Theoretical Study On Adsorption Behaviors Of Surfactants For Enhanced Oil Recovery At Oil/Water Interface

Petroleum resources have traditionally been called "industrial blood".It has many incomparable advantages over other fuels and plays an irreplaceable role in the development of society.Researches have found that after the secondary recovery of crude oil,2/3 of the reserves have not yet been recovered,which has satisfy the people less and less.Oil recovery rate has became an urgent problem to be solved for people.Adding surfactants to water,called "surfactant flooding",will adsorb on the oil/water interface and reduce the interfacial tension,which is of great significance to further improve the oil recovery rate.However,it is still difficult to study the surfactant adsorption properties at oil/water interface at molecular level.With the development of modern computer technology and theoretical chemistry,molecular dynamics simulations have been used to study the surfactant adsorption properties at oil/water interface,revealing the mechanism of surfactant flooding from a microscopic level,and also guiding the selection and design of suitable surfactants for enhanced oil recovery(EOR)This paper mainly studied the surfactant adsorption properties at oil/water interface.Molecular dynamics simulation was used to study the microstructure of the surfactant monolayer and intermolecular interaction.Then,interfacial tension was measured to supplement the study of the interfacial adsorption properties from a macro level.This paper consists of following four partsSection ?:It is mainly introduced the development history of enhanced oil recovery,classification and characteristics of surfactants,mechanism and research progress of surfactant flooding,selection of surfactants for flooding,and basic theory of molecular dynamics simulations.Section ?:The temperature and salt resistance of three types of nonionic surfactants with different structure were analyzed by establishing oil/water interface adsorption models.Results showed that the surfactant adsorption properties decrease sharply with increasing temperature,but the tolerance to temperature is different.Surfactants containing a double bond in tail have the worst temperature resistance.In high-salt reservoir environment,inorganic salt ions can invade into the hydrated layer of the surfactants,which greatly reduces the surfactant adsorption properties.Section III:Combined molecular dynamics simulations and experiments,the synergistic effects of mixed systems of zwitterionic surfactant and anionic surfactant were studied.Results showed that cationic groups in zwitterionic surfactant have an important effect on the interfacial properties.Experiments showed that the three mixed surfactant systems all have synergistic effects,and the interfacial tension is lower than that of pure surfactant systems.The molecular dynamics simulation results showed that different mixed surfactant systems have completely dinfferent interfacial arrangements.The electrostatic interaction and ?-? stacking influence the synergistic effect of mixed systems.Section ?:It mainly includes the summary statement of main work in this paper,which mainly involves the related research on surfactant adsorption properties at oil/water interface,and points out the innovation and deficiencies,as well as the significance of the work and the outlook for future development.