found: Goodman, T.W. Rotary drilling techniques used in the Beckley Coalbed, 1989:pp. 2-4 (the purpose of the study was to drill long methane drainage holes in the Beckley Coalbed allowing the gas to vent into the atmosphere at the surface)
found: Guidebook on coalbed methane drainage for underground coal mines, via WWW, September 19, 2013p. 1 (In order to improve mine safety and decrease downtime as a result of methane in the mine openings, many mines are now using a degasification system to extract much of the coalbed methane from their seams before or during mining. Methane drainage offers the added advantages of reducing the ventilation costs, reducing the development costs of the mine, reducing the global warming threat, and allowing a waste product to be productively utilized.)
found: Coal mine methane recovery, via WWW, September 19, 2013:p. vi (Degasification system: A system that facilitates the removal of methane gas from a mine by ventilation and/or by drainage. However, the term is most commonly used to refer to removal of methane by drainage technology.)