Simulate intersecting 3D hydraulic cracks using a hybrid “FE-Meshfree” method

In this work, a discontinuous hybrid “FE-Meshfree” method is developed to simulate three-dimensional (3D) cracking. Then, an algorithm of Local Adaptive Background Sub-element (LABS-element) is developed in the context of hybrid “FE-Meshfree” method to simulate intersecting cracks. Compared to the extended finite element method (XFEM), the present hybrid “FE-Meshfree” method is not required to increase the size of global stiffness matrix, introduce extra unknowns, and construct special enrichment functions. The present algorithms of LABS-element and “FE-Meshfree” method are validated by intensive numerical tests, which achieves the balance between accuracy and flexibility. Additionally, a hydraulic and mechanical (H-M) coupling model is generated, in which the deformation of rocks and the propagation of cracks are solved by the hybrid “FE-Meshfree” method, meanwhile the fluid flow in cracks is solved by a fluid simulator based on the principle of parallel-plate flow model. This H-M coupling model is then used to investigate the propagation of fluid-driven cracks in rock mass with multiple pre-existing cracks, and the observed fluid pressure feedback is potentially useful during shale oil/gas well simulation.