Study On The Stability And Destabilization Mechanism Of Oil Droplets In Produced Water From Alkali-Surfactant-Polymer Flooding

In 2014,Daqing oilfield was the first to realize industrialization promotion of alkali/surfactant/polymer(ASP)flooding throught the world.The oil recovery of ASP flooding is more than 20 percentage points higher than that of water flooding,which has been determined as one of the leading technologies for sustainable and stable production in Daqing oilfield.With the continuous promotion of ASP flooding technology,the output of ASP flooding produced water is increasing.Because the ASP flooding produced water contains residual oil displacement agent component,resulting in high degree of emulsification degree,good phase stability.Oil-water separation of ASP flooding produced water is much more difficult than that of water flooding and polymer flooding.In order to achieve high efficiency treatment of ASP flooding production water,the stability and destabilization mechanism of the oil droplets in the ASP flooding must be studied.In this paper,the influence of composition of oil displacement agent on oil-water separation characteristics is studied by simulating the ASP flooding produced water in the laboratory.The influence of oil displacing agent on the stability of oil droplets was revealed by studying the influence of the oil displacing agent on the surface properties of the oil droplets.On this basis,using the industrial demulsifier and flocculant to treat simulated ASP flooding produced water,and the processing conditions were optimized.The effect of chemical agents on the surface properties of oil droplets is studied to discuss the mechanism of chemical treatment agent on oil drop instability.The theoretical calculation results show that when the distance between oil droplets is larger,the liquid film life decreases with the increase of the oil droplet diameter;on the contrary,the change is opposite.The liquid film life of oil droplets increases with the increase of the concentration of the surfactant and the concentration of the polymer in the system.The experimental results show that the components of oil displacement agents have an effect on the oil and water separation characteristics,of which the surfactant has the greatest influence.The stability of the oil droplets gradually increases with the increase of the concentration of the surfactant.When the concentration of NaOH is <400mg/L,the stability of oil droplets increases with the increase of concentration.When the concentration of NaOH is >400mg/L,the stability of oil droplets decreases with the increase of concentration.The stability of the oil droplets gradually increases with the increase of the concentration of the surfactant.The effect of polymer on the stability of oil droplets is opposite to that of NaOH,that is,the stability of the droplets decreases and then increases with the increase of the polymer concentration.The demulsification and flocculation tests on the simulated ASP flooding produced water were conducted,and the treatment conditions were optimized: the dosage of the demulsifier,flocculant,settling time,stirring strength and stirring time are 110mg/L,70mg/L,240 min,200r/min,5min,respectively.Through the comparison and analysis of the theoretical and experimental results,the mechanism of demulsification and flocculation is summarized.The demulsifier molecules can be adsorbed onto the oil droplets,replacing the surfactant absorbed on the surface of oil droplet,to reduce the interfacial tension,and weaken interfacial film strength,so that the stability of oil droplets was decreased.At the same time,the demulsifier can also neutralize the negative charge on the surface of the oil droplet,reducing the electrostatic repulsion between the oil droplets,and then be beneficial to the accumulation of oil droplets.The flocculant after demulsification of oil droplets by charge neutralization and adsorption bridging,sweep function together,so that the oil droplets form aggregates,then the synthetic action of the demulsifier and the flocculant causes the oil drop flim to break up,the oil droplet coalescence occurs,so as to achieve the purpose of oil water separation.