Application of air foam composite directional drilling technology in broken soft coal seams

In order to meet the requirements of air screw motor cooling and lubrication, coal dust removal treatment at the orifice and water outlet disposal in the air directional drilling, an air foam composite directional drilling technology for broken soft coal seams has been developed based on the analysis of drilling slag migration characteristics of air directional drilling. The key technologies such as stable and efficient foaming, "mechanical + foam" composite slag discharge and "air + foam" composite drilling were integrated. The technology was also equipped with directional drillrig, foam generation perfusion system, air screw motor, special-shaped drill pipe and measurement while drilling system, etc. The application test was carried out in the coal mine in Suzhou, Anhui Province. The directional borehole with the main hole depth of 232 m was successfully constructed along the coal seams in the broken soft coal seam. Compared with the boreholes using air directional drilling technology, the hole forming depth was increased by 97% and 105% respectively, which significantly improved the hole forming depth of directional drilling along the broken soft coal seams. The technology is helpful to enhance the gas extraction effect in the broken soft coal seams, and to achieve the purpose of cooling and lubricating the air screw motor and reducing the coal dust from the orifice. Finally, it can provide a new technical way for directional drilling construction of broken soft coal seams.