Surfactants employed in conventional and unconventional reservoirs for enhanced oil recovery—A review

Due to the continuous depletion of crude oils in the reserves, and continuous rise in energy demand, there is currently a widespread interest in various methods of chemical enhanced oil recovery (EOR). Surfactants flooding improves oil recovery by combining various mechanisms and this approach has proven to be effective. Surfactant flooding is still threatened by problems which are unstable under excessive adsorption and harsh reservoir conditions. Research has shown that anionic surfactant is most preferred for EOR specifically with sandstone reservoirs. In some cases, after injecting non-ionic, cationic, or both surfactants, into the carbonate reservoirs, better performance has been documented. To produce surfactants for reservoirs with properties such as high/ultra-high temperature, ultra/high oil viscosity, ultra-high salinity, and low/extra-low permeability, new knowledge is needed. An ideal surfactant with highest recovery should possess larger IFT reduction, wettability alteration, and asphaltene inhibition capabilities. This review provides an experimental study on surfactant application to conventional and unconventional reservoirs for EOR. Thus, establishing a good foundation for preparing and designing prospective field-scale chemical supported EOR systems. Furthermore, this study presents the influence of oilfield element variation during surfactant flooding, types and EOR mechanisms, its application in unconventional reservoirs, surfactant adsorption and adsorption mitigation, surfactant phase behavior etc.