Influences and mechanisms of imidazolium-based ionic liquids on oil–water interfacial tension and quartz wettability: Experiment and molecular dynamics simulations

Interfacial tension (IFT) and wettability are two key parameters determining pore-scale oil/water distributions and reservoir-scale hydrocarbon production performances. However, how ionic liquid (IL, a green, stable, and efficient chemical) will manipulate IFT and wettability for EOR in sandstone reservoirs has not been sufficiently investigated yet, and the underlying mechanisms at the micro-level are still unknown. In this study, the influences of two typical ILs at various concentrations (i.e., 0.01, 0.1, 1, and 5 mmol/L) on oil–water IFT and alpha-quartz (α-quartz) wettability were investigated. This study shows that low concentrations of ILs can greatly reduce alkane-water IFT, and gemini IL has higher interfacial activity than mono-cationic IL, which is due to the fact that gemini IL with longer alkyl chains is more likely to form conglomerates at lower concentrations. Both the advancing and receding contact angles increase continuously with concentration in ILs solution, which can be given responsibility for the decrease in IFT and the solid–liquid interaction resulting in an increased capacity of alkane droplets to migrate on the α-quartz surface. Additionally, the molecular dynamic simulations examined the micro-wetting process and interaction energy of the IL-alkane-quartz system, and revealed that ILs can effectively reduce interaction energy between octane droplets and α-quartz surface. These insights have promising applications to enhanced oil recovery and oil contamination removal at subsurface.