煤层气是一种以甲烷为主的清洁型能源，微生物降解煤会生成以甲烷为主的混合气体，补充原始储层含气量，在这个过程中会改变煤的官能团和孔隙结构。微生物降解作用对于不同煤阶煤的降解改造效果不同，进而导致差异煤阶煤的甲烷吸附行为发生不同的改变，所以本文选取6种差异煤阶煤作为研究对象，在室内进行微生物降解煤生烃模拟实验，采用等温吸附、氮气吸附、核磁共振和红外光谱等方法，对降解前后煤的甲烷吸附能力、孔隙结构和官能团进行表征，揭示微生物降解作用对差异煤阶煤的甲烷吸附能力、孔隙结构和表面官能团的影响，探讨微生物降解差异煤阶煤的甲烷吸附行为约束机制。取得的主要认识如下：

经过为期42天的室内研究证明微生物降解煤会生成以甲烷为主的混合气体，随着煤变质程度的加深，甲烷产量逐渐降低，甲烷气体的生成主要经历了三个阶段：缓慢增长期、快速增长期和衰竭期。甲烷产量与煤和微生物的接触面积有关。

在甲烷吸附能力、煤孔隙结构和表面官能团变化方面，微生物降解作用使低阶煤的甲烷吸附能力降低，中高阶煤的甲烷吸附能力呈增加趋势；煤中芳香环侧链、含氧官能团减少，脂肪族长链断裂，富氢、富氧程度降低，芳香化程度和有机质成熟度升高，说明微生物作用能够有效的破坏煤的官能团结构。微生物作用对孔隙的改造行为在低阶煤中表现为扩孔，微孔和过渡孔减少，中孔增多，中高阶煤表现为增孔，微孔、过渡孔和中孔增加。

（3）在甲烷吸附行为方面，R_o,max<0.9%煤的甲烷吸附行为主要受煤孔隙结构的约束。R_o,max>1.4%煤的甲烷吸附行为主要受煤表面芳香族官能团的约束。甲烷最大吸附量与微孔数量和芳香族官能团成正相关，含氧官能团呈负相关。微生物降解后煤中微孔数量在低阶煤中减少，中高阶煤中增加，导致微生物降解后煤最大甲烷吸附量在低阶煤中降低，中高阶煤中升高。说明对于低阶煤，微生物不仅可以产生较多的甲烷，而且还能有效降低煤体甲烷吸附能力，有利于甲烷的解吸，对低阶煤煤层气的开采具有积极意义。

Coalbed methane is a clean energy source mainly composed of methane. Microbial degradation of coal generates a mixture of methane based gases, supplementing the original gas content of the reservoir. During this process, it changes the functional groups and pore structure of coal. The effect of microbial degradation on the degradation and transformation of different coal ranks is different, which leads to different changes in the methane adsorption behavior of different coal ranks. Therefore, this article selects six different coal ranks as the research object and conducts indoor simulation experiments on microbial degradation of coal to generate hydrocarbons. Isothermal adsorption, nitrogen adsorption, nuclear magnetic resonance, and infrared spectroscopy methods are used to investigate the methane adsorption capacity of coal before and after degradation Characterization of pore structure and functional groups reveals the impact of microbial degradation on methane adsorption capacity, pore structure, and surface functional groups of differential coal rank coal, and explores the constraint mechanism of methane adsorption behavior of microbial degradation of differential coal rank coal. The main insights gained are as follows:

After 42 days of indoor research, it has been proven that microbial degradation of coal generates a mixture of gases mainly composed of methane. As the degree of coal metamorphism deepens, methane production gradually decreases. The generation of methane gas mainly undergoes three stages: slow growth, rapid growth, and depletion. Methane production is related to the contact area between coal and microorganisms.

In terms of methane adsorption capacity, coal pore structure, and surface functional group changes, microbial degradation reduces the methane adsorption capacity of low rank coal, while the methane adsorption capacity of medium to high rank coal shows an increasing trend; The reduction of aromatic ring side chains and oxygen-containing functional groups in coal, the fracture of long chains of fatty groups, the reduction of hydrogen and oxygen enrichment, and the increase of aromatization and organic matter maturity indicate that microbial action can effectively destroy the functional group structure of coal. The transformation behavior of pores by microbial action in low rank coal is manifested as pore expansion, reduction of micropores and transition pores, and increase of mesopores. In medium to high rank coal, it is manifested as pore enlargement, and increase of micropores, transition pores, and mesopores.

In terms of methane adsorption behavior, the methane adsorption behavior of coal with R_o,max <0.9% is mainly constrained by the pore structure of the coal. The methane adsorption behavior of coal with R_o,max >1.4% is mainly constrained by the aromatic functional groups on the coal surface. The maximum adsorption capacity of methane is positively correlated with the number of micropores and aromatic functional groups, while it is negatively correlated with oxygen-containing functional groups. After microbial degradation, the number of micropores in coal decreases in low rank coal and increases in medium to high rank coal, resulting in a decrease in the maximum methane adsorption capacity of coal after microbial degradation in low rank coal and an increase in medium to high rank coal. For low rank coal, microorganisms can not only produce more methane, but also effectively reduce the methane adsorption capacity of the coal, which is conducive to methane desorption and has positive significance for the extraction of low rank coal seam methane.

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