基于PFC2D数值模拟的交替压裂中应力阴影效应研究

为了探究应力阴影效应对交替压裂中压裂间距选取的影响，基于优化后的颗粒流离散元流固耦合计算模型，模拟并分析了双初始水力裂缝下因应力阴影效应产生的诱导应力的分布情况，并与理论解析解进行对比，证明了该数值方法的合理性。在此基础上，分析了应力阴影效应在不同各向异性地应力场及初始压裂间距条件下对新水力裂缝的起裂压力及扩展形态的影响，研究结果表明：初始各向异性应力场不改变裂缝周边的应力场，不影响新水力裂缝的起裂压力；随着初始压裂间距的减小，应力阴影效应增强，新水力裂缝的起裂压力逐渐增加。初始水力裂缝间距与初始各向异性应力场共同影响新水力裂缝的扩展形态，随着初始水力裂缝间距或初始水平地应力场差异系数的增大，应力阴影对新水力裂缝的扩展方向的影响逐步减弱；初始水力裂缝对新水力裂缝的扩展有一定的限制作用，在一定程度上不利于形成复杂的裂缝网络。根据以上分析结果，对交替压裂中压裂间距的优化进行了定性的探讨。

Stress shadow effect of alternative fracturing based on numerical simulation of PFC2D

Within the ongoing effort towards a better understanding of the influence of the stress shadow on the choice of fracture spacing in alternative fracturing, an optimised particle flow theory of fluid-solid coupling was applied to simulate the distribution of the induced stress due to the stress shadow around double hydraulic fractures. Numerical results were compared with the theoretical analysis solution to verify its rationality. Numerical simulations under different anisotropic stress fields and initial hydraulic fracture spacing were carried out to investigate the effect of the stress shadow on the initiation pressure and extension forms of the induced fracture with double hydraulic fractures. Experimental results showed that the anisotropic stress field did not change the stress field around the fractures and also did not affect the initiation pressure of the induced fracture. With the decrease of initial hydraulic fracture spacing, the stress shadow effect was enhanced, and the initiation pressure of induced fracture was also increased. Both of the anisotropic stress field and initial hydraulic fracture spacing affected the extension forms of the induced fracture. With the increase of initial hydraulic fracture spacing or the hydraulic differential stress, the influence of stress shadow on the extension direction of new hydraulic fractures gradually weakened. The initial hydraulic fractures exhibit a limitation on the extension direction of the induced fracture, to some extent, which was not conducive to the formation of a complex fracture network. Based on the above results, the optimisation of fracturing spacing in alternate fracturing was qualitatively discussed.