This study develops a hydro-damage-mechanical fully coupled numerical method capable of modelling complex fluid-driven transient dynamic crack propagation in quasi-brittle poroelastic media. In this method, the fluid flow in both fractures and porous media is described by a fluid continuity equation with the modified Darcy-Poiseuille law based on the Biot's poroelastic theory. The fluid pressure and the inertial force of solids are coupled by governing equations of the mesh-insensitive phase-field regularized cohesive zone model that can simulate quasi-brittle multi-crack initiation, propagation, branching and merging without remeshing or crack tracking. The resultant displacement-pressure-damage coupled multiphysics system of equations is solved using an alternative minimization Newton-Raphson iterative algorithm with an implicit Newmark integration scheme within the finite element framework. The new method was first validated by a few 2D problems, including crack branching and deflecting in solids, fracking in a concrete cube, and consolidation and stress wave propagation in poroelastic media, subjected to various impulsive loadings. It was then applied to pressure pulsing fracking of a 40 m granite rock reservoir with extensive parametric studies of fluid viscosity and pulsing injection rate, mode and period. It was found that pulsing injection with higher fluid rates and lower fluid viscosities resulted in more developed crack patterns, and in particular, there existed an optimal pulsing injection period that could promote fracking under relatively low injection pressures. 3D horizontal well problems with multiple non-planar crack propagation and bifurcation were also successfully simulated to demonstrate the capacity and potential of the new method for engineering design and optimization of pressure pulsing fracking.

中文翻译：

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通过水力损伤-机械耦合内聚相场模型模拟多孔弹性介质中的动态脉冲压裂


本研究开发了一种水力损伤机械全耦合数值方法，能够模拟准脆性多孔弹性介质中复杂的流体驱动瞬态动态裂纹扩展。该方法利用基于毕奥多孔弹性理论的修正达西-泊肃叶定律的流体连续性方程来描述裂缝和多孔介质中的流体流动。流体压力和固体惯性力通过网格不敏感相场正则化内聚区模型的控制方程耦合，该模型可以模拟准脆性多裂纹的萌生、扩展、分支和合并，而无需重新网格化或裂纹跟踪。所得到的位移-压力-损伤耦合多物理场方程组通过有限元框架内的隐式纽马克积分方案，使用另一种最小化牛顿-拉夫森迭代算法进行求解。新方法首先通过几个二维问题进行验证，包括固体中的裂纹分支和偏转、混凝土立方体中的压裂以及多孔弹性介质中承受各种脉冲载荷的固结和应力波传播。然后将其应用于 40 m 花岗岩储层的压力脉冲压裂，并对流体粘度和脉冲注入速率、模式和周期进行了广泛的参数研究。研究发现，较高的流体流量和较低的流体粘度的脉冲注入会导致更发育的裂缝模式，特别是存在一个最佳的脉冲注入周期，可以在相对较低的注入压力下促进压裂。 还成功模拟了具有多个非平面裂纹扩展和分叉的 3D 水平井问题，展示了压力脉冲压裂工程设计和优化新方法的能力和潜力。