Study of the mechanism of demulsification of petroleum crude oil emulsions by demulsifiers

Abstract

The formation of stable emulsions during the production of crude oil is an expensive problem faced by the oil industry. Stable emulsions can be encountered during recovery, treatment or transportation of crude oil. Asphaltenes are believed to contribute in formation of stable emulsions by forming an elastic oil/water interface. Though demulsifiers are extensively used in industry to destabilize the emulsions formed, there is a lack of understanding of the mechanism of demulsification. Moreover, potentially informative techniques such as interfacial rheology are of very little use and the value that they can bring to understand the mechanism of demulsification is not known. In this project, asphaltene stabilized emulsions were formulated and the efficiency of the two commercial demulsifiers Tretolite DMO 83262 and Emulsotron OFLP 09/2171 was tested by focusing on their effects on the interfacial rheology properties of the water/oil interface. The experiments showed that both the demulsifiers showed almost the same efficiency. From the bottle tests, it was found that even 1 ppm of demulsifier was effective to achieve complete separation of oil and water. Experimental studies conducted using dilatational rheology and shear rheology indicated that atleast 25-50 ppm of demulsifier is necessary to achieve complete separation. The critical demulsifier concentration (25-50 ppm) determined by the interfacial rheology tests was much higher than the demulsifier concentration (1 ppm) needed for complete separation by the bottle tests. Hence demulsifier efficiency cannot be determined by the critical demulsifier concentration obtained from the interfacial rheology tests. The preliminary studies on the role of various asphaltene sub-fractions separated as a function of polarity was also performed. The results showed a significant difference in the interfacial tension (IFT) and the elastic modulus of the emulsion stabilized by the asphaltene sub-fractions.