CO2-enhanced CH4 recovery technology (CO2-ECBM) can significantly improve methane production efficiency while mitigating greenhouse gas emissions. However, the influence of microstructural evolution of coal under high in-situ stress conditions in deep coal seams on CO2-CH4 competitive adsorption and microscopic gas transport behavior remains insufficiently understood. In this study, molecular dynamics simulations were employed to construct coal structural models under different stress conditions by applying uniaxial loading to the coal molecular framework. The evolution characteristics of the coal pore structure and the mechanisms of fracture formation under different stress conditions were elucidated, and the adsorption characteristics and competitive adsorption behaviors of CH4 and CO2 in coal models subjected to varying stress levels were further analyzed. The results indicate that, with variations in external stress, the pore structure of coal can be classified into a four-stage evolutionary pattern delineated by stress thresholds of 0.2, 0.4, and 0.8 GPa. Stress loading markedly alters the microscopic pore structure of coal and consequently affects gas adsorption behavior, with CO2 consistently exhibiting an adsorption advantage by preferentially occupying high-energy adsorption sites. Under all stress conditions, CO2 consistently exhibits higher adsorption stability and relatively lower mobility, whereas CH4 primarily displays confined diffusion at low stress levels and transitions toward nearly linear diffusion when the applied stress exceeds 0.7 GPa. This study provides a theoretical basis for a deeper understanding of the microscopic controlling mechanisms of CO2-ECBM in deep, high-stress coal seams.

CH4 adsorption in coal is a coupled process involving gas-solid interactions and adsorption-induced heat release. To systematically investigate the temperature response of coal during CH4 adsorption and its influence on adsorption stability, this study carried out CH4 adsorption experiments on coal samples with different ranks under different adsorption equilibrium pressures. By combining mercury intrusion porosimetry, X-ray photoelectron spectroscopy, and molecular simulation, the relationships among pore structure, chemical groups, adsorption capacity, and adsorption thermodynamics were revealed. The results show that the coal temperature during CH4 adsorption exhibits a three-stage variation pattern, higher adsorption pressure leads to a marked increase in the peak temperature rise, and a higher relative content of oxygen-containing functional groups weakens the heat released during CH4 adsorption. Molecular simulation shows that when the adsorption temperature increases from 298 K to 328 K, the CH4 adsorption capacity decreases markedly, indicating that coal heating caused by adsorption-induced heat release weakens the CH4 adsorption capacity. Thermodynamic analysis shows that the Gibbs free energy change, enthalpy change, and entropy change during CH4 adsorption are all negative. This study systematically investigated the mechanisms of CH4 adsorption heat release and temperature variation in coal, providing an important theoretical basis for evaluating coal and gas outburst proneness and predicting outbursts.

The paper uses macroscopic experiments and microscopic molecular dynamics simulations to explore the influence of the difference of DTAB surfactant concentrations and pH conditions on the wettability of coal dust. Through contact angle measurements and Fourier transform infrared spectroscopy (FTIR) to analyze functional groups and wetting behavior in coal, a multiphase wetting and adsorption system of " water-DTAB surfactant-acidic environment-coal " was constructed by molecular dynamics simulation in conjunction with characterization experiments to study the synergistic effects of DTAB surfactant and acidic environment. The comprehensive analysis showed that the wettability of coal dust along with the increase in the concentration of DTAB surfactant showed a tendency to be enhanced and then weakened, and the wettability of coal dust along with the enhancement of the weakly acidic environment is enhanced. The DTAB surfactant at a concentration of 0.075 wt % and a weakly acidic environment with a pH of 3 exhibit optimal wetting performance on coal, which transforms the coal from its original hydrophobic state (contact angle of 99.7 degrees) to a highly hydrophilic state (contact angle reduced to 31.8 degrees), and the total area of the absorption peaks of the hydrophilic groups in the coal increased by 192.45 %, and the diffusion coefficient of water molecules is reduced by 0.2122 & Aring;2/ps; CH3COOH can enhance the interaction energy between DTAB surfactants and coal molecules, as well as between coal and water molecules. It further promoted the adsorption and wetting of water molecules on coal surface, and the effect of wetting action was higher than that of single-factor action.

In the case of sequential mining with single wing arrangement in coal mine working face, the drilling along the working face is easily affected by the support stress of adjacent working faces, leading to drilling failure. At present, research on borehole protection focuses on enhancing the strength of the borehole itself, without proposing solutions to the fundamental factors that affect borehole stability. In order to solve the above problems, a hydraulic fracturing weakening roof borehole protection technology has been proposed. By using hydraulic fracturing to weaken the roof, the peak mining support stress acting on adjacent coal working faces is reduced, and the transmission of high support stress to the surrounding coal bodies in the bedding boreholes is blocked. The entire process of screening is carried out in the bedding boreholes to ensure that the gas escaping from the coal body can enter the bedding boreholes. Numerical simulation is used to analyze the changes in vertical stress and plastic zone of the coal body around the borehole before and after hydraulic fracturing weakening the roof. The results show that by weakening the roof through hydraulic fracturing, the peak vertical stress of the coal body around the borehole decreases from 21.2 MPa to 9.1 MPa, and the plastic zone range of the coal body decreases from 19 m to 11 m. According to the numerical simulation results, hydraulic fracturing parameters are determined and tested on site. The results show that after using hydraulic fracturing weakening roof borehole protection technology, the average volume fraction of gas extraction from boreholes increases from 3.6% to 14.1%. The average mixed flow rate of gas extraction decreases from 1.28 m3/min to 0.464 m3/min. There is no occurrence of coal oxidation and CO production in a large area of bedding boreholes. Therefore, hydraulic fracturing weakening roof borehole protection technology can effectively avoid drilling failure and gas leakage, improve drilling and extraction efficiency, and ensure drilling and extraction safety.

In order to reduce the cost of roadside filling and ensure the stability of the retained roadway system, the 150202 fully mechanized mining face of Shenlei Coal Mine is taken as the background, and the roadside filling body is made of coal gangue and fly ash as the base material, through orthogonal experiments, theoretical analysis, numerical simulation, on-site measurement and other research methods, the optimal ratio of filling materials and the laws of yield stress and deformation of roadway surrounding rock with different filling widths are studied. The results show that the optimal ratio of gangue filling body is water cement ratio 1∶1.85, fly ash replacement cement ratio of 20%, fine coarse aggregate ratio of 35∶65, and sodium silicate content of 6%; the larger the width of the roadside filling body next to the gob-side entry retaining, the lower the deformation of the surrounding rock and the vertical stress of the coal wall; by comprehensively comparing the stress and displacement of surrounding rock under different widths, it is concluded that the reasonable width of the roadside filling body next to gob-side entry retaining is 1.2 m.

The effective extraction layer of the overburden fracture zone in goaf is the basis for arranging high-level extraction boreholes to treat adjacent layers and gas in goaf. Based on the key layer theory, a mathematical model for the effective extraction layer in fracture zones is established, and the upper and lower boundaries of the effective extraction layer are determined. The lower boundary of the effective extraction layer is the first key layer above the collapse zone of the goaf, and the upper boundary is the first key layer below 10 times the mining height of the overburden layer in the goaf. The effective extraction layer includes the lower boundary rock layer and does not include the upper boundary rock layer. According to the mathematical model of the effective extraction layer of the fracture zone, it is calculated that the effective extraction layer of the fracture zone in the 8+9 coal seam of Duanwang Coal Mine is from the medium sandstone at 12.6 m above the coal seam roof to the No. 4 coal at 39.3 m. According to the drilling and observation results of the overburden fracture zone in the goaf, the fracture angle of the working face is about 62°. The height range of the fracture zone is 11.5-40.5 m above the coal seam roof. A high-level drilling and extraction test is conducted at Duanwang Coal Mine. It is found that the actual effective extraction layer of the fracture zone is from medium sandstone at 13.9 m above the coal seam roof to sandy mudstone at 37.4 m. The results of drilling observation analysis and high-level drilling extraction test have verified the accuracy of the mathematical model of effective extraction layer in the fracture zone. The research results can provide theoretical basis for the design of high-level extraction engineering in high gas and coal and gas outburst mines.

In the mining process of 4405 working face, spontaneous combustion of remaining coal is prevented by injecting nitrogen to goaf through buring pipe and continuous injecting nitrogen.Meanwhile, pre-bury beam tubes in the goaf and measure the gas concentration of each measuring point before and after continuous nitrogen injection.Combined with residual coal spontaneous combustion theory in goaf, the distribution variations of "Three Zones"ofgoaf spontaneous combustion were achieved.The safety zone before nitrogen injection was analyzed, explosion and combustion zone were eliminated by nitrogen injection and safetyproduction was ensured.