National Assessment of Oil and Gas

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, 

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Assessment

Units

Appalachian

Basin

Province

0 50 100 MILES

0 50 100 KILOMETERS

EXPLANATION

Utica Shale Gas AU

Utica Shale Oil AU

UNITED STATES CANADA

Figure 1. Location of the oil and gas assessment units (AU) for the Utica Shale in the Appalachian Basin Province.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3116

September 2012
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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EXPLANATION

Utica Shale extent

Point Pleasant 

 Formation extent

TOC in weight percent

2

1

1

2

3

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1

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Figure 2. Map of total organic carbon (TOC) in weight percent from Ryder (2008), and mapped southern limit of Utica Shale (blue 

line) and mapped northern extent of the Point Pleasant Formation (purple line) from Patchen and others (2006).
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; 

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EXPLANATION

Area of combined AUs

CAI

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2

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3 4

Figure 3. Map of conodont alteration index (CAI) for the Utica Oil and Gas Assessment Units (AU) after Repetski and others 

(2008, their fig. 5). The 1+ isograd is used to estimate the generation threshold for oil; the 2 isograd is used to estimate the gas 

threshold.
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EXPLANATION

Gas maximum sweet spot

Oil maximum sweet spot

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Figure 4. Map of maximum extent of the oil and gas sweet spots. The boundaries are based on total organic carbon, extent of 

Point Pleasant Formation, and current (2012) understanding of well completions. See table 1 for percentages.

Assessment input data

Utica Shale Oil AU Utica Shale Gas AU

Minimum Mode Maximum Calculated

mean

Minimum Mode Maximum Calculated 

mean

Potential production area of 

AU (acres)

13,500,000 15,000,000 16,500,000 15,000,000 25,800,000 31,600,000 37,400,000 31,600,000

Average drainage area of 

wells (acres)

 150 250 350 250 120 150 180 150

Percentage of AU in sweet 

spots (%)

 7 14 22 14 9 21 50 27

Input data for sweet spots

Average EUR (MMBO, oil; 

BCFG, gas)

 0.04 0.08 0.2 .086 0.2 0.6 1.1 0.619

Success ratios (%) 70 80 90 80 75 85 95 85

Input data for nonsweet spots

Average EUR (MMBO, oil; 

BCFG, gas)

 0.01 0.03 0.1 0.034 0.04 0.10 0.60 0.128

Success ratios (%) 5 20 35 20 10 40 70 40

[EUR (estimated ultimate recovery per well), well drainage area, and success ratios are from U.S. shale oil and shale gas analogs. MMBO, million barrels of oil; BCFG, 

billion cubic feet of gas; AU, assessment unit; %, percent. The average EUR input is the minimum, median, maximum, and calculated mean]

Table 1. Key assessment input data for shale oil and shale gas assessment units for the Utica Shale in the Appalachian Basin. 
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. 

Provinces,

Total petroleum systems 

(TPS),

and Assessment Units (AU)

AU

probability

Accumulation 

type

Total undiscovered resources

Oil (MMBO) Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Utica-Lower Paleozoic TPS

Utica Shale Gas AU 1.0 Gas 20,601 35,659 59,415 37,273 71 183 382 199

Utica Shale Oil AU 1.0 Oil 590 911 1,386 940 505 897 1,517 939 4 9 16 9

Total unconventional

 resources

 590 911 1,386 940 21,106 36,556 60,932 38,212 75 192 398 208

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. For 

gas accumulations, all liquids are included under the NGL (natural gas liquids) category. Undiscovered gas resources are the sum of nonassociated and associated gas. F95 represents a 95 percent chance of at least the amount tabulated–other fractiles are defined similarly. Fractiles are additive under the assumption 

of perfect positive correlation. AU probability is the chance of at least one well within the AU having a production capacity of the minimum estimated ultimate 

recovery. Gray shading indicates not applicable]

Table 2. Assessment results for potential unconventional oil and gas resources of Utica Shale in the Appalachian Basin.
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).

Hand-tinted photo of Ordovician Utica Shale with interbedded sandstone of the Ordovician 

Lorraine Shale above, Jefferson County, New York. Photograph 1889 by C.D. Wolcott, third Director 

of the USGS. http://library photo.cr.usgs.gov.