Quality and quantity of pre-drainage methane and responding strategies in Chinese outburst coal mines

Abstract

Coal and gas outburst and gas explosion are most important coal mine disasters throughout the world. Pre-drainage is widely accepted and performed to prevent and control methane-related disasters in Chinese outburst mines. Boreholes for pre-drainage are drilled directly into the outburst-prone seams and are theoretically able to capture most of the seam gas that has a high concentration of CH₄. The methane drainage practice in the Huaibei coalfield suggests that high-outburst mines achieved better efficient during pre-drainage and better effects in methane use than the other outburst mines. This implies that pre-drainage was primarily implemented to eliminate the outburst hazards of outburst-prone seams and not to recover methane resource and reduce methane emissions in China. This idea resulted in a greater emphasis on the quantity rather than the quality of pre-drainage methane, and even the quantity of pre-drainage methane itself was not sufficient in eliminating outburst hazards. This idea and related policies on methane drainage should be transformed urgently. Methane pre-drainage can be greatly improved by making full use of those unavoidable intense boreholes. It is suggested that operating a high-efficiency drainage system and developing or popularizing high-efficiency techniques, materials, and equipment for borehole sealing can improve the quality of pre-drainage methane. Simultaneously, extending the pre-drainage time by cooperating with artificial channels can produce the fullest potential of intense boreholes and maximize the quantity of pre-drainage methane. These efforts would benefit the overall mine safety, mine productivity, and methane resource exploitation and usage, as well as the environmental impact, particularly with regard to greenhouse gas emissions.