Efficient drilling technique of 2 311 m ultra-long directionalborehole along coal seam

In view of the need for gas control in the ultra-long working face in Baode Coal Mine, it is suggested to use the domestic high-power directional drilling technology and equipment to carry out the ultra-long directional borehole drilling construction along the coal seam. According to the layout of working face and the geological characteristics of coal seam, the borehole design and drilling equipment selection are optimized. By means of compound directional drilling technology, the friction within borehole is reduced and the drilling pressure transfer in deep borehole is realized. In addition, using the progressive drilling extension technology in coal seam and technology of borehole trajectory control, the drilling rate of coal seam is improved and the precise drilling in deep borehole is realized. To meet the production need of Baode Coal Mine, an ultra-long directional borehole along the coal seam with depth of 2 311 m and diameter of 120 mm has been constructed. The drilling process showed that the drilling equipment is stable and reliable, the drilling technology is advanced, the average daily drilling footage is up to more than 200 m, and the drilling footage within single shift reached 90 m for the borehole with depth more than 2 000 m. The present study can provide an important reference on both the construction of ultra-long directional borehole along coal seam and the control of gas in the ultra-long working face.