Methane (CH4) is a gas formed as part of the process of coal formation. When coal is mined, methane is released from the coal seam and the surrounding disturbed rock strata. Methane can also be released as a result of natural erosion or faulting.
The methane content in coal seams generally increases the deeper the seam, and also with age. As the depth of the coal seam increases, so does the pressure level. This in turn reduces the level of permeability, causing the methane to be much more tightly bound to the coal and surrounding rock strata. Underground mining can therefore produce substantially greater levels of methane than surface mining. In fact, underground mines account for the overwhelming majority (up to 90%) of all methane emissions from the coal sector.
Methane is highly combustible – its release can have serious implications for the safety of mine operations. It is also a potent greenhouse gas (GHG).
Tackling methane emissions is therefore an important step in meeting the challenge of climate change and in ensuring the safety of mining operations. Methane can also act as a valuable source of energy- it is the principal constituent of natural gas - allowing countries to further diversify their energy supplies.
A range of technologies are available to recover methane from coal:
Methane recovered from un-mined coal seams. The coal seams may be mined in the future but this is largely dependent upon geological factors, such as coal depth and quality.
Methane recovered during mining activities as the coal is in the process of being extracted and thus emitting significant quantities of the gas.
Methane recovered from mines that have been abandoned following the completion of mining operations. Significant amounts of methane may remain trapped in the mine or may continue to be emitted from openings.
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