This paper presents results of modeling long-term CO2 storage in a shallow saline aquifer with a commercial black-oil reservoir simulator. Realistic CO2/water phase behavior (pVT properties) covering all pressure, temperature and compositional conditions accounted for during the simulations have been used. The pressure and temperature in the aquifer is above the CO2 supercritical conditions giving rise to the existence of a two-phase fluid system of CO2 as a supercritical fluid ("gas") and CO2 dissolved in the aqueous phase. The objective was to model scenarios of CO2 storage in aquifer with emphasis on the sensitivity of CO2 distribution in the deposit with respect to critical CO2 saturations during the injection period and to residual CO2 saturation for water reentering CO2 filled volumes (hysteresis in fluid saturations). The re-distribution of water occurs after stop of CO2 injection due to gravity segregation of dense CO2 saturated water and CO2-free water. The impact of various reservoir parameters has been studied, including average permeability, vertical to horizontal permeability ratio (kv/kh), relative permeability, and capillary pressure. For the saturation functions the main focus has been on end points and hysteresis effects. It is observed that storage of CO2 as residual gas is most important for low kv/kh ratios.

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