A method for dissolution rate quantification of convection-diffusion mechanism during CO₂ storage in saline aquifers

CO₂storage in deep saline aquifers has been suggested as a way to reduce greenhouse gas emissions. Dissolution of CO₂ into brine causes the density of the mixture to increase. The density gradient induces natural convection in the liquid phase. Correct estimation of dissolution rate is important because the time scale for dissolution corresponds to the time scale over which free phase CO₂ has a chance to leak out. However, for this estimation, a challenging simulation based on the convection-diffusion equation must be performed. In this paper, an analytical method for rapid determination of dissolution rate in a convection-diffusion mechanism is proposed. This will be used to calculate the rate of mass transfer in porous media during CO₂ storage. For this purpose, a new diffusion equation was developed based on the pseudo diffusion coefficient of the system. Experimental tests were conducted in porous media to evaluate this new diffusion coefficient. It is shown that this coefficient can be approximated by a relationship for the Rayleigh number of the system. This relation is entered into the diffusion equation and used as a new diffusion coefficient. The fraction of ultimate dissolution, as a result of the analytical method, is calculated for each test and compared with the experimental data to verify the reliability of the proposed method. We suggest that the analytical method presented herein could be used as a simple and rapid tool to screen the technical or economic feasibility of a proposed CO₂ injection scenario in actual fields.