Technology and application of large-diameter casing hole protection for directional drilling through layers in complex roof
A large-diameter casing hole protection technology based on composite strong slag discharge drilling technology and following pipe casing technology was proposed to address the problems of deviated trajectory,collapse of borehole walls,and low construction effi-ciency in large-diameter high-level directional drilling for complex roof gas extraction in coal mines.The principle of composite strong slag discharge drilling technology was analyzed,and a drilling tool string for casing was designed and tested.An on-site test was conduc-ted in Wangpo Coal Mine in Jincheng mining area,Shanxi Province.Three complex roof high-level directional drilling and layer-crossing hole sections were constructed with large-diameter casing hole protection,with a casing depth of 35 m and a casing diameter of 244.5 mm.The comprehensive construction efficiency was improved by more than 30％.The results show that the large-diameter casing hole protection technology can successfully break through complex and fractured formations,ensure the smooth lowering of the casing hole protection,form reliable supporting for the hole wall of the layer-crossing hole section,and provide technical support for the smooth im-plementation of high-level directional drilling on the roof.
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