井下抽采钻孔瓦斯浓度控制机理及方法研究

Study on control mechanism and method of gas concentration in gas drainage borehole of underground mine

为解决煤矿现场瓦斯抽采浓度偏低的问题,给出了封孔深度确定方法,揭示了空气摄入主控截面位置,提出了考虑吸附作用影响的瓦斯流量控制方程,以及采用多级调节抽采负压控制瓦斯抽采浓度的方法。结果表明:最小封孔深度应超越应力峰值位置;空气摄入主控截面可分为封孔改性区、破裂区、塑性区、弹性损伤区和原岩应力区;煤岩缺陷周围表现出显著应力集中现象的原因为,有效应力较名义应力大,随着瓦斯压力的增大,有效应力有所减小;相同孔隙度条件下,随着名义应力增加,孔隙周围应力集中系数增大;空气摄入量与封孔有效半径表现出负相关关系,与抽采负压表现出正相关关系;工程实践表明,采用优化封孔深度和合理多级调节负压的方法可有效控制钻孔瓦斯抽采浓度。

In order to solve a problem of low gas drainage concentration at the mine site, a method to determine a sealing depth of the bore- hole was provided, a location of the air intake at the main control cross section was revealed, a gas flow control equation was provided in a consideration of the gas adsorption effect influence and a method to control the gas drainage concentration with a multi stage adjusted drain- age negative pressure was provided.The results showed that, a minimum sealing depth of the borehole should he over the location of the stress peak. The main control section of the air intake could be divided into a modification zone of the scaled borehole, cracking zone, plas- tic zone,elastic failure zone and in-situ rock stress zone. There was an obvious stress concentrated phenomenon around the coal and rock failures, because the effective stress was higher than the nominal stress and with the gas pressure increased, the effective stress would be re- duced. Under the condition of the same porosity, with the nominal stress increased, the stress concentrated coefficient around the pores would be increased. The air intake volume and the effective radius of the sealed borehole would be in a negative correlation and the air in- take volume and the drainage negative pressure would be in a positive correlation. The engineering practices showed that a method to opti- mize the borehole sealing depth and the rational multi stage adjusted negative pressure could be applied to effectively control the gas drain- age concentration in the borehole.