Reactive Transport Modeling of the Enhancement of Density-Driven CO(2) Convective Mixing in Carbonate Aquifers and its Potential Implication on Geological Carbon Sequestration

We study the convection and mixing of CO(2) in a brine aquifer, where the spread of dissolved CO(2) is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing. The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system. The extent of convection is quantified in term of the CO(2) saturation volume of the storage formation. Our results suggest that the density increase of resident species causes significant enhancement in CO(2) dissolution, although no significant porosity and permeability alterations are observed. Early saturation of the reservoir can have negative impact on CO(2) sequestration.