Mesoscopic Simulation Of Anionic Surfactant Self-assembly For Oil Displacement

Surfactant flooding is an important part of chemical flooding,which is of great significance for tertiary oil recovery.Surfactants can migrate to the oil-water interface and reduce interfacial tension(IFT),so as to desorb crude oil.Surfactant is a kind of functional molecule with both hydrophobic and hydrophilic groups,which makes it have the trend of adsorption at the two-phase interface.In the field of enhanced oil recovery,research work focuses on the design and synthesis of more active and efficient surfactants,which can reduce IFT to the greatest extent at the lowest concentration.AAS surfactant is an anionic surfactant with excellent interfacial activity and salt resistance.The Po group contained in it can significantly improve the solubility and ion tolerance of the surfactant.In this paper,the structural changes of AAS anionic surfactant multiphase system,which has attracted much attention in the field of surfactant oil displacement,are studied theoretically.By constructing the structure model of AAS surfactant molecule,the structure evolution process in multiphase system was studied at mesoscopic scale by using dissipative particle dynamics(DPD)simulation method.The effects of concentration,number of Po groups and volume fraction of silica nanoparticles on the self-assembly structure,interfacial activity and micelle aggregation number of surfactants were investigated.It provides basic data and theoretical guidance for the molecular design and experimental synthesis of new surfactant oil displacement system.The research results are as follows:(1)It was found that with the increase of surfactant volume fraction,the shape of micelles changed from spherical micelles to rod micelles,and finally aggregated with each other to form larger worm micelles.The final average micelle aggregation number is stable at about 200.The higher the number of Po groups,the higher the micelle compactness.(2)The interfacial activity is related to the coverage of surfactant molecules at the oil-water interface,and the influence of Po groups on the coverage is divided into three aspects: increasing the coverage area of a single AAS surfactant molecule;Lead to the formation of micelles of surfactant molecules at the oil-water interface and reduce the overall coverage area;The effect of intramolecular force,high number of Po groups,surfactant molecules,and the contribution ratio of RMS value of Po groups decreased.(3)The addition of AAS surfactant promotes the aggregation of nanoparticles and oil phase to form hierarchical spherical core aggregates,which can improve the stability of oil-water emulsion.For the surfactant micelle system,silica improves the hydrophobic interaction of the micelle system and enhances the interfacial activity.