Amphoteric surfactants are known for their tolerance to salinity and temperature and are considered as likely candidates for enhanced oil recovery (EOR) application in harsh reservoir environments. This study looked into the phase behavior properties of an amphoteric surfactant, OCT-1 and its interfacial lowering capability over weeks. The surfactant concentrations used ranged from 0.05 to 0.5% active and phase behavior studies were conducted with seawater of salinity 57,000 ppm and crude oil at a reservoir temperature 90°C.
Interfacial tension measurements showed that this surfactant is capable of lowering oil-water interfacial tension (IFT) considerably at low surfactant concentrations. Surfactant concentrations of 0.05% and 0.1 % were able to achieve lowest IFTs till a week into the study. Thereafter, only the 0.2 % concentration was able maintain a low IFT till three weeks. A measurement of surfactant concentrations showed that the aqueous phase surfactant concentration stayed much stable for all surfactant concentrations. An examination of photomicrographs revealed that a tiny amount of the oil partitioned into the aqueous phase enhancing the IFT lowering capability of the aqueous phase at these low concentrations.