天然裂缝分布对水力裂缝扩展及近井筒孔隙压力的影响

Influence of natural fracture distribution on hydraulic fracture extension and near wellbore pore pressure 

张小军 李军 张慧 连威 何龙 刘伟

中国石油大学（北京）石油工程学院，北京 102249 中国石油大学（北京）克拉玛依校区，新疆 克拉玛依 834000 中国石化西南油气分公司，四川 成都 610041）

College of Petroleum Engineering, China University of Petroleum, Beijing 102249, China China University of Petroleum(Beijing) at Karamay, Karamay 834000, China Southwest Oil and Gas Company, SINOPEC, Chengdu 610041, China

页岩气储层发育大量天然裂缝，在水力裂缝扩展过程中，当遇到天然裂缝时，其扩展形式会发生改变，近井筒附近的孔隙压力也会发生一定的变化。文中通过结合现场蚂蚁体预测结果及微地震资料，建立多级压裂数值模型；采用Cohesive孔压单元分别模拟第1压裂段一侧、第1压裂段两侧、相邻压裂段对角侧以及相邻压裂段全局分布天然裂缝4种情况下的水力裂缝扩展规律，并分析了各情况下压裂后近井筒孔隙压力的变化情况；最后分析了压裂簇数、压裂液黏度和排量对孔隙压力的影响。研究结果表明：天然裂缝会促使水力裂缝的扩展发生转向，呈现非均匀扩展的现象，近井筒附近的孔隙压力扰动区也相应地呈现非对称性；当相邻压裂段全局分布天然裂缝时，水力裂缝和天然裂缝的沟通点会明显增多，且孔隙压力的扰动范围和扰动值也会明显增大；在天然裂缝发育段，增加压裂段内的压裂簇数以及适当降低压裂液黏度、排量可以在一定程度上降低孔隙压力的不均匀分布。该研究结果可以为页岩气水平井压裂施工作业提供一定的理论依据。

There are many natural fractures in shale gas reservoirs. In the process of multi-stage fracturing, when hydraulic fractures encounter natural fractures, their expansion forms will change, and the pore pressure near the wellbore will also change to a certain extent correspondingly. This paper establishes a multi-stage fracturing numerical model by combining the on-site ant body prediction and micro-seismic data. Cohesive pore pressure unit was used to simulate the hydraulic fractures propagation of four types, namely natural fractures distributed on one side of the first fracturing stage, on both sides of the first fracturing stage, on diagonal side of an adjacent fracturing stage and on the whole of adjacent fracturing stage. The change of pore pressure near wellbore after fracturing is analyzed. Finally, the effects of fracturing clusters, fracturing fluid viscosity and displacement on pore pressure are analyzed. The results show that natural fractures make hydraulic fractures exhibit non-uniform propagation, and the pore pressure disturbance near the wellbore also presents asymmetry. When natural fractures are wholly distributed in the adjacent fracturing stage, the communication points between hydraulic fractures and natural fractures will increase obviously, and the disturbance range and value of pore pressure will also increase significantly. In the natural fractures section, increasing the number of fracturing clusters in the section and appropriately reducing the viscosity and displacement of fracturing fluid can alleviate the uneven distribution of the pore pressure to a certain extent. The research results can provide a theoretical basis for shale gas horizontal well fracturing operation.

doi:10.6056/dkyqt202206017