Practice and Drilling Technology of Gas Extraction Borehole in Soft Coal Seam

The auger drilling technology and moderate pressure air drilling technology for soft coal seam in underground coal mine are introduced with their corresponding applications. According to the requirements of gas extraction borehole construction and the present status of drilling technology, the drilling problems and the developing trend of new drilling technology in soft coal seam are also discussed. Finally, some suggestions on borehole protection, pulverization dust control in borehole and directional drilling technology by air drilling motor are proposed.