The two most important trapping mechanisms for CO2 storage in saline aquifers, namely residual gas trapping and solubility trapping, are examined. It is shown that a water injector located above the CO2 injector can be used to enhance both residual gas trapping and solubility trapping. Using simulation, the optimal location and operating conditions for the water injector are determined for both a low-permeability aquifer and a high-permeability aquifer. The analysis is performed using the concept of Pareto optimal solutions for multiple-objective optimization. It is shown that for a low-permeability aquifer, the use of a water injector can significantly increase the amount of residual gas trapping, which results in a substantial increase in the total trapped amount. For a high-permeability aquifer, the use of a water injector above the CO2 injector does not increase CO2 trapping.

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