A CHEMICAL, STATISTICAL AND STRUCTURAL
ANALYSIS OF SECONDARY DQLOMITIZATION IN THE
ROGERS CITY ~ DUNDEE FORMATION OF THE
CENTRAL MICHIGAN BASIN

Thesis for the Degree of DI]. D.
MECEIGAN ' {STATE 3N1?! ER'SIT‘Y
Betty M. Tinklepaugh

1957

This is to certify that the
thesis entitled
"A Chemical, Statistical and Structural Analysis
of Secondary Dolomitization in the Rogers-City

Dundee Formation of the Central Michigan Basin."

presented by

Betty M. Tinkleangh

has been accepted towards fulfillment

of the requirements for

Ph. D. degree mm

 

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A CHEMICAL, STATISTICAL AND STRUCTURAL ANALYSIS
OF SECONDARY DOLOMITIZATION IN THE
ROGERS CITY-DUNDEE FORMATION OF
THE CENTRAL MICHIGAN BASIN

by
BETTY M. TINKLEPAUGH

AN ABSTRACT

Submitted to the School of Graduate Studies of Michigan
State University of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Geology

Year 1957

 

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Approved: / - / ‘ WA. l'."‘""Y:““‘L‘-’"‘
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v

BETTY M. TINKLEPAUGH ABSTRACT

The Rogers City-Dundee (Devonian) formation in the
central Michigan basin, although normally a marine lime-
stone, is in many places an extremely porous dolomite. Oil
fields producing from the Rogers City formation are generally
limited to these dolomitic zones. The origin and character-
istcs of these dolomitic zones were the primary concern of
this investigation.

A study of the possible relationships between second-
ary dolomitization, structure, and porosity was made over
an area of approximately 400 square miles chosen in the
Central Michigan basin where four major fields produce oil
from the Rogers City formation.

Chemical analyses for calcium, magnesium, and iron
content were made from samples within the top twenty feet
of the Rogers City formation, in which the pay zones occur.
The methods used were adopted by the author from Standard

Methods for the Examination of Water, Sewage, and Industrial

 

 

Wastes, published by the American Public Health Association,
1955. They were as follows:

1. Calcium analyses were made by the "Compleximetric"
or versene titration methods as used for the
determination of calcium hardness of water.

2. Magnesium and iron analyses were determined by
spectrophotometric methods as adopted from water

hardness tests.

BETTY M. TINKLEPAUGH ABSTRACT
These methods were highly accurate and extremely rapid as
adapted for mass technique analyses.

Structural interpretations were made by an interpo-
lation of a structure contour map of the area. Comparisons
of this map with lithologic magnesium to calcium ratio maps
were made to determine vertical and lateral relationships
between structure and degree of dolomitization.

Statistical comparisons of the data were made by
means of analysis of variance methods to determine rela-
tionships between: (1) dolomitization and structure, (2)
dolomitization and porosity, (3) dolomitization and iron
content of the limestones.

It was concluded from chemical analyses, structural
and lithologic Mg/Ca ratio maps, and statistical analyses
that in the top twenty feet of the Rogers City formation,
including the prolific Goldwater oil field, there is a
definite relationship between the degree of dolomitization
and the magnitude of structure; there is a relationship
between dolomitization and porosity, the nature of which is
neither simple nor direct; and, there would appear to be an
inverse relationship between iron content and the degree of
dolomitization.

The magnesium-calcium ratio in limestones is a very
useful geologic tool. It is especially useful in porosity

Studies and the location of dolomitized zones and structunes-

BETTY M. TINKLEPAUGH ABSTRACT
The rapid and accurate techniques used in this study
can enable geologists and petroleum engineers to make the
Mg/Ca ratio determinations a routine analysis. Statistical
studies may enable them to predict porosity of carbonate
rocks and show the relationship between porosity and dolo-

mitization for many limestones as yet unstudied.

A CHEMICAL, STATISTICAL AND STRUCTURAL ANALYSIS
OF SECONDARY DOIOMITIZATION IN THE
ROGERS CITY—DUNDEE FORMATION OF

THE CENTRAL MICHIGAN BASIN

by
BETTY M. TINKLEPAUGH

A THESIS

Submitted to the School of Graduate Studies of Michigan
State University of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY.

Department of Geology

Year 1957

ACKNOWLEDGMENTS

The author wishes to express her sincere thanks to
Dr. B. T. Sandefur for his aid and helpful suggestions
throughout this investigation. The writer is greatly
indebted to Mr. Irving L. Dahljelm of the Microbiology
department for his advice in the development of the methods
used for the chemical analyses and for the use of his
laboratory facilities, equipment, and reagents.

Grateful acknowledgment is also due to Dr. W. D.
Baten of the Statistics department for his suggestions and
assistance in the choice of statistical methods employed
and statistical interpretations best fitted to this study;
and to Dr. Justin Zinn for a critical reading of the manu-
script.

The writer wishes to thank G. D. Ells of the Michigan
Geological Survey who generously assisted in obtaining well
samples and necessary information required for this study.
'The author is grateful to Dr. A. M. McCarthy for assistance

in editing the manuscript-

ii

VITA
Betty M. Tinklepaugh
candidate for the degree of

Doctor of Philosophy

1957

Dissertation: A Chemical, Statistical and Structural
Analysis of Secondary Dolomitization in
the Rogers City-Dundee Formation of the
Central Michigan Basin

Outline of Studies:

Major subject: Geology
Minor subject: Statistics

Biography:
Born: April 23, 1930, Corunna, Michigan

Undergraduate Studies: Central Michigan College,
A. B. degree, l9A8-l952

Graduate Studies: Michigan State University, Master
of Science degree, 1952-1955; cont. 1955-57.

Experience: Graduate Assistant, Michigan State
University, Geology department, 1954-1955,
Natural Science department, 1956-1957; Graduate
Council Fellowship 1953-1954 and 1955-1956; '
Cartographer, McClure Oil Co., summers 195A, 55;
Instructor in Extension teaching in Geography,
Michigan State University, summer 1955; Instructor
in Natural Science, Michigan State University,l957

Affiliations: Member of the Geological Society of America,
Michigan Academy of Science, American Association
for the Advancement of Science, Michigan Geological
Society, Sigma Delta Epsilon, Associate member
of Society of Sigma X1

111

TABLE OF CONTENTS

LIST OF TABLES.
LIST OF FIGURES
LIST OF MAPS . .

INTRODUCTION

General
Problem .

HISTORICAL Rfssumé OF DOLOMITE.

I. Primary Deposition .
A. Chemical Theory .
B. Organic Theory
C. Clastic Theory .
II. Alteration Theories. . .
A. Marine Alteration . .
B. Ground Water Alteration
C. Pneumatolytic Alteration
III. Leaching Theories . . .
A. Surface Leaching.
B. Marine Leaching
New Classification . . .
A.. Primary dolomites .
B. Diagenetic dolomites
C. Epigenetic dolomites
Dolomitization and Porosity .

FIELD DATA .

Location of Area.
Stratigraphy . . .
Goldwater Oil Field.

LABORATORY PROCEDURE. . . .

Methods.

Samples. .
Source . . . . . .
Sample selection . . .
Sample preparation

Calcium Determination

iv

Page
. vi

vii

. viii

Magnesium Determination.
Magnesium- Calcium Ratios
Iron Determination .
Results of Chemical Analyses

INTERPRETATION OF DATA

Structural and Chemical Interpretation.
Structure Contour Map. .
Structural Interpretation
Lithologic Ratio Maps. .
Interpretation of Lithologic Ratio .Maps.
Goldwater Oil Field . . .
Structure Contour Map.
Lithologic Ratio Map . .
Interpretation of Lithologic Ratio Maps.
Vertical Configuration and Pay Zones.
Statistical Interpretation. . .
Statistical Methods .
Statistical Interpretation of Data
I. Producing "High" Versus Non-
Producing' ‘Low" .
II. Producing "High" VerSus Non-
Producing "High" .
III. Non-Producing "High" Versus Non-
Producing' 'Iow" .
IV. ‘"High" Versus "Low" Structure. .
V. Producing "High" Versus Non-Producing
‘ Low" in Iron Content . . . .

ORIGIN OF DOLOMITE IN THE ROGERS CITY LIMESTONE .
SUMMARY AND CONCLUSION

General Summary
Conclusions. .

SUGGESTIONS FOR FURTHER STUDY .
BIBLIOGRAPHY. .

Page

102
107

107
108

114
115

LIST OF TABLES

Table Page
1. Well Data and Locations. . . . . . . . . 59
2. Data for an Analysis of Variance—-Producing

‘"High" versus Non-Producing'"Low" . . . . 9O
3. Data for an Analysis of Variance—-
A. Producing "High" versus Non-Producing
"High"
B. Non- -Producing "High" versus Non-Producing
n"Low . . . . . . . . . . . 93
A. Data for an Analysis of Variance—~"High"
versus HLow structures. . . . . . . 97
5. Data for an Analysis of Variance--Producing
"High" versus Non- Producing' 'Low‘I -Iron
Content . . . . . . . . . . . . . lOO

vi

Figure

LIST OF FIGURES

Michigan Devonian System--generalized
columnar section. . . .

East-west Cross Section of the Goldwater
Oil Field . . . . . . . . .

North-south Cross Section of the Coldwater
Oil Field . . . . . . .

North-south Cross Section of the Goldwater
Oil Field . . . . . . . . . . .

Analysis of Variance-~Producing "High" versus
Non—Producing "Low" .

Analysis of Variance--Producing "High" versus
Non-Producing "High"

Analysis of Variance--Non- Producing "High"
versus Non- Producing' Low" . . .

Analysis of Variance-4"High" versus "Low"

Analysis of Variance-~Producing "High" versus
Non-Producing "Low"-Iron Content . .

vii

Page

38

85

86

87

91

9M

95
98

101

Map

- O\ U1 J: W R)

LIST OF MAPS

Page
Location of Area-Map of Michigan. . . . . . 36
Structure Contour--Rogers City Formation (Back Pocket)
Magnesium/Calcium Ratio Map-Top 5 Feet (Back Pocket)
Magnesium/Calcium Ratio Map-Top 20 feet (Back Pocket)
Goldwater Oil Field-Structure Contour Map. . . 82

Goldwater 011 Field-Mg/Ca Ratio Map-Top 10 Feet. 83

viii

INTRODUCTION
General

In Michigan a considerable number of petroleum fields
produce from porous zones in locally dolomitized limestones.
. The Rogers City—Dundee (Middle Devonian) formation, in the
central Michigan basin, is normally a fossiliferous, marine
linestone, with no effective porosity. Penetration of the
formation reveals that the upper 10 to 20 feet has been
altered locally in many places to a porous dolomite from
which a large quantity of oil has been obtained.

It is the belief of many geologists that the occur-
rence of secondary dolomitization is related to zones of
weakness, tensional cracks, faults, fissures and the apices
of folded structures within the limestone formations (Geikie,
.1893; Steidtmann, 1917; Hewett, 1931; Hatch, 1938; Landes,
19A6; Jodry, 1955). Because of the great amount of "com-
mercial" porosity which is restricted to dolomitic facies
within limestones, there has been a growing tendency for
geologists to relate porosity to the process of dolomiti-
zation.' Lauer (1917) attributed some porosity in petroleum
reservoir rocks as due to "dolomitization cavities in
altered limestones." Landes (1946) believes that the pro-

cess of dolomitization and porosity is genetically related

and refers to it as "local dolomitization porosity."

R. B. Hohlt (1948) pointed out that "there is no agreement
concerning the origin of porosity through diagenetic and
epigenetic dolomitization" but "that a relationship exists
between porosity and the process or processes of dolomiti-
zation, although no specific relationships have been
established." In recent studies Chilingar and Terry (1954)
conclude that "field evidence suggests that some porosity
forms through dolomitization;" On the other hand, J. E.
Adamd (1934) stated: "The constant use of dolomitization
as an explanation of the increase in porosity in limestone

is one of the theories that appear to be overworked;"

Problem

In an attempt to study the possible relationships
between secondary dolomitization, structure, and porosity
the author chose an area of approximately MOO square miles
in the central Michigan basin in which fields producing oil
from the Rogers City formation are generally limited to
dolomite zones .

A chemical analysis of the Rogers City limestones
from the well samples was made to determine the calcium,
magnesium and iron content. The calcium and magnesium were
recorded for the purpose of determining the Mg/Ca ratio

as a measure of the degree of dolomitization of the lime-

Stone.

D. F. Hewett (1928) recorded that "dolomitized lime-
stones contain more iron than the original rock." Steidtmann
(1917), Tarr (1919) and Cheng, Kuang, and Bray (1952) con-
firmed this in individual observations of dolomitized lime-
stones. But Hewett (1931) found "no evidence of increase
in iron oxide with the process of dolomitization in the.
Qumsprings quadrangle of Nevada." Because of the possi-
lfllity of a relationship existing between iron and dolomit-
ization, the author included a determination of the iron
cxmtent of the limestones in the chemical analysis.

A structural interpretation of the area studied is
cxmmared with lithologic Mg/Ca ratio maps to determine the
Ixmsible relationship between structure and degree of
<kflomitization both vertically and laterally. Statistical
comparisons are made to determine relationships between:
OJ dolomitization and structure, (2) dolomitization and
porosity, and (3) dolomitization and iron content of the
.1imestones.

In order to determine more exactly the degree of
ckflomitization and iron content in the dolomitized lime-
stone formation the author applied methods for the deter—
nunation of calcium, magnesium, and iron from the approved
pmecedures in Standard Methods for the Examination of KEEEE:

Sewage, and Industrial Wastes published by the American

 

Public Health Association, 1955. These methods were

accurate and easily adapted to mass analysis techniques.

i
o‘.

a
.-v

 

 

 

 

HISTORICAL RBSUMB OF DOLOMITE

Deodat Dolomieu, born in Dolomieu, France, was the
first to describe the magnesium carbonate mineral which
he discovered while making an extended tour among the Alps
in 1791 (Knight, 1921). In the following year Saussure
gave it the specific name of "dolomite" in honor of its
first describer (Van Tuyl, 1914).

From this date unto the present the nature and origin
of dolomite has been the subject of much discussion, the
topic of many debates, and’the object of many theories.

In fact, it was noted by Van Tuyl (191M) that Arduino,
in the year 1779: made the first attempt to explain the
formation of "magnesium limestones" by pneumatolytic
alteration of pre-existing calcite limestones in an area
of volcanic activity.

Voluminous literature has appeared on the subject of
dolomite origins and many theories have been proposed since
its discovery. For more than a century recognition of the
presence of exceptional porosity in many dolomites has been
associated with theories on the origin of this rock. The
importance of porosity to the petroleum industry is a known
and established fact. The possible relationship then of
the origin of dolomites and dolomitization to that of

porosity has become an increasingly important problem to

ii

I'll)! id: 1.

 

 

tie petroleum geologist and an added stimulus to a con-
thnung interest in the nature of dolomites.

Although much has been written in regard to the many
cndgins of dolomite and their relationship to porosity, only
atndef resume of the history and present status of the
Inmmlem, as related to the one at hand, will be given here.

The theories of the origin of dolomite may be classi-
fied conveniently in the following manner:

I. Primary deposition theories
A. Chemical
B. Organic
C. Clastic
II. Alteration theories
A. Marine alteration
B. Ground water alteration
C. Pneumatolytic alteration
III. Leaching theories
A. Marine leaching
B. Surface leaching
I. Primary Deposition

A; Chemical Theory

This theory, that dolomite is an original chemical
Iflecipitate on the sea floor, has had many followers, and
mmw geologists still adhere to it today. Bone advocated
this method of origin as early as 1831, and Bertrand-
mxflin (1834) was an early supporter of this theory.
Similarly Wagner (1839) favored the theory that the dolo-

nutes of the French Jura were original deposits rather than

 

alteration products. Coquand (1841), however, concluded
that dolomite had a two-fold origin, being in part a

regular chemical precipitate on the sea bottom, and in part
the product of the action of volcanic agents on limestone.
Wissmann, about this time, expressed the belief that the
dolomites of the Tyrol were original deposits, and Petzholdt
stated that "both the dolomite and the limestone of this
region are chemical precipitates, since they grade into each
other'.‘ (Bischof, 1859). This, Petzholdt believed, would
account for the predominance of limestone in the lower part
of the section and of dolomite in the upper, since MgCO3 is
the more soluble of the two carbonates and would be the
last to be "'thrown out" of solution. Fournet (1849) like-
wise interpreted the dolomite of the same region as an
original chemical precipitate.

Forchhammer (1850), soon after, pointed out that
certain dolomitic nodules in the Cretaceous limestones at
FaxU were probably chemical. These he believed to be the
product of the reaction of the CaCO3 of spring water with
the magnesia of sea water. The presence of material re-
sembling travertine in the rocks and other evidences of
Spring action seemed to lend support to this theory.

Delanoue (1854) was inclined tofavor the chemical
precipitation theory for dolomites in general, regarding

secondary dolomites as only local and of little importance.

 

Hunt (1859) also expressed himself unequivocally in
favor of the chemical precipitation of dolomite, giving as
his opinion, that "dolomites, magnesites, and magnesian
marls have had their origin in sediments of magnesium car-
bonate formed by the evaporation of solutions of bicar-
bonate of magnesia."

Cordier (1862), approaching the problem from a philo-
sophical standpoint, was also led to believe dolomites were
chemical deposits, and Leymerie (1864) entertained similar
beliefs. He pointed out that the dominant salt in the sea
today is NaCl, while MgCl2 and CaC12 are accessory, but
supposed that in early Paleozoic time conditions may have
been reversed.

Von Rosen claimed chemical precipitation as the
probable method of origin of the dolomite and dolomitic
limestone of the Dfina and Welikaja regions in Finland and
Kurland, and Gumbel applied it to the dolomites of the
French Jura and of the southern Tyrol. Zirkel (1894) and
Scheerer (1866) believed that all of the oldest dolomites
represent chemical precipitates.

Loretz (1878) also favored the view that the dolo-
mites of the southern Tryol were original formations and
leaned towards the chemical theory. The preservation of
fine and detailed structures in the rock suggested to him
its primary nature.

. S. F. Emmons (1886) adopted the primary theory for
the origin of dolomites of the Leadville district, Colorado.

He concluded that "the magnesia is an original constituent
of these rocks, having been deposited at the same time as
the lime." Later, Vogt (1898) came out in favor of this
view, stating that certain Norwegian dolomites were chemical.
Ulrich and Schuchert (1901) have also implied that certain
dolomitic limestones were chemical.

The chemical theory has had one of its greatest
champions in Suess (1906), who points out "that in the
Plattenkalk formation beds of dolomite, often containing
more than 40 per cent MgCO3 and of constant thickness and

'and

regular contacts, are interbedded with limestone,"
maintained that “the dolomite was deposited as such from
the sea."

The chemical theory, however, has been elaborated
most fully by Daly in two very descriptive papers. In the
earlier paper (1907) this writer pointed out that in Pre-
Cambrian time, when the scavenger system of the ocean was
not yet developed, the seas must have been depleted in lime
and magnesia due to the precipitating effect of (NHu)2C03
generated from decaying organisms on the sea bottom. “The
magnesium carbonate should have been most abundantly thrown
down in Pre-Cambrian time; its precipitation must have been
lessened through Paleozoic and Mesozoic time and has reached
its minimum since the abysses of the ocean became abundantly

tenanted with scavengers" (Daly, 1907)- In Daly‘s second

paper (1909) this theory was developed still further. The

 

 

. I'-

euternation of clean-cut beds of limestone with beds of
negnesian limestone or dolomite, as illustrated by the Pre-
Cmflndan formations of British Columbia and Montana, also
seemed to him to speak for the original deposition of the
mmncarbonates as against later metamorphism or alteration.

Following closely upon Daly came Linck (1909) as an
mhmmate of the chemical precipitation theory. Basing his
conclusions upon the conditions of his experimental pro-
duction of dolomite, he also assumed'"that (NHu)2C03 derived
from the decay of marine organisms was a competent preci-
pitating agent."

Two years later Steidtmann (1911) concluded a com-
;nehensive study of dolomites with the following statement:
-"Dolomite develops predominantly in the sea, therefore the
decrease in the dolomite content of the sediments in going
up the geologic column is mainly due to a decrease in the
Proportion of dolomite developed in the sea with time;"

Another investigator to express himself as favoring
the chemical hypothesis was Weigelin (1913), who applied it
to the dolomites associated with salt and gypsum in the
Lower Keuper of West wurttemberg. The upward succession
<fi'dolomite, gypsum, and salt here suggested to him that
all these were the products of evaporating seas.

w. A. Tarr (1919, 1920) also considered dolomite to
bezichemical precipitate from shallow marine waters. He

believed freshing of the waters to be the cause of

lO

interbedded pure limestones alternating with the dolomites
in shallow, inclosed seas. Similarly, Stauffer and Thiel
(1933) believed that the direct chemical precipitation from
sea water may have been the process in a few cases of
dolomites in Minnesota but that it is no longer a major one
in the present sea.

Late investigations by W. Stout (1941) of the dolo-
mites of western Ohio have lead him to the conclusion that
"the dolomites are marine in origin, were deposited in
shallow or comparatively shallow water, and in the main are
direct precipitations . . . most certainly they were laid
down in the form we now find them and are not secondary .

11

Recent studies have been made by geologists con-
cerning present day conditions under which dolomites may be
forming by direct chemical precipitation. A. J. Eardley
(1938) and P. Weaver (1946) have published results favorable
to this theory under conditions of high concentrations and

excessive evaporation of the waters studied.

ngkganic Theory

The opinion formerly prevailed in some quarters that
<Hganisms have played an important role in the formation of
dolomite.

Forchhammer showed by a series of analyses as early
as 1850 that the calcareous skeletons of some organisms con-

tained considerable magnesia. The chemical studies of

ll

Damour (1851) also led him to support this theory. Analysis
of calcareous algae ("corals") by him showed a high MgCO3
content in four out of six specimens. Damour- concluded,
therefore, " from the development such forms take on along

the shore and on the sea bottom that deposits of magnesian
limestone are being formed by them today and must have been
formed by them in the past."

Ludwig and Theobold (1852) also emphasized the im-
portance of algae in the deposition of limestone and dolo-
mite. In the travertine of the mineral spring at Nauheim,
in the Wetterau, which is deposited through the agency of
algae, these writers found a magnesia content ranging up
to 11.69 per cent.

The observations of Doelter and Hoernes (1875), who
held that many "weakly dolomitic limestones" were deposited
directly in the sea through the activity of organisms, were
also in accord with the organic theory.

Late investigations by Wallace (1913) tended to lend
weight to this theory, since he believed "that the occur-
rence of dolomitic fucoid-like markings in the Ordovician
limestones of Manitoba is best accounted for on the as-
sumption that algae, bearing considerable magnesia, were
imbedded in the rock at the time it was deposited and that
this magnesia was influential in producing local dolomiti-
zation of the limestone ." Nadson and Walther (1916) advanced

the suggestion that the presence of bacteria in the sea

12

water may possibly influence the process of dolomitization.

C. Clastic Theory

 

That some dolomites may represent ordinary mechanical
sediments derived from the erosion of older dolomitic lime-
stones, seems to have been conceived first by Lesley, in
1879. He suggested this mode of origin for an interbedded
series of limestones and dolomites of the "Calciferous,"
exposed in the old Walton quarry, on the west bank of the
Susquehanna river, opposite Harrisburg, Pennsylvania.

Such a theory of origin was favored by Phillip (1907)
to account for certain impure dolomites associated with
elastic sediments in the Muschelkalk of Germany. He
believed “that the material constituting these dolomites
probably was derived from the residuum of a limestone
originally low in magnesia." This view has been adopted by
Grabau (1913) who holds that '" the upper Silurian waterlimes
and certain dolomitic intercalations in the Salina are
elastic deposits derived from the erosion of older lime-
stones." The same writer (1913) was of the opinion ‘" that
certain interstratifications of limestone and dolomite like-
wise are explainable upon the basis of the clastic theory,"
remarking that "‘the relationship is most satisfactorily
explained as a primary difference in the materials deposited,
that both the limestone and the dolomite are clastic but are
derived from different sources, or that the limestone is

OI‘8anic and the dolomite clastic" (Grabau, 1913).

13

II. Alteration Theories

 

A. Marine Alteration

 

The theory that dolomite has had its origin in the
aflteration of limestone before it emerged from the sea has
hminmny followers and probably is most widely held today.
Mmmg the supporters of this view there has been almost
Irmnimous agreement that the sea water contributed the
nmgnesia. An exception to this is the view of Favre (1879)
Mun basing his suppositions upon the conditions of the
experimental production of dolomite by Marignac, concluded
tflmt "the dolomites of the Tyrol were formed by magnesium
<xmmounds furnished by the action of sulphurous and hydro-
<fifloric acids of volcanic origin on the lava of submarine
nelaphyr eruptions."

The concept that the alteration might be effected by
1mm magnesia of sea water was first suggested by Dana (1843),
unaccount for the dolomitic reef rock of the coral islands
(n‘the Pacific. He hinted, at the time, that "the rock
unght have been formed by the introduction of magnesia
tflmeugh the medium of heated sea water which possibly con—
teined a larger supply of this element than usual;" In
lgflh Dana expressed the view that "the same dolomite had
teen formed in sea water at ordinary temperatures but per—
l“alps in a concentrated state;" In the 4th edition of Dana's

Manual, (1895) this same idea is elaborated without

14

modification, the opinion being held that the concentrated

brines in the lagoon would contain MgCl and MgSOu in a

2
state favorable to the formation of dolomite.

F. Pfaff (1851) likewise regarded the marine alter-
ation theory as the most practicable for the origin of
the dolomites of the French Jura.

Sorby (1856) expressed himself in favor of the marine
alteration theory when he suggested that the formation of
certain dolomites was effected by the alteration of lime-
stone through the agency of soluble magnesian salts of the
sea water "under some peculiar conditions not yet clearly
explained during the period when it became so far concen-
trated that rock salt was frequently deposited . . . .‘"

Similarly, Von Richthofen adopted this theory, in
1860, to explain the formation of the great dolomitic reef
rocks of southern Tyrol (Skeats, 1905). He claimed that
'"these dolomite masses represent dolomitized coral reefs
formed during a period of subsidence and that the St.
Cassian marly and tuffaceous deposits which flank the reefs
represent the deposits of lagoons, bays and channels of the
coral sea.“ R. Harkness (1859) commented along these same
lines on the dolomites formed along the Jointings in the
Devonian rocks around Cork as being due to "magnesium salts
in sea water . . . over consolidated and already Jointed
limestones . . . causing dolomitized rock along Joints,

fractures, and bedding planes in limestones."

15

Monisovics (1879), in his classic memoir on the
dolomite reefs of the same region of Tyrol, proposed a
theory not essentially different from that of Von Richthofen.
He held that the dolomite masses represented altered coral
reefs possibly formed in the same manner as the one de-
scribed by Dana, but doubted if the sea which effected the
alteration was concentrated in lagoons as postulated by
that writer.

Hoppe—Seyler (1875) was also a champion of the marine
alteration theory. He believed that the magnesia for
altering great limestone masses to dolomite could be fur-
nished only by the sea. In like manner, Doelter and Hoernes
(1875) supported this theory in their memoir on dolomite
building, attributing the greater part of the dolomites,
more or less rich in magnesia, to the action of magnesia of
sea water, especially the MgClg, on limestone made up of
the calcareous skeletons of organisms.

F. W. Pfaff (1894), basing his evidence upon the
conditions under which he prepared dolomite artifically,
concluded that coral reefs might be altered to dolomite.

The paucity of fossils in some dolomites was attributed by
Pfaff to the fact that the sea may have been in a concen-
trated state when they were deposited. He, therefore,
believed that dolomitization took place contemporaneously
with deposition in some cases and in support of this he
cited analyses showing a high magnesia content in slimes

dredged from a considerable depth in the modern seas.

16

The View that pressure induced by considerable depth
is an important factor in dolomite formation, however, was
not shared by Phillipi (1907), who pointed out that "'dolo-
mite is associated with sandy sediments in the Rbt and
Keuper and that the presence of calcareous algae in the
dolomite of the Alpine Trias proves that this could not
have been formed in a deep sea as urged by Pfaff, since
algae seldom live below 80 fathoms and never so deep as
200 fathoms." Moreover, Phillipi cited evidence of dolo-
mitization at shallow depths and at ordinary concentration
in the modern seas.

The dolomites of the Aspen District of Colorado were
best explained upon the basis of the marine alteration
theory, according to Spurr (1898), who expressed himself as
' follows: '"The Silurian dolomite . . . was originally de-
posited in quiet seas, and was built up from calcareous
sediments . . . these beds were subsequently altered to
dolomite by the magnesium salts of a great evaporating
shallow inland sea "

Calvin and Bain (1899) adopted an analogous expla-
nation for the origin of the Galena dolomite of the upper-
Mississippi Valley. They stated that "it looks as if dolo-
mitization had affected the limestone . . . after the for-
mation was complete; and that the depth to which the change
descended was, in some instances and to some extent at least

.9

determined by the presence or absence of impervious beds of

Shale .1:

17

Van Hise (1904), on the other hand, tended to mini-
ere the importance of dolomitization before the limestones
emerged from the sea and emphasized the importance of ground
water as a dolomitizing agent.

Brenner (1904) furnished evidence of recent dolo-
mitization through the agency of sea water in an old reef
rock of the stone reefs of Brazil. This rock was found to
bear 12.98 per cent MgC03 and the assumption was made that
part of the lime of the coral rock had been replaced by
magnesium from sea water. The rock is still within reach
of sea water, and dolomitization was believed by him to be
still in progress.

Several examples of altered coral reefs have been
described by Skeats (1903) from the southern Pacific.
Dohmute occurs in several of the elevated coral islands
there, but attains its greatest purity on Christmas Island,
idere it contains as much as 43.3 per cent MgC03. This
sawhor held that "Dana‘s theory with some modification
probably applied here," and he believed that "the view that
limestone is altered dolomite at a considerable depth
mnmesponding to a particular pressure is untenable."
Skeats (1905) was one of the first to recognize both “local"
mwi"regiona1" dolomitization and different causes for each.

Other examples of dolomitization believed to have
teen effected by sea water have been described by Dixon
(1907) as occurring in the Carboniferous limestones of

South Wales .

l8

Peach and Horne (1907) were of the opinion that the
Cambrian dolomites of the Northwest Highlands of Scotland
were formed by the dolomitization of calcareous sediments
on the sea bed itself; but they regarded it as possible
that '"there may have been also an enrichment of magnesia
through the leaching out of the more soluble calcareous
material of a slightly magnesian ooze, possibly made up of
the secretions of unicellular plants of the plankton."

The marine alteration theory was adopted likewise by
Salomon (1908) to explain certain nests and tongue-like
extensions of dolomite in the Ladinic limestones of the
Alps. Similarly Walther (1908) recognized that dolomites
may be produced in this manner.

In favor of some method of alteration capable of
operating over wide areas were the observations of Weller
(1911), who, from a comparison of the faunas of the Galena
and Niagaran dolomites of the Upper Mississippi Valley with
their non-dolomitized equivalents in other regions, con-
cluded that they must have been deposited first as lime-
stone and later metamorphosed.

Blackwelder (1913) also advocated this method of
origin for the Bighorn dolomite of Wyoming; but the low
porosity of the dolomite (1.31 per cent) and its sharp
contact with the limestone interbedded with it and under-
lying it lead him to favor the belief that “it was not

formed by the substitution of magnesium for half the

 

 

19

calcium in normal limestone, but that it has resulted from
progressive alteration during deposition." In this partic-
ular, then, Blackwelder followed Daly (1909), who believed
that the magnesia content of the pre-Devonian limestones
was original and that ‘" in many, if not all, cases the
dolomite crystals may have been formed at or near the sur-
face of the ancient calcareous muds by the interaction of
the magnesium salts of sea-water with the more easily
precipitated calcium carbonate .‘"

The later beliefs of Nahnsen (1913) likewise were in
line with the theory of the alteration of limestone beneath
the sea. He described a horizontal seam of dolomite with
wavy boundaries in the Upper Jurassic limestone of North
Germany, and concluded that '" the alteration probably took
place beneath the sea before the rock solidified, since
solutions would not circulate freely after recrystallization.“

F. M. Van Tuyl (1914, 1915, 1916) held that "'the
great majority of the dolomites, from Cambrian to present,
have resulted from the replacement of limestones before they
emerged from the sea." “The replacement need not be accom-
panied by shrinkage, but may proceed according to the law
of equal volumes, as enunciated by Lindgren (1912)." '"Cer-
tain cases of apparent inter-stratification of limestone
and dolomites cited as evidence in favor of some primary
theory are rather pseudo-inter-stratifications, which have

resulted from selective dolomitization.’n "Examples of

20

limestone mottled with dolomite were interpreted as repre-
senting an incipient stage in the process of alteration."
"Organic factors have exerted a selective influence in some
cases of mottling, but in others the phenomenon is purely
inorganic"? (Van Tuyl, 1914).

E. Steidtmann (1917) stated that "the majority of
dolomites developed in the sea as a sediment either by
direct precipitation or by reactions within the limy sedi-
ments of the sea bottom."

E. W. Skeats (1918) believed that he himself was the
first to develop the hypothesis of a very shallow water
origin for “contemporaneous" or '" regional dolomites.“

Other examples of dolomitization believed to have
been effected by marine alteration have been described by
Clark (1924) and by Stauffer and Thiel (1933). The latter
stated that '" the process of dolomitization must be consid-
ered one of enrichment rather than of original deposition."
"Dolomitization thus appears to have been due largely to a
replacement of part of the calcium in the original more or
less pure calcium carbonate, probably before the resulting
rock had been completely consolidated .‘"

H. R. Greiner (1956) believed the “evidence for re-
placement overwhelming.” He suggested that "contemporan-
eous or penecontemporaneous dolomitization took place on
the sea floor under reducing conditions in shallow, warm
marine waters of high salinity.“ This theory has likewise

been adopted by PettiJohn (1949) .

21

B. Ground Water Alteration

 

That ground water is capable of accomplishing local
dolomitization under favorable conditions there can be no
doubt, and there has been a tendency on the part of some
to believe that this method of alteration is of far-reaching
significance. Most writers who have supported this view
have emphasized the importance of the MgCO3 of ground water
as the dolomitizing agent, but some have advocated that
M'gSOLl was very effective. For instance, Collegno, as early
as 1834, pointed out the frequent association of gypsum and
dolomite in the St. Gothard region and regarded these both
as transformation products resulting from the action of the
M8804 in surface water on limestone. For similar reasons
Haidinger (1827) advocated this method of origin, but since
he found evidence that "under ordinary conditions a solution
of Case), tends to convert dolomite into MgSOh and CaC03'" he
assumed that the contrary change takes place at great depths
and under considerable pressure.

Haidinger (1827) first pointed out that dolomite
might be formed by the partial replacement of calcite by
magnesium carbonate and described a dolomite pseudomorph
after calcite, intimating that it had been formed in this
manner. It remained for Beaumont (1836), however, to put
this theory into definite form. Reasoning on the basis that
"the replacement was molecular and that one out of every

two equivalents of CaCO3 Was replaced by MgCO3‘" he calculated

22

that “the transformation of limestone to dolomite should be
accompanied by a decrease in volume of the rock to the
extent of 12.1 per cent .'" This he believed would explain
the cavernous character of the dolomites of the Tyrol.
Actual porosity determinations of a sample of dolomite from
the Alps by Morlot (1847), who obtained the value of 12.9
per cent, later seemed to confirm this prediction.

Scowler (1838) also favored this view for the origin
of the Carboniferous dolomites of Ireland, believing that
the alteration might readily be accounted for by the in-
filtration of water charged with MgCO3. He suggested that
the magnesia was derived from an igneous or ancient
Paleozoic rock, or from springs.

Discussing the dolomite of the coral island of Metia,
Jackson (1843) suggested that ascending spring water bearing
MgC03 might have effected the change. Likewise, Haussmann
(1854) believed that the dolomite of the Muschelkalk was
produced by the action of MgC03 of ascending thermal springs
on limestone.

It will be observed that most of the foregoing
advocates of the ground water alteration theory attributed
the source of the magnesia to spring water. An entirely
different idea, however, was entertained by Green (1876),
Who suggested that the MgCO3 might be furnished by the
decomposition of olivene sand incorporated in the limestone

at the time it was formed. It was his belief that "'many

 

 

23

magnesian limestones and dolomites as well as serpentinous
streaks in limestone may have been formed in this manner."
There always has been a tendency to regard dolomite
veins in limestone as the product of the reaction of the
MgCO3 of circulating ground waters on limestone. For in-
stance, Schmidt (1875) expressed the view that the dolomit-
ized limestone associated with the ores of the Joplin
district was formed in this way. In like manner, Michael
(1904) attributed the “dolomitization of the Muschelkalk

along lines of disturbance at Tarnowitz, in southeastern

.H

Prussia, to the same cause. The dolomitization there

appeared to be closely bound up with the mineralization
phenomena, the sulphide ore deposits being limited to the
dolomitic areas.

The local dolomitization effects in the Leadville
limestone of the Aspen district of Colorado also were
attributed to the action of the magnesia of ground. water
by Spurr (1898). The limestone is dolomitized along faults
and fractures and '"the local dolomitization almost in-
variably accompanies the ore .‘"

Van Hise (1904) strongly emphasized the importance
01‘ dolomitization through the agency of ground water, and
it would appear that he gave this method of dolomite for-
mation precedence over dolomitization beneath the sea.

Local dolomitization phenomena along fissures in

the Carboniferous limestone of South Wales was attributed

 

24

to the action of ground water by Dixon (1907), who stated
that water percolating downwards from the surface effected
the change. Wichmann (1909) likewise had described local
dolomitization effects in the Korallenoolith (Jura) which
he ascribed to the“ action of ground water bearing MgCO3.

E. Steidtmann (1911, 1917), expressing himself upon
the efficiency of ground water in producing dolomitization,
regarded '"this method of dolomite building as capable of
operating only locally.“

R. A. Smith (1915) stated that “geologic evidence
in favor of the replacement process is so strong that it
has been commonly accepted as the dominant process in dolo-
mitization.'"

D. F. Hewett (1928, 1931) has utilized the local
dolomitization near lead and zinc deposits along fractures
and minor partings as a local aid in searching for ore
bodies.

F. W. Beales (1953) in his study of the dolomitic
mottling in the Palliser (Devonian) limestone regarded it
as the result of '"secondaryalteration and recrystallization
in the rock.'" He believed that there was a “relationship

between dolomitization and organiz remains in the limestone."

LPneumatolytic Alteration
The pneumatolytic theory of the origin of dolomite
was introduced in 1779, by Arduino, to whom we are indebted

for the first attempt to explain the formation of the rock.

 

25

Heim (1894) also entertained similar views as to the origin
of the rock, but it remained for Von Buch (1847) to develop
the theory and put it in definite form in the early twenties
of the last century. In his studies in the Tyrol, he
observed that '" the dolomite was vesicular; that the bedding
planes and the fossils were obliterated and that a brec-
ciated, fissured and crystalline structure had been taken

on ."

He, therefore, concluded that this could represent
no original deposit from the sea, but that it must have
been deposited at first as limestone and subsequently
altered. This alteration, he believed, was accomplished by
"volcanic vapors bearing magnesia, which were given off by
the intrusions of augite porphyry which there penetrate the
rock.“ This belief, however, was not shared by Wissmann
(1859), nor by Fournet (1849), who were unable to find any
constant association of the dolomite with the intrusives.

In 1843, Klipstein adOpted the pneumatolytic theory
to explain the veinlike deposits and irregular masses of
dolomite in the transition limestone of the Lahn district,
holding that "ascending magnesian vapors had effected the
transformation," although he 'was not able to find fissures
extending downwards from the dolomite in all cases (Bischof,
1859).

Karsten (1848) also favored the volcanic theory as
elaborated by Von Buch. Frapolli (1841) similarly has gone

on record in favor of this view, holding that “the dolomites

 

 

26

were formed through the agency of volcanic emanations
either while deposition was going on beneath the sea or
after the rock was deposited.“

D. F. Hewett (1924) explained the dolomitization of
rocks in the Spring Mt. Range of Southern Nevada as due to

solutions from small intrusive bodies of orthoclase porphyry.

III. Leaching Theories
It has been long known that when a magnesian lime-
stone is subjected to solvent action the lime is taken into
solution much more rapidly than the magnesia, giving rise
to a concentration of the latter constituent. Thus many
geologists have held that by the continued leaching of a
limestone originally low in magnesia, either at the surface

or beneath the sea, a dolomite might in time result.

IL. Surface Leaching

The belief that dolomite might result from surface
leaching seems to have been first suggested by Apjohn (1838),
who stated that "'the CaC03 might be removed from limestones
containing some magnesia by the solvent action of carbonated
waters, and that some dolomites might have been produced in
this manner.“ Grandjean subsequently was led to adopt the
Same explanation, in 1844, to account for the dolomites of
the lower Lahn district, and he pointed out that the dolo-
mite was developed to its greatest extent near fissures and

Cracks in the limestone where water had had easy access.

27

The same theory was accepted by Sandberger the following
year for the dolomites of the same district.

In support of this theory are the observations of
Bischof (1859), who showed by experiment that “carbonated
waters do not dissolve out of magnesian limestone more than
a mere trace of magnesia" and concluded '" that dolomite
would ultimately ‘be formed either by the action of surface
water, or of sea water on limestone."

Hardman (1875, 1877) also regarded this as the
plausible theory of dolomite formation, and he sought by
its employment to explain the method of origin of the
Carboniferous dolomites of Ireland.

Later, Hall and Sardeson(1895) favored this theory
in their discussion of the origin of The Magnesian Series
9; the Northwestern States. Phillipi ( 1907), in like
manner, adopted the leaching theory to account for the
Conchodon dolomite of the southern Alps.

E. Steidtmann (1911) recognized "'a little dolomiti—
zation caused due to leaching or weathering of limestone
and leaving magnesium behind."

c. B. Claypool and w. Howard (1928), in studying the
relationship of calcite and dolomite in a sediment as a
criterion for the recognition of an uncomformity, stated
that "porosity is attended by a leaching of the calcite
With a retention of the dolomite.“

Recent studies by Thiel and Sherman (1938), however,

attributed an enriched dolomitic zone in the glaciolacustrine

28

silts of glacial Lake Agassiz to the work of ground waters
rich in magnesium rather than a removal of the calcite with

a retention of the dolomite.

B. Marine Leaching

 

That marine leaching of calcareous deposits low in
magnesia might give rise to dolomite was suggested by
Bischof in 1859, but he made no attempt to elaborate the
idea. Eleven years later, Gfimbel (1870), in making a study
of certain deep sea oozes, found one taken from a depth of
2,350 fathoms in the Atlantic which yielded upon analysis
1.44 per cent magnesia. This magnesia content was accounted
for upon the basis of the solution of a portion of the
original calcareous material, and it was suggested “that by
the same method dolomitic rocks and marly intercalations
might be formed" (Van Tuyl, 1914).

The marine leaching theory, however, has been most
fully developed by Hbgbom (1894). The writer regarded
marine leaching as far more important than surfacing
leaching, since the latter can operate only on that portion
of the limestone exposed. Hbgbom also furnished evidence
of enrichment of magnesia by marine leaching in the coral
reefs of Bermuda.

Judd (1904) was of the opinion that the dolomitic
rock disclosed by the boring at Funafuti was formed, in

part at least, by marine leaching.

29

Peach and Horne (1907) were favorable to the idea
that marine leaching may account in part for the Cambrian
dolomites of the Northwest Highlands of Scotland, sug-
gesting that “unicellular plants which secreted lime may
have existed as plankton, as in the sea today, and that the
small magnesia content of these may have been concentrated
by the abstraction of the more soluble CaCO3." They be-
lieved, however, that some replacement had also taken place.

Murray and Hjort (1912) concurred that the expla-
nation of enrichments of magnesia in deep sea deposits was
to be sought in preferential dissolution of the lime. En-
richment of the magnesia by reaction with sea water did not
seem plausible to them, "since this would require that the

waters be concentrated with MgC03."

New Classificatifon

 

Inasmuch as there is no agreement among the American
geologists as to the meaning of primary and secondary
dolomites (Rodgers, 1954), it is necessary for anyone using
these terms to specify what he means in order to be under-
stood. For instance, another classification of dolomites
has been adopted by Vishnyakov (1951), which includes three

genetic types: (A) primary, (B) diagenetic, (C) epigenetic.

IL. Primary Dolomites
Primary dolomites formed by direct chemical prec1p1_

tation can be recognized easily when associated with other

30

primary sediments. These dolomites lack primary porosity
and caverns and are commonly interlayered with clays, marls,
and gypsums (commonly containing pseudomorphs after gypsum),

(Chilingar, 1956).

B. Diagenetic Dolomites

 

Diagenetic dolomites can be found in the form of
layers or lenses with obscure stratification. They have
slight porosity and fine-grained texture with xenoblastic
grains of irregular form, which are filled with dust-like
inclusions. Relict structure is commonly evident, and the
fauna ordinarily remains in the form of molds (Chilingar,

1956) .

C. Epigenetic Dolomites

The epigenetic dolomites result from alteration of
completely lithified limestones by downward percolating
meteoric solutions or rising hydrothermal solutions.
Epigenetic dolomites are cavernous, having obscure stratifi-
cation, patchy distribution, non-uniform grain size, and
relict structure. Chilingar (1956) noted ”that the (Ia/Ms
ratio of epigenetic dolomites varies widely over short

distances, both vertically and horizontally.‘“

Dolomitization and Porosity
At least four or five major theories have been ad-
vanced to explain the presence of significant porosity in

dolomites. The classic theory, proposed by Elie de Beaumont

31

(1836) stated that molecular replacement of limestone by
dolomite would result in a volume shrinkage of between 12
and 13 per cent. This theory ceased to receive serious
consideration after 1912 when Lindgren in his well known
paper on replacement pointed out that "replacement is on
a volume for volume, and not molecule for molecule, basis"
(Lindgren, 1912). Steidtmann (1917) described field evi-
dence for replacement of limestone by dolomite with volume
change.

The most detailed attack on the Beaumont theory was
made by Murray (1930). He called attention to the fact
that "the presence of oil in porous dolomitic limestones
has led many to believe that the process of dolomitization
has been responsible for the development of the openings in
which the oil occurs." '" The theory that the dolomitization
of a limestone produced porosity appeared in the literature
early in the 19th century. The evidence, if such there was,
which gave it support seems to have been lost while the
theory itself lingers. The writer was unable to find in the
literature any criterion by which porosity by dolomitization
can be distinguished from primary porosity or porosity
developed by leaching and solution. Many dolomites are
described in which the porosity is supposed to have been
caused by this process, but no observer, as far as can be
determined, has ever advanced any evidence in favor of

this conclusion'.‘ (Murray, 1930)-

 

32

The theory that the cavities in porous dolomite are
{reduced by differential leaching of carbonate rocks has
zinumber of adherents. There are three divisions to this
immory, depending upon whether the material leached is
celcite, dolomite, or fossils. The concept of the formation
cfi'cavities through the leaching of calcite is a by-product
cfi'one of the theories of the origin of dolomite advanced
lurHardman (1875-77). According to this idea, the original
carbonate rock was a mixture of calcite and dolomite
crystals which became dolomite through the solution and
removal of the more soluble calcite. '"Such selective
mflution would produce cavities, but not local dolomiti-
zmtion porosity, for the non-dolomitized parts of the
cerbonate rock are not rich enough in dolomite crystals"
(Landes, 1946).

The unusual idea that the leaching of some of the
ckflomite from a dolomitic limestone ooze has produced
Ixmosity was expressed by R. H. Fash (Van Tuyl, 1945).

The vulnerability of dolomite-enclosed fossil shells,
eepecially where calcitic, to leaching by ground waters is
well known (Hatch, Rastall and Black, 1938). The result
(fi'this differential leaching is a highly porous rock in
the zone of weathering. .

Dolomites, in addition to becoming porous through
the dissolving of fossils, can become porous, and even

cavernous, through ground-water solution in the same manner

33

as limestones. Murray (1930) and Howard and David (1936)
pointed out the importance of ground water leaching of
carbonate rocks above the water table. Davis (1930) and
(Rich 1938) emphasized the possibilities of solution below
the water table, either by free or confined water.

Then, there is the theory that dolomite porosity is
produced by recrystallization. This was Orton's conclusion
(1888) for the porous Trenton dolomite in Ohio. J. E. Adams
(1934) believed that: “Recrystallization may also be re-
sponsible for some enlargement of porosity and increase of
permeability." '"It is especially noted in dolomites, but
may also be present in limestones" (Adams, 1934).

K. K. Landes (1946) believed "'that local diastrophism
has produced master fissures in the limestone-containing
section; that an artesian circulation has been developed
which has carried waters through deeper dolomites and up
into the limestone; and that these waters have replaced some
of the limestone by dolomite that is locally porous where
there was an excess of solution over precipitation during
the replacement process."

R. B. Hohlt‘s statement (1948) adequately concludes
this review: '"Because of the great amount of commercial
porosity, which is restricted to dolomitic facies within
limestones, there has been a growing tendency for geologists
to relate porosity to the process of dolomitization.”

.uA relathHShip exists between porosity and the process,

 

34

or processes of dolomitization but what the Specific re-

lationships are have not been established" (Hohlt, 1948).

 

FIELD DATA

Location of Area

 

The area selected for the purpose of determining the
relationships between subsurface structure and the degree
cfi‘dolomitization, as reflected primarily by the Mg/Ca
(Magnesium/Calcium) ratio, centers about Michigan's most
prolific structural-type Rogers City fields. It consists
cfi‘the northwest part of Isabella County, including Nottawa
(T.15 N., R.5 w.), Shaman (T.15 N., R.6 w.), Vernon
(T.16 N., R.4 w.), Gilmore (T.16 N., R.5 w.), and Goldwater
(T216 N., R.6 W.) townships, and the northeast part of
chosta County, including Sheridan (T.15 N., R.7 w.),
Martiny (T.15 N., R.8 w.), Colfax (T.15 N., R.9 w.), Fork
(T. 16 N., R.7 w.) and Chippewa (T.16 N., R.8 w.) townships.
Tfle area, approximately 400 square miles, lies in the center
(fi‘the Michigan basin.(See Map 1.)

Seventy wells were chosen at random from the tract
Emudied with the availability of well samples as a re-
stricting factor to selection. Twenty-five wells were
taken from the Coldwater field exclusively for a more
detailed study as related to a definite prolific structure.
AWootal of ninety-five wells were used to represent the

auea for Mg/Ca ratio studies.

35

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MICHIGAN

 

 

MAP 1

 

 

 

 

Location of Area

 

 

 

 

SCALE

 

MILES

 

40

20
M.

 

Ila“, Dart. of Glul. I Bug.

1

 

I
u
I
I
'
nu.
m
.I
I
‘
1
.I
I
m
o
‘
M
.N
-
I
c

I
It
u
I
9
M
.

 

 

 

 

 

 

I.’

f "T"! "51

 

 

37

Oil fields producing from locally dolomitized lime-
stones of the Rogers City formation are the Coldwater,
Sherman, and Fork fields which lie on a northwest-southeast
structural trend through the central portion of the area
chosen for study. (See Map 2.) These fields were named
by Carl C. Addison as typical examples of oil fields pro-

ducing from locally dolomitized limestones (Landes, 1946).

Stratigraphy

 

The reservoir rock in the area of study is the Rogers
City limestone of Middle Devonian age. It is overlain by
the Bell Shale member of the Traverse group and lies ap-
parently conformable with the Dundee formation. (See
Figure 1.) Before the Rogers City limestone was named
(Ehlers and Radabaugh, 1938) these rocks were placed in the
upperemost Dundee formation and still are so classified in
oil-field terminology. In some areas the formations are
colloquially designated as "Dundee" or "brown lime" for
the Rogers City formation, and "Dundee Restricted" or "black
lime" for the lower, or true Dundee formation. In this
report the formations will be referred to as the Rogers City
for the upper formation and Dundee for the lower formation.
The Dundee consists of a "typical buff to light
brown cherty limestone, dolomitic limestone, and dolomite
varying from approximately 50 to 400 feet thick. Excepting
the southeastern part of Michigan where the Rogers City is

absent, the Dundee is divided into two formations. The

 

 

MICHIGAN DEVONIAN SYSTEM

System Group

R
——:_

Formation

 

)4 2 C) <1 to U

23>

TRAVERSE

Squaw Bay
Thunder Bay
Potter Farm
Norway Point
Four Mile Dam
Alpena

Newt on Creek
Genshaw
Ferron Point
Rockport Quarry
Bell Shale

 

CAZENOVIA

Rogers City

Dundee

 

DETROIT
RIVER

 

 

Lucas
Amherstberg
Flat Rock
Sylvania

Bois Blanc
Garden Island

 

Figure l. Generalized columnar section of
Devonian system in Michigan basin, after
Helen M. Martin, Michigan Geological Survey.

 

39

Rogers City is a typical dark-colored brownish-buff dolo-
mitic limestone or dolomite" (Cohee, etc., 1948). It is
a predominantly fossiliferous, marine limestone altered
locally to dolomite in west-central Michigan and overlaps
the Dundee over the northern two-thirds of the Southern
Peninsula.

'"The underlying Dundee formation restricted, con-
sists typically of buff and light brown limestone, becoming
more dolomitic and even containing some anhydrite in the
lower part in western Michigan" (Cohee, etc., 1948). The
Ihmdee in the east and northeastern areas of the Michigan
basin is a marine limestone, predominantly tan, containing
oolites and stylolites and with a more varied fauna in the
peripheral areas (Knapp, 1956). '"In west-central Michigan,
in a belt extending north and south, a so-called 'primary'
dolomite, crystalline, even-textured, predominantly tan and
lacking in recognizable fossils except for occassional
stromatoporoids" makes up the characteristic lithology of
the Dundee (Knapp, 1956).

It is the contention of some geologists that an un-
confonmity exists at the base of the Traverse group between
the Bell shale and the Rogers City formation. R. B.
Newcombe (1930) states that "the facts strongly indicate
that there is a surface of unconformity at the base of the
Traverse over a large part of southern Michigan, but it

has not yet been clearly established;" Ehlers, working in

 

 

4O

lkesque Isle County, Michigan, states that ”the contact of
3the Rogers City limestone with the overlying Bell shale is
disconformable; the effects of erosion of the Rogers City
limestone prior to the deposition of the Bell shale are
well illustrated" (Ehlers and Radabaugh, 1938).

K. K. Landes (1951) also states "that emergence
followed the deposition of Dundee and Rogers City strata
and subsequent erosion stripped these rocks from the south-
vmstern corner of Michigan and again exposed the Detroit
River group at the surface."

T. S. Knapp (1947), on the other hand, states that
it is not unusual to find evidence of erosion perpheral to
a deposition basin but that cores of the Bell shale-Rogers
City contact "show no visible plane of demarkation between
the two formations; evidence of erosion is absolutely
lacking." "Therefore, in the absence of any reported direct
evidence from cores of post-Rogers City erosion in the
central basin area, it is apparent that the Rogers City was
not eroded on any regional scale. If erosion has occurred
it has been limited to isolated ‘islands' which may or may
not have protruded above the surface of the sea. Cores from
anticlinal structures; such as are occupied by the Reed
City, Coldwater, and Fork oil pools, show continuous depoe
sition from Rogers City into Bell, so present anticlines
mere not necessarily sites of emergence at that time"

(Knapp, 1947).

 

Even—fl —.

 

r~.

 

A“

fl.-. —— —-

 

 

41

Coldwater Oil Field

 

The Coldwater oil field is located in the southwest
quarter of Coldwater township (T.16 N., R.6 w.), Isabella
County, Michigan. It is approximately 10 miles north and
14 miles west of the city of Mt. Pleasant in the west
central part of the Michigan basin.

The Coldwater oil field was discovered in August,
1944. The discovery well flowed 200 barrels of oil the
first 24 hours from the Rogers City dolomite. The top of
the "pay" in the Rogers City lies, in most wells, within
20 feet of the base of the overlying Bell shale.

"A total of eighty-one producing wells and nine dry
holes have been drilled with development substantially
completed by the end of 1946. Subsequent to 1946, seven
producing wells and two dry holes were drilled on the
extreme edges of the field. By 1952 the cumulative pro-
duction was 12,763,000 barrels of oil and 28,800,000 barrels
cfi‘water and there were 69 producing wells" (Criss and Mc-
Cormick, 1953).

The regional dip is northeast and the steepest dips
cfl'the Coldwater structure are along the northeast side of
the field with slightly lesser dips toward synclinal re-
entrants along the north and south sides of the field. The
major axis runs NW-SE and a minor axis trends NE-SW. (See

Map 2.)

 

42

The Rogers City is a secondary dolomite 30 to 35
feet thick in the Coldwater field; the Dundee is primary
dolomite 200 feet thick (Criss and McCormick, 1953). "'Cores
taken from two wells indicated no barrier to vertical fluid
movement at the Dundee-Rogers City contact. Penetration of

the Rogers City zone averaged 11 feet" (Criss and McCormick,

1953).

LABORATORY PROCEDURE

Methods

Conventional chemical methods of determining
nmgnesium and calcium content of limestones and dolomites
are time consuming and tedious, with chemical methods in-
volving precipitation and separation of the two constitu-
ents in solution; whereas, staining methods using silver
chromate, potassium ferricyanide or Lemberg's solution
usually require the preparation of polished thin sections
and detailed examination to determine the amounts of dolo-
mite and calcite present (Keller, 1937; Douglas, 1944; and
Clark, 1924). Spectrochemical and spectrographic analyses,
although conducted with greater speed and at a low cost of
operation, appear to vary in accuracy from 1.5 to 10 per
cent error within a single set of data (Sloss, 1946;
Anderson, 1954; Ahrens, 1950).

G. Schwarzenbach (1946) and co-workers published in

Helvetica Chimica Acta a new simple titration for the deter-

 

nunation of water hardness.l This method consists of the

k

lThe'"theoretica1 hardness of water is the sum of the
concentrations of all the metallic cations other than cations
of the alkali metals, expressed as equivalent calcium car-
bonate concentration. In most waters, nearly all of the
hardness is due to calcium ion and magnesium ion.
(Standard Methods , 1955).

43

44

Lee of ethylenediaminetetraacetic acid (commonly called
versene or abbreviated EDTA) as a titrant for the sum of
celcium and magnesium in water, using the dye known as
Chrome Black T as an indicator.

Schwarzenback (1947) applied this method of titration
to the analysis of alkaline earths and other metals. Later,
Botha and Webb (1952) used this same method for the deter-
ndnation of calcium and magnesium in mineralized waters
containing large concentrations of interfering ions. In
tfie same year Cheng, Kurtz and Bray (1952) adapted this
method to the determination of calcium, magnesium and iron
in.1imestones without the tedious separation of the three
elemenets before analysis.

In an attempt to find the most recent modifications
in the improvement of this method the author reverted back
to the object of its original purpose--ana1ysis of water

hardness. In the Zlatest; edition of Standard Methods for

 

the Examination of Water, Sewage, and Industrial Wastes,

 

 

 

 

(1955) published by the American Public Health Association,
severa1"Compleximetric" or EDTA titration methods, modified
from the original procedure for more accurate results, are
given for: (l) the determination of total hardness of water
(the sum of Ca and Mg ions) and, (2) for the determination
of Ca ion content in the presence of Mg ions using ammonium
purpurate as the indicator.

The second method, as listed above, is recommended

for the most accurate results (accurate to 5 parts per one

45

ndllion or an error of plus or minus .005 per cent) and
vnth the advantage of analyzing for calcium in the presence
cfi‘magnesium (Standard Methods, 1955).

A photometric method was adopted by the author for
tfie determination of magnesium with an accuracy of plus or
nunus 1 per cent error and with the advantage of analyzing
:hlthe presence of calcium salts, directly on the water
sample (Standard Methods, 1955).

The Phenanthroline-photometric method was used for
the determination of the iron content with an accuracy of
{nus or minus 1 per cent error (Standard Methods, 1955).

The three methods used in the chemical analyses for
calcium, magnesium and iron content of the limestone samples
will be described here briefly since the procedure for each
method is clearly outlined, step by step, in the Standard

Methods manual.

Samples

are:

Cable tool and rotary tool samples were used for
analysis, Cable tool samples are quite satisfactory for
use and unless the sample is very fine-grained a represent—
ative portion can be selected megascopically. Samples
cmtained by rotary tool methods are more difficult to work
with due to the necessary separation of foreign material

from the rock to be analyzed. The separation procedure

46

used by the writer was as follows: (1) every "mixed" sample
has sieved, separating that portion between Tyler screens
#20 and~#38 (0.58-0.83mm) which corresponds to Wentworth's

"coarse sand," (2) each sample was

size classification of
examined by means of a binocular microscope with pieces of
caving removed (shale has a tendency to cave into return
Imud fluid, but it can be easily picked out).

Regarding rotary well samples, R. M. Whiteside (1932)
states: '"A sample of rotary cuttings containing less than
2X>per cent of cavings or re-circulated material is con-
sidered as good workable quality." It is the opinion of

the writer that there was considerably less than 20 per cent

cavings in the "mixed" rotary samples.

Sample Selection

 

Samples which represented the top 20 feet of the
Rogers City formation beneath the contact of the Bell shale
were taken from each well. In the case of some wells 3 or
llsamples, taken at 5-7 foot intervals, were necessary to
represent the top twenty feet. Some wells were not repre-
sented by samples for-the entire 20 foot section, but what—
ever samples were available were analyzed. Each well was
assigned a number and the samples from that well were
assigned a letter, for example: Well #6, samples: 6a, 6b,
6c, and 6d.

 

47

Sample Preparation

 

All samples were thoroughly washed with distilled
water. Agitation by shaking and decantation of the wash
water aided in removing rock dust or rotary mud adhering to
the particles. Shale cavings and other foreign material
were removed and all "junk" iron present was picked out by
passing a magnet through the sample. Each sample was then
thoroughly dried over a hot plate within a closed hood.

Samples of 1.00 gram were weighed and placed in 250
nulliliter beakers (Banewicz and Kenner, 1952). Ten milli-
liters of hydrochloric acid (1:1) and 15 milliliters of
distilled water were added to each of the samples. This
was evaporated to dryness, baked for approximately one hour,
and allowed to cool. The residue was taken up with 3 milli-
liters of hydrochloric acid (1:1) and 10 milliliters of
distilled water. Each solution was then filtered, washed,
and made up to 200 milliliters with distilled water. The

samples were now ready for the chemical analyses.

Calcium Determination

 

EDTA Titration Methodl

Reagents

1. EDTA titrant. Dissolve 48 grams of disodium
dihydrogen ethylenediaminetetra acetate dihydrate

lStandard Methods for the Examination of Water,
Sew e, and IndustFIal Wastes (New York: Am. Pub. Health
ASSOC') 955 3 p0 l o ,

 

48

in 9600 milliliters of distilled water. Add
10.32 grams of NaOH. Standardize this solution
against a standard calcium solution by titrating
l milliliter of the standard calcium solution
with EDTA titrant in the manner described under
Calculations.

Standard calcium solution. Dissolve 1.00 gram

of reagent-grade calcium carbonate in dilute HCl,
add 200 milliliters of distilled water and boil
for a few minutes to expel C02. Cool and make

up to 1 liter with distilled water in a volumetric
flask. This standard contains 1.000 milligram
CaCO3 equivalent in each milliliter.

Indicator mixture. Ammonium purpurate (murexide)
is used as the indicator.1 Suspend 50 milligrams
of ammonium purpurate in 50 milliliters of ab-
solute ethyl alcohol. Store in a dropper bottle
and shake before using. The suspension is stable
for at least a year.

Sodium.hydroxide solution. Dissolve 80 grams of
NaOH in 800 milliliters of distilled water; cool;
and dilute to 1 liter.

Essential Apparatus

 

Pgocedure

l.

l 10 ml. microburette--graduated at 0.05 ml
intervals
1 ml pipette
10 ml pipette
50 m1 pipette
250 m1. Erlenmeyer flasks

NHHH

Pipette a l milliliter aliquot of the dilute
sample (1:200) into a 250 milliliter Erlenmeyer
flask. Add 50 milliliters of distilled water.

Add 1 milliliter of the sodium hydroxide solution
and approximately 5 drops of ammonium purpurate
indicator.

Stir the solution and titrate with the standard-
ized EDTA titrant. The end point is reached

1Eastman No. 6373 has been found satisfactory.

 

49

when the color of the solution changes from pink
to purple. (The use of an electric stirrer
during titration kept the solution uniformly
mixed, thus increasin the accuracy of deter-
mining the end point.) The color change at the
end point is very subtle and requires some
practice on the part of the analyst. Check the
end point by adding 1 or 2 more drops of titrant;
no further color change should occur. The
titration must be completed within 5 minutes
from the time of adding the NaOH.

4. Two determinations were made for each sample.
The readings were within 0.05 milliliters of
each other. The average of the two readings
was used.

Standardization of EDTA titrant with standard calcium solution

The standard calcium solution prepared contains 1.00
milligram of CaCO per milliliter of solution. Nine
and five—hundreds (9.05) milliliters of EDTA titrant
were necessary to titrate, to the end point 10 milli-
liters of the standard calcium solution diluted with
50 milliliters of distilled water. Titrating a dis-
tilled water blank, 0.05 milliliters of titrant were
used. The amount of titrant used on the standard
CaCO3 solution then was 9.05 - 0.05 = 9.00 milliliters.
EDTA titrant 10 mg CaCO per 9.00 ml
1.111 mg C CO3 per 1 m1

 

lEthylenediaminetetraacetic acid and its sodium salts

form chelate complexes with metal cations. The calcium and
magnesium complexes are colorless and the calcium-EDTA
complex is more stable than the magnesium-EDTA complex.
EDTA titrant combines with calcium before it combines with
magnesium. At a pH of about 12 ammonium purpurate has a
DUrple color. In the presence of traces of calcium its
color turns to pink. EDTA is capable of extracting calcium
from its purpurate complex and, thus, of restoring the
purple color of ammonium purpurate. Magnesium does not
Change at this pH. These facts permit the titration of
calcium in the presence of magnesium (Standard Methods,
1955, p. 113).

50

Calculations

Calcium as mg/liter CaCO

3

= ml of titrant x 1,000 x 1.111
ml of sample

= 9.00 ml x 1,000 x 1.111
10 ml standard CaCO3

999.99 mg/ liter CaCO3

 

Calcium as mg/ liter Ca

ml of

= titrant

Molecular Wt. Ca

Equivalent Wt. of Calcium
Molecular Wtf'CaCO

3
Equivalent Wt. of Calcium = 40.08 = .4004
100.09
equivalent 01 e mg equivalent wt.
wt. of Ca X V um X of CaCO3 /'ml titrant

 

m1 of sample used

ml of titrant x .4004 x 1000 x 1.111

ml sample

9.00 ml x .4004 x 1000 x 1.111
10 m1

400.395 ml/lit Ca or .4004 mg/ml Ca

Then 1 m1 of titrant = .4004 mg Ca
Using 1 g of sample diluted to 200 milliliters
then 1 m1 = 1 g = .005 g of sample

200 m1

Computation of per cent calcium

If these procedures were followed in the analysis
of a 1 m1 portion of a 1 g sample diluted to
200 m1 and 3.70 ml of titrant were used in the

titration, then:
m1 titrant x .4004 mg Ca/ml x volume =.mg Ca/ml
3.70 x .4004 x 1 ml = 1.4813 mg Ca/ml

1.4813 mg = .0014813 g

51

2. g of sample used : 100% :: g Ca : % Ca
.005 g : 100% :: .0014813 g Ca : % Ca
% Ca = 29.63

Magnesium Determination

 

Two methods for the determination of magnesium are

given in the manual of Standard Methods applicable to all

 

natural waters. Magnesium can be determined by the gravi-
metric method only after prior removal of calcium salts.

It can, however, be determined in the presence of calcium
salts, directly on the water sample by the "Photometric
method." Both methods are applicable to all concentrations
by the selection of suitable aliquots (Standard Methods,
1955). The method used is largely a matter of personal
Ineference, but since it is unnecessary to separate the
calcium from the magnesium before the analysis of the sample

in the "Photometric method" this was adopted by the author.

Photometric Methodl

Pginciple When magnesium hydroxide is precipitated in
‘ffie presence of brilliant yellow, the dye is absorbed
on the precipitate and its color changes from orange
to bri ht red. A stabilizer is added to maintain
the Mg OH)2 in colloidal suspension.

 

Interference Interference from calcium and aluminum is
avoided by raising the concentrations of these ions
to a level where their influence is constant and
predictable.

lStandard'Methods, 1955, p. 135-

 

52

Essential Apparatus

1

[UMP-4mm

Reagents

Spectrophotometer (Bausch and Lomb Spectronic
20), used at 525 millimicrons, providing a light
path of 2.5 cm.
100 m1 volumetric flasks

1 m1 pipette

4 m1 pipette

5 m1 pipette

20 m1 pipette

Standard magnesium stock solution.1 Add 1.000
gram of rough turnings of pure magnesium metal,
not less than 99.9 per cent Mg, to a 500 ml
Erlenmeyer flask. Add 150 milliliters of dis-
tilled water and 5.0 milliliters of sulfuric

acid (1:1). Mix well, allow reaction to subside
and boil 10 minutes. Cool; transfer to a 1 liter
volumetric flask and make up to the mark. The
solution should be water-white and crystal Clear.
1 m1 = 1.000 mg Mg

Standard magnesium working solution. Dilute
100.0 ml of standard magnesium stock solution
to 1 liter with distilled water. This solution
is equivalent to 100 mg/'liter Mg.

Aluminum solution. Dissolve 0.31 g A12(804) .
18H20 in distilled water and dilute to 1 lit r.

Saturated calcium sulfate solution. Saturate
distilled water with CaSOu and filter.

Brilliant yellow solution. Dissolve 0.50 gram
of solid dye (National Aniline Co., Color index
No. 364 or equivalent) in liter of distilled
water. Prepare freshly every 2 or 3 days.

Sulfuric acid solution. Add 0.3 milliliters
concentrated H2804 to 1 liter of distilled water.

Sodium hydroxide solution. Dissolve 200 grams
of NaOH in distilled water; cool; dilute to 1

liter.

1High purity magnesium is available from Dominion
Magnesium Ltd., Suite 1505, 320 Bay Street, Toronto, Ont,

(mnada.

53

8. Stabilizing solution-Colloresin LV. Suspend
1.00 gram of Colloresin LV in 100 m1 of distilled
water by shaking. Place in a refrigerator over-
night, and allow to reach the same temperature of
other reagents before use.

9. Sodium sulfite solution. Dissolve 1.0 gram of
anhydrous Na 803 in 100 ml distilled water.
Prepare fresfily each day.

Procedure

 

l. Pipette 1 m1 of diluted sample (1:200) into a
100 ml volumetric flask (if sample is further
diluted 20 m1 are used).

2. Add 1 m1 of sodium sulfite solution.

3. Add, in order, 1 ml H2804 solution, 20 m1 cal-
cium sulfate solution, and 5.0 ml aluminum
solution.

4. Bring volume to about 80 ml with distilled water
and.mix.

5. Add 5.0 m1 of Colloresin LV, 2.0 m1 of brilliant
yellow solution, and 4.0 ml NaOH solution.

6. Dilute to the mark; shake vigorously; and wait
5 minutes for full color development.

7. Compare photometrically within an hour against
a blank prepared from distilled water and all
of the reagents. Use selected, optically matched,
1 inch test tubes and adjust the difraction
grating in the spectrometer to transmit light
having a wavelength of 525 mmu. Set the instru-
ment at 100% transmittance using this blank.

§§andard Calibration Curve for Magnesium

A standard curve should be drawn on single cycle
semilogarithmic paper with the per cent trans-
mittance plotted on the logarithmic axis and the
concentration of magnesium plotted on the arithmetic
axis. The curve should be drawn through at least

5 points corresponding to .01, .02, .04, .06, .08,
and .10 grams of Mg per 100 milliliters made from

 

54

the dilute standard working solution of Mg. A
new curve should be prepared for each batch of
reagents.

Calculations

Results are read directly from the instrument in
units of per cent light transmittancy through the
colored sample. Referring to the standard cali-
bration curve the concentration of the sample can
be determined in grams of magnesium per 100
milliliters.

% Mg = g Mg/lOO m1 g(read from calibration curve)
m1 aliquot x g of sample/ ml of diluted
original sample

% Mg = grams of Mg/lOO grams of original sample

Computation of Percentage Magnesium

If these procedures were followed and in the analy-
sis of the sample (dilution 1:200) per cent light
transmittancy was read as 79% from the instrument
then the Concentration of Mg in the sample per 100
milliliters is 0.046 g as read from the calibration

curve for magnesium.
%Mg = 0.046g/100 ml = 9.20%
1 m1 x .005 g
Magnesium-Calcium'Ratios
The ratio of calcium to magnesium may vary from 1.50
(in a normal dolomite) to infinity (in a pure limestone).
0n the other hand, the magnesium to calcium ratio will give

results within well defined limits which can be readily

applied to graphs and maps.
The ratio of Mg to Ca can be calculated from the

relative percentages as previously determined.

g‘

1Hawk, Oser and Summerson, "Relation between trans-
nuttance and concentration'" Practical Physiological
W: 12th ed. (1947), p. 469.

55

Example:
Me = 9.20% Mg/Ca = 9.20 =O.3lO
Ca = 29.63% 29.63

(See Table I for Mg/Ca ratios.)
Iron Determlnation
Phenanthroline Method1
(A Colorimetric Method)

The Phenanthroline method has been used for many
years for testing iron in a water supply and is known to
he reliable, if interfering substances are absent. Known
interfering ions are phosphates, chromium, copper, nickel,
cobalt, zinc, mercury, silver, cadmium, bismuth, fluoride,
molybdate, citrate, oxalate, tartrate, and some of the
rarer metals. Complete chemical analysis of dolomites and

limestones indicate none of the above named interfering

ions (Pirsson and Knopf, 1949)-

Egsential Apparatus

1 Spectrophotometer (Bausch and Lomb Spectronic

20), for use at 510 mmu providing a light path
of l to 10 cm.

2 1 m1 pipette
2 10 m1 pipette
12 100 ml volumetric flasks
1 pH meter
Note. All glassware must be acid-washed to
remove iron oxide film.

Reagents

l. Hydrochloric acid. Set aside a supply of con-
centrated HCl for this determination. Because

lStandard‘Methods, 1955, p. 125.

Procedure

10

56

HCl content varies from 35 to 38 per cent, the
sodium acetate solution must be adjusted for
the particular lot of HCl to be used.

Sodium acetate solution. Dissolve 350 grams of
NaC2H30 .3H20 in 500 ml. of distilled water and
dilute 0 approximately 1 liter. Using conc.

HCl and a pH meter adjust the pH of this solution
to a value between 3.2 and 3.3.

Hydroxylamine reagent. Dissolve 10 grams of
NHQOH'H01 in 100 m1 of distilled water.

1,10 Phenanthroline solution. Dissolve 0.12
gram C12H8N2.H 0 in 100 ml of distilled water
by stirring ang heating to 80°C ; do not boil.

Standard iron stock solution. Use electrolytic
iron wire to prepare the standard. Dissolve
0.2000 gram of wire in 20 ml HQSOu(1:5) in a 1
liter volumetric flask. Dilute to mark with
distilled water. This stock solution contains

200.0 mg Fe/liter.

Standard iron working solution. Pipette 5.0 m1
standard iron stock solution into a liter
volumetric flask and dilute to mark with distilled
water. This contains 10.0 mg Fe/liter. Then
pipette 5.0 ml into a 1 liter volumetric flask

and dilute to mark with distilled water. This

contains 1.0 mg Fe/liter.

Add 1 m1 of the dilute sample (1:200) that is
to be analyzed to a 100 m1 volumetric flask.

Add, in order, 1 m1 of hydroxylamine, 10 m1 of
sodium acatate solution and 10 ml of 1,10
phenanthroline solution.

Mix thoroughly and dilute to mark.
Wait 15 minutes for color development.

inst a
Com are hotometrically within an hour aga
blafik prgpared from distilled water and all of
the reagents. Use selected, optically matched,
1 inch test tubes and adjust the difrggtéggthcf
r tin to transmit light hav ng a wa
510 mmfi. Set the instrument at 100% transmittance

using this blank.

57

Standard Calibration Curve for Iron

A standard curve should be drawn on single-cycle
semi-logarithmic paper with the per cent trans-
mittance plotted on the logarithmic axis and the
concentration of iron plotted on the arithmetic
axis. The curve should be drawn through at least
5 points corresponding to .005, .01, .02, .03, .04,
and .05 grams of Fe per 100 milliliters from the
dilute Fe working solution. A new curve should be
prepared for each batch of reagents.

Calculations

 

Results are read directly from the instrument in
units of per cent light transmittancy through the
colored sample. Referring to the standard cal-
ibration curve the concentration of the sample
can be determined in grams of iron per 100 milli-
liters.

%Fe = g Reg/100 ml (gead from calibration curve)
ml aliquot x g of sample/ ml of diluted
original sample

Computation of Percentage Fe

If these procedures were followed and in the
analysis of the sample (dilution 1:200) the
percent transmittancy was read as 53.0% from
the instrument then the concentration of Fe

in the sample per 100 milliliters is 0.0129
gram as read from a calibration curve for iron.

%Fe = 0.0129 g/100 m1 = 2.58%
1 ml X .005 g -

Results of Chemical Analyses

Table I records the ninety-five well locations and

information along with a summary of the chemical analyses

Ofthe 250 samples for calcium, magnesium and iron. The

nMagnesium to calcium ratios are also recorded in Table I.

k

lHawk Oser and Summerson, "Relation betweenltrans-
mittance and’concentration," Practical Physiologic;
fllemistry, 12th ed. (1947), p. 469.

58

These data were used in plotting and drafting
lithologic ratio maps and for statistical interpretations

vduch are presented in the following chapters.

‘(

59
TABLE 1

WELL DATA AND LOCATIONS

 

 

 

 

l
C
Permit Well Name & Top of R. .
No. Operator Location Elev. Formation
16861 Fate & Weis l5N-7W-27 1078.7 3838
Merrill Drilling SW5NW-SW
Co.
4137 Gingrich #1 15N-7W-12 978. 3769
King Drilling W1/2-SE-SW
10043 McCormack #1 16N-8W-23 1072. 3840
Sun Oil Co. Sl/2-SE-SE
5109 Thrush #1 l6N-7W-25 997. 3790
Daily Crude Oil SW-NW-SE
16329 A. McNeely #1 16N-7W-3 1077. 3868
L. Rose NW—NW-NW
4650 Robart #1 l6N—7W—29 1042. 3815
Sun Oil Co. N1/2-NE-NW
6645 wm. Bongard #1 16N-7W-21 1033. 3821
Turner Petr. Co. Sl/2-NW-NE
9663 *Murray #1 16N-7W-5 1068. 3813
Sun 011 Co. Sl/2-NW-SW
2474 Fred Siegel #1 l7N-5W-26 897, 3888
Farwell Oil NW-SE-SE
252“ H. Fordyce #1 16N-5W-34 916. 3943
W. Hunter C-NW-NE
11722 *Cheadle #1 l6N-6W-33 970. 3738
Sohio Petr. Co. N1/2-NW-SE
5242 Stevens #1 16N-6W-13 1030. 3964
Keeler & SW—SW—NW
Chatham Oil
1
Rogers City
*-
Producing Oil Wells
—_¥

 

 

'60

 

TABLE 1--Continued

 

 

 

Smmfle Feet below Pct. Pct. Pct. Mg/Ca
No. top of R.C. Fe Ca Mg Ratio
1 0 - 4 1.50 15.62 30.50 1.953
2a 0 - 6 1.34 22.82 13.20 0.578
2b 6 -11 0.70 25.23 11.00 0.436
3a 0 - 3 2.36 10.66 24.00 2.251
3b 3 - 7 1.54 14.98 23.00 1.535
4a 0 -15 1.48 11.62 25.25 2.173
4b 15 -20 0.80 12.42 37.00 2.979
a 0 - 7 0.90 14.18 27.50 1.939
5b 7 -10 0.64 15.38 17.50 1.138
5c 10 -14 0.50 14.82 21.00 1.417
6 0 - 6.44 20.02 19.00 0.949
6: 3 - 6 2.70 12.18 23.50 1.939
6c 6 - 9 1.10 14.02 23.00 1.6 %
6d 9 -15 0.64 14.50 14.00 0.96
7 0 - 6 0.76 13.62 12.50 0.918
8 0 — 4 1.40 12.58 11.90 0.946
9 0 - 6 1.10 19.22 3.75 0.195
.768

10a 6 - 8 1.20 14.98 11.50 0
10b 8 -13 1.06 14.18 3.00 0.212
4.50 0.328
11a 13 -21 0.90 14.3% 5.50 0 377
11b 21 -26 0.58 1 . 47 0 650

110 25 -33 0.48 14.58 9. .
0 0.335

12 0 - 8 1.24 16.42 5.5

12% 8 -18 1.10 22.82 9.60 0-421

61

TABLE l--Continued

 

 

 

 

1
Permit Well Name & Top of R.C.
No. Operator Location Elev. Formation
15964 J. R. Forbes #1 16N-6w—34 983.6 3775
I. Hartman SW-SE-SW
15796 J. M. Schafer #1 15N-5w-9 906.3 3859
Nottawa Oil SE-SE-NE
12088 Dent #1 15N-6w-5 987.9 3740
Sohio Petr.Co. N1/2-NE-NW
11858 *Diehl #1 15N~6W—29 1047.6 3768
Chartiers Oil N1/2-SW-NW
3725 Lintmuth #32 15N-9W~35 1092.0 3659
Taggart Bros. NW-NW-NW
9608 Wood #1 15N-7W-2 1020.4 3804
C. W. Teater N1/2-Nw-NE
982 Grove #1 15N-7W-14 1021.0 3792
Benedun-Trees Nw-Nw-SE
17892 Floyd Bouck #1' 15N-8w-11 1038.0 3741
Rex 011 & Gas N1/2—NW-NE
14430 Emma Smith #1 15N-8w-10 1047.6 3738
Pure Oil Co. Nw—Nw—NE
11756 V. Minkel #1 14N-8w-7 1027.4 3628
Chapman Oil Co. Sl/E-SW-Sw
19610 G Snyder #1 14N
. - w-6 0
IMO 011 C0. SE-Sg-SE lOO7°6 369
3648 Gorr #1 l6
N-4 -
Chartiers 011 SE-NEYsS 960°C 3951

———~-.—_.___

 

 

 

 

62

TABLE l--Continued

 

 

 

Sample Feet below Pct. Pct. Pct. Mg/Ca
No. top of R.C. Fe Ca Mg Ratio
13 0 - 8 1.68 13.38 10.50 0.785
14a 2 - 6 0.80 13.38 6.25 0.467
14b 6 - 9 0.80 13.62 13.25 0.973
14c 9 -16 (1.64 15.62 9.75 0.624
14d 16 -21 0.70 14.18 10.00 0.705
15a 3 - 6 1.32 12 98 7.00 0.539
15b 6 - 9.5 1.30 13.77 7.87 0.572
16a 0 - 4.5 1.18 14 02 7.87 0.561
16b 4.5 -10.5 1.14 14.98 6.75 0.451
17a 1 - 3 1.80 19.78 4.30 0.217
17b 3 - 8 1.40 25.23 4.08 0.162
18a 0 - 7 1.26 24.98 3.80 0.152
180 7 -15 1.72 28.59 7.16 0.250
18c 15 —23 1.34 26.19 4.60 0.176
19a 3 - 8 2.60 17.78 1.60 0.090
19b 8 -10 2.90 17.62 1.40 0.079
19c 10 -14 1.84 24.82 2.28 0.095
190 14 -20 1.84 23.78 11.40 0.479
20 0 - 7 2.96 12.01 21.00 1.749
21a 0 _ 4 4.16 14 98 21.62 1.443
21b 4 -10 2.86 24.42 20.40 0.835
21c 10 -18 1.80 22.98 5.00 0-218
22a 0 -10 4.70 13.21 5-87 0,444
22b 10 -20 3.70 12.41 3.75 0.302

.669
23a 4 - 8 3.28 8.97 6.00 0
23b 8 -14 2.30 11.77 “-55 823%
23c 14 -19 1.78 6~17 3°00 '
24 0 - 1 0.30 24.58 4.34 0-177

 

 

63

TABLE l--Continued

 

 

1

 

Permit Well Name & Top of R.C.
No. Operator Location Elev. Formation
17389 D. Knox #1 17N-6w-35 1087.7 4055
J. W. Sturman SE-SE-SE
2601 Davy & McLachlan 17N-8W-35 1106. 3911
#1-Sun 011 Co. C-NW—NW
16335 Lloyd #1 17N-7w-34 1038. 3795
Roosevelt Oil NW-NW-SW
16139 State-Garfield 17N-6w-33 1074. 3956
#1—Sam Hindman El/2-NW-NE
16938 Frank Smith #1 16N—7w-4 1055, 3818
I. Hartman NW-NW-NE
15437 Williams #1 16N-7w-24 1073. 3886
J. E. Bauer NW-NW-NW
19195 J. Stockwell #1 16N-8W-22 1086. 3854
McClure Oil NE-NE-SE
17277 D- Church‘"B"#1 l6N-8W-2 1188. 3959
Sun 011 Co. Sl/2-NE-Nw
17151 Sparks #1 16N-8w-15 1143. 3905
Chapman Oil NE-SE-SE
15606 Brewer-Smith #1 l6N-8W- 1
Sohio 011 Co. NE-Nw-SSS 1015'. 377
3428 Waters #1 l6
N-8W-28 8
Taggart & Rowe NW-SW-SE 1100' 3 55

 

 

64

TABLE l--Continued

 

 

A
T
1

 

 

Pct. Mg/ba
F et below Pct. Pct. 1
8611:1136 tip of R.C. Fe Ca Mg Rat o
64 0.180
-10 0.56 20.18 3.
3;: 18 -16 0.56 20.98 5.90 0.281
0.433
- 0.50 22.18 9.60
366 g -l; 0.46 27.39 10.60 0.387
4.83 0.410
27a 0 - 2 1.30 11.7; 4.13 0.308
27b 2 — 5 1.56 13.3 38 0.541
27 5 - 7 0.60 13 62 2'85 0.198
278 '7 - 9 (1.68 :14.41 .
.70 0.712
28a 0 - 4.5 2.00 10.8% 7.88 0.607
28b 4 5 - 7.5 1.32 12.9 10 75 0.746
28c 7.5 -12.5 0.86 14.4% 6.00 0 412
280 12.5 -37.0 0.80 l .
- 0.511
29a 0 - 6 1.46 13.§1 g.g6 0.180
29b 6 - 9 1.70 12. “.20 0 305
290 9 -13 1.00 13.77 .
2.30 0.177
_ 5.50 12.98 0.826
38% g - 8 2.18 13.6% 11.23 0 720
800 8 -13 1.68 14.5 .
0 80 13 77 9.17 0-622
- ' ° 0.2
81: 8 -1§ 0.82 13.38 3.50 6
0.22
32a 0 - 3 2.10 18.17 3.38 O'iig
_ 1.20 . . 0.
8:: 1% 4:: 0.64 23.62 10.60
15.80 1.617
‘ 2'50 9‘77 80 1.876
8%: 18 ’8? 1'90 11'6§ 2214.08 0.291
11 -14 1.20 14.08 “.50 0.358
838 14 -19 0.86 12.5 0 408
1* 0 - 5 2-2“ 1“: 3:22 oizae
£48 5 -10 1.60 14.0 6 O O 486
8 1-96 1338 7:20 0.375
35a g -17 1.10 20.05 13.75 0.609
8%: 17 :24 0.80 22-5

 

65

TABLE l--Continued

 

 

 

 

 

 

Permit Well Name & Top of R.C.
No. Operator Location Elev. Formation
16577 Lake Prop.,#1 16N-7w-36 950.7 3736
Collin & Walton NE-NW-NW
12725 L. Harper #1 16N-7W-3l 1094. 3846
Sun Oil Co. N1/2-SW-NE
19283 Ralph Unit #1 16N—7W-8 1079. 3812
Gulf Refining Co. NE-SW-NW
3357 Hoffman #1 l6N-7W-9 1029. 3793
Daily Crude Oil NW-SW-SE
3516 Cook #1 16N-5w—15 928. 4005
McClanahan Oil NW-NW-SE
1235 Wilson #1 16N-5w-12 945. 3995
F. L. Maire NE-SE-NE
12635 Gamble #1 l6N-5W-23 924. 3970
J. V. Wickland NW-NW-NE
19287 G. Hamilton #1 16N-5w-19 983. 3887
Neyer et a1. NW-SW-SE
19394 Powell #3 16N-5w-30 913, 3802
Neyer et a1. SE—SE-NE
19050 Powell #2 16N-5w-3o 971. 3870
J. Neyer NW—SW-NE

 

66

TABLE l--Continued

 

 

: A 1 w
L _i i _. l .

 

 

 

 

Swmfle Feet below Pct. Pct. Pct. Mg/Ca
No. top of R.C. Fe Ca Mg Ratio
36a 0 - 5 1.90 19.62 3.00 0.153
36b 5 -10 1.00 21.78 6.00 0.275
36c 10 -15 1.36 22.82 4.30 0.188
36d 15 -20 1.20 22.98 2.76 0.120
37a 0 - 5 2.06 18.58 3.40 0.183
37b 5 -11 0.98 23.22 3.30 0.142
37c 11 -17 0.50 24.18 7.16 0.296
37d 17.-26 0.64 24.98 5.74 0.230
38a 0 - 5 3.00 4.16 4.40 1.058
38b 5 -10 1.20 12.81 4.55 0.355
38c 10 -15 1.24 14 02 10.00 0.713
38d 15 -20 2.66 8.01 6.00 0.749
39a 0 - 8 2.16 4.96 4.40 0.887
39b 8 -13 0.80 13.85 3.75 0.271
39c 13 -19 0.70 14.98 4.13 0.275
40a 0 - 4 1.72 16.82 2.00 0.119
40b 4 -12 1.70 18.98 2.00 0.105
40c 12 -17 1.14 21.22 4.60 0.217
41a 0 — 5 2.44 18.18 4.83 0.265
41b 5 — 8 1.50 21.38 9.60 0.449
41c 8 -11 0.80 22.02 9.40 0.427
41d 11 -13 1.10 30.99 1.40 0.045
42a 0 - 5 1.24 18.58 3.86 0.208
42b 5 - 9 1.04 21.38 2.60 0.122
42c 9 -15 0.68 23.22 5.40 0.233
42d 15 -20 0,76 24 18 3.00 0.124
43a 0 _ 6 1, 0 12.58 2.00 0.159
43b 5 -12 0,32 14.18 2.63 0-185
44a 0 - 2 2.00 9.37 4.00 0-“27
44b 2 - 4 1.90 9.21 3.45 O 375
45 ' _ 2.00 12 01 8.95 0.745
L15: (8) -18 850 12.142 5.10 0.41611
45c 10 -13 5.28 14.41 8.13 8°§32
45d 13 -20 1.50 15.38 5.10 .

 

67

 

 

 

TABLE 1--Continued
Permit Well Name & Top of R. C.
No. Operator Location Elev. Formation
18645 Powell #1 16N-5w-30 944.9 3835
J. Neyer N1/2—NE-NE
12512 E. Maybee #1 15N-5w-12 837.8 3770
Merrill Drlg.Co. NE-SE-SE
12779 Frank Bowee #1 15N-5w-23 837.5 3767
Collin & Walton SE-NE-SE
3706 Hicks #1 15N-6w-35 915 4 3640
M. Smith sw-sw-Nw
12956 Carr #1 15N-6w-25 906.0 3688
Bell & ATHA NW-NW-SW
19606 J. a M. Vogel #1 15N—5w-10 900.3 3856
Merrill Drlg.Co. NE-NE-NE
6038 Tillman #1 15N-5w-23 855.7 3821
Teater NE-SE-NW
15781 L. Huber #1 15N-5w-36 832.0 3725
Basin 011 C0. NW—SE-NE
19865 Grewerre & c11ff 15N-5W-19 884.1 3693
Est. #1 SE-NW-NW
Leonard 011
5453 Hauck #1 lSN-SW-l 8 0 0 791
Gulf Ref. Co. sw-Nw—sw3 5 ° 3

 

 

 

 

 

 

TABLE l--Continued

68

 

 

 

Swmfle Feet below Pct. Pct. Pct. Mg/Ca
No. top of R.C. Fe Ca Mg Ratio
46a 0 - 2 1.90 11.21 7.50 0.669
46b 2 ~ 4 2.90 10.81 7.50 0.694
460 4 5 2.58 11.21 2.20 0.196
47a 0 ~ 4 3.66 14.02 5.10 0.364
47b 4 ~ 9 4.50 14.41 1.50 0.104
470 9 ~12 1.34 14.58 3.45 0.237
48a 6 ~11 0.74 14.41 5.10 0.354
48b 11 ~14 0.60 14.82 1.50 0.101
480 14 ~18 0.01 13.77 2.20 0.160
49a 0 ~ 5 0.76 14 18 1.75 0.123
49b 5 ~ 9 0.74 14 02 1.60 0.114
490 9 ~13 0.48 14.82 1.75 0.118
49d 13 ~17 0.30 14.41 5.40 0.375
50a 0 ~ 5 0.70 12.17 1.84 0.151
50b 5 ~12 0.92 10.01 1.50 0.150
500 12 ~19 0.68 12.98 3.75 0.289
500 19 ~24 1.40 10 01 1.28 0.128
51a 0 ~ 0.70 12.81 1.70 0.913
51b 5 ~16 (3.56 13.62 8.40 0.617
52a 0 - 3.5 1.62 11.62 6.16 0.530
52b 3.5 ~12.5 (3.64 13.62 1.10 0.814
520 12.5 ~17 5 0.80 13.21 5.40 0. 09
53a 0 ~ 6 1.14 11.21 5.60 0.500
530 6 ~11 1.04 12 58 5.60 8.435
53c 11 ~18 0.94 14.18 5.40 .3

84
54a 0 - 5 0.94 14.58 5-60 0‘3
54b 5 ~10 0.82 14.82 4.88 g-ggg
54c 10 ~13 0.70 14.82 g. 0 0 423
54d 13 ~18 0.66 14.18 .0 .
0-3 .133 1115 212 8:27
5b ~ . - -
55c 9 ~12 1.20 14.82 8.20 0.553

 

69

TABLE l-~Continued

__=. ma...—

 

 

 

 

 

P it Well Name & Top of R. C.
fig? Operator Location Elev. Formation
4862 *Ryckman #1 15N-6W-33 1003.0 3701

Pure 011 C0. NW—SW-NE
4220 Lawens #4 15N-5W-24 838. 3776
J.V.Wickland Dev. NW-SW-SE
4255 F. Cotter #1 15N~5W~11 838. 3799
C. Weller NE-NE-NE
4663 McClintic B-8 15N—6W-35 952. 3653
Lane Oil Co. sw-sw-sw
3713 Merrihew #1 15N~6W-28 1005. 3736
Turner Petr. Co. SE-SE—NW
6369 *Walch #1 15N~6w-18 996. 3745
Borough SW-SW-NW
19842 State-Sherman 15N~6w~21 925. 3671
'"QN" ~#1 SE-NE-NE
Brazos Oil Co.
19265 Woodin #1 16N-6W-35 962. 3757
Leonard Oil Co. NW-SW-SW
17561 J. 1. Bean #1 15N-6W-8 1005. 3775
Chartiers 011 C0. SW-NW-SW
162““ A- Dent #1 15N~6w-6 977. 3731
J- Neyer N1/2-SE~SE
12936 *Hatcher #1 15N-6W-6 998.5 3754
Pure 011 C0. Nl/2-NE-SE
12378 *1. B. Wilson #2 16N~6w-30 1054.5 3806

Sohio Petr. Co. Nl/2-SW-NE

 

 

 

TABLE l--Continued

70

 

 

 

 

Sample Feet below Pct. Pct. Pct. Mg/Ca
No. top of R.C. Fe Ca Mg Ratio
56a 0 3 1.10 14.41 12.60 0.874
56b 3 ~ 4 0.80 14.41 11.40 0.791
560 4 ~ 5 0.68 15.38 10.60 0.689
572 0 ~ 3 1.06 14.82 11 40 0.769
57b 4 ~ 9 0.90 14.98 12.20 0.814
570 9 ~16 0.66 14.58 12.40 0.850
58a 0 ~ 5 4.04 9.21 3.50 0.380
58b 5 ~12 3.24 10.81 10.25 0.948
580 12 ~14 1.78 13.77 11.20 0.813
59 0 ~ 4 0.98 14 98 12.20 0.814
60a 0 ~12 2.16 10.41 10 50 1.009
60b 12 ~19 1.86 9.61 7.87 0.819
61a 0 -10 2.16 16.02 5.90 0.368
61b 10 ~15 2.04 17.00 3.40 0.200
62a 0 ~ 6 0.98 13.77 9.20 0.668
62b 6 ~12 1.18 12.98 17.92 1.381
620 12 ~22 0.68 14.02 6.16 0.439
23 O -1 3.31 2'28 121:

3b 1.5 ~4.5 1.9 10. . .
630 4.5 ~7.5 1.90 10.17 4.76 0.468
64a 0 - 4 2.96 9.37 4.76 0.508
64b 4 ~10 1.04 7.77 2-20 0-283
64c 10 ~15.5 1.10 13.21 5.00 0.37%
64d 15,5 .205 0.68 13.38 ”.25 0-3
65a 6 ~11 1.24 8.01 5.60 0.699
65b 11 ~16 1.30 17-22 7°34 0°“26
66 0 - 5 2.00 10.81 2.20 0.204

0.813
67a 0 7 0.80 13.77 11.20
67b 7 - 9.5 0.76 14.82 12°68 2.637
670 9.5 -l2.5 0°70 14'58 l ' '

 

71

TABLE l-—Continued

 

 

 

Permit Well Name & Top of R. C.
No. Operator Location Elev. Formation
12911 *Mina DeLong #1 l6N-6W-20 998.1 3748
Mogul 011 C0. s1/2~ss~ss
18337 M. Drallette #1 15N-6W-13 908.0 3707
C. Glavin NE-NW-SW
10131 Gringrich #1 15N-6W-7 943.9 3702
Gordon Oil Co. Wl/2-NW-NW
4741 *Buetler #2 15N-6W-33 1012.0 3710
Laue Oil Co. SW-NW-NE
12187 *Tower #1 15N-6W-5 991.7 3747
Pure Oil Co. N1/2-SE-NW
12464 *0. Dague #3 16N-6W-30 1021.9 3785
Sohio Petr. Co. Nl/2—NW-SE
12681 *E. L. Chapman #2 l6N-6W-30 1054.8 3808
Sohio Petr. Co. S1/2-NW-NE
12182 *E. Chapman #1 l6N-6W-30 1031.9 3768
Sohio Petr. Co. Sl/2-NE-NE
11639 *Conley #2 16N~6w-28 975.0 3750
Sohio Petr. Co. Nl/2-NW-NE
11220 *Rogers #1 l6N-6W-29 1016.5 3732
Cities Service N1/2-SW-SE
12078 *State #1 16N-6W-32 995.0 3757
Cities Service Nl/2—SW-SE
“83 AndePSOH #1 15N-9W-l4 1013.0 3610
Big Rapids Oil NE-NE-NE

 

 

 

TABLE l--Continued

72

 

 

 

 

Sample Feet below Pct. Pct. Pct. Mg/Ca
No. top of R.C. Fe Ca Mg Ratio
68a 0 ~ 2 2.04 10 01 4.00 1.399
68b 2 ~ 9 1.34 12.17 8.60 0.707
680 10 ~11 0.92 13.21 8.40 0.636
69a 0 ~ 4 1.50 11.37 6.16 0.542
69b 4 - 9 0.98 12 98 6.56 0.505
690 9 ~16 0.68 14.58 7.34 0.503
69d 16 ~20 0.64 14.18 5.90 0.416
70a 0 - 7 0.80 23.39 9.00 0.385
70b 7 ~14 0.80 21.22 8.60 0.405
700 14 ~22 0.52 23.78 4.08 0.172
71 17 ~22 1.14 12.42 3.86 0.311
72a 0 ~ 2 2.16 11.77 5.00 0.425
72b 2 5 1.40 14.41 5.40 0.375
73a 0 4 1.18 13.62 6.30 0.463
73b 4 7 0.90 14.18 7.80 0.550
74a 0 ~ 3. 1.60 9.37 3.00 0.320
74b 3.5 - 7. 0.80 13.38 4.92 0.368
75a 0 4 0.60 14.41 5.28 0.366
75b 4 ~ 6 0.52 15.62 6.30 0.403
750 6 9 0.60 14.82 5.90 0.398
76a 0 ~ 6 0.64 14.18 5.60 0.395
76b 6 ~ 9 0.56 13.62 6-56 0.322
760 9 -14 0,30 9.21 4.25 0.
76d 14 ~19 0.40 14.82 5.00 0.337
77a 0 ~ 4. 1.60 9.37 2.75 0-293
77b 4 - 7 1.32 12.42 1.82 8.142
770 7 9 0.80 13.77 6.5 .

. 75
78a 0 - 1.00 12.01 3.30 0 2
78b 3 - 3, 0.74 13.21 6.56 O “97
79 0 ~20 0.98 18-58 ”'92 0'265

 

[til

.1 blit‘

\1

73

TABLE l--Continued

 

 

 

Permit Well Name & Top of R. C.
No. Operator Location Elev. Formation
4075 Hutchins #1 15N-7W-8 1002.2 3717
Daily Crude Oil NW-NW-NW

9806 Helmer #1 l5N-8W-17 1048.2 3765
Gordan 011 C0. Sl/2—NE-NE

11182 *E. s. Cole #1 16N-6W-32 971. 3695
Sohio Petr. Co. N1/2-SW-NE

11218 *Cole #3 16N~6w-32 995. 3737
Sohio Petr. Co. N1/2-NW-SE

11183 *Durkee #1 l6N-6W-32 983. 3704
Sohio Petr. Co. Nl/2-NE-NW

10997 *Cummings #4 16N-6W-32 974. 3688
Sohio Petr. Co. Nl/2-NE-NE

12087 *H. Durkee #1 l6N-6W-31 973. 3726
Sohio Petr. Co. N1/2-NE-SE

11523 *Dague #A-l l6N-6W-3l 1002. 3757
Sohio Petr. Co. N1/2-NE-NE

12827 *Cheadle #1 l6N-6W-33 970, 3744
G.Hanners Nl/2-NE-SE

11524 *F. Sisco #1 l6N-6W- 2 720
Sohio Petr. Co. N1/2-NE-3g 97 ' 3

11321 *W. Sisco #1 16N-6W- 6 6 2
Sohio Petr. Co. Nl/2—NW-gg 97 . 3 9

111“? *Coe #1 l6N-6W- 4
Sohio Petr. Co. N1/2—NW-ga 979' 37 5

 

 

 

74

 

 

 

 

TABLE l--Continued
Sample Feet below Pct. Pct. Pct. Mg/ba
No. top of R.C. Fe Ca Mg Ratio
80a 0 - 7 0.92 21.62 3.00 0.139
80b 7 ~14 0.80 20 98 3.86 0.184
81 0 ~20 1.14 16.02 1.60 0.100
82a 0 ~ 8 1.44 13.62 3.64 0.267
82b 8 ~11 0.68 12 81 5.00 0.390
82c 1 ~13 2.32 10.41 9.47 0.910
83a 0 ~ 4 1.64 13.38 11 20 0.837
83b 4 ~ 8 0.98 14 82 12.90 0.870
830 8 ~12 0.76 14 41 14.80 1.027
84a 0 ~ 3 2.98 10.17 4.92 0.484
84b 3 ~ 9 3.20 9.77 13.25 1.356
85a 0 ~ 5 1.34 12.98 12 40 0.955
85b 5 ~10 1.54 13.77 12.00 0.871
850 0 ~17 1.64 12.42 11.40 0.918
86a 0 1 1.64 13.38 11 00 0.822
86b 1 ~ 6 1.00 14.18 13.52 0.953
860 6 ~13 0.64 14.58 14.30 0.981
87a 0 ~ 4 1.44 11.62 12 40 1.067
87b 4 - 7 0.80 14.41 13.10 0.909
88 0 - 2 0.44 15 38 12 00 0.780
8 0. 0 15.22 12 00 0.788
835 3 ~ 6. 0.56 14.18 11.70 0.825
444
90a 0 - 5 0.90 14 18 6.30 0.
90b 5 - 9 0-98 14.02 5'08 8'57;
900 9 ~14 0.46 14.18 5.2 . .
. 73
1 0 ~ 4 1.78 10.97 3.00 0 2
81: 4 - 9. 0-7“ 14.41 3'23 8'876
910 9,5 -14, 0.52 14.58 . .

 

\I

75

TABLE 1--Continued

 

 

 

 

 

Permit Well Name & Top of R. C.

No. Operator Location Elev. Formation

11337 *R. 0. Dague #2 16N-6W-29 1016.1 3749
Sohio Petr. Co. N1/2-NW-SW

11092 *Rodgers #1 16N-6W-29 1002.2 3719
Sohio Petr. Co. N1/2-SE-SE

11446 *E. L. DeLong #1 16N-6W-29 993.3 3755
Sohio Petr. Co. N1/2-NE-NW

11242 *Watkins #2 16N-6W-29 984.1 3711
Sohio Petr. Co. N1/2-SW-NE

¥

76

TABLE 1~~Cont1nued

 

 

 

Sample Feet below Pct. Pct. Pct. Mg/Ca
No. top of R.C. Fe Ca Mg Ratio
92a 0 ~ 6 1.44 10.97 5.60 0.510
92b 6 -12 0.88 14.41 5.90 0.409
92c 12 -17 0.60 15.38 4.08 0.265
93a 0 ~ 5 2.44 7,21. 9.20 1.276
93b 5 - 9 0.76 13.77 6.30 0.458
93c 9 ~14 0.66 13.38 5.28 0.395
94a 0 - 2 1.64 14.18 5.40 0.381
94b 2 - 3.5 1.24 14.41 4.60' 0.319
958 O - 3 0.68 14.02 4.60 0.328
95b 3 - 6 0.80 12.81 7.16 0.559
950 6 9 0.68 14.41. 3.30 0.229

 

., .t_,_ _
_ ~. _—-_._n—_. _

INTERPRETATION OF DATA
Structural and Chemical Interpretation

Structure Contour Map

A structure contour map was plotted and interpolated
for all available data on the top of the Rogers City-Dundee
formation for the 400 square mile area studied. The
structural interpretation was based exclusively upon samples
for the ninety-five wells studied; and well logs and steel
line readings for all the other wells drilled in the area
which penetrated the top of the Rogers City limestone, but
for which there were no samples available. No interpretation

for the Rogers City-Dundee was made upon data from over— .

lying formations.

Map 2 (See pocket) is the structure contour inter-

pretation on a scale of one inch to the mile and with a

1?

contour interval of 25 feet.

§£ructural Interpretation

The interpretation of the structure contour map for

the area is relatively straight forward. A strong northwest—

Southeast structural alignment occurs across the Fork, Cold-

water and Sherman townships. It is along the axis of this

fold that the three major producing oil fields of the area

are located. The Fork oil field (Fork township) and the

77

78

Coldwater oil field (Coldwater township), situated on the
major fold, both have a minor axis in a northeast-southwest
direction which may line-up with, or tend to parallel, the
structural high occurring in the northern half of Martiny
township (T.15 N., R.8 w.). The Shaman 011 f1e1d (Sherman
township) also lies on the axis of the major northwest-
southeast fold.

Another northwest-southeast fold of a smaller magni-
tude cuts across the northeastern portion of Nottawa
township. A small closure on this fold results in the Beal
City oil field. A small portion of a third northwest-
southeast fold cuts across the northeast corner of the area
studied (1.16 N., 11.4 11.).

A deep synclinal trough lies in the northeastern
portion of Gilmore township and trends parallel with the k
major structural alignment of the area studied.

The regional dip of the entire area is to the north-

east with major folding in a northwest-southeast direction

1?

and a cross-folding of minor importance in a northeast-
southwest direction. Four major oil fields exist in the

area with several minor and one-well fields.

Léthologic Ratio Maps
The ratio of magnesium to calcium provided data for
a lithologic ratio map showing the relative degree of

The
dolomitization at the locations of samples analyzed.

rs
values of the ratios for the top five feet of the Roge

79

City formation were first plotted and lines of equal ratio
values were drawn providing a geometric contour interval.
(Map 3--See pocket.)

An average of the Mg/Ca ratio values was then deter-
mined for each well analyzed and plotted to show the degree
and pattern of dolomitization for the top 20 feet of the

Rogers City limestone. (Map 4-~See pocket.)

Interpretation of Lithologic Ratio Maps

The lithologic Mg/Ca ratio maps show the areal
variation in the degree of secondary dolomitization over
the area studied. Comparing Map 3 with Map 4 a vertical
variability can be observed.

The degree of dolomitization appears, in general,
to increase on the apices of the major folds. There is

a definite relation, in general, between the degree of

dolomitization and the magnitude of the structure. The

Structural trend and the trend existing in the contouring
0f the ratio values show a close correlation in general.
There is an exception to this observation in the

Southeast portion of Chippewa township and the southwest

Portion of Fork township. Here is an area with a high

H H
degree of dolomitization lying in a structural low with
There are a number of reasons which

(1) fracturing

no production of oil.
may be proposed to explain this situation:

and faulting, or original porosity, may have led to

2
Secondary dolomitization in the trough area, 0? ( )

.1. #1. ~..—
nuv I.

80

dolomite-formation may have been complete leaving no
porosity for the accumulation of oil; or (3) there was
porosity in the secondary dolomite but unfavorable con—
ditions for the accumulation of oil.

The degree of dolomitization which appears, in
general, to be related to the minor cross-folding shows a
stronger trend than does the actual structural alignment.
This may be due either to fracturing and fissuring along
the axis of the minor folds, or to an original porosity
in the limestone formed along the apices of the folds
leading to later dolomitization. (Compare Map 2 with Maps
3 and 4.)

Comparing Maps 3 and 4, there would appear to be no
Significant difference in the vertical variation of dolo-
mitization between the upper five feet of the limestone
fermation and a total over-all average of the top twenty
feet, thus, giving no evidence, one way 0? the other, as

to ascending or descending mineralizing waters; assuming

there were such waters.

goldwater Oil Field

A more detailed study was made of the Coldwater oil

field with a chemical analysis of twenty-five samples

Selected from the producing structure. This close-up

SPUdy was made to compare the degree and pattern of dolomit-

ization locally as related to a well defined and prolific

Structure.

1?

 

/ .

L

(“J
‘.>

 

81

Structure contour map.--A structure contour map was

 

plotted and interpolated on the available data for the
Coldwater oil field. (See Map 5.) The regional dip of the
field is to the northeast and the steepest dips of the Cold-
water structure are found along the northeast side of the
field.

The major axis of the field has a northwest-southeast
alignment and a minor axis trending northeast-southwest.
The Coldwater structure has a closure of 40 to 50 feet on

the Rogers City formation.

Lithologic ratio map.--The average Mg/Ca ratios for
approximately the top 10 feet of the Rogers City limestone
were plotted for each of the 25 wells in the field to show
the relative degree of dolomitization and its possible

relationship to that of the Coldwater structure. (See Map 6.)

Interpretation of lithologic ratio map.--The litho-
loglc'Mg/Ca ratio map shows the areal variation in the
degree of secondary dolomitization within the top 10 feet

of the Rogers City limestone of the Coldwater structure.

The pattern of dolomitization coincides closely with

the structure alignment of the field. The degree of dolo-

mitization increases on the apices of the major and minor

folds, with a more pronounced trend appearing along the

minor axis than that evident on the structure contour map.

An exception to the coincidence of structure and

degree of dolomitization is the re-entrant angle in the

1r

3. - (~13-b . -_._ . .. .——

.__—.—-

 

 

 

 

       

0

 

 

 

MAP 5

COLDWATER OIL FIELD
snucrua: couroun

ROGERS CITY FORMATION (o)

I._

 

__..

ON! MILK
CONTOUR INTERVAL l 25 FIIT

 

 

 

 

 

If.

C)

84

pattern of dolomitization on the north side of the field.
This area of reduced secondary dolomitization of the Rogers
City limestone lies parallel to the major axis of the
structure and may be due to a decrease in fissures or

tension cracks on the lower flank of the major axial fold.

Vertical configuration and_pay zones.--Cross sections

 

were drawn to a scale of 4 inches per mile horizontally and

1 inch per 20 feet vertically, to show the configuration of
the top of the Rogers City formation and the pOSition of

the reservoir within it. The pays are shaded in the drawings
and represent actual reservoir Space as determined from the
drilling records of producing wells and dry holes (Knapp,
1950).

Cross section A-A' (Figure 2) shows the east-west
configuration and pay zones across sections 31, 32, and 33
(Coldwater township). Cross sections B-B‘ (Figure 3) and
C-C‘ (Figure 4) give the north-south configuration of the
field through sections 29, 32, (Coldwater township) and 5
(Sherman township) and sections 21 and 33 (Coldwater
township), respectively.

Core analysis records show that lateral permeability
exceeds the vertical permeability due to horizontally bedded
dense and porous zones in the Rogers City formation. The
configuration and pay zone pattern, as observed in the
above cross sections, make it quite "evident that the

Coldwater reservoir is not an open, freely-connected system

85

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88

of spaces" (Knapp, 1950). The lenticular-like chambers are
governed to a certain extent by bedding, whereas, many of
the porous zones (secondary dolomitized limestone) are due
to a haphazard arrangement of vertical fractures consisting
of large, open and continuous fissures and small, short
and completely filled ones (Knapp, 1950).

A combined study of the cross sections of the top
10 feet of the Rogers City formation and the lithologic
Mg/Ca ratio map of the Coldwater field gives a fair picture
of the reservoir system and pay zone configuration of the

Coldwater oil field.

Statistical Interpretation

 

Statistical Methods

The statistical interpretations made in this study
of the laboratory results were based upon the methods of
“analysis of variance;" "Basically the analysis of variance
is a simple arithmetical method of sorting out the compon-
ents of variation in a given set of results" (Goulden, 1952).
The complete analysis of variance actually performs a dual
role. First, there is the sorting out and estimation of
the variance components,1 and secondly, it provides for

tests of significance.

¥

lThe term "component" is used here with reference to
the integral parts, or component parts of the variation
within the set of results.

89

A detailed description of the method and calculations
for an analysis of variance is not given here but can be
found in most statistics texts (Goulden, 1952; Dixon and
Massey, 1951). The "F" ratio was used for the tests of
significance in the analysis of variance; principles and
computations of which are given in all statistics textbooks

(Goulden, 1952; Dixon and Massey, 1951).

Statistical Interpretation of Data

 

I. Producing "high" versus non-producing;"low".--

 

USing the Mg/Ca ratios from nineteen producing wells selected
on "high" structures as compared to the Mg/Ca ratios of
nineteen non-producing wells selected on "low" structures, a
combined analysis of variance was made pertaining to the
variance components: (1) between wells, (2) between pro-
ducing or non-producing structures, (3) between levels of
O to 5 feet and 5 to 10 feet from the top of the Rogers City
formation, and (4) the interactions between structures
times levels and levels times wells. (See Table 2.)

See Figure 5 for the complete analysis of variance

of the above situation.

Conclusion.--There is a highly significant difference
(beyond the 1% level) between the averages of the Mg/Ca
ratios of the thirty~eight wells considered. Although
statistically significant there would appear to be no im—
portant significance geologically as uniform dolomitization

of the limestone would not be expected.

90

TABLE 2

DATA FOR AN ANALYSIS OF VARIANCE

Producing "High" Versus Non-Producing "Low"
Magnesium/Calcium Ratios

 

4—
1

 

 

 

 

 

Producing "High" Well Numbers Non-Producing'"Low"
0.328a 11 2 0.578
0.377b — 0.A36
0.561 16 19 0.090
0.u51 0.087
0.833 56 21 1.4u3
0.689 0.835
0.813 67 23 0.669
0.991 0.387
1.399 68 26 0.u33
0.707 0.387
0.320 7m 28 0.712
0.368 0.607
0.366 75 3h 0.u08
0.401 0.232
0.395 76 36 0.153
0.482 0.275
0.329 82 37 0 183
0.910 0.142
0.837 83 41 0.265
0.870 0.u38
0.h84 84 M2 0.208
1.356 0.122
0 955 85 A9 0.123
0.871 0.114
0.888 86 50 0.151
0.981 0.150
1.067 87 51 0 913
0.909 0.617
0.4uu 90 53 0.500
0-357 0.4u5
0.273 91 54 0.384
0.455 0.270
0.510 92 58 0.380
0.409 0.9u8
1.276 93 64 0.508
0.458 0.283
0.328 95 69 0.542
0.559 0.505

12.406a Total 8.643a
12.601b Total 7.280b
0,658 Average 0.419

 

a0 to 5 foot interval b5 to 10 foot interval

91

PRODUCING'"HIGH" VERSUS NON—PRODUCING "LOW"

 

 

Source of Sums of

Variance D.F.l Squares Mean Square F
Total 75 7.771

Wells 36 4.924 0.1368 2.880**
Types2 1 1.089 1.089 22.930**
Levels3 1 0.021 0.021 0.AA2
Types x Levels 1 0.028 0.028 0.589
Levels x Wells 36 1.709 0.0M?

 

Figure 5. Analysis of variance

1Degrees of freedom
2Producing'"High" and Non-Producing "Low" Structures
3Depth of 0-5 feet and 5-10 feet

**Highly significant beyond the 1% level
The highly significant difference (beyond the 1%
level) between the averages of the Mg/Ca ratios of the pro—
ducing "high" structures and non—producing "low" structures
would tend to show, statistically, a relationship between
increasing dolomitization and producing wells on "high"
structures. The mean of the Mg/Ca ratios for the producing
“high" was 0.658 and for the non-producing "low" 0.419.
There was no statistical difference between the
averages of the Mg/Ca ratios of the upper 0 to 5 feet of
the formation as compared to those of the lower 5 to 10 feet.
There was no significant interactions between types
times levels or between levels times wells. This would
imply that "there is no difference in the means of the

Subgroups after the cell means have been ‘adjusted‘

92

for" well, type and level effects (Dixon and Massey, 1951,
p. 138).

II. Producing;"high" versus non-producing;?high."--

 

USing the Mg/Ca.:ratios .from ten producing wells randomly
selected on "high" structures as compared to the Mg/Ca
ratios of ten non-producing wells selected on "high" struc-
tures, a combined analysis of variance was made pertaining
to the variance components: (1) between wells, (2) between
producing and non-producing wells both on "high" structures,
(3) between levels of 0 to 5 feet and 5 to 10 feet from the
top of the Rogers City formation, and (A) the interactions
between types times levels and levels times wells. (See
Table 3.)

See Figure 6 for the complete analysis of variance

of the above situation.

Conclusion.-- Statistically there is no significant
difference between the averages of the Mg/Ca ratios of the
wells located on "high" structures. This would appear to
indicate that the degree of dolomitization along the "high"
structures is more uniform than between "high" and "low"
structures. There is no significant difference between the
averages of the Mg/Ca ratios of producing and non-producing
wells all located on "high" structures. The mean of the
ME/Ca ratios for the producing wells is 0.590 and for those

of the non-producing wells is 0.558. The relationship as

 

93

TABLE 3
DATA FOR ANALYSIS OF VARIANCE

A. PPOdUC1n8'"HiSh" Versus Non-Producing "High"
B' Non‘PPOdUCing HHigh" Versus Non-Producing "Low"

Magnesium/Calcium Ratios

 

 

Producing "High" Non-Producing "High" Non-Producing'"Low"

 

 

 

 

 

(Random) (Random)
Well N .2Ei_ .183. _£EL.
0. Ca Well No. Ca Well No. Ca
76 0. 395a 27 0.359’01 53 0 . 500a
0.482b 0.370b 0.446b
56 0.833 29 0.511 54 0.384
0.689 0.180 0.270
91 0.273 38 1.058 37 0.183
0.455 0.355 0.142
68 1.399 39 0.887 36 0.153
0.707 0.271 0.275
82 0.329 45 0.745 51 0.913
0.910 0.488 0.617
75 0.366 47 0.364 64 0.508
0.401 0.104 0.283
86 0.888 62 0.668 23 0.669
0.981 1.381 A 0.387
90 0.444 63 1.039 42 0.208
0.357 0.467 0.122
16 0.561 65 0.699 41 0.265
0.451 0.426 0.438
95 0.328 70 0.385 69 0.542
0.559 0.405 0.505
Totala 5.816 6.715 4.325
Totalb 5,992 4.448 3.484
Average 0.590 0.558 0.390

a0 to 5 foot interval

b5 to 10 foot interval

 

94

PRODUCING‘"HIGH” VERSUS NON-PRODUCING'"HIGH"

 

 

J
_

 

 

Source of Sums of

Variance D . F . Squares Mean Square F
Total 39 3.584

Wells 18 2.081 0.1156 1.685
Levels 1 0.109 0.1090 1.589
Types 1 0.010 0.0100 0.146
Types x Levels l 0.150 0.1500 2.187
Levels x Wells 18 1.234 0.0686

 

Figure 6. Analysis of variance

lProducing'"High'" and Non-Producing'"High" structures

determined statistically between the possibility of a pro-
ducing well or a non-producing well depends on factors
other than the degree of dolomitization and structure alone.
A high degree of dolomitization on a favorable structure,
although a good indication, geologically, of a producing
well, is not an exclusive confirmation.

There was no significant interaction between types

and levels or levels and wells.

III. Non-producing "high" versus non-producing
:112w."--Using the Mg/Ca ratios from ten non-producing wells
selected on'"high" structures as compared to the Mg/Ca
ratios of ten non-producing wells randomly selected from
‘"low" structures, a combined analysis of variance was made
pertaining to the variance components: (1) between wells,

(2) between non-producing "high" and "low“ structures,

95

(3) between levels of 0 to 5 feet and 5 to 10 feet from the
top of the Rogers City formation, and (4) the interactions
between types times levels and levels times wells. (See

Table 3.)

See Figure 7 for the complete analysis of variance

of the above situation.

NON-PRODUCING'"HIGH" VERSUS NON-PRODUCING "LOW"

 

 

Source of Sums of

Variance D.F. Squares Mean Square F
Total 39 3.078

Wells 18 1.639 0.0911 1.894
Levels 1 0.242 0.2420 5.031*
Types1 1 0.282 0.2820 5.863*
Types x Levels 1 0.050 0.0500 1.040
Levels x Wells 18 0.865 0.0481

 

Figure 7. Analysis of variance

1Non-Producing‘"High" and Non-Producing "Low" structures
*Significantly different at the 5% level

Conclusion.--Statistically there is a significant

difference (at the 5% level) between the averages of the

MS/Ca ratios of the upper 0 to 5 feet and the 5 to 10 foot

dePths. The means of the Mg/Ca ratios for non-producing

wells on "high" structures at 0 to 5 feet and 5 to 10 feet

are 0.67 and 0.44, respectively; the means of the Mg/Ca

ratios for non-producing wells on "low" structures at 0 to

5 feet and 5 to 10 feet are 0.43 and 0.34, respectively.

96

This comparison, as based upon 20 non-producing wells,
would not appear to be of any geological significance.

The significant differences (at the 5% level) be-
tween the averages of the Mg/Ca ratios for the non-producing
“high" and non-producing "low" structures would tend to
support the belief of a direct relationship of'"high" struc-
ture to increasing degree of dolomitization. The mean of
the Mg/Ca ratios for the "high" structure is 0.558 and for
the "low" structure is 0.39.

There is no significant interaction between types

times levels or between levels times wells.

IV. '"High" versus "low" structure.--Using the Mg/Ca
ratios from nineteen wells selected randomly from "high"
structures as compared to the Mg/Ca ratios of nineteen
wells randomly selected from’"low" structures, a combined
analysis of variance was made pertaining to the variance
Components: (1) between wells, (2) between "high‘and "low"
structures regardless of production or non-production, (3)
between levels of 0 to 7.5 feet and 7.5 to 15 feet from

the top of the Rogers City formation, and (4) the inter-

actions between types times levels and levels times wells.

(See Table 4.)
See Figure 8 for the complete analysis of variance

of the above situation.

97

TABLE 4
DATA FOR AN ANALYSIS OF VARIANCE

‘"High" Versus "Low"--Magnesium/Calcium Ratios

 

 

 

 

 

 

'"High" Well Numbers ‘"Low"
1.939a 5 2 0.578
1.278b 0.436
0'328 11 6 1.439
0.377 1 303
0'305 0.421
0'707 38 14 0.720
0°731 0.624
0.887 39 18 O 152
0.271 0 250
0'578 ”5 19 0.085
0.448 0.287
O 234 47 25 0.180
0.171 0.281
1.009 60 28 0.660
0'819 0.579
0.200 0 720
0.668 62 35 0.486
1.381 0 375
0.813 67 40 0.119
O 991 0.105
0.385 70 41 0.357
0-395 76 43 0,159
0.472 O 185
0.293 77 48 0.354
0.312 0.131
O 874 83 50 0.150
1.027 0.289
0.888 86 58 0.380
0.981 8.792
0.401 0 57 ,
O 365 9 0.850
0.510 92 69 0.542
0.409 0.505
1.276 93 80 0.139
0.427. 0.184 _‘_
‘I2.8 a Total 8.128
11.333b Total 8.709
0.639 Average 0.443

 

a0 to 7.5 foot interval

b7.5 to 15 foot interval

98

.HHIGHH VERSUS “LOW"

 

 

Source of Sums of

Variance D.F. Squares Mean Square F
Total 75 10.177

Wells 36 8.045 0.2235 6.024**
Types1 1 0 .727 0 .7270 19 . 59 6**
Levels 1 0.012 0.0120 0.323
Types x Levels 1 0.058 0.0580 1.563
Levels x Wells 36 1.335 0.0371

 

Figure 8. Analysis of variance

l'"High" and'"Low" structures
**Highly significant beyond the 1% level

Conclusion.--The difference between the averages of
the Mg/Ca ratios of the 38 wells is highly significant
@eyond the 1% level). This would have no significance

geologically as uniform dolomitization would not be expected

over this area.

The highly significant difference (beyond the 1%
level) between the averages of the Mg/Ca ratios, or degree
of dolomitization, between the well samples from'"high"

structures and those of "low" structures is of geologic

importance. It would appear, from statistical evidence,

that there is a direct relationship between the magnitude

0f structure and the degree of dolomitization. In general,

the greater the relief of structure the greater the degree

‘ .l .n
of dolomitization. The mean of Mg/Ca ratios for the high

was 0.639 and for the "low" was 0.443. (See Table 4.)

99

There was no significant interaction between types

times levels or between levels times wells.

V. Producing "high" versus non-producing'"low" in

iron content.-—Using the percentage iron content from nine-

 

teen producing wells selected on "high" structures as
compared to the percentage iron content of nineteen non-
producing wells selected on "low" structures, a combined
analysis of variance was made pertaining to the variance
components: (1) between wells, (2) between producing and
non-producing structures, (3) between levels of 0 to 5 feet
and 5 to 10 feet from the top of the Rogers City formation,
and (4) the interactions between types times levels and
levels times wells. (See Table 5.)

See Figure 9 for the complete analysis of variance

of the above situation.

Conclusion.--There is a highly significant differ-
ence (beyond the 1% level) of the average iron content
between the wells, between the 0 to 5 and 5 to 10 foot
intervals or levels, and between the producing "high" and
the non-producing "low” structures. The iron content is
higher in the non-producing "low" structures with a mean

." ."
0f 1.62% as compared to 1.18 % in the producing high

The 0 to 5 foot interval from the top of the
five

structures.
formation is consistently higher in iron than the next

foot interval. The mean iron content 0f the top 5 feet

100

TABLE 5

DATA FOR AN ANALYSIS OF VARIANCE

Producing'"High" Versus Non-Producing "Low"
Percentage Iron Content

 

 

Producing'"High"

Well Numbers

Non-Producing'"Low"

 

 

 

8:888 11 2 8:88
1.18 16 19 2.60
8:88 67 23 3:88
1:88 68 26 8:38
1.60 74 28 2.00
8.28 75 34 2.2121
.. 3. 12%
1.44 82 37 2.06
2:63 83 41 (2.3%
(3:22 84 42 2.2%
1:38 85 ”9 8:78
8:88 86 50 8:88
8:88 87 51 8:88
8:88 90 53 1:88
8:78 91 5“ 8:88
8283 92 58 8:88
8:88 93 6“ 8:88
8:38 95 69 8:88
777 88:88? 828:} 38:88
1.18 Average 1.62

 

a0 to 5 foot interval

b5 to 10 foot interval

101

for the "high" and "low" structures is 1.64% while that of
the next five foot interval for the combined "high" and

“low" structures is 1.16%.

PRODUCING'"HIG'" VERSUS NON-PRODUCING'"LOW"
IRON CONTENT

 

 

 

Source of Sums of

Variance D.F. Squares Mean Square F
Total 75 55.10 _

Wells 36 41.76 1.160 8.529**
Types1 1 3.79 3.79 27.87 **
Levels 1 4.44 4.44 32.65 **
Types x Levels 1 0.22 0.22 1.60
Levels x Wells 36 4.89 0.136

 

Figure 9. Analysis of variance

1Producing'"High" and Non-Producing'"Low" structures
**Highly significant beyond the 1% level

There is no significant interaction between types
times levels or between levels times wells.

There would appear to be a decrease in the content
of iron with an increase in the degree of dolomitization in

the light of the statistical results.

ORIGIN OF DOLOMITE IN THE

ROGERS CITY LIMESTONE

A number of possibilities exist as to the origin of
the dolomite within the top twenty feet of the Rogers City
Limestone.

The contention of some geologists that an uncon-
formity exists at the top of the Rogers City formation and
the base of the Bell shale, if true, could possibly be the
basis for an explanation of the dolomitized limestone.

R. B. Newcombe (1930) in his studies in western Michigan
proposed that an unconformity exists because of the erosion
of the Dundee beds and because of the non-deposition of the
lower part of the Traverse group and the Bell shale. '"This
Middle Devonian unconformity at the base of the Traverse

group,"

he explained, "amounts to a westward progressive
overlap by which the Bell and Dundee are unrepresented in
the southwestern part of Michigan;" One kind of evidence
Newcombe-(1930) offered to support the contention for this
unconformity was that "the existence of an erosion surface
is shown by dolomitization, character of porosity, and
features of a pre—Traverse topographyg" This erosion sur-

face, he stated, "was due to a sudden drop in sea level

which revived the streams, made the sea more muddy, and led

102

 

103

to extensive erosion of the mantle of Dundee and Monroe
beds" (Newcombe, 1930).‘

Ehlers and Radabaugh (1938) supported this theory
with their study of the Dundee in Presque Isle County,
Michigan. There, they stated: ‘"The contact of the Rogers
City limestone with the overlying Bell Shale is discon-
formable; the effects of erosion of the Rogers City lime-
stone prior to the deposition of the Bell shale are well
illustrated by solution channels, crevices and small caverns
all subsequently filled with the Bell shale“ (Ehlers and
Radabaugh, 1938).

K. K. Landes (1951) stated that "emergence followed
the deposition of Dundee and Rogers City strata and sub-
sequent erosion stripped these rocks from the southwestern
corner of Michigan and again exposed the Detroit River
group at the surface."

If the top of the Dundee were exposed throughout the
entire southern peninsula of Michigan, then the formation
of an erosion surface could result in the highly porous
zone (Rogers City formation) beneath the contact of the
younger Bell shale. The solution channels and cavities
within the limestone would allow easy passage to ascending
waters at the time of dolomitization, possibly at the time
of, or after, the period of folding late in the history of
the Michigan basin.

If the central portion of the Michigan basin was

not entirely exposed the Rogers City formation may be the

104

result of an eroded and redeposited limestone as a clastic
sediment which in turn may have resulted in a more porous
rock that was easily dolomitized later during folding of
the beds in the basin.

The theory of leaching might be applied as an alter-
native to that of the replacement theory in this instance.
“Both calcium carbonate (CaC03) and ferrous hydrocarbonate
(Fe(HCO3)) are more soluble in ground waters, commonly a
carbonic acid solution, than the magnesium carbonate
(MgCO3); thus, they are subject to leaching" (Mellor, 1932).
The removal of the calcium and ferrous carbonates gives
rise to a concentration of the magnesium carbonate. It has
been the view of many geologists that dolomites might have
resulted from surface or marine leaching in this manner.

The theory of leaching might explain the possibility
of a more rapid removal of the calcium and iron from the
fractured and fissured anticlines and little or no leaching
in the troughs or synclines, but it would not explain the
consistent decrease in the iron content from the top of
the formation downward regardless of structure.

Core analyses and well samples show no apparent
break between the Rogers City formation and the contact of
the overlying Bell shale (Knapp, 1950). If this be the
case, and in the light of the present study, it would appear
that with the folding of the sedimentary beds minor frac—

tures and fissures were developed throughout the central.

105

basin. Secondary dolomitization of the limestone formation
probably took place in areas of circulating ground waters,
possibly ascending at the time of dolomitization from lower
depths through older, regional dolomites (Detroit River

and Dundee) and carrying magnesium from those rocks. The
possibility as to why the dolomitization is confined largely
to the upper part of the limestones may be due to the
presence of the overlying Bell shale which might partially
block the ascending solutions so that they spread out and
moved laterally in the upper part of the limestone. The
upper-most portions of the limestones would be the apices
of the anticlinal folds and may explain the relationship

of structure to degree of dolomitization. Also, more
tensional cracks and fissures would tend to form on the
folded anticlines than in the synclinal troughs.

The iron content of the limestone formation exists
in the form of a carbonate. '"The carbonates of iron and
manganese--frequently enter replacing the magnesium car-
bonate (of dolomite) and grade to ankerite" (Dana, 1951).

A replacement of one~third of the Mg atoms by Fe does not
change the character of the dolomite crystalline structure.
Normal dolomite (CaCO3-MgCO3) may readily grade into
ankerite (2CaCo3.MgC03.FeCO3). Minerals that may be classed
as ankerite have in general the same mode of occurrence and
associations as dolomite. As the indices of dolomite

(o = 1.68 and e = 1.50) increase with an increase of iron

106

or manganese it is difficult to distinguish it optically
from ankerite (o = 1.72 and e = 1.53) (Dana, 1951).

It would appear, from all available evidence, that
the magnesium replaced the calcium by solutions ascending
by means of the fractures and fissures concentrated in the
anticlinal structures. 0n the other hand, the ferruginous
waters descending from overlying formations rich in iron
may have concentrated in the trough-like depressions and
replaced the Mg atoms with Fe atoms giving rise to a ferrous
dolomite or possibly an ankerite.

It should be noted, in closing, that the samples
analyzed vary in iron content from 0.46% to 4.16%. This
variation of less than 4.00% may be so insignificant as to
warrant little attention in consideration of the theory of

the origin of the Rogers City dolomite.

SUMMARY AND CONCLUSION

General Summary

 

The rapid and accurate methods described in this
paper for the determination of calcium and magnesium con-
tent of carbonate rocks make it possible to run routine
analyses of a large number of samples. The methods used
were adopted by the author from Standard Methods for the

Examination of Water, Sewage, and Industrial Wastes, pub-

 

lished by the American Public Health Association, 1955,
for the determination of the calcium, magnesium, and iron,
content in water hardness tests. The error encountered in
the chemical analyses ranged from plus or minus .005% for
the calcium test to plus or minus 1% for the magnesium and
iron tests.

The above-mentioned techniques were used to analyze
dolomitic limestones from the Rogers City formation of the
central Michigan basin area. The Rogers City-Dundee for-
mation, normally a marine limestone, is found in many places
to be an extremely porous dolomite. Production is generally
limited to these dolomitic zones in fields producing oil
from the Rogers City formation. It is the nature and origin
of these dolomitic zones which were the concern of this
paper.

107

108

The preparation of lithologic Mg/Ca ratio maps is an
ideal means to depict the lateral variation in the degree
of dolomitization over the area studied. A comparison of
structural maps and Mg/Ca ratio maps make it possible to
observe actual relationships between structure and degree
of dolomitization; whereas, comparison of Mg/Ca ratio maps
determined for different depths of the Rogers City formation
allows one to note vertical variation in the pattern of
secondary dolomitization.

The simultaneous correlations and comparisons of
several variables both laterally and vertically, which could
not be diagramed readily in three dimension, were compared
by the statistical method of the analysis of variance.
Statistically, combinations of variables can be analyzed
for possible relationships that would be impossible or im-

practicable to produce on maps.

Conclusions

 

The comparison of structural and ratio maps of the
Rogers City limestone and the Coldwater oil field reveals,
in general, a significant relationship between the struc-
ture and the degree of dolomitization as indicated by the
Mg/Ca ratio. There would appear to be a direct relation-
ship both regionally and locally between "high" structure
and an increase in the degree of dolomitization.

One exception to this relationship was observed in

the comparison of the structural and ratio maps. An area

109

of locally dolomitized limestone did not coincide with a
structural "high" but was located in a structural trough
or'"low." Unfortunately, then, the discovery of a body of
locally dolomitized limestone does not insure finding gas
or oil. It has been found elsewhere that local dolomites
are non-porous, or that they are so situated structurally
that no suitable trap for oil accumulation exists and
therefore are non-productive. These facts were recognized
by Orton (1888), who pointed out nearly seventy years ago,
that in the Trenton dolomite fields of Ohio and Indiana a
combination of porosity and favorable structural position
was necessary for commercial oil and gas accumulation.
Lacking any further evidence, it would seem that unfavorable
structure may be the cause of non-production in this area
of locally dolomitized limestone.

Upon comparison of the Mg/Ca ratio maps for the top
five feet of the Rogers City limestone with the average
ratios of the top twenty feet there would appear to be no
significant relationship or pattern of dolomitization with
changing depths. The same conclusion was arrived at statis-
tically, showing no significant difference in the pattern
or variation of dolomitization between the top five feet
and the next five feet, or between the top 7.5 feet and
the next 7.5 feet.

In this respect, there is no evidence for, or against,
the possibility of ascending or descending solutions which

may have caused the dolomitization of the limestone.

110

The results of the statistical comparisons were as

follows:

1.

There is a highly significant difference between
the Mg/Ca ratios of the producing wells on ”high"
structures, as compared to those of the non-
producing wells on "low" structures. Expressing
a "producing" well in terms of "porosity,"

there is a relationship between porosity and
degree of dolomitization.

There is no significant difference between the
Mg/Ca ratios of producing wells and non-producing
wells all on "high" structures. The degree of
dolomitization is high for both producing and
non-producing wells. Therefore, there is either
little or no porosity in the replacing dolomite
or other factors are responsible for the non-
productive nature of the wells.

There is a significant difference between the
Mg/Ca ratios of non-producing wells on "high"
structures as compared to those on"low" struc-
tures. The degree of dolomitization is much
smaller in troughs, or "low" structures, as
compared to the structures of greater magnitude.
There is a highly significant difference between
the Mg/Ca ratios of "high" structures as com-
pared to those of "low" structures regardless of

producing or non-producing wells.

111

There would appear to be a direct relationship,
in general, between magnitude of structure and
degree of dolomitization. Although there is a
relationship between degree of dolomitization
and porosity it is no simple and direct relation-
ship which would exist in an ideal case when all
porosity is caused by dolomitization. The lack
of perfect correlation is probably due to the
existence of some pores or fractures prior to
dolomitization.

5. There is a highly significant difference in the
iron content between the producing wells on
"high" structures and the non-producing wells on
"low" structures. The iron content is consis-
tently greater on "low" structure with a minimum
of secondary dolomitization.

6. There is a highly significant difference between
the iron content of the top five foot interval
as compared to the next five foot interval of
the Rogers City formation. The top five feet
of the formation contains a greater per cent of
iron than does the next five foot interval re-
gardless of structural relief.

0n the basis of the thirty-eight wells analyzed

statistically on percentage of iron content it would appear
that the ferrous solutions were descending from overlying

formations with a tendency to concentrate in the troughs or

112

synclinal structures replacing the Mg atom with an Fe atom
in the dolomite crystalline structure. The resulting
secondary replacement is a ferrous dolomite with the even-
tual possibility of grading into the mineral ankerite. The
»concept of descending ferrous solutions would explain the
decrease in per cent iron content from the top of the
Rogers City formation downward. However, the variation of
less than 4.00% in the iron content of the samples analyzed
statistically may be insignificant for a regional consid-
eration and thus warrant little or no attention.

The magnesium to calcium ratio in limestones is a
very useful geologic tool. It is especially useful in
porosity studies of dolomitized limestone formations. The
rapid and accurate techniques used in this study can enable
geologists and petroleum engineers to make the Mg/Ca ratio
determination a routine analysis. Statistical studies may
enable them to predict porosity of carbonate rocks. Statis-
tical studies may also show the relationship between
porosity and dolomitization for many limestones, which have
been reported as lacking such relationship (Chilingar and
Terry, 1954).

Ratio determinations may also be useful in locating
dolomitized structures or trends of structural highs in
areas of little structural control. The Mg/Ca ratios should
aid in locating and following dolomitized zones either along

faults or in areas not related to structure.

113

Lithologic Mg/Ca ratio maps may facilitate the pre—
diction of cross-folding in the Michigan basin which is not
as apparent on structure contour maps.

The author believes that extensive studies of sec-
ondary dolomitized zones in limestone formations by accurate
chemical analyses, detailed structural contouring, careful
interpolation of lithologic Mg/Ca ratio maps, and statistical
‘analyses of resulting data will provide a sound foundation
for a better understanding of secondary dolomitization and
its relationship to structure and porosity of limestone

formations such as the Rogers City.

SUGGESTIONS FOR FURTHER STUDY

For a complete analysis of the relationships existing

between secondary dolomitization and porosity and magnitude

of structure in dolomitic limestone formation of the central

Michigan basin the following suggestions are made:

1.

A systematic plan of sampling and analysis of
the entire Rogers City formation of Michigan,
or any other dolomitized limestone formation
with detailed structural contouring and
lithologic Mg/Ca ratio maps.

A thorough study of the contact between the
Rogers City limestone and the Bell shale to
determine the nature and extent of a possible
unconformity between the two formations.

A detailed study of the Bell shale, chemically,
structurally and petrographically, may shed
more light on the nature of the break between
it and the top of the Rogers City limestone.

The suggested relationship between dolomite

and iron content might be analyzed more carefully
for a detailed explanation.

114

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