U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2018–3076

ver 1.1, March 2020

National and Global Petroleum Assessment

Assessment of Continuous Oil and Gas Resources in the Niobrara 

Interval of the Cody Shale, Wind River Basin Province, Wyoming, 2018

Using a geology-based assessment methodology, the U.S. Geological Survey estimated means of 389 million barrels of oil and 1.8 trillion cubic feet 

of gas in the Niobrara interval of the Cody Shale in the Wind River Basin Province, Wyoming.

Introduction

The U.S. Geological Survey (USGS) quantitatively assessed the 

potential for undiscovered, technically recoverable continuous (unconventional) 

oil and gas resources in the Niobrara interval of the Cody Shale in the 

Wind River Basin Province, Wyoming (fig. 1). In the Wind River Basin, the 

Niobrara interval is represented by gray-to-black shale, calcareous shale, 

marl, and bentonite, with minor amounts of siltstone and sandstone in the 

lower part of the Upper Cretaceous Cody Shale (Finn, 2017). The strata were 

deposited in an epicontinental seaway that occupied an elongate north–south 

foreland basin that was bordered on the west by the tectonically active 

Cordilleran orogenic belt and on the east by the low-lying, stable North 

American craton (DeCelles, 2004). At its maximum extent, the seaway 

extended for more than 3,000 miles from the Arctic Ocean to the Gulf of 

Mexico (Kauffman, 1977). During the Laramide orogeny (Late Cretaceous 

through early Eocene), the central part of the foreland basin was fragmented 

into numerous smaller basins, including the Wind River Basin, that were 

flanked by rising basement-cored uplifts. These 

basins subsided rapidly and were depocenters 

for the accumulation of thick lacustrine and 

continental sediments from latest Cretaceous 

through middle Miocene time (Love, 1988). 

Total Petroleum System and 

Assessment Units

Johnson and others (2007) defined the 

Cretaceous–Lower Tertiary Composite Total 

Petroleum System (TPS) in the Wind River 

Basin Province to include strata from the base 

of the Lower Cretaceous to the base of the 

Paleocene Waltman Shale and to include lower 

Eocene strata where the Waltman is absent. The 

Niobrara interval of the lower part of the Cody 

Shale is an element of the Cretaceous–Lower 

Tertiary Composite TPS and includes both 

source and reservoir rocks. Source rocks occur 

in both the Niobrara interval and the underlying 

Sage Breaks interval and have total organic 

carbon contents of as much as 6 weight percent. 

The organic matter in these source rocks consists 

of Type II and mixed Type II/III kerogen 

with hydrogen index values of as much as 

530 milligrams of hydrocarbon per gram of 

organic carbon. Potential reservoirs have 

carbonate contents of as much as 60 percent. 

The more calcareous zones are often characterized 

by varying amounts of coccolith-rich fecal 

pellets that appear as distinctive “white specks” 

like those described by Hattin (1975). The 

Niobrara interval is more organic rich, oil prone, 

and calcareous in the central and eastern parts of the basin. Thermal maturity 

mapping, based on vitrinite reflectance (Ro

), shows that the Niobrara interval 

is thermally mature for oil generation (0.6–1.35 percent Ro

) along the western 

and southern margins of the basin and mature for gas generation (greater than 

1.35 percent Ro

) in the deeper central and northern parts of the basin (Finn 

and Pawlewicz, 2013). The Late Cretaceous through early Eocene Laramide 

orogeny and post-Laramide burial are considered to have thermally matured 

these organic-rich shales (Roberts and others, 2007).

The geologic model for the Niobrara interval continuous accumulations 

is that oil and gas were generated from oil-prone source rocks primarily 

during Laramide and post-Laramide burial. Oil and gas were partially 

retained within the Niobrara interval following generation and migration 

into adjacent reservoirs. Two assessment units (AUs) were defined: 

(1) the Wind River Niobrara Shale Oil AU encompasses the area within 

the oil-generation window (0.60–1.35 percent Ro

) and (2) the Wind River 

Niobrara Shale Gas AU includes the area where oil has been cracked to gas 

(greater than 1.35 percent Ro

).

CARBON

NATRONA

LINCOLN

SUBLETTE

SWEETWATER

FREMONT

HOT SPRINGS WASHAKIE

PARK

TETON JOHNSON

WYOMING

Wind River Mountains

Absaroka Range

Granite 

Mountains

Casper arch Bighorn Mountains

Owl Creek Mountains

Boysen

Reservoir

Casper

Riverton

Lander

44°

43°

–110° –109° –108° –107°

Base map from U.S. Department of the Interior National Park Service

0 10 20 30 40 KILOMETERS

0 10 20 30 40 MILES EXPLANATION

Wind River Niobrara Shale Gas AU

Wind River Basin Province boundary

Wind River Niobrara Shale Oil AU

WY

MT

ID

UT CO

SD

NE

Map

area

Figure 1. Map showing the continuous oil and gas assessment units (AUs) in the Niobrara 

interval of the Cody Shale in the Wind River Basin Province, Wyoming. Province boundary is 

from Johnson and others (2007).
Assessment input data are summarized in table 1. Input data for 

estimated ultimate recoveries of wells are taken from the geologic analog 

in the Sand Wash Basin part of the Southwestern Wyoming Province.

Undiscovered Resources Summary

The USGS quantitatively assessed continuous oil and gas resources 

in the two delineated AUs (table 2) in the Niobrara interval of the 

Wind River Basin Province, Wyoming. For undiscovered, technically 

recoverable continuous oil and gas resources, the estimated mean totals 

are 389 million barrels of oil (MMBO) with an F95–F5 fractile range 

from 90 to 834 MMBO; 1,831 billion cubic feet of gas (BCFG), or 

1.8 trillion cubic feet of gas, with an F95–F5 fractile range from 377 to 

4,405 BCFG; and 31 million barrels of natural gas liquids (MMBNGL) 

with an F95–F5 fractile range from 6 to 79 MMBNGL.

References Cited

DeCelles, P.G., 2004, Late Jurassic to Eocene evolution of the Cordilleran thrust belt and foreland basin system, western U.S.A.: American Journal of Science, v. 304, no. 2, p. 105–168.

Finn, T.M., 2017, Stratigraphic cross sections of the Niobrara interval of the Cody Shale 

and associated rocks in the Wind River Basin, central Wyoming: U.S. Geological 

Survey Scientific Investigations Map 3370, 19 p., 1 sheet, accessed June 1, 2018, at 

https://doi.org/10.3133/sim3370.

Finn, T.M., and Pawlewicz, M.J., 2013, Maps showing thermal maturity of Upper Cretaceous marine shales in the Wind River Basin, Wyoming: U.S. Geological Survey Scientific Investigations Map 3266, 13 p., 1 sheet, scale 1:500,000, accessed May 1, 2018, at 

http://doi.org/10.3133/sim3266.

Hattin, D.E., 1975, Petrology and origin of fecal pellets in Upper Cretaceous strata of Kansas 

and Saskatchewan: Journal of Sedimentary Petrology, v. 45, no. 3, p. 686–696.

Johnson, R.C., Finn, T.M., Kirschbaum, M.A., Roberts, S.B., Roberts, L.N.R., Cook, T., and 

Taylor, D.J., 2007, The Cretaceous–Lower Tertiary Composite Total Petroleum System, 

Wind River Basin, Wyoming, chap. 4 of USGS Wind River Basin Province Assessment 

Team, Petroleum systems and geologic assessment of oil and gas in the Wind River 

Basin Province, Wyoming: U.S. Geological Survey Digital Data Series DDS–69–J, 96 p.

Kauffman, E.G., 1977, Geological and biological overview—Western Interior Cretaceous 

basin, in Kauffman, E.G., ed., Cretaceous facies, faunas, and paleoenvironments across the 

Western Interior Basin: Denver, Colo., Rocky Mountain Association of Geologists, The 

Mountain Geologist, v. 14, nos. 3–4, p. 75–99.

Love, J.D., 1988, Geology of the Wind River Basin, central Wyoming, in Basins of the 

Rocky Mountain region, chap. 8 of Sloss, L.L., ed., Sedimentary cover—North American 

craton—U.S., v. D–2 of The geology of North America: Boulder, Colo., The Geological 

Society of America, p. 196–200.

Roberts, L.N.R., Finn, T.M., Lewan, M.D., and Kirschbaum, M.A., 2007, Burial history, thermal maturity, and oil and gas generation history of petroleum systems in the Wind River 

Basin Province, central Wyoming, chap. 6 of USGS Wind River Basin Province Assessment Team, Petroleum systems and geologic assessment of oil and gas in the Wind River 

Basin Province, Wyoming: U.S. Geological Survey Digital Data Series DDS–69–J, 26 p.

https://doi.org/10.3133/fs20183076

Table 1. Key input data for two continuous assessment units (AUs) in the Niobrara interval of the Cody Shale in the Wind River Basin 

Province, Wyoming.

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery per well; MMBO, million barrels of oil; BCFG, billion cubic feet of gas. Well drainage area, 

success ratio, and EUR are defined partly using U.S. shale-oil analogs. The average EUR input is the minimum, median, maximum, and calculated mean. Shading 

indicates not applicable]

Assessment input data—

Continuous AUs

Wind River Niobrara Shale Oil AU Wind River Niobrara Shale Gas AU

Minimum Mode Maximum Calculated 

mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,000 713,000 1,264,000 659,333 1,000 719,000 1,198,000 639,333

Average drainage area of wells (acres) 40 120 200 120 80 120 180 126.7

Success ratio (%) 10 50 90 50 10 50 90 50

Average EUR (MMBO, oil; BCFG, gas) 0.06 0.13 0.2 0.132 0.1 0.5 2.0 0.581

AU probability 1.0 1.0

Table 2. Results for two continuous assessment units (AUs) in the Niobrara interval of the Cody Shale in the Wind River Basin Province, Wyoming.

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

estimates. 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. Shading indicates not applicable]

Total petroleum system 

and assessment units (AUs)

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

Cretaceous–Lower Tertiary Composite Total Petroleum System

Wind River Niobrara Shale Oil AU 1.0 Oil 90 346 834 389 90 336 870 389 5 20 55 23

Wind River Niobrara Shale Gas AU 1.0 Gas 287 1,169 3,535 1,442 1 5 24 8

Total undiscovered continuous 

resources 90 346 834 389 377 1,505 4,405 1,831 6 25 79 31

Niobrara Assessment Team 

Thomas M. Finn, Christopher J. Schenk, Tracey J. Mercier, 

Marilyn E. Tennyson, Phuong A. Le, Michael E. Brownfield, 

Kristen R. Marra, Heidi M. Leathers-Miller, Ronald M. Drake II, 

Cheryl A. Woodall, and Scott A. Kinney

For More Information

Assessment results are also available at the USGS Energy 

Resources Program website at https://energy.usgs.gov.

ISSN 2327-6916 (print) ISSN 2327-6932 (online)