Partitioning behaviour of novel surfactant mixture for high reservoir temperature and high salinity conditions

Investigating the use of surfactants in high temperature and high salinity conditions can assist expanding the application of surfactant-based enhanced oil recovery (EOR) to more challenging environments. In the present work, compatibility and thermal stability for alkyl ether carboxylate (AEC) and alkylpolyglucoside (APG) were investigated at anaerobic conditions. The most suitable surfactant formulation was selected after passing the screening criteria of compatibility and thermal stability for the studied offshore field. Interfacial tension (IFT) and partitioning of the selected surfactant formulation were then studied at different surfactant concentrations, brine/oil ratios, temperatures, and salinities. The partitioning behaviour of the AEC:APG mixture was comprehensively examined under the before mentioned conditions. The screening experiments for the individual surfactant AEC have shown poor compatibility and thermal stability. Whereas, a 50:50 ratio of the anionic-nonionic (AEC:APG) mixture has passed the compatibility test criteria. For 90 days, the mixture demonstrated remarkable compatibility and thermal stability at high water salinity (32k ppm) and high temperature (106 °C). The IFT of the AEC:APG mixture was significantly affected by the increase of surfactant concentration, temperature and salinity. The proposed mechanism, through the experimental results, illustrated that as surfactant mixture concentration gradually increased, additional molecules of AEC occupied the interface whereas the APG molecules tend to attach to the existed APG molecules at the interface via hydrogen bonds and they both formed a new interface. The formed interface caused the increment of the IFT values. The outcomes proved that APG was the most dominant surfactant as it had the highest impact on the mixture behaviour. It is believed that the outcomes of this work are expected to provide a better fundamental understanding of the surfactant partitioning behaviour in high temperature and high salinity conditions, as well as providing a basic guideline to design efficient surfactant flooding slugs.