Carbon capture utilizations and storage strategies (CCUS) have recently attracted many interests to mitigate the global warming and reducing CO2 emission in the atmosphere. Injecting CO2 into the depleted hydrocarbon reservoirs and aquifers has been focused as one the main CCUS strategy. This paper presents a comprehensive study on the effects of reservoir heterogeneity that are defined as important physical criteria to determine the success of CCUS projects.

We develop an equation of state (EOS) fluid characterization with 34 components. Wide range of fluid composition from black oil to gas condensate system was generated to capture the degree of fluid heterogeneity in the reservoir. The results of various PVT tests such as CCE, swelling test with CO2 and MMP were compared for different heterogeneous fluid systems. The pseudoized EOS model was optimized to a minimum number of pseudo components that reproduce the physical properties of full-EOS model. The detailed EOS model was then employed by a full compositional reservoir simulation model to study the CO2 injection in a depleted oil reservoir with high degrees of heterogeneities. Various range of porosities, permeabilities, formation temperature and injection pressure scenarios were considered during sensitivity analysis of CO2 storage in depleted reservoir.

Prior to CO2 injection the reservoir depleted from initial reservoir pressure to its abandoned pressure which resulted in forming a gas cap zone with low residual oil saturation. Case scenarios with homogeneous fluid composition, and petrophysical heterogeneity at different reservoir conditions where considered for initialization of the reservoir sector model. Results show that the oil saturation at the abandoned pressure is strongly dependent to the initial condition which effect the CO2 storage efficiency at the later period. During CO2 injection period, the oil recovery profile and the CO2 storage are considerably affected by reservoir heterogeneity, reservoir conditions and different injection scenarios. High CO2 storage was achieved with high CO2 injection pressure with a certain degree of heterogeneity and at low reservoir temperatures.

This paper provides a better understating of CO2 storage mechanism under various range of petrophysical heterogeneity and different reservoir conditions.

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