Coupled hydro-mechanical two-phase flow model in fractured porous medium with the combined finite-discrete element method

This paper presents a time-explicit, fully coupled, hydro-mechanical model to simulate the two-phase flow process in fractured porous media, considering the geomechanical effect. Two solvers are developed, and mutual hydro/mechanical interactions are considered: (i) a novel finite volume discrete fracture–matrix model (FV-DFM) for two-phase flow, through both pores and fractures; and (ii) a combined finite-discrete element method (FDEM) for mechanical responses (e.g., deformation and fracturing). Particularly, a novel two-phase exchange flow model is applied at the matrix–fracture interface, which overcomes the difficulty in realistically capturing the discontinuity (e.g., pressure, saturation, and normal flux) across fractures. Meanwhile, non-uniform time steps of fracture and matrix flow are adopted to improve computational efficiency while maintaining accuracy. The performance of the proposed model is validated against existing results and applied to a practical waterflooding process considering fracture propagation. Results show that the model can well predict the two-phase flow process (e.g., pressure/saturation field, reservoir recovery) in fractured reservoirs, and reveal the important HM coupled effect on the flow process (e.g., the stress-dependent permeability and fracture propagation), with important implication for hydrocarbon reservoirs and CO₂ geological storage.