Effect of Aqueous Phase pH on the Dynamic Interfacial Tension of Acidic Crude Oils and Myristic Acid in Dodecane

Abstract

The time dependence of the interfacial tension between water–acidic crude oil and water–synthetic oil was investigated for aqueous phase pHs ranging from 2 to 9 using the du Noüy ring method at 20°C. Myristic acid in dodecane was selected as a model (synthetic oil) for acidic crude oil containing indigenous surfactants, and the similarities and differences between the dynamic interfacial tension behaviours of the natural and synthetic crude oil systems were compared. The initial interfacial tension and the relaxation of the interfacial tension are sensitive to the aqueous phase pH for both systems. The adsorption kinetics of the indigenous surfactants and myristic acid could be well fitted with the monoexponential model, and the time constants obtained in this manner indicates that reorganization of the indigenous surfactants and myristic acid at the w/o interface are pH dependent. The experimental results also indicate that indigenous surfactants in acidic crude oil and myristic acid in dodecane have similar film formation behaviours at the w/o interface for the range of pHs investigated.

Keywords:

• Acidic crude oil
• dynamic interfacial tension
• indigenous surfactants
• myristic acid
• synthetic oil

Acknowledgements

S. K. acknowledges a Ph.D. grant and financial support from the Multiphase Flow Assurance Centre (FACE), a research cooperation between IFE, NTNU, and SINTEF. The center is funded by The Research Council of Norway, and by the following industrial partners: Statoil AS, Norske ConocoPhillips AS, Vetco Gray Scandinavia AS, Scandpower Petroleum Technology AS, FMC, CD–adapco, ENI Norge AS, Shell Technology Norway AS. The authors also acknowledge discussions with and comments by Dr. Brian Grimes on a first draft of the manuscript.

Notes

^a Karl-Fischer titration.

^b AP PAAR DMA 500 density meter.