Evaluation of the interfacial activity of imidazolium-based ionic liquids and their application in enhanced oil recovery process

•Design of Imidazolium Nitrate-based Ionic Liquids (ILs) with high surface activity cation.•Better EOR potential in Nitrate-based ILs than halogen-based.•ILs with the highest alkyl-chain length exhibited better interfacial activity.•Increasing temperature and salinity improved the interfacial activity of ILs.•Nitrate-based ILs swept the oil from the micromodel with desirable flow distribution. Ionic liquids (ILs) are a growing trend in Enhanced Oil Recovery (EOR) studies as alternatives to commercial surfactants due to their environmentally friendly nature, and their resistance in harsh temperatures and salinities. ILs are customizable and come in an immense variety, and therefore, it is vital that different combinations of cation/anion be investigated for use in the industry. In this work, experiments are designed and performed to evaluate novel ILs’ surface activity and performance in a lab-scale EOR set-up, compatible with Iranian oil reservoir conditions. Three imidazolium-based ionic liquids were used, namely, butyl-methylimidazolium nitrate, hexyl-methylimidazolium nitrate, and octyl-methylimidazolium nitrate. Nitrate anions have a less environmental impact than the often-used halogen anions, but their performance in EOR have not yet been investigated. Aqueous and saline solutions of these ILs were prepared, and subsequently, interfacial tension (IFT) tests and emulsion stability tests were carried out while the IL concentrations were kept to a minimum to account for the procedure’s feasibility. A high reduction in IFT between the saline IL solution, [C8MIm][NO3], and oil was observed compared to ILs with similar alkyl chain length in previous studies. Glass micromodels are exceptional in representing oil reservoirs under chemical EOR, and thus, were utilized to predict the ILs’ contributions to sweep efficiency and recovery factor. Up to 80% oil recovery was obtained in the micromodel flooding tests with a strong sweep efficiency. Tests were repeated at two different temperatures (30 and 75 °C) and several salinities, and it was concluded that the ILs are resistant to harsh reservoir conditions, and can, potentially, improve the production efficiency of oil fields.