The effect of oilfield polymer-flooding wastewater on anion-exchange membrane performance

Polymer-flooding process is one of tertiary oil extraction technologies. It has stepped into industrialization application period in Daqing Oilfield (China) in recent years. It plays an increasingly important role in the oil exploitation, but around 60 million ton polymer-flooding wastewater is produced per day with oil extraction together. Therefore, the treatment and reuse of wastewater becomes very significant. Experiments show that the polymer-flooding wastewater can replace freshwater to be reused to confect polymer solution after removing total dissolved solids (TDS) by electrodialysis technology. This treatment technology can not only decrease environmental pollution resulted by wastewater discharge, but also achieve closed-circuit of polymer-flooding wastewater during crude oil extraction. It has significant effect for protecting environment and saving water resource. After carrying out lots of experiments in the lab, the pilot-test electrodialysis operation has been applied to treating polymer-flooding wastewater and received better economic effect. But serious ion-exchange membrane fouling (especially for anion membrane) is the main problem that holds back this technology's further application. The emphasis of this research is to study the effect of polymer-flooding wastewater on anion membrane performance. Oilfield wastewater is a kind of multiphase system that containing solid suspend, liquid suspend, and dissolved salt. A small-scale 5-compartment electrodialysis was developed to study the effect of main fouling substances of polymer-flooding wastewater (solid suspension, crude oil and polymer) on the performance and apparent characteristics of anion membrane from microcosmic (membrane surface resistance, average current, desalination rate, etc.) and macroscopical (scanning electron microscope and atomic force microscope, AFM) views, respectively. The concentration of cations is measured with atom absorbing spectrum (PERKIN-ELMER 703), the concentration of anions is measured with ion chromatogram (DLONEX 4500i) and the sum amount of ionic concentration is TDS. The experimental results show that fractional solid suspension congregated on the surface of, or inside, anion membrane and fouled membrane. Crude oil formed a compact oil film after being absorbed, which affects ions to get through ion-exchange membrane. The polymer may congregate on the surface of anion membrane, and had some influence for permeation of anion membrane. The membrane fouling changes little with time going on.