Abstract:
The gas control in large panel of underground coal mine objectively requires the length of ultra-long directional drilling along the coal seam to reach more than 3 000 m, however, restricted by the current directional drilling technology and equipment in underground coal mine, the maximum hole depth of directional sliding drilling along coal seam is less than 2 000 m. This paper starts from the point of view of directional drilling technology, the influencing factors of drilling resistance in sliding drilling process of ultra-long directional drilling are analyzed, and on the basis of theoretical analysis and statistics of actual drilling data, the variation law of sliding drilling resistance with hole depth is revealed, it concluded that the friction resistance between the drilling tool and the hole wall increases with the increase of the hole depth, which is the fundamental reason that restricts the drilling depth, based on this, the hydraulic pressure drag reduction drilling technology and the forward and reverse torsional drag reduction drilling technology are developed, it starts from improving the stress state of bottom hole drilling tool and replacing sliding friction with rolling friction, effectively alleviate the problem of supporting pressure of drilling tools in ultra-long directional drilling, the field application was carried out in the 81210 working face of the second plate area of Baode Coal Mine, the test results show that the slow linear growth zone of drilling resistance is improved from less than 1 000 m to less than 1 500 m by hydraulic pressure drilling, the forward and reverse torsional drilling reduced the sliding drilling pressure by 2 MPa to 4 MPa after 2 000 m, using a combination of hydraulic pressure and positive and reverse torsional drilling techniques, directional sliding drilling was successfully achieved to a depth of 2 700 m, effectively improve the control precision of ultra-long directional drilling trajectory and drilling length, and provided technical support for gas extraction in large panel.