储层页岩直剪破断特性及细观演化机制  

Characteristics of shear fracturing and corresponding evolution mechanism at micro-scale in direct shear tests for reservoir shale

作　　者：刘先珊[1,2] 李涛[1,2] 张立君 潘玉华[1,2] 李满 曾南豆 LIU Xianshan;LI Tao;ZHANG Lijun;PAN Yuhua;LI Man;ZENG Nandou(Key Laboratory of New Technology for Construction of Cities in Mountain Area(Chongqing University),Ministry of Education,Chongqing 400045,China;School of Civil Engineering,Chongqing University,Chongqing 400045,China;Hubei Zhanghe Administration Bureau,Jingmen 448156,China)

机构地区：[1]山地城镇建设与新技术教育部重点实验室(重庆大学),重庆400045 [2]重庆大学土木工程学院,重庆400045 [3]湖北省漳河工程管理局,湖北荆门448156

出　　处：《中国石油大学学报（自然科学版）》2022年第5期141-152,共12页Journal of China University of Petroleum(Edition of Natural Science)

基　　金：国家自然科学基金项目(52279094);广西重点研发计划(桂科AB20238036)。

摘　　要：以露头页岩为研究对象,开展不同层理倾角页岩的直剪试验,研究剪切全过程的4个阶段,同时开展基于颗粒离散元的页岩直剪全过程研究,与试验数据对比验证数值模型的可行性,从细观角度分析直剪全过程的能量演化规律,提出各向异性特征表征方法,并通过全过程的声发射变化解释细观裂缝的演化机制,阐明裂缝扩展与细观能量演化机制的一致性,研究不同时刻的层理页岩裂缝扩展规律及力链图,与对应层理倾角页岩的破坏模式进行对比,进一步探讨90°层理页岩剪切破断的裂缝特征,揭示不同层理页岩直剪全过程的裂缝演化机制。结果表明:法向应力增大能更大程度地抑制层理开裂,而剪切速率增大能更快速地达到峰值强度但降低抗剪强度;不同层理倾角页岩的破坏模式各异,0°沿层理面剪切滑移破坏,30°层理开裂为沿层理的雁列状裂缝,60°剪切破裂面呈曲线型。The outcrop shale was taken as a case study,and the direct shear tests with different bedding planes were conducted to describe the four stages during the full process of shearing.Furthermore,numerical simulations based on the particle flow code(PFC)were conducted to describe the shearing process and calibrated by the testing data to prove its feasibility.The energy evolution of the shales in direct shear tests were analyzed from the viewpoint of micro-scale,and the corresponding anisotropy characterization method was proposed.In addition,the mechanism of micro-crack evolution was explained based on the acoustic emission method,showing the agreement between the crack propagation and the energy evolution at the micro-scale.In the meantime,the crack propagation and force chain at different time were deeply investigated for shales with different bedding angles.By comparing with the failure mode of shales with corresponding bedding angles,the shearing and fracturing of the shale with the bedding angle being 90°was deeply discussed,revealing the propagation mechanism of shales with different bedding angles.The results show that increasing the normal stress can further restrain the bedding cracking,however,increasing the shearing speed can accelerate the peak strength but decrease the shearing strength.In addition,the crack modes are distinct for shales with different bedding planes.It can be observed that the bedding angle 0°corresponds to shearing and sliding failure along the bedding plane,the bedding angle 30°corresponds to en-echelon fractures along the bedding planes,and the bedding angle 60°corresponds to the crack surface being curved.

关 键 词：储层页岩 层理 直剪试验 颗粒离散元 各向异性 细观裂缝 

分 类 号：TU45[建筑科学—岩土工程]