Density-driven Natural Convection in Dual Layered and Anisotropic Porous Media with Application for CO2 Injection Project

In this paper we investigate the mass transfer of CO2 injected into a layered and anisotropic (sub)-surface porous formation saturated with water. Solutions of carbon dioxide in water and oil are denser than pure water or oil. We perform our analysis to a rectangular part of the porous medium that is impermeable at the sides except at the top, which is exposed to CO2. For this configuration density-driven natural convection enhances the mass transfer rate of CO2 into the initially stagnant liquid. The analysis is done numerically using mass and momentum conservation laws and diffusion of CO2 into the liquid. This configuration leads to an unstable flow process. Numerical computations do not show natural convection effects for homogeneous initial conditions. Therefore a sinusoidal perturbation is added for the initial top boundary condition. It is found that the development of fingers is fastest for mass transfer enhancement by natural convection is largest for large anisotropy ratio’s and smaller for small ratio's. It is found that the mass transfer increases and concentration front moves faster with increasing Rayleigh number if the high permeability layer is on top. Of particular interest is the case when the Rayleigh number for the high permeable layer is above the critical Rayleigh number (Racr = 40) and smaller than Racr for the low permeable layer. The results of this paper have implications in enhanced oil recovery and CO2 sequestration in aquifers.