CO2 Absorption and Transportation Modes in Porous Media: Numerical Simulation and Comparison with Laboratory Experiment

Abstract

Absorption and mass transfer mechanism of CO2 in a uniformly distributed porous media was analyzed using simulation as well as experimental results. The study was performed in a closed PVT cell containing pressurized CO2 gas above a water saturated porous media. Pressure decay curves obtained from the simulation and the experiments were used to calculate early and late time diffusivity in accordance with analytical model. Mixing regime was visualized over time to comprehend the contribution of natural convection in mass transfer process. Early time diffusion coefficients were two orders of magnitude higher than late time diffusion coefficients in both simulation and experimental results. Density-driven natural convection had a significant impact at early stages giving rise to enhanced mass transfer and hence the disparity in diffusivity. The diffusivity at late stages were close to literature value. Pressure decay observed from large duration simulation results showed that equilibrium was reached at close to theoretical saturation pressure. Three stages of diffusion were observed in both simulation and experimental pressure decay plots. The first stage indicated rapid pressure decline over a short interval of time. At this stage, upper layer of water saturated porous media at liquid-gas interface establishes an equilibrium with gas column above it. The second stage was convection dominated mass transfer followed by the third stage which was diffusion dominated. Finger propagation observed in the porous media was mainly in downward direction before expanding horizontally.