Evaluating Coal-Bed Methane Commercial Viability in Northern and Central Appalachian Basins

David Decker

According to studies conducted by the Gas Research Institute and the U.S. Department of Energy, approximately 109 tcf of pipeline quality gas occluded onto coals in the Northern and Central Appalachian basins. Commercial viability of this large resource will depend on coal permeability, pressure, saturation, and gas content.

Coal-bed methane, as with any gas exploration program, requires prediction of the optimum reservoir properties essential in achieving commercial production. However, geologic methods for predicting ideal coal reservoir properties have been modified from conventional exploration practices. Gas-in-place estimates are determined from total coal thickness and gas content of the coal. Coal gas content may be measured directly from coal core using modified techniques from the coal mining industry. Where direct measurements are not available, source rock evaluation techniques may be used to estimate gas contents. Geologic techniques, such as curvature analysis and remote-imagery fracture analysis, can be applied effectively to determine areas of structurally enhanced coal permeability. Local knowledge of in-situ stresses are necessary to evaluate whether these fracture systems are open. Determining whether coal cleats are currently saturated with water or gas can only be evaluated by close examination of drilling records from wells penetrating coal objectives. Coal reservoir pressure may be established using the available drill-stem and production tests or from hydrologic data.

Aggressive coal-bed methane exploitation programs are under way in the Warrior basin of Alabama and the San Juan basin of southwest Colorado and northwest New Mexico. Ownership of coal-bed methane between coal lessor and oil or gas lessor is being clarified in the Appalachian coalfields. Geologists working these regions will shortly be challenged to select areas for commercial coal degasification.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.