Assessment of undiscovered oil and gas resources of the Ordovician Utica Shale of the Appalachian Basin Province, 2012

Introduction

The U.S. Geological Survey (USGS) assessed unconventional oil and gas resources of the Upper Ordovician Utica Shale and adjacent units in the Appalachian Basin Province. The assessment covers parts of Maryland, New York, Ohio, Pennsylvania, Virginia, and West Virginia (fig. 1). The geologic concept is that black shale of the Utica Shale and adjacent units generated hydrocarbons from Type II organic material in areas that are thermally mature for oil and gas. The source rocks generated petroleum that migrated into adjacent units, but also retained significant hydrocarbons within the matrix and adsorbed to organic matter of the shale. These are potentially technically recoverable resources that can be exploited by using horizontal drilling combined with hydraulic fracturing techniques.

Utica Shale Self-Sourced Reservoirs

The Utica Shale and Late Ordovician age equivalents are the primary source rocks in the Utica–Lower Paleozoic Total Petroleum System (TPS) of Milici and others (2003). The shales are mainly present in New York, Ohio, Pennsylvania, and West Virginia. For this assessment, black shale facies of the Utica are combined with equivalent units — Antes Shale in central Pennsylvania and the Point Pleasant Formation in Ohio and Pennsylvania (Patchen and others, 2006). Thickness of the black shale facies is as much as 700 ft in southwestern Pennsylvania (Patchen and others, 2006) and New York (Ryder, 2008), but typically ranges from 150 to 350 ft (Ryder, 2008).

The facies consist of calcareous to clay-rich mudrock with total organic carbon (TOC) values commonly in excess of 1 weight percent (wt %) (fig. 2). There is a broad northeast-southwest-trending area that extends across western and southern Pennsylvania, eastern Ohio, northern West Virginia, and southeastern New York where TOC values are in the 2 to 3 wt % range (fig. 2; Wallace and Roen, 1989; Ryder and others, 1998). The Utica is an oil-prone source rock containing Type II kerogen (Ryder and others, 1998). Conodont color alteration index (CAI) isograds (fig. 3), based on samples from the Ordovician rocks (Repetski and others, 2008), indicate that a pod of mature Utica source rocks underlies most of the TPS. The Utica source rocks are within a thermal region that generates oil between a CAI of 1 to 2 and generates gas above 2 (fig. 3; Ryder, 2008).

Geologic Model for Assessment

The geologic model used in the assessment of the Utica Shale and adjacent organic-rich shale is that oil and gas were generated in the organic-rich shale and occupies matrix porosity as well as organic porosity in the same shale. A TOC lower cutoff of 1 wt % was used for potential source rocks. The thermal window for oil was based on a CAI greater than 1, and the window for gas and oil cracking to gas used a CAI of 2. A comparison of preliminary production from the Utica in southeastern Ohio confirmed that a CAI of 2 approximates the oil/ gas boundary in eastern Ohio with some degree of confidence; however, all contour lines are subject to geologic uncertainty. The oil/gas boundary is based on a gas-to-oil ratio of 20,000 cubic feet of natural gas per barrel of oil. The

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Utica has little history of production, therefore production data were supplemented with analog data from the Devonian Marcellus Shale, Cretaceous Eagle Ford Shale, and Cretaceous Niobrara Formation. The Marcellus is an analog mainly for its proximity and similar geologic setting, and the Cretaceous units for their facies similarity. Analog data include estimated ultimate recoveries (EUR), mean drainage areas of wells, and ranges of well success ratios. Key assessment input data are listed in table 1.

Assessment Units

The Utica Shale Gas Assessment Unit (AU) is defined where the thermal maturity of the organic matter is greater than a CAI of 2 (fig. 3) and by several constraints that determine the boundaries: total organic carbon (TOC) of greater than 1 wt % (fig. 2), the Allegheny structural front to the southeast, the outcrop of the Utica in New York to the east, and where the unit changes facies into carbonates to the south (see Patchen and others, 2006) (fig. 1).

The Utica Shale Gas AU “sweet spot” is defined as an area in which Utica Shale and equivalents contain TOC greater than 2 wt % and also is underlain by the black shale facies of the Point Pleasant Formation (fig. 4). A possible limiting factor for the sweet spot is whether the Point Pleasant in Ohio and Pennsylvania forms a continuous accumulation with the lower part of the Utica Shale (Flat Creek Member) in New York. A further limiting factor is the possible degradation of reservoir quality in both the deeper and shallower parts of the AU. The sweet spot has been modified to encompass current drilling in the AU where EURs are greater than the minimum cutoff of 0.02 billion cubic feet of gas (BCFG).

The Utica Shale Oil AU (fig. 1) is defined by the presence of the Utica Shale and equivalents based on Ryder (2008) and Patchen and others (2006). It is limited to an area of the Utica that has a thermal maturity greater than a CAI of 1 (Repetski and others, 2008) and TOC content greater than 1 wt% (Wallace and Roen, 1989; Ryder, 2008) (fig. 2). The downdip limit is placed at a thermal maturity greater than a CAI of 2 (fig. 3). The AU boundary also ends at the United States–Canadian border and where the shale changes facies into carbonates to the south (fig. 1).

The Utica Shale Oil AU “sweet spot” encompasses an area of Utica Shale and equivalents and the underlying Point Pleasant Formation (fig. 4), where TOC is consistently greater than 2 wt% (fig. 2; Repetski and others, 2008; Riley and others, 2012). The sweet spot also includes current wells where EURs are considered to be greater than the minimum of 0.002 million barrels of oil (MMBO).

Resource Summary

The USGS assessed technically recoverable continuous (unconventional) oil and gas resources for the two AUs of the Ordovician Utica and Point Pleasant black shale of the Appalachian Basin Province, resulting in estimated means of 940 MMBO, 38.2 trillion cubic feet of gas (TCFG), and 208 million barrels of natural gas liquids (MMBNGL) (table 2).

The Utica Shale Gas AU is an area of about 31,600,000 acres at the mean and is divided into sweet spot and nonsweet spot areas. The estimated mean resource volumes are 37,273 BCFG (range from 20,601 to 59,415 BCFG) and 199 MMBNGL (range from 71 to 382 MMBNGL). Estimates of average drainage area are made for the AU, and separate estimates of average EUR and success ratio are made for the sweet and nonsweet spots (table 1). Because there is a limited amount of existing gas production from the Utica, EUR distributions for sweet spot and nonsweet spots are estimated from distributions of other shale gas AUs (U.S. Geological Survey Oil and Gas Assessment Team, 2012, their fig. 1). Based on these input parameters, recovery of the potential resource would require at the mean about 48,000 wells to be drilled within the sweet spot and an additional 62,000 wells at the mean to be drilled in the nonsweet spot to extract the resource.

The Utica Shale Oil AU is an area of about 15,000,000 acres at the mean and is divided into a sweet spot and a nonsweet spot. The estimated mean resource volumes are 940 MMBO (range from 590 to 1,386 MMBO), 939 BCF of associated gas (range from 505 to 1,517 BCF), and 9 MMBNGL (range from 4 to 16 MMBNGL). Estimates of average drainage area for the AU and separate estimates of average EUR and success ratio are made for the sweet and nonsweet spots (table 1). Because there is a limited amount of existing oil production from the Utica, EUR distributions for sweet and nonsweet spots are estimated from distributions of other shale oil assessment units (U.S. Geological Survey Oil and Gas Assessment Team, 2012, their fig. 4). Based on these input parameters, recovery of the resource would require at the mean about 7,000 wells to be drilled within the sweet spot and an additional 10,500 wells at the mean to be drilled in the nonsweet spot to extract this potential resource.

References Cited

Milici, R.C., Ryder, R.T., Swezey, C.S., Charpentier, R.R., Cook, T.A., Crovelli, R.A., Klett, T.R., Pollastro, R.M., and Schenk, C.J., 2003, Assessment of undiscovered oil and gas resources of the Appalachian Basin Province, 2002: U.S. Geological Survey Fact Sheet 009-03, 2 p.

Patchen, D.G., Hickman, J.B., Harris, D.C., Drahovzal, J.A., Lake, P.D., Smith, L.B., Nyahay, R., Schulze, R., Riley, R.A., Baranoski, M.T., Wickstrom, L.H., Laughrey, C.D., Kostelnik, J., Harper, J.A., Avary, K.L., Bocan, J., Hohn, M.E., and McDowell, R., 2006, A geologic play book for Trenton-Black River Appalachian Basin exploration: U.S. Department of Energy Report, Morgantown, W. Va., DOE Award Number DE-FC26-03NT41856, 582 p., 30 pls.

Repetski, J.E., Ryder, R.T., Weary, D.J., Harris, A.G., and Trippi, M.H., 2008, 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: U.S. Geological Survey Scientific Investigations Map 3006, 41 p., 3 sheets.

Riley, R.A., Erenpreiss, M.S., and Wells, J.G., 2012, Data compilation and source rock mapping of the Upper Ordovician black shale interval in Ohio: Ohio Department of Natural Resources, Division of Geological Survey, contract report funded by U.S. Geological Survey (00200003512), 29 p.

Ryder, R.T., 2008, Assessment of Appalachian Basin oil and gas resources: Utica-Lower Paleozoic Total Petroleum System: U.S. Geological Survey Open-File Report 2008–1287, 29 p.

Ryder, R.T., Burruss, R.C., and Hatch, J.R., 1998, Black shale source rocks and oil generation in the Cambrian and Ordovician of the central Appalachian Basin, USA: American Association of Petroleum Geologists Bulletin, v. 82, no. 3, p. 412–441.

U.S. Geological Survey Oil and Gas Assessment Team, 2012, Variability of distributions of well-scale estimated ultimate recovery for continuous (unconventional) oil and gas resources in the United States: U.S. Geological Survey Open-File Report 2012–1118, 18 p.

Wallace, L.G., and Roen, J.B., 1989, Petroleum source rock potential of the Upper Ordovician black shale sequence, northern Appalachian Basin: U.S. Geological Survey Open-File Report 89–488, 66 p.

Utica Shale Assessment Team

Mark A. Kirschbaum, Christopher J. Schenk (project chief, schenk@usgs.gov), Troy A. Cook, Robert T. Ryder, Ronald R. Charpentier, Timothy R. Klett, Stephanie B. Gaswirth, Marilyn E. Tennyson, Katherine J. Whidden.

For Additional Information

Supporting geologic studies of Utica Shale and Assessment Units, and reports on the assessment methodology used in the assessment can be found at the USGS Energy Resources Program website (http://energy.usgs.gov).

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