The formation of water-in-crude oil (w/o) emulsions during the lifting and pipelining of crude oils is a common issue in petroleum production. In oilfields, emulsions are undesirable due to the increase of fluid viscosity, which consequently drops the production rate. Demulsifiers may be injected at electrical submersible pumps, production lines, and/or the crude oil processing station to deal with the impacts. In a laboratory, emulsion stability and demulsifier efficiency are commonly evaluated by bottle tests, but this approach does not consider the main factors controlling the kinetic stability of water-oil emulsions such as interfacial tension. This study aims to evaluate how the interfacial tension can influence the stability of these w/o emulsions, seeking a microscopic understanding of their phase separation as a function of temperature and demulsifier concentration. The Central Composite Rotatable Design (CCRD) methodology was used to evaluate the effects of the independent variables (temperature and demulsifier concentration) on the interfacial tension and emulsion stability at 50% water-cut. The interfacial tension was determined by a Spinning Drop Tensiometer, and the emulsion stability was determined by measuring the phase separation under a centrifugal field rather than the classical bottle test. We found an intrinsic inverse correlation between the yield of phase separation and interfacial tension, suggesting interfacial tension is an important parameter to assess the demulsifier's effectiveness and the emulsion's stability. Our studies surface important new findings for understanding the stability of emulsions for complex and more realistic crude oil-water systems with commercial demulsifiers.
Freitas et al. (Fri,) studied this question.