The Research And Application Of Fracturing Wastewater Treatment Technology In Hujianshan Area Of Changqing Oilfield

By analyzing the characteristics of fracturing waste liquid in Hujianshan area of Changqing Oilfield,we applied flocculation,deionizing,sludge modifying for the fracturing waste liquid.Through degreasing pre-treatment,flocculant optimization,deionizing optimization,adaptability analysis and parameter optimization of quartz filters,as well as optimization of sludge modifiers,we successfully reinjected and reused fracturing waste fluid.1.The optimization of flocculant types and concentration in application indicates that:Screening experiments on flocculants under different concentration gradients were tested,including polyaluminum chloride(PAC),polyferric sulfate(PFS),Al₂(SO₄)₃,Fe Cl₃.30%of PAC was screened for the best coagulation effect.After treatment,the oil content in fracturing waste fluid decreased from 47mg/L to 7.2mg/L,and suspended solids(SS)decreased from 182mg/L to 14mg/L.10-well field application of the optimized methods shows that both the oil content and suspended solids(SS)in fracturing waste fluid were less than 10 mg/L,and the on-site water quality test results are up to the standard.2.The optimization and screening test of deionizing and waste liquid treatment formula in application indicates that:(1)For Ca²⁺and Mg²⁺,comparing separate treatment using sodium carbonate and sodium hydroxide with the compound system,the compound system not only greatly reduces the dosage and economic cost,but also effectively removes Ca²⁺and Mg²⁺.Meanwhile,the compound system effectively eliminates corrosion products,suspended solids and microorganisms in the waste liquid.The resulting sludge is relatively good in density,dehydration and operability.The finally optimized Ca²⁺and Mg²⁺treatment is compound sodium carbonate and sodium hydroxide,with the compound ratio of 1000:800.(2)For Fe³⁺,both ethylenediaminetetraacetic acid(EDTA)and sodium hydroxide shows effective removal of Fe³⁺.Considering economic cost,the dosage of sodium hydroxide is much lower than that of EDTA and citric acid,and the cost is much smaller.Therefore,sodium hydroxide is finally selected to eliminate Fe³⁺,with 120mg/L dosage.(3)For B³⁺,different proportions of triethanolamine(TEA)and glucose were tried to carry out the post-treatment gel preparation test for the treated fracturing waste liquid.The optimized dosage of TEA and glucose was 30mg/L and 20mg/L respectively when the compound ratio of TEA and glucose was 1:9 And 2:8.Considering the cost,we selected TEA:glucose equals to 2:8 and 20mg/L dosage.The optimized formula of fracturing waste liquid treatment is 30%PAC(1200mg/L)+CPAM(15mg/L)+sodium carbonate(1000mg/L)+sodium hydroxide(800mg/L)+glucose/triethanolamine(20mg/L)+citric acid.After 10-well field application of the optimized formula,fracturing fluid preparation test was carried out with a more than 95%success rate of gel preparation and effective ion removal effect.3.Through the treatment test of fracturing waste liquid,the treatment process of"pretreatment+coagulation+filtration+sludge dewatering"suitable for fracturing waste liquid treatment site was determined,the results indicates that:(1)The inclined pipe oil removal unit is selected as the pre-treatment unit,and can be applied as the pre-treatment oil removal unit when the oil content of fracturing waste liquid per well is less than 100mg/L,which can reduce the oil content in waste liquid to below20mg/l before coagulation,meeting requirements of oil-bearing index of filter inlet.(2)The quartz sand filter was selected for filtration and tested in field application.The optimized filtration speed is 8?10m/h,with 40h-filtration-cycle and backwashing intensity equal to 15 L/m²·s,and the backwashing time is greater than or equal to 3 min.The filtration efficiency is the highest under those conditions.(3)The plate frame filter press was selected as sludge treatment device in waste liquid treatment of single well pad.PAC and Cationic PAM were selected as sludge modifiers,and the optimized dosages of PAC and CPAM are 300-500mg/L and 80-120mg/L respectively.The sludge after modifying is determined by field application test and treated by plate frame filter press,with water content of sludge equals to 60%-70%,which meets the standard requirements.