Study On The Emulsification And Stabilization Of ASP Flooding Produced Liquid

ASP flooding have been widely tested in Daqing Oilfield. While significant decrease of water-cut of produced liquid and increase of oil production have been achieved, residual alkaline, surfactants and polymer in produced liquid have resulted in stable crude oil emulsion, causing great troubles in surface oil-water separation processes.In this work, emulsification and stabilization of o/w ASP flooding produced liquid in Daqing Oilfield were systematically studied on artificial ASP flooding produced liquid and oily water. The influences of alkaline (NaOH), surfactant and polymer (partially hydrolyzed polyacrylamide PAM) on the stability of ASP flooding produced liquid and oily water were tested. Bulk phase rheology and interfacial properties such as interfacial tension, oil droplet Zeta potential and interfacial rheology were tested to reveal the mechanisms of the emulsification and stabilization of ASP flooding produced liquid.Emulsification of o/w ASP flooding produced liquid i.e. breakage of oil droplet is caused by the mechanical shearing force exerted on oil droplets by the surrounding liquid (water). The significant enhancement of the emulsification of chemical flooding produced liquid is mainly caused by the reduction of dynamic oil-water interfacial tension by residual alkaline and surfactant, and the increase of water phase viscosity by residual polymer. Decrease of interfacial tension results in less resistance to oil droplet deformation and thus decrease of energy consumption to break an oil droplet.The enhanced stability of ASP flooding produced crude oil emulsion results mainly from its intensified emulsification by the residual alkaline, surfactant and polymer in it.The stabilization of ASP flooding produced liquid by residual alkaline, surfactant and polymer lies in the enhanced emulsification of produced liquid in which smaller oil droplets are produced, the increase of water phase viscosity by polymer which decreases oil droplet rising velocity and the hindrance of alkaline and surfactant to oil droplet coalescence. Decrease of oil droplet size results inlower o/w ASP flooding produced crude oil emulsion creaming rate and smaller oil droplets in the condense oil droplet layer on top of o/w ASP flooding produced crude oil emulsion, leading to lower oil droplet coalescence rate and smaller water droplets held in oil layer after oil droplet coalescence (tight w/o crude oil emulsion). The increase of water phase viscosity results in slower emulsion creaming, slower draining rate of the water membrane between two approaching oil droplets and thus slower oil droplet coalescence rate in the condense oil droplet layer on top of the o/w crude oil emulsion. In case of high alkaline concentration, alkaline repels the surface-active components on oil-water interface such as indigenous surface-active components in crude oil, the products of chemical reaction between alkaline and indigenous components in crude oil, and the injected surfactant to the oil phase side, resulting in stronger steric hindrance to water droplet coalescence and thus tighter w/o crude oil emulsion on top of o/w chemical flooding produced crude oil emulsion after emulsion creaming and oil droplet coalescence.The phase separation process of o/w chemical flooding produced liquid constitutes of three parallel and successive subprocesses: oil droplet rising (creaming), oil droplet coalescence, and water droplet settling.The influences of indigenous components and injected chemicals on the stabilization of emulsion can be tested by diluting condense emulsion to form dilute emulsions of same droplet size distribution but with different composition.The residual polymer acts to flocculate the oil droplets in ASP flooding produced o/w crude oil emulsion. The flocculating effect of polymer on oil droplets increases with polymer content. The presence of alkaline and surfactant weakens the flocculating effect of polymer on oil droplets.