Relative permeability curves for gas-liquid two-phase flows through rock fractures

In fluid flow simulations for petroleum and geothermal fractured reservoirs, it is important to well understand gas-liquid two-phase fracture flow characteristics. However, gas-liquid two-phase flow characteristics have been poorly understood due to the lack of studies using real rock fractures under confining pressure. In the present study, gas-liquid relative permeability curves have been investigated through nitrogen-water and steam-water two-phase flow experiments and numerical model simulations for a fracture in granite under confining pressure. Experimental and numerical results for nitrogen-water two-phase flow have revealed that relative permeability curves in this system are characterized by the ν type relative permeability curves, which have been reported for liquid-liquid two-phase flows through fractures under influence of capillarity. The ν type relative permeability curves result from very strong interference between phases due to capillarity in a lognormal-like aperture distribution of a real fracture. With the ν type relative permeability curves, it is unlikely for both phases to flow simultaneously. Furthermore, results for steam-water two-phase flow have revealed that relative permeability curves in this system are also characterized by the ν type relative permeability curves. Although several previous studies have suggested that two-phase flow characteristics can be different between steam-water and nitrogen/air-water systems, due to influences of phase change and a different contact angle. The present study has provided no evidence for them. It has been revealed that relative permeability curves are essentially the same for any pairs of fluids.