Research On Treatment Technology And Application Of Produced Water In Xinjiang Oilfield

Karamay oilfield in the Gobi desert of Xinjiang is suffering severe water shortages under fragile ecological environment.As the oilfield enters into a mid-to late period of exploitation,polymer flooding have been applied to some oil wells.The characteristics of produced water from polymer flooding include high viscosity,high emulsification degree,high salinity,etc.The effective treatment for produced water from polymer flooding is of great economic benefit,social benefit and environmental benefit.Then the produced water from polymer flooding in Xinjiang oilfield was taken as the research target in this study.Firstly,coagulation pretreatment was employed to the produced water.After comparing the coagulation effect of coagulant polymeric ferric chloride(PFC)and polyaluminium chloride(PAC),PAC was chosen as the best coagulant eventually and APAM was used at the same time.The influence of PAC and PAM dosage on coagulation is investigated,respectively.The results showed that the oil concentration reduced to zero with 700mg/L of PAC dosage and 0.714 mg/L of PAM dosage as optimized reaction conditions without pH adjustment.When the dosage of PAC and APAM are 700 mg/L and 1.43 mg/L,respectively,the COD of the coagulation effluent could be reduced to 310 mg/L.Then,the influence of Fenton reagent dosage on oxidation is investigated for raw water and the water after coagulation.For the raw water,the removal rate of COD could reach 64.79%under the condition of pH=3,H2O2 dosage of 0.60 g/L,FeSO4 dosage of 0.325 g/L.For the water after coagulation,the removal rate of COD ccould reach 61%under the condition of pH=3,H2O2 dosage of 0.75 g/L,FeSO4 dosage of 0.65 g/L.The advanced treatment of the produced water after coagulation is further studied by electro-catalytic oxidation.The electrochemical performance and electro-catalytic oxidation effect of graphite plate electrode and ruthenium iridium coating titanium mesh electrode were compared,and the influence of current density,plate spacing and hydraulic retention time,acidity and basicity on electro-catalytic oxidation treatment effect were investigated.The experimental results showed that the ruthenium iridium coating titanium mesh electrode has more advantages on electrochemical performance and electro-catalytic oxidation effect.Under the condition of the current density=15 mA/cm2,residence time = 60 min and plate spacing =3 cm,the removal rate of COD reached 81.42%,and the effect in acidic and alkaline conditions are superior to that in the neutral one.The results of orthogonal experiment showed that the influence degree of each factors on the effect is,in order,current density.residence time and plate spacing.Ultimately,coagulation and air flotation was adopted as the the pretreatment process of the produced water from polymer flooding,followed by electro-catalytic and filtration in order.Furthermore,the device design and material selection was improved in pilot test.The inflow of design is 1 m3/h.The appropriate dosage of PAC and APAM are 700 mg/L and 1.4 mg/L,respectively,and the proper current for electro-catalytic oxidation equipment after debugging is 500 A.After running steadily,the COD,oil content,SS and pH value of the effluent from air flotation,electro-catalytic oxidation and filtration were continuously monitored for 15 days.The results can satisfy the requirements of petroleum and natural gas industry standard(SY/T 5329-2012)and integrated wastewater discharge standard(GB 8978-1996).The running cost of the pilot test is calculated as 5.16 yuan per ton of produced water from polymer flooding in Xinjiang oilfield,which has the economic feasibility.