Hydrocarbon Potential of the Devonian Millboro (Marcellus) Shale in the Valley and Ridge Province of Virginia

Catherine B. Enomoto
Virginia Department of Mines, Minerals and Energy, Division of Geology and Mineral Resources, Charlottesville, VA 22903, [email protected]

In 2007, 23.5 billion cubic feet of natural gas were produced from Mississippian sandstone and limestone, and Devonian shale in the Appalachian Plateaus Province in southwest Virginia. In the adjacent Valley and Ridge Province in Virginia, the potential for natural gas resources in Devonian shale may also be significant, but remains relatively untested. In the Virginia portion of the Appalachian Basin, the Devonian Mahantango Formation and the Marcellus Shale are mapped collectively as one unit that is named the Millboro Shale. This unit in Virginia consists of black, fissile shale units, with interbeds of dark gray argillaceous limestone or calcareous shale. Thin, dark gray, aphanitic limestone beds occur near the base. Geophysical logs from wells drilled in Highland and Rockingham counties, Virginia, indicate that the thickness of the Millboro Shale ranges from 368 to 570 feet thick in this region. Geochemical analyses of the Millboro Shale in Virginia indicate there is an organic richness sufficient to generate commercial quantities of hydrocarbons, that the shale contains a kerogen type that is more likely to generate natural gas than liquid oil, and that the shale is in the gas generation phase of maturity.

In 2002, the U.S. Geological Survey estimated the undiscovered, technically recoverable petroleum resources in the Marcellus Shale Assessment Unit to have a mean value of 1,925 billion cubic feet of natural gas and 11.55 million barrels of natural gas liquids. The Marcellus Shale Assessment Unit includes the Millboro Shale in western Virginia.

AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009