Experimental and Simulation Studies of Density-Driven-Convection Mixing in a Hele-Shaw Geometry with Application for CO2 Sequestration in Brine Aquifers

Abstract

Abstract CO2 sequestration in deep formations is being actively considered for the reduction of greenhouse gas emissions. Saline aquifers are considered as one of the most favorable options for this purpose. It has been observed that dissolution of CO2 into brine causes increased density of the mixture. If the corresponding Rayleigh number of the porous medium is high enough to initiate convection flows, density-driven-convection happens and the rate of dissolution increases. Early time dissolution of CO2 in brine is mainly dominated by molecular diffusion while it will be accelerated by density-driven-convection. More contribution of dissolution mechanism for trapping of CO2 decreases the risk of leakage. Density-driven-convection mechanism was investigated in a Hele-Shaw cell with colored-brine and fresh-water instead of CO2-diffusive layer and brine. A convective instability is created by colored-brine diffusing onto the surface of a fresh-water layer. For this configuration, density-driven-convection flow enhances the mass transfer rate of high density fluid into the low density one. The analysis is also done numerically with Eclipse reservoir simulation software. With this analysis, the effects of density-driven-convection on accelerating the rate of dissolution are investigated. Although the horizontal wavelength of the initial instability is small, an increase in the horizontal wavelength of the convective flow with time and depth is observed as the resulting two-dimensional convection develops. Effects of density of fluids and also dip of the systems on convection flows are studied here. Also the changes in geometry of the convection streams with depth and time are investigated. The results have important implications in dissolution trapping of CO2 in brine aquifers.