The elimination of coal and gas outburst disasters by ultrathin protective seam drilling combined with stress-relief gas drainage in Xinggong coalfield

The No. 21 coal seam in Xinggong coalfield belongs to all-layer structured soft coal, with poor permeability and high frequency of coal and gas outbursts. Considering the gas geological condition and gas occurrence regularity of the No. 21 coal seam in Xinggong coalfield, an important technology has been developed for the elimination of coal and gas outburst disasters by ultrathin protective seam drilling combined with stress-relief gas drainage. Ultrathin protective seam with thickness of 0.3–0.5 m was drilled using spiral drilling machine in the field, with improved extraction of stress-relief gas of the No. 21 seam. And the changes of roof and floor displacement and coal seam permeability were systematically studied during the drilling process, together with the flow and drainage rules of stress-relief gas of the No. 21 coal seam. The above results show that after the use of ultrathin protective seam drilling combined with stress-relief gas drainage, gas pressure of the No. 21 seam decreased from 1.2 MPa to 0.15 MPa, with the gas content from 16 m3/t to 4.66 m3/t. The permeability of coal seam increased from 0.0012 mD to 0.4732 mD, nearly 400 times. Coal and gas outburst dangers were completely eliminated of the No. 21 coal seam, and the mining with high safety and efficiency of Xinggong coalfield was successfully realized.