Evaluation of 1-octadecyl-3-methylimidazolium bromide for enhanced oil recovery: interfacial behavior and pore-scale displacement in a glass micromodel

The efficiency of conventional surfactants in chemical enhanced oil recovery (EOR) is often limited by high salinity, elevated temperatures, and adsorption-related chemical losses, particularly in carbonate reservoirs. These limitations have motivated the investigation of alternative surface-active agents with favorable interfacial performance under challenging conditions. In this study, the interfacial and pore-scale displacement performance of the ionic liquid 1-octadecyl-3-methylimidazolium bromide ([C18mim][Br]) was investigated through a combination of interfacial tension (IFT) measurements and flooding experiments in a heterogeneous glass micromodel. A systematic experimental program was conducted to evaluate the effects of ionic liquid concentration, salinity, and temperature on oil–water interfacial behavior and displacement efficiency. The ionic liquid reduced the oil–water IFT from approximately 89 mN/m to below 2 mN/m as the [C18mim][Br] concentration was increased from 0 to 200 ppm, corresponding to a reduction greater than 97%. A pronounced salinity-dependent interfacial response was observed, with an IFT value of approximately 0.36 mN/m at 22,500 ppm NaCl and a nominal ionic-liquid concentration of 50 ppm in the salinity-focused experiments. Micromodel flooding experiments further showed that injection of a nominal 10 ppm [C18mim][Br] solution increased the final recovery factor to approximately 58% relative to conventional water flooding under the tested micromodel conditions. Temperature elevation also improved the observed displacement performance, with recovery increasing from 36.8% at 25 °C to 48.1% at 60 °C. The results further demonstrated that the lowest IFT condition did not necessarily correspond to the highest oil recovery, indicating that pore-scale displacement performance depends on coupled interfacial and flow-related mechanisms. Overall, the findings indicate that [C18mim][Br] provides strong interfacial modification and favorable pore-scale displacement performance at the tested concentrations under the controlled experimental conditions investigated. However, the present study did not quantify ionic-liquid adsorption or retention on carbonate minerals, glass surfaces, or within porous media, and therefore the reported concentrations should not be interpreted as field dosage or as evidence of low chemical consumption at reservoir scale. Accordingly, the results should be regarded as a pore-scale screening assessment that provides a basis for further carbonate-specific validation rather than direct evidence of carbonate-reservoir applicability.