A Study of Caustic Solution-Crude Oil Interfacial Tensions

The results of a study of caustic-solution crude oil interfacial tension measurements on 164 crude oils from 78 fields are presented. Of these crude oils, 131 showed marked surface activity against caustic solutions. Surface activity of crude oil against caustic solution correlates with the acid number, API gravity, and viscosity of the crude. Almost all crude oils with gravities of 20'API or lower that were studied produced a caustic solution--crude oil interfacial tension <0.01 dynes/cm. Ninety percent of the interfacially active samples reached maximum measureable surface activity at a caustic concentration close to 0.1% by wt. The dissolved solids content of the water has a marked influence on the surface activity. Sodium chloride in solution reduces the caustic concentration required to give maximum surface activity. Conversely, calcium chloride in solution suppresses surface activity. (10 refs.)