Interaction between CO2 and oil exhibits complex phase behavior that results in gravity-driven convection and enhanced mixing of CO2 in the oil zone. We have shown that the density of oil increases between 4% and 6% at CO2 concentrations between 65% and 75% by mass. Different cubic EoS give different values for density of CO2-oil mixtures. The increase in oil density leads to an unstable density inversion, instigating convection in a 100 mD aquifer in a few days. The convection enhances the rate of CO2 uptake in the oil, with long-term steady rates from 500 kg/m2/y up to 800 kg/m2/y. The rate has some dependency on the EoS assumed in the computational model. The convective process substantially increases CO2 uptake in the oil zone compared to the diffusion process alone. Enhanced CO2 uptake has important implications for injection into depleted reservoirs and EOR/EGR operations, which is the subject of future work.


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