Separation of Produced Emulsions from Surfactant Enhanced Oil Recovery Processes

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Abstract

Selected cationic and amphoteric surfactants were effective in separating oil-in-water emulsions representative of produced emulsions expected during a surfactant/polymer (SP) process for enhanced oil recovery. The aqueous phase of the emulsion contained an anionic surfactant blend, alcohol, and partially hydrolyzed polyacrylamide. Brine composition was a suitable mixture of formation brine with brines from the surfactant slug and polymer drive. The crude oil had an American Petroleum Institute (API) gravity of 31°. Bottle tests were conducted at ambient temperature, which is near the reservoir temperature. Conventional non-ionic demulsifier resins and polymeric cationic flocculants were not effective in removing oil from the aqueous phase. The water content of the oil phase was still well above specification upon heating the emulsions to 50−60 °C. However, both oil and water phases of acceptable quality were obtained after 6 h of settling upon the addition of 200 ppm of octyltrimethylammonium bromide (C8TAB) at ambient temperature. Additionally, a commercial cationic surfactant at the same concentration yielded acceptable results for both phases in 2 h. Optical microscopy showed significant coalescence after only 1 min in the C8TAB system as the cationic surfactant reduced electrostatic repulsion among drops and shifted system phase behavior toward the balanced state between hydrophilic and lipophilic effects, actions well-known to reduce emulsion stability. Some amphoteric surfactants, such as cocobetaine, were also effective in separating these emulsions. The amount of cationic surfactant required could be reduced by adding it simultaneously with a non-ionic demulsifier resin. A commercial cationic surfactant was also found to significantly improve separation of emulsions produced during an alkaline/surfactant/polymer (ASP) process.

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