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U.S. Department of the Interior

U.S. Geological Survey

Printed on recycled paper

 Introduction

The U.S. Geological Survey (USGS) recently 

completed an assessment of the undiscovered 

oil and gas potential of the Montana Thrust Belt 

Province of northwestern Montana (fig. 1). The 

assessment of the Montana Thrust Belt Province is based on the geologic elements of each 

Total Petroleum System defined in the province, 

including hydrocarbon source rocks (source-rock 

maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and 

petrophysical properties), and hydrocarbon traps 

(trap formation and timing). Using this geologic framework, the USGS defined seven Total 

Petroleum Systems (TPS) and nine Assessment 

Units within these Total Petroleum Systems and 

quantitatively estimated the undiscovered oil and 

gas resources within seven of the nine Assessment Units (table 1).

Resource Summary

The USGS assessed undiscovered conventional oil and gas and continuous (unconventional) oil. The USGS estimated a mean of 8.6 

trillion cubic feet of gas (TCFG), a mean of 109 million barrels of 

oil (MMBO), and a mean of 240 million barrels of total natural gas 

liquids (MMBNGL) in five Total Petroleum Systems. Nearly all (99 

percent) of the undiscovered gas resource is conventional, whereas 

about 75 percent of the undiscovered oil resource is conventional 

(table 1). Of the 8.6 TCFG, about 7.7 TCFG is estimated to be in 

the Paleozoic/Mesozoic Composite Total Petroleum System of 

the Thrust Belt, and 0.68 TCFG is in the Central Montana Trough 

Paleozoic Composite Total Petroleum System of the Helena Salient. 

The remainder of the gas (about 0.28 TCFG) is associated/dissolved 

gas in oil accumulations (table 1). Because the USGS assessment 

of natural gas is for total gas, th

may contain significant percenta

gases, such as carbon dioxide.

The Tertiary Lacustrine Shal

mated to contain a mean of abou

whereas the Marias River Shale 

to contain about 28 MMB of con

Bakken Formation and Jurassic/

were not quantitatively assessed 

Figure 1. Montana Thrust Belt Prov

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8.80 58.20 164.60 68.80 15.10 101.50 309.30 124.10 

11.80 68.60 191.50 80.90 1,100.50 7,132.00 20,674.20 8,526.80 

12.90 25.50 50.60 27.90 46.80 100.10 214.30 111.40 

12.90 25.50 50.60 27.90 46.80 100.10 214.30 111.40 

24.70 94.10 242.10 108.80 1,147.30 7,232.10 20,888.50 8,638.20 

Oil

Oil

Oil

CBG

Continuous Oil and Gas Resources

Tertiary Basins Oil AU

Bakken Continuous Oil

Marias River Shale Continuous Oil

Jurassic/Cretacous Coal-Bed Gas

Total Continuous

Resources

Total Undiscovered

Oil and Gas Resources

Tertiary Lacustrine 

Shale TPS 

Bakken Formation TPS 

Marias River Shale TPS 

Jurassic/Cretaceous TPS 

Total Conventional

Resources

Not quantitatively assessed

Not quantitatively assessed

For Further Information

Supporting geologic studies of Total Petroleum Systems and 

Assessment Units, and reports on the methodology used in the Montana Thrust Belt Province assessment, are in progress. Assessment 

results are available at the USGS Central Energy Team website:

http://energy.cr.usgs.gov/oilgas/noga/

Montana Thrust Belt Assess

Christopher J. Schenk (Task 

R. Charpentier, Troy A. Cook, T

French, Mitchell E. Henry, Tim

Richard M. Pollastro, and Chris

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