Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental Observations

The permeability of more than 70% of coal seams in China is less than 1 mD, creating difficulties in recovering underground coal methane. Therefore, a new technology of high-temperature nitrogen (HTN2) injection into the coal seam was proposed to improve the coal permeability and gas extraction rate. In this paper, the effects of the N2 temperature, injection pressure and cycle number on the permeability of naturally fractured coking coal has...