The Buck Knob anticline of Wise County represents the southwestern extent of coalbed methane production in Virginia. The anticline at depth is a ramp structure developed as a result of overthrusting of the Devonian Shale during the Alleghanian orogeny. Approximately 400 feet of structural closure is expressed at the Pennsylvanian level.
Numerous temperature anomalies and natural gas shows (5-620 MCFPD) were encountered while drilling and logging through the coal section. Reservoirs belong to the Norton and Lee Formations (Morrowan) and range from 650-2450 feet in depth. The coals are of high volatile A to medium volatile bituminous rank. Gas contents range from 60-150 scf/ton. A typical completion contains 6 coal seams with an aggregate thickness of 120 inches. Stimulation is achieved through single stage limited entry fracture treatment.
Average open flow is 50 MCFPD. Average peak rate is 95 MCFPD and is reached within 9-12 months. Exceptional wells have production rates above 200 MCFPD. Current field rate exceeds 1500 MCFPD. Estimated ultimate recoveries are 425 MMCF per well based on 80 acre spacing. Total field recoveries are expected to reach 25-30 BCF.
The field serves as an analog for low rank/low gas content coals producing at economic rates due to enhancement of permeability by natural fractures.
AAPG Search and Discovery Article #90926©1999 AAPG Eastern Section Meeting, Indianapolis, Indiana