Enhanced oil recovery is governed primarily by the role of interfacial tension between crude oil and water. Interfacial tension (IFT) of the crude oil−water system is one of the vital factors in the analysis of the capillary forces affecting trapped oil within the reservoir rocks. High salinity and temperature of the reservoirs tend to make researchers search for new surfactants to lower the interfacial tension in crude oil−water systems. The current study hopes to create a move toward solving the above problem through the use of aromatic ionic liquids (ILs) based on imidazolium as the cation and various anions such as [HSO 4 ] − , and [PF 6 ] − in different concentrations. This work involves the study of the effect of concentration, temperature, time, and brine on the fate of surface tension (SFT) of water and interfacial tension of crude oil− water systems. The present study also addresses the trend in the electrical conductivity of ILs in water along with the effect of temperature and concentration of ILs. The study reveals that these ILs are effective in reducing the SFT and IFT of water and crude oil−water systems at high salinity and temperature conditions. In the IFT measurements, a linear decrement with increase in temperature is observed for crude oil−water in the presence of ILs. The interfacial tension of the various imidazolium-based ionic liquids with the crude oil−water system has been measured as a function of temperature by means of the Wilhelmy plate method. The influence of the nature of cation and anion of ionic liquids and of the chain length on the cationic head of the ILs on interfacial tension is also discussed in detail. At increased salinity conditions, unlike classical surfactants, these ILs are found to be more successful. Enhanced efficiency of the drop in IFT using NaCl and IL mixture has been confirmed by measuring the IFT between crude oil and the aqueous solution of IL. The synergism of salt and IL mixture on the reduction of IFT has been observed.

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Depleted matured reservoirs contain almost two-thirds trapped oil, which remains unrecovered even after primary and secondary oil recovery methods. Chemical enhanced oil recovery (EOR) methods involve the usage of chemical agents that improve the mobility of the residual oil by mechanisms involving alteration of wettability, viscous fingering reduction within the pay zone, and interfacial tension (IFT) between interfaces of fluids (oil/water) and rock, followed by reduced capillary forces during flooding. Chemical EOR methods need more research for high saline reservoir conditions. In this work, the effect of six imidazolium ionic liquids (ILs) on the IFT of alkane–water systems and alteration of wettability of quartz surface was investigated as a function of IL concentration (0–10000 ppm) and temperature (288.15, 298.15, 308.15, and 318.15 K). Initially, the effect of the various ILs on the IFT of the alkane–aqueous IL system was studied and compared with the neat alkane–water system. Subsequently, synergistic behavior of the ILs + NaCl (0–200000 ppm NaCl) on the system of alkane–aqueous IL + NaCl was performed and compared with the alkane–aqueous IL system at zero salinity. Thereafter, the wettability alteration of quartz–alkane–aqueous IL and quartz–crude oil–aqueous IL systems, under both zero and high salinity conditions at 298.15 K at atmospheric pressure, was studied using contact angle measurements. The systems with IL showed an increase of contact angle exhibiting an alteration in the wettability from water wet to oil wet, whereas the systems under saline conditions showed a wettability from oil wet to water wet. A synergistic effect of ILs with salt on IFT reduction and wettability alteration has been detected. It is suggested that longer ILs could be a better option for EOR application.