CO ₂ foam for enhanced oil recovery (EOR) applications using low adsorption surfactant structure

The ability of surfactants to interact with CO ₂ is essential if the CO ₂ foam is intended to augment a water flooding process as a method to displace oil from a reservoir. Apart from improved sweep efficiency of foam, CO ₂ reduces the oil viscosity, causes the oil to swell, lowers the high interfacial tension between oil and rock, dislodges the immobile oil, and hence increases the volumetric sweep efficiency. The surfactant must possess suitable structure to successfully play these roles. In this context, a new surfactant with different functionalities has been synthesized to examine its CO ₂ -philicity. The surfactant was evaluated for the enhanced oil recovery (EOR) suitability by firstly examining the fluid–fluid compatibility in various temperatures, salinity, and hardness conditions. The foaming properties were also assessed. The interfacial tension (IFT) between the surfactant and CO ₂ gas at 90 °C and up to 2700 psi pressure revealed some interesting findings. The IFT of CO ₂ –brine without surfactant dropped from a value of 70 to 30 mN/m when CO ₂ critical pressure approached 1070 psi, and it remained at 30 mN/m at higher pressures. The incorporation of surfactant achieved the lowest IFT of 1.76 mN/m at critical pressure conditions at 90 °C. The foam stability of the surfactants was also evaluated. In the core flooding test, the mobility reduction factor (MRF) values reflected the same trend as that of IFT lowering and foam stability. The three-tailed surfactant showed the MRF of 3.4 while alpha olefin sulfonate (AOS) (commercial surfactant) had the MRF value of 1.3. The three-tailed surfactant provided the highest recovery of 96% of residual oil in place (ROOIP). The adsorption of the surfactant was low at less than 0.5 mg/g.