U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2017–3092

February 2018

National and Global Petroleum Assessment

Assessment of Undiscovered Oil and Gas Resources in the 

North-Central Montana Province, 2017

Using a geology-based assessment methodology, the U.S. Geological Survey estimated mean undiscovered, technically recoverable resources 

of 55 million barrels of oil and 846 billion cubic feet of gas in the North-Central Montana Province.

Introduction

The U.S. Geological Survey (USGS) quantitatively 

assessed the potential for undiscovered, technically recoverable conventional and continuous (unconventional) oil and 

gas resources in the North-Central Montana Province (fig. 1). 

The geologic evolution of the province is the result of a series 

of tectonic events that affected the western margin of North 

America (Petersen, 1986; Anna and others, 2011). These 

events include (1) the development of Neoproterozoic rifts 

and a regional lineament system; (2) an early to middle lower 

Paleozoic passive margin (Cambrian–Silurian); (3) the east–west 

trending central Montana trough coeval with the development of 

the Williston Basin (Petersen, 1986; Maughan, 1989); (4) Late 

Devonian through Mississippian subduction and compression 

during the Antler orogenic event; (5) Pennsylvanian uplift and 

erosion related to the Ouachita event; (6) Jurassic to Early 

Cretaceous high-angle subduction and compression during the 

0 50 100 KILOMETERS

0 50 100 MILES

EXPLANATION

Province boundary

Central Montana

Trough boundary 

(approximate)

Upper Cretaceous–Paleogene 

Biogenic Coalbed Gas AU

Ordovician Red River-Bighorn 

Dolomite AU

Pennsylvanian Tyler

Sandstones AU

Devonian–Mississippian

Carbonates AU

Upper Cretaceous 

Conventional

Biogenic Gas AU

Jurassic–Cretaceous 

Reservoirs AU

CANADA

NORTH

DAKOTA

SOUTH

DAKOTA

Butte

Bozeman

Sweetgrass

 arch

Bears Paw

Mountains

MONTANA

MONTANA

THRUST BELT

PROVINCE

HELENA

SOUTHWEST

MONTANA

PROVINCE

POWDER RIVER

BASIN PROVINCE

WILLISTON BASIN

PROVINCE

 CENTRAL

MONTANA

 TROUGH

Billings

Great Falls

NORTH-CENTRAL 

MONTANA

PROVINCE

–113° –112° –111° –110° –109° –108° –107° –106° –105° –104° –103°

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

48°

49°

47°

46°

45°

MONTANA

IDAHO WYOMING

SOUTH 

DAKOTA

Map area

NORTH 

DAKOTA

CANADA

Figure 1. Map showing the location of six assessment units (AUs) in the North-Central Montana Province.
Sevier event; (7) Late Cretaceous through 

early Tertiary subhorizontal subduction 

and compression from the Laramide 

orogenic event; and (8) uplift, erosion, 

and structural trap formation related to 

the emplacement of intrusive rocks in 

the Eocene (Baker and Johnson, 2000). 

These events shaped the structural and 

stratigraphic evolution and the development of petroleum systems in the NorthCentral Montana Province (fig. 2).

Total Petroleum Systems and 

Assessment Units

The USGS defined four total petroleum systems (TPSs) and six assessment 

units (AUs) within these TPSs, guided by 

previous work (Dyman and others, 1995; 

Anna, 2010). The Upper Cretaceous–

Paleogene Biogenic Gas TPS includes the 

Upper Cretaceous Conventional Biogenic 

Gas AU and the Upper Cretaceous–

Paleogene Biogenic Coalbed Gas AU. 

This TPS is defined by the presence of 

recoverable biogenic gas contained within 

shallow sandstone and coal reservoirs 

(Payenberg and others, 2003; Anna, 2010; 

Fishman and others, 2012). Gas was 

generated through biologic processes 

acting on thermally immature shales and 

coals, and accumulations of biogenic gas 

are the principal petroleum resources in 

the province. 

The Jurassic TPS, which includes 

the Jurassic–Cretaceous Reservoirs AU, 

is poorly understood, and petroleum 

source rocks might be present along the 

flanks of the Sweetgrass arch in the western part of the province (fig. 1). Based on 

limited data, Jurassic source rocks have 

total organic carbon (TOC) values up to 

3.5 weight percent and contain Type II 

organic matter (Aram, 1993).

The Devonian–Mississippian 

Composite TPS may include petroleum 

source rocks of the Bakken, lower part of 

the Madison, and the Heath Formations, 

which were deposited in the central 

Montana trough. These source rocks contain marine Type II organic matter, have 

TOC values up to 12 weight percent, and 

are in the thermal maturity window for oil 

generation (Jarvie, 2001; Jarvie and others, 

2016). Continuous (unconventional) oil 

resources of the Heath TPS were assessed 

previously (Drake and others, 2017). 

The Devonian–Mississippian Composite 

TPS includes oil in the Pennsylvanian 

Tyler Sandstones AU and the Devonian–

Mississippian Carbonates AU. 

The Ordovician TPS was defined 

to encompass oil and gas generated 

from Ordovician marine organic matter 

in the central Montana trough. Similar 

Ordovician organic-rich shales in the 

Williston Basin have TOC values ranging up to 6 weight percent, and hydrogen 

index values to 800 milligrams of hydrocarbon per gram of total organic carbon 

(Nesheim, 2017). Thermal maturity of 

potential Ordovician source rocks is interpreted to be mainly in the oil-generation 

window. The TPS includes the Ordovician 

Red River-Bighorn Dolomite AU. 

Undiscovered oil and gas resources 

within the Ordovician TPS and the 

Devonian–Mississippian Composite TPS 

are focused within the area of the central 

Montana trough, as the trough apparently 

was connected to the Williston Basin 

during the Ordovician Period through the 

Mississippian Subperiod.

The assessment input data are 

summarized in table 1. For the continuous 

assessment unit, well drainage areas, success 

ratios, and estimated ultimate recoveries are 

taken from U.S. coalbed-gas analogs.

Undiscovered Resources Summary

The USGS quantitatively assessed 

undiscovered conventional and continuous 

oil and gas resources in six assessment 

units within the North-Central Montana 

Province (table 2). The estimated mean 

totals for undiscovered resources are 

55 million barrels of oil (MMBO) with 

an F95–F5 range from 0 to 139 MMBO; 

846 billion cubic feet of gas (BCFG) 

with an F95–F5 range from 145 to 

2,144 BCFG; and 6 million barrels of 

natural gas liquids (MMBNGL) with an 

F95–F5 range from 0 to 15 MMBNGL. 

The estimated mean of 55 MMBO is 

subdivided as follows: 3 MMBO are in 

the Jurassic–Cretaceous Reservoirs AU, 

7 MMBO are in the Pennsylvanian Tyler 

Sandstones AU, 25 MMBO are in the 

Devonian–Mississippian Carbonates AU, 

and 20 MMBO are in the Ordovician Red 

River-Bighorn Dolomite AU.

For the Upper Cretaceous 

Conventional Biogenic Gas AU, the estimated mean is 171 BCFG with an F95–F5 

range from 35 to 459 BCFG, and in the 

Upper Cretaceous–Paleogene Biogenic 

Coalbed Gas AU, the estimated mean is 

585 BCFG with an F95–F5 range from 110 

to 1,454 BCFG. Biogenic gas accounts for 

about 90 percent of the estimated mean 

undiscovered, recoverable gas resources in 

the North-Central Montana Province.

Cambrian

Middle

Proterozoic

Interlake 

Stony Mountain

Red River 

Belt

Supergroup

Devils Glen

Winnipeg

Pilgrim

Park

Meagher

Wolsey

Flathead

rocks undiff.

rocks undiff.

Souris River

Duperow

Paleozoic

Devonian Silurian Ordovician

Birdbear

Big Snowy

Group

Mission Canyon

Lodgepole

P TF

Bakken

Charles Castle Reef

Amsden

 Group

Madison

Group

Penn.

Alaska

Bench

Tyler

Heath

Kibbey

Triassic Perm. Mississippian

Otter

Skull Creek Thermopolis

Colorado (basal pt.)

Kootenai

Ellis Group

Morrison

Swift

Piper

Rierdon

Jurassic

Hell Creek

Fox Hills

Bearpaw

Judith River

Telegraph Creek

Greenhorn

Belle Fourche

Mowry

Muddy

Eagle

Claggett

Fort Union and younger rocks

Erathem/

System Tert.

Formations

Central Northern

Niobrara and Carlile, undiff. 

Virgelle

Cretaceous

Cen. Mesozoic

?

Figure 2. Stratigraphic column for the North-Central Montana Province showing the 

stratigraphic extent of the four total petroleum systems defined in this study. Modified from 

Dyman and others, 1995. (Cen., Cenozoic; P, Potlach Formation; Penn.; Pennsylvanian; Perm., 

Permian; pt., part; Tert., Tertiary; TF, Three Forks Formation; undiff., undifferentiated) 
Table 1. Key input data for six assessment units in the North-Central Montana Province.

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

area, and success ratios are defined partly using U.S. coalbed-gas analogs. The average EUR input is the minimum, median, maximum, and calculated mean. Shading 

indicates not applicable]

Assessment input data—

Conventional AUs

Upper Cretaceous Conventional Biogenic Gas AU Jurassic–Cretaceous Reservoirs AU

Minimum Median Maximum Calculated 

mean

Minimum Median Maximum Calculated 

mean

Number of oil fields 1 3 10 3.2

Number of gas fields 1 10 50 11.4 1 2 4 2.1

Sizes of oil fields (MMBO) 0.5 1 10 1.3

Sizes of gas fields (BCFG) 3 6 600 14.9 3 6 60 7.7

AU probability 1.0 0.8

Assessment input data—

Conventional AUs

Pennsylvanian Tyler Sandstones AU Devonian–Mississippian Carbonates AU

Minimum Median Maximum Calculated 

mean

Minimum Median Maximum Calculated 

mean

Number of oil fields 1 5 14 5.3 1 10 40 11.0

Sizes of oil fields (MMBO) 0.5 1 20 1.5 0.5 1 100 2.5

AU probability 0.9 0.9

Assessment input data—

Conventional AU

Ordovician Red River-Bighorn Dolomite AU

Minimum Median Maximum Calculated 

mean

Number of oil fields 1 15 60 16.6

Number of gas fields 1 3 12 3.3

Sizes of oil fields (MMBO) 0.5 1 20 1.5

Sizes of gas fields (BCFG) 3 8 1,500 8.9

AU probability 0.8

Assessment input data—

Continuous AU

Upper Cretaceous–Paleogene Biogenic Coalbed Gas AU

Minimum Mode Maximum Calculated 

mean

Potential production area of AU (acres) 400 5,507,500 11,015,000 5,507,633

Average drainage area of wells (acres) 40 100 160 100

Success ratio (%) 2 7 25 11.3

Average EUR (BCFG) 0.04 0.08 0.3 0.092

AU probability 1.0

Table 2. Assessment results for six assessment units in the North-Central Montana Province.

[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. For gas accumulations, all liquids are included in the NGL category. 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 systems 

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

Upper Cretaceous–Paleogene Biogenic Gas Total Petroleum System

Upper Cretaceous Conventional Biogenic 

Gas AU 1.0 Gas 35 128 459 171 0 0 0 0

Jurassic Total Petroleum System

Jurassic–Cretaceous Reservoirs AU 0.8 Oil 0 3 8 3 0 1 2 1 0 0 0 0

Gas 0 12 30 13 0 0 0 0

Devonian–Mississippian Composite Total Petroleum System

Pennsylvanian Tyler Sandstones AU 0.9 Oil 0 6 16 7 0 1 3 1 0 0 0 0

Devonian–Mississippian Carbonates AU 0.9 Oil 0 19 68 25 0 15 55 20 0 0 0 0

Ordovician Total Petroleum System

Ordovician Red River-Bighorn Dolomite AU 0.8 Oil 0 19 47 20 0 29 76 31 0 6 15 6

Gas 0 20 65 24 0 0 0 0

Total undiscovered conventional resources 0 47 139 55 35 206 690 261 0 6 15 6

Upper Cretaceous–Paleogene Biogenic Gas Total Petroleum System

Upper Cretaceous–Paleogene Biogenic Coalbed 

Gas AU 1.0 Gas 110 467 1,454 585 0 0 0 0

Total undiscovered continuous resources 110 467 1,454 585 0 0 0 0

Total undiscovered resources 0 47 139 55 145 673 2,144 846 0 6 15 6
ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20173092

North-Central Montana Province Assessment Team

Christopher J. Schenk, Tracey J. Mercier, Michael E. Brownfield, Marilyn E. Tennyson, Cheryl A. Woodall, Phuong A. Le, 

Timothy R. Klett, Stephanie B. Gaswirth, Thomas M. Finn, Janet K. Pitman, Kristen R. Marra, and Heidi M. Leathers-Miller

For More Information

Assessment results are also available at the USGS Energy Resources Program website at https://energy.usgs.gov.

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