Gas Production Potential from Gas-Bearing Strata Above Longwall Mining of United States Coal Beds
A. W. Layne, H. J. Siriwardane, C. W. Byrer
Pipeline-quality gas production potential from the highly fractured
methane-bearing strata above longwall-mine coal panels may be many times that of
the gas-in-place estimate for the minable coal bed. The permeability in these
strata is increased significantly due to the fractured zone generated during
longwall mining activity. This presentation assesses the potential production
and influence of well spacing for optimum
drainage of gas from the strata above
coal mine panels. Potential gas reserves were quantified by use of the predicted
extent of the overburden failure zone, the formation gas contents, and geologic
cross sections from the United States coal basins having longwall mining
operations. A finite element method was used to determine the size and shape of
the af ected stratigraphic zones above mining operations.
A two-phase reservoir model was used to compute increased production rates
from methane wells. Production data from actual wells above a longwall coal
panel in the Appalachian basin were matched historically to characterize flow
mechanisms and reservoir properties such as permeability. These properties were
then evaluated in parametric studies to determine the influence of well location
on gas production. Results indicate that cumulative gas production can be
increased by placing wells farther than 1,000 ft apart. The model appears to
make reasonable predictions of the size of the multireservoir area in complex
geologic conditions. The study considered the influence of an advancing mine
face on gas production. Thus, the methodology presented in this paper is
applicable to the optimum
esign of gas wells in highly fractured, multistrata
reservoirs and prediction of long-term gas production from such reservoirs.
AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.