考虑单元劈裂的流-固耦合连续-非连续方法及定向水力压裂模拟

为了更真实地模拟水力压裂过程中的岩石变形、裂缝扩展及流体流动,在自主开发的拉格朗日元与离散元耦合的连续-非连续方法的基础上,发展了一种流-固耦合方法。在该方法中,裂缝可沿四边形单元对角线和单元边界扩展,流体流动满足立方定律。通过与单一裂缝非稳态渗流模型及KGD模型的理论解进行对比,验证了该方法的正确性。由定向射孔水力压裂的模拟结果可以发现,(1)距离射孔越远,流体压力越小;随着时间的增加,裂缝中流体压力降低。(2)随着射孔角度的增加,裂缝起裂和扩展过程中的流体压力及转向距离增加;随着x方向水平应力的增加,裂缝起裂和扩展过程中的流体压力增加;两个方向水平应力之差越大,裂缝转向距离越小。(3)随着时间的增加,裂缝区段数目的增速变慢,这与裂缝体积增加变快有关。

A fluid-solid coupling continuum-discontinuum method considering element splitting and simulation of directional hydraulic fracturing

In order to simulate rock deformations,fracture propagations and fluid flows,a fluid-solid coupling method was developed based on the method that combines the Lagrangian element method and discrete element method.In this method,fractures can propagate along diagonal lines and edges of quadrilateral elements,and fluid flows according to the cubic law.This method was verified by comparing the present results with the theoretical results of the unsteady seepage model with a single fracture and the KGD model.The following results were found from the simulations of hydraulic fracturing containing oriented perforations.(1) With the increase of the distance far away from the perforation,fluid pressures decrease;with the increase of time,fluid pressures in fractures decrease.(2) With the increase of the perforation angle,fluid pressures corresponding to the fracture initiation increase,fluid pressures during the process of the fracture propagation increase,and the turning distances of fractures increase;with the increase of the horizontal stress in the x-direction,fluid pressures corresponding to the fracture initiation increase,and fluid pressures during the process of the fracture propagation increase;the larger the difference between the two horizontal stresses,the smaller the turning distances of fractures.(3) With the increase of time,the number of fracture segments increases,but their increasing speeds decrease,which is related to the increase of the fracture volume.