水平井压裂多裂缝同步扩展数值模拟

摘要

The finite element method was used to simulate the simultaneous propagation of multiple fractures in a horizontal well.Based on the coupling effects of fluid transportation,reservoir deformation and fracturing propagation during fracturing,a mechanical model for the simultaneous propagation of multiple fractures was constructed.Crack element model was used to record the rock cracks coordination,and calculated the cracks propagation paths.Finite element method was used to solve the coupled governing equations,and corresponding code was made to simulate the dynamic fractures initiation,irregular extending trajectory,and turning round of multi-fractures.The results show that breakdown pressure of multiple fractures is similar during simultaneously fracturing,and the propagation pressure of middle fracture is higher than that of the side fractures for stress interference.Because of the effect of stress shadow,deflection range of the main stress direction is increased,promoting the formation of complex fractures.By optimizing the perforation clusters spacing and numbers,which can produce more stronger effects of stress shadow,the complex multiple fractures extending trajectories can be achieved.%采用有限单元法对水平井压裂多裂缝同步扩展问题进行数值分析.考虑压裂过程中高压流体、岩层变形/破裂与裂缝扩展之间的多物理场耦合响应,建立多裂缝同步扩展力学模型;采用裂缝单元记录岩层破裂信息、确定裂缝扩展路径.应用有限元方法求解耦合模型并编制计算程序,模拟水平井多裂缝同步起裂、扩展和转向过程.研究结果表明:水平井多裂缝同步压裂,起裂压力相差较小;延伸压力受缝间应力干扰影响,中间裂缝处压力高于两侧裂缝;随裂缝扩展,多裂缝之间应力干扰效应提高,主应力方向偏转范围增大,促使复杂裂缝的形成;通过优化射孔簇间距与数量可增强裂缝间应力干扰效应,增加水平井多裂缝扩展的复杂性.