不同层理页岩常规三轴压缩力学特性离散元模拟  

Discrete element simulation of the mechanical properties of shale with different bedding inclinations under conventional triaxial compression

作　　者：杨圣奇[1,2] 孙博文 田文岭 YANG Sheng-qi;SUN Bo-wen;TIAN Wen-ling(China State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology,Xuzhou 221116,China;School of Mechanics and Civil Engineering,China University of Mining and Technology,Xuzhou 221116,China)

机构地区：[1]中国矿业大学深部岩土力学与地下工程国家重点实验室,徐州221116 [2]中国矿业大学力学与土木工程学院,徐州221116

出　　处：《工程科学学报》2022年第3期430-439,共10页Chinese Journal of Engineering

基　　金：国家自然科学基金资助项目(42077231)。

摘　　要：页岩作为页岩气储层,在沉积过程中形成部分弱面,在力学特性上表现出各向异性特征.所以,使用离散元软件从微细观层面探讨深部页岩力学各向异性特征具有重要实践意义.基于页岩室内常规三轴压缩试验结果,采用离元程序PFC2D对常规三轴压缩下不同层理倾角页岩进行了颗粒流模拟研究,分析了层理倾角及围压对页岩力学特性的影响规律.结果表明:(1)页岩峰值强度与黏聚力随层理倾角的增加整体呈“U”形变化,但峰值强度在不同围压下的变化趋势有所区别;而内摩擦角随层理倾角的增大呈非线性变化.(2)层理倾角对页岩周围颗粒的位移方向及大小的影响随着层理面与轴向应力的夹角的增大而减小.(3)同一层理倾角试样最终破坏时的微裂纹总数随着围压的升高有所增加;同一围压下,试样最终破坏时的微裂纹数目,随着层理倾角的增加呈现先减少后增多的趋势.(4)同一层理倾角页岩的脆性随围压的增长整体呈下降趋势;低围压情况下,页岩脆性随层理倾角的增加呈两端大中间小的变化规律.With the growth in energy demand,shale gas has attracted considerable attention as an unconventional clean and efficient energy source.In addition,the recoverable reserves of deep shale gas in China far exceed those with a depth less than 3500 m.Thus,deep shale gas is an important replacement field for shale gas production in China.Shale,as a shale gas reservoir,forms many weak surfaces in the deposition process and shows different degrees of anisotropy in the mechanical properties.Therefore,it is of great importance to use particle flow code(PFC)to explore anisotropy of shale from the perspective of micro-level for deep shale gas production in China.Based on the experimental results obtained from the shale specimens under conventional triaxial compression,PFC2D was used to simulate the triaxial mechanical properties of shale with different bedding inclinations.The effects of bedding inclination and confining pressure on the mechanical properties of shale specimens were analyzed.The following results are obtained.(1)With the increase of bedding inclination,the peak strength and cohesion of shale all display a"U"-type variation,but the trend of peak strength is different under different confining pressures and the internal friction angle varied nonlinearly with the bedding inclination increases.(2)The effects of bedding inclinations on the displacement direction and size of surrounding particles decrease with the increase of the angle between the bedding inclination and axial stress.(3)At constant bedding inclination,the number of microcracks at the final failure of the specimen increases with the increase of confining pressure.Under the same confining pressure,the number of microcracks in the final failure of the specimen first decreases and then increases with the increase in bedding inclination.(4)With increased confining pressure,the brittleness of shale with the same bedding angle decreases as a whole.Under low confining pressure,shale brittleness is larger at both ends and smaller in the middle with the incr

关 键 词：页岩 层理倾角 破坏模式 脆性指标 离散元模拟 

分 类 号：TU45[建筑科学—岩土工程]