Effect Of Chemical Oxidation Enhancing Coagulation Treatment On Simulation Alkali-surfactant-polymer (ASP) Flooding Produced Water

ASP(alkaline-surfactant-polymer)flooding is a new type of flooding technology to increase oil recovery,developed on the basis of water flooding and polymer flooding.The produced water of ASP flooding with complicated composition and nature is difficult to treat.Conventional coagulation treatment is difficult to break emulsion stability effectively,leads to poor effect,the treatment of the produced water of ASP flooding has become increasingly prominent problem,attracted people's attention.This topic is based on the effect of pre-oxidation on the coagulation,coagulation effects of the simulated ASP flooding produced water enhanced by potassium permanganate,hydrogen peroxide,potassium persulfate,potassium permanganate-hydrogen peroxide and potassium persulfate-ferrous sulfate were studied respectively.By the tests of coagulation,six kinds of coagulants were filtered.The best coagulant is polymeric ferric sulfate(PFS),which is better than polymeric aluminum ferric chloride,aluminium chloride,ferric sulfate,ferric chloride and aluminum sulfate,The optimum conditions are as follows: the dosage of PFS is 2500 mg/L;the solution temperature of it is 45?;the pH of it is 6;the rapid stirring speed is 250 r/min;the rapid stirring time is 3minutes;the slow stirring speed is 100 r/min and the slow stirring time is 15 minutes;when precipitating 30 minutes,The turbidity removal rate reached 94.4%,the oil removal rate reached 64.5%,and the viscosity decreased to 2.0 m Pa·s.Adding oxidants before coagulation has a significant effect on treatment performance.After coagulation,the oil removal rate,turbidity removal rate and polyacrylamide removal rate of the produced water are all increased,and the viscosity is significantly reduced.The potassium persulfate-ferrous sulfate oxidation combined with coagulation treatment of ASP flooding produced water has the best effect.Through orthogonal experiment,the optimum oxidation conditions are worked out as follows: 1.2 g/L potassium persulfate;0.6 g/L ferrous sulfate;pH=3;45?reaction temperature;60 minutes pre-oxidation time.If the others conditions keep constant,the amount of coagulant used in subsequent coagulation treatment can be reduced to 500 mg/L.The oil removal rate,polyacrylamide removal rate and turbidity removal rate were 92.3%,92.8%,98.8%,respectively.The turbidity decreased to 4.5 NTU,the viscosity decreased to around 0.5 m Pa·s.Through single oxidative degradation of polyacrylamide adsorbed on the oil-water interface,oil-water interfacial film was damaged,the strength,toughness,and viscoelasticity of the interface film was decreased,so that the electrostatic repulsion and space resistance between the oil droplets are weakened and the oil droplets are coalescence and floating,Enhancing the subsequent coagulation effect.The combined oxidation degrades polyacrylamide by generating strong oxidation free radicals,which can reduce the viscosity ofthe produced water,increase the molecular mobility,and destabilize the emulsion.The potassium persulfate-ferrous sulfate was exploited to treating simulated water,the ferrous ions are oxidized to trivalent iron ions and hydrolyzed to produce Fe(OH)3 colloids,which has good flocculation performance and resulting in less dosing of subsequent coagulant and better results.