STRATIGRAPHY AND PETROLEUM GEOLOGY OF THE ALEXANDER SILTSTONE IN THE APPALACHIAN FORELAND BASIN IN DODDRIDGE AND RITCHIE COUNTIES, WEST VIRGINIA, USA

The Upper Devonian Alexander siltstone is an informally named driller’s unit that is associated with the Elk play, occurring throughout the eastern half of the gas producing portion of the Appalachian Basin. The Alexander occurs within the Brallier Formation and lies stratigraphically below the more prolific Benson sand reservoir. The lithology of the Alexander is primarily silt with interbedded shaly intervals and the thickness of the unit ranges from 10 to140 feet throughout the study area. Stratigraphic cross sections constructed for the Alexander indicate three distinct intervals that are referred to as the lower, middle, and upper Alexander in this study. The gamma-ray signatures for each section indicate fining- upward bundles of silt with interlayered shaly intervals that thin basinward, indicative of distal turbidite deposition. The silt bundles are generally thicker at the base and become thinner and less continuous up section. Isopachs for each interval illustrate lobate fans that coalesce in the eastern- southeastern portion of the study area and thin and disappear to the west-northwest. Structure maps for the lower, middle, and upper Alexander indicate a prominent structure in the south-central portion of the study area. This structure is the deeply rooted Arches Fork Anticline, indicating that the traps within the Alexander are likely combination stratigraphic and structural traps. Within the study area, Alexander production is primarily natural gas, although some oil production is also reported. Production data for the Alexander are reported for most wells in Doddridge and Ritchie Counties, however, many are comingled with that of younger Devonian reservoirs.