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.