Numerical modelling of dissolution and convection patterns of CO2 injected into saline aquifers

CO2 injected into saline aquifers is at supercritical pressures and temperatures. This supercritical CO2 is less dense than the surrounding brine and rises to the base of impermeable layers where it becomes trapped. Over longer time periods CO2 dissolves in the brine causing an increase in brine density within the diffusive boundary layer. This density contrast can cause downward convection of CO2 rich brine. Convection will give rise to an acceleration in CO2 dissolution. Dissolution of CO2 into the brine, and therefore convection, is desirable as it reduces the risk of CO2 escaping vertically through the caprock. TOUGH2-MP is a massively parallel version of the TOUGH2 numerical simulation program which models multi-phase fluid and heat flow in porous media. For this work we have used TOUGH2-MP in conjunction with the ECO2N module to study mixtures of water, salt and CO2. Simple models have been developed using TOUGH2-MP/ECO2N to explore the effect of different parameters on CO2 dissolution, convection patterns and timescales. Small scale 2D models with typical aquifer properties have been used. The parameters investigated include flow in the aquifer and the effect of variations in aquifer geometry. An investigation has also been made into the effect of model resolution on convection. These results can then be used as a basis for carrying out more complex, large scale simulations.