Phase Behavior and Interfacial Properties of an Amphoteric Surfactant for a High Temperature and High Salinity Reservoir

The phase behavior of the mixtures of crude oil/aqueous solutions has been well studied to screen appropriate surfactants in the aqueous solution to improve oil production. Several microemulsion types present when aqueous surfactant solution mixes with oils in the presence of electrolytes. By varying the salinity from low to high values, the microemulsion type could pass from Winsor Type I, and Winsor Type III to Winsor Type II. This study looked into the phase behavior properties of an amphoteric surfactant, OCT-9, with a light crude oil from a Middle East representative carbonate reservoir and its interfacial tension (IFT) reduction capability in high temperature and high salinity conditions. The phase behavior study was conducted under salinities ranged from 10,700 mg/L to 185,900 mg/L, containing Ca2+ and Mg2+ at 90 °C with a light crude oil. IFT was estimated using the oil and water solubilization ratios obtained from phase behavior results. Winsor Type III micoemulsion appeared in the salinity ranging from 85,500 mg/L to 138,900 mg/L. The solubilization ratio was 4.7 at the optimum salinity of 128,000 mg/L. This leads to an IFT of 0.014 mN/m by Chun Huh’s equation (Huh 1979). The fitting results modified by the Hydrophilic-Lipophilic Deviation-Net Average Curvature (HLD-NAC) model were in good agreement with the experimental data, which further determined the salinity range of Winsor Type III. IFT was also measured by spinning drop tensiometer. The result was consistent with the value calculated based on phase behavior tests. These results show significant oil production potential using this surfactant for the high temperature and high salinity reservoir.