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This study estimates the plume migration of mobile supercritical phase (flowing), aqueous phase (dissolved), and ionic phase CO 2 (bicarbonate), and evaluates the spatial distribution of immobile supercritical phase (residual) and mineral phase CO 2 (carbonates) when CO 2 was sequestered. This utilized a simulation, in an anticline structure of a deep saline aquifer in the Tiechenshan (TCS) field, Taiwan. All of the trapping mechanisms and different CO 2 phases were studied using the fully coupled geochemical equation-of-state GEM compositional simulator. The mobile supercritical phase CO 2 moved upward and then accumulated in the up-dip of the structure because of buoyancy. A large amount of immobile supercritical phase CO 2 was formed at the rear of the moving plume where the imbibition process prevailed. Both the aqueous and ionic phase CO 2 finally accumulated in the down-dip of the structure because of convection. The plume volume of aqueous phase CO 2 was larger than that of the supercritical phase CO 2 , because the convection process increased vertical sweep efficiency. The up-dip of the structure was not the major location for mineralization, which is different from mobile supercritical phase CO 2 accumulation.

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The purpose of this study is to reduce the risk of leakage of CO2 geological storage by injecting the dissolved CO2 solution instead of the supercritical CO2 injection. The reservoir simulation method is used in this study to evaluate the contributions of the different trapping mechanisms, and the safety index method is used to evaluate the risk of CO2 leakage. The function of the dissolved CO2 solution injection is performed by a case study of a deep saline aquifer. Two scenarios are designed in this study: the traditional supercritical CO2 injection and the dissolved CO2 solution injection. The contributions of different trapping mechanisms, plume migrations, and the risk of leakage are evaluated and compared. The simulation results show that the risk of leakage via a natural pathway can be decreased by the approach of injecting dissolved CO2 solution instead of supercritical CO2. The amount of the CO2 retained by the safe trapping mechanisms in the dissolved CO2 solution injection scenario is greater than that in the supercritical CO2 scenario. The process of CO2 mineralization in the dissolved CO2 solution injection scenario is also much faster than that in the supercritical CO2 scenario. Changing the injection fluid from supercritical CO2 to a dissolved CO2 solution can significantly increase the safety of the CO2 geological storage. The risk of CO2 leakage from a reservoir can be eliminated because the injected CO2 can be trapped totally by safe trapping mechanisms.