Chapter 3

Cretaceous–Tertiary Composite Total 

Petroleum System (503402), Bighorn Basin, 

Wyoming and Montana

By Thomas M. Finn, Mark A. Kirschbaum, Stephen B. Roberts, Steven M. Condon, 

Laura N.R. Roberts, and Ronald C. Johnson

Chapter 3 of

Petroleum Systems and Geologic Assessment of Oil and Gas in the 

Bighorn Basin Province, Wyoming and Montana

By U.S. Geological Survey Bighorn Basin Province Assessment Team

U.S. Geological Survey Digital Data Series DDS–69–V

U.S. Department of the Interior

U.S. Geological Survey

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Volume Title Page
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Finn, T.M., Kirschbaum, M.A., Roberts, S.B., Condon, S.M., Roberts, L.N.R., and Johnson, R.C., 2010, Cretaceous–

Tertiary Composite Total Petroleum System (503402), Bighorn Basin, Wyoming and Montana: U.S. Geological Survey 

Digital Data Series DDS–69–V, 157 p.

ISBN: 1–4113–2667–5.
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Structural and Tectonic Setting...................................................................................................................1

Depositional Setting ......................................................................................................................................7

Stratigraphy ....................................................................................................................................................7

Cloverly Formation..............................................................................................................................11

Thermopolis Shale..............................................................................................................................11

Muddy Sandstone ..............................................................................................................................11

Mowry Shale........................................................................................................................................11

Frontier Formation...............................................................................................................................13

Cody Shale ...........................................................................................................................................13

Mesaverde Formation........................................................................................................................13

Meeteetse Formation, and Lewis and Bearpaw Shales ..............................................................17

Lance Formation..................................................................................................................................18

Fort Union Formation..........................................................................................................................20

Lower Eocene Rocks..........................................................................................................................21

Cretaceous–Tertiary Composite Total Petroleum System (503402).....................................................22

Source Rocks................................................................................................................................................22

Reservoir Rocks ...........................................................................................................................................24

Traps and Seals............................................................................................................................................29

Thermal Maturity..........................................................................................................................................29

Hydrocarbon Generation............................................................................................................................29

Events Chart..................................................................................................................................................32

Assessment Units and Results ..................................................................................................................35

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas 

Assessment Unit (AU 50340261)..........................................................................................38

Mowry Fractured Shale Continuous Oil Assessment Unit (AU 50340262).................................41

Cody Sandstone Continuous Gas Assessment Unit (AU 50340263)............................................43

Mesaverde Sandstone Continuous Gas Assessment Unit (AU 50340264) ................................45

Mesaverde-Meeteetse Formation Coalbed Gas Assessment Unit (AU 50340281)..................49

Fort Union Formation Coalbed Gas Assessment Unit (AU 50340282).........................................52

Cretaceous–Tertiary Conventional Oil and Gas Assessment Unit (AU 50340201)....................54

Acknowledgments.......................................................................................................................................55

References....................................................................................................................................................59

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry 

Fractured Shale Continuous Gas Assessment Unit (50340261) ..............................................67

Appendix B. Input parameters for the Mowry Fractured Shale Continuous 

Oil Assessment Unit (50340262)....................................................................................................80

Appendix C. Input parameters for the Cody Sandstone Continuous 

Gas Assessment Unit (50340263) .................................................................................................93

Appendix D. Input parameters for the Mesaverde Sandstone 

Continuous Gas Assessment Unit (50340264)..........................................................................106
iv

Appendix E. Input parameters for the Mesaverde-Meeteetse 

Coalbed Gas Assessment Unit (50340281) ...............................................................................119

Appendix F. Input parameters for the Fort Union Formation 

Coalbed Gas Assessment Unit (50340282) ...............................................................................132

Appendix G. Input parameters for the Cretaceous-Tertiary 

Conventional Oil and Gas Assessment Unit (50340201) .........................................................145

Figures

1. Index map showing location of the Bighorn Basin Province................................................2

2. Geologic map and cross section of Bighorn Basin, Wyoming and Montana.....................3

3. Tectonic map of Bighorn Basin, Wyoming and Montana ......................................................5

4. Map of Rocky Mountain region showing locations of Laramide 

sedimentary and structural basins and intervening uplifts ...................................................6

5. Map showing extent of the Western Interior Seaway during Campanian time.................8

6. Regional stratigraphic cross section of Cretaceous and Paleocene rocks.......................9

7. Stratigraphic correlation chart of Jurassic to lower Tertiary rocks ..................................10

8. Isopach map of the Muddy Sandstone...................................................................................12

9. Isopach map of the Mowry Shale............................................................................................14

10. Isopach map of the Frontier Formation...................................................................................15

11. Isopach map of the main body of the Cody Shale.................................................................16

12. Isopach map of the Claggett Member of the Cody Shale....................................................17

13. Isopach map of the lower member of the Mesaverde Formation 

and Eagle Sandstone .................................................................................................................18

14. Isopach map of the Mesaverde Formation ............................................................................19

15. Isopach map of the Meeteetse Formation including the Lewis 

and Bearpaw Shales..................................................................................................................20

16. Isopach map of the Lance Formation......................................................................................21

17. Isopach map of the Fort Union, Willwood, and Tatman Formations ..................................23

18. Map showing extent of the Cretaceous–Tertiary Composite Total Petroleum System ..24

19. Plots showing (A) total organic carbon content and (B) hydrogen index 

of Cretaceous marine shales....................................................................................................25

20. Map showing distribution and thickness of coal in the Mesaverde Formation...............26

21. Map showing distribution and thickness of coal in the Meeteetse Formation................27

22. Map showing distribution and thickness of coal in the Fort Union Formation.................28

23. Map showing locations of wells with mud-weight and drillstem test data......................30

24. Pressure-depth plots for five locations in the deep part of the Bighorn Basin ...............31

25. Diagrammatic cross section showing basin-centered gas accumulation.......................33

26. Map showing levels of thermal maturity for the top of the Cody Shale ............................34

27. Map showing levels of thermal maturity for the top of the Mesaverde Formation.........35

28. Timing of gas generation from Type-III gas-prone source rocks .......................................36

29. Timing of oil and gas generation from Type-II oil-prone source rocks..............................37

30. Events chart for the Cretaceous–Tertiary Composite Total Petroleum System...............38

31. Map showing the areal extent of the Muddy-Frontier Sandstone and 

Mowry Fractured Shale Continuous Gas Assessment Unit (50340261).............................39
v

32. Estimated ultimate recovery distributions for wells in the Frontier 

Formation, Muddy Sandstone, and Cloverly Formation and equivalents in the 

Southwestern Wyoming, Wind River Basin, and Bighorn Basin Provinces.....................40

33. Map showing areal extent of the Mowry Fractured Shale Continuous Oil 

Assessment Unit (50340262)......................................................................................................42

34. Estimated ultimate recovery distributions for wells producing from the 

Mowry Shale and Niobrara Formation in the Powder River Basin, Wyoming 

and Montana, and the Spraberry Formation in the Midland Basin, Texas .......................43

35. Map showing areal extent of the Cody Sandstone Continuous Gas 

Assessment Unit (50340263)......................................................................................................44

36. Estimated ultimate recovery distribution for wells in the Cody Sandstone 

Continuous Gas Assessment Unit in the Wind River Basin Province................................45

37. Comparison of well log responses of the upper part of the Cody Shale, 

Bighorn Basin, and Wind River Basin .....................................................................................46

38. Map showing coverage of commercially available seismic surveys 

in the Bighorn Basin, Wyoming and Montana.......................................................................47

39. Map showing areal extent of the Mesaverde Sandstone Continuous 

Gas Assessment Unit (50340264)..............................................................................................48

40. Map showing approximate depth to top of the Teapot Sandstone Member....................49

41. Estimated ultimate recovery distributions for wells producing from the 

Mesaverde, Lance, and Fort Union Formations in the Wind River Basin, Wyoming.......50

42. Map showing areal extent of the Mesaverde-Meeteetse Formation Coalbed 

Gas Assessment Unit (50340281)..............................................................................................51

43. Map showing areal extent of the Fort Union Formation Coalbed Gas 

Assessment Unit (50340282)......................................................................................................53

44. Map showing areal extent of the Cretaceous–Tertiary Composite Conventional 

Oil and Gas Assessment Unit (50340201)................................................................................55

45. Graphs showing grown field size versus discovery year....................................................56

46. Number of new field wildcats by drilling completion year..................................................57

47. Map showing drilling density in the Cretaceous–Tertiary Conventional Oil and Gas 

 Assessment Unit.........................................................................................................................58

Table

1. Summary of assessment results for the Cretaceous–Tertiary Composite 

Total Petroleum System, Bighorn Basin..................................................................................41
vi
Abstract

The Cretaceous–Tertiary Composite Total Petroleum 

System (TPS) produces oil and natural gas mainly from sandstone reservoirs in anticlinal traps around the margins of the 

Bighorn Basin, Wyoming and Montana. The reservoirs range 

from Early Cretaceous to Paleocene in age and are sourced 

by organic-rich Lower and Upper Cretaceous marine shales 

that contain both Type-II oil-prone and Type-III gas-prone 

organic matter, and by Upper Cretaceous and Paleocene coals 

that contain Type-III organic matter. New resource potential 

is expected to be mainly from conventional stratigraphic traps 

and from unconventional continuous-type accumulations. 

The Cretaceous–Tertiary Composite TPS is subdivided 

into (1) three basin-centered gas assessment units 

(AU)—Muddy-Frontier Sandstone and Mowry Fractured 

Shale Continuous Gas AU (50340261), Cody Sandstone 

Continuous Gas AU (50340263), and Mesaverde Continuous 

Gas AU (50340264); (2) one fractured shale oil 

accumulation—Mowry Fractured Shale Continuous Oil AU 

(50340262); (3) two coalbed gas accumulations—MesaverdeMeeteetse Coalbed Gas AU (50340281) and Fort Union 

Coalbed Gas AU (50340282); and (4) one conventional oil and 

gas AU—Cretaceous–Tertiary Conventional Oil and Gas AU 

(50340201). The Cretaceous–Tertiary Conventional Oil and 

Gas AU (50340201) and the Muddy-Frontier Sandstone and 

Mowry Fractured Shale Continuous Gas AU (50340261) both 

have established production; the other AUs have no production 

and are considered hypothetical. The mean estimate for 

undiscovered oil and gas resources that have potential for 

additions to reserves from Cretaceous and Tertiary rocks in the 

Bighorn Basin is about 18 million barrels of oil, 771 billion 

cubic feet of gas, and 5 million barrels of natural gas liquids.

Introduction

The Bighorn Basin Province (5034) is a large sedimentary and structural basin that formed during the Laramide 

orogeny (Late Cretaceous through Eocene). The basin covers 

approximately 10,400 mi2 in north-central Wyoming and a 

small part of south-central Montana (fig. 1). The basin is 

Cretaceous–Tertiary Composite Total Petroleum System 

(503402), Bighorn Basin, Wyoming and Montana

By Thomas M. Finn, Mark A. Kirschbaum, Stephen B. Roberts, Steven M. Condon, Laura N.R. Roberts, and 

Ronald C. Johnson

structurally bounded on the northeast by the Pryor Mountains, 

on the east by the Bighorn Mountains, and on the south by 

the Owl Creek Mountains. The north margin as defined in 

this report includes a zone of faulting and folding referred to 

as the Nye-Bowler lineament (Wilson, 1936). The northwest 

and west margins are formed by the Beartooth Mountains 

and Absaroka Range, respectively. The earliest commercial 

hydrocarbon production from Cretaceous reservoirs in the 

basin was established at Garland field (1906) and Greybull 

field (1907) (Fox and Dolton, 1996). Since then, cumulative 

production from Cretaceous and Tertiary reservoirs is about 

94 million barrels of oil (MMBO) and 830 billion cubic feet 

of gas (BCFG), primarily from sandstone reservoirs associated 

with anticlinal traps around the margins of the basin (fig. 1). 

The purpose of this report is to describe the geologic framework and petroleum geology, and to assess the undiscovered 

oil and gas resources of the Cretaceous and Tertiary rocks in 

the Bighorn Basin.

Structural and Tectonic Setting

Present-day structure of the Bighorn Basin developed 

primarily during the Laramide orogeny, a period of crustal 

instability that began during Late Cretaceous time and ended 

in early Eocene time (Gries, 1983a; Love, 1988). Many of 

the structures are the result of compressional deformation 

characterized by Precambrian basement-involved thrust 

faults (thick-skinned), wrench faults, and strongly folded and 

faulted anticlines and synclines. The northeast, east, and south 

margins of the basin are formed by basement-cored uplifts 

referred to as the Pryor, Bighorn, and Owl Creek Mountains, 

respectively (figs. 1, 2). These uplifts are flanked by highly 

folded and faulted sedimentary rocks that range from Cambrian to Paleocene in age, whereas the central part of the basin 

is covered by nearly flat-lying lower Eocene and undifferentiated Tertiary and Quaternary rocks that mask the structure of 

the older rocks in the central part of the basin (fig. 2).

The basin axis generally trends northwest-southeast but 

locally is north-south, and there is marked asymmetry with 

the steeper basin flank on the west (figs. 2, 3). In the footwall 

of the Oregon Basin fault, the basin axis roughly parallels the 
2 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

T

50

N

T

55

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T

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R94W R90W R85W

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S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

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T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Greybull

Sand Creek

Manderson

Worland

Hidden Dome

Dobie Ceek

Five Mile

Grass Creek

Walker Dome

Little

Grass Creek

Meeteetse

Oregon

Basin

Oregon

Basin, SE

Little

Buffalo

Basin

Badger

Basin

Silver

Tip

Heart

Mountain

Garland

Byron

Big Polecat

North Danker

Elk

Basin, NW

Clark

Fork, N

Elk Basin

Elk Basin, S

Golden

Dome

Dry

Creek

Montana

Wyoming

110°

45°

44°

109° 108° 107°

Precambrian rocks

Tertiary volcanic rocks

Oil field producing from

 Cretaceous or Tertiary

 reservoirs

Gas field producing from

 Cretaceous or Tertiary

 reservoirs

Bighorn Basin Province

Absaroka

Range

Beartooth

Mountains

Creek Mountains

Owl

Mountains

Bighorn 

Mountains

Pryor

Nye-Bowler

Rattlesnake Mountain

anticline

lineament

Big Trails fault

Cloverly Formation

Thermopolis anticline

Sheep 

Mountain

anticline

Byron

Greybull

0 10 20 30 40

MILES

Figure 1. Index map showing location of the Bighorn Basin Province, major structural elements, and oil and gas fields that 

produce from Cretaceous and Tertiary reservoirs.

fault, but toward the north end of the Oregon Basin anticline 

it is offset to the northwest (Blackstone, 1986a) and lies west 

of the Oregon Basin thrust fault (fig. 3). The deep basin trough 

west of the Oregon Basin thrust fault is variously referred to as 

the Clark’s Fork Basin or Clark’s Fork sub-basin (Gingerich, 

1983; Johnson and Finn, 1998a). In this area, the basin axis 

generally trends north-south and passes beneath the eastern 

edge of the Beartooth thrust near the Montana-Wyoming state 

line (fig. 3).

The northern boundary of the Bighorn Basin is formed 

by the Nye-Bowler lineament, a regional anticlinal trend 

extending about 60 mi east-southeast from the northern part of 

the Beartooth mountain front to the Pryor Mountains (figs. 2, 

3). This trend consists of a series of highly faulted anticlines 

and domes that Wilson (1936) interpreted to overlie a leftlateral basement shear zone. The Nye-Bowler lineament forms 

the structural divide separating the Bighorn Basin to the south 

from the Reed Point syncline and Crazy Mountains Basin to 

the northwest (fig. 4). Important petroleum accumulations 

associated with the Nye-Bowler lineament include Golden 

Dome and Dry Creek gas fields (fig.1).
Structural and Tectonic Setting 3

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Oregon Basin West Greybull

monocline

Rio thrust fault

Five Mile trend

Oregon Basin fault

East Hunt Energy 

Loch Katrine Unit 1 True

33-20 Rio

Amoco Production

1 Adams

Moncrief

Michaels Ranch

Forest Oil 

Emblem Bench 5,000

Sea level

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5,000

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A A'

Absaroka

Range

Beartooth

Mountains

Creek Mountains

Owl

Mountains

Bighorn 

Bighorn

Basin

Basin

Powder

River

AB #1

A KL #1 A'

Figure 2 (above and facing page). Geologic map and cross section of Bighorn Basin, Wyoming and Montana. 

Geologic map modified from Green and Drouillard (1994) and Raines and Johnson (1995). Cross section modified in part 

from Blackstone (1986a) and Stone (2004a). Vertical scale of cross section is in feet. AB #1, Amoco Beartooth no. 1 well; 

KL #1, Hunt Loch Katrine no. 1 well. 
4 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Quaternary–Tertiary

 undifferentiated

Miocene(?) sedimentary

 rocks

Oligocene sedimentary

 rocks

Upper Eocene sedimentary

 rocks

Lower Eocene sedimentary

 rocks

Eocene volcanic

 rocks

Paleocene sedimentary

 rocks

Upper Cretaceous

 sedimentary rocks

Lower Cretaceous

 sedimentary rocks

Lower Cretaceous–Jurassic

 sedimentary rocks

Triassic–Pennsylvanian

 sedimentary rocks

Mississippian–Cambrian

 sedimentary rocks

Precambrian crystalline

 rocks

High-angle fault,dashed

 where concealed

Thrust fault, dashed 

 where concealed 

Line of section 

Well location discussed

 in text 

Water features

Bighorn Basin Province 

KJ

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Tel

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pC

MAP UNITS

EXPLANATION

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The northwest margin of the basin is formed by the 

Beartooth Mountains, a Precambrian-cored uplift of Laramide 

age that is thrust fault-bounded and flanked by steeply 

dipping-to-overturned sedimentary strata (Foose and others, 

1961). The west margin is formed by the Absaroka Range, 

which is comprised mainly of Eocene andesitic volcanic and 

volcaniclastic rocks associated with large stratovolcanos 

(Sundell, 1993). These volcanic rocks are believed to unconformably overlie folded and faulted Paleozoic, Mesozoic, and 

lower Tertiary sedimentary rocks (Sundell, 1990). 

Major thrust faults in the Bighorn Basin include the 

Beartooth fault, the Line Creek fault, and the Oregon Basin 

fault on the west side of the basin, the Elk Basin fault in the 

north-central part, and the Rio thrust fault on the east (fig. 3). 

The Beartooth fault is the major basin-bounding fault in the 

northwestern part of the basin (fig. 3). The fault plane dips to 

the west-southwest and displacement is generally to the east 

and northeast, thrusting the Beartooth Mountains over Paleozoic and Mesozoic sedimentary rocks with approximately 

7.5 mi of overhang along the northwest margin of the basin 

(Bonini and Kinard, 1983). The fault was penetrated by the 

Amoco Beartooth #1 well (fig. 2), which was spudded in basement rocks on the Beartooth uplift approximately 1.5 mi west 

of the Precambrian contact. The well drilled through about 

8,400 ft of granitic rock before it encountered the fault zone, 

then drilled through a complexly faulted and folded sequence 

of sedimentary rocks to a total depth of about 13,800 ft (Wise, 

1997; 2000). The Line Creek fault, located in the western part 

of the basin (fig. 3), is an east-directed, west-dipping thrust 

fault that originates in Precambrian rocks and involves strata 

as young as the Paleocene Fort Union Formation (Blackstone, 

1986a). The fault starts near the Montana-Wyoming state line, 

and extends south to southeast approximately 40 mi (fig. 3). 

According to Parker and Jones (1986) the maximum vertical 

and horizontal displacements on the Line Creek fault are estimated to be about 12,000 ft and 10,000 ft, respectively. The 

fault is buried beneath the Eocene Willwood Formation.

The Oregon Basin fault, the major thrust fault along 

the west side of the basin, trends north-south to northwestsoutheast for about 80 mi and separates the relatively undeformed central deep trough of the basin to the east from the 

highly deformed basin margin on the west (fig. 3). According 

to Blackstone (1986a,b) the fault plane dips 40° to 70° to the 

west-southwest, flattening with depth and possibly extending 

beneath many of the anticlines along the west and southwest 

margins of the basin that contain important petroleum accumulations. Blackstone (1986a) estimated that the displacement, although variable, ranges to as much as 25,000 ft in 

the vicinity of Oregon Basin. It is concealed beneath rocks 

of the lower Eocene Willwood Formation but was penetrated 

in the Hunt Oil Company Loch Katrine no. 1 well on the east 

flank of the Oregon Basin anticline (fig. 2), which was drilled 

to evaluate deep gas potential in the subthrust (Rountree, 

1980). The well, spudded in sedimentary rocks west of the 

buried trace of the fault on the northeast flank of the Oregon 

Basin anticline, drilled through steeply dipping Mesozoic and 
Structural and Tectonic Setting 5

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T

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T

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T

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T

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R94W R90W R85W

R95W

R100W

R104W

T

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T

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T

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T

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S

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R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

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R3E

Montana

Wyoming

45°

44°

110° 109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Anticline

Syncline

Thrust fault

High-angle fault, dashed

 where inferred

Physiographic or structural

 feature mentioned in text

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

? ?

8

+ + +

Clark's

Fork

sub-basin

Basin

axis

F

M

7

8

2

5

9

3

4

6

1

Paleozoic sedimentary rocks until it encountered the fault 

zone at around 10,500 ft. Below the fault, the well penetrated 

several thousand feet of vertical to overturned Mesozoic 

rocks before drilling through a relatively flat-lying section of 

Mesozoic and Paleozoic sedimentary rocks to a total depth 

of 23,990 ft (fig. 2) (Parker and Jones, 1986; Blackstone, 

1986a,b; Stone, 1985).

East of and parallel to the northern segment of the 

Oregon Basin fault is the Elk Basin fault (fig. 3) (Ryder, 1987; 

Stone, 1983), a west-dipping, east-directed thrust fault rooted 

in Precambrian crystalline rocks and terminating in Upper 

Cretaceous rocks in the subsurface (Ryder, 1987; Stone, 1983). 

The fault trends north-south about 25 mi but may extend 

southward several miles, merging with the Oregon Basin fault 

in the deep part of the basin trough (Talbot, 1996). Several 

important oil accumulations are associated with, and located 

on, the hanging wall of the Elk Basin thrust, including Elk 

Basin field that has an estimated grown accumulation size of 

about 20 MMBO in Cretaceous reservoirs (fig. 1). The most 

important thrust fault on the east side of the Bighorn Basin 

Figure 3. Tectonic map of Bighorn Basin, Wyoming and Montana, showing major structural features discussed in text (1) 

Beartooth thrust fault, (2) Line Creek thrust fault, (3) Oregon Basin thrust fault, (4) Elk Basin thrust fault, (5) Rio thrust fault, 

(6) Tensleep fault, western extension dashed where inferred, (7) Oregon Basin anticline, (8) Grass Creek anticline, and (9) 

Five Mile trend. Sources of data from Wilson (1936), Ver Ploeg (1985), and Stone (1993, 2004b).
6 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

0 50 100 MILES

MT

ID

MT

WY

ND

SD

WY

CO

NE

ID

UT

UT CO

AZ NM

CO

NM

Black Hills uplift

uplift Casper

arch

Owl Creek uplift

Powder

River Basin

Crazy

Mountains

Basin

Bull

Mountains Basin

Absaroka

volcanics

San

Juan

volcanic

eld

San Juan

Basin

Raton Basin

Denver

Uinta Basin

Piceance

Basin

Greater Green

River Basin

Wind River Basin

Basin

Hanna

Basin

Hartville uplift

Ra

uplif

wlins

t

Uinta uplift

Granite Mountains

uplift

Wind

River uplift

White

River

uplift

Gunnison uplift

Nacimiento

uplift

Rio

Grande rift

Sangre

de

Cristo uplift

Sangre

de

Cristo uplift

Park Range

uplift

Sierra Madre

uplift

Uncompahgre

uplift

Bridger

uplift

Bear

uplif

tooth

t

Miles City arch

San Rafael

Swell

Medicine

Bow uplift

Shirley

Basin

Laramie

Basin

North and Middle

Park Basins

South Park

Basin

Sawatch

uplift

Front Range

uplift

San Juan

uplift

Axial Basin uplift

Teton uplift

Basin

Thrust or

 reverse fault

Cordilleran

orogenic

belt

(Neogene)

NE

SD

WY

Bighorn

Bighorn

Reed Point syncline

Pryor

Mtns.

Nye-Bowler lineament

112° 110° 108° 106° 104°

46°

44°

42°

40°

38°

36°

Figure 4. Map of Rocky Mountain region extending from southern Montana to northern 

New Mexico showing locations of Laramide sedimentary and structural basins (in brown) and 

intervening uplifts. Modified from Dickinson and others (1988).
Stratigraphy 7

is the Rio thrust named by Stone (2004a). It trends about 

35–40 mi northwest-southeast, dips east-northeast, is westsouthwest-vergent, and separates the relatively undeformed 

central deep part of the Bighorn Basin on the west from the 

highly deformed basin margin on the east (figs. 2, 3). The fault 

originates in Precambrian basement rocks, with displacements 

of around 3,000 to 4,000 ft, and dies out in Cretaceous rocks 

in the subsurface (Stone, 2004a). 

The Tensleep fault, located in the southern part of the 

basin, is a major high-angle fault that, according to Allison 

(1983, 1986), extends from the Precambrian core of the Bighorn Mountains due west about 30 mi where it is obscured by 

Upper Cretaceous sedimentary rocks (figs. 2, 3). Stone (1969, 

1985, 1993, 1999, 2004b) extended the fault into the subsurface across the southern part of the Bighorn Basin to the vicinity of Grass Creek anticline and possibly to the eastern edge 

of the Absaroka Range, effectively separating the central part 

of the deep basin trough from the deformed southern margin 

(fig. 3). The nature of the Tensleep fault is questionable and 

has been variously described as a near-vertical normal fault, 

downthrown to the south (Allison, 1983, 1986), and as a leftlateral wrench fault by Stone (1969, 1985, 1993).

Around the margins of the Bighorn Basin are numerous anticlines, many of which are located on the hanging 

walls of the Rio, Oregon Basin and Line Creek thrust faults 

(fig. 3) (Ver Ploeg, 1985; Blackstone, 1986a,b; Stone, 1985, 

2004a). These folds involve sedimentary rocks ranging from 

Paleozoic through Paleocene in age, are typically asymmetric, commonly thrust fault-bounded along their steep flanks, 

and generally trend northwest-southeast. Blackstone (1986b) 

believed that many of these features originated as back-limb 

thrusts on the hanging wall of the Oregon Basin thrust fault. 

Many important oil and gas fields are associated with these 

features—for example, Oregon Basin, Little Buffalo Basin, 

and Grass Creek fields (fig. 1).

The deep central part of the Bighorn Basin is a relatively 

undeformed area that is bounded by the Oregon Basin fault 

on the west, the Rio thrust fault on the east, and possibly the 

western extension of the Tensleep fault on the south (fig. 3). 

This part of the basin is markedly asymmetric with regional 

dip to the west where the deep basin axis is adjacent to or 

overridden by the Oregon Basin thrust fault (fig, 3). According to Johnson and Finn (1998a), the elevation change at the 

Teapot Sandstone Member level is about 11,000 ft from east to 

west. The most prominent structural feature in the central part 

of the basin is referred to as the Five Mile trend by Fox and 

Dolton (1989, 1996), Johnson and Finn (1998a), and Stone 

(2004b). It extends about 50 mi northwest across the deep 

central part of the basin (fig. 3). The Five Mile trend is thrust 

fault-bounded on its northeast flank, plunges to the northwest 

and appears to die out in the deep part of the basin. Important 

fields along the Five Mile trend include Five Mile and Dobie 

Creek (fig. 1).

Depositional Setting

During much of Cretaceous time, the part of Wyoming 

and Montana that is now the Bighorn Basin was located near 

the western edge of the Rocky Mountain foreland basin, an 

elongate north-south structural depression that developed to 

the east of the tectonically active Western Cordilleran highlands. Throughout much of its history, the foreland basin was 

flooded by a broad epicontinental sea, referred to as the Western Interior Seaway (WIS) that developed in response to foreland basin subsidence and eustatic sea-level rise (Steidtmann, 

1993) (fig. 5). At its maximum extent, the seaway extended a 

distance of more than 3,000 mi from the Arctic Ocean to the 

Gulf of Mexico (Kauffman, 1977).

Fluctuations in relative sea level and variations in 

sediment supply along the western shoreline of the seaway 

during much of Cretaceous time resulted in a complex pattern 

of intertonguing marine, marginal marine, and nonmarine 

deposits (fig. 6). Marine deposition ended near the close of 

the Cretaceous Period (early Maastrichtian), as the foreland 

basin gradually filled and the western shoreline of the seaway 

retreated eastward. The uppermost Cretaceous strata also 

record the onset of the Laramide orogeny (Dickinson and 

others, 1988; Johnson and others, 2004), a period of crustal 

instability and compressional tectonics that commenced in 

early Maastrichtian time and fragmented the Rocky Mountain 

foreland basin into numerous smaller structural basins that 

were flanked by rising basement-cored uplifts (fig. 4). Basins 

such as the Bighorn Basin subsided rapidly and became depocenters for thick accumulations of clastic debris eroded from 

the surrounding uplifts during latest Cretaceous and Paleocene 

time. During Eocene time, the basin continued to be filled 

with volcaniclastic debris that originated in the YellowstoneAbsaroka volcanic area to the west (Love, 1988). Volcanic 

activity ended by Oligocene time but basin filling continued as 

Oligocene and Miocene volcaniclastic sediments spilled over 

the crest of the Bighorn Mountains and were deposited in the 

Powder River Basin to the east (McKenna and Love, 1972). 

In middle Miocene time regional uplift initiated the exhumation of the surrounding uplifts and the excavation of the basin 

which continues to the present day (Love, 1988).

Stratigraphy

Figure 7 shows the stratigraphic nomenclature used in 

this report and the change in nomenclature from the Wyoming 

part of the Bighorn Basin to the Montana part. The Wyoming nomenclature is from Keefer and others (1998), and the 

Montana nomenclature is modified from Johnson and Finn 

(2004) for the area in the vicinity of the Nye-Bowler lineament (fig. 1). The change in nomenclature is also illustrated on 

the regional cross section in figure 6, and on the north-south 

stratigraphic cross section presented by Finn (Chapter 6, this 

CD–ROM).
8 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Study

area

?

KILOMETERS

MILES

INTERIOR

WESTERN

SEAWAY

WESTERN

CORDILLERA

PACIFIC

OCEAN

OCEAN

OCEAN

ATLANTIC

ARCTIC

GULF

OF MEXICO

ALASKA

GREENLAND

CANADA

CUBA

MEXICO

Figure 5. Map showing extent of the Western Interior Seaway during Campanian time. Brown areas show 

approximate geographic distribution of land areas. Modified from Gill and Cobban (1973). 
0

0

5 10 15 20 MILES

500

FEET

1,000

Lewis Shale

Meeteetse Formation

Lower member Claggett Member of Cody Shale

Teapot Sandstone Member

Mesaverde Formation (middle part)

Cody Shale

Cody Shale

Cloverly Formation Jurassic rocks, undivided

(part)

Thermopolis Shale

Frontier Formation

"chalk kick

Muddy Sandstone

Mesaverde Formation

?

?

?

Bearpaw Shale

Lennep Sandstone

Eagle Sandstone

Parkman Sandstone

Telegraph Creek Formation

Judith River Formation

Claggett Shale

Virgelle Sandstone Member

Lance Formation

Lance Formation

Hell Creek Formation

Fort Union Formation

(part)

Fort Union Formation

(part)

North Montana Wyoming So

Nye-Bowler

lineament

Badger

Basin

McCulloch

Peak

Cottonwood

Creek

"chalk kick"

Emblem

Bench

Red

Point Fritz Dobie Creek Five Mile Worland

Mowry Shale

Cody Shale

Montana

Wyoming

Figure 6. Regional northwest-southeast stratigraphic cross section of Cretaceous and Paleocene (part) rocks, Bighorn Basin, Wyoming Montana. Colors represent different lithologies and environments of deposition: red, fluvial sandstone and conglomerate; yellow, marine amarine sandstone and siltstone; orange, fluvial and estuarine sandstone; tan, tidal sandstone, siltstone, and shale; various shades of gray, shales; various shades of green, coastal plain and floodplain sandstones, shales, and coals; brown, sandstone, siltstone, shale, coal and cof continental origin.
10 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

PALEOCENE UPPER CRETACEOUS

CRETACEOUS TERTIARY (part)

EOCENE (part)

JURASSIC

(part)

LOWER CRETACEOUS

?

?

System Series

Cody Shale

"chalk kick" "chalk kick" "chalk kick"

Cody Shale Cody Shale

Telegraph Creek Fm.

Mowry Shale

Meeteetse Formation

Lance

Formation

Fort Union

Formation

Muddy Sandstone

Thermopolis Shale

Morrison Formation

Tatman Formation

Claggett Mbr.

Lower

member

Mesaverde Formation

Teapot Ss. Member

Frontier Formation Frontier Formation Frontier Formation

Lewis Sh.

Willwood Formation

Northern Bighorn Basin Northern Bighorn Basin Southern Bighorn Basin

Bearpaw Shale Bearpaw Shale

Lennep Sandstone

Willwood Formation

Wasatch Formation

Mowry Shale Mowry Shale

Muddy Sandstone Muddy Sandstone

Thermopolis Shale Thermopolis Shale

Morrison Formation Morrison Formation

Cloverly

Formation

Cloverly

Formation

Cloverly

Formation

Lance

Formation

Hell Creek

Formation

Meeteetse

Fm. Lewis Sh.

Fort Union

Formation

Fort Union

Formation

Mesaverde Formation

Mesaverde

Formation

(main part)

Mesaverde

Formation

(main part)

Lower

member

Claggett Shale Claggett Mbr.

Eagle Sandstone

Virgelle Ss. Mbr.

Parkman Sandstone

Judith River

Formation

Teapot Ss. Member

Montana Wyoming Reservoirs

Gas Oil

Source rock Coal

Pryor Conglomerate

Mbr.

Pryor Conglomerate

Mbr.

Pryor Conglomerate

Mbr.

Greybull Ss. Mbr. Greybull Ss. Mbr. Greybull Ss. Mbr.

"rusty beds" "rusty beds" "rusty beds"

middle

part

middle

part

S

S

S C

S C

S C

S

S

<1%

<1% <1%

<1%

<1% <1%

<1% <1%

<1% <1%

14%

2%

1.5%

80% 96%

5%

c

Figure 7. Stratigraphic chart showing the Jurassic to lower Tertiary rocks in the Bighorn Basin, Wyoming and 

Montana. Major and minor oil and gas reservoirs indicated by green or red circles, respectively, with relative 

importance shown by size and percentage of production. Source rocks indicated with the letter “S”. Coal-bearing 

units indicated with the letter “C”, with relative importance shown by size. Modified from Keefer and others (1998); 

Johnson and Finn (2004); and Finn, Chapter 6, this CD-ROM.
Stratigraphy 11

Cloverly Formation

The basal Cretaceous rocks are represented by the 

Cloverly Formation, which consists of 210 to 385 ft of 

interbedded sandstone, variegated shale, claystone, and minor 

amounts of conglomerate (Keefer and others, 1998) (fig. 7). 

The basal unit, where present is the Pryor Conglomerate 

Member, consists of sandstone, conglomeratic sandstone, 

and black and gray chert-pebble conglomerate and has an 

irregular distribution. The middle part of the formation is 

comprised of variegated shale and claystone interbedded with 

thin sandstones that accumulated in flood-plain, fluvial, and 

lacustrine environments; Moberly (1960) included these strata 

in his Little Sheep Mudstone and Himes Members. These 

units are overlain by very fine to medium-grained sandstone 

referred to as the Greybull Sandstone Member (Hintze, 1914; 

Mills, 1956; Keefer and others, 1998). The thickness of the 

Greybull is highly variable, ranging from 5 to 70 ft (Keefer 

and others, 1998), but is locally absent. It represents the initial 

marine transgression during Albian time and is interpreted 

to be a fluvial/estuarine channel deposit that accumulated in 

paleovalleys formed on a lowstand surface that developed 

on the nonmarine part of the Cloverly Formation (Mitchell, 

1997; Furer and others, 1997). The uppermost part of the 

Cloverly Formation referred to as the “Rusty beds” by Love 

and others (1945), as the “Rusty Beds Member” by Keefer 

and others (1998), and in this report as the “rusty beds”, 

consist of finely laminated siltstone and shale with minor 

thin sandstone beds that accumulated in tidal flats during the 

continued transgression of the Cretaceous sea during Albian 

time (Moberly, 1960). The “rusty beds” are included in the 

lower part of the overlying Thermopolis Shale by numerous 

authors (for example, Mills, 1956; Eicher, 1962). The Greybull 

Sandstone Member and “rusty beds” have a combined 

thickness of about 100 ft throughout most of the basin but 

range to as much as 160 ft. These units are referred to together 

as the Sykes Mountain Formation by Moberly (1960). Based 

on fission track dating, the age of the Cloverly Formation 

ranges from Neocomian to Albian (Heady, 1992; May and 

others, 1995; Zaleha, 2006).

Thermopolis Shale

The Thermopolis Shale (known as the Skull Creek Shale 

in some other Rocky Mountain Basins), as used in this report, 

refers to the lower part of the Thermopolis Shale of Lupton 

(1916), Mills (1956), and Haun and Barlow (1962); it overlies the “rusty beds” of the Cloverly Formation and underlies 

the Muddy Sandstone. The Thermopolis consists of 125 to 

230 ft of marine shales and siltstones and represents continued 

deposition during sea-level rise in Albian time (Burtner and 

Warner, 1984; Hagen and Surdam, 1984). The shales are dark 

gray to black, organic-rich and contain thin layers of siltstone, 

sandy claystone, and bentonite. The basal contact is gradational with the underlying “rusty beds”; the upper contact may 

be sharp and unconformable or gradational with the overlying 

Muddy Sandstone.

Muddy Sandstone 

In this report, the Muddy Sandstone refers to a sandstonedominated interval located stratigraphically between the 

Thermopolis Shale and the overlying Mowry (Shell Creek) 

Shale (fig. 7). The unit is between about 7 and 125 ft thick 

(fig. 8) and consists of predominantly sandstone interbedded 

with lesser amounts of mudrock, and minor amounts of 

carbonaceous shale and coal. It is thickest in the southeastern 

part of the basin where it is dominated by sandstone and 

thinnest to the north-northwestern part of the basin where it 

consists of thin sandstones enclosed by marine shale. The age 

of the Muddy is latest Albian based on fossil evidence and 

radiometric dates obtained from strata just above and below 

the Muddy (Eicher, 1962; Obradovich, 1993).

According to the USGS database on stratigraphic names, 

the name Muddy was a driller’s term for “muddy” sands in 

the Thermopolis Shale of the Bighorn Basin and other areas 

of Wyoming (Hintze, 1915, p. 20–21; Geolex, 2008). No type 

area was designated, but a reference section was suggested 

by Eicher (1960) for exposures near the Greybull field in 

Bighorn County, Wyoming. Eicher (1960, 1962) used the 

term Muddy Sandstone, following previous workers, and 

provided extensive discussions of the Formation. Paull (1962) 

interpreted depositional environments to include deltaic, bar, 

back-bar, continental, and offshore marine environments. In 

their regional study, Dolson and others (1991) considered 

the Muddy to be a valley-fill complex and interpreted a 

lowstand shoreline in the vicinity of the Bighorn Basin. Long 

(1999) defined two parts to the Muddy, including valley-fill 

sandstones and shale and trangressive marine sandstone. In 

the present study, several cores and outcrops were interpreted 

to indicate a variety of environments—from freshwater to 

marine—within a complex valley-fill succession unit that 

unconformably overlies a lower offshore-marine section, 

generally included in the Thermopolis Shale.

Mowry Shale

The Mowry Shale was defined by Darton (1904) for 

exposures in the northwestern part of the Powder River 

Basin, and the top of the unit was revised by Rubey (1931) to 

include the Clay Spur Bentonite Bed. In the Bighorn Basin no 

definitive correlation can be made to the Clay Spur, but based 

on a comparison with well logs in the northern Wind River 

Basin and the Casper arch area, we placed the Mowry-Frontier 

contact at a distinctive high-gamma geophysical log response 

(Finn, Chapter 6, this CD–ROM; and Johnson, Chapter 7, this 

CD–ROM), which is stratigraphically lower than the contact 

of Goodell (1962) or of Van Houten (1962). According to 

Keefer and others (1998), the Mowry Shale in the Bighorn 

Basin consists of two distinct units. The lower unit consists of 
12 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

20

30

20

20

30

30

40

40

40

30

30

40

40

40

40

20

20

20

50

50

60

70

70

60

30

20

20

20

20

30

30

30

10

10

10

10

10

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Frontier/Mowry/Muddy/

 Thermopolis outcrop

Control point

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Rattlesnake Mountain

anticline

Figure 8. Isopach map of the Muddy Sandstone, Bighorn Basin, Wyoming and Montana; thickness interval 10 ft.

about 160 to 400 ft of soft fissile clay-rich shale similar to the 

Thermopolis Shale and is referred to as the upper Thermopolis 

Shale by several authors including Mills (1956) and Haun 

and Barlow (1962), and as the Shell Creek Shale by Eicher 

(1962). The upper unit consists of about 240 to 400 ft of hard 

brittle siliceous shale. Numerous gray to tan bentonite beds 

are common throughout the Mowry, ranging in thickness from 

less than one inch to about 7 ft (Byers and Larson, 1979).

The siliceous shales are dark brown to black, organic-rich, 

and contain an abundance of fish scales (Burtner and Warner, 

1984). Locally, there are thin fine-grained sandstones in the 

middle to upper part of the siliceous part of the Mowry. These 

units, referred to informally as the “Kimball” and “Octh 

Louie” sands, have produced oil from fields on the east side 

of the basin (Pierce, 1948; Mills, 1956; Cardinal and others, 

1989). Davis (1987) also described two sandstone bodies 

in the Mowry Shale along the east and northeast sides of 

the basin. These sandstones are fine- to medium-grained, 

as much as 15 ft thick, and form elongate bodies that Davis 

(1987) believed were deposited during a fall in sea level. The 
Stratigraphy 13

Mowry Shale is marine in origin with a combined thickness 

for the lower and upper parts ranging from about 400 ft in 

the southeastern part of the basin to more than 800 ft near 

the Beartooth Mountains (fig. 9). Paleontologic evidence 

and radiometric dating indicate that the upper siliceous part 

of the Mowry is largely early Cenomanian in age (Cobban 

and Kennedy, 1989; Obradovich and others, 1996); however, 

radiometric dates for bentonite beds in the basal Mowry (Shell 

Creek equivalent) indicate an Albian (Early Cretaceous) age 

(Obradovich and others, 1996). 

Frontier Formation

The Frontier Formation consists of marine and minor 

marginal-marine shale, siltstone, and sandstone that are generally interpreted to be deltaic or shoreface in origin (Hunter, 

1952; Van Houten, 1962; Goodell, 1962; Siemers, 1975; 

Merewether and others, 1975; Merewether and others, 1998). 

Minor amounts of carbonaceous shale and coal are present in 

the northwestern part of the basin (Siemers, 1975; Merewether 

and others, 1975). The Frontier is early Cenomanian to early 

Coniacian in age and contains at least one major unconformity 

in the upper part (Merewether and others, 1975). The lower 

contact is placed at the top of the Mowry, and the upper contact is typically placed at the top of the uppermost sandstone 

below the Cody Shale. A thin distinctive marker is present in 

the lower part of the overlying Cody Shale (fig. 7), especially 

in the southeastern part of the basin, and it probably represents 

a carbonate or chalk zone equivalent to the Upper Cretaceous 

Niobrara Formation. The main Frontier interval, as defined 

between the top of the Mowry and chalk marker, ranges in 

thickness from 450 ft in the western part of the basin to about 

1,075 ft in the southeastern part of the basin (fig. 10).

There are at least six main sandstone units within the 

Frontier, but not all are present at any one locality. They are 

continuous locally for tens of miles but are subject to truncation due to erosion, mainly by marine-flooding surfaces. The 

maximum thickness of individual sandstones range to as much 

as 130 ft (see Finn, Chapter 6, this CD–ROM; and Johnson, 

Chapter 7, this CD–ROM).

Cody Shale

The Cody Shale in the Bighorn Basin consists of 

marine shale, sandstone, and siltstone deposited during a 

major marine transgressive-regressive cycle that extended 

from Coniacian to Campanian time (Kauffman, 1977). The 

formation ranges in thickness from about 1,700 ft in the 

northern part of the basin to nearly 3,800 ft in the southeastern 

part (fig. 11). The lower and upper contacts are conformable 

and interfinger extensively with the underlying Frontier and 

overlying Mesaverde Formations (fig. 6).

The Cody Shale consists of two main units, the lower 

main body and the upper Claggett Member (Keefer and others, 

1998). The main part interfingers with and extends from the 

top of the Frontier Formation to the base of the Mesaverde 

Fomation and is composed of marine shale with increasing 

amounts of interbedded sandstone in the upper 500–1,200 feet

(fig. 6) (see Finn, Chapter 6, this CD–ROM). The upper sandy 

part is similar to, but somewhat less sandy than, the upper 

sandy member of the Cody Shale in the Wind River Basin (see 

Finn, 2007a, and Johnson, 2007, for descriptions and correlation of the Cody Shale in the Wind River Basin). Many of the 

sandstones in the upper part of the Cody are blanket-like, can 

be traced over many miles, and appear to pinch out into marine 

shale in all directions (see Finn, Chapter 6, this CD–ROM; 

and Johnson, Chapter 7, this CD–ROM). The uppermost 

several hundred feet of the sandy part of the Cody that directly 

underlies the Mesaverde Formation is commonly referred to 

in Montana as the Telegraph Creek Formation (figs. 6, 7). The 

Cody is poorly exposed, however, limited outcrop studies by 

Johnson and others (1998) of uppermost Cody Shale indicate 

that the sandstones are very fine to medium-grained, generally 

laterally persistent, and exhibit a variety of bedding features 

including hummocky cross-bedding, which indicates a nearshore marine origin.

According to Keefer and others (1998), the Claggett 

Member (known as the Claggett Shale in Montana) is a 

westward-thinning tongue of marine shale and fine-grained 

sandstone that is split from the main part of the Cody Shale by 

the lower member of the Mesaverde Formation (Eagle Sandstone in Montana) (figs. 6, 7). The Claggett Member extends 

across the eastern and central parts of the Bighorn Basin, and 

thickens eastward from zero to nearly 500 ft thick at its eastern 

limit, where it merges with the main part of the Cody Shale 

(figs. 6, 12) (see Finn, Chapter 6, this CD–ROM).

Mesaverde Formation

The Mesaverde Formation consists of a basal regressive 

marginal marine sandstone overlain by interbedded nonmarine sandstone, siltstone, shale, carbonaceous shale, and 

coal deposited in coastal plain and marginal marine environments as the western shoreline of the Cretaceous sea retreated 

eastward across the Bighorn Basin (Severn, 1961; Mackenzie, 

1975; Klug, 1993; Johnson and others, 1998). The formation is 

Campanian in age and can be subdivided into a lower member, a middle or main part, and the Teapot Sandstone Member 

(fig. 6) (Keefer and others, 1998; Johnson and others, 1998). 

The lower member of the Mesaverde Formation, referred 

to as the Eagle Sandstone in Montana by Johnson and Finn 

(2004) and as the Eagle Formation of the Mesaverde Group by 

Severn (1961) and Mackenzie (1975), is an eastward-thinning 

wedge of marginal marine and nonmarine strata (figs. 6, 7). 

It conformably overlies and interfingers with the upper sandy 

part of the Cody Shale and is separated from the middle 

member or main body of the Mesaverde by the Claggett 

Member of the Cody Shale (figs. 6, 7). The lower member is 

present in the central and eastern parts of the basin, where it 

consists of very fine to medium-grained sandstone, siltstone, 
14 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

400

500

450

600

550

700

750

650

750

800

Montana

Wyoming

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Control points

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Rattlesnake Mountain

anticline

Frontier/Mowry/Muddy/

 Thermopolis outcrop

Figure 9. Isopach map of the Mowry Shale, Bighorn Basin, Wyoming and Montana; thickness interval 50 ft.

shale, carbonaceous shale, and coal deposited as an eastwardprograding deltaic complex (Mackenzie, 1975; Johnson and 

others, 1998). The basal beds are very fine to fine-grained 

sandstone that were deposited in a marginal marine setting and 

have been referred to as the Virgelle Sandstone Member in 

Montana by Johnson and Finn (2004) or as the Virgelle sandstones by Severn (1961). The basal sandstones grade upwards 

into interbedded shale, carbonaceous shale, coal, and sandstone that were deposited in a delta plain setting (Mackenzie, 

1975). The lower member is thickest at its western limit where 

it is generally around 400–500 ft thick but locally exceeds 

800 ft (fig. 13) (see Finn, Chapter 6, this CD–ROM). It merges 

with the main part of the Mesaverde Formation to the west, 

and thins to zero to the east where is grades into the upper 

part of the Cody Shale (fig. 6). West of the Claggett pinchout, 

the lower and middle Mesaverde members merge as one unit 

simply referred to as Mesaverde Formation.

Where the Claggett Shale is present, that part of the 

Mesaverde Formation overlying it is referred to as the main 

body of the formation by Keefer and others (1998) and as the 
Stratigraphy 15

1,000

900

900

800

800

800

700

700

700

700

600

600

600

600

600

600

500

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Frontier/Mowry/Muddy/

 Thermopolis outcrop

Control point

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Rattlesnake Mountain

anticline

Figure 10. Isopach map of the Frontier Formation, Bighorn Basin, Wyoming and Montana; thickness interval 100 ft.

middle part by Johnson and others (1998). According to Johnson and Finn (2004), it is, in part, equivalent to the Parkman 

Sandstone and the lower part of the Judith River Formation in 

Montana (figs. 6, 7). Severn (1961) referred to this interval, 

together with the overlying Teapot Sandstone Member as the 

Judith River Formation, and Mackenzie (1975) referred to it 

as the Judith River Formation of the Mesaverde Group. It consists of interbedded sandstone, siltstone, shale, carbonaceous 

shale, and coal deposited in marginal marine, coastal plain, 

and fluvial environments (Severn, 1961; Mackenzie, 1975; 

Johnson and others, 1998). The basal strata of the middle 

part are very fine to fine-grained and have been interpreted as 

progradational units that accumulated as shoreface sandstones 

as the western shoreline of the seaway retreated eastward 

across the basin (Keefer and others, 1998; Johnson and others, 

1998). The sandstones in the nonmarine part of the Mesaverde 

are very fine to medium-grained, lenticular, and originated as 

stream channel and crevasse splay deposits (Johnson and others, 1998). The Mesaverde generally thins from west to east 

where a combined thickness of the main part of the Mesaverde 
16 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

2000

2250

2750

2750

1750

1750

2500

3000

3250

3500

3750

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Well control point

Measured section

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Cody Shale outcrop and

 equivalent rocks

Easten limit of lower

 member of Mesaverde

Figure 11. Isopach map of the main body of the Cody Shale excluding the Claggett Member, Bighorn Basin, Wyoming 

and Montana; thickness interval 250 ft. Outcrop data from Hewett (1912).

and Teapot Sandstone Member, excluding the lower member 

or Eagle Sandstone, ranges from greater than 1,200 ft in the 

southwestern part of the basin to less than 500 ft along the 

eastern margin of the basin (fig. 14).

The Teapot Sandstone Member, the uppermost member 

of the Mesaverde Formation, consists of light-gray to white, 

fine- to coarse-grained sandstone and minor amounts of gray 

mudstone (Johnson and others, 1998). Based on outcrop 

studies by Mackenzie (1975) and Johnson and others (1998), 

it is considered to be fluvial in origin throughout most of the 

basin; however, in the eastern part, Johnson and others (1998) 

described hummocky cross-bedding in the lower part of the 

unit, indicating that it is partly marginal marine in origin. The 

thickness of the Teapot Member is highly variable and ranges 

from a few tens of feet to more than 300 ft (Keefer and others, 

1998; Johnson and others, 1998).
Stratigraphy 17

0

50

50

0

100

100

150

150

200

200

250

250

300

350

400 450

400

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Well control point

Measured section

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Cody Shale outcrop and

 equivalent rocks

Figure 12. Isopach map of the Claggett Member of the Cody Shale, Bighorn Basin, Wyoming and Montana; 

thickness interval 50 ft. Outcrop data from Johnson and others (1998).

Meeteetse Formation, and Lewis and Bearpaw 

Shales

The Meeteetse Formation and Lewis and Bearpaw Shales 

are intertonguing marine, marginal marine, and nonmarine 

strata of latest Campanian and early Maastrichtian age (Gill 

and Cobban, 1966; Merewether, 1996) (figs. 6, 7). Johnson 

and Finn (2004) considered the Meeteetse/Lewis/Bearpaw 

interval in the Bighorn Basin to be equivalent to the upper part 

of the Judith River Formation and overlying Bearpaw Shale 

in Montana (figs. 6, 7). The marine strata in this interval are 

included in the Lewis and Bearpaw Shales, and the marginal 

marine and nonmarine strata in the Meeteetse Formation. The 

maximum combined thickness for the formations ranges from 

more than 1,100 ft in the northern and southwestern parts of 

the basin to about 500 ft in the southeastern part (fig. 15).

The Meeteetse Formation is comprised of alternating 

thin beds of very fine to medium-grained sandstone, siltstone, 

shale, carbonaceous shale, and coal that accumulated in poorly 

drained coastal environments along the western shore of the 
18 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

100

0

200

400

300

400

500

600

700

800

300

400

300

400

500

200

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Well control point

Measured section

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Cody Shale outcrop and

 equivalent rocks

Figure 13. Isopach map of the lower member of the Mesaverde Formation and Eagle Sandstone, Bighorn Basin, 

Wyoming and Montana; thickness interval 100 ft. Outcrop data from Johnson and others (1998).

Cretaceous seaway (Keefer and others, 1998). The Lewis 

Shale is a westward-thinning tongue of marine shale and 

sandy shale interbedded with thin sandstone beds. It is present 

in the eastern part of the basin, ranges in thickness from more 

than 300 ft on the east side of the basin, and thins westward to 

zero where it grades into the Meeteetse Formation (Keefer and 

others, 1998). In the northern part of the basin, the Bearpaw 

Shale overlies, and in part intertongues with, the Meeteetse 

Formation and represents the last stages of marine sedimentation in the Bighorn Basin (fig. 6). Where present, the Bearpaw 

is about 80 to 200 ft thick (see Finn, Chapter 6, this CD–

ROM); according to Johnson and others (1998), it consists of 

fissile gray shale and thin beds of very fine grained sandstone. 

Lance Formation

The Lance Formation, referred to as the Hell Creek 

Formation in Montana by Johnson and Finn (2004), consists 

of interbedded sandstone, shale, and minor conglomerate and 
Stratigraphy 19

represents the uppermost Cretaceous rocks in the Bighorn 

Basin. Minor amounts of coal are present locally, but Johnson 

(1998) concluded that it was of minor importance. Sandstone 

is the predominant lithology throughout much of the basin, 

particularly in the lower part of the formation, whereas the 

upper part is largely interbedded sandstone and shale (Keefer 

and others, 1998; Johnson and others, 1998). The sandstones 

are fine- to coarse-grained, locally conglomeratic, and were 

deposited in fluvial systems (Johnson and others, 1998). In 

the northern part of the basin, a sandstone interval in the basal 

part of the Lance overlying the Bearpaw Shale was interpreted 

as a shoreface deposit by Keefer and others (1998), and was 

believed to correlate with the Upper Cretaceous Fox Hills 

Sandstone. Johnson and Finn (2004) referred to this marginal 

marine interval as the Lennep Sandstone in Montana (figs. 6, 

7). The Lance is generally considered to be Maastrichtian 

in age; however, palynogical age determinations by Nichols 

(1998) indicated that locally it is in part earliest Paleocene 

in age. The onset of the Laramide orogeny and initial partitioning of the Rocky Mountain foreland basin into smaller 

1250

1000

500

500

750

750

500

500

500

750

750

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Well control point

Measured section

Western limit of

 Claggett Shale

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Mesaverde outcrop and

 equivalent rocks

Figure 14. Isopach map of the main body of the Mesaverde Formation excluding the lower member and Eagle 

Sandstone, Bighorn Basin, Wyoming and Montana; thickness interval 250 ft. Outcrop data from Hewett (1912) and 

Johnson and others (1998).
20 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

1000

1100

900

600

700

700

700

700

700

600

600

500

500

700

700

800

800

800

900800

800

900

900

900

900

1100

1000

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Well control point

Measured section

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Meeteetse Formation 

 outcrop and equivalent

 rocks

Figure 15. Isopach map of the Meeteetse Formation including the Lewis and Bearpaw Shales, Bighorn Basin, 

Wyoming and Montana; thickness interval 100 ft. Outcrop data from Hewett (1912) and Johnson and others (1998).

Laramide basins is indicated by the Lance thickness patterns 

in the Bighorn Basin, which range from less than 500 ft in 

the southeastern part of the basin to more than 1,500–1,800 ft 

near the basin axis (shown on fig. 3) adjacent to and east of the 

Oregon Basin thrust fault (figs. 3, 16) (Parker and Jones, 1986; 

see Finn, Chapter 6, this CD–ROM). 

Fort Union Formation

The Fort Union Formation, referred to as the Polecat 

Bench Formation by Bown (1975) is composed of sandstone, 

siltstone, conglomeratic sandstone, conglomerate, carbonaceous shale, and coal (Bown, 1975; Johnson, 1998; Keefer and 

others, 1998; Roberts, 1998). The conglomerates accumulated 

mainly as alluvial fans along the northwest margin of the 

Bighorn Basin and as fluvial channel deposits where streams 

flowed into the basin from surrounding highlands (Hickey, 

1980; Johnson and Middleton, 1990; Roberts and Stanton, 

1994; Roberts, 1998). The sandstones are very fine to coarsegrained and represent a variety of fluvial deposits, while the 

finer grained and carbonaceous deposits represent lacustrine 

and swamp deposits (Hickey, 1980; Yuretich and others, 
Stratigraphy 21

1984; Roberts and Stanton, 1994; Hickey and Yuretich, 1997; 

Roberts, 1998). The thickness of the Fort Union indicates 

continued subsidence of the basin trough during the Laramide 

orogeny and reflects the present-day structural configuration 

of the basin. The formation is generally less than 1,000 ft thick 

around the basin margins, thins locally to about 300 ft in the 

north, and thickens to more than 7,500 feet in the structurally 

deepest central part (Moore, 1961; see Finn, Chapter 6, this 

CD–ROM). In outcrops around the margins it unconformably overlies Lance and locally older Upper Cretaceous rocks 

(Bown, 1975; Love and Christiansen, 1985; Keefer and others, 

1998; Roberts, 1998). The Fort Union is Paleocene in age 

based on fossil pollen dating by Nichols (1998) and Roberts 

(1998), and by mammalian faunas reported by Gingerich 

(1983). 

Lower Eocene Rocks

Strata that represent the lowermost Eocene in the Bighorn 

Basin are assigned to the Willwood Formation and consist 

of variegated shales, sandstones, and conglomerates (Van 

500

1000

750

1000

1000 1250

1750

750

1000 1250

500

750

750

1250

1500

1500

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Well control point

Measured section

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Lance Formation outcrop

 and equivalent rocks

Figure 16. Isopach map of the Lance Formation, Bighorn Basin, Wyoming and Montana; thickness interval 250 

ft. Outcrop data from Hewett (1912) and Johnson and others (1998).
22 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Houten, 1944; Bown, 1980). The Willwood is nearly flat lying, 

occupies the central part of the basin, and conceals much of 

the structure of the underlying rocks (fig. 2). Bown (1980) 

reported a maximum thickness of nearly 2,400 ft in exposures 

in the southern part of the basin. The lower Eocene Tatman 

Formation overlies and in part interfingers with the Willwood. 

It is present only as isolated erosional remnants in the southcentral part of the basin (Love and Christiansen, 1985; Bown, 

1980), where it has a maximum thickness of nearly 900 ft, and 

is comprised of fine-grained sandstone and carbonaceous shale 

that accumulated in lakes and swamps (Van Houten, 1944).

Keefer and others (1998) and Finn (Chapter 6, this CD–ROM) 

report a combined thickness for the Willwood and Tatman 

Formations of nearly 5,000 ft in the subsurface along the deep 

axis of the basin. The combined thickness of all lower Tertiary 

rocks ranges from less than 1,000 ft around the margins of the 

basin to greater than 12,000 ft near the basin axis, a pattern 

that reflects the present-day structure of the basin (figs. 3, 17).

Cretaceous–Tertiary Composite Total 

Petroleum System (503402)

The Cretaceous–Tertiary Composite Total Petroleum 

System (TPS 503402) produces oil and natural gas from predominantly sandstone reservoirs in anticlinal traps around the 

margins of the Bighorn Basin (fig. 18). The TPS covers most 

of the central part of the basin and encompasses approximately 

7,900 mi2. The south, east, and northeast boundaries are 

defined generally as the base of Cretaceous outcrops (fig. 18). 

The north boundary is drawn to include the production along 

the Nye-Bowler lineament and coincides with the province 

boundary. The northwest boundary along the Beartooth 

Mountain front is drawn at the contact between Precambrian 

crystalline rocks and younger sedimentary rocks. South of the 

Beartooth Mountains the TPS boundary extends to the eastern 

limit of the Absaroka volcanics, with the exception of the area 

in the vicinity of Rattlesnake Mountain where it is defined as 

the base of exposed Cretaceous rocks (fig.1). Within the TPS 

some areas were excluded with respect to resource potential 

(for example, Sheep Mountain and Thermopolis anticlines, 

fig. 1) because of being eroded deeply enough to have 

removed all Cretaceous and Tertiary rocks. Stratigraphically, 

the TPS includes reservoirs that range from Early Cretaceous 

to Paleocene in age (fig. 7).

Geochemical studies have identified two oil types in 

addition to those associated with the Permian Phosphoria 

Formation, both with characteristics of Cretaceous 

source rocks. One oil type appears to be sourced from the 

Thermopolis Shale and is produced mainly from Muddy 

Sandstone reservoirs, whereas the second has characteristics 

of oils derived from the Mowry Shale and is produced mainly 

from Frontier Formation reservoirs (P.G. Lillis, written 

commun., 2007). Geochemical data also show that there has 

been little or no mixing of the two oil types, indicating that 

the Cretaceous section could theoretically be divided into two 

separate TPSs. However, gas isotope studies by Johnson and 

Keighin (1998) indicate that there has been extensive vertical 

migration of thermogenic gases from deep mature source 

rocks into shallow reservoirs that are immature with respect 

to thermogenic gas generation; in some cases, these gases 

have mixed with biogenic methane generated at the shallower 

depths. Therefore, because of the extensive vertical migration 

and comingling of gases described by Johnson and Keighin 

(1998), and the difficulty in differentiating gas types and 

assigning them to specific source rocks, all Cretaceous and 

Tertiary source rocks, reservoirs, and accumulations have been 

assigned to one composite TPS for this assessment.

Source Rocks

Source rocks in the Bighorn Basin include organicrich marine shales in the Thermopolis Shale, Mowry Shale, 

Frontier Formation, and Cody Shale (fig. 7). The amount and 

type of organic matter in these marine shales are summarized 

in figure 19, and was compiled from Schrayer and Zarrella 

(1963), Nixon (1973), Hagen and Surdam (1984), Burtner and 

Warner (1984), Hagen (1986), Davis (1986), Yin (1997), and 

Finn (Chapter 4, this CD–ROM). Guidelines for evaluating 

kerogen type and organic richness are from Peters and Cassa 

(1994).

The total organic carbon (TOC) content of the Thermopolis Shale ranges from 0.37 to 1.91 percent and averages 

1.23 percent, indicating a fair to good generating potential. 

The hydrogen index (HI), ranging from 79 to 446 with all but 

one sample less than about 200, shows the formation to be 

predominantly gas-prone; however, S2/S3 ratios reported by 

Finn (Chapter 4, this CD–ROM), and associated oil production from the overlying Muddy Sandstone indicates that the 

Thermopolis generated, or has the potential to generate, oil 

(P.G. Lillis, written commun., 2007).

The TOC content for the Mowry Shale ranges from 0.08 

to 3.6 percent with an average of 1.36 percent, indicating a 

poor to very good generating potential, with most samples 

falling in the fair to good range. The HI values range from 10 

to 634, with most samples falling between 50 to 360, so the 

Mowry has the potential to generate both oil and gas.

The TOC content of the marine shales in the Frontier 

Formation ranges from 0.11 to 4.53 percent and averages 

around 1.13 percent, with most samples in the fair to good 

range of generating potential. HI values show the Frontier to 

be gas-prone, with values ranging from 10 to 201.

The TOC content of the Cody Shale ranges from 0.12 

to 5.86 percent, with most samples falling around 1 percent 

or less; thus, the formation has fair generating potential, with 

some excellent potential locally. The HI ranges from 88 to 

337, with most samples less than 200, indicating that the Cody 

is predominantly gas-prone but may be oil-prone locally. However, due to a lack of oil production associated with the Cody 

Shale (for example, from Cody sandstones and interfingering 
Source Rocks 23

Mesaverde sandstones), it is believed to be mainly a gas-prone 

source rock.

In addition to the marine shales, coal beds and carbonaceous shales in the Mesaverde, Meeteetse, and Fort Union 

Formations are considered to be sources of gas in the Bighorn 

Basin (Nuccio and Finn, 1998; Yin, 1997) (fig. 7). However, 

according to Jones and DeBruin (1990) and Johnson (1998), 

the total volume of coal in the Bighorn Basin is considerably less than in the Wind River Basin, a basin of similar size 

where coal is thought to be an important source for gas (Johnson and others, 2007). Also, subsurface mapping by Johnson 

(1998) shows that the distribution of coal beds in the Bighorn 

Basin are limited (figs. 20, 21, 22), so are probably not a major 

source for gas generation.

5000

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7000

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7000

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9000

10000

11000

12000

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Control point

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Lance Formation outcrop

 and equivalent rocks

Figure 17. Isopach map of the Fort Union, Willwood, and Tatman Formations combined, Bighorn Basin, Wyoming 

and Montana; thickness interval 1,000 ft.
24 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

0

5000

-5000

0 0

-5000

-5000

0

0

5000

0

0

0 -10000

-5000

0

5000

0

5000

-15000

-10000

-5000

-5000

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

High-angle fault

Oil well

Gas well

Tertiary volcanic rocks

Bighorn Basin Province

Cretaceous-Tertiary

 Composite TPS 503402

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Cloverly outcrop and

 equivalent rocks

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Rattlesnake Mountain

anticline

Figure 18. Map of the Bighorn Basin Province showing extent of the Cretaceous–Tertiary Composite Total 

Petroleum System (503402), major structural elements, and oil and gas wells that produce from Cretaceous and 

Tertiary reservoirs. Structure contours drawn on top of the Cloverly Formation; contour interval 1,000 ft.

Reservoir Rocks

The most important reservoir in the Cretaceous–Tertiary 

sequence in the Bighorn Basin is the Frontier Formation; 

sandstones with a minimum cumulative production of about 90 

MMBO and 670 BCFG from some 1,250 wells (IHS Energy 

Group, 2007). This accounts for about 96 percent of the total 

oil production and 80 percent of the total gas production from 

all Cretaceous and Tertiary reservoirs combined, and about 31 

percent of the total gas and 3 percent of the total oil production 

from all reservoirs in the basin. Production is from sandstone 

reservoirs encased in marine shale that in some cases pinch out 

across structures (Keefer, 1998). The sandstones are fine- to 

medium-grained, locally shaly, with porosities ranging from 

about 4 to 34 percent and permeabilities ranging from .001 

to 260 millidarcies (mD) (Shapard, 1975; Tonnsen, 1985; 

Cardinal and others, 1989).

The Muddy Sandstone and the Cloverly Formation are 

next in relative importance as reservoirs in the Cretaceous–

Tertiary interval. The Muddy Sandstone has produced a 
Reservoir Rocks 25

Figure 19. Plots showing (A) total organic carbon content and (B) hydrogen index of Cretaceous marine shales in 

the Bighorn Basin, Wyoming and Montana.

TOTAL ORGANIC CARBON, IN WEIGHT PERCENT

0 1 2 3 4 5 6 7

Cody

Frontier

Mowry

Poor

Thermopolis

Fair Good Very good Excellent

0 100 200 300 400 500 600 700

Cody

Frontier

Mowry

Thermopolis

None Gas Oil and gas Oil

HYDROGEN INDEX

A

B
26 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Mesaverde outcrop

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

19 Drill hole—Total coal thickness

 (in ft) shown alongside

Drill hole—No coal identified in

 the Mesaverde Formation

Rattlesnake Mountain

anticline

Silvertip

coaleld

Grass Creek coal field

Mined beds to 8.8 ft thick

Prospects indicate 5 coal

 beds > 3 ft thick and one

 coal bed ≈11 ft thick

Gebo coal field

Subbituminous A or B

> 11 million tons of coal produced

 (> 90% of total coal production)

More than 41 mines

Coal beds to 12 ft thick

4

4

15

15 25

23

27 211812

29 19 19 17

13

10

10 7

7

5 3

3 2

11

11

3

2 2

6

2

4

4 4

10

15

13

7

7

10

8

3

3

3

3

2

2

2

11 8

2

3

2

4

7

6 6

6

15

10

2

9

9

6

2

2

3

18

4

5 4

7

9

9

17

5 5

3 11

6

5

13

6

3 1316

16

13

2

Figure 20. Map showing distribution and thickness (in ft) of coal in the Mesaverde Formation, Bighorn Basin, Wyoming 

and Montana. Data from Glass and others (1975) and Johnson (1998).

minimum of about 1.5 MMBO, and 117 BCFG from about 

105 wells, accounting for about 1.5 percent of the oil and 

14 percent of the gas that have been produced (IHS Energy 

Group, 2007). The reservoirs are generally very fine to 

medium-grained sandstones, with core porosities and 

permeabilities ranging from 1.6 to about 23 percent, and 

0.01 to 8 mD, respectively (Cardinal and others, 1989). The 

Cloverly Formation has produced about 2 MMBO and 41 

BCFG from about 240 wells, which accounts for about 2 

percent of the oil and 5 percent of the gas produced from 

the Cretaceous–Tertiary section (IHS Energy Group, 2007).

The main reservoir in the Cloverly is the Greybull Sandstone 

Member, a fine- to medium-grained sandstone with porosities 

generally ranging from 5 to 20 percent (max up to 30 percent) 

and permeabilities ranging from 0.41 to 50 mD (max 150 

mD) (Hafenbrack and others, 1958; Tonnsen, 1985; BartowCampen, 1986; Cardinal and others, 1989). Additional 

production from the Cloverly is from the basal Pryor 

Conglomerate Member consisting of fine- to coarse-grained 

conglomeratic sandstone, and chert-pebble conglomerate, with 
Reservoir Rocks 27

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R100W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Meeteetse Formation 

 outcrop and equivalent

 rocks

Drill hole—Total coal thickness

 (in ft) shown alongside

19

Drill hole—No coal identified in

 the Meeteetse Formation

Creek Owl

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Rattlesnake Mountain

anticline

2

3

7

5

4

4 2

4 2

2

2

5

5

5

4

4 4 4 4

6

6

6 6

6

13

12

6 2

6 6

6

6

7

7

7

7 17

23 12 12

9

9

9 9

2

3

9

7 2411

11 11

12 13 18

18

10

10

14

14

1820 29

10

9

8

8

8

8

514 6

9 6

3

3

8

5

5

12 8 11

2

2

4

10 7

Basin coal field

Meeteetse coals to

11 ft thick, not mined

Southeastern coal field

6 ft-thick Meeteetse coal mined,

coal beds to 8 ft thick

Gebo coal field

7 Meeteetse coal beds > 3 ft thick

coal beds to 7 ft thick

Oregon Basin coal field

3 ft-thick Meeteetse

coal mined

Figure 21. Map showing distribution and thickness (in ft) of coal in the Meeteetse Formation, Bighorn Basin, 

Wyoming and Montana. Data from Glass and others (1975) and Johnson (1998).

porosities ranging from 8 to 15 percent, and permeabilities 

ranging to as much as 75 mD (Hafenbrack and others, 1958; 

Tonnsen, 1985; Cardinal and others, 1989).

Minor reservoirs include the Mowry and Cody Shales 

and the Mesaverde (including the Eagle Sandstone and Judith 

River Formation), Meeteetse, Lance, and Fort Union Formations. Combined cumulative production from these units is 

about 410 thousand barrels of oil (MBO) and 7 BCFG, which 

accounts for less than one percent of the oil and gas produced 

from all Cretaceous–Tertiary reservoirs in the basin (IHS 

Energy Group, 2007). Reservoirs in the Mowry Shale are 

thin, fine-grained sandstones, referred to as the “Kimball” and 

“Octh Louie” sands, with reported log porosities of 13–16 

percent (Cardinal and others, 1989); future potential from 

the Mowry might include production from fractured shale. 

Reservoirs in the Cody Shale are isolated shallow marine 

sandstones encased in marine shale. These beds are very fine 

to medium-grained, commonly blanket-like, can be traced 

for several miles, and appear to pinch out in marine shale in 

several directions. No porosities or permeabilities have been 
28 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

reported. Production from the Mesaverde and Meeteetse 

Formations (including the Judith River Formation) is from 

lenticular fluvial sandstones that have limited areal extent. 

In addition, some production in the Mesaverde (including 

the Eagle Sandstone) is from blanket-like, marginal marine 

sandstones. The sandstones are generally very fine grained, 

with porosities ranging from 10 to 26 percent (Shapard, 1975; 

Cardinal and others, 1989; Tonnsen, 1985). Potential future 

production from both formations might include coal beds in 

the coastal plain facies of each unit. However, as reported by 

Johnson (1998), coal beds have a limited distribution in the 

basin. Limited production from the Lance and Fort Union 

Formations is from fluvial sandstone reservoirs. Cardinal and 

others (1989) reported log porosities of 20–24 percent for the 

Lance, and 38 percent for the Fort Union, with no permeabilities reported. Potential future production from the Fort Union 

might be coal beds. 

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Fort Union outcrop

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

4

Drill hole—No coal identified

 in the Fort Union Formation

Drill hole—Total coal thickness

 (in ft) shown alongside

Rattlesnake Mountain

anticline

26

4

5 11

8

16

13

12

10 8

6

3

3

3

3

3

10

5

6

3 2

4

4 9

4

Red Lodge-Bearcreek coal field

Coal beds to 11.5 ft thick

8 major coal beds

16 underground mines

Southeastern coal field

Coal beds to 10 ft thick

 (lenticular)

Basin coal field

Mined coal beds to

≈9 ft thick (lenticular)

Grass Creek strip mine

Mayfied coal bed 26 ft thick

Up to 38 ft locally in outcrops

Figure 22. Map showing distribution and thickness (in ft) of coal in the Fort Union Formation, Bighorn Basin, 

Wyoming and Montana. Data from Woodruff (1907), Glass and others (1975), and Johnson (1998).
Hydrocarbon Generation 29

Traps and Seals

Production from conventional oil and gas accumulations 

from Cretaceous and Tertiary reservoirs is from anticlines 

and combination stratigraphic structural traps. To date most 

of the production is from anticlinal traps that formed during 

the Laramide orogeny (Fox and Dolton, 1996). These traps 

are mainly around the margins of the Bighorn Basin, the 

Nye-Bowler lineament (fig. 1), and along the Five Mile trend 

(fig. 3) (Fox and Dolton, 1989). The anticlines are typically 

asymmetric, thrust-fault-bounded along their steep flanks, and 

in many cases produce from more than one reservoir horizon 

(Hafenbrack and others, 1958; Tonnsen, 1985; Cardinal and 

others, 1989). Many of these traps have a stratigraphic component where lenticular or channel sandstones—such as those 

in the Frontier Formation, the Greybull Sandstone Member of 

the Cloverly Formation, and possibly the Muddy Sandstone—

pinch out or are draped across structures (Anonymous, 1958; 

Stone, 1975; Cully, 1985; Mohl, 1989; Keefer, 1998; Talbot, 

1996).

Limited drillstem test and mud log data from wells drilled 

in the structurally deep part of the basin indicate the presence 

of an overpressured basin-centered gas accumulation (BCGA) 

of limited extent in Cretaceous rocks and has been discussed 

in detail by Johnson and Finn (1998b) and Johnson and others 

(1999). Surdam and others (1997) also suggested the presence 

of an overpressured gas compartment in the Bighorn Basin 

based on sonic velocity anomalies. According to Johnson and 

Finn (1998b), the top of overpressuring in the main part of the 

basin generally is at depths between 13,000 and 17,000 ft, and 

in the deepest part of the basin extends from near the base of 

the Meeteetse Formation down to the base of the Cretaceous 

section (figs. 23, 24, 25). In the Clarks Fork sub-basin, the top 

of overpressuring starts at around 14,000 ft in the basal part of 

the Cody Shale and extends to near the base of the Cretaceous 

section (fig. 24E).

Thick sections of marine shale, ranging to as much as 

several thousand feet of strata in the Thermopolis, Mowry, 

Cody, Lewis, and Bearpaw Shales and the Frontier Formation, provide good quality regional seals throughout most of 

the Bighorn Basin (see cross sections by Finn, Chapter 6, this 

CD–ROM; and Johnson, Chapter 7, this CD–ROM). The thick 

marine shales are also important where they isolate marine 

sandstone reservoirs such as those in the Frontier Formation and the Cody Shale. In addition, nonmarine sandstone 

reservoirs are interbedded with shale and mudrock deposited 

in coastal or alluvial plain settings that provide local seals. The 

trap and sealing mechanism for BCGAs is generally believed 

to be formed where high water saturations are updip of gasbearing low-permeability reservoir rocks thereby reducing the 

relative permeability of gas to near zero (Masters, 1979; Law 

and Dickinson, 1985; Spencer, 1989; Law, 2002). Masters 

(1979) referred to this type of trapping mechanism as a water 

block, whereas Law (2002) used the term capillary pressure 

seal. Fine-grained rocks in the Cloverly-Morrison interval act 

as a barrier to downward migration of gas out of the BCGA 

which helps to maintain pressure (Nelson, Chapter 5, this 

CD–ROM).

Thermal Maturity

In outcrop areas of the Bighorn Basin, thermal maturity 

based on vitrinite reflectance (Ro) values for coal-bearing 

strata range from 0.27 to 0.96 percent around the basin 

margins, but generally fall in the range of 0.3 to 0.5 percent 

(Nuccio and Finn, 1998; Finn and Pawlewicz, 2007). In the 

subsurface, Nuccio and Finn (1998) presented maps showing 

the levels of thermal maturity for the top of the Cody Shale 

and the top of the Mesaverde Formation (figs. 26, 27). These 

maps were constructed from data collected from coal-bearing 

strata (outcrop and wells) in the Mesaverde, Meeteetse, 

Lance, and Fort Union Formations (fig. 7). Thermal maturity 

maps for the Cody and Mesaverde show that Ro values are 

less than 0.73 percent around the margins of the basin and 

increase basinward to greater than 1.10 percent in the deeper 

areas (figs. 26, 27). In the Clarks Fork sub-basin, both the 

Mesaverde and the Cody reach a level of thermal maturity 

of around 0.80 percent, and only the Cody reaches a level 

exceeding 1.10 percent in the northern part of the basin 

adjacent to the Beartooth Mountains. The thermal maturity 

trends generally reflect the structural configuration of the 

basin, indicating thermal maturity is related to the structural 

development and burial history of the basin. These levels of 

thermal maturity are much lower than equivalent strata in the 

Wind River Basin and Southwestern Wyoming Province to 

the south. In the central deep part of the Wind River Basin 

both the Cody and the Mesaverde reach Ro levels greater than 

2.0 percent and in one smaller area in the northeastern part, 

the Ro exceeds 3.0 percent (Johnson and others, 2007; Finn, 

2007b). In the Southwestern Wyoming Province, Johnson and 

others (2005) show Ro levels for strata equivalent to the Cody 

Shale and Mesaverde Formation exceeding 2.2 percent. By 

comparison, Ro data collected by Finn and Pawlewicz (2007) 

in the deepest parts of the Bighorn Basin for Cretaceous 

strata older than the Cody Shale show values ranging to only 

around 1.8 percent at depths generally greater than 15,000 ft. 

Petroleum generation modeling by Roberts and others (2008) 

indicated that the Frontier Formation and older Cretaceous 

rocks may have reached an Ro level of 2.0 percent only at 

the Emblem Bench location in the deep part of the basin, 

whereas, equivalent rocks reached or exceeded this level over 

large parts of the Wind River Basin and Southwest Wyoming 

Province (Nuccio and others, 1996; Roberts and others, 2004; 

Roberts and others, 2007).

Hydrocarbon Generation

Roberts and others (2008) modeled the burial history, 

thermal maturity, and timing of petroleum generation for 
30 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Cretaceous and Tertiary source rocks at eight locations in the 

Bighorn Basin that differ in structural settings and represent 

deep, intermediate, and shallow burial depths. Two types 

of modeling were performed at each location to predict the 

timing and type of hydrocarbon generation from Type-III 

gas-prone source rocks, and from Type-II oil-prone source 

rocks. They are (1) time-temperature modeling based on 

vitrinite reflectance, and (2) kinetic modeling based on timetemperature integrated with the results of hydrous-pyrolysis 

experiments.

Time-temperature modeling predicts critical levels of 

thermal maturity based on vitrinite reflectance by integrating 

burial and thermal history and time to model gas generation 

from Type-III gas-prone source rocks. The results, summarized from Roberts and others (2008) in figure 28, indicate 

that in areas where source rocks were buried the deepest, gas 

generation from Type-III source rocks started in the early 

Paleocene (about 63 Ma for Cretaceous source rocks) to early 

Eocene (52 Ma for Fort Union source rocks), reached peak 

generation by early to middle Eocene (44 Ma for Cretaceous 

5000

-5000

-10000

-5000

5000

0 -5000

0

5000

0

0

0 0

-5000

0

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Sellers

Draw

Michael

1-16 Emblem

Bench

Red

Point

McCulloch

Peaks

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Fault

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Mesaverde outcrop

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Control well

Figure 23. Map showing locations of wells with mud-weight and drillstem test data that indicate the presence of an 

overpressured basin-centered gas accumulation in the Bighorn Basin, Wyoming and Montana. Structure contours 

drawn on top of the Teapot Sandstone Member of the Mesaverde Formation are modified from Johnson and Finn 

(1998a); contour interval 1,000 ft. 
Hydrocarbon Generation 31

8.34 lb/gal .433 PSI/FT

9 lb/gal .468 PSI/FT

10 lb/gal .519 PSI/FT

11 lb/gal .571 PSI/FT

12 lb/gal .623 PSI/FT

13 lb/gal .675 PSI/FT

8.34 lb/gal .433 PSI/FT

9 lb/gal .468 PSI/FT

.519 PSI/FT

10 lb/gal

.571 PSI/FT

11 lb/gal 

12 lb/gal .623 PSI/FT

13 lb/gal .675 PSI/FT

8.34 lb/gal .433 PSI/FT

9 lb/gal .468 PSI/FT

.519 PSI/FT

10 lb/gal

11 lb/gal .571 PSI/FT

12 lb/gal .623 PSI/FT

13 lb/gal .675 PSI/FT

8.34 lb/gal .433 PSI/FT

9 lb/gal .468 PSI/FT

.519 PSI/FT

10 lb/gal 

11 lb/gal .571 PSI/FT

12 lb/gal .623 PSI/FT

13 lb/gal .675 PSI/FT

1 2 3 4 5 6 7 8 9 10 11 12

PRESSURE (PSI x 1,000)

Tfu

Kl

Kme

Kmv

Kc

Kf

0

10

15

20

5

DEPTH IN FEET (x 1,000)

Top of overpressure

Kmt Kcv

Twl

Michael 1-16-4D

Kmr

TD

14,828

Mud weight from mud log

?

Jm

?

SIP from DST

PRESSURE (PSI x 1,000)

PRESSURE (PSI x 1,000)

PRESSURE (PSI x 1,000)

Tfu

Kl

Kme

Kmv

Kc

Kf

Kmt

Kcv

Twl

Kmr

TD

18,636

?

Jm

?

Twl Twl

Tfu Tfu

Kl Kl

Kme Kme

Kmv Kmv

TD

15,914

Kc

Kc

Kf

Kmr

TD

18,500

Tfu

Kl

Kme

Kmv

Kc

Kf

Kmt

Kcv

Twl

Kmr

Mud weight from log header

Emblem Bench

Mud weight from mud log— Mud weight from mud log

 Texas Pacic 1 Red Point II

Mud weight from log header—

 Husky 14-25 Unit

SIP from DST—Texas Pacic Red Point II

SIP from DST—Husky 14-25

Red Point 

14-25 Unit Red Point II

Top of overpressure

DEPTH IN FEET (x 1,000)

DEPTH IN FEET (x 1,000) 0

10

15

20

5

0

10

15

20

5

Top of overpressure

1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12

Mud weight from log header

Sellers Draw

Mud weight from mud log

Producing interval

0

10

15

5

DEPTH IN FEET (x 1,000) 20

Top of overpressure (?)

1 2 3 4 5 6 7 8 9 10 11 12

A B

C D

INTERPRETED PRESSURE

GRADIENT

INTERPRETED PRESSURE

GRADIENT INTERPRETED PRESSURE

GRADIENT

INTERPRETED PRESSURE

GRADIENT

Figure 24 (above and next page). Pressure-depth plots for five locations in the deep part of the Bighorn 

Basin, Wyoming and Montana. Abbreviations: DST, drillstem test; lb/gal, pounds per gallon; PSI, pounds 

per square inch; SIP, shut-in pressure; TD, total depth; Jm, Morrison Formation; Kcv, Cloverly Formation; 

Kmt, Thermopolis Shale, Muddy Sandstone, undivided; Kmr, Mowry Shale; Kf, Frontier Sandstone; Kc, 

Cody Shale; Kmv, Mesaverde Formation; Kme, Meeteetse Formation; Kl, Lance Formation; Tfu, Fort Union 

Formation; Twl, Willwood Formation. Well locations shown in figure 23. 
32 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

source rocks), and ended only at the Emblem Bench location by the late Miocene (12 Ma for Frontier source rocks). 

The results are similar for source rocks buried at intermediate 

depths, except that Mesaverde and Meeteetse did not reach 

peak generation until later in the Eocene to early Miocene (47 

to 15 Ma) and Fort Union source rocks did not reach peak 

generation. Timing of gas generation from source rocks buried 

at shallower depths, ranges from onset of gas from the middle 

Paleocene (60 Ma for the Thermopolis) to early Oligocene 

(33 Ma for the Fort Union) and peak generation was reached 

only in the Thermopolis, Mowry, Frontier, and Cody source 

rocks from middle Eocene (47 Ma) to early Miocene (23 

Ma). Sometime after middle Miocene time (about 10 Ma), the 

region was uplifted (including the Bighorn Basin), resulting 

in the exhumation of the basin-bounding mountain ranges and 

removal of large volumes of the basin’s sedimentary fill (Love, 

1988). Subsequently, the basin cooled significantly reducing 

the rates of gas generation during the last 10 Ma (Roberts and 

others, 2008).

Kinetic models were generated for these same well 

locations to model oil generation from Type-II oil-prone 

kerogen. Kinetic modeling by Roberts and others (2008) used 

time and temperature integrated with results from laboratory 

hydrous-pyrolysis experiments by Lewan and Ruble (2002) 

and Tsuzuki and others (1999) to predict the timing and type 

of hydrocarbon generation. The results of this modeling, 

using hydrous-pyrolysis kinetic parameters, are summarized 

in figure 29. The results indicate that in areas where oil-prone 

source rocks of the Thermopolis and Mowry Shales were (1) 

buried the deepest, oil generation occurred from late Paleocene to middle Eocene (58 to 47 Ma); (2) buried at intermediate depths, oil generation occurred from late Paleocene to late 

Eocene (58 to 35 Ma); and (3) buried to shallowest depths, oil 

generation occurred in early Eocene (52 Ma) and ended only 

at Dobie Creek by early Miocene (19 Ma). Continued burial in 

the deeper part of the basin elevated maturities to a level sufficient to initiate cracking of oil to gas between about 37 Ma 

and 16 Ma; however, transformation ratios are only between 

2 and 9 percent, indicating that the cracking of oil to gas does 

not contribute significantly to the gas potential of the basin 

(Roberts and others, 2008). As with gas generation rates of oil 

generation during the last 10 Ma have slowed due to postmiddle Miocene regional uplift and exhumation of the basin 

(Roberts and others, 2008).

Events Chart

The events chart in figure 30 summarizes the essential elements of source rock, reservoir rock, seal rock, and 

overburden rock, and the processes of generation, migration, 

accumulation, and trap formation that are essential to form 

petroleum accumulations. Source rocks include marine shales 

deposited from Early to Late Cretaceous time (≈105–80 Ma) 

and include the Lower Cretaceous Thermopolis Shale, and the 

Upper Cretaceous Mowry and Cody Shales, along with marine 

shales in the Frontier Formation. Coal beds in the Upper 

Cretaceous Mesaverde and Meeteetse Formations and Paleocene Fort Union Formation (≈82–55 Ma) are also believed to 

be gas-source rocks. Reservoir rocks range in age from Early 

Cretaceous to Paleocene (≈134–55 Ma) and include (1) fluvial 

sandstones and conglomerate in the Cloverly Formation, (2) 

fluvial and estuarine sandstones in the Muddy Sandstone, (3) 

sandstone and possibly fractured shale in the Mowry Shale, 

(4) marine sandstones in the Frontier Formation and upper part 

of the Cody Shale, (5) marginal marine and fluvial sandstones 

and coal beds in the Mesaverde and Meeteetse Formations, (6) 

nonmarine sandstones in the Lance Formation, and (7) nonmarine sandstones and coal beds in the Fort Union Formation. 

The Thermopolis, Mowry, Cody, Lewis, and Bearpaw Shales 

provide thick regional seals. In addition, shales interbedded 

with sandstone reservoirs provide local seals.

Important structural traps formed during the Laramide 

orogeny where compressional tectonics formed numerous 

anticlines along the margins of the basin. Permeability in tight 

basin-centered accumulations is thought to be enhanced by 

fractures that resulted from Laramide deformation. Based on 

burial history and petroleum-generation modeling, the amount 

of overburden rock required to reach thermal maturation levels 

8.34 lb/gal .433 PSI/FT

9 lb/gal .468 PSI/FT

10 lb/gal .519 PSI/FT

11 lb/gal .571 PSI/FT

12 lb/gal .623 PSI/FT

13 lb/gal .675 PSI/FT

PRESSURE (PSI x 1,000)

Twl

Tfu

Kl

Kme

Kmv

Kc

Kf

Kmr

Kmt Kcv

TD

15,300

Kl

Tfu

Kmv

Kme

Kc

Kf

TD

14,966

Kl

Kme

Kmv

Kc

Kf

Tfu

TD

16,060

Twl

?

?

?

Twl

1 2 3 4 5 6 7 8 9 10 11 12

15

20

Top of overpressure

10

5

DEPTH IN FEET (x 1,000) 0 Mud weight from mud log—

 McCulloch Peak 2-9

Mud weight from log header—

 Bischo 1

SIP from DST, CIG McCulloch Pk. 1

SIP from DST, McCulloch Pk. 2-9

Producing interval

Mud weight from log header—

 CIG 1 McCulloch Peak

McCulloch

Peak 1

McCulloch

Peak 2-9

1 Bischo

McCulloch Peaks

E

INTERPRETED PRESSURE

GRADIENT

Figure 24.—Continued
Kmv

Kc Kf

Kmr

Tfu

Kl

Kml

Kmv

Kc

Kcv

Oregon Basin

West

Greyb

Five Mile

trend

Tw K

Kf

Kmr

?

?

J–d

J–d

J–d

Oregon Basin

thrust fault

g

g

pe

pe

pe

g

Kmt

MILES

0 5 10

Modied fromBlackstone (1986a)

MoSto

A 

Loch Katrine Unit 1

33-20 Rio Un

M 1 Adams ichaels Ranch 20-1

1 Emblem Bench

5,000

SL

-5,000

-10,000

-15,000

-20,000

A A

R =1.10% o

Kcv

Kmt

Kf

Kmr

Kc

Kmv

Kml

Kl

Tfu

Tw

Precambrian crystalline

 rocks

Paleozoic sedimentay rocks, undivided

Jurassic to Triassic sedimenta rocks, undivided

Lower Cretaceous Cloverly

Formation

Lower Cretaceous Muddy Sandstone and Thermopolis Shale

Upper Cretaceous Frontier

Formation and Mowry Shale

Upper Cretaceous Cody Shale

Upper Cretaceous Mesaverde Formation

Upper Cretaceous Meeteetse

Formation and Lewis Shale

Upper Cretaceous Lance

Formation

Paleocene Fort Union

Formation

Lower Eocene Willwood

Formation

EXPLANATION

J–d

g

pe

Figure 25. Diagrammatic east-west cross section of the central part of the Bighorn Basin, Wyoming and Montana, showing the extent of the ovebasin-centered gas accumulation (shown within the dotted red line). Line of section shown in figure 2. SL, sea level. Modified in part from Blackstand Stone (2004a). 
34 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

1.10

0.73

0.73

0.80

0.80

0.80

0.80

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Well sample point

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Mesaverde outcrop

Clark's

Fork

sub-basin

Figure 26. Map showing levels of thermal maturity based on vitrinite reflectance (in percent) for the top of the Cody Shale in 

the Bighorn Basin, Wyoming and Montana. Modified from Nuccio and Finn (1998).

sufficient to generate hydrocarbons (gas) from the oldest 

source rocks—Mowry and Thermopolis Shales—accumulated by about 63 Ma in the deeper parts of the basin (fig. 28). 

Continued subsidence and deposition progressively buried the 

younger source rocks until they achieved levels of thermal 

maturity sufficient to generate hydrocarbons. Locally in some 

of the deeper parts of the basin, generated oil reached thermal 

maturities sufficient to initiate thermal cracking of oil to gas. 

Gas generated in the deeper parts of the basin migrated vertically, in some cases many thousands of feet into younger, less 

mature reservoirs. Around 10 Ma the Rocky Mountain region, 

including the Bighorn Basin, was uplifted, initiating erosion 

and rapid basin excavation. Subsequent cooling significantly 

reduced the rates of hydrocarbon generation. However, computer modeling indicates that in some parts of the basin minor 

generation may continue to the present day.
Assessment Units and Results 35

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

1.10

0.80

0.73

0.73

0.73

0.80

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Well sample point

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Mesaverde outcrop

Clark's

Fork

sub-basin

Figure 27. Map showing levels of thermal maturity based on vitrinite reflectance (in percent) for the top of the Mesaverde 

Formation in the Bighorn Basin, Wyoming and Montana. Modified from Nuccio and Finn (1998).

Assessment Units and Results 

An assessment unit (AU) is a mappable volume of 

rock within a Total Petroleum System (TPS) that contains 

known or postulated oil and gas accumulations that share 

similar geologic characteristics (Klett and others, 2000). The 

Cretaceous–Tertiary Composite TPS (503402) is subdivided 

into seven AUs. Three are identified as basin-centered gas 

accumulations (BCGA): the Muddy-Frontier Sandstone and 

Mowry Fractured Shale Continuous Gas AU (50340261), 

the Cody Sandstone Continuous Gas AU (50340263), 

and the Mesaverde Continuous Gas AU (50340264). One 

fractured shale oil accumulation, the Mowry Fractured 

Shale Continuous Oil AU (50340262), and two coalbed 

gas accumulations: the Mesaverde-Meeteetse Coalbed 

Gas AU (50340281), and the Fort Union Coalbed Gas AU 

(50340282) were defined. One conventional AU was defined, 

the Cretaceous–Tertiary Conventional Oil and Gas AU 

(50340201). The Cretaceous–Tertiary Conventional Oil and 

Gas AU (50340201) and the Muddy-Frontier Sandstone and 
36 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Late Cretaceous Paleocene Eocene Oligocene Miocene

80 70 60 50 40 30 20 10 0

Age (Ma)

80 70 60 50 40 30 20 10 0

Red Point/Husky

F

E

D

C

B

A

G

Santa Fe Tatman

F

E

D

C

B

A

G

F

E

D

C

B

A

Emblem Bench G

Amoco BN 1 F

E

D

C

B

G

Sellers Draw

F

E

D

C

B

A

G

Dobie Creek F

E

D

C

B

A

G

0.5%Ro

0.8%Ro

2.0%Ro

Minor gas generation

 may continue

Timing of 

gas generation

Burial depth

Source rock (base)

B Mowry Shale

A Thermopolis Shale

D Cody Shale

C Frontier Formation

E Mesaverde Formation

F Meeteetse Formation

G Fort Union Formation

Santa Fe Tatman

 Amoco BN 1

 Doctor Ditch

Emblem Bench

Red Point/Husky

Dobie Creek

Sellers Draw

McCulloch Peak

Deep

Intermediate

Shallow

—Start of gas

—Peak of gas

—End of gas

Doctor Ditch G F

E

D

C

B

A

McCulloch Peak F

E

D

C

B

A

G

Figure 28. Timing of gas generation from Type-III gas-prone source rocks in the Bighorn Basin, Wyoming and Montana. 

From Roberts and others (2008). Ro, vitrinite reflectance.
Late Cretaceous Paleocene Eocene Oligocene Miocene

70 60 50 40 30 20 10

AGE (Ma)

80 0

80 70 60 50 40 30 20 10 0

McCulloch Peak

1

2

1

2

Red Point/Husky

TR 2%

1

2 Emblem Bench TR 6%

TR 9%

Santa Fe Tatman

1

2

Dobie Creek

1

2

Amoco BN 1 2

Doctor Ditch

2

1

1

2

Sellers Draw

Santa Fe Tatman

 Amoco BN 1

 Doctor Ditch

Emblem Bench

Red Point/Husky

Dobie Creek

Sellers Draw

McCulloch Peak

2 Mowry Shale

1 Thermopolis Shale

Start of oil

Peak oil

End of oil

Start of gas

Minor generation

 may continue

Source rocks (middle)

Minor generation

 may continue

Timing of 

oil generation

Timing of 

oil cracking to gas

Burial depth

Deep

Intermediate

Shallow

Figure 29. Timing of oil and gas generation from Type-II oil-prone source rocks in the Bighorn Basin, Wyoming 

and Montana. From Roberts and others (2008). TR, transformation ratio.

Assessment Units and Results 37
38 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

GenerationTrap formation

Overburden rock

Reservoir rock

Seal rock

Source rock

Rock unit

migration-accumulation

MESOZOIC (part) CENOZOIC

Kf Kc Kmv

Cretaceous

Early Late

Paleogene Neogene

Kl Tfu

Eocene Mioc.

Pliocene

Oligocene

Paleocene

Kmr Kmd

Kcv

Kt

Laramide orogeny Ttw

Gas generation from Type-III kerogen 63 Ma

Oil generation from Type-II kerogen 58 Ma

Gas generation from cracking of oil 36 Ma

BCGA

Kme

J

Jm

post-middle

Eocene basin ll

Regional uplift

and erosion

Petroleum

System Events

Geologic Time

Scale

(m.y.b.p.)

125 100 75 50 25 0

Figure 30. Events chart summarizing the essential elements and processes of the Cretaceous–Tertiary Composite Total 

Petroleum System. Jm, Morrison Formation; Kcv, Cloverly Formation; Kt, Thermopolis Shale; Kmd, Muddy Sandstone; 

Kmr, Mowry Shale; Kf, Frontier Sandstone; Kc, Cody Shale; Kmv, Mesaverde Formation; Kme, Meeteetse Formation; 

Kl, Lance Formation; Tfu, Fort Union Formation; Ttw, Tatman and Willwood Formations undivided. BCGA, basin-centered 

gas accumulation.

Mowry Fractured Shale Continuous Gas AU (50340261) both 

have established production; the remaining five AUs have no 

production and are considered hypothetical. (Note: the coding 

numbers follow the worldwide coding system used by the 

USGS). 

Muddy-Frontier Sandstone and Mowry 

Fractured Shale Continuous Gas Assessment 

Unit (AU 50340261)

The Muddy-Frontier Sandstone and Mowry Fractured 

Shale Continuous Gas Assessment Unit (AU 50340261) is 

an established AU that is thought to have additional potential 

to produce gas from low permeability fluvial and estuarine 

sandstone reservoirs, marine deltaic and shoreface sandstone reservoirs, and fractured marine shale reservoirs. The 

AU consists of two areas totaling approximately 1,500 mi2

in the center of the Bighorn Basin and in the deepest part of 

Clark’s Fork subbasin (fig. 31). The AU boundary is defined 

as that part of the petroleum system where the conditions 

favorable for continuous gas accumulations are met using 

the criteria established by Spencer (1987): (1) greater than 

normal pressures, (2) present-day temperatures greater that 

200° F, (3) vitrinite reflectance greater than 0.8 percent, (4) 

presence of low permeability sandstone or fractured shale, 

and (5) no reported gas/water contacts. Based on relatively 

sparse data, these conditions are generally met at a depth of 

around 12,000 ft, except in the Clark’s Fork sub-basin where 

the boundary is placed at a deeper level. These contour lines 

have been modified where information was obtained from (1) 

drillstem test results and (or) mud weights that indicate greater 

than normal pressure gradients, (2) wells with mud logs that 

have gas shows in reservoir units, and (3) vitrinite reflectance 

data for rocks of the AU that show the area is mature for 

gas generation. The south edge of the AU corresponds to a 

fault described by Stone (1999) and also shown by Ver Ploeg 

(1985), which Stone interprets to be a continuation of the 

Tensleep fault (fig. 3). The west boundary of the main assessment area is placed at the projected footwall cutoff of the top 

of the Frontier Formation, which is slightly west of the surface 

trace of the Oregon Basin thrust fault (see fig. 25). 
0

5000

-5000

0 0

-5000

-5000

0

5000

0

0

0

-10000

-5000

0

5000

0

5000

-15000

-10000

-5000

-5000

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Fault

Tertiary volcanic rocks

Cloverly Formation

Producing well

Tested cell

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Cretaceous-Tertiary

 Composite TPS 503402

Muddy-Frontier Sandstone

 and Mowry Fractured Shale

 Continuous Gas AU 50340261

Rattlesnake Mountain

anticline

Figure 31. Map showing the areal extent of the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous 

Gas Assessment Unit (50340261) in the Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming 

and Montana. Structure contours drawn on top of the Cloverly Formation; contour interval 1,000 ft. TPS, Total Petroleum 

System; AU, Assessment Unit.

Potential additions to reserves would come from drilling depths ranging from about 10,500 to 21,000 ft. There are 

about 144 wells within the AU boundary, of which 23 are 

interpreted to be wells tested in the formation. Some of the 

test wells had minor production, gas shows and (or) production, and drillstem tests; others reached their total depth in 

the AU indicating a test. Five wells had production above the 

minimum cutoff of 20 MMCFG; however, only the Sellers 

Draw well (see fig. 23 for location) had production exceeding 

one BCFG. The remaining 121 wells were either drilled in the 

hanging wall of the Oregon Basin thrust fault, and therefore 

did not test the basin center, or did not show sufficient evidence that the operator tested the units for gas; for example, in 

one well the Cretaceous rocks defining the AU were cased off 

and the obvious target was deeper in the Paleozoic strata. The 

paucity of data unit makes most of the area of the AU untested 

and gives rise to considerable uncertainty in the evaluation of 

potential additions to reserves. Analogs are drawn from similar 

Assessment Units and Results 39
40 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

assessment units in the Wind River and Green River Basins 

(Kirschbaum and Roberts, 2005; Johnson and others, 2007).

Input data for assessment of the Muddy-Frontier Sandstones and Mowry Fractured Shale Continuous Gas AU is 

shown on the FORSPAN ASSESSMENT MODEL FORM 

in Appendix A. The minimum and maximum areas for the 

AU are 872,000 acres and 1,066,000 acres, respectively, with 

a calculated mean of 969,000 acres. This range in area size 

reflects the uncertainty of the location of structures in the 

subsurface and the lack of data available to constrain key 

parameters such as the zone of overpressure. The untested area 

within the AU that has potential for additions to reserves is 0.6 

and 22.5 percent, respectively, with a calculated mean of 8.4 

percent (Appendix A). The range in the percentages is based 

on the uncertainty in the amount of area that is interpreted to 

have enhanced permeability due to fracturing, and on a range 

of success ratios that can be applied to these areas based on 

analog data.

The total recovery per cell or estimated ultimate recovery (EUR) for untested cells having potential for additions 

to reserves is 0.02 BCFG at the minimum, 0.35 BCFG at the 

median, and 7.5 BCFG at the maximum, with a calculated 

mean of 0.57 BCFG (Appendix A). The EUR distribution is 

typically based on historical production, but because of the 

lack of data in the Bighorn Basin, analogs from the Southwestern Wyoming Province and Wind River Basin Province 

were used to help estimate a range of production (fig. 32). The 

median and maximum values are conservatively estimated to 

be half the values of the Southwestern Wyoming Province, 

such values being from the largest data set available for rocks 

of similar reservoirs properties but where, it should be noted, 

that the thermal maturities of the source rocks are higher overall than in the Bighorn Basin.

The minimum and maximum area per cell of untested 

cells having the potential for additions to reserves is 40 and 

300 acres, respectively, with a calculated mean of 130 acres. 

This is the most difficult parameter to determine, so these 

estimates are derived directly from the Mowry TPS in the 

Southwestern Wyoming Province (Kirschbaum and Roberts, 

2005), which was based on current and anticipated wellspacing information for that area.

The mean estimate for undiscovered gas resources 

that have potential for additions to reserves in the MuddyFrontier Sandstone and Mowry Fractured Shale Continuous 

Gas Assessment Unit (50340261) is 348 billion cubic feet of 

gas (BCFG); tabulated assessment results are summarized in 

table 1.

0 10 20 30 40 50 60 70 80 90 100

10,000

100

1,000

1

10

100,000

PERCENT OF SAMPLE

EUR (MMCF)

Bighorn Basin Province

Southwest Wyoming Province

Wind River Basin Province

Figure 32. Estimated ultimate recovery (EUR) distributions for wells in the Frontier Formation, 

Muddy Sandstone, and Cloverly Formation and equivalents in the Southwestern Wyoming, Wind 

River Basin, and Bighorn Basin Provinces. The EURs are truncated to remove wells below 10 million 

cubic ft of gas. MMCF, million cubic ft.
Assessment Units and Results 41

Mowry Fractured Shale Continuous Oil 

Assessment Unit (AU 50340262)

The Mowry Fractured Shale Continuous Oil Assessment 

Unit (AU 50340262) is thought to have potential to produce 

oil from fractured marine siliceous shale and interbedded 

siltstones and thin sandstones of the Mowry Shale. It is, however, classed as hypothetical in that there have been no wells 

producing oil from fractured reservoirs nor any wells known 

to have been tested for fractured oil. The AU is approximately 

1,000 mi2 in the eastern and southern parts of the Bighorn 

Basin (fig. 33). The AU boundaries encompass the area 

between the depths of 8,000–12,000 ft to the top of the Mowry 

Shale, such depths approximately matching the oil window for 

Type-II kerogen present in the formation. The Mowry contains 

both Type-II and -III kerogen, and the measured hydrogen 

indices show some oil-prone source rock are present. The transition from oil to gas generation at about the 12,000 ft depth 

in the Mowry was based loosely on the transition to peak gas 

development (0.8 percent Ro) from Type-III organic matter.

Input data for the assessment of AU 50340262 is shown 

on the FORSPAN ASSESSMENT MODEL FORM in Appendix B. The minimum and maximum areas in which are the 

Mowry is considered to have thermal maturity values in the 

oil window are 581,000 and 710,000 acres, respectively, with 

a calculated mean of 646,000 acres. This range-in-sizes area 

reflects high uncertainty in determining the extent of the pod 

of mature source rock, which may, in large part, be due to 

the lack of vitrinite reflectance data available for the Mowry 

in the Bighorn Basin. The area interpreted to have potential 

for additions to reserves ranges from 0.1 to 17 percent of the 

AU. The highest percentage area represents those areas where 

major structures are present in the AU and assumes fractures 

are present in the Mowry. This range in values also reflects the 

uncertainty of this hypothetical AU. The low end of values is a 

worst case scenario.

The closest analog for the Mowry Fractured Shale 

hypothetical AU 50340262 is from the Mowry AU in the 

Powder River Basin (Anna and Cook, 2008); however, the 

Mowry source rock there has higher TOC and Type-II kerogen 

Total Petroleum System 

and Assessment Unit

Field 

Type

Total Undiscovered Resources

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

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

Cretaceous-Tertiary Composite TPS

Muddy-Frontier Sandstone and 

Mowry Fractured Shale Gas AU Gas 119 298 743 348 0 0 1 0

Mowry Fractured Shale Oil AU Oil 2 4 11 5 1 2 6 2 0 0 0 0

Cody Sandstone Gas AU Gas 14 33 80 38 0 0 0 0

Mesaverde Sandstone Gas AU Gas 13 28 63 32 0 0 0 0

Mesaverde-Meeteetse Formation 

Coalbed Gas AU CBG 38 87 196 98 0 0 1 0

Fort Union Formation Coalbed 

Gas AU Gas 14 29 59 32 0 0 0 0

Total Continuous Resources 2 4 11 5 199 477 1,147 550 0 0 2 0

Cretaceous-Tertiary Composite TPS

Cretaceous-Tertiary 

Oil and Gas AU

Oil 4 12 24 13 9 29 66 32 1 2 4 2

Gas 53 176 370 189 1 3 6 3

Total Conventional Resources 4 70212 24 13 62 205 436 221 2 5 10 5

Total Undiscovered 

Oil Resources 6 16 35 18 261 682 1,583 771 2 5 12 5

Continuous 

Resources

Conventional 

Resources

Table 1. Cretaceous–Tertiary Composite Total Petroleum System assessment results.

[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 as NGL (natural gas liquids). F95 represents a 95 percent chance of at least the amount 

tabulated; other fractiles are defined similarly. TPS, total petroleum system; AU, assessment unit. Gray shading indicates not applicable]
42 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

contents (Burtner and Warner, 1984). The estimated ultimate 

recoveries for 17 Mowry wells in the Powder River Basin 

range from 2 to 170 thousand barrels of oil (MBO) (fig. 34). 

The Mowry EURs in the Powder River Basin are also similar 

to the Niobrara EURs in that basin (fig. 34). A larger dataset 

is available from the Permian Spraberry Formation in the 

Midland Basin where there are about 7,000 producing wells. 

Although the depositional environment is different, the Mowry 

and Spraberry have similarities—that is, low permeability 

fractured siltstones and sandstones and similar TOC content 

(Spraberry: 1.1–2.8 weight percent, Handford, 1981; Mowry: 

0.8 to 3.6 weight percent, fig. 19).

For the Mowry Fractured Shale AU 50340262, the minimum recovery is set at 0.002 million barrels of oil (MMBO). 

The maximum is estimated at 0.35 MMBO to reflect a 

slightly lower maximum EUR than in the Powder River Basin 

(fig. 34). Additionally, most of the high end production from 

the maturely explored Spraberry Formation in the Midland 

Basin is also within this range of values. The median EUR is 

estimated at 0.025 MMBO, which is close to the median in 

0

5000

-5000

0 0

-5000

-5000

0

5000

0

0

0

-10000

-5000

0

5000

0

5000

-15000

-10000

-5000

-5000

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Fault

Tertiary volcanic rocks

Cloverly Formation

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Mowry Fractured Shale

 Continuous Oil AU 50340262 

Rattlesnake Mountain

anticline

Cretaceous-Tertiary

 Composite TPS 503402

Figure 33. Map showing areal extent of the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), 

Bighorn Basin, Wyoming and Montana. Structure contours drawn on top of the Cloverly Formation; contour interval 

1,000 ft. TPS, Total Petroleum System; AU, Assessment Unit.
Assessment Units and Results 43

the Powder River Basin. Drainage areas are taken from the 

Powder River Basin analog, with a minimum of 40 acres, a 

mean of 290 acres and a maximum of 640 acres (Larry Anna, 

written commun., 2007).

The mean estimate for undiscovered oil resources in the 

Mowry Fractured Shale Continuous Oil AU (50340262) that 

have potential for additions to reserves is 5 MMBO; tabulated 

assessment results are summarized in table 1.

Cody Sandstone Continuous Gas Assessment 

Unit (AU 50340263)

The Cody Sandstone Continuous Gas Assessment Unit 

(AU 50340263) is a hypothetical AU that is believed to have 

the potential to produce gas from low permeability marine 

sandstone reservoirs in the upper part of the Cody Shale 

(fig. 7). It encompasses approximately 660 mi2 in the central 

part of the Bighorn Basin (fig. 35). The north, east, and south 

boundaries of the AU were drawn, using sparse well data to 

generally outline areas where (1) drillstem test results and (or) 

mud weights indicate greater than normal pressure gradients, 

and (2) mud logs record continuous gas shows in downdip 

areas along the deep trough of the basin (Johnson and Finn, 

1998b). The west boundary is projected beneath the Oregon 

Basin thrust fault and is drawn approximately at the cutoff 

of the Cody Shale in the footwall of the fault (Stone 1993; 

Taylor, 1998). Drilling depths range from about 12,000 to 

19,000 ft. The AU is essentially unexplored, with only nine 

wells penetrating the Cody Shale section (fig. 35). Of these 

wells, none have reported any production from the Cody 

Shale; therefore, the AU is considered 100 percent untested 

and classified as hypothetical. Because of this, the Cody 

Sandstone Continuous Gas AU (50350262) from the Wind 

River Basin assessment was used as an analog because of 

similar geologic characteristics (Johnson and others, 2007).

Input data for the assessment is shown on the FORSPAN 

ASSESSMENT MODEL FORM in Appendix C. The minimum and maximum areas for the AU are 378,000 and 462,000 

acres, respectively, with a calculated mean of 420,000 acres. 

The reason for the wide range is because of the structural 

complexity along the Oregon Basin thrust fault at the west side 

and the small amount of well data used to determine the other 

boundaries. The minimum and maximum percentages of the 

untested AU area that have potential for additions to reserves 

are 0.3 and 19.6 percent, respectively, with a calculated mean 

of 7.6 percent (see Appendix C). These percentages represent well success-ratios (from the Wind River Basin analog) 

applied to possible “sweet spots,” where reservoir permeability may be enhanced by fracture development associated with 

Laramide compression (anticlinal trends and thrust faults) and 

post-Laramide extension (normal faulting).

PERCENT OF SAMPLE

0 10 20 30 40 50 60 70 80 90 100

EUR (MBO) 10,000

1,000

100

10

1

Niobrara Formation, Powder River Basin

Mowry Shale, Powder River Basin

Spraberry Formation, Permian Basin

Figure 34. Estimated ultimate recovery (EUR) distributions for wells producing from the 

Mowry Shale and Niobrara Formation in the Powder River Basin, Wyoming and Montana, and 

the Spraberry Formation in the Midland Basin, Texas. The EURs are truncated to remove wells 

below one thousand barrels of oil (MBO). The cutoff in the Bighorn Basin is 2 MBO. MBO, 

thousand barrels of oil.
44 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

The minimum, median, and maximum total recovery per 

cell for untested cells having potential for additions to reserves 

is 0.02, 0.2, and 5 BCFG, respectively, with a calculated mean 

of 0.34 BCFG (Appendix C). These values are based on the 

low end of the EUR distribution of the analog AU in the Wind 

River Basin (Johnson and others, 2007) because of the general 

lack of reservoir rock in the upper part of the Cody Shale in 

the Bighorn Basin (figs. 36, 37), and overall lower thermal 

maturities in the Bighorn Basin as compared to the Wind River 

Basin (Nuccio and Finn, 1998). Also, most of the wells that 

make up the EUR distribution for the analog Cody Shale AU 

in the Wind River Basin are located on the Madden anticline, a 

large and highly fractured “sweet spot” (fig. 36). Based on the 

extensive seismic data that are available, it is unlikely that a 

similar “sweet spot” is present in the Bighorn Basin (fig. 38).

The minimum and maximum area per cell of untested 

cells having the potential for additions to reserves is 40 and 

640 acres, respectively, with a calculated mean of 280 acres. 

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

5000

-5000

-10000

-5000

0 -5000

0

5000

0

0

0

-5000

0

0

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Fault

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Mesaverde outcrop

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Cretaceous-Tertiary

 Composite TPS 503402

Cody Sandstone

 Continuous Gas AU

 50340263 

Control well

Figure 35. Map showing areal extent of the Cody Sandstone Continuous Gas Assessment Unit (50340263), Bighorn Basin, 

Wyoming and Montana. Structure contours drawn on top of the Teapot Sandstone Member of the Mesaverde Formation; 

contour interval 1,000 ft. TPS, Total Petroleum System; AU, Assessment Unit.
Assessment Units and Results 45

These values are from the Wind River Basin analog and, 

according to Dunleavy and Gilbertson (1986), reflect the variability that is typical of many fractured reservoirs.

The mean estimate for undiscovered gas resources 

in the Cody Sandstones Continuous Gas Assessment Unit 

(50340263) that have potential for additions to reserves is 

38 BCFG; tabulated assessment results are summarized in 

table 1.

Mesaverde Sandstone Continuous Gas 

Assessment Unit (AU 50340264)

The Mesaverde Sandstone Continuous Gas Assessment 

Unit (AU 50340264) is a hypothetical AU that is believed to 

have the potential to produce gas from low permeability fluvial 

and marginal marine sandstone reservoirs in the Mesaverde 

Formation. The AU encompasses approximately 345 mi2 in 

the central part of the Bighorn Basin (fig. 39). The north, east, 

and south boundaries were drawn using sparse well data that 

generally outlines areas where drillstem tests indicate greater 

than normal pressure gradients and (or) mud logs record continuous gas shows in the downdip areas along the deep trough 

of the basin (Johnson and Finn, 1998b). The west boundary is 

projected beneath the Oregon Basin thrust fault and is drawn 

approximately at the cutoff of the Mesaverde Formation in 

the footwall of the fault (Stone, 1993; Taylor, 1998). Drilling 

depths range from about 12,500 to 17,500 ft (fig. 40). Because 

it is classed as hypothetical, analogs were used in the assessment of this AU, including Mesaverde production at Muddy 

Ridge (Johnson and others, 2007), and Lance/Fort Union production at Sand Mesa from the Wind River Basin, Wyoming 

(Troy Cook, written commun., 2008). These areas were chosen 

because they represent production from lenticular fluvial sandstones in areas with lower thermal maturities similar to levels 

in the Bighorn Basin, and because they are not associated with 

major anticlinal structures.

The Mesaverde Sandstone Continuous Gas AU is 

essentially unexplored, with only four wells penetrating the 

Mesaverde section, only one of which reported gas production 

from the formation (fig. 39). According to Cardinal and others 

(1989), the Sellers Draw Unit 1(see fig. 39 for location) was 

initially completed in the Muddy Sandstone in 1978 at a depth 

of about 19,500 ft. According to the Wyoming Oil and Gas 

Conservation Commission (WOGCC), the well was shut-in 

in 1997, then was recently recompleted in the Mesaverde at a 

depth of about 16,100 ft. At the time of this assessment there 

was not enough production history of the well to determine 

if the well will ultimately make the minimum of 0.02 BCFG 

0 10 20 30 40 50 60 70 80 90 100

PERCENT OF SAMPLE

.001

.01

.1

1

10

100 EUR (BCF)

Other wells

Madden anticline wells

Figure 36. Estimated ultimate recovery (EUR) distribution for wells greater than 0.02 billion 

cubic feet of gas in the Cody Sandstone Continuous Gas Assessment Unit in the Wind River 

Basin Province, Wyoming, used as an analog for Assessment Unit 50340263. BCF, billion 

cubic feet.
Wind River Basin Bighorn Basin

Madden anticline

Wickersham Draw 3 BCF–50 BCF

central WRB

≈0.06 BCF

Ocean Lake-Muddy Ridge

Wind River Reservation

≈.06–0.15 BCF

EXPLANATION

Gas producing zone

Marine shale

Marine sandstone

Coastal plain-sandstone, siltstone, shale, and coal

Gas show

Perforated interval

Drillstem test interval

Mesaverde

Formation

Cody Shale

Dolis 2-35 1 Emblem Bench 1 Red Point II 

21-16 Bucy State Tribal 33X-10 GR R

15

GR R

16

GR R

18

17

GR R C

16

17

GR R

11

12

Figure 37. Comparison of well log responses between the sandy interval in the upper part of the Cody Shale in the Bighorn Basin, Montana, and the upper sandy member of the Cody Shale in the Wind River Basin.
Assessment Units and Results 47

to qualify as a producer, therefore the AU is considered hypothetical and essentially 100 percent untested.

Input data for the assessment are shown on the FORSPAN ASSESSMENT MODEL FORM in Appendix D. The 

minimum and maximum areas assigned to the AU are 199,000 

and 243,000 acres, respectively, with a calculated mean of 

221,000 acres; this wide range is because little is known about 

subsurface structure along the west boundary and because of 

the uncertainty over the other boundaries owing to the lack 

of well data. The minimum and maximum percentages of the 

untested AU area that has potential for additions to reserves 

are 0.2 and 8.5 percent, respectively, with a calculated mean 

of 3.6 percent (Appendix D). These percentages represent well 

success-ratios (from the Wind River Basin analogs) applied to 

possible “sweet spots,” where reservoir permeability may be 

enhanced by fracture development associated with Laramide 

compressional features (anticlinal trends and thrust faults) and 

normal faulting associated with post-Laramide extension.

The minimum, median, and maximum total recovery per 

cell for untested cells having potential for additions to reserves 

50340263

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Cloverly Formation

Seismic survey

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Rattlesnake Mountain

anticline

Cretaceous-Tertiary Composite

 TPS 503402

Cody Sandstone Continuous

 Gas AU 50340263 

Figure 38. Map showing coverage (in part) of commercially available seismic surveys in the Bighorn Basin, Wyoming and 

Montana. TPS, Total Petroleum System; AU, Assessment Unit.
48 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

5000

-5000

-10000

-5000

0 -5000

0

5000

0

0

0

-5000

0

0

Sellers Draw

Unit 1

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Fault

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Mesaverde outcrop

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Cretaceous-Tertiary

 Composite TPS 503402

Mesaverde Sandstone

 Continuous Gas AU

 50340264 

Control well

Figure 39. Map showing areal extent of the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), Bighorn 

Basin, Wyoming and Montana. Structure contours drawn on top of the Teapot Sandstone Member of the Mesaverde 

Formation; contour interval 1,000 ft. TPS, Total Petroleum System; AU, Assessment Unit.

is 0.02, 0.2, and 5 BCFG, respectively, with a calculated mean 

of 0.34 BCFG (Appendix D). These values are based on the 

EUR distribution from the analog areas in the Wind River 

Basin, but are lower because of the overall lower volume of 

potential sandstone reservoir rock in the Mesaverde section 

in the Bighorn Basin as compared to the Wind River Basin 

(fig. 41).

The minimum and maximum area per cell of untested 

cells having the potential for additions to reserves is 20 and 

180 acres, respectively, with a calculated mean of 83.3 acres 

and a mode of 50 acres. These values are also from the 

Mesaverde analogs in the Wind River Basin, the smaller 

values reflecting potential future production from lenticular fluvial sandstone bodies and the larger values reflecting 

potential future production from blanket-like marginal marine 

sandstones (Johnson and others, 2007).

The mean estimate for undiscovered gas resources that 

have potential for additions to reserves in the Mesaverde 

Sandstone Continuous Gas AU (50340264) is 32 BCFG; tabulated assessment results are summarized in table 1.
Assessment Units and Results 49

7000

10000

10000

5000

5000

5000

15000

17000

1

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Fault

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Mesaverde outcrop

Figure 40. Map showing approximate depth to top of the Teapot Sandstone Member of the Mesaverde Formation, 

Bighorn Basin, Wyoming and Montana; contour interval 1,000 ft.

Mesaverde-Meeteetse Formation Coalbed Gas 

Assessment Unit (AU 50340281)

The Mesaverde-Meeteetse Formation Coalbed Gas 

Assessment Unit (AU 50340281) is a hypothetical AU that is 

believed to have the potential to produce gas from coal beds 

in the Mesaverde and Meeteetse Formations (Judith River 

Formation and Eagle Sandstone in Montana). These formations were assessed jointly because of general continuity of the 

coal-bearing section extending from the Mesaverde Formation 

upward into the Meeteetse Formation. The AU encompasses 

approximately 2,500 mi2 around the periphery of the Bighorn 

Basin (fig. 42). The upper limit is defined as the base of the 

Mesaverde Formation outcrop or equivalent rocks, and the 

lower limit is defined as the area where coal beds are interpreted to be present at depths of 6,000 ft or less (fig. 40). Coal 

beds at greater depths were not considered due to the potential 

decrease in permeability with increasing depth (Rice and 

others, 1996). 
50 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

0 10 20 30 40 50 60 70 80 90 100

PERCENT OF SAMPLE

100

10

1

.1

.01

.001

EUR (BCF)

6 BCF

2 BCF

Muddy Ridge

Sand Mesa (Lance and Fort Union

 Formations)

Figure 41. Estimated ultimate recovery (EUR) distributions for wells producing from the 

Mesaverde, Lance, and Fort Union Formations in the Wind River Basin, Wyoming. BCF, 

billion cubic feet.

Estimates of the total in-place coal resources in Upper 

Cretaceous and Tertiary strata of the Bighorn Basin are on the 

order of 1.8 billion short tons (R.W. Jones, written commun., 

as reported in Love, 1988). Coal mining in the basin began in 

the late 1800s, and more than 12,000,000 tons were produced 

from Cretaceous coal deposits in the Wyoming part of the 

basin. About 90 percent of the total came from some thirteen 

mines producing coal in the Upper Cretaceous Mesaverde 

Formation near Gebo (Glass and others, 1975); currently there 

are no mines.

Upper Cretaceous coal beds are concentrated in the 

lower and middle parts of the Mesaverde Formation and in 

the upper part of the Meeteetse Formation (Johnson, 1998). 

Individual coal beds are as thick as 12 ft, but typically range 

from 4 to 6 ft or less (Glass and others, 1975; Johnson, 1998). 

In the subsurface, the maximum, combined coal thickness for 

both formations is 38 ft, with the thicker coal accumulations 

primarily in the southern part of the basin. The apparent rank 

of coal beds in the Mesaverde Formation ranges from high 

volatile C bituminous to subbituminous A or B; the bituminous coal is restricted to one coalfield (Silvertip field) near 

the Wyoming-Montana state line (fig. 20). Meeteetse coals 

are subbituminous in rank (Glass and others, 1975). Reported 

thermal maturity (R0) values for coal in the Mesaverde Formation range from a low of 0.27 percent in outcrops in the 

western part of the basin to more than 1.10 percent in the deep 

basin adjacent to the Oregon Basin thrust fault; Meeteetse coal 

thermal maturities range from 0.35 percent in outcrops to more 

than 0.90 percent in the deep basin (Nuccio and Finn, 1998; 

Finn and Pawlewicz, 2007).

Test wells for coalbed gas in the Mesaverde Formation 

have been drilled in Wyoming, adjacent to the WyomingMontana state line, and at one location in the southwestern 

part of the basin near Grass Creek (WOGCC, 2007). However, 

there have been no published results from this drilling and the

AU is essentially 100 percent untested. The AU is classed as 

hypothetical because there is currently no production of coalbed gas from the Mesaverde, Meeteetse, or equivalent strata 

in the basin (WOGCC, 2007), so analogs from the Powder 

River Basin and Piceance Basin (in Colorado) (Flores, 2004; 

Johnson and Roberts, 2003) were used in this assessment on 

the basis that they produce coal of similar rank (primarily 

subbituminous).

Input data for the assessment of AU 50340281 is 

shown on the FORSPAN ASSESSMENT MODEL FORM 

in Appendix E. The minimum and maximum areas for the 

AU are 1,457,000, and 1,781,000 acres, respectively, with 

a calculated mean of 1,619,000 acres. The reason for the 

wide range in acreages is because drill data are lacking for 

determining the depth to or even the presence of coal beds 

in the lower part of the Mesaverde Formation in many areas.

The minimum and maximum percentages of the untested AU 

area that has potential for additions to reserves are 0.5 and 14 

percent, respectively, with a calculated mean of 5.7 percent 
Assessment Units and Results 51

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W

R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Bighorn Basin Province

Cretaceous-Tertiary Composite TPS 503402

Mesaverde-Meeteetse Coalbed

 Gas AU 50340281

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Bighorn 

Mesaverde outcrop

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Rattlesnake Mountain

anticline

Drill hole—Total coal thickness

 (in ft) shown alongside

19

Drill hole—No coal identified in

 the Mesaverde or Meeteetse

 Formation

Cumulative coal thickness (in ft)

 in measured sections of the

 Mesaverde and Meeteetse

 Formations

10

Coalbed gas test 

Mine

CBM test wells

CBM test well

19

16

16

19

11

7

7

7

9

7

7

7

9

8

4

3

2

5

4

4

2

2

6

6

9

9

9

3 3

5 3 5 5

8

10

11

17

13

13

13

18 16

16

6

4

4

4

4

5 5

5

4 9

8

10

12

14

10

3

3

2

2

23

6

6 15

13

20

16

16 21 15

7

3

2

3 3

3

3

7

7

7

9

7 17

9

9

9

9

8 8 8

8

8

3

4

12

15 11

14

10

10

10 10

20

24

11

11

15 15

13

18 6

12

6

6

6

6

23

25

24

33 31 29

24 25 38 22 30 29

21

5

7

13

10

40

Gebo

Figure 42. Map showing areal extent of the Mesaverde-Meeteetse Formation Coalbed Gas Assessment Unit (50340281), 

Bighorn Basin, Wyoming and Montana. Coal thicknesses (in ft) are a composite of Mesaverde and Meeteetse thicknesses 

reported by Johnson (1998). CBM, coalbed methane. TPS, Total Petroleum System; AU, Assessment Unit.

and a mode of 2.5 percent (see Appendix E). The minimum 

area restricts coalbed gas potential to areas in the southern 

part of the basin where total coal thicknesses exceed 30 ft. 

The mode area includes the minimum area, coupled with areas 

where the total coal thickness exceeds 20 ft and additional 

areas where coal beds coincide with subtle anticlinal folds 

at the top of the Mesaverde Formation. The maximum area 

includes the minimum and mode areas plus all remaining areas 

where the total coal thickness exceeds 10 ft.

The estimated minimum, median, and maximum total 

recovery per cell for untested cells having potential for additions to reserves is 0.02, 0.1, and 1.2 BCFG, respectively, 

with a calculated mean of 0.14 BCFG (Appendix E). These 

estimates are based primarily on comparisons to estimated 

ultimate recoveries (EURs) of coalbed gas from wells producing from subbituminous coal in the Powder River Basin 

in Wyoming (Anderson and Canyon coal beds). A minimum 

EUR of 0.02 billion cubic feet of gas (BCFG) was applied to 
52 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

untested cells in AU 50340281; this value is generally considered representative of the minimum gas recovery required for 

a successful well. Median EURs for wells producing from the 

Anderson and Canyon coal beds in the Powder River Basin 

range from about 0.13 to 0.17 BCFG (Troy Cook, written 

commun., 2007). However, a lower median EUR was applied 

to untested cells in this assessment unit because Mesaverde 

and Meeteetse coal beds in the Bighorn Basin are less continuous and significantly thinner than the Anderson and Canyon 

coal beds, which range from 20 to 30 ft in thickness. The 

maximum recovery estimate is essentially equal to maximum 

EURs for the analog Powder River Basin coals (EUR range 

1.2 to 1.3 BCFG).

The minimum and maximum area per cell of untested 

cells having the potential for additions to reserves is 40 and 

240 acres, respectively with a calculated mean of about 127 

acres and a mode of 100 acres. Coalbed gas wells producing 

from coal in the Fort Union Formation (Tongue River Member) in the Powder River Basin, Wyoming, and from coal in 

the Mesaverde Formation in the Piceance Basin, Colorado, 

were used as analogs (Flores, 2004; Johnson and Roberts, 

2003) for estimating cell size (drainage area) because of general similarities in coal rank (primarily subbituminous coal). 

A 40-acre cell size was used at the minimum because of the 

potential for interference between wells producing at a closer 

spacing. A 100-acre cell size (mode) is considered optimal in 

regard to gas volume and recovery, dewatering considerations, 

and reduction (or omission) of interference between adjacent 

wells. The maximum of 240 acres considers the potential 

for increased drainage areas in exceptionally continuous and 

permeable coal reservoirs. Estimated mode and maximum cell 

sizes used in this assessment are slightly larger than estimated 

cell sizes for untested cells in the Powder River Basin (Fort 

Union Formation; Flores, 2004) because the higher thermal 

maturities of Mesaverde and Meeteetse coal in the Bighorn 

Basin coals might enhance their permeability due to better cleat development. Conversely, these values are slightly 

less than drainage-area estimates for coalbed gas wells in the 

Piceance Basin (Mesaverde Formation; Johnson and Roberts, 2003) where Upper Cretaceous coals are more mature, 

generally thicker, and more continuous than coal beds in the 

Bighorn Basin.

The mean estimate for undiscovered gas resources 

that have potential for additions to reserves in the MesaverdeMeeteetse Formation Coalbed Gas Assessment Unit 

(50340281) is 98 BCFG; tabulated assessment results are summarized in table 1.

Fort Union Formation Coalbed Gas Assessment 

Unit (AU 50340282)

The Fort Union Formation Coalbed Gas Assessment Unit 

(AU 50340282) is a hypothetical AU that is believed to have 

the potential to produce gas from coal beds in the Fort Union 

Formation. The AU encompasses approximately 3,800 mi2

in the central part of the Bighorn Basin (fig. 43). The lower 

limit of the AU is defined as the area where coal beds are 

interpreted to be present at depths of 6,000 ft or less; coal 

beds at greater depths were not considered due to the potential 

decrease in permeability with increasing depth. The upper 

limit of the AU is defined as the base of the outcrop of the Fort 

Union Formation. 

Fort Union coals have been mined since the late 1800s, 

and an estimated 30–40 million tons of coal were produced 

from the Red Lodge area (fig. 43) until the 1950s (Rawlins, 

1986). More recent mining has taken place in the Grass Creek 

area (fig. 43), where some 300,000–400,000 tons of Fort 

Union coal were mined between 1989 and 1993 (Resource 

Data International, 1998). Coal and carbonaceous shale beds 

are common in Fort Union Formation outcrops; the 36-ftthick Mayfield coal bed in the Grass Creek area is the thickest 

coal bed identified in the Bighorn Basin (Hewitt, 1926). Near 

Manderson and in the southeastern part of the basin, isolated 

coal beds in outcrops range from 10 to 15 ft thick, although 

most are lenticular. In the Red Lodge area, coal beds range 

from less than 4 ft to 12 ft in thickness (Woodruff, 1907; 

Rawlins, 1986). In most other areas, exposed coal beds are 

generally thin (< 5 ft thick) (Roberts, 1998). Based on limited 

data from oil and gas exploration wells, cumulative (total) 

coal thicknesses in the Fort Union Formation in the subsurface 

range from 3 to 26 ft; the maximum individual coal bed thickness measured in well logs is 11 ft (fig. 43) (Johnson, 1998). In 

many wells throughout the basin, no coal beds were identified. 

The apparent rank of Fort Union coal is subbituminous (Glass 

and others, 1975), and thermal maturity (R0) values for coal in 

the AU range from about 0.36 percent to about 0.87 percent 

in the deep basin adjacent to the Oregon Basin thrust fault 

(Nuccio and Finn, 1998; Finn and Pawlewicz, 2007). The AU 

is considered hypothetical because there is currently no production of coalbed gas from the Fort Union Formation in the 

basin (WOGCC, 2007). To date, there have been no published 

reports of coalbed gas tests, although indirect evidence of gas 

(methane?) in Fort Union coals may be represented by the 

1943 gas explosion in the Smith Mine in the Red Lodge-Bear 

Creek coal field, Montana (Rawlins, 1986).

Input data for the assessment of AU 50340282 is shown 

on the FORSPAN ASSESSMENT MODEL FORM in 

Appendix F. The minimum and maximum areas for the AU are 

2,177,000 and 2,661,000 acres, respectively, with a calculated 

mean of 2,419,000 acres. This wide range in acreages reflects

uncertainty in determining the depth to and (or) the presence 

of Fort Union coal beds in many areas, due to the lack of 

definitive drill-hole data. The estimated minimum and maximum percentages of the untested AU area that has potential 

for additions to reserves are 0.1 and 3 percent, respectively, 

with a calculated mean of 1.4 percent, and a mode of 1.0 

percent (Appendix F). The minimum area restricts coalbed 

gas potential to the Red Lodge-Bearcreek area (fig. 43), where 

there are as many as 8 mapped coal beds in a 32-mi2 area; total 

coal reserves have been estimated in excess of 600 million 

tons (Woodruff, 1907; Rawlins, 1986). The median estimate 
Assessment Units and Results 53

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Fort Union outcrop

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Cretaceous-Tertiary Composite

 TPS 503402

Fort Union Coalbed Gas

 AU 50340282

Rattlesnake Mountain

anticline

Manderson

4

Drill hole—No coal identified

 in the Fort Union Formation

Drill hole—Total coal thickness

 (in ft) shown alongside

Town

26

4

5 11

8

16

13

12

10 8

6

3

3

3

3

3

10

5

6

3 2

4

4 9

4

Red Lodge-Bearcreek coal field

Coal beds to 11.5 ft thick

8 major coal beds

16 underground mines

Southeastern coal field

Coal beds to 10 ft thick

 (lenticular)

Basin coal field

Mined coal beds to

 ≈9 ft thick (lenticular)

Grass Creek strip mine

Mayfied coal bed 26 ft thick

up to 38 ft locally in outcrops

Figure 43. Map showing areal extent of the Fort Union Formation Coalbed Gas Assessment Unit (50340282), Bighorn Basin, 

Wyoming and Montana. Coal thickness data (in ft) from Woodruff (1907), Glass and others (1975), and Johnson (1998). TPS, 

Total Petroleum System; AU, Assessment Unit.

includes the Red Lodge-Bearcreek area coupled with an area 

downdip from coal outcrops near Manderson, where individual coal beds in Fort Union outcrops are locally as thick as 10 

ft. The maximum estimate includes the minimum and median 

areas, and additional untested areas in the east-central part of 

the basin northwest and southwest of Manderson (fig. 43).

Coalbed gas wells producing from coal in the Fort Union 

Formation (Tongue River Member) in the Powder River 

Basin, Wyoming, were used as analogs (Flores, 2004) for estimating cell size (drainage area) and total recovery per cell for 

untested cells (EURs) because of general similarities in coal 

rank (subbituminous coal) and thermal maturity; however, 

coal maturities in some areas of the Bighorn Basin exceed the 

thermal maturity of Powder River Basin coals. The minimum, 

median, and maximum total recoveries per cell for untested 

cells having potential for additions to reserves are estimated 

at 0.02, 0.08, and 1.0 BCFG, respectively, with a calculated 

mean of 0.1 BCFG (Appendix F). These estimates are based 

on EURs for coalbed gas wells producing from the 20- to 

30-ft-thick Anderson and Canyon coal beds in the Powder 
54 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

River Basin. Only the Mayfield coal bed in the Grass Creek 

area is comparable in thickness (fig. 43), but is limited in 

areal extent and not buried deep enough (overburden < 200 ft; 

Stewart, 1975) to be prospective for coalbed gas. Elsewhere in 

the Bighorn Basin, Fort Union coal beds generally range from 

less than 5 ft to 12 ft in thickness. Although no direct correlation has been made between coal thickness, gas content, and 

enhanced production, greater coal volumes associated with 

thicker coal beds should result in a greater volume of coalbed 

gas per unit area of land (for example, see Choate and others, 

1984). Based on this concept, we interpret EURs for untested 

cells in AU 50340282 should be somewhat less than those of 

Fort Union coalbed gas wells in the Powder River Basin. A 

minimum EUR of 0.02 BCFG was applied to untested cells in 

AU 50340282, a value generally considered as representative 

of the minimum gas recovery required for a successful well. 

A median EUR of 0.08 BCFG and a maximum EUR of 1.0 

BCFG were also applied to untested cells. Because of the differences in coal bed thicknesses as discussed previously, these 

EURs are less than EURs from Powder River Basin coalbed 

gas wells, which have median recoveries ranging from 0.13 to 

0.17 BCFG and maximum recoveries ranging from 1.2 to 1.3 

BCFG (Troy Cook, written commun., 2007).

The estimated minimum and maximum areas per cell of 

untested cells having the potential for additions to reserves 

are 40 and 200 acres, respectively, with a calculated mean 

of about 113 acres, and a mode of 100 acres. A 40-acre cell 

size was used at the minimum because of the potential for 

interference between wells producing at a closer spacing. A 

100-acre cell size (median estimate) is considered optimal in 

regard to gas volume and recovery, dewatering considerations, 

and reduction (or omission) of interference between adjacent 

wells. The maximum of 200 acres considers the potential 

for increased drainage areas in exceptionally continuous and 

permeable coal reservoirs. The estimated mode and maximum 

cell sizes used in this assessment are slightly larger than estimated cell sizes for untested cells in the Powder River Basin 

(Flores, 2004), because the slightly higher thermal maturity of 

Fort Union coal in the Bighorn Basin might enhance the permeability due to better cleat development in the more mature 

coal.

The mean estimate for undiscovered gas resources that 

have potential for additions to reserves in the Fort Union 

Formation Coalbed Gas Assessment Unit (50340282) is 32 

BCFG; tabulated assessment results are summarized in table 1.

Cretaceous–Tertiary Conventional Oil and Gas 

Assessment Unit (AU 50340201)

The Cretaceous–Tertiary Conventional Oil and Gas 

Assessment Unit (AU 50340201) is an established AU 

that produces oil and gas mainly from sandstone reservoirs 

associated with anticlinal traps around the margins of the 

Bighorn Basin and along the Five Mile trend (fig. 44); 

however, many of these accumulations have a stratigraphic 

component where sandstone reservoirs pinch out across 

structure (Hafenbrack and others, 1958; Stone, 1975; 

Tonnsen, 1985; Cardinal and others, 1989; Bartow-Campen, 

1986; Keefer, 1998; Talbot, 1996). The AU encompasses 

approximately 7,900 mi2, occupies the entire areal extent 

of the Cretaceous–Tertiary Composite TPS, and includes 

reservoirs ranging from the Lower Cretaceous Cloverly 

Formation through the Paleocene Fort Union Formation 

(figs. 7, 44). The first discovery was from the Frontier 

Formation in 1906 at Garland field (Cardinal and others, 

1989). The AU is heavily explored and since the initial 

discovery at Garland field nearly 12,000 wells have been 

drilled, including about 1,700 wells producing from 

Cretaceous or Tertiary reservoirs. To date, nine oil fields 

and 15 gas fields (NRG Associates, 2007) greater than 

the minimum grown field size of 0.5 million barrels of oil 

equivalent (MMBOE) have been discovered, with a minimum 

cumulative production of 94 MMBO and 833 BCFG gas 

(fig. 45) (IHS Energy Group, 2007).

Input data for the assessment is shown on the Seventh 

Approximation form in Appendix G. The minimum and 

maximum number of oil accumulations greater than the 

minimum field size of 0.5 MMBO expected to be discovered 

are one and 15, respectively, with five most likely (mode). 

The estimated size of the oil accumulations ranges from 0.5 to 

12 MMBO with a median value expected to be 1.5 MMBO.

The minimum and maximum number of gas accumulations 

greater than 3 BCFG expected to be discovered are 1 and 40, 

respectively, with a mode of 10. The estimated size of these 

gas accumulations ranges from 3 to 72 BCFG, with a median 

value expected to be 9 BCFG. Few of these new discoveries are likely to be from structural accumulations, as most 

anticlinal features in the basin have been explored with only 

one accumulation greater than the minimum field size being 

discovered in the last 50 years despite an increase in exploration activity (figs. 45, 46). Some new fields may be discovered 

in subthrust areas where petroleum could be trapped beneath 

the overhang of major thrust faults that flank parts of the basin 

(Gries, 1981, 1983b). However, future discoveries will more 

likely be from stratigraphic traps in the Frontier Formation and 

Cody Shale, where sandstone reservoirs pinch out updip on 

anticlinal noses (Keefer, 1998) or into marine shales along the 

basin flanks, or are draped over structures (Fox and Dolton, 

1996). These accumulations are expected to be small in size 

because larger traps likely would have been discovered by the 

high drilling density that has occurred around the margins of 

the basin (fig. 47). Additional accumulations may also be from 

stratigraphic traps from valley-fill sandstones in the Muddy 

Sandstone and the Greybull Sandstone Member of the Cloverly Formation (Dolson and others, 1991; Fox and Dolton, 

1996).

The mean estimates for undiscovered oil and gas 

resources that have potential for additions to reserves in 

the Cretaceous–Tertiary Conventional Oil and Gas AU 

(50340201) are 13 MMBO and 221 BCFG; tabulated 

assessment results are summarized in table 1.
Acknowledgments 55

0

5000

-5000

0 0

-5000

-5000

0

5000

0

0

0

-10000

-5000

0

5000

0

5000

-15000

-10000

-5000

-5000

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Cloverly Formation

Oil well

Fault

Gas well

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Cretaceous-Tertiary Composite

 TPS 503402 and Conventional 

 Oil and Gas AU 50340201

Rattlesnake Mountain

anticline

Figure 44. Map showing areal extent of the Cretaceous–Tertiary Composite Conventional Oil and Gas Assessment Unit 

(50340201), Bighorn Basin, Wyoming and Montana, and location of wells producing from Cretaceous and Tertiary reservoirs. 

Structure contours drawn on top of the Cloverly Formation; contour interval 1,000 ft. TPS, Total Petroleum System; AU, 

Assessment Unit. 

Acknowledgments

The authors thank Chris Schenk, Rich Pollastro, Ron 

Charpentier, and Tim Klett of the U.S. Geological Survey 

National Oil and Gas Assessment team for discussions regarding the assessment of the Cretaceous–Tertiary Composite Total 

Petroleum System. We also thank Troy Cook and Tim Klett 

for graphs and interpretation of production data; Phil Nelson 

for providing drillstem test and pressure data; and Paul Lillis 

(USGS) for providing geochemical data and for numerous 

discussions and assistance in interpreting the Rock-Eval, TOC, 

and organic geochemistry data. Important geologic input was 

provided by Tom Judkins. Chris Anderson and Wayne Husband (USGS contractors) provided valuable GIS and graphic 

design management and support. The manuscript benefited 

from reviews by William Keefer, Michael Brownfield, Margaret Ellis, Doug Nichols, and Gayle Dumonceaux and their 

suggestions and comments are greatly appreciated.
56 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

1885 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

1885 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

ACCUMULATION DISCOVERY YEAR

ACCUMULATION DISCOVERY YEAR

A

B

0

1

10

100

1

10

100

1,000

GROWN OIL ACCUMULATION SIZE (MMBO) G

ROWN GAS ACCUMULATION SIZE (BCFG)

Figure 45. Graphs showing grown field size versus discovery year for (A) gas fields and (B) oil fields for 

Cretaceous and Tertiary accumulations in the Bighorn Basin, Wyoming and Montana. BCFG, billion of cubic feet 

of gas; MMBO, million barrels of oil. 
Acknowledgments 57

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

DRILLING COMPLETION YEAR

NUMBER OF NEW FIELD WILDCAT WELLS

0

10

20

30

40

50

60

23 discoveries > the minimum

eld size during this time

one discovery > the

minimum eld size

during the last 50 years

Figure 46. Number of new field wildcats by drilling completion year in the Bighorn Basin, Wyoming and 

Montana.
58 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

50340261

50340261

50340263

50340264

T

50

N

T

55

N

T

9

S

T

45

N

T

40

N

R94W R90W R85W

R95W

R100W

R104W

T

50

N

T

55

N

T

57

N

T

9

S

T

5

S

R15E R20E R25E R35E

R101W R95W

R90W R85W

R35E R40E

R105W

T

40

N

T

45

N

T

5

N

R5W R1W R1E R5E

T

8

N

R4W

T

8

N

R3E

Montana

Wyoming

110°

45°

44°

109° 108° 107°

0 10 20 30 40

MILES

Precambrian rocks

Tertiary volcanic rocks

Cloverly Formation

Oil well

Gas well

Dry hole

Bighorn Basin Province

Absaroka

Range

Bear

Mountains tooth

Creek Mountains

Owl

Mountains

Bighorn 

Pryor

Mountains

Nye-Bowler lineament

Big Trails fault

Cretaceous-Tertiary Composite

 TPS 503402 and Conventional

 Oil and Gas AU 50340201

Rattlesnake Mountain

anticline

Figure 47. Map showing areal extent of the Cretaceous–Tertiary Composite Conventional Oil and Gas Assessment Unit 

(50340201) and locations of all wells, including dry holes, within the AU boundary to illustrate the drilling density around the 

margins of the Bighorn Basin, Wyoming and Montana. The boundaries of the three continuous gas AUs that occupy the 

basin center, where no conventional trapping is expected are also shown. TPS, Total Petroleum System; AU, Assessment 

Unit.
References 59

References

Allison, M.L., 1983, Deformation styles along the Tensleep 

fault, Bighorn Basin, Wyoming, in Boberg, W.W., ed., 

Geology of the Bighorn Basin, Wyoming Geological 

Association Guidebook, p. 63–75.

Allison, M.L., 1986, Structural geometry along the Tensleep 

fault, Bighorn Basin, Wyoming, in Garrison, P.B., ed., 

Geology of the Beartooth uplift and adjacent basins: 

Yellowstone Bighorn Research Association-Montana 

Geological Society 50th Anniversary Guidebook, p. 

145–153.

Anna, L.O., and Cook, T.A., 2008, Assessment of the Mowry 

Shale and Niobrara Formation as continuous hydrocarbon 

systems, Powder River Basin, Montana and Wyoming: U.S 

Geological Survey Open-File Report 2008–1367, 1 sheet.

Anonymous, 1958, Golden Dome field, in Abrassart, C.B., and 

others, eds., Montana oil and gas fields symposium: Billings 

Geological Society, p. 153. 

Bartow-Campen, Elizabeth, 1986, Hydrocarbon exploration 

techniques in the Greybull Sandstone, northern Bighorn 

Basin, in Garrison, P.B., ed., Geology of the Beartooth 

uplift and adjacent basins: Yellowstone Bighorn Research 

Association-Montana Geological Society 50th Anniversary 

Guidebook, p. 225–231. 

Blackstone, D.L., Jr., 1986a, Structural geology—Northwest 

margin, Bighorn basin—Park County, Wyoming and Carbon 

County, Montana, in Garrison, P.B., ed., Geology of the 

Beartooth uplift and adjacent basins: Yellowstone Bighorn 

Research Association-Montana Geological Society 50th 

Anniversary Guidebook, p. 125–135.

Blackstone, D.L., Jr., 1986b, Foreland compressional tectonics—Southern Bighorn Basin and adjacent areas, Wyoming: 

Geological Survey of Wyoming Report of Investigations 

no. 34, 32 p. 

Bonini, W.E., and Kinard, R.E., 1983, Gravity anomalies 

along the Beartooth front, Montana—Evidence for a lowangle thrust, in Boberg, W.W., ed., Geology of the Bighorn 

Basin: Wyoming Geological Association Guidebook, 

p. 89–94. 

Bown, T.M., 1975, Paleocene and Lower Eocene rocks in the 

Sand Creek-No Water area, Washakie County, Wyoming, in

Exum, F.A., and George, G.R., eds., Geology and mineral 

resources of the Bighorn Basin, Wyoming: Wyoming 

Geological Association 27th Annual Field Conference 

Guidebook, p. 55–61.

Bown, T.M., 1980, The Willwood Formation (Lower Eocene) 

of the southern Bighorn Basin, Wyoming, and its mammalian fauna, in Gingerich, P.D., ed., Early Cenozoic paleontology and stratigraphy of the Bighorn Basin, Wyoming: 

University of Michigan Papers on Paleontology no. 24, 

p. 127–133.

Burtner, R.L., and Warner, M.A., 1984, Hydrocarbon 

generation in Lower Cretaceous Mowry and Skull Creek 

Shales of the northern Rocky Mountain area, in Woodward, 

J., Meissner, F.F., and Clayton, J.L., eds., Hydrocarbon 

source rocks of the greater Rocky Mountain Region: Rocky 

Mountain Association of Geologists Guidebook, 

p. 449–467.

Byers, C.W., and Larson, D.W., 1979, Paleoenvironments 

of Mowry Shale (Lower Cretaceous), western and central 

Wyoming: American Association of Petroleum Geologists 

Bulletin, v. 63, no. 3, p. 354–361.

Cardinal, D.F., Miller, T., Stewart, W.W., and Trotter, J.F., eds., 

1989, Wyoming oil and gas fields symposium Bighorn and 

Wind River Basins: Wyoming Geological Association, 

555 p.

Choate, R., Johnson, C.A., and McCord, J.P., 1984, Geologic 

overview, coal deposits, and potential for methane recovery 

from coalbeds—Powder River Basin, in Rightmire, C.T., 

Eddy, G.E., and Kirr, J.N., eds., Coalbed methane resources 

of the United States: American Association of Petroleum 

Geologists, Studies in Geology Series 17, p. 335–352.

Cobban, W.A., and Kennedy, W.J., 1989, The ammonite 

Metengonoceras Hyatt, 1903, from the Mowry Shale 

(Cretaceous) of Montana and Wyoming: U.S. Geological 

Survey Bulletin 1787-L, 11 p.

Cully, T.G., 1985, Dry Creek field, in Tonnsen, J.J., ed., 

Montana oil and gas fields symposium: Montana Geological 

Society, p. 441–447.

Darton, N.H., 1904, Comparison of the stratigraphy of the 

Black Hills, Bighorn Mountains, and Rocky Mountain Front 

Range: Geological Society of America Bulletin, v. 15, 

p. 379–448.
60 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Flores, R.M., 2004, Chapter 2—Coalbed methane in the Powder River Basin, Wyoming and Montana: An assessment 

of the Tertiary-Upper Cretaceous Coalbed Methane Total 

Petroleum System, in USGS Powder River Basin Province 

Assessment Team, Total petroleum system and assessment 

of coalbed gas in the Powder River Basin Province, Wyoming and Montana: U.S. Geological Survey Digital Data 

Series DDS–69–C, CD–ROM.

Foose, R.M., Wise, D.U., and Garbarini, G.S., 1961, Structural 

geology of the Beartooth Mountains, Montana and Wyoming: Geological Society of America Bulletin, v. 72, no. 8, 

p. 1143–1172.

Fox, J.E., and Dolton, G.L., 1989, Petroleum geology of the 

Wind River and Bighorn Basins, Wyoming and Montana: 

U.S. Geological Survey Open-File Report 87–450P, 41 p.

Fox, J.E., and Dolton, G.L., 1996, Petroleum geology of the 

Bighorn Basin, north-central Wyoming and south-central 

Montana, in Bowen, C.E., Kirkwood, S.C., and Miller, T.S., 

eds., Resources of the Bighorn Basin: Wyoming Geological 

Association Guidebook, p. 19–39. 

Furer, L.C., Kvale, E.P., and Engelhardt, D.W., 1997, Early 

Cretaceous hiatus much longer than previously reported, in

Campen, E.B., ed., Bighorn Basin—50 years on the frontier: Yellowstone Bighorn Research Association-Wyoming 

Geological Association-Montana Geological Society, 1997 

Field Trip and Symposium, p. 47–56.

Geolex, accessed 2008, Geologic Names Lexicon: U.S. 

Geological Survey National database, http://ngmdb.usgs.

gov/Geolex/geolex_home.html

Gill, J.R., and Cobban, W.A., 1966, Regional unconformity in 

Late Cretaceous, Wyoming: U.S. Geological Survey Professional Paper 550–B, p. B20–B27.

Gill, J.R., and Cobban, W.A., 1973, Stratigraphy and geologic 

history of the Montana Group and equivalent rocks, 

Montana, Wyoming, and North and South Dakota: U.S. 

Geological Survey Professional Paper 776, 37 p.

Gingerich, P.D., 1983, Paleocene-Eocene faunal zones and a 

preliminary analysis of Laramide structural deformation 

in the Clark’s Fork Basin, Wyoming, in Boberg. W.W. 

ed., Geology of the Bighorn Basin: Wyoming Geological 

Association 34th Annual Field Conference Guidebook,

p. 185–195.

Glass, G.B., Westervelt, K., and Oviatt, C.G., 1975, Coal 

mining in the Bighorn coal basin of Wyoming, in Exum, 

F.A., and George, G.R., eds., Geology and mineral 

resources of the Bighorn Basin, Wyoming: Wyoming 

Geological Association 27th Annual Field Conference 

Guidebook, p. 221–228.

Davis, H.R., 1986, Amount and type of organic matter in the 

Cretaceous Mowry Shale of Wyoming: U.S. Geological 

Survey Open-File Report 86–412, 17 p.

Davis, H.R. 1987, Deposition of the Lower Cretaceous Mowry 

Shale: Madison, University of Wisconsin, Ph.D. 

dissertation, 217 p.

Dickinson, W.R., Klute, M.A., Hayes, M.J., Janecke, S.U., 

Lundin, E.R., McKittrick, M.A., and Olivares, M.D., 1988, 

Paleogeographic and paleotectonic setting of Laramide 

sedimentary basins in the central Rocky Mountain region: 

Geological Society of America Bulletin, v. 100, no. 7, 

p. 1023–1039.

Dolson, John, Muller, Dave, Evetts, M.J., and Stein, J.A., 

1991, Regional paleotopographic trends and production, 

Muddy Sandstone (Lower Cretaceous), central and northern Rocky Mountains: American Association of Petroleum 

Geologists Bulletin v. 75, no. 3, p. 409–435.

Dunleavy, J.M., and Gilbertson, R.L., 1986, Madden anticline: 

growing giant, in Noll, J.H., and Doyle, K.M., eds., Rocky 

Mountain Oil and Gas Fields: Wyoming Geological 

Association, p. 107–157.

Eicher, D.L., 1960, Stratigraphy and micropaleontology of the 

Thermopolis Shale: Peabody Museum of Natural History, 

Yale University Bulletin 15, 126 p. 

Eicher, D.L., 1962, Biostratigraphy of the Thermopolis, 

Muddy, and Shell Creek Formations, in Enyert, R.L., and 

Curry, W.H., eds., Symposium on Early Cretaceous rocks of 

Wyoming and adjacent areas: Wyoming Geological Association 17th Annual Field Conference, p. 72–93. 

Finn, T.M., 2007a, Subsurface stratigraphic cross sections 

of Cretaceous and lower Tertiary rocks in the Wind River 

Basin, central Wyoming, Petroleum Systems and Geologic 

Assessment of Oil and Gas Resources in the Wind River 

Basin Province, Wyoming: U.S. Geological Survey Digital 

Data Series DDS–69–J, Chapter 9, 28 p., CD–ROM.

Finn, T.M., 2007b, Source rock potential of Upper Cretaceous 

marine shales in the Wind River Basin, Wyoming, 

Petroleum Systems and Geologic Assessment of Oil 

and Gas Resources in the Wind River Basin Province, 

Wyoming: U.S. Geological Survey Digital Data Series 

DDS–69–J, Chapter 8, 24 p., CD–ROM.

Finn, T.M., and Pawlewicz, M.J., 2007, New vitrinite 

reflectance data for the Bighorn Basin, north-central 

Wyoming and south-central Montana: U.S. Geological 

Survey Open-File Report 2007–1246, 9 p.
References 61

Goodell, H.G., 1962, The stratigraphy and petrology of the 

Frontier Formation of Wyoming, in Enyert, R.L., and 

Curry, W.H., eds., Symposium on Early Cretaceous rocks 

of Wyoming and adjacent areas: Wyoming Geological 

Association 17th Annual Field Conference Guidebook, 

p. 175–210.

Green, G.N., and Drouillard, P.H., 1994, The digital geologic 

map of Wyoming in ARC/INFO format: U.S. Geological 

Survey Open-File Report 94–0425, 10 p.

Gries, R.R., 1981, Oil and gas prospecting beneath the 

Precambrian of foreland thrust plates in the Rocky 

Mountains: The Mountain Geologist, v. 18, no. 1, p. 1–18.

Gries, R.R., 1983a, North-south compression of Rocky 

Mountain foreland structures, in Lowell, J.D., and Gries, 

R.R., eds., Rocky Mountain foreland basins and uplifts: 

Rocky Mountain Association of Geologists, p. 9–32.

Gries, R.R., 1983b, Oil and gas prospecting beneath the Precambrian of foreland thrust plates in the Rocky Mountains: 

American Association of Geologists Bulletin, v. 67, no. 1, 

p. 1–28. 

Hafenbrack, J.H., Chuman, R.W., and Shannon, P., eds, 1958, 

Montana Oil and Gas Fields Symposium 1958: Billings 

Geological Society, 240 p. 

Hagen, E.S., 1986, Hydrocarbon maturation in Laramidestyle basins—Constraints from the northern Bighorn Basin, 

Wyoming and Montana: Laramie, University of Wyoming, 

Ph.D. dissertation, 215 p. 

Hagen, E.S., and Surdam, R.C., 1984, Maturation history and 

thermal evolution of Cretaceous source rocks of the Bighorn 

Basin, Wyoming and Montana, in Woodward, J., Meissner, 

F.F., and Clayton, J.L., eds., Hydrocarbon source rocks 

of the greater Rocky Mountain Region: Rocky Mountain 

Association of Geologists Guidebook, p. 321–338.

Handford, C. R., 1981, Sedimentology and genetic stratigraphy of Dean and Spraberry Formations (Permian), Midland 

Basin, Texas: American Association of Petroleum Geologists Bulletin, v. 65, p. 1602–1616.

Haun, J.D., and Barlow, J.A., 1962, Lower Cretaceous stratigraphy of Wyoming, in Enyert, R.L., and Curry, W.H., 

eds., Symposium on Early Cretaceous rocks of Wyoming 

and adjacent areas: Wyoming Geological Association 17th 

Annual Field Conference Guidebook, p. 15–22. 

Heady, E.C., 1992, A detailed stratigraphic analysis and fission 

track study of the Morrison and Cloverly Formations in the 

vicinity of Shell, Big Horn County, Wyoming: Hanover, 

New Hampshire, Dartmouth College, M.S. thesis, 89 p.

Hewett, D.F., 1912, The Shoshone River section, Wyoming: 

U.S. Geological Survey Bulletin 541, p. 89–115.

Hewett, D.F., 1926, Geology and oil and coal resources of the 

Oregon Basin, Meeteetse, and Grass Creek Basin quadrangles: U.S. Geological Survey Professional Paper 145, 111 p.

Hickey, L.J., 1980, Paleocene stratigraphy and flora of the 

Clark’s Fork Basin, in Gingerich, P.D., ed., Early Cenozoic 

paleontology and stratigraphy of the Bighorn Basin, 

Wyoming: University of Michigan Papers on Paleontology 

no. 24, p. 33–49. 

Hickey, L.J., and Yuretich, R.F., 1997, The Belfry Member of 

the Fort Union Formation, an allocyclic lacustrine deposit 

of late middle Paleocene age in the Bighorn Basin, Montana 

and Wyoming, in Campen, E.B., ed., Bighorn Basin—50 

years on the frontier: Yellowstone Bighorn Research Association-Wyoming Geological Association-Montana Geological Society, 1997 Field Trip and Symposium, p. 38–42.

Hintze, F.F., 1914, The Basin and Greybull oil and gas fields: 

Wyoming Geological Survey Bulletin 10, 60 p. 

Hunter, L.D., 1952, Frontier Formation along the eastern 

margin of the Big Horn Basin, Wyoming, in Spalding, R.W., 

and Wold, J.S., eds., Southern Big Horn Basin: Wyoming 

Geological Association 7th Annual Field Conference 

Guidebook, p. 63–66.

IHS Energy Group, 2007, [includes data current as of 

December, 2007], PI/Dwights Plus US Well Data: 

Englewood, Colo., IHS Energy Group; database available 

from IHS Energy Group, 15 Inverness Way East, D205, 

Englewood, CO 80112, U.S.A.

Johnson, R.C., 1998, Coal in the deep subsurface of the 

Bighorn Basin, Wyoming and Montana, in Keefer, W.R., 

and Goolsby, J.E., eds., Cretaceous and lower Tertiary rocks 

of the Bighorn Basin, Wyoming and Montana: Wyoming 

Geological Association 49th Guidebook, p. 199–209.

Johnson, R.C., 2007, Detailed measured sections, cross sections, and paleogeographic reconstructions of the Upper 

Cretaceous and Lower Tertiary nonmarine interval, Wind 

River Basin, Wyoming, Petroleum Systems and Geologic 

Assessment of Oil and Gas Resources in the Wind River 

Basin Province, Wyoming: U.S. Geological Survey Digital 

Data Series DDS–69–J, Chapter 10, 49 p., CD–ROM.

Johnson, R.C., Crovelli, R.A., Lowell, B.A., and Finn, T.M., 

1999, An assessment of in-place gas resources in the 

low-permeability basin-centered gas accumulation of the 

Bighorn Basin, Wyoming and Montana: U.S. Geological 

Survey Open-File Report 99-315-A, 123 p.
62 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Johnson, R.C., and Finn, T.M., 1998a, Structure contour map 

on top of the Upper Cretaceous Mesaverde Formation, 

Bighorn Basin, Wyoming and Montana, in Keefer, W.R., 

and Goolsby, J.E., eds., Cretaceous and Lower Tertiary 

rocks of the Bighorn Basin, Wyoming and Montana: 

Wyoming Geological Association 49th Guidebook, 

p. 197–198. 

Johnson, R.C., and Finn, T.M., 1998b, Is there a basincentered gas accumulation in Upper Cretaceous rocks in the 

Bighorn Basin?, in Keefer, W.R., and Goolsby, J.E., eds., 

Cretaceous and Lower Tertiary rocks of the Bighorn Basin, 

Wyoming and Montana: Wyoming Geological Association 

49th Guidebook, p. 257–273.

Johnson, R.C., and Finn, T.M., 2004, Structural and 

stratigraphic framework and hydrocarbon potential of 

the Cretaceous and Lower Tertiary rocks of the Crazy 

Mountains Basin, Montana, Stratigraphic framework, 

structure, and thermal maturity of Cretaceous and lower 

Tertiary rocks in relation to hydrocarbon potential, Crazy 

Mountains Basin, Montana: U.S. Geological Survey 

Scientific Investigations Report 2004–5091, Chapter A, 

44 p., CD–ROM.

Johnson, R.C., Finn, T.M., Kirschbaum, M.A., Roberts, S.B., 

Roberts, L.N.R., Cook, T.R., and Taylor, D.J., 2007, The 

Cretaceous-Lower Tertiary Composite Total Petroleum 

System, Wind River Basin, Wyoming, Petroleum Systems 

and Geologic Assessment of Oil and Gas Resources in the 

Wind River Basin Province, Wyoming: U.S. Geological 

Survey Digital Data Series DDS–69–J, Chapter 4, 96 p., 

CD–ROM.

Johnson, R,C., Finn, T.M., and Roberts, S.B., 2004, Regional 

stratigraphic setting of Maastrichtian rocks in the central 

Rocky Mountain region, in Robinson, J.W., and Shanley, 

K.W., eds., Jonah field–Case study of a tight-gas fluvial 

reservoir: American Association of Petroleum Geologists 

Studies in Geology Series no. 52, and Rocky Mountain 

Association of Geologists 2004 Guidebook, p. 21–35.

Johnson, R.C., Finn, T.M., and Roberts, L.N.R., 2005, 

The Mesaverde Total Petroleum System, Southwestern 

Wyoming Province, Petroleum Systems and Geologic 

Assessment of Oil and Gas Resources in the Southwestern 

Wyoming Province, Wyoming, Colorado, and Utah: U.S. 

Geological Survey Digital Data Series DDS–69–D, 

Chapter 8, 38 p., CD–ROM.

Johnson R.C., Keefer, W.R., Keighin, C.W., and Finn, T.M., 

1998, Detailed outcrop studies of the upper part of the 

Upper Cretaceous Cody Shale and The Upper Cretaceous 

Mesaverde, Meeteetse, and Lance Formations, Bighorn 

Basin, Wyoming, in Keefer, W.R., and Goolsby, J.E., eds., 

Cretaceous and Lower Tertiary rocks of the Bighorn Basin, 

Wyoming and Montana: Wyoming Geological Association 

49th Guidebook, p. 59–78.

Johnson, R.C., and Keighin, C.W., 1998, Origins of natural 

gasses from Upper Cretaceous reservoirs, Bighorn Basin, 

Wyoming and Montana, and comparison with gases from 

the Wind River Basin, Wyoming, in Keefer, W.R., and 

Goolsby, J.E., eds., Cretaceous and Lower Tertiary rocks 

of the Bighorn Basin, Wyoming and Montana: Wyoming 

Geological Association 49th Guidebook, p. 233–249.

Johnson, R.C., and Roberts, S.B., 2003, The Mesaverde Total 

Petroleum System, Uinta-Piceance Province, Utah and 

Colorado, Petroleum Systems and Geologic Assessment 

of Oil and Gas Resources in the Uinta-Piceance Province, 

Utah and Colorado: U.S. Geological Survey Digital Data 

Series DDS–69–B, Chapter 7, 62 p., CD–ROM.

Johnson, S.J., and Middleton, L.T., 1990, Tectonic significance of Paleocene alluvial sequence, Clark’s Fork Basin, 

Wyoming-Montana, in Specht, R.W., ed., Wyoming sedimentation and tectonics: Wyoming Geological Association 

41st Field Conference Guidebook, p. 69–87. 

Jones, R.W., and DeBruin, R.H., 1990, Coalbed methane in 

Wyoming: Geological Survey of Wyoming Public Information Circular no. 30, 15 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: The Mountain Geologist, v. 14, nos. 

3 and 4, p. 75–99.

Keefer, W.R., 1998, Silver Tip and South Elk Basin South 

fields—Examples for stratigraphic traps in Upper 

Cretaceous Frontier Formation, northern Bighorn Basin, 

Wyoming, in Keefer, W.R., and Goolsby, J.E., eds., 

Cretaceous and Lower Tertiary rocks of the Bighorn Basin, 

Wyoming and Montana: Wyoming Geological Association 

49th Guidebook, p. 275–278. 

Keefer, W.R., Finn, T.M., Johnson, R.C., and Keighin, C.W., 

1998, Regional stratigraphy and correlation of Cretaceous 

and Paleocene rocks, Bighorn Basin, Wyoming and Montana, in Keefer, W.R., and Goolsby, J.E., eds., Cretaceous 

and Lower Tertiary rocks of the Bighorn Basin, Wyoming 

and Montana: Wyoming Geological Association 49th 

Guidebook, p. 1–30.
References 63

Kirschbaum, Mark A. and Roberts, Laura N.R., 2005, 

Geologic assessment of undiscovered oil and gas resources 

of the Mowry Composite Total Petroleum System, 

Southwestern Wyoming Province, Wyoming, Colorado, 

and Utah, in Petroleum Systems and Geologic Assessment 

of Oil and Gas in the Southwestern Wyoming Province, 

Wyoming, Colorado, and Utah: U.S. Geological Survey 

Digital Data Series DDS–69–D, Chapter 5, 27 p., 

CD–ROM.

Klett, T.R., Schmoker, J.W., Charpentier, R.R., Ahlbrandt, 

T.S., and Ulmishek, G.F., 2000, Glossary, U.S. Geological 

Survey World Petroleum Assessment 2000—description 

and results: U.S. Geological Survey Digital Data Series 

DDS–60, CD–ROM.

Klug, B., 1993, Cyclic facies architecture as a key to 

depositional controls in a distal foredeep—Campanian 

Mesaverde Group, Wyoming, USA: International Journal 

of Earth Sciences, v. 82, no. 2, p. 306–326.

Law, B.E., 2002, Basin-centered gas systems: American 

Association of Petroleum Geologists Bulletin, v. 86, no. 11, 

p. 1891–1919.

Law, B.E., and Dickinson, W.W., 1985, Conceptual model for 

origin of abnormally pressured gas accumulations in lowpermeability reservoirs: American Association of Petroleum 

Geologists Bulletin, v. 69, no. 8, p. 1295–1304.

Lewan, M.D., and Ruble, T.E., 2002, Comparison of petroleum generation kinetics by isothermal hydrous and nonisothermal open-system pyrolysis: Organic Geochemistry, 

v. 33, p. 1457–1475.

Long, M.S., 1999, Facies architecture and sequence stratigraphy of the Lower Cretaceous Muddy Formation in the 

southeastern Bighorn Basin, Wyoming: Provo, Brigham 

Young University, MS thesis, 86 p.

Love, D.J., and Christiansen, A.C., 1985, Geologic map of 

Wyoming: U.S. Geological Survey, scale 1:500,000.

Love, J.D., 1988, Geology of the Bighorn Basin, northern 

Wyoming and southern Montana in Chapter 8—Basins of 

the Rocky Mountain Region, in Sloss, L.L., ed., Sedimentary Cover—North American Craton, U.S.: The Geology of 

North America: Geological Society of America, v. D-2, 

p. 201–204.

Love, J.D., Thompson, R.M., Johnson, C.O., Sharkey, H.H.R., 

Tourtelot, H.A., and Zapp, A.D., 1945, Stratigraphic 

sections and thickness maps of Lower Cretaceous and 

nonmarine Jurassic rocks of central Wyoming: U.S. 

Geological Survey Oil and Gas Investigations Preliminary 

Chart 13. 

Lupton, C.T., 1916, Oil and gas near Basin, Big Horn County, 

Wyoming: U.S. Geological Survey Bulletin 621, 

p. 157–190. 

Mackenzie, M.G., 1975, Stratigraphy and petrology of the 

Mesaverde Group Southern part of the Big Horn Basin, 

Wyoming: New Orleans, Tulane University, PhD. dissertation, 155 p. 

Masters, J.A., 1979, Deep basin trap, western Canada: 

American Association of Petroleum Geologists Bulletin, 

v. 63, no. 2, p. 152–181.

May, M.T., Furer, L.C., Kvale, E.P., Suttner, L.J., Johnson, 

G.D., and Meyers, J.H., 1995, Chronostratigraphy and 

tectonic significance of Lower Cretaceous conglomerates 

in the foreland of central Wyoming, in Dorobek, S.L., 

and Ross, G.M., eds., Stratigraphic evolution of foreland 

basins: Society for Sedimentary Geology (SEPM) Special 

Publication 52, p. 97–110.

McKenna, M.C., and Love, J.D., 1972, High-level strata containing Early Miocene mammals on the Bighorn Mountains, 

Wyoming: American Museum Novitiates, no. 2490, 31 p. 

Merewether, E.A., 1996, Stratigraphy and tectonic implications of Upper Cretaceous rocks in the Powder River Basin, 

northeastern Wyoming and southeastern Montana: U.S. 

Geological Survey Bulletin 1917-T, 92 p.

Merewether, E.A., Cobban, W.A., and Ryder, R.T., 1975, 

Lower Upper Cretaceous strata, Bighorn Basin, Wyoming 

and Montana in Exum, F.A., and George, G.R., eds., 

Geology and mineral resources of the Bighorn Basin: 

Wyoming Geological Association 27th Annual Field 

Conference Guidebook, p. 73–84.

Merewether, E.A., Tillman, R.W., Cobban, W.A., and 

Obradovich, J.D., 1998, Outcrop-sections of the Upper 

Cretaceous Frontier Formation, southeastern Bighorn 

Basin, Wyoming in Keefer, W.R., and Goolsby, J.E., eds., 

Cretaceous and lower Tertiary rocks of the Bighorn Basin, 

Wyoming and Montana: Wyoming Geological Association 

49th Guidebook p. 31–42.

Mills, N.K., 1956, Subsurface stratigraphy of the pre-Niobrara 

Formations in the Bighorn Basin, Wyoming, Wyoming 

Stratigraphy, Part I, Subsurface stratigraphy of the preNiobrara Formations in Wyoming: Wyoming Geological 

Association, p. 9–22.

Mitchell, J.R., 1997, Regional distribution of the Greybull Ss. 

Member of the Thermopolis Shale, and related petroleum 

deposits, Wyoming & Montana, in Campen, E.B., ed., 

Bighorn Basin—50 years on the frontier: Yellowstone 

Bighorn Research Association-Wyoming Geological 

Association-Montana Geological Society, 1997 Field Trip 

and Symposium, p. 37. 
64 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Moberly, R.M., 1960, Morrison, Cloverly, and Sykes Mountain Formations, northern Bighorn Basin, Wyoming and 

Montana: Geological Society of America Bulletin, v. 71, 

no. 8, p. 1137–1176. 

Mohl, K.L., 1989, Greybull, in Cardinal, D.F., and others, eds., 

Wyoming oil and gas fields symposium, Bighorn and Wind 

River Basins: Wyoming Geological Association, p. 209. 

Moore, D.A., 1961, Isopachous map Fort Union Formation 

Bighorn Basin, in Wiloth, G.J., Hale, L.A., Randall, A.C., 

and Garrison, L., eds., Symposium on Late Cretaceous 

rocks Wyoming and adjacent areas: Wyoming Geological 

Association 16th Annual Field Conference, p. 200–204.

Nichols, D.J., 1998, Palynological age determinations of 

selected outcrop samples from the Lance and Fort Union 

Formations in the Bighorn Basin, Wyoming and Montana,

in Keefer, W.R., and Goolsby, J.E., eds., Cretaceous and 

Lower Tertiary rocks of the Bighorn Basin, Wyoming and 

Montana: Wyoming Geological Association 49th Guidebook, p. 117–129.

Nixon, R.P., 1973, Oil source beds in Cretaceous Mowry 

Shale of northwestern interior United States: American 

Association of Petroleum Geologists Bulletin, v. 57, no. 1, 

p. 136–161.

NRG Associates, 2007, The significant oil and gas fields of the 

United States: Colorado Springs, Colo., NRG Associates, 

Inc.; database available from NRG Associates, Inc., P.O. 

Box 1655, Colorado Springs, CO 80901, U.S.A. 

Nuccio, V.F., and Finn, T.M., 1998, Thermal maturity and 

petroleum generation history of Cretaceous and Tertiary 

source rocks, Bighorn Basin, Wyoming and Montana,

in Keefer, W.R., and Goolsby, J.E., eds., Cretaceous and 

Lower Tertiary rocks of the Bighorn Basin, Wyoming and 

Montana: Wyoming Geological Association 49th Guidebook, p. 211–231.

Nuccio, V.F., Finn, T.M., and Johnson, R.C., 1996, Thermal 

maturity data used for the assessment of gas resources in 

the Wind River Basin, Wyoming: U.S. Geological Survey 

Open-File Report 96–064, 57 p.

Obradovich, J.D., 1993, A Cretaceous time scale, in Caldwell, 

W.G.E., and Kauffman, E.G., eds., Evolution of the Western 

Interior Basin: Geological Association of Canada Special 

Paper 39, p. 379–396.

Obradovich, J.D., Cobban, W.A., Merewether, E.A., and 

Weimer, R.J., 1996, A time framework for the late Albian 

and early Cenomanian strata of northern Wyoming and 

Montana: Geological Society of America Abstacts with 

Programs, 1996 Annual Meeting, Denver, Colorado, p. 

A-66.

Parker, S.E., and Jones, R.W., 1986, Influence of faulting 

on Upper Cretaceous-Lower Tertiary deposition, Bighorn 

Basin, Wyoming, in Garrison, P.B., ed., Geology of the 

Beartooth uplift and adjacent basins: Yellowstone Bighorn 

Research Association-Montana Geological Society 50th 

Anniversary Guidebook, p. 137–144.

Paull, R.A., 1962, Depositional history of the Muddy 

Sandstone, Big Horn Basin, Wyoming, in Enyert, R.L., and 

Curry, W.H., eds., Symposium on Early Cretaceous rocks 

of Wyoming and adjacent areas: Wyoming Geological 

Association 17th Annual Field Conference Guidebook, 

p. 102–117. 

Peters, K.E., and Casa, M.R., 1994, Applied source rock 

geochemistry, in Magoon, L.B., and Dow, W.G., eds, The 

petroleum system-from source to trap: American Association of Petroleum Geologists Memoir 60, p. 93–120. 

Pierce, W.G., 1948, Geologic and structure contour map of 

the Basin-Greybull area, Bighorn County, Wyoming: U.S. 

Geological Survey Oil and Gas Investigations Preliminary 

Map 77, scale 1:48,000. 

Raines, G.L., and Johnson, B.R., 1995, Digital representation 

of the Montana state geologic map; a contribution to the 

Interior Columbia River basin ecosystem management 

project: U.S. Geological Survey Open-File Report 95–691, 

20 p.

Rawlins, J.H., 1986, Bearcreek coal field, in Garrison, P.B., 

ed., Geology of the Beartooth uplift and adjacent basins: 

Yellowstone Bighorn Research Association-Montana 

Geological Society 50th Anniversary Guidebook, p. 

253–255.

Resource Data International, Inc., 1998, COALdat database: 

Coal database, 1320 Pearl Street, Suite 300, Boulder, CO 

80302.

Rice, D.D., Young, G.B.C., and Paul, G.W., 1996, Methodology for assessment of technically recoverable resources of 

coalbed gas, in Gautier, D.L., Dolton, G.L., Takahashi, K.I., 

and Varnes, K.L, eds., 1995 National assessment of United 

States oil and gas resources—Results, methodology, and 

supporting data: U.S. Geological Survey Digital Data Series 

DDS–30, CD–ROM. 

Roberts, L.N.R., Finn, T.M., Lewan, M.D., and Kirschbaum, 

M.A., 2008, Burial history, thermal maturity, and oil and 

gas generation history of source rocks on the Bighorn Basin, 

Wyoming and Montana: U.S. Geological Survey Scientific 

Investigations Report 2008–5037, 27 p.
References 65

Roberts, S.B., 1998, An overview of the stratigraphic and 

sedimentologic characteristics of the Paleocene Fort Union 

Formation, southern Bighorn Basin, Wyoming, in Keefer, 

W.R., and Goolsby, J.E., eds., Cretaceous and lower Tertiary 

rocks of the Bighorn Basin, Wyoming and Montana: Wyoming Geological Association 49th Guidebook, p. 91–116.

Roberts, S.B., and Stanton, R.W., 1994, Stratigraphy and 

depositional setting of thick coal beds in the Grass Creek 

coal mine, southwestern Bighorn Basin, Wyoming, in

Flores, R.M., Mehring, K.T., Jones, R.W., and Beck, T.L., 

eds., Organics and the Rockies Field Guide: Wyoming State 

Geological Survey Public Information Circular no. 33, 

p. 125–138.

Rountree, Russ, 1980, Deep Bighorn Basin test attracts area 

interest: Western Oil Reporter, October, p. 60–61.

Rubey, W.W., 1931, Lithologic studies of fine-grained Upper 

Cretaceous sedimentary rocks of the Black Hills region, 

in Shorter contributions to general geology, 1930: U.S. 

Geological Survey Professional Paper, 165-A, p. A1–A54.

Ryder, R.T., 1987, Oil, gas, and coal resources of the 

McCullough Peaks Wilderness study area, Bighorn Basin, 

Wyoming: U.S. Geological Survey Open-File Report 

87–646, 59 p.

Schrayer, G.J., and Zarrella, W.M., 1963, Organic geochemistry of shale—I Distribution of organic matter in siliceous 

Mowry Shale of Wyoming: Geochimica et Cosmochimica 

Acta, v. 27, no. 10, p. 1033–1046.

Severn, W.P., 1961, General stratigraphy of the Mesaverde 

Group, Bighorn Basin, Wyoming, in Wiloth, G.J., Hale, 

L.A., Randall, A.C., and Garrison, L., eds., Symposium 

on Late Cretaceous rocks Wyoming and adjacent areas: 

Wyoming Geological Association 16th Annual Field 

Conference Guidebook, p. 195–199.

Shapard, G.W., 1975, Dry Creek, in Doroshenko, J., Miller, 

W.R., Thompson, E.E., and Rawlins, J.H., eds., Energy 

resources of Montana: Montana Geological Society 22nd 

Annual Publication, p. 64–67. 

Siemers, C.T., 1975, Paleoenvironmental analysis of the upper 

Cretaceous Frontier Formation, northwestern Bighorn 

Basin, in Exum, F.A., and George, G.R., eds., Geology and 

mineral resources of the Bighorn Basin: Wyoming Geological Association 27th Annual Field Conference Guidebook, 

p. 85–100.

Spencer, C.W., 1987, Hydrocarbon generation as a mechanism 

for overpressuring in Rocky Mountain region: American 

Association of Petroleum Geologists Bulletin, v. 71, no. 4, 

p. 368–388. 

Spencer, C.W., 1989, Review of characteristics of low-permeability gas reservoirs in western United States: American 

Association of Petroleum Geologists Bulletin, v. 73, no. 5, 

p. 613–629.

Steidtmann, J.R., 1993, The Cretaceous foreland basin and 

its sedimentary record, in Snoke, A.W., Steidtmann, J.R., 

and Roberts, S.M., eds., Geology of Wyoming: Geological 

Survey of Wyoming Memoir no. 5, p. 250–271.

Stewart, W.W., 1975, Grass Creek coalfield, Hot Springs 

County, in Exum, F.A., and George, G.R., eds., Geology 

and Mineral resources of the Bighorn Basin: Wyoming 

Geological Association 27th Annual Field Conference 

Guidebook, p. 229–233.

Stone, D.S., 1969, Wrench faulting and Rocky mountain 

tectonics: The Mountain Geologist, v. 6, no. 2, p. 67–79.

Stone, D.S., 1975, Discovery of Silver Tip South field, Park 

County, Wyoming, in Exum, F.A., and George, G.R., eds., 

Geology and mineral resources of the Bighorn Basin: 

Wyoming Geological Association 27th Annual Field 

Conference Guidebook, p. 189–201.

Stone, D.S., 1983, Seismic profile—South Elk basin, in Bally, 

A.W., ed., Seismic expression of structural styles: American 

Association of Petroleum Geologists Studies in Geology 

Series no. 15, v. 3. p. 3.2.2-20–3.2.2-24. 

Stone, D.S., 1985, Geologic interpretation of seismic profiles, 

Bighorn Basin, Wyoming, Part I—East flank, in Gries, R.R., 

and Dyer, R.C., eds., Seismic exploration of the Rocky 

Mountain Region: Rocky Mountain Association of Geologists-Denver Geophysical Society, p. 165–174.

Stone, D.S.,1993, Basement-involved thrust-generated folds 

as seismically imaged in the subsurface of the central 

Rocky Mountain foreland, in Schmidt, C.J., Chase, R.B., 

and Erslev, E.A., eds., Laramide basement deformation in 

the Rocky Mountain foreland of the western United States: 

Geological Society of America Special Paper 280, 

p. 271–318. 

Stone, D.S., 1999, Foreland basement-involved structures—

Discussion: American Association of Petroleum Geologists 

Bulletin, v. 83, no. 12, p. 2006–2016. 

Stone, D.S., 2004a, Rio thrusting, multi-stage migration, and 

formation of vertically segregated Paleozoic oil pool at 

Torchlight field on the Greybull platform (eastern Bighorn 

Basin)—Implication for exploration: The Mountain 

Geologist, v. 41, no. 3, p. 119–138.

Stone, D.S., 2004b, Structures of the Rocky Mountain foreland—Fivemile fault-related fold trend, central Bighorn 

Basin: The Mountain Geologist, v. 41, no. 3, p. 140–142.
66 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Sundell, K.A., 1990, Sedimentation and tectonics of the 

Absaroka Basin of northwestern Wyoming, in Specht, 

R.W., ed., Wyoming sedimentation and tectonics: Wyoming 

Geological Association 41st Field Conference Guidebook, 

p. 105–122. 

Sundell, K.A., 1993, A geologic overview of the Absaroka 

volcanic province, in Snoke, A.W., Steidtman, J.R., and 

Roberts, S.M., eds., Geology of Wyoming: Geological 

Survey of Wyoming Memoir No. 5, p. 480–506.

Surdam, R.C., Jiao, Z.S., and Heasler, H.P., 1997, Anomalously pressured gas compartments in Cretaceous rocks of 

the Laramide basins of Wyoming—A new class of hydrocarbon accumulation, in Surdam, R.C., ed., Seals, traps, and 

the petroleum system: American Association of Petroleum 

Geologists Memoir 67, p. 199–222. 

Talbot, C.L., 1996, The Tertiary and Upper Cretaceous 

potential in the Bighorn Basin, in Bowen, C.E., Kirkwood, 

S.C., and Miller, T.S., eds., Resources of the Bighorn Basin: 

Wyoming Geological Association 47th Guidebook, 

p. 59–62. 

Taylor, D.J., 1998, Processing and interpretation of 2-D 

seismic data from the Bighorn Basin, Wyoming, in

Keefer, W.R., and Goolsby, J.E., eds., Cretaceous and 

Lower Tertiary rocks of the Bighorn Basin, Wyoming 

and Montana: Wyoming Geological Association 49th 

Guidebook, p. 179–196. 

Tonnsen, J.J., editor, 1985, Montana oil and gas fields 

symposium 1985: Montana Geological Society, 1217 p. 

Tsuzuki, N., Takeda, N., Suzuki, M., and Yoki, K., 1999, The 

kinetic modeling of oil cracking by hydrothermal pyrolysis 

experiments: International Journal of Coal Geology, v. 39, 

p. 227–250.

Van Houten, F.B., 1944, Stratigraphy of the Willwood and 

Tatman Formations in northwestern Wyoming: Geological 

Society of America Bulletin, v. 55, no. 2, p. 165–210.

Van Houten, F.B., 1962, Frontier Formation, Bighorn 

Basin, Wyoming in Enyert, R.L., and Curry, W.H., eds., 

Symposium on Early Cretaceous rocks of Wyoming and 

adjacent areas: Wyoming Geological Association 17th 

Annual Field Conference Guidebook, p. 221–231.

Ver Ploeg, Alan J., 1985, Tectonic map of the Bighorn Basin, 

Wyoming: Wyoming Geological Survey Open-File Report 

85–11.

 Wilson, C.W., Jr., 1936, Geology of the Nye-Bowler lineament, Stillwater and Carbon Counties, Montana: American 

Association of Petroleum Geologists Bulletin, v. 20, no. 9, 

p. 1161–1188.

Wise, D.U., 1997, Pseudo tear faults at Red Lodge, MT—

Late-stage basin understuffing and tectonics of the greater 

Beartooth block, in Campen, E.B., ed., Bighorn Basin—50 

years on the frontier: Yellowstone Bighorn Research 

Association-Wyoming Geological Association-Montana 

Geological Society, 1997 Field Trip and Symposium, 

p. 71–99. 

Wise, D.U., 2000, Laramide structures in basement and 

cover of the Beartooth Uplift near Red Lodge, Montana: 

American Association of Petroleum Geologists Bulletin, 

v. 84, no. 3, p. 360–375.

Woodruff, E.G., 1907, The Red Lodge coalfield, Montana: 

U.S. Geological Survey Bulletin 341, p. 92–107.

Wyoming Oil and Gas Conservation Commission (WOGCC) 

accessed on (2007), at http://wogcc.state.wy.us/.

Yin, P. 1997, Source rock maturation and diagenetic modeling 

in Badger Basin, in Campen, E.B., ed., Bighorn Basin—50 

years on the frontier, part II: Yellowstone Bighorn Research 

Association-Wyoming Geological Association-Montana 

Geological Society, 1997 Field Trip and Symposium, 

p. 41–44.

Yuretich, R.F., Hickey, L.J., Gregson, B.P., and Hsia, Y.L., 

1984, Lacustrine deposits in the Paleocene Fort Union 

Formation, northern Bighorn Basin, Montana: Journal of 

Sedimentary Petrology, v. 54, no. 3, p. 836–852. 

Zaleha, M.J., 2006, Sevier orogenesis and nonmarine basin 

filling—Implications of new stratigraphic correlations of 

Lower Cretaceous strata throughout Wyoming, U.S.A,: 

Geological Society of America Bulletin, v. 118, no. 7/8, 

p. 886–896.
Appendix A 67

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas Assessment 

Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, 

barrel of natural gas liquids; m, meters; A.U., assessment unit]

Assessment Geologist: M.A. Kirschbaum and S.M. Condon Date: 19-Feb-08

Region: North America Number: 5

Province: Bighorn Basin Number: 5034

Total Petroleum System: Cretaceous-Tertiary Composite Number: 503402

Assessment Unit: Muddy-Frontier Sandstone and Mowry Fractured Shale Number: 50340261

 Continuous Gas

Based on Data as of: IHS Energy (2007); Cardinal and others (1989)

Notes from Assessor:

Assessment-unit type: Oil (<20,000 cfg/bo) or Gas (>20,000 cfg/bo), incl. disc. & pot. additions Gas

What is the minimum total recovery per cell? 0.02 (mmbo for oil A.U.; bcfg for gas A.U.)

Number of tested cells: 23

Number of tested cells with total recovery per cell > minimum: 5

Established (discovered cells): X Hypothetical (no cells):

Median total recovery per cell (for cells > min.): (mmbo for oil A.U.; bcfg for gas A.U.)

 1st 3rd discovered 2nd 3rd 3rd 3rd

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an untested cell with total recovery > minimum. 1.0

2. ROCKS: Adequate reservoirs, traps, seals for an untested cell with total recovery > minimum. 1.0

3. TIMING: Favorable geologic timing for an untested cell with total recovery > minimum. 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

1. Total assessment-unit area (acres): (uncertainty of a fixed value)

calculated mean 969,000 minimum 872,000 mode 969,000 maximum 1,066,000

2. Area per cell of untested cells having potential for additions to reserves (acres): (values are inherently variable)

calculated mean 130 minimum 40 mode 50 maximum 300

uncertainty of mean: minimum 100 maximum 160

3. Percentage of total assessment-unit area that is untested (%): (uncertainty of a fixed value)

calculated mean 99.6 minimum 99.2 mode 99.7 maximum 99.9

IDENTIFICATION INFORMATION

FORSPAN ASSESSMENT MODEL FOR CONTINUOUS

ACCUMULATIONS--BASIC INPUT DATA FORM (NOGA, Version 9, 2-10-03)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

CHARACTERISTICS OF ASSESSMENT UNIT
68 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas Assessment 

Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of 

gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; 

bngl, barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 5034

4. Percentage of untested assessment-unit area that has potential for additions to reserves (%):

( a necessary criterion is that total recovery per cell > minimum; uncertainty of a fixed value)

calculated mean 8.4 minimum 0.6 mode 2 maximum 22.5

Geologic evidence for estimates:

Total recovery per cell for untested cells having potential for additions to reserves:

(values are inherently variable; mmbo for oil A.U.; bcfg for gas A.U.)

calculated mean 0.57 minimum 0.02 median 0.35 maximum 7.5

Oil assessment unit: minimum mode maximum

 Gas/oil ratio (cfg/bo)

 NGL/gas ratio (bngl/mmcfg)

Gas assessment unit:

 Liquids/gas ratio (bliq/mmcfg) 0 0.5 2

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

 (Continued)

AVERAGE COPRODUCT RATIOS FOR UNTESTED CELLS, TO ASSESS COPRODUCTS

TOTAL RECOVERY PER CELL

(uncertainty of fixed but unknown values)
Appendix A 69

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

Oil assessment unit: minimum mode maximum

 API gravity of oil (degrees)

 Sulfur content of oil (%)

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

Gas assessment unit: minimum mode maximum

 Inert-gas content (%) 0.00 0.50 2.00

 CO2 content (%) 0.00 3.00 5.00

 Hydrogen sulfide content (%) 0.00 0.00 0.00

 Heating value (BTU) 950 1000 1100

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

3000 3500 4000 5800 6700

Success ratios: calculated mean minimum mode maximum

Future success ratio (%) 35 10 20 75

Historic success ratio, tested cells (%) 22

Completion practices:

1. Typical well-completion practices (conventional, open hole, open cavity, other) conventional

2. Fraction of wells drilled that are typically stimulated 100

3. Predominant type of stimulation (none, frac, acid, other) hydrofrac

4. Fraction of wells drilled that are horizontal 0

SELECTED ANCILLARY DATA FOR UNTESTED CELLS

(values are inherently variable)

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas 

Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, 

billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of 

oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued
70 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

P4

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

Surface Allocations (uncertainty of a fixed value)

1. Wyoming represents 100 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 100

2. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO STATES

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous 

Gas Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin 

Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, 

million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., 

assessment unit]—Continued
Appendix A 71

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas 

Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, 

billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of 

oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued
72 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 6

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

Surface Allocations (uncertainty of a fixed value)

1. Federal Lands represents 75.09 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 75

2. Private Lands represents 19.95 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 20

3. Tribal Lands represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. Other Lands represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. WY State Lands represents 4.96 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 5

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO GENERAL LAND OWNERSHIPS

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas 

Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, 

billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of 

oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix A 73

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas 

Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, 

billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel 

of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued
74 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 8

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

Surface Allocations (uncertainty of a fixed value)

1. Bureau of Land Management (BLM) represents 72.58 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 74.9

2. BLM Wilderness Areas (BLMW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. BLM Roadless Areas (BLMR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. National Park Service (NPS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. NPS Wilderness Areas (NPSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. NPS Protected Withdrawals (NPSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO FEDERAL LAND SUBDIVISIONS

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas 

Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, 

billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, 

barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix A 75

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

7. US Forest Service (FS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. USFS Wilderness Areas (FSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. USFS Roadless Areas (FSR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. USFS Protected Withdrawals (FSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. US Fish and Wildlife Service (FWS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. USFWS Wilderness Areas (FWSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous 

Gas Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin 

Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, 

million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., 

assessment unit]—Continued
76 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

13. USFWS Protected Withdrawals (FWSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

14. Wilderness Study Areas (WS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

15. Department of Energy (DOE) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

16. Department of Defense (DOD) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

17. Bureau of Reclamation (BOR) represents 2.51 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 0.1

18. Tennessee Valley Authority (TVA) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous 

Gas Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin 

Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, 

million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., 

assessment unit]—Continued
Appendix A 77

Assessment Unit (name, no.)

19. Other Federal represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

20. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas 

Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion 

cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, 

barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued
78 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

Surface Allocations (uncertainty of a fixed value)

1. Bighorn Basin (BHBA) represents 85.95 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 80

2. Yellowstone Highlands (YSHL) represents 14.05 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 20

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO ECOSYSTEMS

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous 

Gas Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin 

Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, 

million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., 

assessment unit]—Continued
Appendix A 79

Assessment Unit (name, no.)

Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas, 50340261

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix A. Input parameters for the Muddy-Frontier Sandstone and Mowry Fractured Shale Continuous Gas 

Assessment Unit (50340261), Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, 

billion cubic feet of gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of 

oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued
80 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]

Page 1

Assessment Geologist: M.A. Kirschbaum Date: 19-Feb-08

Region: North America Number: 5

Province: Bighorn Basin Number: 5034

Total Petroleum System: Cretaceous-Tertiary Composite Number: 503402

Assessment Unit: Mowry Fractured Shale Continuous Oil Number: 50340262

Based on Data as of: IHS Energy (2007)

Notes from Assessor: Powder River Basin Mowry Continuous Oil (50330261) assessment unit used as

analog.

Assessment-unit type: Oil (<20,000 cfg/bo) or Gas (>20,000 cfg/bo), incl. disc. & pot. additions Oil

What is the minimum total recovery per cell? 0.002 (mmbo for oil A.U.; bcfg for gas A.U.)

Number of tested cells: 0

Number of tested cells with total recovery per cell > minimum: 0

Established (discovered cells): Hypothetical (no cells): X

Median total recovery per cell (for cells > min.): (mmbo for oil A.U.; bcfg for gas A.U.)

 1st 3rd discovered 2nd 3rd 3rd 3rd

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an untested cell with total recovery > minimum. 1.0

2. ROCKS: Adequate reservoirs, traps, seals for an untested cell with total recovery > minimum. 1.0

3. TIMING: Favorable geologic timing for an untested cell with total recovery > minimum. 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

1. Total assessment-unit area (acres): (uncertainty of a fixed value)

calculated mean 646,000 minimum 581,000 mode 646,000 maximum 710,000

2. Area per cell of untested cells having potential for additions to reserves (acres): (values are inherently variable)

calculated mean 290 minimum 40 mode 185 maximum 640

uncertainty of mean: minimum 240 maximum 340

3. Percentage of total assessment-unit area that is untested (%): (uncertainty of a fixed value)

calculated mean 100 minimum 100 mode 100 maximum 100

IDENTIFICATION INFORMATION

FORSPAN ASSESSMENT MODEL FOR CONTINUOUS

ACCUMULATIONS--BASIC INPUT DATA FORM (NOGA, Version 9, 2-10-03)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

CHARACTERISTICS OF ASSESSMENT UNIT
Appendix B 81

Page 2

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

4. Percentage of untested assessment-unit area that has potential for additions to reserves (%):

( a necessary criterion is that total recovery per cell > minimum; uncertainty of a fixed value)

calculated mean 6 minimum 0.1 mode 1.25 maximum 17

Geologic evidence for estimates:

Total recovery per cell for untested cells having potential for additions to reserves:

(values are inherently variable; mmbo for oil A.U.; bcfg for gas A.U.)

calculated mean 0.04 minimum 0.002 median 0.025 maximum 0.35

Oil assessment unit: minimum mode maximum

 Gas/oil ratio (cfg/bo) 500 1000 1500

 NGL/gas ratio (bngl/mmcfg) 30 60 90

Gas assessment unit:

 Liquids/gas ratio (bliq/mmcfg)

AVERAGE COPRODUCT RATIOS FOR UNTESTED CELLS, TO ASSESS COPRODUCTS

TOTAL RECOVERY PER CELL

(uncertainty of fixed but unknown values)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

 (Continued)

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
82 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 3

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

Oil assessment unit: minimum mode maximum

 API gravity of oil (degrees) 40 45 50

 Sulfur content of oil (%) 0 0.1 0.3

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

2400 2800 3000 3300 3600

Gas assessment unit: minimum mode maximum

 Inert-gas content (%)

 CO2 content (%)

 Hydrogen sulfide content (%)

 Heating value (BTU)

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

Success ratios: calculated mean minimum mode maximum

Future success ratio (%) 28 10 25 50

Historic success ratio, tested cells (%)

Completion practices:

1. Typical well-completion practices (conventional, open hole, open cavity, other) conventional

2. Fraction of wells drilled that are typically stimulated 100

3. Predominant type of stimulation (none, frac, acid, other) hydrofrac

4. Fraction of wells drilled that are horizontal 90

SELECTED ANCILLARY DATA FOR UNTESTED CELLS

(values are inherently variable)

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix B 83

Page 4

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

Surface Allocations (uncertainty of a fixed value)

1. Wyoming represents 100 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity 100

Gas in gas assessment unit:

 Volume % in entity

2. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO STATES

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
84 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 5

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix B 85

Page 6

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

Surface Allocations (uncertainty of a fixed value)

1. Federal Lands represents 74.43 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity 75

Gas in gas assessment unit:

 Volume % in entity

2. Private Lands represents 20.77 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity 21

Gas in gas assessment unit:

 Volume % in entity

3. Tribal Lands represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. Other Lands represents 0.18 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity 0

Gas in gas assessment unit:

 Volume % in entity

5. WY State Lands represents 4.62 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity 4

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO GENERAL LAND OWNERSHIPS

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
86 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 7

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix B 87

Page 8

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

Surface Allocations (uncertainty of a fixed value)

1. Bureau of Land Management (BLM) represents 73.04 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity 74.9

Gas in gas assessment unit:

 Volume % in entity

2. BLM Wilderness Areas (BLMW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. BLM Roadless Areas (BLMR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. National Park Service (NPS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. NPS Wilderness Areas (NPSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. NPS Protected Withdrawals (NPSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO FEDERAL LAND SUBDIVISIONS

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
88 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 9

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

7. US Forest Service (FS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. USFS Wilderness Areas (FSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. USFS Roadless Areas (FSR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. USFS Protected Withdrawals (FSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. US Fish and Wildlife Service (FWS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. USFWS Wilderness Areas (FWSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix B 89

Page 10

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

13. USFWS Protected Withdrawals (FWSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

14. Wilderness Study Areas (WS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

15. Department of Energy (DOE) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

16. Department of Defense (DOD) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

17. Bureau of Reclamation (BOR) represents 1.39 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity 0.1

Gas in gas assessment unit:

 Volume % in entity

18. Tennessee Valley Authority (TVA) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
90 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 11

Assessment Unit (name, no.)

19. Other Federal represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

20. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix B 91

Page 12

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

Surface Allocations (uncertainty of a fixed value)

1. Bighorn Basin (BHBA) represents 100.00 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity 100

Gas in gas assessment unit:

 Volume % in entity

2. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO ECOSYSTEMS

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
92 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 13

Assessment Unit (name, no.)

Mowry Fractured Shale Continuous Oil, 50340262

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix B. Input parameters for the Mowry Fractured Shale Continuous Oil Assessment Unit (50340262), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix C 93

Page 1

Assessment Geologist: T.M. Finn and R.C. Johnson Date: 19-Feb-08

Region: North America Number: 5

Province: Bighorn Basin Number: 5034

Total Petroleum System: Cretaceous-Tertiary Composite Number: 503402

Assessment Unit: Cody Sandstone Continuous Gas Number: 50340263

Based on Data as of: IHS Energy (2007)

Notes from Assessor: Wind River Basin Cody Sandstone Continuous Gas (50350262) assessment unit used

as analog.

Assessment-unit type: Oil (<20,000 cfg/bo) or Gas (>20,000 cfg/bo), incl. disc. & pot. additions Gas

What is the minimum total recovery per cell? 0.02 (mmbo for oil A.U.; bcfg for gas A.U.)

Number of tested cells: 0

Number of tested cells with total recovery per cell > minimum: 0

Established (discovered cells): Hypothetical (no cells): X

Median total recovery per cell (for cells > min.): (mmbo for oil A.U.; bcfg for gas A.U.)

 1st 3rd discovered 2nd 3rd 3rd 3rd

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an untested cell with total recovery > minimum. 1.0

2. ROCKS: Adequate reservoirs, traps, seals for an untested cell with total recovery > minimum. 1.0

3. TIMING: Favorable geologic timing for an untested cell with total recovery > minimum. 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

1. Total assessment-unit area (acres): (uncertainty of a fixed value)

calculated mean 420,000 minimum 378,000 mode 420,000 maximum 462,000

2. Area per cell of untested cells having potential for additions to reserves (acres): (values are inherently variable)

calculated mean 280 minimum 40 mode 160 maximum 640

uncertainty of mean: minimum 160 maximum 400

3. Percentage of total assessment-unit area that is untested (%): (uncertainty of a fixed value)

calculated mean 100 minimum 100 mode 100 maximum 100

IDENTIFICATION INFORMATION

FORSPAN ASSESSMENT MODEL FOR CONTINUOUS

ACCUMULATIONS--BASIC INPUT DATA FORM (NOGA, Version 9, 2-10-03)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

CHARACTERISTICS OF ASSESSMENT UNIT

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of 

natural gas liquids; m, meters; A.U., assessment unit]
94 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 2

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

4. Percentage of untested assessment-unit area that has potential for additions to reserves (%):

( a necessary criterion is that total recovery per cell > minimum; uncertainty of a fixed value)

calculated mean 7.6 minimum 0.3 mode 3 maximum 19.6

Geologic evidence for estimates:

Total recovery per cell for untested cells having potential for additions to reserves:

(values are inherently variable; mmbo for oil A.U.; bcfg for gas A.U.)

calculated mean 0.34 minimum 0.02 median 0.2 maximum 5

Oil assessment unit: minimum mode maximum

 Gas/oil ratio (cfg/bo)

 NGL/gas ratio (bngl/mmcfg)

Gas assessment unit:

 Liquids/gas ratio (bliq/mmcfg) 0 0.015 1

AVERAGE COPRODUCT RATIOS FOR UNTESTED CELLS, TO ASSESS COPRODUCTS

TOTAL RECOVERY PER CELL

(uncertainty of fixed but unknown values)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

 (Continued)

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of 

natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix C 95

Page 3

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

Oil assessment unit: minimum mode maximum

 API gravity of oil (degrees)

 Sulfur content of oil (%)

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

Gas assessment unit: minimum mode maximum

 Inert-gas content (%) 0.00 0.50 2.00

 CO2 content (%) 0.00 3.00 5.00

 Hydrogen sulfide content (%) 0.00 0.00 0.00

 Heating value (BTU) 950 1050 1100

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

3750 4575 5800

Success ratios: calculated mean minimum mode maximum

Future success ratio (%) 40 10 40 70

Historic success ratio, tested cells (%)

Completion practices:

1. Typical well-completion practices (conventional, open hole, open cavity, other) conventional

2. Fraction of wells drilled that are typically stimulated 100

3. Predominant type of stimulation (none, frac, acid, other) hydrofrac

4. Fraction of wells drilled that are horizontal 0

SELECTED ANCILLARY DATA FOR UNTESTED CELLS

(values are inherently variable)

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
96 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 4

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

Surface Allocations (uncertainty of a fixed value)

1. Wyoming represents 100 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 100

2. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO STATES

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix C 97

Page 5

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of 

gas; mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, 

barrel of liquid; bngl, barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued
98 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 6

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

Surface Allocations (uncertainty of a fixed value)

1. Federal Lands represents 81.21 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 88

2. Private Lands represents 13.68 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 8

3. Tribal Lands represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. Other Lands represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. WY State Lands represents 5.11 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 4

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO GENERAL LAND OWNERSHIPS

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of 

natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix C 99

Page 7

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
100 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 8

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

Surface Allocations (uncertainty of a fixed value)

1. Bureau of Land Management (BLM) represents 81.01 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 88

2. BLM Wilderness Areas (BLMW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. BLM Roadless Areas (BLMR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. National Park Service (NPS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. NPS Wilderness Areas (NPSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. NPS Protected Withdrawals (NPSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO FEDERAL LAND SUBDIVISIONS

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix C 101

Page 9

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

7. US Forest Service (FS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. USFS Wilderness Areas (FSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. USFS Roadless Areas (FSR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. USFS Protected Withdrawals (FSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. US Fish and Wildlife Service (FWS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. USFWS Wilderness Areas (FWSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
102 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 10

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

13. USFWS Protected Withdrawals (FWSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

14. Wilderness Study Areas (WS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

15. Department of Energy (DOE) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

16. Department of Defense (DOD) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

17. Bureau of Reclamation (BOR) represents 0.20 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 0

18. Tennessee Valley Authority (TVA) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix C 103

Page 11

Assessment Unit (name, no.)

19. Other Federal represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

20. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, 

barrel of natural gas liquids; m, meters; A.U., assessment unit]—Continued
104 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 12

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

Surface Allocations (uncertainty of a fixed value)

1. Bighorn Basin (BHBA) represents 87.49 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 92

2. Yellowstone Highlands (YSHL) represents 12.51 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 8

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO ECOSYSTEMS

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix C 105

Page 13

Assessment Unit (name, no.)

Cody Sandstone Continuous Gas, 50340263

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix C. Input parameters for the Cody Sandstone Continuous Gas Assessment Unit (50340263), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
106 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 1

Assessment Geologist: T.M. Finn and R.C. Johnson Date: 19-Feb-08

Region: North America Number: 5

Province: Bighorn Basin Number: 5034

Total Petroleum System: Cretaceous-Tertiary Composite Number: 503402

Assessment Unit: Mesaverde Sandstone Continuous Gas Number: 50340264

Based on Data as of: IHS Energy (2007); Cardinal and others (1989); MGS (1985)

Notes from Assessor: Wind River Basin Mesaverde-Meeteetse Sandstone Gas (50350264) assessment unit

used as analog.

Assessment-unit type: Oil (<20,000 cfg/bo) or Gas (>20,000 cfg/bo), incl. disc. & pot. additions Gas

What is the minimum total recovery per cell? 0.02 (mmbo for oil A.U.; bcfg for gas A.U.)

Number of tested cells: 1

Number of tested cells with total recovery per cell > minimum: 0

Established (discovered cells): Hypothetical (no cells): X

Median total recovery per cell (for cells > min.): (mmbo for oil A.U.; bcfg for gas A.U.)

 1st 3rd discovered 2nd 3rd 3rd 3rd

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an untested cell with total recovery > minimum. 1.0

2. ROCKS: Adequate reservoirs, traps, seals for an untested cell with total recovery > minimum. 1.0

3. TIMING: Favorable geologic timing for an untested cell with total recovery > minimum. 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

1. Total assessment-unit area (acres): (uncertainty of a fixed value)

calculated mean 221,000 minimum 199,000 mode 221,000 maximum 243,000

2. Area per cell of untested cells having potential for additions to reserves (acres): (values are inherently variable)

calculated mean 83.3 minimum 20 mode 50 maximum 180

uncertainty of mean: minimum 60 maximum 100

3. Percentage of total assessment-unit area that is untested (%): (uncertainty of a fixed value)

calculated mean 100 minimum 100 mode 100 maximum 100

IDENTIFICATION INFORMATION

FORSPAN ASSESSMENT MODEL FOR CONTINUOUS

ACCUMULATIONS--BASIC INPUT DATA FORM (NOGA, Version 9, 2-10-03)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

CHARACTERISTICS OF ASSESSMENT UNIT

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit].
Appendix D 107

Page 2

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

4. Percentage of untested assessment-unit area that has potential for additions to reserves (%):

( a necessary criterion is that total recovery per cell > minimum; uncertainty of a fixed value)

calculated mean 3.6 minimum 0.2 mode 2.1 maximum 8.5

Geologic evidence for estimates:

Total recovery per cell for untested cells having potential for additions to reserves:

(values are inherently variable; mmbo for oil A.U.; bcfg for gas A.U.)

calculated mean 0.34 minimum 0.02 median 0.2 maximum 5

Oil assessment unit: minimum mode maximum

 Gas/oil ratio (cfg/bo)

 NGL/gas ratio (bngl/mmcfg)

Gas assessment unit:

 Liquids/gas ratio (bliq/mmcfg) 0 3 6

AVERAGE COPRODUCT RATIOS FOR UNTESTED CELLS, TO ASSESS COPRODUCTS

TOTAL RECOVERY PER CELL

(uncertainty of fixed but unknown values)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

 (Continued)

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
108 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 3

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

Oil assessment unit: minimum mode maximum

 API gravity of oil (degrees)

 Sulfur content of oil (%)

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

Gas assessment unit: minimum mode maximum

 Inert-gas content (%) 0.00 0.50 4.00

 CO2 content (%) 0.00 0.25 1.00

 Hydrogen sulfide content (%) 0.00 0.00 0.00

 Heating value (BTU) 1000 1150 1300

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

3800 4270 5340

Success ratios: calculated mean minimum mode maximum

Future success ratio (%) 30 10 30 50

Historic success ratio, tested cells (%)

Completion practices:

1. Typical well-completion practices (conventional, open hole, open cavity, other) conventional

2. Fraction of wells drilled that are typically stimulated 100

3. Predominant type of stimulation (none, frac, acid, other) hydrofrac

4. Fraction of wells drilled that are horizontal 0

SELECTED ANCILLARY DATA FOR UNTESTED CELLS

(values are inherently variable)

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix D 109

Page 4

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

Surface Allocations (uncertainty of a fixed value)

1. Wyoming represents 100 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 100

2. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO STATES

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
110 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 5

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix D 111

Page 6

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

Surface Allocations (uncertainty of a fixed value)

1. Federal Lands represents 78.83 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 92

2. Private Lands represents 15.64 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 0

3. Tribal Lands represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. Other Lands represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. WY State Lands represents 5.52 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 8

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO GENERAL LAND OWNERSHIPS

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
112 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 7

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix D 113

Page 8

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

Surface Allocations (uncertainty of a fixed value)

1. Bureau of Land Management (BLM) represents 78.83 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 92

2. BLM Wilderness Areas (BLMW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. BLM Roadless Areas (BLMR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. National Park Service (NPS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. NPS Wilderness Areas (NPSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. NPS Protected Withdrawals (NPSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO FEDERAL LAND SUBDIVISIONS

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
114 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 9

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

7. US Forest Service (FS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. USFS Wilderness Areas (FSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. USFS Roadless Areas (FSR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. USFS Protected Withdrawals (FSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. US Fish and Wildlife Service (FWS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. USFWS Wilderness Areas (FWSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix D 115

Page 10

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

13. USFWS Protected Withdrawals (FWSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

14. Wilderness Study Areas (WS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

15. Department of Energy (DOE) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

16. Department of Defense (DOD) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

17. Bureau of Reclamation (BOR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

18. Tennessee Valley Authority (TVA) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
116 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 11

Assessment Unit (name, no.)

19. Other Federal represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

20. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix D 117

Page 12

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

Surface Allocations (uncertainty of a fixed value)

1. Bighorn Basin (BHBA) represents 78.23 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 83

2. Yellowstone Highlands (YSHL) represents 21.77 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 17

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO ECOSYSTEMS

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
118 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 13

Assessment Unit (name, no.)

Mesaverde Sandstone Continuous Gas, 50340264

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix D. Input parameters for the Mesaverde Sandstone Continuous Gas Assessment Unit (50340264), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix E 119

Page 1

Assessment Geologist: S.B. Roberts Date: 20-Feb-08

Region: North America Number: 5

Province: Bighorn Basin Number: 5034

Total Petroleum System: Cretaceous-Tertiary Composite Number: 503402

Assessment Unit: Mesaverde-Meeteetse Formation Coalbed Gas Number: 50340281

Based on Data as of: IHS Energy (2007)

Notes from Assessor: Powder River Basin Fort Union Formation and Piceance Basin Mesaverde Formation

coalbed gas wells used as analogs.

Assessment-unit type: Oil (<20,000 cfg/bo) or Gas (>20,000 cfg/bo), incl. disc. & pot. additions Gas

What is the minimum total recovery per cell? 0.02 (mmbo for oil A.U.; bcfg for gas A.U.)

Number of tested cells: 16

Number of tested cells with total recovery per cell > minimum: 0

Established (discovered cells): Hypothetical (no cells): X

Median total recovery per cell (for cells > min.): (mmbo for oil A.U.; bcfg for gas A.U.)

 1st 3rd discovered 2nd 3rd 3rd 3rd

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an untested cell with total recovery > minimum. 1.0

2. ROCKS: Adequate reservoirs, traps, seals for an untested cell with total recovery > minimum. 1.0

3. TIMING: Favorable geologic timing for an untested cell with total recovery > minimum. 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

1. Total assessment-unit area (acres): (uncertainty of a fixed value)

calculated mean 1,619,000 minimum 1,457,000 mode 1,619,000 maximum 1,781,000

2. Area per cell of untested cells having potential for additions to reserves (acres): (values are inherently variable)

calculated mean 127 minimum 40 mode 100 maximum 240

uncertainty of mean: minimum 80 maximum 170

3. Percentage of total assessment-unit area that is untested (%): (uncertainty of a fixed value)

calculated mean 99.9 minimum 99.9 mode 99.9 maximum 99.9

IDENTIFICATION INFORMATION

FORSPAN ASSESSMENT MODEL FOR CONTINUOUS

ACCUMULATIONS--BASIC INPUT DATA FORM (NOGA, Version 9, 2-10-03)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

CHARACTERISTICS OF ASSESSMENT UNIT

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]
120 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 2

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

4. Percentage of untested assessment-unit area that has potential for additions to reserves (%):

( a necessary criterion is that total recovery per cell > minimum; uncertainty of a fixed value)

calculated mean 5.7 minimum 0.5 mode 2.5 maximum 14

Geologic evidence for estimates:

Total recovery per cell for untested cells having potential for additions to reserves:

(values are inherently variable; mmbo for oil A.U.; bcfg for gas A.U.)

calculated mean 0.14 minimum 0.02 median 0.1 maximum 1.2

Oil assessment unit: minimum mode maximum

 Gas/oil ratio (cfg/bo)

 NGL/gas ratio (bngl/mmcfg)

Gas assessment unit:

 Liquids/gas ratio (bliq/mmcfg) 0 2 5

AVERAGE COPRODUCT RATIOS FOR UNTESTED CELLS, TO ASSESS COPRODUCTS

TOTAL RECOVERY PER CELL

(uncertainty of fixed but unknown values)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

 (Continued)

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix E 121

Page 3

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

Oil assessment unit: minimum mode maximum

 API gravity of oil (degrees)

 Sulfur content of oil (%)

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

Gas assessment unit: minimum mode maximum

 Inert-gas content (%) 0.10 0.30 1.00

 CO2 content (%) 0.50 1.80 20.00

 Hydrogen sulfide content (%) 0.00 0.00 0.00

 Heating value (BTU) 850 950 1050

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

150 650 750 1150 1800

Success ratios: calculated mean minimum mode maximum

Future success ratio (%) 47 20 40 80

Historic success ratio, tested cells (%)

Completion practices:

1. Typical well-completion practices (conventional, open hole, open cavity, other) conventional

2. Fraction of wells drilled that are typically stimulated 0

3. Predominant type of stimulation (none, frac, acid, other) none

4. Fraction of wells drilled that are horizontal none

SELECTED ANCILLARY DATA FOR UNTESTED CELLS

(values are inherently variable)

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
122 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 4

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

Surface Allocations (uncertainty of a fixed value)

1. Wyoming represents 85.50 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 99

2. Montana represents 14.50 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 1

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO STATES

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix E 123

Page 5

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
124 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 6

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

Surface Allocations (uncertainty of a fixed value)

1. Federal Lands represents 58.63 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 90

2. Private Lands represents 35.11 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 7

3. Tribal Lands represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. Other Lands represents 0.16 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 0

5. WY State Lands represents 5.49 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 2

6. MT State Lands represents 0.61 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 1

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO GENERAL LAND OWNERSHIPS

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix E 125

Page 7

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
126 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 8

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

Surface Allocations (uncertainty of a fixed value)

1. Bureau of Land Management (BLM) represents 56.89 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 89

2. BLM Wilderness Areas (BLMW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. BLM Roadless Areas (BLMR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. National Park Service (NPS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. NPS Wilderness Areas (NPSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. NPS Protected Withdrawals (NPSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO FEDERAL LAND SUBDIVISIONS

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix E 127

Page 9

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

7. US Forest Service (FS) represents 0.37 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 0

8. USFS Wilderness Areas (FSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. USFS Roadless Areas (FSR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. USFS Protected Withdrawals (FSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. US Fish and Wildlife Service (FWS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. USFWS Wilderness Areas (FWSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
128 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 10

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

13. USFWS Protected Withdrawals (FWSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

14. Wilderness Study Areas (WS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

15. Department of Energy (DOE) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

16. Department of Defense (DOD) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

17. Bureau of Reclamation (BOR) represents 1.37 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 1

18. Tennessee Valley Authority (TVA) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix E 129

Page 11

Assessment Unit (name, no.)

19. Other Federal represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

20. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
130 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 12

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

Surface Allocations (uncertainty of a fixed value)

1. Bighorn Basin (BHBA) represents 74.38 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 97

2. Powder River Basin (PRBA) represents 4.18 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 1

3. Yellowstone Highlands (YSHL) represents 21.44 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 2

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO ECOSYSTEMS

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix E 131

Page 13

Assessment Unit (name, no.)

Mesaverde-Meeteetse Formation Coalbed Gas, 50340281

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix E. Input parameters for the Mesaverde-Meeteetse Coalbed Gas Assessment Unit (50340281), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic 

feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural 

gas liquids; m, meters; A.U., assessment unit]—Continued
132 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), Cretaceous-Tertiary 

Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of gas; 

cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, 

meters; A.U., assessment unit]

Page 1

Assessment Geologist: S.B. Roberts Date: 20-Feb-08

Region: North America Number: 5

Province: Bighorn Basin Number: 5034

Total Petroleum System: Cretaceous-Tertiary Composite Number: 503402

Assessment Unit: Fort Union Formation Coalbed Gas Number: 50340282

Based on Data as of: IHS Energy (2007)

Notes from Assessor: Powder River Basin coalbed gas wells used as analog.

Assessment-unit type: Oil (<20,000 cfg/bo) or Gas (>20,000 cfg/bo), incl. disc. & pot. additions Gas

What is the minimum total recovery per cell? 0.02 (mmbo for oil A.U.; bcfg for gas A.U.)

Number of tested cells: 0

Number of tested cells with total recovery per cell > minimum: 0

Established (discovered cells): Hypothetical (no cells): X

Median total recovery per cell (for cells > min.): (mmbo for oil A.U.; bcfg for gas A.U.)

 1st 3rd discovered 2nd 3rd 3rd 3rd

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an untested cell with total recovery > minimum. 1.0

2. ROCKS: Adequate reservoirs, traps, seals for an untested cell with total recovery > minimum. 1.0

3. TIMING: Favorable geologic timing for an untested cell with total recovery > minimum. 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

1. Total assessment-unit area (acres): (uncertainty of a fixed value)

calculated mean 2,419,000 minimum 2,177,000 mode 2,419,000 maximum 2,661,000

2. Area per cell of untested cells having potential for additions to reserves (acres): (values are inherently variable)

calculated mean 113 minimum 40 mode 100 maximum 200

uncertainty of mean: minimum 60 maximum 160

3. Percentage of total assessment-unit area that is untested (%): (uncertainty of a fixed value)

calculated mean 100 minimum 100 mode 100 maximum 100

IDENTIFICATION INFORMATION

FORSPAN ASSESSMENT MODEL FOR CONTINUOUS

ACCUMULATIONS--BASIC INPUT DATA FORM (NOGA, Version 9, 2-10-03)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

CHARACTERISTICS OF ASSESSMENT UNIT
Appendix F 133

Page 2

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

4. Percentage of untested assessment-unit area that has potential for additions to reserves (%):

( a necessary criterion is that total recovery per cell > minimum; uncertainty of a fixed value)

calculated mean 1.4 minimum 0.1 mode 1 maximum 3

Geologic evidence for estimates:

Total recovery per cell for untested cells having potential for additions to reserves:

(values are inherently variable; mmbo for oil A.U.; bcfg for gas A.U.)

calculated mean 0.1 minimum 0.02 median 0.08 maximum 1

Oil assessment unit: minimum mode maximum

 Gas/oil ratio (cfg/bo)

 NGL/gas ratio (bngl/mmcfg)

Gas assessment unit:

 Liquids/gas ratio (bliq/mmcfg) 0 0.25 0.5

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

 (Continued)

AVERAGE COPRODUCT RATIOS FOR UNTESTED CELLS, TO ASSESS COPRODUCTS

TOTAL RECOVERY PER CELL

(uncertainty of fixed but unknown values)

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), Cretaceous-Tertiary 

Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of gas; 

cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, 

meters; A.U., assessment unit]—Continued
134 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 3

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

Oil assessment unit: minimum mode maximum

 API gravity of oil (degrees)

 Sulfur content of oil (%)

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

Gas assessment unit: minimum mode maximum

 Inert-gas content (%) 0.10 0.30 1.00

 CO2 content (%) 0.50 1.80 20.00

 Hydrogen sulfide content (%) 0.00 0.00 0.00

 Heating value (BTU) 850 950 1050

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

150 580 600 1100 1800

Success ratios: calculated mean minimum mode maximum

Future success ratio (%) 40 10 40 70

Historic success ratio, tested cells (%)

Completion practices:

1. Typical well-completion practices (conventional, open hole, open cavity, other) conventional

2. Fraction of wells drilled that are typically stimulated 0

3. Predominant type of stimulation (none, frac, acid, other) none

4. Fraction of wells drilled that are horizontal none

SELECTED ANCILLARY DATA FOR UNTESTED CELLS

(values are inherently variable)

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), Cretaceous-Tertiary 

Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of gas; 

cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, 

meters; A.U., assessment unit]—Continued
Appendix F 135

Page 4

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

Surface Allocations (uncertainty of a fixed value)

1. Wyoming represents 88.26 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 30

2. Montana represents 11.74 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 70

3. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO STATES

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), Cretaceous-Tertiary 

Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of 

gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas 

liquids; m, meters; A.U., assessment unit]—Continued
136 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 5

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), Cretaceous-Tertiary 

Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of gas; 

cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, 

meters; A.U., assessment unit]—Continued
Appendix F 137

Page 6

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

Surface Allocations (uncertainty of a fixed value)

1. Federal Lands represents 66.41 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 34

2. Private Lands represents 28.58 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 64

3. Tribal Lands represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. Other Lands represents 0.08 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 0

5. WY State Lands represents 4.28 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 1

6. MT State Lands represents 0.64 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 1

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO GENERAL LAND OWNERSHIPS

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), Cretaceous-Tertiary 

Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million cubic feet of gas; 

cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel of natural gas liquids; m, 

meters; A.U., assessment unit]—Continued
138 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 7

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix F 139

Page 8

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

Surface Allocations (uncertainty of a fixed value)

1. Bureau of Land Management (BLM) represents 63.40 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 34

2. BLM Wilderness Areas (BLMW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

3. BLM Roadless Areas (BLMR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

4. National Park Service (NPS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. NPS Wilderness Areas (NPSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. NPS Protected Withdrawals (NPSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO FEDERAL LAND SUBDIVISIONS

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
140 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 9

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

7. US Forest Service (FS) represents 0.81 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 0

8. USFS Wilderness Areas (FSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. USFS Roadless Areas (FSR) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. USFS Protected Withdrawals (FSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. US Fish and Wildlife Service (FWS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. USFWS Wilderness Areas (FWSW) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix F 141

Page 10

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

13. USFWS Protected Withdrawals (FWSP) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

14. Wilderness Study Areas (WS) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

15. Department of Energy (DOE) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

16. Department of Defense (DOD) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

17. Bureau of Reclamation (BOR) represents 2.19 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 0

18. Tennessee Valley Authority (TVA) represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
142 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 11

Assessment Unit (name, no.)

19. Other Federal represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

20. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix F 143

Page 12

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

Surface Allocations (uncertainty of a fixed value)

1. Bighorn Basin (BHBA) represents 81.18 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 30

2. Powder River Basin (PRBA) represents 2.91 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 0

3. Yellowstone Highlands (YSHL) represents 15.91 area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity 70

4. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

5. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

6. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO ECOSYSTEMS

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
144 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Page 13

Assessment Unit (name, no.)

Fort Union Formation Coalbed Gas, 50340282

7. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

8. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

9. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

10. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

11. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

12. represents area % of the AU

Oil in oil assessment unit: minimum mode maximum

 Volume % in entity

Gas in gas assessment unit:

 Volume % in entity

Appendix F. Input parameters for the Fort Union Formation Coalbed Gas Assessment Unit (50340282), CretaceousTertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; mmcfg, million 

cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of liquid; bngl, barrel 

of natural gas liquids; m, meters; A.U., assessment unit]—Continued
Appendix G 145

SEVENTH APPROXIMATION

DATA FORM FOR CONVENTIONAL ASSESSMENT UNITS (Version 6, 9 April 2003)

Assessment Geologist: T.M. Finn, M.A. Kirschbaum, and S.M. Condon Date: 19-Feb-08

Region: North America Number: 5

Province: Bighorn Basin Number: 5034

Total Petroleum System: Cretaceous-Tertiary Composite Number: 503402

Assessment Unit: Cretaceous-Tertiary Conventional Oil and Gas Number: 50340201

Based on Data as of: NRG (2007, data current through 2005); IHS Energy (2007)

Notes from Assessor: Cardinal and others (1989); NRG reservoir growth factor, 30 years

Powder River Basin Sussex-Shannon (50330302) and MesaverdeLewis Sandstones (50330303) assessment units used as analogs

CHARACTERISTICS OF ASSESSMENT UNIT

Oil (<20,000 cfg/bo overall) or Gas (>20,000 cfg/bo overall): Oil

What is the minimum accumulation size? 0.5 mmboe grown

(the smallest accumulation that has potential to be added to reserves)

No. of discovered accumulations exceeding minimum size: Oil: 9 Gas: 15

Established (>13 accums.) X Frontier (1-13 accums.) Hypothetical (no accums.)

Median size (grown) of discovered oil accumulations (mmbo):

1st 3rd 3.7 2nd 3rd 1.5 3rd 3rd

Median size (grown) of discovered gas accumulations (bcfg):

1st 3rd 19.3 2nd 3rd 40.3 3rd 3rd 59.6

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an undiscovered accum. > minimum size: 1.0

2. ROCKS: Adequate reservoirs, traps, and seals for an undiscovered accum. > minimum size: 1.0

3. TIMING OF GEOLOGIC EVENTS: Favorable timing for an undiscovered accum. > minimum s 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

UNDISCOVERED ACCUMULATIONS

No. of Undiscovered Accumulations: How many undiscovered accums. exist that are > min. size?: 

 (uncertainty of fixed but unknown values)

Oil Accumulations: minimum (>0) 1 mode 5 maximum 15

Gas Accumulations: minimum (>0) 1 mode 10 maximum 40

Sizes of Undiscovered Accumulations: What are the sizes (grown) of the above accums?: 

 (variations in the sizes of undiscovered accumulations)

Oil in Oil Accumulations (mmbo): minimum 0.5 median 1.5 maximum 12

Gas in Gas Accumulations (bcfg): minimum 3 median 9 maximum 72

IDENTIFICATION INFORMATION

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]
146 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

AVERAGE RATIOS FOR UNDISCOVERED ACCUMS., TO ASSESS COPRODUCTS

(uncertainty of fixed but unknown values)

Oil Accumulations: minimum mode maximum

Gas/oil ratio (cfg/bo) 1200 2500 3800

NGL/gas ratio (bngl/mmcfg) 30 60 90

Gas Accumulations: minimum mode maximum

Liquids/gas ratio (bliq/mmcfg) 8 16 24

Oil/gas ratio (bo/mmcfg)

SELECTED ANCILLARY DATA FOR UNDISCOVERED ACCUMULATIONS

(variations in the properties of undiscovered accumulations)

Oil Accumulations: minimum mode maximum

API gravity (degrees) 36 45 50

Sulfur content of oil (%) 0 0.1 0.3

Depth (m) of water (if applicable)

minimum F75 mode F25 maximum

Drilling Depth (m) 150 3000 4600

Gas Accumulations: minimum mode maximum

Inert gas content (%) 0 1.5 10

CO2 content (%) 0 0.3 1

Hydrogen-sulfide content (%) 0 0 0

Depth (m) of water (if applicable)

minimum F75 mode F25 maximum

Drilling Depth (m) 150 3000 4600

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued
Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

Surface Allocations (uncertainty of a fixed value)

1. Wyoming represents 90.88 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 99

Gas in Gas Accumulations:

Volume % in entity 99

2. Montana represents 9.12 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 1

Gas in Gas Accumulations:

Volume % in entity 1

3. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

4. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

5. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

6. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO STATES

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued

Appendix G 147
148 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

7. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

8. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

9. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

10. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

11. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

12. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued
Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

Surface Allocations (uncertainty of a fixed value)

1. Federal Lands represents 58.70 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 70

Gas in Gas Accumulations:

Volume % in entity 70

2. Private Lands represents 33.39 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 25

Gas in Gas Accumulations:

Volume % in entity 25

3. Tribal Lands represents 1.01 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 0

Gas in Gas Accumulations:

Volume % in entity 0

4. Other Lands represents 0.23 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 0

Gas in Gas Accumulations:

Volume % in entity 0

5. WY State Lands represents 6.19 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 5

Gas in Gas Accumulations:

Volume % in entity 5

6. MT State Lands represents 0.47 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 0

Gas in Gas Accumulations:

Volume % in entity 0

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO LAND ENTITIES

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued

Appendix G 149
150 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

7. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

8. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

9. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

10. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

11. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

12. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued
Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

Surface Allocations (uncertainty of a fixed value)

1. Bureau of Land Management (BLM) represents 55.09 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 70

Gas in Gas Accumulations:

Volume % in entity 70

2. BLM Wilderness Areas (BLMW) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

3. BLM Roadless Areas (BLMR) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

4. National Park Service (NPS) represents 0.11 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 0

Gas in Gas Accumulations:

Volume % in entity 0

5. NPS Wilderness Areas (NPSW) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

6. NPS Protected Withdrawals (NPSP) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO FEDERAL LAND SUBDIVISIONS

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued

Appendix G 151
152 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

7. US Forest Service (FS) represents 1.78 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 0

Gas in Gas Accumulations:

Volume % in entity 0

8. USFS Wilderness Areas (FSW) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

9. USFS Roadless Areas (FSR) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

10. USFS Protected Withdrawals (FSP) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

11. US Fish and Wildlife Service (FWS) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

12. USFWS Wilderness Areas (FWSW) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued
Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

13. USFWS Protected Withdrawals (FWSP) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

14. Wilderness Study Areas (WS) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

15. Department of Energy (DOE) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

16. Department of Defense (DOD) represents 0.05 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

17. Bureau of Reclamation (BOR) represents 1.67 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 0

Gas in Gas Accumulations:

Volume % in entity 0

18. Tennessee Valley Authority (TVA) represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued

Appendix G 153
154 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Assessment Unit (name, no.)

Paleozoic-Mesozoic Conventional Oil and Gas, 50340101

19. Other Federal represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

20. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued
Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

Surface Allocations (uncertainty of a fixed value)

1. Bighorn Basin (BHBA) represents 74.11 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 95

Gas in Gas Accumulations:

Volume % in entity 95

2. Bighorn Mountains (BHMT) represents 0.09 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 0

Gas in Gas Accumulations:

Volume % in entity 0

3. Powder River Basin (PRBA) represents 1.53 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 0

Gas in Gas Accumulations:

Volume % in entity 0

4. Yellowstone Highlands (YSHL) represents 24.27 area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity 5

Gas in Gas Accumulations:

Volume % in entity 5

5. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

6. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

ALLOCATIONS OF POTENTIAL ADDITIONS TO RESERVES TO ECOSYSTEMS

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued

Appendix G 155
156 Cretaceous–Tertiary Composite Total Petroleum System, Bighorn Basin, Wyoming and Montana

Assessment Unit (name, no.)

Cretaceous-Tertiary Conventional Oil and Gas, 50340201

7. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

8. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

9. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

10. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

11. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

12. represents area % of the AU

Oil in Oil Accumulations: minimum mode maximum

Volume % in entity

Gas in Gas Accumulations:

Volume % in entity

Appendix G. Input parameters for the Cretaceous-Tertiary Conventional Oil and Gas Assessment Unit (50340201), 

Cretaceous-Tertiary Composite Total Petroleum System, Bighorn Basin Province. [bcfg, billion cubic feet of gas; 

mmcfg, million cubic feet of gas; cfg, cubic feet of gas; mmbo, million barrels of oil; bo, barrel of oil; bliq, barrel of 

liquid; bngl, barrel of natural gas liquids; mmboe, million barrels of oil equivalent; m, meters]—Continued
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