压裂中顶底板对缝高控制作用的数值模拟研究

裂缝在缝高方向的延伸会导致裂缝有效长度的降低,影响压裂效果;也可能直接穿过水层,造成压裂施工的失败。因此,基于FEPG有限元平台,利用网格开裂技术,开展了煤层气井压裂数值模拟研究,对垂向裂缝起裂、扩展及穿层的全过程进行分析。数值模拟结果表明:煤层气井压裂过程中,控制裂缝是否向隔层扩展主要取决于作业的净压力与隔层水平地应力差之间的关系;与储集层岩石力学性质相比,储集层的地应力剖面是影响裂缝垂向扩展范围的主要因素;T型缝、工型缝等复杂缝是由储集层的岩石力学性质和地应力共同作用的结果。这对于提高现场煤层气井水力压裂的效果具有重要的指导意义。

Numerical Simulation on the Effect of Crack Height of Roof and Floor Rock in Fracturing

Crack extension in the direction of fracture height can decrease the effective fracture length and influence the fracturing effect; at the same time it may directly go through the water layer, which leads to the failure of fracturing. Therefore, based on the finite element of FEPG platform and with the help of a grid cracking technology, numerical simulation of coalbed methane wells fracturing is carried out to simulate the dynamic process of the crack propagation, including the whole process of fracture initiation, expansion and cross layer in extension. The result of numerical simulation shows that during the coal bed methane well fracturing process whether the controlled cracks to expand to interlayer is dependent on the differential pressure between net pressure and interlayer stress; compared with rock mechanics properties, geostress in the reservoir is the main factor that influences the vertical cracks extending area; complex cracks such as T shape crack and I shape crack, are mainly due to the joint action of rock mechanics properties and the crustal stress. It is significant that can improve the effect of hydraulic fracturing coal bed methane well.