Study on the stress relief and permeability increase in a special low-permeability thick coal seam to stimulate gas drainage.

Underground coal seam gas drainage is an effective method to lower the risk of coal and gas outburst disaster. However, it is difficult to drainage gas in the low-permeability coal seam, especially low-permeability thick coal seam with a tectonic coal sub-layer. Due to the special structure of this coal seam, many conventional technologies are inefficient. In this paper, to stimulate the coal seam gas drainage, we proposed a hydraulic flushing cavitation technology. Theory analysis, numerical simulation and field tests ware carried out to study the stress relief and permeability increase after adopting this technology. The results indicated that a large hole was formed in the coal seam, which enlarged the scope of stress relief and plastic damaged, and the coal seam permeability and gas drainage efficiency increased significantly. [ABSTRACT FROM AUTHOR]