煤层原生CO钻孔探测试验

当前不少研究均得出煤层赋存原生CO气体的结论,但是未考虑钻孔施工过程中产生CO后被煤体吸附的可能。为探究西北地区易自燃煤层是否存在原生CO的问题,采用原始煤层原位钻孔探测方法进行原生CO探测试验。在未受采动影响的实体煤区域沿巷帮一字排开布置3个测试钻孔,钻孔密封后采用高纯N₂置换密闭气室内气体,采用专用抽气泵抽取钻孔内气体,消除原位探测钻孔施工过程中煤体氧化产生CO对试验结果的影响。在分析煤层原生CO来源可能性及其涌出理论的基础上,探讨了密闭钻孔内气体浓度随时间变化特征,结果表明:密封后钻孔内O₂和CO体积分数随密封时间的延长而迅速降低,12 d后O₂体积分数稳定在2%以下;12 d后CO体积分数低于10^-12,气相色谱仪未检测到CO气体;钻孔内气体主要为N₂。由此推断,待测煤层中无原生CO气体。N₂环境破煤试验和煤样常温恒温氧化试验结果表明,封孔初期检出的CO气体来源于钻孔施工破煤作业。

Borehole detection test of primary CO in coal seam

At present,many studies have come to the conclusion that the coal seam contains primary CO gas,but the possibility of CO being adsorbed by coal after CO generated in drilling construction is not considered.In order to explore whether there is primary CO in spontaneous combustion coal seam in Northwest China,the original coal seam in-situ drilling detection method is used to detect primary CO.Three test boreholes are arranged in a row along the roadway side in the solid coal area not affected by mining.After the boreholes are sealed,high-purity N₂ is used to replace the gas in the closed gas chamber,and the gas in the boreholes is extracted by a special air pump,so as to eliminate the impact of CO generated by coal oxidation on the test results during the construction of in-situ detection boreholes.On the basis of analyzing the source possibility of primary CO in coal seam and its emission theory,the variation characteristics of gas concentration in closed borehole with time are discussed.The results show that the volume fraction of O₂ and CO in the sealed borehole decrease rapidly with the extension of sealing time,and the volume fraction of O₂ is stable below 2%after 12 days.After 12 days,the CO volume fraction is lower than 10^-12,and no CO gas is detected by gas chromatograp.The gas in the borehole is mainly N₂.It is concluded that there is no primary CO gas in the tested coal seam.The results of coal breaking test in N₂ environment and coal sample oxidation test at normal temperature and constant temperature show that CO gas detected at the initial stage of borehole sealing comes from coal breaking operation in drilling construction.