水力压裂中裂纹扩展的数值模拟

水力压裂是在高压粘滞流体或清水作用下地层内裂缝起裂与扩展的过程。由于包含岩石断裂和流-固耦合等复杂问题,对该过程的数值模拟具有相当大的挑战性。本文建立基于有限元与离散元混合方法的裂纹模型,模拟岩石裂纹扩展,实现了连续向非连续的转化;建立双重介质流动模型,裂隙流作为孔隙渗流的压力边界,孔隙渗流反作用裂隙的压力求解,处理了流体在基岩与人工裂缝中的协调流动;将裂纹模型与流体流动模式进行结合,建立断裂-应力-渗流耦合形式的力学模型,进一步分析了水力压裂的基本过程,综合多种数值计算方法,编写程序,在验证岩体裂纹模型与双重介质流动模型有效性的基础上,对压裂过程进行复现,将模拟结果与文献结果进行了对比,并讨论了所构建模型的优缺点。

Numerical simulation of hydraulic fracturing

Hydraulic fracturing is a process which fractures initiate and propagate due to hydraulic loading applied by fluid inside the fractures.To simulate the process is a great challenge because of the strong nonlinear coupling between the viscous flow of fluid and fracture propagation.In this work,a crack model based on the combined finite-discrete element method is built.The transition from continuum to dis-continuum can be efficiently simulated.In order to simulate fluid flow in the porous media and fracture,a dual-media model is created.In the model,fracture flow works as the pressure boundary condition of pore flow,while,pore discharge counteracts hydraulic head calculation.A fracture-stress-seepage coupling mechanical model is created based on the crack model and flow model mentioned above which are validated in some cases.The process of hydraulic fracturing is analyzed.Using a variety of numerical methods,a computer program is coded to simulate the process.The result is compared with another one simulated by distinct element method.The advantages and drawbacks of the proposed numerical model is discussed in details.