The effects of oil displacement agents on the stability of water produced from ASP (alkaline/surfactant/polymer) flooding

Alkaline/surfactant/polymer (ASP) flooding technology has been successfully used in Chinese oil fields, such as Daqing and Shengli. However, water produced from ASP flooding contains large quantities of residual chemicals (alkali, surfactant and polymer) making it a complex and stable emulsion system which is difficult to treat. The emulsion stability of water produced from ASP flooding was investigated by conducting settling experiments and measuring the oil-water interfacial properties. The experimental results showed that the addition of polymer (HPAM, hydrolyzed polyacrylamide) degrades the emulsion stability when its concentration is below 300 mg/L for the 1.2 x 10(7) MW polymer, and 800 mg/L for the 3.0 x 10(6) MW polymer. But it enhances the emulsion stability when polymer concentrations are above those levels. At low polymer concentrations, flocculation induced by the polymer on oil droplets in the produced water is the dominant factor, while at high polymer concentrations the produced water viscosity plays an important role in the emulsion stability. The adsorption of surfactant on the oil-water interface increases the zeta potentials and decreases interfacial tension, and thus remarkably enhances the emulsion stability. Furthermore, the emulsion stability is enhanced gradually with the increase of NaOH concentration up to 300 mg/L due to the increase of zeta potentials and decrease of interfacial tension, and then weakened with the further increase of NaOH concentration, which is attributed to the decreased strength of the interfacial film. A pilot experiment for the treatment of simulated water was done, and the result showed that the simulated produced water from ASP can be successfully treated by using a leaching solution of alkaline white mud. (C) 2010 Elsevier B.V. All rights reserved.