Research On Biochemical Treatment Of Fracturing Flowback Fluid

The fracturing operation,put into use universally in each oilfield,is one of major measures to increase production of oil and gas well.The fracturing flowback fluid generated in this process has already become one kind of wastewater source in oilfields.It has a profound meaning for controlling the environmental pollution of oilfield to deeply research treatment methods for the fracturing flowback fluid.This thesis systematically analyzed the sources,compositions,pollutional characteristics and current status of controlling of fracturing flowback fluid,adopted biochemical method to treat fracturing flowback fluid,and emphatically studied the feasibility and influential factors of the biochemical treatment method.In the chemical pretreatment experiment,coagulated treatment was taken and home-made polysilicate ferric aluminum(PSFA)was used as the coagulant.Design-Expert was applied to design orthogonal experiment to inspect PSFA's properties influences due to the factors,that is,the concentration of SiO2,the mole ratio of Si VS sum of Fe and Al,as well as pH value,moreover,optimizing PSFA's preparation condition.And the results showed that the mole ratio of Si VS sum of Fe and Al and p H value had great influence,and the optimal matching was w(SiO2)=3.4%,n(Si)/n(Fe+Al)=1.3,pH=1.8.Compared with traditional coagulants-PAC and PAM's treatment effects,PSFA was better;the removal rate of turbidity of fracturing flowback fluid treated by PSFA was able to reach 88.63%,which reduced the difficulty for the subsequent biological treatment.In the biological experiment,fracturing flowback fluid treated by coagulant was used to confect improved nutrient solution,in which chlorella vulgaris was cultured partially curing.Design-Expert was applied to design orthogonal experiment to inspect the influences of the concentrations of fracturing flowback fluid,activated carbon and ?-mannase.After one cycle-7d,the turbidity and algae cell density of each improved nutrient solution group were measured respectively,optimizing treatment project.The experiments' results showed that the optimal matching of improved culture solution was c(Fracturing flowback fluid)=200mL/L,c(Activated carbon)=100g/L,c(?-mannase)=171.08mg/L.The algae cell density of chlorella vulgaris turned from 0.0774×107/mL to 0.4149×107/mL,the removal rate of turbidity reached 91.61%,and the turbidity reached 2.29mg/L,which accorded with the First Grade of the National Standard for Wastewater Discharge.In order to verify the biochemical treatment's effect for removal of organics in fracturing flowback fluid,the paper eventually introduced the removal rate of COD as a test index.With the "Coagulation-Anaerobic-Microcosmic" craft,chlorella vulgaris was cultivated in the optimal improved culture solution.Finally,the removal rate of COD reached 91.3% and the COD was degraded with 56.38mg/L,which accorded with the First Grade of the National Standard for Wastewater Discharge.It verified the biochemical treatment method's feasibility and efficiency.