高效开发煤层气不仅能够遏制煤矿瓦斯事故，而且对于缓解我国天然气供给压力和优化能源结构具有重大战略意义。煤中多组分气体的吸附和扩散机理是煤层气开采过程中的关键问题。本文基于巨正则蒙特卡洛方法和分子动力学方法，从微观角度探究了多组分气体在煤狭缝微孔中的竞争吸附和扩散规律。

       基于煤的微晶结构参数，建立了不同分子结构的煤狭缝孔隙模型，并对煤的芳香单元延展度、芳香单元堆砌层数、表面缺陷及含氧官能团四个因素对CO2和CH4竞争吸附和扩散的影响机制进行研究。发现CO2和CH4的吸附量、平均等量吸附热和扩散系数均随芳香单元延展度增加显著增大；随着芳香单元堆砌层数的增加，CO2和CH4的吸附量及平均等量吸附热有所减小，扩散系数呈现先增大后减小的趋势；表面缺陷导致CO2和CH4吸附量、平均等量吸附热和扩散系数均减小；表面含氧官能团降低了CO2和CH4的吸附能力和扩散能力。

       基于不同种类煤的分子结构，建立了褐煤、烟煤和无烟煤的狭缝孔隙模型，探讨了煤阶对多组分气体竞争吸附和扩散的影响。发现多组分气体吸附能力随煤阶升高而增强；CH4/CO2、N2/CH4和CO2/H2O在不同煤阶煤狭缝微孔中的吸附选择性大小关系为褐煤<烟煤<无烟煤；不同煤阶煤与气体的相互作用能大小关系为褐煤<烟煤<无烟煤；多组分气体在煤狭缝微孔中扩散系数大小随煤阶的升高而增大；吸附和扩散膨胀比均随煤阶升高而增大。

       通过构建不同体系的煤-水-纳米颗粒改性表面活性剂模型，探究了纳米颗粒改性表面活性剂对煤体润湿性以及CH4吸附和扩散的影响。发现纳米颗粒改性表面活性剂可以促进水和煤的结合与吸附，CH4优先吸附在煤的狭缝孔隙中，含表面活性剂压裂液可抑制CH4的吸附和扩散。

         结合山西寺河煤矿的矿井条件和气体吸附理论，开展分子模拟的工程应用，对3号煤层中CH4的含气量进行预测，发现与实测值吻合较好，研究对预防煤与瓦斯突出及瓦斯治理具有指导意义。

    The efficient development of coalbed methane (CBM) can not only curb coal mine gas accidents, but also has important strategic significance for relieving natural gas supply pressure and optimizing China's energy structure. The mechanism of multi-component gases adsorption and diffusion in the coal is still a key problem in the process of CBM exploitation. The adsorption and diffusion mechanism of multi-component gases in coal slit micropores and its influencing factors were explored from the microscopic level using the Grand Canonical Monte Carlo (GCMC) method and Molecular Dynamics (MD) method.

     According to the microcrystal structure parameters of coal obtained from experiments, the influence of molecular structure on the competitive adsorption and diffusion of CO2 and CH4 was investigated by constructing different coal slit models with different extension degree of basic structural unit, the number of basic structural unit, surface defects, and oxygen-containing functional groups. It is found that the adsorption capacity, the isosteric heat of adsorption and diffusion coefficients of CO2 and CH4 increase significantly with the increase of the extension degree of basic structural unit. With the increase of the number of basic structural unit, the adsorption capacity and the isosteric heat of adsorption of CO2 and CH4 increase, and the diffusion coefficients show a trend of frist increasing and then decreasing. The surface defects lead to the decrease of CO2 and CH4 adsorption capacity, the isosteric heat of adsorption and diffusion coefficients. The presence of surface oxygen-containing functional groups can reduce the adsorption and diffusion capacity of CO2 and CH4.

    Based on the molecular structure of different types of coal, slit models of brown coal, bituminous coal and anthracite coal were established to investigate the effect of coal rank on competitive adsorption and diffusion of multi-component gases. It is found that the multi-component gases adsorption capacity increase with the increase of coal rank. The adsorption selectivity of CH4/CO2, N2/CH4 and CO2/H2O in three rank coal slit micropores is brown coal < bituminous coal < anthracite coal. The interaction energy relationship between the three coal molecules and the multi-component gases is brown coal < bituminous coal < anthracite coal. With the increase of coal rank, both the diffusion coefficients of multi-component gases and the swelling ratio of adsorption and diffusion increase in coal slit micropores.

     The influence of nanoparticles modified surfactant on coal wettability and CH4 adsorption and diffusion was investigated by constructing different system models. The results show that the nanoparticle modified surfactant can promote the bonding and adsorption of H2O and coal, and reduce the interaction between coal surface and H2O, and the hydrophobic effect of surfactant decreases obviously. CH4 is preferentially adsorbed in slit pores of coal, and the fracturing fluid containing surfactant can inhibit the adsorption and diffusion of CH4 in coal seam.

    Combined with the mine conditions of Sihe Coal mine in Shanxi Province and gas adsorption theory, the engineering application of molecular simulation was studied, and the gas content of CH4 in No.3 coal seam was predicted, which is of great significance to the prevention of coal and gas outburst and gas control.

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