The relationship between the pore structure of coal and gas-dynamic behaviour of coal seams

Abstract

An explanation of the process of methane emission from coal and associated strata from the general viewpoint of recent British and Soviet physicochemical research, concerning the pore structure, sorptive capacity and sorption-kinetic properties of these materials, is attempted. The control exerted by the geological environment of a coal seam, particularly the degree of structured disturbance and the distribution of mineral matter, on the gas-dynamic behaviour of coal and associated strata in both the laboratory and in mine workings is examined. The temperature effects accompanying methane emission are also discussed. Experimental results show that the mineral matter content of a sample determines its sorptive capacity, whilst the rate of methane emission depends on the number and distribution of the macropores and fractures present in a unit volume of the sample. A strong relationship between the degree of molecular damage suffered by coal, expressed in terms of the concentration of unpaired electrons (paramagnetic centres), and its sorption-kinetic characteristics is demonstrated. It is shown that these characteristics are strongly related to other phenomena such as the rule of methane emission from deep boreholes and the resulting reduction in temperature of the walls of coal boreholes. Large variations in such characteristics of coal are shown in occur over short distances as the geological structure of the seam changes, both vertically and horizontally. Consequently, they may be used to quantify the risk of outburst inherent to disturbed areas of coal and to predict the general level of methane emission from the seam.