--> Silurian Tuscarora Sandstone in Western West Virginia: Will It Work as a Geothermal Reservoir Rock?

2019 AAPG Eastern Section Meeting:
Energy from the Heartland

Datapages, Inc.Print this page

Silurian Tuscarora Sandstone in Western West Virginia: Will It Work as a Geothermal Reservoir Rock?


More than twenty years of bedrock mapping experience with the Silurian Tuscarora Sandstone in the Fold and Thrust Belt of eastern West Virginia suggests that it should be a low-permeability reservoir rock because of deformation and associated heavy silica cementation. Therefore, the choice of the Tuscarora as the target reservoir for a geothermal energy project in north-central West Virginia generated a great deal of scientific interest . . . and some surprise. At the proposed well location on the West Virginia University campus in Morgantown, WV, the Tuscarora is approximately 10,000 feet (3000 m) below surface, lies on the eastern margin of the Rome Trough, and is approximately 300 feet (90 m) thick. A search of the WVGES core and sample inventory yielded thin sections and drill core for wells from Kanawha, Clay, Harrison, and Preston counties in West Virginia, all reasonably close Morgantown. Thin sections from Kanawha 2751, Kanawha 3914, Clay 513, and Preston 119 were examined with the intent of estimating “visual” porosity and searching for features that might contribute or detract from permeability. Petrographic analysis yielded rare instances of “visual” porosity as high as 25%; typical porosity estimates were 1-2% or less. Not readily apparent in most of the thin sections was extensive silica overgrowth and cementation expected based on experience with exposures of Tuscarora in eastern West Virginia. Because of its proximity (37 miles; 60 Km) to Morgantown, Preston 119 was chosen for permeability analysis. Air-injection-permeability sampling concentrated primarily on observed fractures but also included matrix and unusual features (such as bioturbation and stylolites) encountered in the core. Fracture lengths, widths, and orientations were measured and recorded together with permeability. Fracture permeabilities as high as a Darcy were observed; the sandstone matrix was typically “tight” with less than 1-2 mD of permeability. Whether or not higher observed fracture permeabilities are present and accessible at the proposed well site remains to be seen. However, large, open voids associated with vertical and oblique fractures in the Preston 119 core suggest that rock with properties amenable to geothermal fluid circulation may be present in the Tuscarora.