Experimental investigation on the interactions of asphaltenes and ethylene–vinyl acetate (EVA) copolymeric flow improvers at the interface between brine water and model oil

In oil fields, ethylene–vinyl acetate copolymers (EVA) are often added to the produced fluid as flow improvers. Asphaltenes in the crude oil and EVA can both adsorb at the interface and form a protective interfacial layer, affecting the emulsion stability of produced fluid. In this study, the effects of the interactions between asphaltenes and EVAs with different VA contents on the oil/water interfacial properties are investigated. To explore the adsorption behavior of asphaltenes and EVAs, the dynamic interfacial tension is firstly measured with droplet shape analysis method. The effects of the interactions between asphaltenes and EVAs are observed by analyzing the dynamic interfacial tension of the binary system and that of the single system. The added EVAs participate in the formation of interfacial layer and motivate the interfacial activity of asphaltenes to different degrees by influencing the dispersion state of asphaltenes in the model oil. The dilational modulus is then obtained by interfacial small-amplitude oscillation method. The addition of EVAs decreases the modulus, weakening the structure of interfacial layer. The conductivity experiment, asphaltene precipitation experiment and dynamic lighting scattering experiment are combined to explore the effect of EVAs on the dispersion state of asphaltenes. The polar moieties of EVAs interact with asphaltenes and form composite particles with peripheral nonpolar moieties, thus inhibiting asphaltenes from aggregation and improving the dispersion state. Among all the EVAs in this study, the EVA with 30% VA content has the strongest influence on the dispersion state of asphaltenes.