Stability Dynamic Characteristic of Oil-in-Water Emulsion from Alkali-Surfactant-Polymer Flooding

Abstract

The relationship model between the droplet lifetime and interface properties is established to characterize the stability of oil droplets, and then, the influence of the alkali-surfactant-polymer (ASP) concentration on the lifetime is analyzed by theoretical calculations. The stability dynamic characteristics of oil-in-water (O/W) emulsions from ASP flooding were evaluated using the emulsion stability model (Civan model) based on two-phase separation. The effect of ASP on dynamic characteristics of the emulsion was explored by analyzing film strength qualitatively and measuring interfacial tension and ζ potential. The results showed that the Civan model was suitable to evaluate the stability of the O/W emulsion and to obtain the corresponding dynamic characteristics. The O/W emulsions became more stable with the increasing alkali concentration first at a low alkali concentration (cNaOH < 200 mg/L) and then became less stable with the increasing alkali concentration at a high alkali concentration (cNaOH > 200 mg/L). The stabilities of O/W emulsions were improved with the increasing concentrations of the surfactant and polymer. The mechanism of stabilization of the O/W emulsion by ASP is as follows. The surface-active substances formed by the reaction of alkali and acidic substances in the oil phase, together with surfactants, adsorb at the oil-water interface, reducing the interfacial tension and increasing the strength of the oil-water interface film. The polymer only increases the strength of the interface film by increasing the viscoelasticity of the oil-water interface film.