Surfactant chemical-enhanced oil recovery plays a crucial role in achieving ultralow interfacial tension between remaining crude oil and injected water, thereby enhancing oil recovery rates. This study aims to investigate the impact of pressure and gas/oil ratios (GORs) on surfactant flooding for enhanced oil recovery, focusing on high-pressure and high-temperature (HPHT) conditions. High-temperature salinity screening was employed to identify optimal surfactant formulations for Type III microemulsions. HPHT phase behavior tests were conducted to examine water and oil solubilization under pressure, with a particular focus on how GOR affects these parameters. The research utilized a unique approach to analyzing GOR variations at different pressure levels in a crude oil sample through salinity screening experiments and HPHT phase behavior tests using methanecontaining live oil. With increasing pressure, while maintaining a lower GOR, the water solubilization ratio in the microemulsion increased dramatically, whereas the solubilization ratio of oil decreased. Furthermore, both oil and water solubilization ratios decreased at higher GOR and pressure compared to dead oil results. The optimum salinity was found to be equal to 17,283 ppm at a GOR of 180 scf/stb and decreased to 14,403 ppm at a GOR of 280 scf/stb, validating that the optimum salinity decreases with increasing GOR value. The tendency of microemulsion generation also decreased with increasing GOR from 180 to 280 and 380 scf/stb. Additionally, the minimum bubble point pressure required to solubilize the total amount of gas in the oil increased from 2500 psi at a GOR of 280 scf/stb to 3000 psi at a GOR of 380 scf/stb. The microemulsion was not observed at any pressure level and at any salinity at a higher GOR (380 scf/stb). This study provides valuable insights into the petroleum industry, offering potential improvements in reservoir management, forecasting accuracy, and recovery efficiency. The research's innovative approach to analyzing GOR variations and its impact on surfactant flooding under HPHT conditions contributes to the field's knowledge and could lead to more effective and efficient oil recovery strategies.
