Effects of Gravity on the Relative Permeability Curves of Supercritical CO2 and Brine: An Experimental Study Using Surrogate Fluids

This study investigates the influence of gravity on relative permeability-saturation (k r -S) relationships.Steady-state relative permeability tests were conducted using a 1 m-long column designed by the authors and surrogate fluids.Both upward and downward flow conditions were tested across three intrinsic permeabilities and three total flow rates.The measured k r -S curves clearly exhibited directional dependence on gravity.Downward flow yielded a more stabilized flow front and more consistent non-wetting phase saturation, whereas upward flow promoted flow instability, resulting in greater spatial variability.Endpoint relative permeability (k r,end,NWP and k r,end,WP ) results suggest that k r,end,NWP is governed mainly by connected flow pathways at steady state, whereas k r,end,WP can increase even at similar residual non-wetting phase saturation during imbibition because the spatial configuration of stranded non-wetting phase clusters constrains wetting-phase connectivity.These results highlight the importance of gravity-controlled directional dependency of the k r -S relationship and the need to incorporate this behavior into reservoir-scale models.