Assessment of Undiscovered Oil and Gas Resources of the Devonian Marcellus Shale of the Appalachian Basin Province, 2011
By James L. Coleman, Robert C. Milici, Troy A. Cook, Ronald R. Charpentier, Mark Kirshbaum, Timothy R. Klett, Richard M. Pollastro, and Christopher J. Schenk, USGS - - Republished from USGS Fact Sheet 2011-3092
Using a geology-based assessment methodology, the U.S. Geological Survey (USGS) estimated a mean undiscovered natural gas resource of 84,198 billion cubic feet and a mean undiscovered natural gas liquids resource of 3,379 million barrels in the Devonian Marcellus Shale within the Appalachian Basin Province. All this resource occurs in continuous accumulations.
Marcellus Total Petroleum System
In 2011, the USGS completed an assessment of the undiscovered oil and gas potential of the Devonian Marcellus Shale within the Appalachian Basin Province of the eastern United States (Figure. 1). The Appalachian Basin Province includes parts of Alabama, Georgia, Kentucky, Maryland, New York, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia. The assessment of the Marcellus Shale is based on the geologic elements of this formation's total petroleum system (TPS) as recognized in the Appalachian Basin Province. These elements incorporate the characteristics of the TPS as a petroleum source rock (source rock richness, thermal maturation, petroleum generation, and migration) as well as a reservoir rock (stratigraphic position and content and petrophysical properties).
Defining the Marcellus Shale Assessment Unit
Together, these components confirm the Marcellus Shale as a continuous petroleum accumulation. Using this geologic framework, the USGS defined one TPS and three assessment units (AUs) within this TPS and quantitatively estimated the undiscovered oil and gas resources within the three AUs (table 1). For the purposes of this assessment, the Marcellus Shale is
considered to be that Middle Devonian interval that consists primarily of shale and lesser amounts of bentonite, limestone, and siltstone occurring between the underlying Middle Devonian Onondaga Limestone (or its stratigraphic equivalents, the Needmore Shale and Huntersville Chert) and the overlying Middle Devonian Mahantango Formation (or its stratigraphic equivalents, the upper Millboro Shale and middle Hamilton Group).
The USGS assessed the technically recoverable, undiscovered continuous (unconventional) gas within the Marcellus Shale and estimated a mean of 84,198 billion cubic feet of gas and a mean of 3,379 million barrels of total natural gas liquids. The entire undiscovered gas and natural gas liquids resource is in a continuous accumulation and is contained within a single TPS, the Devonian Shale-Middle and Upper Paleozoic TPS (Table 1 - below). Ninety-six percent of the estimated resource resides within the Interior Marcellus AU.
The Marcellus Shale is divided into three AUs within the formation's extent in the Appalachian Basin-the Western Margin Marcellus AU, which encompasses the western extent of the formation and west of the Appalachian Structural Front (ASF); the Interior Marcellus AU, which is the central extent of the trend and west of the ASF; and the Foldbelt Marcellus AU,which is east of the ASF. The total area of these three AUs extends from southern New York to northeastern Tennessee and from central Ohio to western Virginia and Maryland.
Western Margin Marcellus AU
The Western Margin Marcellus AU includes the formation where it is less than 50 feet (ft) thick, ranges in depth from less than 2,000 ft to more than 9,000 ft, and contains strata that range in current levels of thermal maturity from pre-peak oil to past-peak gas.
Interior Marcellus AU
The Interior Marcellus AU contains the Marcellus Shale that is 50 feet thick or more, ranges in depth from less than 2,000 ft to more than 11,000 ft, and contains strata that range in current levels of thermal maturity from peak oil to past-peak gas.
Foldbelt Marcellus AU
The Foldbelt Marcellus AU contains the Marcellus Shale within the Appalachian fold and thrust belt, ranges in thickness from a few feet to more than 350 ft thick, ranges in depth from outcrop to more than 11,000 ft, and contains strata that range in current levels of thermal maturity from peak gas to past-peak gas.
|Figure 1. Map of the Appalachian Basin Province showing the three Marcellus Shale assessment units, which encompass the extent of the
Middle Devonian from its zero isopach edge in the west to its erosional truncation within the Appalachian fold and thrust belt in the east. Click image to enlarge.
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