Modified Method for Estimating Petroleum Source-Rock 

Potential Using Wireline Logs, With Application to the 

Kingak Shale, Alaska North Slope

Scientific Investigations Report 2016–5001

U.S. Department of the Interior

U.S. Geological Survey
Cover. Outcrop along Hue Creek at the northern front of the Shublik Mountains, northeast Brooks Range. A geologist examines the 

steeply dipping, overturned contact between the Jurassic Kingak Shale (left-center) and Lower Cretaceous Kemik Sandstone (right). 

The light-colored rocks (upper left) are Proterozoic Katakturuk Dolomite, thrust northward over the Kingak Shale. The Kingak-Kemik 

contact is the Lower Cretaceous unconformity. Photograph by David W. Houseknecht, U.S. Geological Survey.
Modified Method for Estimating Petroleum 

Source-Rock Potential Using Wireline Logs,

With Application to the Kingak Shale, 

Alaska North Slope

By William A. Rouse and David W. Houseknecht

Scientific Investigations Report 2016–5001

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

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Suggested citation:

Rouse, W.A., and Houseknecht, D.W., 2016, Modified method for estimating petroleum source-rock potential using 

wireline logs, with application to the Kingak Shale, Alaska North Slope: U.S. Geological Survey Scientific Investigations Report 2016–5001, 40 p., http://dx.doi.org/10.3133/sir20165001.

ISSN 2328-0328 (online)
iii

Contents

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

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

Geologic Background....................................................................................................................................1

Source-Rock Characterization With Wireline Logs.................................................................................7

Methodology...................................................................................................................................................8

Discussion.....................................................................................................................................................12

Conclusions...................................................................................................................................................12

Acknowledgments.......................................................................................................................................12

References Cited..........................................................................................................................................16

Appendix 1. Workflow for Calculating Key Parameters.......................................................................19

Calculating Shale Volume (Vsh).........................................................................................................19

Calculating Log R ................................................................................................................................21

Creating a Cross Plot of Log R versus DT .......................................................................................24

Calculating DTlogR ................................................................................................................................29

Calculating ∆DT Curve Separation ..................................................................................................32

Calculating ∆DTz .................................................................................................................................35

Finding ∆DTx ...............................................................................................................................35

Finding hnet ..................................................................................................................................38

Exporting the Spreadsheet.......................................................................................................39
iv

Figures

1. Diagram showing generalized chronostratigraphy for the Alaska North Slope ...............2

2. Map of northern Alaska showing areas of inferred source-rock quality in the 

Kingak Shale and outlines of shale-oil and shale-gas assessment units ...........................3

3. Schematic summary of inferred depositional sequence sets in the Kingak Shale 

in the National Petroleum Reserve in Alaska ...............................................................................4

4. Map of the National Petroleum Reserve in Alaska (NPRA) showing thickness 

of Kingak Shale sequence set K1 and inferred clinoform dip directions ............................5

5. Wireline-log response in the K1 sequence set........................................................................6

6. Part of a wireline log illustrating overlay of sonic and resistivity logs to define 

∆log R separation in an unidentified organic-matter-rich interval ......................................7

7. Chart relating ∆log R, total organic carbon, and thermal maturity expressed 

as level of organic metamorphism.............................................................................................8

8. Cross plot of log resistivity versus sonic travel time within the K2 sequence set 

of the Kingak Shale in the Ikpikpuk No. 1 well.........................................................................9

9. Map of ∆DTx in the lower Kingak Shale for that part of the Alaska North Slope

where requisite wireline-log data are available ...................................................................10

10. Map of ∆DTz in the lower Kingak Shale for that part of the Alaska North Slope

where requisite wireline-log data are available ...................................................................11

11. Gamma-ray log in American Petroleum Institute units, DT log in microseconds

per foot, and total organic carbon content in weight percent of the Kingak 

Shale K1 and K2 sequence sets in the North Inigok well ...................................................13

12. Well logs from cross section A–A' illustrating regional change in ∆DT related

to location in Kingak Shale K1–K3 sequence sets................................................................14
v

Conversion Factors

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m) 

mile (mi) 1.609 kilometer (km)

Datum

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Abbreviations

API American Petroleum Institute

∆log R delta-log resistivity 

DT sonic travel time 

GR gamma-ray 

HGR high-gamma-ray 

LAS Log ASCII Standard 

LCU Lower Cretaceous unconformity 

μsec/ft microseconds per foot

NPRA National Petroleum Reserve in Alaska 

ohm-m ohm-meters 

RILD resistivity 

RMA reduced major axis 

TOC total organic carbon 

USGS U.S. Geological Survey

Modified Method for Estimating Petroleum Source-Rock 

Potential Using Wireline Logs, With Application to the 

Kingak Shale, Alaska North Slope

By William A. Rouse and David W. Houseknecht

Abstract

In 2012, the U.S. Geological Survey completed an 

assessment of undiscovered, technically recoverable oil and 

gas resources in three source rocks of the Alaska North Slope, 

including the lower part of the Jurassic to Lower Cretaceous 

Kingak Shale. In order to identify organic shale potential in 

the absence of a robust geochemical dataset from the lower 

Kingak Shale, we introduce two quantitative parameters, ∆DTx

and ∆DTz, estimated from wireline logs from exploration wells 

and based in part on the commonly used delta-log resistivity 

(∆log R) technique. Calculation of ∆DTx and ∆DTz is intended 

to produce objective parameters that may be proportional 

to the quality and volume, respectively, of potential source 

rocks penetrated by a well and that can be used as mapping 

parameters to convey the spatial distribution of source-rock 

potential. Both the ∆DTx and ∆DTz mapping parameters show 

increased source-rock potential from north to south across the 

North Slope, with the largest values at the toe of clinoforms 

in the lower Kingak Shale. Because thermal maturity is not 

considered in the calculation of ∆DTx or ∆DTz, total organic 

carbon values for individual wells cannot be calculated on the 

basis of ∆DTx

 or ∆DTz alone. Therefore, the ∆DTx and ∆DTz

mapping parameters should be viewed as first-step reconnaissance tools for identifying source-rock potential. 

Introduction

In 2012, the U.S. Geological Survey (USGS) completed 

an assessment of undiscovered, technically recoverable oil 

and gas resources in three source-rock systems (fig. 1) of 

the Alaska North Slope: (1) the Triassic Shublik Formation; 

(2) the lower part of the Jurassic to Lower Cretaceous Kingak 

Shale; and (3) the Cretaceous pebble shale unit, Hue Shale, 

and parts of the Paleogene Canning Formation, collectively 

called the Brookian shale (Houseknecht, Rouse, Garrity, and 

others, 2012). Maps of inferred source-rock richness were 

constructed using three parameters because of differences in 

lithology and wireline-log response among the source rocks. 

The map used for the Kingak Shale is highly generalized 

(fig. 2) because no quantitative mapping parameter had been 

defined. The study summarized in this report was initiated 

to evaluate the efficacy of the delta-log resistivity (∆log R) 

technique (Passey and others, 1990) for estimating an objective and quantitative parameter for evaluating source-rock 

potential from wireline-log data. This parameter may be useful 

as an evaluation tool for individual wells and, when calculated 

for multiple wells, as a mapping parameter. However, due to 

software limitations for digital calculation of ∆log R and the 

absence of a robust geochemical dataset for calibration of 

∆log R, we sought to develop a modified version of ∆log R

that yields two parameters that may serve as proxies of 

source-rock quality and volume. This report documents the 

digital workflow developed for calculating a modified version 

of ∆log R and presents the results of applying the technique to 

evaluate source-rock potential of the lower Kingak Shale.

Geologic Background

The Jurassic to Lower Cretaceous Kingak Shale contains 

both marine and terrigenous organic matter deposited in a 

marine siliciclastic setting influenced by pulses of syndepositional uplift of the Beaufort rift shoulder (also known as 

the Barrow arch; see figs. 3 and 4) during opening of the 

Canada Basin (Magoon and Claypool, 1984; Hubbard and 

others, 1987; Bird and Houseknecht, 2011). Houseknecht and 

Bird (2004) identified four depositional sequence sets in the 

Kingak Shale (fig. 3, K1–K4) that define a northern-sourced 

southward-offlapping succession of Beaufortian strata in the 

National Petroleum Reserve in Alaska (NPRA), and these 

sequence sets subsequently have been mapped eastward 

beyond the NPRA on the basis of seismic and well data. 

The basal K1 sequence set is 1,000 to more than 

1,250 feet (ft) (300 to 380 meters [m]) thick across a broad 

area in the north-central NPRA that extends to the south 

as a lobe in the central NPRA (fig. 4). North of the zone of 
2 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

.

Ellesmerian

Franklinian

Beaufortian

Brookian

Nonmarine clastics

Marine shelf clastics

Marine basin clastics

Condensed marine shale

Marine carbonates

Metasedimentary

Granite

Hiatus or erosion

.. . ..

Main oil-prone 

 source rocks

EXPLANATION

360

Age

(Ma)

Tectonostratigraphy

50

100

144

208

245

286

320

2

Jurassic Cretaceous Cenozoic Mississippian

Penn

Permian Triassic Pre-Miss

Pebble shale unit

SOUTHWEST NORTHEAST

Gubik Fm

Kingak

Shale

Shublik Fm

Lisburne Group

Sag River Sandstone

Torok Fm

Canning Fm

GRZ (gamma-ray zone)

Hue Shale

Endicott Group

Sadlerochit Group

Seabee Fm

Sagavanirktok Fm

Canning Fm

Prince Creek Fm

Schrader Bluff Fm

T

N

F

1

2

3a

3b

3c

B

Basement

Otuk Fm

LCU

JU

Figure 1 Figure 1. Diagram showing generalized chronostratigraphy for the Alaska North Slope (from Houseknecht, Bird, 

and Garrity, 2012). Oil-prone source-rock systems discussed in text are indicated at right: 1, Triassic source-rock 

system, composed of the Shublik Formation and the Triassic part of the Otuk Formation; 2, Jurassic source-rock 

system, composed of the lower part of the Kingak Shale and the Blankenship Member (B) of the Otuk Formation; 

and 3, Cretaceous to Cenozoic source-rock system, composed of (a) the Lower Cretaceous pebble shale unit and 

gamma-ray zone (GRZ), (b) Upper Cretaceous organic-matter-rich tongues of the Hue Shale, and (c) lower Paleogene 

organic-matter-rich tongues of the Canning Formation. Italicized labels (Otuk Formation and B) indicate units that 

crop out in the Brooks Range frontal thrust belt and that represent southern distal facies equivalents of formations 

present beneath the Alaska North Slope. Arctic Alaska stratigraphy modified from Lerand (1973), Bird (1985, 2001), 

Hubbard and others (1987), and Mull and others (2003); ages from Gradstein and others (2004) Abbreviations used: 

B, Blankenship Member of the Otuk Formation; F, Fortress Mountain Formation; Fm., Formation; GRZ, gamma-ray 

zone; JU, Jurassic unconformity; LCU, Lower Cretaceous unconformity; Ma, mega-annum, or million years ago; 

N, Nanushuk Formation; PENN, Pennsylvanian; Perm, Permian; Pre-Miss, pre-Mississippian; T, Tuluvak Formation.
Geologic Background 

3

Figure 2. Map of northern Alaska showing areas of inferred source-rock quality in the Kingak Shale and outlines of shale-oil and shale-gas assessment units (AUs). Average and maximum total organic carbon (TOC) content of the Kingak Shale from public-domain data (Threlkeld and others, 2000; Peters and others, 2006). Areas of inferred source-rock quality south of well control are based on sequence stratigraphic interpretations (Houseknecht and Bird, 2004), seismic observations, and outcrops of the Kingak Shale and coeval rocks in the Brooks Range foothills. Note that the source-rock-quality map does not extend beyond the State-Federal offshore boundary and that only selected other information is shown beyond that boundary. Modified from Houseknecht, Rouse, and Garrity (2012).

UNITED STATES

ALASKA

Map area

0 Base map modified from U.S. Geological Survey

1:1,000,000-scale digital files from The National MapProjection is Alaska Albers

50 100 MILES

0 50 100 KILOMETERS

1002 Area

B R O O K S

R A N G E Hope

Basin

Point Barrow

Prudhoe

Bay

Beaufort Shelf

Chukchi Shelf

Herald

A

r

c

h Arctic National Wildlife Refuge

Alpine Endicott

Milne

Point

Absent (non-deposition or erosion)

Absent (erosion)

Absent

(erosion)

CANADA National Petroleum Reserve in Alaska

Inferred source-rock quality

Selected control wellExploration well

EXPLANATION

Figure 2.

TOC, in percent

0 to 2>2 to 4>4

Average TOCMaximum TOC

Kingak Shale Oil AUKingak Shale Gas AUState-Federal offshore boundaryOil field boundary

Good (oil-prone)Poor (gas-prone)Poorly known Normal fault—Hachures on 

Federal land boundaryTrans-Alaska Pipeline SystemThrust fault downthrown side

—Teeth on upper plate

69°

165°

71°70°68°

160° 155° 150° 145°
4 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

Distal Proximal

K4 K3 K2 K1

LCU

Barrow

Arch A

B

Pebble

shale

unit

200 200 Sinemurian

Pliensbachian

Toarcian

Aalenian

Bajocian

Bathonian

Callovian

Vertical scale change

Oxfordian

Kimmeridgian

Tithonian

Berriasian

Valanginian

Hauterivian

Cretaceous

Jurassic

Age (Ma)

Neocomian

Kingak Shale

Hettangian

Barremian

Triassic

180

160

160

150

140

130

120

180

160

160

150

140

130

120

Stage Age (Ma)

LCU

LCU

Kuparuk A

Walakpa

Kuyanak Alpine

Simpson

Barrow

Nuiqsut

Nechelik

LCU

LCU

Kuparuk C?

Shublik Formation Sag River Sandstone

Pebble shale unit (Kuparuk D and Kalubik)

K1 (lower Kingak Shale)

K2 (upper Kingak Shale)

K3 (Miluveach and Kuparuk A-B)

K4 (Kuparuk C?) Kuparuk C?

Eroded on flank

of Barrow Arch

Figure 3 Houseknecht & Bird

NOT TO SCALE

Figure 3. Schematic summary of inferred depositional sequence sets in the Kingak Shale in the National Petroleum Reserve 

in Alaska (modified from Houseknecht and Bird, 2004). A, Cross section from south (distal) to north (proximal) showing lithostratigraphic relations among four depositional sequence sets (K1–K4) and general aspects of internal stratal geometry. 

Note that the Lower Cretaceous unconformity (LCU) bevels Kingak Shale strata northward to extinction on the Barrow arch. 

B, Diagram showing chronostratigraphy of sequence sets in the Kingak Shale. Shown in parentheses are stratigraphic names 

widely applied to approximate age-equivalent strata of the four sequence sets. Names in italics show approximate positions of 

sandstone reservoirs and potential reservoirs. Vertical lines denote time gaps between sets. Note scale change near center of 

diagram. Geologic timescale from Gradstein and Ogg (1996). Abbreviation used: Ma, mega-annum, or million years ago.
Geologic Background 

5

Figure 4. Map of the National Petroleum Reserve in Alaska (NPRA) showing thickness of Kingak Shale sequence set K1. Modified from Houseknecht and Bird (2004). Abbreviations used: AU, assessment unit; LCU, Lower Cretaceous unconformity.

UNITED STATES

ALASKA

Map area

0 50 100 MILES0 50 100 KILOMETERS

1002 Area

B R O O K S

R A N G E Hope

Basin

Point Barrow

Prudhoe

Bay

Beaufort Shelf

Chukchi Shelf

Herald

A

r

c

h Arctic National Wildlife Refuge

National Petroleum Reserve in Alaska

Absent (non-deposition or erosion)

Absent (erosion)

Absent

(erosion)

CANADA 250 500 750 1,000 500

1,250 1,250

1,000 250

250

EXPLANATION

Kingak Shale Oil AUKingak Shale Gas AUState-Federal offshore 

 boundary Normal fault—Hachures on 

Federal land boundaryTrans-Alaska Pipeline SystemThrust fault downthrown side

—Teeth on upper plate

Well location and name

Line of equal thickness of Kingak Shale—

K1 sequence set. Interval 250 feet

K1 beveled to north by truncation beneath LCUTop of K1 truncated to north at base of K2

Figure 4.

Inigok

Walakpa 1

Ikpikpuk

Inigok

69°

165°

71°70°68°

160° 155° 150° 145°

Base map modified from U.S. Geological Survey1:1,000,000-scale digital files from The National MapProjection is Alaska Albers
6 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

maximum thickness in the central NPRA, the K1 sequence set 

thins gradually where seismic data show an erosional contact 

between the K1 and K2 sequence sets. Farther north, the 

K1 sequence set abruptly thins to a zero edge along the trend 

of the Barrow arch, where it is beveled beneath the Lower 

Cretaceous unconformity. South of the zone of maximum 

thickness, the K1 sequence set abruptly thins in a radial 

pattern to less than 500 ft (150 m) in the western NPRA and 

to less than 250 ft (76 m) in the southeastern NPRA.

Wireline-log responses within the K1 sequence set in 

the northern NPRA commonly exhibit thin (<200 ft [61 m]) 

coarsening-upward trends consisting of mudstone grading 

upward to siltstone (for example, fig. 5, Walakpa 1 well, 

2,980- to 2,800-ft [908- to 853-m] depth) or mudstone 

grading upward to sandstone (for example, fig. 5, Walakpa 1 

well, 3,200- to 3,050-ft [975- to 930-m] depth). In contrast, 

fining-upward transitions commonly are abrupt between 

sandstone and siltstone (for example, fig. 5, Walakpa 1 well, 

~3,050-ft [930-m] depth) or between siltstone and mudstone 

(for example, fig. 5, Walakpa 1 well, ~2,990-ft [911-m] depth), 

with an additional few thin fining-upward successions also 

present (for example, fig. 5, Walakpa 1 well, 2,800- to 2,770-ft 

[853- to 844-m] depth; Houseknecht and Bird, 2004).

Within the zone of maximum thickness in the central 

NPRA, wireline-log responses within the K1 sequence set 

display subtle coarsening-upward successions capped by 

siltstone abruptly overlain by shale, as well as repetitive 

intervals of silty mudstone locally punctuated by shale 

(fig. 5, Ikpikpuk well). The wireline-log response in the most 

distal well penetrations of the K1 sequence set in the eastern 

NPRA displays an off-the-scale gamma-ray response in a thin 

interval of silty mudstone near or beyond the toe of K1 clinoforms (fig. 5, Inigok well). 

The distal increase in gamma-ray response within the 

K1 sequence set was interpreted as increased organic matter 

content and coalescence of time lines (that is, it is a condensed 

section) in a distal direction by Houseknecht and Bird (2004). 

Biostratigraphic data from NPRA wells indicate that the K1 

sequence set is Early to Middle Jurassic, equivalent to the 

lower Kingak Shale in the central North Slope (Carman and 

Hardwick, 1983; Masterson and Paris, 1987). Conventional oil 

accumulations at the Alpine, Endicott, Milne Point, and Prudhoe 

Bay fields were sourced entirely or partly from the lower 

Kingak Shale (fig. 2; Seifert and others, 1980; Claypool and 

Magoon, 1985; Premuzic and others, 1986; Sedivy and others, 

1987; Masterson, 2001; Magoon and others, 2003; Peters 

and others, 2006). The potential for self-sourced, continuous 

accumulations of recoverable oil and gas in lower Kingak Shale 

source rocks is assumed to exist (Houseknecht, Rouse, and 

Garrity, 2012) but has not been confirmed by well completions.

Figure 5. Wireline-log response in the K1 sequence set. Well locations are shown in figure 4. Wireline-log measured 

depth ticks below kelly bushing are at 100-foot (ft) (30-meter) intervals, and numbers are ×1,000 ft. Modified from 

Houseknecht and Bird (2004). Abbreviations used: ohm-m, ohm-meter; API, American Petroleum Institute.

MRS

- 3 -

c

c

c

MFS

MRS

MRS

MFS

Sag River Sandstone

R

T

R

T>

S2

S1

K1 sequence set boundary

Candidate sequence boundary

Basal K2 (Oxfordian) flooding surface

Basal K1 (Hettangian?) flooding surface

 K1 sequence set

A

A

B

B

c core

MRS maximum regressive surface

MFS maximum flooding surface

R regressive systems tract

S1 sequence 1

S2 sequence 2

T transgressive systems tract

Lower

Barrow

sandstone

? ?

Abbreviations

EXPLANATION

Sequence boundary

Ikpikpuk

0.2 ohm-m 2,000

Resistivity

0 API 150

Gamma ray

- 9 -

Basinal condensed section - 10 -

Walakpa 1

0 API 150

Gamma ray Resistivity

0.2 ohm-m 200

- 3 -

c

c

c

0 API 150

Gamma ray

0.2 ohm-m 2,000

Resistivity

Inigok

- 12 -

- 11 -

c

c

Figure 5 Houseknecht & Bird
Source-Rock Characterization With Wireline Logs 7

Source-Rock Characterization With 

Wireline Logs

Petroleum source rocks typically are shale or limestone 

containing more than 1 or 2 weight percent of organic matter 

(Tissot and Welte, 1984). Direct geochemical measurements 

on source rocks are generally sparse, resulting in the increased 

use of common wireline logs from exploration and development wells for identifying source-rock intervals and estimating 

organic matter content. Recognition of organic-matter-rich 

strata from wireline logs is based on the unique physical 

properties of organic matter as compared to minerals in 

the host rock. These properties include higher radioactivity 

(Beers, 1945; Schmoker, 1981), lower density (Schmoker, 

1979), higher resistivity (Nixon, 1973; Meissner, 1978; 

Schmoker and Hester, 1989), and slower sonic velocity or 

higher sonic travel time (Dellenbach and others, 1983).

Previous assessments of technically recoverable shale-gas 

resources by the USGS have used a high-gamma-ray (HGR; 

gamma-ray greater than 150 American Petroleum Institute 

[API] units) mapping parameter as a possible indication 

of source-rock richness (Houseknecht and others, 2014). 

Whereas gamma-ray response increases distally within the 

lower Kingak Shale, gamma-ray values rarely exceed 150 API

except for a thin interval near the base of the formation in 

distal parts of the depositional system, precluding the use 

of the HGR mapping parameter in identifying source-rock 

potential and necessitating an alternative methodology. 

Meyer and Nederlof (1984) developed a method 

involving a combination of density, resistivity, and sonic logs 

that discriminates between source rocks and non-source rocks 

without attempting to quantify the organic-matter richness 

from the combination of logs. Their technique uses cross 

plots of density versus resistivity and of sonic travel time 

versus resistivity; strata with relatively high resistivity and 

either relatively high sonic travel time or low bulk density 

represent a potential source rock. A regression line is fit 

through the cross-plot data, the equation of which becomes 

the discriminant function for separating potential source rock 

from non-source rock.

Passey and others (1990), using a principle similar to that 

of Meyer and Nederlof (1984), developed a method called 

delta-log resistivity (∆log R) that identifies potential source 

rocks by overlaying the sonic curve and the resistivity curve 

in a baseline interval consisting of clay-rich rocks (mudstone 

or shale) that are not of source-rock quality (fig. 6). Potential 

source rocks in other depth intervals of the well are identified 

by a separation of the two curves through the parameter 

quantified in the following equation:

2,200

FEET

2,300

2,400

Resistivity, in ohm-m

0.01 0.1 1.0 10 100

Sonic, in μsec/ft Gamma ray,

in API units

200 0 200 150 100 50 0

∆log R

Resistivity

Sonic

Baseline

interval {

Figure 6. Figure 6. Part of a wireline log illustrating overlay of 

sonic and resistivity logs to define ∆log R separation 

in an unidentified organic-matter-rich interval. Scaling 

of the sonic and resistivity curves is adjusted so that 

50 μsec/ft on the sonic log corresponds to one decade 

of resistivity. The values in the center of the sonic 

and resistivity log track correspond to the Rbaseline and 

∆t

baseline values (for this example, Rbaseline = 1 ohm-m, 

and ∆tbaseline =100 μsec/ft). Wireline-log measured 

depth ticks below kelly bushing are at 100-foot (ft) 

(30-meter) intervals. Figure from Passey and others 

(1990). Abbreviations used: ohm-m, ohm-meter; 

μsec/ft, microsecond per foot; m, meter; API, American 

Petroleum Institute.
8 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

R

R

∆log R log 0.02 ( ) ∆t ∆t baseline

= 10 baseline 









 ×+ − (1)

where

∆log R is the curve separation measured in 

logarithmic resistivity cycles;

R is the resistivity measured in ohm-meters 

(ohm-m); 

∆t is the measured sonic travel time in 

microseconds per foot (μsec/ft);

Rbaseline is the resistivity corresponding to the 

∆t

baseline value when the curves are 

overlain in non-source, clay-rich rocks; and

0.02 is based on the ratio of -50 μsec/ft per 

resistivity cycle. 

Passey and others (1990) found a linear correlation between 

∆log R separation and total organic carbon (TOC) content in 

multiple source rocks as a function of thermal maturity (fig. 7). 

The original calibration of the ∆log R technique (Passey and 

others, 1990) was for source rocks in the oil window, as there 

was no calibration at that time to include rocks of higher 

thermal maturity (Passey and others, 2010). Sondergeld and 

others (2010) proposed using a correction multiplier to obtain 

log-derived TOC using the ∆log R technique for overmature 

shale-gas formations: 

TOC=∆log R×10(2.297–0.1688×LOM )×C (2)

where

TOC is the total organic carbon measured in 

weight percent,

LOM is the level of organic metamorphism 

(Hood and others, 1975), and

C is a correction factor.

0

Figure 7.

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

0

2

4

6

8

10

12

14

16

18

20

∆log R, in logarithmic resistivity cycles

Total organic carbon, in weight percent

Calibration limit for LOM<7 (Ro<0.48)

Calibration limit for LOM>10.5 (Ro>0.90)

LOM=7 (Ro=0.48)

LOM=8 (Ro=0.56)

LOM=9 (Ro=0.67)

LOM=10 (Ro=0.82)

Methodology

The methodology used in this study for identifying 

organic shale potential is based on a combination of the 

cross-plot and ∆log R methods (Meyer and Nederlof, 1984; 

Passey and others, 1990) and follows an example presented 

by Bowman (2010). Our digital workflow was developed 

and tested using IHS Kingdom® version 8.8 software. The 

following procedures were performed on a well-by-well basis.

To assure adequate non-source-rock strata with which to 

determine a baseline for sonic and resistivity data, we defined 

a target stratigraphic interval that includes both the K1 and the 

overlying K2 sequence sets (fig. 3) in the Kingak Shale, where 

the K2 sequence set is assumed to consist of predominately 

non-source-rock strata. The target stratigraphic interval was 

identified by examining wireline-log and seismic data across 

the North Slope. To constrain the analysis to clay-rich intervals within the K2 and K1 sequence sets, shale volume was 

calculated for each well using the following equation:

GRlog –GRclean

GRshale –GRclean

Vsh = 









 (3)

where

Vsh is the shale volume (decimal percent),

GRlog is the API value from the gamma-ray 

log curve,

GRclean is the API value of a “clean” sand, and 

GRshale is the API value of a shale. 

GRclean and GRshale values were computed for each well 

using the IHS Kingdom® version 8.8 software Petrophysics 

module. Only strata consisting of at least 60 percent shale 

Figure 7. Chart relating ∆log R, total organic carbon, and thermal maturity expressed as level of 

organic metamorphism (LOM) (Hood and others, 1975). Abbreviations used: Ro, vitrinite reflectance.
Methodology 9

by volume (Vsh≥0.6) were considered suitable as a baseline 

(Tom Wild, President and Owner, Tom Wild Petrophysical 

Services LLC, written commun., February 27, 2013). Fiftyfour wells were identified with suitable shale intervals and 

complete digital gamma-ray (GR), resistivity (RILD), and 

sonic travel time (DT) wireline-log data that extend through 

the K2 and K1 sequence sets.

The inability to display linear and logarithmic data on 

the same log track in IHS Kingdom® version 8.8 software 

precluded digital curve manipulation of the ∆log R methodology (Passey and others, 1990) to determine baseline values 

for non-source-rock shale intervals. As an alternative, cross 

plots of sonic travel time versus resistivity were constructed 

for each well (Bowman, 2010). Cross-plot data were 

constrained to the assumed non-source-rock K2 sequence 

set and a reduced major axis (RMA) regression line was 

fit through the data, thus automating the determination of 

Bowman’s (2010) low-resistivity shale line. The resultant 

correlation equation then was used to calculate a pseudosonic 

log DTlogR which transformed resistivity data into sonic travel 

time units (μsec/ft), thereby enabling the direct comparison 

of sonic and resistivity log data within the same unit space 

and scaling the resistivity data to overlie the sonic data in the 

assumed non-source-rock interval (equation 4, fig. 8). 

DTlogR=b –m×log R (4)

where

m is the slope and

b is the y-intercept of a line.

In two cases where individual wells exhibited an inverse 

regression trend (positive m value), values for b and m were 

substituted from the nearest well. The DTlogR curve calculation 

(equation 4) then was applied to both K2 and K1 sequence 

sets. Curve separation within the lower Kingak Shale 

K1 sequence set was calculated using the following equation:

∆DT=DT–DTlogR (5)

where ∆DT is the separation between DT and DTlogR curves 

(in units of μsec/ft), a transform functionally similar to ∆log R

of Passey and others (1990). 

It should be noted that whereas ∆DT is functionally 

similar to ∆log R of Passey and others (1990), the application 

of the RMA transform in the calculation of DTlogR ultimately 

distorts the resistivity data. Thus, ∆DT values may not be 

equivalent to ∆log R values in all cases.

We assumed the existence of a positive relationship 

between ∆log R and TOC, as documented by Passey and 

others (1990, 2010) (fig. 7), to infer qualitatively the presence of potential source-rock intervals in the lower Kingak 

Shale K1 sequence set. Although this revised methodology 

addressed the presence of potential source rocks by the calculation of ∆DT, our objectives also included the development of 

a parameter that may be proportional to the volume of potential 

source rocks in a well. We therefore introduced an additional 

 0.2 0.3 0.4 0.5 0.6 0.7 

 70 

 75 

 80 

 85 

 90 

 95 

 100 

 105 

 110 

 115 

 120 

log R, in ohm-m 

Figure 8.

DT, in microsecond per foot

DTlogR = 120.27–69.68*log R

parameter, ∆DTz, which incorporated both the magnitude and 

thickness of the ∆DT curve separation, defined as:

∆DTz= ∆DTx×hnet ,∆DT >0 (6)

where 

∆DTx is the mean of positive ∆DT values calculated 

within the stratigraphic interval of interest 

(K1 sequence set, in this example) and

hnet is the net vertical interval in feet, over 

which ∆DT exceeds zero within the 

subject interval.

∆DTx may be used as a proxy of the overall source-rock 

quality in a stratigraphic interval of interest. ∆DTx and ∆DTz

were only calculated where ∆DT was greater than zero, as 

positive values represent higher resistivity and higher sonic 

travel times indicative of possible source rocks. Definition of 

∆DTz to include both the magnitude and thickness of positive 

∆DT values was intended to produce an objective parameter 

that may be proportional to the volume of potential source 

rocks penetrated by each well. Following the calculation of 

∆DTx and ∆DTz for each well, the results for the lower Kingak 

Shale K1 sequence set were mapped (figs. 9, 10) using a 

gridding algorithm in IHS Kingdom® version 8.8 software. 

A digital workflow for calculation of ∆DTx and ∆DTz using 

IHS Kingdom® 8.8 software is presented in appendix 1.

Figure 8. Cross plot of log resistivity (log R) versus sonic travel 

time (DT) (both derived from wireline logs) within the K2 sequence 

set of the Kingak Shale in the Ikpikpuk No. 1 well (location shown 

in figures 9 and 10). The equation of the reduced major axis (RMA) 

regression line is used to transform resistivity-log data into sonic 

travel time units, enabling the direct comparison of sonic- and 

resistivity-log data within the same unit space. Abbreviations used: 

ohm-m, ohm-meter; μsec/ft, microsecond per foot.
10 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale Figure 9. Map of 

∆DTx in the lower Kingak Shale for that part of the Alaska North Slope where requisite wireline-log data are available. Blue contours modified from 

Houseknecht and Bird, 2004. Abbreviations used: AU, assessment unit; LCU, Lower Cretaceous unconformity; 

∆DTx is the mean of positive 

∆DT values calculated within 

the stratigraphic interval of interest, and may be used as a proxy of the overall source-rock quality.

Alpine Endicott

Milne

Point

UNITED

STATES

ALASKA

Map area

0 50 100 MILES0 50 100 KILOMETERS

1002 Area

B R O O K S R A N G E Hope

Basin

Point Barrow

Prudhoe

Bay

Beaufort Shelf

Chukchi Shelf

Herald Arch Arctic National Wildlife Refuge National Petroleum Reserve in Alaska

Absent (non-deposition or erosion)

Absent (erosion)

Absent

(erosion)

CANADA

250

500

750 1,000

500

1,250 1,250

1,000

250

A'

A

Kugrua Ikpikpuk

North Inigok

EXPLANATION

Kingak Shale Oil AUKingak Shale Gas AUState-Federal offshore

boundary Normal fault—Hachures on 

Federal land boundaryTrans-Alaska Pipeline SystemThrust fault downthrown side

—Teeth on upper plate

Figure 9.

250

≤5>5 to 10>10 to 15>15 to 20>20

∆DTx in the lower Kingak Shale,

 in microseconds per foot

– Line of equal thickness of Kingak Shale

—

K1 sequence set. Interval 250 feet

K1 beveled to north by truncation beneath LCUTop of K1 truncated to north at base of K2Selected control wellWell used in cross section

69°

165°

71°70°68°

160° 155° 150° 145°

Base map modified from U.S. Geological Survey1:1,000,000-scale digital files from The National MapProjection is Alaska Albers
Methodology 11 Figure 10. Map of ∆DTz in the lower Kingak Shale for that part of the Alaska North Slope where requisite wireline-log data are available. Blue contours modified from Houseknecht and Bird, 2004. Abbreviations used: AU, assessment unit; LCU, Lower Cretaceous unconformity; ∆DTz incorporates both the magnitude and thickness of the ∆DT curve separation, and is intended to produce an objective parameter that may be proportional to the volume of potential source rocks penetrated by each well.

Alpine Endicott

Milne

Point

UNITED STATES

ALASKA

Map area

0 50 100 MILES0 50 100 KILOMETERS

1002 Area

B R O O K S

R A N G E Hope

Basin

Point Barrow

Prudhoe

Bay

Beaufort Shelf

Chukchi Shelf

Herald

A

r

c

h Arctic National Wildlife Refuge

National Petroleum Reserve in Alaska

Absent (non-deposition or erosion)

Absent (erosion)

Absent

(erosion)

CANADA 250 500 750 1,000 500

1,250 1,250

1,000 250

A'

A

Kugrua Ikpikpuk

North Inigok

EXPLANATION

Kingak Shale Oil AUKingak Shale Gas AUState-Federal offshore

boundary Normal fault—Hachures on 

Federal land boundaryTrans-Alaska Pipeline SystemThrust fault downthrown side

—Teeth on upper plate

Figure 10.

∆DTZ in the lower Kingak Shale,

 in microseconds per foot

≤1,000 >1,000 to 2,000>2,000 to 3,000>3,000 to 4,000>4,000

250 Line of equal thickness of Kingak Shale—

K1 sequence set. Interval 250 feet

K1 beveled to north by truncation beneath LCUTop of K1 truncated to north at base of K2Selected control wellWell used in cross section

69°

165°

71°70°68°

160° 155° 150° 145°

Base map modified from U.S. Geological Survey1:1,000,000-scale digital files from The National MapProjection is Alaska Albers
12 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

Discussion

The ∆DTx and ∆DTz parameters were developed to serve 

as proxies for potential source-rock quality and volume, 

respectively, in the absence of geochemical and thermal 

maturity data necessary for the direct correlation of TOC 

log and geochemical data. Geochemical data from the lower 

Kingak Shale are sparse and largely derived from cuttings 

collected over intervals of 10 to 100 ft (3 to 30 m). Moreover, 

most of the available TOC data were concentrated in relatively 

proximal parts of the Kingak Shale depositional system that 

lack organic-matter-rich and oil-prone source rocks, making a 

direct comparison of TOC and ∆DT in potential source-rock 

intervals difficult. However, where TOC measurements were 

available in potential source-rock intervals, ∆DT and TOC 

values were positively correlated (for example, North Inigok; 

fig. 11). 

Maps of ∆DTx and ∆DTz

 in the K1 sequence set reveal 

an increase in potential source-rock quality and volume, 

respectively, from north to south. The potentially richest area 

in the eastern NPRA corresponds to a re-entrant in the K1 

shelf margin, as defined by a K1 isopach map (figs. 9, 10). 

Within the NPRA, ∆DTx and ∆DTz values are inversely related 

to the thickness of the K1 sequence set, with the greatest 

values where the K1 sequence set thins distally (fig. 12). These 

findings agree with Houseknecht and Bird’s (2004) interpretation of a distal increase in organic matter content within the 

K1 sequence set in the NPRA. Outside of the NPRA, ∆DTx

and ∆DTz values gradually decrease eastward toward the 

Arctic National Wildlife Refuge (figs. 9, 10). An exception to 

this regional trend occurs in the Prudhoe Bay area, where a 

pod of large ∆DTx and ∆DTz values highlight a potential rich 

source-rock area, although the controls are not understood 

(figs. 9, 10). 

The large ∆DTz value calculated for the Kugrua well 

(location shown in figure 10) is attributed to elevated methane 

concentrations within shale of the K2 interval (Hayba and 

others, 2002), skewing the shale baseline values meant to be 

derived in a non-source-rock interval. This results in an offset 

of the DT and DTlogR log curves within the K1 interval, where 

the curves otherwise would be superimposed. This small curve 

separation (as evident in figure 9), combined with the thickness of the K1 sequence set preserved in the proximal portion 

of the basin, result in a large ∆DTz value that is unlikely to 

correspond to a large volume of potential source rock. 

Conclusions

The methodology outlined in this report can be used in 

a completely digital workflow to evaluate the richness and 

volume of potential source rocks, both in individual wells 

and in a map area containing multiple wells, provided that a 

non-source-rock interval of mudstone or shale can be identified to establish a baseline for comparison. Use of ∆DTx

 and 

∆DTz parameters delineates regional source-rock potential in 

the lower Kingak Shale, and map results are consistent with 

known patterns of lithofacies and geochemistry. However, 

because thermal maturity was not considered in the calculation of these parameters in the Kingak Shale test case, TOC 

values cannot be estimated for individual wells or regionally. 

Therefore, the ∆DTx and ∆DTz mapping parameters should 

be viewed as first-step reconnaissance tools for identifying 

possible source-rock potential. 

Acknowledgments

We thank Tom Wild, President and Owner of Tom Wild 

Petrophysical Services LLC, for insightful discussion on 

geophysical-log interpretation. 
Discussion 13

Figure 11. Gamma-ray log, sonic travel time, and total organic carbon content of 

the Kingak Shale K1 and K2 sequence sets in the North Inigok well (location shown 

in figures 9 and 10). Greater positive separation of the DT and DTlogR curves (∆DT; 

highlighted in red) in the K1 sequence set correlates with high total organic carbon 

values. Depths are below kelly bushing. Abbreviations: API, American Petroleum 

Institute; DT, sonic travel time.

Sonic travel time,

in microseconds per foot

5075100125

Gamma ray,

in API units

0 50 100 150

8,500

FEET

9,000

9,500

10,000

Total organic carbon,

in weight percent

1 2 3 4 5

DT

DTlogR

∆DT

North Inigok

K1

K2

Figure 11.
14 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

DT

DTlogR

∆DT

Not included

in calculation

GR, in API units

0 150

GR, in API units

0 150

GR, in API units

0 150

DT, in μsec/ft

150 50

DT, in μsec/ft

150 50

DT, in μsec/ft

150 50

Kugrua South Meade Ikpikpuk 

8

9

7

8

9

8

9

10

K1

K2

K3

LCU

A 

Figure 12.

Figure 12. Well logs from cross section A–A' illustrating regional change in ∆DT (highlighted in red) related to location 

in Kingak Shale K1–K3 sequence sets. Intervals with curve separation highlighted in gray have less than 60 percent shale 

content and were not included in the calculation of ∆DT. Wireline-log measured depth ticks below kelly bushing are at 100-foot 

(ft) (30-meter) intervals. Cross section hung on the Lower Cretaceous unconformity (LCU). Location of cross section shown in 

figures 9 and 10. Abbreviations: API, American Petroleum Institute; DT, sonic travel time; GR, gamma ray; μsec/ft, microseconds 

per foot.
Discussion 15

GR, in API units

0 150

GR, in API units

0 150

GR, in API units

0 150

DT, in μsec/ft

150 50

DT, in μsec/ft

150 50

DT, in μsec/ft

150 50

Kokoda 5 North Inigok Inigok

8

9

8

9

10

11

10

10

11

12

A'

DTlogR

∆DT

DT

Not included

in calculation

Figure 12. Well logs from cross section A–A' illustrating regional change in ∆DT (highlighted in red) related to location 

in Kingak Shale K1–K3 sequence sets. Intervals with curve separation highlighted in gray have less than 60 percent shale 

content and were not included in the calculation of ∆DT. Wireline-log measured depth ticks below kelly bushing are at 100-foot 

(ft) (30-meter) intervals. Cross section hung on the Lower Cretaceous unconformity (LCU). Location of cross section shown in 

figures 9 and 10. Abbreviations: API, American Petroleum Institute; DT, sonic travel time; GR, gamma ray; μsec/ft, microseconds 

per foot.—Continued
16 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

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Williston basin, North Dakota: Transactions of the Thirtieth 

Society of Petrophysicists and Well Log Analysts Annual 

Logging Symposium, paper H.

Sedivy, R.A., Penfield, I.E., Halpern, H.I., Drozd, R.J., 

Cole, G.A., and Burwood, R., 1987, Investigation of source 

rock-crude oil relationships in the northern Alaska hydrocarbon habitat, in Tailleur, Irv, and Weimer, Paul, eds., 

Alaskan North Slope Geology: Pacific Section, Society of 

Economic Paleontologists and Mineralogists and Alaska 

Geological Society 50, v. 1, p. 169–179.

Seifert, W.K., Moldowan, J.M., and Jones, R.W., 1980, Application of biological marker chemistry to petroleum exploration: Proceedings of the 10th World Petroleum Congress, 

Bucharest, Romania, September 9–14, 1979, p. 425–440.
18 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

Sondergeld, C.H., Newsham, K.E., Comisky, J.T., Rice, M.C.,

and Rai, C.S., 2010, Petrophysical considerations in 

evaluating and producing shale gas resources: Society of 

Petroleum Engineers Unconventional Gas Conference, 

Pittsburgh, Pennsylvania, February 23–25, 2010, Society 

of Petroleum Engineers Paper 131768, 34 p.

Threlkeld, C.N., Obuch, R.C., and Gunther, G.L., 2000, 

Organic geochemistry data of Alaska: U.S. Geological 

Survey Digital Data Series DDS–59, accessed 

November 24, 2014, at http://pubs.usgs.gov/dds/dds-059/.

Tissot, B.P., and Welte, D.H., 1984, Petroleum formation and 

occurrence: New York, Springer-Verlag, 699 p. [Also available at http://dx.doi.org/10.1007/978-3-642-96446-6.]
Appendix 1. Workflow for Calculating Key Parameters 19

Appendix 1. Workflow for Calculating Key Parameters

The following workflow was compiled using IHS Kingdom® version 8.8 software with the EarthPAK® module. This 

workflow assumes that a project has already been populated with well locations, digital gamma-ray, resistivity, and sonic 

wireline-log data in LAS format, and formation tops that bound the stratigraphic interval of interest. For instructions on 

how to input these data, the reader is referred to the IHS Kingdom® version 8.8 software help files. This workflow uses 

input parameters specific to the Alaska North Slope Kingak Shale that may not be applicable to all shale plays. 

Calculating Shale Volume (Vsh)

Note: The Petrophysics module is available with an EarthPAK license.

1. From the Logs menu, select Petrophysics... to proceed to the Petrophysics dialog box.

2. In the Quick-Look Analysis Navigator window, select Zone-related Parameters. 

3. In the Zone-related Parameters window, from the Select an Existing Zone drop-down menu, select Borehole 

(Public). Under Select Lithology and Porosity Model, from the Reservoir Lithology drop-down menu, select 

the appropriate reservoir lithology (sandstone in this example). Accept all other defaults.
20 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

4. In the Quick-Look Analysis Navigator, under Zone-related Parameters, select Vshale Indicators. Calculated values 

for clean and shale baselines for gamma-ray (GR) and spontaneous potential (SP) are displayed; these may be accepted 

or manually adjusted. 

5. In the Quick-Look Analysis Navigator, select 

Run All Wells to proceed to the Select Logs 

to Save dialog box.

6. Select VShale from the curve selection 

window.

7. Under Save Options, toggle Create New Curves 

Only and accept the default prefix 

of SMT. 

8. Click OK.
Appendix 1. Workflow for Calculating Key Parameters 21

Calculating Log R

1. From the Logs menu, select Calculations → Equation to proceed to the Select or Enter an Equation dialog box.

2. In the Equation Category window, type Other.

3. In the Equation window, type LOGR=. In the Functions window below, double click on LOG10(x) to place it in 

the equation and replace (x) with R. The resulting equation should read LOGR=LOG10(R).

4. In the Description window, type LogR from resistivity.

5. Click Next > to proceed to the Assign Variables dialog box.
22 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

6. To assign R to the resistivity (RILD) log curve, in the Select the Variable to Assign window, select R; then toggle 

on Log Curves, and select RILD from the drop-down menu and click Assign.

7. Click Next > to proceed to the Depth Range Selection dialog box.

8. Toggle on by Zone Intervals and select Borehole (Public) from the drop-down menu.

9. Click Next > to proceed to the Output dialog box.
Appendix 1. Workflow for Calculating Key Parameters 23

10. In the Output Log Curve Name window, type LOGR.

11. From the Output Log Curve Type drop-down menu, select Other.

12. Toggle on Create new log curve and replace existing curve.

13. Click Finish.
24 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

Creating a Cross Plot of Log R versus DT

Note: The following exercise assumes that the user has predefined zones within the interval of interest. For these 

exercises, the K1 TO KBASE zone is the interval that is assessed for probable source rock potential and the 

K2 TO K1 zone is the assumed non-source rock interval used to create baseline sonic and resistivity data.

1. From the Tools menu, select Crossplot → New to proceed to the Select Data dialog box.

2. In the Category window, select Log.

3. In the Attributes drop-down menu, select a well that contains gamma-ray, sonic, and resistivity log curves 

and for which you have calculated VSH and LOGR. 

4. In the Attributes window, select the LOGR curve; from the Axis/Filter window, select X and click >.

5. In the Attributes window, select the DT curve; from the Axis/Filter window, select Y and click >.

6. In the Attributes window, select the SMTVSH curve; from the Axis/Filter window, select Filter and click >. 

In the Min Value window, type 0.6 and keep the default Max Value. 

7. Click Depth Range to proceed to the Crossplot Depth Range Selection dialog box.
Appendix 1. Workflow for Calculating Key Parameters 25

8. Toggle on By Zone Intervals and select the assumed non-source rock interval zone.

9. Click OK to return to proceed to the Select Data dialog box.

10. Click OK to proceed to the Crossplot window.
26 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

11. Click on the regression icon to proceed to the Regression dialog box.
Appendix 1. Workflow for Calculating Key Parameters 27

12. Under Regression Method, toggle on Numerical Regression.

13. Under Equation, toggle on Polynomial and Reduced Major Axis (RMA).

14. Click OK to return to the Crossplot window. 
28 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

15. The regression equation is shown under the x-axis. Record the slope and intercept of the regression line for 

each well in order to calculate DTLOGR.
Appendix 1. Workflow for Calculating Key Parameters 29

Calculating DTlogR (DTLOGR)

Note: Calculation of DTlogR must be done on a well-by-well basis. When using this workflow, make sure that only one 

well is selected in the project, otherwise the calculation will be applied to all wells selected.

1. From the Logs menu, select Calculations → Equation to proceed to the Select or Enter an Equation dialog box.

2. In the Equation Category window, type Other.

3. In the Equation window, type DTLOGR=B-M*LOGR.

4. In the Description window, type DTLOGR from Crossplot of LogR vs. DT.

5. Click Next > to proceed to the Assign Variables dialog box.
30 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

6. Assign B to the y intercept of the regression equation for the well by selecting B in the Select the Variable to Assign

window, toggling on Constant, entering the intercept value in the window, and clicking Assign.

7. Assign LOGR to the LOGR log curve by selecting LOGR in the Select the Variable to Assign window, toggling on 

Log Curves, selecting LOGR from the drop-down menu, and clicking Assign.

8. Assign M to the slope of the regression equation for the well by selecting M in the Select the Variable to Assign

window, toggling on Constant, entering the slope value in the window, and clicking Assign.

9. Click Next > to proceed to the Depth Range Selection dialog box.
Appendix 1. Workflow for Calculating Key Parameters 31

10. Toggle on by Zone Intervals and select the zone to be assessed for probable source rock potential from the 

drop-down menu.

11. Click Next > to proceed to the Output dialog box.

12. In the Output Log Curve Name window, type DTLOGR.

13. In the Output Log Curve Type window, select Other from the drop-down menu.

14. Toggle on Create new log curve and replace existing curve.

15. Click Finish.
32 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

Calculating ∆DT Curve Separation

1. From the Logs menu, select Calculations → Equation to proceed to the Select or Enter an Equation dialog box.

2. In the Equation Category window, type Other.

3. In the Equation window, type DELTADT=DT-DTLOGR.

4. In the Description window, type Curve separation between DT and DTLOGR.

5. Click Next > to proceed to the Assign Variables dialog box.
Appendix 1. Workflow for Calculating Key Parameters 33

6. Assign DT to the DT log curve by selecting DT in the Select the Variable to Assign window, toggling on 

Log Curves, selecting DT from the drop-down menu, and clicking Assign.

7. Assign DTLOGR to the DTLOGR log curve by selecting DTLOGR in the Select the Variable to Assign

window, toggling on Log Curves, selecting DTLOGR from the drop-down menu, and clicking Assign.

8. Click Next > to proceed to the Depth Range Selection dialog box.
34 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

9. Toggle on by Zone Intervals and select the zone to be assessed for probable source rock potential from the 

drop-down menu.

10. Click Next > to proceed to the Output dialog box.

11. In the Output Log Curve Name window, type DELTADT.

12. In the Output Log Curve Type window, select Other from the drop-down menu.

13. Toggle on Create new log curve and replace existing curve.

14. Click Finish.
Appendix 1. Workflow for Calculating Key Parameters 35

Calculating ∆DTz

Note: As of this publication, calculation of ∆DTz entirely in IHS Kingdom® version 8.8 software is not possible. 

However, the key variables in the equation, and hnet, can be obtained using the Kingdom software. 

Finding ∆DTx

In order to restrict the calculation of ∆DTz to positive ∆DT values:

1. From the Logs menu, select Calculations → If-Then-Else to proceed to the If-Then-Else for Log Curves

dialog box.

2. Under IF, select DELTADT from the Log Curve Name drop-down menu, select GE (greater than or equal to) 

from the is drop-down menu, toggle on Constant and type 0.

3. Under THEN, toggle on Log Curve Name and select DELTADT from the drop-down menu.

4. Under ELSE, toggle on Missing (NULL).

5. Under Save As, type +DELTADT in the Log Curve Name window.

6. Click OK.
36 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

In order to further restrict the calculation of ∆DTz to intervals containing at least 60 percent shale (Vsh ≥ 0.60):

7. From the Logs menu, select Calculations → If-Then-Else to proceed to the If-Then-Else for Log Curves

dialog box.

8. Under IF, select VSH from the Log Curve Name drop-down menu, select GE (greater than or equal to) from 

the is drop-down menu, toggle on Constant and type 0.6.

9. Under THEN, toggle on Log Curve Name and select +DELTADT from the drop-down menu.

10. Under ELSE, toggle on Missing (NULL).

11. Under Save As, type +DELTADT VSH>0.6 in the Log Curve Name window.

12. Click OK.
Appendix 1. Workflow for Calculating Key Parameters 37

Finally, to find the mean ∆DT value (∆DTx  ):

13. From the Logs menu, select Calculations → Simple Statistics to proceed to the Log Curve Statistics dialog box.

14. Under Log Curves, select +DELTADT VSH>0.6.

15. Under Zones, select the zone to be assessed for probable source rock potential.

16. Click the check box next to Arithmetic Mean (AM) and type DDTAM.

17. Click OK.
38 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

Finding hnet

1. From the Zones menu, select Zone Attribute Calculator to proceed to the Zone Attribute Calculator dialog box.

2. In the Attributes tab, under Attributes to Calculate, check the box next to Net and type HNET in the window.

3. Check the box next to Correct for TVD (Elev. Ref.).

4. Under Select One or More Zones, select the zone to be assessed for probable source rock potential.

5. Under Conditions, check the box next to Other, select the +DELTADT VSH>0.6 log curve from the drop-down 

menu and choose the default values for Minimum and Maximum.

6. Click OK.
Appendix 1. Workflow for Calculating Key Parameters 39

Exporting the Spreadsheet

The user can complete the calculation of ∆DTz by exporting and hnet to an Excel spreadsheet. To accomplish this:

1. From the Zones menu, select View Attribute Values by Zone to proceed to the Select Data for Spreadsheet 

dialog box.

2. Under Select Category, select Zone Information.

3. Under Zones, select the zone to be assessed for probable source rock potential from the drop-down menu.

4. Under Attributes, select DDTAM and HNET by clicking on each while holding down the ‘ctrl’ button.

5. Under Field, select Value.

6. Click > to move your selections to the Selected Items window.

7. Click OK to proceed to the Spreadsheet.
40 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

From the spreadsheet, the user can copy and paste the data into an Excel workbook.
Manuscript approved January 6, 2016

Prepared by the USGS Science Publishing Network

Publishing Service Centers

Edited by Natalie Juda and David A. Shields, Reston

Layout and illustrations by Caryl J. Wipperfurth, Raleigh

For more information concerning this report, contact:

Director, Eastern Energy Resources Science Center

U.S. Geological Survey

12201 Sunrise Valley Drive

Mail Stop 956

Reston, VA 20192

http://energy.usgs.gov/

http://energy.usgs.gov/GeneralInfo/ScienceCenters/Eastern.aspx
Rouse and Houseknecht—Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale—Scientific Investigations Report 2016–5001

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20165001