Emulsions in Produced Crude Oil

In the production of crude oil, the greatest part of the crude oil occurs as a water-in-oil emulsion. The composition of the continuous phase depends on the water/oil ratio, the natural emulsifier systems contained in the oil, and the origin of the emulsion. The natural emulsifiers contained in crude oils have a complex chemical structure, so that, to overcome their effect, petroleum-emulsion demulsifiers must be selectively developed. As new oil fields are developed, and as the production conditions change at older fields, there is a constant need for demulsifiers that lead to a rapid separation into water and oil, as well as minimal-residual water and salt mixtures. 

The emulsion must be separated by the addition of chemical demulsifiers before the crude oil can be accepted for transportation. The quality criteria for a delivered crude oil are the residual salt content and the water content. For the oil to have a pipeline quality, it is necessary to reduce the water content to less than approximately 1.0%. 

The separated saltwater still contains certain amounts of residual oil, where now preferentially oil-in-water emulsions are formed. The separation of the residual oil is necessary in oil field water purification and treatment for ecologic and technical reasons, because the water is used for secondary production by waterflooding, and residual oil volumes in the water would increase the injection pressure. 

The presence of water-in-oil emulsions often leads to corrosion and to the growth of microorganisms in the water-wetted parts of the pipelines and storage tanks. 

At the refinery, before distillation, the salt content is often further reduced by a second emulsification with freshwater, followed by demulsification. Crude oils with high salt contents could lead to breakdowns and corrosion at the refinery. The object of using an emulsion breaker, or demulsifier, is to break the emulsion at the lowest possible concentration and, with little or no additional consumption of heat, to bring about a complete separation of the water and reduce the salt content to a minimum. 

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