Gas Permeability Evolution Mechanism and Comprehensive Gas Drainage Technology for Thin Coal Seam Mining

Wang, Fangtian; Chen, Jianhang; Ningning, Liang

doi:10.3390/en10091382

Cited by 36 publications

(18 citation statements)

References 39 publications

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“…(1) e subsurface subsidence could have a significant in uence on the performance of the gob well degasi cation system [29,30], migration of groundwater [31,32], and subsurface mine structures [33]. e KS theory shows that the subsidence of a KS can represent a set of strata displacements and the subsurface subsidence can be predicted by KS subsidence.…”

Section: Application Analysis Of the Vbs Formulaementioning

confidence: 99%

Subsidence Prediction of Overburden Strata and Surface Based on the Voussoir Beam Structure Theory

2018

Advances in Civil Engineering

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The hard and stiff strata (key strata) bear the overburden load in the form of a voussoir beam structure (VBS) after break. The VBS affects both the surface subsidence and the stope underground pressure. Therefore, the reasonable method to predict the surface subsidence is based on the whole subsidence formulae of the VBS. This study first establishes the subsidence formulae of the VBS analytically. The influence of the block length on the subsidence curve and the VBS level on the zero-subsidence range are then analyzed based on the subsidence formulae of the VBS. The results show the half-subsidence curve of the VBS is an S-shaped curve. The block length hardly affects the S-shaped subsidence curve determined by the width of the undercompacted zone. Furthermore, a greater undercompacted zone width corresponds to a greater offset distance of the inflection point. The higher the VBS level, the farther the zero-subsidence range, and the flatter the subsidence curve. The subsidence of the highest VBS can approximately represent the surface subsidence when the topsoil is thin enough.

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Section: Application Analysis Of the Vbs Formulaementioning

confidence: 99%

Subsidence Prediction of Overburden Strata and Surface Based on the Voussoir Beam Structure Theory

2018

Advances in Civil Engineering

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“…In sedimentary formations, shear slip of fractured rock associated with dilation or compaction can significantly change fracture permeability, thus affecting fluid flow [13][14][15]. Enhanced fluid flows may be beneficial for desorbing of coal seam gas and increasing geothermal energy extraction [16][17][18][19][20][21], but this enhanced flow will be disadvantageous for groundwater protection and mining [22]. Therefore, to achieve safe and efficient mining in coal seams, knowledge of the evolution of fracture permeability with shearing is very important.…”

Section: Introductionmentioning

confidence: 99%

Shear-induced Permeability Evolution of Sandstone Fractures

et al. 2018

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In underground coal mines, shear-induced changes in regional fluid flow are a major factor causing water inrushes from faults into working faces. Shear slip along preexisting fractures tends to be activated during hydraulic fracturing, and this movement can either enhance or diminish hydraulic fracturing efficiency. To prevent water inrush disasters and further hydraulic fracturing, understanding the evolution of shear-induced permeability in fractures in sedimentary rock is very important. In this study, the evolution of shear-induced permeability in saw-cut sandstone fractures with three different types of surface roughness was investigated by conducting triaxial shear tests and examining the 3-D topography of the unsheared and sheared fracture surfaces. The results allow several important conclusions to be drawn. (1) The permeability of fractures follows a three-stage shear-displacement-dependent evolution. The permeability remains unchanged in the first stable stage. After that, permeability decreases sharply with increasing shear displacement. Finally, the permeability enters a second stable stage. (2) The shear stress versus shear-displacement curves can also be divided into three stages, namely, a stress adjustment stage, a stage of increasing stress, and a stable stage. During the experiments, the fractures always experienced stick-slip shear in the stable stage. The oscillations of the shear stress in the stick-slip stage had a higher frequency for fractures with rougher surfaces. In addition, the rougher surfaces exhibited a greater permeability drop after shearing than that shown by smoother fracture surfaces. (3) The 3-D scanning results imply that the coupled effects of grinding (plus scraping) and sealing lead to decreased permeability. During shearing, the fracture walls grind and scrape against each other resulting in partial flattening of the fracture surface and the production of fault gouge in the fracture. This leads in turn to the flow pathways being partially sealed by crushed mineral grains.

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“…To raise the gas flow rate and concentration from a mining seam and reduce the suction pressure loss in the pipeline, Qin and Xu [10] established an opportunity election model of secondary borehole sealing and also developed a dynamic secondary borehole-sealing device. Wang et al [11] presented gas permeability evolution mechanisms and gas seepage rules of protected seams close to protective seams and applied comprehensive gas extraction technologies to creating a favorable environment for the safe mining of coal and gas outburst seams. e existence of truly undesorbable residual gas in coal seams and its impacts on the sorption model and gas drainage efficiency were studied [12].…”

Section: Introductionmentioning

confidence: 99%

Gas Distribution Law for the Fully Mechanized Top‐Coal Caving Face in a Gassy Extra‐Thick Coal Seam

Wang¹,

Wang

et al. 2018

Advances in Civil Engineering

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Mine gas overflow is a serious threat to the safe and efficient longwall mining of gassy coal seams. Based on the field mining conditions and gas extraction of the fully mechanized top-coal caving face of a gassy coal mine, the space volume fraction distribution and emission (extraction rate) of gas in the face were tested by an arrangement of measuring points in the stereo grid. The isograms of gas volume fraction distribution for each measurement section and air direction in the face are drawn. The research shows that each measurement section gas volume fraction distribution is presented for an asymmetric concave curve along the vertical direction of the coal wall in the air-inlet side and the air-return side of the face; on the working face air-return side, the determination of gas volume fraction distribution of the section appears as falling straight line along the vertical direction of the coal wall. Before the first weighting, the absolute quantity of gas emission in the working face increased with the advancing of the working face, reached the maximum at the time of the first weighting, and then remained stable.

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Gas Permeability Evolution Mechanism and Comprehensive Gas Drainage Technology for Thin Coal Seam Mining

Cited by 36 publications

References 39 publications

Subsidence Prediction of Overburden Strata and Surface Based on the Voussoir Beam Structure Theory

Subsidence Prediction of Overburden Strata and Surface Based on the Voussoir Beam Structure Theory

Shear-induced Permeability Evolution of Sandstone Fractures

Gas Distribution Law for the Fully Mechanized Top‐Coal Caving Face in a Gassy Extra‐Thick Coal Seam

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