Experimental Study On Ultrafiltration Technology For The Advanced Treatment Of Oilfield Polymer Flooding Produced Water

With the tertiary Enhanced Oil Recovery (EOR) technology further carrying on and developing, the polymer-flooding and alkali-surfactant-polymer (ASP)-compound-flooding have been applied on a large scale and a large amount of oil wastewater with polymer and oil has been produced during oil exploring with polymers in Daqing. In view of the complex wastewater system containing polymer and oil, the original flooding wastewater treatment processes haven't met the increasingly complex demands of wastewater disposal in the oilfield yet. Thus, this thesis conducts in-depth research on ultrafiltration membrane technology treating the oilfield polymer flooding produced water on the basis of the comparison of the advantages and disadvantages of various watertreatment technologies according to unique polymer flooding produced water quality of the Daqing oilfield.The bench-scale experiment, with the strongly anticontaminated PVDF ultrafiltration membraneh well separating the oil and water as the experiment object, systematically inspected the effect of the key parameters on membrane separation process from foundmental experiment to theory, inspected the permeate quality indexes of ultrafiltration for long-term operation and studied the technology of controling membrane fouling, such as the physical and chemical cleaning methods.The results show that the optimum operating conditions are a crossflow velocities between 3.0~3.5 m·s-1, a transmembrane pressures between 0.30~0.35 MPa, a feed temperature between 35~40°C and a volume concentration ratio 10, under which the perfect permeate flux and operation effect can be gained. The oil concentration, suspended solid and particle median diameter in the ultrafiltration permeate fully meet the reinjection water quality standard, and the ultrafiltration also has considerable effect on the removal of COD, turbidity and HPAM.The main elements causing membrane fouling have been analyzed in the methods of AFM, SEM, EDX and GC-MS. The results show that the basis causing membrane fouling is the crude oil and suspended solid from the wastewater. The former is absorbed on the membrane surface and the latter enters the the memrabne pore, which lead to the decrease of the infiltration speed. The research of the memrabne fouling mechanism shows that the concentration polarization is the most main factors making for flux decline and then is the gel layer formed by pollutant adsorption on membrane surface.According to the analysis of the pollutant component on the ultrafiltration membrane surface, this paper proposes the short-time chemical cleaning technology combined with the acid-alkali joint cleaning technology. The experiment shows that this kind of the cleaning technology can dispose the inorganic and organic foulants on the membrane surface and in the membrane pore in order to resume the membrane flux.To ensure the industrialized application feasibility of the ultrafiltering polymer-flooding produced water further, the pilot-scale research is enhanced on the basis of the bench scale to inspect the technology's adaptability to the oilfield production and the stability of the permeate water quality during the long-time operation.The ultrafiltration pilot apparatus with a capacity of 300 m3 water per day has made the permeate water quality of ultrafiltration fully meet the the reinjection water quality standard of Daqing oilfield with oil concentration less than 1.5 mg·L-1, the suspension content less than 1.5 mg·L-1, no particle median diameter checked and the obvious effect on the removal of the polymers and turbidity after the continuous operation more than three months. In the economic evaluation, this project has the remarkable economic benefit because the cost of the treatment of produced water for reinjection is lower than that of buying the fresh water for reinjection in Daqing.All in all, it is perfect to use the ultrafiltration to treat the polymer-flooding produced water. This technology can't only decrease the environmental pollution from the wastewater discharge further but also it can save the water and reduce the cost of affusion. Therefore, it is worth widely spreading this technology according to the economic and social benefit.