Mechanistic studies of enhanced oil recovery by imidazolium-based ionic liquids as novel surfactants

Abstract

Ionic liquids are recently considered as an alternation to surfactants for their application in enhanced oil recovery (EOR) because of their promising surface-active properties. In the present study, the ability of a series of synthesized ionic liquids (C8mimBF4, C10mimBF4 and C12mimBF4) to reduce interfacial tension (IFT) and change the wettability of oil-wet rock have been investigated. Results demonstrated that all three synthesized ionic liquids enhanced interfacial properties and rock-wetting characteristics. The ionic liquids were able to significantly reduce IFT and remained stable at high temperature and saline conditions. Addition of organic alkali also showed a synergistic effect on IFT reduction between crude oil and ionic liquid solution. FTIR and zeta potential measurements were conducted to establish the mechanism of wettability alteration of oil-wet rock. Emulsification tests confirmed the capability of the ionic liquids to emulsify the trapped oil, which is an important mechanism of chemical EOR. The loss of ionic liquids by adsorption on rock surface was studied, and the adsorption data were analyzed by Langmuir and Freundlich models. Microemulsion study showed Winsor type III behavior with ultra-low IFT, which is beneficial for EOR application. Sand pack flooding experiments were conducted to study the EOR efficiency using the synthesized ionic liquids and around 32.28% additional recovery was observed after the conventional water flooding with injection of ionic liquid, polymer and alkali slugs.