Study Of The Separation Of Produced Liquid And Oil In Back Water After The Polymer Flooding

The Polymer flooding in Daqing Oilfield has resulted in EOR rates respective 14% over water flooding. However, they have also resulted in tighter crude oil emulsion in produced liquid, leading to poorer oil/water separation of both produced liquid and oily water. As a result, qualities of the effluent water of some oily water treatment facilities have gone out of specifications. Aiming at improving the qualities of the effluent water of oily water treatment facilities in Daqing Oilfield, this paper focuses on the following subjects:(1) Mechanisms concerning the stabilization of the crude oil emulsion in polymer flooding produced oily water were studied. It was determined that the enhanced stability of crude oil emulsion in polymer flooding produced oily water results primarily from adsorption of colloidal particles on oil droplets which exerts steric hindrance to oil droplet coalescence and decreases the density difference between the oil droplets and the water phase. It was also found that residual polymer in polymer flooding produced oily water enhances the stability of the oily water by promoting adsorption of colloidal particles on oil droplet surface and increasing water phase viscosity, leading to lower oil droplet coalescence rate and lower oil droplet rising velocity.(2)The oil/water separation properties of reverse crude emulsion and mass transfer of demulsifier in reverse crude oil emulsions were studied. One emulsion type oil/water separation agent and one micro-emulsion type oil/water separation agent, suitable respectively for settling and flotation treatment of polymer flooding produced oily water, were developed on the basis of the oil/water separation characteristics of reverse crude oil emulsions and the mass transfer process of demulsifier in reverse crude oil emulsions. The micro-emulsion type oil/water separation agent was applied to improve the quality of the effluent water of an oily water treatment facility troubled long by out-of-specification effluent water. The two oil/water separation agents are both nonionic and their primary mechanism on polymer flooding produced liquid and oily water lies in their abilities to replace other surface active species on the surface of oil droplets and thus depress the negative charge on the surface of oil droplets. Another mechanism of the micro-emulsion type oil/water separation agent on polymer flooding produced liquid and oily water lies in its ability to depress the steric hindrance to oil droplets coalescence exerted by fine particles resting on the surface of oil droplets and its ability to improve the flowability of the surface of oil droplets by removing fine particles on the surface of oil droplets through wettability variation. In comparison with treating the produced liquid and oily water respectively with a state-of-art polyalkoxide demulsifier upstream of FWKOs and with a cationic flocculant or coagulant, treating the produced liquid with an oil/water separation agent has the advantages of no generation of sticky flocs, less sludge deposition in oily water treatment facilities, less oil content and looser reverse crude oil emulsion in the effluent oily water of FWKOs, and better qualities of the effluent oily water of oily water treatment facilities.