济阳拗陷页岩储层水平井裂缝扩展数值模拟

Numerical Simulation of Fracture Propagation in Horizontal Wells of Shale Reservoirs in Jiyang Depression

薛仁江 郭建春 赵志红 周广清 孟宪波

XUERenjiang GUOJianchun ZHAOZhihong ZHOUGuangqing MENGXianbo

“油气藏地质及开发工程”国家重点实验室·西南石油大学, 四川 成都 610500 中国石化胜利石油工程有限公司井下作业公司, 山东 东营 257000 中国石化胜利油田分公司油气勘探管理中心, 山东 东营 257000

State key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China Downhole Service Company of SINOPEC Shengli Petroleum Engineering Co. Ltd., Dongying, Shandong 257000, China Manage Center of Oil & Gas Exploration of SINOPEC Shengli Oilfield Company, Dongying, Shandong 257000, China

由于物理实验受到实验条件、数量的限制，难以对裂缝扩展规律开展大规模的研究。因此，在有了一定的岩石力学测试、页岩压裂破裂方式测试以及页岩压裂裂缝扩展物模试验的基础上，开展了页岩压裂裂缝起裂及扩展规律数值模拟研究。基于流固耦合Biot固结理论、Darcy渗流定律，采用最大拉伸强度准则和Mohr Coulomb准则损伤阈值进行单元损伤判断，引入全新的材料分布算法，建立了水力压裂裂缝扩展的有限元计算模型。进行了岩石样本的参数标定试验。采用有限元计算方法研究了地应力、页岩脆性指数、压裂液黏度和层理特征等关键物理参数对页岩裂缝扩展的影响。结果表明，当脆性指数较小时，水力裂缝主要沿最大主应力方向在页岩基质中扩展，难以转向形成复杂缝网。层理胶结强度较高时，水力作用即便在局部压开天然层理，也难以持续以大角度偏离，而只能形成比较单一的裂缝。地应力比、压裂液黏度越低，层理密度等特性越高时，裂纹网络越复杂。

Physical experiments are limited by experimental conditions and the number of experimental samples available. Thus, it is difficult to conduct large-scale studies on fracture propagation patterns. Hence, a numerical simulation study on fracture initiation and propagation patterns during hydraulic fracturing of shales is conducted based on certain mechanical tests of rocks, rupture tests on hydraulic fracturing of shales, and physical model tests on fracture propagation during hydraulic fracturing of shales. Based on fluid-solid coupling through Biot's consolidation theory and Darcy's seepage law, the maximum tensile strength criterion, and the Mohr-Coulomb criterion as a damage threshold for damage determination of units, a new material distribution algorithm is introduced to construct a finite element calculation model of fracture propagation during hydraulic fracturing. Parameter calibration tests were performed on rock samples, and the influences of key physical parameters on fracture propagation in shales were investigated through the finite element calculation method. The key physical parameters are ground stresses, brittleness indices of shales, the viscosity of fracturing fluids, and bedding characteristics. The general view is that when brittleness indices are small, hydraulic fractures propagate in the shale matrix mostly along the direction of the maximum principal stress. The fractures hardly change direction to form a complex network of fractures. For highly cemented beds, hydraulic actions cannot deviate at a large angle continuously, even in partially open natural beds, and thus form only relatively uniform fractures. Fracture networks become more complex when ground stress ratios and the viscosity of fracturing fluids are lower, and bedding densities are higher.

10.11885/j.issn.1674-5086.2018.05.21.01