Demulsification of o/w emulsion produced by polymer flooding injecting anionic polymeric surfactant

Abstract

Anionic amphiphilic polymers (polymeric surfactant) have been applied in polymer flooding to improve its adaptability to reservoirs of low permeability, high salinity and high temperature. Some pilot and extended polymer flooding projects injecting anionic polymeric surfactants with interfacial activities produced very stable o/w emulsion, bringing about high oil carry-over in produced water which was very difficult to remove to meet re-injection specifications. Factors contributing to the stability of o/w emulsion produced by a polymer flooding project injecting an anionic amphiphilic polymer were investigated by means of phase separation test, interfacial tension and Zeta potential measurements, emulsion microscopic structure observation and determination, and identification of interfacial active species. Major mechanisms hindering the aggregation and coalescence of oil droplets in the stable o/w emulsion were identified as the electrostatic repulsion and steric repulsion exerted by the polymer coils attached to the surfaces of oil droplets. A novel combination of a nonionic block polyether SP-2002 and a low molecular weight anionic surfactant AS-2001was designed to effectively demulsify the stable o/w emulsion produced by the polymer flooding project. Field trial of SP-2002 and AS-2001, together with a chelating agent WS-2001, brought about much looser o/w emulsion and significantly reduced oil carry over in produced water separated by field 3-phase production separators and skim tanks. The average OIWs of produced water dropped from 790 ppm before the trial to 482 ppm during the second stage of the trial. OIW of the produced water at the end of the trial dropped from 426 ppm to 90 ppm after 24 h static settling at 35 °C and further reduced to 17 ppm after bench-top media filtration.