Foam drilling technology and application for broken soft coal seam in underground coal mine

Aiming at the limitation of middle pressure air drilling for gas drainage in soft and broken coal seam, such as limited drill cutting removal capacity, and dust pollution, foam drilling technique research in underground coal mines was carried out. CFD simulation of the flow field during the drilling process was conducted to obtain the optimized drilling tool structure parameters for efficient drill cutting transportation. Optimal structural parameters of wide-blade milled auger drill rod with the number of heads 3, the groove width 26 mm, and the pitch 110 mm were determined. A foam perfusion system suitable for underground coal mining was developed. Field test applications show that foam drilling technique and assorted wide-blade milled auger drill rods have high efficiency of cutting transportation. Rotatory resistance was reduced in a range of 42%-48%. The technique can improve drilling depth in soft and broken coal seam and provide a reference for similar deep coal mine drilling construction.