Mechanism studies on the application of the mixed cationic/anionic surfactant systems to enhance oil recovery

[Display omitted] •Electrostatic attraction caused the fabrications of pseudo two-tailed co-surfactants.•The mixed M12/SDS systems showed the remarkable surface/interfacial activity.•Molecular dynamics simulation was employ to explore the surface/interfacial activity.•The mixed M12/SDS systems effectively modified oil-wet surface to be more water-wet.•The mixed M12/SDS systems improved oil recovery by more than 10% in harsh conditions. Mixed cationic/anionic surfactant systems have showed great potential in various fields. Ionic liquids with extraordinary physical and chemical properties are regarded as novel alternatives to traditional surfactants. In this report, we evaluated the performances of the mixed surfactant systems comprising a cationic surface-active ionic liquid 1-dodecyl-3-methylimidazolium chloride (M12) and an anionic surfactant sodium dodecyl sulfate (SDS) in terms of surface/interfacial tension reduction, emulsifying ability, wettability alteration and core flooding tests. Molecular dynamic simulation was employed to explore the surface/interfacial activity of the mixed surfactant systems. The interfacial tension (IFT) between the mixed surfactant solutions and crude oil could be dramatically decreased to the ultralow level (