| In the process of shale gas exploitation,hydraulic fracturing technology is needed to increase the recovery rate.Hydraulic fracturing is accomplished by injecting a large amount of fracturing fluid into the formation to improve reservoir permeability.After the fracturing operation is completed,most of the fracturing fluid will be returned to the ground after breaking the rubber to form shale gas fracturing flowback fluid.A variety of additives are often added to the fracturing fluid to meet the requirements of sand carrying and drag reduction.At the same time,it will contact with oil and gas,water and rocks in the stratum during the fracturing process,resulting in many types of pollutants in the fracturing fluid.The viscosity is high and the treatment is difficult.If it is not treated,it will cause environmental pollution.The development of shale gas fracturing flowback fluid treatment and reuse technology is of great significance for shale gas development and environmental protection.The paper takes the gas shale gas-splitting and discharge of the Shaanbei shale as the treatment object,and studies the oxidized flocculation treatment and the treated water nanofiltration treatment technology to form a“catalytic oxidation-flocculation sedimentation-nanofiltration”shale gas fracturing flowback fluid recycling process.?1?The viscosity and COD of shale gas fracturing flowback fluid are as high as 18.1mPa·s and 3992.7 mg/L,respectively,and the chromaticity,suspended matter content and salinity are 1330 degrees,2490 mg/L and 2472.15 mg/L,respectively.?2?At room temperature,when the dosage of oxidant hydrogen peroxide and ferrous sulfate are 0.3%and 100 mg/L respectively,and the dosage of catalyst cerous sulfate is 100mg/L,the viscosity of shale gas fracturing flowback fluid can be reduced from 18.1 mPa·s to less than 2 mPa s after 25 minutes of Fenton catalytic oxidation treatment.?3?When the catalytic oxidation of shale gas fracturing fluid flowback at the pH value is 7,PAC and cationic PAM are added in amounts of 800mg/L,20mg/L,and the dosing interval of flocculant and coagulant is 40s,the suspended matter content and oil content of the post-water reached 0.9 mg/L and 4.32 mg/L,respectively.The salinity of the water before and after treatment was 2472.15 mg/L and 2886.61 mg/L,respectively,and the corrosion rate decreased to 0.041 mm·a-1.The water quality standard for re-injection water is reached.At the same time,a"catalytic oxidation-flocculation sedimentation"reinjection treatment process is formed.?4?The water treated by the"catalytic oxidation-flocculation sedimentation"process is adjusted to a pH of 7 at room temperature for nanofiltration.Calcium,magnesium,sulfate,carbonate and boron ions in the water samples before treatment are 30.62 mg/L,18.48 mg/L,158.04 mg/L,58.81 mg/L and 58.72 mg/L,respectively.After treatment,they are reduced to0.36 mg/L,0.21 mg/L,6.21 mg/L,0 mg/L and 2.08 mg/L.The water quality index of the fracturing fluid is reached,and a shale gas fracturing fluid flowback treatment process“catalytic oxidation-flocculation sedimentation-nanofiltration”is formed. |
PDF Full Text Request