Computer-Assisted Interpretation of 

Geophysical Well Logs in a 

Coal Depositional Environment, 

Illinois Basin, Kentucky · 

GEOLOGICAL SURVEY BULLETIN 1509 

Comp:uter-Assisted Interpretation of 

Geophysical Well Logs in a 

Coal Depositional Environment, 

Illinois Basin, Kentucky 

By JEFFREY J. DANIELS and JAMES H. SCOTT 

GEOLOGICAL SURVEY BULLETIN 1509 

Physical properties associated with various 

lithologies in a coal depositional environment are 

interpreted from digital geophysical well-log measurements 

UNITED STATES GOVERNi\1ENT PRINTING OFFICE, WASHINGTON: 1980 
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

H. William Menard, Director 

Library of Congress Cataloging in Publication Data 

Daniels, Jeffrey J. 

Computer-assiSted interpretation of geophysical well logs in a coal depositional environment, Illinois Basin, Kentucky. 

(Geological Survey Bulletin 1509) 

Bibliography: p. 29 

Supt. of Docs. no.: I 19.3:1509 

1. Coal mines and mining-Kentucky-Data processing. 2. Geophysical well loggingKentucky-Data processing. 3. Coal mines and mining-Illinois Basin-Data processing. 

4. Geophysical well logging-Illinois Basin-Data processing. 

I. Scott, James H., joint author. II. Title. III. Series: United States Geological Survey 

Bulletin 1509. 

QE75.B9 no.1509 [TN805.K3] 557.3s S0-'-607932 [622'.1824'02854] 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 
CONTENTS 

Page 

Abstract ···················································································································· 1 

Introduction ············································································································· 1 

Well-log response characteristics·······································································-··· 2 

Density ··············································································································· 3 

Resistivity ·········································································································· 4 

Gamma-ray ········································································································ 4 

Neutron ·············································································································· 4 

Induced polarization (IP) ·················································································· 5 

Computer-assisted approach to interpretation of lithology·································· 5 

Geology ····················································································································· 6 

Interpretation using individual well logs ······················································-········ 9 

Composite well-log interpretation ··········································································· 25 

Conclusions ··············································································································· 28 

References cited ···························································································-······-··· 29 

Appendix A 

Lithology interpreted from the geophysical well logs for each hole··············· 31 

AppendixB 

Product and ratio well logs, and composite lithologic interpretation for drill 

holes 2 through 6 ································································································ 39 

ILLUSTRATIONS 

Page 

FIGURE 1. Sketch showing location of study areas and of the six drill 

holes with respect to the mine workings near Centertown, Ky 7 

2. General lithologic logs, interpreted from drill-cutting samples, 

for drill holes 8 

3-12. Types of well logs and lithologic interpretation: 

3. Density, holes 1, 2, and 3 10 

4. Density, holes 4, 5, and 6 11 

5. Neutron-neutron, holes 1, 2, and 3 14 

6. Neutron-neutron, holes 4, 5, and 6 15 

7. Sixteen-inch normal resistivity, holes 1, 2, and 3 --- 16 

8. Sixteen-inch normal resistivity, holes 4, 5, and 6 --- 17 

9. Gamma-ray, holes 1, 2, and 3 18 

10. Gamma-ray, holes 4, 5, and 6 19 

11. Induced polarization (IP), holes 1, 2, and 3 22 

12. Induced polarization (IP), holes 4, 5, and 6 23 

13. Product and ratio well logs, and composite lithologic 

interpretation for drill hole 1 24 

14. Composite lithologic interpretation for drill holes 1 

through6 27 

III 
IV CONTENTS 

FIGUREA1-A6. Sections showing lithology as interpreted from density, 

neutron, resistivity, gamma-ray, and IP well logs for: 

A1. Drill hole 1 32 

A2. Drill hole 2 33 

A3. Drill hole 3 34 

A4. Drill hole 4 35 

A5. Drill hole 5 36 

A6. Drill hole 6 37 

B 1-B5. Product and ratio well logs, and composite lithologic interpretation for: 

B 1. Drill hole 2 40 

B2. Drill hole 3 41 

B3. Drill hole 4 42 

B4. Drill hole 5 43 

B5. Drill hole 6 44 

TABLES 

TABLE 1. Relative response levels of well-logging probes in coal depositional 

envrronments----------~---------------------------

2. Composite well-log interpretation for individual and combined 

lithologies using product and ratio well logs -----------------

Page 

5 

26 
COMPUTER-ASSISTED INTERPRETATION 

OF GEOPHYSICAL WELL LOGS IN A 

COAL DEPOSITIONAL ENVIRONMENT, 

ILLINOIS BASIN, KENTUCKY 

By jEFFREY J. DANIELS andjAMES H. SCOTT 

ABSTRACT 

Physical properties detected by well-logging probes include density, porosity, water 

content, resistivity, electrical polarizability, and natural gamma-ray radiation. Welllogging probes respond primarily to physical properties of the rock surrounding the 

drill hole, but are also affected by the properties of the fluid in the hole and by 

irregularities of the hole surface. A particular lithology may be characterized by 

physical properties that are measured by one type of geophysical well-logging device 

and not by another. Therefore, the geologic section near a borehole must be inter· 

preted by using more than one type of well log to selectively determine individual 

lithologies. 

Interpretations of lithologies from borehole geophysical measurements are based 

on the fact that different rock types exhibit characteristic physical properties that 

can be measured by the probes. For example, the following response values (relative 

to the average probe response values in a sedimentary environment) can be used for 

lithologic identification: (1) coal yields a low density response, (2) limestone 

conglomerate and sandstone have high neutron and resistivity responses, and (3) 

kaolinite shale has a high gamma-ray response. Interpretation of lithologies in a 

shallow sedimentary coal environment can be facilitated by using products and ratios 

of well logs. Coal is characterized by a low density, a low natural gamma-ray count 

rate, and a high induced polarization response. The density and gamma-ray responses 

of black shale are slightly higher than those of coal. Limestone conglomerate and 

sandstone both have high resistivity and neutron responses and low gamma-ray 

responses, but the product of the resistivity and neutron response is higher for 

limestone conglomerate than for sandstone. The approximate amount of shale in 

shaly sandstone can be determined by the product of the resistivity and neutron well 

logs. In shale that contains only clay, the induced polarization well log can be used to 

distinguish the clays with a high cation-exchange capacity from those with a low 

cation-exchange capacity. After the geologic section has been interpreted using product and ratio well logs, the stratigraphic features in an area can be determined by 

comparing composite interpretations from drill hole to drill hole. 

INTRODUCTION 

Density, gamma-ray, and single-point resistance well logs are now 

commonly used by mining geologists and engineers for identification 

of coal deposits and for lateral correlation of stratigraphic units 
2 GEOPHYSICAL WELL LOGS, ILLINOIS BASIN, KENTUCKY 

associated with coal deposits. Authors of previous papers on well-log 

analysis in coal deposits have limited their topics to identification of 

coal seams and to analysis of the economic and engineering 

parameters of the seams (Weltz, 1976; Kowalski and Fertl, 1976; 

Reeves, 1976). For example, Bond and others (1969) discussed the 

following applications of well-log analysis to coal-prospect evaluation: (1) identification of coal seams, (2) measurement of coal seam 

thickness, (3) evaluation of lithology and moisture index of formations surrounding coal seams, (4) determination of a strength index 

for formations penetrated by the drill hole, and (5) analysis of coal 

quality. Bond's paper implies that all these problems can be easily 

solved to a high degree of accuracy with conventional well logs 

(gamma-ray, density, sonic, neutron, laterolog, and caliper) that are 

commercially available and are used routinely in the petroleum industry. Unfortunately, most well-logging tools that are used in the 

petroleum industry require a minimum drill-hole diameter of 6 inches, 

but most holes drilled for coal exploration and development are less 

than 5 inches in diameter. Also, interpretive parameters developed 

for consolidated sedimentary environments, such as those used in 

petroleum exploration, are not valid for unconsolidated or poorly consolidated sediments that are characteristic of sub-bituminous and 

bituminous coal environments. 

No single type of well log can be used to completely interpret the 

lithology of rock surrounding a drill hole. However, detailed 

lithologic and stratigraphic interpretations of shallow sedimentary 

coal depositional environments can be made by using combinations 

of well logs that measure several different physical properties of the 

rocks. The following well logs, all of which can be obtained with commercially available small-diameter probes ( < 6 em (centimeter)), are 

discussed in this paper: gamma-ray, density, resistivity, neutron, and 

induced polarization (IP). A computer-aided interpretive technique is 

described for determining the following geologic features in a coal 

depositional environment: (1) the lithologic section, (2) the presence of 

pyrite, (3) the presence of high cation-exchange capacity clays, and (4) 

the presence of lateral facies changes. 

WELL-LOG RESPONSES CHARACTERISTICS 

It is important to understand the response characteristics of different types of geophysical well-logging probes in terms of the 

physical properties of the rocks. A single well-logging probe can yield 

similar response values in different lithologies. Conversely, different 

types of well-logging probes can yield different lithologic interpretations in the same drill hole. 
WELL-LOG RESPONSE CHARACTERISTICS 3 

Geophysical well-logging probes can be divided into two groups 

based upon the complexity of their response characteristics: (1) welllogging probes that respond to specific physical properties, and 

(2) well-logging probes that respond to combinations of physical 

property changes. The gamma-ray probe detects the amount of 

natural gamma radiation emanating from potassium-40 and 

uranium-series isotopes in a rock unit. Resistivity and neutron 

probes respond to a combination of physical characteristics of a rock 

unit, primarily its water content which reflects porosity and, to a 

lesser degree, the __intrinsic resistivity of minerals in the rock. The 

density-probe response is primarily a function of the rock bulk density; however, the electron density of the rocks (the density of the 

rock that is measured by the gamma-gamma density probe) is also affected by secondary physical properties including porosity, water 

content, and invasion of drilling mud, and by the chemical composition of the rocks as it affects the ratio of average atomic number to 

average atomic weight, Z/ A (Robbins, 1979). In addition, a 

geophysical well-log measurement is a function of the volume of rock 

investigated by the probe and the vertical resolution of the probe 

("thin" bed resolution). Therefore, the response recorded by a 

geophysical well-logging probe that responds to combinations of 

physical properties should always be thought of as an "apparent", 

rather than a "true", measure of a physical property value. The functions and response characteristics of individual well-logging probes 

in a shallow sedimentary coal environment can be summarized as 

follows: 

DENSITY 

The density probe consists of a gamma-ray source and one or more 

gamma-ray detectors. Gamma rays emitted by the source are scattered by the enclosing rock wall and absorbed as a direct function of 

the electron density of the rock unit. The Compton-scattered gamma 

radiation that is measured at the gamma-ray detector on the probe is 

inversely related to the electron density of the rock. When two detectors at different spacings from the source are used to measure the 

scattered gamma radiation, the local effects of error-producing 

borehole conditions (rugosity, invasion of drilling mud, and presence 

of borehole fluid between probe and rock) on the calibrated density 

measurement can be compensated, and the computed density is approximately equal to the electron density of the rocks (Scott, 1977). 

The apparent density of coal is commonly the lowest response 

value on the density well log, averaging less than 1.6 g/cm3 (grams 

per cubic centimeter) for sub-bituminous and bituminous coal. The 

bulk density of coal is a function of the ash content, where ash is 
4 GEOPHYSICAL WELL LOGS, ILLINOIS BASIN, KENTUCKY 

defined as the nonburnable percentage of the coal. The densities of 

other interbedded sediments are a function of the porosity and grain 

density of the individual rock units. Clays and shales exhibit low densities (2.2-2.5 g/cm3), sandstone has an intermediate density 

(2.5-2.65 g/cm3

), and limestone has a high density (2.7-2.9 g/cm3). 

RESISTIVITY 

Resistivity is a measure of the pore water resistivity and the grain 

resistivity of a rock. Clay has an apparent resistivity of generally less 

than 10 ohm meters, shale has a resistivity of less than 50 ohm 

meters, sandstone has a resistivity between 50 and 200 ohm meters, 

and limestone and bituminous coal have resistivities of more than 

200 ohm meters. Shale partings can significantly decrease the apparent resistivity of coal,' sandstone, and limestone. The wide range of 

resistivity values (from less than 10 to more than 500 ohm meters) 

recorded in shallow sedimentary rocks makes resistivity a good indicator of lithologic changes in logged sections. 

GAMMA RAY 

The gamma-ray probe measures the natural gamma radiation emitted by the rocks surrounding the borehole. The principal sources of 

natural gamma radiation in shallow sedimentary rocks are uraniumseries isotopes and potassium-40. Pure limestone contains practically 

no natural gamma-ray emitting elements. Shale and clay containing 

potassium-40 have an tntermediate gamma-ray response. Coal is 

associated with a reducing environment that enhances the deposition 

of uranium, but coal itself rarely contains significant concentrations 

of uranium minerals. Uranium may be concentrated in some detrital 

sediments by the presence of organic matter. Uranium-bearing black 

shales commonly have extremely high gamma-ray levels and are 

therefore importal'lt marker horizons for between-hole stratigraphic 

correlations. 

NEUTRON 

The neutron well-logging probe consists of a neutron source and a 

neutron detector that is located on the probe approximately 40 em 

from the source. The count rate of the neutron detector is inversely 

related to the hydrogen content of the rocks surrounding the 

borehole, and is primarily a measure of the amount of water and 

hydrocarbons in the rocks. Coal has a low neutron count rate because 

of its high hydrocarbon content, whereas low-porosity limestone has 
COMPUTER ASSISTED APPROACH TO INTERPRETATION OF LITHOLOGY 5 

TABLE I.-Relative response levels of well-logging probes in coal depositional 

environments 

(The lowest response is assigned the value of 1; the highest reponse is ~signed the value of 7. For some probes, 

certain rock types exhibit a range of values which overlap or are essentially coincident; these values are shown in 

the table by two or more "level" values] 

Gray Black Sand- Lime- Con- Clay 

Probe type Coal shale shale stone stone glomerate 

Density------------- 1 4 2 5,6 7 5,6 3 

Resistivity--------- 6,7 3 2 4,5 6,7 4,5 1 

Gamma-ray----------- 2,3,4 6 7 2,3,4 1 2,3 5 

Neutron------------- 1 2,3,4 2,3,4 5',6 7 5,6 2,3,4 

Induced polarization 2,1,4 5,6 7 2,3,4 1 2,3,4 5,6 

a high neutron count rate because of its low water content. Sandstone 

and shale (intermediate porosity and high porosity, respectively) 

have intermediate and low neutron count rates. The neutron response 

is also affected by the borehole fluid and the rugosity of the borehole. 

INDUCED POLARIZATION (IP) 

The IP is measured by recording the decay voltage (emitted from 

an ''on-off'' current source) at a two-potential electrode that is positioned on the probe at a spacing of 10-40 em from an electrical current source. The rate of decay of the potential during the current off 

time is related to the electrical polarizability of the rock, and is called 

the induced potential (IP) effect. A high IP response may be caused 

by the presence of pyrite or cation-rich clays (such as montmorillonite 

or illite). A high IP response in black shale or coal usually indicates 

the presence of pyrite. 

The relative range of values for these five types of well-logging 

probes are listed in Table 1 for various shallow sedimentary rock 

types. The relative response values listed in this table are subjective. 

COMPUTER-ASSISTED APPROACH TO INTERPRETATION 

OF LITHOLOGY 

As stated previously, each individual well-logging probe responds 

to physical properties associated with the drill hole and the rock surrounding the drill hole. Physical properties detected by well-logging 

probes used in this study include density, porosity, water content, 

resistivity, electrical polarizability (IP effect), and natural gammaray radiation. Interpretation of physical properties from geophysical 

well logs assumes that the effects of borehole conditions on the welllog response values have been quantitatively considered in the 
6 GEOPHYSICAL WELL LOGS, ILLINOIS BASIN, KENTUCKY 

analysis, or that the physical condition of the borehole can be considered to have the same effect on the well-log response throughout 

the intervals being logged. Not all well-logging probes respond to 

every change in the geology because: ( 1) the response values of the 

well-logging probe to lithologic variations depends upon the range of 

values of the physical properties, and (2) a particular rock type may 

be characterized by a physical property that is measured by one type 

of well-logging probe, and not measured by another probe. In order to 

interpret a geologic section from physical-properties measurements, 

the measurements from several different well-logging probes must be 

used and a composite interpretation must be made that considers all 

of the physical properties characteristic of a particular lithology. 

The interpretation procedure that was followed in this study involves the following steps. After visual inspection of the geophysical 

logs and the driller's logs, the interpreter assigns (1) a well-log 

response value range to each geologic parameter of interest and uses 

the computer to assign a lithology for those depth intervals where the 

individual well log values are within the assigned value ranges. (2) 

These individually interpreted well logs are compared to existing 

geologic information (such as cores -and driller's well logs) to find 

where gaps exist and where interpretations are unreasonable. (3) To 

fill in the gaps and to correct unreasonable interpretations, products 

and ratios of different types of well logs are calculated and assigned 

lithologies based upon specified value ranges. (4) A final interpretation is made that includes all the individual and product-ratio 

geophysical well-log interpretations as well as all the available 

geologic information. The final interpretation is subjective and 

utilizes the well-log response, or combination of well-log responses, 

that best characterize a particular lithology. 

GEOLOGY 

The six holes in this study were drilled into the Carbondale Formation of Middle Pennsylvanian age at a site located approximately 1 

mile south of Centertown in Ohio County, Kentucky. Detailed 

descriptions of the geology of the Carbondale Formation are not 

available in the literature; the descriptions and interpretations of the 

unit are based upon geological information provided by coal-company 

geologists. 

The areal positions of the six drill holes and old mine workings are 

shown in figure 1. Lithologic well logs for each of the six drill holes 

are shown in figure 2. These lithologic well logs were compiled from 

the driller's and company geologist's descriptions of sample cuttings 

taken at the time these holes were drilled. The three major coal seams 
GEOLOGY 7 

penetrated by the drill hole were the Nos. 9, 10, and 11 coals, all of 

which are classified as bituminous. Only the No. 9 coal has economic 

value at the present time. The No. 9 coal is approximately 1.2 m 

(meters) thick; the Nos. 10 and 11 coals are each approximately 0.3 m 

thick. The driller's logs note three types ot'shale and clay: (1) fire clay, 

(2) gray shale, and (3) black shale. The shale referred to in the remainder of the present text is gray shale, unless otherwise noted. 

The lithology above the No. 11 coal is primarily shale and sandy 

shale with some sandstone string¢rs. The interval between the No. 10 

and No. 11 coals includes shale, shaly sandstone clay, and sandstone, 

but the facies distribution in this interval varies from hole to hole. 

Coal interbedded with shale overY,es the No. 10 coal in holes 2, 3, and 

6. Clay described by the drillers as fire clay underlies the No. 11 coal 

in holes 2-6, but not in hole 1. 

:u .. 'Study area 

------l 

L-, 

1 

• 

KENTUCKY 

6 • 

L---------------------_r----., 

MINE WORKINGS 

I 

I 

I 

I 

,-----------------1 ,---..., I 

I I L----...l 

I L_~ 

______ _j 

3 • 2 

• 

FIGURE I.-Location of study area and of the six drill holes with respect to the mine 

workings near Centertown, Ky. 
00 

2 3 4 5 6 EXPLANATION 0 , ___ , 0 1-::::--1 0 , ___ , 0 , _ __,..., 

0~ om ··.·.:.·.·· [D Sandstone . 

0 

t;rj 

10~ 10~ 10~ 10~ 10 i :~±z~ 10~ ~Gray shale 0 

~ 

::t:: 

Clay ~ 

--;-:;:_ Shaly sandstone 00 

(/) 20 20 20 20 20 20 Coal -

0 

a: No. 11 No. 11 > t""4 w No. 11 Limestone ~ 1-30 30 30 30 30 30 No. 11 conglomerate t;rj 

w No. 11 t""4 

~ No. 11 t""4 

t""4 No. 10 No. 10 0 z 40 40 No. 10 40 40 40 40 0 

No. 10 sn No. 10 

No. 10 -t""4 

X~~ 50 ~~ 50 50 50 50 t""4 

~~~ .... 

1- :'::-:·: ·:v:: -z ·.·:.·: 

{1~::· .· .... ;. 

~~ 0 a.. 

~~t -

00 

w 60 60 60 60 60 60 t:C 0 ·;:;~~: ·+~t". 

:~:r~ ~-·::.-

:::.·:: > ~#:;: ~~f~~ 00 No.9 ~-~~;· 

.-.·:.-: No.9 lZ - 70 +:;·.·:;f- 70 No.9 70 ~-~~ 70 70 ~~!~·:::: 70 ~ 

!?Jt~} No.9 t;rj 

No.9 80. z No.9 t-3 

80 -i :+±:q- 80-l :+~~ 80 -1:·::.:-3- 80 ..... '!!":..-': 80 c::: 

0 

~ 

~ 

~ 

FIGURE 2.-Generallithologic logs, interpreted from drill-cutting samples, for each of the six drill holes in this study. Location of the Nos. 9, 10, 

and 11 coals is indicated on each of the lithologic logs. 
INTERPRETATION USING INDIVIDUAL WELL LOGS 9 

The stratigraphic section between the No. 9 and No. 10 coals is 

about 30 m thick and consists of a clay, a shale, or a sandy shale. A 

thick shale overlies the No.9 coal in holes 1 and 6, but is nearly absent in holes 2-5. Limestone is present in holes 1 through 4 not as an 

independent rock type, but as fragments in a conglomerate whose 

matrix is composed of calcite-cemented sand (Marc Silverman, oral 

communication, 1979). This conglomerate is important because it is 

the basal conglomerate for channel-sandstone sequences. The 

presence of channel sandstones cannot readily be inferred from the 

lithologic well logs. Also, these logs do not show any obvious lateral 

correlation of lithologic units or stratigraphic features between the 

No. 9 and No. 10 coals. The lithology below the No. 9 coal is primarily 

shaly sandstone, shale, and sandy shale and there are no correlatable 

stratigraphic features in any of the drill holes below the No. 9 coal. 

INTERPRETRATION USING INDIVIDUAL WELL LOGS 

The density well logs for holes 1 through 6 are shown in figures 3 

and 4. The density well log clearly defines the low-density coals (Nos. 

9, 10, and 11) better than does any other geophysical well log. The 

range of density values for noncoallithologies is small (2.0 g/cm3 for 

some clays and shale to 2.9 g/cm3 for dense limestone), and these 

lithologies are difficult to differentiate from the density well logs 

alone. The value ranges for lithologies shown in figures 3 and 4 

emphasize this point; from the density well log alone it is difficult to 

distinguish between clay and shale, or to determine the relative 

amounts of sandstone and shale in a mixed-lithology rock strata. 

The lowest apparent density values on the well logs are for the 

Nos. 9, 10, and 11 coals. Low-density values are also associated with 

black shale, which is present above the No. 10 coal in each of the six 

drill holes. The low apparent density of the black shale is evidence 

that it contains a large amount of organic material. The No. 11 coal in 

drill hole 1 has an apparent density higher than l.S g/cm3 and is consequently interpreted as a black shale. 

A comparison of the lithologic well logs that are interpreted from 

the density well logs indicates the following about the noncoal 

lithology: 

1. There is more shale above the No. 11 coal in drill holes 1 and 6 

than in drill holes 2, 3, 4, and 5. 

2. There is more shale present between the No. 10 and No. 11 

coals in drill holes 1, 5, and 6 than is present in drill holes 2, 

3, and4. 

3. There is more shale present between the No. 10 and No.9 coals 

in drill holes 1 and 5 than in drill holes 2, 3, 4, and 6. 
HOLE 1 HOLE 2 HOLE 3 

Density, lnterpre- Density, lnterpre- Density, lnterpre-

...... 

0 

in g/cm' tation in g/cm• tation in g/cm3 tation EXPLANATION 0 12 3 12 3 12 3 tr:l 

0 0+-t 0 O+-t 0 l t On 100. ~ 

Coal ...::: 10-l f ~ 10~ 10-l \ ~ 10-F!:i- 10-l ) ~ 10-j·~~~~ 150 ;!3 ... () 

: 20 J 20 I~.· 20 4 20 1 .. = .. ·~.:t 20 ~ 20 I f 200 .,", ••• ,. ~ 1- . .~ ~ • a> Shale t:"'l 

w 30 30 -:-:-:- 30 30 30 30 ° 250 t:"'l 

~ ,,.. 0 

0 

z 40 1 l ~ 40 ~ 40 -1 ~ ~ 40 ~ 40 -1 .S ~ 40 -L.Bl- 300 ~::::::~ Li~~~~~~erate ~ t:"'l 

I-

:I: 50 J 501 50 ~ 50~":: · ... ·. 50 ! 50~·:": ....... -

00 

~ ·-· ": ·:· .~.,.~ t:O 

Q.. 60 60 60 60 ·~~.:. 60 60 :·.~~::. > ~ -~~ '7"'7 :.~;~ ~ 

10 1 ( ~ 10 ~ 10 1 ~ ~ 10 -iiiiii 10 1 r ~ 10 -E3- ~ 

tr:l 

z 

~ 

80 1 ~ ~ 80 ~ 80 -l 1 ~ 80 4<~+ 80 -l ~ 80 4 ~ c:: 

FIGURE 3.-Density well logs and lithologic interpretation of density well logs for holes 1, 2, and 3. Lithologic symbols and corresponding den· 

sit,y value ranges that were used for interpretation are shown in explanation. g/cm3

, grams per cubic centimeter. 

() 

~ 

...::: 
HOLE 4 HOLE 5 HOLE 6 

Density, lnterpre- Density, lnterpre- Density, Inter prein g/cm3 tat ion in g/cm3 tation in g/cm3 tation EXPLANATION 1 2 3 1 2 3 1 2 3 0 0 ;-----t 0 orr 0 0 100 ~ 

' ~ z "I t-3 

101 ! ~ 10~ 10 1 

t 

10 10 Coal tJ:j 

150 ~ 

~ 'i:l (/) ~ Ol tJ:j a: 20 20 20 20 :~~.:. 20 20 .£ 200 Black shale t-3 w 301 i- > 1- ·;; t-3 c: Shale ~ 

Q) 

w 0 30 30 30 30 30 0 250 Shaly sandstone z 

;~1 ~I Sandstone c:: 

00 Limestone ~ 

40 40 40 40 300 conglomerate z 

.. ! 0 

~ 

z :I: 50 

n 00; 50 { 50 50 t:l 

I < 1-

60 :+!:+ 

. 

..; a... ~ 

t:l W6Q 60 60 60 c:: 0 . .;...-:-..:.. > t"'4 

701 ~~ 70 f ;:'J 701 J I :I 70 70 ~ tJ:j 

t"'4 

t"'4 

~J t"'4 801 ~ ~ 80 1 Z'-!:~ 80 1 80 80 0 

0 • • .l.":""..:..· 00 

FIGURE 4.-Density well logs and lithologic interpretation of density well logs for holes 4, 5, and 6. Lithologic symbols and corresponding density value ranges that were used for interpretation are shown in explanation. g/cm3, grams per cubic centimeter. ....., 

...... 
12 GEOPHYSICAL WELL LOGS, ILLINOIS BASIN, KENTUCKY 

The sandstone-shale facies can be defined more completely from 

neutron and resistivity well logs, which will be discussed later. 

The neutron well logs for holes 1 through 6 are shown in figures 5 

and 6. The neutron well log is primarily an indicator of the amount of 

hydrogen in hydrocarbons and water in the rock strata. A variation 

in porosity of the rocks is accompanied by a variation in water content and a corresponding inverse variation in the neutron well-log 

response. Clays and shales have a higher porosity than sandstones in 

this lithologic sequence, whereas limestone has a lower porosity than 

sandstone. Coal has the lowest neutron response seen in the neutron 

well logs in holes 4 and 5. The broad dynamic range of values of the 

neutron well-log record makes it particularly useful for determining 

the relative concentration of individual (noncoal) lithologic components such as sandstone, clay, and shale in a rock unit. 

Interpretation of the neutron well logs shows more variability in 

the sand-to-shale ratio than is indicated on the driller's well logs. The 

well-log response value ranges that were chosen identify the coal 

layers with the following exceptions: (1) the No. 11 coal in drill hole 1 

has the neutron response of a shale, and (2) a clay layer at a depth of 

43 m on the driller's well log in drill hole 5 is interpreted as a coal on 

the neutron well log. 

A low-porosity zone that is interpreted as a limestone conglomerate 

is present in drill holes 2, 3, 4, 5, and 6 at depths of 51, 59, 48, 58, and 

50 m, respectively. A low-porosity zone is also present above the 

No. 9 coal in drill holes 2, 3, and 5 at depths of 66, 73, and 7 4 m, 

respectively. The neutron well logs show that the porosity steadily increases above these limestone conglomerates, and indicates that the 

low-porosity limestone conglomerate may be the base of a finingupward channel sequence. The lower channel sequence is absent in 

drill holes 1, 4, and 6. The upper channel sequence is not interpreted 

in drill hole 1; however, there is an indication of a low-porosity zone at 

a depth of 46 m in this drill hole. 

A sandy shale that is not clearly defined on the driller's well logs is 

present between the No. 10 and No. 11 coals in drill holes 1, 4, and 6 

in the depth intervals from 27 to 33 m, from 28 to 34 m, and from 34 

to 39m, respectively. This sandy shale may also be present in drill 

holes 2 and 5 (in the depth intervals of from 31 to 34m, and 38 to 

42 m, respectively), but the sandy shale in these drill holes has a 

higher apparent porosity (more shale) than does the same layer in 

drill holes 1, 4, and 6. 

The 16-inch normal resistivity measurement is one of the best 

geophysical well logs for defining the relative amounts of the main 

lithologic constituents (other than coal) in a shallow sedimentary environment. Daniels and others (1977) showed the nearly linear relationship between increasing clay content and decreasing resistivity 
INTERPRETATION USING INDIVIDUAL WELL LOGS 13 

for samples taken from a shallow sedimentary uranium deposit in 

south Texas. Limestone, or limestone conglomerate, has a relatively 

high resistivity. The apparent resistivity of thin coal seams is often 

less than the apparent resistivity of limestone conglomerate or 

limestone. 

The apparent resistivity of the coals is generally less than the 

resistivity of the limestone conglomerate; therefore, the highresistivity coals are difficult to distinguish from the limestone conglomerates by use of the resistivity log alone. Smith (1967) also noted 

this problem in his investigations. The thin coal beds also yield apparent resistivity values that are much lower than the true resistivity 

of the coal. The coal layers penetrated by drill holes 1 through 6 are 

interpreted as sandstone, sandy shale, or limestone conglomerate, 

depending upon the amount of ash contained in the coal and the 

thickness of the coal seam. 

The resistivity well logs, and corresponding lithologic interpretations, for holes 1 through 6 are shown in figures 7 and 8. A high 

resistivity zone, that is interpreted as a limestone conglomerate, is 

present in drill holes 1, 2, 3, 4, and 6 at depths of 46, 52, 59, 49, and 

52 m, respectively. The resistivity well logs show that the resistivity 

values steadily decrease above these limestone conglomerates in drill 

holes 1, 2, and 4. The lower resistivity is caused by an increasing 

amount of clay-size material that results in an increase in porosity. 

The lack of interpretive agreement between the neutron and resistivity well logs for these high-resistivity, low-porosity zones may be 

caused by differences in the lateral distances into the formation that 

the two well logging tools investigate. A high-resistivity zone is also 

present above the No.9 coal in drill holes 2, 3, and 5 at depths of 66, 

73, and 74 m, respectively. This high-resistivity layer is located at the 

same depth as the base of the fining-upward channel sequence seen 

on the neutron welf logs in figures 5 and 6. 

The gamma-ray probe measures the natural gamma radiation, 

primarily from potassium-40 in shale and from uranium-series 

istopes in black shale and sandstone. The organic matter in black 

shale provides a reducing environment that is conducive to the 

accumulation of uranium were a source of uranium present during 

deposition or later. In the shallow sedimentary environment of this 

study, the general order of gamma radiation, from highest to lowest, 

is as follows: (1) black shales, (2) shales and clays, (3) sandstone, (4) 

coal, and (5) limestone. However, coal can yield a higher gammaradiation count if it contains uranium, or a high percentage of clay 

(low-grade coal). 

Figures 9 and 10 show the gamma-ray well-log response and interpretation of the gamma-ray well logs for holes 1 through 6. In all 

these logs, the coal is characterized by its low gamma-ray count, with 
Neutron, 

in c/s 

HOLE 

1600 9600 

0 

10 

(/) 

a: 20 L.U 

1-

L.U 30 

~ 

z 40 

J: 50 

ln. 

L.U 60 

0 

70 

80 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

80 

Neutron, 

in c/s 

HOLE 2 

1600 9600 

0 

10 

20 

30 

40 

50 

60 

70 

80 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

80 

Neutron, 

in c/s 

HOLE 3 

1600 9600 

0 

10 

20 

30 

40 

50 

60 

70 

80 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

80 

EXPLANATION 

<1.1 ..... 

tJ 

2000 

3000 

4000 

.!: 5000 

c· 

0 

-5 6000 Q) 

z 

7000 

8000 

Coal 

Shale 

Sandstone 

and shale 

Shaly 

sandstone 

Sandstone 

Limestone 

9000 +:•:•:+ conglomerate 

FIGURE 5.-Neutron-neutron well logs and lithologic interpretation of neutron-neutron well logs for 'holes 1, 2, and 3. Lithologic symbols and 

corresponding density value ranges that were used for interpretation are shown in explanation. c/s, counts per second. 

~ 

~ 

0 

t.%j 

0 

1-C 

::c: 

t< 

en 

0 

> r 

~ t.%j 

r 

r 

r 

0 

0 

sn 

-r 

r 

z 

0 

-

en 

C:l 

> en 

_z 

~ 

t.%j 

2: 

1-3 

c:: 

(j 

~ 

t< 
Neutron, 

in c/s 

HOLE 4 

1600 9600 

0 

10 

en 

a: 20 

w 

1-

LU 30 

~ 

z40 

50 J: 

1-

a.. 60 LU 

0 

70 

80 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

80 

Neutron, 

in c/s 

HOLE 5 

1600 9600 0 +--...____"--'--+ 

10 

20 

30 

40 

50 

60 

70 

80 

90 L.._ __ _J 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

Neutron, 

in c/s 

HOLE 6 

1600 9600 

0 

10 

20 

30 

40 

50 

60 

70 

80 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

80 

EXPLANATION 

"' u 

2000 

3000 

4000 

.!: 5000 

c 

0 

~ 6000 Q) 

z 

7000 

8000 

9000 

Coal 

Shale 

Sandstone 

and shale 

Shaly 

sandstone 

Sandstone 

Limestone 

conglomerate 

FIGURE G.-Neutron-neutron well logs and lithologic interpretation of neutron-neutron well logs for holes 4, 5, and 6. Lithologic symbols and 

corresponding density valul ranges that were used for interpretation are shown in explanation. c/s, counts per second. 

z 

~ ~ 

~ 

~ 

trl 

~ ~ 

8 

z 

c::: 

00 

z 

0 

z 

tj 

< 8 

c::: 

> t"'4 

~ t"'4 

t"'4 

t"'4 

0 

0 

00 

...... 

01 
HOLE 

Resistivity, 

in ohm meters 

0 300 600 o~~.___.-;. 

10 

(f) 

a:20 

IW30 

~ 

Z40 

I 50 

1-

a.. 60 w 

Cl 

70 

80 u._~~---" 

Interpretation 

10 

20 

30 

40 

50 

60 

70 

80 

HOLE 2 

\. Resistivity, 

in ohm meters 

0 300 600 

0 

10 

20 

30 

40 

50 

60 

70 

80 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

80 

HOLE 3 

Resistivity, 

in ohm meters 

0 300 600 0 

10 

20 

30 

40 

50 

60 

70 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

0 

50 

100 

150 

"' 200 (D 

~ 250 

] 300 0 

.s 350 

i 

:~ 400 

-~ 450 a: 

500 

550 

600 

650 

700 

EXPLANATION 

Clay shale 

..... Shale and sandstone 

:±*~ Shaly sandstone 

Jsandstone 

ml~·~ 

~=~=~::·. 

Sandstone and limestone 

conglomerate 

Limestone 

conglomerate 

FIGURE 7.-Resistivity well logs and lithologic interpretation for 16-inch normal resistivity well logs for holes 1, 2, and 3. Lithologic symbols 

and corresponding velocity value ranges that were used for interpretation are shown in explanation. 

......... 

~ 

0 

trl 

0 

1-d 

::r: 

~ 

r.n 

-

0 

> t"" 

~ trl 

t"" 

t"" 

t"" 

0 

0 

sn 

-t"" 

t"" 

z 

0 

00 

ttl 

> r.n 

~ 

~ 

trl 

z 

1-3 

c 

0 

~ 

~ 
HOLE 4 HOLE 5 HOLE 6 

Resistivity, lnterpre- Resistivity, lnterpre- Resistivity, lnterprein ohm meters tation in ohm meters tation in ohm meters tation EXPLANATION 

0 300 600 0 300 600 0 300 600 - 0 0 t---t 0 0 t--t 0 0 t---t 0 z 

~ 

50 Clay shale tr:l 

::0 10 1 ~ 101 ~ 10 -j ~ 101 ~ 101\ ~ 10 ~ 100 ·-t>:+ Shale and sandstone ~ 

:20 t 20 I 20 20 I 20 I 20 1

. 150 

w "' 200 ~~ \HB· Sandstone 

::~ .. :,:·"""' and ~ :j t- _ a> ::::: limestone 0 -- ~ 250 •••••• conglomerate z w 30 30 ·; 30 30 30 30 E :::::: C::: 

~ : ~ 3oo :::::: en 

~ 350 :::::: z 

z4o-lf ~ 4o ~ 4o-R ~ 4o~ 4o11 ~ 4om ·:::_ :::::: o 

J: 50 ~ 50 1·: ·-· 50 ~ 501 50 r 50 I'•• i : 500 ~~I~~ :•:•:• Um"'""' conglomerate ~ ..... 1- i\'~ • • • t;j 

: 60 60 60 60 :::~= 60 60 . ~~+ 550 ~~~~~~ ~ 

0 ~···~· 600 :::::: $l 70 70 ,,, 70 70 ... :;:~ 70 70 650 :::::: ~ 

:·:·:· t"" 700 •••••• t"" 

BOil ~ 80 sH· 80-l\.. ~ 80~]- 80-l/ ~ SO.§!} g 

FIGURE B.-Resistivity well logs and lithologic interpretation for 16-inch normal resistivity well logs for holes 4, 5, and 6. Lithologic symbols 

and corresponding velocity value ranges that were used for interpretation are shown in explanation. 

en 

...... 

'I 
HOLE 1 HOLE 2 HOLE 3 

Gamma ray, Inter pre- Gamma ray, Inter pre- Gamma ray, Inter prein c/s tat ion in c/s tat ion in c/s tation EXPLANATION 1200 0 1200 0 1200 0~ 0 0+--+ 0 +n-ot Limestone 

conglomerate 

~ ~ 10 1:+±+~ 200 Sandstone 10-l ;. ~ 10-§3- 10-l ~ 1- 10~ 10 i 

Shaly 

400 sandstone (/) Shale a: 20 20 20 20 20 20 ~ w <.> 600 .: 1-

> w 30 30 30 30 30 30 ~ 800 .., ~ E 

~ 1000 z 40 40 40 40 40 40 (!) Black shale 

1200 

('=l WI 50 tJ :i 50 

t ~~ ·+~+ 1400 

~-

60 60 60 60 60 -~~. w 1600 

.·:~:: 0 //// ... ··;,_=i-;,.' -· 70 ..• :';7. 70 70 ••• 70 70 .:!~!: 

80 -r-1- 80i r ~ 80 -E3- '-----' 

FIGURE 9.-Gamma-ray well logs and lithologic interpretation of gamma-ray well logs for holes 1, 2, and 3. Lithologic symbols and corresponding density value ranges that were used for interpretation are shown in explanation. c/s, counts per second. 

..... 

()) 

0 

t_:l:j 

0 

'i:l 

:I: 

...( 

00· 

-

{j 

> t"' 

~ t_:l:j 

t"' 

t"' 

t"' 

0 

0 

rn 

-t"' 

t"' 

-z 

0 

-

00 

t:D 

> 00 

~ -

~ t_:l:j 

z 

1-3 

c::: 

{j 

~ 

...( 
HOLE 4 HOLE 5 HOLE 6 

Gamma ray, lnterpre- Gamma ray, lnterpre- Gamma ray, lnterprein c/s tation in c/s tation in c/s tation EXPLANATION 1200 0 1200 0 1200 

Ot--t 0 I > I Ot--t 0 0-t=:-:-t 0 ~ Limestone 

conglomerate 

200 Sandstone 10 -L-J ~ 10 ·L:'~~ 10 ~ l ~ 10~ 101 ; ~ 10~ Shaly 

400 sandstone en Shale a: 20 20 20 20 20 20 

w "' <> 600 

f- .!: 

>. w 30 30 30 30 30 30 ~ 800 

t 

(Q 

E 

~ 1000 40 40 40 40 40 (!) Black shale 

1200 

~~~ ~~ 50 

t ~I "I ~{ ... 1400 

: ,:: 0..60 60 60 <: 60 60 ~:~ w 1600 

~· 

0 

70 70 70 :t:· 70 70 

80~ i ~ 80~ 80~ ..:; ~ 80~ 80 ~ > ~ 80~ 

FIGURE 10.-Gamma-ray well logs and lithologic interpretation for gamma-ray well logs for holes 4, 5, and 6. Lithologic symbols ~nd 

corresponding density value ranges that were used for interpretation are shown in explanation. c/s, counts per second. 

-

z 

1-3 

t::rj 

~ 

'"C 

~ 

t::rj 

1-3 

> 1-3 

-

0 

z 

c:: 

00 

-z 

0 

-

z 

t::! 

-

< -t::! 

c::: 

> t-t 

~ t::rj 

t-t 

t-t 

t-t 

0 

0 

00 

cc """'"' 
20 GEOPHYSICAL WELL LOGS, ILLINOIS BASIN, KENTUCKY 

a high gamma-ray count rate recorded for the overlying black shale. 

This is particularly true for the No. 10 coal. A pure limestone should 

be characterized by a near-zero gamma-ray response; limestones that 

are defined on the driller's logs have a low, but nonzero, gamma-ray 

count rate. Because the gamma-ray count rate is higher for the 

limestones than for the coal layers, the limestones must contain impurities. 

The gamma-ray well-log response indicates the following concerning the shale content in the drill holes: 

1. There is more shale above the No. 11 coal in drill holes 1, 2, and 

5 than in drill holes 3, 4, and 6. 

2. There is more shale present between the No. 10 and No. 11 

coals in drill holes 2, 5, and 6 than is present in drill holes 1, 

3, and4. 

3. There is more shale present between the No.9 and No. 10 coals 

in drill holes 1, 4, and 6 than in drill holes 2, 3, and 5. 

The gamma-ray response below the No. 11 coal is high in each of the 

drill holes. This high response is interpreted as being caused by black 

shale and is located at depths of 27, 31, 34, 28, 38, and 34m, in drill 

holes 1, 2, 3, 4, 5, and 6, respectively. Other high gamma-ray response 

values are in each of the drill holes below the No. 10 coal and above 

the No. 9 coal. Only in the No. 9 coal is the black shale layer apparently located above the coal. 

The induced-polarization well logs and interpretations are shown in 

figures 11 and 12 for each of the six drill holes. Of all of the well-log 

responses, the IP well log is the most difficult to interpret individually. The IP response in shallow sedimentary environments is 

primarily affected by the presence of pyrite and clays with a high 

cation-exchange capacity (montmorillonite or illite). Therefore, if the 

IP log is to be interpreted with minimum ambiguity, the relative 

sand and shale content must first be established. Later in 'this paper 

it will be shown that the IP well log-can be used to determine certain 

mineralogic components when the IP log is interpreted simultaneously with other types of well-log responses. 

The interpretation procedure that was found to work best for indi 

vidual geophysical well logs in the shallow sedimentary coal environment of this study includes the following: 

1. Determination and depth correction of the coal seams on the 

driller's well logs with the density well logs. 
INTERPRETATION USING INDIVIDUAL WELL LOGS 21 

2. Refinement of the determination of sandstone and shale shown 

on the driller's well logs with the neutron, gamma-ray, and 

16-inch normal resistivity well logs. 

3. Determination of the depths and relative amounts of limestone 

conglomerate from the resistivity well log. 

4. Determination of the depth and relative amounts of black shale 

and fire clay from the gamma-ray and IP well logs. 

5. Determination of pyrite-bearing zones within the sandstone 

and shale from the IP well logs. 

The following conclusions can be drawn from the preceding interpretation of individual well logs in a coal depositional environment: 

1. The density well log is the only well log that clearly and consistently defines the coal seams. However, organic black 

shale can yield a low-density response on the density well log 

and can be misinterpreted as a coal layer. 

2. Limestone conglomerate produces a high neutron response and 

a high resistivity response. But a very thin limestone conglomerate will not be detected by the resistivity well log and 

a well-cemented sandstone (calcite or silica matrix cement) 

can also yield a high neutron and a high resistivity well-log 

response. Coal can also be misinterpreted as limestone conglomerate from the resistivity well'log. 

3. Shale can generally be identified from the gamma-ray well 

log. However, variations in the potassium content of the 

shale can lead to false interpretations of the amount of shale 

in the geologic section. 

Comparison of the interpretations for the six different types of well 

logs reveals the inadequacy of individual geophysical well logs for 

interpreting lithology. (The lithologic well logs interpreted from the 

individual well logs are shown in Appendix A for each hole.) Different 

types of well logs often yield different geologic interpretations. To 

overcome this limitation, the interpreter must apply his knowledge of 

geology and of the physical properties of the rocks to all of the 

available information, and make a final composite interpretation of 

the well-log data. Thus, the interpreter must recognize well-log 

response values and combinations of well-log response values from 

the various well-log responses that are indicative of certain geologic 

media. 

A refined interpretation for each well can be achieved by comparing 

the interpreted lithology and mineralogy for each individual type of 

well log (driller's, neutron, gamma-ray, resistivity, and IP well logs). 
HOLE 1 HOLE 2 HOLE 3 

~ 

~ 

IP, lnterpre- IP, lnterpre- IP, lnterprein percent tation in percent tation in percent tation EXPLANATION 0 

01234 01234 01234 tz:l 0 0 

-t--t 0 ~ 0 0 0 Limestone 0 conglomerate =:g 

Sandstone 

10 1 \._ ~ 10 ~ 10 10 10 10 ~ 

f 50 Shale 0 00 > a: 20 20 20 20 20 20 High cation- :;;; 

w · exchange clay <:: 

1- 100 ·/iE ~ 

" 

w " 

{ 

~ ao I 3o 3o 

...... 

3o 3o ... 

~ :·l!l' 

::~1l! Pyrite 

'""""""· 

in s ~ Q) ·:·:~11 0 

z 40 1 c-- ~ 4o ~ 4o 1 > ~ 4o ~ 40 1 ~ ~ 40 ~ ~ 150 ::: sn 

g; ::: F 

1- :I: 50 ~ 501 

::::::· 50 t 501 ...... 50~ 501·~:~:~ ...... 200 ;~; • Pyrite in shale 

0 

~ - ~ ~ 00 60 60 :::::: 60 60 • ..:::: 60 60 C::t w ....... ••• > 0 250 ::: 00 

10 10 10 70 = 10 10 ::: ~z :: ~ 300 •• tz:l 

8011 ~ 80~ soi? ~ so~ so.J ~ so-I...._J ~ 

FIGURE 11.-Induced polarization (IP) well logs and lithologic interpretation for IP well logs for holes 1, 2, and 3. Lithologic symbols and corresponding IP value ranges that were used for interpretation are shown in explanation. 

c:: 

("') 

~ 
HOLE 4 

IP, 

in percent 

0 1 2 3 4 o+-~ 

10 

(/) 

a: 20 

w 

1-

w 30 

:::2: 

z 40 

-50 

I 

1-

a.. 60 

w 

0 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

80 

HOLE 5 

IP, 

in percent 

0 1 2 3 4 

0 

10 

20 

30 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

HOLE 6 

IP, 

in percent 

0 1 2 3 4 0 +--..__...__.--+ 

10 

20 

30 

40 

50 

60 

Interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

EXPLANATION 

0 

50 

100 

1:: 

Q) 

~ 

~ 150 

·= 9,:. 

200 

250 

Limestone 

conglomerate 

Sandstone 

Shale 

High cationexchange clay 

Pyrite in 

sandstone 

Pyrite in shale 

FIGURE 12.-lnduced polarization (IP) well logs and lithologic interpretation for IP well logs for holes 4, 5, and 6. Lithologic symbols and corresponding IP value ranges that were used for interpretation are shown in explanation. 

1-4 

~ ~ ~ 

tt:l 

1-4 

~ 0 

z 

c:: 

00 

z 

0 

z 

t:l 

1-4 

<: 

8 

c:: 

> t-t 

~ t-t 

t-t 

t-t 

0 

0 

00 

t...:l 

~ 
gr/ip, 

in c/s 

percent 

0 2000 4000 

0 ~ 

10 

(/) 20 

a: 

w 

1-30 

w 

~ 

\. .. / ,I 

\. 

r.·:;. 

.. ~ 

t 

J 

z40 1( ~· 

;!:';: .:. 

\ 

~ 

:x:50 

1-

Cl... 

w60 

0 

l 

~l .... . ·- ... 

··,~\' .. 

70 -1<, .. 

~ 

\.' 80 ' ( 

ip/dc, 

in percent 

g/cm3 

0.0 1.0 2.0 0 +--'---L-'--+ 

10 

,J_ , .. 

~ 

~ 30\ 

'( 

'1 .. :. ®\ 

::r 

70-l \ 

~ 

( 80 

:,,~ .... 

nn x rs, 

in c/s x 

ohm meters 

0 500,000 0+--'--~-~~ 

::~) ( 30 

.,_ . 

./, 40-l··~· ....... 

50 

60 

-_-:.., 

s· .. (' 

'? 

,::':( .. /· 

70-1 

r· 80 

·.-:.. ... 

nn/gr 

unitless 

0 50 100 

0 

10 

l 

20-1) 

t ~~~ 

(' 

40-lt 

<. 

. ..,. 

~-1{ 

} 

so<J 

··~. 

m-1\. {' 

80 ' f 

Composite 

interpretation 

10 

20 

30 

40 

50 

60 

70 

80 

EXPlANATION 

Coal 

Black shale 

Limestone 

conglomerate 

Sandstone 

Percent Sandstone 75 

Shale 25 

Sandstone 50 

Shale 50 

Sandstone 25 

Shale 75 

Shale (high 

cation exchange) 

Shale (low 

cation exchange) 

FIGURE 13.-Product and ratio well logs, and composite lithologic interpretation for drill hole 1. Neutron, induced polarization, resistivity, 

density, and gamma-ray well logs are represented by the symbols nn, ip, res, de, and gr, respectively. c/s, counts per second; g/cm3

, grams 

per cubic centimeter. 

t-:) 

~ 

0 

tr:l 

0 

'"0 

:I: 

><: 

00 

(j 

-

> t""' 

:E 

tr:l 

t""' 

t""' 

t""' 

0 

0 

sn 

t=: 

t""' 

-

z 

0 

-

00 

t:C 

> 00 

::z -

~ 

tr:l 

z 

~ 

c::: 

(j 

~ 

><: 
COMPOSITE WELL-LOG INTERPRETATION 25 

COMPOSITE WELL-LOG INTERPRETATION 

To overcome the ambiguity associated with individual well-log 

interpretation, simultaneous interpretation of several combinations 

of individual well logs is advantageous. Composite interpretation 

utilizes combinations of physical properties that characterize a particular lithology or mineralogy, and can be implemented by choosing 

response values from two or more well logs and cross-plotting these 

response values. Good examples of cross-plotting have been given by 

Keys (1979). The primary disadvantage of this technique is the difficulty of relating cross-plotted values to depth intervals on the 

original well logs. 

An alternative to the cross-plotting technique is to interpret product and ratio values of two or more well logs. Product values can be 

used for interpretation when the values of two or more well logs increase or decrease in response to a particular lithology. Ratio values 

can be used when the values of one well log increase and the values of 

another well log decrease in response to the physical properties 

associated with a particular lithology. The interpretation of prod1:1ct 

and ratio well logs can }:>e facilitated by the use of a digital computer. 

Figure 13 illustrates the use of product and ratio well logs for interpreting the lithology for drill hole 1. Product and ratio well logs for 

holes 2 through 6 are shown in ''Appendix B.'' The value ranges and 

order of interpretation that were used to obtain the final lithologic 

interpretation are listed in table 2. 

The order of interpretation is important because once a lithology 

has been assigned to a depth interval, the computer program does not 

consider that depth interval in future lithologic assignments. 

Lithologies that are the easiest to identify must be interpreted first. 

The low gamma-ray, low-density, and high IP response of coal 

enables the effective use of the gamma-ray/induced polarization and 

induced polarization/density logs for identifying coal and black shale. 

The high IP response is caused by the presence of pyrite in the strong 

reducing environment associated with coal and black shale. 

Limestone conglomerate and sandstone both have high neutron 

responses and low gamma-ray responses. However, limestone conglomerate has a higher neutron-resistivity product-log response than 

does sandstone. These responses are due to the fact that although 

both limestone conglomerate and sandstone contain relatively low 

concentrations of gamma-ray emitting minerals (such as kaolinite), 

they both have low porosities, with the high degree of cementation in 

limestone conglomerate giving it a slightly higher neutron-toresistivity product log response than sandstone. 

Other than coal, .black shale, and limestone conglomerate, the sorting of detrital sedi:fitentary rocks varies greatly, ranging from shale 
26 GEOPHYSICAL WELL LOGS, ILLINOIS BASIN, KENTUCKY 

TABLE 2.-Composite well-log interpretation for individual and combined lithologies 

using product and ratio well logs 

(The neutron, induced polarization, resistivity, density, and gamma-ray well logs are represented by the symbols 

nn, ip, res, de, and gr, respectively. gr/ip = counts per second/percent; ip/dc = percent/grams per cubic centimeter; nn x res = counts per second x ohm meters; nn/gr is unitless. sh, shale; Is cong, limestone conglomerate; 

ss, sandstone; pet, percent) 

Order of Value range 

interpre- Product or of product or 

tat ion Lithology. ratio well log ratio well log 

Coal------------- gr/ip 0-130 

ip/dc 0.58-1.5 

2 Black sh--------- gr/ip 130-500 

ip/dc 0.58-1.5 

3 ls cong---------- nn x res 2,000,000-5,000,000 

nn/gr 20-5,000 

4 ss--------------- nn x res 675,000-2,000,000 

nn/gr 20-5,000 

5 ss (75 pet), 

sh (25 pet)---- nn x res 478,000-675,000 

6 ss (50 pet), 

sh (50 pet)---- nn x res 285,000-478,000 

7 ss (25 pet), 

sh (7 5 pc t) ---- nn x res 88,000-285,000 

8 sh (high-cation)- nn x res O-R8,000 

gr/ip 0-500 

9 sh (low-cation)-- nn x res 0-88,000 

gr/ip 500-5,000 

to shaly or silty sandstone. The relative amount of shale in a sandstone can be roughly estimated by the neutron-resistivity product 

log. The lithology is interpreted as shale when the values on the 

neutron-resistivity product log are low. Varying amounts of different 

types of clay (high- and low-potassium clay) make it impossible to use 

the gamma-ray log for interpreting the amount of shale in a sandy 

shale. When the rock consists only of shale, the ratio of the gammaray well log to the induced-polarization well log can be used to determine the type of clay in the shale. High cation-exchange capacity clay 

minerals (illite and montmorillonite) have low gamma-ray responses 

(low potassium-40 content), and low cation-exchange capacity clay 

minerals (such as kaolinite) have high gamma-ray response values. 

The composite lithologic well logs for holes 1 through 6 are shown 

in figure 14. Some lithologic details indicated by these logs include 

the following: 
Hole 1 

composite 

0 

10 

(/) 20 

a: 

w 

lw30 

:::!! 

Z40 

:I: 50 

1-

a.. 

w 

0 60 

70 

80 

No. 11 

No. 10 

No.9 

Hole 2 

composite 

0 

10 

20 

No. 11 

30 

40 No. 10 

50 

60 

70 No.9 

80 

Hole 3 

composite 

0 

10 

20 

30 

40 

No. 10 

50 

60 

70 

No.9 

80 

Hole 4 

composite 

0 

10 

20 

No. 11 

30 

40 No.10 

50 

60 

No.9 

70 

80 

Hole 5 

composite 

0 

10 

20 

30 

No. 11 

40 

No.10 

50 

60 

70 

No.9 

80 

Hole 6 

composite 

0 

10 

20 

30 No. 11 

40 

No. 10 

50 

60 

70 No.9 

80 

FIGURE 14.-Composite lithologic interpretation for drill holes 1 through 6. 

EXPLANATION 

Coal 

Black shale 

Limestone 

conglomerate 

Sandstone 

Percent 

Sandstone 75 

Shale 25 

Sandstone 50 

Shale 50 

Sandstone 25 

Shale 75 

Shale (high cation exchange) 

Shale (low 

cation exchange) 

(") 

0 

== ~ 

0 

00 

-

1-3 

t.rl 

~ t"" 

t"" 

~ 

0 

0 

z 

~ ~ 

~ 

;; 

1-3 

:> 

1-3 

-

0 

z 

t-o:) 

-.:] 
28 GEOPHYSICAL WELL LOGS, ILLINOIS BASIN, KENTUCKY 

1. There is a dominance of high-potassium clay above the No. 11 

coal. 

2. With the exception of hole 6, there is a dominance of highpotassium clay between the No. 11 and No. 10 coals. 

3. There are two limestone conglomerates in drill holes 2 and 3 

between the No. 9 and No. 10 coals, but there is only one 

limestone conglomerate in drill holes 1, 4, and 6 between 

the No. 9 and No. 10 coals. 

4. Sandstone is the dominant lithology between the No. 9 and 

No. 10 coals in drill hole 5. 

The composite well logs indicate considerable lateral facies changes 

over a small area in the interval between the No. 9 and No. 10 coals. 

With th~ exception of hole 5, there is an inverse correlation between 

the presence of limestone conglomerates near a drill hole and the 

amount of shale in the geologic section. There are two cycles of finingupward sedimentation recorded in drill holes 2 and 3. Upward fining 

generally characterizes the stratigraphic interval between the No. 9 

and No. 10 coals in drill holes 1, 4, and 6, whereas the same interval in 

drill hole 5 is a relatively uniform sandstone. 

The lateral facies changes occur in intervals of nearly uniform 

thickness between drill holes. This fact implies that the area was 

slowly subsiding· during the time interval of deposition of the 

sediments between the No. 9 and No. 10 coals. A stream channel was 

cut into the sediments near drill holes 2 and 3 shortly after the No. 9 

coal was deposited. Strata penetrated by drill holes 1, 4, and 6 indicate similar steady deposition above the No.9 coal. Another channel 

was cut later (as indicated by the limestone conglomerate) near all of 

the drill holes except drill hole 5. 

CONCLUSIONS 

The interpretation of lithologies from geophysical well logs is 

necessarily subjective. This is particularly true when individual 

types of geophysical well logs are interpreted without regard for the 

response of other types of well logs. Adequate interpretations must 

rely on combinations of well-log data that best characterize each individual lithology. The final interpretation must also agree with the 

available geologic data (that is, core descriptions, driller's logs). In 

fact, a good geophysical well-log interpretation is one that adds 

detailed information to the geologic information obtained from rock 

samples taken from the well. The study presented in this paper illustrates that only a limited lithologic interpretation can be made when 
REFERENCES CITED 29 

only one type of well log is used for the interpretation. A more 

consistent and accurate interpretation of the geologic section can be 

made by interpreting the product and ratio values of more than one 

type of well log. 

REFERENCES CITED 

Bond, L. 0., Alger, R. P., and Schmidt, A. W., 1969, Well log applications in coal mining and rock mechanics: American Institute of Mining, Metallurgical, and 

Petroleum Engineers, preprint number 69-F -13, 11 p. 

Daniels, J. J., Scott, J. H., Blackman, P. D., and Starkey, H. S., 1977, Borehole 

geophysical investigations in the south Texas uranium district: U.S. Geological 

Survey Journal of Research, v. 5, no. 3, p. 343-357. 

Keys, W. S., 1979, Borehole geophysics in igneous and metamorphic r,ocks: SPWLA 

[Society of Professional Well Log Analysts] 20th Annual Logging Symposium 

Transactions, p. 001-0026. 

Kowalski, John, and Fertl, W. H., 1976, Application of geophysical well logging to 

coal mining operation: Houston, Tex., Dresser Atlas, Technical Memorandum, v. 

7, no. 8,11 p. 

Reeves, D. R., 1976, Development of slimline logging systems for coal and mineral 

exploration: SPWLA 17th Annual Logging Symposium Transactions, p. 

KK1-KK16. 

Robbins, S. L., 1979, Density determinations from borehole gravity data from a 

· shallow lignite zone within the Denver Formation near Watkins, Colorado: 

SPWLA 20th Annual Logging Symposium Transactions, p. JJ1-JJ19. 

Scott, J. H., 1977, Borehole compensation algorithms for a small diameter, dualdetector density well-logging probe: SPWLA 18th Annual Logging Symposium 

Transactions, p. S1-S17. 

Smith , G. E., 1967, Pennsylvanian cross sections in western Kentucky; Coals of the 

Lower Carbondale Formation, Part I: Kentucky Geological Survey Report bf Investigations 6,.p. 7-14 

Weltz, L. S., 1976, Log evaluation of sub-bituminous coals in Magallanes, Chile: 

SPWLA 17th Annual Logging Symposium Transactions, p. K1-K33. 

APPENDIX A 

Lithology interpreted from the geophysical well logs for each hole 
DRILLERS LOG 

10 

CJl 20 

a: 

w 

1-

w 30 

::?: 

z 40 

J: 50 1-

a.. 

w 

0 60 

70 

80 

DENSITY 

0 

10 

20 

30 

40 

50 

60 

70 

80 

NEUTRON RESISTIVITY 

0 0 

10 10 

20 20 

30 30 

40 40 

50 50 

60 60 

70 70 

80 80 

GAMMA RAY 

0 0 

10 10 

20 20 

30 30 

40 40 

50 50 

60 60 

70 70 

80 80 

IP EXPLANATION 

Sandstone 

Shale 

Clay 

Shaly 

sandstone 

Coal 

Black shale 

Shale 

(high cationexchange) 

Pyrite 

Limestone 

conglomerate 

FIGURE Al.-Lithology interpreted from density, neutron, resistivity, gamma-ray, and induced polarization (IP) well logs for drill hole 1. 

Clj 

~ 

0 

trj 

0 

'"0 

::c: 

to<: 

r:n 

0 

> t"-4 

~ trj 

t"-4 

t"-4 

s 

0 

sn 

-t"-4 

t"-4 

z 

0 

-

r:n 

t:l:l 

> r:n 

~ 

~ 

trj 

z 

t-3 

c:: 

C':l 

~ 

to<: 
DRILLERS LOG DENSITY NEUTRON RESISTIVITY GAMMA RAY IP EXPLANATION 

O+=t Ot---t ot---t 

on ormrr 0 

I I HH Sandstone 

10~ 10~ 10-1 ~ 101 t 10~ 10 I E3 Shale 

i 20~ I~~~~ Cloy 

en 20 20 20 20 20 a: 

w jti Shaly 

...... . ...... :tft sandstone 

w 30 30 30 30 30 30 

:E I I Cool 

z 40 40 40 40 40 40 

. 

Black shale 

J: 50 

~t~ ~a 

~~ ~-....... ······· ~~ . ...... I Shol• ...... (high cation- T.~.!' ::-:t. Q.. 

60 ·:~;~ •• ::o::. exchange) 

w 60 60 .• +J: 60 .~T~ 

0 .~..;. ... · ·····:· 

~ 70~ 701 

t······t . .. Pynte 

70 70 70 70 

. 

••• Limestone 

conglomerate 

t"i j-·~'i ~q~ ll il ~ < .. '":. ~ 80 ·~~i 80 ~-;.;,;. 80 .: 80 

. 

80 80 -!! 

FIGURE A2.-Lithology interpreted from density, neutron, resistivity, gamma-ray, and induced polarization (IP) well logs for drill hole 2. 

;J> 

'"C 

'"C 

trj 

z 

tj 

-:>< 

;J> 

~ 

~ 
DRILLERS LOG 

0 

10 

(/) 20 

a: 

w 

fw 30 

::::!: 

Z4o 

J: 

f- 50 

n. 

w 

0 60 

70 

80 

DENSITY 

0 

10 

20 

30 

40 

-:~~1·1 

so, .. ,,., ... , 

::.~~f:l 

60' :;:t: 

70 

80 

.~'":"~ 

.... -:-. 

NEUTRON 

0 

10 

20 

30 

40 

50 

60 

70 

80 

RESISTIVITY 

0 

10 

20 

30 

40 

50 

60 

70 

GAMMA RAY 

0 0 

10 10 

20 20 

30 30 

40 40 

50 50 

60 60 

70 70 

80 

IP EXPLANATION 

Sandstone 

Shale 

Clay 

Shaly 

sandstone 

Coal 

Black shale 

Shale 

(high cationexchange) 

Pyrite 

Limestone 

conglomerate 

FIGURE A3.-Lithology interpreted from density, neutron, resistivity, gamma-ray, and induced polarization (IP) well logs for drill hole 3. 

Clj 

~-

0 

tz:j 

0 

~ 

::I: 

~ 

CJJ. 

-

n 

> t"'4 

$! 

tz:j 

t'"4 

t"'4 

t'"4 

0 

0 

sn 

-t"'4 

t'"4 

z 

0 

-

CJJ. 

t:cl 

> CJJ. 

~ ~ 

tz:j 

~ C! 

n 

~ 

~ 
DRILLERS LOG 

10 

(/) 20 

a: 

w 

1-

w 30 

::2 

z40 

I 

1- 50 

n. 

w 

060 

70 

80 

DENSITY 

0 

10 

20 

30 

40 

50 

60 

NEUTRON RESISTIVITY 

0 0 

10 10 

20 20 

30 30 

40 40 

50 50 

60 60 

70 70 

GAMMA RAY 

0 0 

10 10 

20 20 

30 30 

40 40 

50 50 

60 60 

70 70 

80 80 

IP EXPLANATION 

Sandstone 

Shale 

Clay 

Shaly 

sandstone 

Coal 

Black shale 

Shale 

(high cationexchange) 

Pyrite 

Limestone 

conglomerate 

FIGURE A4.-Lithology interpreted from density, neutron, resistivity, gamma-ray, and induced polarization (IP) well logs for drill hole 4. 

> 'i:l 

~ z 

tj 

:;< 

> 

Clj 

01 
DRILLERS LOG 

0 1.::;~. 

·:::~·~::·: 

00 '" Iii a: 20 

w 

fw30 

:2: 

Z40 

:I: 50 

fa. 

w 60 

0 

~%~i i·E.~~~t 

~t~:~ 70 1~~ .. ~:;· ~[[{' 

80 

DENSITY 

0 

10 

20 

30 

40 

50 

60 

70 

80 

NEUTRON RESISTIVITY 

0 0 

10 10 

20 20 

30 30 

40 40 

50 50 

60 

70 

80 80 

90 

GAMMA RAY 

0 

10 

20 

30 

40 

50 

"'L,,._ 1..:;;·. 

70 ,~~~~*: 

80 

0 

10 

20 

30 

40 

50 

60 

70 

80 

IP EXPLANATION 

Sandstone 

Shale 

Clay 

Shaly 

sandstone 

Coal 

Black shale 

Shale 

(high cationexchange) 

Pyrite 

Limestone 

conglomerate 

FIGURE AS.-Lithology interpreted from density, neutron, resistivity, gamma-ray, and induced polarization (IP) well logs for drill hole 5. 

Clj 

~ 

0 

tr:l 

0 

~ 

:I: 

to<! 

00 

.... 

<1 

)> 

~ 

~ tr:l 

~ 

~ 

~ 

0 

0 

sn 

.... 

~ 

~ 

z 

0 

.... 

00 

t::tl 

)> 

00 

~ ~ 

tr:l 

z 

t-3 

c:: 

<1 

~ 

to<! 
DRILLERS LOG 

0 

10 

(/) 20 

a: 

w 

fw 30 

~ 

z 40 

J: 50 

1-

~ 

w 

0 60 

70 

80 

DENSITY 

0 

10 

20 

30 

40 

50 

60 

70 

80 

NEUTRON 

0 

10 

20 

30 

40 

50 

60 

70 

80 

RESISTIVITY 

0 

10 

20 

30 

40 

50 

60 

70 

80 

GAMMA RAY 

0 0 

10 10 

20 20 

30 30 

40 40 

50 50 

60 60 

70 70 

80 80 

IP EXPLANATION 

Sandstone 

Shale 

Clay 

Shaly 

sandstone 

Coal 

Black shale 

Shale 

(high cationexchange) 

Pyrite 

Limestone 

conglomerate 

FIGURE A6.-Lithology interpreted from density, neutron, resistivity, gamma-ray, and induced polarization (IP) well logs for drill hole 6. 

> ""0 

""0 

tz:j 

z 

t:l 

>< 

> 

CoA:l 

-.J 

APPENDIX B 

Product and ratio well logs, and composite lithologic interpretation for drill holes 2 through 6 
gr/ip, ip/dc, nn x rs, nn/gr Composite 

in c/s ir1 eercent in c/s x unitless interpretation percent g/cm3 ohm meters EXPLANATION 0 2000 4000 o.o 1.0 2.0 0 500,000 0 50 100 0 0 0 0 0~ ..... Coal 

101 f- 10-l ~ 10-! ~ 10-l ~ 10 i ~ ~~ Black shale 

Limestone 

conglomerate ... (/) 20 20 20 20 20 a: Sandstone 

, .. •' .1 {· w Percent .... Sandstone 75 ( t- .. \ 30 <· Shale 25 30 30 30 30 w < ... -~.\ Sandstone 50 

::1! 

·:~ i. Shale 50 

•.: ·::~:· ,. Sandstone 25 z40 40 :.··.·· 40 40 40 

~ ... \.) Shale 75 

Shale (high /.':.· cation exchange) 

;~r c <_.. 

50 ( 50 ~--....... 50 ''.'·,:,.,·:· 50 Shale (low 

cation exchange) '.•. }'~ 

t- ( 

'· ·\ a.. 60 60 60 60 ·· .. 60 t ., : :.:;: ( ~ 

_-._-_: ~_,. 

\' ~ 

70 ~. .... 70 .f .. -·: 70 < .... 

. ' ~-. 70 70 ,. <.·: 

oo} 

•:: ..:·"' ~· .. 'i•' ( ,.. _,\' 

80-l \ 80 ! (~ 80 { 80 

FIGURE Bl.-Product and ratio well logs, and composite lithologic interpretation for drill hole 2. Neutron, induced polarization, resistivity, 

density, and gamma-ray well logs are represented by the symbols nn, ip, res, de, and gr, respectively. c/s, counts per second; g/cm3

, grams 

per cubic centimeter. 

.,j:::o. 

0 

Q 

tlj 

0 

'"0 

:r: 

-< en 

-(") 

> t"' 

~ tlj 

t"' 

t"' 

t"' 

0 

Q 

sn 

t= 

t"' 

z 

0 

-

en 

ttl 

)> 

en 

~ ~ 

tlj 

z 

~ 

c 

(") 

~ 

-< 
gr/ip, ip/dc, nn x rs, nn/gr Composite 

in c/s in percent in c/s x unitless interpretation 

percent g/cm3 ohm meters EXPLANATION 0 2000 4000 1.0 2.0 0 500.000 50 100 

0 0 0 

- Coal 

10-1 ~ 101 101 101 

f 

10i 

~ Black shale 

Limestone 

: 20~ ~ conglomerate 

20 20 20 20 :: Sandstone 

Percent 

; 30 j f 30j 

Sandstone 75 

30 30 30 Shale 25 

Sandstone 50 

Shale 50 

z 40 i ,:;.·~- 40 ~ :( ··., .. ( Sandstone 25 40 40 f .. 40 Shale 75 . -~· ( .l Shale (high \··r·. }. '-~-. ( cation exchange) 

I 50 50 50 -~ 50 f ·f •. -_, 50 Shale (low ..... ·.·,. ( ': . f- 1.)~.~; cation exchange) 

a_ •:;~. f :o', 

UJ 60 (' 60 f 60 t 

___ -_~.> 

...... 60 l.<' ~ 60 

0 _;{ ··,'\ 

"··;· 

l'l. ( :, 

: ·:·:·. 

1o-1l' 70 70 ·- 70 r-: .. ·· j- 70 

'z, (.. -~~~:;;1 ... ,, .. ,.·· , . <. 

80 ~ 80 80 80 ~ 80 

FIGURE B2.-Product and ratio well logs, and composite lithologic interpretation for drill hole 3. Neutron, induced polarization, resistivity, 

density, and gamma-ray well logs are represented by the symbols nn, ip, res, de, and gr, respectively. c/s, counts per second, g/cm3

, grams 

per cubic centimeter. 

> '"tJ 

'"tJ 

tz:j 

z 

t::1 

~ 

:><: 

t:C 

~ 

1-' 
gr/ip, ip/dc, 

in c/s in ~ercent 

percent g/cm3 

0 2000 4000 o.o 1.0 2.0 

.:n 0 

10 

IJ) 

.~1 l ...... · ... 20 20 a: ·······' w .... ( 

( 1- ... w30 '.~:::~· 30 

::iE t 

c:.·( ) .. 

(" Z40 ..... 40 

·~:: ..... ~ . i .. 

~~f 50 > 

~> 

C_ w60 ) 60 0 t, 

~~ ... t 

70 1'<\,,:·· { 70 

? 

80~ \ J 80 

nn x rs, 

in c/s x 

ohm meters 

0 500,000 

0 0 

10 10 

~ 20 20 

30 

!~.·· "<;i- :" 30 

'I ''·:.• 

40 <.I 40 

\\. .... ·•··· 

50 -----:,..,. ,---- __ ..., __ 50 

1 ..... 

t 

I ~~. " 

60 i 60 ,• 

·'' I 

_ ... ' .... ·,,. 70 .. . ~ .. · .:.~ 70 I 

.,::. ... I 

I \ 80 80 

nn/gr 

unitless 

0 50 

l 

">.. 

~~·~ .. r ~·. 

\ 

(.?.. 

{ .. :J•: 

l 

\: 

{' 

100 

Composite 

interpretation 

0 

10 

20 

30 

40 

60 

70 

80 

EXPLANATION 

Coal 

Black shale 

Limestone 

conglomerate 

Sandstone 

Percent 

Sandstone 75 

Shale 25 

Sandstone 50 

Sl)ale 50 

Sandstone 25 

Shale 75 

Shale (high 

cation exchange) 

Shale (low 

cation exchange) 

FIGURE B3.-Product and ratio well logs, and composite lithologic interpretation for drill hole 4. Neutron, induced polarization, resistivity, 

density, and gamma-ray well logs are represented by the symbols nn, ip, res, de, and gr, respectively. c/s, counts per second, g/cm3, grams 

per cubic centimeter. 

N:;o. 

~ 

0 

t_:l:j 

0 

"'d 

:I: 

~ 

00 

-("",) 

> t"'4 

:E 

t_:l:j 

t"'4 

t"'4 

t"'4 

0 

0 

sn 

-t"'4 

t"'4 

-

z 

0 

-

00 

~ 

> 00 

:z: -

~ t_:l:j 

z 

o-3 

c:: 

("",) 

~ 

~ 
gr/ip, ip/dc, nn x rs, nn/gr Composite 

in c/s in Qercent in c/s x unitless interpretation 

percent g/cm3 ohm meters EXPLANATION 

0 2000 4000 1.0 2.0 0 500.000 50 100 0 0 0 -- Coal 

10 -l 1- 10 10 10 10 Black shale 

Limestone 

:20! ,> ' 

conglomerate 

20 20 / 20 

J 

20 Sandstone 

w ·;t Percent 

1- .1' Sandstone 75 <, Shale 25 

;'· \:>- 30 30 30 30 

..... Sandstone 50 

~·-. ( 1 Shale 50 

Sandstone 25 Z40..J'i .. 40 40 40 '} 40 Shale 75 

i<'~i~ ( .... ~., 

l r. -.~ t Shale (high 

cation exchange) 

J: 50 ..... \." 50 

\ 50 ·~i 50 t 50 Shale (low .. •1,', ,. cation exchange) 1- ( ;\··:. a.. •' w 60 60 60 /~I 60 1- 60 

0 ] .. · ... \{.~:-

{/' ::-:~ 

70 ') 70 70 < 70 --~: . . J- 70 '} ~ . 

•, ~ ...... -#..._==· 

80lf ,. 

:~· 

80 -l ":.~ ... .··) 8of~·' I 80 \ . ... •·. 1- 80 

l> ·, 5.> ~ 

FIGURE B4.-Product and ratio well logs, and composite lithologic interpretation for drill hole 5. Neutron, induced polarization, resistivity, 

density, and gamma-ray well logs are represented by the symbols nn, ip, res, de, and gr, respectively. c/s counts per second, g/cm3

, grams 

per cubic centimeter. 

> "t:l 

"t:l 

trj 

z 

t:l 

-:>< 

tc 

~ 

Cl:) 
Ul 

Cl 

~ 

"' :u 

z 

~ z 

-1 

11 

:u 

3 

z 

Cl 

~ g 

! 

~ 

gr /ip, 

in c/s 

percent 

0 2000 4000 

0 

10 

(/) 20 

a: 

LJ.J 

;30R 

z 40-lt 

\ ::c 50,) 

In. ·~ 

~ "i) 

70 -l_. 

l. 

80j 

ip/dc, 

in percent 

g/cm3 

0.0 1.0 2.0 o~~____._...__--~, 

10 

20 

30 .. < ... 

~ 

f·f 

\' ... ~ 

40 

I~ •' ' 

50'\' 

r l };.· 60 

70 

80 

nn x rs, 

in c/s x 

ohm meters 

0 500,000 0 +--1---'--L_-J10 

20 

30-1.[' 

~ 

) l' . 40-l { 

~ .... 

~-. 50-{---;~--; 

c· --~~· \ ..... 

60-l : 

I )' , .. 

I ,. 

: \"' 

70~ f ,..1 

~ ~. 

'~ '· 

80.J;' 

nn/gr 

unitless 

0 50 100 

0+--'-----'--"--+ 

10 

20 

30-t' 

ir 40-li' 

l 50-l 0 

"i.' 

( 

( 

"'{ 

70il 

.. .. ~; 

·\ 80-1 ,(' 

Composite 

interpretation 

0 

10 

20 

30 

40 

50 

60 

70 

80 

EXPLANATION 

Coal 

Black shale 

Limestone 

conglomerate 

Sandstone 

Percent 

Sandstone 75 

Shale 25 

Sandstone 50 

Shale 50 

Sandstone 25 

Shale 75 

Shale (high 

cation exchange) 

Shale (low 

cation exchange) 

FIGURE B5.-Product and ratio well logs, and composite lithologic interpretation for drill hole 6. Neutron, induced polarization, resistivity, 

density, and gamma-ray well logs are represented by the symbols nn, ip, res, de, and gr, respectively. c/s counts per second, g/cm3, grams 

per cubic centimeter. 

~ 

~ 

0 

t;rj 

0 

""0 

::z:: 

~ 

00 

,...., 

(j 

> t"" 

~ t;rj 

t"" 

t"" 

t"" 

0 

0 

sn 

..... 

t"" 

t"" 

z 

0 

,...., 

00 

tc 

> 00 

~ 

~ 

t;rj 

z 

t-3 

c:: 

(j 

~ 

~