Chapter 7

Fischer Assay Histograms of Oil Shale 

Drill Cores and Cuttings from the 

Piceance Basin, Northwestern Colorado

By Jesse G. Self, Michael E. Brownfield, Ronald C. Johnson, and 

Tracey J. Mercier

Chapter 7 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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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:

Self, J.G., Brownfield, M.E., Johnson, R.C., and Mercier, T.J., 2010, Fischer assay histograms of oil shale drill cores 

and cuttings from the Piceance Basin, northwestern Colorado: U.S. Geological Survey Digital Data Series DDS–69–Y, 

chp. 7, 9 p.

ISBN: 1–4113–2668–2
iii

Contents

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

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

CD–ROM..........................................................................................................................................................1

Oil-Yield Histograms ......................................................................................................................................4

References Cited............................................................................................................................................9

Figures

1. Geologic map of northwestern Colorado showing generalized outcrops of the 

Mesaverde Formation and Group, and the Wasatch, Green River, and Uinta 

Formations in the Piceance Creek Basin..........................................................................................2

2. Stratigraphic nomenclature and correlation chart for oil shale zones for the 

north-central part of the Piceance Basin, Colorado.......................................................................3

3. Geologic map of northwestern Colorado showing generalized outcrops of 

the Mesaverde Formation and Group, and the Wasatch, Green River, 

and Uinta Formations and locations of drill holes within the Piceance 

Creek Basin....................................................................................................................................5

4. Part of the histogram plot showing Fischer assay oil-yield data in gallons 

per ton for borehole C0002 in the Piceance Basin, northwestern Colorado ......................8

Tables

1. Names and definitions from the column headers for the Colorado oil 

shale borehole information spreadsheet..................................................................................6

2. Names and definitions for the column headers for the Fischer assay 

data spreadsheet..........................................................................................................................7
Abstract

This CD–ROM chapter presents oil-yield histograms of 

samples of cores and cuttings from exploration drill holes in 

the Eocene Green River Formation in the Piceance Basin of 

northwestern Colorado. A database was compiled that includes 

319,996 Fischer assays from 780 oil shale exploration holes. 

Most of the oil-yield data are from analyses performed by the 

former U.S. Bureau of Mines oil shale laboratory in Laramie, 

Wyo., with some analyses made by private laboratories. Location data for these 780 Colorado oil shale drill holes are listed 

in a spreadsheet that is included in the CD–ROM.

These Colorado Fischer assays and histograms are part 

of a much larger collection of oil shale information, including geophysical and lithologic logs, water data, chemical, 

and X-ray diffraction analyses on the Green River oil shale 

deposits in Colorado, Utah, and Wyoming held by the U.S. 

Geological Survey. Because of an increased interest in oil 

shale, this CD–ROM containing Fischer assay data and oilyield histograms for the Piceance Basin oil shale deposits in 

northwestern Colorado is being released to the public.

Microsoft Excel spreadsheets included with this chapter 

contain the Fischer assay data from the 780 holes as well as 

data on the company name, drill-hole name, and well location. 

Histograms of the oil yields obtained from the Fischer assays 

are presented in PDF format. Fischer assay text-data files are 

also included in the CD–ROM.

Introduction

For several decades, the U.S. Geological Survey (USGS) 

has collected core, cuttings and other subsurface data from 

boreholes drilled to evaluate the oil shale deposits in the 

Eocene Green River Formation in the Piceance Basin of 

northwestern Colorado (fig. 1). In Colorado, the Green River 

Formation was deposited in Lake Uinta during early to middle 

Eocene time, with the richest oil shale deposits in the Garden 

Gulch and Parachute Creek Members (fig. 2). It was from this 

area, rich in oil shale, that data were collected and preserved 

for use by researchers and industry in anticipation of the 

time when Green River oil shale deposits would become an 

economically practical alternate source of fossil energy.

The types of data collected include: (1) thousands of 

Fischer (shale oil) assays (American Society for Testing and 

Materials, 1980) on cores, and cuttings from rotary-drilled 

holes; (2) geophysical and lithologic logs of drill holes; (3) 

chemical, water-quality, and X-ray diffraction analyses; as 

well as (4) rock mechanics data. Dyni (1998) in cooperation 

with the U.S. Department of Energy published original Fischer 

assay data on 737 oil shale exploration holes containing 

about 298,500 assays in text format. Fischer assay data and 

histograms for 780 drill holes, of which 186 were cored, are 

included in this report. Figure 3 shows the general locations 

of these drill holes in northwestern Colorado. Each drill hole 

was assigned a unique 4-digit number preceded by “C” for 

Colorado (for example, C0001). The database created for this 

assessment contains 319,996 samples. Although this data set is 

far from complete, it most likely represents the largest single 

source of available subsurface information on the Green River 

Formation oil shale deposits in northwestern Colorado.

Most of the Fischer assays on oil shale samples were 

conducted by the former U.S. Bureau of Mines (USBM) laboratory in Laramie, Wyo. (Dyni, 1998), with some also done by 

private laboratories. From the late 1940s to the early 1980s, 

the USBM analyzed core splits and drill cuttings from holes 

drilled by Federal agencies in the Green River Formation 

oil shale deposits in Colorado, Utah, and Wyoming. A large 

amount of data was also obtained from energy companies that 

drilled exploratory holes on private or leased oil shale lands in 

the region. Many of these companies generously donated analytical data as well as drill cores and cutting samples, which 

are being stored by the USGS.

CD–ROM

This CD–ROM chapter reports on data from three directories: Histograms, Spatial, and Spreadsheets. The Histogram 

directory contains oil-yield histograms, in scaled Adobe PDF 

format (Adobe Systems, Inc., San Jose, Calif.), for 780 drill 

holes with Fischer assay data derived from an assay database 

(CO_Oil_Shale_Assays.mdb). The Spatial directory contains 

Fischer Assay Histograms of Oil Shale Drill Cores and 

Cuttings from the Piceance Basin, Northwestern Colorado

By Jesse G. Self, Michael E. Brownfield, Ronald C. Johnson, and Tracey J. Mercier
2 Fischer Assay Histograms of Oil Shale Drill Cores and Cuttings from the Piceance Basin, Northwestern Colorado

City, town

Extrusive and intrusive

 igneous rocks

Mesaverde Formation 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

Delta

Eagle

Garfield

Gunnison

Mesa

Moffat

Pitkin

Rio Blanco

Routt

40

40

70

70

50

50

Grand 

Junction

Gunnison

Montrose

Craig

Glenwood

Springs

39°00'

41°00'

40°00'

109°00' 108°00' 107°00'

Colorado River

G

Yampa River

reen

River

Meeker

Rangely

Steamboat

Springs

64

13

13

139

Montrose

Rifle

Piceance

 Basin

Figure 1. Geologic map of northwestern Colorado showing generalized outcrops of the Mesaverde 

Formation and Group, and the Wasatch, Green River, and Uinta Formations in the Piceance Creek Basin. 

Modified after Brownfield, Hettinger, and Johnson (2000).
CD–ROM 3

Donnell and Blair,

(1970); Cashion and

Donnell (1972)

A-groove A-groove

B-groove B-groove

Rich oil shale

zone R-6

Rich oil shale

zone R-5

Rich oil shale

zone R-4

Rich oil shale

zone R-3

Rich oil shale

zone R-2

Mahogany

zone

Correlation chart of stratigraphic

nomenclature for oil shale zones

Parachute Creek Member (part)

Green River Formation (part)

Rich oil shale

zone R-1

Rich oil shale

zone R-0

Lean oil shale zone L-2

Lean oil shale zone L-1

Lean oil shale zone L-0

Lean oil shale

zone L-4

Lean oil shale zone L-3

Lean oil shale

zone L-5

Uinita Formation

(part)

Wasatch

Formation

(part)

Eocene

Age Unit Green River Formation Garden Gulch

Member Parachute Creek Member

Dyni (1974)

Garden Gulch

Member

Lower

Middle

Upper

Zone 9

Zone 10

Zone 11

Zone 12

Zone 13

Zone 8

Zone 2

Zone 3

Zone 4

Zone 5

Zone 6

Zone 1

Zone 7

Mahogany zone

Figure 2. Stratigraphic nomenclature and correlation chart for oil shale zones for the north-central part of the 

Piceance Basin, Colorado. This assessment uses the nomenclature of Donnell and Blair, (1970) and Cashion 

and Donnell (1972) shown in yellow.
4 Fischer Assay Histograms of Oil Shale Drill Cores and Cuttings from the Piceance Basin, Northwestern Colorado

data for these drill holes along with 211 additional wells that 

have no analyzed samples. These 211 drill holes are included 

on figure 3. The majority of the locations were digitized using 

ArcGIS ver. 9.1, based on footage measurements east and 

west of Public Land Survey System (PLSS) section corners 

contained in the original database. A custom tool described 

in chapter 1, this CD-ROM, was used to measure and place 

points. Source PLSS files used for plotting locations were 

obtained from the Bureau of Land Management in Colorado 

and projected to North American Datum 27 (NAD27). Where 

footage measurements were not available, locations were 

digitized as being in the center of the quarter-quarter section, 

quarter section, or the center of the section—that is, the best 

location data available in the original database were used. In 

a minimal number of cases where location data in the original 

database were questionable, locations were verified using the 

State of Colorado Oil and Gas Conservation Commission’s 

online database. ASCII and Google Earth Keyhole Markup 

Language (KML) file formats of the locations of the drill holes

are also included in the Spatial folder. 

The Spreadsheets folder includes Microsoft EXCEL 

(Microsoft, Corp., 2006) spreadsheets (CO_Borehole.xls; 

CO_Oil_Shale_Assays.xlsx; and so forth) and one Microsoft 

Access database (CO_Oil_Shale_Assays.mdb). The CO_Borehole.xls spreadsheet contains information on 780 core and 

rotary holes with Fischer assays, and the 211 holes without 

analyses. The drill holes are sorted with the USGS unique 

4-digit borehole number (C0001). The file includes well locations, operator and well name, surface elevation, core-hole 

location when known, depths of lithologic log units, geophysical logs that were run, and other data. Table 1 defines the 

column headers in the Colorado borehole spreadsheet. 

The Fischer assay data (Spreadsheet folder) included 

in this CD–ROM are presented in spreadsheet format (CO_

Oil_Shale_Assays.xls) and database format (CO_Oil_Shale_

Assays.mdb). The CO_Oil_Shale_Assays.xlsx spreadsheet 

includes the 319,996 assays from the original laboratory 

Fischer assay reports. In a few cases, separate analyses were 

taken from the same drill hole and these sets of data are 

following the USGS drill-hole number, whereas core holes 

Fischer assay data sets.

Where samples were not analyzed, the Fischer assay data 

-

gram to be created. Missing sample intervals can be detected 

in the database by the lack of a USBM laboratory number 

(LABNO, table 2) followed by “0” in all of the Fischer assay 

Oil-Yield Histograms

Oil shale-yield histograms were created for the 780 holes 

with Fischer assay data, in Grapher 7 (Golden Software, Inc., 

(c0001.grf). Due to restrictions on spreadsheet size in Grapher 

7, the single Excel spreadsheet (CO_Oil_Shale_Assays.

xlsx) had to be divided into seven smaller Excel spreadsheets (CO_Oil_Shale_Assays_1-100.xls, CO_Oil_Shale_

Assays_101-200.xls, and so forth) which are also included 

in the Spreadsheet folder on this CD-ROM. The histograms 

were created using the “Step Plot” feature in Grapher 7 using 

data from one of the seven newly created spreadsheets (for 

example, CO_Oil_Shale_Assays_1-100.xls). Once created, the 

histograms (or step plots) were then exported in PDF (c0001.

pdf) format and opened in Adobe Illustrator, where they were 

scaled vertically to 1 in. = 50 ft and exported again in PDF 

format (c0001.pdf, found in the Support Data, Histogram folder). 

Figure 4 is an example of part of the oil-yield histogram plot for 

a borehole in the histogram folder. As with the Fischer assay 

-

larly, histograms of drill holes with two separate analyses are 

If errors or omissions of data are found in this disc, 

at mbrownfield@usgs.gov or Ronald C. Johnson at 

rcjohnson@usgs.gov. 
Oil-Yield Histograms 5

City, town

Extrusive and intrusive

 igneous rocks

Mesaverde Formation 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

Oil shale wells

0 50 MILES

Colorado

Index map

Delta

Eagle

Garfield

Gunnison

Mesa

Moffat

Pitkin

Rio Blanco

Routt

40

40

70

70

50

50

Grand 

Junction

Gunnison

Montrose

Craig

Glenwood

Springs

39°00'

41°00'

40°00'

109°00' 108°00' 107°00'

Meeker

Rangely

Steamboat

Springs

64

13

13

139

Montrose

Rifle

Colorado River

G

Yampa River

reen

River

Figure 3. Geologic map of northwestern Colorado showing generalized outcrops of the Mesaverde 

Formation and Group, and the Wasatch, Green River, and Uinta Formations and locations of drill holes 

within the Piceance Creek Basin.
6 Fischer Assay Histograms of Oil Shale Drill Cores and Cuttings from the Piceance Basin, Northwestern Colorado

Table 1. Names and definitions from the column headers for the Colorado oil shale borehole information spreadsheet 

(CO_Borehole.xls).

[USGS, U.S. Geological Survey; Wyo.,Wyoming]

Column name Column definition

USGSID Unique ID assigned by staff geologist

CMPNYPROJ Name of the company or agency that drilled the borehole or project name

NAME Name of the borehole assigned by the company or agency that drilled it

EASTWEST Distance, in ft, measured east or west from section line

NORSOU Distance, in ft, measured north or south from section line

QQ Quarter-quarter section

SEC Section

TWP Township 

RNG Range

LATITUDE Latitude, in decimal degrees, North American Datum 1927, software-calculated, original record

LONGITUDE Longitude, in decimal degrees, North American Datum 1927, software-calculated, original record

X_CALC Latitude, in decimal degrees, North American Datum 1927, digitized, software-calculated, this report

Y_CALC Longitude, in decimal degrees, North American Datum 1927, digitized, software-calculated, this report

LOCSOURCE Source of the borehole location, usually from the Fischer assay file, geophysical log, lithologic log, or survey.

COUNTY Name of county in Colorado 

ELEVFT Borehole reference elevation from which downhole depths were measured: ground level (GL), rotary (Kelly) 

bushing (KB), or rotary table, top of collar (TC), derrick floor (DF), drill pipe collar (Col.), mine level (ML), top 

of drill collar (DC), mine floor (MF), or top of casing (Cg).

COREDINTV Depths, in ft, of the sequence that was cored in the borehole

ELEVSRC Source of elevation, usually from the Fischer assay file, geophysical log, lithologic log, or survey

TOTDEPTFT Total depth of the borehole, in ft

QUAD Name of 7.5-minute USGS topographic map, borehole may or may not be shown on map

ARCHIVED Core archived yes or no

YRDRILLED Year that the borehole was drilled

LOCCORE Physical location of the core from core hole, for example, USGS Core Research Center

SHOWNMAP Indicates whether the actual borehole location is shown on the topographic map

LITHFT Top and bottom borehole depths, in ft, of sequence of core or rotary cuttings for which a lithologic log was prepared.

PHOTOFT Top and bottom borehole depths, in ft, of photographic record of drill core

ELECFT Top and bottom depths, in ft, of electric log of borehole

GAMMAFT Top and bottom depths, in ft, of gamma ray log of borehole

DENSFT Top and bottom depths, in ft, of density log of borehole

SONICFT Top and bottom depths, in ft, of sonic log of borehole

NEUTRONFT Top and bottom depths, in ft, of neutron log of borehole

CALIPERFT Top and bottom depths, in ft, of caliper log of borehole

RQDFT Top and bottom borehole depths, in ft, of rock quality data log

TEMPFT Top and bottom depths, in ft, of temperature log of borehole

OTHERLOGS Top and bottom depths, in ft, of other geophysical logs

FISCHASSY Top and bottom depths, in ft, of sequence analyzed by Fischer assays

LAB Name of laboratory where Fischer assays were performed

ALUMINAFT Top and bottom depths, in ft, of sequence analyzed for alumina

NUMBASSYS Number of Fischer assays that were made

USBMNUMBR Lab number assigned to the report of Fischer assays made by the former U.S. Bureau of Mines, Laramie, Wyo.
Oil-Yield Histograms 7

Table 1. Names and definitions from the column headers for the Colorado oil shale borehole information spreadsheet 

(CO_Borehole.xls).—Continued

[USGS, U.S. Geological Survey; Wyo.,Wyoming]

Column name Column definition

LOCATNOTE Additional information, commonly used where there is a problem with the location

NAHCOLTFT Top and bottom depths, in ft, of sequence analyzed for nahcolite

XRDFT Number of X-ray diffraction analyses made on samples from the borehole

ELEVNOTE Additional information, commonly used where there is a problem with the elevation

MISCNOTE Miscellaneous information, such as publications related to the borehole, and other data

REVISDATE Date of last revision for original borehole data

Table 2. Names and definitions for the column headers for the Fischer assay data spreadsheet (CO_Oil_Shale_Assays.xlsx). 

[USGS, U.S. Geological Survey; Wyo.,Wyoming]

Column name Column definition

USGSID Unique drill-hole number assigned by the USGS

LABNO U.S. Bureau of Mines, Laramie, Wyo., laboratory number

TOPFT Depth, in ft, measured from surface datum to top of sampled interval

BOTFT Depth, in ft, measured from surface datum to base of sampled interval

SHLOILPCT Amount of shale oil in weight percent

WATERPCT Amount of water in weight percent

SHLRSDPCT Amount of shale residue in weight percent

GASPLSPCT Amount of “gas plus loss” in weight percent

OILGPT Shale oil, in U.S. gallons per short ton of rock

WTRGPT Water, in U.S. gallons per short ton of rock

SPCFGRAV Specific gravity of shale oil

COKETEND Tendency for spent shale to coke
8 Fischer Assay Histograms of Oil Shale Drill Cores and Cuttings from the Piceance Basin, Northwestern Colorado

1,500

C0002

Wolf Ridge Minerals Corp.

Dunn 20-1

sec. 20, T. 1 S., R. 98 W.

TD 2,621 ft

OIL YIELD, IN GALLONS PER TON

OIL YIELD, IN GALLONS PER TON

100806040200

DEPTH, IN FEET

C0002

Wolf Ridge Minerals Corp.

Dunn 20-1

sec. 20, T. 1 S., R. 98 W.

TD 2,621 ft

1,600

1,700

1,800

1,900

2,000

100806040200

Total depth of well

Oil-yield histogram—In gallons 

 per ton

EXPLANATION

Location (section, township, range)

Well name

Company name

USGS number

Figure 4. Part of the histogram plot showing Fischer assay oil-yield data in gallons per ton for 

borehole C0002 in the Piceance Basin, northwestern Colorado.
References Cited 9

References Cited

Adobe Systems, Inc., 2007, Adobe Design Premium CS3.

American Society for Testing and Materials, 1980, Standard 

method of test for oil from oil shale: Annual Book of ASTM 

Standards, Part 25, Designation D 3904-80, p. 513–515.

Brownfield, M.E., Hettinger, R.D., and Johnson, E.A., 2000, 

A summary of the stratigraphy, coal resources, and coalbed 

methane potential of northwest Colorado, Chapter I, in

Kirschbaum, M.A., Roberts, L.N.R., and Biewick, L.R.H., 

eds., Geological assessment of coal in the Colorado Plateau: 

Arizona, Colorado, New Mexico, and Utah, compiled by 

Colorado Plateau Coal Assessment Group: U.S. Geological 

Survey Professional Paper 1625-B, ver. 1.0, p. I1–I25, 

CD–ROM.

Cashion, W.B., and Donnell, J.R., 1972, Chart showing 

correlation of selected key units in the organic-rich 

sequence of the Green River Formation, Piceance Basin, 

Colorado, and Uinta Basin, Utah: U.S. Geological Survey 

Oil and Gas Investigation Chart OC–65. 

Donnell, J.R., and Blair, R.W., Jr., 1970, Resource appraisal 

of three rich oil shale zones in the Green River Formation, 

Piceance Creek Basin, Colorado: Colorado School of Mines 

Quarterly, v. 65, no. 4, p. 73–87.

Dyni, J.R., 1974, Stratigraphy and nahcolite resources of the 

saline facies of the Green River Formation, Rio Blanco 

County, Colorado: U.S. Geological Survey Open-File 

Report 74–56, 28 p.

Dyni, J.R., 1998, Fischer assays of oil shale drill cores and 

rotary cuttings from the Piceance Creek Basin, Colorado: 

U.S. Geological Survey Open-File Report 98–483, 7 p., 

CD–ROM.

Golden Software, Inc., 2007, Grapher 7.

Microsoft Corporation, 2006, Microsoft Access and Excel 

(part of Microsoft Office 2007).

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