Does coal mining induce methane emissions through the lithosphere/atmosphere boundary in the Ruhr Basin, Germany?

Underground coal mining is associated with the release of substantial quantities of coal bed methane. While the quantities of methane released from mine shafts are well known, little information is available about the extent of direct firedamp emissions across the earth's surface. On some farm lands, inflammable firedamp escapes have been reported to persist for more than 30 years. These incidents are restricted to hard coal mining areas in the Ruhr Basin and may indicate a causal link between underground coal panels and firedamp surface emissions. To investigate this, a study was initiated in which the emission and consumption rates for methane at the lithosphere/atmosphere boundary were measured using flux chambers. Only emission sites are presented here. As a result, methane emissions were traced not only inside coal mining regions, but for the first time outside the area of mining activities alongside natural normal faults also. The methane release at these faults was found to be correlated negatively to the atmospheric pressure. Furthermore, gas permeabilities for different rock units were calculated from hydraulic conductivities of these rocks and fluid characteristics. They allow the determination of the range of methane emissions possible through different rock units. Having compared these theoretical emission rates with the observed ones, the reason for some of the emission points might be natural, but others can be explained only by underground coal mining, disrupting the rock fabric, increasing the permeabilities and hence giving way to firedamp emissions. (C) 2001 Elsevier Science B.V. All rights reserved.