Underground coal mining of CH₄ gas-rich tectonic coal seams often induces methane outburst disasters. Investigating gas permeability evolution in pores of the tectonic coal is vital to understanding the mechanism of gas outburst disasters. In this study, the triaxial loading–unloading stresses induced gas permeability evolutions in the briquette tectonic coal samples, which were studied by employing the triaxial-loading–gas-seepage test system. Specifically, effects of loading paths and initial gas pressures on the gas permeability of coal samples were analyzed. The results showed the following: (1) The gas permeability evolution of coal samples was correlated with the volumetric strain change during triaxial compression scenarios. In the initial compaction and elastic deformation stages, pores and cracks in the coal were compacted, resulting in a reduction in gas permeability in the coal body. However, after the yield stage, the gas permeability could be enhanced due to sample failure. (2) The gas permeability of the tectonic coal decreased as a negative exponential function with the increase in initial gas pressure, in which the permeability was decreased by 67.32% as the initial gas pressure increased from 0.3 MPa to 1.5 MPa. (3) Coal samples underwent a period of strain development before they began to fail during confining pressure releasing. After the stress releasing-induced yield stage, the coal sample was deformed and cracked, resulting in a quickly increase in gas permeability. With a further releasing process, failure of the sample occurred, and thus induced rapidly increasing gas permeability. These obtained results could provide foundations for gas outburst prevention in mining gas-rich tectonic coal seams.

This study investigated the patterns of gas occurrence in the coal seam structural zones of the northeastern margin of the Qinshui Basin, with a focus on the Sijiazhuang Coal Mine. Using laboratory experiments, theoretical analysis, and field exploration, we examined how geological structures influence gas distribution. The results show that gas content and pressure near normal faults are generally higher than those in reverse fault areas. However, fault-induced gas occurrence is complex, with stress superposition potentially reversing this trend. When a normal fault intersects modern tectonic stress at a perpendicular or large angle, the fault zone may transition to a compressional state, enhancing gas preservation. Fold structures were found to play a significant role in gas distribution, with anticline zones exhibiting the highest gas content, followed by syncline and normal zones. Collapse columns were shown to affect gas occurrence within a range of 15 to 180 m, with the impact depending on factors such as surrounding rock properties, hydrogeological conditions, and fault activity during collapse formation. Additionally, mirror-like sliding surfaces, formed by multiple factors, are prevalent in the coal seam structures of this region. These sliding surfaces are closely linked to structural zones and serve as valuable indicators for geological predictions in coal seam development.

Nanoparticles are ubiquitous in nature and are also found in raw coal, which plays an irreplaceable role in the global economy. In this study, raw coal samples were obtained from Gaojiapu Coal Mine in Shanxi Province, China. The elementary composition of nanoparticles was determined using energy-dispersive X-ray spectroscopy. The structural and chemical characteristics of nanoparticles were analyzed using transmission electron microscopy. Results revealed that there were multiple types of nanoparticles in the raw coal, such as S-, Ca-, Ba-, Ni-, Cr-, Si-, Sr-, and V-bearing nanoparticles. These nanoparticles exhibited various sizes and complex, irregular shapes. Our findings revealed that elemental nanoparticles occur in raw coal. These nanoparticles include celestite and barite nanoparticles. In addition, nanoparticles with Ni, Cr, and V in composition are also included in raw coal. These nanoparticles, which contain heavy metal elements, have great potential to harm the human body. Meanwhile, compared with the characteristics of nanoparticles produced by coal combustion, the nanoparticles in raw coal may be an important potential source of the nanoparticles produced by coal combustion.

Deep hot dry rock (HDR) geothermal energy is a widespread and sustainable renewable energy that could be extracted for the decarbonisation of electricity generation. Measurements are essential for hydraulic fracturing in HDR monitoring, which can be used for assessing the current state and predicting the future performance of geothermal systems. However, a major challenge is that it is difficult to implement hydraulic fracturing for HDR under high-temperature and high-pressure (HTHP) conditions. Similarly, it is hard to conduct laboratory-scale hydraulic fracturing experiments under HTHP due to the sealing failure of injection pipes in boreholes. Therefore, in this paper, we proposed a novel sealing technique by using a wedge-shaped structure for sealing injection pipes under HTHP environments. By conducting numerical simulations and experimental verifications, we discovered that (1) compression stress should be applied on the seal to achieve pre-sealing. Specifically, a compression displacement of between 2 mm and 6 mm is suggested. (2) Copper material with good ductility, high-temperature bearing performance, and excellent thermal expansion is preferred for manufacturing the seal components. (3) Heating-induced thermal expansion of sealing is conducive to re-sealing rocks.