Geochemical Characteristics and Significance of shale Gas Well Flowback Fluid in Zheng’An Block, Guizhou

Analysis of fracturing flowback fluids from 14 shale gas wells across 7 platforms in the Zheng'an block, Guizhou, reveals that the fluids are characterized by high salinity, elevated Na\(^+\) and Cl\(^-\) concentrations, and high levels of chemical oxygen demand (COD) and ammonia nitrogen. Na\(^+\) concentrations range from 7370 to 27396~mg/L (mean 18689~mg/L), Cl\(^-\) from 9000 to 43000~mg/L (mean 29438~mg/L), and total salinity from 17074 to 70950~mg/L (mean 48744~mg/L). The dominant microbial populations comprise iron bacteria (FEB), saprophytic bacteria (TGB), and sulfate-reducing bacteria (SRB). These characteristics indicate that the flowback fluid cannot be discharged directly without treatment. However, following appropriate pretreatment—including advanced oxidation for COD reduction, chemical flocculation for suspended solids removal, and biocide addition for microbial control—the fluid can be either recycled for further shale gas development or discharged after meeting the required standards, such as those specified in the Guizhou Province Pollution Discharge Standard (DB 52/864-2022). Sulfate-reducing bacteria and other microorganisms contribute to scaling, corrosion, and perforation of downhole tubing, surface equipment, and gas transmission pipelines; such damage can be effectively mitigated by regular biocide application during shale gas production. These findings provide critical data support for the treatment and recycling of shale gas flowback fluids in Guizhou, contributing to improved shale gas reserve development and production efficiency in the region.