Assessment of Appalachian basin oil and gas resources: Utica-Lower Paleozoic Total Petroleum System

The Utica-Lower Paleozoic Total Petroleum System (TPS) in the Appalachian Basin Province is named for the Upper Ordovician Utica Shale, which is the source rock, and for multiple lower Paleozoic sandstone and carbonate units that are the important reservoirs. The total organic carbon (TOC) values for the Utica Shale are usually greater than 1 weight percent. TOC values ranging from 2 to 3 weight percent outline a broad, northeast-trending area that extends across western and southern Pennsylvania, eastern Ohio, northern West Virginia, and southeastern New York. The Utica Shale is characterized by type II kerogen, which is a variety of kerogen that is typically prone to oil generation. Conondont color-alteration index (CAI) isograds, which are based on samples from the Upper Ordovician Trenton Limestone (or Group), indicate that a pod of mature Utica Shale source rocks occupies most of the TPS.

The following strata (in ascending stratigraphic order) are the most important reservoir rocks for oil and gas in the Utica-Lower Paleozoic TPS: (1) the Upper Cambrian Copper Ridge dolomite in Ohio; (2) the Upper Cambrian Rose Run sandstone in Ohio; (3) the Upper Ordovician Black River Limestone (or Group) and Trenton Limestone in New York, West Virginia, and Ohio; (4) the Lower Silurian “Clinton” sandstone, Medina sandstone, Medina Group sandstones, and Tuscarora Sandstone in Ohio, Pennsylvania, New York, and West Virginia; and (5) the Lower and Upper Silurian Lockport Dolomite (also known as the Newburg zone) in Ohio. Strata containing oil and gas reservoirs of secondary importance are sandstone reservoirs in the Upper Ordovician Queenston Shale in New York, the Upper Ordovician Bald Eagle Sandstone in Pennsylvania, and the Upper Silurian Williamsport Sandstone (also known as the Newburg sandstone) in West Virginia. The Upper Ordovician Utica Shale may be an important gas and oil(?) reservoir in the future. In about 2011, after this report was written, commercial natural gas and oil was discovered in the Utica Shale in eastern Ohio.

Both conventional oil and gas resources and continuous (unconventional) gas resources are present in the UticaLower Paleozoic TPS. Conventional oil and gas resources in the Utica-Lower Paleozoic TPS were assessed by the U.S. Geological Survey (USGS) in 2002 in the following assessment units (AU): (1) the Lower Paleozoic Carbonates in Thrust Belt AU, (2) the Knox Unconformity AU, (3) the Black River-Trenton Hydrothermal Dolomite AU, and (4) the Lockport Dolomite AU. The total estimated undiscovered oil and gas resources for these four AUs, at a mean value, was about 46 million barrels of oil (MMBO) and about 3 trillion cubic feet of gas (TCFG), respectively. In contrast, continuous (unconventional) gas resources in the TPS were assessed by the USGS in 2002 in four AUs associated with the “Clinton” sandstone, Medina sandstone, Medina Group sandstones, Tuscarora Sandstone, and sandstones in the Queenston Shale. The total estimated undiscovered gas for these four AUs, at a mean value, was about 26.8 TCFG. A hypothetical Utica Shale AU for oil(?) and continuous gas is identified in this report. In 2012, the Utica Shale was recognized by the USGS as a continuous AU and was assessed by Kirschbaum and others (2012).