陆相页岩压裂试验与数值模拟

Experiment and numerical simulation of hydraulic fracturing in lacustrine shale： Taking the Ordos Basin as an example

李晓 郭鹏 胡彦智 李士祥 杨伟伟

Xiao LI Peng GUO Yanzhi HU Shixiang LI Weiwei YANG

鄂尔多斯盆地三叠系延长组7段（长7段）页岩油资源潜力巨大，是增储上产的重要领域。然而由于陆相页岩黏土矿物含量高、纹层发育、结构和力学非均质性强，压裂改造难度大，亟需针对其压裂缝网演化特征进行研究。通过开展压裂试验与非连续数值模拟，获取了地应力和压裂液黏度对水力裂缝扩展的影响规律。研究认为：①当垂向应力差为15 MPa时，水力裂缝扩展主要受陆相页岩层理弱面控制，裂缝高度较小；当垂向应力差高于20 MPa时，水力裂缝扩展高度逐渐增大。②提高压裂液黏度能促进水力裂缝穿过层理弱面垂向扩展。③陆相页岩储层岩体结构是形成复杂缝网的基础，压裂裂缝最主要为被激活的天然裂缝。④压裂缝网主要由水平层理缝和与层理近似垂直的裂缝构成，当水平缝和垂直缝占比接近时，压裂改造效果较好。

The 7 member of the Triassic Yanchang Formation in Ordos Basin is rich in shale oil and has been regarded as one of the key targets for reserve growth and production increase. However， the oil-bearing lacustrine shale with its broad lamination and bedding， high content of clay minerals， and heterogeneity in terms of structure and mechanism， responds poorly to hydraulic fracturing， calling for a better understanding to the evolution characteristics of hydraulic fracture network. In this paper， the effects of in-situ stress difference and fracturing fluid viscosity on hydraulic fracture propagation in lacustrine shale are determined through laboratory fracturing tests and numerical simulation analysis. The results show that the hydraulic fracture propagation is mainly controlled by weak bedding planes with fracture height being limited when the vertical stress difference is 15 MPa and gradually increasing when the vertical stress difference is larger than 20 MPa. Fluid with higher viscosity enhances the vertical propagation of hydraulic fractures across weak bedding planes. The rock mass of lacustrine shale reservoirs is the basis for the generation of complex hydraulic fracture networks of mostly activated natural fractures. The hydraulic fracture network is mainly composed by activated horizontal bedding-parallel fractures and nearly bedding-perpendicular fractures.

10.11743/ogg20230416