Study On Dynamic Character And The Influence Of Negative Pressure Along Axial Direction Of Gas Drainage Bore

The research of dynamic character and the influence of negative pressure along the gas drainage bore are important theoretical and realistic significance for selecting the rational parameter, raising the gas drainage effect, eliminating blank zone of gas drainage and exploitation safety. This paper takes Jiulishan coalmine of Jiaozuo Energy Coal Group and Dning coalmine as research background and test site where the research on dynamic character of negative pressure along the gas drainage bore and the influence to parameter and effect of gas drainage through theoretical analysis, laboratory test, numerical simulation, field test and other methods.Based on the systematic analysis of the distributing of negative pressure and many factors, including negative pressure at spot face, diameter of drilling, gas emission, etc. the distributing regular of negative pressure along the drilling hole is concluded. The negative pressure along the drilling hole is not a constant value. It is reduced gradually along the drilling hole length. And obey the negative index relationship,xxep×-×+=eba. The gas emission is reduced gradually along the drilling hole length too. And obey the negative index relationship, xd xec Q×-×=44.The diameter of drilling hole, the negative pressure, the coalseam permeability, and the drainage time are constant value; the distribution of gas pressure is V type around the drilling hole. It is different to the U type traditionally. The effect of negative pressure transient on gas extraction parameters was analyzed based on modeling results and field tests data. A new concept, the effective gas extraction radius at different depth of borehole, was provided. This indicated that the effective gas extraction radius not only related to the gas extraction time, borehole diameter and coal seam permeability, but also related to the depth of borehole. And obey the relationship,)/(5.05.0LBAtp Rn×+×××=fl. The following reasonable gas extraction parameters were obtained for Jiulishan coal mine: the negative pressure in borehole collar ranges from 26.7k Pa to 39.9k Pa, the drilling diameter is 94 mm to 113 mm.According to the application at Jiulishan coalmine, with the increase of the depth of drillinghole, the negative pressure along the drillinghole is decreased obviously, and the loss of per 100 meters is 19.73 ~ 22.64%. The research shows that the amount of initial gas drainage enhanced to 0.0203m3/min, gas flow attenuation coefficient reduced to 0.0042. The concentration and emission of pump are enhanced significantly. According to the application at Daning coalmine, when the length before 810 m, the drainage quantity increased with the length of the drilling hole, when the length reached 810 m, the average drainage quantity unchanged basically. The rational length of drilling hole is 810 m.