Low volumetric sweep efficiency, early breakthrough of injected fluid, and high risk of gas leakage from the reservoir are the major technical challenges associated with direct gas and water injection into oil reservoirs. Injection of carbonated water (CW) into oil reservoirs is a carbon dioxide-augmented water injection technique, which results in improved oil recovery and possible CO 2 storage in the reservoir. In this paper, the potential of carbonated water injection (CWI) into an Iranian carbonate reservoir for the purpose of improving oil recovery was investigated. In addition, the interfacial tension (IFT) of crude oil and two different carbonated brines (carbonated formation brine and carbonated seawater) as well as CO 2 solubility in these two carbonated brines was determined. Experimental results showed that CO 2 solubility in both brines increases with pressure and decreases with temperature. However, CO 2 solubility was more promising in seawater compared to formation brine because of the lower salinity. The IFT results showed that increasing the temperature from 40 to 100°C and increasing the pressure from 1000 to 2500 psi had a positive impact on reducing the IFT between carbonated brines and oil. In addition, core flooding experiments showed that oil recovery increased with CWI as compared to conventional water flooding (WF). However, secondary carbonated water injection (SCWI) resulted in higher oil recovery compared to tertiary carbonated water injection (TCWI). A maximum oil recovery of 21.75%, 61.63%, and 52.58% was achieved with conventional WF, SCWI, and TCWI, respectively.

The main purpose of this study is to investigate the effect of reaction temperature and NH4HCO3 on the overall performance of a pH swing mineral carbonation. The overall performance of the pH swing process is investigated in terms of carbonation efficiency and product purity. Initially, 2 M H2SO4 is used for red gypsum dissolution at 70 °C. Then in the second stage, NH4OH is added for increasing the solution pH and removing the impurities from solutions. Finally, CO3 2is introduced to calcium rich solution in the form of pure CO2 and NH4HCO3. The experimental results show that using NH4HCO3 improves carbonation efficiency and product purity. 2 Carbonation efficiency attains a maximum value at 75 °C and then decreases gradually with increasing temperature up to 300 °C, with both CO2 and NH4HCO3. In this research, CaCO3 with the maximum purity of 99.05% is produced successfully when NH4HCO3 is used as a CO3 2source.

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