Study Of Residual Gas Content Diversity Between Soft And Hard Coal Under The Condition Of Gas Predrainage From Virgin Coal Seam

The general method of regionally predicting coal and gas outburst is coal seam gas parameters combined with gas geology analysis according to the 42th article of"The rule of control coal and gas outburst".While meathen content is always chosen to be a common used index in mining. However ,there is a certain thickness of soft coal layer in some coal seam which may have risk of gas outburst when the risk of gas outbrust of hard coal is eliminated. So not only residual gas content inspection site is decorated in the soft coal or the hard one blindly when the risk of outburst is examined, but also this phenomenon is often neglected when the drainage borehole was designed. In view of this, this article studied the difference between soft coal and hard coal such as microscopic pores, permeability and adsorption ability of meathen by laboratory experiment.The difference of residual gas content between the soft and hard coal is studied by theory analysis and numerical simulation which based on the experiment.Mercury injection experiment shows that microscopic pore volume of soft coal is mainly distributed in the pore, the diameter of which is larger than 100nm and mean volume diameter is 375.8 nm. But hard coal is mainly distributed in the pore, the diameter of which is larger than 10000nm and mean volume diameter is 90812.7 nm.There is much pore looks like ink-bottles in the coal ,the number of which is much more in the soft coal contrasted with the hard one. Cryogenic nitrogen adsorption experiment shows that there is great difference between specific surface area of two kinds of coal: soft coal is 25.468m~2/g while hard coal is 1.285m~2/g. The isothermal adsorption of methane shows that soft coal adsorption capacity is stronger than hard coal.The difference is obvious when the pressure is below 1MPa, is soft coal Langmuri pressure is greater than the hard one in the eyes of numerical expression. Permeability test shows that the law between permeability and confining pressure of both kinds of coal is negative exponent regularity, however permeability of hard coal is great larger than the soft coal.Residual gas content under the condition of different arrangement way of drainage borehole is numerical simulated by constructing equations using Comsol software.Result shows that:residual gas content of the soft coal is greater than the one of hard coal during drainaging gas when drilling space is greater than 2m or the distance of drainage borehole from soft layer is greater than 1.5m. Otherwise ,residual gas content of hard coal is greater.