| The large-scale development of shale gas has led to major changes in the world’s energy structure,but it will also produce a large amount of high COD,high heavy metal content,and high TDS fracturing flowback fluids.From the perspective of ecological environmental protection,the rational,effective and timely treatment of flowback fluid is the key to the sustainable development of shale gas development.In this paper,the typical fracturing flowback fluid in Changning area of Sichuan Province is taken as the research object,and the treatment of fracturing flowback fluid is taken as the research purpose.The water quality analysis of flowback fluid samples and the comparison of the water quality characteristics of flowback fluid at home and abroad are carried out;the influencing factors and the optimal treatment process conditions of three treatment technologies of gravity sedimentation,chemical coagulation and artificial zeolite softening are studied;the gravity sedimentation chemical coagulation place A study on the treatment of flowback fluid and the preparation of slick hydraulic fracturing fluid by the combination of GSCPand GSCZ.The results show that:(1)There are significant differences in the water quality of fracturing flowback fluids generated by shale gas development at home and abroad,mainly manifested as high SS content,high salt content,and large fluctuation range of water quality.The content of TDS and SS in foreign return fluid is within 2.3×10~5mg/L and 1.4×10~5mg/L,while the content of domestic TDS and SS is below 8×10~4mg/L and8×10~2mg/L,respectively,the content is significantly higher In China;Domestic reports on the quality of the returned water are not rich and comprehensive,and need to be supplemented and improved.(2)The turbidity of the water sample after gravity sedimentation decreased from 232.5NTU to 27.95NTU,the turbidity removal rate reached 88.0%,and gravity sedimentation can effectively reduce the turbidity of the return fluid.(3)The four inorganic coagulants FC,AS,PFS,and PAC have obvious removal effects on COD and turbidity in water samples.Under the best coagulation conditions,the turbidity of the water sample drops from 27.95NTU after gravity sedimentation to below 1NTU,the removal rate can reach 96%,the COD content decreases from 612.8mg/L to about 150mg/L,and the removal rate reaches 75.5%Above;The p H and temperature of the water sample have an effect on the coagulation effect of the four coagulants.At the optimal p H and temperature,the removal rate of COD in the water sample can reach 78.59%,and the turbidity drops to 0.36NTU.(4)Due to the high concentration of calcium and magnesium ions in the flowback fluid treated by GSCP process,the compatibility of the formation water used to prepare the fracturing fluid failed to meet the performance index of slippery water fracturing fluid.(5)The concentration of calcium and magnesium ions in the water sample after artificial zeolite softening decreased from 528mg/L and 38.4mg/L before softening to 128mg/L and 26.4mg/L respectively,and the removal rates reached 75.8%and 31.2%,respectively;The flowback fluid processed by the GSCZ process can be used as the base fluid for the preparation of slippery water fracturing fluid.The slippery water fracturing fluid prepared by it meets the performance indexes of fracturing construction.The research results provide a theoretical basis for further engineering application research of shale gas development fracturing flowback fluid reuse treatment technology. |
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