Investigation On The Synergistic Treatment For Fracturing Flow-back Fluid By The Oxidation Of Potassium Ferrate And Electrochemical Process

Hydraulic fracturing technology plays an irreplaceable role in ensuring high and stable production of oil and gas fields.However,the discharge of the fracturing flowback fluid brings harm to the environment,thus it has become one of the important contents of environmental protection in oil and gas field.In this paper,the source,composition,pollutant composition,environmental pollution and the main treatment methods of fracturing flowback fluid(wastewater)were analyzed.Moreover,The green oxidant K2 Fe O4 was proposed to degrade the characteristic pollutant guar gum solution,and with the cooperation of electrochemical method,the fracturing flowback fluid was treated.we calculated the thermodynamic and dynamic of the experiment.Meanwhile,based on the results the main mechanism of degradation was put forward and the scheme of flocculation pretreatment-the oxidation by K2 Fe O4-secondary flocculation-electrochemical depth treatment was determined.The results showed that the guar gum with the concentration of 0.3‰,simulated as the model compound of fracturing flowback fluid,was degraded by K2 Fe O4 after full swelling.When the K2 Fe O4 addition of 0.5 g/L,the temperature of 30 oC and the p H value of 12,the viscosity of guar gum solution decreased by 89.27% and the removal ratio was 36.27%.The reaction product was trivalent iron,which was green and pollution-free.Based on the kinetic study and thermodynamic calculation of guar gum degradation,the reaction mechanism of guar gum degradation was proposed.The scheme of flocculation pretreatment-the oxidation by K2 Fe O4-secondary flocculation-electrochemical method was employed to deal with the fracturing flowback fluid.(1)Poly aluminium chloride(PAC)was optimized for the pretreatment of flocculation via the flocculation experiment with PAC,polyferric sulfate(PFS)and polyacrylamide(PAM).When the p H value of 7.0,the addition of flocculant of 0.4 g/L,the flocculation temperature of 25 oC and the flocculation time of 30 min,the turbidity lowered by 18.5%,the removal ratio of SS was approximately 68.9% and the removal ratio of COD was approximately 29.4%.(2)K2Fe O4 was used for the oxidation treatment of fracturing flowback fluid after the sediment and filtration.When the temperature of 25 oC,the p H value of 11.0 and the K2 Fe O4 addition of 3.0 g/L and the oxidation time of 40 min,the removal ratio of COD for the fracturing flowback fluid increased to 68.69% and the viscosity was reduced to 2.58 m Pa·s.Unforturnately,the chroma and turbidity of the fracturing flowback fluid increased significantly after the aboving treatment.Therefore,the additional flocculation process was needed.(3)PAM was optimized for the secondary flocculation process.When the addition of PAM of 0.1 g/L,the flocculation time of 20 min,the COD for the fracturing flowback fluid decreased by 73.74%,the viscosity slightly evaluated for the introduciton of PAM.(4)Taking the DSA as anode and titanium sheet as cathode,the eletrochemical process was used for the deep oxidation treatment as the final step.Under the decomposition voltage of 8.0 V and the decomposition time of 90 min,the removal ratio of COD was approximately 95.61% and the viscosity was approximately 0.925 m Pa·s,moreover,the turbidity and SS value reached the highest emission standard of category II pollutants for national comprehensive sewage(GB-8978-1996).