exist several micromechanics models for the determination of the effective moduli of microcracked solids, and crack density is the only parameter in these models that characterizes the effect of microcracking. A numerical hybrid BEM method, in conjunction with a unit cell model, is proposed in the present paper to evaluate these micromechanics models. A unit cell, which can be considered as a representative block in the solid, contains randomly distributed microcracks. The unit cell is then assumed to be periodic in the solid so as to account for interactions between cracks inside and outside the cell. There are stochastic variations of the estimated moduli for different microcrack distributions. Two groups of microcracks with the same crack density, one with a low number of large cracks and the other with a large number of small cracks, show the same range of stochastic variations and the same mean of effective moduli for random distributions of microcracks. The effective moduli based on this numerical method for randomly distributed cracks and parallel cracks are compared with those from various micromechanics models. While the differential method provides the closest estimation to the mean of the numerical results at low crack density, the generalized self-consistent method is much more accurate at relatively high crack density
[334]	Huang Y, Hu K, Chandra A.1994. A generalized self-consistent mechanics method for microcracked solids . Journal of the Mechanics and Physics of Solids, 42: 1273-1291. DOI      URL      [本文引用: 1]      摘要 A CRACK-MATRIX-COMPOSITE model is proposed and studied for microcracked solids. The model properly accounts for the effect of crack interactions on the effective moduli of microcracked solids. Approximate formulas for randomly distributed penny-shaped cracks and tunnel cracks are given. The difference between the crack-matrix-composite model and that of the dilute or non-interacting solution is of the order 07 for penny-shaped cracks and 07 for tunnel cracks, where 07 is the crack density. The results from an accurate numerical method for arbitrarily distributed cracks, based on a pseudo-traction approach, verify the present crack-matrix-composite model.
[335]	Hudson J A.1981. Wave speeds and attenuation of elastic waves in material containing cracks . Geophysical Journal International, 64: 133-150 DOI      URL      [本文引用: 1]      摘要 Summary. Expressions now exist from which may be calculated the propagation constants of elastic waves travelling through material containing a distribution of cracks. The cracks are randomly distributed in position and may be randomly orientated. The wavelengths involved are assumed to be large compared with the size of the cracks and with their separation distances so that the formulae, based on the mean taken over a statistical ensemble, may reasonably be used to predict the properties of a single sample. The results are valid only for small concentrations of cracks. Explicit expressions, correct to lowest order in the ratio of the crack size to a wavelength, are derived here for the overall elastic parameters and the overall wave speeds and attenuation of elastic waves in cracked materials where the mean crack is circular, and the cracks are either aligned or randomly orientated. The cracks may be empty or filled with solid or fluid material. These results are achieved on the basis of simply the static solution for an ellipsoidal inclusion under stress. The extension to different distributions of orientation or to mixtures of different types of crack is quite straightforward.
[336]	Hunsweck M J, Shen Y, Lew A J.2013. A finite element approach to the simulation of hydraulic fractures with lag . International Journal for Numerical and Analytical Methods in Geomechanics, 37: 993-1015. DOI      URL      [本文引用: 2]      摘要 We presented a finite-element-based algorithm to simulate plane-strain, straight hydraulic fractures in an impermeable elastic medium. The algorithm accounts for the nonlinear coupling between the fluid pressure and the crack opening and separately tracks the evolution of the crack tip and the fluid front. It therefore allows the existence of a fluid lag. The fluid front is advanced explicitly in time, but an implicit strategy is needed for the crack tip to guarantee the satisfaction of Griffith's criterion at each time step. We enforced the coupling between the fluid and the rock by simultaneously solving for the pressure field in the fluid and the crack opening at each time step. We provided verification of our algorithm by performing sample simulations and comparing them with two known similarity solutions. Copyright 2012 John Wiley & Sons, Ltd.
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[338]	Ibanez W D, Kronenberg A K.1993. Experimental deformation of shale: Mechanical properties and microstructural indicators of mechanisms. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts. 30: 723-734. DOI      URL      [本文引用: 5]      摘要 The mechanical properties and deformation mechanisms of an illite-rich shale have been investigated in triaxial compression experiments at varying confining pressures (P
[339]	Irwin G R.1968. Linear fracture mechanics, fracture transition, and fracture control . Engineering Fracture Mechanics, 1: 241-257. DOI      URL      [本文引用: 1]      摘要 As an analysis viewpoint, fracture mechanics treats the leading edge of a crack as a line disturbance zone in a manner similar to the treatment of dislocation lines in dislocation mechanics. Linear fracture mechanics analysis is adequate for most practical applications and permits estimates of two new length factors: the approximate size of the plastic zone, 2 r Y, and the crack border opening displacement, δ = 65/σ Y. Studies of crack extension behaviors as a function of the stress field parameters K and 65, and their interpretation with the assistance of length factors, have clarified general understanding of fracture in ways which impinge strongly on various fields of investigation such as stress corrosion cracking, fatigue, brittle transition temperature, and fracture control methods. As an example, the paper discusses interpretation of the brittle-ductile transition in terms of relative plastic zone size, and allowable-load estimates which include fracture strength in a rational way. Fracture control methods which do not rely on prior fracture failure experience are needed for new structures now under consideration. Correspondingly, the need for training and experience in fracture mechanics is urgent.
[340]	Ishida T, Aoyagi K, Niwa T, Chen Y, Murata S.2012. Acoustic emission monitoring of hydraulic fracturing laboratory experiment with supercritical and liquid CO$_{2}$ . Geophysical Research Letters, 39: 1-6. DOI      URL      [本文引用: 1]      摘要 Carbon dioxide (CO) is often used for enhanced oil recovery in depleted petroleum reservoirs, and its behavior in rock is also of interest in COcapture and storage projects. COusually becomes supercritical (SC-CO) at depths greater than 1,000 m, while it is liquid (L-CO) at low temperatures. The viscosity of L-COis one order lower than that of normal liquid water, and that of SC-COis much lower still. To clarify fracture behavior induced with injection of the low viscosity fluids, we conducted hydraulic fracturing experiments using 17 cm cubic granite blocks. The AE sources with the SC- and L-COinjections tend to distribute in a larger area than those with water injection, and furthermore, SC-COtended to generate cracks extending more three dimensionally rather than along a flat plane than L-CO. It was also found that the breakdown pressures for SC- and L-CO2 injections are expected to be considerably lower than for water.
[341]	Islam M A, Skalle P.2013. An experimental investigation of shale mechanical properties through drained and undrained test mechanisms . Rock Mechanics and Rock Engineering, 46: 1391-1413. DOI      URL      [本文引用: 1]      摘要 AbstractShale mechanical properties are evaluated from laboratory tests after a complex workflow that covers tasks from sampling to testing. Due to the heterogeneous nature of shale, it is common to obtain inconsistent test results when evaluating the mechanical properties. In practice, this variation creates errors in numerical modeling when test results differ significantly, even when samples are from a similar core specimen. This is because the fundamental models are based on the supplied test data and a gap is, therefore, always observed during calibration. Thus, the overall goal of this study was to provide additional insight regarding the organization of the non-linear model input parameters in borehole simulations and to assist other researchers involved in the rock physics-related research fields. To achieve this goal, the following parallel activities were carried out: (1) perform triaxial testing with different sample orientations, i.e., 0°, 45°, 60°, and 90°, including the Brazilian test and CT scans, to obtain a reasonably accurate description of the anisotropic properties of shale; (2) apply an accurate interpretative method to evaluate the elastic moduli of shale; (3) evaluate and quantify the mechanical properties of shale by accounting for the beddings plane, variable confinement pressures, drained and undrained test mechanisms, and cyclic versus monotonic test effects. The experimental results indicate that shale has a significant level of heterogeneity. Postfailure analysis confirmed that the failure plane coincides nicely with the weak bedding plane. The drained Poisson’s ratios were, on average, 4002% or lower than the undrained rates. The drained Young’s modulus was approximately 4802% that of the undrained value. These mechanical properties were significantly impacted by the bedding plane orientation. Based on the Brazilian test, the predicted tensile strength perpendicular to the bedding plane was 1202% lower than the value obtained using the standard isotropic correlation test. The cyclic tests provided approximately 602% higher rock strength than those predicted by the monotonic tests.
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[354]	Kanamori H, Rivera L.2006. Energy partitioning during an earthquake . Earthquakes: Radiated Energy and the Physics of Faulting, 3-13. DOI      URL      [本文引用: 2]      摘要 We investigate the partitioning of energy released during an earthquake to radiated, fracture and thermal energies in an attempt to link various observational results obtained in different disciplines. The fracture energy, E, used in seismology is different from that commonly used in mechanics where it is the energy used to produce new crack surface. In the seismological language it includes the energies used for off-fault cracking, and various thermal processes. The seismic moment, M, the radiated energy, E, and rupture speed, V, are key macroscopic parameters. The static stress drop can be a complex function of space, but if an average can be defined as Δτ, it is also a useful source parameter. From the combination of M, E, and, Δτ we can estimate the radiation efficiency η, or Ewhich can also be estimated independently from V.ηprovides a link to the results of dynamic modeling of earthquakes which determines the displacement and stress on the fault plane. Theoretical and laboratory results can also be compared with earthquake data through η. Also, the fracture energy estimated from the measurement of the volume and grain size of gouge of an exhumed fault can be linked to seismic data through η. In these comparisons, the thermal energy is not included, and it must be estimated independently from estimates of sliding friction during faulting. One of the most challenging issues in this practice is how to average the presumably highly variable slip, stress and frictional parameters to seismologically determinable parameters.
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[356]	Kaneko K, Murata K.1997. An analytical method of micropore filling of a supercritical gas . Adsorption, 3: 197-208. DOI      URL      [本文引用: 1]      摘要 The supercritical gas adsorbed in the micropore having a strong molecular field was presumed to transform into the quasi-vapor to be filled in the micropore (quasi-vaporization adsorption mechanism). The Dubinin-Radushkevitch (DR) equation for micropore filling of vapor was extended to the quasi-vaporized supercritical gas using the quasi-saturated vapor pressure P 0 q and the inherent micropore volume W L . The reason why the concepts of P 0q and W L were introduced was explained with the molecule-pore interaction potential theory which is based on the Lennard-Jones interaction. The extended DR equation was named the supercritical DR equation. The W L was evaluated by the Langmuir plot of the adsorption isotherm for a supercritical gas and both of P 0q and W L provided the single reduced adsorption isotherms of supercritical NO, N 2 , and CH 4 on activated carbon fibers and high surface area carbons were analyzed by the supercritical DR plots. The wide applicability of the reduced adsorption isotherm to these adsorption data was explicity shown. The two phase model of the organized and confined fluids was proposed in order to improve the quasi-vaporization adsorption mechanism.
[357]	Kao H, Shan S J.2004. The source-scanning algorithm: Mapping the distribution of seismic sources in time and space . Geophysical Journal International, 157: 589-594. DOI      URL      [本文引用: 3]      摘要 We introduce a new method, which we call the Source-Scanning Algorithm (SSA), for imaging the distribution of seismic sources in both time and space. Using trial locations and origin times, the method calculates the 'brightness' function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times. The spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness. The greatest advantages of this method are that: (1) it exploits waveform information (both arrival times and relative amplitudes) without the need to calculate high-frequency synthetic seismograms; and (2) it requires neither pre-assembled phase-picking data nor any a priori assumptions about the source geometry. A series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval. Finally, we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip (ETS) sequence in the northern Cascadia subduction zone.
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[373]	Kushch V I, Sevostianov I, Mishnaevsky L.2009. Effect of crack orientation statistics on effective stiffness of mircocracked solid . International Journal of Solids and Structures, 46: 1574-1588. DOI      URL      [本文引用: 1]      摘要 This paper addresses the problem of calculating effective elastic properties of a solid containing multiple cracks with prescribed orientation statistics. To do so, the representative unit cell approach has been used. The microgeometry of a cracked solid is modeled by a periodic structure with a unit cell containing multiple cracks; a sufficient number is taken to account for the microstructure statistics. The developed method combines the superposition principle, the technique of complex potentials and certain new results in the theory of special functions. A proper choice of potentials provides reducing the boundary-value problem to an ordinary, well-posed set of linear algebraic equations. The exact finite form expression of the effective stiffness tensor has been obtained by analytical averaging the strain and stress fields. The convergence study has been performed; the statistically meaningful results obtained show dependence of the effective elastic stiffness on angular scattering of cracks. Comparison has been made with the selected simple micromechanical models, namely, non-interaction approximation, differential scheme and modified differential scheme. It is found that, among these models, the differential scheme provides the best fit of the numerical data.
[374]	La Rocca M, McCausland W, Galluzzo D, Malone S, Saccorotti G, Pezzo E D.2005. Array measurements of deep tremor signals in the Cascadia subduction zone . Geophysical Research Letters, 32. DOI      URL      [本文引用: 1]      摘要 Preliminary analysis of deep tremor recorded during July, 2004, in the Cascadia Subduction zone shows that the use of small aperture arrays can resolve the slowness and back azimuth of seismic waves with a useful resolution. Data were collected by three dense arrays of short-period seismometers specifically deployed in the Puget Sound area under an US-Italy-Canada cooperative effort. Slowness analyses at the three arrays indicate that the 2-4 Hz tremor wave-field is composed by waves propagating with apparent velocities higher than 4 km/s. Combining this with polarisation analysis show these waves to be transverse (SH) waves. However, P-waves, though smaller in amplitude, can be detected by different slowness values obtained for the radial and transverse components. The intersection of wave vectors determined by the back azimuth and slowness values measured at the three arrays provides a preliminary estimate of source location for a sample of the recorded deep tremor.
[375]	Lecampion B, Desroches J.2015. Simultaneous initiation and growth of multiple radial hydraulic fractures from a horizontal wellbore . Journal of the Mechanics and Physics of Solids, 82: 235-258. DOI      URL      摘要 61A numerical model for the simultaneous initiation and propagation of an array of radial hydraulic fractures driven by fluid injection from a horizontal well.61Single radial hydraulic fracture initiation experiments can be fully predicted by the model.61Fluid partitioning between multiple hydraulic fractures is governed by stress interaction and the local pressure drop at the connection between wellbore and fractures.61A dimensionless number separates preferential growth from simultaneous growth.
[376]	Lecampion B.2009. An extended finite element method for hydraulic fracture problems . International Journal for Numerical Methods in Biomedical Engineering, 25: 121-133. DOI      URL      [本文引用: 2]      摘要 In this paper, the extended finite element method (X-FEM) is investigated for the solution of hydraulic fracture problems. The presence of an internal pressure inside the crack is taken into account. Special tip functions encapsulating tip asymptotics typically encountered in hydraulic fractures are introduced. We are especially interested in the two limiting tip behaviour for the impermeable case: the classical LEFM square root asymptote in fracture width for the toughness-dominated regime of propagation and the so-called 090500 asymptote in fracture width for the viscosity-dominated regime. Different variants of the X-FEM are tested for the case of a plane-strain hydraulic fracture propagation in both the toughness and the viscosity dominated regimes. Fracture opening and fluid pressure are compared at each nodes with analytical solutions available in the literature. The results demonstrate the importance of correcting for the loss of partition of unity in the transition zone between the enriched part and the rest of the mesh. A point-wise matching scheme appears sufficient to obtain accurate results. Proper integration of the singular terms introduced by the enrichment functions is also critical for good performance. Copyright 0008 2008 John Wiley & Sons, Ltd.
[377]	Lecampion B.2009. An extended finite element method for hydraulic fracture problems . Communications in Numerical Methods in Engineering, 25: 121-133. DOI      URL      摘要 In this paper, the extended finite element method (X-FEM) is investigated for the solution of hydraulic fracture problems. The presence of an internal pressure inside the crack is taken into account. Special tip functions encapsulating tip asymptotics typically encountered in hydraulic fractures are introduced. We are especially interested in the two limiting tip behaviour for the impermeable case: the classical LEFM square root asymptote in fracture width for the toughness-dominated regime of propagation and the so-called 090500 asymptote in fracture width for the viscosity-dominated regime. Different variants of the X-FEM are tested for the case of a plane-strain hydraulic fracture propagation in both the toughness and the viscosity dominated regimes. Fracture opening and fluid pressure are compared at each nodes with analytical solutions available in the literature. The results demonstrate the importance of correcting for the loss of partition of unity in the transition zone between the enriched part and the rest of the mesh. A point-wise matching scheme appears sufficient to obtain accurate results. Proper integration of the singular terms introduced by the enrichment functions is also critical for good performance. Copyright 0008 2008 John Wiley & Sons, Ltd.
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[419]	Mohammadnejad T, Khoei A R.2013. An extended finite element method for hydraulic fracture propagation in deformable porous media with the cohesive crack model . Finite Elements in Analysis and Design, 73: 77-95. DOI      URL      [本文引用: 1]      摘要 61A fully coupled XFEM model is used for hydraulic fracture propagation of porous media.61The governing equations of porous media are derived using the generalized Biot theory.61The fluid flow within the fracture is modeled using the cubic law in the Darcy law.61The cohesive crack model is used for the nonlinear fracture process zone.61The fluid leak-off and the length of crack growth are obtained during the solution.
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[445]	Paterson M S.1958. Experimental deformation and faulting in Wombeyan marble . Bull. Geol. Soc. Am, 69: 465--476. DOI      URL      [本文引用: 3]      摘要 Abstract In Compressive Stress-Strain Tests On A Coarse-Grained Marble At Various Confining Pressures Up To 1000 Kg Cm-2, Special Attention Has Been Paid To The Transition From Brittle To Ductile Behavior. The Application Of Low Confining Pressures Suppresses The Longitudinal Fractures Characteristic Of Failure At Atmospheric Pressure, And Well-Defined Shear Failures Develop. The Formation Of The Localized Shear Zones Accompanies A Gradual Decrease In The Stress Needed For Continued Deformation But Does Not Lead Immediately To Complete Fracture. This Behavior May Be Initiated By A Type Of Plastic Instability. Its Relevance To Geological Faulting Is Discussed, Since The Shear Zones Developed In The Marble Specimens Appear To Be Similar To Geological Faults. At Confining Pressures Above About 300 Kg Cm-2, The Stress-Strain Curves Rise Continuously Without Reaching A Maximum, And The Deformation Is Distributed Throughout The Specimen Instead Of Being Localized In Shear Zones Or Faults. This Suggests That There Is A Depth In The Earth'S Crust Below Which Faulting Cannot Be Expected In This Rock. The Stress-Strain Curves Have Been Analyzed To Show The Effect Of Confining Pressure On The Yield Stress And On The Stress At The Maximum Load. A Few Measurements On A Fine-Grained Limestone Are Also Included In An Appendix. Coloration Of The Marble By X Radiation Occurs After Deformation At Low Confining Pressures, But The Effect Becomes More Marked At Higher Confining Pressures.
[446]	Peirce A, Detournay E.2008. An implicit level set method for modeling hydraulically driven fractures . Computer Methods in Applied Mechanics and Engineering, 197: 2858-2885. DOI      URL      [本文引用: 1]      摘要 We describe a novel implicit level set algorithm to locate the free boundary for a propagating hydraulic fracture. A number of characteristics of the governing equations for hydraulic fractures and their coupling present considerable challenges for numerical modeling, namely: the degenerate lubrication equation; the hypersingular elastic integral equation; the indeterminate form of the velocity of the unknown fracture front, which precludes the implementation of established front evolution strategies that require an explicit velocity field; and the computationally prohibitive cost of resolving all the length scales. An implicit algorithm is also necessary for the efficient solution of the stiff evolution equations that involve fully populated matrices associated with the coupled non-local elasticity and degenerate lubrication equations. The implicit level set algorithm that we propose exploits the local tip asymptotic behavior, applicable at the computational length scale, in order to locate the free boundary. Local inversion of this tip asymptotic relation yields the boundary values for the Eikonal equation, whose solution gives the fracture front location as well as the front velocity field. The efficacy of the algorithm is tested by comparing the level set solution to analytic solutions for hydraulic fractures propagating in a number of distinct regimes. The level set algorithm is shown to resolve the free boundary problem with first order accuracy. Further it captures the field variables, such as the fracture width, with the first order accuracy that is consistent with the piecewise constant discretization that is used.
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[452]	Rafiee M, Soliman M Y, Pirayesh E.2012. Hydraulic fracturing design and optimization: A modification to zipper frac//Society of Petroleum Engineers, San Antonio, SPE 159786 . [本文引用: 1]
[453]	Raghavan R, Chen C.2013. Fractional diffusion in rocks produced by horizontal wells with multiple, transverse hydraulic fractures of finite conductivity . Journal of Petroleum Science & Engineering, 109: 133-143. DOI      URL      摘要 Assuming diffusion in the rocks to be anomalous, a flux law that is nonlocal in space and time is used to develop a mathematical model for fractured rocks drained by a horizontal well produced through multiple transverse hydraulic fractures. As a result the governing differential equation is fractional in character. The conductivity of the fractures is assumed to be finite and their properties (width, length, permeability, etc.) maybe variable. Expressions for the well response that produces at a constant rate or at a constant pressure are derived in terms of the Laplace transformation. Approximate analytical solutions are derived and the analytical development provides perspectives on short and long-time well behaviors. In addition to outlining characteristic features of the model, the analytical solutions are useful in verifying numerical computations. The computational results obtained by the Stehfest algorithm establish the robustness and viability of the mathematical model. Comparisons with classical diffusion are noted. (C) 2013 Elsevier B.V. All rights reserved.
[454]	Rahman M M, Rahman M K.2010. A review of hydraulic fracture models and development of an improved pseudo-3D model for stimulating tight oil/gas sand . Energy Source Part A, 32: 1416-1436. DOI      URL      [本文引用: 2]      摘要 Many injection/production wells have been hydraulically fractured to enhance injectivity/productivity. Various engineering models for fracture geometry have been developed, which define the propagation of a fracture with time and wellbore treatment pressure. These models combine with elasticity, fluid flow, material balance, and propagation criterion/in-situ stresses. When this combination describes the fracture dimensions, the fracture-geometry can be of two-dimensional (2D) and three-dimensional (3D), depending on the number of dimensional variables. For design purposes, several 2D and 3D models are already developed. But it is still a concern in the oil industry as to which model is beneficial to design optimum treatment parameters for a particular tight sand, because despite many successes, there have been many wells of poor post-fracture productivity. This article provides a review of 2D and 3D fracture models for prediction of fracture geometry. A P-3D (pseudo) model has been improved by incorporating Carter solution of material balance for the first time and was named P-3D-C model, which has predicted higher fracture conductivity. The improved model is highly potential for repetitive computation in hydraulic fracture design optimization.
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[456]	Ren Q W, Dong Y W, Yu T T.2009. Numerical modeling of concrete hydraulic fracturing with extended finite element method . Science in China Series E: Technological Sciences, 52: 559-565. DOI      URL      [本文引用: 1]      摘要 The extended finite element method (XFEM) is a new numerical method for modeling discontinuity. Research about numerical modeling for concrete hydraulic fracturing by XFEM is explored. By building the virtual work principle of the fracture problem considering water pressure on the crack surface, the governing equations of XFEM for hydraulic fracture modeling are derived. Implementation of the XFEM for hydraulic fracturing is presented. Finally，the method is verified by two examples and the advan-tages of the XFEM for hydraulic fracturing analysis are displayed.
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[466]	Ross D J K, Bustin R M.2007. Shale gas potential of the Lower Jurassic Gordondale Member northeastern British Columbia, Canada . Bulletin of Canadian Petroleum Geology, 55: 51-75. DOI      URL      [本文引用: 1]
[467]	Ross D J K, Bustin R M.2008. Characterizing the shale gas resource potential of Devonian-Mississippian stratain the Western Canada sedimentary basin: Application of anintegrated formation evaluation . AAPG Bulletin, 92: 87-125. DOI      URL      [本文引用: 3]
[468]	Ross D J K, Bustin R M.2009. The importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs . Marine & Petroleum Geology, 26: 916-927. DOI      URL      摘要 The effect of shale composition and fabric upon pore structure and CH sorption is investigated for potential shale gas reservoirs in the Western Canadian Sedimentary Basin (WCSB). Devonian–Mississippian (D–M) and Jurassic shales have complex, heterogeneous pore volume distributions as identified by low pressure CO and N sorption, and high pressure Hg porosimetry. Thermally mature D–M shales (1.6–2.5%02VRo) have Dubinin–Radushkevich (D–R) CO micropore volumes ranging between 0.3 and 1.202cc/10002g and N BET surface areas of 5–3102m/g. Jurassic shales, which are invariably of lower thermal maturity ranging from 0.9 to 1.3%02VRo, than D–M shales have smaller D–R CO micropore volumes and N BET surface areas, typically in the range of 0.23–0.6302cc/10002g (CO) and 1–902m/g (N).High pressure CH isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon (TOC) content. Methane sorption in D–M shales increases with increasing TOC and micropore volume, indicating that microporosity associated with the organic fraction is a primary control upon CH sorption. Sorption capacities for Jurassic shales, however, can be in part unrelated to micropore volume. The large sorbed gas capacities of organic-rich Jurassic shales, independent of surface area, imply a portion of CH is stored by solution in matrix bituminite. Solute CH is not an important contributor to gas storage in D–M shales. Structural transformation of D–M organic matter has occurred during thermal diagenesis creating and/or opening up microporosity onto which gas can sorb. As such, D–M shales sorb more CH per weight percent (wt%) TOC than Jurassic shales.Inorganic material influences modal pore size, total porosity and sorption characteristics of shales. Clay minerals are capable of sorbing gas to their internal structure, the amount of which is dependent on clay-type. Illite and montmorillonite have CO micropore volumes of 0.78 and 0.7902cc/10002g, N BET surface areas of 25 and 3002m/g, and sorb 2.9 and 2.102cc/g of CH, respectively (dry basis) – a reflection of microporosity between irregular surfaces of clay platelets, and possibly related to the size of the clay crystals themselves. Mercury porosimetry analyses show that total porosities are larger in clay-rich shales compared to silica-rich shales due to open porosity associated with the aluminosilicate fraction. Clay-rich sediments (low Si/Al ratios) have unimodal pore size distributions
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[483]	Shakib J T.2013. Numerical modeling of hydraulic fracture propagation: Accounting for the effect of stresses on the interaction between hydraulic and parallel natural fractures . Egyptian Journal of Petroleum, 22: 557-563. DOI      URL      [本文引用: 1]      摘要 This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of According to EGYJP committee’s decision and after precise investigation ,It is ultimately obvious that the article titled: “Numerical Modeling of Hydraulic Fracture Propagation: Accounting for the Effect of Stresses on The Interaction Between Hydraulic and Parallel Natural Fractures” by its auther Jaber Taheri Shakib is totally plagiarized from the thesis titled: “Analysis of hydraulic fracture propagation in fractured reservoirs: an improved model for the interaction between induced and natural fractures” by Arash Dahi Taleghani; http://hdl.handle.net/2152/18381; beginning from the abstract passing through chapter 3. Even the conclusion of chapter 3 is copied directly from the thesis: “Analysis of hydraulic fracture propagation in fractured reservoirs: an improved model for the interaction between induced and natural fractures” A matter which leads the committee to take its final decision of retracting the mentioned article from volume no. 22 issue 4 and blacklisting its author Dr. Jaber Taheri Shakib from our journal. Hoping that this decision is taken promptly from your honored side.
[484]	Shao J F, Jia Y, Kondo D, Chiarelli A S.2006. A coupled elastoplastic damage model for semi-brittle materials and extension to unsaturated conditions . Mechanics of Materials, 38: 218-232. DOI      URL      [本文引用: 1]      摘要 In this paper, a coupled elastoplastic damage model is proposed for semi-brittle materials. This model is applied to a specific semi-brittle sedimentary rock material. A brief account of experimental investigations is presented in the first part. The data obtained show an important plastic deformation coupled with stress-induced damage corresponding to initiation and growth of microcracks. Influences of mineral compositions and water content on the mechanical behaviour are also investigated. Based on these experimental evidences, the general formulation of the model is presented in the second part of the paper. The effective elastic properties of isotropic damaged material are determined based on relevant considerations from micromechanics. Damage evolution law and plastic damage coupling are described by using the framework of irreversible thermodynamics. A non-associated plastic flow rule is used. The model is extended to partially saturated conditions in order to study coupled hydromechanical behaviours in drying etting processes. Comparisons between numerical simulations and test data are performed for various loading paths. It is shown that the proposed model is able to describe the main features of mechanical behaviour observed in this class of materials.
[485]	Shao J F, Zhu Q Z, Su K.2003. Modeling of creep in rock materials in terms of material degradation . Computers and Geotechnics, 30: 549-555. DOI      URL      [本文引用: 1]      摘要 In this paper, we present a constitutive model for creep deformation in rock materials. Starting from an elastoplastic model for the description of short term behavior, the time-dependent deformation is described in terms of evolution of microstructure, leading to progressive degradation of elastic modulus and failure strength of material. The proposed model is applied to predict material responses in creep and relaxation tests. There is a good agreement between numerical simulations and experimental data. The proposed model is able to describe the main features observed in most cohesive frictional geomaterials (rocks and concrete), such as plastic deformation, damage, volumetric dilation, pressure sensitivity, rate dependency and creep.
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[487]	Shen L, Li J.2004. A numerical simulation for effective elastic moduli of plates with various distributions and sizes of cracks . International Journal of Solids and Structures, 41: 7471-7492. DOI      URL      [本文引用: 1]      摘要 A fast convergent numerical model is developed to calculate the effective moduli of plates with various distributions and sizes of cracks, in which the crack line is divided into parts to obtain the unknown traction on the crack line. When =1, the model reduces to Kachanov's approximation method [Int. J. Solids Struct. 23 (1987) 23]. Six types of crack distributions and three kinds of crack sizes are considered, which are four regular (equilateral triangle, equilateral hexagon, rectangle, and diamond) and two random distributions (random location and orientation, and parallel orientation and random location), and one, two and random crack sizes. Some typical examples are also analyzed using the finite element method (FEM) to validate the present model. Then, the effective moduli associated with the crack distributions and sizes are calculated in detail. The present results for the regular distributions show some very interesting phenomena that have not been revealed before. And for the two random distributions, as the effective moduli depend on samples due to the randomness, the effect of the sample size and number are analyzed first. Then, effective moduli for plates with the three sizes of cracks are calculated. It is found that the effect of crack sizes on the effective moduli is significant for high crack densities, and small for low crack densities, and the random crack size leads to the lowest effective moduli. The present numerical results are compared with several popular micromechanics models to determine which one can provide the optimum estimation of the effective moduli of cracked plates with general crack densities. Furthermore, some existing numerical results are analyzed and discussed.
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[510]	Sun H, Yao J, Gao S, Fan D, Wang C, Sun Z.2013. Numerical study of CO$_{2}$ enhanced natural gas recovery and sequestration in shale gas reservoirs . International Journal of Greenhouse Gas Control, 19: 406-419. DOI      URL      [本文引用: 2]      摘要 Due to the ultra-fine pore sizes, Darcy's law is not applicable in shale gas reservoir. On the basis of the multiple binary gas transport mechanisms including viscous flow, Knudsen diffusion and ordinary diffusion, a new dual-porosity mathematical model is established to investigate the CO2 sequestration with enhanced natural gas recovery (CSEGR) in shale gas reservoirs. Meanwhile, the transfer function and well flow model considering the multiple mechanisms are developed. The mathematical model is implemented by the finite element simulation software COMSOL, and the accuracy of the numerical solution is verified by comparison with the classic analytical solution. Three sets of simulations were conducted to investigate the influence of CO2 injection on the development of shale gas reservoirs. The results show that CSEGR is feasible to achieve CO2 sequestration and enhance CH4 recovery in shale gas reservoirs, the CO2 storage and natural gas production rate can be improved highly with the increase of injection pressure. The CSEGR process can be divided into three stages including the early depressurization production period, the intermediate CO2 adsorption and CH4 replacement period and the late period of CH4 and CO2 produced simultaneously. In addition, the concentration variation and storage pattern of CH4 and CO2 gas are analyzed during the CSEGR process in shale gas reservoirs.
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[514]	Taleghani A D.2009. Analysis of hydraulic fracture propagation in fractured reservoirs: An improved model for the interaction between induced and natural fractures. [PhD Thesis]. Austin: The University of Texas. DOI      URL      [本文引用: 1]      摘要 Large volumes of natural gas exist in tight fissured reservoirs. Hydraulic fracturing is one of the main stimulating techniques to enhance recovery from these fractured reservoirs. Although hydraulic fracturing has been used for decades for the stimulation of tight gas reservoirs, a thorough understanding of the interaction between induced hydraulic fractures and natural fractures is still lacking. Recent examples of hydraulic fracture diagnostic data suggest complex, multi-stranded hydraulic fracture geometry is a common occurrence. The interaction between pre-existing natural fractures and the advancing hydraulic fracture is a key condition leading to complex fracture patterns. Large populations of natural fractures that exist in formations such as the Barnett shale are sealed by precipitated cements which could be quartz, calcite, etc. Even though there is no porosity in the sealed fractures, they may still serve as weak paths for fracture initiation and/or for diverting the path of the growing hydraulic fractures. Performing hydraulic fracture design calculations under these complex conditions requires modeling of fracture intersections and tracking fluid fronts in the network of reactivated fissures. In this dissertation, the effect of the cohesiveness of the sealed natural fractures and the intact rock toughness in hydraulic fracturing are studied. Accordingly, the role of the pre-existing fracture geometry is also investigated. The results provide some explanations for significant differences in hydraulic fracturing in naturally fractured reservoirs from non-fractured reservoirs. For the purpose of this research, an extended finite element method (XFEM) code is developed to simulate fracture propagation, initiation and intersection. The motivation behind applying XFEM are the desire to avoid remeshing in each step of the fracture propagation, being able to consider arbitrary varying geometry of natural fractures and the insensitivity of fracture propagation to mesh geometry. New modifications are introduced into XFEM to improve stress intensity factor calculations, including fracture intersection criteria into the model and improving accuracy of the solution in near crack tip regions.
[515]	Tanmay M S.2014. LPG-Based Fracturing: An alternate fracturing technique in shale reservoirs. SPE170542//SPE nconventional Resources Conference.
[516]	Tayari F, Blumsack S, Dilmore R, Mohaghegh S D.2015. Techno-economic assessment of industrial CO$_{2}$ storage in depleted shale gas reservoirs . Journal of Unconventional Oil and Gas Resources, 11: 82-94. DOI      URL      [本文引用: 1]      摘要 The long-term storage of carbon dioxide (CO2) via injection into deep geologic formations represents a promising technological pathway to reducing greenhouse gas emissions to the atmosphere. Geologic storage in deep saline aquifers has been studied extensively, and the injection of CO2 for enhanced oil recovery (EOR) from conventional (porous and permeable) formations has been practiced for decades. This study is focused on developing a preliminary assessment of the economic feasibility of storing CO2 in depleted unconventional natural gas-bearing shale formations. Using a surrogate reservoir model (SRM) and a flexible environment for techno-economic analysis, this paper presents site-scale estimates of long-term CO2 sequestration costs in depleted shale gas formations and discussion of the likely major cost drivers. This analysis focuses on the transportation of CO2 from industrial point sources in the Pennsylvania Marcellus Shale region, and the transition of Marcellus wells from production to CO2 injection. This approach couples techno-economic analysis with reservoir simulation models to estimate costs associated with transportation, injection, CO2 separation and post-injection monitoring of CO2 storage permanence from large industrial point sources in depleted shale-gas reservoirs. We also consider potential revenue from incremental CH4 recovery (effectively enhanced gas recovery) in reservoir scenarios where such production is significant. The techno-economic model boundary includes pipeline transport from an industrial source (excludes the cost of capture of CO2 at that source), site preparation and CO2 flooding operations, and long-term monitoring and post-injection site care (PISC) at the storage site. Under an operational scenario where a Marcellus shale gas well is in primary production for 42years prior to the initiation of CO2 injection, it is estimated that CO2 could be transported and stored at a levelized cost of $40 $80 per metric tonne, in present value terms. These costs are shown to be highly sensitive to assumptions regarding well spacing, bottomhole pressure, CO2 transport distance and the future price of natural gas. In most of the scenarios considered, transportation and injection costs were dominant factors, while CO2 separation, pore space acquisition and post-injection site care/monitoring did not significantly influence levelized costs.
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[518]	Thiel S, Heinson G.2010. Crustal imaging of a mobile belt using magnetotellurics: an example of the Fowler Domain in South Australia . Journal of Geophysical Research: Solid Earth, 115: 1-18. DOI      URL      [本文引用: 1]      摘要 [1] A long-period magnetotelluric data set was obtained in 2005 along a two-dimensional profile across the western part of the late Archaean-early Proterozoic Gawler Craton, South Australia. The study is aimed at delineating the electrical conductivity structure of the crust and upper mantle underneath an east-west trending profile extending from the Gawler Range Volcanics in the east, crossing the Nuyts Domain and the highly prospective Meso-Proterozoic Fowler Domain, and terminating in the Eucla Basin to the west. The resistivity model shows a very electrically resistive crust and upper mantle underneath the Nuyts and Fowler Domain, possibly representing the cratonic root of the Gawler Craton extending to depths of 160 km. The resistive cratonic root is closer to the surface underneath the Fowler Domain compared to the Nuyts Domain which supports findings from outcrops of metasediments of higher metamorphic grade in the Fowler Domain. A subvertical conductor marks the western terminus of the Fowler Domain and is imaged to upper mantle depths. On the eastern side of the Fowler Domain, another subvertical conductor extends to similar depths. These features spatially coincide with the Tallacootra and Coorabie shear zone at the surface, respectively, and their higher conductivity is likely due to a reduction in grain size of olivine associated with an increase in influence of grain boundary diffusion and thus enhanced conductivity. A comparison of the results with other surveys across mobile belts worldwide shows a more resistive response of the interpreted mobile belt of the Fowler Domain raising questions as to the nature of the domain.
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[520]	Thomsen L.1995. Elastic anisotropy due to aligned cracks in porous rock . Geophysical Prospecting, 43: 805-829. DOI      URL      [本文引用: 2]      摘要 All theoretical expressions which relate the characteristics of saturated aligned cracks to the associated elastic anisotropy are restricted in some important way, for example to the case of stiff pore fluids, or of the absence of equant porosity, or of a moderately high frequency band. Because of these restrictions, previous theory is not suitable for application to the upper crust, where the pore fluid is brine (K f K 8 20) , the equant porosity is often substantial ( p > 0.1), and the frequency band is sonic to seismic. This work removes these particular restrictions, recognizing in the process an important mechanism of dispersion. A notable feature of these more general expressions is their insensitivity, at low frequency, to the aspect ratio of the cracks; only the crack density is critical. An important conclusion of this more general model is that many insights previously achieved, concerning the shear-wave splitting due to vertical aligned saturated cracks, are sustained. However, conclusions on crack orientation or crack aspect ratio, which were derived from P-wave data or from shear-wave'critical angles', may need to be reconsidered. Further, the non-linear coupling between pores and cracks, due to pressure equalization effects, means that the (linear) Schoenberg-Muir calculus may not be applied to such systems. The theory receives strong support from recent data by Rathore et al . on artificial samples with controlled crack geometry.
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[529]	Wang H L, Cai Z H, Guo Z L.2009. Lattice Boltzmann simulation of gas transfusion in compact porous media . Chinese Journal of Computational Physics, 26: 389-395. DOI      URL      [本文引用: 1]      摘要 In order to describe microscale flows in compact porous media with lattice Boltzmann method,we extend a model proposed by Guo et al designed for micro gas flows in a single channel to porous medium.The extended model is used to simulate two simplified porous structures.Dependence of permeability on Knudsen number and averaged pressure is studied and analyzed theoretically.Simulated results are consistent with experimental results reported.It shows that the lattice Boltzmann method can serve as a promising tool for simulating gas flows through a compact porous medium.
[530]	Wang H, Li G, Shen Z.2012. A feasibility analysis on shale gas exploitation with supercritical carbon dioxide . Energy Sources Part A: Recovery Utilization & Environmental Effects, 34: 1426-1435. DOI      URL      [本文引用: 1]      摘要 Supercritical CO2 (SC-CO2) fluid has the properties of low viscosity and high diffusion capacity near gas and higher density near liquid, so it showed great vitality at the beginning of its use in drilling technology at the end of the last century. This article analyzes the thermophysical properties of SC-CO2 fluid, and the properties of shale gas and reservoir are analyzed at different aspects of drilling and reservoir formation, while the characteristics of shale gas development are summarized also. Combining the characteristics of SC-CO2 fluid and shale gas reservoir exploitation, the feasibility of shale gas exploitation with SC-CO2 is demonstrated in detail. Meanwhile, the technical and economic superiorities of it are also analyzed. It is believed that the shale gas exploitation with SC-CO2 will achieve great success in economic and technical aspects, and it will provide much more clean energy and make a great contribution to protecting the environment.
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[533]	Wang T, Zhou W, Chen J, Xiao X, Li Y, Zhao X.2014. Simulation of hydraulic fracturing using particle flow method and application in a coal mine . International Journal of Coal Geology, 121: 1-13. DOI      URL      [本文引用: 2]      摘要 61The hydraulic fracturing of a coal seam is simulated.61The connections between different scales are researched.61The empirical formula of breakdown pressure is deduced.61The empirical formula of fracture radius is deduced.
[534]	Wang Y C.2008. Discrete element simulation of hydraulic fracturing and induced seismicity in engineered geothermal systems//Proc . Australian Geothermal Energy Conference. URL      摘要 In this paper the Discrete Element Model (DEM) `ESyS_Particle', previously used to modelfracture of brittle rocks and earthquake processes, is further developed to be able to be applied tothe hydraulic fracturing process in Engineered Geothermal Systems (EGS). The advantage of DEM is that large deformations and dynamic process can be modelled easily. ESyS_Particle has been used to successfully model fracture of brittle rocks and earthquake processes in the past 15 years.Currently it incorporates thermal-hydro-mechanical coupling based on Darcy's Law and Biottheory. A simple simulation of a hydraulic fracture is provided, which reproduces the most basicfeatures of hydraulic fracture. I hope to model induced seismicity in the future.
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[536]	Wangen M.2011. Finite element modeling of hydraulic fracturing on a reservoir scale in 2D . Journal of Petroleum Science and Engineering, 77: 274-285. DOI      URL      摘要 78 A unified finite element formulation for the fracture, the rock and the fluid flow. 78 The fracture criterion is based on bond-strength. 78 The model is validated against 1D and 2D analytical solutions. 78 Case studies: Hydraulic fracturing in homogeneous and inhomogeneous rock.
[537]	Wangen M.2013. Finite element modeling of hydraulic fracturing in 3D . Computational Geosciences, 17: 647-659. DOI      URL      [本文引用: 1]      摘要 A procedure based on the finite element method is suggested for modeling of 3D hydraulic fracturing in the subsurface. The proposed formulation partitions the stress field into the initial stress state and an additional stress state caused by pressure buildup. The additional stress is obtained as a solution of the Biot equations for coupled fluid flow and deformations in the rock. The fluid flow in the fracture is represented on a regular finite element grid by means of "fracture" porosity, which is the volume fraction of the fracture. The use of the fracture porosity allows for a uniform finite element formulation for the fracture and the rock, both with respect to fluid pressure and displacement. It is demonstrated how the fracture aperture is obtained from the displacement field. The model has a fracture criterion by means of a strain limit in each element. It is shown how this criterion scales with the element size. Fracturing becomes an intermittent process, and each event is followed by a pressure drop. A procedure is suggested for the computation of the pressure drop. Two examples of hydraulic fracturing are given, when the pressure buildup is from fluid injection by a well. One case is of a homogeneous rock, and the other case is an inhomogeneous rock. The fracture geometry, well pressure, new fracture area, and elastic energy released in each event are computed. The fracture geometry is three orthogonal fracture planes in the homogeneous case, and it is a branched fracture in the inhomogeneous case.
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[542]	Watanabe N, Wang W, Taron J, Görke U J, Kolditz O.2012. Lower-dimensional interface elements with local enrichment: Application to coupled hydro-mechanical problems in discretely fractured porous media . International Journal for Numerical Methods in Engineering, 90: 1010-1034. DOI      URL      [本文引用: 2]      摘要 In this study, we develop lower-dimensional interface elements to represent preexisting fractures in rock material, focusing on finite element analysis of coupled hydro-mechanical problems in discrete fractures orous media systems. The method adopts local enrichment approximations for a discontinuous displacement and a fracture relative displacement function. Multiple and intersected fractures can be treated with the new scheme. Moreover, the method requires less mesh dependencies for accurate finiteelement approximations compared with the conventional interface element method. In particular, for coupled problems, the method allows for the use of a single mesh for both mechanical and other related processes such as flow and transport. For verification purposes, several numerical examples are examined in detail. Application to a coupled hydro-mechanical problem is demonstrated with fluid injection into a single fracture. The numerical examples prove that the proposed method produces results in strong agreement with reference solutions. Copyright 2012 John Wiley & Sons, Ltd.
[543]	Waters G A, Lewis R E, Bentley D.2011. The effect of mechanical properties anisotropy in the generation of hydraulic fractures in organic shales//SPE Annual Technical Conference and Exhibition. Society of Petroleum Engineers. [本文引用: 1]
[544]	Weber N, Fries T P.2013. The XFEM with an Implicit-Explicit Crack Description for a Plane-Strain Hydraulic Fracture Problem//Proceedings in Applied Mathematics and Mechanics , 13: 83-84. [本文引用: 1]
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[546]	Wei Y J.2008. On micro-cracking, inelastic dilatancy, and the brittle-ductile transition in compact rocks: A micro-mechanical study . International Journal of Solids and Structures, 45: 2785-2798. DOI      URL      [本文引用: 3]      摘要 This work introduces a micro-mechanical grain-aggregate model and numerical simulation capability to study the combined effects of grain-boundary slip and separation, as well as grain-interior plasticity on the overall deformation of compact rocks. Two major conclusions can be drawn from our simulation study: (i) At sufficiently low confining pressures, the widely-observed inelastic dilatant response in compact rocks under compression is attributable to the geometrically-mismatched grain-boundary sliding and concomitant formation of triple-junction cracks which result in an increase in volume. Failure patterns change from splitting-fracture at low confining pressures, to distributed micro-cracking in macroscopic “shear”-bands as the confining pressure increases. (ii) When the confining pressure increases to an amount such that grain-boundary sliding is suppressed due to frictional effects, the inelastic dilatancy effects disappear, and isochoric grain-interior plasticity takes over to accommodate the imposed external deformation, and this is the major cause of the brittle-ductile transition in these materials.
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[548]	White C M, Mungal M G.2008. Mechanics and prediction of turbulent drag reduction with polymer additives . Annual Review of Fluid Mechanics, 40: 235-256. DOI      URL      [本文引用: 1]      摘要 This article provides a review of recent progress in understanding and predicting polymer drag reduction (DR) in turbulent wall-bounded shear flows. The reduction in turbulent friction losses by the dilute addition of high molecular weight polymers to flowing liquids has been extensively studied since the phenomenon was first observed over 60 years ago. Although it has long been reasoned that the dynamical interactions between polymers and turbulence are responsible for DR, it was not until recently that progress had been made to begin to elucidate these interactions in detail. These advancements come largely from numerical simulations of viscoelastic turbulent flows and detailed turbulence measurements in flows of dilute polymer solutions using laser-based optical techniques. This review presents a selective overview of the current state of the numerics and experimental techniques and their impact on understanding the mechanics and prediction of polymer DR. It includes a discussion of areas in which our understanding is incomplete, warranting further study.
[549]	White J E, Mihailova N, Lyakhovitsky F.1975. Low-frequency seismic waves in fluid-saturated layered rocks . The Journal of the Acoustical Society of America, 57: S30. DOI      URL      [本文引用: 3]      摘要 Expressions are derived for speed and attenuation of compressional waves travelling normal to the boundaries of a laminated medium which consists of alternating layers of two fluid﹕aturated porous solids. Fluid flow across boundaries is taken into account through approximate expressions, applicable at low frequencies, derived through extension of the approach used by Gassmann. Calculations show that when one of the saturating fluids is gas, substantial dispersion and extreme attenuation may result.
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[551]	Williams J G, Ewing P D. Fracture under complex stress-the angled crack problem . International Journal of Fracture, 1984, 26: 346-351. DOI      URL      [本文引用: 1]      摘要 Experiments are described in which thin plates of polymethylmethacrylate were fractured with cracks set at various angles to an applied uniaxial stress. While there is substantial agreement with previous analytical predictions, it is shown that inclusion of the stress component parallel to the crack can improve the correlation between linear theory and experiment, using a critical stress at a critical distance interpretation of the stress intensity factor criterion.
[552]	Wu K L, Chen Z X, Li X F, Guo C H, Wei M Z.2016. A model for multiple transport mechanisms through nanopores of shale gas reservoirs with real gas effect--adsorption-mechanic coupling . International Journal of Heat and Mass Transfer, 93: 408-426. DOI      URL      [本文引用: 1]      摘要 Multiple transport mechanisms coexist in nanopores of shale gas reservoirs with complex pore size distribution and different gas-storage processes, including continuum flow, slip flow and transition flow of bulk gas and surface diffusion for adsorbed gas. The force between gas molecules and the volume of the gas molecules themselves cannot be negligible in shale gas reservoirs with high pressure and nanoscale pores, influences gas transport and must be taken into account as a real gas effect. During depressurization development of shale gas reservoirs, the adsorbed gas desorption and a decrease in an adsorption layer influence gas transport. Meanwhile, due to the stress dependence, decreases in intrinsic permeability, porosity and a pore diameter also influence gas transport. In this work, a unified model for gas transport in organic nanopores of shale gas reservoirs is presented, accounting for the effects of coupling the real gas effect, stress dependence and an adsorption layer on gas transport. This unified model is developed by coupling a bulk gas transport model and an adsorbed gas surface diffusion model. The bulk gas transport model is validated with published molecular simulation data, and the adsorbed gas surface diffusion model is validated with published experimental data. The results show that (1) in comparison with the previous models, the bulk gas transport model developed on the basis of a weighted superposition of slip flow and Knudsen diffusion can more reasonably describe bulk gas transport, (2) surface diffusion is an important transport mechanism, and its contribution cannot be negligible and even dominates in nanopores with less than 2 nm in diameter, and (3) the effect of stress dependence on fluid flow in shale gas reservoirs is significantly different from that in conventional gas reservoirs, and is related to not only the shale matrix mechanical properties and the effective stress but also the gas transport mechanisms.
[553]	Wu K L, Chen Z X, Li X F, Xu J Z, Li J, Wang K, Wang H, Wang S H, Dong X H.2017. Flow behavior of gas confined in nanoporous shale at high pressure: Real gas effect . Fuel, 205: 173-183. DOI      URL      [本文引用: 2]
[554]	Wu K L, Chen Z X, Li X F.2015. Real gas transport through nanopores of varying cross-section type and shape in shale gas reservoirs . Chemical Engineering Journal, 281: 813-825. DOI      URL      [本文引用: 1]      摘要 A model for real gas transport in nanopores of shale gas reservoirs (SGRs) was proposed on the basis of the weighted superposition of slip flow and Knudsen diffusion, where the ratios of the intermolecular collisions and the molecule anopore wall collisions to the total collisions are the weighted factors of slip flow and Knudsen diffusion, respectively. The present model takes account of slip effect and real gas effect, additionally, the effects of cross-section type and its shape of nanopores on gas transport are also considered in this paper. The present model is successfully validated against existing molecular simulation data collected from different sources in literature. The results show: (1) the present model is reasonable to describe all of the gas transport mechanisms known, including continuum flow, slip flow and transition flow in nanopores of SGRs; (2) the cross-section type and shape of nanopores both affect gas transport capacity: at the same cross-sectional area, gas transport capacity of nanopores with a circular cross section is greater than that with a rectangular cross section, and gas transport capacity of nanopores with a rectangular cross section decreases with an increasing aspect ratio; compared to the cross-section type, the effect of the cross-section shape on gas transport capacity is stronger; (3) a real gas effect improves gas transport capacity, which becomes more obvious with an increasing pressure and a decreasing pore size; (4) and compared to nanopores with a circular cross section, the effect of real gas effect on gas transport capacity of nanopores with a rectangular cross section is stronger, and the effect increases with an increasing aspect ratio. The proposed model can provide some theoretical support in numerical simulation of reservoir behavior in SGRs.
[555]	Wu K L, Chen Z X, Wang H.2015. A model for real gas transfer in nanopores of shale gas reservoirs//EUROPEC 2015, Madrid, Spain: Society of Petroleum Engineers, 1-14.
[556]	Wu K L, Li X F, Wang C C.2014. Apparent permeability for gas flow in shale reservoirs coupling effects of gas diffusion and desorption . Advanced Materials Research, 3702: 2305-2309. DOI      URL      [本文引用: 1]      摘要 The Cretaceous age Glauconitic sandstone formation is present across a large area of Central Alberta, Canada. The majority of the play involves multi-stage horizontal wells for tight gas exploitation. This case study focuses on channel sand Glauconitic oil pools. These semi-conventional pools were initially exploited with hydraulically fractured vertical wells. The implementation of multi-stage fractured horizontal wells has breathed new life into the play, with much higher production rates, recoveries and better economics. The historical fracturing technique used in the Glauconitic consisted of a gelled hydrocarbon fluid system, due to known reservoir fluid sensitivities to water. The operator had completed a number of multi-stage horizontal wells using this fracture fluid system, and was uncertain if this was the optimum fracture design or fluid system. Production analysis of the existing multi-stage horizontal wells was used to determine how effective the fractures were, as well as drainage areas and estimated ultimate recoveries, etc. The study concluded the gelled hydrocarbon fracture design was not optimal in terms of effective fracture half lengths, or net present value (NPV). A new fracture design was proposed, involving the use of foamed, solids free, viscoelastic surfactant water based fracture fluids, much larger fracture sizes and higher conductivities. This new design was implemented on approximately seven multi-stage fractured horizontal wells (MFHW) during 2013. The new design approach has increased well productivities and enhanced the economics significantly compared to the old design. Other benefits include: much better capital efficiency, better cleanup, accelerated positive cash flow, reduced safety issues and reduced sand flow-back problems. The paper will discuss the initial phase of the optimization process, the early production results, enhanced economics and net present value.
[557]	Wu R, Germanovich L N, Van Dyke P E, Lowell R P.2007. Thermal technique for controlling hydraulic fractures . Journal of Geophysical Research: Solid Earth, 112: 1-15. DOI      URL      [本文引用: 1]      摘要 [1] A simple technique is introduced to control hydraulic fractures in laboratory samples. This is achieved by heating or cooling samples prior to injecting the fracturing liquid, so that the induced thermal stresses govern the fracture orientation. We developed a simple theoretical model to parameterize experiments in laboratory settings and for materials that are different from ours. We also illustrate the utility of the technique with two examples: (1) mixed mode I+III hydraulic fracture propagation and (2) visualization of the fluid flow in the created fracture. In some cases, a similar technique may also be applicable for controlling the orientation of hydraulic fractures in field conditions.
[558]	Xu W, Thiercelin M J, Ganguly U, Weng X, Gu H, Onda H.2010. Wire-mesh: A Novel Shale Fracture Simulator//SPE Papers of the CPS/SPE International Oil and Gas Conference and Exhibition held in Beijing , China, 8-10. [本文引用: 2]
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[562]	Yun M, Yu B, Cai J.2011. A fractal model for the starting pressure gradient for Bingham fluid in porous media embedded with randomly distributed fractal-like tree networks . Advances in Water Resources, 34: 1574-1580. DOI      URL      [本文引用: 2]      摘要 An analytical expression is derived for the starting pressure gradient for Bingham fluids in porous media embedded with randomly distributed fractal-like tree networks based on fractal theory and technique. The proposed model relates the flow rate and the starting pressure gradient to the structural parameters of porous media and microstructural parameters of fractal-like tree networks, the yield stress and fractal dimensions of porous media and maximum mother diameter of randomly distributed fractal-like tree networks. The results show that the starting pressure gradient decreases with the increase of porosity of matrix material, fractal dimension for mother diameters, diameter ratio and permeability, and the starting pressure gradient increases with the increase of the length ratio and the yield stress. The model predictions from the present model for the starting pressure gradient are in good agreement with the available expression.
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[564]	Zeng W, Zhang J, Ding W, Zhao S, Zhang Y, Liu Z, Jiu K.2013. Fracture development in Paleozoic shale of Chongqing area (South China). Part one: Fracture characteristics and comparative analysis of main controlling factors . Journal of Asian Earth Sciences, 75: 251-266. DOI      URL      摘要 Natural macro- and micro-fractures in the Longmaxi shale (Lower Silurian) from Yuye-1 well and the Niutitang shale (Lower Cambrian) from Yuke-1 well are characterized. Regional geological structural evolution and shale geochemistry (including TOC and mineral composition, etc.) are analyzed. The controlling factors of natural fractures in Palaeozoic shale in the southeast of Chongqing have been confirmed, which have been analyzed qualitatively or semi-quantitatively. The results show that fractures are abundant, in both the Longmaxi Shale and Niutitang shale, due to the multiphase strong tectonic movement in the southeast of Chongqing. Therefore, tectonic factors are the principal factors that control fracture development in the Paleozoic shale of this region, followed by the mineral composition of the shale. Vertically, the mineral composition of shale in Yuke-1 well has a high dispersion degree and a strong heterogeneity (the dispersion coefficients of quartz and dolomite were 0.48 and 1, respectively), therefore, the development and distribution of fractures are controlled by quartz and dolomite content in the Niutitang shale, moreover, the quartz content shows positive correlation with the fractures quantity, and fractures are most abundant where dolomite content up to 64.7%. While the mineral composition of shale in Yuye-1 well has a low dispersion degree and a strong homogeneity in a vertical position (the dispersion coefficients of quartz and plagioclase were 0.15 and 0.26, respectively), which shows unconspicuous control effect for fractures, therefore, the development and distribution of fractures are mainly controlled by the TOC content, moreover, the TOC content shows positive correlation with the fractures quantity. Fractures are sealed by calcite, quartz and pyrite. Although sealed fractures do not contribute to the permeability of the reservoir, they are important planes of weakness that tend to be reactivated by hydraulically induced fractures. SEM images show that intergranular pore is connected by microfractures, thereby, the validity of porosity has been improved. The mixed network of microfractures and micropore provide enhanced permeability or storage capacity for the reservoir. (C) 2013 Elsevier Ltd. All rights reserved.
[565]	Zeng X, Wei Y.2016. The influence of crack orientation distribution on the mechanical properties of pre-cracked brittle media . International Journal of Solids and Structures, 96: 64-73. DOI      URL      [本文引用: 4]      摘要 Cracks in kerogen-rich shales and other brittle rock-like materials have a tremendous impact on their elastic properties and strength. In this paper, we investigate the effective mechanical properties of shale plates with pre-existing cracks. We employ the extended finite element method (XFEM) to investigate a pre-cracked medium with an elastic, isotropic and brittle shale matrix. We show how the mechanical properties of the orthotropic shale plates are dependent on the crack density and the standard deviation of crack angles. Both the Young's modulus and the Poisson's ratio of the cracked media exhibit a linear dependence on the standard deviation of crack angles, in contrast to the nonlinear dependence of the strength on the angle deviation. Finally, we propose mechanical models to capture the relationship between the mechanical properties and the distribution characteristics of pre-existing cracks in shales. These phenomenological models could be applied to estimate the fracking behavior of shales in engineering practice.
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[567]	Zhan S, Wang T, Han X.1999. Analysis of two-dimensional finite solids withmicrocracks . International Journal of Solids and Structures, 36: 3735-3753. DOI      URL      [本文引用: 1]      摘要 A general method is presented for solving the plane elasticity problem of finite plates with multiple microcracks. The method directly accounts for the interactions between different microcracks and the effect of outer boundary of a finite plate. Analysis is based on a superposition scheme and series expansions of the complex potentials. By using the traction-free conditions on each crack surface and resultant forces relations along outer boundary, a set of governing equations is formulated. The governing equations are solved numerically on the basis of a boundary collocation procedure. The effective Young's moduli for randomly oriented cracks and parallel cracks are evaluated for rectangular plates with microcracks. The numerical results are compared with those from various micromechanics models and experimental data. These results show that the present method provides a direct and efficient approach to deal with finite solids containing multiple microcracks.
[568]	Zhang H, Liu J, Elsworth D.2008. How sorption-induced matrix deformation affects gas flow in coal seams: A new FE model . Int J Rock Mech Min Sci, 45: 1226-1236. DOI      URL      [本文引用: 1]      摘要 The influence of sorption-induced coal matrix deformation on the evolution of porosity and permeability of fractured coal seams is evaluated, together with its influence on gas recovery rates. The porosity-based model considers factors such as the volume occupied by the free-phase gas, the volume occupied by the adsorbed phase gas, the deformation-induced pore volume change, and the sorption-induced coal pore volume change. More importantly, these factors are quantified under in situ stress conditions. A cubic relation between coal porosity and permeability is introduced to relate the coal storage capability (changing porosity) to the coal transport property (changing permeability). A general porosity and permeability model is then implemented into a coupled gas flow and coal deformation finite element model. The new FE model was used to compare the performance of the new model with that of the Palmer ansoori model. It is found that the Palmer ansoori model may produce significant errors if loading conditions deviate from the assumptions of the uniaxial strain condition and infinite bulk modulus of the grains. The FE model was also applied to quantify the net change in permeability, the gas flow, and the resultant deformation in a coal seam. Model results demonstrate that the evolution of porosity and of permeability is controlled by the competing influences of effective stresses and sorption-based volume changes. The resulting sense of permeability change is controlled by the dominant mechanism.
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