Improvement of drainage gas of steep gassy coal seam with underground hydraulic fracture stimulation: a case in Huainan, China

The paper introduced a new technique named underground hydraulic fracture stimulation to improve gas drainage efficiency. And the technique was successfully applied in a steep gassy coal seam in Huainan of China. Application results showed that water injection changed water/gas content distribution greatly and gas drainage efficiency was improved greatly. After the stimulation, central part of coal seam around fracturing borehole showed lower water content and much higher gas content than other parts. Average pure gas flow rate for single borehole of central part is 3 similar to 8 times higher than that of original part. The upper and below part showed higher water content and lower gas content than central part. The phenomenon is closely related to the steep structure of coal seam. In consideration of the wide distribution of steep gassy coal seam in China, the results have great significance for popularization and application of the technique in Chinese coal mines.