Advanced treatment of produced water from ASP (alkali/surfactant/polymer) flooding with polyether sulfone UF membrane for reinjection

Alkali/surfactant/polymer (ASP) flooding technology, as an important technology of tertiary oil extraction, has been successfully and widely applied in Daqing Oil Field (China). However, large amounts of produced water from ASP flooding (PWFAF) are always generated concomitantly. PWFAF is a more complex and stable emulsion system compared with the conventional produced water, and it is more difficult to reduce the oil content to meet the criteria of injection water by conventional water treatment systems, especially for low and ultra-low permeability reservoirs. In the present paper, advanced treatment of PWFAF with polyethersulfone (PES) ultrafiltration (UF) membranes in dead-end filtration was conducted, and the main purpose was to evaluate the effectiveness of the membrane on advanced treatment of PWFAF for reinjection. The effects of trans-membrane pressure (TMP), pH and total dissolved solids (TDS) on membrane flux decline were examined; the rejection rates of anionic polyacrylamide (APAM), sodium dodecyl benzene sulfonate (SDBS), especially oil as well as membrane cleaning methods were also investigated. The results demonstrated that TMP exhibited a more significant influence on membrane flux decline compared with pH and TDS, but the TMP, pH and TDS all exhibited little influence on the rejection rates of oil. The rejection rate of oil was more than 95%, and the oil content was always below 5 mg L-1 in the permeate. A flux recovery rate of 95% could be obtained by a combined cleaning method of citric acid solution (0.5 wt. %) soak, sodium hydroxide solution (0.5 wt. %) soak and SDBS solution (0.5 wt. %) soak. Scanning electron microscopy (SEM) was employed for intuitive observation and comparison of the membrane morphology. It was concluded that the PES UF membrane had a potential feasibility and application for advanced treatment of the PWFAF.