Three-dimensional continuous-discrete pore-fracture mixed seepage model and hydro-mechanical coupling model to simulate hydraulic fracturing

Abstract

A three-dimensional (3D) continuous-discrete seepage mixed model is presented, which considers the fluid exchange and the pore pressure discontinuity at the fracture. In this model, both the fracture seepage and pore seepage are considered simultaneously. Moreover, the node sharing connection of the neighboring elements near the fracture are dynamically updated during fracture propagation. The pore pressure discontinuity and fluid exchange at the fracture can be well considered but the virtual joint element and its very large exchange coefficient do not need to be introduce. The mixed model is coupled with finite discrete element method (FDEM) to create a hydro-mechanical coupling model for simulating hydraulic fracturing. Three examples are given to verify the mixed seepage model and hydro-mechanical coupling model. Finally, a hydraulic fracturing experiment is simulated by using the coupling model. The simulation results demonstrate that the differences in in-situ stress and approach angle are the most important factors controlling the fracture propagation behavior, and the shear strength of natural fractures also affects the intersection mode.