Improvement on gas drainage of soft gassy coal seam with underground hydraulic flushing and fracturing: a case study in Huainan

The low gas drainage efficiency of soft coal seam is a key factor that induces gas disasters, such as gas explosion and outburst, in China. This study aims to improve the gas drainage efficiency of a soft coal seam in Huainan, China, by conducting field trials with a new stimulation technique. The stimulation technique comprises two significant procedures: (1) fracturing the coal seam with a fracturing borehole and (2) flushing wet coal and water out with the adjacent fracturing borehole. Coal seam stress is released by such actions because much coal could be flushed out of the coal seam through the process. Therefore, an artificial fracture network could be created in the coal seam, and the gas drainage efficiency could be improved. Results of field trials show a significant improvement in gas drainage efficiency of up to eight times higher than that of the original part.