Key technology and practice of deep borehole pneumatic directional drilling in broken-soft coal seam in Yangquan mining area

Objective In response to the need for precise, proactive, and regional management of gas in the broken-soft coal seam of the Yangquan Mining Area, a technical scheme utilizing pneumatic directional drilling for pre-drainage boreholes was proposed.

Methods Based on the analysis of the technical challenges in pneumatic directional drilling, a series of technologies suitable for the broken-soft coal seam in the Yangquan Mining Area were developed. These include stable operation technology for pneumatic downhole motors, precise control technology for drilling boreholes, efficient deep-hole slag discharge technology, and pneumatic milling and salvage technology. The pneumatic directional drilling equipment was optimized, and field industrial trials were conducted in the broken-soft coal seam of the Yangquan Mining Area.

Results and Conclusions The results indicate:(1) Through the optimization of the structure and technological process of the pneumatic downhole motor, as well as the design of low wind resistance pipelines, abnormal braking of the pneumatic downhole motor was effectively resolved, achieving stable and efficient operation. (2) The optimization of borehole trajectory and technological parameters, the design of large-angle deflecting drilling tool combinations, and the development of pneumatic impact downhole motors ensured precise control of the borehole trajectory and improved the penetration rate of the coal seam. (3) The application of forced slag discharge with slide and rotary drilling and short-lifting drilling tools significantly enhanced slag discharge efficiency. (4) By adopting pneumatic milling and salvage technology, along with the specially designed retractable overshot, the complex downhole accident handling requirements in the broken-soft coal seam of the Yangquan Mining Area were met, successfully resolving two severe sticking incidents. (5) In a certain mine in the Yangquan Mining Area, ten directional boreholes with a diameter of 120 mm were completed, each reaching depths of over 450 m, with the maximum borehole depth being 607 m and the maximum single-shift footage being 76 m. The directional boreholes in the broken-soft coal seam achieved significant gas drainage results, with the maximum pure gas drainage from a single borehole reaching 971.96 m³, thereby enabling long-term stable gas drainage in the broken-soft coal seam of the Yangquan Mining Area. The research results provide a novel technical approach for the efficient management of gas in the broken-soft coal seam of the Yangquan Mining Area, demonstrating significant potential for practical application and widespread adoption.