Oil Has a Higher Methanogenic Potential than Coal in an Oil-Bearing Coal Seam

The presence of oil in coal seams from coal-oil symbiosis areas poses a serious threat to the safe and efficient mining of coal. However, the information about the application of microbial technology in oil-bearing coal seams was insufficient. In this study, the biological methanogenic potential of coal and oil samples in an oil-bearing coal seam was analyzed by anaerobic incubation experiments. The results showed that the biological methanogenic efficiency of the coal sample increased from 0.74 to 1.06 from day 20 to day 90, and the biological methanogenic potential of the oil sample was about twice as high as that of the coal sample after 40 days of incubation. The Shannon diversity and observed operational taxonomic unit (OTU) number of oil were lower than those in coal. The major genera in coal were Sedimentibacter, Lysinibacillus, Brevibacillus, etc., and the major genera in oil mainly included Enterobacter, Sporolactobacillus, and Bacillus. The methanogenic archaea in coal mainly belonged to the order Methanobacteriales, Methanocellales, Methanococcales, etc., and the methanogenic archaea in oil mainly belonged to the genera Methanobacterium, Methanobrevibacter, Methanoculleus, and Methanosarcina. In addition, metagenome analysis showed that functional genes belonging to processes such as methane metabolism, microbial metabolism in different environments, and benzoate degradation were in a higher abundance in the oil culture system, while genes belonging to sulfur metabolism, biotin metabolism, and glutathione metabolism were in a higher abundance in the coal culture system. The metabolites specific to coal samples mainly belonged to phenylpropanoids, polyketides, lipids, and lipid-like molecules; meanwhile, the metabolites specific to oil were mainly organic acids and their derivatives. In summary, this study has a reference value for the elimination of oil from coal in oil-bearing coal seams and can be used to separate oil from oil-bearing coal seams and reduce the hazard brought by oil for coal seam mining.