水射流卸压增渗及抽采瓦斯效果的渗流力学数值解

为提高低渗煤体的瓦斯抽采性能,以重庆天府三矿为研究目标区,采用低温液氮吸附法和压汞法测定了煤层孔隙结构,分析了重庆天府矿区煤体低渗的原因,结果表明,煤体孔隙多为两端开口的平板状、管状孔,孔隙的连通性好,压汞渗透率是原位煤体渗透率的2×105倍,煤体孔隙本身的渗透性较好,煤层低渗为高地应力所致。进行了底板穿层钻孔高压水射流卸压增渗试验,试验表明,卸压后煤层渗透率增加了90倍,抽采率从17%提高到了58%,抽采量增加了4.8倍。建立了瓦斯抽采的渗流力学方程,解算了卸压增渗透前后的不同抽采时间条件下的抽采半径,优化了合理布孔间距、抽采时间,为水射流卸压抽采瓦斯效果评价提供了理论指导。

Stress relief and permeability increasing by water jet and numerical method of seepage mechanics equation for gas extraction effect

In order to improve gas extraction capability of low permeability coal seam of Tianfu mine in Chongqing, the paper showed the pore structure of coal seam measured by low temperature nitrogen adsorption method and mercury intrusion method and analysed the reason why coal seam in Tianfu, was low permeable. The results show that most pores, in plate type of two open-ends and tube type, were usually of good connectivity. Further, the permeability measured by mercury intrusion method is 2 × 10^5 times than that by field test. Even though the permeability of coal itself was good, the low permeability of coal seam resulted from higher ground stress. So pressure relief and permeability increasing technology by water jet through the cross-drilling from the bottom was carried out. The results indicate that the permeability of coal seam increased by 90 times,the gas extraction from 17% to 58% ,and the quantity of gas extraction by 4.8 times after stress relief. Based on the data by field test, the seepage mechanics equation was established and the gas extraction radius of drilling at different extraction time was calculated. The distance of drillings and gas extraction time was improved rationally. Hence, it provides the theory guidance for evaluation of stress relief and permeability increasing technology by water jet.