Flow-coupled cohesive interface framework for simulating heterogeneous crack morphology and resolving numerical divergence in hydraulic fracture

Abstract

A user-friendly and generic finite element framework for simulating hydraulic fracture with a complex crack network in unconventional oil and gas exploitation is developed in this work with the following unique features. While the cohesive zone model (CZM) removes crack singularities, its finite element simulations suffer numerical convergence problem during crack nucleation and growth, which can be regularized by a fictitious viscosity approach. The decoupling of cohesive-cracked solid and fluid into separate free body diagrams allows the development of a weak-form finite element formulation for the former and a finite-difference approach for the transport analysis in the latter. Enforcing the Kirchhoff condition in polycrystalline geomaterials allows the study of the fluid-driven complex fracture propagation process. Our method has been verified by analytical solutions, and then employed to simulate the synergistic roles of confining pressure and grain boundary anisotropy on the fracking morphology. Numerical implementation into a user-defined element (UEL) subroutine in ABAQUS provides easy adaptation and further development for the research community.