Jessica Pierson Moore, Philip A. Dinterman, Ronald R. McDowell, Joel R. Sminchak, and Gary W. Daft
The Tuscarora Sandstone in the Indian Creek field in Kanawha County, West Virginia produces commercial volumes of food-grade carbon dioxide (CO
2) as a constituent of the natural gas stream. Commercial production of naturally occurring CO
2 in the Appalachian basin is unique to the Indian Creek field, providing a natural laboratory for the effects of potential carbon storage and a unique opportunity to examine an analog for long-term carbon storage. Because the mechanisms of this CO
2 generation and trapping are not fully understood, researchers examined thin sections, well logs, drilling and completion reports, and core from wells inside the Indian Creek field and compared these data to wells from nearby fields that do not produce significant amounts of CO
2 in gas accumulations. The resulting geologic cross-sections and isopach maps of the Tuscarora were augmented with Computed Tomography (CT) scans of the cores to assess potential fracture networks and migration pathways. Pores in thin sections of Tuscarora taken from a well drilled inside the field exhibit thin, incomplete, linings of calcite that appear to be an early cement partially dissolved by later pore fluids to produce CO
2. A second possibility for CO
2 generation is suggested by the presence of pores lined with framboidal pyrite typically associated with bacterial degradation of organic matter such as hydrocarbons. Thin sections from core reveal bedding-parallel stylolites, often filled with heavy minerals and/or clays, as well as thick quartz overgrowths, and sutured grain contacts. Sediments in this core are burrowed; the burrows are backfilled with very fine to silt-sized quartz. Porosity is fracture-enhanced and contained within burrows rather than the matrix.
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