Study On Structure-Property Relationship Of Petroleum Sulfonates For Enhanced Oil Recovery

At present,the surfactants used for enhanced oil recovery are mainly petroleum sulphonates and heavy alkyl benzene sulfonates.Heavy alkyl benzene sulfonates can only perform good behavior in the presence of strong alkaline.Stong alkaline may destroy stratum, the weak base system is preferred for enhanced oil recovery.Recent research results indicate that petroleum sulfonates have good behavior while buffered alkaline is being adopted.So the less expensive petroleum sulfonates would be important products to be developed in next stage.However,it's difficult to satisfy the request for stable and high efficient enhanced oil recovery since the petroleum sulfonates are extremely uncertain.Therefore,further researches on the relationship between the components and properties of petroleum sulfonates are needed.Three fractions with different average molecular mass were isolated from petroleum sulfonates by extraction,which are used for further research.The composition and structure of the three fractions were investegated by ESI/MS,IR,¹H-NMR,¹³C-NMR and elemental analysis.The results indicated that the fraction extracted with benzene may result in a greater decrease in the dynamic interfacial tension than other fractions,so the former plays a vital role in reducing interfacial tension.However,petroleum sulfonates before separation exhibit better interfacial activity than all the fractions,which can lower interfacial tension to 10^-5 mN·m^-1,which indicates that there exists obvious synergism between these different fractions. But these fractions are also mixtures.It's important to synthesize a series of alkyl aromatic sulfonates to explore the relationship between surfactant molecular structure and displacement efficiency.In this dissertation,a series of alkyl aromatic surfonate surfactants have been synthesized on the basis of "tailoring technology".The alkylation of aromatic hydrocarbon including benzene,toluene,xylene,tetrahydronaphthalene,and methylnaphthalene with long-chain olefins has been performed in the presence of self-chosed catalyst,the reaction conditions are optimized.The products and unreacted reactants do not dissolve in catalyst.Therefore catalyst can be isolated and reused easily.The synthesized intermediates are sulfonated by using 20% oleum as sulfonating agent.Alkyl aromatic sulfonates of high purity(more than 95%by two-pahse titration) are obtained after separation from redundant acid,neutralization and desalting,and characterized by ESI/MS,IR.The dynamic interfacial tensions(DIT) between crude oil from Daqing Oilfield and series of alkyl aromatic sulfonates,including alkyl benzene sulfonates,alkyl methylbenzene sulfonates,alkyl dimethylbenzene sulfonates,alkyl tetrahydronaphthalene sulfonates and alkyl methylnaphthalene sulfonates,flooding systems have been measured.Effects of concentration of surfactants,alkalinity and salinity on the DIT behavior are investigated.It's found that under the appropriate conditions,DIT can be lowered to ultralow values,and even to reach 10^-5 mN·m^-1 at the optimum conditions.The dynamic interfacial behavior of mix surfactants were investigated,the results show that the dynamic interfacial behavior of mixed surfactant system were much better than single surfactant system,flooding system in which surfactants of different molecular mass were mixed has stronger ability to reduce interfacial tension,and DIT can maintain ultralow values for a very long time.