Bio-based surfactant for enhanced oil recovery: Interfacial properties, emulsification and rock-fluid interactions

Anionic surfactants are very effective for application in enhanced oil recovery (EOR) in sandstone reservoirs because of their promising surface-active properties. Considering the non-biodegradability of some of the commercial surfactants, the present study deals with an anionic surfactant synthesized from naturally occurring soap-nut oil with excellent interfacial properties for application in EOR. The soap-nut surfactant showed the promising properties of interfacial tension (IFT) reduction, emulsification, rock wettability alteration, which are desirable for its application in EOR. An ultra-low IFT value of 2.123 x 10( -2) mN/m between crude oil and surfactant solution was obtained at critical micelle concentration (CMC), which was further reduced to 2.037 x 10( -3) mN/m at optimum salinity. Phase behaviour studies showed the formation of Winsor III emulsion phase which is beneficial for recovery of the trapped oil from the fine pores of the reservoir by miscibility mechanism. The surfactant exhibited favourable rock-wetting ability from oil-wet rock to water-wet condition. The loss of surfactant by adsorption on the rock surface was studied, and the adsorption data were analysed by Langmuir and Freundlich models. Injection of a small pore volume of surfactant-slug augmented with polymer slug as mobility buffer recovered more than 30% of original oil in place (OOIP) after the conventional water-flooding.