| The research and exploration of shale gas get rapid development in China in recent years,while the commercialization of shale gas in American and Canada.According to the report,hydraulic fracturing technology is an important stimulation for gas production,and the skill of horizontal drilling and multiple staged fracturing is the key to hydraulic fracturing.However,lots of fracturing liquid is produced after fracturing operation,furthermore,the liquid has become one of the main environmental pollution sources in the process of shale gas for the characteristic of large capacity,high stability,complicated composition and difficult treatment.The pollutant composition in the fracturing liquid from SINOPEC Southwest Oilfield Company Deyang Xinye HF-1 well was analyzed,and the results showed that the fracturing wastewater was weak acidity because of pH of 6.52,moreover,the contamination in the wastewater exceeded quota seriously because of CODCr value of 2 679.2 mg/L,sodium chloride concentration of 53 533 mg/L,total iron of 12.40 mg/L,SS concentration of 60.85 mg/L.Analysis of GC-MS showed that the fracturing liquid contaimed organic matter of paraffin,esters and benzene.Gel breaking by CaO and preliminary oxidation by NaClO were adopted in the experiment of preprocess of fracturing liquid,the effects of pH value in gel breaking and preliminary oxidation separately,CaO dosage,NaClO dosage and reaction time in the experiment of preliminary oxidation on pollutants removal were studied.Under the optimum conditions of pH value of 9.5,CaO dosage of 4 000 mg/L in the gel breaking,pH value of 5.5,NaClO dosage of 80 mL/L and the reaction time of 60 min,the pollutants in the effluent of oxidation were sharply decreased,CODCr,SS,oil content,NaCl,K+,Mg2+,total iron,Ca2+ and bacteria was decreased to 1 170.2 mg/L,7.92 mg/L,0.53 mg/L,67 870 mg/L,10.33 mg/L,0.33 mg/L,620.06 mg/L,0.59 mg/L and 2.5 cell/L respectively,the chroma was droped to 20 times.The effluent of the treatment has reached the first grade criteria of standard of reuse water quality of shale gas fracturing fackflow wastewater.The effluent of pretreatment of the water was used for confecting fracturing fluid,and the single-factor experiment in the process of confecting found that the concentration of K+,Na+ and Mg2+ in the water had no impact on the fluid viscosity and effect of crosslinking,while the concentration of Ca2+ and total iron ion below 800 mg/L and 80 mg/L respectively,fluid viscosity of fracturing fluid was above 40 mPa·s steadily,and for the effect of crosslinking,the concentration of Ca2+ and toaal iron ion need to decrease to 800 mg/L and 120 mg/L.The gel fracturing fluid prepared by treated water had good pick hang and elasticity,and rheological properties had little difference in performance compared to blank test.The combination of wet oxidation and vacuum membrane distillation was used to remove the organic pollutants and salt in the effluent of pretreated of fracturing liquid,effectively,so that the final effluent quality could meet the discharge standard.In the experiment of wet oxidation treatment,found that the reaction temperature had the greatest effect on the processing effort,and followed by mixing speed,oxidation time and oxygen partial pressure through single-factor and orthogonal tests.Various factors that affect the processing effort were discussed,the results showed that under the optimal reaction conditions of reaction tempreture of 230?,mixing speed of 240 r/min,reaction time of 180 min,oxygen partial pressure of 3.50 MPa,CODCr concentration in the fracturing fliud from 1170.2 mg/L fell to 299.8 mg/L,removal rate reached 74.38%,effluent colority reduced to 5 times.In the experiment of vacuum membrane distillation,found that the temperature of feed liquid and condensation had a greater influence on the processing effort,while vacuum degree and reaction time had less effect through single-factor and orthogonal tests.And the tests aslo showed that under the optimum technological conditions of feed liquid temperature of 80?,condensate temperature of 8?,vacuum degree of 0.090 MPa,reaction time of 60 min,the membrane flus of up to 1 750 mL/m2·h,the CODCr concentration in the effluent of membrane distillation of 92.15 mg/L,the effluent quality met the first grade criteria of integrated wastewater discharge standard(GB8978-1996),eventually.In addition,in the produced water of membrane distillation,the conductivity was 63 uS/cm,the sodium chloride concentration was 1.1680 mg/L,which could reduce the salinization damage on the surrounding soil by the effluent of fracturing fluid flowback effectively. |
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