岩石定向起裂水压裂缝的转向扩展模型研究.pdf

国家自然科学基金项目（51274149）资助 国家优秀青年科学基金项目（51522406）资助 硕士学位论文 岩石定向起裂水压裂缝的转向扩展模型研究 Reorientation Model for Hydraulic Fracture after Directional Initiation in Rock 作 者张佳兴 导 师黄炳香 教授 中国矿业大学 二〇一七年五月 中图分类号 TD8 学校代码 10290 UDC 622 密 级 公开 国家自然科学基金项目（51274149）资助 国家优秀青年科学基金项目（51522406）资助 中国矿业大学 硕士学位论文 岩石定向起裂水压裂缝的转向扩展模型研究 Reorientation Model for Hydraulic Fracture after Directional Initiation in Rock 作 者 张佳兴 导 师 黄炳香 申请学位 工学硕士 培养单位 矿业工程学院 学科专业 采矿工程 研究方向 岩体力学与岩层控制 答辩委员会主席 谢耀社 评 阅 人 盲审 二○一七年五月 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 致 谢 致 谢 时光荏苒，亦如白驹过隙，转眼间研究生三年的时光即将结束，毕业近在眼 前。回首往昔，我已在矿大度过了七年的时光，在这里我播撒过汗水与青春，我 对这片热土亦爱的深沉。值此毕业之际，谨向我的母校致以我最崇高的敬意，向 求学路上所有给予过我帮助和曾经伴我前行的人致以最诚挚的感谢和最美好的 祝愿 首先，我要深深感谢我的导师黄炳香教授。本论文是在导师的悉心指导下完 成的，倾注了导师大量的心血与汗水。感谢导师三年来对我论文的悉心指导，以 及对我学术道路上的帮助和指引。相识于 2011 年，初次见面便被导师儒雅的气 质、敏锐的洞察力以及长远的眼光所深深折服。师生六载，科研上，手把手教我 科研的方法与精神；生活上，用实际行动教给我许多做人做事的道理。感谢多年 来导师对我科研上的启蒙，对我生活上的关心和照顾。导师高尚的品格以及伟大 的学术精神，是我不断学习的榜样，也是我一生中宝贵的精神财富。在此，再次 向导师表达我深深的感谢与祝福 感谢刘江伟师兄、卢卫永博士、赵兴龙博士对我论文思路和细节上的无私指 导和帮助，在自己担负着繁重科研任务的同时，仍对我的硕士论文给予大量的关 心和帮助，并提出宝贵的意见和建议 感谢杨帆硕士在硕士学习期间的相互帮助、鼓励和支持。感谢课题组师弟田 泽础、张权、徐杰、张新、王常委在数值模拟、物理实验以及声发射方面的无私 帮助 感谢国家自然科学基金委对本论文的资助 感谢我的父母， 在我多年的求学生涯中给予我无微不至的关怀以及精神上和 经济上的支持 感谢所有曾给予过我帮助的老师、同学和朋友 感谢百忙之中评审论文的各位专家、学者 张佳兴 2017 年 5 月 10 日 I 摘 要 摘 要 煤矿中的坚硬厚煤层综放开采、坚硬顶板控制、冲击矿压、低渗透性煤层瓦 斯抽采、煤与瓦斯突出等问题一直以来严重影响着矿井的安全生产。煤岩体定向 水力致裂技术是解决这些问题的有效措施之一。 水压裂缝的扩展是水力致裂的重 要研究内容。本文采用物理实验、理论分析、数值模拟等方法对定向起裂后水压 裂缝的转向扩展问题进行了研究。 应用大尺寸真三轴水力致裂实验系统以及 RFPA3D-Flow 数值模拟软件进行 了定向水力致裂水压裂缝的转向扩展基本规律研究。结果表明在定向水力致裂 过程中，水压裂缝一般能够沿预割缝边缘起裂，但是起裂方向往往与预割缝所在 的平面有一定的夹角。水压裂缝沿预割缝边缘起裂后，其扩展方向会慢慢朝着最 大主应力 1 σ所在的方向旋转， 最终旋转到与最大主应力平行的方向， 之后其扩展 方向基本保持不变。 水压裂缝转向扩展的快慢与距离决定了定向水力致裂水压裂 缝的有效扩展范围，进而影响煤岩体结构定向改造的效果。 基于水压裂缝转向扩展基本规律的物理实验和数值模拟研究， 采用最大拉应 力准则，提出了水压裂缝转向扩展的宏、细观概念模型，建立了水压裂缝转向扩 展的力学模型。水压裂缝的转向扩展可以看作是以下过程在裂缝尖端局部应力 场的作用下，裂缝前沿周围会产生拉应力。在裂缝前沿不同的方位，拉应力的大 小不同，拉应力在某一特定的方位达到最大值，该最大拉应力所在的方位即微裂 纹产生和扩展的方位，也就是宏观水压裂缝下一步的扩展方向。分析得出，裂缝 的转向扩展受到缝尖水压力、主应力差、水压裂缝方位角等因素的影响。 选择了预割缝长度、主应力差、致裂排量以及预割缝数目四个因素进行物理 实验和数值模拟，研究了它们对水压裂缝转向扩展结果的影响。在单割缝定向水 力致裂中， 主应力差对水压裂缝的起裂和转向的影响程度最大， 预割缝深度次之， 致裂排量的影响程度最小。在多割缝定向水力致裂中，沿不同预割缝边缘起裂的 转向裂缝之间没有相互贯通， 而是沿相反的方向朝最大主应力的方向进行旋转， 转向扩展过程相对独立， 与单割缝定向水力致裂中转向裂缝的扩展规律基本一致。 在定向水力致裂的现场应用中， 应根据工程问题的具体特征， 合理设计钻孔方位、 间距、预割缝深度、数目以及致裂工艺参数，从而使定向水力致裂的效果能最大 程度满足工程需要。 本论文有图 63 幅，表 6 个，参考文献 90 篇。 关键词关键词水压裂缝；转向扩展；力学模型；影响因素 II Abstract Fully mechanized top coal caving with hard thick coal seam, the control of hard roof, gas extraction in coal seam with low permeability and coal and gas outburst are issues threating the safety mining at present. Directional hydraulic fracturing is an effective way to solve the above problems. In directional hydraulic fracturing, the propagation of hydraulic fracture is an important issue to be investigated. In this thesis, the reorientation law of hydraulic fracture after initiating from the prefabricated slot is studied by laboratory experiments, numerical simulation and theoretical analysis. Laboratory experiments are pered by large-size true triaxial hydraulic fracturing experimental system and numerical simulation with RFPA3D-Flow software are carried out to study the reorientation law of hydraulic fractures. The results show that in directional hydraulic fracturing, hydraulic fractures usually initiate along the edge of the prefabricated slot. However, the angle between the initiated hydraulic fracture and the prefabricated slot is not 0. During the propagation of hydraulic fracture, the propagation direction will gradually turn towards the direction parallel to the maximum principal stress. When the propagation direction of hydraulic fractures have been parallel to the maximum principal stress, it will not change anymore. The reorientation speed and distance has great impact on the effective propagation range of hydraulic fracture and the transation of coal and rock mass. Based on the laboratory experiments and numerical simulation, macro and micro conceptual models for the reorientation of hydraulic fracture tip are proposed. Then, a mechanical model for hydraulic fracture reorientation is established on the basis of Maximum Tensile-Stress Criterion. The reorientation process of hydraulic fracture can be regarded as follows under the effect of local stress field, tensile stress will occur around the hydraulic fracture tip. The magnitude of tensile stress changes with the direction around the hydraulic fracture tip. The tensile stress will reaches the maximum at a certain direction around the hydraulic fracture tip, which is the reorientation direction for hydraulic fracture. The mechanical model shows that the reorientation of hydraulic fracture is affected by the fracture water pressure, the differences of principal stresses and the initial azimuth angle of the hydraulic fracture. Physical experiments and numerical simulation are carried out to study the influence of the length of the prefabricated slot, the differences of principal stresses, the III water injection rate and the number of prefabricated slot on hydraulic fracture reorientation. In directional hydraulic fracturing with one prefabricated slot, the differences of principal stresses has the greatest impact on the hydraulic fracture reorientation among the three factors, while the influence of the water injection rate on hydraulic fracture reorientation is the least important. If two prefabricated slot exist, the reoriented hydraulic fractures initiated from different prefabricated slots are not connected. The reorientation processes of hydraulic fractures initiating along different prefabricated slot are relative independent. In field application of directional hydraulic fracturing, characteristics of the engineering problem must be taken into consideration. The location, dip angle and spacing of borehole, the length and number of the prefabricated slot and other technological parameters should be determined reasonably to achieve the best effect. There are 63 figures, 6 tables and 90 references in this thesis. Keywords hydraulic fracture; reorientation; mechanical model; influencing factors IV 目 录 目 录 摘摘 要要 ........................................................................................................................... I 目目 录录 ........................................................................................................................ IV 图清单图清单 ........................................................................................................................ VI 表清单表清单 .......................................................................................................................... X 1 绪论绪论 ........................................................................................................................... 1 1.1 问题的提出 ............................................................................................................. 1 1.2 研究现状及发展趋势 ............................................................................................. 2 1.3 本文的研究内容和研究路线 ................................................................................. 7 2 水压裂缝的转向扩展基本规律研究水压裂缝的转向扩展基本规律研究 ....................................................................... 9 2.1 物理模拟实验研究 ................................................................................................. 9 2.2 数值模拟研究 ....................................................................................................... 24 2.3 本章小结 ............................................................................................................... 28 3 水压裂缝的转向扩展模型水压裂缝的转向扩展模型 ..................................................................................... 30 3.1 水压裂缝的转向扩展概念模型 ........................................................................... 30 3.2 力学模型的建立 ................................................................................................... 34 3.3 本章小结 ............................................................................................................... 39 4 水压裂缝的转向扩展影响因素分析水压裂缝的转向扩展影响因素分析 ..................................................................... 41 4.1 定向预割缝长度 ................................................................................................... 41 4.2 主应力差 ............................................................................................................... 46 4.3 致裂排量 ............................................................................................................... 51 4.4 预割缝数目 ........................................................................................................... 52 4.5 本章小结 ............................................................................................................... 55 5 主要结论主要结论 ................................................................................................................. 57 参考文献参考文献 ..................................................................................................................... 59 作者简历作者简历 ..................................................................................................................... 65 学位论文原创性声明学位论文原创性声明 ................................................................................................. 66 学位论文数据集学位论文数据集 ......................................................................................................... 67 V Contents Abstract ........................................................................................................................ II Contents ....................................................................................................................... V List of Figures ............................................................................................................ VI List of Tables ................................................................................................................ X 1 Introduction ............................................................................................................... 1 1.1 Problem Description ................................................................................................ 1 1.2 Research Situation and Development ...................................................................... 2 1.3 Research Contents and s .............................................................................. 7 2 Basic Reorientation Law of Hydraulic Fractures .................................................. 9 2.1 Physical Simulation Experiments ............................................................................ 9 2.2 Numerical Simulation ............................................................................................ 24 2.3 Brief Summary ....................................................................................................... 28 3 Reorientation Model for Hydraulic Fracture in Directional Hydraulic Fracturing ................................................................................................................... 30 3.1 Conceptual Models for Reorientation of Hydraulic Fracture ................................ 30 3.2 Establishment of the Mechanical Model ................................................................ 34 3.3 Brief Summary ....................................................................................................... 39 4 Analysis of Affecting Factors of Hydraulic Fracture Reorientation .................. 41 4.1 The Length of the Prefabricated Slot ..................................................................... 41 4.2 Differences of Principal Stresses ........................................................................... 46 4.3 Water Injection Rate ............................................................................................... 51 4.4 The Number of Prefabricated Slot ......................................................................... 52 4.5 Brief Summary ....................................................................................................... 55 5 Main Conclusions .................................................................................................... 57 References ................................................................................................................... 59 Author Resume .......................................................................................................... 65 Declaration of Thesis Originality ............................................................................. 66 Thesis Date Collection ............................................................................................... 67 VI 图清单 图清单 List of Figures 图序号 图名称 页码 图 1-1 技术路线图 8 Figure 1-1 Technology road map 8 图 2-1 大尺寸真三轴水力致裂实验系统 9 Figure 2-1 True triaxial hydraulic fracturing experimental system 9 图 2-2 弯曲封孔器 10 Figure 2-2 Bending hole packer 10 图 2-3 模拟预割缝圆盘 11 Figure 2-3 Discs to simulate prefabricated slot 11 图 2-4 带有预割缝圆盘的封孔器 11 Figure 2-4 Hole packer with prefabricated slot 11 图 2-5 定向预割缝试块效果图 12 Figure 2-5 Schematic diagram of test block with prefabricated slot 12 图 2-6 试块放入真三轴加载框架内效果图 12 Figure 2-6 Test block placed in the experiment system 12 图 2-7 试块 C-1 的实验过程 13 Figure 2-7 Experimental process of test block C-1 13 图 2-8 试块 C-1 水压力和注水量曲线 13 Figure 2-8 Curves of water pressure and injected water volume against time of test block C-1 13 图 2-9 试块 C-1 水压力和声发射事件数曲线 14 Figure 2-9 Curves of water pressure and events number against time of test block C-1 14 图 2-10 试块 C-1 水压力和声发射能量曲线 14 Figure 2-10 Curves of water pressure and AE energy of test block C-1 14 图 2-11 试块 C-1 水压力与声发射幅值曲线 14 Figure 2-11 Curves of water pressure and AE amplitude against time of test block C-1 14 图 2-12 试块 C-1 致裂后上表面 15 Figure 2-12 Upper surface of test block C-1 after hydraulic fracturing 15 图 2-13 试块 C-1 致裂后侧面 15 Figure 2-13 Side surfaces of test block C-1 15 图 2-14 水压裂缝将试块分成 I、II 两部分 16 Figure 2-14 The test block is divided into two parts 16 图 2-15 剖开的试块 C-1 16 Figure 2-15 The splitted test block C-1 16 图 2-16 沿预割缝定向起裂后水压裂缝扩展的空间形态 17 Figure 2-16 Morphology of hydraulic fracture initiated along the edge of the slot 17 图 2-17 裂缝转向角度示意图 18 VII Figure 2-17 Schematic diagram for orientation angle of hydraulic fracture 18 图 2-18 局部放大的裂缝扩展转向效果图 18 Figure 2-18 Magnified local morphology of orientation of hydraulic