Objective  The study aims to explore the microbial community composition and evolution process in flowback water from the initial drainage stage to the production stage in shale gas well.

Method 16S rRNA sequencing was used to test microbial community composition in flowback water and to analyze the relative abundance of phyla and genera.

Result The relative abundance of the microbial communities in the flowback water decreased successively during the initial drainage and gas production stage, final drainage and gas production stage, and the formal production stage. And the difference in microbial community composition among the three stages was obvious. The Proteobacteria, Campylobacterota, Firmicutes, and Desulfobacterota were abundant in the sample from the initial drainage and gas production stage. The dominant genera included Marinobacter, Paracoccus and so on. The dominant genus for the final drainage and gas production stage was Bacillus. The microbial community composition of the formal production stage was similar to that for the initial drainage and gas production stage to some degree at the genus level, because the appearance of some dominant genera for one stage was also found for another, such as Desulfomicrobium. But these dominant genera, such as Desulfovibrio and Shewanella were found in the gas production stage.

Conclusion  The difference in microbial community compositions among the three stages is more dominant than the similarity. The dominant microbial community in shale gas fields undergo significant evolution from the drainage stage to the production stage.