采空区渗透率演化规律及卸压开采效果研究

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。

Research on permeability evolution law of goaf and pressure-relief mining effect

In order to study the permeability evolution law and distribution characteristics of goaf dur-ing protective seam mining and its pressure-relief mining effect, a calculation model to calculate gas flow rate of drilling well extracting gas from goaf and pressure-relieved seams has been simplified. This model has made full use of gas extraction monitoring data of the working face 1242(1) of a coal mine in Huainan city. Combined with Darcy’s law, the equivalent permeability of goaf has been obtained. Meanwhile, by fitting gas extraction volumes from protected seam, thedecline coefficient of gas extrac-tion has been obtained. A decrease multiples ofdecline coefficient has been introduced to reflect the pressure-relief performance of protective seam mining. The results have shown that: 1) The permeability evolution of goaf has experienced three stages including sharp rise stage, the decline stage, and the sta-ble stage. Longwall face advancing distances of the first two stages are 19.24 m and 186.2 m respec-tively. The permeability in the middle of the compacted goaf is much smaller than the permeability on the edge of goaf, and presents O shape trend after longwall face mining. 2) Gas extraction volume from protected seam has also experienced three stages including sharp rise stage, the decline stage and the stable stage. The time of the first two stages are 10 d and 125 d. 3) Decrease multiples of decline coeffi-cient of 1# drilling well is as high as 7.7, which has indicated that the protective seam mining has great pressure-relief effect.