In alkaline flooding, Interfaclal properties of acidic oil/aqueous caustic play an important role. Although lots of experimental results concerning the effect of various parameters upon interfacial tension and surface charge density have been reported, the mechanism is still not well clarified. C. J. Radke, T. F. Yen and D. T. Wasan have already presented their chemical models for interfacial phenomena of this system, but they all ignore the possibility of forming micelles in the aqueous phase. This article deals with an improved equilibrium chemical model of acidic oil/caustic system. Taking the effect of NaOH-NaCI concentration on the micelles formation into consideration, an expression of interfacial activity is proposed on the basis of Davies theory of the ionic monolayer. Using kerosene containing oleic acid/aqueous solution of hydroxide-sodium containing sodium chloride as the model system, the data of interficial tension (7) and electrophoretic mobility (U) with various concentration of sodium hydroxide and sodium chloride in aqueous phase and acid value of oil phase are presented. The critical micelle concentration of sodium oleate under the various ionic strength is determined and the relation between the micelle concentration and ionic strength is employed in the simulation calculation. γmin and U max thus obtained from the model calculations agree well with the experimental results in regard to the varying trend of parameters used. The mechanisms for the presence of γ min are also suggested. This model may be used in practical numerical simulation for alkline flooding with reasonable option of physicochemical parameters.

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