宣东二号矿布设施工的大口径瓦斯抽放井以小口径导向钻进，后逐级扩孔成井。
Mine used small-diameter pilot drilling, then gradually reaming the borehole and finally completed to designed size.
宣东二号矿布设施工的大口径瓦斯抽放井以小口径导向钻进，后逐级扩孔成井。
The large-diameter gas drainage well laid out in the Xuandong No. 2 Mine used small-diameter pilot drilling, then gradually reaming the borehole and finally completed to designed size.
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