Laboratory study of the phenomenon of methane and coal outburst

Abstract

Gas and rock outbursts occur in virtually all coalfields around the globe [1,2]. Chinese mining has currently been affected by the problem most; nearly one-third of all outbursts take place in China. High levels of outburst threat also occur in Ukraine, Poland, and Australia. Since the phenomenon of outburst is by all means a complex one, its study must be interdisciplinary. It thus involves various aspects of geomechanics, gas study, chemistry, statistics, risk assessment, and many others. In Ref. [3] there are over 30 factors mentioned which might influence outburst threat. Currently, scientists’ views around the world suggest a number of parameters that encourage rock and gas outburst. These are, among others, increased gas capacity of the medium, extremely high diffusivity and increased porosity of coal, and very low gas permeability in natural conditions [4,–6]. According to many authors, coalbed methane capacity constitutes a crucial parameter in the evaluation of outburst and methane threat in coal mines [1]. Methane content in coal seam is not constant; it alters with changes of the properties of coal and of geological conditions in the vicinity of the seam [7,8]. It is assumed that free gas (sorptive unbounded) represents the main source of energy that may lead to destruction of coal structure and the occurrence of rock and gas outburst [9]. The relative amount of free gas in the whole quantity of gas in coal is very important for the assessment of methane and rock outburst threat. The ratio of the free gas quantity to the sorbed gas quantity in the coalbed may vary. Sorptive bounded gas is mainly responsible for the transport of outburst masses [10,11]. Thus it is important in the process of sustaining the outburst. Devising methods of measuring coalbed methane pressure in coal, which would be both effective and reliable, seems to be a significant issue. Various authors [12–14] and others write about