Permeability of bituminous coal and its stress sensitivity under liquid nitrogen fracturing
© 2020, Editorial Board of Journal of Mining & Safety Engineering. All right reserved. In order to study the evolution law of the permeability of bituminous coal and its stress sensitivity under liquid nitrogen (LN2) fracturing, the experiment of LN2 multiple fracturing on bituminous coal with natural moisture content from Xutuan coal mine has been carried out, and the permeability under different stresses before and after LN2 fracturing has been analyzed. The effect of LN2 fracturing on the stress sensitivity of coal has been studied. The experimental results have indicated that the permeability decreases first and then increases with the decrease of effective stress under constant confining pressure, which is consistent with the quadratic function distribution. LN2 multiple fracturing can effectively enhance the permeability of coal, and the permeability increases with the number of fracturing, with the growth rate gradually slowing down. The fluctuation range of permeability value caused by changing gas pressure is represented by permeability dispersion. The permeability dispersion has an obvious increase after the first LN2 fracturing, while the remaining cycles have a smaller fluctuation range. Under the same gas pressure, the confining pressure sensitivity coefficient decreases with the increase of confining pressure, and the permeability damage rate increases with the increase of the number of fracturing and gas pressure. The first LN2 treatment has the most significant effect on coal permeability and stress sensitivity, while the effects of the following ones were smaller.