基于改进PFC流固耦合算法的页岩水力压裂裂缝扩展研究  

Propagation investigation of hydraulic fractures for shales considering improved hydro-mechanical coupling algorithm based on PFC software

作　　者：刘先珊[1,2] 曾南豆 李涛[1,2] 张立君 LIU Xianshan;ZENG Nandou;LI Tao;ZHANG Lijun(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;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：《中南大学学报（自然科学版）》2022年第9期3545-3560,共16页Journal of Central South University:Science and Technology

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

摘　　要：针对颗粒流软件PFC中传统流固耦合算法的局限性,提出使用几何图形定义流动管道替换接触定义流通管道的流固耦合分析技术,解决基本算法中因为接触破坏而流动管道失效的问题,能更准确地描述页岩破坏后裂缝的优先流效应。在此基础上,通过设定额外属性区分管道流和裂隙流,提出水力压裂裂缝开度的计算公式,并建立储层页岩水力压裂模型,分析不同地应力作用下的完整页岩裂缝扩展模式,验证水力压裂模型的可靠性。研究结果表明:不同地应力组合的压裂裂缝扩展模式不同,不同方向的地应力相差较大时,裂缝依然沿着最大主应力方向延伸,当层理倾角不同时,压裂裂缝以较大角度逼近层理面,且较易穿过层理面,当压裂裂缝逼近角较小时,易被层理捕获并延伸;注水压力增大时,基质裂缝迅速萌生扩展,流体流入扩展的裂缝中,压裂裂缝的延伸模式差异显著;当页岩层理密度越小时,起裂注水压力越大,但层理密度较大对裂缝延伸的阻碍效应更明显。Aimed at the deficiency of the traditional fluid−solid coupling algorithm based on particle flow code(PFC),a new algorithm was proposed to use the geometrical shapes to replace the particles contacts,which solved the failure of the flow channels induced by the failure of the particles contact,practically describing the flow superiority of the cracks.And then,the extra properties were designed to distinguish the channel flow and crack flow,corresponding formula were proposed to calculate the cracks aperture in the process of the hydraulic fracturing.And also,a hydraulic fracturing model was conducted to analyze the cracks propagation,and verify the feasibility of the fracturing model.The results show that the propagation modes are obviously different considering different stress combination,and greater difference between the stresses in directions causes cracks extending to the maximum principle stress,especially when the bedding angles are greater,the cracks will be close to the bedding planes with larger angle and more easily crosses the bedding plane,and the cracks will more easily be captured by the bedding planes when the cracks are close to the bedding planes with smaller angles.The water injection pressure increases,the cracks in the rock masses rapidly initiates and propagates,and the fluid rapidly flows in the propagated cracks,resulting in obvious difference in the cracks formation.The density of the bedding planes is lower,and the initiation pressure is greater,but greater density of the bedding planes gives more blocks for the cracks extension.

关 键 词：水力压裂 颗粒流软件(PFC) 流固耦合 裂缝开度 裂缝扩展 

分 类 号：TU45[建筑科学—岩土工程]