Study On Migration Law Of Gas With Pressure Relief And Technology Of Efficient Gas Drainage In The First-mined Face During High Gas Coal Seams Group

Coal mines are mostly occurrence conditions for the high gas seams group in our country, characterized by the "three high and one low", more than80percent of major or fatal accidents have some connection with gas, the gas control is a worldwide problem. On the condition that4.2m mining height, up and down range of pressure-relief will enlarge, gas of adjacent layers flood into working face. The gas is difficult to control."pressure-relief and increase-through" mechanism of the first coal seam mining can achieve the efficient pressure relief gas drainage of the neighboring coal seam. This article mainly study the mining upper strata cracks evolution law and pressure-relief gas enrichment regularity under the condition of4.2m mining height during close-distance high gas coal seams group in western region of our country.based on this, First put forward pressure-relief gas drainage of fractured zone by the large diameter (Φ=250mm) borehole group instead of inclined high drainage roadway,which has realized gas comprehensive management in first-mined face during close-distance high gas coal seams group and Guaranteed the safe and efficient mining in the working face.Based on the coal seam characteristics and geological conditions of shaqu face24207in Shanxi to build up the FLAC3D three-dimensional mechanical model with4.2m large mining coal seam height, through the simulation, the comprehensive analysis of the movement-destruction law of the overlying strata in the seam, the stress re-distribution law, the stress relief characteristics and relief range, cracks space-time evolution, and finally get the3D cracks distribution patterns of mining overburden and pressure-relieved gas migration and enrichment regularity.The simulation results shows,50m before harvest, roof above1～5times the mining height is stress increases area; below10times the mining height of the roof rock and50m range of post-harvest belong to the stress release area that is the sufficient relief area; stress recovery in the post-harvest150～200m within. Post-harvest about100m and10times the mining height is the scope of the relief influence of overlying strata. Mine goaf roof more than7～10times the mining height is cracks zone, and five times the mining height within belongs to the coal and rock crushing caving zone, while the fracture zone, lateral bed separation cracks, longitudinal breaking cracks and ring distribution cracks become a good channel for gas migration and temporary storage space, and the fissure turns on each other is that the gas concentrated rich region.Based on the results of simulation analysis, First put forward technology of pressure-relief gas drainage by the large diameter (Φ=250mm) borehole group instead of inclined high drainage roadway. Through the drainage effect analysis verified the research results. The whole period of the mining face, the total gas emission in20.76～78.52m3/min, the average is42.35m3/min, the average Wind row the amount of gas is11.53m3/min; after implementation of the gas comprehensive control measures, the total gas extraction quantities in9.14～66.51m3/min, and the average is30.81m3/min; Among them,the average extraction quantity of hing drainage roadway is6.18m3/min,the average gas extraction quantity of large diametet borehole group is12.13m3/min,the top is33.14m3/min, Large diameter borehole group general pipeline gas drainage quantity for an average of16.02m3/min, accounting for51.45%of the total extraction,that is the large diameter borehole group can be substituted for high drainage roadway to realized pressure relief gas drainage efficiency; during the face mining period, the face gas average extraction rate is71.20%and gas concentration is below0.6%that ensure the safe and efficient mining in the working face.