Comprehensive Review on the Role of Surfactants in the Chemical Enhanced Oil Recovery Process

With a constant upsurge in energy demand, production from depleted and harsh reservoirs through enhanced oil recovery techniques (EOR) has significantly increased. Among many EOR techniques, chemical EOR (cEOR) is one of the most widely used methods of oil extraction. Surfactants used in cEOR are instrumental in reducing interfacial tension (IFT) and altering the wettability of rock, which leads to additional oil recovery. This review draws attention to detail on surfactants from fundamentals to field scale. Properties of surfactants like phase behaviors, critical micelle concentration (CMC), hydrophilic–lipophilic balance and deviation, zeta potential, and their importance are discussed in depth. The presence of a saline environment, polymer, cosurfactant, and other factors affecting the performance of surfactant during the cEOR process are also elaborated. Key findings on surfactant adsorption on reservoir rock with other influencing aspects have also been reported in this study. Types of surfactants, from basic to the likes of polymeric, viscoelastic, Gemini, natural, and their effects on oil recoveries have been analyzed and compared. Special emphasis on emerging aids for surfactant flooding such as applications of nanotechnology, use amphoteric Janus particles, and synergies of surfactant–low salinity water flooding, along with their mechanisms and recent advances have been thoroughly duscussed. Lastly, the review delineates discerning criteria for the selection of surfactants, reviews recent field applications, and outlines the challenges that the industry faces while implementing surfactant cEOR. It has been found that exhaustive studies have been conducted on sandstones with success. However, extreme temperature and saline conditions in the case of carbonate reservoirs limit the applicability of surfactants, and the pursuit to accomplish its efficacy continues.