Coal Quality Variations and Paleoenvironmental Controls of the Badaowan for Mation Coal in Fukang Mine, South Junggar Basin

The coal-bearing strata in the Fukang mining area exhibit favorable potential for coalbed methane exploration. To elucidate the vertical variations in coal lithology and coal quality and their constraints on the coal-forming environment, this study systematically analyzed the characteristics of coal lithology and coal quality at different stratigraphic levels based on weighted average values from multiple borehole coal samples. Furthermore, the controlling effects of the coal-forming environment on their formation were explored by integrating indicators such as sedimentary facies, coal facies, and ash content parameters. The results indicate that: ① Vertically, the vitrinite content shows a pattern of ″high-low-relatively high,″ while ash yield exhibits the opposite trend. The coal is characterized by carbon enrichment, low sulfur content, and oxides rich in silicon and aluminum. ② The peat swamp was a low-salinity inland freshwater environment. It evolved from an early-stage forest swamp facies with high and stable water levels to a mid-stage herbaceous swamp facies with frequent water activity, and then transformed into a late-stage humid forest swamp facies. The redox conditions successively corresponded to a reducing-weakly oxidizing-weakly reducing environment. ③ The evolution of the coal-forming swamp significantly influenced the V/I value and ash yield of the coal seams. As the swamp properties changed in stages, the coal lithology and coal quality exhibited periodic evolution. The coal seams in the lower member of the Badaowan Formation demonstrated the optimal coal lithology and coal quality, representing the most favorable interval for coalbed methane exploration and development.