Experimental Research Of Fracturing Flow-back Fluid For Reinjection Treatment In Oilfield

Fracturing technology is one of the important methods for promoting the production of oil and gas well.There was a large amount of water flows which with high viscosity,high COD and high suspended back to the surface after fracturing and become one of the main sources of pollution in the oil field.This will cause serious pollution to the surroundings if it discharged directly without any treatment.This study carried out the removal process of contaminants on the basis of analyzing the main pollution components of fracturing flow-back fluid,the results showed that:（1）fracturing flow-back fluid pH was 9.4,viscosity was 102mPa·s,suspended solids content,oil content and COD content was respectively 1814.3,78 and 2518.5 mg·L^-1.c(Ca²⁺),c(Mg²⁺),c（Cl^-）,c(Fe²⁺),c(PO₄^3-),c（NO₃^-）and c(SO₄^2-)was respectively 2440,263.8,6018,100,2319.05,61.75 and 316.7 mg·L^-1.The average corrosion rate was 0.0163 mm·a^-1,sulfate reducing bacteria and saprophytic bacteria was respectively 2.0×10³ and 2.5×10³.（2）Gel breaking process.Research the effect of gel breaking by dosage of enzyme,temperature,pH,stirring speed and time,and selected the best gel breaking condition through orthogonal experiment,when the dosage was 40 mg·L^-1,temperature was 40,pH was 7,stirring speed was 600rpm,time was 150min,the viscosity of fracturing flow-back fluid can be controlled under 2mPa·s.（3）Oxidation process.Single factor experiment were investigated the effect of dosage for ammonium persulfate with sodium bisulfite,hydrogen peroxide,sodium hypochlorite and potassium permanganate,and compounded ammonium persulfate with sodium bisulfite,hydrogen peroxide and enzyme breaker.The results showed that when the ammonium persulfate,sodium bisulfate,hydrogen peroxide and enzyme was respectively6000 mg·L^-1,2000 mg·L^-1,3000 mg·L^-1 and 20 mg·L^-1,the viscosity of flow-back fluid was controlled under 1mPa·s.（4）Coagulation process.Single factor experiment investigated the effect of pH,type and dosage of coagulant and flocculant,and compounded the selected coagulant.The result showed that when pH was about 7⁸,c（PAC）,c（PAM）and c（J1）was respectively 600,10 and 10 mg·L^-1,the removal rate of suspended solids content and oil contentwasreached97.8%and98.7%,respectively.（5）“Gel breaking-Oxidation-Coagulation-Neutralization-Filtration”processing technique has formed by the research of each unit treatment process,the result showed that pH was 7.4,the viscosity was 1.2mPa·s,suspended solids content was 4.6mg·L^-1,oil content was 1.0mg·L^-1after treatment,and all the indicators of fracturing flow-back fluid after treatment can reach the standard of reinjection.（6）Research of compatibility of corrosion and fouling.Mixture the treated effluent and water sewage station with the ratio of 0:10,2:8,4:6,5:5,6:4,8:2 and10:0,the result showed that it has good compatibility with precipitation and low corrosive,the loss of Ca²⁺was under 10%,the average corrosion rate was under 0.076 mm·a^-1.This paper provided basis of theoretical and guidance for the reinjection requirements,experiment basis for design and implementation of disposing of fracturing flow-back fluid treatment devices.