Pneumatic directional drilling technology and equipment for broken-soft coal seams in underground coal mines
-
-
Abstract
Objective The geological conditions of coal seams in China are complex, with a wide distribution of broken-soft coal seams, and a large number of wells have the problems of high gas and coal-gas outburst. Currently, borehole gas drainage is an effective measure for preventing and controlling the gas disasters. Methods In response to the problems of uncontrollable drilling trajectory, shallow drilling depth, large blind spots of drainage in conventional rotary drilling process of broken-soft coal seams, as well as multiple stuck drilling accidents, great difficulty in drilling and low drilling efficiency in conventional directional drilling processes, the development history and application status of drilling technologies for the broken-soft coal seams in underground coal mines was systematically introduced. Accordingly, the pneumatic directional drilling (PDD) equipment composed of pneumatic screw drilling tools, directional drilling rig, measurement while drilling system, dust removal pump truck, air compressor/nitrogen generator and oil mist lubrication device, as well as the key supporting technologies such as PDD technology and screen completion technology, has been developed to overcome the challenges of directional drilling in broken-soft coal seams and ensure the effectiveness of gas drainage. Besides, directional drilling test using the complete set of technology and equipment was conducted in the broken-soft coal seams of mines in Huainan, Huaibei, Shanxi, Guizhou and other regions. Results and Conclusions The research showed that: (1) The PDD technology is an effective technical means for gas control in broken-soft coal seam drilling. Its drilling depth generally reaches over 200 m, with a maximum drilling depth of 607 m. Besides, it can effectively control the extension of the drilling trajectory in the target coal seam, and the coal seam drilling encounter rate reaches over 90%. (2) The field test showed that the pneumatic directional drilling has good drilling results and high drilling efficiency, with a maximum drilling efficiency of 3 594 m per month with one rig, effectively promoting the application of PDD technology from in small-scale testing to large-scale industrialization. Based on the current application status of this complete set of technology and equipment and the development needs of safe and efficient production in coal mines for the drilling technology and equipment, the expanding application direction of PDD technology and equipment in coal mines, as well as the practical needs and inevitable trends towards automation, intelligence and intensification, was proposed.
-
-