Leakage Risks
Associated with Coal Sequestration in Some Areas of The
Central
Appalachians: Subsurface, Seismic and Geomechanical
Evaluations
Wilson, Tom1, Hema Siriwardane2, Xiaochao
Tang3, Brian Connelly1, Jamie Tallman1 (1)
West Virginia University, Morgantown, WV (2) West Virginia University,
Morgantown, Algeria (3) West Virginia University, Morgantown,
Potential risks associated with carbon
dioxide sequestration in coal seams are examined in an unmined
area of central West Virginia between the Northern
and Central Appalachian coal regions. The study incorporates subsurface
mapping, 2D seismic interpretation and geomechanical
simulation. Isopach maps of interpreted low density
coal bearing zones reveal significant thickness variation and discontinuity throughout
the 12 square kilometer study area. Systematic thinning and thickening observed
in isopach maps of 200 to 300 foot coal bearing
intervals suggest that deeper faults were periodically active during
deposition. Interval transit time variations observed in 2D seismic lines
across the area also reveal syndepositional
reactivation of deeper faults in the area. Reactivation during and following
deposition is likely to have opened and extended fracture systems through coal
bearing intervals and into overlying strata. Isopach
maps of coal bearing zones suggest that coals in the area have pod-like
distribution. Low hydrostatic pressures limit injection to gaseous phase CO2. A
geomechanical model was developed for the site using
sonic (DT shear and DT compressional) and density
logs from a key well in the area. Geomechanical
simulations predict surface displacements and pore pressures in response to CO2
injection. The likelihood that overburden fracture systems are enhanced through
late stage deformation and the presence of considerable heterogeneity and
discontinuity in coal distribution, combined with overburden deformations
produced by CO2 injection, all represent increased risk of leakage for any coalbed sequestration activities that might be conducted in
this or similar areas of the basin.