The Investigation of Two-Phase Fluid Flow Structure Within Rock Fracture Evolution in Terms of Flow Velocity: The Role of Fracture Surface Roughness and Shear Displacement

Understanding the structural evolution of two-phase fluid flow in fractured rock is of great significance for related rock engineering, including underground oil and gas extraction, contaminant storage and leakage, etc. Considering that rock fracture is the fundamental element of fractured rock, we conduct a series of numerical simulations to investigate the role of fracture aperture, surface roughness and shear displacement in the transition of two-phase fluid flow. The roughness fracture surfaces were generated by a MATLAB code we developed according to successive random addition algorithms. The level set method was applied to describe two-phase fluid flow and the numerical solution of the governing equations in COMSOL 6.2, and its effectiveness was verified by comparing it with the results of previous experiments. Numerical simulation results indicated the following: the water saturation (Sw) in the fracture decreases with an increase in the gas–water flow rate ratio; with an increase in roughness, the water saturation contained within the fracture gradually increases; the effect of fracture roughness on the two-phase fluid flow structure is enhanced; with an increase in dislocations, the water saturation in the low-roughness fracture increases, and the water saturation in the high-roughness fracture first increases and then decreases. The results of this study can provide reference significance for the study of gas–water two-phase fluid flow and provide theoretical guidance in related engineering.