Abstract
Coal 3 in group A is employed as a protective layer to release long-distance coal 4 in group B in Paner colliery (approximately 80 m vertical interval) as the mining depth extends downward, which is the first engineering test in the Huainan coal mining area. To evaluate the validity of the scheme, the permeability distribution, and evolution law, gas pressure distribution characteristics, swelling deformation, pressure relief range, and gas drainage volume of the protected coal seam are analyzed using a FLAC3D numerical simulation and field measurements. Therefore, different stress-permeability models are adopted for caved, fractured, and continuous deformation zones, and a double-yield model is applied in the goaf based on compaction theory to improve the accuracy of the numerical simulation. The results indicate that the extraction of coal 3 has a positive effect on permeability enhancement and pressure relief gas drainage. However, the dip angle of coal measurements causes asymmetric strata movement, which leads to the pressure relief and permeability enhancement area shifting to the downhill side, where the permeability enhancement effect of the downhill side is better than that of the uphill side. The permeability enhancement zone is an inverted trapezoid, but the effective pressure relief range is a positive trapezoid. The permeability of the protected coal seam in the pressure relief zone is significantly higher than that in the compressive failure zone. The permeability in the pressure relief zone will decrease again due to the recompaction of the coal seam with an advancement of the longwall face. Thus, pressure relief gas drainage is suggested during long-distance protective coal seam mining to eliminate gas hazards.
Highlights
Coalbed methane is an associated product of coal resources
Because of points B, C, D, and E located in the pressure relief zone, the permeabilities sharply increase to approximately 1.04 mD when the working face advances to a certain distance (Figure 8(b)). en, the permeability in the protected coal seam (PDCS) gradually decreases due to goaf compaction
The gas pressure on the downhill side of the working face is effectively reduced, while the gas pressure at the uphill side decreases slightly, and the local gas pressure is still higher than 0.74 MPa. e permeability of the PDCS in the recompaction zone was recovered to the state before pressure relief mining, and the free gas was readsorbed, resulting in the gas pressure here still being higher than the threshold value
Summary
Coalbed methane is an associated product of coal resources. It is a clean resource, but it threatens coal mining safety. Pressure relief mining has been the primary method to remove gas and coal outbursts and achieve simultaneous coal and gas extraction in deep, high gas, and low-permeability coal seams. E #3 coal seam of the Paner coal mine has entered deep mining, and remote pressure relief of the #4 coal seam is an attempt in the mining area, which has guiding significance for other similar geological settings in the future Based on this background, this study analyzes the permeability distribution and evolution characteristics, gas pressure, pressure relief range, dynamic change in the gas drainage volume, and coal seam expansion deformation using a FLAC3D seepage module simulation and a field engineering measurement method to judge the feasibility of long-distance pressure relief mining in deep high-gas coal seams.
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