Microbial community in produced water from typical coalbed methane wells and its geological significance in Guizhou and Yunnan Provinces, China

The produced water from coalbed methane (CBM) wells contains abundant geochemical and microbiological information. The microbial communities in the produced water of 14 CBM wells from four coal-bearing synclines in Guizhou and Yunnan were successfully tested by using 16S rRNA amplicon sequencing technology. The results showed that the produced water contained a large number of archaea and bacteria. The bacteria mainly included the orders Bacteroidales and Clostridiales, accounting for 37.4% and 32.92%, respectively. The water contained more than 30 species of bacteria and 15 species of methanogens. Macellibacteroids was the dominant genus, followed by the genus Citrobacter. The methanogens mainly included the orders Methanobacteriales and Methanosarcinales, accounting for 57.46% and 26.49%, respectively. Methanobacterium was the dominant genus, followed by the genus Methanothrix. There were three kinds of metabolism: hydrogenotrophic methanogens, acetoclastic methanogens, and methylotrophic methanogens. The main influencing factors of archaea were coalbed properties, such as burial depth and R_o,max, while the influencing factors of bacteria were mainly the physical and chemical properties of groundwater, including Cl⁻, total dissolved solids, and HCO₃⁻. The microbial communities were segmented in the vertical direction of the coal measure strata, which can be consistent with the distribution characteristics of multiple superposed fluid systems, and the main microbial species in each section were preliminarily identified. Combining carbon and hydrogen isotopes of methane, and dissolved inorganic carbon stable carbon isotopes of produced water from CBM wells, the results showed that the microbial reduction in the Tucheng and Enhong synclines were strong and that there were obvious secondary biogases. A reduction in hydrogen-trophic methane bacteria is an important way to produce secondary biogases in the study area. These synclines are suitable to carry out microbially enhanced coalbed methane research, expanding and extending CBM stimulation technology in the later stage.