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The density-driven convection coupled with chemical reaction is the preferredmechanism for permanently storing CO2 in saline aquifers. This study uses a 2Dvisual Hele-Shaw cell to evaluate and visualize the density-driven convectionformed due to gravitational instabilities, also known as Rayleigh-Taylorinstability. The primary goal of the experiments is to understand the variousmechanisms for the mass transfer of gaseous CO2 into brine with differentinitial ionic concentrations and flow permeability. Moreover, the impact of CO2flow rates, injection locations, reservoir dipping angle, and permeabilityheterogeneity is also investigated. We observed that the presence of saltsresulted in earlier onset of convection and a larger convective fingerwavelength than the case with no dissolved salts. In addition, experimentaldata showed a higher lateral mixing between CO2 fingers when dipping isinvolved. The visual investigation also revealed that the CO2 dissolution rate,measured by the rate of the convective fingers advance, depends on the type andconcentration of the ions present in the brine. The CO2 dissolution forsolutions with varying salt dissolved, indicated by the area of thepH-depressed region, is observed to be 0.38-0.77 times compared to when no saltis present. Although convective flow is slowed down in the presence of salts,the diffusive flux is enhanced, as observed from both qualitative andquantitative results. Moreover, the reduced formation permeability, introducedby using a flow barrier, resulted in numerous regions not being swept by thedissolved CO2, indicating an inefficient dissolution. We also investigated theeffect of discrete high conductivity fractures within the flow barriers, whichshowed an uneven vertical sweep and enhanced flow channeling. Lastly, theparameters regarding CO2 leakage risk during storage are identified anddiscussed.

Fundamental Investigation of Reactive-Convective Transport: Implications for Long-Term Carbon dioxide (CO2) Sequestration