Enhanced convective dissolution due to an A + B → C reaction: control of the non-linear dynamics via solutal density contributions

Abstract

Chemical reactions can have a significant impact on convective dissolution in partially miscible stratifications in porous media and are able to enhance the asymptotic flux with respect to the non-reactive case. We numerically study such reactive convective dissolution when the dissolving species A increases the density of the host phase upon dissolution and reacts with a reactant B present in the host phase to produce C by an A + B → C reaction. Upon varying the difference ΔR_CB = R_C − R_B between the Rayleigh numbers of the product C and the reactant B, we identify four regimes with distinct dynamics when the diffusion coefficients are the same. When ΔR_CB < 0, the density profiles are non-monotonic and the non-linear dynamics are seen to depend on the relative values of the density at the interface and the initial density of the host phase. For ΔR_CB > 0, the monotonic density profiles are destabilizing with respect to the non-reactive case above a certain critical value ΔR_cr. We analyze quantitatively the influence of varying ΔR_CB and the ratio β = B₀/A₀ of the initial concentration of B and the solubility of A on the asymptotic steady flux, the wavelength of the fingers and the position of the reaction front. In the context of CO₂ geological sequestration, understanding how such reactions can enhance the dissolution flux is crucial for improving the efficiency and safety of the process.