Pore-scale modeling of multiple fluids flow transport kinetics for CO2 enhanced gas recovery

Carbon storage with enhanced gas recovery (CSEGR) is a promising technology in the era of energy transition. The changes in the gas-liquid interface and the miscibility of fluids in the CO2-CH4-brine system are the key and difficult issues of mutual coupling. Therefore, this study develops a fully coupled multiphase flow and mass transfer model that considers both convective and diffusive interactions between gases while simulating the gas-liquid interface. This model explores the multiphase flow and diffusion characteristics of various fluids at the pore scale. Additionally, the study examines the profound impacts of pore pressure and wettability. The findings are as follows: The high density and viscosity of CO2 causes it to flow in the center of the dominant channels, while CH4 and water prefer to be distributed along the pore walls. At lower pore pressures, diffusion becomes a key factor in interphase gas exchange. As pressure increases, the effect of convection exceeds that of diffusion, resulting in a more dynamic mixing of CO2 and CH4. For highly hydrophilic reservoirs, water film will hinder the flow of CO2 and cause gas retention. Moderately hydrophilic reservoirs provide the best conditions for CO2 displacement while reducing gas mixing. Weakly hydrophilic reservoirs have minimal water resistance, which is conducive to CO2 displacement, but will lead to sufficient mixing between CO2 and CH4. This study aims to elucidate the interactions among various fluids and the impact of pore structures on flow behavior through numerical simulation, thereby offering a more comprehensive scientific basis for optimizing design.