A new technology for the drilling of long boreholes for gas drainage in a soft coal seam

The geostatic stress, coal mine gas and disturbances produced by external loading can undermine the stability of a borehole and cause the borehole to collapse in a soft coal seam, which results in a poor efficiency of drilling long boreholes and draining gas in a soft coal seam. To improve the efficiency of drilling boreholes and draining gas in a soft coal seam, we propose a drilling technology of protecting the borehole by spraying foam...