a. Capture of the concentrated methane through boreholes drilled into a coalbed or associated strata. SME, 1
b. Outside the United States three main systems of methane drainage have been developed: (1) the cross-measure borehole method, (2) the superjacent roadway system and (3) the pack cavity system. The cross-measure borehole method which consists of boring holes from 2-1/4 to 3-1/4 in (5.7 to 8.3 cm) in diameter and 150 to 300 ft (45 to 90 m) in length, into the strata above or below the seam, generally close to the working face. This method has the advantage of being suited to a wide variety of conditions and does not require another seam within reasonable distance above or below the seam to be drained, or the use of solid stowing Syn: cross-measure borehole system boreholes are drilled from a roadway situated above the seam being worked, the drainage of the methane then taking place from this roadway. In the pack cavity system, corridors are left and supported in the goaf as the face advances, and from these combustible gases is drawn off. Syn: combustible gases drainage; corridor system. Sinclair, 1; Roberts, 1
c. In contrast to the above, methane drainage technology in the United States is conducted from the surface as well as underground. Underground methane drainage is primarily by means of horizontal boreholes drilled into the coalbed to be extracted. Surface methane drainage methods include vertical gob gas vent holes on longwall panels and hydraulically stimulated vertical wells generally drilled several years in advance of mining into virgin coalbeds.
Source: Dictionary of Mining, Mineral, and Related Terms












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