Crude-Oil Emulsions: A State-Of-The-Art Review

Summary The formation of emulsions during oil production is a costly problem, both in terms of chemicals used and production lost. This paper discusses production and operational problems related to crude-oil emulsions and presents a review that will be useful for practicing engineers. The first part of this paper presents why emulsions form during oil production, the types of emulsions encountered, and new methods for characterizing them. Crude-oil emulsions are stabilized by rigid interfacial films that form a "skin" on water droplets and prevent the droplets from coalescing. The stability of these interfacial films, and hence, the stability of the emulsions, depends on a number of factors, including the heavy material in the crude oil (e.g., asphaltenes, resins, and waxes), solids (e.g., clays, scales, and corrosion products), temperature, droplet size and droplet-size distribution, pH, and oil and brine composition. The effects of these factors on emulsion stability are reviewed within this paper. The second part of this paper presents methods to tackle crude-oil emulsions. The focus is on the destabilization of emulsions and the demulsification process. Emulsions are destabilized by increasing temperature and residence time, removal of solids, and controlling emulsifiers. The mechanisms involved in demulsification (e.g., flocculation, aggregation, sedimentation, creaming, and coalescence) are discussed in terms of the stability of the interfacial films. The methods involved in demulsification—including thermal, mechanical, electrical, and chemical are also presented. Experience and economics determine which methods are used, and to what degree, for emulsion treatment. Finally, a section on field applications also is included that should be useful for the practicing engineer who deals with emulsions either regularly or on a limited basis. Herein the field-emulsion treatment program is discussed, and more importantly, methods to prevent emulsion problems are highlighted. Recommendations are made for reducing and optimizing demulsifier dosage and controlling emulsion problems.