Relative permeability of two-phase fluid flow through rough fractures: The roles of fracture roughness and confining pressure

The relative permeability of two-phase fluid flow through rough fractures was investigated by conducting the triaxial two-phase fluid flow experiment on sandstone fractures. The relative permeability in rough rock fractures is greater than that predicted by the Corey model and the viscous coupling model due to interphase resistance. Therefore, the flow resistance between two-phase fluids is lower than that of the Corey model and viscous coupling model. The resistance between two-phase fluids increases with the increase of fracture roughness and confining pressure, causing the decrease of relative permeability of two-phase fluid flow. It is also found that the influence of fracture roughness on relative permeability of water phase is more obvious than that of gas phase, while the influence of confining pressure on relative permeability of gas phase is more obvious than that of water phase. The relative role of fracture roughness and confining pressure in two-phase fluid flow decreases while the relative permeability approaching the equal-permeability point. Based on the influence of fracture roughness and confining pressure, a relative permeability model for rough rock fractures under the effect of confining pressure is established. This model describes the two-phase fluid flow behavior in rough rock fracture under different confining pressure well. Further analysis on relative permeability in terms of fractional flow of water was conducted. It shows that the confining pressure and fracture surface roughness play a hindering role in the twophase fluid flow. This hindering effect is mainly on nitrogen at the low fractional flow of water and mainly on water at the high fractional flow of water.