水力压裂过程中射孔冲蚀效应的数值模拟研究

Numerical simulation of perforation erosion effects during hydrualic fracturing treatment

针对水力压裂过程中射孔冲蚀效应使得射孔簇处射孔数目难以确定的问题,使用FrackOptima全三维水力压裂软件和前期研究建立的射孔冲蚀模型建立算例。通过边界元进行网格离散,使用时间步长算法进行流固耦合数值模拟,定量研究射孔冲蚀效应对裂缝最终形态、压裂液流量分布、射孔摩阻、射孔直径、流量系数、井底压力这6个压裂结果参数的影响规律。研究结果表明:传统非限流压裂过程中射孔摩阻的值和射孔冲蚀导致的摩阻瞬时动态变化较小,因此可以忽略射孔冲蚀效应;而在使用同时多簇限流压裂方法开发非常规油气的过程中,射孔摩阻的值较大且射孔冲蚀导致的摩阻瞬时动态变化较明显,所以必须考虑射孔冲蚀效应。在算例参数条件下,选取8孔/簇可以获得较合适的射孔摩阻,从而较好地平衡应力阴影效应,获得较均匀的多条裂缝发育;同时,确保井底压力在实际压裂安全范围内。

To solve the problem that it is hard to determine perforation numbers at clusters due to the perforation erosion effects during hydraulic fracturing treatment,we set up numerical examples with a fully�three-dimensional simulator FrackOptima and a perforation erosion model established in a previous study.We investigated the effects of perforation erosion on six resulting parameters of fracturing treatment by using the boundary element method for discretization and the time-step algorithm for numerical simulation of coupled mechanics of solid and fluid.The six resulting parameters are configurations of final fractures,fracturing�fluid distribution,perforation pressure drop,perforation diameter,discharge coefficient,and downhole pressure.The results demonstrate that the effects of perforation erosion are negligible during conventional non�limited-entry treatment because both the value of perforation pressure drop and its instant change induced by perforation erosion are small,while they can not be neglected in simultaneous multi-fracture limited-entry treatment for development of unconventional reservoirs because the value of perforation pressure drop is large and its instant change induced by perforation erosion is significant.An eight-perforation per cluster produces appropriate perforation pressure drop to mitigate stress shadow effects,leading to a relatively uniform propagation of multiple fractures and ensuring downhole pressures in safe range for practical fracturing.