A series of coal and gas outburst tests were conducted on coal seams in north China to determine the important order of gas pressure, in situ stress, and coal strength during coal and gas outbursts. And the typical phenomena of coal and gas outbursts were investigated. In addition, improved outburst energy equations were built to study the coal energy evolution process during coal and gas outbursts. The results show that the coal strength has the strongest influence on coal and gas outbursts, followed by the gas pressure and the in situ stress. The weights of pulverized coal with a particle size of less than 0.28 mm are consistent with the changing trend of the total weights of the pulverized coal particles in the corresponding outburst interval. Furthermore, the results suggest that the gas pressure monitored by the sensors close to the outburst hole begins to drop first and lasts for the longest time. The outburst coal presents obvious fracture and pulverization damage characteristics, and the pulverization damage features of the coal near the outburst hole are more obvious. In addition, the improved outburst energy equation was established, and the rationality of the improved outburst energy equation was verified by using the outburst orthogonal simulation experimental data and the on-site outburst accident cases. The results of this experiment have important guiding significance for preventing and controlling the occurrence of coal and gas outbursts and ensuring safe and efficient mining of coal mines.

The height of the water-conducting fracture zones (WCFZ) is crucial for ensuring safe coal mining beneath aquifers, particularly considering the secondary development of the WCFZ in upper seams due to repeated mining in close distance coal seams. Accurately predicting this height is essential for mine safety, groundwater protection, and optimal coal resource use. This study compiles extensive measured data from various mining areas in China to analyze the coupling relationship between the WCFZ development height and six influencing factors: mining thickness, mining depth, coal seam spacing, hard rock lithology ratio, and the slope length of working face. Using principal component analysis and fuzzy comprehensive evaluation, we derived the combined weights of these factors. We developed a prediction model based on multiple regression analysis that incorporates the weighted influences of these factors, further refined into a multivariate nonlinear regression model for greater accuracy. Compared against a multivariate linear regression model, empirical formulas, and measured results, our model demonstrated higher accuracy, stability in both absolute and relative errors, and practical applicability. It was successfully applied and validated on the 100,501 working face of Nanyaotou Coal Mine in Shanxi Province, offering a new scientific approach for predicting the WCFZ.

The permeability of marine sediments is critical to the gas production assessment of hydrate reservoirs. In this work, the sample of natural marine sediments was obtained from Shenhu Area of South China Sea at the depth of 1600 m, and the gas permeability of the sample was measured in the laboratory under various confining pressures. The porosity of the sample decreased from 41.82% to 29.54%, and the effective gas permeability of the sample decreased from 2.638 × 10⁻¹⁶ m² to 0.872 × 10⁻¹⁶ m² as the confining pressure increased from 0 to 23 MPa. The gas permeability of the natural sediments was determined to be 1.535 × 10⁻¹⁶ m² with confining pressure of 15 MPa and porosity of 32%. The deformation of sample in longitudinal direction was sensitive to the confining pressure, and the compressibility in the radial direction was limited. On the basis of the experimental results, the particle size term in the classical Kozeny–Carman equation was revised by correction factor N, and the experimental results fitted well with the curves with N = 2.40. Moreover, the gas production potential at the site of W–17 in the Shenhu Area was numerically studied based on the measured gas permeability. The simulation results showed that the cumulative volume of produced gas was approximately 1.46 × 10⁶ ST m³ after 30 years. A new enlarged permeable well wall method was proposed to improve the poor gas production caused by low permeability. The cumulative gas production increased by 2.7 times as the permeable well wall radius increased from 0 to 5 m. Regarding the gas and water production rates, water production increased with the increase of permeable well wall radius. Spatial distributions of hydrate and gas saturations, pressure, and temperature were investigated as well.