Enhancing carbonated water efficiency in the fluid and rock surface activity and swelling behavior of crude oil using an anionic CO2-philic surfactant

• To enhance carbonated water, its formulation was adjusted by adding a CO 2 -philic anionic surfactant. • The fluid and rock surface activity and swelling behavior of crude oil were investigated. • IFT trends show that optimal salinity plays an important role at low pressures, but at high pressures, it decreases with increasing salinity. • Oil swelling varies from 2.31% to 23.51% depending on the conditions, and at different salinities, it increases with increasing pressure. • The lowest contact angle is achieved at 42.78° at a salinity of 30,000 ppm and a pressure of 750 psi. Both carbonated water injection and surfactant flooding are efficient techniques for enhanced oil recovery (EOR). Carbonated water enhances oil recovery through mechanisms such as oil swelling, altering the wettability of reservoir rocks, and lowering interfacial tension (IFT). Similarly, surfactants reduce IFT, which subsequently decreases capillary pressure in the reservoir, facilitating the extraction of residual oil after natural and secondary recovery stages. However, the IFT in the carbonated water method does not reach the minimum possible to affect capillary pressure. The behavior of carbonated water is influenced by the interactions and solubility of carbon dioxide (CO 2 ) in both water and oil. In this research, we altered the formulation of carbonated water by incorporating a CO 2 -philic anionic surfactant to improve its characteristics and studied its impact on the primary mechanisms. The experimental temperature was considered equal to the reservoir temperature and the parameters of CO 2 pressure, surfactant concentration, and salinity were varied. The results indicated the positive effect of improving the carbonated water formulation with the specific surfactant, such that at a pressure of 750 psi and salinities of 0, 10 K, 30 K, and 74 K ppm, the IFT reached 1.613, 1.045, 0.837, and 0.713 mN/m, respectively. The IFT trends showed that at low pressures, the optimal salinity played an important role, but at high pressures, IFT decreased with increasing salinity. The oil swelling varied from 2.31 % to 23.51 %, depending on the conditions, and at different salinities, the oil droplet volume increased with increasing pressure. The contact angle at CMC decreased in proportion to salinity with its lowest value being 42.78° at the optimal salinity of 30,000 ppm and the highest pressure of 750 psi, indicating hydrophilicity.