Experimental study of gas pressure and effective stress influencing on gas seepage characteristics of bituminous coal in both axial and radial directions

The effects of factors including effective stress, gas pressure, and Klinkenberg effect on the axial and radial gas seepage characteristics of bituminous coal, and the strain of the coal in the radial seepage process, are investigated with self-built GFDTA system. The concept of effective stress sensitivity coefficient is proposed, and the sensitivity of the permeability to the effective stress is negligible when the effective stress sensitivity coefficient is 0.01. It is concluded that the effective stress sensitivity coefficient decreases with increasing effective stress, and increases with increasing gas pressure. With the confining pressure and gas pressure increasing, the effect of unloading on the decrease degree of coal axial permeability decreases. In the axial seepage process, the sensitivity of permeability to confining stress is higher than that of axial pressure. In the radial seepage process, the influence of gas pressure on permeability is larger than that of axial pressure. [Received: September 21, 2017; Accepted: December 1, 2017]