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在1984年澳大利亚水井与钻探协会国际会议年会上,澳大利亚煤矿工业研究所介绍了用于排放瓦斯的地下煤层水平孔和向下斜孔的钻进技术。据介绍水平孔最深达824米,
At the 1984 Annual Meeting of the Australian Association of Wells and Drilling Associations, the Australian Institute of Coal Mining introduced the drilling techniques for horizontal and downcomer holes in underground coal seams for gas drainage. It is reported that the horizontal hole up to 824 meters deep,