受地质因素影响的煤体结构能够影响煤层气井的产气能力，且在实际地质条件下，煤储层往往含有甲烷，使得含甲烷煤体的力学性质与储层压裂改造的效果密切相关。通过工业分析、元素分析、核磁共振碳谱(13C-NMR)和X射线光电子能谱(XPS)等手段测试和分析了山西沁水盆地寺河矿无烟煤的元素组成、原子比和官能团类型与分布等分子结构特征，构建了其大分子结构模型，模型的碳含量和密度与实测值具有较好的一致性。采用蒙特卡洛法模拟计算了甲烷在无烟煤中的吸附量、吸附位和吸附热，得到了甲烷在无烟煤中的吸附构型。结果表明:甲烷在无烟煤中的饱和吸附量为22.4个/晶胞，Langmuir压力为1.12 MPa，无烟煤模型中的芳香碳、吡啶型氮和吡咯型氮以及羧基是甲烷分子主要吸附位，等温吸附热随吸附压力的升高呈对数下降，说明甲烷在低压力时率先占据无烟煤表面的高能吸附位;甲烷在无烟煤中的吸附热介于22.65 ~25 kJ/mol，远小于42 kJ/mol，属于物理吸附。采用分子动力学方法对无烟煤的含气力学性质进行了模拟，定量研究了含气量对无烟煤的体积模量、杨氏模量、剪切模量和泊松比的影响。结果表明，无烟煤的体积模量、杨氏模量和剪切模量等随着含气量的增大呈对数规律降低，而泊松比随吸附量的增大呈线性增大;与不含甲烷的无烟煤相比，体积模量、杨氏模量和剪切模量最高降低了38.5%,24.4%和27.1%，表明吸附甲烷能够显著降低无烟煤的力学强度，其机理为无烟煤的体积和膨胀率随吸附量的增加呈指数增大，使得无烟煤基质之间的相互作用力降低，进而导致无烟煤的强度降低，抵抗变形的能力减弱。无烟煤的范德华能在吸附甲烷的过程中降幅最大，说明范德华能是保持煤体结构和力学性质稳定的主导因素。

The coal structure affected by geological factors can affect the gas production capacity of CBM wells,and under the actual geological conditions,coal reservoirs often contain methane,so the mechanical properties of methane bearing coal bodies are closely related to the effect of reservoir fracturing.By means of industrial analysis,element analysis,13C NMR and XPS,the molecular structure characteristics of Sihe anthracite in Qinshui Basin were tested and analyzed,including element composition,atomic ratio,type and distribution of functional groups.The macromolecular structure model was established,and the carbon content and density of the model were in good agreement with the measured values.The adsorption capacity,adsorption site and adsorption heat of methane in anthracite were simulated by Monte Carlo method,and the adsorption configuration of methane in anthracite was obtained.The results show that the saturated adsorption capacity of methane in anthracite is 22.4/cell,and the Langmuir pressure is 1.12 MPa.Aromatic carbon,pyridine nitrogen,pyrrole nitrogen and carboxyl group in anthracite model are the main adsorption sites of methane molecules.The isothermal adsorption heat decreases logarithmically with the increase of adsorption pressure,which indicates that methane occupies the high energy adsorption sites on the surface of anthracite at low pressure.The adsorption heat of anthracite is between 22.65-25 kJ/mol,far less than 42 kJ/mol,which belongs to physical adsorption.Molecular dynamics method was used to simulate the mechanical properties of anthracite.The effect of gas content on bulk modulus,Young’s modulus,shear modulus and Poisson’s ratio of anthracite was quantitatively studied.The results show that the bulk modulus,Young’s modulus and shear modulus of anthracite decrease logarithmically with the increase of gas content,while Poisson’s ratio increases linearly with the increase of adsorption capacity.Compared with the anthracite without methane,the bulk modulus,Young’s modulus and shear modulus decrease by 38.5%,24.4% and 27.1% respectively,which indicates that the adsorption of methane can significantly reduce the mechanical strength of anthracite.The mechanism is that the volume and expansion rate of anthracite increase exponentially with the increase of adsorption capacity,which makes the interaction force between anthracite matrix decrease,and then the strength of anthracite decreases and the ability to resist deformation is weakened.The van der Waals energy of anthracite decreases most in the process of adsorption of methane,which indicates that van der Waals energy is the dominant factor to maintain the stability of coal structure and mechanical properties.