Understanding the interaction of CH₄ with kaolinite is significant for researchers in the fields of coalbed CH₄ and shale gas. The diffusion behaviors of CH₄ in kaolinite with water contents ranging from 0 to 5 wt% have been analyzed by molecular dynamics simulations. The results of the simulations indicate that CH₄ molecules can jump between adjacent holes in the kaolinite matrix. CH₄ diffusion coefficient was very low (3.28 × 10⁻⁹ m²/s) and increased linearly with the increasing of water content. As the water content decreased, the value of radial distribution function first peak between CH₄ and oxygen was larger, meaning that with lower water content, the interaction energy between CH₄ and oxygen in kaolinite is stronger. The interaction between CH₄ and water is linearly positively correlated with water content, in contrast, the interaction energy between kaolinite and water as well as between kaolinite and CH₄ decreased linearly with increasing water content. On the other hand, the diffusion of CH₄ molecules adsorbed on the surfaces also can be accelerated by the fast diffusion of water molecules in the middle micropore of the kaolinite.

To better understand the methane adsorption behavior after microwave exposure, the importance of quantitatively characterizing the effect of cyclical microwave exposure on the molecular structures of coals cannot be overemphasized, with implications for enhancing coalbed methane (CBM) extraction. Thus, cyclical microwave exposure experiments of three different metamorphic coals were conducted, and the methane adsorption capacity before and after each microwave exposure (10 in total) for 120 s was evaluated. Fourier transform infrared spectroscopy analysis and peak fitting technology were applied to quantitatively characterize the changes in the structural parameters of coal molecules. The results showed that after modification, the structural parameters like aromatic carbon fraction (f_a–F), aromaticity (I₁ and I₂), degree of condensation (DOC₁ and DOC₂), and the maturity of organic matter (“C”) gradually increased with increasing exposure times, while the length of the aliphatic chain or its branching degree (CH₂/CH₃) and the hydrocarbon generating capacity (“A”) showed a decreasing trend. The Langmuir volume (V_L) of three different rank coal samples decreased from 29.2, 32.8, and 40.4 mL/g to 25.7, 29.3, and 35.7 mL/g, respectively; the Langmuir pressure (P_L) increased from 0.588, 0.844, and 0.942 MPa to 0.626, 1.007, and 1.139 MPa, respectively. The modification mechanism was investigated by analyzing the relationship between the methane adsorption behaviors and molecular structures in coals. The release of alkane side chains and the oxidation of oxygen-containing functional groups caused by microwave exposure decreased the number of methane adsorption sites. As a result, the methane adsorption capability decreased. In addition, the decomposition of minerals affects methane adsorption behaviors in coals. This work provides a basis for microwave modification of coal as well as in situ enhancement of CBM extraction using microwave exposure.

Molecular simulation was used to study methane adsorption and its effect on kaolinite swelling. The effects of temperature and pressure were also analysed. The comparisons which validate the force field and model in our paper were made between simulation and experiment. Simulation results demonstrate that adsorption behaviour of methane exhibit Langmuir adsorption behaviour. The temperature has a negative effect on gas adsorption, the adsorption amounts will decrease with increasing temperature at a given pressure. A quantitative relationship between the methane adsorption and the kaolinite swelling was provided. The kaolinite–methane interaction dominates and the methane–methane interaction contributes less than 20% to the total interaction energy. The first peak in the RDFs increases with the increasing pressure, illustrating that the system becomes less structured at higher pressure. Compared with the higher temperature, the first peaks at lower temperature increase as a higher amount of methane adsorbed indicating that the interaction between the kaolinite and methane increase with decreasing temperature. Methane is strongly adsorbed on the sites of the hydrogen and oxygen atoms in kaolinite molecules.

Because the coal seam is particularly thick and the mining intensity is large, the mining of extremely thick coal seams often causes a wide range of disturbed fractures, which in turn induces the phenomenon of strong underground pressure such as induced support crushing and water inrush. Through theoretical analysis, laboratory similarity simulation test, and other methods, this paper studies the effect of mining thickness on overburden movement and underground pressure characteristics for extremely thick coal seams by sublevel caving with high bottom cutting height. Some conclusions can be drawn as follows: (i) under the “beam‐hinged cantilever beam rocks” structure theory, the rock pillar thickness which needs to be controlled increases linearly as a function of mining thickness is achieved, and the reason of increased of support resistance in full‐mechanized caving mining in extremely thick seams is explained in the theory; (ii) based on the results of the theoretical analysis and the lab simulation tests, the law of the abutment pressure peak is inverse to the full‐seam mining thickness, and the distance between abutment peak and working face is proportional to the full‐seam mining thickness, that is to say that the damage range of overlying strata increased; (iii) there are three working states of loading support in extrathick coal seams, such as normal circumstance, lower main roof pressure, and higher main roof pressure, meanwhile these states keep changing; (iv) under the guarantee of stope safety conditions, due to lower support strength, it will benefit the special thick seam top‐coal caving under normal circumstance; (v) increasing the supporting strength can balance the impact loading under the lower main roof pressure, guaranteeing valid support for roof strata; (vi) by releasing high pressure, due to lower production, lower recovery rate of coal and other measures guarantee the stability of the stope support in the case of the higher main roof pressure.