EVOLUTION OF UPPER DEVONIAN MARGINAL MARINE SANDSTONE LITHOFACIES IN THE APPALACHIAN BASIN: IMPLICATIONS FOR BASIN EVOLUTION, LITHOSTRATIGRAPHY AND CARBON STORAGE POTENTIAL

Upper Devonian sandstones of the Appalachian basin have been the subject of oil and gas exploration for more than 150 years. While these units are characterized by demonstrated ease of drilling and an abundance of data that allow detailed delineation of zones of enhanced reservoir quality, they generally have not been widely considered as carbon storage prospects due to limited size, uncertain reservoir quality, extensive penetration from legacy wells, and shallow depth. New detailed basin-scale correlation and lithofacies mapping, focused on marginal marine sandstone lithofacies, indicates large areas of sandstone-rich strata occurring at depths suitable for carbon storage in the basin. Initial sandstone mapping was accomplished via relative baselining (50% volume of shale cut-off) for more than ~2,350 well logs that span ~270 miles of strike and ~50 miles of dip. Changing basin-scale sand distribution patterns observed in these maps record the progressive infill of the basin as shorelines generally progressed westward. Further, in accordance with waning tectonism and progressive basin infill, the overall transition from moderately sand-rich, offset-stacked and mixed dip- and strike-trending (Frasnian and early Famennian), to sand-rich, vertically stacked, and predominantly strike-trending (late Famennian) systems is observed. Although Frasnian and lower Famennian sandstones are locally thick and of good reservoir quality, those of late Famennian age are perhaps the most prospective due to higher sand-shale ratio and greater lateral continuity. The detailed regional mapping also provides an opportunity to refine lithostratigraphic terminology and relationships. While an informal terminology that reflects approximate chronostratigraphic intervals is well developed and widely used for subsurface correlation, subsurface formal lithostratigraphic terminology that recognizes the time-transgressive nature of the prospective sandstone lithofacies is less complete and poorly integrated with formal nomenclature established in the outcrops to the east. Further work will progress toward characterization of specific carbon storage capacities in potential reservoirs of specific interest.