Mass Transfer of CO₂ in a Carbonated Water–Oil System at High Pressures

In this paper, CO₂ diffusion coefficients in a carbonate water–oil system are determined by measuring the pressure buildup in the closed water–oil system experimentally and modeling the pressure change mathematically. The mathematical method of investigating one-dimensional, time-dependent heat conduction in a composite medium is adopted to solve the mass transfer problem between two liquid phases. The model is combined with well-designed trial-and-error method to determine diffusion coefficients of CO₂ in both water and oil phases at the same time. The model considers a moving interface between carbonated water and oil as well as variations of interface concentrations of CO₂ in these two phases, which more effectively conforms to reality. Results show that the pressure buildup during the diffusion process resulted from the increased density and swelling of the oil phase. The diffusion coefficient of CO₂ in the water phase plays a major role in the interphase mass transfer process.