页岩气藏压裂缝网扩展数值模拟

为探究页岩气藏水力压裂复杂裂缝网络的形成机理,开展了缝网扩展的数值模拟研究.考虑应力阴影和天然裂缝作用,建立了井筒和裂缝中流体流动模型,利用位移不连续方法求解应力与位移不连续量,然后构建了压力与裂缝宽度的迭代方程,并采用牛顿迭代法求解.通过比较数值解经典模型解析解,验证了模型和迭代解法的正确性.多簇裂缝同步扩展时裂缝间距越小,压裂液分配到各条裂缝越不均匀,靠近井筒跟部的裂缝的分流量越大,从而裂缝宽度越大;考虑天然裂缝作用时,逼近角越小或者应力各向异性越弱,水力裂缝越容易发生转向扩展,裂缝网络越复杂. 

NUMERICAL MODELING OF FRACTURE NETWORK PROPAGATION IN SHALE RESERVOIRS

To investigate the forming mechanism of complex fracture network during the process of hydraulic fracturing in shale gas reservoirs, numerical simulation of fracture network propagation has been carried out. Taking the e ects of stress shadowing and natural fractures into account, coupled mathematical model of fluid flow in the wellbore and fractures is established. The stress and displacement discontinuity are solved by using displacement discontinuity method. New iterative algorithm of pressure and fracture widths has been constructed and solved with Newton iteration method. The mathematical model and numerical algorithm are validated by comparing numerical solutions to analytical solutions with consideration of leak-o e ect. Parameters sensitivity analysis is performed to study the influencing factors of hydraulic fractures propagation. As to simultaneous propagation of multiple cluster fractures: the smaller fracture spacing is, the more unevenly fracturing fluid is distributed to each fracture; the fracture near the heel of wellbore receives more fluid than other fractures and becomes wider; When taking the e ect of natural fractures into account, the smaller approaching angle is or the weaker stress anisotropy is, the more possibly hydraulic fractures change propagation direction and the more complex fracture networks become.