AbstractWe study the convection and mixing of CO₂ in a brine aquifer, where the spread of dissolved CO₂ 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 CO₂ saturation volume of the storage formation. Our results suggest that the density increase of resident species causes significant enhancement in CO₂ dissolution, although no significant porosity and permeability alterations are observed. Early saturation of the reservoir can have negative impact on CO₂ sequestration.