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

Protective layer mining is one of the most effective measures to control outbursts of coal seam gas in coal mines. Accurately grasping the overlying rock movement and pressure-relief gas migration patterns under protective layer mining conditions is a prerequisite for efficient surface coalbed methane extraction; it is the basis for green emission reduction in coal mines. A physical model was established using the Ji15-33200 working face of Pingmei Shi Mine as the research object, and a method combining theoretical calculation and numerical simulation was used to obtain the overlying rock movement. In situ stress distribution characteristics of the stope after the upper protective layer was mined to explore the upper protective layer migration rules of pressure-relief gas after mining. On this basis, the location and layer of surface coalbed methane production wells was determined. The research results show that the coal and rock formations on the floor of the goaf experienced a deformation process of compression → expansion → rebalance during the mining process; the stress changes of the overlying and underlying coal strata in the goaf have experienced a process of increasing → decreasing → rebalance; and gas migrates upward through the fissure zone in the coal layer and slowly diffuses in other microfissure areas. When the pressure reaches a certain value, it is enriched in the crack development area and the upper part of the fissure zone; combined with the relevant geological conditions of the study area, it was determined that the upper part of the roof of the Ji16-17 coal seam is a gas-rich area. By comparing three mining vertical wells at different positions in the horizontal direction, it was found that the extraction effect was significant in the "O″ ring, near the excavation face.

Characteristics of Acid Leaching and Vibration Coupling Desorption of Gas-Saturated Coking Coal.

Permeability is a key factor affecting efficient gas drainage from coal seams, and acidification and vibration shock are effective means to increase permeability in original low-permeability coal seams. To study the gas desorption characteristics of coking coal under the coupling effect of mining disturbance and acidification permeability enhancement, taking the coal seam of Shoushan No. 1 coal as the research object, a self-built adsorption-desorption vibration test platform was used. Acid leaching vibration coupling desorption experiments at vibration frequencies of 0, 30, 60, and 100 Hz were conducted on selected particle coals with particle sizes of 0.18-0.25 and 1-3 mm. The experimental results show that the gas desorption amount of particle coal with the same particle size first increases and then decreases with the increase of vibration frequency, among which the desorption effect is the best under 60 Hz vibration condition. Under the condition of fixed vibration frequency, the desorption amount, initial desorption velocity, and velocity attenuation coefficient of particle coal increase as the particle size decreases. Under the same particle size and vibration frequency conditions, the acid leaching and vibration of coal samples have a synergistic effect on gas desorption, which is manifested in the promotion of gas desorption on the outer surface of the coal sample and the surface of open macropores. The research can provide theoretical reference for coal seam acidification and permeability enhancement under the influence of mining disturbance.