Chapter 1

An Assessment of In-Place Oil Shale 

Resources in the Green River Formation, 

Piceance Basin, Colorado

By Ronald C. Johnson, Tracey J. Mercier, Michael E. Brownfield, 

Michael P. Pantea, and Jesse G. Self

Chapter 1 of 7

Oil Shale and Nahcolite Resources of the Piceance 

Basin, Colorado

By U.S. Geological Survey Oil Shale Assessment Team

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

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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Suggested citation:

Johnson, R.C., Mercier, T.J., Brownfield, M.E., Pantea, M.P., and Self, J.G., 2010, An assessment of in-place oil 

shale resources in the Green River Formation, Piceance Basin, Colorado: U.S. Geological Survey Digital Data Series 

DDS–69–Y, chp. 1, 187 p.

ISBN: 1–4113–2668–2
iii

Contents

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

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

Acknowledgments.........................................................................................................................................5

Previous Assessments..................................................................................................................................5

Stratigraphy of the Green River Formation and Definition of the Rich and Lean Zones that 

Comprise the Oil Shale Section .....................................................................................................6

Factors Affecting the Precision of Oil-Yield Measurements................................................................11

Determining the Volume of Oil in a Given Volume of Rock...........................................................11

Broken Core and Missing Core Intervals........................................................................................12

Comparing Gallons Per Ton Data Points From This Assessment With Those Used in the 

Previous Assessment ...........................................................................................................39

Reproducibility of Fischer Assay Analysis .....................................................................................39

Problems Related to Saline Minerals..............................................................................................39

Methods Used to Generate Isopach Maps and Isoresource Maps ...................................................51

Detailed Description and Assessment Results of Oil Shale Zones .....................................................53

R-0 Zone................................................................................................................................................64

L-0 Zone................................................................................................................................................64

R-1 Zone................................................................................................................................................66

L-1 Zone................................................................................................................................................66

R-2 Zone................................................................................................................................................83

L-2 Zone................................................................................................................................................83

R-3 Zone................................................................................................................................................98

L-3 Zone................................................................................................................................................98

R-4 Zone................................................................................................................................................98

L-4 Zone..............................................................................................................................................120

R-5 Zone..............................................................................................................................................120

L-5 Zone..............................................................................................................................................120

R-6 Zone..............................................................................................................................................136

B-Groove ............................................................................................................................................136

Mahogany Zone ................................................................................................................................152

A-Groove ............................................................................................................................................163

The Interval Above A-Groove .........................................................................................................163

Discussion...................................................................................................................................................176

References Cited........................................................................................................................................185
iv

Figures

1. Geologic map of the Piceance Basin, northwest Colorado showing Upper 

Cretaceous and Lower Tertiary stratigraphic units ................................................................2

2. Map showing extent of Uinta and Piceance Basins and Greater Green River 

Basin, and approximate extent of oil shale in the Green River Formation..........................3

 3. North-south cross section through the Piceance Basin, northwest Colorado..................7

4. East-west cross section through the Piceance Basin, the Douglas Creek arch, 

and the eastern part of the Uinta Basin....................................................................................8

5. Photograph of an outcrop of the Mahogany ledge in the south-central part of the 

Piceance Basin ...........................................................................................................................10

6. Photograph of a typical sample of oil shale in the Parachute Creek Member 

displaying organic-rich layers and organic-lean layers ......................................................10

7. Rich and lean zones for the Green River Formation .............................................................11

8. Photograph of nahcolite aggregates in rich oil shale, Piceance Basin, Colorado..........12

9. Photograph of an outcrop of “blebby” oil shale displaying organically 

lean marlstone clasts in rich oil shale matrix ........................................................................13

10. Photograph of an outcrop of oil shale displaying disrupted bedding due 

to movement of the floor of Lake Uinta prior to lithification................................................13

11. Photograph showing intertonguing of volcaniclastic sandstones of the 

Uinta Formation and marlstones of the Green River Formation..........................................14

12. Graph showing the relationship between oil yield for Green River oil shales 

and specific gravity ....................................................................................................................19

13. Map showing percent of missing intervals, number of missing intervals, 

and thickest missing interval for core holes drilled through the R-0 zone, 

Piceance Basin, Colorado.........................................................................................................20

14. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the L-0 zone, 

Piceance Basin, Colorado.........................................................................................................21

15. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the R-1, 

Piceance Basin, Colorado.........................................................................................................22

16. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the L-1 zone, 

Piceance Basin, Colorado.........................................................................................................23

17. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for both core holes and rotary holes drilled through 

the R-2 zone, Piceance Basin, Colorado.................................................................................24

18. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for both core holes and rotary holes drilled through 

the L-2 zone, Piceance Basin, Colorado .................................................................................25

19. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the R-3 zone, 

Piceance Basin, Colorado.........................................................................................................26

20. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the L-3 zone, 

Piceance Basin, Colorado.........................................................................................................27
v

 21. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the R-4 zone, 

Piceance Basin, Colorado.........................................................................................................28

22. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the L-4 zone, 

Piceance Basin, Colorado.........................................................................................................29

23. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the R-5 zone, 

Piceance Basin, Colorado.........................................................................................................30

24. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the L-5 zone, 

Piceance Basin, Colorado.........................................................................................................31

25. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for both core holes and rotary holes drilled 

through the R-6 zone, Piceance Basin, Colorado..................................................................32

26. Map showing percent of missing intervals, number of missing intervals, and 

thickest missing interval for core holes drilled through the Mahogany zone, 

Piceance Basin, Colorado.........................................................................................................33

27. Map showing locations of 13 closely spaced core holes in the northwest part 

of the basin that were used to study affects of missing core intervals on the 

overall oil yields obtained from the core ................................................................................36

28. Percent missing interval versus average oil yield for the oil shale zones 

from the L-0 zone through Mahogany zone for 13 closely spaced core 

holes in the northwest part of the basin .................................................................................37

29. Oil-yield histograms for two closely spaced rotary holes in the eastern 

part of the basin ..........................................................................................................................40

30. Oil-yield histograms listing percent missing intervals and average oil yield 

in gallons per ton for four core holes (A–D) in the northwest part of the basin..............41

31. Map showing gallons per ton measurements used in both this assessment and the 

previous one to assess the R-5 zone.......................................................................................42

32. Map showing barrels per acre measurements used in both this assessment 

and the previous one to assess the R-5 zone ........................................................................43

33. Map showing gallons per ton measurements used in both this assessment and the 

previous one to assess the L-5 zone .......................................................................................44

34. Map showing barrels per acre measurements used in both this assessment and the 

previous one to assess the R-5 zone.......................................................................................45

35. Ratio of gallons per ton calculated here with that calculated by Pitman and 

others (1989) for 49 core holes that penetrated the R-5 zone compared with 

percent missing intervals ..........................................................................................................49

36. Ratio of barrels per acre calculated here with that calculated by Pitman and 

others (1989) for 49 core holes that penetrated the R-5 zone compared with 

percent missing intervals ..........................................................................................................49

37. Ratio of gallons per ton calculated here with that calculated by Pitman and 

others (1989) for 61 core holes that penetrated the L-5 zone compared with 

percent missing intervals ..........................................................................................................50

38. Ratio of barrels per acre calculated here with that calculated by Pitman and 

others (1989) for 61 core holes that penetrated the L-5 zone compared with 

percent missing intervals ..........................................................................................................50
vi

39. Barrels per acre map for the R-5 zone plotted using the Radial Basis Function 

Method (RBF) using the same core holes and the same barrels per acre 

values used by Pitman and others (1989) ...............................................................................54

40. Barrels per acre map for the L-5 zone plotted using the Radial Basis Function 

Method (RBF) using the same core holes and the same barrels per acre 

values used by Pitman and others (1989) ...............................................................................55

41. Isopach map of the R-0 zone using both core hole and rotary hole data .........................65

42. Isoresource map of the R-0 zone showing the oil yield in gallons per ton (GPT) ............67

43. Isoresource map of the R-0 zone showing oil yields in barrels per acre (BPA) ..............68

44. Isoresource map of the R-0 zone showing total number of barrels of oil in 

each township.............................................................................................................................69

45. Isopach map of the L-0 zone using both core hole and rotary hole data..........................71

46. Isoresource map of the L-0 zone showing the oil yield in gallons per ton (GPT).............72

47. Isoresource map of the L-0 zone showing oil yields in barrels per acre (BPA)...............73

48. Isoresource map of the L-0 zone showing total number of barrels of oil in 

each township.............................................................................................................................74

49. Isopach map of the R-1 zone using both core hole and rotary hole data .........................76

50. Isoresource map of the R-1 zone showing the oil yield in gallons per ton (GPT) ............77

51. Isoresource map of the R-1 zone showing oil yields in barrels per acre (BPA) ..............78

52. Isoresource map of the R-1 zone showing total number of barrels of oil in 

each township using only core hole data...............................................................................79

53. Isopach map of the L-1 zone using both core hole and rotary hole data..........................84

54. Isoresource map for the L-1 zone showing the oil yield in gallons per ton (GPT) ...........85

55. Isoresource map of the L-1 zone showing oil yields in barrels per acre (BPA)...............86

56. Isoresource map of the L-1 zone showing total number of barrels of oil in 

each township.............................................................................................................................87

57. Isopach map of the R-2 zone using the Radial Basis Function Method (RBF) 

of contouring ...............................................................................................................................91

58. Isoresource map of the R-2 zone showing the oil yield in gallons per ton 

(GPT) using only core hole data ...............................................................................................92

59. Isoresource map for the R-2 zone showing oil yields in barrels per acre (BPA) 

using only core hole data. .........................................................................................................93

60. Isoresource map of the R-2 zone showing total number of barrels of oil in 

each township using only core hole data...............................................................................94

61. Isopach map of the L-2 zone using the Radial Basis Function Method (RBF) 

of contouring ...............................................................................................................................99

62. Isoresource map of the L-2 zone showing the oil yield in gallons per ton 

(GPT) using only core hole data .............................................................................................100

63. Isoresource map of the L-2 zone showing oil yields in barrels per acre 

(BPA) using only core hole data.............................................................................................101

64. Isoresource map of the L-2 zone showing total number of barrels of oil in 

each township using only core hole data.............................................................................102

65. Isopach map of the R-3 zone using the Radial Basis Function Method (RBF) 

of contouring .............................................................................................................................106

66. Isoresource map for the R-3 zone showing the oil yield in gallons per ton 

(GPT) using only core hole data .............................................................................................107

67. Isoresource map for the R-3 zone showing oil yields in barrels per acre 

(BPA) using only core hole data.............................................................................................108
vii

68. Isoresource map of the R-3 zone showing total number of barrels of oil in 

each township using only core hole data.............................................................................109

69. Isopach map of the L-3 zone using the Radial Basis Function Method (RBF) 

of contouring .............................................................................................................................113

70. Isoresource map of the L-3 zone showing the oil yield in gallons per ton 

(GPT) using only core hole data .............................................................................................114

71. Isoresource map of the L-3 zone showing oil yields in barrels per acre 

(BPA) using only core hole data.............................................................................................115

72. Isoresource map of the L-3 zone showing total number of barrels of oil 

in each township using only core hole data ........................................................................116

73. Isopach map of the R-4 zone using the Radial Basis Function Method 

(RBF) of contouring...................................................................................................................121

74. Isoresource map of the R-4 zone showing the oil yield in gallons per 

ton (GPT) using only core hole data ......................................................................................122

75. Isoresource map of the R-4 zone showing oil yields in barrels per 

acre (BPA) using only core hole data....................................................................................123

76. Isoresource map of the R-4 zone showing total number of barrels of 

oil in each township using only core hole data ...................................................................124

77. Isopach map of the L-4 zone using the Radial Basis Function Method 

(RBF) of contouring...................................................................................................................128

78. Isoresource map of the L-4 zone showing the oil yield in gallons per ton 

(GPT) using only core hole data .............................................................................................129

79. Isoresource map of the L-4 zone showing oil yields in barrels per acre 

(BPA) using only core hole data.............................................................................................130

80. Isoresource map of the L-4 zone showing total number of barrels of oil 

in each township using only core hole data ........................................................................131

81. Isopach map of the R-5 zone using the Radial Basis Function Method 

(RBF) of contouring...................................................................................................................135

82. Isoresource map of the R-5 zone showing the oil yield in gallons per ton 

(GPT) using only core hole data .............................................................................................137

83. Isoresource map of the R-5 zone showing oil yields in barrels per acre 

(BPA) using only core hole data.............................................................................................138

84. Isoresource map of the R-5 zone showing total number of barrels of oil in 

each township using only core hole data.............................................................................139

85. Isopach map of the L-5 zone using the Radial Basis Function Method 

(RBF) of contouring...................................................................................................................143

86. Isoresource map of the L-5 zone showing the oil yield in gallons per ton 

(GPT) using only core hole data .............................................................................................144

87. Isoresource map of the L-5 zone showing oil yields in barrels per acre 

(BPA) using only core hole data.............................................................................................145

88. Isoresource map of the L-5 zone showing total number of barrels of oil in 

each township using only core hole data.............................................................................146

89. Isopach map of the R-6 zone using the Radial Basis Function Method 

(RBF) of contouring...................................................................................................................150

90. Isoresource map of the R-6 zone showing the oil yield in gallons per ton 

(GPT) using only core hole data .............................................................................................151

91. Isoresource map of the R-6 zone showing oil yields in barrels per acre

(BPA) using only core hole data.............................................................................................153
viii

92. Isoresource map of the R-6 zone showing total number of barrels of oil in 

each township using only core hole data.............................................................................154

 93. Isopach map of B-groove using both core hole and rotary hole data.............................157

94. Isoresource map of B-groove showing the oil yield in gallons per ton 

(GPT) using only core hole data .............................................................................................158

95. Isoresource map of B-groove showing oil yields in barrels per acre 

(BPA) using only core hole data.............................................................................................159

96. Isoresource map of B-groove showing total number of barrels of oil in 

each township using only core hole data.............................................................................160

97. Isopach map of the Mahogany zone using both core hole and rotary hole data..........162

98. Isoresource map of the Mahogany zone showing the oil yield in gallons 

per ton (GPT)..............................................................................................................................164

99. Isoresource map of the Mahogany zone showing oil yields in barrels per 

acre (BPA)..................................................................................................................................165

100. Isoresource map of the Mahogany zone showing total number of barrels 

of oil in each township using only core hole data...............................................................166

101. Isopach map of A-groove using both core hole and rotary hole data.............................170

102. Isoresource map of A-groove showing the oil yield in gallons per ton 

(GPT) using only core hole data .............................................................................................171

103. Isoresource map of A-groove showing oil yields in barrels per acre 

(BPA) using only core hole data.............................................................................................172

104. Isoresource map of A-groove showing total number of barrels of oil in 

each township using only core hole data.............................................................................173

105. Detailed north-south cross section showing the intertonguing of the Uinta 

Formation with the upper part of the Green River Formation in the 

Piceance Basin, Colorado.......................................................................................................174

106. Isopach map of Bed 44 to A-groove using both core hole and rotary hole data...........175

107. Isoresource map of bed 44 to A-groove showing the oil yield in gallons 

per ton (GPT) using only core hole data ...............................................................................177

108. Isoresource map of bed 44 to A-groove showing oil yields in barrels per 

acre (BPA) using only core hole data....................................................................................178

 109. Isoresource map of bed 44 to A-groove showing total number of barrels of 

oil in each township using only core hole data ...................................................................179

110. Map showing total in-place oil in millions of barrels for each township in 

the Piceance Basin, Colorado ................................................................................................183
ix

Tables

1. Original volume-weight oil-yield relationships of Green River Formation oil shale ........15

2. Recalculated volume-weight oil-yield relationships of Green River Formation 

oil shale ........................................................................................................................................17

3. Detailed analysis of 13 closely spaced core holes from a four-square-mile 

area in the northwest part of the basin...................................................................................34

4. Gallons per ton, barrels per acre, and percent missing intervals for 49 

selected core holes that were used to assess the R-5 zone in both this 

assessment and the assessment of Pitman and others (1989)...........................................46

5. Gallons per ton, barrels per acre, and percent missing intervals for 61 

selected core holes that were used to assess the L-5 zone in both this 

assessment and the assessment of Pitman and others (1989)...........................................47

6. Number of control points used to assess each oil shale zone in this 

assessment and the previous assessment ............................................................................52

7. Comparing total barrels per township for the R-5 zone using the Radial 

Basis Function Method (RBF) here with the results using kriging by 

Pitman and others (1989)...........................................................................................................56

8. Comparing total barrels per township for the L-5 zone using the Radial 

Basis Function Method (RBF) here with the results using kriging by 

Pitman and others (1989)...........................................................................................................58

9. Estimating thicknesses, gallons per ton (GPT), and barrels per acre (BPA) 

for surface sections ...................................................................................................................60

10. Total number of in-place barrels of oil per acre (BPA) in each township 

for the R-0 zone calculated here using the Radial Basis Function Method (RBF)...........70

11. Total number of in-place barrels of oil per acre (BPA) in each township for 

the L-0 zone calculated here using the Radial Basis Function Method (RBF) .................75

12. Total number of in-place barrels of oil per acre (BPA) in each township for the 

R-1 zone calculated here using the Radial Basis Function Method (RBF)........................80

13. Total number of in-place barrels of oil per acre (BPA) in each township for 

the L-1 zone calculated here using the Radial Basis Function Method (RBF) .................88

14. Total number of in-place barrels of oil per acre (BPA) in each township for 

the R-2 zone calculated here using the Radial Basis Function Method (RBF).................95

15. Total number of in-place barrels of oil per acre (BPA) in each township 

for the L-2 zone calculated here using the Radial Basis Function Method (RBF) .........103

16. Total number of in-place barrels of oil per acre (BPA) in each township for 

the R-3 zone calculated here using the Radial Basis Function Method (RBF)...............110

17. Total number of in-place barrels of oil per acre (BPA) in each township for 

the L-3 zone calculated here using the Radial Basis Function Method (RBF) ...............117

18. Total number of in-place barrels of oil per acre (BPA) in each township for the 

R-4 zone calculated here using the Radial Basis Function Method (RBF)......................125

19. Total number of in-place barrels of oil per acre (BPA) in each township for 

the L-4 zone calculated here using the Radial Basis Function Method (RBF) ...............132

20. Total number of in-place barrels of oil per acre (BPA) in each township for 

the R-5 zone calculated here using the Radial Basis Function Method (RBF)...............140

21. Total number of in-place barrels of oil per acre (BPA) in each township 

for the L-5 zone calculated here using the Radial Basis Function Method (RBF) .........147
x

22. Total number of in-place barrels of oil per acre (BPA) in each township for the 

R-6 zone calculated here using the Radial Basis Function Method (RBF)......................155

23. Total number of in-place barrels of oil per acre (BPA) in each township for 

B-groove calculated here using the Radial Basis Function Method (RBF) ....................161

24. Total number of in-place barrels of oil per acre (BPA) in each township for the 

Mahogany zone calculated here using the Radial Basis Function Method (RBF) ........167

25. Total number of in-place barrels of oil per acre (BPA) in each township for 

A-groove calculated here using the Radial Basis Function Method (RBF) ....................169

26. Total number of in-place barrels of oil per acre (BPA) in each township for 

the interval from the top of A-groove to the top of bed 44.................................................180

27. Total in-place oil for each of the rich and lean oil shale zones in the 

Piceance Basin, Colorado.......................................................................................................181

28. Barrels of in-place oil in each township in the Piceance Basin, Colorado ....................182

29. Comparing the results of this assessment using the Radial Basis Function 

Method (RBF) with the results from the previous assessment of 

Pitman and others (1989) using kriging .................................................................................184
Abstract

A comprehensive assessment of in-place oil, regardless 

of richness, in oil shales of the Green River Formation of 

the Piceance Basin of western Colorado is presented here. A 

considerable amount of oil-yield data was collected after the 

previous in-place assessment was published in 1989, and these 

data have been incorporated into this new assessment. About 

twice as many oil-yield data points (2,178 versus 1,083) were 

used in this assessment. Estimated total in-place oil in the 

Piceance Basin is about 1.5 trillion barrels, or about 50 percent 

larger than the previous in-place assessment of about one trillion barrels. Almost all of this increase is due to (1) new areas 

being assessed that had too little data to assess in the previous 

assessment, and (2) new intervals being assessed that were 

not assessed previously. Much of this previously unassessed 

resource is of low grade and is unlikely to be developed. The 

Radial Basis Function (RBF) extrapolation method was used 

to generate isopach maps, isoresource maps, and to calculate resources. The RBF method created more geologically 

reasonable models than kriging, and a comparison of the two 

methods using the same data points showed little difference in 

the results.

Introduction

This report presents an in-place assessment of the oil 

shale resources of the Green River Formation in the Piceance 

Basin of western Colorado (fig. 1). The Piceance Basin is one 

of three large structural and sedimentary basins that contain 

vast amounts of oil shale resources in the Green River Formation of Eocene age. The other two basins, the Uinta Basin 

of eastern Utah and westernmost Colorado, and the Greater 

Green River Basin of southwest Wyoming, northwestern 

Colorado, and northeastern Utah also contain large resources 

of oil shale in the Green River Formation (fig. 2), and these 

two basins will be assessed separately. The previous assessment of the Piceance Basin by the U.S. Geological Survey 

(USGS) estimated that there was about 1 trillion barrels of 

oil-in-place (Pitman and Johnson, 1978; Pitman, 1979; Pitman 

and others, 1989), based on Fischer assay results from coreholes drilled to evaluate oil shale, making it the largest known 

oil shale deposit in the world (Dyni, 2003). 

The Fischer assay method is a standardized laboratory 

test for determining the oil yield from oil shale that has been 

almost universally used to determine oil yields for Green 

River Formation oil shales (Stanfield and Frost, 1949; ASTM, 

1980). The Fischer assay standard method consists of heating 

a crushed and screened (-8 mesh (2.38-mm mesh) 100-gram 

sample in a small aluminum retort to 500° C at a rate of 12° C 

per minute and then held at that temperature for 40 minutes. 

The volatile vapors of shale oil, gas, and water pass through a 

condenser cooled with ice water (about 5° C) and collected in 

a graduated centrifuge tube. The oil and water are then separated by centrifuging and weighed. The quantities reported in 

the original sample are the weight percentages of shale oil, 

water, shale residue (contains carbon char), and “gas plus loss” 

(noncondensable gas yield) by difference. The specific gravity 

of the shale oil is measured and used to calculate the oil yield 

in gallons per ton (GPT).

The Fischer assay method does not determine the total 

amount of hydrocarbons in an oil shale sample and the method 

does not measure the amount or composition of the gases 

released during the heating of the sample. These gases—

chiefly light hydrocarbons, hydrogen, and carbon dioxide—are 

reported as the “gas plus loss.”

Fischer assay does not necessarily measure the maximum amount of oil that an oil shale can produce, and there 

are retorting methods that yield more than the Fischer assay 

yield (see Dyni, 2003, p. 196 for a discussion of methods to 

determine oil yields). However, the oil yields achieved by 

other technologies are typically reported as a percentage of the 

Fischer assay oil yield, and thus Fischer assay is still considered the standard by which other methods are compared.

Fischer assay analysis was done on cuttings from a 

significant number of rotary holes drilled for oil and gas in the 

basin. These analyses are quite old, mainly from the 1950s 

and 1960s, and were done to supplement the limited core hole 

data available at the time. There are many unresolved issues 

with the cuttings data, and no cuttings data were used in the 

assessment of Pitman and Johnson (1978), Pitman (1979), and 

Pitman and others (1989) or the assessment presented here. 

An Assessment of In-Place Oil Shale Resources in the 

Green River Formation, Piceance Basin, Colorado

By Ronald C. Johnson, Tracey J. Mercier, Michael E. Brownfield, Michael P. Pantea, and Jesse G. Self
2 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Chaffee Delta

Eagle

Garfield

Grand

Gunnison

Hinsdale

Jackson

Lake

Larimer

Mesa

Moffat

Montrose

Ouray

Park

Pitkin

Rio Blanco

Routt

Saguache

San Miguel

40

40

40

285

70

70

50

Grand 

Junction

Gunnison Salida

Montrose

Craig

Glenwood

Springs

39°

38°

41°

40°

109° 108° 107° 106°

Colorado River

Green

River

Lake

Granby

Meeker

Rangely

Steamboat

Springs

64

13

13

139

Rifle

City, town

Extrusive and intrusive

 volcanic rocks

Mesaverde Fm. and Mesaverde

 Group coal-bearing rocks

Undivided Quaternary, Tertiary,

 Mesozoic, and Paleozoic

EXPLANATION

TERTIARY

CRETACEOUS

County line Uinta Formation and undivided

 Tertiary

Green River Formation

Wasatch Formation and undivided

 lower Tertiary

0 50 MILES

Colorado

Index map

Fig. 4 Fig. 3

A’

A

B B’

Figure 1. Geologic map of the Piceance Basin, northwest Colorado showing Upper Cretaceous and Lower 

Tertiary stratigraphic units. Locations of figures 3 and 4 are shown.
Introduction 3

112° 111° 110° 109° 108° 107° 106°

40°

39°

38°

41°

42°

43°

Piceance

Basin

Sand Wash

Basin

Washakie

Basin

Great Divide Basin

Uinta Basin

COLORADO

UTAH

WYOMING

IDAHO

Provo

Price

Utah

Lake

Vernal

Rangely

Grand

Junction

Green River

Salt Lake City

Meeker

Rifle

Craig

Baggs

Rawlins

Rock Springs

Green

Evanston River

Green River

Basin

Great Salt Lake

Yampa River

Green River

White

White

Colorado River

Colorado River

River

River

River

Green

River

Yampa

40

40

40

40

287

287

187

187

189

189

40

50

50

80

80

80

80

70

70

70 50

160

50

Gunnison

64

44

414

318

318

430

789

13

13

13

28

33

139

Southwestern Wyoming

Province Boundary

Uinta-Piceance

Province Boundary

EXPLANATION

U.S. Geological Survey

 Oil and Gas Province

Oil-shale bearing rocks City or town

Major highway or road

Figure 2. Map showing extent of Uinta and Piceance Basins and Greater Green River Basin, and 

approximate extent of oil shale in the Green River Formation. Extent of the Uinta and Piceance 

Basins is the same as the Uinta-Piceance Province boundary (Uinta and Piceance Assessment 

Team, 2003). Extent of the Greater Green River Basin is the same as the Southwest Wyoming 

Province boundary (Southwest Wyoming Province Assessment Team, 2005). For the extent of oil 

shale in the Piceance Basin, the base of the Parachute Creek Member as mapped by Tweto (1979) 

was used for all but the northwest part of the basin where the base of the lower member of the 

Green River Formation is used. For the extent of oil shale in the eastern part of the Uinta Basin, the 

base of the Parachute Creek Member of the Green River Formation as mapped by Cashion (1973) 

and Rowley and others (1985) was used. In the western part of the basin the top of the Mahogany 

bed, as mapped by Witkind (1995), was used. In the northern part of the Uinta Basin, only those 

areas where oil shale occurs at a depth of 6,000 ft or less are shown. This area was determined 

using a structure contour map of the top of the Mahogany oil shale bed compiled by Johnson 

and Roberts (2003). For the Sand Wash, Washakie, Great Divide, and southeastern part of the 

Green River Basin, the base of the Tipton Shale Member, as mapped by Tweto (1979) and Love and 

Christiansen (1985), was used as the extent of oil shale. For the western part of the Green River 

Basin, the base of the Wilkins Peak Member of the Green River Formation, and for the northern 

part of the Green River Basin, the base of the Laney Shale Member of the Green River Formation, 

as mapped by Love and Christiansen (1985), was used. 
4 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

A considerable amount of oil-yield data was collected 

subsequent to this previous assessment, and these data have 

been incorporated into the present oil shale assessment. About 

twice as many data points (2,178 versus 1,083) were used in 

this assessment when compared with the previous one. Much 

of this additional data was donated by private industry after 

interest in developing oil shale waned in the 1980s. In addition, five oil shale intervals that were not included in the previous assessment are assessed here.

This effort has been hampered by difficulties in recovering the digital files that were used in the previous assessments 

by the USGS and the former U.S. Bureau of Mines (USBM). 

Much of the data that was used by the USGS was stored on 

outdated digital mediums that had either degraded to a point 

that they were no longer readable, or a suitable computer or 

software that could read the data could not be found. The 

USBM was disbanded in 1996, and the considerable amount 

of oil shale data stored on their computers is, at present, not 

accessible. In many cases, only computer printouts of the data 

remained that had to be scanned and tediously rectified. 

The previous USGS assessment (Pitman and Johnson, 

1978; Pitman, 1979; Pitman and others, 1989) subdivided the 

oil shale interval into a series of oil-rich and oil-lean zones 

that could be traced across most of the basin (Cashion and 

Donnell, 1972), and each zone was assessed separately. We 

attempted to use the same set of rich and lean zones in order 

to make the two assessments comparable. Only a computer 

printout of part of the file listing the tops for these rich and 

lean zones in the drill holes that were used in the previous 

assessment was recovered, and this information was incorporated into our new digital tops file. In addition, a considerable 

amount of core hole information was collected subsequent 

to the previous assessment, and tops had to be picked for 

these additional holes. A series of stratigraphic cross sections 

was constructed to aid in this effort, and these are published 

separately (Self and others, chapter 5, this CD-ROM). Different workers in the past have used slightly different picks for 

the tops of some of the rich and lean zones. An attempt was 

made to use the same stratigraphic contacts for the rich and 

lean zones that were used in the previous USGS assessment, to 

make the two assessments as comparable as possible. In some 

isolated instances, we corrected minor errors in the tops file 

used in the previous assessment. 

There have been considerable advances in computational 

power and computer programming since the last assessment 

was published, and this current assessment tries to take full 

advantage of these advancements. Pitman and others (1989) 

used geostatistical interpolation by kriging in part to generate 

their resource maps and resource numbers. Pitman and others (1989) found that kriging gave good results in areas with 

large numbers of control points but calculated unreasonable 

resource numbers with unreasonably large error limits in areas 

with little control, and they resorted to hand contouring and 

hand calculating resources in these areas. In this assessment 

we tried two extrapolation methods for spatial interpolation 

and extrapolation, the Radial Basis Function (RBF) method, 

and the Inverse Distance Weighted (IDW) method. Both 

methods gave similar results and we ultimately decided that 

the RBF method produced the most geologically reasonable 

results. The RBF method has been shown to give comparable 

results to those from kriging (Rusu and Rusu, 2006). We also 

compared the results using the RBF method with those from 

kriging for the same set of data points used in the previous 

assessment and found that the two methods calculated similar 

resource numbers.

The area underlain by Green River Formation oil shale 

occupies only a very small portion of the north-central part of 

the Piceance Basin structural and sedimentary basin (fig. 2). 

The isopach maps and assessment maps generated for this 

assessment cover only that portion of the Piceance structural 

and sedimentary basin that is underlain by Green River oil 

shale excluding Grand Mesa (fig.2). The oil shale resources 

on Grand Mesa are limited and were not assessed here. When 

describing the various oil shale zones, we will be referring to 

only that part of the Piceance structural and sedimentary basin 

that is underlain by Green River oil shale. For instance, if we 

refer to the depocenter in the north-central part of the basin we 

are referring to the north-central part of the overall Piceance 

structural and sedimentary basin that is underlain by Green 

River oil shale. 

Additional core data acquired since the previous assessment helped considerably with this present assessment, but 

there was still insufficient core data in many marginal areas 

of the basin to establish oil-shale-richness trends. A large 

number of surface stratigraphic sections have been measured 

and described in detail in these marginal areas in the past (for 

example, see Johnson and others, 1988), and a reasonably 

good idea of how oil shale richness varies in these marginal 

areas was obtained from these sections. Much of this surface 

information was published after the previous assessment 

and was not used in that assessment. In addition, a number 

of previously unpublished surface sections, described by the 

authors, were included in this assessment. These sections are 

included in another publication on this CD-ROM (Self and 

others, chapter 5). 

All of the Fischer assay data, corehole-location data, and 

oil shale zone tops file have been assembled into one Access 

database (see Mercier and others, chapter 3, this CD-ROM). 

Due to the number of data records (approximately one-half 

million) and the complexity of the spatial data involved in the 

assessment, Microsoft Access database management software 

and ESRI ArcGIS software were used to combine, store, and 

analyze the raw data. The ability to create custom forms in 

Access was a crucial element in the assessment methodology 

as it allowed staff to write Visual Basic scripts and SQL statements to filter subsets of the data and perform the necessary 

calculations using Access form controls. The public benefits 

from this process as the original forms used to calculate 

resources also serve as the end-user interface to view the 

raw data in a more simplified and meaningful manner. After 

resources were calculated for each core hole, the resultant 

Access tables were linked seamlessly with ESRI ArcGIS 
Previous Assessments 5

software to model, extrapolate, and quantify the data spatially. 

The end product is a large database of tables (spreadsheets), 

forms to view the data, and a series of maps quantifying the 

results of those calculations. A complete description of how 

to use this database is presented in Mercier (chapter 3, this 

CD-ROM).

This assessment does not attempt to estimate the amount 

of oil that is economically recoverable, largely because there 

has not been an economic method developed to recover oil 

from Green River oil shale. In a recent report published by the 

RAND Corp. concerning the prospects for oil shale development in the United States, Bartis and others (2005, p. 5) state 

that: “Usually, estimates of recoverable resources are based on 

an analysis of the portion of the resources in place that can be 

economically exploited with available technology. Because oil 

shale production has not been profitable in the United States, 

such estimates do not yield useful information. Instead, calculations of recoverable resources have generally been based on 

rough estimates of the fraction of the resources in place that 

can be accessed and recovered, considering mining methods 

and processing losses.” 

Previous estimates of the amount of oil shale that is technically recoverable without considering economics are 45 percent (Taylor, 1987) and 55 to 75 percent (Prien, 1974) of the 

oil in place using room-and-pillar mining methods, whereas 

estimates of technically recoverable resource using open-pit 

mining are as much as 80 percent of the oil in place (Taylor, 

1987). At present, there are no estimates of the percent of the 

resource that could be recovered using the in-situ methods that 

are currently being developed, however, Taylor (1987) stressed 

that the amount of oil that can be recovered from any in-situ 

process depends on both the percent of oil that can be recovered from within the retort and the amount of oil left behind in 

the areas between retorts. There are currently no estimates of 

the percent of in-place oil that can be recovered using in-situ 

methods currently being developed.

Although we cannot estimate recoverable shale oil at this 

time, one of our goals here is to lay the groundwork so that 

estimates of economically recoverable shale oil can be made 

in the future once suitable extraction methods are developed. 

For instance, Mercier (chapter 6, this CD-ROM) calculates 

cubic meters of overburden on the Mahogany oil shale zone 

throughout the basin. These calculations can be compared 

with estimates of in-place oil to generate “strip ratio” maps 

for strip mining the oil shale. Brownfield and others (chapter 

2, this CD-ROM) estimates the in-place nahcolite resource in 

the basin, and for the first time, breaks down the resources into 

discrete zones. The presence of nahcolite (sodium bicarbonate) 

is a major concern for in-situ oil shale processes, because it 

breaks down to sodium carbonate (natrite) and carbon dioxide 

at temperatures from about 120° C to 350°C, depending on 

the fugacity of carbon dioxide, or significantly below retort 

temperatures. Nahcolite is considered a leasable mineral thus 

must be recovered either by solution mining prior to retorting 

or by solution mining the natrite after retorting and recombining it with carbon dioxide to again produce nacholite. 

Acknowledgments

The authors would like to thank Jim Otton of the U.S. 

Geological Survey and Jerry Boak of the Colorado School of 

Mines for their many thoughtful and helpful comments. The 

authors would also like to acknowledge the tireless and mostly 

thankless work by Jack Dyni and John Donnell over the past 

25 years to preserve oil shale data for the Eocene Green River 

Formation during a period when there was little to no interest 

in developing the oil shale resources in the United States. This 

assessment would not have been possible without their efforts.

Previous Assessments

Winchester (1916) published the first estimate of oil 

in the Green River Formation in the Piceance Basin, and he 

estimated that the basin could produce about 20 billion barrels 

of oil. After further study, Winchester (1928, p. 13) increased 

his estimate to 79.6 billion barrels of oil with 47.6 billion 

barrels “recoverable.” Until recently, it was believed that 

mining and surface retorting of oil shale would be the 

predominant method of extraction, thus there were many 

attempts to separate out that part of the resource that could be 

potentially mined by eliminating intervals that were too lean 

to be mined. Only oil shale that exceeded minimum cutoffs, 

such as 15 ft of 15 gallons per ton (GPT) was assessed. The 

USGS in 1951 estimated that the Piceance basin contained 

750 billion barrels of oil-in-place in shale yielding 15 gallons 

per ton (GPT) or greater (U.S. Congress, Senate Committee 

on Interior and Insular Affairs, 1951). Donnell (1961) divided 

the oil shale resources of the Piceance Basin into “indicated” 

and “inferred,” with indicated resources generally occurring 

within 6 miles of a core hole and inferred resources occurring 

at greater than 6 miles from a core hole. Donnell (1961) 

estimated total in-place oil averaging 15 GPT or more in 

continuous sequences of 15 ft or more thick was 292.2 billion 

barrels of indicated and 666.9 billion barrels of inferred 

resource for a total of 959.1 billion barrels. Pitman and 

Donnell (1973) assessed an interval in the uppermost part of 

the oil shale interval, above the Mahogany zone, and estimated 

that it contained 128.5 billion barrels of oil-in-place. Duncan 

and Swanson (1965) and Donnell (1979) both estimated that 

the Piceance Basin contained about 1.1 trillion barrels of 

oil-in-place in sequences averaging 15 GPT or greater. Smith 

(1980) estimated about 1.0 trillion barrels of total resource. 

Pitman and others (1989) estimated the in-place resources, 

including all grades of oil shale of 1,008 billion barrels. 

Several resource estimates have been made of just 

the Mahogany zone. The Mahogany zone has received 

considerable attention because it is one of the richest oil 

shale zones in the basin, and because it crops out around the 

margins of the basin where it can easily be mined. Donnell 

(1961) estimated that oil shale “in and adjacent to the 

Mahogany zone” contained indicated reserves of 6.8 billion 
6 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

barrels and another 0.7 billion barrels of inferred reserves 

in sequences averaging 45 GPT in a continuous section and 

5 ft or more thick. Using an average of 30 GPT in an interval 

25 ft thick or greater, Donnell (1961) estimated that there 

were 36.8 billion barrels of indicated reserves and 54.7 billion 

barrels of inferred reserves. Using a 25 GPT and 15 ft cutoff, 

he estimated that there were 55.2 billion barrels of indicated 

reserves and 99.2 billion barrels of inferred reserves. Donnell 

and Blair (1970) estimated 164 billion barrels of oil in the 

Mahogany in intervals 10 ft thick or greater with an average 

yield of 15 GPT or greater. Pitman and Johnson (1978) 

estimated total resources in the Mahogany, regardless of 

grade, at 173 billion barrels, while Pitman and others (1989) 

estimated 178 billion barrels regardless of grade.

Computer programs written in FORTRAN were constructed in the 1970s and 1980s to calculate gallons per ton 

and barrels per acre (BPA) from Fischer assay analysis for 

any specified interval in a core hole. Although it was seldom 

stated, it is believed that these programs were used in most 

if not all the assessments made during that period. In addition, some of these programs included special algorithms to 

identify the longest sequence in an assayed core or section 

that maintained a specified average yield of oil in GPT. This 

was done to identify specific intervals thick enough and rich 

enough to be potentially mined. The algorithm could be used, 

for example, to determine the total amount of oil in intervals 

averaging at least 15 ft thick and 15 GPT or averaging at least 

25 ft thick and 25 GPT. The algorithm also could exclude 

too much low-grade oil shale in these intervals. For example, 

intervals that average less than 10 GPT and were greater than 

10 ft thick could be excluded. 

Recent evaluation of the software by the authors has 

revealed some problems, the most significant being that the 

software will not function if zero values for oil yields are present in the Fischer assay tables. There are typically many missing core intervals in oil shale core holes, and these are listed in 

the Fischer assay tables as zero values for oil yields. Although 

it was never stated in any of the previous assessments, oilyield values had to be assigned to all the missing intervals in 

order to make the FORTRAN programs function. It is unclear 

how values were assigned to all of the missing intervals, and 

it is possible that no consistent method was used. According 

to Janet Pitman (written commun., 2008) a missing interval was assigned the average of the oil-yield values of the 

intervals immediately above and below the missing interval. 

John R. Donnell (oral commun., 2008) recalls that values were 

assigned to missing intervals by comparing with nearby core 

holes where the intervals were not missing. We recovered a 

large number of computer printouts of oil-yield histograms 

that appear to date from the period when the last assessment 

was made and found examples of each. However, because 

the original files from the last assessment were not recovered, 

we are unable to ascertain which method of handling missing 

intervals was ultimately used. 

Making estimates of thicknesses of oil shale that fit a set 

of criteria may not have the importance that it once had. Such 

estimates are a critical first step to determining the amount of 

oil shale that can be economically mined in underground or 

open-pit mines under various scenarios. But such estimates are 

less important for in-situ processes of retorting oil shale, the 

favored method being considered today, as all oil shale in a 

thick column would be heated and retorted regardless of grade. 

Stratigraphy of the Green River 

Formation and Definition of the Rich 

and Lean Zones that Comprise the Oil 

Shale Section

The rich oil shale interval in the Green River Formation 

of the Piceance Basin was deposited in Eocene Lake Uinta, 

a large, internally drained lake that extended across both the 

Piceance Basin and the Uinta Basin to the west. The Green 

River Formation oil shales of the Greater Green River Basin 

(fig. 2) were deposited in a separate but largely contemporaneous lake, Lake Gosiute. Lake Uinta, which started out as 

a fresh or near freshwater lake, became increasingly saline 

through time and ultimately vast quantities of the potentially 

valuable sodium bicarbonate mineral nahcolite (NaHCO3

) 

and halite were deposited during periods when the lake 

receded into a comparatively small area in the middle of the 

Piceance Basin. The nahcolite deposits in the Piceance Basin 

are assessed in another report in this CD-ROM (Brownfield 

and others, chapter 2). Nahcolite is used as a raw material in 

the manufacture of a variety of basic industrial chemicals and 

to remove sulfur dioxide from power-plant emissions, and 

it is presently being solution mined in the basin. Dawsonite, 

a hydrated aluminum carbonate mineral (NaAl(OH)2

CO3), 

which can be used as a source of aluminum, also occurs in 

vast quantities in the middle of the basin. These nahcolite and 

dawsonite deposits are disseminated in and interbedded with 

some of the richest oil shale deposits in the basin, and in the 

1970s and 1980s, plans to exploit the oil shale resources of the 

saline depocenter of the Piceance Basin commonly included 

plans to recover the nahcolite and dawsonite resources as well 

(see for example, Nielson, 1969; Beard and others, 1974). 

Several members of the Green River Formation are 

recognized, although the member designations have not 

always been applied the same way by all workers (figs. 3 and

4). In the oil shale section deposited in the offshore areas of 

the lake, the name Garden Gulch Member is generally applied 

to the illitic oil shales that were deposited in the early history 

of Lake Uinta, and the name Parachute Creek Member is 

applied to the dolomitic oil shales deposited later. The name 

Douglas Creek Member is applied to marginal lacustrine rocks 

along the west and southwest margins, and the name Anvil 

Points Member is applied to marginal lacustrine rocks along 

the east and southeast margins of the Piceance Basin. The 

names Garden Gulch Member, Parachute Creek Member, and 

Douglas Creek Member were first used by Bradley (1931), 
Stratigraphy of the Green River Formation 7

Top of Mahogany

oil shale zone

Long Point

 bed

 Top of 

Cretaceous

South

North

R0 and L0 zones

R1 zone

L1 zone

R2, L2, R3, L3 

 zones

R4, L4, R5 zones

L5 zone

R6 zone and 

B-groove

Mahogany zone

 Uinta 

Formation

 Uinta 

Formation

 Wasatch 

Formation

 Wasatch 

Formation

Wasatch

Formation

 Fort

 Union

Formation

Cow Ridge Member,

Green River Formation

Parachute

Creek 

Member

Douglas

Creek 

Member

Garden Gulch Member

Green

River

Formation

Parachute

Creek Mbr.

Top of Bed 44

of Donnell (2008)

Stage 1

Stage 2

Stage 3

Stage 4

Stage 5

A

A’

Fresh-water lacustrine and paludal rocks with molluscs

 and thin coal beds 

Lean dolomitic oil shale 

Rich dolomitic oil shale with nahcolite and halite

Variegated mudstone, sandstone, and siltstone

Lean illitic oil shale

Rich illitic oil shale

Carbonate-rich marginal lacustrine mudstone with 

 ostracodal, oolitic, and stromatolitic limestones

Volcanoclastic rocks

Disseminated nahcolite in oil shale

Nahcolite and halite

0 20,000 60,000 FEET

10 KILOMETERS

0

500

1,000

1,500

400

200

FEET METERS

Vertical exaggeration x 40

EXPLANATION

Figure 3. North-south cross section through the Piceance Basin, northwest Colorado showing member 

subdivisions, stages of Lake Uinta as defined by Johnson (1985), and some of the rich and lean zones defined by 

Cashion and Donnell (1972).

whereas Donnell (1953) was the first to use the name Anvil 

Points Member. The name Uinta Formation is applied to a 

sequence of sandstones and siltstones containing abundant 

volcanic debris that interfinger with the upper part of the 

Green River Formation (Cashion and Donnell, 1974). 

Johnson (1985) subdivided the history of Lake Uinta 

into five roughly time-stratigraphic periods or stages with the 

change from one stage to the next corresponding to a significant change in conditions in the lake (figs. 3 and 4). The 

first two stages are generally equivalent to the Garden Gulch 

Member, and the last three are generally equivalent to the 

Parachute Creek Member. The beginning of stage 1 is marked 

by the initial transgression of Lake Uinta, the Long Point 

transgression that caused two comparatively small freshwater 

lakes, one in the Piceance Basin and one in the Uinta Basin 

to form one large lake that spanned across the intervening 

Douglas Creek arch. The illitic-rich oil shales from this stage 

deposited in the offshore areas of the lake generally average less than 15 GPT, and because of their great depth and 

low grade, there has been little interest in their development. 
8 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Unconformity at

top of Cretaceous

Unconformity at

top of Cretaceous

Unconformity at top of Cretaceous

Cretaceous

rock

undivided

Land

surface

 Land

surface

White River Uplift

FEET METERS

2,000

1,000

0 0

600

400

200

Douglas Creek

Member

Wasatch

Formation

Green River

Formation

Black Sulfur Tongue

of Green River Formation

Tongue of

Uinta Formation

Base of

R-4 rich

oil-shale

zone

Parachute Creek

Member of Green

River Formation

Garden Gulch Member

Cow Ridge

Member of

Green River

Formation

Tongue of

Uinta Formation

Tongue of

Uinta Formation

Thirteenmile Creek

Tongue of Green

River Formation

Black Sulfur Tongue

of Green River Formation

Tongue of Uinta

Formation

Top of Mahogany

oil-shale zone

Base of R-2 rich

oil-shale zone

Anvil Points

Member

Datum is base of Long

Point Bed of Garden

Gulch Member

Wasatch

Formation

Fort Union

Formation

Fort

Union

Formation

WasatchFort Union

Formation

contact

UTAH COLORADO

Douglas Creek Arch

Piceance Basin

Uinta Basin

Fresh-water lacustrine and paludal rocks with

 molluscs and thin coal beds 

Rich dolomitic oil shale with nahcolite and halite

Variegated mudstone, sandstone, and siltstone

Lean illitic oil shale

Rich illitic oil shale

Carbonate-rich marginal lacustrine mudstone

 with ostracodal, oolitic, and stromatolitic limestones

Volcanoclastic rocks

EXPLANATION

0

0 10 20 30 40 KILOMETERS

10 20 30 MILES

Stage 1

Stage 2

Stage 3

Stage 4

Stage 5

Intersection of cross

sections shown in

figures 1, 3 and 4

West

East

B B’

Figure 4. East-west cross section through the Piceance Basin, the Douglas Creek arch, and the eastern part of the Uinta Basin 

showing member subdivisions, stages of Lake Uinta as defined by Johnson (1985), and some of the rich and lean zones defined 

by Cashion and Donnell (1972).

Average oil yield increases abruptly at the beginning of the 

second stage, to a maximum of about 27 GPT averaged for the 

entire interval in the central part of the Piceance Basin, with 

thin beds averaging nearly 60 GPT. There has been some interest recently in exploiting these shales using an in-situ method. 

A gradual shift from illitic-rich to carbonate-rich oil 

shales occurred at the beginning of the third stage, and for the 

first time nahcolite was deposited near the center of the lake. 

Nahcolite occurs disseminated in oil shale, as aggregates, and 

as beds (Dyni, 1974; 1981). Bedded nahcolite grades laterally 

into halite beds towards the middle of the saline depocenter. 

All oil shales deposited after the beginning of stage 3 are 

carbonate-rich with dolomite being the dominant carbonate 

(Robb and Smith, 1974). The fourth and fifth stages are 

marked by expansions of Lake Uinta. The fourth stage began 

with a relatively minor transgression that may have been 

caused by increased outflow from Lake Gosiute in the Greater 

Green River Basin into Lake Uinta (Johnson, 1985; 2007). 

The transgression at the start of the fifth stage was almost 

certainly related to increased outflow from Lake Gosuite, 

as volcaniclastic sediments thought to be derived from the 

Absaroka volcanic field in northwest Wyoming reached 

the north margin of Lake Uinta shortly after maximum 

transgression (Surdam and Stanley, 1980). The Mahogany 

zone (Mahogany ledge where exposed) was deposited during 

the early part of the fifth stage. These volcaniclastic sediments 
Stratigraphy of the Green River Formation 9

could only have reached Lake Uinta once Lake Gosiute was 

largely filled in, as prior to its infilling, Lake Gosiute would 

have acted as a sediment sink. The volcaniclastic sediments 

gradually filled in the Piceance Basin part of Lake Uinta thus 

ending oil shale deposition (Johnson, 1985). 

Individual oil shale units in the Piceance Basin can be 

traced great distances. Bradley (1931) traced the Mahogany 

ledge throughout most of the Piceance and Uinta Basins 

(fig. 5). In general, the oil shales are well bedded and on a 

small scale display fine laminations or “varves” (fig. 6) that 

have been attributed by many workers to seasonal variations in 

amount of organic matter and mineral matter raining down and 

settling on the bottom of the lake (see for example: Bradley, 

1929). Cashion and Donnell (1972) recognized that the entire 

Parachute Creek Member and Garden Gulch Member could 

be subdivided into a sequence of oil-rich zones (R-zones) and 

oil-lean zones (L-zones) that could be recognized throughout 

much of the central part of the Piceance Basin and eastern 

part of the Uinta Basin (fig. 7). These zones appear to roughly 

form time-stratigraphic units representing changing rates of 

organic matter production and preservation that occurred 

simultaneously throughout Lake Uinta. The rich- and 

lean-zone stratigraphy formed the basis of the previous USGS 

assessment with in-place resources in each of the zones being 

assessed separately (Pitman and Johnson, 1978; Pitman, 1979; 

and Pitman and others, 1989). The lower zones, from the 

L-0 zone through the L-1 zone are clay rich and contain little 

carbonate, and comprise the Garden Gulch Member. All zones 

above the L-1 zone are dolomitic and comprise the Parachute 

Creek Member. On a finer scale many individual rich and 

lean beds within each rich and lean zone can be traced for 

great distances as well. Donnell (2008) traced individual oil 

shale beds above the Mahogany zone across large areas of the 

Piceance and Uinta Basins, and many beds within and below 

the Mahogany zone can also be traced for great distances. 

All of these oil shale zones grade into marginal lacustrine 

rocks towards the margins of the basin. Johnson and others 

(1988) were able to trace many of the oil shale zones into 

marginal lacustrine equivalents around the west and southwest margins of the basin. Many of the oil shale zones have 

been subsequently traced into marginal lacustrine equivalents 

along the northern and eastern margins of the basin as well 

(Self and others, chapter 5, this CD-ROM). One of the biggest 

issues with the previous resource assessment (Pitman and 

others, 1989) was that oil-shale-richness trends were poorly 

constrained around the basin margins leading to poor results in 

these areas. Tracing rich and lean zones into marginal lacustrine equivalents allowed us to better constrain richness trends 

towards the margins of the basin leading to better estimates of 

oil shale richness in these areas. 

The distinctive vertical pattern of rich and lean beds 

and rich and lean zones breaks down somewhat in the saline 

depocenter, making exact correlation more difficult. Here a 

rich bed can be present in one core hole and seemingly absent 

in another core hole nearby, and the overall patterns of rich 

and lean beds used elsewhere to define the zones is somewhat 

muted. Part of the problem is that the diameter of the core may 

be too small to obtain a representative sample in the saline 

interval where nahcolite aggregates as much as 40 cm across 

(fig. 8) are scattered throughout much of the section (Dyni, 

1981, p. 30). Another problem is that many of the thick beds 

of nahcolite and halite that were once present in the saline 

depocenter have been leached out by relatively recent groundwater activity causing widespread collapse and rubblization. 

The exact vertical and lateral extent of the saline zone prior to 

leaching is not known. There are no saline minerals or persistent breccias preserved today above the lower part of the L-5 

zone (fig. 7), indicating that thick beds of nahcolite and halite 

may never have been present in that interval (Dyni, 1974). 

There are, however, vugs that were presumably once filled 

with saline minerals in this interval (Trudell and others, 1970; 

Pipiringos and Johnson, 1976).

A major cause of correlation problems near the depocenter of the lake is mass-movement processes prior to lithification. Evidence for this mass movement includes contorted 

“breccias” or “blebby” oil shale (Bradley, 1931; Dyni, 1981: 

Dyni and Hawkins, 1981) (fig. 9) and disrupted bedding 

(fig. 10). Brecciated or “blebbly” oil shale beds from a few 

centimenters to 11-m thick have been described (Dyni, 1981). 

They consist of organically lean marlstone clasts floating in a 

darker organic-rich matrix (fig. 9). Typically, these blebby oil 

shales are higher in kerogen content than laminated marlstones 

(Bradley, 1931; Dyni, 1981), suggesting that high amounts of 

organic matter contributed to instability in the lake sediments. 

Dyni (1981) and Dyni and Hawkins (1981) believed that the 

blebby oil shale beds were transported across the floor of the 

lake by turbidity currents and traced one of these beds over an 

area of 175 square km. Dyni and Hawkins (1981) estimated 

that as much as 50 percent of the oil shale deposited in the 

depocenter of the lake consists of the blebby type, suggesting 

that redistribution of the most organic-rich sediments in Lake 

Uinta occurred on a massive scale. 

A significant interval of oil shale occurs above the 

Mahogany zone in about the southern half of the basin (fig. 3). 

Pitman and Donnell (1973) subdivided this interval into four 

oil shale units and estimated the in-place oil shale resources 

in gallons per ton and barrels per acre for each of the four 

units. Individual oil shale beds in this interval are extremely 

persistent and can be traced over great distances (Donnell, 

2008). Towards the north this oil shale interval intertongues 

and grades into sandstones of the Uinta Formation, a sandy 

unit consisting largely of volcaniclastic sediments sourced by 

the Absaroka volcanic field in northwest Wyoming (Johnson, 

1981a). Unlike the continuous oil shale section to the south, 

the intertonguing interval has been highly affected by massmovement processes prior to lithification (Johnson, 1981a) 

(fig. 11), and correlation of individual oil shale beds is only 

rarely possible. One slump block covering several square 

kilometers was mapped by Johnson (1981b). 
10 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Figure 5. Outcrop of the Mahogany ledge in the south-central part of the Piceance Basin (sec. 16, T. 5 S., R. 

98 W.). The Mahogany bed is the most persistent bed in the middle of the ledge. B-groove is the buff re-entrant 

at the base of the cliff.

Figure 6. A typical sample of oil shale in the Parachute Creek Member displaying 

organic-rich layers (dark brown) and organic-lean layers (white).
Factors Affecting the Precision of Oil-Yield Measurements 11

500

1,000

1,500

2,000

2,500

3,000

500

1,000

1,500

2,000

2,500

3,000

Oil in gallons per ton Nahcolite in weight percent

20406080100 0 20 40 60 80 100

C0034

U.S. Bureau of Mines–

Atomic Energy Commission

Colorado 1

Sec 13, T. 1 N., R. 98 W.

A-groove

Mahogany

zone

B-groove

R-6

L-5

L-4

R-4

L-3

R-3

L-2

R-2

L-1

R-1

L-0

R-0

R-5

Oil in gallons per ton Nahcolite in weight percent

20406080100 0 20 40 60 80 100

Orange marker

Depth 

in Feet

Figure 7. Rich and lean zones for the Green River Formation 

originally defined by Cashion and Donnell (1972) for the 

Piceance Basin, western Colorado and the Uinta Basin of 

eastern Utah and western Colorado. Graphs show oil in 

gallons per ton (red lines) and nahcolite in weight percent 

(black lines). The upper part of the R-0 zone is marked in the 

central part of the basin by a distinctive increase in resistivity 

on electric logs known informally as the orange marker, 

named for the color of pen used to mark it on geophysical 

logs (Chancellor and others, 1974; Ziemba, 1974). The orange 

marker, which comprises about the upper 30 ft of the R-0 

zone, is caused by a slight increase in carbonate in the illitic 

sediments. The orange marker is equivalent to the carbonate 

marker in the Uinta Basin part of Lake Uinta, which also 

represents a temporary increase in carbonate precipitation 

(Johnson, 1989). 

Factors Affecting the Precision of 

Oil-Yield Measurements

Determining the Volume of Oil in a Given 

Volume of Rock

Determining gallons per ton from a Fischer assay is 

a straightforward calculation as the weight of the original sample is known and the volume of oil generated is 

known. Unfortunately, the density of the sample prior to 

retorting is not routinely measured, as this density must 

be known in order to calculate the amount of oil present 

in a prescribed interval over a prescribed area. Typically 

in-place oil in the Green River Formation is given in the 

rather arcane unit of barrels of oil per acre (BPA). The 

method used to convert GPT into BPA in the previous 

assessment (Pitman and others, 1989) was not discussed 

in their publication. An equation that computes BPA was 

recovered with the FORTRAN program that was used at 

the time of the previous assessment. The equation was 

isolated from the rest of the program, and it does seem to 

generate reasonable results. But there was no reference to 

where the equation came from and how the many constants used in the equation were generated, and thus we 

decided not to use it. 

For this report, the determination of oil shale resource 

numbers in BPA for the Piceance Basin were generated 

from average GPT data from oil-yield Fischer assay 

analyses from core holes in the basin. Stanfield and others 

(1954) report summary data on volume-weight oil-yield 

relationships from about 20,500 USBM oil-yield analyses 

(table 1). Smith (1956) reported that oil-yield values 

were related to the specific gravity of the oil shale. Table 

1 contains original values for oil yield, gallons per ton, 

as well as specific gravity, and was regenerated using 
12 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Figure 8. Nahcolite aggregates in rich oil shale, Piceance Basin, Colorado.

Microsoft Excel and values for weight of oil shale, volume 

of oil shale, and oil yield per unit volume were updated using 

currently accepted formulas (table 2). A third-order trendline 

with a R2

 value of 0.9998 was generated comparing oil yield 

versus specific gravity (fig. 12). As the original table contained 

only integer values for GPT, new records were inserted to fill 

in values to one decimal place (0.1 ft) creating a new look-up 

table. A linear trend series fill function in Microsoft Excel 

2007 was then used to calculate specific-gravity values for 

each 0.1 ft value for the GPT column. A third-order trendline 

was then regenerated comparing new oil-yield versus specific 

gravity data yielding a R2

 value of 0.9997. Values for weight 

of oil shale, volume of oil shale, and oil yield per unit volume 

were then calculated using the new values for oil yield and 

specific gravity. The final lookup table contained records for 

oil yield (GPT), specific gravity, and oil yield per unit volume 

for interval thicknesses from 1.0 to 80.0 ft.

Shale-oil-resource numbers in BPA were calculated using 

the formula: oil shale interval thickness * 43,560 

(sq. ft/acre) *oil yield per unit volume (from the final look-up 

table, containing values on a 0.1 GPT basis /42 (gals/barrel 

of oil).

Broken Core and Missing Core Intervals

As previously discussed, oil-yield values were assigned 

to all of the missing intervals in order to make the FORTRAN 

program function. There are 15,805 missing intervals in the 

Fischer assay data file for the Piceance Basin, and because of 

time constraints, a simple method of dealing with these intervals had to be devised. The method used here simply calculates an average oil yield for all core recovered in a particular 

core hole for an oil shale zone in question, and that average is 

assigned to all the missing intervals in the zone. A brief discussion of some of the problems posed with missing intervals is 

presented here. 

Core can be moderately to severely broken by the coring 

process itself, and a quantity of rubble is recovered instead 

of a complete core. The onsite geologist might decide that 

the rubble is more or less representative of the entire interval 

and spread the rubble out in the core boxes between whole 

pieces of recovered core. Because the rubble was largely 

homogenized, the original variation in oil yield through the 

interval is lost. In addition, it is possible that the recovered 

rubble is not representative of the average oil yield for the 

entire interval. For instance, leaner oil shale may be more 
Factors Affecting the Precision of Oil-Yield Measurements 13

Figure 9. Outcrop of “blebby” oil shale displaying organically lean marlstone clasts in 

rich oil shale matrix. The sediment was transported laterally on the floor of Lake Uinta by 

mass-movement processes (NW 1⁄4 sec. 16, T. 5 S., R. 98 W., approximately 200 ft below top 

of Mahogany ledge). Lens cap for scale.

Figure 10. Outcrop of oil shale displaying disrupted bedding due to movement of the 

floor of Lake Uinta prior to lithification (sec. 15, T. 6 S., R. 99 W., approximately 500 ft 

above top of Mahogany ledge). Pencil for scale.
14 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Figure 11. Intertonguing of volcaniclastic sandstones of the Uinta Formation (brown) and 

marlstones of the Green River Formation (white). The sandstones underwent slumping on 

the floor of Lake Uinta prior to lithification (sec. 14, T. 3 S., R. 99 W).

prone to disintegration than rich oil shale resulting in the 

recovered rubble being skewed towards the richer oil shale in 

the interval. If the amount of rubble is small and the rubblized 

interval is quite long, the geologist might decide to assign the 

rubble to only part of the interval and assume that the rest of 

the interval is missing. In either case, oil-yield values obtained 

are compromised, and the distinctive pattern of rich and lean 

beds that characterize the oil shale zones in the Piceance Basin 

is lost for the core being studied. 

The missing core problem also affects the isopach maps 

to some degree. When calculating GPT, we had to place 

the top of a rich or lean zone at the top or base of an actual 

assayed interval. For instance, if the top of the Mahogany zone 

occurs within a 30-ft missing interval, we had to place the 

contact at either the top or the base of the overlying or underlying assayed interval in order to construct the isopach maps 

and make the resource calculations. Thus, the uncertainty of 

each data point will be different depending on whether or not 

the contact of the rich or lean zone in question occurs within a 

thick missing interval. This problem would not only affect the 

uncertainty of points on the isopach maps but also the uncertainty of points on the resource maps, because the BPA maps 

were constructed by multiplying average GPT by the thickness 

of the zone. Thus if the thickness is off because there is a thick 

missing interval at the contact, then the point on the BPA map 

will be affected as well.

Figures 13–26 plot the percent missing interval in each 

oil shale zone in each core hole. The number of missing 

intervals (in red) and thickest single missing interval in each 

zone (in blue) is also shown. The percent missing intervals 

for individual oil shale zones range to as high as 62 percent. 

Clearly missing intervals are a major source of uncertainty in 

the precision of each data point. 

A detailed analysis of 13 closely spaced core holes from 

a four-square-mile area in the northwest part of the basin 

(table 3, fig. 27) was undertaken to test the validity of applying the average of the recovered core to the missing intervals. 

The average oil yield for all oil shale zones from the L-0 zone 

through the Mahogany zone was plotted along with the percent of missing interval in figure 28. There are not enough data 

points for the R-0 zone to make a plot. Distance between the 

core holes needed to be kept to a minimum to limit the effect 

of regional variations in oil-yield values. Even though the core 

holes are closely spaced, there is still a noticeable decrease in 

oil yields towards the west across the study area. Average oil 

yields are lower overall in the two westernmost core holes in 

the study area, C261 and C265 (fig. 28). For most of the oil 

shale zones, this decrease is minimal, but it is significant in the 

L-3 oil shale zone, which decreases from 17.7 GPT in C283 

in the eastern part of the study area to 9.5 GPT in C265 in 

the western part. With the exception of the L-3 zone, there is 

remarkably little correlation between the percentage of missing core and the average oil yield. For example, oil yields vary 

little for the Mahogany zone between the core holes despite 

the missing core totals varying from 0 to over 40 percent. One 

major concern was that richness of the oil shale affected the 

probability of it being preserved during coring. For instance, if 

rich beds were more likely to be preserved than lean beds, then 

the average oil yield for a zone should go up as the percentage of missing core increases. These results suggest that, in 
Factors Affecting the Precision of Oil-Yield Measurements 15

Table 1. Original volume-weight oil-yield relationships of Green River Formation oil shale. From Stanfield and others (1954).

[GPT, gallons per ton; gm/cc, grams per cubic centimeter; lbs/ft3, pounds per cubic foot; ft3/ton, cubic feet per ton; gal/ft3, gallons per cubic foot]

Oil yield by 

assay, (GPT)

Specific gravity of 

oil shale (gm/cc)

Weight of oil 

shale, (lbs/ft3

)

Volume of oil 

shale, (ft3/ton)

Oil yield, per unit 

volume, (gal/ft3)

1 2.740 170.98 11.70 0.085

2 2.715 169.42 11.80 0.169

3 2.690 167.86 11.91 0.252

4 2.655 166.30 12.03 0.333

5 2.640 164.74 12.14 0.412

6 2.618 163.36 12.24 0.490

7 2.596 161.98 12.35 0.567

8 2.574 160.61 12.45 0.642

9 2.552 159.24 12.56 0.716

10 2.530 157.87 12.67 0.789

11 2.508 156.49 12.78 0.860

12 2.486 155.12 12.89 0.930

13 2.464 153.75 13.01 0.999

14 2.442 152.38 13.13 1.067

15 2.420 151.01 13.24 1.133

16 2.400 149.76 13.35 1.198

17 2.380 148.51 13.47 1.262

18 2.360 147.26 13.58 1.325

19 2.340 146.02 13.70 1.387

20 2.320 144.77 13.80 1.448

21 2.302 143.64 13.92 1.508

22 2.284 142.52 14.03 1.567

23 2.266 141.40 14.14 1.625

24 2.248 140.78 14.26 1.683

25 2.230 139.15 14.37 1.740

26 2.216 138.28 14.46 1.797

27 2.202 137.40 14.56 1.854

28 2.188 136.53 14.65 1.910

29 2.174 135.66 14.74 1.966

30 2.160 134.78 14.83 2.022

31 2.147 133.97 14.92 2.077

32 2.134 133.16 15.02 2.131

33 2.121 132.35 15.11 2.184

34 2.108 131.54 15.20 2.236

35 2.093 130.73 15.30 2.288

36 2.082 129.92 15.44 2.339

37 2.069 129.11 15.49 2.389

38 2.056 128.29 15.59 2.438

39 2.043 127.48 15.69 2.486

40 2.030 126.67 15.79 2.534

41 2.018 125.92 15.88 2.581

42 2.006 125.17 15.98 2.628
16 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 1. Original volume-weight oil-yield relationships of Green River Formation oil shale. From Stanfield and 

others (1954).—Continued

[GPT, gallons per ton; gm/cc, grams per cubic centimeter; lbs/ft3, pounds per cubic foot; ft3/ton, cubic feet per ton; gal/ft3, gallons per cubic foot]

Oil yield by 

assay, (GPT)

Specific gravity of 

oil shale (gm/cc)

Weight of oil 

shale,(lbs/ft3

)

Volume of oil 

shale, (ft3/ton)

Oil yield, per unit 

volume, (gal/ft3)

43 1.994 124.43 16.07 2.674

44 1.982 123.68 16.17 2.720

45 1.970 122.93 16.27 2.766

46 1.959 122.24 16.36 2.811

47 1.948 121.56 16.45 2.856

48 1.937 120.87 16.55 2.901

49 1.926 120.18 16.64 2.945

50 1.915 119.50 16.74 2.938

51 1.904 118.81 16.83 3.030

52 1.893 118.12 16.93 3.071

53 1.882 117.44 17.03 3.112

54 1.871 116.79 17.12 3.152

55 1.860 116.06 17.23 3.192

56 1.849 115.38 17.33 3.231

57 1.838 114.69 17.44 3.269

58 1.827 114.00 17.54 3.306

59 1.816 113.32 17.65 3.343

60 1.805 112.63 17.76 3.379

61 1.794 111.95 17.87 3.414

62 1.783 111.26 17.98 3.449

63 1.772 110.57 18.09 3.483

64 1.761 109.89 18.20 3.516

65 1.750 109.20 18.32 3.549

66 1.740 108.58 18.42 3.582

67 1.730 107.95 18.53 3.615

68 1.720 107.33 18.63 3.648

69 1.710 106.70 18.74 3.681

70 1.700 106.08 18.85 3.713

71 1.690 105.46 18.96 3.744

72 1.680 104.83 19.08 3.774

73 1.670 104.21 19.19 3.804

74 1.660 103.58 19.31 3.833

75 1.650 102.96 19.43 3.861

76 1.640 102.34 19.54 3.889

77 1.630 101.71 19.66 3.916

78 1.620 101.09 19.78 3.943

79 1.610 100.46 19.91 3.969

80 1.600 99.84 20.03 3.994

90 1.500 93.75 21.33 4.219
Factors Affecting the Precision of Oil-Yield Measurements 17

Table 2. Recalculated volume-weight oil-yield relationships of Green River Formation oil shale. From Stanfield and others (1954).

[GPT, gallons per ton; lbs/ft3, pounds per cubic foot; ft3/ton, cubic feet per ton; gal/ft3, gallons per cubic foot; gm/cc, grams per cubic centimeter]

Oil yield by 

assay, (GPT)

Specific gravity of 

oil shale, (gm/cc)

Weight of oil 

shale, (lbs/ft3

)

Volume of oil 

shale, (ft3/ton)

Oil yield, per unit 

volume, (gal/ft3)

1 2.740 171.06 11.69 0.086

2 2.715 169.50 11.80 0.169

3 2.690 167.94 11.91 0.252

4 2.655 165.75 12.07 0.332

5 2.640 164.82 12.13 0.412

6 2.618 163.44 12.24 0.490

7 2.596 162.07 12.34 0.567

8 2.574 160.69 12.45 0.643

9 2.552 159.32 12.55 0.717

10 2.530 157.95 12.66 0.790

11 2.508 156.57 12.77 0.861

12 2.486 155.20 12.89 0.931

13 2.464 153.83 13.00 1.000

14 2.442 152.45 13.12 1.067

15 2.420 151.08 13.24 1.133

16 2.400 149.83 13.35 1.199

17 2.380 148.58 13.46 1.263

18 2.360 147.33 13.57 1.326

19 2.340 146.09 13.69 1.388

20 2.320 144.84 13.81 1.448

21 2.302 143.71 13.92 1.509

22 2.284 142.59 14.03 1.568

23 2.266 141.47 14.14 1.627

24 2.248 140.34 14.25 1.684

25 2.230 139.22 14.37 1.740

26 2.216 138.34 14.46 1.798

27 2.202 137.47 14.55 1.856

28 2.188 136.60 14.64 1.912

29 2.174 135.72 14.74 1.968

30 2.160 134.85 14.83 2.023

31 2.147 134.04 14.92 2.078

32 2.134 133.23 15.01 2.132

33 2.121 132.41 15.10 2.185

34 2.108 131.60 15.20 2.237

35 2.093 130.67 15.31 2.287

36 2.082 129.98 15.39 2.340

37 2.069 129.17 15.48 2.390

38 2.056 128.36 15.58 2.439

39 2.043 127.54 15.68 2.487

40 2.030 126.73 15.78 2.535

41 2.018 125.98 15.88 2.583

42 2.006 125.23 15.97 2.630
18 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 2. Recalculated volume-weight oil-yield relationships for Green River Formation oil shale. From Stanfield and others 

(1954).—Continued

[GPT, gallons per ton; lbs/ft3, pounds per cubic foot; ft3/ton, cubic feet per ton; gal/ft3, gallons per cubic foot; gm/cc, grams per cubic centimeter]

Oil yield by 

assay, (GPT)

Specific gravity of 

oil shale, (gm/cc)

Weight of oil 

shale, (lbs/ft3

)

Volume of oil 

shale, (ft3/ton)

Oil yield, per unit 

volume, (gal/ft3)

43 1.994 124.49 16.07 2.676

44 1.982 123.74 16.16 2.722

45 1.970 122.99 16.26 2.767

46 1.959 122.30 16.35 2.813

47 1.948 121.61 16.45 2.858

48 1.937 120.93 16.54 2.902

49 1.926 120.24 16.63 2.946

50 1.915 119.55 16.73 2.989

51 1.904 118.87 16.83 3.031

52 1.893 118.18 16.92 3.073

53 1.882 117.49 17.02 3.114

54 1.871 116.81 17.12 3.154

55 1.860 116.12 17.22 3.193

56 1.849 115.43 17.33 3.232

57 1.838 114.75 17.43 3.270

58 1.827 114.06 17.53 3.308

59 1.816 113.37 17.64 3.344

60 1.805 112.69 17.75 3.381

61 1.794 112.00 17.86 3.416

62 1.783 111.31 17.97 3.451

63 1.772 110.63 18.08 3.485

64 1.761 109.94 18.19 3.518

65 1.750 109.25 18.31 3.551

66 1.740 108.63 18.41 3.585

67 1.730 108.00 18.52 3.618

68 1.720 107.38 18.63 3.651

69 1.710 106.76 18.73 3.683

70 1.700 106.13 18.84 3.715

71 1.690 105.51 18.96 3.745

72 1.680 104.88 19.07 3.776

73 1.670 104.26 19.18 3.805

74 1.660 103.63 19.30 3.834

75 1.650 103.01 19.42 3.863

76 1.640 102.39 19.53 3.891

77 1.630 101.76 19.65 3.918

78 1.620 101.14 19.78 3.944

79 1.610 100.51 19.90 3.970

80 1.600 99.89 20.02 3.996

90 1.500 93.65 21.36 4.214
Factors Affecting the Precision of Oil-Yield Measurements 19

Figure 12. Graph showing the relationship between oil yield for Green River oil shales and specific gravity. 

Data from Stanfield and others (1954).

general, rich and lean oil shale is equally likely to go missing 

during the coring process. 

Both the number of missing intervals and thickness of 

individual missing intervals in a zone are important because 

lots of thin missing intervals randomly distributed throughout 

an oil shale zone are less likely to affect the average for that 

zone than if most of the missing core is concentrated in a 

single or a few missing intervals. For instance, if 25 percent 

of a certain zone is missing and the missing intervals are 

numerous and fairly thin then the overall average of the zone 

will probably not be highly affected. However, if that 25 

percent missing interval consists of a single interval, then the 

chances are much greater that the missing core will affect 

the average. Figure 29 shows oil-yield histograms for two 

closely spaced rotary holes in the east-central part of the basin 

and demonstrates the potential problem when an individual 

missing interval is thick. There are no missing intervals in 

the Mahogany zone in C0599R, and the average for the zone 

is 23.7 GPT. The second drill hole is missing one 70 ft thick 

interval in the Mahogany zone, but this missing interval 

includes the Mahogany bed, the richest part of the Mahogany 

zone. As a result, average oil yield for the Mahogany zone in 

this hole is only 16.4 GPT. 

Figure 30 shows the oil-yield histograms for four of 

the 13 closely spaced core holes discussed previously. The 

average of 22.8 GPT for the Mahogany zone in C0265 

(fig. 30A) should be close to the true average because there is 

no missing core. Core hole C0261 (fig. 30B), which had only 

9.3 percent missing core in intervals no thicker than 3.6 ft, 

averages 22.6 GPT or similar to the complete core. Core hole 

C0273 (fig. 30C) has more missing core, 16.3 percent, but the 

individual intervals are relatively thin, no greater than 3.9 ft. 

Average oil yield for this core hole is somewhat greater than 

expected at 25.8 GPT. Core hole C0266 (fig. 30D) is missing 

41.1 percent of the Mahogany zone, yet the average oil yield 

of 21.6 GPT is close to the expected value of 22.8 GPT from 

Specific Gravity vs. Oil Yield, Green River Oil Shale

y = -1E-06x

3

 + 0.0003x

2

 - 0.0265x + 2.7656

R

2

 = 0.9998

0.000

0.500

1.000

1.500

2.000

2.500

3.000

OIL YIELD IN GALLON PER TON (GPT)

0 2010 30 40 50 60 70 80 90 100

SPECIFIC GRAVITY 

EXPLANATION

Specific gravity

Trendline
20 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

2

4

1

2

5

4

1

2

34

1

2

1

2

2

11 4

19

0.3

5.6

5.9

24

1

5.7

1

0.5

8.9

1

2

0.9 0.9

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

R–0 missing core—In percent

< 1

1.1–2.5

2.6–5

5.1–10

> 10

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 13. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing interval 

(blue) for core holes drilled through the R-0 zone, Piceance Basin, Colorado.
Factors Affecting the Precision of Oil-Yield Measurements 21

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1.7

6

11.1

5

0.6 2

9

2 2.5

1.9

2

12.3

2.1

0.4

6.6

1 1

3

2.8

1.1

0.5

1

1

1

2

1 1

1

4

2

1

1

1

2

3

1

5

1

1

1

1

1

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

L–0 missing core—In percent

< 5

5.1–10

10.1–20

20.1–40

> 40

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 14. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for core holes drilled through the L-0 zone, Piceance Basin, Colorado.
22 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

8.3

3

3

9

1.1

9

4

3

22.3

12.7 5.9

5.5

21.5 1

6.4

0.9 3.6

4.7

8

6.5

8.9 6

8.8 6.3

0.3 3.8

4

1.6

3.2

13

13.7 0.8

2.2

1

3

1

4.2

1.5

0.7

2.7

31.7

1

1

1.5

1.6

11 1.1

3

10

12

6.6

1

20.4

13

10

0.3

1.9

0.5

6

3

1

2

1

3

1

1

4

2 2

3

1 2

3

3 2 2

2

3

6 12

4 8 1

3

16

1 8

11

3 2

3

40

2

1

1

2

1

8

6

1

1

1

1

5 2

1

3

3

5

1

4

4

3

1

7

3

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

R–1 missing core—In percent

< 1.5

1.6–5

5.1–10

10.1–20

> 20

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 15. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for core holes drilled through the R-1, Piceance Basin, Colorado.
Factors Affecting the Precision of Oil-Yield Measurements 23

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

4

3

1

2

2

3

1

1

1 1

1

3 2

1

3

2

5 2

1

2

1

3

3

15

1

4

1

1

1

1

1

2

1

1

2

1

4

1

3

1

1

1.5

0.6

6.6

0.5

9

1.3

41.1

1

1

1.8

3

12.9

5.1

1

2 2

2.6 5.9

2.7

4.4

3.2

8

21

3

1

1

3.8

0.1

1

0.3

3

4

14.9

2.4

6

1

2.4 0.8

0.6

3.7

1.5

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

L–1 missing core—In percent

< 2

2.1–5

5.1–10

10.1–25

> 25

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

Figure 16. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for core holes drilled through the L-1 zone, Piceance Basin, Colorado.
24 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

3

2

2

2

1

1

1

3

1

2

1

2

1

2

10

2

1

1

1

5

3

2

4

1

3 1

3

2

1

1

1

1

13

2

2

3

2

1

1

1

2

2

1

1

3

3

1

1

2

1

1

0.7

0.1

4

1

18.4

0.8

1

0.3

5.2

1

37

7

1

3.7

2

1

0.9

2.4

23

4.5

6.1 0.5

2.3

4.8 2.8

3.3

0.7

7

2

1 1

3

0.6

0.6

5

0.8

48

5

1

5.6

3

6

5.2

0.3

0.8 0.8

0.2

1

12.7

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

R–2 missing core—In percent

< 2

2.1–5

5.1–10

10.1–30

> 30

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 17. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for both core holes and rotary holes drilled through the R-2 zone, Piceance Basin, Colorado.
Factors Affecting the Precision of Oil-Yield Measurements 25

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.3 0.7

1.4

0.3

0.7

0.8

3.3

0.7 0.6

2

2

0.9

3.8

0.3

4.6

2.7

0.8

8

2

1

15.4

2.3 1

4.7

16.6 3 2.8

4.8

1.3

2

2.3

4

0.3

3

1

1

1

0.5

0.3

2

0.3

1

8.3

13.2

2.2

5

1.6

0.6

1 1

1

1 2

1

1

1 1

1

1

1

1

3

1

1

1

1

1

1

4

1 1

2

2 2 1

5

1

2

2

1

1

2

1

10

1

1

2

1

3

1

1

1

1

1

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

L–2 missing core—In percent

< 1.5

1.6–5

5.1–15

15.1–30

> 30

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 18. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for both core holes and rotary holes drilled through the L-2 zone, Piceance Basin, Colorado.
26 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

2

1

1 1

2

1

1

2

1

3

1

1

2

2

2

3

3

4

5

3 5

4 6

1

1

2

1

5

5

4

1

1

4

5 5

6 8

4

7

3

1

3

10

1

1

4

1

1

1

11

1

1

3

1

12

1

2

1

5

2

1

1

1

0.1

4

5

1

3

0.7

1.8

0.2

0.6

0.5

1.3 3

10

0.9

2.3

2.5

2

6.2 12.5

7.2 4.9

0.1

4

6

4

8

4.7

8.3

1 2.2

5.7 35 9.7

4.4

3.2

5.6 6.1

8.5

1

6.7

9

2

0.2

0.8

7

1

1

0.5

2

1.2

0.5

1.3

2

1

4

8.8

7

5.6

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

R–3 missing core—In percent

< 10

11–20

21–30

31–50

> 50

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 19. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for core holes drilled through the R-3 zone, Piceance Basin, Colorado.
Factors Affecting the Precision of Oil-Yield Measurements 27

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

2

1

1

2

1

1

1

1

1

1 1 1 1 1

2

2 2

1 1

2

1

1

2

1

3

3

1

1

2

7

2

2

1

1

1

1

1

1

1

1

1

2

0.6

4

4

6

0.4

0.5

1.8

1

1

0.4 2.2

1.5 1.3

0.3

2.9

8

1.7 0.2 4.7

5.6 1.9

1.5 2.6

2.8

2.3

1.7

0.2

9.1

1

0.2

0.1

0.2

1

6

3

0.7

0.5

1.4

0.4

0.2

2.1

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

L–3 missing core—In percent

< 1.5

1.6–5

5.1–10

10.1–20

> 20

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

COLORADO

0 5 10 2.5 KILOMETERS

Figure 20. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for core holes drilled through the L-3 zone, Piceance Basin, Colorado.
28 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1 1

1

2

1

4

1

1

1

1 1

1

3

1

1

1

1

3

1

1

1 1

3 3

1

3

2 1

4

4

4

3 3 3 4

4

2 6

3

2 2

3

1 4

1

2

1 4

3

12

1

2

3

9

4

1

1

1

8

2

2

1

1

8 1

1

2

2

2

4 3

4

9

8 1

0.2

0.9

2.4

0.4

0.5

2

1.9

1.1 0.5

6.5

2

1

0.2

0.6

0.6

2

6.2

1.9 0.3

3.2 2.8

0.1

2

2 4

5.2

10.7

16

1 1 2 8

5.9 1.4

2.1 5.5

4 3.9

5

5

4.2

2

9.1

0.2

0.9

3

1

0.5

0.5

4.5

1.5

0.1

2.9

9.5

1.4

8

9.9

0.9

1.5

7.9 0.7

0.6

0.6

0.6

1.9

6

1.1

0.4

1.3 0.4

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

R–4 missing core—In percent

< 2

2.1–5

5.1–10

10.1–15

> 15

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 21. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for core holes drilled through the R-4 zone, Piceance Basin, Colorado.
Factors Affecting the Precision of Oil-Yield Measurements 29

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.3 0.3

0.1

3.5

5

1

9 3 1

0.8

3.6

1

10.9

2.5

2

2

6

5.9

1.1

29

2.3

5 2

21

5

1

5.5

2

2

1.4

0.7

4

1

0.9

6.3

4

10.6

5.4

3.8

2.9

23

2.2

1

2

10.4

4.7 4.1 2.7 1.3 24

5.3

7.7

1.7

2.9 2.6

4.3

2

4

2.3

7

22.9 5.9

2.8

43.3

4

9

6

0.5

1.5

2.4

0.4

1.1

0.7

1.9

1.3

0.6

0.7

1

6.3

1

8.7 1

5

0.6

7

8

6.9 1

0.8

6.6 8.3

0.7

0.6

1.5

2

2.7 3.1

0.3 2.3

0.5

2 1

2 4

2

1

3 5 1

2

6

1

9

3

1

1

2

6

1

1

1

4 3

2

1

1

1

1

4

2

2

1

1

1

2

1

4

1

3

3

1

1

2

1

3

2 3 1 4

4

4 5

4

1

2 1

5

2

7

12

5

2

1

2

1

3

10

1

4

5

1

3

2

7

1

1

1

1

2

1

1 1

1

2

1

4

2 1

4

9 1

2

1

1

4

4

2 4 1

6

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

L–4 missing core—In percent

< 2

2–5

5.1–15

15.1–30

> 30

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 22. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for core holes drilled through the L-4 zone, Piceance Basin, Colorado.
30 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1.3 2.2

0.9

4

1.3

8

4.2

4

12

6

3 22

0.4

6.4

2.6

9.5

20.8

23.3

3

5.9

27.2

3.5

0.8

34

23.6

4

2

2

2

5

5.1

5.5

6.2

4.4

4

2.3

0.4

2

22.9

4.6

11.9 6.6

6.5

0.5

2.4

2.8

0.4

1

6

5

2

3

4

2

5

15.8

5.4 14 8.2

1.3

10.8

8.2

6.9 3 8

5.2

3.8

26.7

11.5

5.1

5.8

1

5.3

6.2

2

2 11.2

13 7

5.9

2 19

2

2.9

1.4

1.4

1

1

13.6

3.5

16.3

1.1

1

3.5

1

8.2

0.8

1.4

13

3.9

14.7

24.1 21

16.3

1.2

0.7

9

1.5

7

8

10.9

4

9

1.3

6.2

1

6

2.9

0.5

1.7

0.4

3.7

2.5

1.8

1 3

1.5

1.1

2

4 4

5 7

2

7

9

20

5

7

7 9

3

9

18

7

17 6

5

29

7

8

1

4

7

14 11

2

1

1

3

8

1

6

4

1

2

5

3

11

7

5

9

2

4

8

1

1

1

1

6

7

4

1

1

9

4

9

11

5 12

7

8 5 8

10

1

3

6 4

3

1

6

10

1

1

10

15

13

3

3

5 31

6

6

12

5

7

11

12

15

2

1

16

1

10

3

8

4

13 9 12 8

10

12

2

11 2

7

6

7 3

3 14

9

2

1

1

1

1

1

6

5 4 5 2

1

25

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

R–5 missing core—In percent

< 2.5

2.6–5

5.1–10

10.1–20

> 20

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 23. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for core holes drilled through the R-5 zone, Piceance Basin, Colorado.
Factors Affecting the Precision of Oil-Yield Measurements 31

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

2.3

0.4

7

24

8

0.5

1

25

7

3 17

13.9

7.2

10

7

3.2

2

40.7

7

14.9

1

8.9

9

12

2 5

3

3

1

18

10

2.4

1.2

0.7

24.5

10

5.6

4 12.5

1.5

5

1.4

8.5

3

10.6

4.1 10.5 4.6

6.7 11.7

3 2 2.6

1

12

2

6.2 8.6

6

11

19.2

26 17.7

5.5

7.7

6

5 3

0.9

0.5

1

2.5

0.8

5

0.5

6

9.5

0.3

2.8

0.3

1

2

2

1.6

4.5

2

4.9

1.2

1

4.6 1

6.8

12

21

36

6

5.5

5

13.3

0.6

8.4

1.3

6.3

1.1

3.4

0.6

3.9

2.1

1.9

0.3

1.8

2 4.4

0.6

1.3

2

1.3

1

6

2

6

10 10

3

1

2

6 4 6

22

4

1

11

3

1

16

5

10

1

10

4

2

9

1

2

1

1

3

7

1

5

1

6

1

2 2

3

2

4

4

13

2

2

1 2 3 5

6

3

2

1

3

4 1

6

2

3

4

8

6 8

1

2

7

3

18

3

3

4

5

3

2

3

6

8

1

3

1

1

1

2

1

6

3

16

4

1

7 4

8

3

7

3

7

3

1

5

2

3

2 10

4

1

1

1

5

2

1 3

2 6

2

1

4

23

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

L–5 missing core—In percent

< 2.5

2.6–10

10.1–20

20.1–40

> 40

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 24. Map showing percent of missing intervals, number of missing intervals (red), and thickest 

missing interval (blue) for core holes drilled through the L-5 zone, Piceance Basin, Colorado.
32 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

3

1

2.3 1.6

0.7 4.2

7

7

10

4 4

7

5

14

7.8

5.6

3.2

4.5

2

2.2

4.1

1

6

6.1

1

3.8

1

4.4

6.2

9

8 2

4

1

1

6

3.9

10.9

2

5.8

1

1.3

3.3

1

12.6

6.5

5.4 4.7

4.3

4

3.9

5.1

8

1.4

1

1

4

8.4

7.4

3 9.9

22

2.2

6.7

8.8

5.4

7 4 27.7

3.6 8 3.2

5.3

3

4.2

4

6

17.2 11.6

1

5.5

6

10

1

1.2

1.5

1.6

0.8

1

2

0.7

3.5

2

6.7

7.6

34 1

1.8

3

2

4 5.4

15.9

6

7

4

0.5

1.8

1

3.9

2

1.8

1

4

10.3

1.2 6

9

17

5

12.9

11.3

4.5

2.2

4.3

5 6

1.7 1.4 0.4

1.5

0.4

1

4.1 1.1

6.3 3.4 1.8

9.5

1.9 1.4

0.3

2

1

1 2 1.4

1 3

4

2 1.1

11.6

4.7 1.2

1 1.8

1

1.8

1.9

2

2

3

6 5 4

5

12

10

22

3

6 10 9

28

7

16

6

1

5

6

2

15

23

3

13 2

20

6

6

2

6

4

1

2

2

2

7

1

7

1

8

11

1

6

1

5

9

8

19

12

19

4

2

2

1 3 3

9 6

11 10

3

10

11

5

7

5 5 6 4

8

3

6

7

1

8

15

14

1

3

4

4

25

5

4

9

1

10

26

9

4

17

16

16

1 5

1

5

1

9 11

12

1

3

1

2

8

1

11

1

12

1

15

11

31

7

9

7

5

1

10

11

9

7

13 11

5 1 1

1

1

2 10

10

8

2

11

9

4 3

1 4

1

1

1 3

1 2

5

3 3 6

4

3

1 2

1

2

32

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

R–6 missing core—In percent

< 2.5

2.6–5

5.1–10

10.1–25

> 25

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 25. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for both core holes and rotary holes drilled through the R-6 zone, Piceance Basin, Colorado.
Factors Affecting the Precision of Oil-Yield Measurements 33

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

1

1

1 1

1 1

1

1

1

1

1

1

1

1

1 1

1

1

1

1

1

1 1 1

1 1

1

1

1

1

1 1

1

1 1 1

1

1

1

1

1

1

1 1

1

1

1

1

1

1

1

1

1 1

1

1

1

1

1

1

1 1

1

1 1

1

1

1

1

1

1

1

1

1

1

1

1

1 1 1

1

1

1

1

1 1 1

1

1

1

1

1

1

1 1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1 1

1

1

1 1

1

1 1

1

1 1 1 1 1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1 1

1

1 1

1 1

1 1

1

1

1 1

1

1

1

1 1

1

1

1

1

1

11 1

1 1

1

1

1

1

1 1

1 1

1

1

1

1 1

1

1

1 1

1 1

1

2

5

1.1

0.7 1.2

0.3

0.6

3.7

1.4

3.7

3

3

3

3

3

3 5

3

27.8

6.1

2

1

2 3 2

1.5

3

1.5

8.5

4.8

1.5

1.4 0.4

0.3

3.5 1.3

0.5

2.5

1

4

15.4

2.3

1

4.8 1.9

4

10

3.3

4 2

2.5

3

9

1.5

2.3

3

37

1.3

2.2

3.1

1

1.9

3

1.3 3.9

4 5 8

3

1.4

0.1

6

2

1

3

2.4

1.3

12

14.2

7.1

4.7

7.9 7.5

40

2.1

3.6 2

1.5

2.9 3.9 1.6

8

3.4

4

3.9

1.2 1

10.4

15.5 13.8

3

5

6

3

2

2

1

0.5

1.2

2.4

1.5

9

2.8

2.1

1.4

0.7

2.6

2.5

6.9

15

0

3.4

2.1

1

3.7

8.1

2.6

1

1 1

3

1.3 1.1

10

2 2

1 1

0.5

5.3

4.6

1.5

2.9

0.5

1

2.3

2.9

1

1

2.4

0.8

2.1 7

6

4

6

3.9

18.7

4.2

1.6

0.9

4.9

3

4

2

5

5.5

0.9

0.7

3 0.6

1 2 0.3

3.2

1

1.7 0.9

2 0.6

1.7

9.5

4.1

0.5

5

3.1

1.2

2

1.7

1.9

1.5

1.4

0.5

2.3

1

2

2

1.4

2

5

1

1.5 1.7

1.7 1.2

0.6

3

0.6

1.9

2.4

0.5

2.9 0.9 1

1.1 0.6

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Mahogany Ledge outcrop

Base of Parachute Creek Member

Mahogany Zone missing core—In percent

< 2

2.1–5

5.1–15

15.1–20

> 20

2

6.5 Thickest missing interval—Shown in blue

 Number of missing records—Shown in red

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 26. Map showing percent of missing intervals, number of missing intervals (red), and thickest missing 

interval (blue) for core holes drilled through the Mahogany zone, Piceance Basin, Colorado.
34 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 3. Detailed analysis of 13 closely spaced core holes from a four-square-mile area in the northwest part of the basin showing 

variations in average gallons per ton and percent missing interval for all 13 oil shale zones assessed. Locations of core holes shown 

on figure 27.

USGS 

ID

Mahogany 

gallons 

per ton

Mahogany 

percent 

missing 

interval

R-6 

gallons 

per ton

R-6 

percent 

missing 

interal

L-5 

gallons 

per ton

L-5 

percent 

missing 

interval

R-5 

gallons 

per ton

R-5 

percent 

missing

L-4 

gallons 

per ton

L-4 

percent 

missing

C0206 23.4 6.9 20.6 13.4 13.4 0.7 28 3.6 21.9 1.3

C0207 24.6 2.7 19.9 0.7 12.5 0 31.7 17.5 21.6 0

C0214 23.4 8.1 22.3 13.3 11.9 6 28.2 6 19.8 8.7

C0217 26.5 5.7 22.2 14.8 13.4 13.9 31.6 3.5 24.7 8.7

C0237 24.7 5.5 20.9 5.1 12.7 0 32.1 5 24.2 3.3

C0238 23.3 3.2 20.4 10.8 12.4 4.2 29.3 7.5 21.7 3.1

C0261 22.6 9.3 17.9 9.5 10.7 5.5 27.3 15.3 18.4 24.8

C0262 23 4.4 20 15.1 12.5 3.8 30.3 5.8 22.1 0

C0265 22.8 0 15.4 0 15 0 24.7 2.6 19.9 0

C0266 21.6 41.1 17.8 10.2 10.2 8 26 24 18.4 22.3

C0267 24.1 7.5 19.2 12.8 14.8 36.3 28.7 16.6 20.7 0

C0273 25.8 16.3 19.8 11.1 12 41.8 30.7 18.7 23.1 19.4

C0384 26.7 13.4 22.2 9.3

Table 3. Detailed analysis of 13 closely spaced core holes from a four-square-mile area in the northwest part of the basin showing 

variations in average gallons per ton and percent missing interval for all 13 oil shale zones assessed. Locations of core holes shown 

on figure 27.—Continued

USGS 

ID

R-4 

gallons 

per ton

R-4 

percent 

missing

L-3 

gallons 

per ton

L-3 

percent 

missing

R-3 

gallons 

per ton

R-3 

percent 

missing

L-2 

gallons 

per ton

L-2 

percent 

missing

R-2 

gallons 

per ton

R-2 

percent 

missing

C0206 33.7 2.9 13 6 25.8 6.1 15.4 0 29.2 0

C0207 33.5 2.3 16.5 0 28.8 6 16.5 0 32.6 0

C0214 33.8 0.4 11.1 6.5 26.2 26.7 14.4 0 28.7 0

C0217 35.4 8.5 16.1 3.5 30.9 30.1 18.1 0 30.1 0

C0237 36.3 0 16.4 0 29.4 4.7 18.3 0 31.7 0

C0238 34 9.1 11.8 0 26 16.5 15.4 3.7 30.2 0

C0261 32.6 22.8 10.3 17 23.7 18.1 15.1 53.7 27 28.9

C0262 36.3 2.9 15 0 31.1 47.8 15.5 0 29.1 0

C0265 29.6 0 9.5 0 20.7 0 10.9 0 26.7 0

C0266 36 21.4 12.5 11.1 22.7 32 9.7 28.6 27.4 22.5

C0267 32.5 7.6 13.2 6.5 26.8 14.3 18.1 0 29.7 0

C0273 36.3 12.9 17.7 15.7 28.7 35.6 18 9 31.2 14.4

C0384
Factors Affecting the Precision of Oil-Yield Measurements 35

Table 3. Detailed analysis of 13 closely spaced core holes from a four-square-mile area in the 

northwest part of the basin showing variations in average gallons per ton and percent missing 

interval for all 13 oil shale zones assessed. Locations of core holes shown on figure 27.—

Continued

USGS 

ID

L-1 

gallons 

per ton

L-1 

percent 

missing

R-1 

gallons 

per ton

R-1 

percent 

missing

L-0 

gallons 

per ton

L-0 

percent 

missing

R-0 

gallons 

per ton

C0206

C0207 8.4 0 17.7 3.1 6.4 0 12.4

C0214 8.4 4.4 19.2 0 4.9 0

C0217

C0237

C0238

C0261 6.5 18.2 17.5 11.7 5.1 0

C0262 8.4 7.7 20.7 12 5.9 0

C0265 8 0 17.9 0 5.5 0

C0266 6.5 35.5 16.9 12.2 9.9 12.8

C0267 6.4 0 16.2 0 13.4 0

C0273 5.7 21.9 20.1 13.4 7.5 15.8

C0384
36 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

C2003X

C1000

C0886R

C0885R

C0884R

C0678R

C0838R

C0813U

C0812R

C0808R

C0807U

C0806U

C0805U

C0804U

C0759R

C0758R

C0748R

C0675R

C0673R

C0672

C0844R

C0998R

C0811R

C0810R

C0809R

C0802U

C0801R

C0800U

C0799

C0754R

C0751R

C0749

C0747R

C0745R

C0677R

C0676R

C0674R

C0714R

C0713R C0217

C0519

C0518

C0517

C0516

C0515

C0508 C0507

C0594R

C0563R

C0579R

C0021

C0022

C0570R

C0689R C0560R

C0540R

C0235

C0543R

C0266

C0589R

C0349

C0685R

C0017

C0649R C0384

C0651R

C0544R

C0664R

C0316

C0522

C0622R

C0710R

C0681

C0609R

C0466S

C0355

C0347

C0310 C0309

C0308

C0307

C0273

C0272

C0270

C0269

C0268

C0265C0267

C0264

C0263 C0262

C0261

C0239

C0238

C0237

C0236

C0234

C0215

C0214

C0213

C0208

C0207

C0206

C0200

C0199

C0173

C0152

C0035

C0031

C0030

C0029 C0028 C0025

C0024

C0023

C0020

C0018

C0680R

C0679R

C0521

C0514

C0513

C0512

C0511

C0510

T. 1 S. T. 2 S. T. 1 N. T. 3 S.

R. 100 W. R. 101 W. R. 99 W. R. 98 W.

c0217

COLORADO

0 1 2 0.5 KILOMETERS

Mahogany Outcrop

Base of Parachute Creek Member—

 Dashed where inferred

EXPLANATION

0 0.5 1 2 MILES

Figure 27. Map showing locations of 13 closely spaced core holes (red numbers) in the northwest part of the 

basin that were used to study effects of missing core intervals on the overall oil yields obtained from the core. 

Number designations are from Dyni (1998). Core holes and rotary holes not used in this comparison shown in 

black. Rotary holes are distinguished from core holes by the “R” at the end of the number. Brown line is top of 

Mahogany ledge as mapped by Hail and Smith (1994). Green line is base of Parachute Creek Member of the 

Green River Formation as mapped by Hail and Smith (1994). 
Factors Affecting the Precision of Oil-Yield Measurements 37

0

2

4

6

8

10

12

14

16

18

20

L–3 gallons per ton

L–3 percent missing

 interval

0

10

20

30

40

50

60

R–3 gallons per ton

R–3 percent missing

 interval

0

10

20

30

40

50

60

L–2 gallons per ton

L–2 percent missing

 interval

0

5

10

15

20

25

30

35

R–2 gallons per ton

R-2 percent missing

 interval

0

5

10

15

20

25

30

35

40

L–1 gallons per ton 

L–1 percent missing

 interval 

0

5

10

15

20

25

R–1 gallons per ton

R–1 percent missing

 interval

0

2

4

6

8

10

12

14

16

18

L–0 gallons per ton

L–0 percent missing

 interval

A B

C D

E F

G

Figure 28. Percent missing interval versus average oil yield for the oil shale zones from the L-0 zone through Mahogany 

zone for 13 closely spaced core holes in the northwest part of the basin. Locations of core holes shown on figure 27.
38 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

0

5

10

15

20

25

30

35

40

45

Mahogany gallons per ton

Mahogany percent missing

 interval 

0

5

10

15

20

25

R–6 gallons per ton

R–6 percent missing

 interal

0

5

10

15

20

25

30

35

R–5 gallons per ton

R–5 percent missing

 interval

0

5

10

15

20

25

30

35

40

45

L–5 gallons per ton

L–5 percent missing

 interval

0

5

10

15

20

25

30

L–4 gallons per ton

L–4 percent missing

 interval

0

5

10

15

20

25

30

35

40

R–4 gallons per ton

R–4 percent missing

 interval

I

J K

L M

H

Figure 28. Percent missing interval versus average oil yield for the oil shale zones from the L-0 zone through 

Mahogany zone for 13 closely spaced core holes in the northwest part of the basin. Locations of core holes shown on 

figure 27.—Continued
Factors Affecting the Precision of Oil-Yield Measurements 39

the full core. One of the missing intervals is 18.7 ft thick, 

which represents 15.3 percent of the total thickness of the 

Mahogany zone. 

What is clear from this discussion is that the reliability of 

each control point used to construct the resource maps varies 

depending on the amount of missing interval. The issue of 

missing intervals clearly warrants further study, but for this 

assessment, we did not eliminate any control points because of 

excessive amounts of missing intervals. 

Comparing Gallons Per Ton Data Points From 

This Assessment With Those Used in the 

Previous Assessment

Although the computer files used in the previous assessment (Pitman and others, 1989) were not recovered, the 

thickness of oil shale zones, gallons per ton values, and barrels 

per acre values for each data point are shown on the isopach 

maps and assessment maps published with that assessment. 

In areas where core holes are widely spaced, we could, in 

many instances, identify the core holes used in the previous 

assessment and thus we could compare their results with ours. 

Figures 31–34 shows locations of selected core holes that were 

used to compare GPT and BPA determinations for the R-5 and 

L-5 zones in both this assessment and the assessment of Pitman and others (1989). The results are listed in tables 4 and 5 

and graphed in figures 35–38. As expected, for core holes with 

no missing intervals, the GPT values are nearly the same for 

the two assessments except that the values used in the previous 

assessment were rounded off to the nearest integer (figs. 31, 

33). As the percentage of missing interval increases, the ratio 

between GPT used here and GPT used in the previous assessment increases and there is an increase in scatter (figs. 35–38). 

In addition, most but not all of the BPA values used in this 

assessment are higher than those used in the previous assessment even when there were no missing intervals (figs. 31, 33, 

34, 37). This difference is generally quite small but can be 

as much as 35 percent particularly for core holes in marginal 

areas. This indicates that our method for assigning values to 

missing intervals and for converting GPT into BPA overall 

produces slightly greater resource numbers than the method 

used in the previous assessment. Our method, however, is 

fully documented, and it would be relatively easy to use different formulas and generate a new set of resource numbers using 

the Access table presented in Mercier and others (chapter 3, 

this CD-ROM).

Reproducibility of Fischer Assay Analysis

Fischer assay has been the standard method to measure 

the oil potential of oil shale for almost 60 years (Stanfield and 

Frost, 1949). Dyni (2003) discusses the Fischer assay method 

and how it compares with other methods to determine oil 

yields in oil shales. Reproducibility of Fischer assay results 

has been studied by many workers in the past. Keighin (1980) 

studied variations in assay results on: 1) the same samples 

using the same analytical technique by the same lab, 2) the 

same samples analyzed by different labs using the same 

analytical technique, 3) the same samples run by different labs 

using slightly different analytical techniques, and 4) samples 

from two closely spaced holes run by two different labs 

using slightly different analytical techniques. Results were 

variable, with a correlation coefficient (r) of 0.9207 for the 

first scenario, r values of 0.9946 and 0.9604 for the second, 

r values of 0.9947 and 0.9973 for the third, and an r value of 

only 0.7994 for the fourth scenario. For the third case of two 

labs analyzing the same samples but using slightly different 

analytical techniques one lab gave consistently higher results 

than the other. The poor correlation for the fourth case of two 

laboratories using slightly different analytical techniques on 

two sets of samples from nearby core holes suggests that there 

may be significant problems with assigning values to missing 

core intervals based on results from a nearby core hole. 

The analytical errors should be minimal for a typical oil 

shale zone that averages from 50 to about 200 ft thick that was 

sampled and analyzed for oil content every foot or so, as the 

errors should be averaged out by the relatively large number 

of analyses. No attempt was made here to identify assays that 

were run by the lab that gave consistently higher results, but 

this should be investigated in the future. 

Problems Related to Saline Minerals

Much of the oil shale section in the saline depocenter 

contains the saline minerals nahcolite and halite. When nahcolite is dispersed in the oil shale or occurs as aggregates or thin 

beds, it is generally not removed prior to assaying. The presence of nahcolite in a sample can generally be detected from 

Fischer assay results because it breaks down producing carbon 

dioxide during retorting, increasing the amount of “gas plus 

loss” over that of nahcolite-free oil shale. In fact, this increase 

in “gas plus loss” due to the breakdown of nahcolite can be 

used to estimate the amount of nahcolite originally present in 

the sample (see Brownfield and others, chapter 2, this CDROM). The assay results are thus diluted by the presence of 

these minerals and lower GPT measurements are obtained than 

if the minerals had been leached prior to assaying. This dilution does not greatly affect the calculation of in-place oil as 

the diluted GPT value is applied to the entire section, including the nahcolite.

However, thick beds of nahcolite and halite are also 

present in the saline depocenter. These beds are generally not 

assayed and appear as zeros in the Fischer assay results. One 

bed of halite and nahcolite is as much as 65 ft thick (Dyni, 

1974, p. 117). Missing intervals also appear as zeros in the 

assay results, and great care was taken to distinguish the zero 

assay results from these saline beds from zero results from 

missing intervals. As previously discussed, true missing intervals were assigned an oil yield value equivalent to the average 
40 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

C0598R

Sec. 2, T. 2 S., R. 96 W.

C0599R

Sec. 3, T. 2 S., R. 96 W. Mahogany zone

Mahogany

zone

0 20 40 60 80 100 0 20 40 60 80 100

GALLONS PER TON GALLONS PER TON

MAHOGANY AVERAGE: 

23.7 GALLONS PER TON

MAHOGANY AVERAGE:

16.4 GALLONS PER TON

DEPTH IN HUNDREDS OF FEET

DEPTH IN HUNDREDS OF FEET

13

14

15

16

17

18

19

12

13

14

15

16

17

18

A B

Figure 29. Oil-yield histograms for two closely spaced rotary holes in the eastern part of the basin. 

In the first hole (A), the Mahogany zone is complete and averages 23.7 gallons per ton. A 70 ft thick 

interval is missing in the second hole (B). The missing interval includes the Mahogany bed, the 

richest part of the Mahogany zone. Having the Mahogany bed missing depresses the average of the 

remaining core in the Mahogany zone to 16.4 gallons per ton.
500

300

0 20 40 60 80 100

Gallons per ton

500

400

0 20 40 

Gallon

21.6 Gallons 41.1 percent 7 missing inteMaximum thica single missin

Rio Blanco Oil 

 Sec. 5, T. 

C

0 20 40 60 80 100

700600800900

25.8 Gallons per ton16.3 percent of Mahogany is missing10 missing interalsMaximum thickness of a siingle missing interval: 3.9 ft

C

Rio Blanco Oil Shale Co., C-15

 Sec. 10, T. 2 S., R. 99 W.

C0273

Gallons per ton

22.6 Gallons per ton9.3 percent of Mahogany is missing5 missing intervalsMaximum thickness of a single missing interval: 3.6 ft

B

C-a Project, C-1

Sec. 32, T. 1 S, R. 99 W.

C0261

100

200

300

0 20 40 60 80 100

0

Gallons per ton

22.8 Gallons per tonNo missing intervals

A

Gulf-Standard of Indiana

(C-a Project), CH-7

Sec. 5, T. 2 S., R. 99 W.

C0265

600 400

Figure 30. Oil-yield histograms listing percent missing intervals and average oil yield in gallons per ton for four core holes (A–D) in the no

part of the basin. Black lines bracket the Mahogany zone. Locations are shown on figure 27.
42 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

21

14

18

8 8 7

4

8

11

15

13 13

13 9

12

15 18

16

20

18

23

19

14 8

13

29

23

34

34

24

27

19

26

37

35 37

21

23

24

24

23

21

29

27

22 21 25

21

28

20

12 22

0

0.3

0.9

5

12.5

15.9

5.9

4.9

0

0.6

6.4

0

3

3.6

0

24.8

3.8

8

0

24.2

18.8

0.4

17.8

0.2

5.1

0

10.9

0.4

3

5.3

5.6

6.4

0

23.6

0

0

4.5

0

22.7

1.6

17.2

21.8

20

11.5

0

0

0

11.9

5.4

9 0.5

0.1

10.6

12.7

16

13.8

35.5

23.3

28

21.5

8.4

8.6

25.8

18

24.1

15.8

18

25.7

19.1

22.7

7.1

26.5

21.5

7.9

21

12.5

14.3

20.9

21.6

17.9

26.3

35.6

23.5

16.8

24.6

21

11.5

8.1

22.4

13.2

31.3

27.8

22.9

26.2

27.5

36.2

7.9

4.1

12.6

13.9

38.5

38.1

21.7 24

10.2

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO 0 5 10 2.5 KILOMETERS

20 10.9 21.6

EXPLANATION

Mahogany Outcrop

Base of Parachute Creek Member

Oil shale core hole—Gallons per ton

this assessment (shown in black); 

gallons per ton Pitman and others 

(1989, shown in red); and 

percent of missing intervals this 

assessment (shown in green)

Figure 31. Map showing gallons per ton measurements used in both this assessment and the previous one 

to assess the R-5 zone. The black values are for this assessment, and the red values are from the previous 

assessment. The green numbers are the percent of missing interval in the R-5 zone. The brown line is the outcrop 

of the top of the Mahogany ledge, and the green line is the outcrop of the base of the Parachute Creek Member 

(digitized from Hail and Smith, 1994; 1997).
Factors Affecting the Precision of Oil-Yield Measurements 43

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

539

133

135

71

57 46

36

132

143

206

169 175

193 146

160

234 195

191

271

238

291

278

157 212

228

405

319

467

474

289

241

179

324

506

450 535

552

568

535

505

486

522

487

460

343 371 469

478

533

295

212 471

0

0.3

0.9

5

12.5

0.8

15.9

5.9

4.9

0

0.6

6.4

0

3

3.6

0

24.8

3.8

8

0

24.2

18.8

0.4

17.8

0.2

5.1

0

10.9

0.4

3

5.3

5.6

6.4

0

23.6

0

0

4.5

0

22.7

1.6

17.2

21.8

20

11.5

0

0

0

11.9

5.4

9 0.5

1

153

179

198

223

499

87

526

516

504

142

154

570

243

342

214

142

246

188

250

49

466

354

167

309

171

203

377

328

250

329

473

517

214

479

311

228

75

496

240

460

556

491

573

339

514

59

42

185

139

545

563

566 531

10.2

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO 0 5 10 2.5 KILOMETERS

20 10.9 21.6

EXPLANATION

Mahogany Outcrop

Base of Parachute 

 Creek Member

Oil shale core hole—Gallons per ton

this assessment (shown in black); 

gallons per ton Pitman and others 

(1989, shown in red); and 

percent of missing intervals this 

assessment (shown in green)

Figure 32. Map showing barrels per acre measurements used in both this assessment and the previous one 

to assess the R-5 zone. The black values are for this assessment and the red values are from the previous 

assessment. The green numbers are the percent of missing interval in the R-5 zone. The brown line is the outcrop 

of the top of the Mahogany ledge, and the green line is the outcrop of the base of the Parachute Creek Member 

(digitized from Hail and Smith, 1994; 1997).
44 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

2

2

1

4

1

2

2 1

4

7

7

10

9 11

9 4

9

13

10

10

11 11 13

12

12

13 6 11

11

12

10

19

17

14

16

17

15

14

12

10

10

14

14 15

14

11

14

13

14

15

14

15

9

11

7 7

6

14

14

10

4

8 9

10

5

2.5

6.7

0.4

16.8

25.9

25.4

27

52.7

11.8

1

0.6

0.2

3.4

0.2

36.6

1.3

6.1

0

1.2

2.5

12

21.3

5.4

49.6

22.4

12.9 5.3

25.7

28

3.1

0

41.5

2.7

0

0

28.3

1.3

44.5

0.7

0

0

18.2

0

0

22.2

1

0

0

13.6

0

32.9

0

7

30.3

0

0

0

0

13.2

47.8

12.1

21.3

42.5

11.8

6.3

8.9

2.4

10.9

13.3

11.9

17.2

22.4

14.3

13.8

1.3

4.2

1.9

4.1

18.2

14.1

13.1

14.2

10.9

9.9

11.1

9.3

1.3

13.8

9.8

6.1 12.9 17.7

10.3

8.6

10.6

11.6

12.5

10.1

14

15.6

4.2

12.9

6.7 6.1

12.5

13

4.7

2.2

10.8

13.5

11.5

9.7

14.9

14.7

15.5

7.1

13.3

18.3

1.7

4.1

1.8

11.1

7.1

14.9

9.9

16.6

15.1

12.7

14.5

38

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO 0 5 10 2.5 KILOMETERS

20 10.9 21.6

EXPLANATION

Mahogany Outcrop

Base of Parachute 

 Creek Member

Oil shale core hole—Gallons per ton

this assessment (shown in black); 

gallons per ton Pitman and others 

(1989, shown in red); and 

percent of missing intervals this 

assessment (shown in green)

Figure 33. Map showing gallons per ton measurements used in both this assessment and the previous one 

to assess the L-5 zone. The black values are for this assessment, and the red values are from the previous 

assessment. The green numbers are the percent of missing interval in the L-5 zone. The brown line is the 

outcrop of the top of the Mahogany ledge and the green line is the outcrop of the base of the Parachute Creek 

Member (digitized from Hail and Smith, 1994; 1997).
Factors Affecting the Precision of Oil-Yield Measurements 45

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

21

14

11

31

14

33

28 18

47

49

32

64

60 79

73 51

48

57 87

53

61 62 89

89

93

106 96 77 112

109

112

128

127

91

107

119

103

75

85

79

75

120

89 104

188

177

127

91

124

126

122

144

118

135

85 75 44

110

132

104

55

137 137 140 65

2.5

6.7

0.4

16.8

25.9

25.4

27

52.7

11.8

1

0.6

0.2

3.4

0.2

36.6

1.3

6.1

0

1.2

2.5

12

21.3

5.4

49.6

22.4

12.9 5.3

25.7

28

3.1

0

41.5

2.7

0

0

28.3

1.3

44.5

0.7

0

0

18.2

0

0

22.2

1

0

0

13.6

0

32.9

0

7

30.3

0

0

0

0

13.2

47.8

12.1

21.3

42.5

11.8

1

50

63

33

85

65

126

122

154

130

115

18

49

26

52

137

130

90

95

66

62

83

72

12

141

128

77 108 85

68

88

143

121

94

78

94

146

57

73

76 45

99

114

68

22

171

105

112

116

146

130

183

79

76

130

15

44

23

83

33

134

177

117

170

184

105

38

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO 0 5 10 2.5 KILOMETERS

20 10.9 21.6

EXPLANATION

Mahogany Outcrop

Base of Parachute 

 Creek Member

Oil shale core hole—Gallons per ton

this assessment (shown in black); 

gallons per ton Pitman and others 

(1989, shown in red); and 

percent of missing intervals this 

assessment (shown in green)

Figure 34. Map showing barrels per acre measurements used in both this assessment and the previous one 

to assess the R-5 zone. The black values are for this assessment and the red values are from the previous 

assessment. The green numbers are the percent of missing interval in the R-5 zone. The brown line is the 

outcrop of the top of the Mahogany ledge, and the green line is the outcrop of the base of the Parachute Creek 

Member (digitized from Hail and Smith, 1994; 1997).
46 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 4. Gallons per ton, barrels per acre, and percent missing intervals for 49 selected core holes that were used 

to assess the R-5 zone in both this assessment and the assessment of Pitman and others (1989).

[GPT, gallons per ton; BPA, barrels per acre]

GPT here, 

R-5

GPT Pitman, 

R-5

BPA here, 

R-5

BPA Pitman, 

R-5

Percent 

missing

GPT here/GPT 

Pitman

BPA here/BPA 

Pitman

11.5 12 228 212 0 0.958 1.075

22.4 22 496 471 4.5 1.018 1.053

24.6 25 479 460 0 0.984 1.041

20.9 21 377 371 0 0.995 1.016

21.5 22 354 343 18.8 0.977 1.032

19.1 19 188 179 3.8 1.005 1.050

21.6 20 328 295 10.9 1.080 1.112

26.3 26 329 324 3 1.012 1.015

38.5 37 545 506 11.9 1.041 1.077

25.8 24 570 535 6.4 1.075 1.065

23.3 21 526 539 15.9 1.110 0.976

21.7 21 566 552 9 1.033 1.025

26.2 23 573 568 21.8 1.139 1.009

21.5 21 504 478 4.9 1.024 1.054

22.9 21 491 522 17.2 1.090 0.941

24 24 531 505 0.5 1.000 1.051

29 28 516 487 5.9 1.036 1.060

23.5 23 517 486 5.6 1.022 1.064

26.5 27 466 460 24.2 0.981 1.013

18 18 142 135 0 1.000 1.052

35.6 35 473 450 5.3 1.017 1.051

38.1 37 563 535 5.4 1.030 1.052

35.5 34 499 474 12.5 1.044 1.053

36.2 34 514 467 11.5 1.065 1.101

13.2 13 240 228 0 1.015 1.053

27.5 24 339 289 20 1.146 1.173

16.8 16 214 191 6.4 1.050 1.120

24.1 23 342 319 3 1.048 1.072

31.3 29 460 405 22.7 1.079 1.136

22.7 20 250 271 8 1.135 0.923

21 23 309 291 17.8 0.913 1.062

21 19 311 278 23.6 1.105 1.119

13.8 14 223 212 5 0.986 1.052

7.9 8 167 157 0.4 0.988 1.064
Factors Affecting the Precision of Oil-Yield Measurements 47

Table 4. Table listing gallons per ton, barrels per acre, and percent missing intervals for 49 selected core holes 

that were used to assess the R-5 zone in both this assessment and the assessment of Pitman and others 

(1989).—Continued.

[GPT, gallons per ton; BPA, barrels per acre]

GPT here, 

R-5

GPT Pitman, 

R-5

BPA here, 

R-5

BPA Pitman, 

R-5

Percent 

missing

GPT here/GPT 

Pitman

BPA here/BPA 

Pitman

13.9 14 139 133 0 0.993 1.045

12.5 12 171 160 0.2 1.042 1.069

15.8 15 214 195 3.6 1.053 1.097

18 18 243 234 0 1.000 1.038

16 15 198 206 0.9 1.067 0.961

17.9 18 250 238 0.4 0.994 1.050

12.7 13 179 169 0.3 0.977 1.059

12.6 13 185 175 0 0.969 1.057

11 10.6 153 143 0 1.038 1.070

14.3 13 203 193 5.1 1.100 1.052

8.4 8 142 132 0 1.050 1.076

8.6 9 154 146 0.6 0.956 1.055

7.1 7 49 46 0 1.014 1.065

7.9 8 59 57 0 0.988 1.035

8.1 8 75 71 0 1.013 1.056

Table 5. Gallons per ton, barrels per acre, and percent missing intervals for 61 selected core holes that were 

used to assess the L-5 zone in both this assessment and the assessment of Pitman and others (1989).

[GPT, gallons per ton; BPA, barrels per acre]

GPT here, 

L-5

GPT Pitman, 

L-5

BPA here, 

L-5

BPA Pitman, 

L5

Percent 

missing

GPT here/GPT 

Pitman

BPA here/BPA 

Pitman

4.7 5 68 65 0 0.940 1.046

12.7 10 184 140 42.5 1.270 1.314

10.8 9 171 137 22.2 1.200 1.248

9.9 8 177 137 4.7 1.238 1.292

4.2 4 57 55 1.3 1.050 1.036

6.7 7 76 85 0.7 0.957 0.894

7.1 7 79 75 0 1.014 1.053

6.1 6 45 44 0 1.017 1.023

10.6 11 143 135 0 0.964 1.059

9.8 9 128 118 22.4 1.089 1.085

9.3 10 72 79 21.3 0.930 0.911

11.6 10 121 104 41.5 1.160 1.163

10.1 10 78 75 0 1.010 1.040

14.9 14 134 120 13.2 1.064 1.117

14.1 14 130 127 1.3 1.007 1.024

14.9 14 146 132 13.6 1.064 1.106

15.1 14 170 188 21.3 1.079 0.904

15.5 11 183 177 32.9 1.409 1.034

13.8 14 115 110 1 0.986 1.045

14.7 15 130 126 0 0.980 1.032
48 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 5. Gallons per ton, barrels per acre, and percent missing intervals for 61 selected core holes that 

were used to assess the L-5 zone in both this assessment and the assessment of Pitman and others (1989).—

Continued

[GPT, gallons per ton; BPA, barrels per acre]

GPT here, 

L-5

GPT Pitman, 

L-5

BPA here,

 L-5

BPA Pitman, 

L5

Percent 

missing

GPT here/GPT 

Pitman

BPA here/BPA 

Pitman

14.3 14 130 122 11.8 1.021 1.066

15.6 14 146 124 28.3 1.114 1.177

11.1 12 83 85 12 0.925 0.976

14 14 94 89 0 1.000 1.056

16.6 15 117 104 12.1 1.107 1.125

22.4 17 154 119 52.7 1.318 1.294

17.2 16 122 107 27 1.075 1.140

18.3 15 130 103 30.3 1.220 1.262

18.2 17 137 127 36.6 1.071 1.079

9.7 10 116 112 0 0.970 1.036

14 13.3 76 75 7 1.053 1.013

12.9 10 73 53 44.5 1.290 1.377

13.3 11 65 61 25.9 1.209 1.066

11 10.9 66 62 1.2 1.009 1.065

14.2 14 95 91 0 1.014 1.044

13.5 13 105 89 1 1.038 1.180

17.7 19 85 128 25.7 0.932 0.664

12.5 12 99 93 0 1.042 1.065

12.9 13 108 106 12.9 0.992 1.019

11.5 12 112 109 0 0.958 1.028

13 11 114 96 18.2 1.182 1.188

11.9 11 126 112 25.4 1.082 1.125

6.1 6 77 77 5.3 1.017 1.000

7.1 7 33 32 0 1.014 1.031

10.3 9 68 48 28 1.144 1.417

13.1 13 90 87 6.1 1.008 1.034

10.9 10 85 64 16.8 1.090 1.328

12.5 12 94 89 2.7 1.042 1.056

8.9 9 63 67 6.7 0.989 0.940

11.1 11 83 79 0 1.009 1.051

6.3 7 50 49 2.5 0.900 1.020

8.6 9 88 73 3.1 0.956 1.205

4.2 4 49 47 0.2 1.050 1.043

4.1 4 52 51 0.2 1.025 1.020

2.4 2 33 33 0.4 1.200 1.000

1.9 2 26 28 3.4 0.950 0.929

1.3 1 18 18 0.6 1.300 1.000

2.2 2 44 31 0 1.100 1.419

1.3 1 12 11 5.4 1.300 1.091

1.7 2 15 14 8 0.850 1.071

2.2 2 22 21 10.4 1.100 1.048
Factors Affecting the Precision of Oil-Yield Measurements 49

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

0 5 10 15 20 25 30

R-5 ZONE

GALLONS PER TON THIS ASSESSMENT VERSUS 

GALLONS PER TON PITMAN AND OTHERS (1989)

PERCENT MISSING INTERVAL

Figure 35. Ratio of gallons per ton calculated here with that calculated by Pitman and others 

(1989) for 49 core holes that penetrated the R-5 zone compared with percent missing intervals.

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

0 5 10 15 20 25 30

PERCENT MISSING INTERVAL

R-5 ZONE

BARRELS PER ACRE THIS ASSESSMENT VERSUS 

BARRELS PER ACRE PITMAN AND OTHERS (1989)

Figure 36. Ratio of barrels per acre 

calculated here with that calculated 

by Pitman and others (1989) for 49 

core holes that penetrated the R-5 

zone compared with percent missing 

intervals.
50 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

0 10 20 30 40 50 60

GALLONS PER TON THIS ASSESSMENT VERSUS 

GALLONS PER TON PITMAN AND OTHERS(1989)

PERCENT MISSING INTERVAL

R-5 ZONE

Figure 37. Ratio of gallons per 

ton calculated here with that 

calculated by Pitman and others 

(1989) for 61 core holes that 

penetrated the L-5 zone compared 

with percent missing intervals.

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

0 10 20 30 40 50 60

BARRELS PER ACRE THIS ASSESSMENT VERSUS 

BARRELS PER ACRE PITMAN AND OTHERS (1989)

PERCENT MISSING INTERVAL

L-5 ZONE

Figure 38. Ratio of barrels per 

acre calculated here with that 

calculated by Pitman and others 

(1989) for 61 core holes that 

penetrated the L-5 zone compared 

with percent missing intervals.
Methods Used to Generate Isopach Maps and Isoresource Maps 51

of the recovered core for that oil shale zone. We did not want 

to assign oil-yield values to unassayed saline beds as it would 

falsely increase the in-place oil shale calculations. 

Leaching of nahcolite and halite beds in the R-5 and L-5 

zones in the saline depocenter by relatively recent groundwater movement has created an unknown but significant 

amount of void space (Dyni, 1981). Void space occurs in 

collapse breccias, formed by the collapse due to leaching of 

thick halite and nahcolite beds, and in vugs and other spaces 

formed by the leaching of nahcolite aggregates and disseminated nahcolite. Leaching saline minerals out of a sample 

increases the GPT measured with Fischer assay, because the 

saline minerals no longer dilute the results. Applying this 

enhanced Fischer assay result to the entire interval including 

the void space results in an overestimation of the oil in place. 

This problem was not discussed in the previous assessment 

by Pitman and others (1989). However, descriptions of core 

taken in the leached zone rarely give estimates of the amount 

of void space, and thus it is unlikely that this problem has ever 

been systematically addressed. Thus, in-place oil estimates 

in the leached zone have probably been overestimated by 

an unknown amount in this assessment as well as the previous assessment. It should be possible to address this problem 

by careful core analysis and possibly by analyzing available 

geophysical logs, but strict time constraints did not allow us to 

pursue these possibilities at this time. 

Methods Used to Generate Isopach 

Maps and Isoresource Maps

Pitman and others (1989) used geostatistical interpolation by kriging to generate their resource maps and resource 

numbers. According to Pitman and others (1989), statistical 

tests done prior to kriging determined that oil shale resource 

values were “statistically homogeneous” or that BPA resource 

values for oil shale core holes spaced a short distance apart 

tended to be more alike than values for core holes that were 

farther apart. Pitman and others (1989) used a computer 

program called BLUEPACK to determine that variations in 

oil yield were linear for all of the oil shale zones except the 

L-5 and R-2 zones. For these two zones there was a significant 

amount of variation that could not be predicted from available 

data and a “nugget-only” model was used to try to capture 

this variability. Pitman and others (1989) found that universal 

kriging gave good results in areas with good control, but in 

areas with little control such as basin margin areas universal 

kriging calculated very large error limits—as much as +1,298 

percent, and several townships had insufficient control for 

universal kriging to calculate any resource numbers at all. 

Pitman and others (1989) manually determined in-place oil 

shale resources using isoresource contours and compared the 

results with the results from kriging. Pitman and others (1989) 

found that resource estimates determined by kriging compared 

favorably with resource values determined manually in areas 

with good control, however in areas with limited control, such 

as the basin margin areas, universal kriging dramatically overestimated resources. For example, in the township with the 

+1,298 percent error, kriging estimated 1.1 billion barrels of 

oil in place in the R-5 zone while hand contouring estimated 

only 219 million barrels. 

As our study required close to 200 unique models to 

construct the isopach, GPT, BPA, and nahcolite assessments, 

we chose to use an RBF-multiquadric function instead of 

kriging as it facilitated the generation of quicker models while 

providing similar results. The RBF-multiquadric function in 

ESRI Geostatistical Analyst provided us with a quick, exact 

interpolator, and kept the model within our methodology’s 

native software format (ESRI ArcGIS). Rusu and Rusu (2006) 

recently demonstrated that “soft computing methods” such as 

Radial Basis Functions (RBF) compare favorably with conventional “hard computing methods” such as kriging. In their 

study, they compared results when the RBF method and kriging were applied to the same data set. Rusu and Rusu (2006) 

cited a recent study where the Radioactivity Environmental 

Monitoring Group (REM) of the Institute for Environment 

and Sustainability at the Joint Research Center (JRC) of the 

European Commission invited participants to apply both RBF 

and kriging to a data set depicting variations in daily mean 

values of gamma-ray doses in southwest Germany. Part of the 

data points were hidden, and the participants were asked to 

estimate values at these hidden locations using the data points 

given. In general, both the RBF method and kriging were 

equally good at predicting the right results, except for areas 

with limited data where a proper variogram required for kriging is difficult to construct. In these areas, the RBF method 

gave better results. According to Rusu and Rusu (2006, p. 126) 

“The results and the execution time are quite similar for RBF 

and kriging, but the ease of use of RBF is overwhelming, 

compared to the use of kriging. When using RBF, the user has 

to choose only the radial functions type and the smoothing 

parameter. When using kriging, complex variogram modeling 

has to be done.” The problems with generating a proper variogram with limited data may be in part why in the previous 

assessment kriging gave values with unacceptable margins of 

error for areas with limited data.

Some of the problems encountered with the previous 

assessment have largely been alleviated by the addition of a 

large number of new data points. Table 6 compares the number 

of data points used for each oil shale zone in the previous 

assessment with the number used in this assessment. In all, 

2,178 data points are used here which compares with 1,083 

used for the last. For the Mahogany zone, 396 data points were 

used this time as opposed to 131 in the previous assessment, 

whereas the number of data points used for the R-6 zone 

increased from 67 to 235. Despite these increases, there were 

still problems establishing trends in the marginal areas of the 

basin, and estimates from surface sections were added as a 

supplement to the core-hole data. The importance of having 
52 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

detailed measured sections and good geologic mapping in 

these marginal areas to help fix regional oil-yield trends cannot 

be overemphasized. 

Four maps were generated for each oil shale zone 

assessed here: 1) an isopach map, 2) a map showing variations 

in oil yield in GPT, 3) a map showing variations in BPA, and 

4) a map showing total in-place oil in each 36-section township in the basin. We compared two methods for spatial interpolation, the RBF method discussed above, and the Inverse 

Distance Weighted (IDW) method. Resource models were 

created using ESRIs ArcGIS GeoStatistical Analyst extension. 

IDW interpolation explicitly implements the assumption that 

things that are close to one another are more alike than those 

that are farther apart. To predict a value for any unmeasured 

location, IDW will use the measured values surrounding that 

location. Those measured values closest to the prediction location will have more influence on the predicted value than those 

farther away. Thus, IDW assumes that each measured point 

has a local influence that diminishes with distance. 

The RBF method in GeoStatistical Analyst (GA) is an 

exact interpolator that will honor all data points and not introduce any error at those locations unless a smoothing function 

is used. If a smoothing function is used, the RBF can also 

extrapolate values above or below the actual values outside the 

data-point locations. The final resource models were created 

with the RBF method using a sampling method containing 

eight moving window sectors with eight neighbors in each 

sector. No smoothing function was used. After numerous iterations, we found that the RBF method using these parameters 

yields surfaces that we believe best fit what was happening 

geologically. Both the RBF method and IDW method gave 

fairly similar results in areas with large numbers of control 

points, but the RBF method seemed to generate more reasonable results in marginal areas with little control. 

Although the RBF method does not generate as complete an error estimate as kriging, it does give the difference 

between the predicted and measured value for each control 

point, and it does give an overall error for an entire map. To 

obtain the difference between the predicted value and the measured value the RBF method predicts a value at a given control 

point from the eight nearest control points without knowing 

the actual value measured at that control point. That predicted 

value is then compared with the measured value, and the difference between the two is calculated. 

The barrels-per-township maps were generated by first 

intersecting the Piceance township polygon file with the 

outcrop polygon files. The resultant files included only those 

polygonal areas of each township that contained the desired 

zones to be assessed—one file for the Mahogany and those 

zones above the Mahogany, one file for B-groove and R-6, and 

one file for all zones below the R-6 (fig. 7). Using ESRIs Spatial Analyst’s Zonal Statistics function, we were able to quantify each township in each barrels-per-acre resource model (1 

acre = 63.615 meter cell size) by using each “clipped” township polygon (the result of intersecting the township polygon 

with the outcrop polygon) as the zone to quantify. In short, as 

the cell size in the model is one acre, the function sum totals 

all of the cells contained by each polygon to be assessed in the 

zone dataset. The resultant summary table contains a sum total 

of barrels for each township, as well as several other statistics. 

The maps were then generated by joining the summary table 

to each zone polygon file. For a more complete explanation 

Table 6. Number of control points used to assess each oil shale zone in this 

assessment and the previous assessment by Pitman and Johnson (1978), 

Pitman (1979), and Pitman and others (1989). Oil shale zones from Cashion 

and Donnell (1972).

Oil shale zone Number of control points

This assessment Previous assessment

Mahogany zone 392 131

R-6 zone 235 67

L-5 zone 186 105

R-5 zone 176 107

L-4 zone 173 101

R-4 zone 171 104

L-3 zone 171 92

R-3 zone 158 93

L-2 zone 155 85

R-2 zone 148 85

L-1 zone 122 63

R-1 zone 91 50

Total 2178 1083
Detailed Description and Assessment Results of Oil Shale Zones 53

of this procedure see Mercier and others (chapter 3, this 

CD-ROM).

Here we compare the results of the RBF method and 

kriging using the same data sets that were used in Pitman and 

others (1989). Figures 39 and 40 are maps showing barrels per 

acre for the R-5 and L-5 zones generated using the RBF and 

using only the data shown on the kriged R-5 assessment map 

of Pitman and others (1989). The R-5 and L-5 zones were used 

for this comparison because they had the most data points of 

all the oil shale zones that were kriged (table 6). The Mahogany zone had more data points, but kriging was not used to 

assess it. Tables 7 and 8 list the barrels per acre for each township using the RBF method and kriging. A comparison was 

also made between only the best townships, those where kriging in the assessment of Pitman and others (1989) estimated an 

error of 20 percent or less at the 95 percent confidence level. 

For the R-5 zone, the overall results using RBF were 5.15 

percent higher than the kriged results and only 0.13 percent 

higher when only the best townships were compared (table 8). 

For the L-5 zone, our overall results were 6.28 percent higher 

than kriged results and 7.50 percent higher for the best townships (table 9). Townships where kriging gave greater results 

are shown in red and those where the RBF method gave 

greater results are shown in blue on figures 39 and 40. For the 

R-5 zone, kriging gave higher results throughout much of the 

central part of the basin (fig. 39), whereas for the L-5 zone 

only a few scattered townships gave higher results using kriging (fig. 40). Some of the discrepancy in the marginal areas is 

because we used a new outcrop line that encompasses a larger 

area than the previous assessment. 

Detailed Description and Assessment 

Results of Oil Shale Zones

This study presents an in-place assessment of the Green 

River Formation in the Piceance Basin and, for comparative 

purposes, this assessment uses the same two sets of maps 

used in the previous in-place assessment by Pitman and others 

(1989): 1) maps showing variations in oil yield measured in 

GPT, and 2) maps showing variations in BPA. A table was 

compiled that lists the in-place resource for each oil shale 

zone in each township in the basin similar to the one compiled 

by Pitman and others (1989). This allows us to compare our 

results with Pitman and others (1989) who estimated total oil 

in each township using both hand contouring and kriging. 

The extent of each oil shale zone around the margins 

of the basin had to be estimated in order to define the limits 

of the assessed area. With the exception of the Mahogany 

zone, the oil shale zones have been incompletely mapped 

in outcrop around the margins of the basin because many 

of them have graded into largely marginal lacustrine rock 

and cannot be identified. Pitman and others (1989) did not 

specify what outcrop line was used to define the limits of 

their assessed areas. Only the outcrop of the Mahogany zone 

is shown on their assessment maps, and it is assumed that 

that line was used to define the limits of all their assessment 

areas. Two outcrop lines are shown in our assessment maps: 

the top of the Mahogany ledge, and the base of the Parachute 

Creek Member of the Green River Formation. The base of 

the Parachute Creek Member, as mapped around the basin 

margins, is variably placed at the base of the R-2 zone to the 

base of the R-4 zone, and the base of the Mahogany zone 

(see for example, Johnson and others, 1988). The contacts are 

from Hail and Smith (1994, 1997). For zones R-6 and above, 

we used the top of the Mahogany ledge as the limit of the 

assessed area, and for zones below the R-6, we used the base 

of the Parachute Creek Member. Using these two outcrop lines 

results in slightly underestimating the area underlain by the 

R-6 zone and higher, and slightly overestimating the areas of 

the zones below R-6.

As noted above, nahcolite that was present in either disseminated or aggregate form in a core was typically assayed 

along with the oil shale thus diluting the overall oil yield for 

the sample. This resulted in a lower gallons per ton measured 

for the assayed interval than if the nahcolite had been removed 

prior to assaying. However, a bed of almost pure halite or 

nahcolite or both that was encountered during coring in the 

saline depocenter was typically not assayed and shows up as 

a zero oil-yield value on the oil-yield histograms. These beds 

were not included when calculating the average GPT for the 

enclosing oil shale zone, and thus the average for the oil shale 

zone was not reduced by the presence of nearly pure nahcolite 

and (or) halite beds. 

Oil-yield trends are poorly constrained in many of the 

marginal areas of the basin where core holes are sparse, and 

resource maps generated early in this project appeared to overestimate or underestimate oil yields in these areas based on our 

knowledge of the geology. To better constrain oil-yield trends 

in these areas we estimated oil yields in 14 of the 20 surface 

sections that were used to help construct the isopach maps of 

the oil shale zones (table 9). Without these surface sections, 

the RBF method extrapolated to negative values in many of 

these marginal areas. Many of the oil shale zones have graded 

into marginal lacustrine lithologies with little or no kerogen 

content in these surface sections. We could not assign zero values, however because the interpolation program required that 

these points have some minimal value. Oil yield was placed 

at 0.1 GPT and barrels per acre was placed at 1,000 for these 

sections (table 4). 

We did not attempt to assess the amount of oil shale in 

the basin that adheres to a defined set of criteria such as the 

total amount of oil in intervals averaging at least 25 ft thick 

and 25 GPT, as some earlier assessments had done. This is, in 

part, because the FORTRAN program used for these calculations needs to be rewritten in modern computer code, but also 

because we need to seriously rethink the whole process used 
54 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

387

314

309

350

539

586

482

318

133

135

172

71

57

46

36

132

143

206

169 175 193 146

160

195 234

225 191

241

240

203 271

238

291

278

157

239

338 271 212

228

325 320

310 316

411

405

319

467

474

460

541

289

371 304

282

249 275 394

349 312 376

336 399

241

179

324

506

450 521

491

535 516

582

552

568

535

527

465

505

505

486

522

487

485

471

460

343

174

180 159

371 469

457

337

247 227

221 180 262 175

154

478

533

295

418 471 212

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO 0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed

Base of Parachute Creek Member

Core hole—Barrels per acre, in

 thousands of barrels

405

R–5 zone—Barrels per acre

< 100,000

101,000–

 200,000

201,000–

 300,000

301,000–

 400,000

401,000–

 500,000

501,000–

 600,000

RBF gave 

 higher results

Kriging gave

 higher results

Figure 39. Barrels per acre map for the R-5 zone plotted using the Radial Basis Function Method (RBF) using the 

same core holes and the same barrels per acre values (in black) used by Pitman and others (1989).
Detailed Description and Assessment Results of Oil Shale Zones 55

EXPLANATION

Top of Mahogany Bed

Base of Parachute Creek Member

Core hole—Barrels per acre, in

 thousands of barrels

405

L–5 zone—Barrels per acre

< 25,000

25,001–

 50,000

50,001–

 75,000

75,001–

 100,000

100,001–

 125,000

125,001

 150,000

150,001

 175,000

175,001

 200,000

RBF gave 

 higher results

Kriging gave 

 higher results

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W

T

2

N

67

21

14

11

31

14

33

18 28

47

49

32

64

60 79 73 51

48

57 87

70 53

61

62

89 102

89

110

93

77 106 96 112

109

112

109 105

104 103

128

127

91

107

119

103

138

75

86 65

71

68 79 87

86 81 80 79 85

85

79

75

120

89 104 138 134 157

188

177

127

123

106

172

91

124

126

122

121

109

144

118 61

69

35

135

114 164 169

104

93 81

75 66

85 40

44

110

132

104

55

71

137 137

140 65

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO 0 5 10 2.5 KILOMETERS

Figure 40. Barrels per acre map for the L-5 zone plotted using the Radial Basis Function Method (RBF) using the 

same core holes and the same barrels per acre values (in black) used by Pitman and others (1989).
56 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 7. Comparing total barrels per township for the R-5 zone using the Radial Basis Function Method (RBF) here with the 

results using kriging by Pitman and others (1989). Townships highlighted in yellow are those in which kriging by Pitman and 

others (1989) indicated an error of 20 percent or less at the 95 percent confidence level.

Township, Range Kriging (Pitman and others, 

1989) R-5 95 percent confidence RBF using Pitman's data Percent diff. RBF vs kriging

1N 96W 1,419,119,000 ±22 1,794,120,000 26.42

1N 97W 5,921,871,000 ±5 6,109,330,000 3.17

1N 98W 8,882,764,000 ±14 9,292,230,000 4.61

1N 99W 5,785,083,000 ±23 5,966,310,000 3.13

1N 100W 220,454,000 ±82 965,061,000 337.76

2N 97W 187,961,000 ±85 432,532,000 130.12

2N 98W 218,723,000 ±1298 3,576,110,000 1534.99

2N 99W –-

2N 100W

1S 95W –-

1S 96W 6,708,348,000 ±31 7,329,560,000 9.26

1S 97W 11,746,252,000 ±5 11,674,400,000 -0.61

1S 98W 12,581,545,000 ±4 12,612,100,000 0.24

1S 99W 9,627,029,000 ±7 9,560,800,000 -0.69

1S 100W 2,743,627,000 ±33 3,481,780,000 26.90

2S 94W

2S 95W 3,875,865,000 ±88 3,922,430,000 1.20

2S 96W 7,483,801,000 ±17 7,332,360,000 -2.02

2S 97W 10,877,714,000 ±9 10,807,300,000 -0.65

2S 98W 10,094,247,000 ±8 10,058,000,000 -0.36

2S 99W 6,651,097,000 ±15 6,695,290,000 0.66

2S 100W 1,676,860,000 ±57 2,031,350,000 21.14

3S 94W –-

3S 95W 3,085,710,000 ±79 3,643,140,000 18.06

3S 96W 5,834,195,000 ±13 5,907,430,000 1.26

3S 97W 7,077,905,000 ±8 6,944,300,000 -1.89

3S 98W 5,882,000,000 ±12 5,855,370,000 -0.45

3S 99W 4,045,525,000 ±49 4,003,880,000 -1.03

3S 100W 150,523,000 ±216 472,698,000 214.04

4S 94W 1,406,316,000 ±153 1,090,650,000 -22.45

4S 95W 3,709,025,000 ±60 3,831,660,000 3.31

4S 96W 4,733,460,000 ±35 4,686,960,000 -0.98

4S 97W 4,840,702,000 ±16 4,831,700,000 -0.19

4S 98W 3,626,276,000 ±31 3,760,870,000 3.71

4S 99W 2,211,771,000 ±119 2,666,560,000 20.56

4S 100W –-

4S 101W –-

5S 94W 1,659,768,000 ±175 1,679,310,000 1.18

5S 95W 2,635,176,000 ±33 2,714,700,000 3.02

5S 96W 3,099,056,000 ±53 3,114,720,000 0.51

5S 97W 3,375,428,000 ±35 3,360,190,000 -0.45
Detailed Description and Assessment Results of Oil Shale Zones 57

Table 7. Comparing total barrels per township for the R-5 zone using the Radial Basis Function Method (RBF) here with the 

results using kriging by Pitman and others (1989). Townships highlighted in yellow are those in which kriging by Pitman and 

others (1989) indicated an error of 20 percent or less at the 95 percent confidence level.—Continued

Township, Range Kriging (Pitman and others, 1989) 

R-5 95 percent confidence RBF using Pitman's data Percent diff. RBF vs kriging

5S 98W 1,760,651,000 ±198 2,143,860,000 21.77

5S 99W –-

5S 100W –-

5S 101W –-

6S 94W –-

6S 95W 561,821,000 ±199 633,172,000 12.70

6S 96W 838,119,000 ±142 845,871,000 0.92

6S 97W –-

6S 98W 856,785,000 ±114 913,930,000 6.67

Total: 168,092,572,000 176,742,034,000

Percent difference using RBF. 5.15

Sum best townships kriged: 100,850,025,000

Sum best townships RBF: 100,985,320,000

Percent difference using RBF: 0.13
58 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 8. Comparing total barrels per township for the L-5 zone using the Radial Basis Function Method (RBF) here with the results 

using kriging by Pitman and others (1989). Townships highlighted in yellow are those in which kriging by Pitman and others (1989) 

indicated an error of 20 percent or less at the 95 percent confidence level.

Township, 

Range

Kriging, Pitman 

and others (1989) L-5 95 percent confidence RBF using Pitman's data

Percent 

diff RBF 

vs Kriging

1N 96W 481,007,000 ±36 597,498,000 24.22

1N 97W 1,742,788,000 ±10 1,947,430,000 11.74

1N 98W 2,191,041,000 ±16 2,721,310,000 24.20

1N 99W 2,074,246,000 ±33 1,879,500,000 -9.39

1N 100W 120,010,000 ±54 377,498,000 214.56

2N 97W 59,849,000 ±54 91,961,300 53.66

2N 98W –-

2N 99W –-

2N 100W

1S 95W –-

1S 96W 2,120,861,000 ±29 2,601,150,000 22.65

1S 97W 2,949,845,000 ±10 3,145,710,000 6.64

1S 98W 2,866,351,000 ±8 3,371,510,000 17.62

1S 99W 2,293,272,000 ±13 2,397,060,000 4.53

1S 100W 1,143,711,000 ±38 1,399,940,000 22.40

2S 94W

2S 95W 2,533,654,000 ±53 2,038,080,000 -19.56

2S 96W 2,605,432,000 ±18 2,785,940,000 6.93

2S 97W 2,850,288,000 ±9 2,983,640,000 4.68

2S 98W 2,218,631,000 ±10 2,336,020,000 5.29

2S 99W 1,663,017,000 ±24 1,654,860,000 -0.49

2S 100W 745,547,000 ±71 862,447,000 15.68

3S 94W 57,906,000 ±384 248,785,000 329.64

3S 95W 1,771,464,000 ±66 1,750,070,000 -1.21

3S 96W 2,157,516,000 ±17 2,227,300,000 3.23

3S 97W 2,181,891,000 ±10 2,353,650,000 7.87

3S 98W 1,630,335,000 ±17 1,544,520,000 -5.26

3S 99W 1,072,910,000 ±50 1,105,750,000 3.06

3S 100W 81,431,000 ±115 167,073,000 105.17

4S 94W 604,929,000 ±115 415,039,000 -31.39

4S 95W 1,504,636,000 ±25 1,525,650,000 1.40

4S 96W 1,863,716,000 ±18 1,818,460,000 -2.43

4S 97W 1,693,348,000 ±20 1,712,340,000 1.12

4S 98W 1,064,422,000 ±47 1,095,160,000 2.89

4S 99W 565,643,000 ±235 712,652,000 25.99

4S 100W –-

4S 101W –-

5S 94W 462,398,000 ±131 475,563,000 2.85
Detailed Description and Assessment Results of Oil Shale Zones 59

Table 8. Table comparing total barrels per township for the L-5 zone using the Radial Basis Function Method (RBF) here with the 

results using kriging by Pitman and others (1989). Townships highlighted in yellow are those in which kriging by Pitman and others 

(1989) indicated an error of 20 percent or less at the 95 percent confidence level.—Continued

Township, 

Range

Kriging, Pitman 

and others (1989) L-5

95 percent confidenceRBF using 

Pitman's data

Percent 

diff RBF 

vs Kriging

5S 95W 979,482,000 ±40 988,904,000 0.96

5S 96W 1,133,047,000 ±30 1,220,350,000 7.71

5S 97W 1,134,248,000 ±46 1,225,900,000 8.08

5S 98W 478,075,000 ±206 635,610,000 32.95

5S 99W –-

5S 100W –-

5S 101W –-

6S 94W –-

6S 95W 185,888,000 ±259 223,354,000 20.16

6S 96W 270,021,000 ±74 302,842,000 12.15

6S 97W 709,285,000 ±74 617,220,000 -12.98

6S 98W 270,399,000 ±70 272,452,000 0.76

Total: 52,532,540,000 55,830,198,300

Percent difference using RBF:

Sum best townships Kriged:

Sum best townships RBF:

Percent difference using RBF:

6.28

27,086,938,000

29,117,590,000

7.50
Table 9. Estimating thicknesses, gallons per ton (GPT), and barrels per acre (BPA) for surface sections. Data was used to control isopach maps and GPT maps in basin margin areas. Name Reference Notes Location Latitude Longitude B thicknesPhiladelphia Creek Johnson and others (1988) 32-1S-100W 39°55'18" 108°38'03" 18 Little Burma Road Johnson and others (1988) 18-4S-100W 39°42'04" 108°39'27" 10 Spring Creek Unpublished sur. Sec. 11-2N-99W 40°09'48" 108°27'48" 81 Yellow Creek Unpublished sur. Sec. 15-2N-98W 40°08'57" 108°22'39" 98 Deep Channel Creek Unpublished sur. Sec. Assumes top Ss is top R-0 36-4N-96W 40°16'37" 108°07'04" Anvil Points Unpublished sur. Sec. Assumes top red is top R-0 18-6S-94W 39°31'4" 107°55'29" Rio Blanco Unpublished sur. Sec. 5-4S-94W 39°44'15" 107°57'24" Horsethief Mtn. Johnson and May (1978) Assumes top Ss is top R-0 18-9S-96W 39°16'37" 108°08'34" Kissinger Gulch Pipiringos and Johnson (1976) Assumes "C" bed is top R-0 14-1N-96W 40°03'31" 108°08'14" Sec. D Wagon Track Ridge Johnson and May (1978) Top R-0 is top big Ss below Km tuff 21-8S-98W 39°20'29" 108°19'54" Sec. C Wagon Track Ridge Johnson and May (1978) Top R-0 is top big Ss below Km tuff 32-8S-99W 39°19' 108°26'52" Sec B Left Hand Draw Johnson and May (1978) Top R-0 tied to Km, base 1st algal below Km 23-8S-100W 39°20'27" 108°31'13" Sec A Middle Dry Fork Johnson and May (1978) Top R-0 tied to Km, base 1st algal below Km 7-8S-100W 39°22'52" 108°35'37" Munger Creek Johnson and others (1988) 12-7S-102W 39°27'46" 108°43'10" Baxter Pass Johnson and others (1988) Base L-1 is base 1st good oil shale 24-5S-103W 39°36'20" 108°53'59" Evacuation Creek Johnson and others (1988) Base L-1 is base 1st good oil shale 1-12S-25 E 39°47'59" 109°04'28" Hell's Hole Johnson and others (1988) Base L-1 is base 1st good oil shale 31-1S-103 39°54'52" 108°59'35" Powell Park Pipiringos and Johnson (1975) R-0, L-0 all Ss with some red beds 28-1N-95W 40°01'50" 108°03'52" Lower Piceance Creek Pipiringos and Johnson (1976) Top "C" is top L-0 11-1N-97W 40°04'10" 108°14'33" Douglas Pass Johnson and others (1988) 25-5S-102 39°35'36" 108°47'05"
Table 9. Estimating thicknesses, gallons per ton (GPT), and barrels per acre (BPA) for surface sections. Data was used to control isopach maps and basin margin areas.—Continued

Name R6 thickness L5 thickness R-5 thickness L-4 thickness R-4 thickness L-3 thickness R-3 thickness L-2 thicknes

Philadelphia Creek 98 100 100 50 50 27 54 27 

Little Burma Road 113 59 60 30 30 13 25 13 Spring Creek 292 192 145

Yellow Creek 537 256

Deep Channel CreekAnvil PointsRio BlancoHorsethief Mtn.Kissinger GulchSec. D Wagon Track RidgeSec. C Wagon Track RidgeSec B Left Hand DrawSec A Middle Dry ForkMunger CreekBaxter PassEvacuation CreekHell's HolePowell ParkLower Piceance CreekDouglas Pass
Table 9. Estimating thicknesses, gallons per ton (GPT), and barrels per acre (BPA) for surface sections. Data was used to control isopach maps and margin areas.—Continued Name L-1 thickness R-1 thickness L-0 thickness R-0 thickness L-5 GPT L-5 BPA R-5 GPT R-5 BPA L-4 GPT L-4 BPhiladelphia Creek 75 288 25 195 Little Burma Road 150 392 15 75 Spring Creek Yellow Creek Deep Channel Creek 463 Anvil Points 585 Rio Blanco 390 Horsethief Mtn. 20 260 0.1 500 0.1 500 0.1 50

Kissinger Gulch 20 500 Sec. D Wagon Track Ridge 20 245 Sec. C Wagon Track Ridge 20 232 Sec B Left Hand Draw 20 162 Sec A Middle Dry Fork 135 255 20 166 0.1 50Munger Creek 248 30 142 Baxter Pass 120 314 20 98 Evacuation Creek 175 403 20 72 Hell's Hole 177 324 20 60 Powell Park Lower Piceance Creek Douglas Pass
Table 9. Estimating thicknesses, gallons per ton (GPT), and barrels per acre (BPA) for surface sections. Data was used to control isopach maps and margin areas.—Continued

Name L-3 GPT L-3 BPA R-3 GPT R-3 BPA L-2 GPT L-2 BPA R-2 GPT R-2 BPA L-1 GPT L-1 BPA R-1 GPT R-1 BPA 

Philadelphia CreekLittle Burma Road 0.1 500 0.1 500 0.1 500 0.1 500

Spring Creek Yellow CreekDeep Channel Creek 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500 

Anvil Points 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500 

Rio Blanco 0.1 500 0.1 500 

Horsethief Mtn. 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500 

Kissinger GulchSec. D Wagon Track Ridge 0.1 500 0.1

Sec. C Wagon Track Ridge 0.1 500 0.1

Sec B Left Hand Draw 0.1 500 0.1

Sec A Middle Dry Fork 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500 0.1

Munger CreekBaxter Pass 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500 0.1

Evacuation Creek 0.1 500 0.1 500 0.1 500 0.1 500

Hell's Hole 0.1 500 0.1 500 0.1 500 0.1 500

Powell Park 0.1 500 0.1 500 

Lower Piceance Creek Douglas Pass 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500 0.1 500
64 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

for these calculations because of the many issues raised here 

with missing core intervals. As previously discussed, missing intervals had to be assigned values in order to make the 

FORTRAN program function. The program uses a special 

algorithm to identify the longest sequence in an assayed core 

or section that maintained a specified average yield of oil in 

GPT and also has restraints that exclude intervals of low-grade 

shale that were too thick. Unless the individual is extremely 

skillful at assigning values to missing core, it would seem that 

the algorithm would not calculate very meaningful results. 

R-0 Zone

The R-0 and L-0 zones comprise the first stage of 

Lake Uinta as defined by Johnson (1985) and have not been 

assessed prior to this assessment. The R-0 oil shale zone is the 

first oil shale zone deposited after the Long Point transgression when two much smaller freshwater lakes in the Piceance 

and Uinta Basins expanded and connected across the Douglas 

Creek arch to form one large lake, Lake Uinta (figs. 3 and 4) 

(Johnson, 1985). The base of the R-0 zone is the base of the 

Long Point bed, the basal transgressive bed of the Long Point 

transgression, which is marked in outcrop around much of 

the basin margins by a mollusk-rich bed overlying the variegated mudstones of the fluvial Wasatch Formation (Johnson, 

1989). The base of the R-0 zone can be identified throughout 

much of the deeper parts of the basin as a distinctive resistivity “kick” on electric logs (see for example, Johnson, 1989). 

Along the northwest margin of the basin, the R-0 zone overlies 

freshwater lacustrine rocks of the Cow Ridge Member of the 

Green River Formation, and in this area, the base of the R-0 

zone is marked by a change from mollusk-bearing freshwater 

lacustrine rocks below to low-grade oil shale above (Johnson, 

1985; Johnson and others, 1988). The R-0 zone grades into 

sandstones towards the eastern margin of the basin.

The upper part of the R-0 zone is marked in the central 

part of the basin by a distinctive increase in resistivity on 

electric logs known informally as the orange marker, named 

for the color of pen used to mark it on geophysical logs 

(Chancellor and others, 1974; Ziemba, 1974). The orange 

marker, which comprises about the upper 30 ft of the R-0 zone 

(fig. 7), is caused by a slight increase in carbonate in the illitic 

sediments. The orange marker is equivalent to the carbonate marker in the Uinta Basin part of Lake Uinta, which also 

represents a temporary increase in carbonate precipitation 

(Johnson, 1989). 

This slight increase in carbonate content is not conspicuous in outcrop, and the top of the R-0 zone is difficult 

to identify in marginal lacustrine rocks exposed around the 

margins of the basin. However, the top of the overlying L-0 

zone or base of the R-1 zone is thought to occur at the base 

of the first illitic moderate to rich oil shale bed of the R-1 oil 

shale zone. Table 4 lists approximate thicknesses for the R-0 

and overlying L-0 zones from detailed measured sections 

and surface locations published by Johnson and May (1978), 

Johnson and others (1988), and Johnson (unpub. surface sections). In addition one thickness for the R-0 zone, the Powell 

Park locality (table 4) was estimated from surface mapping 

by Pipiringos and Johnson (1976). The contact between the 

R-0 and L-0 zones cannot be distinguished in most of these 

surface locations, and the thickness of the R-0 zone is obtained 

by assuming that the L-0 zone is 20 ft thick, the approximate 

thickness in nearby drill holes.

The R-0 zone is thinnest in the westernmost part of the 

basin, along the Douglas Creek arch (fig. 2) where it is about 

75 ft thick (fig. 41). It thickens and becomes sandy to the 

southeast, east, and northeast, reaching a maximum thickness of about 585 ft thick at Anvil Points, just west of Rifle, 

Colo. (fig. 2) in the southeast part of the basin where it is 

predominantly fluvial and consists of variegated mudstone 

and lenticular sandstone. The R-0 zone is typically included in 

the Wasatch Formation in areas along the eastern margins of 

the basin where it is predominantly fluvial (see for example, 

O’Sullivan, 1986), but its equivalent can generally still be 

recognized because it includes some lacustrine lithologies 

including ostracodal and oolitic limestones (Johnson, unpub. 

measured section at Anvil Points). The R-0 zone is included 

in the Anvil Points Member of the Green River Formation 

in the eastern part of the basin where it is very sandy but not 

predominantly fluvial. 

The R-0 zone was assayed in just 34 core holes in the 

Piceance Basin. Using only these core holes, oil-yield values 

are remarkably uniform, from 10 to 20 GPT, throughout 

a broad area of the central part of the basin with yields 

decreasing in a regular fashion towards the basin margins 

(fig. 42). Oil yields are very low along the east margins of 

the basin where the zone is predominantly sandstone, and 

oil-yield estimates in surface sections there were set at the 

minimum value (table 8). There is no oil-yield data for the 

R-0 zone for much of the south and southwestern parts of 

the basin, but in these areas, the zone is predominantly shale 

that probably contains some kerogen. No attempt to estimate 

kerogen content in the surface sections was made here (table 

4). Barrels per acre in the central part of the basin varies from 

150,000 to 250,000 and decreased in a regular fashion outward 

(fig. 43). Maximum in-place oil is in T. 1 S., R. 98 W. with 

over 4.8 billion barrels (fig. 44). Estimated total in-place oil in 

the R-0 zone is just over 83.4 billion barrels (table 10). 

L-0 Zone

The L-0 zone is a thin lean zone, with a thickness of 

from 13 to 35 ft throughout most of the basin, but it attains a 

thickness of 77 ft in one anomalous well in sec. 26, T. 3 S., R. 

99 W. (fig. 45). The L-0 zone thickens in an irregular fashion 

towards the east margin of the basin, where it grades into 

sandstone. Maximum recorded thickness in the eastern part of 

the basin is 90 ft in sec. 28, T. 3 S., R. 95 W. In outcrop, along 

the eastern margin of the basin, the L-0 zone occurs within an 

overall sandy interval and cannot be recognized. 
Detailed Description and Assessment Results of Oil Shale Zones 65

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

142

166

162

232

245

500

260

390

585

75

143.3

139 152

137

177

183 163 155

153

163

158

160

166 128

133

110

123

131

148

122

125

134 128

162

125

165

147

148

155

165163 165

163

173

138

142 145

148

162

168187

142

265

172

172 172 169

169

160

159

163 165 165

170 153

155

143

146 157

150

135 135 135 132

138136 140

139142

166 187 190

136 133

168

152

172 182 245

240

160 153

184 195 232

275

214 243

235

290

285

138 166

172

165 128

132

215 215 153

184 182 435

179

250

168

179

138

79

131

136

144

171

147.9

140

155

163

160.7

153

208

249.9

136.6

139.6

152

159

277.3

172

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

110

R–0 interval—Thickness in feet

101–200

201–300

301–400

401–500

501–600

< 100

Figure 41. Isopach map of the R-0 zone using both core hole and rotary hole data. Radial Basis Function Method 

(RBF) method was used for contouring. Contour interval in feet is variable.
66 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

The L-0 zone was assessed in 74 core holes. Oil yields 

vary from 5.0 to 14.3 GPT in the central part of the basin, in 

approximately the same area of high oil yields for the underlying zone, and decrease in a regular fashion towards the basin 

margins (fig. 46). Trends towards the east margin of the basin 

are controlled by surface sections in which oil yields were set 

at the minimum value of 0.1 GPT—the extrapolation program 

required some value above zero (table 8). Maximum in-place 

resources in the L-0 zone varies from 7,500 to 32,000 BPA in 

the central part of the basin and decrease outwards (fig. 47). 

Maximum in-place oil in a township is just over one-half 

billion barrels in T. 2 S., R. 97 W. (fig. 48). Total in-place oil 

in the R-0 zone is estimated to be 8.3 billion barrels (table 11). 

R-1 Zone

The R-1 zone consists of illite-rich oil shale similar to 

the underlying R-0 zone but much richer. It varies in thickness 

from about 100 to 125 ft in the central part of the basin to over 

350 ft along much of the eastern, southeastern, and southwestern margins (fig. 49). Unlike the underlying R-0 and L-0 

zones, which thicken mainly towards the east, the R-1 zone 

thickens in all directions away from the central part of the 

basin (fig. 49). Of note, the interval thickens markedly towards 

the southwest, with much of the thickening due to the insertion 

of discrete, southwestward thickening, kerogen-poor, mudstone and sandstone wedges into the oil shale interval (Johnson, 1985; 1989; Johnson and others, 1988; Pitman and others, 

1989). The wedges appear to be predominantly lacustrine, 

consisting of non-laminated to laminated carbonate-rich mudstone in the center of the basin, grading to the southwest first 

into sandstone and mudstone that is, in part, highly contorted, 

and then into carbonate-rich mudstone and ripple laminated 

sandstone with stromatolitic, ostracodal, and oolitic limestone 

(Johnson, 1985; Johnson and others, 1988). One wedge thickens from about 8 ft in the center of the basin to about 230 ft 

along the southwest margin (Johnson, 1985, p. 264), suggesting that it was deposited comparatively rapidly. 

The R-1 zone was assessed in 91 core holes in the basin. 

Oil-yield trends towards the east and south were established 

by assuming oil-yield values of 0.1 GPT in surface sections 

there (table 8), as the R-1 zone has graded into marginal lacustrine, kerogen-poor rocks in these areas. Estimated oil yield 

varies from about 20–29 GPT in the central part of the basin 

with oil yields decreasing markedly towards the basin margins 

(fig. 50). 

Estimated in-place oil varies from 300,000 to 435,000 

BPA through a broad crescent-shaped depocenter (fig. 51) 

that is somewhat south of the depocenter for the underlying 

L-0 zones. Oil yields are lower in this depocenter then farther 

to the north, but this is due largely to the insertion of clastic 

wedges into the R-1 interval discussed earlier. Maximum 

in-place oil occurs in T. 4 S., R. 97 W. in the middle of 

the depocenter, with an estimated 9.4 billion barrels of oil 

(fig. 52). Total in-place oil in the R-1 zone is estimated at 

195.4 billion barrels (table 12). 

Pitman and others (1989) estimated 115.4 billion barrels 

of oil in place in the R-1 zone using a manual “extrapolated” 

method and 137.0 billion barrels using kriging (table 12), 

but they assess fewer townships than were assessed here. 

Their kriged number is larger than their extrapolated number 

because they assessed two more townships using kriging than 

they did manually (table 12). If only the townships that were 

assessed by Pitman and others (1989) are compared to our 

results in those townships using only core holes, our results 

are 4.52 percent higher than their “extrapolated” results and 

7.65 percent lower than their kriged results. 

Considerably more control was available for this assessment than for Pitman and others (1989), and comparison was 

only made of townships where sufficient control was available 

at the time they made their assessment. When only townships 

where the kriged results from Pitman and others (1989) estimated an error of 20 percent or less at the 95 percent confidence level are compared, our results are 15.7 percent higher 

than their extrapolated results and 8.89 percent higher than 

their kriged results. The results of Pitman and others (1989) 

for the R-1 zone are in question, however. Their results list 

unreasonably high assessment numbers for T. 1 N., R. 100 W., 

and T. 2 N., R. 97 and 98 W. (table 12, shown in red). Their 

assessment numbers for these townships are far higher than 

geologically reasonable for these areas, and their small estimated errors for their kriged results are inconsistent with the 

very limited control available at the time of their assessment in 

these townships. These three townships were not included in 

the comparison of best townships presented above.

L-1 Zone

The L-1 zone is also illite-rich, similar to the underlying 

R-1 zone and is, in essence, the highest of the southwestthickening clastic wedges that entered Lake Uinta during the 

illitic phase of the lake. The L-1 zone is similar in lithology to 

the clastic wedges in the underlying R-1 zone. One hundred 

twenty two holes were used to assess the L-1 zone as compared to 63 in the previous assessment (Pitman and others, 

1989). The zone varies from about 10 to 45 ft thick throughout 

the north-central part of the basin. It thickens to the east to 

a maximum of about 100 ft and to the southwest to a maximum recorded thickness of 168 ft in sec. 13, T. 6 S., R. 98 W. 

(fig. 53). 

Maximum oil yields are from about 5 to 25 GPT in the 

north-central part of the basin (fig. 54). The BPA map (fig. 55) 

shows a depocenter with from 20,000 to 80,000 barrels per 

acre in the south-central part of the basin, the same area as the 

depocenter during the previous R-1 zone, but several much 

smaller areas with high in-place oil occur scattered throughout the northern part of the basin. Maximum in-place oil in a 

township is 876 million barrels in T. 3 S., R. 97 W. (fig. 56). 
Detailed Description and Assessment Results of Oil Shale Zones 67

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

10 Core hole—Average oil yield in

R–0 interval—Average oil yield in gallons per ton

< 5

5.1–10

10.1–15

15.1–20

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

0.1

0.1

0.1

14.3

9.6

10.5

10.3

7.4

9.1

11.4

14.1

15.5

6.9

9.3

7

12

10.7

14

13.1

13.9

12.4

11.5

12.1

15.2

7.6

14.7

13.8

13.6

12.9

6.3

15.7

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 42. Isoresource map of the R-0 zone showing the oil yield in gallons per ton (GPT). The Radial Basis 

Function Method (RBF) was used for contouring.
68 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

R–0 zone—In barrels per acre

< 50,000

50,001–

 100,000

100,001–

 150,000

150,001–

 200,000

> 200,001–

 250,000

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

1

1

1

162

125

137

140

79

99

136

165

160

45

100

80

139

145

164

143

171

162

149

149

247

159

158

153

164

165

133

210

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 43. Isoresource map of the R-0 zone showing oil yields in barrels per acre (BPA). The Radial Basis 

Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 69

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

36,740,300

601,009

0

0

0

0

0

0

16,166,700

167,095,008

79,719,000

240,432,992 57,346,500

982,979

50,860,200

197,836,992

331,716,000

629,142,976

1,056,049,984

345,852,992

184,504,992 1,726,930

127,525,000 324,220,992

1,193,319,936 1,558,550,016

2,150,749,952

1,523,760,000 783,686,976

143,810,000

57,914,000

666,574,016

2,268,900,096 2,739,030,016 3,270,710,016 2,449,070,080 1,190,950,016

91,127,904

4,833,770

731,129,984

2,960,790,016 3,696,499,968 3,548,699,904 2,936,600,064 1,438,659,968 78,645,504 374,624,000

3,508,290,048 4,323,480,064 3,570,449,920 2,467,069,952 1,286,649,984 15,906,300 1,353,830,016

1,737,699,968

1,577,619,968

153,724,992

10,656,100

3,977,929,984 4,807,900,160 2,895,849,984 1,306,029,952

458,312,000

1,964,359,936

2,961,750,016 3,437,060,096 1,309,350,016

90,712,200

493,067,008

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

R–0 zone shale oil, total in-place resource—In millions of barrels

< 250

251–780

781–2,000

2,001–3,000

3,001–4,800

Top of Mahogany zone

Base of Parachute Creek Member

R–0 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 44. Isoresource map of the R-0 zone showing total number of barrels of oil in each township. 
70 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Township and Range SUM R-0 zone (BPA)

1N 96W 90,712,200

1N 97W 1,309,350,000

1N 98W 3,437,060,000

1N 99W 2,961,750,000

1N 100W 493,067,000

2N 97W 153,725,000

2N 98W 1,577,620,000

2N 99W 1,737,700,000

2N 100W 10,656,100

1S 95W 458,312,000

1S 96W 1,306,030,000

1S 97W 2,895,850,000

1S 98W 4,807,900,000

1S 99W 3,977,930,000

1S 100W 1,964,360,000

2S 94W 15,906,300

2S 95W 1,286,650,000

2S 96W 2,467,070,000

2S 97W 3,570,450,000

2S 98W 4,323,480,000

2S 99W 3,508,290,000

2S 100W 1,353,830,000

3S 94W 78,645,500

3S 95W 1,438,660,000

3S 96W 2,936,600,000

3S 97W 3,548,700,000

3S 98W 3,696,500,000

3S 99W 2,960,790,000

3S 100W 374,624,000

4S 94W 91,127,900

4S 95W 1,190,950,000

4S 96W 2,449,070,000

4S 97W 3,270,710,000

4S 98W 2,739,030,000

4S 99W 2,268,900,000

4S 100W 731,130,000

4S 101W 4,833,770

5S 94W 143,810,000

5S 95W 783,687,000

5S 96W 1,523,760,000

5S 97W 2,150,750,000

5S 98W 1,558,550,000

Township and Range SUM R-0 zone (BPA)

5S 99W 1,193,320,000

5S 100W 666,574,000

5S 101W 57,914,000

6S 94W 1,726,930

6S 95W 184,505,000

6S 96W 345,853,000

6S 97W 1,056,050,000

6S 98W 629,143,000

6S 99W 331,716,000

6S 100W 324,221,000

6S 101W 127,525,000

7S 93W 0

7S 94W 0

7S 95W 982,979

7S 96W 57,346,500

7S 97W 240,433,000

7S 98W 79,719,000

7S 99W 167,095,000

7S 100W 197,837,000

7S 101W 50,860,200

8S 93W 0

8S 94W 0

8S 95W 601,009

8S 96W 23,395

8S 99W 36,740,300

8S 100W 16,166,700

8S 101W 1,762,280

9S 94W 0

9S 95W 0

9S 96W 0

Total: 83,416,642,063

Table 10. Total number of in-place barrels of oil per acre (BPA) in each township for the R-0 zone calculated here using the Radial 

Basis Function Method (RBF).
Detailed Description and Assessment Results of Oil Shale Zones 71

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

30

20

20

20

20

15

24.8

18 52

25

46

22

23 24 20

23

27

22

24.6

22

20 20

27

20

22

22

16 28

23

21

22

77

23

20 22

20

12 23 20 18

22

24 23

23

58

48 65

30

90

25

23

20 24 21

21.8

13

22

2425 23 22

25 22

23

25

22

20

23

25

22

32 22

25 25

25 26 26

24 27 22

22 24

1525 26 29 35

34

24

23

28 30 36

46

31 20

30

40

41

45

22 26

28

25

25 22

24

25

31 31 27

32 27 33

26

35

20

28

32

20

33

13

18

24

22.6

26

21.6

30

22

21

20

25 21

22.6

23.5

34.5

26 28

18 15.5

22

20 24

24.1

20 22

16

22 25 28.6

26

17

26 15.1 20 22

24

22.4

18.7

32 24

34

24

25 28.6

30.6

27.3

32

27 18.7

34.2

8

20

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

10

L–0 interval—Thickness in feet

< 20

21–40

41–60

61–80

81–100

Figure 45. Isopach map of the L-0 zone using both core hole and rotary hole data. Radial Basis Function 

Method (RBF) was used for contouring. Contour interval in feet is variable.
72 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in 

 gallons per ton

10

L–0 interval—Average oil yield in gallons per ton

2.6–5

5.1–7.5

7.6–10

10.1–12.5

12.6–15

< 2.5

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

0.1

0.1

8.3

4.5

5.5 4.7

4.8 3.9

4.5

7.9

8.2

8.6

9.9 12.6

6

7.1

8.5

6.2

3.5

5.9

2.8

8

8

8.5

7.5

7.4

7.8

7.2

6.7 4.8

8.3

7.8

4.1

7.5 2.9

6.65.4

5.513.4 7

6.5 7.5

5.9

5.1

9.2 7 6.3

9

7.3

6.2 4.9

5.56.4

7.5

5.1

6.1

10.9

8.7

4.7

14.3

4.3 5.4

10.3

8.5

12.7

9.4 8.6

5.4

12.4

5.2

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 46. Isoresource map of the L-0 zone showing the oil yield in gallons per ton (GPT). The Radial Basis 

Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 73

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

L–0 zone—In barrels per acre

< 7,500

7,501–

 15,000

15,001–

 22,500

22,501–

 30,000

> 30,000

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

1

1

17

8

11

9

8 7

10

11

15

13

18 32

13

29

15

14

17

4

9

6

15

17

15

19

14

14

12

14 9

16

15

12

16 7 10

7

13 11 21

13

10 14

7

17 15 15

19

10

13

6 9 12

15

10

10

28 17

14

27

9 13

26

19

32

21 13

16

8

9

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

108°30' 108°00'

40°00'

39°30'

Figure 47. Isoresource map of the L-0 zone showing oil yields in barrels per acre (BPA). The Radial Basis 

Function Method (RBF) was used for contouring.
74 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

136,234 636,775

2,837,420 6,663,140 2,703,620

0

1,485,560

12,915,700

6,458,220 23,180,200

5,671,820

2,245,060

2,021,990

5,358,950 17,990,700

24,829,500

48,764,900

89,019,800

31,968,500

19,985,700 738,457

10,056,900 27,330,000

90,241,504

122,824,000

166,788,992

126,108,000 69,854,496

24,261,700 6,514,140

53,284,200

157,906,000 218,254,000 265,960,000 207,751,008 109,662,000

16,066,400

608,437

56,810,300

234,558,000 304,328,000 398,755,008 287,412,000 158,236,992 12,585,100 31,056,300

296,480,992 354,292,000 508,633,984 358,495,008 178,486,000 2,417,260

122,880,000

131,635,000 137,500,000 21,475,700

854,738

286,158,016 460,332,000 448,852,000 271,215,008

81,788,600

162,628,000

223,735,008

347,055,008 291,732,992

78,619,400

37,088,300

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

L–0 zone shale oil, total in-place resource—In millions of barrels

< 38

39–90

91–180

181–300

301–510

Top of Mahogany zone

Base of Parachute Creek Member

L–0 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 48. Isoresource map of the L-0 zone showing total number of barrels of oil in each township.
Detailed Description and Assessment Results of Oil Shale Zones 75

Township, Range SUM L-0 zone (BPA)

1N 96W 78,619,400

1N 97W 291,733,000

1N 98W 347,055,000

1N 99W 223,735,000

1N 100W 37,088,300

2N 97W 21,475,700

2N 98W 137,500,000

2N 99W 131,635,000

2N 100W 854,738

1S 95W 81,788,600

1S 96W 271,215,000

1S 97W 448,852,000

1S 98W 460,332,000

1S 99W 286,158,000

1S 100W 162,628,000

2S 94W 2,417,260

2S 95W 178,486,000

2S 96W 358,495,000

2S 97W 508,634,000

2S 98W 354,292,000

2S 99W 296,481,000

2S 100W 122,880,000

3S 94W 12,585,100

3S 95W 158,237,000

3S 96W 287,412,000

3S 97W 398,755,000

3S 98W 304,328,000

3S 99W 234,558,000

3S 100W 31,056,300

4S 94W 16,066,400

4S 95W 109,662,000

4S 96W 207,751,000

4S 97W 265,960,000

4S 98W 218,254,000

4S 99W 157,906,000

4S 100W 56,810,300

4S 101W 608,437

5S 94W 24,261,700

5S 95W 69,854,500

5S 96W 126,108,000

5S 97W 166,789,000

Township, Range SUM L-0 zone (BPA)

5S 98W 122,824,000

5S 99W 90,241,500

5S 100W 53,284,200

5S 101W 6,514,140

6S 94W 738,457

6S 95W 19,985,700

6S 96W 31,968,500

6S 97W 89,019,800

6S 98W 48,764,900

6S 99W 24,829,500

6S 100W 27,330,000

6S 101W 10,056,900

7S 93W 0

7S 94W 2,021,990

7S 95W 2,245,060

7S 96W 5,671,820

7S 97W 23,180,200

7S 98W 6,458,220

7S 99W 12,915,700

7S 100W 17,990,700

7S 101W 5,358,950

8S 93W 0

8S 94W 2,703,620

8S 95W 6,663,140

8S 96W 89,019

8S 99W 2,837,420

8S 100W 1,485,560

8S 101W 197,084

9S 94W 5,379

9S 95W 636,775

9S 96W 136,234

Total: 8,265,472,203

Table 11. Total number of in-place barrels of oil per acre (BPA) in each township for the L-0 zone calculated here using the 

Radial Basis Function Method (RBF).
76 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

110

R–1 interval—Thickness in feet

101–200

201–300

301–400

401–500

501–600

< 100

 

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

248

255

392

288 119

306 354

200

352

252

144 118 145

162

180

178

181 152

188 330

236

455

361

372 421

327

304

318

248 225

210

190

361 322 195 176

315

159 152

129

322

317 330

246 300

420

370

237

168 127

150

179

218

166

143

100

92 142 131

130 111

116

165 170

122

136

157

153

135

135 118

122 126 150

145 165

190 218 252

165 160

180 183

153 240 323

310

172

162

193 240 262

397

324 397

325

345

349

377

184 115

130

138

123 117

131

144

181

181

138

108

218 178

140

383

194

235

290

148

365

173

227

184

78

239

264

127.3

122

237.1

276.8

136

148

175

257

274 202

208.4

117.8

168

248.7

149

142

160

168134 134 186 138.9

133.1

158

173

188 213 228.4

161

222

140 173 145 160

195

152.6

322.3

120

134

257

116

203 192.4

191.6

146.3

127

190 149.7

209.5

119

132

120

120

120

206

259.6

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 49. Isopach map of the R-1 zone using both core hole and rotary hole data. Radial Basis Function Method 

(RBF) was used for contouring. Contour interval in feet is variable.
Detailed Description and Assessment Results of Oil Shale Zones 77

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in 

 gallons per ton

10

R–1 interval—Average oil yield in gallons per ton

5.1–10

10.1–15

15.1–20

20.1–25

25.1–30

< 5

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

26.3

18.9

17.2

19.5

7 18.1

12.5

14.9

23.3

24.1

16.2

16.9

26

21.2

26.7

23

24.3

19.3

21.1

22.9

22.8

13.5

12.8

6.9

26.4

27.4

6.5

20.8

24.4

17.7

22

17.8

10.3 14.3

23.3

25.9

22.7

14.7

20.1

18 21.3

18.5

17.9 16.2 23.7

20.7

22.2 20.7 17.5

22.1 19.8 19.4

21.2

22.4

21.9

19.2 19.4 17.7

21.6

20.8

13.7

27.4

24.3

17.5

26.3

18.6 22.9

24.6

24.4

25.7

18.9 28

20.6

24.9 28.3

26.9

24.5

27.5

22.2

14.8

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 50. Isoresource map of the R-1 zone showing the oil yield in gallons per ton (GPT). The Radial Basis 

Function Method (RBF) was used for contouring.
78 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

1

1

1

1

1

1

1

224

255

240

224

260 194

213

435

358

308

377

233

267

268

225

233

254

157

272

382

308

84

225

152

241

238

129

430

241

201

285

350

230 228

355

219

280

287

225

225

220236

255 232168

215

218

244

232

307 317 334

254

367

227 251 212217

312

237

350

234

236

345

218

287 323

341

259

235

272 297

323

238 238 230

213

234

338

302

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

R–1 zone—In barrels per acre

< 100,000

100,001–

 200,000

200,001–

 300,000

300,001–

 400,000

> 400,001–

 500,000

COLORADO

0 5 10 2.5 KILOMETERS

Figure 51. Isoresource map of the R-1 zone showing oil yields in barrels per acre (BPA). The Radial Basis 

Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 79

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

53,146,100 5,098,450 0

0

0

0

0

16,529,500

431,748,000

208,364,000

702,017,984

170,291,008

5,492,010

58,700,200

336,289,984

1,033,230,016

2,004,860,032

3,362,650,112

1,111,149,952

576,910,976

6,937,410

259,204,000

842,068,992

3,777,319,936

5,272,849,920

7,082,520,064

4,985,710,080 2,606,030,080

592,638,976

132,587,000 1,941,629,952

6,319,220,224 8,031,779,840 9,439,639,552 7,468,619,776 3,986,710,016

419,321,984

14,813,300

2,249,359,872

6,438,080,000 7,159,300,096 7,209,920,000 7,690,240,000 5,038,419,968 331,396,000

906,361,024

5,924,599,808 5,684,980,224 6,012,890,112 6,331,140,096 4,416,889,856 64,976,900

3,120,140,032

3,194,779,904

2,590,340,096

235,424,992

26,336,400

5,697,930,240 5,327,170,048 6,068,660,224 5,125,459,968

1,644,140,032

3,998,569,984

5,711,779,840

6,010,240,000

5,233,070,080

1,474,419,968 1,198,220,032

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

R–1 zone shale oil, total in-place resource—In millions of barrels

< 710

711–2,200

2,201–4,400

4,401–6,400

6,401–9,400

Top of Mahogany zone

Base of Parachute Creek Member

R–1 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 52. Isoresource map of the R-1 zone showing total number of barrels of oil in each township using only 

core hole data.
Table 12. Total number of in-place barrels of oil per acre (BPA) in each township for the R-1 zone calculated here using the Radial Basis Function Mhighlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the 95 percent confidence levefrom Pitman and others (1989) using manual extrapolation and kriging are also listed with percent differrence using the RBF method here. Numbers hbe errors in the calculations made by Pitman and others (1989). Township, Range SUM R-1 no rotary holes Extrapolated (Pitman and others,1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence 

1N 96W 1,474,420,000 468,274,000 ±27 

1N 97W 5,233,070,000 5,921,654,000 ±30 1N 98W 6,010,240,000 1N 99W 5,711,780,000 1,052,800,000 4,658,980,000 443 1,593,772,000 ±30 

1N 100W 1,198,220,000 4,171,420,000 -2,973,200,000 -71 5,680,672,000 ±9 -2N 97W 235,425,000 6,183,100,000 -5,947,675,000 -96 6,762,724,000 ±10 -2N 98W 2,590,340,000 5,874,550,000 -3,284,210,000 -56 6,011,643,000 ±12 -2N 99W 3,194,780,000 316,470,000 2,878,310,000 910 405,566,000 ±32 

2N 100W 26,336,400 1S 95W 1,644,140,000 1S 96W 5,125,460,000 4,741,400,000 384,060,000 8 6,197,299,000 ±27 -1S 97W 6,068,660,000 6,149,250,000 -80,590,000 -1 6,011,335,000 ±8 

1S 98W 5,327,170,000 5,490,100,000 -162,930,000 -3 5,401,393,000 ±9 1S 99W 5,697,930,000 5,510,250,000 187,680,000 3 5,729,628,000 ±11 

1S 100W 3,998,570,000 2,990,600,000 1,007,970,000 34 3,454,415,000 ±22 

2S 94W 64,976,900 2S 95W 4,416,890,000 2S 96W 6,331,140,000 5,819,750,000 511,390,000 9 7,110,359,000 ±16 

2S 97W 6,012,890,000 5,814,585,000 198,305,000 3 5,742,464,000 ±7 

2S 98W 5,684,980,000 5,478,935,000 206,045,000 4 5,508,761,000 t8 

2S 99W 5,924,600,000 5,317,830,000 606,770,000 11 5,354,657,000 ±11 

2S 100W 3,120,140,000 2,537,392,000 582,748,000 23 2,559,034,000 ±19 

3S 94W 331,396,000 3S 95W 5,038,420,000 3S 96W 7,690,240,000 7,935,200,000 -244,960,000 -3 8,141,686,000 ±8 3S 97W 7,209,920,000 6,738,825,000 471,095,000 7 6,789,007,000 ±4 

3S 98W 7,159,300,000 6,992,980,000 166,320,000 2 6,656,552,000 ±7 

3S 99W 6,438,080,000 5,266,500,000 1,171,580,000 22 6,461,536,000 ±22 

3S 100W 906,361,000 370,695,000 535,666,000 145 457,762,000 ±42 

4S 94W 419,322,000
Table 12. Total number of in-place barrels of oil per acre (BPA) in each township for the R-1 zone calculated here using the Radial Basis Function Mhighlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the 95 percent confidence levefrom Pitman and others (1989) using manual extrapolation and kriging are also listed with percent differrence using the RBF method here. Numbers hbe errors in the calculations made by Pitman and others (1989).—Continued

Township, 

Range

SUM R-1 

no rotary 

holes

Extrapolated (Pitman 

and others,1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence 

4S 95W 3,986,710,0004S 96W 7,468,620,000 5,430,480,000 2,038,140,000 38 9,876,394,000 ±26 -4S 97W 9,439,640,000 8,740,125,000 699,515,000 8 9,734,521,000 ±7 4S 98W 8,031,780,000 6,428,240,000 1,603,540,000 25 8,984,729,000 ±13 4S 99W 6,319,220,0004S 100W 2,249,360,0004S 101W 14,813,3005S 94W 592,639,0005S 95W 2,606,030,0005S 96W 4,985,710,0005S 97W 7,082,520,0005S 98W 5,272,850,0005S 99W 3,777,320,0005S 100W 1,941,630,0005S 101W 132,587,0006S 94W 6,937,4106S 95W 576,911,0006S 96W 1,111,150,0006S 97W 3,362,650,0006S 98W 2,004,860,0006S 99W 1,033,230,0006S 100W 842,069,0006S 101W 259,204,0007S 93W 07S 94W 07S 95W 5,492,0107S 96W 170,291,0007S 97W 702,018,0007S 98W 208,364,0007S 99W 431,748,000
Table 12. Total number of in-place barrels of oil per acre (BPA) in each township for the R-1 zone calculated here using the Radial Basis Function Mhighlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the 95 percent confidence levefrom Pitman and others (1989) using manual extrapolation and kriging are also listed with percent differrence using the RBF method here. Numbers hbe errors in the calculations made by Pitman and others (1989).—Continued Township, Range SUM R-1 no rotary holes Extrapolated (Pitman and others,1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence 

7S 100W 336,290,000 7S 101W 58,700,200 8S 93W 0 8S 94W 0 8S 95W 5,098,450 8S 96W 199,313 8S 99W 53,146,100 8S 100W 16,529,500 8S 101W 576,316 9S 94W 0 9S 95W 0 9S 96W 0 Totals: 195,372,090,899 115,351,477,000 137,015,837,000 Sum of townships used here and Pitman and others (1989) extrapolated: 120,566,026,000 Sum of townships used here and kriging: Percent difference between RBF and kriging: 127,273,516,000 Percent difference using RBF here and Pitman and others (1989) extrapolated: 4.52 -7.65 Sum of best townships RBF (20 percent) 91,167,010,000 Sum of best townships extrapolated: 78,953,462,000 Sum of best townships kriging: 8

Percent difference RBF vs extrapolation for best townships: 15.47 Percent difference RBF vs kriging for best townships: 8.89
Detailed Description and Assessment Results of Oil Shale Zones 83

Total in-place oil in the L-1 zone is estimated to be just over 

15 billion barrels (table 13).

Pitman and others (1989) estimated 10.7 billion barrels using manual extrapolation and 11.2 billion barrels using 

kriging for the L-1 zone (table 12), but again, they assessed 

fewer townships than were assessed here. None of the results 

from Pitman and others (1989) for individual townships for 

the L-1 zone appears to be geologically unreasonable. When 

only those townships that were used in both assessments are 

compared, our assessment is 6.44 percent higher than their 

manually extrapolated results and 3.43 percent higher than 

their kriged results (table 13). When only the townships with 

the best control are compared (those with 20 percent or less 

estimated error in the kriged results of Pitman and others, 

1989), our results are 4.02 percent less than their manually 

extrapolated results and 0.91 percent higher than their kriged 

results (table 13). 

R-2 Zone

The R-2 zone marks the beginning of the third stage 

of Lake Uinta as defined by Johnson (1985) and represents 

the transition from illitic-rich oil shales to carbonate-rich oil 

shales. In electric logs this shift is represented by a distinctive 

increase in resistivity informally known as the blue marker 

(Ziemba, 1974) because a blue pencil was used to mark it 

on geophysical logs. The first occurrence of disseminated 

nahcolite, a sodium bicarbonate mineral (NaHCO3), is in the 

upper part of the L-2 zone in the north-central part of the basin 

(Dyni, 1974; 1981). Dawsonite, a hydrated aluminum carbonate mineral (NaAl(OH)2

CO3) appears for the first time in 

the lower part of the R-2 zone, about 65–75 ft below the first 

occurrence of nahcolite (Dyni, 1981), and increases in abundance upwards. Illite correspondingly decreases in abundance 

upwards though the R-2 zone (Dyni, 1974; 1981; Robb and 

Smith, 1974). Dyni (1981) suggested that the alkaline lake 

waters destroyed much of the fine-grained detritus in the sediments, including the clays. These fine-grained sediments were 

replaced by a suite of authigenic minerals including dawsonite, authigenic feldspars, and authigenic quartz. Authigenic 

quartz in the saline interval is so clean and well crystallized 

that it has been used as an internal standard for d-spacing measurements in x-ray diffraction (Smith and Robb, 1966; 1973). 

One hundred forty eight core holes were used to assess 

the R-2 zone here as compared to 85 in the previous assessment (Pitman and others, 1989). The zone is thickest along 

an east-to-northeast trending belt across the south-central and 

northeastern parts of the basin where it ranges from about 90 

to 155 ft thick (fig. 57). The interval thins generally towards 

the southwest in the direction that the previous R-1 and L-1 

zones had thickened markedly. Along the south and west 

margins of the basin, the R-2 zone cannot be separated from 

the overlying L-2, R-3, and L-3 zones, and thus all four zones 

are generally lumped together (Johnson, and others, 1988). 

Here, the four zones have a combined thickness of about 75 

to 155 ft and consist of marlstone oil shale beds and stromatolites. In outcrop the underlying L-1 zone is much sandier and 

the overlying R-4 zone includes more rich oil shale beds than 

this distinctive interval (Johnson and others, 1988). In surface 

sections used for isopaching, this interval is arbitrarily proportioned so that the two rich zones are twice as thick as the two 

lean zones (table 4, Philadelphia Creek and Little Burma Road 

sections).

The oil shale depocenter during deposition of the R-2 

zone is in the north-central part of the basin and north of the 

area where the zone is thickest (figs. 58–60). Here, maximum 

oil yield reaches 45 GPT, and decreases in a radial pattern 

outward. Oil yields reach near zero around the southeastern 

and southwestern margins and about 10–15 GPT around the 

northern and northwestern margins (fig. 58). Estimated inplace oil in barrels per acre reaches a maximum of 240,000 

in this depocenter and decreases outward (fig. 59). Maximum 

in-place oil in a township is in T. 1 S., R. 98 W. with over 4 

billion barrels (fig. 60). Total in-place oil in the basin in the 

R-2 zone is estimated to be 66.8 billion barrels (table 14). 

As in all of the oil shale zones assessed here, we were 

able to assess more townships than were assessed by Pitman 

and others (1989) due largely to more control. When only 

those townships that were assessed in both assessments are 

compared, our assessment of the R-2 zone is 10.25 percent 

higher than the manually extrapolated result and 3.01 percent 

higher than the kriged result of Pitman and others (1989) 

(table 14). Six townships listed in Pitman and others (1989) 

gave either unreasonably high or unreasonably low results, 

based on the control points they used and current geologic 

knowledge. These values are shown in red in table 14. When 

only the townships with the best control are compared (those 

with 20 percent or less estimated error in the kriged results of 

Pitman and others, 1989), our results are 4.87 percent higher 

than the manually extrapolated results and 4.47 percent higher 

than the kriged results of Pitman and others (1989) (table 14). 

We did not include any of the six townships with questionable 

results, even though two of them had estimated errors using 

kriging of significantly less than 20 percent.

L-2 Zone

Thickness and oil shale richness patterns for the L-2 zone 

are similar to those for the R-2 zone with the area of maximum 

thickness rimming the south end of the oil shale depocenter 

(fig. 61). The L-2 zone reaches a maximum thickness of 115 

ft in this area. Maximum oil yield for the L-2 zone is about 

34 GPT in the oil shale depocenter, with oil yields decreasing 

in a radial pattern outwards (fig. 62). Maximum BPA in the 

L-2 zone is 112,000 barrels (fig. 63), and maximum in-place 

resources in a township is just over 1.5 billion barrels in T. 

1 S., R. 97 W. (fig. 64). Total in-place oil in the L-2 zone is 

estimated to be 24.2 billion barrels (table 15).

Using only those townships that were assessed in both 

this assessment and the previous assessment by Pitman and 
84 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

135

150

75 26.2

91

75

102

75

58

68 46 30

30

40

68 64

62 66

96 76 123

64 46.8

76

96

108 72

102

90 105

158

85

128

121

117

98 60 65 94

53

63

54

48

100

89 95

70 68

70

80

74

86

53 56 53

42

22

65 17

6275 20 60

25 39

31

38 39

35

20

34

32 27 29 28

25 24

29 34 30

46 44 60

35 45

35 32 14 52 82

56

34 30

35 43 53

75

73 65

68 63

59

60

57 21

22

24

28

15

33

22

23

25

25

21

51

38 30

80

55

33

40

122

24

50

27

134

26

96

168

14

21.4

16

24

22

118.3

0

0

17

38.4

62

99

135

94 69

85

75

92.6

28.7

41

28 31

36

34

72

32 45

18 16 24 24

27.9

31

33

47 47 64

42

30

16

32

45

140

90

10

84.6

20

34 46

30

26

108

52

46

26

119

28 20

98

77

44

29

123

15

113.1

71.2

43.3

29.5

48

30

15.7

38

28.3

32 28

28

25

25

28

29

87.9

84.4 85.8

127

91

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

10

L–1 interval—Thickness in feet

< 40

41–80

81–120

121–160

161–200

Figure 53. Isopach map of the L-1 zone using both core hole and rotary hole data. The Radial Basis Function 

Method (RBF) of contouring. Contour interval in feet is variable.
Detailed Description and Assessment Results of Oil Shale Zones 85

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in 

 gallons per ton

10

L–1 interval—Average oil yield in gallons per ton

5.1–10

10.1–15

15.1–20

20.1–25

25.1–30

< 5

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

8.2

6.1 5.6

5.95.7

4.4 2.6 0.6

2.9 6.2

1.4

2.2

3.1

5.4

3.7

6.2

6.5

12.3

6.3

10

11.5

12.7 11.4

7

11.5

3.9

13.9

1.4

1.2

7.4

6.8

13.4

7.4

4

4.2

12.3

5.8

9.9

4.2

3.4

2.2 5.3

2.5

5.8

5.3

10

14.8

7.9 11.4

5.7

8.1

3

2.8

3.8

3 6.4 8

10.4

15.2 8.4 6.5

5.17 5.4

8.4

7.4

7.3

7.7

5

3.3

1.3

5.5

0.5

9.7

8.45.4

10.5

8.4

3.8

6.1

5.9

8.9

1.8

18.2

8.8

5.9

4.9

25.3

8.1

0.4

10.8

4

4.8

9.2

13

3

8

12.8

11.4

11.8

10.2 14

7.8

5.6

6

14.7

13.3

1.9

2.1 1.2

2.6

2

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 54. Isoresource map for the L-1 zone showing the oil yield in gallons per ton (GPT). The Radial Basis 

Function Method (RBF) was used for contouring.
86 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

L–1 zone—In barrels per acre

< 20,000

20,001–

 40,000

40,001–

 60,000

> 60,001–

 80,000

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

1

1

1

1

1

1

18

35 30

3132

36 17 7

14 24

12

21

33

43

22

29

23

17

21

23

22

15 21

30

25

45

29

12

18

9

12

17

15

8

43

17

19

50

36

40

18 31

19

36

41

24

48

18

29

17

23

19

8

15

5 9 16

20

22 33 18

28 20 29

29

19

10

21

19

40

10

5

4

16

24 21

26

18

35

27

23

19

19

39

15

48

32

80

20

4

13

39

29

33

31

13

20

16

35

27

35

23

18

12

13

32

31

15

16

9

29

16

108°30' 108°0'

40°0'

39°30'

0 3 6 12 MILES

40°00'

39°30'

COLORADO

0 5 10 2.5 KILOMETERS

Figure 55. Isoresource map of the L-1 zone showing oil yields in barrels per acre (BPA). The Radial 

Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 87

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

57,768 140,342

4,935,180

581,489

0

0

1,677,890

32,231,400

15,852,000

27,461,100 5,378,030 353,586

994

5,016,580

25,114,300

67,498,496

143,583,008

171,556,992

29,280,500

13,086,800 473,895

17,110,400 52,268,200

216,696,992 275,372,000

290,686,016

173,120,000 56,931,800

11,852,500

8,333,000 114,429,000

381,284,992 591,379,968 635,224,000 415,140,992 185,068,000

16,080,300

1,055,170

135,202,000

456,446,016 719,788,992 876,163,008 691,401,984 355,328,992

27,925,800

69,403,296

430,512,992 562,617,024 582,444,992 677,638,016 452,879,008 7,814,390

202,112,992

223,716,992 181,746,000 23,064,100

1,666,990

591,715,008 512,150,016 631,329,984 651,281,984

253,502,000

376,603,008

400,099,008 401,776,000 413,012,992

88,664,496

82,375,400

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

L–1 zone shale oil, total in-place resource—In millions of barrels

< 33

34–140

141–290

291–510

511–880

Top of Mahogany zone

Base of Parachute Creek Member

L–1 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 56. Isoresource map of the L-1 zone showing total number of barrels of oil in each township.
88 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 13. Total number of in-place barrels of oil per acre (BPA) in each township for the L-1 zone calculated here using the 

Radial Basis Function Method (RBF). Results for the L-1 zone from Pitman and others (1989) using manual extrapolation and kriging 

are also listed with percent difference using the RBF method here. Townships highlighted in yellow are those in which kriging by 

Pitman and others (1989) indicated an error of 20 percent or less at the 95 percent confidence level. 

Township, 

Range SUM L-1

"Extrapolated" 

(Pitman and 

others, 1989)

Difference Percent 

difference

Kriged (Pitman and 

others 1989)

95 percent 

confidence

1N 96W 88,664,500 9,176,000 79,488,500 866 13,554,000 ±138

1N 97W 413,013,000 102,512,000 ±311

1N 98W 401,776,000

1N 99W 400,099,000 105,280,000 294,819,000 280 85,744,000 ±90

1N 100W 82,375,400 417,142,000 -334,766,600 -80 369,524,000 ±29

2N 97W 23,064,100 337,260,000 -314,195,900 -93 465,107,000 ±36

2N 98W 181,746,000 256,344,000 -74,598,000 -29 392,027,000 ±75

2N 99W 223,717,000 7,535,000 216,182,000 2,869 35,684,000 ±91

2N 100W 1,666,990

1S 95W 253,502,000

1S 96W 651,282,000 545,261,000 106,021,000 19 543,029,000 ±72

1S 97W 631,330,000 688,716,000 -57,386,000 -8 540,687,000 ±24

1S 98W 512,150,000 549,010,000 -36,860,000 -7 546,565,000 ±22

1S 99W 591,715,000 587,760,000 3,955,000 1 527,804,000 ±30

1S 100W 376,603,000 119,624,000 256,979,000 215 335,612,000 ±57

2S 94W 7,814,390

2S 95W 452,879,000

2S 96W 677,638,000 698,370,000 -20,732,000 -3 686,079,000 ±33

2S 97W 582,445,000 498,393,000 84,052,000 17 620,790,000 ±18

2S 98W 562,617,000 424,897,000 137,720,000 32 536,230,000 ±19

2S 99W 430,513,000 508,662,000 -78,149,000 -15 409,720,000 ±45

2S 100W 202,113,000 170,786,000 31,327,000 18 288,845,000 ±60

3S 94W 27,925,800

3S 95W 355,329,000 333,645,000 21,684,000 6 545,476,000 ±99

3S 96W 691,402,000 838,864,000 -147,462,000 -18 764,002,000 ±19

3S 97W 876,163,000 1,064,025,000 -187,862,000 -18 767,124,000 ±13

3S 98W 719,789,000 563,950,000 155,839,000 28 622,691,000 ±24

3S 99W 456,446,000 337,056,000 119,390,000 35 512,766,000 ±70

3S 100W 69,403,300 17,109,000 52,294,300 306 43,798,000 ±95

4S 94W 16,080,300 –-

4S 95W 185,068,000 183,592,000 1,476,000 1 –-

4S 96W 415,141,000 429,913,000 -14,772,000 -3 478,261,000 ±37

4S 97W 635,224,000 559,368,000 75,856,000 14 724,812,000 ±34

4S 98W 591,380,000 367,328,000 224,052,000 61 282,314,000 ±116
Detailed Description and Assessment Results of Oil Shale Zones 89

Table 13. Total number of in-place barrels of oil per acre (BPA) in each township for the L-1 zone calculated here using the 

Radial Basis Function Method (RBF). Results for the L-1 zone from Pitman and others (1989) using manual extrapolation and kriging 

are also listed with percent difference using the RBF method here. Townships highlighted in yellow are those in which kriging by 

Pitman and others (1989) indicated an error of 20 percent or less at the 95 percent confidence level.—Continued

Township, 

Range SUM L-1

"Extrapolated" 

(Pitman and 

others, 1989)

Difference Percent 

difference

Kriged (Pitman and 

others 1989)

95 percent 

confidence

4S 99W 381,285,000

4S 100W 135,202,000

4S 101W 1,055,170

5S 94W 11,852,500

5S 95W 56,931,800

5S 96W 173,120,000 78,452,000 94,668,000 121

5S 97W 290,686,000

5S 98W 275,372,000

5S 99W 216,697,000

5S 100W 114,429,000

5S 101W 8,333,000

6S 94W 473,895

6S 95W 13,086,800

6S 96W 29,280,500

6S 97W 171,557,000

6S 98W 143,583,000

6S 99W 67,498,500

6S 100W 52,268,200

6S 101W 17,110,400

7S 93W 0

7S 94W 994

7S 95W 353,586

7S 96W 5,378,030

7S 97W 27,461,100

7S 98W 15,852,000

7S 99W 32,231,400

7S 100W 25,114,300

7S 101W 5,016,580
90 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 13. Total number of in-place barrels of oil per acre (BPA) in each township for the L-1 zone calculated here using the 

Radial Basis Function Method (RBF). Results for the L-1 zone from Pitman and others (1989) using manual extrapolation and kriging 

are also listed with percent difference using the RBF method here. Townships highlighted in yellow are those in which kriging by 

Pitman and others (1989) indicated an error of 20 percent or less at the 95 percent confidence level.—Continued

Township, 

Range SUM L-1

"Extrapolated" 

(Pitman and 

others, 1989)

Difference Percent 

difference

Kriged (Pitman and 

others 1989)

95 percent 

confidence

8S 93W 0

8S 94W 0

8S 95W 581,489

8S 96W 54,224

8S 99W 4,935,180

8S 100W 1,677,890

8S 101W 100,561

9S 94W 0

9S 95W 140,342

9S 96W 57,768

15,066,851,989 10,697,518,000 11,240,757,000

Sum of townships used here and Pitman and others 

(1989) extrapolated:

11,386,537,300 Sum of townships used here and 

kriging 

11,441,362,300

Percent difference using RBF here and Pitman and 

others (1989) extrapolated:

6.44 Percent difference betwee RBF 

and kriging:

1.78

Sum of best townships (RBF) 2,712,627,000

Sum of best townships extrapolated: 2,826,179,000

Sum of best townships kriged: 2,688,146,000

Percent difference betwee RBF and extrapolation 

best townships:

4.19

Percent difference between RBF and kriging best 

townships: 

0.91
Detailed Description and Assessment Results of Oil Shale Zones 91

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

110

R–2 interval—Thickness in feet

31–60

61–90

91–120

121–150

151–180

< 30

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

25

54 75.7

123

68 68

7074

64 70 49

59 65.2

75

76

143

117

108

105

58

65

66

76

73

83

93 84

113

110 120

107 125

113

50

72 70

59 90

155

63

147

64

53

100

88

66

46

72

80

82

57.7

114.5

58

77.1

90

138

133

66 64

74

63

125.2

71

64

54.6 58

70

54

57

103

77 68

58 64 66 51

51 49.8 61.9

122

107 108 112

93

64

58

40

58

54

57

56

50

62

146

93

77.7

46

46

67.7

46

6050

70

56

60

58

53

55.4

111.5

99

55.6

55

62

63.8

60

129.1

77

60

42

48

64 68

103

112

84

56

88

67

132.5

111.4

85.3

62.3

54

64

6647

70

67.5

78.8

60

49.3

60.5

67

64

71

82

75

66

67

76 74

80 74.1

72

66

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 57. Isopach map of the R-2 zone using the Radial Basis Function Method (RBF) of contouring. Contour 

interval in feet is variable.
92 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

0.1

0.1

0.1

34.2

24.4

23.8 25

23.5 16.5 11.8

14.7 24.9

7.3

10.5

15.9

23.9

15.4

28.5

27.4

33.2

26.6

35.5

31.5

36.8 33.8

28

31

12.4

32.2

4.3

7.3

2.3

23.6

16.2

36

36

35.9

11.9

13

35.5

32.5

23.8

16.6

9

16.1 24

21.5

19.2

19

37.3

30.6

21.2 28.4

24.3

31.2

33.6

7.4

23.3 24.9

30 26.7 29.7

37.1

34.2

2729.1

19.5

24.1 20.7 21

25.3

26.9

20.3

16

20.2

30.6

30.2

31.7

34

27.7

12.7

6.9

7.1

13.5

30.1

3.9

33.6

28.7 26.9

23.7

24.5

19.9

26.1

32.6

29.2

13.2

23.6

31.2

33.7

23.8

32.5

22.2

8.2

28.1

16.5

17

38.9

38.4

18.8

16.2

45.3

26.8

2.1

34.6

17.3

19.5

27.2

37.2

29.2

20.7

20.8

19.7

21.5

36.8

1.8

3.3

37.7

29

33.9 40.1

33.5

35

29.2

41.3

35.4

22.2 16.2

18 13.7

13

11.7

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in 

 gallons per ton

10

R–2 interval—Average oil yield in gallons per ton

10.1–20

20.1–30

30.1–40

40.1–50

< 10

Figure 58. Isoresource map of the R-2 zone showing the oil yield in gallons per ton (GPT) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 93

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

R–2 zone—In barrels per acre

< 50,000

50,001–

 100,000

100,001–

 150,000

150,001–

 200,000

> 200,001–

 250,000

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

1

1

1

176

109 120

121134

110 89 47

117 68

46

65

177

204

130

117

127

150

144

175

109

178 162

117

136

146

142

20

61

18

114

58

175

194

198

55

119

139

173

156

177

99

82 112

118

91

180

177

136

86

116

123

117

131

64

116139

134 126 121 127

119 102

119

179

188 167 175

170

123

88

50

88

115

120

123

116

122

148

53

46

49

97

23

106

121 96

121

99

90

109

119

114

117

171

120

127

108

143

98

88

153

5463

165

173

147

141

242

107

16

158

176

164

165

155

111

99102

70

112

167

13

17

124

123

176 148

163

194

154

178

160

125 93 110 80

75

62

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 59. Isoresource map for the R-2 zone showing oil yields in barrels per acre (BPA) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
94 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

9,361 161,490

7,182,360 1,532,570 0

0

0

1,960,750

38,747,900

23,378,100 90,282,400

21,263,100

408,365

1,997,280

21,517,500

71,333,800

164,674,000 316,496,000

97,268,496

47,896,000 2,211,320

5,370,070 36,440,200

249,302,000 436,656,992

702,371,008 616,886,016

306,576,992

155,564,992

531,160

63,299,200

781,390,976 1,436,889,984 1,945,459,968 1,589,769,984 915,452,032

181,711,008

7,897

113,454,000

1,664,150,016 3,443,689,984 3,900,499,968 3,139,000,064 1,476,809,984 153,476,000

140,575,008

2,624,659,968 3,376,420,096 3,778,050,048 3,093,129,984 1,827,289,984 29,542,300

936,625,024

1,502,560,000

1,350,169,984

145,575,008 10,933,500

2,851,520,000 4,017,469,952 3,562,769,920 2,296,150,016

941,001,984

1,637,280,000

2,393,750,016 3,041,920,000 1,995,890,048

531,279,008

460,867,008

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

R–2 zone shale oil, total in-place resource—In millions of barrels

< 120

121–460

461–940

941–2,400

2,401–4,000

Top of Mahogany zone

Base of Parachute Creek Member

R–2 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 60. Isoresource map of the R-2 zone showing total number of barrels of oil in each township using only 

core hole data.
Table 14. Total number of in-place barrels of oil per acre (BPA) in each township for the R-2 zone calculated here using the Radial Basis Function MResults for the R-2 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF mTownships highlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the 95 percent confiNumbers highlighted in red appear to be errors in the calculations made by Pitman and others (1989).

Township, 

Range SUM R-2 Extrapolated (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Difference 

1N 96W 531,279,000 34,410,000 496,869,000 1,444 85,904,000 ±42 445,375,000 

1N 97W 1,995,890,000 703,950,000 1,291,940,000 184 964,014,000 ±84 1,031,876,000 

1N 98W 3,041,920,0001N 99W 2,393,750,000 427,700,000 1,966,050,000 460 387,551,000 ±27 2,006,199,000 

1N 100W 460,867,000 1,896,100,000 -1,435,233,000 -76 1,874,660,000 ±4 -1,413,793,000 

2N 97W 145,575,000 2,922,920,000 -2,777,345,000 -95 2,957,579,000 ±14 -2,812,004,000 

2N 98W 1,350,170,000 2,221,648,000 -871,478,000 -39 2,405,777,000 ±21 -1,055,607,000 

2N 99W 1,502,560,000 135,630,000 1,366,930,000 1,008 150,421,000 ±50 1,352,139,000 

2N 100W 10,933,5001S 95W 941,002,0001S 96W 2,296,150,000 1,825,439,000 470,711,000 26 1,985,566,000 ±47 310,584,000 

1S 97W 3,562,770,000 3,640,356,000 -77,586,000 -2 3,628,422,000 ±7 -65,652,000 

1S 98W 4,017,470,000 3,771,460,000 246,010,000 7 3,814,808,000 ±8 202,662,000 

1S 99W 2,851,520,000 2,914,310,000 -62,790,000 -2 2,857,124,000 ±16 -5,604,000 

1S 100W 1,637,280,000 1,121,475,000 515,805,000 46 1,390,669,000 ±28 246,611,000 2S 94W 29,542,300

2S 95W 1,827,290,000 1,324,850,000 502,440,000 38 3,046,240,000 ±76 -1,218,950,000 

2S 96W 3,093,130,000 2,560,690,000 532,440,000 21 2,932,199,000 ±25 160,931,000 

2S 97W 3,778,050,000 3,678,615,000 99,435,000 3 3,696,804,000 ±8 81,246,000 

2S 98W 3,376,420,000 3,086,094,000 290,326,000 9 3,171,693,000 ±10 204,727,000 

2S 99W 2,624,660,000 2,265,858,000 358,802,000 16 2,451,198,000 ±14 173,462,000 

2S 100W 936,625,000 878,328,000 58,297,000 7 1,059,230,000 ±33 -122,605,000 

3S 94W 153,476,0003S 95W 1,476,810,000 1,156,636,000 320,174,000 28 802,979,000 ±120 673,831,000 

3S 96W 3,139,000,000 3,106,064,000 32,936,000 1 2,923,854,000 ±9 215,146,000 

3S 97W 3,900,500,000 3,783,200,000 117,300,000 3 3,737,419,000 ±5 163,081,000 3S 98W 3,443,690,000 3,022,772,000 420,918,000 14 3,099,380,000 ±11 344,310,000 

3S 99W 1,664,150,000 863,706,000 800,444,000 93 1,533,706,000 ±41 130,444,000 

3S 100W 140,575,000 121,667,000 ±100 18,908,000 

4S 94W 181,711,000
Table 14. Total number of in-place barrels of oil per acre (BPA) in each township for the R-2 zone calculated here using the Radial Basis Function MResults for the R-2 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF mTownships highlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the 95 percent confiNumbers highlighted in red appear to be errors in the calculations made by Pitman and others (1989).—Continued Township, Range SUM R-2 Extrapolated (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Difference 

4S 95W 915,452,000 917,960,000 -2,508,000 0 782,210,000 ±98 133,242,000 

4S 96W 1,589,770,000 1,697,025,000 -107,255,000 -6 1,619,528,000 ±36 -29,758,000 

4S 97W 1,945,460,000 1,631,490,000 313,970,000 19 1,763,993,000 ±21 181,467,000 

4S 98W 1,436,890,000 1,010,152,000 426,738,000 42 1,014,718,000 ±49 422,172,000 

4S 99W 781,391,000 4S 100W 113,454,000 4S 101W 7,897 5S 94W 155,565,000 5S 95W 306,577,000 5S 96W 616,886,000 470,712,000 146,174,000 31 541,644,000 ±262 75,242,000 

5S 97W 702,371,000 5S 98W 436,657,000 5S 99W 249,302,000 5S 100W 63,299,200 5S 101W 531,160 6S 94W 2,211,320 6S 95W 47,896,000 6S 96W 97,268,500 6S 97W 316,496,000 6S 98W 164,674,000 6S 99W 71,333,800 6S 100W 36,440,200 6S 101W 5,370,070 7S 93W 0 7S 94W 0 7S 95W 408,3657S 96W 21,263,1007S 97W 90,282,4007S 98W 23,378,1007S 99W 38,747,900
Table 14. Total number of in-place barrels of oil per acre (BPA) in each township for the R-2 zone calculated here using the Radial Basis Function MResults for the R-2 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF mTownships highlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the 95 percent confiNumbers highlighted in red appear to be errors in the calculations made by Pitman and others (1989).—Continued

Township, 

Range SUM R-2 Extrapolated (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Difference 

7S 100W 21,517,5007S 101W 1,997,2808S 93W 08S 94W 08S 95W 1,532,5708S 96W 91,8018S 99W 7,182,3608S 100W 1,960,7508S 101W 87,1329S 94W 09S 95W 161,4909S 96W 9,361

66,768,689,056 53,069,550,000 56,800,957,000

Sum of townships used here 

and Pitman and others (1989) extrapolated:

58,510,064,000 Sum of townships used here and 

kriging:

58,510,064,000

Percent difference using RBF 

here and Pitman and others (1989) extrapolated:

10.25 Percent difference between RBF 

and kriging:

3.01

Sum of best townships RBF (20 

percent):

30,694,080,000 Sum of best townships extrapolated: 29,268,729,000 Sum of best 

townships kriging:

29,380,702,000

Percent difference RBF vs 

extrapolation for best TSPS:

4.87

Percent difference RBF vs 

kriging for best TSPS:

4.47
98 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

others (1989) our assessment of in-place oil for the L-2 zone is 

8.28 percent higher than the manually extrapolated results and 

4.83 percent higher than the kriged assessment of Pitman and 

others (1989) (table 15). When only the townships with the 

best control are compared (those with 20 percent or less estimated error in the kriged results of Pitman and others, 1989), 

our results are 0.47 percent lower than the manually extrapolated results and 6.21 percent higher than the kriged results of 

Pitman and others (1989) (table 15). 

R-3 Zone

The saline depocenter in the north-central part of the 

basin became well established during deposition of the R-3 

zone with several thick beds consisting of predominantly 

nahcolite scattered throughout the zone in this area (Dyni, 

1974; 1981; Brownfield and others, chapter 2, this CD-ROM). 

Unlike the underlying R-2 and L-2 zone, in which maximum 

thicknesses were south and east of the oil shale and saline 

depocenter, the R-3 zone is thickest in the depocenter itself 

where it is over 150 ft thick. The R-3 zone thins in a radial 

pattern outward (fig. 65). The presence of several thick 

nahcolite beds in the R-3 zone is at least in part responsible 

for this thickening trend. The R-3 zone reaches a maximum 

of over 43 GPT and 381,000 BPA in this depocenter (figs. 66, 

67). Maximum in-place oil in a township is nearly 6.5 billion 

barrels in T. 1 S., R. 98 W. in the heart of the oil shale and 

saline-mineral depocenter (fig. 68). Total in-place oil in 

the R-3 zone is estimated to be nearly 68.1 billion barrels 

(table 16).

Using only those townships that were assessed in both 

this assessment and the previous assessment by Pitman and 

others (1989) our assessment of in-place oil for the R-3 zone 

is 5.17 percent higher than the manually extrapolated results 

and 6.22 percent higher than the kriged assessment of Pitman 

and others (1989) (table 16). Results from seven townships 

assessed by Pitman and others (1989) are questionable based 

on the control available at the time and our knowledge of the 

basin, and these are highlighted in red on table 16. When only 

the townships with the best control are compared (those with 

20 percent or less estimated error in the kriged results of Pitman and others, 1989), our results are 5.33 percent higher than 

the manually extrapolated results and 3.90 percent higher than 

the kriged results of Pitman and others (1989) (table 16). The 

questionable townships mentioned above were not included in 

this comparison of best townships.

L-3 Zone

One hundred fifty eight core holes were used to assess 

the L-3 zone in this assessment as compared to 93 in the 

previous assessment (Pitman and others, 1989). The L-3 zone 

is a comparatively thin oil shale zone that represents a near 

cessation of nahcolite deposition. Interestingly, the zone is 

thickest along the south margins of the oil shale depocenter 

similar to the R-2 and L-2 zones. Here the L-3 zone reaches a 

maximum thickness of 68 ft. (fig. 69). The oil shale depocenter during deposition of the L-3 zone occupies the same area 

in the north-central part of the basin as the previous R-3 zone 

(figs. 70–72). Maximum oil yields in this depocenter are about 

35 GPT (fig. 70) and maximum in-place oil is about 94,000 

BPA (fig. 71). Maximum in-place oil in a township is nearly 

1.6 billion barrels in T. 2 S., R. 97 W. (fig. 72). Total in-place 

oil in the L-3 zone is estimated to be about 22.5 billion barrels 

(table 17).

Using only those townships that were assessed in both 

this assessment and the previous assessment by Pitman and 

others (1989) our assessment of in-place oil for the L-3 zone is 

7.45 percent higher than the manually extrapolated results and 

2.18 percent higher than the kriged assessment of Pitman and 

others (1989) (table 17). When only the townships with the 

best control are compared (those with 20 percent or less estimated error in the kriged results of Pitman and others, 1989), 

our results are 6.39 percent higher than the manually extrapolated results and 0.48 percent higher than the kriged results of 

Pitman and others (1989) (table 17). 

R-4 Zone 

The base of the R-4 zone through the base of the 

Mahogany ledge comprises the fourth stage of Lake Uinta of 

Johnson (1985). A comparatively minor transgression marks 

the beginning of this stage, extending oil shale deposition into 

areas of the lake where marginal lacustrine facies previously 

predominated (Johnson, 1985; 1988). In some locations along 

the south and west margins of the basin, the transgression is 

marked by a shift from a marginal lacustrine sequence containing abundant thick stromatolite units to oil shale interbedded with marlstone and thin stromatolites (Johnson and 

others, 1988, sheet 1, measured section 4). In other locations 

the transgression is marked by a shift from interbedded oil 

shale and marlstone to predominantly oil shale (Johnson and 

others, 1988, sheet 1, measured section 2). The presence of 

stromatolites both above and below the base of the R-4 zone 

in some sections possibly suggests that the increase in average 

water depth after this transgression may not have been great. 

It should be remembered that water level probably fluctuated 

constantly throughout the history of this closed saline lake, 

but average water levels appear to have been somewhat higher 

beginning with the deposition of the R-4 zone than previously. 

Nahcolite is all but absent from the lower part of the R-4 zone 

in the saline depocenter, and only a few comparatively thin, 

persistent beds high in nahcolite occur in the R-4 zone overall 

(Dyni, 1974; 1981). This would suggest that lake water was 

less saline after the transgression than before.

One hundred seventy one core holes were used to assess 

the R-4 zone here as compared to 104 core holes in the previous assessment (Pitman and others, 1989). The R-4 zone is 
Detailed Description and Assessment Results of Oil Shale Zones 99

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

13

27 42.5

44

48 36

4438

54 52 25

28 36

20

32

28

86

86

60

45

48 29

38

47

40 45 71

52

55 52

65 50

65

30

42 41

41 50

70

45

66

41

37

23

30

40

32

22

31.6

24

48

24.3

57.4

41

49.3

72

115

45

42 52

55

56

82.1

27

30.4

53.1

33 40

44

41

28

57

44 46

32 26 34 32 32

32.2

41.5

50

45 61 52

44

34

26

16

22

40

27

32

30

44

62

31.8

36.6

12

40

39.7

35

32 38

54

26 30

76

30

28

50

65

34.4

34

42

44.2

40

40.6

32

40

15

12

36

15 21

50 38

58

52

48

35

27

43.5

112.7

54.5

65

33

45.7

41

28

24

34

38

73

41.9

14

40

39.7

48.9

45 30

41

49

52

44

43

66 46

54 42

43

29

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

10

L–2 interval—Thickness in feet

< 25

26–50

51–75

76–100

101–125

Figure 61. Isopach map of the L-2 zone using the Radial Basis Function Method (RBF) of contouring. Contour 

interval in feet is variable.
100 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in

 gallons per ton

10

L–2 interval—Average oil yield in gallons per ton

< 7.5

7.6–15

15.1–22.5

22.6–30

30.1–37.5

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

0.1

0.1

0.1

22.5

8.2 9.8

8.811

8.9 5.7 4.4

10.3 6.4

3.9

4.4

10.2

4.9

10.6 7

14.5

9.7

18.9

13.5

20.4

20.5

20.3 21.9

21.7

19

5

20.6

6.3

1.8

4.4

1.4

10.5

8.9

21

21.6

24.6

7.5

7.5

21.1

19.4

11.5

6.8

4.9

5.4 9.5

10.3

9.2

9.1

0.6

22

20.7

13.5 15.6

13.6

18

16.5

4.6

14.6 13.1

15.5 10.9 18.1

20.6

18.6

15.5 15.1

10.5

15 12.2 11.7

14.4

14.7

11.2

11.3

10.5

19.3

15.4

18.3

19.1

15.6

5.4

4.6

3.7

8.8

18.1

3.4

19

14.4

15.3

12.5

12.3

10.9

4.6

16.5

15.4

6.9

13.9

13.9

22.3

12.6

19.4

12

4.1

16.5

10.8

8.5

12.4

9.3

12.3

22.8

19.8

10

8.8

34.1

14.6

1.5

19.4

6.6

9.9

9.5

13.9

20.6

15.3

10.9

10.6

12.8

12.6

12.8

21

1.6

2

23.8

17

20.6 23.3

18.8

19.6

19.3

23.4

18.7

5.2 7.5

5.5 4.8

5

5.3

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 62. Isoresource map of the L-2 zone showing the oil yield in gallons per ton (GPT) using only core 

hole data. The Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 101

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

1

1

1

70

33 29

3234

40 25 9

15 30

7

12

23

36

74

35

55

23

54

50

61

46

64 66

66

65

28

63

19

4

11

5

27

16

49

38

86

15

36

64

72

67

65

19

19 41

46

43

62

1

49

82

35 49

47

56 36

22

53

46

3044 31

49

45 39

49

43

53 60 49

50

39

24

15

19

58

32

45

43

54

28

13

12

9

55

12

50

36 45

54

26 27

30

38

34

29

72

38

56

42

65

39

14

41

13

8

36

1121

84 57

48

38

112

40

4

64

62

44

51

36

70

49

25

21

35

38

75

66

2

7

69

64

77 46

59

72

76

75

61

20 41

25 17

18

13

0 3 6 12 MILES

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

L–2 zone—In barrels per acre

< 25,000

25,001–

 50,000

50,001–

 75,000

75,001–

 100,000

100,001–

 125,000

COLORADO

0 5 10 2.5 KILOMETERS

108°30' 108°00'

40°00'

39°30'

Figure 63. Isoresource map of the L-2 zone showing oil yields in barrels per acre (BPA) using only 

core hole data. The Radial Basis Function Method (RBF) was used for contouring.
102 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

141,391

660,733

1,259,120 6,503,770

3,395,740

270,436

555,180

5,685,770

4,695,510

22,310,800

5,996,400

1,855,670

2,216,060

1,240,190

5,421,290

13,045,700

40,038,700

98,460,600

46,696,300

32,731,200 1,544,860

1,916,340 7,459,390

46,517,300 98,498,200

198,512,000 190,238,000

145,776,000

87,699,200

1,416,990

13,803,100

144,602,000 283,212,992 549,811,968 376,908,992 268,010,000

67,745,104

25,259

24,019,500

560,449,984 1,160,339,968 1,281,789,952 934,408,000 480,718,016

58,880,500

31,652,100

1,007,590,016 1,411,000,064 1,420,649,984 1,315,280,000 769,420,032 12,729,900 248,452,000

560,718,976 532,768,000 47,132,900

3,695,390

1,185,049,984 1,504,349,952 1,539,670,016 1,192,259,968

469,140,000

473,636,992

933,542,016

1,306,470,016 657,993,984

173,195,008

142,620,992

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

L–2 zone shale oil, total in-place resource—In millions of barrels

< 68

69–200

201–380

381–770

771–1,500

Top of Mahogany zone

Base of Parachute Creek Member

L–2 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 64. Isoresource map of the L-2 zone showing total number of barrels of oil in each township using only 

core hole data.
Table 15. Total number of in-place barrels of oil per acre (BPA) in each township for the L-2 zone calculated here using the Radial Basis Function Mthe L-2 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method herein yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.

Township, 

Range SUM L-2 Extrapolated (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Diffe

1N 96W 173,195,000 22,940,000 150,255,000 655 25,132,000 ±85 14

1N 97W 657,994,000 140,790,000 517,204,000 367 784,995,000 ±73 -12

1N 98W 1,306,470,0001N 99W 933,542,000 131,600,000 801,942,000 609 78,716,000 ±144

1N 100W 142,621,000 758,440,000 -615,819,000 -81 634,651,000 ±20 -49

2N 97W 47,132,900 1,124,200,000 -1,077,067,100 -96 1,242,144,000 ±28 -1,19

2N 98W 532,768,000 491,326,000 41,442,000 8 848,223,000 ±122 -31

2N 99W 560,719,000 13,563,000 547,156,000 4,034 101,135,000 ±98 45

2N 100W 3,695,3901S 95W 469,140,0001S 96W 1,192,260,000 924,573,000 267,687,000 29 1,035,633,000 ±60 15

1S 97W 1,539,670,000 1,598,805,000 -59,135,000 -4 1,187,460,000 ±14 35

1S 98W 1,504,350,000 1,766,380,000 -262,030,000 -15 1,341,564,000 ±11 16

1S 99W 1,185,050,000 1,175,520,000 9,530,000 1 1,229,485,000 ±23 -4

1S 100W 473,637,000 269,154,000 204,483,000 76 507,642,000 ±63 -3

2S 94W 12,729,9002S 95W 769,420,000 529,940,000 239,480,000 45 530,605,000 ±307 23

2S 96W 1,315,280,000 1,163,950,000 151,330,000 13 1,173,075,000 ±29 14

2S 97W 1,420,650,000 1,281,582,000 139,068,000 11 1,399,168,000 ±10 2

2S 98W 1,411,000,000 1,341,780,000 69,220,000 5 1,231,889,000 ±10 17

2S 99W 1,007,590,000 971,082,000 36,508,000 4 974,440,000 ±19 3

2S 100W 248,452,000 207,383,000 41,069,000 20 480,258,000 ±57 -23

3S 94W 58,880,5003S 95W 480,718,000 400,374,000 80,344,000 20 275,185,000 ±355 20

3S 96W 934,408,000 884,208,000 50,200,000 6 927,150,000 ±24 

3S 97W 1,281,790,000 1,418,700,000 -136,910,000 -10 1,092,010,000 ±14 18

3S 98W 1,160,340,000 1,127,900,000 32,440,000 3 905,320,000 ±22 25

3S 99W 560,450,000 273,858,000 286,592,000 105 361,049,000 ±117 19

3S 100W 31,652,100 106,990,000 ±501 -7

4S 94W 67,745,1004S 95W 268,010,000 275,388,000 -7,378,000 -3 246,409,000 ±175 2
Table 15. Total number of in-place barrels of oil per acre (BPA) in each township for the L-2 zone calculated here using the Radial Basis Function Mthe L-2 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method herein yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.—C

Township, Range SUM L-2 Extrapolated (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Diffe

4S 96W 376,909,000 362,032,000 14,877,000 4 565,147,000 ±39 -18

4S 97W 549,812,000 349,605,000 200,207,000 57 519,824,000 ±67 2

4S 98W 283,213,000 344,370,000 -61,157,000 -18 4S 99W 144,602,000 4S 100W 24,019,500 4S 101W 25,259 5S 94W 87,699,200 5S 95W 145,776,000 5S 96W 190,238,000 196,130,000 -5,892,000 -3 179,051,000 ±550 1

5S 97W 198,512,000 183,224,000 15,288,000 8 5S 98W 98,498,200 201,972,000 -103,473,800 -51 5S 99W 46,517,300 5S 100W 13,803,100 5S 101W 1,416,990 6S 94W 1,544,860 6S 95W 32,731,200 6S 96W 46,696,300 6S 97W 98,460,600 91,785,000 6,675,600 7 6S 98W 40,038,700 53,220,000 -13,181,300 -25 6S 99W 13,045,700 6S 100W 7,459,390 6S 101W 1,916,340 7S 93W 87 7S 94W 2,216,060 7S 95W 1,855,670 7S 96W 5,996,400 7S 97W 22,310,800

7S 98W 4,695,5107S 99W 5,685,7707S 100W 5,421,2907S 101W 1,240,190
Table 15. Total number of in-place barrels of oil per acre (BPA) in each township for the L-2 zone calculated here using the Radial Basis Function Mthe L-2 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method herein yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.—C

Township, 

Range SUM L-2 Extrapolated (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Diffe

8S 93W 270,4368S 94W 3,395,7408S 95W 6,503,7708S 96W 95,8438S 99W 1,259,1208S 100W 555,1808S 101W 70,6149S 94W 8,2779S 95W 660,7339S 96W 141,391Totals: 24,216,677,409 20,075,774,000 19,984,350,000Sum of townships used here 

and Pitman and others (1989) extrapolated:

21,737,311,900 Sum of townships used here and kriging: 20,949,658,000

Percent difference using RBF 

here and Pitman and others (1989)extrapolated:

8.28 Percent difference between RBF and kriging: 4.83

Sum of best townships RBF (20 

percent): 7,416,028,000 Sum of best townships extrapolated: 7,450,955,000 Sum of best townships kriging: 6,98

Percent difference RBF vs extrapolation for best TSPS: -0.47Percent difference RBF vs kriging 

for best TSPS:

6.21
106 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

110

 R–3 interval—Thickness in feet

31–60

61–90

91–120

121–150

151–180

< 30

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

25

54 127.4

51

52 58

53 62

52 46 22

32 55

34

30

36

52

79

98

63.1

60

74

81

124

111

115 75 62

48

60 48

53 47

48

85

153 121

119 50

62

101

66

97

43

77

23

42

36

60 42

38

133.4

137

129

27.3

56.2

108

147.4

132

86

47

41 56

52

46

70.9

34

127.8

90.9

68

92

66

90

102

50

85

86.4

97 78 86

89.3 93 80.3 74.6

73

116 91.2

78

130

80

50

28

48

86

85

86

84

84

67

38.8

35

34

72

31

91

88 86

80

90

48

88

87

83

56.6

102.7

77

93.9

80

113.2

48

45.3

107

60 42

34

64

33 45

146

136

62

66

136

84

29

102.5

80.5

67

80

120.7

110.1

94

54

64

60

62

86.9

106.8

25.2

30

108.8

88.2

132 144

111

146

137

148

93

44 54

48 38.2

37.3

28

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 65. Isopach map of the R-3 zone using the Radial Basis Function Method (RBF) of contouring. Contour 

interval in feet is variable.
Detailed Description and Assessment Results of Oil Shale Zones 107

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in 

 gallons per ton

10

R–3 interval—Average oil yield in gallons per ton

10.1–20

20.1–30

30.1–40

40.1–50

< 10

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

0.1

0.1

0.1

30

18 19.2

19.5 19.7

18.5

15.2

10.2

12.9 19.1

8.9

9.1

8.9

13.1

11.6

17.9 16.4

22.2

22.7

25.9

21.5

28.3

24.1

27.8 27.5

25.3

26.4

10.2

28.2

9.8

11.1

6.2

10.7

4.7

23.9

23.6

16.7

28.1

28.7

27.1

16.5

10.7

26.9

25.5

19.8

14.7

9

10.6 19.4

19.4

16.9

17.8

5.4

26.9

28.3

23.3 24.9

22.4

28.7

28

9.1

27.4 22.9 29.6 20.7 26.8

33.6

34.5 31.1 23.7

19.6

21.1 18.9 20.1

22.1

23

20.5

21.1

22.9

30.1

26 33.7

25.1

9.4

9.2

9.4

19.3

30.9

8.9

33.7

26.2 24.5

20.6

20.8

22.5

21.1

28.8

25.8

12.6

20.7

24.8

33.6

20

28.1

21

9.6

24.9

23.6

20.3

24

24.3

20.2

26.3

26.7

18.3

19.1

43.5

24.1

6.3

25.8

14.4

18.9

16.8

24.6

30.7

26

20.1

21

20

20.6

24

4.9

7.2

28.7

26.3

28.2 26.9

23.1

27.3

24.4

31.6

31.4

17.3

13.3 14.7 11.9

11.8

10.9

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 66. Isoresource map for the R-3 zone showing the oil yield in gallons per ton (GPT) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
108 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

R–3 zone—In barrels per acre

< 75,000

75,001–

 150,000

150,001–

 225,000

225,001–

 300,000

300,001–

 375,000

375,001–

 450,000

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

1

1

1

267

72 84

7892

73 18 55

33 80

25

23

27

54

74

134 80

121

135

231

177

230

149

302 236

217

191

55

194

35

69

12

37

14

73

103

49

265

277

249

35

49

207

270

197

99

35

35 82

76

60

97

15

245

182

116 166

109

182 202

38

166 145

164 201 121

205

201 188

129

108

182 131 118

212

135

77

44

81

181

159

177

194

152

52

29

27

50

155

23

210

165 153

123

140

80

138

177

154

57

159

138

216

120

225

75

36

193

72

52

112

58

68

275

259

86

95

381

147

15

190

91

96

104

215

235

175

81

94

94

93

134

187

11

18

220

166

276 263

188

284

243

324

202

7247

55 37

35

25

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 67. Isoresource map for the R-3 zone showing oil yields in barrels per acre (BPA) using only core 

hole data. The Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 109

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

128,546 749,814

8,543,330 8,328,180 31,173

0

2,683,380

47,371,500

20,806,100

87,776,000

21,957,900

2,957,990

282,329

5,578,450

35,823,700

76,402,704 139,666,000

280,955,008

112,565,000

72,108,000 2,667,860

15,263,600 61,356,600

214,880,992 315,614,016

480,104,000

453,046,016 326,164,000

170,803,008

4,171,350

80,703,800

401,710,016 644,401,024 1,030,739,968 897,001,024 576,412,032

119,549,000

39,939

76,448,000

1,072,220,032 2,376,519,936 3,263,150,080 2,034,620,032 854,417,024 87,627,696 57,027,100

3,004,470,016 5,177,650,176 4,813,799,936 2,999,680,000 1,289,440,000 16,472,100

470,617,984

1,612,729,984 1,321,600,000

119,142,000

12,129,300

4,329,569,792 6,462,239,744 5,236,089,856 2,552,270,080

698,678,016 1,176,290,048

3,106,599,936

3,891,739,904

2,301,639,936

467,192,000

482,952,000

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

R–3 zone shale oil, total in-place resource—In millions of barrels

< 290

291–900

901–2,000

2,001–3,900

3,901–6,500

Top of Mahogany zone

Base of Parachute Creek Member

R–3 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 68. Isoresource map of the R-3 zone showing total number of barrels of oil in each township using only 

core hole data.
Table 16. Total number of in-place barrels of oil per acre (BPA) in each township for the R-3 zone calculated here using the Radial Basis Function Mthe R-3 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method herein yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level. Nuappear to be errors in the calculations made by Pitman and others (1989). Township, Range SUM R-3 "Extrapolated" (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence 

1N 96W 467,192,000 57,350,000 409,842,000 715 46,180,000 ±121 

1N 97W 2,301,640,000 422,370,000 1,879,270,000 445 272,661,000 ±461 2

1N 98W 3,891,740,000 31N 99W 3,106,600,000 329,000,000 2,777,600,000 844 387,412,000 ±44 2

1N 100W 482,952,000 1,896,100,000 -1,413,148,000 -75 2,176,476,000 ±7 -1

2N 97W 119,142,000 3,822,280,000 -3,123,602,000 -82 3,744,418,000 ±17 -32N 98W 1,321,600,000 2,969,318,000 -417,048,000 -14 3,083,941,000 ±25 

2N 99W 1,612,730,000 94,941,000 5,141,149,000 5,415 110,960,000 ±103 5

2N 100W 12,129,300 6

1S 95W 698,678,000 4

1S 96W 2,552,270,000 1,943,974,000 -767,684,000 -39 2,135,441,000 ±60 

1S 97W 5,236,090,000 5,411,340,000 -5,292,198,000 -98 5,037,376,000 ±9 -4

1S 98W 6,462,240,000 6,206,200,000 -4,884,600,000 -79 6,038,495,000 ±8 -4

1S 99W 4,329,570,000 4,408,200,000 -2,795,470,000 -63 4,291,099,000 ±11 -2

1S 100W 1,176,290,000 897,180,000 -885,050,700 -99 968,840,000 ±60 

2S 94W 16,472,100 

2S 95W 1,289,440,000 1,192,365,000 97,075,000 8 1,557,951,000 ±117 

2S 96W 2,999,680,000 3,259,060,000 -259,380,000 -8 2,996,821,000 ±27 

2S 97W 4,813,800,000 4,343,139,000 470,661,000 11 4,668,916,000 ±11 

2S 98W 5,177,650,000 5,143,490,000 34,160,000 1 4,906,089,000 ±9 

2S 99W 3,004,470,000 2,543,310,000 461,160,000 18 2,924,846,000 ±18 

2S 100W 470,618,000 414,766,000 55,852,000 13 325,491,000 ±162 

3S 94W 87,627,700 

3S 95W 854,417,000 444,860,000 409,557,000 92 426,256,000 ±314 

3S 96W 2,034,620,000 1,768,416,000 266,204,000 15 1,858,767,000 ±22 

3S 97W 3,263,150,000 3,050,205,000 212,945,000 7 3,208,191,000 ±9 

3S 98W 2,376,520,000 1,804,640,000 571,880,000 32 2,286,908,000 ±16 

3S 99W 1,072,220,000 842,640,000 229,580,000 27 844,997,000 ±158 

3S 100W 57,027,100 57,030,000 -2,900 0 
Table 16. Total number of in-place barrels of oil per acre (BPA) in each township for the R-3 zone calculated here using the Radial Basis Function Mthe R-3 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method herein yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level. Nuappear to be errors in the calculations made by Pitman and others (1989).—Continued

Township, 

Range SUM R-3

"Extrapolated" 

(Pitman and 

others, 1989)

Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence 

4S 94W 119,549,000 

4S 95W 576,412,000 688,470,000 -112,058,000 -16 560,013,000 ±211 

4S 96W 897,001,000 950,334,000 -53,333,000 -6 892,895,000 ±97 

4S 97W 1,030,740,000 1,002,201,000 28,539,000 3 920,011,000 ±45 

4S 98W 644,401,000 642,824,000 1,577,000 0 394,900,000 ±178 

4S 99W 401,710,000 

4S 100W 76,448,000 

4S 101W 39,939 5S 94W 170,803,000 

5S 95W 326,164,000 

5S 96W 453,046,000 431,486,000 21,560,000 5 306,460,000 ±403 

5S 97W 480,104,000 503,866,000 -23,762,000 -5 275,889,000 ±570 

5S 98W 315,614,000 370,282,000 -54,668,000 -15 100,584,000 ±2351 

5S 99W 214,881,0005S 100W 80,703,8005S 101W 4,171,3506S 94W 2,667,8606S 95W 72,108,0006S 96W 112,565,0006S 97W 280,955,000 348,783,000 -67,828,000 -19

6S 98W 139,666,000 122,080,000 17,586,000 14

6S 99W 76,402,7006S 100W 61,356,6006S 101W 15,263,6007S 93W 07S 94W 282,329

7S 95W 2,957,9907S 96W 21,957,9007S 97W 87,776,000
Table 16. Total number of in-place barrels of oil per acre (BPA) in each township for the R-3 zone calculated here using the Radial Basis Function Mthe R-3 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method herein yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level. Nuappear to be errors in the calculations made by Pitman and others (1989).—Continued Township, Range SUM R-3 "Extrapolated" (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence 

7S 98W 20,806,100 7S 99W 47,371,500 7S 100W 35,823,700 7S 101W 5,578,450 8S 93W 0 8S 94W 31,173 8S 95W 8,328,180 8S 96W 171,246 8S 99W 8,543,330 8S 100W 2,683,380 8S 101W 120,597 9S 94W 0 9S 95W 749,814 9S 96W 128,546 Totals: 68,084,658,284 58,382,500,000 57,749,284,000 Sum of townships used here and Pitman and others, (1989) extrapolated: 61,399,867,100 Sum of townships used here and kriging 61,342,840,000 Percent difference using RBF here and Pitman and others (1989) extrapolated: 5.17 Percent difference between RBF and kriging 6.22 Sum of best townships RBF (20 percent): 34,663,490,000 Sum of best townships extrapolated: 32,910,524,000 Sum of best townships kriging: 33,361,920,000 Percent difference RBF vs ex- trapolation for best TSPS: 5.33 Percent difference RBF vs kriging for best TSPS: 3.90
Detailed Description and Assessment Results of Oil Shale Zones 113

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

10

L–3 interval—Thickness in feet

< 15

16–30

31–45

46–60

61–75

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

13

27 34.4

37

30 30

3028

26 16 15

27 27

35.3

34

34

30

30

24

36

61

50.9

35

32

27

49

68

40 43 48

62

35 45

42 43

42

39

35 37.4 39

49 40

30

34

47

30

52

27

36

8

32

32

34

30

34

18

43.1

34

32

27.8

36.3

0

0

0 0

43

32.3

66

52

29

19

34

33

23

50.7

16

45.2

44

39.2 46

38

42

40

48

27.6 38

40 38 30

36.227.7

25

33

58

61 51.8 60

53

34

32

34

30

36

33

40

34

42

29

27.9

29.4

28

37

30

25.8

34 34

40

28

34

36

34

39

35

40.5

57.3

33.2

33.1

40

42

38

23.5

43

32 33

21

32

32

24

36 34

56

56

40

30

17

45.2

46

57.7

48

70.4

40.9

38

44

39

30

34

32

32

45.1

48.9

15.8

44

35.6 45

27

46.2

48.1

46

38

44

34

28

40

43

45.4

17.3 30

22 13.8

12.7

13

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 69. Isopach map of the L-3 zone using the Radial Basis Function Method (RBF) of contouring. Contour 

interval in feet is variable.
114 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in

 gallons per ton

10

L–3 interval—Average oil yield in gallons per ton

< 7.5

7.6–15

15.1–22.5

22.6–30

30.1–37.5

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

0.1

0.1

0.1

16.5

8.3 9.1

8.2

8.3

7.6

8.5 7

7.1 9

4.1

6.3

5.4

7.5

6.3

10.1

6.5

8

7.8

12.9

12.5

19.5

13.8

18.2

17.8

19.8 23.4 19.1

22.8

13.6

17.3

7.5

20.7

8.1

6.7

2.5

5.7

3

11.7

10.2

12.7

6.8

20.4

21.3

20.7

7.4

7.3

21.7

16.4

10.9

6

6.9

9.3 8.7

8.6

7.2

7.1

4

19.4

18.1

14.1 16.4

12.2

17.7

15.1

4.9

14.815.1

17.2 9.5 13.2

19.8

20.6

15

10.3

8.9

9.7 7.2 8.3

10.9

15.6

10.4 8.7

9

16

11.8

16.4

19.4

14.7

6.6

6.7

4.9

8.3

16.1

4.5

16.8

11.111.3

13.5

12.3

11

13.4

13.1

16.5

13

7.7

10.2

11.3

17.7

11.7

16.6

11

6.7

16.6

10.5

8.4

10.7

12.8

9.9

19.5

16.8

9.2

7.5

34.7

12.1

3.6

19.7

6.9

8.4

8

14.6

18.6

17.7

19.1

11.5

9.3

9.8

10.8

8.8

8.8

19.9

3.6

1.8

5.9 3.6

7.5

21

17.8

19.9 21.3

22.1

18.5

16.6

22.1

18.2

18

8.97.4

7.3 7

6.3

7.7

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 70. Isoresource map of the L-3 zone showing the oil yield in gallons per ton (GPT) using only core hole data. 

The Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 115

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

1

1

1

44

21 23

2019

17 11 9

16 20

12

18

15

19

16

20

20

41

33

33

27

72

74

56

53

64 52 56

82

37

62

19

80

18

20

2

15

8

32

25

35

10

66

54

49

17

22

69

41

58

26

17

15 25

24

14

30

6

66

61

44

58

37

57 47

20

44 33

50 42 23 41

56 29

28

43

49 31 41

47

41

27 25

22

45

31

51

50

48

16

16

12

19

46

12

33

31 31

43

28

30

38

36

50

36

26

48

30

45

38

54

34

13

55

28

15

28

33

19

53

44

43

35

94

29

5

67

26

40

32

81

58

52

64

36

23

27

28

23

33

73

5

7

18 14

17

72

66

73 57 72

48

36

65

60

62

11 22

13

8

7

8

108°30' 108°00'

40°00'

39°30'

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

L–3 zone—In barrels per acre

< 20,000

20,001–

 40,000

40,001–

 60,000

60,001–

 80,000

80,001–

 100,000

0 3 6 12 MILES

Figure 71. Isoresource map of the L-3 zone showing oil yields in barrels per acre (BPA) using only core hole data. 

The Radial Basis Function Method (RBF) was used for contouring.
116 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

153,388 810,447

3,239,330 8,845,360 1,688,610 4,196

1,195,130

19,278,100

8,944,000

34,682,400

9,712,970

3,516,820

3,005,740

4,162,670

19,282,600

48,089,200

83,162,304

160,492,000

81,159,400

78,132,200 3,508,330

14,044,400 43,380,700

200,692,000 246,024,000

319,980,992

266,082,000 232,836,992

168,438,000

4,856,840

82,313,400

324,220,992 369,384,992 453,608,000 420,609,984 349,907,008

103,140,000

152,784

70,767,400

301,676,992 682,460,032 1,008,670,016 798,265,024 457,003,008

59,379,600 13,972,900

744,926,976 1,287,360,000 1,569,080,064 1,031,550,016 517,760,000 8,928,400

141,342,000

406,371,008 435,708,000 35,921,800

2,539,220

1,145,200,000 1,415,689,984 1,396,080,000 954,772,992

313,855,008

344,366,016

820,372,992 1,317,689,984 726,380,032

204,318,000

118,689,000

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

L–3 zone shale oil, total in-place resource—In millions of barrels

< 110

111–270

271–520

521–1,000

1,001–1,600

Top of Mahogany zone

Base of Parachute Creek Member

L–3 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 72. Isoresource map of the L-3 zone showing total number of barrels of oil in each township using only 

core hole data.
Table 17. Total number of in-place barrels of oil per acre (BPA) in each township for the L-3 zone calculated here using the Radial Basis Function Mfor the L-3 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hhighlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidenc

Township, 

Range SUM L-3

"Extrapolated" 

(Pitman and 

others, 1989)

Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confi- dence Differ

1N 96W 204,318,000 164,500,000 39,818,000 24 154,595,000 ±45 49,

1N 97W 726,380,000 625,713,000 100,667,000 16 711,063,000 ±7 15,

1N 98W 1,317,690,000 1,169,168,000 148,522,000 13 1,174,470,000 ±23 143,

1N 99W 820,373,000 598,136,000 222,237,000 37 810,883,000 ±36 9,

1N 100W 118,689,000 19,591,000 99,098,000 506 26,287,000 ±155 92,

2N 97W 35,921,800 17,205,000 18,716,800 109 24,426,000 ±97 11,

2N 98W 435,708,000 140,790,000 294,918,000 209 433,335,000 ±102 2,

2N 99W 406,371,0002N 100W 2,539,2201S 95W 313,855,0001S 96W 954,773,000 734,917,000 219,856,000 30 868,808,000 ±54 85,

1S 97W 1,396,080,000 1,451,223,000 -55,143,000 -4 1,411,881,000 ±10 -15,

1S 98W 1,415,690,000 1,718,640,000 -302,950,000 -18 1,462,488,000 ±10 -46,

1S 99W 1,145,200,000 1,028,580,000 116,620,000 11 1,099,224,000 ±14 45,

1S 100W 344,366,000 209,342,000 135,024,000 64 239,795,000 ±86 104,

2S 94W 8,928,400

2S 95W 517,760,000 503,443,000 14,317,000 3 471,596,000 ±163 46,

2S 96W 1,031,550,000 1,000,997,000 30,553,000 3 1,021,110,000 ±28 10,

2S 97W 1,569,080,000 1,685,043,000 -115,963,000 -7 1,538,031,000 ±12 31,

2S 98W 1,287,360,000 1,207,602,000 79,758,000 7 1,265,613,000 ±15 21,

2S 99W 744,927,000 647,388,000 97,539,000 15 874,582,000 ±27 -129,

2S 100W 141,342,000 170,786,000 -29,444,000 -17 232,584,000 ±95 -91,

3S 94W 59,379,6003S 95W 457,003,000 400,374,000 56,629,000 14 352,433,000 ±160 104,

3S 96W 798,265,000 748,176,000 50,089,000 7 769,126,000 ±22 29,

3S 97W 1,008,670,000 945,800,000 62,870,000 7 1,044,790,000 ±12 -36,

3S 98W 682,460,000 676,740,000 5,720,000 1 646,242,000 ±23 36,

3S 99W 301,677,000 337,056,000 -35,379,000 -10 475,943,000 ±94 -174,

3S 100W 13,972,900 32,317,000 -18,344,100 -57 20,533,000 ±361 -6,
Table 17. Total number of in-place barrels of oil per acre (BPA) in each township for the L-3 zone calculated here using the Radial Basis Function Mfor the L-3 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hhighlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidenc

Township, Range SUM L-3 "Extrapolated" (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confi- dence Differ

4S 94W 103,140,000 4S 95W 349,907,000 130,215,000 ±614 219,

4S 96W 420,610,000 407,286,000 13,324,000 3 429,568,000 ±86 -8,

4S 97W 453,608,000 442,833,000 10,775,000 2 418,367,000 ±61 35,

4S 98W 369,385,000 344,370,000 25,015,000 7 298,384,000 ±86 71,

4S 99W 324,221,000 308,280,000 15,941,000 5 296,540,000 ±201 27,

4S 100W 70,767,400 4S 101W 152,784 5S 94W 168,438,000 5S 95W 232,837,000 5S 96W 266,082,000 215,743,000 50,339,000 23 222,338,000 ±174 43,

5S 97W 319,981,000 320,642,000 -661,000 0 306,488,000 ±87 13,

5S 98W 246,024,000 201,972,000 44,052,000 22 213,387,000 ±382 32,

5S 99W 200,692,000 5S 100W 82,313,400 5S 101W 4,856,840 6S 94W 3,508,330 6S 95W 78,132,200 6S 96W 81,159,400 6S 97W 160,492,000 165,213,000 -4,721,000 -3 6S 98W 83,162,300 78,480,000 4,682,300 6 6S 99W 48,089,200 6S 100W 43,380,700 6S 101W 14,044,400 7S 93W 0 7S 94W 3,005,740

7S 95W 3,516,8207S 96W 9,712,9707S 97W 34,682,400

7S 98W 8,944,000
Table 17. Total number of in-place barrels of oil per acre (BPA) in each township for the L-3 zone calculated here using the Radial Basis Function Mfor the L-3 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hhighlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidenc

Township, 

Range SUM L-3

"Extrapolated" 

(Pitman and 

others, 1989)

Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confi- dence Differ

7S 99W 19,278,1007S 100W 19,282,6007S 101W 4,162,6708S 93W 4,1968S 94W 1,688,6108S 95W 8,845,3608S 96W 123,8618S 99W 3,239,3308S 100W 1,195,1308S 101W 95,0169S 94W 3,0599S 95W 810,4479S 96W 153,388 153,388

Totals: 22,504,056,571 18,718,346,000 19,445,125,000

Sum of townships used here 

and Pitman and others (1989) extrapolated:

20,112,821,000 Sum of townships 

used here and kriging:

19,869,166,700

Percent difference using RBF 

here and Pitman and others (1989) extrapolated:

7.45 Percent difference 

between RBF and kriging:

2.18

Sum of best townships RBF 

(20 percent):

9,346,725,000 Sum of best 

townships extrapolated:

8,785,064,000 Sum of best 

townships kriging:

9,302,

Percent difference RBF vs 

extrapolation for best TSPS:

6.39

Percent difference RBF vs 

kriging for best TSPS:

0.48
120 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

thickest along a southeast-trending belt extending from the 

oil shale depocenter in the north-central part of the basin to 

the east margin of the basin, reaching a maximum thickness 

of about 165 ft along this trend (fig. 73). Oil yield reaches a 

maximum of about 43 GPT in the saline depocenter (fig. 74). 

The area of at least 20 GPT extends farther towards the 

margins of the basin during R-4 deposition than any of the 

previous oil shale zones except the R-1 zone (figs. 46, 50, 54, 

58, 62, 66, 70). Maximum BPA is about 424,000 in the middle 

part of the saline and oil shale depocenter in the north-central 

part of the basin (fig. 75). Maximum in-place oil in a township 

is over 8.9 billion barrels in T. 1 S., R. 98 W. (fig. 76). Total 

in-place oil in the R-4 zone is estimated to be over 127 billion 

barrels (table 18).

Using only those townships that were assessed in both 

this assessment and the previous assessment by Pitman and 

others (1989), our assessment of in-place oil for the R-4 zone 

is 7.45 percent higher than the manually extrapolated results 

and 2.18 percent higher than the kriged assessment of Pitman 

and others (1989) (table 18). When only the townships with 

the best control are compared (those with 20 percent or less 

estimated error in the kriged results of Pitman and others, 

1989), our results are 6.39 percent higher than the manually 

extrapolated results and 0.48 percent higher than the kriged 

results of Pitman and others (1989) (table 18). 

L-4 Zone

One hundred seventy three core holes were used here 

to assess the L-4 zone as compared to 101 core holes in the 

previous assessment (Pitman and others, 1989). The L-4 

zone is thickest in about the same southeast trending belt as 

the underlying R-4 zone reaching a maximum thickness of 

184 ft in the saline depocenter (fig. 77). Oil yields gradually 

decline in the lower part of the L-4 zone (fig. 7). The L-4 zone 

contains large amounts of nahcolite in the saline depocenter, 

and several persistent nahcolite beds have been traced 

throughout the depocenter (Dyni, 1974; 1981). Oil yields 

are significantly lower overall in the L-4 zone than in the 

underlying R-4 zone, with a maximum of about 34 GPT in the 

saline depocenter and lower values throughout the marginal 

areas of the basin (fig. 78). Maximum BPA is about 426,000 

in the saline depocenter (fig. 79). Maximum in-place oil in a 

township is over 6 billion barrels in T. 1 S., R. 98 W. (fig. 80). 

Total in-place oil in the L-4 zone is estimated to be over 

69.1 billion barrels (table 19).

Using only those townships that were assessed in both 

this assessment and the previous assessment by Pitman and 

others (1989) our assessment of in-place oil for the L-4 zone 

is 7.47 percent higher than the manually extrapolated results 

and 5.98 percent higher than the kriged assessment of Pitman 

and others (1989) (table 19). When only the townships with 

the best control are compared (those with 20 percent or less 

estimated error in the kriged results of Pitman and others, 

1989), our results are 4.09 percent higher than the manually 

extrapolated results and 5.09 percent higher than the kriged 

results of Pitman and others (1989) (table 19). 

R-5 Zone

A significant increase in oil yield marks the base of the 

R-5 zone (fig. 7). The basal bed of the R-5 zone contains 

abundant nahcolite in the oil shale depocenter, and thick beds 

of halite and nahcolite occur throughout the lower part of the 

R-5 zone starting about 15–20 ft above the base (fig. 7) (Dyni, 

1974; 1981). Thinner beds of halite and nahcolite occur in the 

upper part of the R-5 zone, and nahcolite levels, in general, are 

comparatively high in the R-5 zone when compared to previous oil shale zones. 

One hundred seventy six core holes were used to assess 

the R-5 zone here as compared to 107 in the previous assessment (Pitman and others, 1989). The R-5 zone is thickest 

through a broad band that extends from the oil shale depocenter southeastward to near the basin margin (fig. 81). Maximum 

thickness for the zone is in the oil shale and saline-mineral 

depocenter where thickness ranges from 225 to 380 ft. A silty 

and sandy zone about 60 ft thick occurs in the lower part of 

the R-5 zone along the east margin of the basin in about the 

same stratigraphic interval as the thick halite beds in the saline 

depocenter (Carter Oil Co. no. 2 upper Piceance Creek core 

hole in sec. 9, T. 3 S., R. 95 W., labeled 253 ft on fig. 81). This 

wedge appears to be eastern sourced as it wedges out to the 

west, and no similar wedge occurs along the southern, western, and northern margins of the basin. 

The R-5 zone contains as much as 41.4 GPT in the oil 

shale and saline depocenter in the north-central part of the 

basin with oil yields generally decreasing in a radial pattern 

outward (fig. 82). Maximum BPA varies from about 400,000 

to 870,000 in the oil shale and saline depocenter (fig. 83). 

Maximum in-place oil in the R-5 zone in a township is almost 

13.4 billion barrels in T. 1 S., R. 98 W. (fig. 84). Total in-place 

oil in the R-5 zone is estimated to be over 198.2 billion barrels 

(table 20).

Using only those townships that were assessed in both 

this assessment and the previous assessment by Pitman and 

others (1989) our assessment of in-place oil for the R-5 zone is 

6.32 percent higher than the manually extrapolated results and 

8.61 percent higher than the kriged assessment of Pitman and 

others (1989) (table 20). When only the townships with the 

best control are compared (those with 20 percent or less estimated error in the kriged results of Pitman and others, 1989), 

our results are 2.64 percent higher than the manually extrapolated results and 5.73 percent higher than the kriged results of 

Pitman and others (1989) (table 20). 

L-5 Zone

The lower part of the L-5 zone contains huge deposits 

of halite and nahcolite in two beds about 20 ft a part with 

each bed reaching a maximum thickness of 60–65 ft (Dyni, 
Detailed Description and Assessment Results of Oil Shale Zones 121

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

110

R–4 interval—Thickness in feet

61–90

91–120

121–150

151–180

< 60

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

30

50 151.6

125

58 66

6369

66

66

51

66 46

75

75.3

78

69

74

84 78

67 77

96

107

150

72

73

145

131

148 155 117

133 140

135

135

97

121

158

157.5

150.6

146

143

117

84

148

78

154

74

81

67

80

72

94

92

106

80

74

144.9

149

149

82.5

74.2

0

0

0

0

163

157.5

119

94

76

54 61

57

50

95.9

78

150.3

157.8

114.9

126

104

92.2

85.4

139

70

72

79 91 76

102

104.8 83

72.4

103

116

115

114 114.3 106

135

128

100

74

94

77

85

108

84

79

76.5

78

84

88

79.4

110.2

74 72

120

116

100

116

92

88

75

81.4

115

75.3

117

120

149

96

71.5

142

108

84

79

121

79

108

164

162

95

90

144

123

87

146.1

89.1

102.2

124

136.5

153.5

148.9

151.9

91

100

110

106

106

98

151.1

82

102

70 85

145.8

143.7

165 121 154

162

156

156

145

149.9

70 64.3

64 65

62

62

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 73. Isopach map of the R-4 zone using the Radial Basis Function Method (RBF) of contouring. Contour 

interval in feet is variable.
122 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in 

 gallons per ton

10

R–4 interval—Average oil yield in gallons per ton

10.1–20

20.1–30

30.1–40

40.1–50

< 10

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

35.3

27.6 29.1

28.3 28.4

28.1

24.9 19

21.8 29.4

13.3

16.5

15.3

15

16.1

18.2 15.8

19.7 28.3

28.8 19.3

31

36

33.5

29.5

34.9

7

37.8

38.533

33.8

33.3

27

24.9

30.3

23.7

33.3

21.8

24.8

10.5

20.5

10.3

27.8 25.3

30.8

10.9

19.2

35.9

38.3

37.8

16.2

23.4

32.5

34.5

27.4

25

19.2

23.2 27.9

28.9

29.2

26.9

4.8

35

31.8

26.9 32.9

28.3

36.3

36.1

9.4

33.5 31.1

37.3 32.5

29.6 40.7 40.8

36.3 32.6

26.6

25.5

27

27.8

27.4 27.2

30.1

29.7

25

21.4

22.9

36.4

34

36.3

40.8

34.2

23.7

17

15.9

18.3

35.4

14

39.4

33.8 33.3

26.6

29.2

26.1

27.6

32.5

33.7

24.4

28.2

34.2

39.7

28.5

34.2

24.5

20.6

31.7

29.7

21.7

27.8

22.9

23.6

38.1 34

26.9

21.6

43.1

25.2

7.6

31

25.1

24.8

19

31

36.7

34.4

35.3

33.3

25.9

25.3

24.7

30.2

34.2

6

4.2

17.1 11.7

39.9

33.2

38.6 33.6

34.4

35.4

33.4

41.8

35.3

32.6

22.4 27.9

25.2 20.8

20.6

18.4

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 74. Isoresource map of the R-4 zone showing the oil yield in gallons per ton (GPT) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 123

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

362

114 135

126 138

131

73 119

136 74

79

96

93

80

92

117

96

99 154

195

156

155

177

333

271

350

57

305

358

402

348

333

275

151

313

135

352

119

145

57

123

61

185

168 227

71

107

351

379

375

104

127

365

369

232

170

110

92

121

116

103

184

32

357

347

220

285

208

225 208

108

151

165

177 227 158 272

280 203

162

196

213

221

225 223 205

284

266

180

118

165

230

179

208

288

196

137

100

96

117

211

88

286

171 164

228

238

187

227

206

202

173

144

229

175

306

241

347

170

110

311

56

153

127

239

133

186

416

376

182

144

400

224

55

315

161

183

179

294

378

349

363

208

186

193

190

207

352

42

37

92 80

383

327

310 379

358

388

357

424

346

336

106 138

116 101

95

87

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

R–4 zone—In barrels per acre

< 100,000

100,001–

 200,000

200,001–

 300,000

300,001–

 400,000

400,001–

 500,000

Figure 75. Isoresource map of the R-4 zone showing oil yields in barrels per acre (BPA) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
124 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1,273,500 9,949,750

21,911,100 161,276,000

201,040,000 83,815,600 5,542,230

120,981,000

79,165,904

335,768,000

90,020,304

60,734,000

160,738,000

24,045,000

92,915,904

249,835,008

567,456,000

1,176,850,048

530,916,992

470,380,992 28,850,900

90,764,704 216,186,000

904,979,968 1,283,570,048

1,863,920,000

1,700,240,000 1,459,020,032

1,051,720,000

47,440,000 469,136,992

1,551,640,064 2,241,349,888 2,708,379,904 2,695,350,016 2,110,899,968

603,963,008

3,501,940

494,132,000

2,226,099,968 3,948,709,888 4,893,660,160 3,879,439,872 2,439,389,952

341,067,008

230,256,992

4,122,510,080 6,879,680,000 7,722,109,952 5,327,000,064 2,936,509,952

52,051,200 1,183,920,000

2,168,900,096 1,841,360,000

243,592,992

17,857,800

6,739,630,080 8,922,470,400 7,977,039,872 5,192,260,096

1,861,570,048

2,046,909,952

5,121,739,776 6,682,880,000 4,241,890,048

1,155,680,000

782,504,000

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

R–4 zone shale oil, total in-place resource—In millions of barrels

< 610

611–1,700

1,701–2,900

2,901–5,300

5,301–8,900

Top of Mahogany zone

Base of Parachute Creek Member

R–4 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 76. Isoresource map of the R-4 zone showing total number of barrels of oil in each township using only 

core hole data.
Table 18. Total number of in-place barrels of oil per acre (BPA) in each township for the R-4 zone calculated here using the Radial Basis Function Mthe R-4 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hereyellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.

Township, 

Range SUM R-4

"Extrapolated" 

(Pitman and 

others, 1989)

Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence 

1N 96W 1,155,680,000 822,500,000 333,180,000 41 884,370,000 ±20 

1N 97W 4,241,890,000 4,171,420,000 70,470,000 2 4,179,006,000 ±4 

1N 98W 6,682,880,000 6,745,200,000 -62,320,000 -1 6,328,486,000 ±11 

1N 99W 5,121,740,000 4,699,640,000 422,100,000 9 5,006,541,000 ±15 

1N 100W 782,504,000 210,980,000 571,524,000 271 202,729,000 ±50 

2N 97W 243,593,000 86,025,000 157,568,000 183 129,359,000 ±46 

2N 98W 1,841,360,000 703,950,000 1,137,410,000 162 1,069,300,000 ±125 

2N 99W 2,168,900,0002N 100W 17,857,8001S 95W 1,861,570,000 968,400,000 893,170,000 92

1S 96W 5,192,260,000 3,793,120,000 1,399,140,000 37 4,701,730,000 ±25 

1S 97W 7,977,040,000 7,994,025,000 -16,985,000 0 7,978,416,000 ±5 

1S 98W 8,922,470,000 8,951,250,000 -28,780,000 0 8,809,130,000 ±3 

1S 99W 6,739,630,000 6,734,750,000 4,880,000 0 6,510,680,000 ±6 

1S 100W 2,046,910,000 1,570,065,000 476,845,000 30 1,653,401,000 ±31 

2S 94W 52,051,2002S 95W 2,936,510,000 2,649,700,000 286,810,000 11 3,107,714,000 ±62 

2S 96W 5,327,000,000 5,517,123,000 -190,123,000 -3 5,339,945,000 ±13 

2S 97W 7,722,110,000 7,642,026,000 80,084,000 1 7,479,641,000 ±7 

2S 98W 6,879,680,000 6,440,544,000 439,136,000 7 6,578,515,000 7 

2S 99W 4,122,510,000 3,699,360,000 423,150,000 11 3,866,316,000 ±14 

2S 100W 1,183,920,000 1,097,910,000 86,010,000 8 858,717,000 ±63 

3S 94W 341,067,0003S 95W 2,439,390,000 2,113,085,000 326,305,000 15 1,922,713,000 ±72 

3S 96W 3,879,440,000 3,990,272,000 -110,832,000 -3 3,772,921,000 ±11 

3S 97W 4,893,660,000 4,776,290,000 117,370,000 2 4,831,391,000 ±7 

3S 98W 3,948,710,000 3,879,976,000 68,734,000 2 3,817,762,000 ±14 

3S 99W 2,226,100,000 1,895,940,000 330,160,000 17 1,594,671,000 ±64 

3S 100W 230,257,000 171,090,000 59,167,000 35 52,442,000 ±376 

4S 94W 603,963,000
Table 18. Total number of in-place barrels of oil per acre (BPA) in each township for the R-4 zone calculated here using the Radial Basis Function Mthe R-4 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hereyellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.—Con

Township, Range SUM R-4 "Extrapolated" (Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence D

4S 95W 2,110,900,000 1,996,563,000 114,337,000 6 1,976,776,000 ±64 

4S 96W 2,695,350,000 2,715,240,000 -19,890,000 -1 2,647,708,000 ±35 

4S 97W 2,708,380,000 2,680,305,000 28,075,000 1 2,650,651,000 ±18 

4S 98W 2,241,350,000 2,158,052,000 83,298,000 4 1,963,386,000 ±38 

4S 99W 1,551,640,000 1,651,500,000 -99,860,000 -6 1,745,768,000 ±210 

4S 100W 494,132,000 4S 101W 3,501,940 5S 94W 1,051,720,000 5S 95W 1,459,020,000 5S 96W 1,700,240,000 1,608,266,000 91,974,000 6 1,572,093,000 ±59 

5S 97W 1,863,920,000 1,878,046,000 -14,126,000 -1 1,813,757,000 ±38 

5S 98W 1,283,570,000 1,228,663,000 54,907,000 4 1,188,388,000 ±167 

5S 99W 904,980,000 5S 100W 469,137,000 5S 101W 47,440,000 6S 94W 28,850,900 6S 95W 470,381,000 6S 96W 530,917,000 6S 97W 1,176,850,000 6S 98W 567,456,000 540,640,000 26,816,000 5 78,746,000 ±282 

6S 99W 249,835,000 6S 100W 216,186,000 6S 101W 90,764,700 7S 93W 80,964 7S 94W 160,738,000 7S 95W 60,734,0007S 96W 90,020,300

7S 97W 335,768,0007S 98W 79,165,9007S 99W 120,981,000
Table 18. Total number of in-place barrels of oil per acre (BPA) in each township for the R-4 zone calculated here using the Radial Basis Function Mthe R-4 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hereyellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.—Con

Township, 

Range SUM R-4

"Extrapolated" 

(Pitman and 

others, 1989)

Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence 

7S 100W 92,915,9007S 101W 24,045,0008S 93W 83,815,6008S 94W 201,040,0008S 95W 161,276,0008S 96W 1,183,3208S 99W 21,911,1008S 100W 5,542,2308S 101W 238,0059S 94W 325,5069S 95W 9,949,7509S 96W 1,273,500Total: 127,150,178,615 107,781,916,000 106,313,169,000

Sum of townships used here and Pitman and others 

(1989) extrapolated:

114,265,185,000 Sum of townships used here and kriging: 112,403,615,000

Percent difference using RBF here and Pitman and 

others (1989) extrapolated:

6.02 Percent difference between RBF and kriging: 5.73

Sum of best townships RBF 

(20 percent):

80,322,820,000 Sum of best townships 

extrapolated:

78,744,681,000 Sum of best townships 

kriging:

78,033,771,000

Percent difference RBF vs 

extrapolation for best TSPS:

2.00

Percent difference RBF vs 

kriging for best TSPS:

2.93
128 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

10

L–4 interval—Thickness in feet

< 50

51–100

101–150

151–200

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

30

50

121.6

50

58 65

58.6 57

50.7

35 46

67 48

53.4

55.7

60

62

43

54

72 72

58 73

80

83

60 57

99

96

107 157 123

95

71

94.1

156 156

158.5

164

128

168

78

157

65

146

64

68

31

70

46

90

74

108

70

171.8

159

167.7

56.9

69.5

0

0

0

0

158

165.1

88

74

61

52

52

51

59

106

28

173.2

120.2

111.4 142

118

63.8 66.6

100

64 61

63 73 58 66.7 83

68

60.6

84

87

84

86 86.7 93

81

128

90

100

66

65

61

83

58

69

49.4

61.7

76

67.8

60.6

81

62 59.8

140

134

100

136

97

61

69

69.5

81.3

72.5

93

134

171

94

53.7

154

100.5

84

66

96

165 74

75

154

146

81

105

184

125

30

153.2

70.3

104.5

130

82.7

155

170.5

166.1

69

98

109

138

73

98.8

27.1

98

58 65

96.3

144.5

143 126 106

152

159

144

147

154.9

47 53.6

50 42.7

46

40

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 77. Isopach map of the L-4 zone using the Radial Basis Function Method (RBF) of contouring. 

Contour interval in feet is variable.
Detailed Description and Assessment Results of Oil Shale Zones 129

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in

 gallons per ton

10

L–4 interval—Average oil yield in gallons per ton

< 7.5

7.6–15

15.1–22.5

22.6–30

30.1–37.5

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

0.1

22

6.3

14.3 17.3

16.7 18

18.4

15.8 13.2

10.2 16.1

8.1

11.5

9.6

8

10.2

10.2

13.5

9.6

14.1 14.1

16.8

12.8

19.5 18.4

28.9

17.7

26.1

2.5

22.6

24.3

25.3 19.2

20.3

18.1

16.5

12.2

20

13.7

19.6

13.5

12.9

7.8

11.5

6.4

13.8

12.7

17.4

6.9

22.4

22

24

9.7

13.6

20.3

21.3

14.7

14.3

11.7

14.2 16.4

18.8

15

16.5

1.5

23

19.2

17 18.1

12.9

23.1 23.5

6.8

22.1 18.6

24.9 20.7

19.9 28.8

22.1 28

18.4

13.4

15.7

15.6

17 15 15.5

18

15.6

13.1 12.7

24.3

21.7

24.2

27.3

21.1

10.1

9.9

10

8.5

24.7

9

27.3

19.8 21.8

13.6

15.7

13.3

18.4

21.6

21.9

12.7

17.3

22.3

26.7

13.7

17.6

10.4

12.6

17.2

14.6

12.3

8.9

12.2 12.6

9.8

19.5

18.9

15

11.5

33.9

10.1

2

18

17.6

12.6

9.6

22.3

21.7

18.7

21.5

22.8

12.7

14.1

13.7

11.1

18.2

26.2

1.8

1

10 7.3

27.7

17.5

19.3

31.1 23.6

22.7

20.7

25.3

20

21.6

17.2 14.3

15.4 13.9

15.3

13.1

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 78. Isoresource map of the L-4 zone showing the oil yield in gallons per ton (GPT) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
130 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

1

198

26

65 86

76 78

71 37 57

84 39

36

52

47

41

35

45

77 57

65 81

104 85

8088

201

130

200

16

157

266

289 227

250

177

213

76

236

71

216

69

70

20

65

25

98 75 144

40

284

259

293

45

75

240

261

102

83

58

58 66

73

69

135

4

292

175

146 196

122

108

114

57

104

86

97 131 87

132 168 111 85

89

106

102

113 102 112

111

156

94

102

116

105

107

161

91

57

40

51

54

121

45

157

92 97

151

164

114

144

136

98

112

71

108

119

177

146

231

80

54

204

115

83

49

128

167 73 60

226

209

95

98

426

103

5

211

95

105

103

136

249

242

256

116

100

118

124

101

185

4

9

48 40

189

194

272 209

183

254

246

263

221

248

71 53

60 47

55

42

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

L–4 zone—In barrels per acre

< 100,000

100,001–

 200,000

200,001–

 300,000

300,001–

 400,000

400,001–

 500,000

Figure 79. Isoresource map of the L-4 zone showing oil yields in barrels per acre (BPA) using only core 

hole data. The Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 131

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

123,777 930,210

0

17,331,300 24,522,000

13,078,700

163,675

13,020,100

11,348,300 41,342,800

11,629,200

7,987,650

23,881,800

9,451,320

17,731,400

73,907,600

195,922,000

367,244,992

199,336,000

160,692,992 8,952,190

35,529,600 64,290,200

356,792,992 514,169,984

869,177,984

813,064,000 742,963,008

463,945,984

19,658,900

190,020,000

760,926,976 1,022,190,016 1,528,540,032 1,427,760,000 1,144,450,048

297,371,008

1,360,510

230,220,000

1,252,790,016 2,053,779,968 2,586,680,064 2,056,729,984 1,289,400,064

168,587,008

115,551,000

2,192,049,920 4,406,569,984 4,003,379,968 2,792,610,048 1,567,830,016 26,040,000

623,329,984

846,958,976

818,329,984

100,603,000

7,372,390

3,809,769,984 6,087,860,224 5,220,360,192 2,862,560,000

918,806,016

1,241,660,032

2,614,720,000

4,156,199,936 2,633,999,872

590,492,992

400,646,016

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

L–4 zone shale oil, total in-place resource—In millions of barrels

< 380

381–920

921–1,600

1,601–2,900

2,901–6,100

Top of Mahogany zone

Base of Parachute Creek Member

L–4 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 80. Isoresource map of the L-4 zone showing total number of barrels of oil in each township 

using only core hole data.
Table 19. Total number of in-place barrels of oil per acre (BPA) in each township for the L-4 zone calculated here using the Radial Basis Function MResults for the L-4 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF mTownships highlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percenlevel. Township, Range SUM L-4 "Extrapolated" ( Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Differen

1N 96W 590,493,000 493,500,000 96,993,000 20 449,032,000 ±49 141,461

1N 97W 2,634,000,000 2,237,398,000 396,602,000 18 2,390,068,000 ±9 243,932

1N 98W 4,156,200,000 4,047,120,000 109,080,000 3 3,892,694,000 ±21 263,506

1N 99W 2,614,720,000 2,563,440,000 51,280,000 2 2,445,509,000 ±39 169,211

1N 100W 400,646,000 82,885,000 317,761,000 383 117,631,000 ±108 283,015

2N 97W 100,603,000 40,145,000 60,458,000 151 44,700,000 ±164 55,903

2N 98W 818,330,000 281,580,000 536,750,000 191 1,113,185,000 ±117 -294,855

2N 99W 846,959,000 –- 2N 100W 7,372,390 1S 95W 918,806,000 1,162,080,000 -243,274,000 -21 –- 1S 96W 2,862,560,000 1,778,025,000 1,084,535,000 61 2,474,188,000 ±60 388,372

1S 97W 5,220,360,000 5,165,370,000 54,990,000 1 5,080,789,000 ±9 139,571

1S 98W 6,087,860,000 6,158,460,000 -70,600,000 -1 5,845,892,000 ±7 241,968

1S 99W 3,809,770,000 3,722,480,000 87,290,000 2 3,581,630,000 ±14 228,140

1S 100W 1,241,660,000 897,180,000 344,480,000 38 1,094,622,000 ±59 147,038

2S 94W 26,040,000 2S 95W 1,567,830,000 1,059,880,000 507,950,000 48 1,770,113,000 ±136 -202,283

2S 96W 2,792,610,000 2,793,480,000 -870,000 0 2,847,929,000 ±32 -55,319

2S 97W 4,003,380,000 3,892,212,000 111,168,000 3 3,972,225,000 ±16 31,155

2S 98W 4,406,570,000 3,958,251,000 448,319,000 11 4,023,784,000 ±15 382,786

2S 99W 2,192,050,000 1,919,043,000 273,007,000 14 2,040,114,000 ±33 151,936

2S 100W 623,330,000 585,552,000 37,778,000 6 482,466,000 ±139 140,864

3S 94W 168,587,000 –- 3S 95W 1,289,400,000 1,000,935,000 288,465,000 29 1,019,020,000 ±168 270,380

3S 96W 2,056,730,000 1,949,792,000 106,938,000 5 1,883,547,000 ±29 173,183

3S 97W 2,586,680,000 2,175,340,000 411,340,000 19 2,357,505,000 ±21 229,175

3S 98W 2,053,780,000 2,030,220,000 23,560,000 1 1,992,887,000 ±30 60,893

3S 99W 1,252,790,000 1,032,234,000 220,556,000 21 942,027,000 ±134 310,763

3S 100W 115,551,000 47,525,000 68,026,000 143 51,756,000 ±474 63,795

4S 94W 297,371,000 306,684,000 ±595 -9,313
Table 19. Total number of in-place barrels of oil per acre (BPA) in each township for the L-4 zone calculated here using the Radial Basis Function MResults for the L-4 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF mTownships highlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percenlevel.—Continued 

Township, 

Range SUM L-4

"Extrapolated" 

( Pitman and 

others, 1989)

Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Differen

4S 95W 1,144,450,000 1,032,705,000 111,745,000 11 1,008,033,000 ±155 136,417

4S 96W 1,427,760,000 1,470,755,000 -42,995,000 -3 1,365,793,000 ±85 61,967

4S 97W 1,528,540,000 1,561,569,000 -33,029,000 -2 1,500,457,000 ±39 28,083

4S 98W 1,022,190,000 1,010,152,000 12,038,000 1 1,013,869,000 ±91 8,321

4S 99W 760,927,000 770,700,000 -9,773,000 -1 416,019,000 ±881 344,908

4S 100W 230,220,000 –-4S 101W 1,360,510 –-5S 94W 463,946,000 –-5S 95W 742,963,000 825,084,000 -82,121,000 -10 807,997,000 ±108 -65,034

5S 96W 813,064,000 784,520,000 28,544,000 4 775,926,000 ±146 37,138

5S 97W 869,178,000 893,217,000 -24,039,000 -3 868,413,000 ±97 765

5S 98W 514,170,000 420,775,000 93,395,000 22 382,440,000 ±644 131,730

5S 99W 356,793,000 –-5S 100W 190,020,000 –-5S 101W 19,658,900 –-6S 94W 8,952,1906S 95W 160,693,000 –-6S 96W 199,336,000 460,350,000 -261,014,000 -57 234,311,000 ±425 -34,975

6S 97W 367,245,000 367,140,000 105,000 0 –-

6S 98W 195,922,000 174,400,000 21,522,000 12 173,299,000 ±397 22,623

6S 99W 73,907,6006S 100W 64,290,2006S 101W 35,529,6007S 93W 12,7797S 94W 23,881,8007S 95W 7,987,6507S 96W 11,629,2007S 97W 41,342,8007S 98W 11,348,3007S 99W 13,020,100
Table 19. Total number of in-place barrels of oil per acre (BPA) in each township for the L-4 zone calculated here using the Radial Basis Function MResults for the L-4 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF mTownships highlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percenlevel.—Continued Township, Range SUM L-4 "Extrapolated" ( Pitman and others, 1989) Difference Percent difference Kriging (Pitman and oth- ers, 1989) 95 percent confidence Differen

7S 100W 17,731,400 7S 101W 9,451,320 8S 93W 13,078,700 8S 94W 24,522,000 8S 95W 17,331,300 8S 96W 120,131 8S 99W 0 8S 100W 163,675 8S 101W 87,442 9S 94W 32,789 9S 95W 930,210 9S 96W 123,777 Totals: 69,126,949,762 60,845,494,000 60,766,554,000 Sum of townships used here and Pitman and others (1989) extrapolated: 65,391,961,000 Sum of townships used here and kriging: 64,403,281,000 Percent difference using RBF here and Pitman and others (1989) extrapolated: 7.47 Percent difference between RBF and kriging: 5.98 Sum of best townships RBF (20 percent): 26,161,940,000 Sum of best townships extrapolated 25,134,171,000 Sum of best townships kriging: 24,894,388,000 Percent difference RBF vs ex- trapolation for best TSPS: 4.09 Percent difference RBF vs kriging for best TSPS: 5.09
Detailed Description and Assessment Results of Oil Shale Zones 135

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

110

R–5 interval—Thickness in feet

76–150

151–225

226–300

301–375

376–450

< 75

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

60

100

145

221.7

172

136 143

138.2 138

137.3

122

109

132 145

176.8

176

174

186

152

150.6

178

158.9 199

176

182 204

154

144

208

190

227

221

207

175

227.9

367.4

310 354

357.1

260

329

174

252

173

297

170

173

116 216

176

162

184

188

216

204

215.8

341.9

322.6

360.5

165.6

176.7

0

0

0 0

227

354.2

195

177

174

103

140

133

130

149.8

82

309.7

246

221.8

295

264

173

160

253

159 149

181 196.8 146 177

176 163 154

197.4

228

203 198.8

206 211

233

284

202

182

161

179

189

152

158

170.3

179.9

156

178.9

194

192

168 167.2

270

242

192

242

205

176.7

159

182.6

191.9

174.8

196.7

258

301

238

165.3

269

231.5

168

166

231

148 261 159

360

341

199

216

347

245

111

300.5

149.6

190

228

211.9

282

350.6

358.6

169

196

200 196

206

173.3

210.7

89.9

118

183 195

126

213.3

281

286

222

214

379

374

230.2

280

303.8

119.4 152.4

126 111.3

115

107

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 81. Isopach map of the R-5 zone using the Radial Basis Function Method (RBF) of contouring. Contour 

interval in feet is variable.
136 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

1974; 1981). These two beds are the highest preserved saline 

beds in the section, but there is a persistent collapse breccia 

near the top of the L-5 zone indicating that a saline bed was 

probably once present. The two thick nahcolite and halite beds 

have been leached out over much of their previous extent and 

replaced by collapse breccias. 

One hundred eighty six core holes were used to assess the 

R-5 zone here as compared to 105 core holes in the previous 

assessment (Pitman and others, 1989). The isopach map for 

the L-5 zone (fig. 85) shows complex thickening trends that 

are significantly different from underlying oil shale zones 

and highly modified by the relatively recent leaching of the 

thick nahcolite and halite beds. Throughout much of the 

basin, the L-5 zone thickens in a fairly regular pattern to the 

east-northeast. The approximate area where the two beds 

are preserved forms a conspicuous “bulls eye” in T. 1 S., R. 

97 and 98 W. The L-5 zone thickens from about 80 to 100 

ft where the beds have been leached to nearly 230 ft where 

the beds are still preserved. This thick area may once have 

covered much of the saline depocenter as the thickest areas 

in many of the previous isopach maps. In a completely new 

trend, the L-5 zone thickens markedly toward the northern 

part of the basin (fig. 85). This thickening is due to an influx 

of clastics from the north that Johnson (1985; 2007) suggested 

may be related to outflow from Lake Gosiute to the north. 

Estimated GPT for the L-5 zone ranges from 14.2 to 22.4 

in the oil shale and saline depocenter with values decreasing outward in a general radial pattern (fig. 86). In-place oil 

ranges to as high as 274,000 BPA in the depocenter with 

values decreasing rapidly toward the southwest and northeast 

and more slowly towards the southeast (fig. 87). Maximum inplace oil in a township is over 4 billion barrels in T. 1 S., 

R. 98 W. (fig. 88). Total in-place oil in the L-5 zone is estimated to be just over 66 billion barrels (table 21).

Using only those townships that were assessed in both 

this assessment and the previous assessment by Pitman and 

others (1989) our assessment of in-place oil for the L-5 zone is 

5.31 percent higher than the manually extrapolated results and 

9.35 percent higher than the kriged assessment of Pitman and 

others (1989) (table 21). When only the townships with the 

best control are compared (those with 20 percent or less estimated error in the kriged results of Pitman and others, 1989), 

our results are 7.97 percent higher than the manually extrapolated results and 18.10 percent higher than the kriged results of 

Pitman and others (1989) (table 21). 

R-6 Zone

The R-6 zone contains no preserved nahcolite or halite, 

but some solution cavities that may once have been filled with 

nahcolite were described in the upper part of the R-6 zone in 

outcrop near the mouth of Piceance Creek in the north-central 

part of the basin (Pipiringos and Johnson, 1976). There are no 

breccia zones in the R-6 zone (Dyni, 1974), thus it is doubtful 

that thick beds of halite and nahcolite, like those found in the 

underlying L-5 zone, ever existed in the R-6 zone. According 

to Dyni (1974, p. 119) the highest solution breccia occurs in 

the middle of his zone 12 (the L-5 zone) and “No unleached 

saline beds equivalent to this breccia, or younger solution 

breccias, are known to exist in the Piceance Creek basin.” 

Two hundred thirty five core holes were used to assess 

the R-6 zone here as compared to just 67 for the previous 

assessment (Pitman, 1979). One reason that so few holes were 

used in the previous assessment was that it was published a 

decade prior to the assessment of the zones below the R-6 

zone (Pitman and others, 1989), and there were far fewer core 

holes available. The R-6 zone thickens generally towards the 

east-northeast across the basin to a maximum of about 250 ft 

in the eastern part of the basin, then thins abruptly to 106 ft 

along the northeast margin (fig. 89). There is no thickening 

towards the saline depocenter in the north-central part of the 

basin as in previous oil shale zones that contain abundant 

saline minerals. There is a pronounced thickening to 537 ft 

towards the north-central part of the basin, in the vicinity of 

where the underlying L-5 zone thickened, suggesting again a 

source of sediment from the north.

Maximum oil yields for the R-6 zone range from about 

23 to 33 GPT through an elongate south-southeast-trending 

area that extends for a considerable distance to the southeast from the former oil shale and saline mineral depocenter 

(fig. 90). This trend toward expansion of the oil shale depocenter towards the southeast was apparent in the underlying 

L-5 zone (figs. 86, 87) but less pronounced. The southeast 

expansion of the oil shale depocenter is very conspicuous on 

the map showing estimated BPA with the area of maximum 

in-place oil, from about 300,000 to 425,000 BPA, extending 

to the upper reaches of the Parachute Creek drainage north 

of the Colorado River (fig. 91). Maximum in-place oil in a 

township is over 8.5 billion barrels in T. 1 S., R. 97 W. (fig. 92, 

table 22). Total in-place oil in the R-6 zone is estimated to be 

over 185 billion barrels (table 22).

The R-6 zone was originally assessed by Pitman (1979) 

by manual extrapolation. Pitman and others (1989) did not 

reassess the R-6 zone using kriging but instead included the 

extrapolated numbers from the 1979 publication in their final 

assessment for the basin. Using only those townships that were 

assessed in both this assessment and the assessment of Pitman 

(1979) our results are 16.99 percent higher than the manually 

extrapolated results of Pitman (1979). Pitman (1979) had very 

few control points to use for the assessment (67 as compared 

to 235 here), and thus it is difficult to compare the two assessments. Five townships were visually picked out that seemed to 

have adequate control in the 1979 assessment, and using only 

those townships, our assessment is 7.43 percent higher than 

the assessment of Pitman (1979) (table 22).

B-Groove

B-groove is a comparatively thin interval that represents 

a major decrease in oil yields that occurs throughout the oil 
Detailed Description and Assessment Results of Oil Shale Zones 137

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in 

 gallons per ton

10

R–5 interval—Average oil yield in gallons per ton

10.1–20

20.1–30

30.1–40

40.1–50

< 10

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

33

9

18.7 21.9

21.2

24.3

24.8 21

17.9

14.8 19.1

10.6

12.7

12.6

10.5

11.3

11.7

11

16 13.2

20.4

23.8

13.8

25.926

35.5

26.8

36.3

34.4

6.8

25.7

28.5

29.823.7

23.3

28

21.5

15.5

26.7

18.3

23.1

17.3

19.6

12.2

22.4

15.9

9.6

16.8 15.5

19.6

8.4

8.6

23.2

25.8

23.2

13.9

18

30.1

22

24.1

19.3

15.8

18 25.8

25.7

19.1

22.7

7.1

24.4

26.5

21.5

20.7

13.4

30.7

32.6

7.9

2526.6

31.1 28.7

24.7 37.5

35.7

30.3

27.3

21

21.8

21.4

23.9 21 21.8

27.6

21.3

15.6 14.9

32.4

29.3

32.1

28

19

12.5

14.3

12.8

31.6

11.6

32.3

28.2

28.9

15.6

21.2

20.9

21.6

31.7

28

17.9

24.2

26.3

35.6

17.5

23.5

11.5

16.8

24.6

15.9 14.1

12.4

18.6

15.6 13.9 14.8

22.2

21.7

21

16.5

37.5

11.5

8.1

22.4

23.5

18.3

13.2

31.3

27.8

22.9

26.2

33

15.1

16.3

12.3

27.5

36.2

7.9

4.1

12.6 11.1

13.9

38.5

21

38.1 31.6

33.7

21.7

18.6

41.4

24.6

24

22.3 20

20.8 18.7

18.6

18.5

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 82. Isoresource map of the R-5 zone showing the oil yield in gallons per ton (GPT) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
138 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

502

128

193 232

218 243

246 191

149

151 210

153

179

176

159

139

142

159

198 209

269

316

223

286

269

499 363

554

517

87

421

657

518512

526

516

504

210

481

241

503

226

256

114

357

218

122

239 227

319

142

154

575

570

612

182

243

477

576

342

258

214

142 259

246

188

250

49

548

466

354 456

281

370 359

167

283 287 391 398 261

443

424

345

299

309

368

323 346

322 341 457

450

246

227

406

331

397

444

301

227

171

203

160

392

182

428

335 340

328

382

250

377

328

388

315

250

337

329

473

347

517

221

214

479

286

187

165

327

180 309 185

551

510

311

276

869

228

75

496

257

265

240

460

556

491

573

383

232

258 248

203

339

514

59

42

185 176

139

545

440

563 586

493

566

505

621

499

531

251 179

196 158

163

151

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

R–5 zone—In barrels per acre

< 200,000

200,001–

 400,000

400,001–

 600,000

600,001–

 800,000

> 800,000

Figure 83. Isoresource map of the R-5 zone showing oil yields in barrels per acre (BPA) using only core hole data. 

The Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 139

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

651,761 6,661,440

37,373,900 128,425,000

149,607,008 61,913,400

14,733,200

188,511,008

122,810,000

462,312,000

118,594,000

55,770,800

134,504,000

74,182,400

206,452,992

436,441,984

1,048,540,032

1,983,840,000

878,177,024

682,654,976 37,536,500

206,615,008 415,455,008

1,629,680,000

2,274,380,032

3,538,299,904

3,243,389,952 2,881,679,872

1,802,370,048

119,444,000

967,750,976

2,827,290,112 3,960,320,000 4,845,949,952 4,964,980,224 4,214,380,032

1,173,309,952

10,227,200

1,004,769,984

4,180,000,000 6,624,390,144 7,446,490,112 6,253,969,920 3,927,010,048

571,958,016

431,857,984

7,090,780,160 11,176,999,936 11,062,400,000 7,192,459,776 4,128,260,096 76,573,904

2,112,339,968

2,358,299,904

2,489,139,968

321,636,992 18,028,000

10,141,899,776 13,357,500,416 12,056,599,552 7,548,340,224

2,711,600,128

3,471,160,064

6,041,549,824 9,373,939,712

6,313,399,808

1,867,629,952

980,272,000

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

R–5 zone shale oil, total in-place resource—In millions of barrels

< 1,300

1,301–2,900

2,901–5,000

5,001–7,500

7,501–13,000

Top of Mahogany zone

Base of Parachute Creek Member

R–5 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 84. Isoresource map of the R-5 zone showing total number of barrels of oil in each township using only 

core hole data.
Table 20. Total number of in-place barrels of oil per acre (BPA) in each township for the R-5 zone calculated here using the Radial Basis Function Mthe R-5 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hereyellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level. Township, Range SUM R-5 "Extrapolated" ( Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Diff

1N 96W 1,867,630,000 1,908,200,000 -40,570,000 -2.13 1,419,119,000 ±22 4

1N 97W 6,313,400,000 6,636,350,000 -322,950,000 -4.87 5,921,871,000 ±5 3

1N 98W 9,373,940,000 9,443,280,000 -69,340,000 -0.73 8,882,764,000 ±14 41N 99W 6,041,550,000 6,088,170,000 -46,620,000 -0.77 5,785,083,000 ±23 21N 100W 980,272,000 233,585,000 746,687,000 319.66 220,454,000 ±82 72N 97W 321,637,000 172,050,000 149,587,000 86.94 187,961,000 ±85 2N 98W 2,489,140,000 1,126,320,000 1,362,820,000 121.00 218,723,000 ±1298 2,22N 99W 2,358,300,000 1,525,480,000 832,820,000 54.59 –- 2N 100W 18,028,000 1S 95W 2,711,600,000 1,291,200,000 1,420,400,000 110.01 –- 1S 96W 7,548,340,000 6,519,425,000 1,028,915,000 15.78 6,708,348,000 ±31 8

1S 97W 12,056,600,000 11,929,545,000 127,055,000 1.07 11,746,252,000 ±5 31S 98W 13,357,500,000 12,412,400,000 945,100,000 7.61 12,581,545,000 ±4 7

1S 99W 10,141,900,000 9,183,750,000 958,150,000 10.43 9,627,029,000 ±7 51S 100W 3,471,160,000 2,990,600,000 480,560,000 16.07 2,743,627,000 ±33 7

2S 94W 76,573,900 2S 95W 4,128,260,000 3,444,610,000 683,650,000 19.85 3,875,865,000 ±88 22S 96W 7,192,460,000 7,449,280,000 -256,820,000 -3.45 7,483,801,000 ±17 -22S 97W 11,062,400,000 10,917,180,000 145,220,000 1.33 10,877,714,000 ±9 

2S 98W 11,177,000,000 10,622,425,000 554,575,000 5.22 10,094,247,000 ±8 1,0

2S 99W 7,090,780,000 6,705,090,000 385,690,000 5.75 6,651,097,000 ±15 4

2S 100W 2,112,340,000 1,829,850,000 282,490,000 15.44 1,676,860,000 ±57 4

3S 94W 571,958,000 –- 3S 95W 3,927,010,000 2,669,160,000 1,257,850,000 47.13 3,085,710,000 ±79 

3S 96W 6,253,970,000 6,236,160,000 17,810,000 0.29 5,834,195,000 ±13 4

3S 97W 7,446,490,000 7,684,625,000 -238,135,000 -3.10 7,077,905,000 ±8 33S 98W 6,624,390,000 6,203,450,000 420,940,000 6.79 5,882,000,000 ±12 7

3S 99W 4,180,000,000 3,791,880,000 388,120,000 10.24 4,045,525,000 ±49 3S 100W 431,858,000 209,110,000 222,748,000 106.52 150,523,000 ±216 2

4S 94W 1,173,310,000 813,240,000 360,070,000 44.28 1,406,316,000 ±153 -2
Table 20. Total number of in-place barrels of oil per acre (BPA) in each township for the R-5 zone calculated here using the Radial Basis Function Mthe R-5 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hereyellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.—Continued

Township, 

Range SUM R-5

"Extrapolated" 

( Pitman and 

others, 1989)

Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Diff

4S 95W 4,214,380,000 3,442,350,000 772,030,000 22.43 3,709,025,000 ±60 54S 96W 4,964,980,000 4,977,940,000 -12,960,000 -0.26 4,733,460,000 ±35 2

4S 97W 4,845,950,000 5,011,005,000 -165,055,000 -3.29 4,840,702,000 ±16 4S 98W 3,960,320,000 3,673,280,000 287,040,000 7.81 3,626,276,000 ±31 34S 99W 2,827,290,000 2,422,200,000 405,090,000 16.72 2,211,771,000 ±119 64S 100W 1,004,770,000 –-

4S 101W 10,227,200 –-

5S 94W 1,802,370,000 1,407,700,000 394,670,000 28.04 1,659,768,000 ±175 

5S 95W 2,881,680,000 2,686,320,000 195,360,000 7.27 2,635,176,000 ±33 2

5S 96W 3,243,390,000 3,138,080,000 105,310,000 3.36 3,099,056,000 ±53 5S 97W 3,538,300,000 3,435,450,000 102,850,000 2.99 3,375,428,000 ±35 5S 98W 2,274,380,000 1,683,100,000 591,280,000 35.13 1,760,651,000 ±198 55S 99W 1,629,680,000 1,732,800,000 -103,120,000 -5.95 –-

5S 100W 967,751,000 –-

5S 101W 119,444,000 –- 

6S 94W 37,536,500 –-

6S 95W 682,655,000 697,550,000 -14,895,000 -2.14 561,821,000 ±199 

6S 96W 878,177,000 1,841,400,000 -963,223,000 -52.31 838,119,000 ±142 

6S 97W 1,983,840,000 1,835,700,000 148,140,000 8.07 –-

6S 98W 1,048,540,000 697,600,000 350,940,000 50.31 856,785,000 ±114 6S 99W 436,442,0006S 100W 415,455,0006S 101W 206,615,0007S 93W 59,8717S 94W 134,504,0007S 95W 55,770,8007S 96W 118,594,0007S 97W 462,312,0007S 98W 122,810,0007S 99W 188,511,000
Table 20. Total number of in-place barrels of oil per acre (BPA) in each township for the R-5 zone calculated here using the Radial Basis Function Mthe R-5 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hereyellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.—Continued Township, Range SUM R-5 "Extrapolated" ( Pitman and others, 1989) Difference Percent difference Kriging (Pitman and others, 1989) 95 percent confidence Diff

7S 100W 206,453,000 7S 101W 74,182,400 8S 93W 61,913,400 8S 94W 149,607,000 8S 95W 128,425,000 8S 96W 942,763 8S 99W 37,373,900 8S 100W 14,733,200 8S 101W 1,814,340 9S 94W 178,871 9S 95W 6,661,440 9S 96W 651,761 198,239,468,346 178,718,890,000 168,092,572,000 Sum of townships used here and Pitman and others (1989) extrapolated: 192,609,169,000 Sum of townships used here and in kriging: 183,925,749,000 Percent difference using RBF here and Pitman and others (1989) extrapolated: 6.32 Percent difference between RBF and kriging: 8.61 Sum of best townships RBF (20 percent): 105,744,320,000 Sum of best townships extrapolated: 103,020,820,000 Sum of best townships kriging: 100,0

Percent difference RBF vs extrapolation for best TSPS: 2.64 Percent difference RBF vs kriging for best TSPS: 5.73
Detailed Description and Assessment Results of Oil Shale Zones 143

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

256

59

100

192

97.7

108

64

100 100

99.2 98

78 80.9 67

101 93

94.3

86

132

152 158

84

94

74.3

81

95.9 105

61

72

131

10886

92

93

115

100

98

128

121

186 115

105

106

130

77

171.9

72

77

112 110

99

60

83

122

112

110 132

154

154

136

155

147.6

36

98.4

99.1

116.4

78.8

154.9

86.3

0

0

0 0

129

165

85

74

76

76 80

92 94

94.8

102

107.4

129.1

159.2

139

156

55

88

151

84

77

84.2 80 60 85 99 97

110

104.6

72

102

80.2 103 105

63

140

130

120

84

96

85

90

74

90

80.7

123.7

92

83.3

120

87

81 72

240

166

142

158

129.4

89.3

101.9

93.6

103.8

94.8

85.3

158

120

158

70.4

150

136

127

89

161

181 97 125

108 157

99

110

116

169

115

194.5

98

120

146

102.2

125

113

227.4

75

132

158

152

71.4

93.2

101.1

125

142

92 160

55 59 60

114.8

217.6

91 107

102

183

93

106.1

152

181

92.2

78 52

80 66

60

67

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

10

L–5 interval—Thickness in feet

51–100

101–150

151–200

201–250

251–300

< 50

Figure 85. Isopach map of the L-5 zone using the Radial Basis Function Method (RBF) of contouring. Contour 

interval in feet is variable.
144 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in

 gallons per ton

10

L–5 interval—Average oil yield in gallons per ton

< 5

5.1–10

10.1–15

15.1–20

20.1–25

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

0.1

16.9

4.6

6.3

8.9 9.9

10.59.9

9.4 11.1

7.6

6.8 9.1

6.3

8.9

7.3

5.9 2.4

7.7

8.1

7.2

8.4

10.9

8.3

13.3

12.5

11.9

11.9

10.2

17.2

22.4

17.7

17.4

14.8

10.6

19.9 14.3

13.8

6.2

12.8

11.4

12.1

11.2

12.6

5.2 4.5

5

3.1 14.6

9.2

3.6

6.6

6.8

7.9

1.3

4.2

1.9

4.1

1.8

18.2

16

14.1

17.3

4.8

13.1

13.3

12.6

14.2

10.9

9.9

8.3 10.9

11.1

9.3

13.5

1.3

18.7

13.8

9.8

10.7

5.6

12

12.9

6.1

11.3

12.2

12.3 15 14.8

12.1 12.5 14.4 10.7

15

14.5

13.4

13.8 12.9 12.9

17.7

13.2

6.7 7

13.4

12.4

12.7

13.3

12.7

11.6

10.3

8.6

4.7

13.4

6.8

13.9

11.9 11.7

7

10.6

7

9.2

11.6

12.5

13.4

12.5

13.8

10.1

14

8.9

15.6

4.2

12.9

9.8

6.7

6.5

6.1

7.9

6.5 5

6.4

17

14.2

12.5

13

18.3

4.7

2.2

10.8

13.5

11.5

9.7

20

14.9

14.7

15.5

15.2

7.1

7.3

5.8

13.3

18.3

1.7

4.1

1.8

11.1 5.9

7.1 8.6 5.9

14.9

9.9

16.6 20.4

15.4

15.1

15.1

17.1

14.9

12.7

14.5

8.7 9.3 9.8 9.7

9.5

9.2

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 86. Isoresource map of the L-5 zone showing the oil yield in gallons per ton (GPT) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 145

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

1

127

43

34

74 81

8580

70

63

43

76

53

50

63

81

75 33

54

63

45

57

85 72

65

72

126

8290

122

154

156

134

114

105

274 130

115

55

133

71

167

65

78

49 42

42

16

95

93

35

73

62 101

18

49

26

52

6

137

123

130

105

64

90

136

167

95

66

62

52 71

83

72

102

12

152

141

128

121

73

53 91

77

77

75

79 98 71 112 83

97

96

123

82

109

88

106 108

85

147

67 76

89

95

86

95

75

84

68

88

37

89

68

96

78 68

141

143

84

120

121

89

109

94

113

78

94

116

146

57

73

121

76 69

45

106

41 87 67

141

162

99

114

162

68

22

171

105

112

116

153

146

130

183

89

79

97

74

76

130

15

44

23

83 79

33 42 30

134

177

117 163

123

170

110

140

178

184

105

40 56

64 53

47

51

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

L–5 zone—In barrels per acre

< 50,000

50,001–

 100,000

100,001–

 150,000

150,001–

 200,000

200,001–

 300,000

Figure 87. Isoresource map of the L-5 zone showing oil yields in barrels per acre (BPA) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
146 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

665,404 5,209,930

4,645,070 79,015,104 87,158,000

27,051,800

695,816

42,997,100

32,005,200

153,380,000

44,171,400

30,711,100

67,435,296

6,967,040

33,558,300

137,734,000

313,681,984

738,651,008

374,983,008

288,172,992 13,122,800

33,187,700 103,646,000

579,083,008 869,300,992

1,285,609,984

1,412,850,048 1,121,240,064

489,820,992

17,126,500

245,103,008

860,363,008 1,426,390,016 1,936,790,016 2,031,250,048 1,672,029,952

428,264,000

1,423,240

246,114,000

1,059,830,016 1,693,740,032 2,423,419,904 2,374,109,952 1,827,500,032 246,787,008

104,852,000

1,594,800,000 2,691,170,048 3,204,270,080 2,840,819,968 2,062,850,048 39,496,400 663,529,984

1,250,380,032

1,163,469,952

96,235,904

8,292,300

2,741,839,872 4,023,310,080 3,238,020,096 2,672,969,984

1,196,009,984

1,262,560,000

2,060,380,032

3,276,529,920 2,000,489,984

634,131,968

369,625,984

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

L–5 zone shale oil, total in-place resource—In millions of barrels

< 160

161–740

741–1,400

1,401–2,400

2,401–4,000

Top of Mahogany zone

Base of Parachute Creek Member

L–5 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 88. Isoresource map of the L-5 zone showing total number of barrels of oil in each township using only 

core hole data.
Table 21. Total number of in-place barrels of oil per acre (BPA) in each township for the L-5 zone calculated here using the Radial Basis Function Mthe L-5 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hereyellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.

Township, 

Range SUM L-5

Extrapolated 

(Pitman and 

others, 1989)

Difference Percent difference Township, Range Kriging, Pitman and others, (1989) 95 percent confidence 

1N 96W 634,132,000 473,760,000 160,372,000 34 1N 96W 481,007,000 ±36 1N 97W 2,000,490,000 1,744,412,000 256,078,000 15 1N 97W 1,742,788,000 ±10 1N 98W 3,276,530,000 2,585,660,000 690,870,000 27 1N 98W 2,191,041,000 ±16 

1N 99W 2,060,380,000 2,349,820,000 -289,440,000 -12 1N 99W 2,074,246,000 ±33 

1N 100W 369,626,000 45,210,000 324,416,000 718 1N 100W 120,010,000 ±54 2N 97W 96,235,900 34,410,000 61,825,900 180 2N 97W 59,849,000 ±54 2N 98W 1,163,470,000 281,580,000 881,890,000 313 2N 98W –-

2N 99W 1,250,380,000 2N 99W –-

2N 100W 8,292,300 2N 100W1S 95W 1,196,010,000 322,800,000 873,210,000 271 1S 95W –-

1S 96W 2,672,970,000 237,070,000 2,435,900,000 1,028 1S 96W 2,120,861,000 ±29 

1S 97W 3,238,020,000 3,394,386,000 -156,366,000 -5 1S 97W 2,949,845,000 ±10 1S 98W 4,023,310,000 3,389,540,000 633,770,000 19 1S 98W 2,866,351,000 ±8 

1S 99W 2,741,840,000 2,449,000,000 292,840,000 12 1S 99W 2,293,272,000 ±13 

1S 100W 1,262,560,000 1,046,710,000 215,850,000 21 1S 100W 1,143,711,000 ±38 

2S 94W 39,496,400 2S 94W2S 95W 2,062,850,000 1,722,305,000 340,545,000 20 2S 95W 2,533,654,000 ±53 

2S 96W 2,840,820,000 2,793,480,000 47,340,000 2 2S 96W 2,605,432,000 ±18 

2S 97W 3,204,270,000 3,203,955,000 315,000 0 2S 97W 2,850,288,000 ±9 2S 98W 2,691,170,000 2,348,115,000 343,055,000 15 2S 98W 2,218,631,000 ±10 2S 99W 1,594,800,000 1,502,865,000 91,935,000 6 2S 99W 1,663,017,000 ±24 

2S 100W 663,530,000 487,960,000 175,570,000 36 2S 100W 745,547,000 ±71 

3S 94W 246,787,000 3S 94W 57,906,000 ±384 

3S 95W 1,827,500,000 1,445,795,000 381,705,000 26 3S 95W 1,771,464,000 ±66 

3S 96W 2,374,110,000 2,267,200,000 106,910,000 5 3S 96W 2,157,516,000 ±17 3S 97W 2,423,420,000 2,482,725,000 -59,305,000 -2 3S 97W 2,181,891,000 ±10 

3S 98W 1,693,740,000 1,556,502,000 137,238,000 9 3S 98W 1,630,335,000 ±17 3S 99W 1,059,830,000 779,442,000 280,388,000 36 3S 99W 1,072,910,000 ±50 

3S 100W 104,852,000 19,010,000 85,842,000 452 3S 100W 81,431,000 ±115 4S 94W 428,264,000 180,720,000 247,544,000 137 4S 94W 604,929,000 ±115 
Table 21. Total number of in-place barrels of oil per acre (BPA) in each township for the L-5 zone calculated here using the Radial Basis Function Mthe L-5 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF method hereyellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.—Con

Township, Range SUM L-5 Extrapolated (Pitman and others, 1989) Difference Percent difference Township, Range Kriging, Pitman and others, (1989) 95 percent confidence 

4S 95W 1,672,030,000 1,606,430,000 65,600,000 4 4S 95W 1,504,636,000 ±25 

4S 96W 2,031,250,000 1,923,295,000 107,955,000 6 4S 96W 1,863,716,000 ±18 4S 97W 1,936,790,000 1,724,718,000 212,072,000 12 4S 97W 1,693,348,000 ±20 4S 98W 1,426,390,000 1,056,068,000 370,322,000 35 4S 98W 1,064,422,000 ±47 4S 99W 860,363,000 616,560,000 243,803,000 40 4S 99W 565,643,000 ±235 4S 100W 246,114,000 4S 100W –- 4S 101W 1,423,240 4S 101W –- 5S 94W 489,821,000 361,980,000 127,841,000 35 5S 94W 462,398,000 ±131 

5S 95W 1,121,240,000 959,400,000 161,840,000 17 5S 95W 979,482,000 ±40 5S 96W 1,412,850,000 1,274,845,000 138,005,000 11 5S 96W 1,133,047,000 ±30 

5S 97W 1,285,610,000 1,282,568,000 3,042,000 0 5S 97W 1,134,248,000 ±46 5S 98W 869,301,000 538,592,000 330,709,000 61 5S 98W 478,075,000 ±206 5S 99W 579,083,000 5S 99W –- 5S 100W 245,103,000 5S 100W –- 5S 101W 17,126,500 5S 101W –- 6S 94W 13,122,800 10,092,000 3,030,800 30 6S 94W –- 6S 95W 288,173,000 199,300,000 88,873,000 45 6S 95W 185,888,000 ±259 

6S 96W 374,983,000 662,904,000 -287,921,000 -43 6S 96W 270,021,000 ±74 6S 97W 738,651,000 642,495,000 96,156,000 15 6S 97W 709,285,000 ±74 6S 98W 313,682,000 226,720,000 86,962,000 38 6S 98W 270,399,000 ±70 6S 99W 137,734,000 6S 99W 6S 100W 103,646,000 6S 100W 6S 101W 33,187,700 6S 101W 7S 93W 31,560 7S 93W 7S 94W 67,435,300 7S 94W 7S 95W 30,711,100 7S 95W

7S 96W 44,171,400 7S 96W7S 97W 153,380,000 134,694,000 18,686,000 14 7S 97W

7S 98W 32,005,200 7S 98W7S 99W 42,997,100 50,592,000 -7,594,900 -15 7S 99W
Table 21. Table listing total number of in-place barrels of oil per acre (BPA) in each township for the L-5 zone calculated here using the Radial BasiResults for the L-5 zone from Pitman and others (1989) using manual extrapolation and kriging are also listed with percent difference using the RBF mhighlighted in yellow are those in which kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidenc

Township, 

Range SUM L-5

Extrapolated 

(Pitman and 

others, 1989)

Difference Percent difference Township, Range Kriging, Pitman and others, (1989) 95 percent confidence 

7S 100W 33,558,300 7S 100W

7S 101W 6,967,040 7S 101W

8S 93W 27,051,800 8S 93W8S 94W 87,158,000 8S 94W8S 95W 79,015,100 8S 95W8S 96W 601,341 8S 96W

8S 99W 4,645,070 8S 99W

8S 100W 695,816 8S 100W

8S 101W 11,921 8S 101W

9S 94W 135,517 9S 94W

9S 95W 5,209,930 9S 95W

9S 96W 665,404 9S 96W

Totals: 66,063,806,739 52,415,685,000 66,063,806,739 Totals: 52,532,540,000Sum of townships used here 

and Pitman and others (1989) extrapolated:

62,735,363,800 Sum of townships used here and in 

kriging:

60,413,170,900

Percent difference using RBF 

here ahd Pitman and others (1989) extrapolated:

5.31 Percent difference between RBF and 

kriging:

9.35

Sum of best townships RBF 

(20 percent):

32,538,970,000 Sum of best townships extraploated 30,138,270,000 Sum of best 

townships kriging

27,551,106,000

Percent difference RBF vs 

Kriging for best townships:

18.10

Percent difference RBF vs 

extrapolation for best townships:

7.97
150 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

110

R–6 interval—Thickness in feet

151–200

201–250

251–400

401–500

< 150

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

537

113

98

292

174.5

138 119

111

106

108

106

108

170 163.4

154.3

146

134

143.1

116

172 160

126 130131

132 126

124 127

122 124

119

117 120 120.2

118

122

120126124

118

119

119 119

130.2

137.7

199

200.6 208

207.2

195.2

201.6

242 250

112

109

104 108

118

115

114

113

112

115

110

118

129.5

136.8

138.2 206

223 125

148

154

186

206

134 127

148

151

183

158

159

215 106

137.9

183.1

174 195

211 249

204

207

149

239.1

131

150

142.1 142

179

180

146

238

214

254

175

176 186

227

205.7

229.9

209.4 111

291

167

179.4

190

189.4

214.2

160.6

1572

1482

1588.6 1470

202

180.8

153

151

122.3

143

133

151

165

163.8

148

176.9 193.9

238.7

236

272

132

234

136

132

146 111.3 178

154

134 145 139.8

189

181

179 178.9

194 177.8

172.6

242

240 240

130

143

137

147

133

154

118.7

203

192

143

202

149.1

132

134

274

234

242

228

184

143.4

164.3

177.9

147.2

145

240

212

238

129.7

230

273 211

184

251

190

301

216

167 168

186

191

167.4

211

169

253.2

169

210

164.3

210.2

199

190

138

250

238

123

123.3

276

139.4

142

151.4

143

222

152 210

120 118

115

167.7

261.9

130

170

164

164

191

175

163.7

238

239

161

150

154

142 152

139.5 147

138

131

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 89. Isopach map of the R-6 zone using the Radial Basis Function Method (RBF) of contouring. Contour 

interval in feet is variable.
Detailed Description and Assessment Results of Oil Shale Zones 151

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

26.2

12.9

17.4

14.6

16.3

15.3

14.9

16.7 17

17.6 17.6

20.7 18.3 16.2

15.6 16.8

12.7

14.8

15.3

14.3 13.4

13 13.8 14.1 14.1

15.4

15.1

14.8

15.415.1

15 15.8

15.7 15.2

15.2

15.2

17.9

15.1

16

20

19.6

20.6 17.7

20.8

21.2 22

7.1

4.2

16.3

17.4

16.3 16.8

18.8 17.4

17.7

17

16.5

15.6

17.9 16.4

16.9

18.1

21.8 22

17 19

25.5

24.8

26.3

25

19.9

17.8

30.4

33.1

26.5

28

26.1

2.6

22.2

19.7

28.2 24.6

22.6 11.2

15.3

23.4

22.8

21.1

24

23.4

14.2 13.8

26.7

23

10.1

16.7

15.8

17.1

27.9

28.1

27.2

6

13.8

7.8

13.8

4.2

2.2

27.8

24.4

24.5

24.7

11.9

24.4

22.4

24

24.2

22.1

21.5

16.6 19.3

18.7

17.3

26

4.7

28.8

27

20.2

21.6

15.1

19.8

15.4

21.6 18.8

19.2 21.6 15.4 19.6

20 22

17.9

28.6

25.9

26.3

27

24.5 26.4

28.2

19.5

16

22

20.4

20.9

23.5

21

24.2

19.6

22.2

11.6

22.2

20.6

22.8

22.3

19.9

14.3

20

16.6

19.8

18.1

19.9

20.6

25.4

26.4

18.4

22.6

17.8

25

13.3

22

16.6

14.6

14.4

12.5

17.1

13.7

13.7 14.7

26.3

26

27

26.1

28.1

13.8

7

20.4

26.8

21.8 31.5

22.9

21.7

24.7

23

14.4

12.9

19.5

20.8

13.9

26.2

27.8

6

10

6.5

21.4 16

18

18.9

14.8

24.4

19.7

22

24.6 29.2

26.1

23.1

22.3

27.9

24.6

24

24.3

11.2

18.1 20.7

18.7 17.7

17.5 17.6

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in 

 gallons per ton

10

R–6 interval—Average oil yield in gallons per ton

7.6–15

15.1–22.5

22.6–30

30.1–37.5

< 7.5

Figure 90. Isoresource map of the R-6 zone showing the oil yield in gallons per ton (GPT) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
152 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

shale areas of the Piceance and Uinta Basins. It is one of the 

most distinctive and easily recognizable units on geophysical 

logs and oil-yield histograms in the entire oil shale interval 

(fig. 7). B-groove had never been previously assessed. Three 

hundred fifty two core holes were used to assess B-groove 

here. An additional 68 rotary holes were used to construct the 

isopach map. B-groove varies from 5 to 40 ft thick throughout 

most of the basin (fig. 93) and thickens markedly towards both 

the north, where it reaches a thickness of almost 100 ft and 

towards the east, where it reaches a maximum of 90 ft thick 

(fig. 93). The B-groove is very sandy in these marginal areas 

where it is thickest (Johnson, unpub. sections; Donnell, 1961, 

his plate 49). It appears to represent a major contraction of the 

lake that brought sandy sediments much farther into the lake 

than during the previous R-6 interval or the Mahogany interval 

that followed. It is unclear why organic productivity was so 

much lower during this contraction of the lake than during 

previous contractions.

B-groove is organically poor overall, with oil yields 

ranging from less than 1 GPT to about 10 GPT throughout 

most of the basin, but oil yields of as much as 25 GPT occur 

locally in the central part of the basin (fig. 94). The overall 

pattern is a general increase in oil yield towards about the 

same southeast-trending oil shale depocenter as for the 

underlying R-6 zone (figs. 90, 94) but with a high degree of 

scatter. In-place oil is also higher in this depocenter (fig. 95) 

but again, there is a high degree of scatter. Maximum in-place 

oil in a township is almost 460 million barrels in T. 3 S., R. 

97 W. (fig. 96, table 23). Total in-place oil in B-groove is 

estimated to be over 7.8 billion barrels (table 23).

Mahogany Zone 

The Mahogany zone and the strata above it comprise the 

fifth stage of Lake Uinta as defined by Johnson (1985). The 

Mahogany zone has been the target of most oil shale extraction 

projects thus far because of its richness and because it crops 

out around the margins of the basin where it can be easily 

reached by underground mining. The base of the Mahogany 

zone is marked by a significant increase in oil yields (fig. 7). 

Oil yields generally increase upwards in the Mahogany zone 

culminating in deposition of the Mahogany bed, one of the 

richest and probably the most widespread oil shale beds in 

both the Piceance Basin and Uinta Basin to the west (fig. 

7). The Mahogany bed is the only significant oil shale bed 

remaining in the Green River Formation throughout much of 

the southern part of the Uinta Basin to the west, where most 

of the Green River Formation is marginal lacustrine (Cashion, 

1967, his plate 3). It represents the culmination of a major 

transgression of Lake Uinta that began at the base of the 

Mahogany zone. 

The Mahogany bed can be recognized throughout most, if 

not all, the area where the Green River Formation is preserved 

except near the mouth of Yellow Creek in T. 2 N., R. 98 W. in 

the north-central part of the Piceance Basin were it grades into 

organically lean marlstone, siltstone, and sandstone. Johnson 

(1985; 2007) believed that the Mahogany zone graded into 

clastics in this area due to outflow from Lake Gosiute to the 

north, and that the expansion of the lake during deposition of 

the Mahogany was caused by the increase in water supplied to 

Lake Uinta due to this outflow. The Mahogany bed represents 

the maximum extent of Lake Uinta when oil shale was deposited across nearly all the areas that had previously been marginal lacustrine. Oil yields gradually decline in the Mahogany 

zone above the Mahogany bed. The expansion of the oil shale 

depocenter towards the southeast that began during deposition 

of the L-5 zone continued with the Mahogany zone with rich 

oil shale being deposited across much of the southeastern part 

of the basin. 

A single core hole near the mouth of Yellow Creek in 

sec. 20, T. 2 N., R. 98 W. (C19 in Dyni, 1998) appears to have 

cored and assayed the Mahogany zone. The only significant oil 

shale encountered in the hole extends from a depth of 855 to 

980 ft. The zone resembles the Mahogany zone in other core 

holes in the area but with much lower oil yields—6.9 GPT 

(fig. 97). Because this is the only control point in this unique 

area, it was included in the assessment calculation. Without it, 

isovalue lines for estimated gallons per ton for the Mahogany 

zone overestimated the richness throughout a large area of the 

northernmost part of the basin. 

Three hundred ninety two core holes were used to assess 

the Mahogany zone here. An additional 73 rotary holes were 

used in the alternative set of resource maps that used both 

core holes and rotary holes. Only 131 core holes were used to 

assess the Mahogany zone in the previous assessment (Pitman 

and Johnson, 1978). The Mahogany zone varies from 150 to 

250 ft thick through a broad northwest-trending swath in the 

middle of the Piceance basin (fig. 97). It thins towards the 

west, south, and east but thickens and grades into marlstone, 

siltstone, and sandstone near the mouth of Yellow Creek. 

Oil yield for the Mahogany zone varies from about 22 to 33 

GPT throughout the oil shale depocenter (fig. 98). In-place 

oil using only the core holes shows that the Mahogany zone 

contains from 200,000 to 427,000 BPA in the richest part of 

the depocenter with values decreasing in a regular fashion 

outward (fig. 99). Maximum in-place oil in a township is 

over 8.7 billion barrels in place in T. 1 S., R. 97 W. (fig. 100, 

table 24). Total in-place oil in the Mahogany zone using only 

core holes is estimated to be 191.7 billion barrels (table 25). 

The Mahogany zone was originally assessed by Pitman 

and Johnson (1978) using hand extrapolation and was not 

reassessed using kriging by Pitman and others (1989). Using 

only those townships that were assessed in both this assessment and the assessment of Pitman and Johnson (1978), our 

results are 8.97 percent higher than the manually extrapolated 

results of Pitman and Johnson (1978). 

Nine townships were visually picked out that seemed to 

have adequate control in the 1978 assessment, and using only 

those townships, our assessment is 5.10 percent higher than 

the assessment of Pitman and Johnson (1978) (table 24).
Detailed Description and Assessment Results of Oil Shale Zones 153

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

R–6 zone—In barrels per acre

< 100,000

100,001–

 200,000

200,001–

 300,000

300,001–

 400,000

400,001–

 500,000

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

328

142

148

122

136

127

126

219 214

208

197

207 200 146

182 223

128

151

157 141 129 142

139

136

143

138 139

142

142

143

148

152 150

140141 163

141

162

207

294

309 282

322

308 328

144 90

141 146

131 140

168

154 155

148

143

140

151 150

169

189

223 335

292 180

272

276

350

372

200

173

314

343

347

313

297

24

226

272

347 347

351 226

244

354

250

376

229

257

159 155

341

304

121

307

263

334

346350

360

115

225

150

40 229

33

329

318

337

339

205

284

334

316

269

247

195

183 194

214

219

305

60

359

373

362 378

322

197

281

218

188

162 234

214 227

236 201

191

381

337

337 344

367 316

344

356

298269

211

218

214

252

208

271

175

333

180

234

311

250

217200

309

351

310

340

254

201

221

301

336

206

241

327

383

252

211

295

313

239

184

330

206 327 249

315

313

358

357

333

231

99

387

323

339

359

353

320

340

233

284

245

181

191

304

262

280

77

117

120

242 261

165 169 134

297

388

211

349

292

307

323

288

324

424

410

284

140

235 196 198 199

176 186

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 91. Isoresource map of the R-6 zone showing oil yields in barrels per acre (BPA) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
154 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

77,451,504

255,790,000

658,067,968

200,086,000

219,280,000 503,567,008 533,440,992

1,106,720,000

2,311,660,032

1,468,839,936

1,454,550,016 75,149,296

103,179,000 1,129,539,968

2,060,039,936 2,705,870,080

4,096,450,048

4,796,210,176 4,782,839,808

2,316,049,920

1,207,480,064

4,227,300,096 5,773,389,824 6,915,160,064 6,579,420,160

1,499,459,968

5,840,640,000 7,376,379,904 7,757,859,840 5,927,050,240

433,596,000

4,854,459,904 6,617,410,048 7,655,860,224 6,985,569,792 3,038,560,000

7,849,059,840 8,520,929,792 6,580,230,144

1,762,019,968

260,559,008 7,794,809,856

1,616,960,000 216,098,000

2,503,069,952

5,764,129,792

1,612,989,952

5,052,839,936

2,998,860,032 6,226,679,808

2,163,160,064

439,848,992

3,107,899,904

3,931,630,080

10,284,900

280,375,008

730,241,024 902,561,024

348,551,008

221,552,992

584,062,016

152,064,992

25,824,700 74,790,600

12,212,700 65,216,600

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

R–6 zone shale oil, total in-place resource—In millions of barrels

< 900

901–1,800

1,801–3,100

3,101–5,100

5,101–8,500

Top of Mahogany zone

Base of Parachute Creek Member

R–6 zone shale oil in-place resource—

 By township, in barrels 228,800,000

Figure 92. Isoresource map of the R-6 zone showing total number of barrels of oil in each township using only 

core hole data.
Detailed Description and Assessment Results of Oil Shale Zones 155

Table 22. Total number of in-place barrels of oil per acre (BPA) in each township for the R-6 zone calculated here using the Radial 

Basis Function Method (RBF). Results for the R-6 zone from Pitman and others (1989) using manual extrapolation and kriging are also 

listed with percent difference using the RBF method here. Townships highlighted in yellow are those in which kriging by Pitman and 

others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.

Township, Range SUM R-6 Extrapolated Pitman and 

others, 1989 Difference Percent difference

1N 96W 1,612,990,000 1,655,359,000 -42,369,000 -2.56

1N 97W 5,764,130,000 5,208,895,000 555,235,000 10.66

1N 98W 7,794,810,000 6,369,959,000 1,424,851,000 22.37

1N 99W 5,052,840,000 4,009,833,000 1,043,007,000 26.01

1N 100W 260,559,000 126,207,000 134,352,000 106.45

2N 97W 216,098,000 115,671,000 100,427,000 86.82

2N 98W 2,503,070,000 1,613,707,000 889,363,000 55.11

2N 99W 1,616,960,000 1,009,920,000 607,040,000 60.11

2N 100W

1S 95W 1,762,020,000 1,295,776,000 466,244,000 35.98

1S 96W 6,580,230,000 6,007,621,000 572,609,000 9.53

1S 97W 8,520,930,000 8,131,159,000 389,771,000 4.79

1S 98W 7,849,060,000 7,282,021,000 567,039,000 7.79

1S 99W 6,226,680,000 5,812,091,000 414,589,000 7.13

1S 100W 2,998,860,000 1,597,541,000 1,401,319,000 87.72

2S 94W

2S 95W 3,038,560,000 2,583,613,000 454,947,000 17.61

2S 96W 6,985,570,000 6,328,320,000 657,250,000 10.39

2S 97W 7,655,860,000 7,198,068,000 457,792,000 6.36

2S 98W 6,617,410,000 6,044,955,000 572,455,000 9.47

2S 99W 4,854,460,000 4,553,164,000 301,296,000 6.62

2S 100W 2,163,160,000 1,194,530,000 968,630,000 81.09

3S 94W 433,596,000 156,239,000 277,357,000 177.52

3S 95W 5,927,050,000 4,748,567,000 1,178,483,000 24.82

3S 96W 7,757,860,000 7,206,961,000 550,899,000 7.64

3S 97W 7,376,380,000 6,972,504,000 403,876,000 5.79

3S 98W 5,840,640,000 5,519,544,000 321,096,000 5.82

3S 99W 3,931,630,000 3,744,312,000 187,318,000 5.00

3S 100W 439,849,000 317,119,000 122,730,000 38.70

4S 94W 1,499,460,000 904,019,000 595,441,000 65.87

4S 95W 6,579,420,000 5,600,159,000 979,261,000 17.49

4S 96W 6,915,160,000 6,528,163,000 386,997,000 5.93

4S 97W 5,773,390,000 5,439,115,000 334,275,000 6.15

4S 98W 4,227,300,000 4,146,597,000 80,703,000 1.95

4S 99W 3,107,900,000 2,937,954,000 169,946,000 5.78

4S 100W 1,207,480,000

4S 101W 10,284,900 1,523,000 8,761,900 575.31

5S 94W 2,316,050,000 2,189,722,000 126,328,000 5.77

5S 95W 4,782,840,000 4,165,623,000 617,217,000 14.82

5S 96W 4,796,210,000 4,520,973,000 275,237,000 6.09
156 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 22. Total number of in-place barrels of oil per acre (BPA) in each township for the R-6 zone calculated here using the Radial 

Basis Function Method (RBF). Results for the R-6 zone from Pitman and others (1989) using manual extrapolation and kriging are also 

listed with percent difference using the RBF method here. Townships highlighted in yellow are those in which kriging by Pitman and 

others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.—Continued

Township, 

Range SUM R-6 Extrapolated Pitman and others, 1989 Difference Percent difference

5S 97W 4,096,450,000 3,909,584,000 186,866,000 4.78

5S 98W 2,705,870,000 2,177,218,000 528,652,000 24.28

5S 99W 2,060,040,000 1,490,416,000 569,624,000 38.22

5S 100W 1,129,540,000 529,666,000 599,874,000 113.26

5S 101W 103,179,000 25,244,000 77,935,000 308.73

6S 94W 75,149,300 64,327,000 10,822,300 16.82

6S 95W 1,454,550,000 910,968,000 543,582,000 59.67

6S 96W 1,468,840,000 1,150,043,000 318,797,000 27.72

6S 97W 2,311,660,000 2,137,386,000 174,274,000 8.15

6S 98W 1,106,720,000 896,155,000 210,565,000 23.50

6S 99W 533,441,000 439,179,000 94,262,000 21.46

6S 100W 503,567,000 255,751,000 247,816,000 96.90

6S 101W 219,280,000 42,813,000 176,467,000 412.18

7S 93W 272,072

7S 94W 584,062,000

7S 95W 221,553,000

7S 96W 200,086,000 144,121,000 55,965,000 38.83

7S 97W 658,068,000 583,481,000 74,587,000 12.78

7S 98W 152,065,000 130,897,000 21,168,000 16.17

7S 99W 255,790,000 217,319,000 38,471,000 17.70

7S 100W 280,375,000 94,796,000 185,579,000 195.77

7S 101W 77,451,500 9,688,000 67,763,500 699.46

8S 93W 348,551,000

8S 94W 902,561,000

8S 95W 730,241,000

8S 96W 7,040,600

8S 99W 74,790,600

8S 100W 25,824,700

8S 101W 2,735,640 45,000 2,690,640 5,979.20

9S 94W 2,068,020

9S 95W 65,216,600

9S 96W 12,212,700

Sum: 185,366,007,632 158,446,601,000

Sum of townships used in both assessments: 181,184,134,340

Percent higher this assessment: 16.99

Best townships this assessment: 28,558,330,000

Best townships previous assessment: 26,583,077,000

Percent difference: 7.43
Detailed Description and Assessment Results of Oil Shale Zones 157

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

10

B–groove interval—Thickness in feet

< 20

21–40

41–60

61–80

81–100

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

98

10

18

81

16.1

20 22

12 16 14

12 16

12 13 13 14 15 12

1514 12 14

14

14

15 14

15

10

13

14

20 14 14

15 20

24

17

18 20 10

20

20

20

16.6

14.5

18

16 18 18

20 20

17 17

31.7

80

16.5

26.3 16

18

18

18 16 17 18 16 16

15 14

12 15 16

15 16

18 17

22 16 16 16

14

11 16 17

13

17 24.3

18 18

16

19 12

16

19

23

23.5

26.6

21 22

25

19.7

17.4

23.8 22

24

20.5

23

23.6

57 90

1513

15 16

14

14 16

15

14

10

15

10 13

9 14.2

10

14.2

18 13

20

15

20

25

20

10 15

20

17

13

16

13.118

19 14 10 14

15

20 20

20

2020

19.8

17

21

20

20

15

23 14

12

24 14

17 13

36 16 20 14

15 20

20

21 15

20

22 1525 18

20 17 28

20 20 22

26 20

20 15

21

24

18 35 27

2025 28

27 20 24

67

20 33

15

31

30 22

15

15.6

18

18.9

22

22

22

23

25

30

30

21

22

30 22

41

42 50

34

15

30

30

24

23

15

20

13

26.8

15

11

29

12

14

24

18

18.1 20

18

29 27

22 30

18

21

32

36

28

18.6

17.5 17.1

58

36

60

36.3

26

53.1

32.2

11

14.1

17

15.8

22.5

8.6

42.8

13.4

18.6

22

17 21.3

25

18.2

18

18

12.7

17 31 18

22

28.4

18

17

27.1

22

35.3

18 16 18

15

12

32

46

18

18

14 18

14 14.7

12 14

18

18

16.2

19

6.3

12 19

26.1

20

20.2

17.4

30

36 30

20

15

11

16

18

20

15

15

16.9

21.7

34

15

14

16.9

15 16

30

33

32

34

23.1

19.1

17

18

6

19.1

22.2

15

36

32

54

9.4

18

20

37 38

34.5

15

35 37

35

8.3

21 17

24

24

12.6

27

32

25.9

14

22

13

20

21.3

10.9

28.3

29

17

17

19.9

20.5 18.1 17.3

19.3

19.2

30

30

42

23.8

12.7

23.4

18.3

36

18.4

20.1

41.2

16.6

25.6

25

15

28

24

19

24

88

63

68

22

15

13

22

18

34

25

60

18 12 12

11

14

10

17

10

10

15

13

10 5

10

14

21.6

20.3

21

10

15 16

16

31

19

11.5

20

33

57

16

24

24

20

22 19

18 18

14.5 16

16

17

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

Figure 93. Isopach map of B-groove using both core hole and rotary hole data. The Radial Basis Function Method 

(RBF) was used for contouring.
158 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in

 gallons per ton

10

B– groove interval—Average oil yield in gallons per ton

< 5

5.1–10

10.1–15

15.1–20

20.1–25

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

8.4

3.2

3.8 3.2 3.3

3.2 5.4

3.3

3.4 3.8

4.5

4.1 3.7

3.7 4.7 3.8 4.3

3.5

2.8

6.7 3.9

4.5

5.4

3.4 4.1 3.1 4.1

3.8 3.3

3.4 3.8

4.4 3.6 4.7

2.4 3.9

3.1

1.3

3.3

2.4

2.8

4

4 4.3

3.9

3.5 4.2

3.7 3.4

4.4 3.3

3.3 4.53.9

3.5 4

3.64.9 3.5 3.6 3.6

3.6

3.2 4.54.2 7.1

2.2 6

4.43

4.5

4.4 3.8

4 4.6

5.2

6.8

5.9

5.1

5.7

4.2 4.5

3.5 5.2 5

4.8 4.6

4.6

4.3

2.1

1.3

3.93.6

6.6 5

4.3 4.1

4.8

3.8 3.2

4.1

3.7

3.5 4.4

6 3.7

4.3

4.5

5.8

4.7

4.9 7.8 5

5

5 7.3

3.6

5.2

7.7

19.2

6.7

8

4

1.2

5.4

4.2

11 6.1

7.7

3.4

2

3

4.9

3.5

6.8

5.5

4

5.9

4.8

5

2.7

2.6

2.8 2.2

7.2

2.7 2.4

2.5 2.5

5.7

3.3

2.8 3.5 3.4

5.6

6.1

5

2

2

4

1.5

2.4

3.2

0.2

2.5

7.2

7

5.9

6.1

3.3

5.1

5.8

5.6

6.5 4.7

5.5

6.3

7.2

6

5.4

3.1 5.2

16.9

4.9

15.6

2 1.3

6.1

8.9

5.4

4

3.9

3.7

3.4

4.7

5.3

3.6

6.6

4.1

4.2

5.95.7 4.1 3.9 3.2

6.64.9

4

6.6

8

13.2

5.4

25.2

5.9 4.5 13.7

4.1

3.2 2.2

3.7

3.5

4.5

4.2

5.2

4.8

5.1

17.5

4.6

7

2.2

4.4

3.1

7.6

4.7 5.7

3.8

5.1

2.8

4.7

4.3

5.8

4.5

6.2

5.1

6.9

5.5

4.7

7.7

4.5

1.7

3.6

5.8

9.8

7

3.1

1.8

5.4

4 2.6

2.5

3.5

8.6

5

7.6

12.2

4.9

2.6

1.9

3.9

4.2

6.2

6.1

4

2.2

5.4

11.3

6.7

6.4

3.4

6.1 4.3 4.1

10.4

11.6

3.3

2.6

4.1

6.7

4.1

6.2

5.5

2.8

7.4

6.2

2.7

3.3

3.2

2

1.9

2.5

3

4.4

2.9

3.4

2

1.8

7.1

3.8

4.1

8

4.5

5.1

4

3

3.4 3.5 6.8

3.7

4 4.4

4.6

3.14.1 4.9 2.5

13.5 5.8 4.7

3.5

8.3

7

10.8

5.3

7.9

13.2 5.7

19.2

5.5

8.7

4.8 4

3.4

2.8

3.6 4.5 4.3

4.6 4.1

3.9 3.8

5

3.4

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 94. Isoresource map of B-groove showing the oil yield in gallons per ton (GPT) using only core 

hole data. The Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 159

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of 

 barrels per acre 10

B–groove—In barrels per acre

< 10,000

10,001–

 20,000

20,001–

 30,000

30,001–

 40,000

40,001–

 50,000

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

11

6

4 4 4

3 7

4 4 3 6 5 4 5 6 4 5

4

3

8 5

6

6

5 6 44

5

7 5

4 6

6 6 7

3 7

5

4

23

3

4 6

6

7 5 5 5 6

5

6 4 3

65

5

5

6 7

5 5 5

4

3 6

6

8

3 12

7

5

6

7

4

6

7

10

13

13

9 11

9 8 510

10

10 8

9

9

11 10

5 4

8 7

5 6 54 6

4

5

3 5

3 7

5

7

7

8

10 7 6

6

6

13

4

5

15

19

8

12

7

2

7

7

20 13

14 12

9

8

10

7

15

7

4

14

5

6

6

4

4 4

11

7 6

5 7

9

6

8

11

8

9 9

7

10

11

12

3

11

9

0

3

10

9

11

4

12

6

9

10

12 7

12

10

11

9

6

5 8

40

9

35

3 2

14

16

16

6 6 5

4

5

14

14

10

6

5

9

5 7 4

4 8

10

6

10 4

20

5

47

10 8

19

11

10

6

6

5

4

6

8

8

6

20

7

13

7

6

4

11

6 8

10

14

8

14

9

9

7

9

3

11

10

6

23

12

8

3

9

16

22 10

5

7

8 12

8

3

15 7

15

24

5

6

5

9

5

11

7

7

4

13

27

10

9

6

10 7 6

16

18

9

7

15

13

4

12 8

9

11

10

10

5

7

4

3 6

6

7

6 26

11 11

13

5

5

15

7

15

9

16

5 4 7

4

5

4

7

3 3 6

3

11 2

4

4

15

12

18

4

16 11

8

45

9 8

8

11

5

6

6

8 7

6 7

5 5

7 5

108°30' 108°00'

40°0'

39°30'

0 3 6 12 MILES

40°00'

39°30'

Figure 95. Isoresource map of B-groove showing oil yields in barrels per acre (BPA) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
160 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

5,233,940

17,350,600

33,382,700

11,094,900

10,195,900 25,653,000 28,704,300

62,267,000

100,903,000

56,103,600

135,555,008 6,495,840

3,333,520

47,044,800

83,444,896 141,404,000

167,323,008 158,638,000

180,204,000

202,151,008

63,209,400

134,387,008 180,430,000 190,139,008 205,568,992

75,703,904

177,115,008 459,128,000 256,216,992 180,344,992

16,678,500

172,284,992 281,612,992 233,279,008 195,262,000 99,318,496

299,043,008 361,604,992 300,176,000

81,408,704

6,143,830

231,555,008

63,095,600

82,267,000 6,846,780

219,568,000

78,290,400

136,238,000

104,700,000 244,488,992

106,632,000

34,336,300

110,206,000

173,324,000

312,383

20,722,200

157,132,992

251,714,000

119,811,000

42,825,800

153,335,008

9,968,410

2,468,120 5,581,790

2,500,960 13,503,600

EXPLANATION

B-groove shale oil, total in-place resource—In millions of barrels

< 15

16–47

48–120

121–240

241–460

Top of Mahogany zone

Base of Parachute Creek Member

B-Grove shale oil in-place resource—

 By township, in barrels 228,800,000

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 96. Isoresource map of B-groove showing total number of barrels of oil in each township using 

only core hole data.
Detailed Description and Assessment Results of Oil Shale Zones 161

Township, 

Range SUM B-groove

1N 96W 78,290,400

1N 97W 219,568,000

1N 98W 231,555,000

1N 99W 136,238,000

1N 100W 6,143,830

2N 97W 6,846,780

2N 98W 82,267,000

2N 99W 63,095,600

2N 100W

1S 95W 81,408,700

1S 96W 300,176,000

1S 97W 361,605,000

1S 98W 299,043,000

1S 99W 244,489,000

1S 100W 104,700,000

2S 94W

2S 95W 99,318,500

2S 96W 195,262,000

2S 97W 233,279,000

2S 98W 281,613,000

2S 99W 172,285,000

2S 100W 106,632,000

3S 94W 16,678,500

3S 95W 180,345,000

3S 96W 256,217,000

3S 97W 459,128,000

3S 98W 177,115,000

3S 99W 173,324,000

3S 100W 34,336,300

4S 94W 75,703,900

4S 95W 205,569,000

4S 96W 190,139,000

4S 97W 180,430,000

4S 98W 134,387,000

4S 99W 110,206,000

4S 100W 63,209,400

4S 101W 312,383

5S 94W 202,151,000

5S 95W 180,204,000

5S 96W 158,638,000

5S 97W 167,323,000

5S 98W 141,404,000

Township, 

Range SUM B-groove

5S 99W 83,444,900

5S 100W 47,044,800

5S 101W 3,333,520

6S 94W 6,495,840

6S 95W 135,555,000

6S 96W 56,103,600

6S 97W 100,903,000

6S 98W 62,267,000

6S 99W 28,704,300

6S 100W 25,653,000

6S 101W 10,195,900

7S 93W 88,884

7S 94W 153,335,000

7S 95W 42,825,800

7S 96W 11,094,900

7S 97W 33,382,700

7S 98W 9,968,410

7S 99W 17,350,600

7S 100W 20,722,200

7S 101W 5,233,940

8S 93W 119,811,000

8S 94W 251,714,000

8S 95W 157,133,000

8S 96W 1,285,000

8S 99W 5,581,790

8S 100W 2,468,120

8S 101W 196,117

9S 94W 520,796

9S 95W 13,503,600

9S 96W 2,500,960

Total: 7,819,053,970

Table 23. Total number of in-place barrels of oil per acre (BPA) in each township for B-groove calculated here using the Radial Basis 

Function Method (RBF).
162 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

176.4

102

114

126

94 98 89

88 99

93 94 93 90 96 91 94 98 102

96

92

91 98 97

114

170

115

99

95

104 162

174

123

122 160

180

167

126 121

123.2

120

116

112 93

112 126

72

64 62

88.2

88.1

88.3

90.2

76

60 63

65 96.5

134

76.2 89

92

92

93

91 92

89 92

92 92

92

91

89 94 94

93

92

93

97 95 94 95

94

91 94

95

94

94

86.394 109.8

114 118

115

118

131

135.2

132.8

139.7

144 134

140.6

138.1

136 140.6

141

141.3

142.6

137 126

119 93 116 105

97 92 92

95

98

97 95

99 94

91

96

94 97

103 93

120

113

121.6 130

160

151

155

165

137

172

101 104104

110

98

125

135

138.9

135

133

129

152 145

135

154 160

167

157

165

169.5

176

169.7

175

124

110 123

122 122

149 158

145

166

164

149 160 128

153 167

168

175 171

160

150

168

174 172150 178

178178

170 150

172 175 172 178

172

180 180

185 210 180

152

162 155

168

175

170 61

84

130.2

162

153

177

201

168

183

188

206

206 176

186

190 180

137

177

160

174

143

205

137.1

112

95

200.2

131

112

216

118

140

98

98

107 106

88

176

121 120

132

120 129

128

141

128

123

143

158

128

122

118

99

182

174

196

96

168.4

176.9 179.7

115

131

124

128

90

138

118

124

139.4

69

189.9

99.2

178

186

176.3

174

145.4

142

183.4

180

1567.3

183

181

176.2

163.2

141.3

115

115 116

103

123

158.2

68 68

180

182.4

200.5

114 117 116 111

126

106

208

127.8

182

118 124.5

124 124125 142

133 129 123

179 190.7

184

184

171 172.9 187

176.3

212

200

93

101

131

131

140

124

132

108.8

139.8

142

138

174

184

178.5 176.5

132

144 125

124

207

186

146.5

124

128.7

160.5

181

171

174

137.3

208

194

105.1

151

210

165

169.5

222 162

81

180 176

165.4

173

176.3

161.7

93

242.4

128

112.5

161

180

107.6

182.4

190.5

181

178

141

108.6 109.7 98.7 105.6

110.2

96.1

101.3 90.2

100.5 111.1 118.6

108.7

119.2

130

194

190

98.4

112.6

126.1

130

200

136

166.4

152.3

84.5 62.9

80

64.2 94

101

99

106

109

94

97.5

122

96

88

92 112

60

97 89.5

111

106

116

127 126 123

133

141

85 120 105

72 91 93 84

90 89

88

98 101 93 99

104.5 96

102

101

165.7

249.1

111

106

176

152 168

172

175

228

180.6

96

109

107

121

120 114

114 109

112 105.1

111 98

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

10

Mahogany zone interval—Thickness in feet

< 100

101–150

151–200

201–250

Figure 97. Isopach map of the Mahogany zone using both core hole and rotary hole data. The Radial Basis 

Function Method (RBF) was used for contouring. Contour interval in feet is variable.
Detailed Description and Assessment Results of Oil Shale Zones 163

A-Groove

A-groove represents another comparatively thin interval, 

similar to B-groove that contains low oil yields. Three hundred 

eighty four core holes were used to assess A-groove here, 

with an additional 36 rotary holes use for the isopach map. 

A-groove has never been assessed before. It varies from 5 to 

25 ft throughout most of the basin (fig. 101), and thickens to 

the north to 71 ft in one control point about eight miles south 

of the mouth of Yellow Creek in the north-central part of the 

basin. A-groove could not be identified in outcrop near the 

mouth of Yellow Creek. 

Oil yields for A-groove vary from less than 1 GPT to 

about 22 GPT in a highly irregular fashion (fig. 102). Total 

in-place oil also shows a high degree of irregularity, but in 

general, in-place oil is highest along approximately the same 

southeast-trending area where in-place oil was highest for the 

underlying Mahogany zone (fig. 103). This southeast-trending 

area of high in-place oil is also reflected in the map showing 

total barrels of oil in B-groove for each township (fig. 104). 

Total in-place oil in A-groove is estimated to be nearly 6.3 billion barrels (table 25).

The Interval Above A-Groove

The interval above A-groove is complex with marlstones 

and oil shales of the Green River Formation intertonguing 

with volcanic-rich sandstone and siltstone of the Uinta 

Formation (figs. 3, 105). The interval represents the infilling 

stage of Lake Uinta, when the Piceance Basin part of the 

lake was largely, if not completely, filled in. Thick wedges of 

volcaniclastic sediments derived from the Absaroka volcanic 

field in northwestern Wyoming prograded from north to south 

across the Piceance Basin starting from a point source near the 

mouth of Yellow Creek in the north-central part of the basin 

(Johnson, 1981a; 1985) (fig. 3). The southward progradation 

of these volcaniclastics occurred over a significant period 

of time, with intervals of oil shale deposited during periods 

when the rate of volcaniclastics supplied to the basin from the 

north diminished or ceased entirely. These oil shale intervals 

coalesce towards the south end of the basin as the intervening 

clastic wedges pinch out creating a nearly continuous interval 

of oil shale several hundred feet thick in the southern part of 

the basin (fig. 3). 

Only the interval from the top of A-groove to the top of 

bed 44 of Donnell (2008) is assessed here, although there is 

clearly significant oil shale above this interval in the southernmost part of the basin (fig. 105). The interval above bed 44 is 

complexly intertongued with the Uinta Formation, and is not 

assessed here. As previously mentioned, Pitman and Donnell 

(1973) also assessed the interval from the top of A-groove to 

the top of bed 44 and estimated that it contained 128.5 billion 

barrels of oil in place. They subdivided the interval into four 

units that were assessed separately. In this report the entire 

interval is assessed as a single unit. Pitman and Donnell 

(1973) did not define the exact area that was assessed, but 

their assessment did not apparently extend as far north as our 

assessment of this interval here. 

Figure 106 is an isopach map of the interval from the 

top of A-groove to the top of the “Big Three” oil shale beds 

of Cashion and Donnell (1972) or bed 44 of Donnell (2008). 

The map used a significant number of previously unpublished 

surface points that were used by Johnson (1981a) when he created an isopach map for the interval from the base of A-groove 

or top of the Mahogany zone to the top the Thirteenmile Creek 

Tongue of the Green River Formation (Johnson, 1981a, his 

fig. 2), the top of which is just slightly above the top of bed 44 

(fig. 105). The interval includes much of the richest oil shale 

above the Mahogany zone, but there is clearly significant oil 

shale above the top of bed 44 particularly in the southernmost part of the basin (fig. 105). The interval thickens from 

about 150 ft along the southwest margin of the basin to over 

1,500 ft in the north-central part of the basin (fig. 106) where 

it consists of predominantly volcaniclastic sandstone with a 

few thin zones of marlstone. The interval is similar to the one 

isopached by Johnson (1981a, his fig. 2) but does not include 

A-groove.

Typically only part of this interval is cored and assayed, 

thus some additional points from partial cored intervals were 

added to constrain the resource maps. Six core holes were 

used, and for these six core holes data had to be assigned 

to the missing intervals based on geologic inference. In 

core holes C0011 and C0158 only the lower part of the 

Thirteenmile Creek Tongue of the Green River Formation was 

cored. The tongue was assumed to be 90 ft thick and averaged 

10 GPT based on C0176 in sec. 21, T. 3 S., R. 96 W. where 

the entire tongue was cored and assayed. In C0176 the tongue 

averages about 12–13 GPT, but based on the partial interval 

of the Thirteenmile Creek Tongue in core holes C0011 and 

C0158 the tongue is somewhat leaner in these two core holes. 

The top of bed 44 is estimated to be at 550 ft in C0174 based 

on surface mapping and sample descriptions. The assayed 

interval in C0174 begins at 900 ft, but visual estimates of 

oil yields were made for the interval from 500 ft to 900 ft 

by the geologist processing the core. These visual estimates 

are clearly approximations, but these are the only data 

available and are used here. In C0034, the top of bed 44 or the 

Thirteenmile Creek Tongue is 420 ft above the well bore based 

on surface mapping. This interval is largely sandstone, and 

thus it is assumed that it contains only a trace of oil. In C0293, 

the top of the Thirteenmile Creek Tongue is at about 125 ft in 

the hole based on surface mapping. In C0035, the top of the 

Thirteenmile Creek Tongue is assumed to be at 150 ft based on 

surface mapping. Assays start at 315 ft, and the interval from 

150 to 315 ft is assumed to contain only a trace of oil.

Estimated oil yield for the interval varies from about 16 

GPT to 22 GPT throughout much of the south central part 

of the basin with oil yields dropping off rapidly to the north, 

as the interval becomes intertongued with the Uinta Formation, and more gradually to the east, south, and west, due to 

an overall decrease in oil yields (fig. 107). In-place oil varies 
164 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in

 gallons per ton

10

Mahogany zone interval—Average oil yield in gallons per ton

< 7.5

7.6–15

15.1–22.5

22.6–30

30.1–37.5

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

28.3

25.3

24.1 23.5

22.1

22.6 23.6

23.8

23.2

23.323.5

25.2 22.9

22.9 24.124.4

24

22.6

21.6 24.624.7

25

23.4

22.4

22.7

20.4 21.7

21.8

22.2

23.6 22.8 18

19.1 20.6

19.8

21.3

23.7

24.1

24.3 24.1

13

18.7 20.2

20.2

25

28.2 19.6

23.6 23.5

24.7

23.7

23.5 25.5 24.2 23.2

23.4 24.1

23.7 24.2

24.5 24.2

23.6 23.5

24.4 24.8

23.6

23.9

24.5 24.72425.8 24.8

24.6

28.1 26.4 25.6

27.3 25.4

26.3

27.8

27.6

28.1

25.4

26.6

27.9

28.9

27.3

27.9

28.3 25.5

26.4

27

26.1

27.2 23.7

25.5 17.4 11 24.5 24.9

25.6 24.6

26.1

26.3 23.3

26.4

25.2

25.2

25.2

25.7

24.4 27.1

24.6 25.6

26

28.4

30.4

28.3

28.4

27.4

14.3

25.8

24.2 24.8

27

28.5

27.9

27.7

22.7 21.6

31.8

27.9

25.3

26.7

26.3

7.7

26.7

20.8

25.8 27.7

22.8

17.6

14.2

25.3

26.3

27.7

25.7

22.6

26.5

27.8

23.6

23.8

26.4 25.2

17.1 30.4

27.7 26.8

25.8

29 24.7

27.6

26

26.624.2

27.7

27.4

27.1 27.9

25.6

25.5

19.3

19.5

20.3

23.9

28.1 29.2 24.6

23.9

22.6

25.2

21.2

13.3

26.5

25.1

25.8

11.1

7.5

23.9

28.8

29.4

26.5

28.1

16

28.6

26.9

27.1

26.7

24.1

27.8

27.6

25.2

26.6

21.820.4

24.1

22

30.4

20 20.3

29.6

28.2

23.3

25.927.5

26.2 25.9

26.9

25.9

23.5

25.8

24.2

22.2 22.1

24.7 22.8 24.1 23.3

23 24.9 22.6

29.9 29.3

29.9

28 30.7 30.1 28.8

33.1

21.6

16.8

27.2

27.1

24.5

23.3

25.7

25.7

28

25.6

25.8

15.6

26

29

29.9

30.6 29.3

26.5 24.8

23.425.4

21

19.5

20.8

24.6

23.4

24.4

24.9

26.4

28.8

26

21.8

24.3

25.7

28.1

26.5

17.7

13.7 17.7 15.5

19.2

28.5

29.1

28.4

28.3

29.3

15.5

23.2

20.3

28.1

27.4

28.9

23.9

25.7

31.1

25

27

27.9

29.8

28.2 27.6 26.7

25.7 27

24.5

26.6 29.6

27.6 27.7 26.5

26.6

26.7

26.4

17.5

17.2

25.3

26

27 26

14.7

29.6

29.9

16

23.8 22.4

24.1

19.5 25.2

25.7

24.9

26.9

28.7

25.1

24.8

27.7 24.6

25.5

24.8

27.1

18

28

26.3

25.6

27.4

26 25 28.1

27.2

27.1

23.5 26.3 22.6

19.3 24.123.7 22.8

22.4

23.6

22.5

23.424.7 24.9 25.3

24

22

25.1

24.8

25.7

22.4

21.4

25.3

6.9

28.7 28.9

27.6

26.7

27.4

26.1

26

22.5

27.3

26.5

27.4 27.2

24.6 22.6

23.2 22.9

22.8

23.2

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 98. Isoresource map of the Mahogany zone showing the oil yield in gallons per ton (GPT). The Radial 

Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 165

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

353

186

172

161

145

146 171

161

160

153 160

174 153158 172 181

168

153

146 173175

208

169

157

174

192 195

199 197

200

128 188

135 194

107

101

152

154

156

158

79

91

89

98 174

267

113

153 158

164

161

156 169

156 160 156

157161

157

156167 165 160

158165 170 162

165

167

163

164

176 169

167

172178

202

221

216

217

233

257

269243

266

285

273

273

273

258 272

266

272

267

265 218

218 155 94 165

175

169 164

178

167 183

180

180 171

165

177

166 187

171 184

211

244

339

302

311

322

154

187

183 186

267

292

335

334

204

195

348

328

312

320

328

39

246

238

373 369

312 239

179

250

377

257

207

359

224

276

169

170

202 193

116

373

238 229

245

215 263

251

263

243 216

281

308

247

241

217

182

265

256

298

167

335 369315

200

206

233

142

146

224

225

258

62

119

173

361

384

334

346

181

287

352

348

349

317

347

320

257

219

186 177

181

200

336

102 103

374

364

342

212

227

220

206

242

197

357

237

320

193

203

208 219 222

242

239 218

205

374

392

385

365 366

380 364

400

340

259

180

195

233

223

227

259

229

262

200

259

173

257

355

385

376 367

250258

214 227

324

274

227

221

220

284

326

323

353

256

336

342

194

300

398

224

184 301 196

118

362

360

332

346

363

196

158

369

255

219

328

313

199

394

344

348

352

294

217 215 188

195 212

171

193 187

197 218 225 207

227

246

261

251

179

210

235

250

231

282

348

189

147 104

140

94

171

187

178

203

221

170

175

240

171 161

165 216

83

192

152

209 195

226

237 227245

258

272

146 226 175

105 163157

141

149

153

146

168 181 167

181

183 156

185

181

306

411

176

193

72

356

309

329

328

341

427

337

159

208

229

234 221

203 181

190 177

186

166

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

Mahogany zone—In barrels per acre

< 100,000

100,001–

 200,000

200,001–

 300,000

300,001–

 400,000

> 400,000

COLORADO

0 5 10 2.5 KILOMETERS

Figure 99. Isoresource map of the Mahogany zone showing oil yields in barrels per acre (BPA). The Radial 

Basis Function Method (RBF) was used for contouring.
166 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

136,932,000

435,366,016

1,058,710,016

323,312,992

279,000,000 655,296,000 755,475,968

1,631,059,968

3,328,920,064

1,919,929,984

2,010,700,032 104,496,000

135,299,008

1,288,560,000

2,422,309,888

3,082,830,080

4,640,820,224

4,644,919,808 4,944,050,176

3,427,429,888

1,391,079,936

3,641,750,016 4,538,399,744 5,834,740,224 6,535,600,128 6,420,539,904

1,465,500,032

436,356,000

4,157,580,032 6,058,930,176 7,966,009,856 7,545,469,952 6,222,470,144 401,102,016

1,965,479,936

5,258,359,808 7,124,939,776 7,983,070,208 6,843,010,048 3,219,130,112

1,311,129,984

1,639,459,968 171,400,992

2,581,550,080 6,151,920,128 8,034,570,240 8,747,780,096 6,549,130,240

1,688,440,064

212,840,000

4,031,950,080

6,700,009,984

5,581,219,840

1,505,319,936

13,897,900

522,751,008

1,009,070,016

1,072,019,968

405,640,000

303,455,008

704,193,024

227,375,008

54,142,000

130,336,000

18,553,400 94,429,800

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

EXPLANATION

Mahogany zone shale oil, total in-place resource—In millions of barrels

< 330

331–1,000

1,001–2,600

2,601–5,300

5,301–8,800

Top of Mahogany zone

Base of Parachute Creek Member

Mahogany zone shale oil in-place resource—

 By township, in barrels 228,800,000

COLORADO

0 5 10 2.5 KILOMETERS

Figure 100. Isoresource map of the Mahogany zone showing total number of barrels of oil in each township 

using only core hole data.
Detailed Description and Assessment Results of Oil Shale Zones 167

Table 24. Total number of in-place barrels of oil per acre (BPA) in each township for the Mahogany zone calculated here using 

the Radial Basis Function Method (RBF). Results for the Mahogany zone from Pitman and others (1989) using manual extrapolation 

and kriging are also listed with percent difference using the RBF method here. Townships highlighted in yellow are those in which 

kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.

Township, 

Range

SUM Mhg, no 

rotary holes

"Extrapolated" Pitman 

and others, (1989) Difference Percent difference

1N 96W 1,505,320,000 1,503,776,000 1,544,000 0

1N 97W 5,581,220,000 5,097,122,000 484,098,000 9

1N 98W 6,700,010,000 5,740,681,000 959,329,000 17

1N 99W 4,031,950,000 3,464,872,000 567,078,000 16

1N 100W 212,840,000 167,481,000 45,359,000 27

2N 97W 171,401,000 161,069,000 10,332,000 6

2N 98W 1,639,460,000 1,053,367,000 586,093,000 56

2N 99W 1,311,130,000 786,834,000 524,296,000 67

2N 100W

1S 95W 1,688,440,000 1,272,147,000 416,293,000 33

1S 96W 6,549,130,000 6,108,594,000 440,536,000 7

1S 97W 8,747,780,000 8,349,431,000 398,349,000 5

1S 98W 8,034,570,000 7,472,206,000 562,364,000 8

1S 99W 6,151,920,000 5,812,983,000 338,937,000 6

1S 100W 2,581,550,000 2,044,619,000 536,931,000 26

2S 94W

2S 95W 3,219,130,000 2,557,731,000 661,399,000 26

2S 96W 6,843,010,000 6,378,481,000 464,529,000 7

2S 97W 7,983,070,000 7,680,361,000 302,709,000 4

2S 98W 7,124,940,000 6,869,942,000 254,998,000 4

2S 99W 5,258,360,000 5,234,224,000 24,136,000 0

2S 100W 1,965,480,000 1,767,740,000 197,740,000 11

3S 94W 401,102,000 226,265,000 174,837,000 77

3S 95W 6,222,470,000 4,835,740,000 1,386,730,000 29

3S 96W 7,545,470,000 7,098,816,000 446,654,000 6

3S 97W 7,966,010,000 7,447,163,000 518,847,000 7

3S 98W 6,058,930,000 5,819,722,000 239,208,000 4

3S 99W 4,157,580,000 4,160,823,000 -3,243,000 0

3S 100W 436,356,000 425,763,000 10,593,000 2

4S 94W 1,465,500,000 1,281,420,000 184,080,000 14

4S 95W 6,420,540,000 5,918,413,000 502,127,000 8

4S 96W 6,535,600,000 6,255,423,000 280,177,000 4

4S 97W 5,834,740,000 5,708,767,000 125,973,000 2

4S 98W 4,538,400,000 4,538,500,000 -100,000 0

4S 99W 3,641,750,000 3,540,981,000 100,769,000 3

4S 100W 1,391,080,000 1,104,739,000 286,341,000 26

4S 101W 13,897,900 8,142,000 5,755,900 71

5S 94W 3,427,430,000 3,123,880,000 303,550,000 10

5S 95W 4,944,050,000 4,443,359,000 500,691,000 11

5S 96W 4,644,920,000 4,440,714,000 204,206,000 5

5S 97W 4,640,820,000 4,474,505,000 166,315,000 4
168 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 24. Total number of in-place barrels of oil per acre (BPA) in each township for the Mahogany zone calculated here using 

the Radial Basis Function Method (RBF). Results for the Mahogany zone from Pitman and others (1989) using manual extrapolation 

and kriging are also listed with percent difference using the RBF method here. Townships highlighted in yellow are those in which 

kriging by Pitman and others (1989) indicated an error of 20 percent or less at the at the 95 percent confidence level.—Continued

Township, 

Range

SUM Mhg, no rotary 

holes

"Extrapolated" Pitman 

and others, (1989) Difference Percent difference

5S 98W 3,082,830,000 2,759,827,000 323,003,000 12

5S 99W 2,422,310,000 2,185,995,000 236,315,000 11

5S 100W 1,288,560,000 1,028,917,000 259,643,000 25

5S 101W 135,299,000 114,055,000 21,244,000 19

6S 94W 104,496,000 106,495,000 -1,999,000 -2

6S 95W 2,010,700,000 1,750,875,000 259,825,000 15

6S 96W 1,919,930,000 1,856,525,000 63,405,000 3

6S 97W 3,328,920,000 3,251,134,000 77,786,000 2

6S 98W 1,631,060,000 1,331,957,000 299,103,000 22

6S 99W 755,476,000 661,725,000 93,751,000 14

6S 100W 655,296,000 544,470,000 110,826,000 20

6S 101W 279,000,000 154,240,000 124,760,000 81

7S 93W 560,240

7S 94W 704,193,000 461,287,000 242,906,000 53

7S 95W 303,455,000 1,030,937,000 -727,482,000 -71

7S 96W 323,313,000 252,052,000 71,261,000 28

7S 97W 1,058,710,000 391,432,000 667,278,000 170

7S 98W 227,375,000 390,007,000 -162,632,000 -42

7S 99W 435,366,000 90,079,000 345,287,000 383

7S 100W 522,751,000

7S 101W 136,932,000

8S 93W 405,640,000

8S 94W 1,072,020,000

8S 95W 1,009,070,000

8S 96W 11,006,200

8S 99W 130,336,000 130,982,000 -646,000 0

8S 100W 54,142,000 64,696,000 -10,554,000 -16

8S 101W 5,344,020 3,077,000 2,267,020 74

9S 94W 2,250,500

9S 95W 94,429,800

9S 96W 18,553,400

Sum: 191,716,681,060 172,937,560,000

Sum of townships used in both assessments 188,443,467,920

Percent higher this assessment 8.97

Best townships this assessment 43,344,160,000

Best townships previous assessment 41,242,220,000

Percent difference 5.10
Detailed Description and Assessment Results of Oil Shale Zones 169

Township, Range SUM A-Groove

1N 96W 27,325,600

1N 97W 102,764,000

1N 98W 173,953,000

1N 99W 160,764,000

1N 100W 8,491,410

2N 97W 3,881,950

2N 98W 81,503,600

2N 99W 86,044,300

1S 95W 118,608,000

1S 96W 305,327,000

1S 97W 265,201,000

1S 98W 189,827,000

1S 99W 161,456,000

1S 100W 89,708,200

2S 94W

2S 95W 194,306,000

2S 96W 281,241,000

2S 97W 228,800,000

2S 98W 139,030,000

2S 99W 140,256,000

2S 100W 63,972,700

3S 94W 18,355,000

3S 95W 180,307,000

3S 96W 203,941,000

3S 97W 176,088,000

3S 98W 178,398,000

3S 99W 180,859,000

3S 100W 15,663,800

4S 94W 98,852,300

4S 95W 198,158,000

4S 96W 180,224,000

4S 97W 150,252,000

4S 98W 148,461,000

4S 99W 137,507,000

4S 100W 57,933,300

4S 101W 632,008

5S 94W 150,121,000

5S 95W 164,825,000

5S 96W 116,492,000

5S 97W 133,574,000

5S 98W 98,785,300

Township, Range SUM A-Groove

5S 99W 90,309,600

5S 100W 67,244,000

5S 101W 7,936,200

6S 94W 4,110,210

6S 95W 71,477,200

6S 96W 45,456,200

6S 97W 87,814,100

6S 98W 49,263,200

6S 99W 23,809,500

6S 100W 36,409,300

6S 101W 19,021,900

7S 93W 37,909

7S 94W 59,871,200

7S 95W 14,211,200

7S 96W 9,194,890

7S 97W 33,481,600

7S 98W 14,512,700

7S 99W 26,374,100

7S 100W 30,199,900

7S 101W 8,608,690

8S 93W 45,042,000

8S 94W 79,982,000

8S 95W 28,895,200

8S 96W 278,680

8S 99W 10,060,000

8S 100W 3,889,010

8S 101W 396,943

9S 94W 119,303

9S 95W 2,612,740

9S 96W 586,794

Total 6,283,095,737

Table 25. Total number of in-place barrels of oil per acre (BPA) in each township for A-groove calculated here using the Radial Basis 

Function Method (RBF).
170 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

10

A–groove interval—Thickness in feet

10.1–15

15.1–20

20.1–25

25.1–30

> 30

5–10

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

14

9 10

12

10 11

11

12 10

12

9 11 10 10

10 10 12

8

9

12

10 10

12

20

12 11

9

1112

12

18

12

15 15

12

15

14 15

15 14

12

13 9

12 13

5

11

9.5

9.3

10.8 10.8

12

31

10 10

9 7

12 9.8 9 8

10 10

9 13 9 9 10

10 10

10

8 8 9

11

10

9

9 10

11 10

10

11

12 10

11

11

9

9.7 10

10

11

11

9

9.3

12

13

11 12

13.3

10

13 13

12.5 10

12 6

12

9.9 12 14

16 17 15 10

10

10 12

9

10

11 11 10 11

12

10

10 12

9 10.4

10

10.4

12

12 13.5

14

17.8

16 13

14

14

11

14 15 28

30

10

10 7

12

20

8

18

20 17 15 13

20

25

20

9

2016

14.7

17

17.3

20

12 13

16

16

10

17 9

15 14

20 16

14 15

17

13

20

20

14

11 15 30

25 22 20

18

20 17

12 20

18

15 20

14

13 20

16

20

17

16

22

20 22

20 20

21

25

30

18

15

20

15

11

10

10

10

8

10.6 10

13

10

10

15

11

13 10 12

13 10 12 12

10

13

13

16

8

13

18

13.8 10

14

13

13

12

13 13

18.4

12.2

6

12.7

11.2

13

14

15

18

15

17

14.6

12.8

15.7

12

13 12

16

13

13.6

10 9

13

17.6

9 11 11

10

9 8.8

10 6

26

12.4

20

15 15.5

14 16 15 6

14 14

15

13 14

14

13

11

14 17.1

14.7

22

9

9

14

12

14

14

14

9

11.2

11.2

14 12

10 12

17

18.4

12

12.5

15

13

14.7

10.5

18

21

10

14 14

14.6

16

14

11

8

10.5

10.5

11

10

8.8

14.7

14

17

14

11

12.1

10.6 12 12.4

12 13.1

9

11

10 9.3

10.1 9.2

10.7 12 5.3

8.9

10

15

8.8

9 9.4

10 13.5

18

7.1

8

9.5

10.1

8.2

8 17

9

11.8 10

10

7

10

11.1

10

13.5

8

13.8

14

14

14 10

10

9 9.5

10 7

9

11

10

10 9 11

7.5

13

9

19 15 1516

11 11

11

8

7 9 7

11

10.5

10

10 11

12

10.712 8

15.8

16.9

9 11

9 16

9 11

9

15

11

8

10

13

10.5

11 12

17

14.4

11

11

11

9

11 10

12 13

10 12.9

10

12

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 101. Isopach map of A-groove using both core hole and rotary hole data. The Radial Basis Function 

Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 171

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in

 gallons per ton

10

A-groove interval—Average oil yield in gallons per ton

< 5

5.1–10

10.1–15

15.1–20

> 20

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

7.9

7.4

5.8 7.1

5.9

7.6 8.5

8.2 6.4 7 7.2 6.9

6.6 7 8.64.9

5.8

7.4

5.8 9.7 8.2

10.9 6.2

6.8

5.1

6.9

4.7 5.1

5.75.7

6.8

3.8 5.6

6 5.3

2.6

5.7

5

5.2

5.5 5.1

5.1

3.6

5.6

5.3

6.1

9.7

6.3

5.9 5.6

7.3 5.9

6.5 6.8

6.4

6.9

6.8 6.76.9

7 10.46.8

6.7

10.2 7.7

8.8

5.3 8.7 6.8

7.5

10.3 11

7.4 8.4

5.5

6.4 12

11.1

10.9

7.4

8.4

5.5

8.5

7.3

9 9

8.2

6.5

10.9 6.9 5

6.7 6.6

8.6

6.3 5.8 7.3 5.5

9.8 10.2 4.2 7.6

6.6

7.1

13.9

9.1

6.3

8.6 13.6

12.2 8.9

9.6

7.7

6.2 8.8

8.1 6.6

7.9

5.5

6.8

6.2 6.6

8.3

8.5

8.8 7.8

7.5

5.7

6.5

7.5 5.1

3.7

8.1 6.3 5.6

11.6

6.8

10.5

6.7

5.2 5.6 6.8

5.6

9.7

4.8

8.9

11.8

4.9

5.6

5.8

4.1

3.6

7.1

13

6.1

9.3

6.3

4.9

6.3

6.3 5.3

2.4

8.2

7.3

8

6.1

6.5

5.8 7

9.1 5.2

3.7

5.9

7

11

5.3

9.7

8.8

7.7

6.2

5.6

8.1

4.4 5.6

12.6

4.9

6.1

5.9

8.5

9

8

7.7

6.8

6.2

7.7

7.8

7.3

7

8

4.9 4.1

7

7.2

5.9

6.3 5.6

11

19.1

6.4 7.2 8

6.8 6.6

5.7

11.3 22

3.1

5.9

4.6

10.9

8.8

4.4 6.6 5.6

8.6 6.7 5.5 6

8.8

7.2

6.7

7.7

9.5 9

8.4

4.1

6.4

7.2

7.2

4.7

7.1

6

6.1

4.5

5.7

5.6

6.2 5

5.9 6.2

4.9

8.7

5.5

5.2

9

8.3

5.3

5.8

12.7

6.8

7.2

6.1 6.2

8.4

6.9

6.1

6.3

20.4

8.7

6.2

11

5.5

5.9

5.8

6

6.4

3.3

5.9

5.8

6.4

6.2

5.69.3

5.3

6.1

6.1 7.2

9.3 9.2

6 8.8 7.1 6.8

7.7

9.2

10.3

6.2 5.7

6.2 8.4

1

6.7

6.3

12.3

6.1

1.3

0.8 9.3

6

6.4

6.3

6.6

6.4

6.4

6

7.3

9.4

5.2

5.6

6

5.7

5.6 13.6

7.2

6.7

7.3

6.2

5.5

7.2

7 8 7.7

7.9

6.1

6.4

8.3 4.66 4

7.2 7.2

7.4

6.8

5.1

7.6

9.6 7.4

10.2

7.6

10.1 6.8

7.4

5.5

7.6 9.1

5.6

2.7

3.9 11.6

9.5 12.5

5 7.1

10.4

13.5

6.1

6.4

6.1

5.9

5.6

5.4

7.2

5.6

4.9

8.2

5.3

6 5.8

6.1 6.1

5.4 6.4

6.7

7.4

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 102. Isoresource map of A-groove showing the oil yield in gallons per ton (GPT) using only core hole 

data. The Radial Basis Function Method (RBF) was used for contouring.
172 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

9

5

5 7 5

8 7

8 4 6 6 6 6 6 9 3

4

7

5 8 8

11 6

5 5

7

6 6

7 7

7 3 6

6 5

1

5

4

4 5 5

5

10

4 5

5

10

5 4 4

6

4 5

5 5 7 6 6

6

6 7

5 4 8

6 37 7 5

611 8

7

8

4

5 10

8 10

7

6

4 8

8

8 9

5 9

12 7 5

6

4 7

5 6

7 6

13 14

5

6 6

6 13 7

5 11 12 8 7

9

6

5 9

6

5

7

4

7

7 7

10

13

12 8

9

7

6

9 6 9

4 5 5

7

7

13

10

5 6

6

4

11

5

10

10

6

8

8

7 8

12

16

6

8

5

4

4

5 4

3

7

6

9

6 7

5 7

10 3

4

5

8

12

4

10

10

6

7

6

8

5

6

18

5

3

6

8

10

9

10

10

8

11

9

8

9

8

5 4

9

8

7

5 4

12

25

5 7 7

6

5

4

9 3

7

6

8

13

11

6 8

7 4

6 7

8

9

8

8 9 8

10

10

8

5

5

8

5

8

7

7

3

5

5

7 5

5 6

7

13

6

5

11

9

6

5

18

12

6

7 7

10

9

7

6

11

7

5

10

4 5

6

9

7

3

6

5

6 6 10 5

3 5

5 6

7 7

5 9 3 5

6

11

6

4 4

5 9

2

4

4

9

5

1

1

13

5

4 5

6

4

5

6

6

3

4

6

7

7

7 11

6

5

6

5

5

6

6 6 6

1

7

5

7

10 68

7 7

7

2

3 6 6

7

9

6

8 6

7

5 8 6

7

4

2 10

7 16

4 7

8

16

6

4

5

6

5

5

10

7

5

8

3 6 5

6 7

5 7

5

7

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre 10

A–groove—In barrels per acre

< 5,000

5,001–

 10,000

10,001–

 15,000

15,001–

 20,000

> 20,000

COLORADO

0 5 10 2.5 KILOMETERS

Figure 103. Isoresource map of A-groove showing oil yields in barrels per acre (BPA) using only core hole data. The 

Radial Basis Function Method (RBF) was used for contouring.
Detailed Description and Assessment Results of Oil Shale Zones 173

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

8,608,690

26,374,100

33,481,600

9,194,890

19,021,900 36,409,300 23,809,500

49,263,200

87,814,096

45,456,200

71,477,200 4,110,210

7,936,200

67,244,000

90,309,600 98,785,296

133,574,000

116,492,000 164,824,992

150,120,992

57,933,300

137,507,008 148,460,992 150,252,000 180,224,000 198,158,000

98,852,304

15,663,800 180,859,008 178,398,000 176,088,000 203,940,992 180,307,008

18,355,000

63,972,700 140,256,000 139,030,000 228,800,000 281,240,992 194,306,000

86,044,304 81,503,600 3,881,950

89,708,200 161,456,000 189,827,008 265,200,992 305,327,008

118,608,000

8,491,410

160,764,000 173,952,992 102,764,000

27,325,600

632,008

30,199,900

28,895,200

79,982,000 45,042,000

14,211,200

59,871,200

14,512,700

3,889,010

10,060,000

586,794 2,612,740

108°30' 108°00'

40°0'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

A-groove shale oil, total in-place resource—In millions of barrels

< 20

21–75

76–150

151–200

> 200

Top of Mahogany zone

Base of Parachute Creek Member

A-Grove shale oil, in-place resource—

 By township, in barrels 228,800,000

Figure 104. Isoresource map of A-groove showing total number of barrels of oil in each township using only 

core hole data.
350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 

1050 1000 950 900 850 800 750 700 650 600 550 500 450 400 350 300 800 850 900 950 1000 1050 1100 1150 1200 1250 1300 1300 1250 1150 1000 950 900 850 800 750 700 650 600 550 500 605854524440383226221812AMB C0035 U.S. Bureau Of Mines- Atomic Energy Commission, Colorado 2 Sec. 14, T. 1 S., R. 99 W. C0254 Arco (C-b Project), Sorghum Gulch 11 Sec. 7, T. 3 S., R. 96 W. C0333 Getty Oil Co., 32-27 Sec. 27, T. 5 S., R. 97 W. 

U.S. Bur

Trian

Sec

C0034 U.S. Bureau Of Mines- Atomic Energy Commission, Colorado 1 Sec. 13, T. 1 N., R. 98 W. 0 20 40 60 80 0 20 40 60 80 0 20 40 60 80 0 20 40 60 80 

? ??? ? 1050 1100 1200 66 ? 64 ? 

North 

Depth (ft)

Figure 105. Detailed north-south cross section showing the intertonguing of the Uinta Formation (yellow) with the upper part of the Green River FoPiceance Basin, Colorado (blue) (from Donnell, 2008). Abbreviations used: MB, Mahogany bed; A, base of A-groove; Tggc, Marlstone at GreasewooMarlstone at Trail Canyon; Tgm, Marsltone at Mare Canyon; Tgy, Yellow Creek Tongue; Tgd, Dry Fork Tongue; Tgt, Thirteenmile Creek Tongue; Tgb, BTongue; Tgc, Cough’s Creek Tongue; Tgs, Stewart Gulch Tongue; Tgsl, Tgi, Marlstone at Barnes Ridge and Marder bed at Bull Fork; Tgsk, Marlstone Numbers between C0333 and C0037 are persistent oil shale beds defined by Donnell (2008).
Detailed Description and Assessment Results of Oil Shale Zones 175

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

517

492

187

153

295

666

522

652

555 583 586

658 633

618

575

485

392 337

362

382

351

357 426

411

411

472

502

469 451

490 536

571

496

479

557 553

652 751

791 1019

780

730

648

1033

1119

1119

1135

1076

1096

1067

1064

1206 1174

946 897

762

834 777 886

985

1061

1125

1168 1197

1221 1278 1214

1099

1249 1294

1298

1298

1298

1181

1149

1060

1157

1128 1143

1202 1177

1079

958

902

817

717

767

1012976 866

661

696

1124

1317

1372

1349 1354

1370

1427

1379

13841387

1289

13301457 1422

1390

1365

1510

15641508

1277

1334

1417

1259

1396

1352

1302

1356

1333 1018 1055

1043

1039

221 225 248

230

499 472

359

177

181

187

183

140

252

162

188

214 214 186

195 203 202

199 209206

214 213

218

212

214

213 220

214 218

222

252

260 264

259

265 270

260

263

264 260 281

211 214

214230 231

227

225 232

248

270

267.5

306

314

324

354 364

330

276

241

293

200

206

227 228

266

257

235.5

272 254

234

271

277

247

255

287

358 370

334

139

225

421.8

380

397

259

232.9

370.3

237

257

227 229 236 236

159

165

162 220

215

236

236

296

174 195

222

310

257

245

224

243

250 233

346 338

320 311

288

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of oil shale

 interval in feet

330

A-groove to bed 44 interval—Thickness in feet

301–600

601–900

901–1,200

1,201–1,500

1,501–1,800

< 300

Figure 106. Isopach map of Bed 44 to A-groove using both core hole and rotary hole data. The Radial Basis 

Function Method (RBF) was used for contouring.
176 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

from 375,000 to 475,000 BPA in this area and diminishes in 

a more-or-less radial pattern outward (fig. 107). Interestingly, 

the area with maximum in-place oil is about 12 miles to the 

north of the area with maximum oil yields (figs. 107 and 108). 

Maximum in-place oil in a township is over 10 billion barrels 

in T. 2 S., R. 97 W. (fig. 109). Figures 107 and 108 show total 

in-place oil assuming that the entire assessed interval is preserved. However, the interval crops out in the townships north 

of the blue line in figure 109, and thus the interval is only 

partially preserved. The outcrop pattern for this interval in this 

area is highly complex, and it is difficult to assess exactly how 

much of the oil shale is preserved. As a result, we included 

only those townships south of this line in the final assessment (table 26). Total in-place oil in the interval from the top 

of A-groove to bed 44 of Donnell (2008) is estimated to be 

nearly 186.6 billion barrels (table 26). This is nearly as much 

oil in place as in the Mahogany zone (table 24). 

Discussion

This study presents a comprehensive assessment of 

in-place oil in the Green River Formation of the Piceance 

Basin that includes most oil shale zones and nearly all the 

oil-shale-bearing part of the Piceance Basin. Total in-place 

oil for all zones assessed using oil core-hole data is over 1.5 

trillion barrels (table 27), making the oil shale deposits of the 

Piceance Basin by far the largest oil shale deposit in the world 

(see Dyni, 2003). Total in-place oil in each township in the 

Piceance Basin is shown on Figure 110 and listed in table 28. 

Maximum in-place oil in a township is over 74.4 billion barrels in T. 2 S., R. 97 W. Most of the increase over the previous 

assessment of just over one trillion barrels (Pitman and others, 

1989) is due to: 1) areas being assessed here that had too little 

data to assess in the previous assessment, and 2) intervals 

being assessed here that were not assessed previously: R-0 

zone, A-groove, B-groove, and the interval above A-groove. 

Some of the differences in the results are from the townships 

around the basin margins where Pitman and others (1989) 

appear to have only calculated resources to the outcrop of the 

Mahogany zone, whereas we extended the assessment outward 

to the base of the Parachute Creek Member for the lower oil 

shale zones. These increases are limited, because oil yields for 

most of the oil shale zones are quite low in the marginal areas. 

Using only those townships and those oil shale zones 

that were assessed both here and by Pitman and others (1989) 

the assessment presented here is 8.86 percent higher than the 

manually extrapolated assessment and 4.83 percent higher 

than the kriged assessment of Pitman and others (1989). If 

only the best townships are used, the assessment presented 

here is 5.87 percent higher than the manually extrapolated 

assessment and 6.27 percent higher than the kriged assessment 

of Pitman and others (1989) (table 29). Our results are higher 

for all the oil shale zones assessed here and by Pitman and others (1989) except for the L-2 zone where our results were 0.41 

percent lower than theirs using manual extrapolation in only 

the townships with the most control. These slightly higher 

results for our assessment appear to be largely the result of the 

method used to convert GPT into BPA. As shown for the R-5 

and L-5 zones, our barrels-per-acre calculations for the same 

core holes are overall somewhat higher than those of Pitman 

and others (1989). Because Pitman and others (1989) did not 

publish the formula that they used to convert GPT to BPA, we 

cannot explore the causes of this consistent but fairly minor 

discrepancy. Using the Access form presented in Mercier and 

others (chapter 3, this CD-ROM), future workers could easily 

insert a different formula for this conversion and calculate different in-place resources. 

In-place resources in the leached zone have almost 

certainly been overestimated in this assessment as well as in 

previous assessments because the void space created by the 

leaching of saline minerals was not taken into account. This 

void space can occur in collapse breccias, formed by the collapse of overlying rock once a thick halite and nahcolite bed 

has been leached out, and vugs and other void spaces formed 

by the leaching of nahcolite aggregates and disseminated 

nahcolite. The volume of this void space is not measured prior 

to submitting samples for Fischer assay, and it does not appear 

that the amount of void space in core has been systematically 

recorded in the past. Evaluating void space in the leached zone 

may require a re-examination of a significant amount of the 

core taken of the leached zone.

Although we assessed more intervals and more areas than 

previous assessments, there are still significant intervals that 

have yet to be assessed in this remarkably hydrocarbon-rich 

basin. The interval from A-groove to bed 44 was assessed only 

in townships where the interval is complete, and the interval 

above bed 44 was not assessed at all, yet it contains significant resources in the southern part of the basin. There is also a 

significant thickness of low-grade oil shale in the Cow Ridge 

Member of the Green River Formation that was not assessed. 

The Cow Ridge Member was deposited in the freshwater 

lacustrine lakes that proceeded the development of saline Lake 

Uinta. About 330 ft of the Cow Ridge Member was cored and 

assessed in the Humble Oil No. 1 Yellow Creek hole (C-157) 

in sec. 2, T. 1 S., R. 97 W. where it consists of mostly lowgrade oil shale in the range of 5 to 10 GPT. 
Discussion 177

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Average oil yield in

 gallons per ton

10

A-groove to bed 44 interval—Average oil yield in gallons per ton

< 5

5.1–10

10.1–15

15.1–20

20.1–25

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

16.2

15.9

5.5

6.9

10

14.2

14.4

14.6

12.1

13.8

15.9

14.1 15.8 16.8

17.3

15.9

16.7 16.3

16.8

16.4 16.1 16.7

16.6 16.8

16.4 16.3

16

16.1 17.5

17.1

18.1

16.7

16.1

16.6

16.3

16.7

16.4 15.7

15.6

17.1 16.2 17 14.8

17 16.7

17.3

16.7 17.2

16.8

17.4 17.2

16.5 16 17.1

15.6

14.4

13.8

14.6 13.6

15.8

10.5

17

15.8

15.7

14.9

16.5

16.5 15.4

9.1

15.8

15.5

15.1 15.6

16

15.7

14.5

15.7

15.5

9.3 9.1

16.3

13.2

4.4

21.5

9.4

15

15

16

15.9

15.2

6.5

12

15.9

15.9

15.9

15.3

15.6 15.5

12.9 14

14.7 16.8

17.4

17

16.3

15.9

15.1 15.3

15.3

16.1

3.4

1.4

15.2

16.2

16.7

16.6 17.8

10.6 10.7

11.2 12

13.6

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 107. Isoresource map of bed 44 to A-groove showing the oil yield in gallons per ton (GPT) using only core 

hole data. The Radial Basis Function Method (RBF) was used to construct the map.
178 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

277

284

231

271

293

207

204

214

178

153

312 180 231

277

285 230 246

261

262

253268

257

275 276

269 275

264

266 295

280300

286

315

334 333

334

336 329

316

346 332 341 326

276 276

276304 306

294

301 304

317 350 336

372

356

354

406 393

406

443

362

296

358

234

263

288 274

200

316

283

322 309

290

339

282

311

346

274 278

422

146

414

359

326

447

467

321

288

440

358

475

291

315

280 273 285 283

162

182

184 285

285

307

297

366

205 232

265

387

300

114

303

308

313

321 318

299 294

290 300

310

108°30' 108°00'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

40°00'

39°30'

EXPLANATION

Top of Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—In thousands of

 barrels per acre

10

A-groove to bed 44 interval—In barrels per acreÊ

< 200,000

200,001–

 300,000

300,001–

 400,000

 400,001–

 500,000

Figure 108. Isoresource map of bed 44 to A-groove showing oil yields in barrels per acre (BPA) using only 

core hole data. The Radial Basis Function Method (RBF) was used to construct the map.
Discussion 179

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

212,914,000

588,188,032

1,446,489,984

438,598,016

506,996,000 1,053,470,016 1,071,830,016

2,263,300,096

4,652,460,032

2,503,130,112

2,861,280,000

192,598,000

256,327,008 2,223,040,000

3,778,769,920 5,008,439,808

7,126,060,032

6,110,430,208 6,483,440,128

5,832,410,112

2,303,529,984

5,872,869,888 7,017,090,048 7,962,169,856 8,162,229,760 8,512,920,064

2,933,400,064

705,659,008 6,395,670,016 8,189,660,160 9,963,750,400 9,721,990,144 9,014,209,536 895,036,992

3,135,569,920

7,297,939,968 8,432,090,112 10,081,000,448 9,832,810,496 8,416,260,096

1,854,770,048

1,680,249,984 125,004,000

3,228,720,128 6,734,949,888 7,054,799,872 7,929,350,144 8,285,830,144

4,458,420,224

239,176,000

3,885,090,048

3,647,680,000

3,511,290,112

1,803,000,064

29,611,000

724,332,032

1,827,529,984

2,243,209,984

950,534,976

534,870,016

1,438,669,952

329,641,984

74,257,000

181,760,992

31,841,600 164,846,000

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

EXPLANATION

A-groove to bed 44 interval, total in-place resource—In millions of barrels

< 450

451–1,700

1,701–4,500

4,501–7,300

7,301–10,000

Top of Mahogany zone

Base of Parachute Creek Member

Bed 44 shale oil in-place resource—

 By township, in barrels 228,800,000

Bed 44 resource boundary—In-place

 shale oil resource numbers, north of

 line, not included in assessment

Figure 109. Isoresource map of bed 44 to A-groove showing total number of barrels of oil in each township using 

only core hole data. The interval is only partially preserved north of the blue line, and because of complexities in 

determining how much of the original resource is preserved in these townships the resources in these townships 

were not included in the total.
180 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Township and 

Range

In-place gas in townships 

where interval complete

2S 96W 9,832,810,000

2S 97W 10,081,000,000

2S 98W 8,432,090,000

2S 99W 7,297,940,000

3S 100W 705,659,000

3S 94W 895,037,000

3S 95W 9,014,210,000

3S 96W 9,721,990,000

3S 97W 9,963,750,000

3S 98W 8,189,660,000

3S 99W 6,395,670,000

4S 100W 2,303,530,000

4S 101W 29,611,000

4S 94W 2,933,400,000

4S 95W 8,512,920,000

4S 96W 8,162,230,000

4S 97W 7,962,170,000

4S 98W 7,017,090,000

4S 99W 5,872,870,000

5S 100W 2,223,040,000

5S 101W 256,327,000

5S 94W 5,832,410,000

5S 95W 6,483,440,000

5S 96W 6,110,430,000

5S 97W 7,126,060,000

5S 98W 5,008,440,000

5S 99W 3,778,770,000

6S 100W 1,053,470,000

6S 101W 506,996,000

6S 94W 192,598,000

6S 95W 2,861,280,000

6S 96W 2,503,130,000

6S 97W 4,652,460,000

6S 98W 2,263,300,000

Table 26. Total number of in-place barrels of oil per acre (BPA) in each township for the interval from the top of A-groove to the top of 

bed 44 of Donnell (2008) calculated here using the Radial Basis Function Method (RBF).

Township and 

Range

In-place gas in townships 

where interval complete

6S 99W 1,071,830,000

7S 100W 724,332,000

7S 101W 212,914,000

7S 93W 1,279,450

7S 94W 1,438,670,000

7S 95W 534,870,000

7S 96W 438,598,000

7S 97W 1,446,490,000

7S 98W 329,642,000

7S 99W 588,188,000

8S 100W 74,257,000

8S 101W 8,163,650

8S 93W 950,535,000

8S 94W 2,243,210,000

8S 95W 1,827,530,000

8S 96W 18,650,600

8S 99W 181,761,000

9S 94W 4,525,830

9S 95W 164,846,000

9S 96W 31,841,600

Total 186,467,922,130
Discussion 181

Table 27. Total in-place oil for each of the rich and lean oil shale zones in the Piceance Basin, 

Colorado. Total in-place oil estimated here is 1.52 trillion barrels. Most of the increase from the 

previous assessment by Pitman and others (1989) is because more townships and more zones 

were assessed here.

Oil shale zone Oil in place (barrels)

Top A-groove-top bed 44 186,467,922,130

A-groove 6,283,095,737

Mahogany zone 191,716,681,060

B-groove 7,819,053,970

R-6 185,366,007,632

L-5 66,063,806,739

R-5 198,239,468,346

L-4 69,126,949,762

R-4 127,150,178,615

L-3 22,504,056,571

R-3 68,084,658,284

L-2 24,216,677,409

R-2 66,768,689,056

L-1 15,066,851,989

R-1 195,372,090,899

L-0 8,265,472,203

R-0 83,416,642,063

Total this assessment: 1,521,928,302,463

Total of same townships and zones assessed by Pitman and others (1989): 1,097,395,260,860

Total of new townships and zones assessed here: 424,533,041,603
182 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Township, 

Range Total

1N 100W 6,036,961,940

1N 96W 10,580,261,100

1N 97W 39,786,532,000

1N 98W 58,143,829,000

1N 99W 41,771,811,000

1S 100W 23,930,842,200

1S 95W 15,198,880,300

1S 96W 46,360,433,000

1S 97W 68,166,838,000

1S 98W 73,270,942,000

1S 99W 56,282,758,000

2N 100W 120,362,128

2N 97W 1,941,758,130

2N 98W 18,746,052,600

2N 99W 19,071,980,900

2S 100W 15,478,364,700

2S 94W 352,949,050

2S 95W 27,985,579,500

2S 96W 60,564,766,000

2S 97W 74,430,168,000

2S 98W 69,927,302,000

2S 99W 50,264,972,000

3S 100W 4,139,053,800

3S 94W 3,903,083,700

3S 95W 41,267,276,000

3S 96W 58,561,675,000

3S 97W 64,779,254,000

3S 98W 54,308,290,000

3S 99W 37,246,154,000

4S 100W 10,455,659,900

4S 101W 92,787,637

4S 94W 9,590,565,900

4S 95W 38,640,538,000

4S 96W 46,927,565,000

4S 97W 48,511,796,000

4S 98W 39,030,221,000

4S 99W 29,649,688,000

5S 100W 9,643,476,500

5S 101W 926,068,600

5S 94W 17,091,087,400

5S 95W 27,288,119,300

5S 96W 31,331,184,000

5S 97W 35,112,948,000

Table 28. Barrels of in-place oil in each township in the Piceance Basin, Colorado.

Township, 

Range Total

5S 98W 24,305,139,500

5S 99W 17,894,381,300

6S 100W 4,468,497,590

6S 101W 1,851,081,510

6S 94W 491,120,802

6S 95W 9,160,820,100

6S 96W 9,832,814,000

6S 97W 20,284,023,500

6S 98W 10,492,102,100

6S 99W 4,977,324,800

7S 100W 2,588,315,790

7S 101W 688,700,410

7S 93W 2,423,814

7S 94W 3,334,217,413

7S 95W 1,289,931,030

7S 96W 1,544,319,410

7S 97W 5,451,079,000

7S 98W 1,347,109,440

7S 99W 2,443,651,270

8S 100W 223,969,841

8S 101W 21,997,678

8S 93W 2,055,713,132

8S 94W 5,019,633,143

8S 95W 4,177,070,568

8S 96W 41,957,336

8S 99W 584,342,600

9S 94W 10,173,846

9S 95W 366,519,671

9S 96W 69,036,584

Grand total 1,521,928,302,462
Discussion 183

EXPLANATION

Total in place shale oil resource—In millions of barrels

< 15,000

15,001–25,000

25,001–50,000

50,001–65,000

> 65,000

Top of Mahogany zone

Base of Parachute Creek Member

Total in-place shale oil resource—

 By township, in millions of barrels 74430

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

69 367

584

4,177

5,020

2,056 224

2,444

1,347 5,451

1,544

1,290 3,334

689 2,588

4,977

10,492

20,284 9,833 9,161 491

1,851 4,468

17,894 24,305

35,113 31,331

27,288

17,091

926

9,643

29,650 39,030 48,512 46,928 38,641

9,591 93 9,248

37,246 54,308, 64,779 58,562 41,267 4,139 3,903

50,265 69,927 74,430 60,565 27,986

353 15,478

19,072 18,746 1942 120

56,283 73,271 68,167 46,360

15,199 27,160

41,772 58,144 39,787

10,580

6037

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

COLORADO

0 5 10 2.5 KILOMETERS

Figure 110. Map showing total in-place oil in millions of barrels for each township in the Piceance Basin, 

Colorado.
184 An Assessment of In-Place Oil Shale Resources in the Green River Formation, Piceance Basin, Colorado

Table 29. Comparing the results of this assessment using the Radial Basis Function Method (RBF) with the results 

from the previous assessment of Pitman and others (1989) using kriging. Only those townships that were assessed 

in both assessments are used. When only those townships and zones that were assessed both here and by Pitman 

and others (1989) are compared, our assessment is 8.86 percent higher than the hand-extrapolated results and 4.83 

percent higher than the kriged results of Pitman and others (1989). When only those townships in which kriging by 

Pitman and others (1989) estimated an error of 20 percent or less are compared, our assessment is 5.87 percent 

higher than the hand-extrapolated results and 6.27 percent higher than the kriged results of Pitman and others 

(1989).

Barrels

Sum all townships used here and in Pitman extrapolation: 1,097,395,260,860

Sum all townships used here and in Pitman kriging: 721,997,242,700

Total Pitman extrapolation: 1,008,089,335,000

Total Pitman kriging: 688,761,145,000

Percent difference using RBF vs extrapolation: 8.86

Percent difference using RBF versus kriging: 4.83

Sum of best townships RBF here and extrapolated: 492,652,335,000

Sum of best townships extrapolated Pitman: 465,350,950,000

Percent difference RBF vs extrapolation best townships: 5.87

Sum of best townships here and kriging Pitman: 420,749,845,000

Sum of best townships kriging Pitman: 395,936,440,000

Percent difference RBF vs kriging best townships: 6.27
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