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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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