ABSTRACT
The water separated out at the demulsification stage at the oilfield-processing facilities contains residual oil and finely dispersed solids. The oil is present as a dispersion in water or oil-in-water emulsion (inverse emulsion). The concentration of residual oil is usually too high for discharge of the water to be allowed into the environment, plus the residual oil also has economic value.1 For example, a new discharge standard for oil and grease in produced water in the Northeast Atlantic and North Sea area of 30 ppm (30 mg/L, previously 40 mg/L) became effective on January 1, 2007. Elsewhere, this level may be set as low as 5-10 mg/l, which can be difficult to achieve. In addition, if the water is to be reinjected, the solids may plug the pore throats in the near-well area of the injection wells, or plug filters, raising backpressures, which wastes energy, damages equipment, or can even lead to shutdown. Therefore, the water needs to be treated to remove the oil and dispersed solids. The chemical method of doing this is to add a flocculant, also called a “water clarifier,” “deoiler,” “oil-in-water demulsifier,” “reverse emulsion breaker,” or “polyelectrolyte.” Flocculants can also be useful in wellbore cleanup operations.2
