Experimental studies of CO2 and CH4 diffusion coefficient in bulk oil and porous media

Abstract

This paper presents the results of experimental studies on diffusion coefficient of CO2 and CH4 in bulk oil and porous media. A series of tests were performed and diffusion coefficients were estimated from pressure profile as a function of time coupled with semi-analytical solution of the one-dimensional diffusion equation. The pressure-time profiles were measured from experiments. For each run, the gas diffusion coefficient was used as adjustable parameter to fit the pressure-time profile predicted by semi-analytical model to the experimentally measured profile. The diffusion coefficient resulting from the best-fit curve was considered as the average diffusion coefficient. Three main conclusions were obtained from these experiments: (i) diffusion coefficients for both solvents, CO2 and CH4, increase linearly with temperature; (ii) diffusion coefficients of CO2 are higher than those of CH4, and (iii) the effective diffusion coefficients of CO2 in porous media have lower values when compared to bulk oil. The importance of this study is linked to a better understanding of the molecular diffusion coefficient, which is significant in several oil recovery and CO2 storage processes since it is often considered as the rate controlling mechanism.