Comparison of relative permeability hysteresis in oil-brine and gas-brine systems: A pore-scale investigation

Relative permeability ( k r ) hysteresis reflects the complex interplay between capillary forces and fluid distributions in porous media, which affects multiphase flow predictions. Although traditional hysteresis models have been widely applied to oil–brine systems, gas–brine systems can exhibit reverse hysteresis behavior, and direct pore-scale comparisons between the two systems remain limited. This study compares k r hysteresis of oil-brine and gas-brine systems using a simple glass-bead system that allows for precise pore-scale measures of fluid morphology during drainage and imbibition cycles. Our comparison confirms that gas-brine and oil-brine glass bead systems exhibit different hysteresis behaviors, with the gas-brine system showing a reversed trend where imbibition k r is placed above drainage k r . We find that the origin of the reverse trend results from changes in the behavior of the interfacial area ( A n w ) during drainage and imbibition, while all other morphological measures follow traditional hysteresis models. In general, we observe consistent trends between A n w and k r hysteresis behaviors. Based on these findings, we present a k r hysteresis model that reflects the observed trends and provides a framework for further investigation of the relative permeability in such systems. These findings contribute to a better understanding of multiphase flow in porous media, particularly in systems where gas transport is affected by hysteresis. The insights gained are especially relevant for cases exhibiting gas-brine hysteresis reversal behavior, offering a basis for further research into improving gas transport models in relevant applications. Plain Language Summary The flow of gas and water through porous materials is important for various applications, including subsurface energy storage. Here, we study how gas and brine flow through porous rocks using an analog glass bead system imaged with high-resolution X-ray, which provides 3-dimensional images of the fluids within the glass beads at a resolution that is one-tenth the diameter of human hair. Unlike typical models, we found that brine flows more easily after gas injection (imbibition) than during gas entry (drainage), which is the opposite of what is expected when water and oil are used. To confirm this, we repeated the process for an oil-brine system and found the opposite trend in the gas-brine flow. A detailed analysis of the fluid structures within the porous material shows that this behavior is linked to the surface areas of the fluids within the porous rock. Based on our findings, we developed a model to explain the observed unique flow behavior, which is important for understanding gas transport in porous media. • Gas-brine systems can exhibit different relative permeability hysteresis patterns compared to oil-brine systems. • A new relative permeability hysteresis model is proposed for systems that exhibit reverse hysteresis behavior. • The observed hysteresis trends correlate strongly with specific interfacial area changes.