Evolution of fissures and pressure discharge of gas caused by mining of the upper protective layer of a coal seam

Abstract

The evolution of fissures and permeability associated with mining of the upper protective layer of the coal seam is crucial for pressure relief gas drainage of the underlying seam. To understand the influence of mining the upper protective layer on gas drainage within the underlying coal seam, this study utilized the M16 and M18 seams in the Qinglong Coal Mine in Guizhou. Theoretical analysis, discrete element numerical simulation, and field tests were used to characterize the evolution of fractures associated with mining of the upper protective layer and the effects of pressure relief gas drainage within the protected coal seam. The results show that mining-related stress changes controlled the development of fractures, altering the permeability values of coals. An analysis of the crack development in the coal mass caused by mining of the upper protective layer shows that during the initial stage of mining, the produced cracks exhibited a butterfly shape network. Yet, with further development of the mining, these cracks and the stress changes gradually produced an inverted butterfly shape network. According to simulations, the areas of maximum deformation via expansion in the protected coal seam were located near the open cut and the mining end line of the working face. The maximum deformation values were 29.06 and 26.68 mm, respectively, and the corresponding deformation rates were 9.37‰ and 8.61‰, which are greater than the required 3‰. The findings of this study provide a new reference for gas control in pressure relief coal seams under similar working conditions.

Research on how acidification affects the coal's microscopic pore structure in the Guizhou mining region

“…The most abundant elements in the two coal samples were carbon and oxygen, as well as traces of silicon and calcium, suggesting the presence of quartz, kaolinite, and calcite. Among them, the acidified coal contains almost nonexistent Si and Ca because HCl and HF fully react with minerals, and Si and Ca are dissolved in the liquid in the form of ions, resulting in a large loss of Si and Ca on the surface of the coal sample 38,39 . The proportion of C elements on the surface of the coal sample increases by 15.5% and 6.7%, respectively, after acidification.…”

“…Among them, the acidified coal contains almost nonexistent Si and Ca because HCl and HF fully react with minerals, and Si and Ca are dissolved in the liquid in the form of ions, resulting in a large loss of Si and Ca on the surface of the coal sample. 38,39 The proportion of C elements on the surface of the coal sample increases by 15.5% and 6.7%, respectively, after acidification. Because when the content of other elements decreases, the relative content of C increases, and in an acid environment, the crystalline minerals buried in the coal body migrate to the surface, and these minerals contain C, which is conducive to the formation of corrosive pore networks inside the coal body.…”

Optimization of the Layer Location of Extraction Wells Based on the Unpressurized Gas Transport Law

“…Cheng et al 28 also conducted simulation studies on the mechanical effects of coal and rock mass under different protective layer mining modes, revealing the pressure relief and deformation resistance mechanism after protective layer mining. Xie et al 29 established a coal seam pressure-relief gas model, discovered the impact of the evolution of coal and rock mass cracks in protective layer mining on gas migration, and used the results to optimize the layout of pressure-relief gas drainage boreholes. In addition, Wang et al, 30 by studying the gas channels in the fissures of coal strata, proposed that the floor coal stratum in the mining direction be divided into the original stress zone, the pressure relief and permeability enhancement zone, and the recompaction zone.…”

Acidification-Induced Micronano Mechanical Properties and Microscopic Permeability Enhancement Mechanism of Coal

“…However, stable and efficient exploitation of CBM requires two fundamental conditions of the coal seam: first, the methane in the coal seam should be rapidly desorbed by injecting CO 2 to displace the methane within the coal; second, the coal seam must possess good permeability . This involves implementing various measures to enhance coal seam permeability as these measures are crucial for efficient exploitation of CBM. − …”