Effects of geochemical reaction on double diffusive natural convection of CO2 in brine saturated geothermal reservoir

Abstract

In order for mitigation of greenhouse gas emissions, as we know, the storage of CO2 in deep geological formations is considered as a promising option. Besides convective mixing an understanding of geochemical reaction that affects the long term storage process in deep saline aquifers is of great importance. In this study we numerically investigate double diffusive natural convection of CO2 in brine saturated geothermal reservoir which is anisotropic in permeability variations, impervious from the sides, and is open to CO2 at the top. Our primary objective is to understand effects of geochemical reactions of different rates and orders on density driven natural convection of CO2 due to concentration and geothermal gradients. We present propagation of CO2 plumes over long period of time by analyzing different combination of problem parameters: Damkohler number (0.01⩽Da⩽105) with variation of 1st, 2nd, and 3rd order reactions; solutal Rayleigh number (500⩽Ras⩽2000); the buoyancy ratio (2⩽N⩽100); Dykstra–Parsons coefficient (0.35⩽Vdp⩽0.85); and fixed Lewis and Prandtl numbers. Reaction order is set from relevant stoichiometric ratio. In each case results are quantified in term of percentage of CO2 deposition. It is found that mineral interactions make traceable difference of depositions as reaction rate increases, especially when Da>103. In one hand, compared to very minimum geochemical interaction (Da∼0.01) the strong reaction effects (Da∼104) can make difference of more than 5% in the period of 500years of trapping. On the other hand, at a fixed equivalent Da reaction order also makes substantial distinction as deposition time passes. Heterogeneity plays a vital role. Geothermal gradient has very negligible effect, however only after very long time (>500years).