Synergistic Effect of Ionic Liquid and Surfactant for Enhancing Imbibition in Carbonate Reservoirs

Abstract

Abstract Chemical imbibition technology is an effective way to enhance oil production for fractured carbonate reservoirs. Surfactants have been reported frequently in the literature to enhance imbibition process, while the combination of ionic liquid and surfactants is less investigated. This study aims to analyze the synergic mechanisms of the combination contributing to imbibition process to assist in the application of chemical imbibition technology. The laboratory experiments consisted measurement of several parameters: contact angle, interfacial tension (IFT), and zeta potential. Effectiveness of chemicals were evaluated by spontaneous imbibition using Amott cells. Three functional surfactants and four ionic liquids were investigated. Carbonate core plugs and chips were aged in crude oil at 95°C for more than 3 weeks to render them oil-wet prior to spontaneous imbibition and contact angle tests, respectively. Effect of ionic liquids on wettability alteration, IFT change and ultimate imbibition potential were analyzed. The three surfactants and four ionic liquids were used with different IFT and wettability alteration ability. The ionic liquids have limited effects on IFT change and zeta potential on carbonate rock surface for all the tested surfactants, while the ionic liquid EMIM Ac and one anionic surfactant can modify the oil-wet carbonate surface to water-wet effectively, with contact angle reduced from ∼140° to ∼56°. The ionic liquid can enhance the stability of oil-water interface film, thus keeping the water-wetness status longer, compared with surfactant alone. Using the combination of ionic liquid and surfactant, the imbibition production can be improved by at 6 % compared with surfactant imbibition. The more water-wetness caused by ionic liquid contributes to the incremental oil production. An optimized imbibition agent formulation with high imbibition production potential and relatively lower chemical cost was developed for up-scale consideration. This study investigated the synergistic effect of ionic liquid and surfactant on different parameters, especially the wettability alteration, which helps better understand the complex chemical imbibition phenomenon. The optimized imbibition agent has potential for further investigation.