The effect of heterogeneity on the character of density-driven natural convection of CO2 overlying a brine layer

The efficiency of mixing in density-driven natural-convection is largely governed by the aquifer permeability, which is heterogeneous in practice. The character (fingering, stable mixing or channeling) of flow-driven mixing processes depends primarily on the permeability heterogeneity character of the aquifer, i.e., on its degree of permeability variance (Dykstra–Parsons coefficient) and the correlation length. Here we follow the ideas of Waggoner et al. (1992) [13] to identify different flow regimes of a density-driven natural convection flow by numerical simulation. Heterogeneous fields are generated with the spectral method of Shinozuka and Jan (1972) [13], because the method allows the use of power-law variograms. In this paper, we extended the classification of Waggoner et al. (1992) [13] for the natural convection phenomenon, which can be used as a tool in selecting optimal fields with maximum transfer rates of CO2 into water. We observe from our simulations that the rate of mass transfer of CO2 into water is higher for heterogeneous media.

Research highlights► Our numerical simulations demonstrate three flow regimes (fingering, dispersive, and channeling) for density-driven natural convection flow in heterogeneous media. ► Numerical simulations in homogenous porous media underestimate the mass transfer rate of CO2 into water. The rate of CO2 dissolution in heterogeneous media is larger than in homogeneous media. This means that larger volumes of CO2 can be stored in heterogeneous media. ► We found no correlation between the mass of dissolved CO2 in water and the heterogeneity measures.