Investigation on the effects of cationic surface active ionic liquid/anionic surfactant mixtures on the interfacial tension of water/crude oil system and their application in enhancing crude oil recovery

The surface active ionic liquids (SAILs) have been widely employed in various aspects of the petroleum industry, and the mixed surfactant systems exhibited greater interfacial activity in enhanced oil recovery (EOR). To systematically explore the effects of the molecular structure and the intermolecular interaction on the interfacial activity of the mixed SAIL/surfactant systems, the interfacial properties of various SAIL/surfactant mixtures containing typical cationic SAILs (N-dodecyl-N-methylpyrrolidinium bromide (L12), 1-dodecyl-3-methylimidazolium bromide (M12), or 1-hexadecyl-3-methylpyrrolidinium bromide (L16)) and anionic surfactants (sodium dodecyl sulfate (SDS) or sodium dodecyl benzene sulfonate (SDBS)) with different molar ratios were investigated. The temperature and salt tolerances of various SAIL/surfactant systems were also investigated. A series of core flooding experiments were carried out to verify the advantages of the mixed SAIL/surfactant systems. It was found that both M12/SDS and L12/SDS mixtures could greatly decrease the IFT to about 10−2 mN/m at the SAIL/surfactant molar ratio of 1:2, whereas the moderate interfacial activity of other systems might be attributed to the poor matching degree of molecular structures and weak intermolecular interaction between SAIL and surfactant. The mixed systems showed superior oil displacement efficiency than single component systems, and the oil recovery was further improved with additional polymer and sodium chloride. The present study demonstrated the mixed SAIL/surfactant systems are efficient and promising chemical flooding agents for EOR application in harsh conditions.