Systematic Investigation Of The Effects Of Surface Active Ionic Liquid On Interfacial Tension Of Water/Oil System

Surfactant flooding has been a promising method for mobilizing residual oil from mature reservoirs for many decades.Focus on the EOR of the unconventional reservoirs with more complex conditions,the conventional surfactants cannot satisfy the operating requirements of the harsh environments,therefore it is highly desirable to research the novel high-performance surfactants.ILs with the long alkyl chains resembles traditional surfactants and can be referred to as novel surface active ionic liquids(SAILs).The SAILs have been successfully employed in multiple applications because of the specific physical chemical,biological,and electrical properties.So we focus on the EOR process and explore the potential of its potential applicationA new type of anionic-halogen-free ionic liquid,1-butyl-3-methylimidazolium dodecyl sulfate([C4mim][C12SO4]),was synthesized for potential application in EOR processes.In this way,we investigated the effects of the ionic liquid[C4mim][C12SO4],temperature,model oil type and concentrations of salts on interfacial tensions between[C4mim][C12SO4]solutions and model oils.It's showed that the new type SAIL[C4mim][C12SO4]has remarkably highly effective abilities in reducing the IFT of aromatic hydrocarbon/water system.Interestingly,in the presence of salinity at higher temperature,ultra-low IFT can be achieved.Moreover,with using the molecular mechanics,we calculated the interaction energies between[C4mim][C12SO4]moleculars and different model oil molecules which could explain the further reasons of ultra-low IFT.Ionic liquid-type gemini surfactants are kinds of ionic liquids with special structure,which have the advantages of both a surface active ionic liquid and a gemini surfactant.They have been applied in different fields.We introduced a series of ionic liquid-type Gemini imidazolium surfactants with a four-methylene spacer group(CnD,n=8,10,12)for chemical enhanced oil recovery(CEOR).The CnD had obvious effects on the interfacial tension(IFT)between water and a model oil(toluene and n-decane,v:v=1:1),which appears to be closely related to the length of hydrocarbon chain.Moreover,the addition of NaCl could cause abnormal variations in the IFT.Based on the phase behaviour of the surfactants in phase,we proposed a mechanism to explain the relationship between the surfactant concentration and the effects of salt,which was verified by measuring the IFT between a homologous series of alkanes with different alkane carbon numbers and the surfactant solutions.The temperature effects were further evaluated to explore the effects of the CnD molecular structures on the IFT.Zwitterionic surface active ionic liquids(SAILs),3-(1-hexadecyl-3-imi dazolio)propanesulfonate(C16IPS)and 3-(1-hexadecyl-3-imidazolio)propanesulfonate ?-naphthalene sulfonate(C16IPS-Nsa),their possible application in chemical enhanced oil recovery(CEOR)were studyed.The zwitterionic SAILs had a higher interfacial activity better than the traditional surface active ionic liquids.Moreover,the C16IPS-Nsa molecule had a greater ability for reducing the interfacial tension between water and crude oil due to their large hydrophobic group p-naphthalene sulfonate.Interestingly,the proposed mechanism of the novel ionic liquids effects on the IFT was confirmed by the investigations of the salt effects,temperature and the dynamic IFT.Moreover,The C16IPS-Nsa system performed a satisfactory displacement performance(15.3%of IOIP).