Quantification of density-driven natural convection for dissolution mechanism in CO ₂ sequestration

Dissolution of CO ₂ into brine causes the density of the mixture to increase. The density gradient induces natural convection in the liquid phase, which is a favorable process of practical interest for CO ₂ storage. Correct estimation of the dissolution rate is important because the time scale for dissolution corresponds to the time scale over which free phase CO ₂ has a chance to leak out. However, for this estimation, the challenging simulation on the basis of the convection-diffusion equation must be done. In this study, a pseudodiffusion coefficient is introduced which accounts for the rate of mass transferring by both convection and diffusion mechanisms. Experimental tests in fluid continuum and porous media were performed to measure the real rate of dissolution of CO ₂ into water during the time. The pseudo-diffusion coefficient of CO ₂ into water was evaluated by the theory of pressure decay and this coefficient is used as a key parameter to quantify the natural convection and its effect on mass transfer of CO ₂. Measured CO ₂ mass transfer rate from experiments are in reasonable agreement with values calculated from diffusion equation performed on the basis of pseudo-diffusion coefficient.