基于三维CT重构的油页岩复杂水力裂缝网络分形表征  

Fractal characterization of complex hydraulic fracture networks of oil shale via 3D CT reconstruction

作　　者：何强 李凤霞[2] 史爱萍[2] 何柏[1,3,4] 陈江 谢凌志[1,3,4] HE Qiang;LI Fengxia;SHI Aiping;HE Bo;CHEN Jiang;XIE Lingzhi(College of Architecture and Environment,Sichuan University,Chengdu City,Sichuan Province,610211,China;Petroleum Exploration and Production Research Institute,SINOPEC,Beijing City,100083,China;State Key Laboratory of Hydraulics and Mountain River Engineering,Sichuan University,Chengdu City,Sichuan Province,610065,China;Institute of New Energy and Low-Carbon Technology,Sichuan University,Chengdu City,Sichuan Province,610207,China)

机构地区：[1]四川大学建筑与环境学院,四川成都610211 [2]中国石化石油勘探开发研究院,北京100083 [3]四川大学水,力学与山区河流开发保护国家重点实验室,四川成都610065 [4]四川大学新能源与低碳技术研究院,四川成都610207

出　　处：《油气地质与采收率》2021年第5期116-123,共8页Petroleum Geology and Recovery Efficiency

基　　金：国家自然科学基金项目“页岩三维重构及压裂缝网扩展模拟试验研究”(11872258);四川省科技厅国际合作项目“页岩高温破断行为及热-流-固耦合压裂数值模拟研究”(2019YFH0121)。

摘　　要：通过压裂形成的复杂裂缝网络是提高致密油气藏产能的关键措施。采用真三轴实验系统对鄂尔多斯盆地中生界三叠系延长组油页岩试件进行水力压裂物理模拟实验,并对压裂前后试件的裂缝网络进行三维CT重构。基于分形理论和数字图像处理技术,对室内水力压裂前后裂缝网络的复杂性进行研究。结果表明,基于立方体覆盖法压裂前后裂缝网络的分形维数变化率为0.45%~3.64%。分形维数变化率与水平应力比之间始终存在负相关关系。然而,在不同压裂液黏度下,分形维数变化率先增大后减小,在黏度为5.0 mPa·s时分形维数变化率最大。在较低的水平应力比和相对较低的压裂液黏度下,更容易形成复杂的裂缝网络,而过低或过高的压裂液黏度均限制了复杂裂缝网络的形成。The complex fracture networks produced by hydraulic fracturing are crucial to the higher gas/oil production capacity from tight reservoirs.In this study,the physical simulation experiments on hydraulic fracturing were conducted by a true triaxial test system with the oil shale samples from the Triassic Yanchang Formation,and 3D CT reconstruction was performed on the fracture networks of the samples before and after fracturing.The complexity of the fracture networks were quantitatively described on the basis of the fractal theory and the digital image processing technology.The results indicate that the change rate of the fractal dimension of fracture networks are 0.45%-3.64%before and after fracturing based on the cube covering method.A negative correlation is always between the change rates of the fractal dimension and the horizontal stress ratio.Moreover,the change rate of the fractal dimension grows first and then declines as the fracturing fluid viscosity varies,and it reaches the maximum at the fluid viscosity of 5.0 mPa·s.A low horizontal stress ratio and a low fluid viscosity can intensify the complicated morphology of fracture networks,while over low or high fracturing fluid viscosity restrains the formation of fracture networks.

关 键 词：油页岩 水力压裂 分形维数 裂缝网络 三维CT重构 鄂尔多斯盆地 

分 类 号：TE357.1[石油与天然气工程—油气田开发工程]