Numerical simulation of hydraulic fracturing using a three-dimensional fracture model coupled with an adaptive mesh fluid model

Abstract

A three-dimensional fracture model developed in the context of the combined finite-discrete element method is incorporated into a two-way fluid-solid coupling model. The fracture model is capable of simulating the whole fracturing process. It includes pre-peak hardening deformation, post-peak strain softening, transition from continuum to discontinuum, and the explicit interaction between discrete fracture surfaces, for both tensile and shear fracture initiation and propagation. The fluid-solid coupling model can simulate the interactions between moving fluids and multi-body solids. By incorporating the fracture model into the coupling model, a methodology of using the new coupling model to capture fracturing behaviour of solids in fluid-solid coupling simulations is proposed. To solve the problem in the coupling model of having adaptive continuous meshes being used by the fluid code and discontinuous meshes in the solid code, a scheme to convert different meshes is developed. A single fracture propagation driven by fluid pressures is simulated and the results show that the modelling obtains the correct critical load and propagation direction for fluid-driven fracturing. Several important phenomena, such as stress concentration ahead of the fracture tip, adaptive refinement of fluid mesh as a response to the fracture propagation and fluids flowing into fractures, are properly captured.