Destabilization of oil droplets in produced water from ASP flooding

Produced water from alkali/surfactant/polymer (ASP) flooding was more difficult to treat than that from water flooding due to large quantities of residual chemicals (alkali, surfactant and polymer) in the produced water. Surfactant was mainly responsible for the stability of oil droplets, decreasing oil-water interfacial tension and zeta potential on the surface of the oil droplets. Flocculation and demulsification were conducted to remove the stable oil droplets in the produced water. Due to the large dose of the flocculants and some viscous sediment formed, flocculation was not suitable for the wastewater treatment. Demulsification was an effective method to accelerate oil-water separation for the produced water. Of the numerous demulsifiers screened, DODY68 was found to be the most effective in treating the wastewater. The zeta potential of oil droplets increased after addition of the demulsifier to the produced water from ASP flooding, which indicated that the approach and coalescence of small oil droplets became easier due to the decrease in electrostatic repulsion between oil droplets.