Petroleum source rock potential of the Upper Ordovician black shale sequence, northern Appalachian basin

Abstract

In the Appalachian basin, the widespread black shales of Mississippian through Devonian age and of Late Ordovician age are sufficiently rich in organic matter to be hydrocarbon source rocks. The younger Devonian and Mississippian sequence is less deeply buried and better exposed within the basin than the Upper Ordovician sequence. As a result, the Upper Ordovician shales have not been evaluated as extensively for their hydrocarbon potential. An appraisal of the Upper Ordovician black shale sequence has been made for the northern part of the basin west of the Allegheny front in New York, Pennsylvania, Ohio, and West Virginia. The region contains a relatively continuous sequence of dark-gray to grayish-black shale of Late Ordovician age. Within the Upper Ordovician black shales, a sequence was delineated based on its physical properties that were indicative of a potential source rock. This unit, informally defined here as the Utica sequence comprises all or part of the Utica Shale and its correlatives, the Antes Shale, the lower part of the Reedsville Shale, the lower part of the Martinsburg Shale, the Point Pleasant Formation, and the basal part of the undivided Cincinnatian Series.The thickness of the Utica .sequence ranges from less than 200 feet in western Ohio to more than 600 feet along the Allegheny front in southwestern Pennsylvania. Structure contours indicate that the base of the Utica sequence is about 2,000 feet below sea level in central Ohio and plunges eastward to about 12,000 feet below sea level in central and northeastern Pennsylvania.Geochemical analyses of 175 samples from the Utica sequence from 104 localities in New York, Ohio, Pennsylvania, and West Virginia.indicate that the sequence has an average total organic carbon content of 1.34 weight percent. Conodont alteration indices and the production index for these rocks indicate the maturation, with respect to hydrocarbon generation, ranges from diagenetic in the shallow western part of the basin to catagenetic in the deep eastern part of the basin. This data is supported by the temperatures of maximum pyrolytic hydrocarbon generation. The 400 to 600 ft. sequence of shale in eastern New York and central and eastern Pennsylvania is in the middle to upper catagenetic stage and is now in the gas window, but probably also produced oil; the 200 to 300 ft. sequence of shale in the western part of New York, Pennsylvania, and West Virginia and the eastern part of Ohio is in the lower catagenetic stage and is now in the oil window.The genetic potential of the shales in New York, Pennsylvania, and West Virginia where they are deepest, indicates that the potential for further generation of oil from these shales is poor and the potential for further gas generation is fair. However, in Ohio, the potential for further generation oil in the shale is fair to good.

Assessment of Appalachian Basin Oil and Gas Resources: Utica-Lower Paleozoic Total Petroleum System

“…Total organic carbon (TOC) values (in wt percent) for the Utica Shale are usually greater than 1 percent, and TOC values in the 2 to 3 percent range outline a broad, northeast-trending area that extends across western and southern Pennsylvania, eastern Ohio, northern West Virginia, and southeastern New York (Wallace and Roen, 1989;Ryder and others, 1998) (fig. 8).…”

Thermal Maturity Patterns (CAI and %Ro) in Upper Ordovician and Devonian Rocks of the Appalachian Basin: A Major Revision of USGS Map I-917-E Using New Subsurface Collections

“…The most plausible source rock for the oil and gas fields in Cambrian and Ordovician reservoirs in Ohio, Pennsylvania, New York, and West Virginia is the Upper Ordovician Utica Shale (Cole and others, 1987;Jenden and others, 1993;Laughrey and Baldassare, 1998;Ryder and others, 1998). The Utica Shale is 150 to 300 ft thick across much of Ohio, Pennsylvania, New York, and the northern part of West Virginia (Wallace and Roen, 1989). In southeastern New York, the Utica Shale increases in thickness to as much as 800 ft (Martin, 2005;Martin and others, 2005).…”

Overview of the potential and identified petroleum source rocks of the Appalachian basin, eastern United States

“…In all of the maps presented in this study, the TOC values incorporated from the Brown and Ruth study are neither the maximum values recorded nor the arithmetic averages, so that neither the very few high values nor the very numerous low values overweigh the aggregate. The values from the Brown and Ruth study were incorporated along with additional data from outcrops, wells, and maps from Schmoker (1980); Snowdon (1984); Cole and others (1987); Wallace and Roen (1989); Carroll and others (1995); Ryder and others (1998Ryder and others ( , 2005Ryder and others ( , 2007; Milici and Swezey (2006); Patchen and others 2006…”