Biodegradation of coal organic matter associated with the generation of secondary biogenic gas in the Huaibei Coalfield

Although the biodegradation of coal-measure organic matter (OM) provides a crucial material basis for the formation of secondary biogenic gas (SBG), few studies to date have focused on the effect of OM biodegradation on SBG enrichment. Therefore, the compositional characteristics of saturated hydrocarbons and aromatic hydrocarbons in coal and coal-measure mudstone in the Huaibei Coalfield were analyzed to investigate their biodegradation characteristics and the impact on SBG enrichment. The biodegradation analysis of biomarkers showed that all samples had experienced different degrees of biodegradation; however, the degradation of saturated hydrocarbons and aromatic hydrocarbons differed significantly. In saturated hydrocarbons, long-chain n-alkanes showed more extensive degradation than short-chain alkanes, while aromatic compounds with low substituent numbers degraded more rapidly than that with high substituent numbers in the same series. Naphthalene was strongly biodegraded, and the degradation of biphenyl and dibenzofuran was more heavily than that of phenanthrene series compounds. In contrast, phenanthrene and dibenzothiophene compounds showed slight biodegradation. In terms of the biodegradation degree of saturated hydrocarbons, the biodegradation level reached 4 -5 levels, while the biodegradation level of aromatic hydrocarbons was as high as 5 -7 levels. Obviously, the degradation of biomarkers in coal is remarkably different from the phenomenon found in oil. Nevertheless, while microbial degradation provides a sufficient material basis for the generation of SBG, strong biodegradation does not necessarily lead to the best occurrence of SBG. The preservation of SBG is also affected by the characteristics of structural fractures, the preservation conditions of CBM, and so on.

Automated summary

In this study, the compositional characteristics of saturated hydrocarbons and aromatic hydrocarbons in coal and coal-measure mudstone were analyzed to investigate their biodegradation characteristics and impact on secondary biogenic gas (SBG) enrichment. The research found that saturated hydrocarbons and aromatic hydrocarbons experienced different degrees of biodegradation, with varying levels of degradation observed.