In accordance with the Paris Agreement, many nations have set out a global framework to stabilise and prevent greenhouse gas (GHG) emissions to mitigate climate change. This study reviewed the literature on the GHG protection and control (GHGPC) impacts of overburden fractures in relation to coal mining. Different factors, such as geological conditions, mining conditions, and gas extraction methods, were compared because they influence GHGPC. Carbon emissions, coal mining safety, and environmental protection are crucial parameters. GHGPC can (1) improve the safety and efficiency of mining, (2) reduce GHG emissions, and (3) generate clean gas resources. During mining, cracks appear in overburden strata, causing GHG emissions. Various techniques, including scanning electron microscopy, nuclear magnetic resonance, two-dimensional and three-dimensional physical similarity simulations, permeability testing, and numerical simulations, have been adopted to determine the macroscopic and microscopic features of overburden fractures. Finally, the extraction method of GHG was optimised through field practice, namely, roadway, borehole, and pipe extraction, were analysed, and the comprehensive GHG extraction method was preferred to achieve superior management results. This paper reviewed studies that examine the development of fractures to elucidate the significance of GHGPC. Moreover, this article provides new insights into the achievement of the “dual carbon strategy” with particular reference to coal mining; it also summarises the holistic life cycle of gas management in terms of overburden activity, gas transport patterns, reservoir characteristics and typical technologies. It also summarises the holistic life span of GHGPC management in terms of overburden activity, GHG transport patterns, reservoir characteristics, and typical technologies. Finally, the authors discuss and conclude the article with proposed methods for future research directions. 

Greenhouse gas protection and control based upon the evolution of overburden fractures under coal mining: A review of methods, influencing factors, and techniques

Gas is associated with coal mining; it commonly exists in the coal seam. It is one of the major dangers during the production because its reaction between the coal masses may induce the gas-coal outburst as well as it being an expositive matter. The gas accident has caused a huge amount of property damage and casualties. Therefore, the primary precaution for coal mining is gas control. At present, drilling and extraction are the main approaches for gas accident prevention. After drilling, the ground pressure will be released; the gas which is in a free state or absorbed in the coal seam will be easy to extract as the migration channel is enhanced. Hence, one of the most concerned problems is the stress redistribution of the coal and rock mass around the borehole. In practical engineering, there are many joints distributed in the coal and rock strata, so it is necessary to investigate the effect of the drilling in the jointed coal and rock mass. In this paper, the boundary element model of the borehole in the jointed coal and rock mass is established to study the influence of joints on the stress and displacement field. The following results can be obtained. The number of joints has a significant effect on the maximum displacement of the coal and rock mass. The maximum displacement increases with the number of the joint. The position of the maximum displacement shifts from the boundary of the borehole to the far field. Meanwhile, it can be found that the displacement may reach a peak value when the joint angle is 30° and if the joint number is less than 4, and the maximum displacement may occur under the joint angle of 45° and if the joints number continuous increases. The von Mises stress has a trend of increasing with the number of joints when the joint angle is less than 30°, while it has a decreasing trend when the joint angle is larger than 30°. The max stress may occur at the joint angle of 15°. The maximum shear stress occurs mostly in the No. 4 joint and the No.7 joint. When the joint angle is 30°, the maximum shear stress occurs in the No. 3 joint and the No. 4 joint. The overlap of the position of the maximum von Mises stress or the maximum displacement with different joint angles or different numbers of joint leads to a reexploration of such positions. The position of the maximum von Mises stress and the maximum displacement is relatively steady, which locates symmetrically around the borehole. The line between the points that behaves as the maximum von stress is approximately perpendicular to the joint direction.

/pdf/parametric-study-of-the-borehole-drilling-in-jointed-rock-25xwjpiglc.pdf

Parametric Study of the Borehole Drilling in Jointed Rock Mass

Coal mining causes the pressure releasing from coal reservoir,the coal reservoir parameters' great changing,and has the enormous influence on the coalbed methane storage and the migration. The experiment achievement of Luling coal mine,concerning ground well drainage from pressure release area and related ground well and underground well integrated drainage technology,indicated that the coalbed methane drainage from coal seams with low permeability in the release area of pressure is not only an advantageous to the coal mine safety production,but also can enhance recovery ratio of the coalbed methane enormously and enhances the economic efficiency of the coalbed methane development.

Integrated technology of coalbed methane drainage with ground well in Luling coal mine

Extraction of coalbed gas in overlying mining-disturbed area of working face through surface wells can well resolve the difficult problems of gas drainage in coal seams with low permeability.However,the low ratio of successful well completion severely limits the application of the technology.Trough the study of the key factors influencing well completion such as well layout,well structure,gas drainage by well,extraction horizons,drilling technology and drilling management etc.,by applying well completion technology for gas extraction trough surface wells in Xinji No.1 mine,all 12 wells for surface gas extraction have been successfully completed,providing guarantee for the successful application of gas extraction by surface wells.

Completion technology of surface gas extraction wells

Effective gas control is of significance for safe efficient coal mining in Haizi Coal Mine and other mines with similar geological conditions. This study concentrates on gas control theories and techniques in multiple coal seams of Haizi Coal Mine (No. 7, No. 8, No. 9, and No. 10 coal seam from top to bottom). To minimize risk of high gas emission and outburst hazard, No. 10 seam was mined first as a protective seam prior to the mining of its overlying outburst-prone No. 7, No. 8, and No. 9 seam. Four gas drainage measures were determined for gas control, including cross-measure boreholes into overlying coal seams, surface goaf wells, roof boreholes, and roof gas drainage roadway. These gas control measures, if implemented through entire coal seam extraction, would be possibly uneconomic. An investigation was undertaken to analyze effects of those four measures on gas emission, methane concentration, and gas drainage quantity in No. 2 1024 mining panel of No. 10 seam. Results indicate that the highly expensive gas drainage measure of a roof roadway has poor drainage performance and could be effectively replaced by roof boreholes. When adopting the optimized combination of gas drainage measures, drainage efficiency of No. 7 seam, No. 8 seam, and No. 9 seam could reach 58.64% and decrease gas pressure to be below 0.74 MPa. Outcomes of this study could provide beneficial guidance not only for gas drainage design optimization in Haizi Coal Mine but also for other multiple-seam mines with similar mining and geological conditions, for increasing gas drainage efficiency and guaranteeing mining safety.

Study on Gas Control Methods Optimization for Mining Safety

To study the behavior of gas extraction from the protected layer by surface drilling, the common characteristics of gas extraction concentration and gas extraction quantity are summarized through the collection of key parameters of surface drilling and a combination of data and figures, with the background of 11−2 coal protection 13−1 coal in the Huainan mining area. The research results show that the flow of pressure relief gas extraction of the protected layer by surface drilling has three stages: a rising period, stable period, and decay period. When the extraction processes of multiple surface wells on the same working face are coordinated, the extraction flow is superimposed, and the extraction volume of surface drilling shows an increasing trend and fluctuates with the location of the drilling. The extraction flow rate before ground drilling is relatively small, and the extraction flow rate increases after ground drilling. This behavior is further confirmed by field observation of mining changes in the protective layer and the expansion and deformation of the protected layer. The periodic variation in the surface drilling and extraction quantity is affected primarily by the mining movement of the working face of the protective layer. Specifically, it is affected by factors such as the mining progress of the working face of the protective layer, mining height, degree of compacted goaf, degree of pressure relief of the protected layer, original gas content, and other measures taken to extract the protected layer.

/pdf/characteristics-of-pressure-relief-gas-extraction-in-the-1e4wbpzq79.pdf

Characteristics of Pressure Relief Gas Extraction in the Protected Layer by Surface Drilling in Huainan

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Characteristics of Pressure Relief Gas Extraction in the Protected Layer by Surface Drilling in Huainan