Gas injection process for more oil recovery and in particular CO2 injection is a well-established method to increment oil recovery from underground oil reservoirs. CO2 sequestration which takes place during this enhanced oil recovery (EOR) method has positive impact on reducing the greenhouse gas emission which causes global warming. Direct gas injection into depleted oil reservoirs, encounters several shortcomings such as low volumetric sweep efficiency, early breakthrough (BT) and high risk of gas leakage in naturally fractured carbonate oil reservoirs. Carbonated water injection (CWI) has been recently proposed as an alternative method to alleviate the problems associated with gas injection. In this paper, the results of extensive experimental tests of ultimate oil recovery efficiency as both secondary and tertiary CWI tests and their CO2 storage capacity for an Iranian carbonate reservoir are presented. Besides, the CWI recovery efficiencies are compared with traditional water flooding (WF) test. The results showed that higher ultimate oil recovery is achieved when carbonated water is injected as secondary technique compared to tertiary process. The results showed 40.54% and 56.74% more oil recovery during tertiary carbonated water injection (TCWI) and secondary water injection (SCWI) compared to the corresponding water flooding, respectively. However, the CO2 storage capacities for both TCWI and SCWI cases were almost the same, as it was measured to be more than half of the total delivered CO2.

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