压裂的孔隙压力梯度作用机制与扰动应力致裂效应研究.pdf

博士学位论文 压裂的孔隙压力梯度作用机制与扰动应力致裂效应研究 The Mechanism of Pore Pressure Gradient Effect and the Fracturing Effect Induced by Disturbing Stress during Hydrofracturing 作 者赵兴龙 导 师黄炳香 教 授 中国矿业大学 二Ο一九年六月 国家优秀青年科学基金项目（51522406）资助 国家自然科学基金面上项目（51774272）资助 学位论文使用授权声明 学位论文使用授权声明 本人完全了解中国矿业大学有关保留、使用学位论文的规定，同意本人所撰 写的学位论文的使用授权按照学校的管理规定处理 作为申请学位的条件之一， 学位论文著作权拥有者须授权所在学校拥有学位 论文的部分使用权，即①学校档案馆和图书馆有权保留学位论文的纸质版和电 子版，可以使用影印、缩印或扫描等复制手段保存和汇编学位论文；②为教学和 科研目的，学校档案馆和图书馆可以将公开的学位论文作为资料在档案馆、图书 馆等场所或在校园网上供校内师生阅读、浏览。另外，根据有关法规，同意中国 国家图书馆保存研究生学位论文。 （保密的学位论文在解密后适用本授权书） 。 作者签名 导师签名 年 月 日 年 月 日 中图分类号 TD8 学校代码 10290 UDC 622 密 级 公开 中国矿业大学 博士学位论文 压裂的孔隙压力梯度作用机制与扰动应力致裂效应研究 The Mechanism of Pore Pressure Gradient Effect and the Fracturing Effect Induced by Disturbing Stress during Hydrofracturing 作 者 赵兴龙 导 师 黄炳香 申请学位 工学博士 培养单位 矿业工程学院 学科专业 采矿工程 研究方向 煤岩体压裂 答辩委员会主席 曹胜根 评 阅 人 盲 审 二○一九年六月 国家优秀青年科学基金项目（51522406）资助 国家自然科学基金面上项目（51774272）资助 致致 谢谢 本论文是在导师黄炳香教授的悉心指导和严格要求下完成的， 没有导师的指 导、鼓励及经费上的大力支持，论文是不可能得以顺利完成的。师从多载，收获 颇丰。感谢导师将我纳入门下，悉心栽培，带我走上科研这条道路。黄老师广博 的专业知识、活跃的学术思想、严谨的治学态度、务实的工作作风、掌控全局的 能力、富有远见的卓识、忘我的工作精神及谦和的为人风范给学生树立起潜移默 化的典范作用，是我人生当中的一笔宝贵财富，将永远激励我在今后的人生道路 上不断进取。值此拙文完成之际，谨向我的导师致以最崇高的敬意和最衷心的感 谢同时感谢师母程庆迎老师在生活上给予的关怀和帮助 感谢外导英属哥伦比亚大学 Malcolm Scoble 教授和多伦多大学 Giovanni Grasselli 教授在我博士联合培养期间给予的指导和帮助 感谢课题组陈树亮老师、 卢卫永博士、 蔡青旺博士、 李浩泽博士、 徐杰硕士、 王常委硕士、张新硕士、邵鲁英硕士、赵龙硕士、陈斌硕士、金峰硕士、张昕硕 士、李丁硕士在物理模拟实验及现场试验方面给予的帮助 感谢多大联培期间课题组王玙硕士、 Earl Magsipoc 硕士、 Yusheng Qiu 硕士、 Aly Abdelaziz 博士、Johnson Ha 硕士在数值模拟和 CT 扫描方面给与的帮助 求学二十余载，特别感谢父母和家人一直以来对我的理解、支持和鼓励。在 外求学已有九年，不能陪伴在父母左右，心中十分愧疚 感谢女友李雯在我撰写博士论文期间给予我默默地支持、鼓励和体谅，在我 到国外进行博士联合培养期间依旧不离不弃。两年时间聚少离多，十分愧疚 感谢攻博期间曾给予我帮助的老师、同学和朋友 最后，感谢在百忙之中评审本论文和参加答辩的各位专家，期待得到您的指 正和赐教 赵兴龙 2019 年 5 月 I 摘摘 要要 高瓦斯煤层的水力致裂实践及前期原理性实验研究表明 水力致裂的破裂压 力可能随着孔隙压力（梯度）的增大而增大，传统的水力致裂理论无法解释该现 象。 本文以压裂的孔隙压力梯度作用机制为切入点， 采用实验室实验、 理论分析、 数值模拟相结合的方法，较为系统的研究了压裂的孔隙压力及其梯度作用规律、 考虑孔隙压力及其梯度作用的岩石压裂细观破裂机制、 压裂的围岩应力扰动规律、 及压裂的扰动应力致裂效应，取得了以下主要创新性成果 （1）开展了初始均匀孔隙压力作用下的岩石水力致裂实验。实验结果表明 随着初始孔隙压力的增大，水力致裂的破裂压力线性增大。孔壁破裂瞬间声发射 能量也相应增大，相同泵注时间内裂缝的扩展范围和张开度也越大。 （2）开展了孔隙压力梯度作用下的岩石水力致裂实验。实验结果表明孔隙 压力梯度越大，由试样内部孔隙结构变形不协调导致开裂瞬间破裂范围越大，破 裂后的压力降也越大。相同泵注排量致裂相同时间时，初始孔隙压力梯度越大， 水压裂缝的张开度越大。 （3）建立了考虑孔隙压力及其梯度作用的岩石压裂细观破裂准则。岩石在 细观上是由颗粒和孔隙组成的，基于岩石的细观结构，对岩石压裂过程进行了细 观力学分析，建立了考虑孔隙压力及其梯度作用的岩石压裂细观破裂准则，并根 据实验结果对该破裂准则的合理性进行了验证。 （4）水力致裂引起了围岩应力发生变化，即水力致裂的应力扰动效应。水 力致裂的应力扰动包括孔隙压力扰动和骨架应力扰动两个方面。 随着水压裂缝的 扩展， 水压裂缝前沿及两侧的孔隙压力和骨架应力随泵注压力的波动而同步波动， 且距离水压裂缝越近波动越明显。 （5）水压裂缝尖端前沿及两侧的孔隙压力和骨架应力分布均遵循指数衰减 规律，随着泵注排量的增大，衰减速率逐渐减小。相同泵注排量下水压裂缝扩展 过程中裂缝两侧的孔隙压力衰减速率小于裂缝尖端前沿，因此，水压裂缝两侧的 渗透区范围大于水压裂缝尖端的渗透区范围。 （6）孔隙压力升高的地方骨架应力也相应升高，并且均沿着远离裂缝的方 向逐渐以指数规律衰减。骨架应力衰减速率小于孔隙压力的衰减速率，水压裂缝 尖端前沿及两侧的骨架应力扰动区范围大于孔隙压力扰动区（渗透区）范围。水 压裂缝两侧孔隙压力与骨架应力之间的变化关系符合自然对数衰减关系。 （7）压裂引起的应力扰动效应，既有有利的一面，也有不利的一面。在工 程施工中，应根据具体的工程背景，基于应力扰动的评价，采取相应的措施，做 到趋利避害。提出了基于应力梯度和应力增速的应力扰动评价方法，分别评价应 II 力扰动在时间和空间上的变化程度大小。 （8）当水压裂缝尖端前沿或两侧存在天然裂缝等弱结构时，压裂产生的扰 动应力会使天然裂缝面的剪应力增大，当剪应力达到天然裂缝的抗剪强度时，压 裂的扰动应力诱导天然裂缝发生剪切破坏，即压裂的扰动应力致裂效应。 该论文有图 121 幅，表 12 个，参考文献 150 篇。 关键词关键词压裂；初始孔隙压力；孔隙压力梯度；细观破裂；应力扰动；扰动 应力致裂 III Abstract The application of hydraulic fracturing in the gassy coal seam and preliminary principle experiment show that the breakdown pressure of hydraulic fracturing may increases with the increase of initial pore pressure, which cannot be explained by the traditional hydrofracturing theory. In this study, the mechanism of the pore pressure gradient effect of hydrofracturing was taken as the entry point, the laboratory experiment, theoretical analysis, and numerical simulation s were adopted to systematically study the effect of initial pore pressure and its gradient on hydraulic fracturing, the mesoscopic fracturing mechanism of rock hydrofracturing, the stress disturbance induced by hydrofracturing, and the fracturing effect induced by disturbing stress of hydrofracturing. The main innovative results are summarized as follows. 1 The rock hydraulic fracturing experiment under different initial unily distributed pore pressure was pered. The experimental results indicated that with the increase of initial pore pressure, the breakdown pressure of hydraulic fracturing increases linearly, and the acoustic emission energy increases correspondingly at the moment of fracture initiation. The propagation range and opening degree of hydraulic fractures are also larger in the same pumping time. 2 The rock hydraulic fracturing experiment under different initial pore pressure gradient was pered. The experimental results indicated that the larger the pore pressure gradient is, the larger the deation of the internal pore structure is, and the greater the pressure drop after the fracture initiation. When fracturing by the same pumping rate for the same time, the larger the initial pore pressure gradient, the greater the opening degree of the hydraulic fracture. 3 A mesoscopic fracture criterion for rock hydrofracturing considering pore pressure and its gradient was established. The rock is composed of particles and pores on the mesoscopic scale. Based on the mesostructure of the rock, the meso- mechanical analysis of the rock hydrofracturing process was carried out, and the mesoscopic fracture criterion for rock hydrofracturing considering pore pressure and its gradient was established. According to the experimental results, the reasonability of the fracture criterion was verified. 4 Hydraulic fracturing causes a change in the stress of the surrounding rock, that is, the stress disturbance effect of hydraulic fracturing. The stress disturbance IV effect of hydraulic fracturing includes pore pressure disturbance and matrix stress disturbance. With the hydraulic fracture propagation, the pore pressure and matrix stress at the front and sides of the hydraulic fractures fluctuate synchronously with the fluctuation of the pumping pressure, and the closer to the hydraulic fractures, the more obvious the fluctuation. 5 The pore pressure and matrix stress distribution at the front of fracture tips and both sides of the hydraulic fracture follow the exponential decay law. As the pumping rate increases, the decay rate decreases. The pore pressure decay rate on both sides of the fracture during the hydraulic fracture propagation is smaller than the front of the fracture tip under the same pumping rate. Therefore, the penetration range on both sides of the hydraulic fracture is larger than the penetration range at the front of the fracture tip. 6 The matrix stress at the point where the pore pressure increases also increased correspondingly and both gradually decay exponentially along the direction away from the fracture. The matrix stress decay rate is less than the pore pressure, therefore the range of the matrix stress disturbance zone around the hydraulic fracture is larger than the pore pressure disturbance zone permeate zone. The relationship between the pore pressure and the matrix stress on both sides of the hydraulic fracture follow the natural logarithmic decay. 7 The stress disturbance effect caused by hydrofracturing has both advantages and disadvantages. In the engineering construction, according to the specific engineering background, based on the uation of stress disturbance, take corresponding measures to achieve profit and avoid disadvantages. A stress disturbance uation based on stress gradient and stress growth rate is proposed to uate the stress disturbance in time and space. 8 When there is a weak structure such as natural fractures on the front or both sides of the hydraulic fracture, the disturbing stress generated by the hydrofracturing will increase the shear stress of the natural fractures. When the shear stress reaches the shear strength of the natural fractures, the disturbing stress of hydrofracturing can induce shear failure of natural fractures, that is, the fracturing effect induced by disturbing stress during hydrofracturing. There are 121 figures, 12 tables and 150 references in this study. Keywords Hydrofracturing; initial pore pressure; pore pressure gradient; mesoscopic fracturing mechanism; fracturing induced by disturbing stress V 目目 录录 致致 谢谢............................................................................................................................ 1 摘摘 要要 ........................................................................................................................... I 目目 录录 .......................................................................................................................... V 图清单图清单 ........................................................................................................................ IX 表清单表清单 .................................................................................................................... XVII 1 绪绪 论论 ....................................................................................................................... 1 1.1 研究背景及意义 .................................................................................................... 1 1.2 研究现状与发展趋势 ............................................................................................ 2 1.3 研究内容与研究方法 ............................................................................................ 8 1.4 主要创新点 .......................................................................................................... 10 2 初始均匀孔隙压力对岩石水力致裂的影响研究初始均匀孔隙压力对岩石水力致裂的影响研究 ................................................. 12 2.1 实验原理 .............................................................................................................. 12 2.2 物理模型实验 ...................................................................................................... 13 2.3 初始均匀孔隙压力对裂缝起裂的影响 .............................................................. 17 2.4 初始均匀孔隙压力作用下的水压裂缝扩展形态 .............................................. 21 2.5 实验结果与经典模型的对比分析 ...................................................................... 23 2.6 岩石水力致裂的孔隙压力作用机制 .................................................................. 24 2.7 小 结 .................................................................................................................. 24 3 孔隙压力梯度对岩石水力致裂的影响研究孔隙压力梯度对岩石水力致裂的影响研究 ......................................................... 26 3.1 实验原理 .............................................................................................................. 26 3.2 物理模型实验 ...................................................................................................... 27 3.3 孔隙压力梯度对裂缝起裂的影响 ...................................................................... 31 3.4 孔隙压力梯度对裂缝扩展的影响 ...................................................................... 36 3.5 致裂过程中上下端渗透压的变化规律 .............................................................. 38 3.6 小 结 .................................................................................................................. 39 4 考虑孔隙压力及其梯度作用的岩石压裂细观破裂机理考虑孔隙压力及其梯度作用的岩石压裂细观破裂机理 ..................................... 40 4.1 典型岩石细观结构模型的构建 .......................................................................... 40 4.2 岩石水力致裂过程的渗流现象 .......................................................................... 41 4.3 岩石压裂过程的细观力学模型 .......................................................................... 42 VI 4.4 岩石压裂的细观破裂准则 .................................................................................. 46 4.5 细观破裂准则的验证与分析 .............................................................................. 48 4.6 小 结 .................................................................................................................. 49 5 水力致裂的围岩应力扰动规律研究水力致裂的围岩应力扰动规律研究 ..................................................................... 51 5.1 物理模型实验方案 .............................................................................................. 51 5.2 水压裂缝扩展过程及裂缝形态 .......................................................................... 58 5.3 水压裂缝扩展过程中的孔隙压力和骨架应力演化规律 .................................. 61 5.4 水压裂缝扩展过程中的孔隙压力和骨架应力分布规律 .................................. 76 5.5 水压裂缝扩展过程中的孔隙压力与骨架应力相互作用规律 .......................... 78 5.6 水力致裂的应力扰动评价 .................................................................................. 85 5.7 小 结 ................................................................................................................ 101 6 压裂的扰动应力致裂效应研究压裂的扰动应力致裂效应研究 ........................................................................... 103 6.1 FDEM 数值计算原理 ......................................................................................... 103 6.2 FDEM 数值模型设计 ......................................................................................... 106 6.3 水压裂缝前沿扰动应力诱导天然裂缝张开扩展 ............................................ 109 6.4 水压裂缝两侧扰动应力诱导天然裂缝剪切破坏 ............................................ 118 6.5 小 结 ................................................................................................................ 119 7 结论与展望结论与展望 ........................................................................................................... 121 7.1 主要结论 ............................................................................................................ 121 7.2 研究展望 ............................................................................................................ 123 参考文献参考文献 ................................................................................................................... 125 作者简历作者简历 ................................................................................................................... 135 学位论文原创性声明学位论文原创性声明 ............................................................................................... 139 学位论文数据集学位论文数据集 ....................................................................................................... 140 VII Contents Abstract ...................................................................................................................... III Contents .................................................................................................................... VII List of Figures ............................................................................................................ IX List of Tables .......................................................................................................... XVII 1 Introduction ............................................................................................................... 1 1.1 Research Background and Significance .................................................................. 1 1.2 Literature Review ..................................................................................................