Coalbed Methane Resources in the Northern Appalachian Coal Basin, Southwestern Pennsylvania and North-Central West Virginia
MARKOWSKI, ANTONETTE K., Pennsylvania Geological Survey, Harrisburg, PA; GRADY, WILLIAM C., and MATCHEN, DAVID L., West Virginia Geological and Economic Survey, Morgantown, WV
A mapping investigation of the regional geology of coal-bearing intervals
and its influence on coalbed methane (CBM) potential focused on and showed
that the Allegheny Formation of northern West Virginia (Allegheny Group
of southwestern Pennsylvania) and basal part of the Monongahela Group (Pittsburgh
coal) of these two areas contain the most prospective methane-producing
coals. An "operational" Allegheny Formation/Group was defined for coal
beds in the subsurface. Total in-place coalbed gas resource estimates to
date are 61 Tcf for the Northern Appalachian Coal Basin.
Pennsylvania's Campbells Mill pool, Indiana County, is the largest
commercial CBM project with 26 producing wells. Higher gas contents, increasing
rank, and possibly tighter folding indicate more favorable conditions for
production at the northeastern end of the study area in Indiana County.
The "potential" for CBM is affected by coal-quality parameters, particularly
ash yield, rank, and petrographic composition. In West Virginia and Pennsylvania,
vitrinite-rich bituminous coals range in reflectance from 0.5 to 1.9%,
the rank range over which most thermally derived CBM is known. Only coals
constrained by geographic (primarily tectonic) and stratigraphic (primarily
depth of burial) rank factors could potentially contain commercial quantities
of methane.
In West Virginia, development of Pittsburgh and Allegheny coals has
been attempted with mixed results. Seven Pittsburgh mine gob wells have
reportedly produced 0.47 Bcf since 1922. According to a recent well survey,
low initial flow tests reported in old (1800 to 1929) Allegheny wells may
be caused by the presence of numerous oil and conventional gas wells that
were drilled to deeper targets, left open and abandoned, resulting in the
release of much of the available CBM.
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