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为了研究保护层开采过程中采空区渗透率的演化规律、分布特征以及对被保护层卸压增透效果,在充分利用淮南某矿1242(1)工作面抽采监测数据的基础上对地面钻井抽采卸压煤层及采空区瓦斯的流量计算模型进行了简化,结合达西定律给出了采空区等效渗透率的计算模型。在此基础上,通过拟合被保护层瓦斯抽采量得出各钻井的瓦斯衰减系数,并引入瓦斯涌出衰减系数减小倍数来反映保护层卸压增透效果。研究结果表明:1)采空区渗透率随着保护层工作面的推进经历急剧升高、缓慢降低以及稳定3个阶段,前2个阶段对应的工作面推进长度分别为19.24,186.2 m;工作面回采结束后,采空区中部渗透率最低,向边缘逐渐增大,呈横“O”型分布。2)被保护层瓦斯抽采同样经历3个阶段:急剧升高阶段、衰减阶段以及稳定阶段,前2个阶段经历的平均时间分别为10 d和125 d。3)1#钻井的瓦斯涌出衰减系数减小倍数高达7.7,表明了保护层卸压效果十分显著。
In order to study the evolution law and distribution characteristics of permeability in the mined-out area and the relief effect on the protected layer, based on the monitoring data of the extraction of 1242 (1) face in a mine in Huainan, The flow calculation model for drilling and extracting pressure relief coal seam and goaf is simplified. The calculation model of equivalent permeability of goaf is given with Darcy’s law. On this basis, the gas attenuation coefficient of each drilling well is obtained by fitting the gas drainage amount of the protected layer, and the reduction factor of gas emission is introduced to reflect the effect of pressure relief and permeability enhancement of the protective layer. The results show that: 1) The permeability of goaf increases rapidly, slowly decreases and stabilizes with the advancement of the working face of the protective layer, and the corresponding propulsive lengths of the first two stages are 19.24 and 186.2 m respectively; Face after the end of mining, the lowest permeability in the central area, gradually increasing edge, was horizontal “O ” type distribution. 2) The gas drainage in the protected area also experiences three stages: rapid rise stage, decay stage and stable stage. The average time of the first two stages is 10 d and 125 d, respectively. 3) The reduction factor of gas emission attenuation coefficient of No.1 drilling well reaches as high as 7.7, indicating that the pressure relief effect of the protective layer is very significant.