Imidazolium based ionic liquids for enhanced oil recovery on the carbonate reservoir

• The ionic liquids alters the rock wettability from strongly oil-wet into water-wet. • The diluted concentration of ionic liquids improve the oil recovery substantially. • The longer alkyl chain ionic liquids works more effectively than the shorter chain ones. • The measured wettability and interfacial tension data supports the oil recovery mechanisms. • Low retention of ionic liquids are considered to be the viable additives for the deep reservoir oil recovery. Improving the oil recovery by changing the wettability using chemicals often possess huge challenges in the harsh oil-wet carbonate reservoirs, such as chemical instability, high retention, lack of deliverability in the deep reservoir, etc. In this study, we investigated the adsorptive behavior of imidazolium-based ionic liquids (ILs) on the carbonate reservoir, and also evaluated their performance in the oil recovery using the high temperature and high pressure coreflood setup. The measured adsorption values are well within the limit of field requirements. In which, the ILs with longer alkyl chains had shown less adsorption than the shorter ones. Next, in the coreflood oil recovery studies, the injection of ILs after waterflooding increased the oil recovery by 12–26% additionally. As expected, the lengthier alkyl chain containing ILs work more effectively than the shorter chain ones. For a case of reference, we also studied a few conventional surfactants (anionic, cationic, nonionic, and zwitterionic). We also extracted the unsteady state two-phase relative permeability curves of the SW and ILs flooding coreflood experiments to understand the flow characteristics of oil and water while injecting SW, and ILs. It was observed that the ILs improved the oils’ flowability, k ro, and reduced the water’s mobility, k rw . All these experiments were performed at the Saudi Arabian reservoir conditions of 100 °C, and at 4500 psi confining pressure, and at high salinity (TDS = 240, 000 ppm). In addition, we also demonstrated the wettability and interfacial tension (IFT) measurements in order to analyze the oil recovery mechanism. It was noted that both the ILs and surfactants alter the rock wettability from strongly oil-wet into intermediate-wet, while in the IFT measurements, the surfactants outperformed the ILs. Hence, it can be conceded that the oil recovery with ILs was dominated by the wettability modification, and for the surfactants, it was the combined effect of both wettability alteration and interfacial tension reduction. The use of dilute concentration of ILs (10–500 ppm) can be considered as the most profitable, and the best alternative over the costlier surfactant flooding.