Research On The Disposal Technology Of Fracturing Wastewater In Shengli Oilfield

In order to enhance oil recovery and water injection,fracturing techniques are applied widely in oilfield.While in the process of fracturing a large amount of fracturing wastewater is produced,which makes the disposal research of fracturing wastewater increasingly important.This paper was mainly aimed at the fracturing wastewater discharged by Fan district in Shengli oilfield.The main control index of wastewater treatment was identified with wastewater analysis.The conditions of oxidation,flocculation and catalytic oxidation were investigated respectively,and the mechanism of treatment conditions on the flocculation effect was discussed through scanning electron microscopy,Zeta potential and floc size analysis.Combined with the specific water quality in experimental area and the effect of reagent adding sequence on the removal of organics,the "five step" process was proposed.Water quality and pollutants evaluation of fracturing wastewater were analyzed.The results showed that the wastewater composition was complicated,which was high iron content and turbidity with high concentration of suspended matter and organics.Corrosion rate,content of suspended matter and oil were decreased obviously by filtration,while the COD was still as high as 7000 mg·L-1,which was the main control index for following treatment.In the process of chemical oxidation,treatment parameters of H₂O₂,NaClO and KMnO₄ were studied respectively.The results indicated that: COD removal rates of H₂O₂,NaClO and KMnO₄ were 39.8%,27.5%,21.3% under the optimum experimental conditions.Considering chroma,H₂O₂ was chose as chemical oxidation treatment agentia,with optimal conditions: pH 6.5,80 m L·L-1 H₂O₂,reaction time 60 min.In the process of flocculation,the optimum formula of APAM: at room temperature,pH 9,100 mg·L-1 APAM.The reaction between APAM and organics is adsorption,cross-linking and sweeping.By increasing pH,the electric repulsion among hydrolytic aggregate of APAM is enhanced,which reduces the integrity and uniformity of network structure.The degradation of APAM is promoted and aggregation structure is destroyed for an increase in temperature,which affecting the removal rate on organics.The preferred treatment formula of PAC（I）: pH 10,200 mg·L-1 PAC（I）.Dosage affects the quantity and charge of PAC（I）hydrolysates,which lead to the change of flocculation characteristics and system stability.p H influences PAC（I）hydrolysates’ form: polymeric chloride aluminum and aluminum hydroxide gel produced under basic conditions are conducive to the removal of organics with adsorption and sweeping.In the process of catalytic oxidation,influence factors of Fenton reagent on oxidative degradation were discussed by orthogonal experiment.The results showed that COD removal rate was more affected by dosage of H₂O₂ and Fe²⁺ than pH and reaction time.Optimum formula for catalytic oxidation: pH 3,50 m L·L-1 H₂O₂,3000 mg·L-1 Fe²⁺,reaction time 60 min.The combined efficiency of five step treatment（filtering pretreatment-chemical oxidation-flocculation sedimentation-catalytic oxidation-filtration aftertreatment）was researched.Water quality analysis indicated: the treated water was neutral and low corrosion ratle;contents of suspended matter and oil were reduced to 2.6 mg·L-1 and 1.4 mg·L-1 respectively;removal rate of COD was 91%,which demonstrated that the combined treatment on fracturing wastewater in experimental block was feasible.