Entry Process Of Oil Droplet To The Gas/liquid Interface Of Foam Films:A Coarse-grained Simulation Study

As a new type of tertiary oil recovery method,foam flooding has the high apparent viscosity and selective plugging,is a promised technology of tertiary oil recovery.During the process of foam flooding,the oil phase can dispersed in the foam films as the emulsified oil droplets,which may decrease the foam stability.And then,the oil recovery could be limited.There are still lack the systematic studies of the effects to the defoaming mechanism of the type and concentration of the surfactant.Therefore the coarse grained molecular dynamics method has been carried out to investigate the defoaming process of the emulsified oildrop in the SDS foam and C₁₂E₅ foam individually.The effects of the concentration of surfactant?N_i?and the emulsifying degree?N_e?have been investigated,and the microscopic mechanism of the entry process of the emulsified oil has been analysed in depth according to the dynamic process and the interaction between each component.Firstly,the effects of surfactant concentration to the foam stability have been investigated.The results showed that the more the surfactants,the harder for the emulsified oil to enter into the interface,and the foam is more stable.Particularly,there is an unusual phenomenon for the SDS foam that the emulsified oil can entry to the interface while N_i>CMC and N_e>N_em.Secondly,the interaction between each component in the foam system has been studied.For the SDS foam,the hydrophobic interaction between the tail of SDS and the oil can stimulate the emulsified oildrop move to the interface,while the electrostatic repulsion between the interfacial SDS and the emulsifying SDS can prevent the emulsified oildrop move to the interface.For the C₁₂E₅ foam,the attraction effect between the surfactants and between the surfactants and the oil phase can stimulate the emulsified oildrop move to the interface,while the strong attraction effect between the water phase and the emulsifying SDS can prevent the emulsified oildrop move to the interface.Finally,the defoaming mechanism has been proposed according to the entry process and interaction between each component.The defoaming mechanism of SDS foam can be divided into three kinds,which are the“Hole”mechanism(N_i<CMC,N_e<N_em),the“Attraction”mechanism(N_i?CMC,N_e<N_em)and the“Budding”mechanism(N_i>CMC,N_e>N_em).While for the C₁₂E₅ foam,the defoaming mechanism can be only divided into two kinds,which are the“Hole”mechanism(N_i is less,N_e<N_em)and the“Attraction”mechanism(N_i is larger,N_e<N_em).The defoaming mechanism has been supplemented from the micro level by the present study,and the microscopic understanding to foam flooding has been enhanced.