Five Categories of Organic-Rich Shale, and Their Gas-Bearing Potential in the Eastern United States
Christopher S. Swezey and James L. Coleman, Jr.
U.S. Geological Survey, Reston, VA 20192,
[email protected]
Most organic-rich shale in the eastern United States may
be grouped according to stratigraphical and depositional
setting into the following five categories, which may be
useful for developing exploration portfolios:
(1) Lacustrine shale in rift basins. Shale category 1 includes
shale in the Precambrian Nonesuch Formation (Michigan
Basin) and Triassic shale in Virginia and North Carolina.
(2) Marine shale that overlies carbonate platform deposits
and that is part of a 10-40 Ma interval of siliciclastic rocks.
Shale category 2 includes the Ordovician Utica Shale
(Appalachian Basin) and equivalent strata, and the Devonian
Marcellus Shale (Appalachian Basin) and equivalent strata.
(3) Deep-water marine shale adjacent to carbonate platform
deposits. Shale category 3 includes the Mississippian
Lillydale Shale in Virginia (and other shale units basinward of
the Mississippian carbonate platform, such as the
Mississippian Barnett Shale in Texas).
(4) Shallow marine and marginal marine shale associated
with evaporite deposits. Shale category 4 includes shale in
the Ordovician Foster Formation (Michigan Basin), the
Ordovician Ancell Group (Illinois Basin), and the Silurian
Niagara and Salina Groups (Michigan Basin).
(5) Marine shale associated with coal beds. Shale category 5
consists of Pennsylvanian shale in the Appalachian,
Michigan, and Illinois Basins.
According to U.S. Geological Survey, Devonian strata of shale category 2 may contain approximately 2 to 10 trillion cubic feet (tcf) of undiscovered gas resources per basin in the eastern United States. Commercial gas production has not yet been established from shale categories 1, 3, 4, or 5 in the eastern United States.
AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009