Reservoir Geology of the Dundee Limestone, West Branch Field, Michigan

Home , Amherstburg Formation, Bell Shale, Dundee Limestone, Lucas Formation, Rogers City Limestone, Sylvania Sandstone

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Master's Theses Graduate College

12-1990

Reservoir Geology of the Dundee Limestone, West Branch Field, Michigan

Brendan Ciaran Curran

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Recommended Citation Curran, Brendan Ciaran, "Reservoir Geology of the Dundee Limestone, West Branch Field, Michigan" (1990). Master's Theses. 1053. https://scholarworks.wmich.edu/masters_theses/1053

This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. RESERVOIR GEOLOGY OF THE DUNDEE LIMESTONE, WEST BRANCH FIELD, MICHIGAN

Brendan Ciaran Curran

A Thesis Submitted to the Faculty of The Graduate College in partial fulfillment of the requirements for the Degree of Master of Science Department of Geology

Western Michigan University Kalamazoo, Michigan December 1990

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RESERVOIR GEOLOGY OF THE DUNDEE LIMESTONE, WEST BRANCH FIELD, MICHIGAN

Brendan Ciaran Curran, M.S.

W estern Michigan University, 1990

West Branch field is a low-relief, NW-SE-trending anticline near the

center of the Michigan basin. Since 1934, the Dundee Limestone (Middle

Devonian) has produced over 12 million barrels of oil from this field. From

core studies, six depositional facies types were recognized in the Dundee.

These are dominated by bioclastic carbonate sand facies deposited in normal-

marine shelf settings. Although burial cements have occluded some porosity,

carbonate sand facies have retained significant primary interparticle porosity

and are the most important reservoir rocks. Micritic facies with restricted

faunal assemblages are present at the top of the Dundee. The top 10 to 15

feet were dolomitized before the deposition of the overlying Rogers City

Limestone. This dolomite has hiigh porosity but very low permeability. Cross

sections from well logs show that facies distribution in the Dundee is largely

lenticular. This understanding of distribution of porous and nonporous units

will allow design and evaluation of waterflood programs.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS

I thank my advisor, Dr. William B. Harrison III (Western Michigan

University, Kalamazoo), for his encouragement and support throughout the

course of this project I would also like to thank Neil F. Hurley (Marathon

Oil Company, Littleton, Colorado) for the generous contribution of his time

and valuable advice.

Special thanks go to David A. Barnes (Western Michigan University) for

many helpful discussions and suggestions. Special thanks are also extended

to Lise Brinton (Marathon Oil Company) for her suggestions and constructive

criticism, and assistance with petrographic work and microsampling. Thanks

also go to K. C. Lohmann (University of Michigan, Ann Arbor) for his

assistance with isotopic analyses, and to Joyce M. Budai (University of

Michigan) for her assistance with ultraviolet fluorescence microscopy.

Research was supported by a grant from Marathon Oil Company, the

American Association of Petroleum Geologists’ Grants-in-Aid program, a grant

from The Graduate College of Western Michigan University, and the W. David

Kuenzi Memorial Research Award from the Western Michigan University

Department of Geology.

Brendan Ciaran Curran

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Reservoir geology of the Dundee Limestone, West Branch Field, Michigan

Curran, Brendan Ciaran, M.S.

Western Michigan University, 1990

UMI 300 N. ZeebRd. Ann Arbor, MI 48106

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Copyright by Brendan Ciaran Curran 1990

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS

ACKNOWLEDGEMENTS...... ii

LIST OF TABLES ...... vii

LIST OF FIGURES ...... viii

LIST OF PLATES ...... x

INTRODUCTION...... 1

Research Objectives ...... 1

Research Contributions ...... 2

Previous W ork ...... 4

Field History: Dundee Reservoir ...... 5

M ethods ...... 6

GEOLOGIC SETTING ...... 9

Stratigraphy ...... 9

Regional Structure ...... 16

SEDIMENTOLOGY OF THE DUNDEE LIMESTONE...... 20

Facies Types ...... 23

Crinoid Grainstone ...... 23

Skeletal-Peloidal Grainstones and Packstones ...... 27

Skeletal Wackestone ...... 32

Restricted Mudstones and Wackestones ...... 35

iii

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Stromatoporoid-Coral Floatstone ...... 42

Fenestral-Cryptalgal Lam inite ...... 44

Sedimentary Cyclicity...... 45

SEDIMENTOLOGY OF THE ROGERS CITY LIMESTONE 51

Nodular Wackestone ...... 51

Composition ...... 51

Common Diagenetic Effects ...... 52

Permeability and Porosity...... 52

Depositional Environment ...... 53

Skeletal Packstone ...... 53

Composition ...... 53

Common Diagenetic Effects ...... 53

Permeability and Porosity ...... 54

Depositional Environment ...... •...... 54

FIELD-WIDE STRATIGRAPHIC CORRELATIONS...... 56

Dundee Limestone Correlations ...... 58

Rogers City Limestone Correlations ...... 64

DIAGENESIS...... 65

Early Marine Fabrics ...... 67

C h e rt ...... 72

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Matrix-Replacive Dolomite ...... 72

Calcite Cem ent ...... 76

Syntaxial Cem ent ...... 76

Intercrystalline Calcite Microspar ...... 78

Scalenohedral and Blocky Cements ...... 80

Cement Associated With Stylolites ...... 82

Saddle Dolomite Cement ...... 82

Other Burial Cements ...... 85

STRUCTURAL EVOLUTION: WEST BRANCH FIELD...... 88

F ractu res...... 88

Small-Scale Compactional Fractures...... 91

Fractures Associated With Stylolites ...... 91

Through-Going Macrofractures ...... 93

Timing of Deformation ...... 94

Nature of Movement ...... 95

DISCUSSION...... 97

Facies Interpretation ...... 97

Disconformity at the Top of the Dundee Limestone ...... 99

Diagenesis ...... 101

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Fracture-Controlled Dolomite Hyposthesis ...... 103

Timing of Structural Development ...... 106

Economic Considerations ...... 107

CONCLUSIONS...... 109

APPENDICES

A. Plates 1-1 Through 1-38, Core Description Sheets ...... I ll

B. Plates II-l Through 11-11, Well Summary Sheets ...... Pocket

C. Plates III-l Through III-5 Field Cross Sections ...... Pocket

BIBLIOGRAPHY...... 154

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES

1. Facies Characteristics, Dundee Limestone ...... 21

2. Frature Intensity From Core, Normalized to 100 feet ...... 90

vii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES

1. Location of West Branch and Other Nearby Middle Devonian Oil Fields ...... 10

2. Regional Isopach Map of the Dundee Limestone ...... 13

3. Typical Log Signature and Stratigraphic Units, West Branch Area ...... 14

4. Basement Province Map of Michigan ...... 17

5. Structure Contour Map of the Top of the Rogers City Limestone, West Branch Area ...... 19

6. Characterisitics of Carbonate Sand Facies, Dundee Limestone ...... 24

7. Characteristics of Restricted Mudstones and Wackestones, and the Dundee-Rogers City Contact ...... 36

8. Stromatoporoid-Coral Floatstone and Fenestral-Cryptalgal Laminite Facies, Dundee Limestone ...... 43

9. Idealized Coarsening Upward Hemicycle, Dundee Limestone ...... 47

10. Plot of Normalized Cycle Frequency vs. Distance From the First Well in Cross Section A-A’” ...... 49

11. Location of Cross Sections on Structure Contour Map of the Top of the Rogers City Limestone ...... 57

12. Simplified Version of Stratigraphic Cross Section A-A’”, Plate? III-l through III-3 ...... 59

13. Simplified Versions of Stratigraphic Cross Sections B-B’ and C-C, Plates III-4 and III-5 ...... 60

viii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Figures-Continued

14. Paragenetic Sequence Determined for the Dundee Limestone, West Branch Field ...... 66

15. Early Marine Calcite Cement and Replacive Chert, Dundee Limestone ...... 68

16. Isotopic Signatures of Early Calcite Fabrics Compared to Published Devonian Marine Signatures ...... 70

17. Isotopic Signature of Replacive Dolomite ...... 75

18. Calcite Cements, Dundee Limestone ...... 77

19. Isotopic Signatures of Calcite Cements ...... 79

20. Pore-Filling Saddle Dolomite Cement, Dundee Limestone .... 84

21. Isotopic Signature of Saddle Dolomite Cem ent ...... 86

22. Small-Scale Fractures Associated With a Sutured-Seam Stylolite ...... 89

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF PLATES

1-1. Heintz #9 Core Description, 2777’-2810’ ...... 116

1-2. Heintz #9 Core Description, 2810’-2845’ ...... 117

1-3. Heintz #9 Core Description, 2845’-2878’...... 118

1-4. Donovan #6 Core Description, 261T-2637’ ...... 119

1-5. Donovan #6 Core Description, 2687-2720’ ...... 120

1-6. Donovan #6 Core Description, 2720’-2748’ ...... 121

1-7. Cox tfl Core Description, 2715’-2750’ ...... 122

1-8. Cox #2 Core Description, 2750’-2785’ ...... 123

1-9. Cox ft! Core Description, 2785’-2797’ ...... 124

I-10. Estey E-8 Core Description, 2643’-2680’ ...... 125

1-11. Estey E-8 Core Description, 2680’-2715’ ...... 126

1-12. Estey E-8 Core Description, 2715’-2750’ ...... 127

1-13. Doran #5 Core Description, 2634’-2670’ ...... 128

1-14. Doran #5 Core Description, 2670’-2705’ ...... 129

1-15. Doran #5 Core Description, 2705’-2712’ ...... 130

1-16. Hart #2 Core Description, 2509’-2545’ ...... 131

1-17. Hart #2 Core Description, 2545’-2580’ ...... 132

1-18. Hart #2 Core Description, 2580’-2615’ ...... 133

1-19. H art #2 Core Description, 2615’-2650’ ...... 134

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Plates-Continued

1-20. H art ff2 Core Description, 2650’-2685’ ...... 135

1-21. Hart #2 Core Description, 2685V2689’ ...... 136

1-22. H art #1 Core Description, 2603’-2626’ ...... 137

1-23. Hart ffl Core Description, 2655’-2687’ ...... 138

1-24. Reinhardt #3 Core Description, 261T-2645’ ...... 139

1-25. Reinhardt #3 Core Description, 2645’-2680’ ...... 140

1-26. Reinhardt #3 Core Description, 2680’-2685’ ...... 141

1-27. Buckingham ff4 Core Description, 2568’-2605’ ...... 142

1-28. Buckingham ff4 Core Description, 2605’-2640’ ...... 143

1-29. Buckingham ff4 Core Description, 2640’-2675’ ...... 144

1-30. Buckingham #4 Core Description, 2675’-2679’ ...... 145

1-31. Grow if4 Core Description, ..2570’-2605’...... 146

1-32. Grow ff4 Core Description, ..2605’-2640’...... 147

1-33. Grow ff4 Core Description, ..2640'-2675’...... 148

1-34. Grow ft4 Core Description, ..2675’-2710’...... 149

1-35. Grow if4 Core Description, 2710’-2716’ ...... 150

1-36. Grow ff9 Core Description, 2624’-2660’ ...... 151

1-37. Grow ff9 Core Description, 2660’-2674’ ...... 152

1-38. Grow ff9 Core Description, 2726V2752’ ...... 153

II-1. Heintz ft9 Well Summary S h e e t ...... Pocket

with permission of the copyright owner. Further reproduction prohibited without permission. List of Plates-Continued

II-2. Donovan ft6 Well Summary Sheet ...... Pocket

II-3. Cox ft2 Well Summary Sheet ...... Pocket

II-4. Estey E-8 Well Summary Sheet ...... Pocket

II-5. Doran #5 Well Summary Sheet ...... Pocket

II-6. H art #2 Well Summary Sheet ...... Pocket

II-7. Hart ft1 Well Summary Sheet ...... Pocket

II-8. Reinhardt #3 Well Summary Sheet ...... Pocket

II-9. Buckingham ff4 Well Summary Sheet ...... Pocket

11-10. Grow ft4 Well Summary Sheet ...... Pocket

11-11. Grow ff9 Well Summary S h e e t ...... Pocket

III-l. Sratigraphic Cross Section A-A’ ...... Pocket

III-2. Stratigraphic Cross Section A’-A” ...... Pocket

III-3. Stratigraphic Cross Section A”-A’” ...... Pocket

III-4. Stratigraphic Cross Section B-B’ ...... Pocket

III-5. Stratigraphic Cross Section C-C’ ...... Pocket

xii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION

Dundee Limestone (Middle Devonian) reservoirs have produced over 351

million barrels of oil in Michigan. This is more oil production than any other

formation in the Michigan basin (Michigan Department of Natural Resources,

1989). Dundee oil fields are generally found in the central region of the basin

and are all located on structural highs. On the western side of the basin, the

Dundee is commonly dolomitized and contains laminated and nodular

anhydrite. Most Dundee fields in the central and eastern side of the basin

contain no anhydrite, are much less dolomitic, and produce from primary

porosity zones that occur directly below the overlying micritic Rogers City

Limestone (Gardner, 1974).

West Branch field has produced hydrocarbons from the Ordovician St

Peter Sandstone and five Middle Devonian formations: Amherstburg, Lucas,

Dundee and Rogers City (commonly treated as the "Dundee" reservoir), and

Traverse Limestone. The Dundee Limestone has been the main producing

unit in West Branch since the field was discovered in 1934, and has produced

over 12 million barrels of oil.

Research Objectives

This study is concerned with understanding the stratigraphy,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sedimentology, and diagenesis of the Dundee Limestone and the structural

development of West Branch field. The research objectives are:

1. Describe Dundee depositional facies and the nature of the contact between

the Dundee and the overlying Rogers City Limestone.

2. Characterize the lateral continuity of porous units for evaluation of current

and future waterflood programs.

3. Establish the paragenetic sequence of diagenesis and hydrocarbon

emplacement Use cathodoluminescence and stable isotope geochemistry to

investigate the origin of calcite cements and dolomites.

4. Document fracture abundance in core. Evaluate a published model

(Prouty, 1989a, 1989b; Ten Have, 1979) for fracture-controlled dolomite in this

reservoir. If they exist, project fracture-controlled dolomite fairways or trends

down to deeper reservoirs.

5. Compare structural timing and sedimentary response in West Branch to

observations of pre-sedimentary folding made in the nearby Buckeye field

(Montgomery, 1986).

Research Contributions

The major contributions of this research are:

1. Detailed descriptions were constructed of cores from the Dundee and

Rogers City Limestones. Six depositional facies types were recognized in the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dundee; four of these facies occur above the oil-water contact in the reservoir.

Two facies were recognized in the Rogers City. The contact between the

Dundee and Rogers City is a corroded or bioeroded, pyritized surface. This

disconformity represents a sequence boundary between deposition of the

Dundee and Rogers City formations. This surface marks the drowning of the

shallow water Dundee shelf.

2. Porosity and permeability distribution in both the Rogers City and Dundee

were found to oe controlled by depositional facies types. The distribution of

facies in the Dundee is largely lenticular throughout the field. The Rogers

City is dominated by a facies that is generally nonporous. The other facies

present in the Rogers City (with marginal porosity and permeability) is

correlative throughout the field in two discrete beds.

3. Early diagenesis of the Dundee is characterized by early marine carbonate

cements in many facies and the early dolomitization of the top 10 to 15 feet

(3 to 5 meters). Burial diagenesis resulted in a limited amount of porosity

occlusion by pore-lining calcite, and syntaxial calcite cement, and pore-filling

saddle dolomite. Stylolitization occurred throughout much of the burial history

of these sediments. Hydrocarbon emplacement occurred before or during the

precipitation of the last carbonate cement (saddle dolomite).

4. The presence of throughgoing macrofractures, and small-scale fractures

associated with stylolite seams were documented in detailed core descriptions.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dolomite appears to be facies-controlled rather than fracture-controlled.

Therefore, the published model of fracture-controlled dolomite (Prouty, 1989a,

1989b; Ten Have, 1979) in this reservoir is judged to be in error.

5. Correlation of Dundee and Rogers City facies on well logs and comparison

of thicknesses of units overlying the Rogers City show no evidence of an

existing structural high in the study area during the Middle Devonian.

Previous Work

West Branch Held has been the subject of several studies since its

discovery in 1934. Newman (1936) discussed the early history and geology

of this oil field. Ten Have (1979) studied the structural aspects of the field

and mineralogy of the Dundee reservoir. He concluded that late

dolomitization enhanced porosity in this field. From maps of dolomite

concentrations in well cuttings, he suggested that vertical faults and fractures,

inferred from a structure map, controlled the lateral distribution of dolomite

in the field. Based on the work of Ten Have (1979), Prouty (1989a., 1989b)

cited the West Branch Dundee Limestone as an example of a fracture-

controlled dolomite reservoir.

Vugrinovich and Matzkanin (1981) stressed the significance of the

development of secondary porosity through dolomitization in West Branch

field. They also stated that different productive intervals in wells "seem to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. be connected" in the field. Vugrinovich and Matzkanin (1981) considered a

waterflood initiated in 1977 in a unitized area of the field to be a success.

Montgomery (1986) studied depositional facies in the Dundee Limestone

of Buckeye oil field, about 30 miles southwest of West Branch. His study,

based on observations of 12 cores, concluded that depositional facies controlled

the distribution of oil producing zones in the Dundee. He also concluded that

structural movement occurred before Dundee deposition and carbonate

buildups resulted in approximately 200 feet of thickening in the Dundee over

the paleohigh.

Park (1987) addressed the origin and distribution of porosity in the Lucas

Formation at West Branch field. The Lucas directly underlies the Dundee.

Significant findings by Park (1987), in the context of this paper, include the

interpretation that structural movement at West Branch post-dated deposition

of the Lucas Formation, and that dolomitization of the Lucas was

penecontemporaneous with deposition.

Field History: Dundee Reservoir

The West Branch Dundee oil reservoir was discovered in 1934 with the

completion of Pure Oil Company’s Fisk #1 well (Sec. 27, T22N-R2E). Top

of the Dundee was at 2625 ft and initial production was 21 barrels a day.

Field development began on a 10 acre spacing (Newman, 1936).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In 1966, the central area of the field was unitized and a Dundee

waterflood program was initiated by Marathon Oil Company. The waterflood

utilized a five-spot well pattern (Vugrinovich and Matzkanin, 1981). In 1989,

95 injection wells were operating in this unitized area A smaller area of the

field was unitized by Muskegon Development Company in 1978 and a

waterflood began in 1981 with 4 injection wells (Lintemuth, 1989).

Before initiation of waterflood programs, the production ratio of water

to oil (on a field-wide basis) was 1:15. After the Marathon waterflood began,

water production steadily increased every year, and exceeded oil production

in 1970. By 1980, annual water production was approximately six times as

great as oil production (Vugrinovich and Matzkanin, 1981).

In 1986, 206 oil wells were active from this reservoir and 99 water

injection wells were operating. Vugrinovich and Matzkanin (1981) calculate

that the Dundee at West Branch has 1870 reservoir acres. Historically, an

average value of -1785 ft (subsea depth) has been used for the oil-water

contact in this reservoir.

Methods

This project is based on observations and test results from 11

conventional cores (average length about 100 feet) taken from West Branch

field by Marathon Oil Company. The cores generally cover the majority of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the producing section of the Dundee and often include part of the overlying

Rogers City Limestone. All cores were subject to whole-core or core-plug

porosity and permeability analyses prior to the initiation of this study.

Slabbed core was examined using a low-power binocular microscope

during preparation of detailed core description sheets. Cores were described

using the format of Bebout and Loucks (1984) (Appendix A, Plates 1-1 through

1-38). In addition, individual well-summary plates for all cored wells were

constructed to correlate rock descriptions, log signatures, and core analyses

(Plates II 1 through 11-11).

Well logs from 58 wells were used to create subsurface cross sections.

These cross sections show the distribution and lateral continuity of facies

recognized in core throughout the field (Plates III-l through III-5).

After core descriptions were completed and depositional facies were

recognized, 106 thin sections were cut from selected intervals for petrographic

studies. One-half of each thin section was stained with Alizarin Red-S and

potassium ferricyanide. This staining allowed easy discrimination of calcite

from dolomite, and ferroan carbonates from non-ferroan carbonates (Dickson,

1966). These thin sections were used to study depositional and diagenetic

fabrics.

To help determine the paragenetic sequence, 45 thin sections were

polished and examined under cathodoluminescence (CL) microscopy. This

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. work was done in preparation for microsampling of unaltered marine

sediments and cements. Luminescence microscopy allowed inferences to be

drawn regarding the contamination of primary fabrics by later diagenesis and

also allowed the recognition of changing trace-element concentrations in

cements that commonly looked homogeneous under plane light

Microsamples with a mass of 0.2 to 0.5 mg were drilled from cements

and marine fabrics for carbon and oxygen isotope analysis. The samples were

drilled from polished thin section chips using a low-power binocular

microscope and a fixed dental drill bit 500 microns in diameter. Forty-eight

microsamples were drilled from 35 polished chips. Sixteen of these were

analyzed at the University of Miami (Florida), and thirty-two were analyzed

at the University of Michigan, Ann Arbor. All results are reported using the

per-mil nomenclature with respect to the Peedee Belemnite (PDB) standard.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GEOLOGIC SETTING

Stratigraphy

West Branch field (Figure 1) is located in central Michigan, slightly

northwest of the Middle Devonian depocenter of the Michigan basin.

Phanerozoic sediments in this basin exceed 16,000 feet in thickness (Fisher,

Barratt, Droste, and Shaver, 1988). The Michigan basin is located over a

Keweenawan rift sequence related to the mid-continent rift Known

Precambrian sediments in the basin are composed predominantly of siliciclastic

sediments (Catacosinos, 1981). The Cambrian through Silurian sedimentary

section contains sandstones, shales, dolomites, and evaporites. Fisher et al.

(1988), Catacosinos (1973), and Lilienthal (1978) addressed the gross lithologies

and stratigraphic relationships of these lower Paleozoic formations.

The reservoir of interest at West Branch field is the Dundee Limestone.

The term "Dundee Limestone" was first used by Lane (1895) to describe

limestones that crop out in southeast Michigan. Stratigraphically, these rocks

lie between dolomites of the Detroit River Group and shales of the Traverse

Group. Bassett (1935) described the stratigraphy and paleontology of these

same outcrops. Ehlers and Radabaugh (1938) originally defined the overlying

Rogers City Limestone from outcrop studies in northeastern Michigan. Cohee

and Underwood (1945) used outcrop and subsurface data to address the 9

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. /[OGEMAW " " 1 IOSCO j ^ j I Rose City I

I ^ ^ s t ! j Branch \ J ___ f e u J t- — V a X ARENAC j North j [ Buckeye ! ^ = 7 ! / South Buckeye

25 Miles 40 km

100 Miles 4 180 Icm

Figure 1. Location of West Branch and Other Nearby Middle Devonian Oil Fields.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. regional lithology and thickness of the Dundee and Rogers City formations

throughout the Michigan basin.

Bloomer (1969), Gardner (1974), and Sanford (1967) discussed various

aspects of Dundee-Rogers City stratigraphy and facies in the Michigan basin.

The Dundee is underlain by the Lucas Formation and is overlain by the

Rogers City Limestone and Bell Shale. Conodont research from outcrop

samples (Bultynck, 1976) indicates that the Dundee Limestone and the Rogers

City Limestone are upper Eifelian (Middle Devonian) in age. Bultynck (1976)

also concluded that the contact between Eifelian and Givetian sediments is

near the base of the Bell Shale. Conodont research done by Orr (1971)

agrees that the Dundee is Eifelian and the Bell is lower Givetian. Although

it is implied that the Rogers City is upper Eifelian, Orr (1971) does not

speculate on the stratigraphic location of the Eifelian-Givetian boundary.

During the Middle Devonian, the Michigan basin was apparently 20 to

30 degrees south of the equator (Scotese, 1984). The climate was arid, as

indicated by thick evaporite and sabka dolomites of the Lucas Formation

(Park, 1987). Transgressing Middle Devonian seas returned well-circulated

normal-marine waters to the Michigan basin to initiate deposition of the

Dundee Limestone. According to Gardner (1974), the Dundee is a biostromal

shelf carbonate. He does note, however, that on the extreme western margin

of the basin, sabka-lagoonal deposits predominate.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2 is a regional isopach map of the Dundee Limestone. Note that

the basin depocenter is only 50 miles southeast of West Branch field.

The overlying Rogers City Limestone is described as a dark-gray, nodular,

massive, aphanitic limestone (Cohee and Underwood, 1945; Gardner, 1974;

Montgomery, 1986; and Sanford, 1967). This unit is interpreted here to

represent deposition in water depths significantly greater than those

encountered during Dundee deposition.

Figure 3 is a typical log from West Branch field. This log illustrates

thickness and lithology of stratigraphic units from Lower Devonian to surface.

At the base of the Lower Devonian lie the cherty limestones of the Bois

Blanc Formation. The Bois Blanc is overlain by the Detroit River Group

(Lower and Middle Devonian), made up of the Sylvania Sandstone,

Amherstburg Formation, and Lucas Formation. The Sylvania Sandstone is

generally absent in the West Branch area. The Amherstburg (predominantly

limestone) and the Lucas (evaporites and dolomite) are known hydrocarbon

reservoirs in the field. The contact between the Lucas Formation and the

overlying Dundee Limestone is believed by Sanford (1967) to be a major

unconformity. This contact is a problematic pick on well logs and is picked

by some workers (e.g., Gardner, 1974) at the first anhydrite below the Dundee.

In this study, the top of the Lucas was picked at the top of the pervasive

dolomite below the limestone of the Dundee.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13

OUTCROP AREA

■250-]

_ J.

32 km

Figure 2. Regional Isopach Map of the Dundee Limestone (modified from Cohee and Underwood, 1945).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. HARATHON #M8 BOHLIR (See. 18, T22N-RZE GAMMA PAY LITHOLOGY l« NEUTRON POROSITY Ml -All HEIST GLACIAL DRIFT Unconsolidated sand and gravel

Shale, gray, occasional beds of m e slltstone, tan to gray, slightly calcareous

Shale, brown to black Shale, gray to greenish gray, D M - REA trace of sandstone ANTRIM Shale, gray to black, pyrltlc

Limestone, shaley, light gray, fosslHferous

Limestone, light brown to tan, microcrystal 11ne, fosslHferous, some gray shale Interbeds

BELL Shale, medium gray, calcareous Limestone, dark gray, mlcrocrystalHne Limestone, light brown to tan, foss 11 Iferous ______

Dolomite, tan to medium brown, Inter bedded with anhydrite, limestone, and LUCAS salt

Limestone, light to medium brown, AMHERSTBURG slightly fosslHferous, dolomltlc

Limestone, light to medium brown, BOIS BLANC abundant chert

Figure 3. Typical Log Signature and Stratigraphic Units, West Branch Area

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Dundee Limestone is generally represented by light brown to tan

limestone with some preserved primary porosity in the central and eastern

parts of Michigan and by dolomites in the western side of the state (Gardner,

1974). Sanford (1967) believes the contact between the Dundee Limestone

and the overlying Rogers City Limestone to be conformable. The micrite-

rich, nodular Rogers City Limestone is identified by its dark color.

Although outcrop and early subsurface studies treated the Dundee and

Rogers City separately (Cohee and Underwood, 1945; Knapp, 1947), many

recent workers have informally grouped these two formations together under

the name Dundee Limestone (e.g., Gardner, 1974; Lilienthal, 1978; Ten Have,

1979). In this paper these formations are treated separately.

An abrupt contact exists between the Rogers City, which has a very low

gamma ray signature on well logs, and the overlying Bell Shale, which has a

very high gamma ray signature. This provides one of the most easily

identified contacts in the subsurface of Michigan. Although this contact is an

unconformity in basin-margin outcrops, it is believed to be conformable in the

deeper subsurface (Gardner, 1974). The Bell Shale is the basal member of

a sequence of shales and limestones in the Traverse Group. The Traverse

Limestone of this group produced minor oil and gas in the early development

of the West Branch field.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Above the Traverse Group is a thick package of mainly Upper Devonian

and Mississippian shales. The Mississippian Coldwater Shale is the thickest

formation in this package and subcrops beneath glacial till on the crest of the

West Branch structure.

Regional Structure

Structural trends observed in Paleozoic rocks in Michigan probably

represent the interaction of extrabasinal stresses and preexisting lines of

weakness in the Precambrian basement rocks of the region (Hinze, Kellogg,

and O’Hara, 1975). From a limited number of drill holes and geophysical

techniques, Hinze et al. (1975) constructed a basement province map of the

Michigan basin (Figure 4). The Precambrian provinces present are: (1) the

Penokean province in the central and northern areas of the basin, (2) Central

province in the southwest, (3) Grenville province in the southeast, and (4)

Keweenawan rift zone which cuts across the basin trending roughly northwest-

southeast Each province is believed to have its own lines of weakness that

developed during its long tectonic history.

West Branch is located over the Penokean province which is associated

with predominantly northwest-southeast structural trends (Hinze et al., 1975).

The West Branch anticline and other local structures reflect this trend.

Clayton field, about 8 miles to the southeast of West Branch is a smaller, yet

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17

MAFIC LEGEND VOLCANIC ROCKS Granvlll* (O.B-I.IB.Y) K*w»»na»ori (1.05-1.I4B.Y.) Central (1.2- 1.5B Y.) Penokaan (1.6- 1.8 B.Y.) METAVOLCANIC Predominant mafic extrusive METASEOIMENTARY, ROCKS Structural 9 iNTRUSiVE NOCKS GNEISSES Trend -

EXTRUSIVE ROCKS, /m afic/ /\ I METASEOIMENTARY/ / INTRUSIVE ROCKS, METAVOLCANIC ^ROCKS GNEISSES ' 9 GNEISSES a META- / SEDIMENTARY ROCKS

METAVOLCANIC ROCKS MAFIC GNEISSES

MAFIC INTRUSIVE ROCKS gneisses a GRANULITE

granite , felsic a / n"tru 3TVE3 - MAFIC GNEISSES. a EXTRUSIVES EXTRUSIVE a \ , mafic gneiss ETASEDIMENTARY ROCKS

Figure 4. Basement Province Map of Michigan (from Hinze e. al, 1975).

..... Further reproduction prohibited without permission. Reproduced with permission of me copynght owner. Further repr similar structure, aligned with West Branch (Figure 1). These two structures

are probably related to the same basement feature. Approximately 9 miles to

the north of West Branch is the Rose City field (Figure 1). This structure is

a low-relief, gentle anticline with the same orientation as the West Branch and

Clayton structures.

Figure 5 is a structure contour map on top of the Rogers City Limestone

in West Branch. Several features of this structure map are notable. The

structure here is asymmetric, dipping about 350 feet per mile on the

northeastern side and about 250 feet per mile on the southwestern side. The

Clayton anticline exhibits a similar asymmetry (Versical, 1989, 1990). This

provides further evidence of a close genetic relationship between these two

structures. West Branch anticline also appears somewhat irregular in shape.

Ten Have (1979) separated the structure into six principle folds based on the

orientation of structural highs and saddle areas observed on his structure map.

The crest of the West Branch fold migrates to the northeast with depth,

indicated by the recent drilling activity about 2 miles north of the Rogers

City/Dundee structural crest in wells targeting the gas-producing St Peter

Sandstone.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. R3E § 2 ‘ • • •• Hjrt R2E , 1 6 0 0 -

1.6 km 1.6 J J ml R1E 22 R. Dow, and W. Cheek. All contours are based on well-log tops. Off-structure contours are based on seismic and log tops. Figure 5. Structure ContourContour Map interval of the = Top 40 of feetthe Rogers City Circled Limestone. dots = cored wells of this study. Adapted from maps by M. Fahy, i

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SEDIMENTOLOGY OF THE DUNDEE LIMESTONE

From study of core and thin sections, six facies types were identified.

These are: (1) crinoid grainstones, (2) skeletal-peloidal grainstones and

packstones, (3) skeletal wackestones, (4) restricted mudstones and wackestones,

(5) stromatoporoid-coral floatstones, and (6) fenestral-cryptalgal Iaminites.

Various subfacies have been defined within these groups. All facies generally

represent shallow-water, marine-shelf depositional environments. This section

describes the depositional facies characteristics and cyclicity observed in core.

Table 1 summarizes the characteristics of each facies type recognized. For

each facies type, major diagenetic effects are briefly described in this section.

These are discussed more thoroughly in a later section. Appendix A (Plates

I-1 through 1-38) contains detailed core-description sheets of each core. Plates

II-1 through 11-11 summarize core-analysis, well-log, and core-description data

for each cored well. Field wide cross sections (Plates III-l through III-5) show

the lateral continuity of facies groups.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 1

Facies Characteristics, Dundee Limestone

Facies types

Crinoid Skeletal-Peloidal Skeletal Grainstone Sand Facies Wackestone

Coarse-grained Medium-grained Crinoid ossicles, crinoid ossicles. crinoid & brach brachiopods Carbonate Also brachiopod, iopod parts, and (commonly Grain Types bryozoan, coral fine-grained articulated), line algae, and peloids. Also corals, and other trilobite parts other normal- normal marine marine fossils fossils

Internal Limited amount Coarsening Horizontal Structures of parallel bed upward burrows and ding hemicycles. Cyclicity Burrows. Rare of parallel bedding.

Porosity 5 to 15% 1 to 12% nil and Permeability 5 to 10 md 0.1 to 8 md nil

Depositional Quiet water Extensive Quiet subtidal Setting crinoid meadow shallow water environment shoal

Low in section, Present through Present in present in NW out field, 60 to different parts of Distribution one half of field. 80 feet thick, section, in Field 13 to 15 feet main lithofacies correlative thick in cored within oil pro laterally for wells, thickens to ducing interval miles. Less than NW on cross 10 ft thick, most section common in SE end of field

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 1-Continued

Facies types

Restricted Stromatoporoid- Fenestral-Crypt- Micritic Facies Coral Floatstone algal Laminite

Ostracods, Hemispherical Very few fossils f o r a m s , and encrusting in laminated Carbonate Grain gastropods, stromatoporoids muds. Storm lags Types tentaculitids, and a n d corals. contains a wide peloids Matrix of diversity of fossil bioclastic sand types dominated by crinoid ossicles

Horizontal None recognized Cryptalgal Internal burrows and laminations Structures and some parallel Cyclicity laminations

1 to 15% Porosity (highest where 6 to 10% 5 to 10% and dolomitized) Permeability 0 to 2 md 0.2 to 10 md 1 to 90 md (highest where dolomitized)

Depositional Restricted lagoon Shallow subtidal Supratidal Setting environment

Top 10 to 30 ft Low in section Low in section o f Dundee (below oil-water (below oil-water Distribution (largely contact in cored contact), present in Field dolomitized). wells), present in in two cores, not Also present low two cores, not correlative on in the section in correlative on log cross sections t w o cores log cross sections (undolomitized)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Facies Types

Crinoid Grainstone

This facies was cored in the Heintz #9 and the Cox #2 wells (Figure 5).

The zone is 13 to 15 feet thick in these wells and is correlative in the

northwest one-half of the field (Plates III-l and III-2). Although low in the

reservoir (approximately 80 feet below the Rogers City-Dundee contact), this

facies appears to be productive in the Heintz #9 and Cox #2 wells.

Composition

This moderately-sorted, medium-grained sand is made up largely of

pelinatozoan parts. Other common constituents include brachiopod, bryozoan,

calcareous algal, and trilobite skeletal material (Figure 6). Neither micrite nor

non-skeletal grains were observed. Two microfacies with subtle differences are

present in this lithotype. The first is a moderate to well-sorted grainstone that

contains 80-95% coarse-grained crinoid ossicles. The other microfacies is a

moderately sorted grainstone that contains an admixture of other skeletal grain

types. These two microfacies are represented in about equal proportions in

this facies and are irregularly interbedded on scales ranging from less than

about 2 cm to more than 30 cm (Figure 6). Bedding is most commonly

horizontal. In some areas however, contacts between these microfacies appear

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24

Figure 6. Characteristics of Carbonate Sand Facies, Dundee Limestone.

(A) Crinoid grainstone with some interparticle porosity. Brachiopod valves ("B") appear to have been articulated before physical compaction, suggesting a low energy setting. Plane light, scale = 1 mm. Heintz #9, 2862.6’. (B) Crinoid grainstone. Bedding of two microfacies are highlighted by oil stain in the dominantly crinoidal microfacies. Scale = 3 cm. Heintz #9, 2862.5’. (C) Peloidal-skeletal packstone. Labeled are: brachiopod ("B"), crinoid ("C"), and peloids ("P"). Crossed polars, scale = 0.5 mm. Cox #2, 2756.7’. (D) Skeletal-peloidal grainstone with interparticle porosity. Crinoid stems ("C") are the main allochem. Brachiopod grains ("B") are rounded fragments of original skeletoa Peloids ("P") are common. Plane light, scale = 0.25 mm. Estey E- 8, 2721.0’.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to be churned or disturbed, probably due to bioturbation. Brachiopod shells

show no preferred orientation in either of these microfacies, and some

brachiopods are articulated. This suggests that bedding is non-current induced.

Common Diagenetic Effects

The grains in this facies show no signs of early marine cementation.

They appear to have experienced significant early compaction. Delicate grains

(e.g., brachiopod, bryozoan, and trilobite parts) were commonly broken

between crinoid ossicles as the sediment was compacted.

Pressure solution has also occurred in this facies, mainly through the

suturing of grain contacts. Stylolite solution seams are rare in this lithotype.

The mixed skeletal microfacies experienced more pressure solution than the

dominantly crinoidal microfacies.

Little burial cement is present in this facies. Crinoid ossicles are covered

with thin syntaxial overgrowths. Other skeletal grains generally have no

cements on their surfaces. Saddle dolomite (discussed in more detail later in

this paper) occurs in trace amounts in intergranular pores of this facies.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Permeability and Porosity

Porosity and permeability are both relatively high; porosity ranges from

5-11%, and permeability is 1 to 50 md (Plates II-l and II-3). The nature of

the porosity is interparticle, and it is the result of preservation of primary

porosity. Diagenesis has reduced porosity through compaction (physical and

chemical) and, to a lesser extent, precipitation of syntaxial cements.

Depositional Environment

The depositional environment of this facies is interpreted to be a quiet-

water crinoid meadow below wave base. The interpretation is based on: (1)

the lack of abrasion or rounding of skeletal grains, (2) no preferred orientation

of easily hydrodynamically influenced grains (i.e., brachiopods and bryozoans),

(3) the presence of some articulated brachiopods, (4) lack of early marine

cements, and (5) the absence of cyclicity in this facies.

This environment was probably areally extensive; on cross section A-A’”

(Plates III-l and III-2) this facies is correlated for approximately 6 miles. It

thickens considerably to the northwest. To the southeast, this facies thins and

grades laterally into finer-grained, higher-energy skeletal-peloidal carbonate

sand that contains coarsening upward hemicycles.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Skeletal-Peloidal Grainstones and Packstones

This facies is represented in all cores examined and is the most common

lithotype observed in the Dundee Limestone. This facies is about 60 to 70

feet thick throughout the field and is present higher in the section in the

northwest end of the field. This facies group consists of two subfacies that

represent deposition in different energy conditions: (1) a lower-energy peloidal-

skeletal packstone, and (2) a higher-energy skeletal-peloidal grainstone. These

two subfacies are interbedded throughout the field. Skeletal-peloidal

grainstones are typically less than five feet thick, whereas peloidal-skeletal

packstones are commonly greater than five feet thick. In generalized core

descriptions and field cross sections, thin grainstones are grouped with peloidal-

skeletal packstones. Grainstone units are differentiated only where they are

thicker than 5 feet

Composition

The lower-energy end member is a muddy packstone that contains fine

grained peloids and skeletal grains and various amounts of micrite (Figure 6).

Peloids range in size from about 0.08 to 0.2 mm in diameter. The most

common skeletal grain types are crinoid, brachiopod, bryozoan, and coral

parts. Average grain size of this skeletal material is about 0.25 to 0.35 mm,

although many larger fossils are present (e.g., brachiopod valves, rugose corals,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and tabulate corals). Sorting is poor to moderate. Many skeletal grains show

signs of abrasion, particularly the finer grained material that makes up the

bulk of this facies. Also present in some parts of this subfacies are whole,

unabraded, articulated fossils. The texture in these areas is usually micrite-

rich.

The only sedimentary structures commonly observed in peloidal-skeletal

packstones are burrows. Two major types of burrows have been recognized.

One type appears to have been a lined living chamber. These burrows were

observed in orientations from horizontal to vertical, and are 4 to 7 mm in

diameter. This burrow type is commonly filled with sediment, although some

are filled with later diagenetic cements. Also present are burrows with

preserved spriten structures. These structures were found only in the micrite-

rich areas of this subfacies. Most burrows of this type are near horizontal and

3 to 4 mm in diameter. It appears that much more burrowing occurred

without leaving discrete structures. This accounts for the churned appearance

of this lithotype.

The other subfacies in this carbonate sand facies is skeletal-peloidal

grainstone, deposited in higher-energy conditions than the peloidal-skeletal

packstone. The skeletal grains in this subfacies average about 0.2 to 0.35 mm

in diameter and are dominated by crinoid stems, although brachiopod parts are

also very common (Figure 6). Other bioclastic material present includes

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. bryozoans, solitary corals, trilobites, tabulate corals, coralline algae, and

stromatoporoids. Stromatoporoids in this subfacies most commonly have an

encrusting or bulbous morphology. Peloids are common and range in size

from 0.10 to 0.15 mm, and appear to have been hardened so that they support

other framework grains. Grains in this subfacies are moderately to well-sorted.

The smaller size of the peloids results in bimodal sorting.

Evidence for abrasion and rounding of bioclastic grains is abundant in

this subfacies. Fossils, especially brachiopods, display a high degree of

fragmentation and rounding. Some crinoid grains appeared slightly micritized.

Whereas delicate fossils were preserved in some parts of the peloidal-skeletal

packstone, none were found in the skeletal-peloidal grainstone.

Many of the multicrystalline skeletal grains (e.g., brachiopods, bryozoans,

and trilobite parts) are partly covered by an early marine cement crust This

crust is commonly obscured by later burial cement This early cement appears

to have been a crust of acicular carbonate cement If the peloids in this

subfacies are of biogenic origin, they may have been hardened by early marine

cementation.

The only preserved primary sedimentary structure observed in this

subfacies is a two foot interval with planar bedding of fine skeletal material

observed in the Cox #2 core (Appendix A, Plate 1-8). Inclined beds of

disarticulated brachiopod valves were occasionally observed in this subfacies.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. These may represent the only remaining indication of ripple marks or cross

bedding.

Common Diagenetic Effects

This carbonate sand facies shows little or no sign of physical compaction.

Peloids are not deformed, brachiopod and bryozoan parts do not appear

broken by physical compaction, burrows do not appear to be deformed, and

many oversized interparticle pores remain open in grainstones. This lack of

physical compaction is probably due to the presence of an open framework

caused by early marine cements that encrusted many skeletal grains and

hardened peloids.

This facies contains abundant stylolites. Although the grainstones are

largely unaffected by pressure solution, micrite-poor packstones typically

contain numerous sutured-seam stylolites with amplitudes between 1 and 5 cm.

Micrite-rich packstones contain both sutured-seam stylolites and microstylolitic

swarms. Sutured-seam stylolites in this facies commonly have fracture sets

associated with them. These fractures are between 2 and 30 cm long. Many

of these are open, especially near the solution seam. These fractures are

vertical and, in individual core pieces, have consistent orientations. Such

fractures have been documented elsewhere by Nelson (1981) and Watts (1983).

The most common cement in this facies, particularly in grainstones, is

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. syntaxial crinoid calcite overgrowths. Overgrowths 10 to 15 fim are common

around crinoid columns.

As mentioned above, ghosts of acicular cement crusts have been observed

on multicrystalline skeletal remains in this facies. Other calcite cements

present in this facies are scalenohedral pore-lining cement and equant, blocky

pore-filling cements. These two cement types are most common in relatively

large pores (e.g., inside articulated brachiopods, gastropod molds, or open

fractures).

Pore-filling euhedral saddle dolomite is present in trace amounts in this

facies. This cement was found scattered in all pore types.

Poiosity. and Permeability

The primary pore type is interparticle with a limited amount of

intraparticle porosity. This porosity is what remains of the primary pore space

after limited early compaction, neomorphism of micrite, and occlusion of

porosity by burial cements. Porosity is highest in the skeletal-peloidal

grainstone subfacies. Core-analysis porosity and permeability from this facies

range from 4-12% and 0.2 to 20 md, respectively. Peloidal-skeletal packstones

have core analysis porosity generally ranging from 2-8% and permeability

between zero and 10 md.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Some relatively low-porosity peloidal-skeletal packstones show very high

permeabilities in the 100 md range. A comparison of core descriptions and

core analyses suggests that these permeability highs are produced by stylolite-

related fracture sets. The Cox #2 core between 2730 and 2756 is the best

example of this relationship (Plate II-3, and Appendix A, Plates 1-7 and 1-8).

Isolated coral pieces in this facies group retained much of their original

intraparticle porosity, but this is a very minor contributor to overall porosity.

Depositional Environment

This facies group represents shallow-water platform sedimentation, often

at or above normal wave base. This facies group may be somewhat analogous

to the "platform interior sand blanket" described by Ball (1967) from the Great

Bahama Bank. Ball’s descriptions of allochem types, discrete burrows, lack of

primary sedimentary structures, presence of marine cements, and the large

areal extent of the environment fit observations from the Dundee cores very

closely.

Skeletal Wackestone

This lithotype occurs in different parts of the Dundee Limestone section

and is generally correlative for miles in cross sections. Although thin, this

facies may be of considerable importance for enhanced or secondary recovery

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. projects at West Branch because of its very low porosity and permeability.

Composition

Common skeletal allochems in this facies include crinoid, brachiopod,

bryozoan, coral, ostracod, foram, trilobite, and stromatoporoid parts. Fine

grained peloids are also present These grains show no signs of abrasion.

Articulated brachiopods, some with the spiralia well-preserved, are common in

this facies. Also present in a few places are colonies of tabulate corals

preserved in growth position.

The only sedimentary structures observed within this facies were burrows.

The most common type of discrete burrow is generally horizontal, about 4 mm

in diameter, with preserved spriten structure. Also present, although rare in

this facies, are lined burrows that are nearly vertical, about 5 mm wide, and

5 cm long. These burrows are filled with unstructured sediment similar to that

surrounding the burrow.

Common Diagenetic Effects

It is difficult to assess the amount of compaction that has occurred in

this facies. However, examination of horizontal burrows with preserved spriten

and branching tabulate coral colonies suggest that some (<30%) physical

compaction did occur.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Pressure solution has taken place in this facies in the form of

microstylolites and microstylolitic swarms. Contacts with other facies are

usually sharp, especially at the base of this facies. These contacts are

commonly sites of thick sutured-seam stylolites.

Few cements were observed in this facies because of the very low volume

of porosity available for cementation. Intraparticle porosity associated with

corals and stromatoporoids was commonly filled with fine scalenohedral calcite

crusts which coarsened outward from the pore wall. Rarely, small rhombs of

saddle dolomite were seen in a few of these pores.

Porosity and Permeability

This facies is very tight and impermeable. Core analysis porosity is

typically 2 % or less, and permeability is generally 0.1 md or zero. The only

observable porosity in core or in thin section is small amounts of isolated

intraparticle porosity in scattered corals and stromatoporoids.

Depositional Environment

This facies represents deposition in quiet water, probably below storm

wave base. Sharp contacts with other, underlying facies suggests that

transgressions happened rapidly and may have occurred (or resulted) in

conditions that made continued deposition of the previous facies impossible

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (e.g., temporary increase in water turbidity).

Restricted Mudstones and Wackestones

This facies is present in all cores examined in this study. The top 10 to

15 feet of the Dundee Limestone were invariably found to be of this facies

(Plates II-1 through 11-11). This facies was also found to be present very low

in the section near the base of the Grow #4 core (Plate 11-10). This facies

group is represented by two end-member subfacies: restricted mudstone

subfacies and restricted wackestone subfacies.

The restricted mudstone subfacies contains very few skeletal grains in its

predominantly micritic fabric (Figure 7). Fossils include forams, ostracods, and

numerous spore cases 100 p m in diameter (Tasmanitesl. Small, high-spired

gastropods are also present, though rare. Ostracods are commonly articulated,

indicating that they were deposited under very low energy conditions. Fabric

has been nearly completely obliterated by neomorphism and diagenesis. Some

fine laminations are present and horizontal burrows are common in some

zones. These burrows are 4 to 7 mm in diameter. Rock texture appears

mottled in some areas-it is unclear whether this represents burrowing or a

diagenetic fabric.

The restricted wackestone subfacies contains a slightly more diverse faunal

assemblage that includes forams, ostracods, trilobites, tentaculitids, crinoids, and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36

m m

Figure 7. Characteristics of Restricted Mudstones and Wackestones, and the Dundee-Rogers City Contact

(A) Restricted mudstone containing spore case ("SC") and ostracod m old C O ”). Micrite is not pelleted. Plane light, scale = 0.25 cm. Reinhardt #3, 2616.5’. (B) Restricted wackestone facies with tentaculitid ("T") and brachiopod spine ("B"). Matrix is peloidal in this example. Plane light, scale = 0.25 mm. G row #9, 2665.7’. (C) Bioerosional contact at the top of the dolom itized restricted mudstone facies, Dundee Limestone ("DL"). The overlying Rogers City Limestone ("RCL") displays the nodular wackestone texture typical of Rogers City nodular wackestone facies. Scale = 3 cm. Reinhardt #3, 2585.3’.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. brachiopods (Figure 7). Brachiopods are rare in the facies compared to their

abundance in the rest of the Dundee. Some horizontal fine laminations are

present in this facies, and in these areas the rock fabric may be a fine-grained

packstone. This facies occurs as various thicknesses in the cored wells and

always forms a gradational contact with the overlying restricted mudstone

facies.

The grains in restricted wackestones show no signs of abrasion, but

articulated, delicate fossils are very rare. Some crinoid stems in this subfacies

have micrite envelopes.

Common Diagenetic Effects

In the restricted mudstone facies near the top of the Dundee Limestone,

bioeroded, mineralized surfaces that appear to be hardgrounds are common.

In the top 30 cm of the Dundee, several cores show as many as three of these

distinct surfaces. The uppermost surface is most dramatic. This surface has

a pyritized rind a few millimeters thick in most cores, and appears highly

bioeroded in the Buckingham #4 core. This surface is overlain by darker,

nodular micritic sediments of the Rogers City Limestone (Figure 7).

The restricted mudstone subfacies (and in some cores, the top 3 to 5 feet

of the underlying restricted skeletal wackestone subfacies) has been pervasively

dolomitized. This is especially true of cores from the southeast end of the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. field. Cores taken more to the northwest (i.e., Estey E-8, Cox #2, Donovan

#6, Hientz #9) show less pervasive dolomitization of this facies and commonly

have thin (less than 30 cm), interbedded streaks of undolomitized mudstone

remaining.

Matrix-replacive dolomite occurs in a wide range of crystal sizes, from

less than 3 p m to greater than 200 /tm. These different crystal sizes occur

together to produce a highly tortuous pore network.

The mudstone unit recognized low in the section in the Grow #4 has not

been dolomitized and does not contain any recognizable hardgrounds.

In areas where the restricted mudstone has not been replaced by

dolomite, it is difficult to tell if these muds were compacted during burial.

Fossils appear undeformed but it is possible the unconsolidated carbonate

mud could have compacted without deforming more rigid particles (e.g., Shinn

and Robbin, 1983). In dolomitized sediments, however, it is apparent that

some post-replacement physical compaction has occurred. Skeletal fragments

are broken and the spherical spores that are well preserved in unreplaced

mudstone are very deformed.

The contact between dolomitized and undolomitized mudstone is

commonly sharp. Where a bed of undolomitized mudstone is thin, there

commonly are many irregular, high-angle fractures that cut through the

unaltered mudstone. Such fractures generally do not continue into the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. dolomite.

Some unreplaced mudstones contain microstylolites, and where skeletal

grains are locally concentrated, sutured-seam stylolites have developed. A few

of the contacts between unaltered mudstone and dolomite have also developed

sutured-seam stylolites. Sutured-seam stylolites in this facies typically have an

associated set of fractures similar to those discussed in the previous section

that concerned the peloidal-skeletal packstone facies. Some fracture sets

associated with stylolites in the mudstone facies are, however, much longer;

some are over 30 cm in length.

The restricted wackestone subfacies contains a large amount of chert,

especially in cores from the southeast end of the field. Much of the chert

is clearly nodular, but in some places the entire core is chert for up to six

inches. In these areas it is possible that chert is bedded. The chert is most

commonly a light buff color, lighter than the surrounding light brown

limestone. All but the largest skeletal grains are replaced by chert Fine

textures in the original sediment are very well-preserved, especially burrows

that contain spriten. Chert also seems to have preserved trace fossils of other

burrowers whose effect on the sediment is not as obvious as other burrows.

These burrows are about the same width (5 mm), but they seem to be more

random. This gives the sediment a churned appearance. Such subtle textures

are not preserved in the adjacent carbonate.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. As with the other matrix-supported facies, examination of the limestone

fabric of this rock provides few clues for assessing the amount of physical

compaction the sediments have experienced. However, many of the chert

nodules have numerous vertical fractures, which indicates some physical

compaction has taken place. Many of these fractures have been partly filled

by carbonate sediment that flowed into the open space.

Stylolitization has also occurred in this facies, creating sutured-seam

stylolites, microstylolites and microstylolitic swarms. As in the other facies,

sutured-seam stylolites commonly have associated fracture sets. As in the

peloidal-skeletal carbonate sand facies, these fractures range in size from 5 to

20 cm long and have consistent orientations in each sample.

Porosity and Permeability

Unreplaced, restricted mudstone interbedded with dolomitized sediment

near the top of the Dundee and the restricted mudstone unit deep in the

section cored in the Grow #4 have no observable porosity in thin sections,

and no core analysis was performed on this part of the core. Near the top

of the Dundee in the southeast, where this facies is pervasively dolomitized,

core-analysis data indicate that intercrystalline porosity is generally 1-15% and

permeability is generally 0.1 md to zero in the top 5 feet, and between 0.1

and 2.0 md below. The low permeability is believed to be the result of the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. wide range of crystal sizes present and the tight, random packing of the

dolomite rhombs.

The restricted wackestone subfacies has generally very low porosity and

permeability as well, although the chert has some microporosity visible when

viewed in thin section. In unreplaced limestone fabric, core analysis for this

subfacies indicate porosity is 3-6% and permeability of zero to 2.0 md. In

the southeast where the top few feet of this subfacies is dolomitized, however,

intercrystalline porosity ranges between 1 and 15 %, and permeability between

zero and 4.0 md (Plates II-5 through 11-11).

Pepositional Environment

This facies group represents deposition in a low-energy subtidal

environment The relatively low diversity faunal assemblage suggests that the

seawater present during deposition had limited circulation with normal-marine

waters and that environmental stresses in this setting were too high for many

normal marine fauna. The gradational contact between the restricted

wackestone subfacies and the overlying restricted mudstone subfacies and the

decreasing faunal diversity upward indicate that restriction of seawater

continued with time. The hardgrounds that cap the Dundee Limestone may

be related to further restriction of environmental conditions in this setting.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Str.omatoporoid-Coral Floatstone

This facies occurs low in the Dundee section, below the oil-water contact

as interpreted from electric logs. This facies is thin (2 to 3 feet) and is

present in the cores of two wells, the Estey E-8 and the Grow #4 (Plates II-

4 and 11-10). This facies is not correlative in cross sections. Although not

believed to be a reservoir rock, it is included in this discussion for

completeness of discussion of Dundee lithofacies.

Composition

The main constituents of this facies are bulbous hemispherical

stromatoporoids (ranging in size from less than 2 cm to over 30 cm in

diameter), smaller encrusting stromatoporoids and branching colonial tabulate

corals (approximately 1 to 2 cm in diameter). These fossils are typically

overturned and they are no longer in growth position. The sediment between

these larger fossils is a medium to fine-grained, well-sorted bioclastic sand that

contains crinoid ossicles, brachiopod parts, and many unidentified fossil

fragments (Figure 8).

Pepositional Environment

The well-sorted, mud-free nature of the bioclastic sand and the

morphology of the stromatoporoids (encrusting and bulbous forms) indicate

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 8. Stromatoporoid-coral Floatstone and Fenestral-cryptalgal Laminite Facies, Dundee Limestone.

(A) Stromatoporoid-coral floatstone facies. Coral ("C") and stromatoporoid C'S") in a matrix of bioclastic sand. Scale = 3 cm. Estey E-8, 2740.5’. (B) Fenestral-cryptalgal laminite facies. Top 2 to 3 cm contain cryptalgal laminations. The underlying micritic rock contains some saddle dolomite filled vertical tubes and numerous isolated bubble-shaped voids or fenestrae. Scale = 3 cm. Estey E-8, 2747.5’.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. that this facies was deposited in a subtidal environment of moderate to high

energy, and was probably above wave-base.

Fenestral-Crvptalgal Laminite Facies

This facies is present in only two cores in this study and it occurs at the

base of these cores (Estey E-8 and Grow #4, Plates II-4 and 11-10). In both

cores, this facies occurs well below the oil-water contact In all areas, this

rock type is light tan to cream colored. The facies is discussed here to

document the presence of this lithotype in the Dundee Limestone.

Composition

The main fabric present in this facies is a fine-grained carbonate silt or

mud that contains many vertical and horizontal fenestral pores (present in

both cores). No other structures are visible in this fabric type. Some areas

also contain numerous skeletal parts. Fauna represented by these skeletal

grains mainly include bryozoans, corals, stromatoporoids, brachiopods, and

crinoids. Intraclasts are also common.

The other fabric type is a fine-grained laminated carbonate which contains

many fine (100 to 500 fim) fenestral pores. Commonly, these pores are

concentrated just below the sharp contacts of these laminations. Most

laminations are between 0.25 and 0.5 cm thick (Figure 8). This laminated

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. fabric type is present only in the Estey E-8 core. This fabric matches algal-

laminated sediments described by Shinn (1983).

Also present in both cores are fine-grained (sand to silt size) zones that

appear to be disrupted. Tnese zones contain irregular clasts of sediment and

some large irregular pores filled with geopetal sediment, sparry calcite, and

saddle dolomite. These areas also have vertical disturbances similar to

burrows, but they are irregular in size and shape. These areas are interpreted

to be soil clast zones (Shinn, 1983).

Pepositional Environment

The presence of cryptalgal laminations and soil clast zones in this light

colored (oxidized?) sediment indicate that the environment of deposition was

supratidal (Shinn, 1983). Coarser grained beds of skeletal material probably

represent storm deposits.

Sedimentary Cyclicity

Coarsening upward hemicycles are present in the skeletal-peloidal

carbonate grainstones and packstones. These hemicycles are 2 to 18 feet

thick (average thickness about 8 ft) and they were recognized in all cores

examined in this study. These coarsening upward hemicycles consist of (in

descending order): (1) Skeletal-peloidal grainstone (1 to 8 ft thick), (2)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Peloidal-skeletal packstone (between 2 and 17 ft thick), that contains increasing

amounts of micrite downward, and (3) Skeletal wackestone (usually less than

2 ft thick, rare).

Figure 9 summarizes this hemicyclicity and diagrammatically displays the

common structures and allochems. Many of the hemicycles identified in core

are incomplete. They lack either a weil-developed grainstone at the top or a

wackestone at the base, or both. Where hemicycles are not complete, the

skeletal wackestone is most commonly absent

In most recognized cycles, the facies changes within a single cycle are

gradational. Contacts between hemicycles are typically abrupt Grainstones

near the top of these cycles commonly contain surfaces that appear to have

been cemented into a hardground and were either scoured or bored before

being covered by more grainstone. Oversized pores are also common; these

may indicate early cementation.

Coarsening upward hemicycles are interpreted to represent the shoaling

upward of an extensive shallow water environment in response to fluctuations

in relative sea level. The evidence of sea floor lithification (hardgrounds) in

the grainstones at the top of hemicycles, and abrasion of the skeletal material

in this subfacies suggests deposition had slowed considerably. The allochems

present in these areas were probably at the sediment-water interface for an

extended period of time. The abrupt contact between grainstones and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47

Skeletal—Peloidal G rainstone Hardground % Rugose Horn Coral ☆ I ☆

Vertical Lined Burrow

Peloidal—Skeletal 8 ft P a c k sto n e

Articulated Brachiopod

Skeletal CS23&32? * Horizontal Burrows W ack esto n e Wispy Laminations

KEY TO SYMBOLS YV Crinoid Ossicles cd Fine-Grained Peloids *’"**• Brachiopod Snells /=> Shell Fragments

Figure 9. Idealized Coarsening Upward Hemicycle, Dundee Limestone.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. overlying wackestones or packstones suggests a rapid rise in relative sea level

before the initiation of deposition in each new cycle. Contributing to the

apparent abruptness of these inter-cycle contacts is the effect of lag-time. Lag

time is the period that carbonate environments take to re-establish sediment

production after a period of non-productivity (Schlager, 1981).

The change from deposition of packstone to grainstone represents

shallowing of the local environment until the sediment surface is in a zone

of significant wave energy. Grainstones were deposited first in the shallower

areas of the carbonate ramp and spread out laterally as shoaling continued.

Shoaling and spreading of this environment continued until the deepening

event that started deposition of the next cycle; whether or not these cycles

were alio- or autocyclic. Therefore, when a rise in relative sea level occurred,

sediments from shallower water areas more commonly had well-developed

grainstone caps that created a recognizable coarsening upward hemicycle in the

rock record. Sediments deposited in relatively deep water would be expected

to contain fewer recognizable coarsening upward hemicycles than sediments

deposited in shallower water.

To test this idea, gross interval thicknesses and coarsening upward

hemicycles were recorded for each core (Plates II-1 through 11-11). These

frequencies were normalized to a gross interval of 100 feet so that they could

be meaningfully compared. Figure 10 is a plot of the normalized frequency

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49 30-1

t 25- O O G9 O HZ G4 05 £5 20 - □ l

o 10- a : LU CD 2 Z> Z

10,000 20,000 30,000 40,000 50,000 NW SE DISTANCE FROM WELL #A -1 (IN FEET)

WELL LOCATION MAP KEY 4>A- H9 HEINTZ #9 D6 C2 COX §2 D6 DONOVAN #6 E8 ESTEY E -8 D5 DORAN #5 H2 HART #2 1 mAf H7 HART #7 R3 REINHARDT §3 B4- BUCKINGHAM §4 Structure Contour Wap G4 GROW #4 West Branch Reid, Michigan G9 GROW #9

Figure 10. Plot of Normalized Cycle Frequency vs. Distance From the First Well in Cross Section A-A’”.

Cored wells have been projected into a line that runs N65°W from well A-l on Plate 111-1. Note cyclicity increases markedly to the southeast

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of hemicycles in each well versus the distance of that well from the

northwestern end of cross section A-A’”(Plate III-l). Cores from the

northwestern end of the field have a normalized cyclicity of 12.5 to 15.7 per

100 ft, whereas wells in the southeastern part of the field have between 17.6

and 26.7 cycles per 100 ft If, as discussed above, shallower water settings are

more sensitive to fluctuations in relative sea level, decreasing values of

normalized cyclicity to the northwest suggests that the depositional setting of

the skeletal-peloidal grainstones and packstones sloped in that general

direction. Note that this direction is away from, rather than toward, the

depocenter of the Michigan basin during the Middle Devonian (Figure 2).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SEDIMENTOLOGY OF THE ROGERS CITY LIMESTONE

Although the Dundee Limestone is the focus of this study, several cores

(Donovan #6, Cox #2, Doran #5, Hart # 2 , Hart # 1 , Buckingham #4, and

Grow #4) have been described from the Rogers City Limestone. Two main

facies types were recognized-nodular wackestones, and skeletal packstones.

For completeness, the following section describes these Rogers City facies.

Nodular Wackestone

Composition

Common skeletal allochems in this facies are ostracods, forams, trilobites,

tentaculitids, and echinoderms. Megafauna are very rare in this facies and

include calcareous sponges, small gastropods, and large crinoid parts. This

facies appears dark gray on rough-cut surfaces, but is dark to medium brown

when etched with a weak hydrochloric acid solution.

This facies has an obvious nodular texture, with nodules 5 to 8 cm in

height and commonly greater than 7 cm wide surrounded by darker limestone.

This darker fabric contains numerous wispy laminations and microstylolites that

appear compacted around the nodular areas. Horizontal burrows about 5 mm

wide are preserved in the nodular areas, but obliterated in the highly

compacted limestone surrounding the nodules. 51

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Common Piagenetic Effects

Nodules are interpreted to represent differential early cementation of

the carbonate mud on the sea floor and subsequent burial compaction. No

evidence that this nodular texture could be attributed to the actions of

burrowing organisms was observed. Some of these nodules have small

fractures (less than 2 cm long) around their outer edges that are interpreted

to represent burial compaction of early cemented nodules.

Microstylolites are commonly present around the nodules and may have

formed along thin organic laminations in these inter-nodular areas.

Cements observed in this facies occur as pore-fdling calcite and saddle

. dolomite, although these cements are uncommon, mainly because visible pore-

space is rare in this facies. Most pores are small, wide fractures in nodules

or rare skeletal molds.

Permeability and Porosity

Core analysis was rarely performed on rocks from this facies type.

Limited plug analysis indicates a porosity range of 1-3% and a permeability

range of zero to 1.0 md. The only whole-core analysis performed (Cox #2,

Plate II-3) indicates porosity of about 1 % with no measurable permeability.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dap.ositional Environment

This facies is the dominant lithotype of the Rogers City Limestone. The

depositional environment is interpreted to be a deeper-water setting than the

depositional environments of the Dundee Limestone.

Skeletal Packstone

No thin sections were made from this facies; therefore, all observations

are from slabbed and polished core.

Composition

The most common allochems in this facies are crinoid ossicles ranging

in size from less than 1 mm to 20 mm in diameter. Some crinoid stems are

still largely articulated. Other fossils present are pelecypods, calcareous

sponges, and trilobite parts.

Common Piagenetic Effects

This Rogers City facies also appears to have been differentially cemented

before significant burial. However, since this facies is a packstone (grain-

supported fabric), little or no differential physical compaction has occurred

around these cemented areas.

Observations with a low-power binocular microscope indicate that pore-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 lining calcite is present in fossil molds. Pore-lining fluorite is also present in

some molds. Sutured-seam stylolites are common in this facies.

P_ermeabilitv and Porosity

Core analysis of this facies in the Donovan #6 core indicate porosity as

high as 7 % and permeability up to 2.0 md. Porosity and permeability values

appear to be dependent on the amount of skeletal material present vs. mud

and how much of the sediment has been differentially cemented. Porosity is

highest where there is little mud or intergranular cement The main pore type

is interparticle with some moldic porosity.

Depositional Environment

The poor-sorting of this facies and the presence of articulated crinoid

stems and intact calcareous sponges indicate that the depositional environment

was a low-energy setting. The differential cementation of this facies appears

similar in scale and style to the cementation observed in the Rogers City

nodular wackestone facies. The main difference between these facies is the

abundance of benthic megafauna hard parts in the skeletal packstone facies

that form a grain-supported framework. The depositional environment of this

facies is similar to that of the Rogers City nodular wackestone (deeper, quiet

water), except something changed to allow the proliferation of benthic

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. megafauna. The accumulation of the skeletal material of these animals was

fast enough relative to micrite deposition to form a packstone with a degree

of interparticle porosity.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FIELD-WIDE STRATIGRAPHIC CORRELATIONS

Previous sections have shown that a complex group of facies exists in the

Dundee and Rogers City Limestones. These facies are commonly arranged

in hemicyclic, shoaling upward sequences. Vertical heterogeneities in facies

and reservoir properties are clearly illustrated in Plates II-1 through 11-11.

Lithologic changes commonly correspond to changes in log signatures. As a

measure of lateral heterogeneity, the next logical step is to construct and

correlate field-wide cross sections. Features such as pinch-outs, blanket-like

permeability barriers, and gradual facies transitions can be detected with such

cross sections.

Three field-wide cross sections (Plates III-l through III-5) have been

constructed from well logs. One cross section is parallel, and two are

perpendicular to the trend of the field (Figure 11). Each cross section

includes well logs from cored wells examined in this study. These sections

are hung on the contact between the Bell Shale and the Rogers City

Limestone. Units identified in core were correlated in the cross sections in

both the Rogers City and Dundee Limestones to examine lateral variations.

Cross section wells were chosen because: (1) they were generally on-trend

with the chosen path of the cross section, and (2) they had been logged with

"modem" logs in the last 20 years. Preferred wells had gamma ray, neutron

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 CD -o o Q. C o CD Q.

"O CD

C/5 (f) R1E R2E R3E

O "Oo

3 CD

3. 3" CD -5 CD B ■o « *>*»• • •••'•*!> • (3 • .1600• • • • •• —sO Q. C 2 . o' 3 -o o—i

CDa

1.6 km oc Figure 11. Location of Cross Sections (Plates 111-1 through 111-5) on Structure "O CD Contour Map of the Top of the Rogers City Limestone.

C/> C/5 o' Map adapted from same sources listed in Figure 5. Contour interval 40 feet. 3 porosity, bulk density, and electrical resistivity logs. Many wells did not have

neutron porosity/bulk density logs, so sidewall neutron porosity logs were used

instead. It is important to have included resistivity logs in the cross sections.

This is because porosity logs alone generally did not have high enough

resolution to allow confident correlation of marker beds.

Figures 12 and 13 are simplified versions of the cross sections constructed

from well logs (Plates III-l through III-5). Wells in these figures were

projected into straight lines drawn along the trend of the cross sections.

Dundee Limestone Correlations

Thirteen markers in the Dundee were correlated in the cross sections.

The markers were picked by comparing distinctive lithologic units in core to

the correlative log signatures. Contacts between rock units identified in core

commonly appeared as markers on logs because the rock properties of

overlying and underlying units contrasted with one another.

Markers D1 and D2 were found to be correlative throughout the entire

field. Marker D1 represents the contact between the nodular, micritic

limestone of the Rogers City and the underlying dolomitized Dundee. This

contact is present in six of the cores examined and is a distinct hardground

at the top of the Dundee. Marker D2 is the base of the dolomitized

restricted mudstone. In the northwest one-third of the field, the lithotype

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. NW A

-J 1----- ) ■ ! U R 1 (DATUM)

>< E-i W R2 I—I £ o o C/D H C/D R3 « W W 0 *—iS O «

CD D2 > w O £ Q o D4 H C/D W S D10

w H Q D11 £ 0 Q

L1 L1 ______g Figure 12. Simplified Version of Stratigraphic Cross Section A-A’”, Plates III-l C/3 i—i Through III-3. < J H / !.v y ^ Datum is the Bell Shale/Rogers City Limestone contact Core control p s indicated by texture logs and lithology symbols. Tick marks along the top line O are wells used in the cross section and projected into a line N65°W. P*h Abbreviations of well names in index map: H9 = Heintz #9, D6 = Donovan Struct^ # 6 , C2 = Cox # 2 , EE-8 = Estey E-8, H2 = Hart //2, B4 = Buckingham West^E #4, G4 = Grow # 4 , and G9 = Grow if9.

-*— i— i------1_ -J 1------1------L- R1 (DATUM)

nr R2

a> KEY =tt= Symbol Lithology o CD Dolomitized Mudstone CD 'CD D2 CD WR Restricted Wackestone 'WR 03 WS Skeletal Wackestone D7 Peloidal—Skeletal Packstone ws yrsi Skeletal—Peloidal Grainstone D8 ☆ Crinoid Grainstone D9

Cored Interval Carbonate Textures

) Grafn3tone 013 ( Packstone \ Wackestone J Mudstone INDEX MAP

" ’*00 4 0 ft re Contour Mop ranch Reid, Michigan 5,000 ft

w ------R2 HHH £ u o cn H CO R3 « w W o t—Is o 1-4 K

W WR £ o D3 EH co W S3 D10 D11 w w Q £ INDEX MAP Q

£ L1 - O C O J r - 1 Cj

Figure 13. Simplified Versions of Stratigraphic Cross Sections B-B’ and C-C\ Plates III-4 and

Datum is Bell Shale/Rogers City Limestone contact Core control indicated by texture logs ai symbols (key for lithology symbols on figure 12). Tick marks along the top line are wells used sections and projected into a line N2°E for cross section B-B’, and N80°E for cross se Abbreviations of well names in index map: EE-8 = Estey E-8, D5 = Doran it5 , H2 = Hart , = H art #7.

- R2 R2

- R3 R3

- D1 CJ icy D2 - D2 m WR WR D3 n D3 D7

D10 D 11 D9 D12

INDEX MAP

Structure Contour Map West Branch Reid, Michigan oss Sections B-B’ and C-C\ Plates III-4 and III-5. ct Core control indicated by texture logs and lithology rick marks along the top line are wells used in the cross •oss section B-B’, and N80°E for cross section C-C’. = Estey E-8, D5 = Doran ft5, H2 = Hart ft2, and H7

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. below the dolomitized mudstone is the skeletal-peloidal carbonate sand. In the

southeast two-thirds of the field, the restricted skeletal wackestone facies

underlies the D2 marker.

The contact between restricted skeletal wackestone and underlying

skeletal-peloidal carbonate sand is correlated as marker D3. This marker

appears on well logs as a distinctive change from low porosity, high resistivity

wackestones to underlying higher porosity, lower resistivity skeletai-peloidal

carbonate sands. The D3 marker is correlative in the southeastern two-thirds

of the field. The restricted wackestone facies (between D2 and D3) thickens

from the southeast end of the field toward the center of the field. The D3

marker and the generally low porosity, high resistivity signature of the

restricted wackestone facies gradually disappears between the Estey E-8 and

Cox # 2 wells (A-18 and A-10, respectively, Plates III-2 and III-l). This

suggests a gradational contact between laterally equivalent skeletal-peloidal

carbonate sand and the restricted wackestone facies present in these wells

below the D2 marker. This lateral facies relationship implies that the

depositional environment deepened to the northwest, where marine packstones

were deposited, and shallowed to the southeast, where lagoonal wackestones

were deposited.

Markers D4 through D9 all occur within the skeletal-peloidal grainstones

and packstones. Markers D4, D5, and D8 all mark the tops of coarsening

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. upward hemicycles that contain unusually thick skeletal-peloidal grainstones.

These created interparticle porosity zones that were thick enough to be

confidently recognized and correlated on well logs. All three of these markers

were correlative for about two miles on the log cross section constructed

parallel to the field trend (Figure 12 and cross section A-A”\ Plates III-l

through III-3). Markers D4 and D5 are present in the northwestern half of

the field, and D8 is present lower in the section in the southeastern half of

the field.

Markers D6, D7, and D9 all mark the tops of low porosity skeletal

wackestone or tight peloidal-skeletal packstone facies. These units create low

porosity and very high resistivity responses on well logs and were very

correlative for 2 to 3 miles on cross sections (Figures 12 and 13). Marker

D7 occurs in the southeast half of the field in a thick section otherwise

dominated by peloidal-skeletal packstones (Plates II-4, II-9, 11-10, and 11-11).

Marker D6 is in the northwest half of the field and occurs about 11 ft below

marker D5. The unit between D5 and D6 has high porosity and permeability

(between 4 and 11 %, and 0.1 and 8 md on core analyses, Plates II-2 and II-

3) relative to the rock above and below this unit Markers D8 and D9

bracket a similar high porosity and permeability unit in the southeastern half

of the field.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The crinoid grainstone facies is delimited by markers DIO and Dll.

These markers are present relatively low in the section in the northwestern

half of the field. The DIO marker is the contact between the crinoid

grainstone facies and the overlying skeletal-peloidal grainstones and packstones.

The crinoid grainstone, which has excellent porosity and permeability, overlies

a tight skeletal wackestone. This sharp contact is correlated as marker Dll.

In a traverse from NW to SE (well A-l through A-19, Plates III-l and III-2),

log signatures of the rocks between DIO and D11 indicate gradually decreasing

porosities and increasing resistivities. Interval thickness also decreases in this

direction. Examination of this DIO to D ll unit in the Estey E-8 core (Plate

II-4, and Appendix A, Plates I-11 and 1-12) indicates that the porosity zone in

this area is a skeletal-peloidal grainstone that contains two coarsening upward

hemicycles. This lateral facies change from crinoid grainstone to skeletal-

peloidal grainstone indicates an up-dip change in environment of deposition

(shallower, higher-energy environment in the Estey E-8 area than further to

the northwest in the Cox # 2 and Heintz #9).

Markers D12 and D13 are present low in the section at the extreme

southeast end of cross section A-A’” and at the southern end of cross section

C-C (Figures 12 and 13). These markers are the only lines correlated in the

cross sections without core control. The area between the markers is a thick

correlative unit of low resistivity and high porosity that appears to thicken to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the southeast Thin gamma-ray peaks of unknown origin occur in this interval.

Marker LI correlates the inferred contact between the Dundee Limestone

and the underlying Lucas Formation. This marker was correlated on well logs

at the first large inflection toward higher porosity and higher density associated

with Lucas dolomite.

Rogers City Limestone Correlations

Correlated markers in the Rogers City Limestone consist of the very

sharp contact with the overlying Bell Shale (labeled Rl, Plates III-l through

III-5), and the tops of two relatively high porosity and permeability zones

(labeled R2 and R3 in cross sections). Immediately below each of these two

markers (R2 and R3) are poorly-sorted, medium-grained skeletal packstones

that represent times when benthic megafauna produced enough skeletal

material to create packstones with some interparticle porosity. The R2 and

R3 log markers were picked at the top of these porosity zones, as indicated

by the inflection to lower resistivity on electric logs. The Rl marker is

defined by a sharp drop in gamma ray counts from the overlying Bell Shale

to the Rogers City Limestone.

Correlation of these markers shows no lateral variation of these units

throughout the West Branch field. The correlation lines are virtually parallel

to the Bell Shale /Rogers City Limestone datum.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DIAGENESIS

Core and thin section examination has shown the presence of a number

of diagenetic phases. These include marine cements, syntaxial overgrowths,

scalenohedral and blocky calcite cements, matrix-replacive dolomite, saddle

dolomite, and chert Pressure solution, compaction, and stylolitization are

common in some facies. One remarkable feature, important from a reservoir

standpoint, is the abundance of primary porosity in these rocks.

This section presents the results of plane light, cathodoluminescent (CL),

and ultraviolet fluorescent microscopy of thin sections, and carbon and oxygen

stable isotope analysis of microsampled rock fabrics. The purpose of

diagenetic work was to unravel the paragenetic sequence, determine a marine

isotopic signature from pristine allochems and micrite, and investigate the

origin of dolomite. Dolomite origin is important in light of the fracture-

controlled dolomite models developed by Prouty (1989a, 1989b) and Ten Have

(1979) for the Dundee Limestone in West Branch field.

Figure 14 shows the paragenetic sequence determined in this study.

Early marine cementation was followed by chertification and dolomitization of

restricted facies. Various calcite cements were deposited and stylolitization

occurred upon burial. Saddle dolomite and late non-carbonate cements are the

most recent diagenetic phases. The following discussion focuses on the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o\ o\ Precipitation Non—Carbonate of Late Cements Youngest Events Macro—Fractures Development of Saddle Dolomite Precipitation Precipitation of Blocky Calcite Stylolitization (and Development of Associated Fracture Sets) Precipitation of Syntaxial Calcite Precipitation of Scalenohedral Calcite Figure 14. Paragenetic Sequence Determined for the Dundee Limestone, West Branch Field. Restricted Facies Isotopic Overprint of Dolomite Dolomitization of Chertification Oldest Oldest Events Early Marine Carbonate Cementation

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. evolution of diagenesis in these rocks.

Early Marine Fabrics

Precipitation of early marine carbonate cement was common in some of

the depositional environments of the Dundee Limestone. In the skeletal-

peloidal grainstone subfacies, acicular cement crusts grew on some skeletal

parts (Figure 15). Peloids in this subfacies are undeformed framework grains

and therefore are believed to have been hardened on the sea floor by early

marine cementation (Figure 6). Also, rare hardgrounds in this subfacies

provide further evidence sea floor cementation.

The preservation of limestone beds in the dolomitized, restricted

mudstone facies is attributed to early marine cementation. After cementation,

these beds were then impermeable to fluids that later dolomitized the

surrounding sediment The way these beds deformed when physically

compacted also supports the conclusion of early lithification (Figure 15).

Certain marine rock components were examined and microsampled for

stable isotope analysis to provide an isotopic "starting point" to which the

stable isotope composition of cements could be compared. The ideal starting

point is the original marine isotopic composition of calcite precipitated from

Dundee-age seawater. The effects of neomorphism and precipitation of burial

cements, however, make this determination of original marine signature

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 15. Early Marine Calcite Cement and Replacive Chert, Dundee Limestone. (A) Acicular early marine carbonate cement crust ("MC") on a brachiopod substrate ("B"). Dark area ("BC") is blocky calcite cement extinct under crossed polars. Scale = 0.005 mm. Cox #2, 2730.2’. (B) Boudins of a calcite bed ("C") surrounded by dolomite ("D"). Bed is interpreted to have been cemented on the sea-floor and fractured during the early stages of burial compaction. Marine cementation apparently protected this bed from dolomitization by reducing permeability. Scale = 3 cm. Grow #9, 2625.5'. (C) Chert nodule in the restricted wackestone facies. Fractures ("F") in chert and compaction of dark laminations in limestone ("L") around chert nodule ("C") indicate physical compaction. Scale = 3 cm. Estey E-8, 2655.6’.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. difficult, if not impossible. Work done by Popp, Anderson, and Sandberg

(1986) on Middle Devonian carbonate rock constituents indicated that

brachiopod skeletal material is commonly very stable in the burial

environment It is commonly thought that brachiopod valves are secreted as

stable low-magnesium calcite. In their study, Popp et al. (1986) found that

brachiopods that appeared pristine when examined using a scanning electron

microscopy were non-luminescent under CL microscopy. They determined a

5I80 value of -3.7 + 0.2°/„» for an original marine signature of Middle

Devonian biogenic calcite (Figure 16).

Hurley and Lohmann (1989) sampled Late Devonian brachiopods, marine

cement, micrite, and subtidal stromatolites for isotopic analysis. They

determined an original marine signature of -4.5 5'80 ±0.5°/o0and +2.0 <513C

±0.5° / 0o for the Late Devonian of the Canning basin (Figure 16). This

compared well with other Late Devonian results from Australia, Canada, and

Belgium.

In this study, non-luminescing brachiopods were microsampled in an

attempt to obtain an estimate of the original marine isotopic composition of

these sediments. Not all brachiopods were non-luminescing. In fact, many

brachiopods luminesced dull red to orange, and most were contaminated with

cements that precipitated in microfractures that were common in these fossils.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o (PDB) (513C Variation, 0 - 4 — 6 --2 -2 -4

6 - 2 Signature, This Study Inferred Middle Devonian Middle Devonian (Popp and others, 1986) R ange of D- \ \ \ \ \ \ \ \ \ - 4 O KEY L qb O O JZ Brachiopods (Luminescing) Brachiopods (Non—Luminescing) CP □ Non—Luminescing Micrite - 8 O O O 1 9 8 9 ) (Hurley and Lohmann, Marine Signature Mean Late Devonian - 1 0 -12 (PDB) (5 (5 0 Figure 16. Isotopic Signatures of Early Calcite Fabrics Compared to Published Devonian Marine Signatures. - 1 4

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission Rock chips that contained non-luminescent brachiopods were re-examined

under CL after isotope microsamples were drilled. Unfortunately, some of the

samples were contaminated by diagenetically altered matrix and/or cements

within brachiopods. Analyses of contaminated samples ranged from 6180=-7.39

to -3.40°/«■ and 5I3C=0.12 to 1.86°/on . Uncontaminated brachiopods had

isotopic signatures from S180=-4.79 to -3.40°/<,<, and 513O=1.10 to 1.33°

(Figure 16).

Non-luminescent micrite from the undolomitized restricted mudstone

facies (present near the bottom of the Grow if4 core, Plate 11-10) was also

sampled. This mudstone facies is now very impermeable and non-porous.

Carbonate muds typically have high porosities (50-70%, Bathurst, 1975) before

lithification. Subsequent lithification and neomorphism is believed to occur

early in the burial history of micritic sediments (Bathurst, 1975). If this were

the case, then the result was a very impermeable rock, and the calcite in this

facies might be protected from further rock-water reactions. If so, the stable

isotope signature would reflect conditions of the early burial environment

These samples were taken assuming that if the isotopic signature was

preserved from a shallow burial environment, it may be near the original

marine signature and may help define the general values for the original

marine signature. Two samples of this type were taken and the results ranged

from 5l80=-5.53 to -5.38°/0aand 613C=1.10 to 1.13°/„. (Figure 16).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72 Chert

Chert nodules occur in the restricted wackestone facies (Figure 15). The

presence of chert in this one lithotype strongly suggests that its distribution is

facies controlled. The original sediment may have contained relatively large

amounts of amorphous silica. However, no sources of silica were observed.

The formation of chert nodules is interpreted as being relatively early

(eogenetic) as indicated by the preservation of very delicate sedimentary

textures. Further evidence comes from compaction of laminae around chert

nodules. Many chert nodules contained trace amounts of scattered dolomite.

This dolomite was typically euhedral and averaged about 100 ^m in diameter.

The dolomite looks like the matrix-replacive dolomite that surrounds some of

the chert nodules, and may or may not be related. Replacement of carbonate

sediments by chert is interpreted to have occurred during or before

dolomitization of the top 10 to 15 feet of the Dundee Limestone.

Matrix-Replacive Dolomite

The top 10 to 15 feet of the Dundee Limestone at West Branch is largely

dolomite. This occurrence of dolomite coincides with the presence of the

restricted mudstone facies and, in some places, the top few feet of the

restricted wackestone facies. The base of this dolomitized zone appears to be

gradational with underlying limestones. The upper contact of this dolomite

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. zone is the top of the Dundee. It is abruptly overlain by the undolomitized

Rogers City Limestone.

Dolomitization of this zone is most pervasive in the seven cores from the

southeast half of the field (Buckingham #4, Doran #5, Grow #4, Grow #9,

Hart #2, H art #1, and Reinhart #3; Figure 5). The remaining four wells in

the central and northwest parts of the field show an increased amount of

unaltered limestone in this interval, although the relative proportions of calcite

and dolomite have not been quantified.

This dolomite occurs as euhedral rhombs that range in size from 1 to

250 /tm. A wide range of crystal sizes is typically visible in each thin section.

Dolomite rhombs appeared dull red when examined using CL microscopy and

showed none of the zoning observed in all other cement types. Evidence to

suggest more than one episode of dolomitization was not found.

Fossils preserved in pervasively dolomitized samples show signs of

physical compaction that appear to be post-replacement Similar fossils

observed in the same facies, but in areas not replaced by dolomite show no

signs of compaction. Several cores contain beds of unaltered micritic

limestone that range from 2 to 15 cm in thickness in otherwise pervasively

dolomitized rock. These beds typically show some fracturing. Some are

broken into rotated boudins (Figure 15). These observations suggest that the

dolomitized sediments experienced the effects of burial compaction, whereas

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. some streaks of micritic sediment resisted both dolomitization and compaction,

probably due to early calcite cementation.

Preservation of primary textures is poor where dolomitization occurred.

Horizontal burrows are the only structures still visible. Some areas display

textures that may be burrows or diagenetic mottling.

While drilling microsamples for carbon and oxygen isotope analyses, an

attempt was made to sample areas that were more coarsely or finely

crystalline to see if any separation in stable isotope values would emerge.

Samples were considered finely crystalline when the bulk of the dolomite was

less than 100 /*m in diameter, and coarsely crystalline when most dolomite was

greater than 100 p m in diameter. The results of carbon and oxygen isotope

analyses show practically no separation of these different size fractions. The

results group between -9.8 to -7.7 5180 and 1.1 and 2.5 5'3C with two samples

deviating significantly from this range (samples at -5.97 5180 and 1.69 5I3C, and

-12.81 5I80 and -0.45 613C, Figure 17).

To summarize, matrix-replacive dolomite appears to be an early diagenetic

phase. Some dolomite is encased in chert which is thought to be early.

Matrix-replacive dolomite is confined to a thin zone in the upper Dundee.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75

L. Figure Figure 17. Isotopic Signature of Replacive Dolomite.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Calcite Cement

Syntaxial Cement

Syntaxial cements occur as overgrowths on crinoid ossicles. These

overgrowths are the most common cement type in the grainy facies

(packstones and grainstones) and are responsible for about 2-10% porosity

occlusion (visual estimates). Overgrowths in the crinoid grainstone facies are

generally thin (<10 fim ), whereas overgrowths are commonly much thicker in

the skeletal-peloidal grainstone subfacies (>500 n m; Figure 18). These

overgrowths, where pore space is available, grow thickest over the flat surfaces

of crinoid columns. This direction (perpendicular to the flat surfaces of

columns) is parallel to the C-axis in crinoid ossicles (Bathurst, 1975).

Potassium ferricyanide staining revealed thin zones of iron-rich calcite in

many crinoid overgrowths. These ferroan calcite zones were even more

apparent when examined using CL microscopy. Zones that stained blue with

potassium ferricyanide were invariably areas of dark luminescence under CL.

Otherwise, the general CL character of this cement is relatively bright orange,

especially near the crinoid substrate. These cements commonly contain

numerous thin, darker orange bands, especially near the outer edges of

crystals.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77

Figure 18. Calcite Cements, Dundee Limestone.

(A) Syntaxial calcite overgrowth ("OG") on a crinoid stem f’C’’). Saddle dolomite rhomb ("SD”) is present in interparticle pore. Plane light, scale = 0.25 mm. Reinhardt ft3, 2683.0’. (B) Scalenohedral calcite ("S”) that has grown on a brachiopod substrate ("B"). Blocky calcite cement (”BC") present as a pore-filling cement Plane light, scale = 0.25 mm. Grow #4, 2669.9'. (C) Stylolite in a micrite-poor peloidal-skeletal packstone. Local cementation around the stylolite has occluded interparticle porosity. Porous areas in the core appear darker due to oil stain, most visible on the unpolished surface (right side of photo). Note fracture ("F") associated with stylolite. Scale = 3 cm. Hart #2, 2647.5’.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Two different types of microsamples were drilled in this cement type.

The first type of sample was drilled from crinoid overgrowths that were just

thick enough to microsample without risk of contamination from original

crinoid skeletal material. Where overgrowths in a sample were well-developed

and had grown into larger pore spaces, only the outermost edge of the crystal

was sampled. Five microsampies of whole overgrowths and three of just the

outer edges were taken.

Whole overgrowths plotted in a tight group from -6.4 to -7.5 <5'80 and 1.2

to 1.5 S13C. Results from samples of the outer edges of these crystals had a

similar C13 range, but they ranged from -7.0 to -9.0 <5I80 (Figure 19).

Intercrvstalline Calcite Microspar

Several samples of the dolomitized restricted mudstone facies contain a

fine-grained calcite cement that occludes intercrystalline porosity. The cement

is anhedral and is generally about 4 to 5 microns in diameter.

Three areas rich in this cement type were sampled for stable isotope

analyses. Because the intercrystalline pores in the dolomite where this cement

is present are far smaller than the diameter of the drill used in microsampling

(500 /zm), each of sample consisted of a mixture of dolomite and calcite

cements. These isotopic analyses were intended to be compared with the

isotopic signature of dolomite sampled with no intercrystalline calcite cement

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 1 2 (PDB) (513 C (513 - 2 - -- 6 - - 4 -2 - 4 Signature _ Marine ^ KEY n Q Q Scalenohedral Calcite Crinoid OvergrowthsGrowth Zone) (Outer Most (Contaminated With Dolomite) Intercystalline Calcite Whole Crinoid Overgrowths 8 - 6 - 4 - 2 □ ■ o A ■ o ^ - 1 0

■

'1 '1 o

00 c>, (PDB) Figure 19. Isotopic Signatures of Calcite Cements. I" I" " 14 - 1 2

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission The results of isotopic analyses of these three samples yielded results from -8.2

to -8.6 5 180, and 1.30 and 1.93 8'3C (Figure 19).

Scalenohedral and Blockv Cements

Two other types of calcite cement were observed during thin section

examination: (1) pore-lining scalenohedral calcite, and (2) pore-lining and

pore-filling blocky calcite (Figure 18). These cements were found to be most

common in pore spaces of samples that contained a significant fraction of

micrite, especially peloidal-skeletal packstones. Pore-lining scalenohedral

cement was most abundant on brachiopods, and was generally oriented

perpendicular to the skeletal substrate. This cement was also present in

mollusk molds and stylolite-related fracture sets in micritic packstones. This

cement typically coarsens outward into the pore and crystals are commonly 400

p m long and 150 /im wide. Staining with potassium ferricyan.ide revealed the

presence of some iron-rich zones in this calcite cement Some scalenohedral

cements displayed "fir-tree" zoning of ferroan calcite (Raven and Dickson,

1989).

In some thin sections it appeared that the scalenohedral cement contained

dust rim relics of a thin isopachous, acicular cement near the base of the

substrate.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. One microsample was drilled from scalenohedral cement for isotopic

analysis. The cement was drilled from a large gastropod mold in which the

scalenohedral calcite had grown. The isotopic signature of this sample was

-8.18 5I80 and 1.35 5I3C (Figure 19).

Blocky calcite cement occurred as both a pore-lining cement and as a

pore-filling cement that showed little dependence on pore-wall substrates.

Where present as a pore-lining cement, the calcite coarsens rapidly outward

away from the substrate. The most common substrate for this cement was

pore walls made up of micritic fabric. Commonly, the cement nearest the

pore wall appeared to be inclusion-rich. This suggests that some of the

substrate had been replaced. In pores that were interpreted to have an early

origin (e.g., open burrows, shelter porosity, etc.), ghosts of an earlier, thin

isopachous acicular cement appeared to be present in the cement nearest the

pore wall The size of the pore-lining crystals is typically about 50 pm .

Cement further out in the pore is commonly coarser than 400 pm .

As with the scalenohedral calcite, some of the blocky cement locally

contained crystal zones that stained blue with potassium ferricyanide. No

samples of this cement type were taken for isotopic analysis.

These two cements commonly occurred together in the same pore space,

especially in pores that had an early origin. In such pores the scalenohedral

cement texturally predated the blocky cement

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cement Associated With Stvlolites

During core description, stylolites with associated tight zones on either

side of insoluble seams were observed in some places (e.g., Appendix A,

Plate 1-11, Estey E-8 at 2682.0’, 2682.5’, and 2684.4’). These tight streaks are

typically only a few centimeters thick and are most common in the peloidal-

skeletal packstone subfacies where this lithotype is micrite-poor (Figure 18).

These zones were not sampled for petrographic study. It is unclear what these

zones are; they maybe the result of extensive grain suturing or localized

cementation associated with stylolitization.

Saddle Dolomite Cement

Trace amounts of saddle dolomite were observed in pore spaces of every

facies type in this study (Figure 18 and 20). Saddle dolomite occurred as

pore-filling and pore-lining cement Saddle dolomite is generally euhedral, and

displays the curved crystal facies and undulose extinction pattern diagnostic of

this cement type (Radke and Mathis, 1980). Crystal size generally ranged

from 4 /Xm to 500 /xm. When examined in core the dolomite is white to light

brown. Thin section examination revealed that this dolomite was inclusion-

rich. Staining with potassium ferricyanide indicated the presence of distinct

ferroan zones within many saddle dolomite crystals. Many crystals showed five

or more distinct (ferroan and non-ferroan dolomite) zones. Ferroan dolomite

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. zones lacked the numerous inclusions that most non-ferroan zones contained.

Cathodoluminescence microscopy also revealed numerous distinct zones

within saddle dolomite rhombs. Luminescence character of these zones ranged

from completely black to bright red. The contact between zones of different

CL character is very distinct in this cement type (Figure 20).

Ultraviolet-fluorescence microscopy showed the presence of hydrocarbon-

filled fluid inclusions in many saddle dolomite crystals (Figure 20). These

inclusions are very small (less than 2 microns) and are concentrated in the

nonferroan (unstained), brightly luminescent growth zones of saddle dolomite

crystals. Cercone and Lohmann (1987) observed a similar relationship of

hydrocarbon fluid inclusions in brightly luminescent saddle dolomite growth

zones in samples from Silurian carbonates in the Michigan basin.

This cement type texturally post-dates all other carbonate cements.

Saddle dolomite commonly occurs in fractures associated with stylolites, and

also forms resistant pinnacles in stylolite seams. This indicates that pressure

solution was an on-going process throughout much of the burial diagenesis of

these rocks.

One thin section (from the Doran #5 core at 2660.7 ft) contains saddle

dolomite that appears to have replaced pre-existing fine-grained calcite.

Coarse-grained skeletal fragments remain unreplaced. Dolomite rhombs here

are between 200 and 500 /im in size. Compromise boundaries with other

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 20. Pore-filling Saddle Dolomite Cement, Dundee Limestone.

(A) Saddle dolomite rhomb ("SD") and anhydrite cement ("AN") in fracture associated with a stylolite. Note the three distinct growth zones ("1", "2", and "3") in the dolomite rhomb. Zone "3" is darkest because it is the most inclusion-rich, whereas zone "1" is the most inclusion-poor. Crossed polars, scale = 0.25 mm. Doran #5, 2660.7’. (B) Saddle dolomite cathodoluminescence displaying growth zones with distinct luminescent characteristics. Scale = 0.25 mm. Doran #5, 2660.7’. (C) Saddle dolomite in a shelter pore (open burrow) as seen in plane light (left), and under an ultraviolet (UV) light source (right). Fluid inclusions fluoresce when examined with UV light due to the presence of hydrocarbons in these inclusions. The inclusions are interpreted to be primary. Scale = 0.25 mm. Grow #4, 2595.9’.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. saddle dolomite crystals are very common. This was the only sample where

replacement by this cement type was observed.

Twelve microsamples were drilled from saddle dolomite crystals for stable

isotope analysis. Two of these samples were taken from the specimen that

contained replacive saddle dolomite. The other ten samples were drilled from

pore-filling saddle dolomite. Six of these samples were drilled from the

outermost growth zone of crystals as identified using CL microscopy before

sampling. Two very large saddle dolomite crystals from different wells were

sampled twice; the first samples of each were drilled from a discrete CL zone

in the center of the crystal, the second samples were drilled from another CL

zone toward the outer edge of each crystal. This was done to see if any

isotopic trends from early to late saddle dolomite were apparent

The stable isotope signatures of eleven saddle dolomite samples ranged

from -8.35 to -4.85 <5I80 and 1.43 to 2.7 5'3C (Figure 21). One very anomalous

signature of -8.75 <5I80 and -5.85 5 I3C was measured for one of the

microsamples taken from the replacive saddle dolomite (Figure 21).

Other Burial Cements

Three other cement types were recognized-anhydrite, fluorite, and pyrite.

These cements are very rare and all texturally post-date saddle dolomite.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oo a\ KEY Replacive Saddle Dolomite Void—Filling SaddleVoid—Filling Dolomite A O (PDB) <513C -6 - 2 - - 4 -2 -4 Signature _ Marine - 4 - 2 2 4 o

1 © 6 cs)(§© A (PDB) <51S0 from single crystals. Figure 21. Isotopic Signature of Saddle Dolomite Cement Arrows indicate the relationship between inner (at base of arrow) and outer (at tip of arrow) growth zones 14 -12 -10 -8 -6

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Anhydrite occurs as a pore-filling cement Crystals occurred as long

(usually 3 to 4 mm), thin laths with planar contacts with other anhydrite

crystals. In many pores filled with anhydrite, pore walls showed evidence of

anhydrite replacement of pre-existing calcite cements and sediments. Saddle

dolomite also commonly appeared to be in various stages of replacement by

anhydrite where these two cements are adjacent (Figure 20).

Late pyrite was observed in four thin sections as a subhedral pore-filling

cement In one sample a saddle dolomite rhomb appeared completely

surrounded by late pyrite.

Fluorite was observed in thin section and in core. This cement occurred

as sub- to euhedral crystals in sizes from less than 50 /im to greater than 5

mm across.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. STRUCTURAL EVOLUTION: WEST BRANCH FIELD

The purpose of this section is to: (a) describe fractures observed in core,

(b) determine the timing of structural development of West Branch relative

to deposition of the Dundee Limestone, and (c) consider the style of structural

deformation in the West Branch area.

Fractures

Three types of fractures were observed during core examination: (1)

Small-scale compactional fractures in chert nodules and restricted mudstone

beds surrounded by dolomite (Figure 15); (2) Fracture sets associated with

sutured-seam stylolites in the peloidal-skeletal packstone subfacies (Figure 22);

(3) High-angle, through-going macrofractures.

Various types of fractures are recorded on core description sheets

(Appendix A). It is important to be able to compare fracture intensities from

one well to another. One approach is to count the number of fractured feet

in a core, then express this as a percentage of the total cored footage. Any

foot of core with 1 or more fractures is counted as 1 fractured foot Table

2 shows the normalized fracture intensities for all Dundee cores examined in

this study.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89

Figure 22. Small-scale Fractures Associated With a Sutured-seam Stylolite.

Sample is peloidal-skeletal packstone (unpolished core slab). Scale = 3 cm. Cox »2, 2743.5’.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2

Fracture Intensity From Core, Normalized to 100 Feet

Core Well Name Normalized fracture intensity

Heintz #9 44'

Donovan #6 29

Cox # 2 71

Estey E-8 57

Doran ft5 40

H art ft2 49

Hart ff l 56

Reinhardt #3 48

Buckingham tt \ 44

Grow #4 83

Grow tt9 58

Approximately 40% of this core is sealed in paraffin (Appendix A). Therefore, normalized fractured foot count may be unreliable.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Small-Scale Compactional Fractures

The small-scale compactional fractures found in chert and mudstones are

believed to be the result of relatively early compaction and are discussed in

the sedimentology section. These will not be discussed here further.

Fractures Associated With Stvlolites

These fractures occur most abundantly in the peloidal-skeletal packstone

subfacies. The fractures are generally between 2 and 30 cm long and are

vertical. Fractures in a set associated with the same stylolite have the same

relative trend. From the examination of core and thin sections, it is clear that

these fractures are extensional, not shear related. These are by far the most

common type of fracture observed in this study (Figure 22). Nelson (1981)

has reported similar fractures. Watts (1983) suggests that stylolite-related

fractures are the major fluid conduits in a North Sea chalk reservoir.

These fractures typically contain some amount of burial cement, although

some are completely unfilled. Common cement types in these fractures are

pore-lining scalenohedral calcite, pore-filling saddle dolomite, and less

commonly, anhydrite. Several fractures that contained no calcite cement were

connected to fractures that were lined with calcite cement This relationship

indicates that the unlined fractures formed after the formation and

cementation of earlier fractures.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Saddle dolomite is present in fractures with and without calcite cement

Saddle dolomite filled some fractures completely. Several dolomite-filled

fractures are now resistant pinnacles along solution seams. This relationship

indicates that stylolitization continued after the formation and filling of some

fractures with saddle dolomite.

Various cement-fracture relationships indicate that the formation of

sutured-seam stylolites and associated fracture sets occurred over an extended

period of time. It is not clear if the formation of these structures occurred

as separate events or in one continuous process.

Fracture sets indicate the presence of triaxial stress conditions during

stylolitization, with the stylolites forming perpendicular to the principal stress

direcfion (overburden) and associated extension fractures forming normal to

the horizontal paleo-stress minimum (Nelson, 1981). These fractures may be

related to the same stress conditions responsible for the formation of the West

Branch anticline.

The presence of these fracture sets has an influence on core analysis

results and electric log response. The best example of this effect is in the

Cox #2 core. In this core, a large number of sutured-seam stylolites with

associated fracture sets are present in the relatively thick unit of peloidal-

skeletal packstone present between 2730’ and 2756’ (Appendix A, Plates 1-7

and 1-8). This packstone has low interparticle porosity and permeability typical

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of this subfacies, but the presence of numerous fracture sets results in very

high permeability from core analysis (around 100 md) and low resistivity on

well logs (Plate II-3).

The distribution of this fracture type is largely limited to the peloidal-

skeletal packstone, the depositional facies that contains most of the sutured-

seam stylolites.

Through-Going Macrofractures

Macrofiractures occur as high-angle (non-conchoidal) fractures. The

surfaces of these fractures commonly have many small irregularities and they

do not show any component of slip. It is unclear how many true

macrofractures exist in the core examined because many areas exist where

the core was broken and abraded during coring. Some of these areas may

have been sites where macrofractures were present Only twenty three

macrofractures were identified in over 1,000 ft of core examined in this study.

The only evidence for relative timing comes from cement observed in

these fractures. Saddle dolomite is the only cement observed in

macrofractures. Saddle dolomite was very rare, but unequivocally present,

even if only in small amounts. The absence of other cement types may or

may not be significant, due to the low number of macrofractures observed

and because these fracture surfaces were difficult to sample for thin section.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Core examination does not indicate any localized diagenetic alteration

of the surrounding rock fabric in the proximity of these fractures. For

example, dolomite haloes are not present to suggest that these fractures served

as conduits for dolomitizing fluids.

Macrofractures were observed in all facies types except the crinoid

grainstone and skeletal-peloidal grainstone. Although the low number of

fractures recognized makes it speculative, this may indicate that these

lithotypes avoided fracturing because other types of strain were more easily

achieved (e.g., grain rotation, suturing, or calcite twinning).

The orientation of these fractures is unknown, and no mechanism of

deformation will be assumed in this study.

Prouty (1989a, 1989b) and Ten Have (1979) state that shear faults exist

in the West Branch Dundee Limestone. Fracture types documented from core

in this study show no component of shear.

Timing of Deformation

The structural development of the West Branch anticline apparently did

not begin before or during deposition of the Dundee Limestone. There is

no evidence for development of shallow-water build-ups over the structure

similar to those in Buckeye field (Montgomery, 1986). The lateral continuity

of facies markers in cross sections (especially those perpendicular to the field

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. trend) strongly suggests that little or no structural movement occurred prior to

deposition (Figures 12 and 13).

Isopach maps were examined to see if any of the overlying formations

thinned over the structure. Thinning would indicate that structural

development predated deposition of the unit examined. The results were

inconclusive due to the low number of off-structure control points. However,

thicknesses of Mississippian shales from wells in on-structure areas (e.g., wells

in Sec. 28, T22N-R2E) were compared with thicknesses in off-structure wells

(e.g., States Petroleum Grezeszak # 1-16, Sec. 16, T22N-R2E, and Amoco Rau

#1-21 in Sec. 21, T22N-R2E). This comparison showed that shales are on

average only about 2-4% thicker in off-structure areas to the north over a

distance of about 1.5 miles. This is interpreted to indicate that practically no

structurally related paleohigh was present during deposition of the

Mississippian shales.

In summary, the only age constraint on structural movement at West

Branch is the fact that deformation post-dated the Mississippian Coldwater

Shale and Marshall Sandstone and pre-dated Pleistocene glacial tills.

Nature of Movement

The similarity of the West Branch and Clayton structures has been

discussed in an earlier section. To review, these structures are en echelon

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. asymmetrical anticlines that dip more steeply on their northeastern flanks.

The crest of the West Branch anticline migrates to the northeast with depth.

Also, the top of the West Branch anticline appears to be relatively flat on

structure contour maps (Figure 5).

Versical (1989, 1990) relates the development of the West Branch and

Clayton structures to strike-slip movement on a fault in the Precambrian

Penokean basement He used seismic data from a line shot perpendicular to

the Clayton field. Faults believed to be helical Riedel shears that form a

"tulip" structure were observed in Lower Paleozoic sediments below the Salina

Formation (Silurian). "Tulip" structures are believed to occur in settings where

basement-induced wrench faulting has deformed overburden (Naylor, Mandl,

and Sijpesteijn, 1986). In the seismic line across Clayton, Versical (1990)

noted that the fault on the north side of the structure has considerably more

vertical displacement than the fault on the south side of the structure. This

probably caused the asymmetry observed in these fields.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DISCUSSION

Facies Interpretation

The Dundee Limestone consists of a complex facies mosaic of crinoid

grainstones, skeletal-peloidal grainstones and packstones, skeletal wackestones,

restricted mudstones and wackestones, and rare stromatoporoid-coral

floatstones and fenestral-cryptalgal laminites. Hemicyclic, shoaling upward

sequences are common. These contribute to vertical heterogeneity. Lateral

heterogeneity has been established by comparing core descriptions to log

signatures, then correlating logs in a series of field-wide cross sections.

During deposition of the normal marine facies, the northwest end of the

study area was apparently in deeper water than the southeast This

interpretation is based on the following evidence:

1. The crinoid grainstone facies is present only in the northwestern one-third

of the field (Figure 12). This facies is interpreted to represent deposition in

a deeper water, lower energy environment than laterally equivalent facies in

the central and southeastern parts of the field (i.e., the skeletai-peloidal

grainstones and packstones).

2. Cross sections show the crinoid grainstone facies reaches its maximum

thickness in the northwestern part of the field. To the southeast, this facies

gradually thins and grades into higher-energy, cyclic skeletal-peloidal 97

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. grainstones (Figures 12 and 13).

3. The frequency of shoaling upward hemicycles in the skeletal-peloidal

packstones and grainstones increases to the southeast (Figure 10). This

suggests that shallower depositional environments existed to the southeast

4. The restricted wackestone facies between markers D2 and D3 (Figure 12

and 13) grades into skeletal-peloidal sands to the northwest This gradation

from restricted to open-marine facies suggest that the seaward direction was

to the northwest

5. Dolomite abundance varies in the zone between markers D1 and D2 at the

top of the Dundee. This layer is pervasively dolomitized in the southeast part

of the field, and less dolomitized to the north west Dolomite is an early,

matrix-replacing mineral in this zone. Uwdolomitized layers appear to be

marine cemented. The observed variation in degree of dolomitization may

suggest that the seaward, more cement-prone depositional environment was to

the northwest

All lines of evidence suggest that the Dundee shelf or platform sloped

to the northwest This is in direct conflict with the fact that the Dundee

depocenter was to the southeast (Figure 2). It is probable that the

"depocenter" defined by the thickest isopach is not equivalent to the deepest

water areas of the Michigan basin during the deposition of the Dundee

Limestone.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Disconformity at the Top of the Dundee Limestone

The top of the Dundee is marked by a mineralized or bioeroded

hardground in all cores examined in which this contact was present (Figure

7). This previously undocumented surface indicates a drowning event that

terminated deposition on the shallow-water Dundee carbonate ramp. As such,

the surface is a sequence boundary between the Dundee and Rogers City

Limestones. It is unknown at this point what conditions were responsible for

creating this disconformity. The processes and conditions present during this

hiatus resulted in the lithification and pyritization of this hardground and also

caused early replacement of underlying lime muds with dolomite or a

protodolomite precursor.

The lateral extent of this surface is unknown beyond the study area.

Considering the fact that the West Branch area is near the depocenter of

Middle Devonian sediments (Gardner, 1974), the exceptional conditions

responsible for this hiatus probably had recognizable regional effects.

Schlager (1981) stated that drowning events in carbonates that do not

involve the introduction of elastics to the depositional setting must be caused

by short-term processes. Ecologic stress (to suppress the growth potential of

carbonate producing organisms) and rapid rises in relative sea level are the

two-short term processes that can accomplish this type of drowning. Either

process can accomplish drowning (in the presence of longer term eustacy and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. subsidence), but when both occur together, drowning of shallow water

carbonate settings is even more likely (Schlager, 1981). Faunal diversity

decreases in the uppermost Dundee Limestone, (the restricted micritic facies).

This indicates that environmental conditions had become too stressful for

normal-marine fauna (i.e., brachiopods, corals, and crinoids).

The Middle Devonian rate of subsidence for the central Michigan basin

is calculated to be 70 cm /1000 yrs by Gardner (1974). This high rate of

subsidence would have an additive effect on rising eustatic sea level to make

drowning a more likely occurrence (Schlager, 1981).

Johnson, Klapper, and Sandberg (1985) published a eustatic "sea-level

curve" of Devonian time based on rocks from the western United States, the

U.S. Appalachians, and Europe. Correlation of the Dundee drowning event

is difficult due to discrepancies of stratigraphic correlation from the study

areas of Johnson et al. (1985) to the Michigan basin and the conflicting

assignment of Michigan basin strata to different established conodont zones

(e.g., Bultynck, 1976 and Rickard, 1984). However, Johnson et al. (1985)

suggest a transgressive-regressive cycle began near the end of Eifelian time.

The beginning of this cycle, recognized by Johnson et al. (1985) in other areas

of North America, may be time equivalent with the drowning of the Dundee

depositional setting in the Michigan basin.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In the West Branch locality, a decrease in carbonate productivity due to

environmental stress seems to be related to the drowning of the Dundee

depositional environment This drowning is also probably related to a eustatic

sea level rise, although correlation to similar transgressive events outside the

Michigan basin is limited by contradictory conclusions of recent research that

has tried to establish the biostratigraphy of the region.

Diagenesis

Core descriptions, thin-section petrography (plane light, CL, and

fluorescence) and carbon/oxygen isotope geochemistry have been used to

determine a paragenetic sequence in the Dundee Limestone. Early marine

cementation was followed by chert and dolomite replacement of matrix. A

series of calcite cements predate and post-date pressure solution/compaction.

Open fractures commonly formed as a result of stylolitization. Saddle

dolomites and other minor late stage minerals line some pores and fractures.

Even though a complex series of diagenetic events has occurred in the Dundee

Limestone, primary interparticle porosity is largely preserved in many areas.

Isotopic analyses of early marine fabrics (brachiopods and micrites) yield

results that are compatible with published Devonian values. The heaviest

brachiopod analyzed in this study (-3.40 5lsO and 1.33 613C) is taken to be the

Dundee "marine signature." Other samples were more or less contaminated

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. by later diagenetic overprints and had lighter oxygen values.

The distribution of replacive dolomite in this field—laterally persistent

with a gradational contact to the underlying limestone and a sharp contact

with the limestone of the Rogers City-strongly suggests an early replacement

of the restricted mudstone facies. Textural evidence from core and thin

sections shows no indication of subaerial exposure or evaporative conditions

at the top of the Dundee where this dolomite is present A "mixing zone"

environment (Badiozamani, 1973) is probably inappropriate here, although not

enough is known about the regional paleotopography.

Isotopic results shed some light on considerations of the origin of matrix-

replacive dolomite. The oxygen isotopic signature is very depleted (-8 to -9

5l80). The carbon signature is slightly enriched in l3C (about 0.5 ° /„» )

compared to the inferred marine signature (Figures 12 and 13). The light

oxygen is not characteristic of marine or evaporitic dolomite. Both of these

would be heavier, not lighter, than the marine signature. Light oxygen occurs

when there is either high temperature or significant meteoric water involved

in dolomitization. Evidence for meteoric influence has not been observed.

The coincidence in isotopic composition between matrix-replacive dolomites,

all types of calcite cements, and saddle dolomites (Figures 17, 19, and 21)

suggests that some late diagenetic event may have homogenized the isotopic

signatures of these fabrics.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fracture-Controlled Dolomite Hypothesis

Ten Have (1979) studied cuttings from wells drilled in the West Branch

field and created subsurface maps based on reported formation tops. He

concluded that epigenetic dolomitization, localized in the vicinity of faults,

enhanced the porosity of the Dundee Limestone. Based on this work, Prouty

(1989a, 1989b) cited the West Branch Dundee Limestone as an example of a

fracture-controlled dolomite reservoir.

The results of this study conflict with almost all of the major conclusions

of Ten Have (1979). The following is a summary of the major points of

disagreement:

1. Ten Have (1979) concluded that matrix-replacive dolomite in the Dundee

is structurally related based on distribution of dolomite in well cuttings. In

this study, matrix-replacive dolomite is interpreted to have a syngenetic origin,

based on textural evidence and observed distribution in core.

2. Ten Have (1979) calculated percent dolomite of well cuttings from

different depth intervals below the Bell Shale and used this data to create

"dolomite ratio maps" for each depth interval. The depth interval 80 to 110

feet below the hase of the Bell Shale (the top of the Dundee is approximately

90 feet below the base of the Bell) is the depth interval in which Ten Have

(1979) found the highest concentrations of dolomite. This corresponds to the

occurrence of replacive dolomite observed in this study. However, Ten Have

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (1979) found dolomite percentages to vary greatly (from 2.5-43%) in this

interval from well to well. This lateral variability in dolomite distribution was

not observed in this study. Three cored wells with similar amounts of

replacive dolomite (Hart # 2, Hart #7, and Doran #5 cores, Plates II-5, II-6,

and II-7) were posted on Ten Have’s (1979) dolomite ratio map. Two wells

were outside the 5% "isodol," whereas the third well (Hart §2) was between

the 25 and 30% "isodols". This suggests that these dolomite percentage maps

do not provide an accurate picture of lateral dolomite distribution.

Also, the well log cross sections constructed in this study (Plates III-l

though III-5) do not show rapid lateral variation in log response. Porous

zones were found to be laterally persistent on a scale of miles.

3. The depth interval between 80 and 110 feet below the Bell Shale was

calculated to contain an average of 20% dolomite by Ten Have (1979). Depth

intervals 110 to 140, and 140 to 170 feet below the Bell Shale were calculated

to contain an average of about 10% and 5% dolomite, respectively. From the

examination of core and thin sections, the percent dolomite estimated by Ten

Have (1979) of these two intervals is too high. Perhaps his cuttings were

contaminated by cavings. The only dolomite observed in these intervals was

trace amounts of saddle dolomite and local, trace amounts of finely-crystalline

dolomite associated with stylolite seams. The over-estimation of dolomite

from X-ray analysis can be attributed to the inherent error in using well

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cuttings and bulk sample analysis for this type of quantitative use.

4). Ten Have (1979) noted that chert was most common in cuttings between

80 and 170 feet below the base of the Bell Shale. This is inconsistent with

observations in core, where chert was only observed in the restricted

wackestone facies. This facies is less than twenty feet thick in most cores.

Estey E-8 is the exception, where the restricted wackestone facies is about 30

feet thick. This facies occurs between 100 and 130 feet below the Bell Shale

(about 8 to 38 feet below the top of the Dundee Limestone, Figures 12 and

13). This is further evidence that suggests that cavings contaminated the

cuttings used in his study.

5. Ten Have (1979) attributed local thickening in an isopach map made of

the Traverse Group (which immediately overlies the Rogers City and includes

the Bell Shale) to sags in the Dundee (and Rogers City) Limestone due to

dolomitization along fractures. No such sags are apparent on well log cross

sections (Plates III-l through III-5), even at great vertical exaggeration (Figures

12 and 13).

In summary, the interpretation that fracture-related epigenetic dolomite

is present in the West Branch field is based on the X-ray analysis of well

cuttings. The results of X-ray analyses do not accurately reflect the

distribution of dolomite in the subsurface as observed in eleven cores in this

field. This illustrates the danger of doing a study restricted to cuttings when

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. core is available. The fracture-related epigenetic dolomite model for the

Dundee Limestone in this Held is inaccurate and is not a useful concept for

understanding the nature of this reservoir.

Timing of Structural Development

Montgomery (1986) demonstrated that structural development of the

Buckeye field occurred before deposition of the Dundee Limestone. The

resulting paleo-high was evidenced by rapid on- and off-structure facies

changes and over 200 feet of thickening of the Dundee over the structure as

compared to off-structure areas. From facies analysis and the construction of

well-log cross sections, no similar evidence can be found in the Dundee

Limestone at West Branch field. Neither the Roger’s City nor the Dundee

Limestone show a change in thickness on cross sections perpendicular the

trend of the structure (Figure 13). Facies also did not show rapid lateral

variation that could be related to structural position.

Comparison of thickness of Mississippian shales in on- and off-structure

wells indicated that no paleohigh was present in the study area during the

deposition of those shales, as would be expected if structural development

had occurred before that time.

Deformation of the Coldwater Shale and Marshall Sandstone, which

outcrop and subcrop over and around the crest of the West Branch structure

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (Newman, 1936), indicates that development of this structure was probably

post-Mississippian and did not affect the deposition of the Dundee Limestone.

Economic Considerations

The Dundee Limestone in West Branch field is currently under

waterflood. A number of aspects of this study could have economic

implications:

1. Laterally discontinuous porous and permeable zones have been identified.

In addition, laterally extensive permeability barriers, such as the skeletal

wackestone facies, have been documented. It would be useful to look at

completion records and injection profiles in the context of this study to see if

improvements could be made in areal sweep efficiency.

2. This study has shown that fine-scale fractures are present in cherts and

limestone interbeds in the uppermost Dundee Limestone. Matrix porosities

and permeabilities are poor in this zone. If many wells are completed in this

interval, and if a lot of fluid is being lost into those perforations,

recompletions may be in order.

3. Extensional fractures associated with stylolites are common in skeletal-

peloidal packstone facies. These facies have been identified in core studies,

and they have been correlated in field-wide cross sections. Stylolite-related

fractures may behave as permeable conduits to channel significant volumes of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. injected water. If this is known to be the case in certain parts of the

waterflood, gel or cement conformance treatments may be in order.

4. One of the original goals of this project was to see if fairways of fracture-

controlled dolomite existed in the Dundee. If so, it would be useful to project

those down to deeper reservoirs. Unfortunately, the fracture-controlled

dolomite model does not apply to the West Branch Dundee Limestone.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CONCLUSIONS

1. Six depositional facies types were recognized from core studies, four

of which are present above the oil-water contact in this field: crinoid

grainstone facies, skeletal-peloidal grainstones and packstones, skeletal

wackestone facies, and the restricted mudstones and wackestones. The crinoid

grainstone and skeletal-peloidal grainstones and packstones contain interparticle

porosity. The restricted mudstone is largely replaced by dolomite and contains

intercrystalline porosity with very low permeability. The skeletal wackestone

is practically nonporous and nonpermeable. The stromatoporoid-coral

floatstone facies and the fenestral-cryptalgal laminite facies both have high

permeability and porosity properties, but they lie below the oil-water contact

in this field.

2. The contact between the Dundee and Rogers City Limestones is a

disconformity represented by a mineralized hardground that shows bioerosion

in some cores. This is interpreted as a sequence boundary that corresponds

to the drowning of the Dundee platform.

3. Porous units identified in core and on well logs are related to

depositional facies. The zone of high porosity associated with the dolomitized

restricted mudstone facies is correlative field wide, whereas porosity zones that

are interparticle in nature are more lenticular, and correlate between two and

six miles along the field. Two thin, nonporous skeletal wackestone facies were

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. also found to be correlative in part of the field for several miles. Knowledge

of the distribution of porous and nonporous units in this field should prove

valuable in the design and evaluation of waterflood programs.

4. Dolomitization of the restricted mudstone facies at the top of the

Dundee is believed to have occurred early, before deposition of the Rogers

City Limestone. Replacement probably occurred on the sea floor during the

hiatus in sedimentation at the end of Dundee deposition. The stable isotope

signature of this dolomite is depleted in l80 relative to other marine and

diagenetic fabrics sampled in this study. This signature is attributed to

diagenetic overprinting of the dolomite in the burial environment

Primary porosity in grainy facies has been partly occluded by calcite

cements, mainly crinoid overgrowths. Some porosity destruction has occurred

due to pressure solution. Saddle dolomite and other late cements precipitated

to occlude minor amounts of porosity.

5. Based on the results of this study, the fracture-related dolomite model

for porosity enhancement at West Branch (Ten Have, 1979) is judged to be

in error. His study was based on bulk-sample analysis of cuttings. His

conclusions are inconsistent with extensive core data available in this reservoir.

6. The anticlinal structure that now defines this field was not present

during deposition of the Dundee or Rogers City formations and does not

appear to have formed before Early Mississippian time.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Appendix A

Plates 1-1 Through 1-38, Core Descriptions Sheets

111

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. KEY TO CORE DESCRIPTIONS*

P o r e Type Mineral Composition Logged in percent BP = Interparticle WP = Intraparticle BC = Intercrystalline a Dolomite MO = Moldic C alcite

A AA FE = Fenestral A A A C hert V ■ ■ ■ SH = Shelter Right ■ s E P y rite FR = Fracture

Nature of Contact

S = Sharp ST = Stylolite

SI = Sharp irregular G = Gradational

UK = Unknown

*Modified from Bebout and Loucks, 1984.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Key to Core Descriptions-continued

Carbonate Texture

Left Intraclasts

Skeletal grains

(J) 0 Pellets $

o O o Peloids

Right Micrite

Highly altered. Superimpose over interpreted texture.

Carbonate Fabrics

M = Mudstone P = Packstone

W = Wackestone G = Grainstone

F = Floatstone

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Key to Core Descriptions-eontinued

Stuctures

T ype

Stylolite A^\_AXV. Ripple marks

Microstylolites T \ VV Cross bedding X Fracture (filled) A Hardground X Fracture (partly filled) Burrows "U~ Vertical Fracture (open) X cj Horizontal Through^going \ macrofracture Clast Borings o Cloudy appearance u s Scoured surface F Fenestral Lamina types- Geopetal sketch diagrammatically, e.g. irregular Vug laminations

S iz e

This column used to record maximum amplitude of sutured seam stylolites.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Key to Core Descriptions—continued

Color

L = Light G = Gray M = Medium B = Brown D = Dark C = Cream m = Mottled Bk= Black

Example: MB = Medium Brown

Fossils

Fossil types listed at top of core form. Names often abbreviated, (e.g., Brach = Brachiopod, Pelecy = Pelecypod). Relative fossil abundance logged as shown below.

Not present

P resent

Common

Abundant

Cement Cement observed in large pores.

AN = Anhydrite C = Calcite SD = Saddle dolomite F = Fluorite P = Pyrite B = Bitumen

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w e ll QorioMM * . . - STA TE STRATIGRAPHIC INTERVAL ■ p u H c i < £ e L O G G ED BY ( 5 DATE

S lU ttt sue MINCRAL 3 "I STnUCTUA(( *! In pAUAAtlYtftb OO ^O H tfl- C**STAi UZfl Is:I 38 ~ 3

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Plate 1-5

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WELL T>r~*tn tn v ft (e (Cc02,2?\ . COUNTY - - STATE STRATIGRAPHIC INTERVAL , LOGGED 8V PATE

CHAIN 3 K I I ------V ' 5 H tN lflU COMPOSITION e=i., ifj 1-5.311^1 3 P o h s S e IINCl. PONOSITV) 1 * YZfce- tjy&hoooo- ■ / s / ! ■ * ~ pSw#pfeP S o p f e iiKjSMtvcZca-41

'&O0OO0O? s.R.

rfP ■ f c M psB ^ I- \m z ^ ~ S3> ttsc

m » 5 ? T «? t f £ / u iw'AI J Mckb o* * • j}J? STVo*. i Ufeaoop--- tf'SP ' | » R WB t> s c i ■ I j h S ? |> 5 * •~ 5 d Z73fF ■ H t>5? lW h r cepo;. I | } S ? i -VC* S T ? Ufiooseo-;, 1 1 'Jtpocoo — j s * > m s » 'ibeeoooo-..\ '^Ufioccoa-] i> si? yU l .’JnUceo.. -i n V*1 ■ ytioca* 'iAoo- • * I 3 s ? fM£tsoao- -\ 5 D 'sl>i6oocC-. }SR ■■ |M 5 ' * r • ? ! Z7V5"! m a L - At-Zm Vh ,. UUj x p -" 3 > B JSE* AH m s? ® * " JS?

’ I

Plate 1-6

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W E L L R u W i C a X * 2 . C O U I C & Z A /U J .

STRATIQHAPHtC INTEnVAI.'RpjtfS £ > f y /D tA H iL e A . L » i e t n LOQGEO BV B . £ U ( fa-V\

3“ STMUCTURII St' COIVOtlTION ;«f 05 lINCL 3? f^etes ...... ! !

j f c c ; v . l&tJ'yzAL'.',* * rJard<*)rz**'vS

3 -Vrf \yS

;2b55rsAD£ 4-?yr>'TfZeJ EtatWctf! £! fafdqroun^

. Erctii heft. on^. OO F.'/ie-^ratned y*itiOO flhnsyial fpwrtl wcJiil bbkbbfeooo-ip: Telctds), lidrfe/) fetfcbttto tpo *■ • , I* •Afr y* !i yOO f7«>OoJ- icocWta AaS^ .F txCea^LTppnxf^ LLtt* f&r\*6rvi' AS**ll ^fACKKVit O r pi \ y ^ r / S ^ l i ^ C prejjenf.' n **+&] tU<5 afioii, ^/V» r;) /v - . ..‘J > 6 ^ 2 7 3 5 1 — w f a t O IL- • * ^ 1 » ?,iX ■*-V - witbto**" W • * y > A ^ u '

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:£=. ! ikfcfci*

2 ( x ,f c t < 3

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WELL Jiixth .C&y* ^2- COUNTY STATE STRATIQRAPHIC INTERVAL _L5l/\.H d-e-S. LOQQEO BY 3 . m*\ 0AT6 FOSSILS MINf *Al CHAIN >111 . COMPOSITION ioocomiti- ir* S "5 i 3 ¥1 <3 r ttNCL. "’"V i"1, i- s -j 1 ’ ft.e POUOSITV) p A ff e c ...... I tjjttbcio . WUz Kt«>o- •Vv. ■*■ 6 1 U60 O * h u e " 0

r-i^ & boo- U-7- " tp Y i A ^ Z E « m ' ZKS- ■ I I Ifcfcfcloo- TV-~ , :, tktkfcooe fctt-t®6- ^{j.bOodo *V“ ICiiAooe .aM 000 ^aoo- JckOoo' Jaboa o • ,T,i'o0o“~ |£»kf»6o©^ r S ^ 1 L t e » o t^SOV ■■• ■ "T' LUv>crcr . _ JP'«0O''L^f,l//W-j t -/IS Ubn&°- jLl&hsa: ■ J,b6otP°°' -, / / / / > k£iUt&eo “ &TQ- — - / / , y MBI klo&AAAAi' • tAitooo • I B | *w ' ItWasw **&! &.WP 1 » SuWftti s^MxtQ- » t t f e - w o t st)loir& s L-* 5 ^tfcoo | '1 z m - . -&&Z 1 <+**• zjtu>y^°' MCi j f ULU°°‘ \ji~ l%tJoLoc-- I ->v,i LUoao. ■ vCL SE fetU e I! 1 MS 111 ■f-A av AevI 2-780 .jtfkiU* 1 ^Lcvac'* • • (j/ciu/ai D u | *"Sf ■.■<■»« V' - lsUU(J>b(> l i S r f (£&or.-- MG ■ S t . * ^ _ „ l ‘Jcf fit ■ LA/i«UL- 2 7 3 5 "

Plate 1-8

Reproduced with permission of the copyright owner Further reproduction prohibited without permissiorr WELL £-OJ< COUNTY O ^e-M a t-j stati STRATIGRAPHIC INTERVAL T^Ufld&e LOOQED BY £>. CjJ-TtfO-A °*T t INfrtflAl 3j. trUUCTUttlS unaun tits V 11 ' COMPOSITION ;* a idoiomiti- 5ri S i j I Jj 5 r gc JINCI 23 ------PONOSlTt) «3, , m '&r?8S~

<- "V-v, -h tb b b b V

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Plate 1-9

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. COUNTY C ^^JVIC XO J STATE w e l l 9 STRATIORAPHIC INTERVAL ~L^> U r ) J-&& LOOQEDBY l i ^ > PATE QNAM SIZC - . - - r ------r • - MlNlftAl 8- STRUCTUNIS ioolouiis. >r 5 1 ^ = £ Sge C I COMPOSITION i*3 csmsizz, g c 'i ic Mot'es

^ Z C C & / - f •*}* •/ V

.iT

ooo»* ,40 / /«&

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Z6Z5"i

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. w e l l £ - 3 - COUNTY - - - STATE STRATIGRAPHIC INTERVAL .. LOOQEOBY 3 'CsH/SaH, DRAIN tlZC lOOtOMITI- i 5r, 5 It-? “Id 'S >->. - i cmm tizci ;|[ g tt e h j - ^ a '2r^ vt r-^4 ri? r£ v52 Vi i

V* . ( ' L d l i J M l

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W f vV. •U&6----- ■ '/ // / , Mo V / / ^ M6

Lacai Cer*e*\&!o*m &C&ur\a Z+yvlltt5

Z7IS P

Plate 1-11

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. _ STATE ___ WELL g s k y S - B COUNTY Cj&tW titaCd . . . . ®T STRATIGRAPHIC INTERVAL LOGGED BY -

GRAIN SIZK i ______- g g S . . . m 3-!IfRUCTURII tOOkOHITC. J f ; $ 1 - ^ ^ . « g V, § £ , * COMPOSITION I-* TtlTURI ,c™ ”\ ^ s ! 5 ! ': \h~ ~"

CeMg/fbf hfrt j around SV^/.’M j Lowar’*|i,d CifiS5 1 6 beds

FrrU*

'AvJw-H VVX . :A6

27% )’

^ ,1 iu wfcfcm.

(akTTnilf SFVrv)

UiXO- ~P ■Z7HS cv I— ttW-CCO t v {UjM- o- y %. m u , - , filqA. i-a+'tfiae ■

p ' ^ $ " * 1 ffl* Vf^ & £yvta/l TU//WS 1

Plate 1-12

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W E L L ______£2.^jSu«fV U -?______STATE STRATIQRAPHIC INTERVAL _ / j g Z ^iu fc k ^ - & -C .ut:rjAa ______DATE ------MAIN tUf MNCftAL (QOIOMITC coi»o>nioN CftVSTAL s i n t (INCt. pofiosiro

Pfrmssl cJ*sf

C o d * c f S tyS> C.h'tS f«'h'-z,€ cl.

oa ■pM/it CPUtri-itMces'1- Ctfc\ piylrfes?) T&fufe AtxvmT b* peforw/

Orcfan

■V^- OOQoCCOOO < / / / / / Co Os. 8 CoK&r\ -A» ,->CCOOOQ5000 * CXCOQ3C00O fl .' cooaxcacO "7 I. ccooooaooc •v -

5f 'v”“ br>t» ( j ■ ‘ x— c«^bbbbO SD |<-’ I « ctbfctb^ Ef * f W r f e 1txh«n>J- It Tbs^IaHbll»l>bDyA- — vv -x __m!5®2^5^' SD |s«4^ EfclWft. I Plate 1-13

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. weu. _ _Ui.Ca.fea ------county *T A T E------LODGED BY &-C**CTGin------DATE STRATIORAPHIC INTERVAL ZCutiJae. afuiN »w FCftlLI 1DOLOWTI CflVITAL ttZIl

Missinp Core

bUtO

Core urate* CirvA yUrViblcA pafc-es rM.'ss.'ng

Milie JoUi .Ibklkbo-- £Ai5SL04_

ttU tU o o ^xsoxgc- ,U<>...... A iu ib io ffarjgraurvd ■ F*-3 6oul^ "Surf.' *“ tfwr^nxinei

btU SKi tta, , trcs-'"-"- -1 II

Ufetioiteuu*-'-! P

66-a0- *1 f w - M&o* *

^iuU /o°°-\ P t

Plate 1-14

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WELL _ _ Jr* _ COUNTY - Q g a V A - L g - ______LOQQEOBV . 8TRATIQRAPHIC INTERVAL _ _

Plate 1-15

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. •TATI ______WELL _3I Haft COUNTY _<5§€rtlA.^ ------ETBATIORAPHIC INTERVAL ------LOOgtOBY — - DATE _SLlJt ------

(MAIN tun MNCRAL [OOtOMfTC COMPOSITION CflVSTAL M W IINCL. p o r o s it y ) ; 5 . : s r III! liL.I

-AliUJNMCwk

itttttoo crtotu XbtUco MS

W>t>kb<>° jfefeWCO

Jhbooo sfafe Lbbbooo 'm & h -v*" ^ ’LLUiflO 'JLyx&Xr

Law®---

v*- __ JJyidhCCi ^CtfWC fCCOCO T !| CtiOD O _ ptb0®*. ZtfLffc it* ,k>o- ~ \p O O O O o • • pOpOCV 'fiilOOCQ ■JgOOOCO p lb & V f doOooo boo

Plate 1-16

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. COUNTY _ STATE ______WELL s J U - l & z . , ______LODGED BY (^1 .. _ DATE STAATIORAPHIC INTERVAL gc>#z/S. C t roiuu MMRtt COtWOtlTION IIMCL. » O fto irrr>

A* 2

Plate 1-17

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W ELL - — COWNTY _ , ------s t a t e ------STRATIQRAPHIC INTERVAL . lo ao eo av J3+ C't\&?VA- — p*te F O IS Ill (WAIN t i l l MMinia IPO .O W T I c o k » o t i n o N CMCTM. tlZ tt IINCL. POftOttTYI ^ W vo;

^ '■55 3 Cm.

-/--Ju.' .. /L Z - k a

f)*€ fyaf LQ*>t*er*. CG6G0 * »• • * p?

= -

Plate 1-18

Reproduced with permission of the copyright owner Further reproduction prohibited without permission. ______«TA TE _ WELL _7L - - STRATKWAPHIC INTERVAL JL2tut\sLe£- LOGGED BV _ 'Bi_£

M■ -d

CfeCOO* *

£ DO • &<*> bSfw-

CjlVrtJ kla^tCe/ledl t,fco^«t4-3a"*

jMt'SV/ig 6d(2

6fcfe66oc !& g c?o ■^sJoiM^00' LULlP

Plate 1-19

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. C O U N TY _ - - r ------»T*T«------WELL

STRATIQRAPHIC INTERVAL _L^M JA cleji ______LOOPED BY _(3,-C-M ffrat.lA'... _ OATE

n imucruMii

* "p

" ° * J ' ’MJoUoOO" ttr

IbUc fc^66s- SSSE&So

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yjco \SV0bQo(& zcbbUrb®

fetb^fc^o

'iMdd>U=",

'$'£Qjobbb°‘

z£ $ ot j

Plate 1-20

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WELL COUNTS OATE STRATIQRAPHIC INTERVAL

OjrC

Plate 1-21

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. COUNTY STATE _ _ w e u _

STRATIQRAPHIC INTERVAL _ LOQOEOST T3-(LUnjQZ*- --•■-■ — ------l» — 11 I I l « « /« ..« I. , , CUMIN X H FOWL* (OotoMirc -3-r 'a J| $ v." CWTtTEO. t l t t l vjo3,‘S'w IOCS'S1^ Itff

y/// 4 ihsi

m y flrsstyy ’

4 -

Plate 1-22

Reproduced with permission of the copyright owner. Further reproduction prohibited without permissioh. _ 3 JWELL C OUNTY Q ^ t j * 6 A l A J — _ STATE _ STRATIQRAPHIC INTERVAL LOQQEO BY 25. - DATE

MINFIUI COMPOSITION (INC*. McfeS> ponosini $T? I : S ; 55EESS

ODOOOO' ' ' eoooao *<50000

be boys ?L

M UlUbgoo ILiihbDP U DO' ’ ttll|°oon t-1

clat^tLy

4 ^ s-g** (.SllgkrL dX0c ^ o i ‘jiifti

L j-r -l ^ ^ s s ir A S f as*r -*»-»••« •00* I

Plate 1-23

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WELL _ i x i . ^ 3 ------. COUNTY *iJ ------•TKATIORAPHIC INTERVAL _ _ LOCOED BY S . C s U rtO llA ------DATE

MNCKAi comounot* CMtTAL SUI) (IN CL. .rOMOMTT)

e ■ * tJu/vycua or B'occa-Her

a» o « o .. 9»OMI • JvoC'fui''S ? ft**, iaflfe L**V>\4f lo/iS 4/Mors 1

lCtAuc*

TV.T-'nf-1 52&- q.Iom*5 ■C^.’Kti MUo- HU

Uj ibit>£ ill>Uito ^UOfao

Plate 1-24

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WELL COUNTY *T A T * ------STRATIQRAPHIC INTERVAL ------______LOOOfD BV - d a t e ------

o j u j n k z i mmnti (Datoam- CQMFCSJTTOM •4 1. E {mo. CftYfTM.*XI) M t i s s n PMOtirv) ;s.:::: ? 3-i I I 1. . . . . -i c* £z g & & -■

t b t l Z o P a*‘nj cLUULo- ULVcO"- 4AUW** M U U o - UUlioo / x *d| UiL Llri UUU°--' x x ^ .gHD&RhZ. 'M U & o * >;x \> J * z .

MULL o' Xtop G»/*3 £ . < m x Elites ft/\* 3 (Vow. s - X X y ULLULo LLLlULL0 ’,U&LILo m t s j w ? U M o X UM Ml, pttcro* -V_ >U>AU X y ubt&to ■/ 'V / y - 3D r a ' / ' y . 'Z -io te y fflx •? XX ~rH, / "■"V UUL- , X ✓ A \ i h r * ^SD m r X Z&O- r 3 Vj* j* klfetio / < k -- _^li(>oo *6 U U U ° ' / i ILlUUo • ' / UL X 2-675= « s * f IUWjOO m u loo v0*?r"i“ ilJ>LLLoo c v/V P ! SD - - i».rUiUUo ib U U 'w Sf E E is.'V f !i J ,' y y “ “ t t t y ' y ' / ZUO ffiS - /.... ' ...05 i

Plate 1-25

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission WELL j& rtC O U N T Y STATE ------

ETRATlaBAPHIC INTERVAL J _ J t ^ c L e ^ _ L O G G E D BV _ £ 5 | _ C - J U 5 l a £ V------OATE ------

looiotfiri

U M U fo Ih /ka ieL dtrstlrtS

4-M-

4-4- r - |- 1 - T-f-j--

Plate 1-26

Reproduced with permission of the copyright owner Further reproduction prohibited without permission. weu JBocbvy W*l COUNTY _ ^ g j n a c M l ------tTATK

STRATIQRAPHIC INTERVAL ______£ < W / C SQ g f/L p ! & tU £ £ - ^ I A & LOQOEO ST — r 3 —C> {*■ & jc x y ^ r ~ — O A T S ------— - ~ ** ' * i -.. - | | — f . ' ■ i~ T~ M A M ttn fOOtOMTT*- CftYITM U Z t) 5 = .*a':s I I I I-1,1-1

J S—»fcP»iwyl .

m -

v.r*K. mm/v* J« r>oK5

wmm ■w w

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of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission «nx JBucki.Atf haM- ~ y ~~, COUNTY C * j r e / t ¥ U d______*TATI ------LOQQCD IT OATC anuTKuupHic int £ rv a l _ X)xuAcL£e. QAAMtttXft [D O c o ttm - carrm »r»? m j ;9.!S33 u ccOiv5 \? "uywttyvm ECw- L±J m ■Wi/ P«£.S f« J-bP

•tieLLiitttfi

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ftUUifa 'iU W X rr UJJA

»3c£rf -SyV PiU.HU

UilLv .WVI

UUW> u u u C1BQ0 ULk&L*- oUtrS.'acA

Plate 1-28

Reproduced with permission of the copyright owned Further reproduction prohibited without permission tTATt WELL _ C O U N TY J ^ i -

STRATIQRAPHIC INTERVAL _ . 'D M c l ^ ______L O O O tD B Y J 3 > L±U {fa.t\- ° * T t

coi^otirioNimcu AJottsS POftOUnri

bibbU^bbO-' r U t t 0 yLlUitik ouef s ‘-ze

lILUJ>o ■

" « v r '3

Plate 1-29

Reproduced with permission of the copyright owner Further reproduction prohibited without permission. COUNTY C x u y & u ^ - WELL \ — I— DATE 8TRATI0 RAPHIC INTERVAL _ J ^ U P l A s ^ - LOQQCD BY

Plate 1-30

Reproduced with permission of the copyright owner Further reproduction prohibited without permission. w eu._ls.i3f , , county - Q g & / X A l J ------STATE____ «m*nnnAowir interval Jc / ? 5 Q M*"V L LOQQCOaY wiNinw. (UUM VU coM^oiirioN tf j (POiOMirv M o res (met. | I cnriTALtim : i AOMOtinri 8*! 8 5

firj'.'t.wia.rzd fcpcds

•^m rWik'tai find U 1d ti> <- 7%>s h * C*S*5-

0oO I poow OOf f?»e ro»

i* i ” ...... v ^ V^fyfekkU LL vw ^ I Co^c3pi9^rH iV«

5o*c *V3Sl^ ■ ,

Laj |^ ^ |^ '''.‘”'l'v! f t iUU.tiir.; JUjbb^t ktt * 'iob^knTf'A f / Cbfa

Plate 1-31

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. COUNTY stats WELL d .& m o ------OATE ______STRATIQRAPHIC INTERVAL jGW LOQOEOBY ! S . ‘C ___ IOIU1 M NIRA1 (OOlOM tTI COMPOtlTlOH CNViTAL t t n i (INCL. POMOtlTY)

Ubbbtbo (jUib^aC

vvh tlUlU,* Ubtibf

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bbl

r M

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, Uabbw^Cr • PB? diM M fi00 ^bbhihpfaC

E t e

Plate 1-32

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ______STATE WELL STRATIQRAPHIC INTERVAL LOQOEO BY FOISItl

-* cS O j S?-i Q 5<1 v!*w- Sit,m ^ 5 S s .<= f 3 -3 s s R, s 1~xi = ^ M tC '~ .n .T-? h r-W S ::

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t a . .

lUklobb^lj^ XtfduceX i Prcxdof'C bVWf''0 UbtaUo I boo CUUit* ;tbfctW.«o iifcttttoo Uoo bOO

‘E/iivC ? & M\>U»

■ f-> t;asiw ij

iM W ^ 0 MUU*>o

*-v** kll«^ i*/1 SoJjLle, kelo .' a /i< i •PletM'irc*

,Ufet>£»*

fiUUL

■ y f

Plate 1-33

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WELL COUNTY - ° § * 4 STRATIQRAPHIC INTERVAL V^tQJ/L. (oocouiriQAAIN 11X1 CHVITAL UZI!

Bn ^1S SfMl jt/K'cwU^

oDfr-3«.r{?0C

l\Li)6bblfO bikiifaO''

yiuofibz- ypfe cmim*

*l£oUn hi AiWli £kkU-fcJ jJCsfods £ntr*$ft*y ^•CM^dO' I Wj tiooo v»5 Ss&tefZy,/^

v'JL !-'" ...66 itOuS'VJ- ‘jokl/^&d*»;li > • L “ S i m t

t/wusA'*/

Z£?/'b>Z7QOft Cotti.'pfe o P , c«ft,/s and Sfra* r 3t(MUed rtuJr.'x of 5"^ f ; osWcbd^s JAitW- Siia|e^

j A h u tc J - st^k'f <-t)

G>fi * 1,'fkt , Cfljim Os\o<~ Coal'd; zeifj

fB'c/i^st' in s e r t, 3 SU)« y

Plate 1-34

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. COUNTY J _ _ ------»t*t* DATE STRATIQRAPHIC INTERVAL LOQOEO7 BY B jG u i& tn _ _

SE>

Plate 1-35

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WBLL COUNTV . . C ' ^ i A l / O . y r ------STRATIQRAPHIC INTERVAL ~D/AlAd£&- Loooto a r O , C ^ s J / Q t

tTM UCTUAft I ! H eh = S

SOHt "3'oTuro.

/tf

2i»recuS t-W / S D * r s»-< B ^ sa p r n A '. t'oM'fc hjc*y\

««w- - tW/VW /ivd GSD l/C •*(<:'a "i f;M ^/SI)

^UjbU>0 ; ,CTTfQ/ LfifC !

UUUU-jl OlUH W oUj *>

Plate 1-36

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. w eu C o > te * " £ ) COUNTY »T A T E------STRATIGflAPHIC INTERVAL ______LOGGED BY O A T t------

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Plate 1-37

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WELL COUNTY _ _ _ _ *T A T « ------STRATIGRAPHfC INTERVAL LOGQEO BY I&--C.U//TZ14 - - DATE______F O IIIL l UIN C RU 13*- fcS 9? 55 (IMCk POftOsirY) JM ^

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~~Plate 1-38~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BIBLIOGRAPHY~~

~~Badiozamani, K., 1973, The dorag dolomitization m odel-application to Middle Ordovician of Wisconsin: Journal of Sedimentary Petrology, v. 43, p. 965- 984.~~

~~Ball, M. M., 1967, Carbonate sand bodies of Florida and the Bahamas: Journal of Sedimentary Petrology, v. 37, p. 556-591.~~

~~Bassett, C. F., 1935, Stratigraphy and paleontology of the Dundee Limestone of southeastern Michigan: Geological Society of America Bulletin, v. 46, p. 425-462.~~

~~Bathurst, R. G. C., 1975, Carbonate Sediments and Their Diagenesis: Developments in Sedimentology, v. 12, Elsevier, New York, 658 p.~~

~~Bebout, D. G., and Loucks, R. G., 1984, Handbook for Logging Carbonate Rocks: Bureau of Economic Geology, Austin, Texas, 43 p.~~

~~Bloomer, A. T., 1969, A regional study of the Middle Devonian Dundee Dolomites in the Michigan basin: Unpublished Master’s thesis, Michigan State University, East Lansing, 67 p.~~

Bultynck, P. L., 1976, Comparative study of Middle Devonian conodonts from north Michigan (USA) and the Ardennes (Belgium-France), in Conodont Paleoecology: Geologic Association of Canada, Special Paper no. 15, p. 119-141.

~~Catacosinos, P. A., 1973, Cambrian lithostratigraphy of Michigan basin: American Association of Petroleum Geologists Bulletin, v. 57, p. 2404- 2418.~~

~~Catacosinos, P. A., 1981, Origin and stratigraphic assessment of pre-Mt Simon elastics (Precambrian) of Michigan basin: American Association of Petroleum Geologists Bulletin, v. 65, p. 1617-1620.~~

Cercone, K. R., and Lohmann, K. C., 1987, Late burial diagenesis of Niagaran (Middle Silurian) pinnacle reefs in Michigan Basin: American Association of Petroleum Geologists Bulletin, v. 71, p. 156-166.

~~154~~

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cohee, G. V., and Underwood, K. K., 1945, Lithology and thickness of the Dundee Formation and the Rogers City Limestone in the Michigan Basin: U. S. Geological Survey Oil and Gas Investigations Preliminary Map 38.

~~Craig, H., 1957, Isotopic standards for carbon and oxygen and correction factors for mass spectrometric analysis of carbon dioxide: Geochim. Cosmochim. Acta, v. 12, p. 133-140.~~

~~Dickson, J. A. D., 1966, Carbonate identification and genesis as revealed by staining: Journal of Sedimentary Petrology, v. 36, p. 491-505.~~

~~Ehlers, G. M., and Radabaugh, R. E., 1938, The Rogers City Limestone, a new Middle Devonian formation in Michigan: Academy of Sciences, Arts, and Letters, Paper 23, p. 441-446.~~

Fisher, J. H., Barratt, M. W., Droste, J. B., and Shaver, R. H., 1988, Michigan basin, in Sloss, L. L. (ed.), Sedimentary cover—North American craton, U.S.: Geological Society of America, Decade of North American Geology, v. D-2.

~~Gardner, W. C., 1974, Middle Devonian stratigraphy and depositional environment in the Michigan Basin: Michigan Basin Geological Society, Special Papers no.l, p. 43-48.~~

Hinze, W. J., Kellogg, R. L„ and O’Hara, N. W., 1975, Geophysical studies of basement geology of Southern Peninsula of Michigan: American Association of Petroleum Geologists Bulletin, v. 59, p. 1562-1584.

~~Hurley N. F., and Lohmann, K. C., 1989, Diagenesis of Devonian reefal carbonates in the Oscar Range, Canning Basin, Western Australia: Journal of Sedimentary Petrology, v. 59, p. 127-146.~~

~~Johnson, J. G., Klapper, G., and Sandberg, C. A., 1985, Devonian eustatic fluctuations in Euramerica: Geological Society of America Bulletin, v. 96, p. 567-587.~~

~~Knapp, T.S., 1947, A theory of Rogers City and Dundee Relationships in central Michigan: unpublished report~~

~~Lane, A. C., 1895, The geology of lower Michigan with reference to deep borings: Michigan Geologic Survey Report, v. 5, p. 25-26.~~

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Lilienthal, R. T., 1978, Stratigraphic cross-sections of the Michigan Basin: Michigan Geologic Survey Division, Report of Investigations no. 19, Lansing, Michigan, 27 p.

Lintemuth, R., 1989, Ogemaw County continues to make mark among busiest oil, gas exploration areas; Amherstburg, PdC join list, is Antrim next?: Michigan’s Oil and Gas News, v. 95, no. 21, p. 24-26, 33, and 60.

Michigan Department of Natural Resources, 1989, Michigan’s oil and gas fields 1985 and 1986: Oil and Gas Statistical Summary 84, State of Michigan Department of Natural Resources, Geological Survey Division, East Lansing.

~~Montgomery, E. L., 1986, Facies development and porosity relationships in the Dundee Limestone of Gladwin County, Michigan: Unpublished Master’s thesis, Western Michigan University, Kalamazoo, 82 p.~~

~~Naylor, M. A., Mandl, G., and Sijpesteijn, C. H. KL, 1986, Fault geometries in basement-induced wrench faulting under different initial stress states: Journal of Structural Geology, v. 8, p. 737-752.~~

~~Nelson, R. A., 1981, Significance of fracture sets associated with stylolite zones: American Association Petroleum Geologists Bulletin, v. 65, p. 2417- 2425.~~

~~Newman, E. A., 1936, Geology of Ogemaw County and West Branch oil field: State of Michigan Progress Report no. 2.~~

~~Orr, R. W., 1971, Conodonts from Middle Devonian strata of the Michigan basin: Indiana Department of Natural Resources, Geologic Survey, Bulletin 45, 125 p.~~

Park, S. G., 1987, Deposition, diagenesis, and porosity development of the Middle Devonian Lucas Formation in West Branch Oil Field, Ogemaw County, Michigan: Unpublished Master’s thesis, Western Michigan University, Kalamazoo, 102 p.

Popp, B. N., Anderson, T. F., and Sandberg, P. A., 1986, Textural, elemental, and isotopic variations among constituents in Middle Devonian limestones, North America: Journal of Sedimentary Petrology, v. 56, p. 715-728.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Prouty, C. E., 1989a, Trenton exploration and wrenching tectonics-Michigan basin and environs, in Keith, B. D. (ed.), The Trenton Group (Upper Ordovician Series) of Eastern North America: American Association of Petroleum Geologists Studies in Geology, no. 29, p. 207-236.

Prouty, C. E., 1989b, Shearing mechanics and reservoir rock development in producing linear structures-Michigan basin (abs.): Michigan Geological Survey Symposium, Michigan: Its Geology and Geologic Resources, Program and Abstracts, p. 20-21.

~~Radke, B. M., and Mathis, R. L., 1980, On the formation and occurrence of saddle dolomite: Journal of Sedimentary Petrology, v. 50, p. 1149-1168.~~

~~Raven, M. J., and Dickson, J. A. D., 1989, Fir-tree zoning: an indicator of pulsed crystallization in calcite cement crystals: Sedimentary Geology, v. 65, p. 249-260.~~

~~Rickard, L. V., 1984, Correlation of the subsurface Lower and Middle Devonian of the Lake Erie region: Geological Society of America Bulletin, v. 95, p. 814-828.~~

~~Sanford, B. V., 1967, Devonian of Ontario and Michigan, in International Symposium on the Devonian System: Alberta Society of Petroleum Geologists, v. II, p. 973-999.~~

~~Schlager, W., 1981, The paradox of drowned reefs and carbonate platforms: Geological Society of America Bulletin, v. 92, p. 197-211.~~

Scotese, C. R., 1984, Paleozoic paleomagnstism and the assembly of Pangea, in Van der Voo, R., Scotese, C. R., and Bonhommet, N., eds., Paleozoic paleomagnetism: American Geophysical Union Geodynamic Series, vol. 12, p. 1-10.

Shinn, E. A., 1983, Tidal flat environment, in Scholle, P. A., Bebout, D. G., and Me ore, C., H. (eds.), Carbonate Depositional Environments: American Association of Petroleum Geologists Memoir 33, p. 171-210.

~~Shinn, E. A., and Robbin, D. M., 1983, Mechanical and chemical compaction in fine-grained shallow-water limestones: Journal of Sedimentary Petrology, v. 53, p. 595-618.~~

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 158 Ten Have, E. L., 1979, Relationship of dolomite/limestone ratios to the structure and producing zones of the West Branch oil field, Ogemaw County, Michigan: Unpublished Master’s thesis, Michigan State University, East Lansing, 100 p.

Versical, R. T., 1989, Calcite strain analysis in relation to the origin of structural trends in Paleozoic rocks of the Michigan basin (abs): Geologic Society of America Abstracts with Programs, v. 21, no. 6, p. 367.

Versical, R. T., 1990, Tulip structures in Michigan? A new look at the origin and structural styles of some Michigan basin oil and gas fields (abs.): American Association of Petroleum Geologists Bulletin, v. 74, p. 1311.

~~Vugrinovich, R. G., and Matzkanin, A. D., 1981, West Branch field Dundee oil pool: Department of Natural Resources Geological Survey Division Secondary Recovery Report no. 8, Lansing Michigan, 13 p.~~

Watts, N. L., 1983, Microffactures in chalks of Albuskjell field, Norwegian sector, North Sea: possible origin and distribution: American Association of Petroleum Geologists Bulletin, v. 67, no. 2, p. 201-234.

~~Wilson, J. L., 1975, Carbonate Facies in Geologic History: Springer-Verlag, New York, 471 p.~~

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~~Oversize maps and charts are filmed in sections in the following manner:~~

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~~copies and is inserted into the inside of the back cover.~~

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~~2 RXO/RT -0.5 R (ILS) w • m •0.05 AP 0.45 0 GR 150 R(ILM) i2-m s...cat..is 30_" JO . JW CNSI. _0 _ J O ♦ R(lLD)ft-m jooo 20 Q . GR. -130 2 p«] 3~~

* 2600

~~b q i i q a CORE~~

~~^CAL~~

~~ucnoM Iffir~~

~~10LOG~~

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission GENERALIZED CORE DESCRIPTION DOLOMITIZED MUDSTONE - Fair to poor InlorcrvatalUno poroaltv and pormooblllly. Contnlns ------. a low diversity of fossil typos. Very correlative In all field cross sections (Plates 111-1 through ill-5).

______- Fair to good Interparticle porosity and pormoablllty. Contains many coarsening upwartf homlcycles. Bases ot these hemlcyclos are usually low porosity, polold-rlch packstones. Better sorted, coarser grained skeletal packstones and gralnstonos with good Inlorpartlcle porosity aro common near the top of the hemlcycles. A wide range ot fossil types are represented, although medium grained crinold ossicles aro the most common grain type. Most skolotal grains show signs of abrasion and many show signs of early marine cementation. This is the most common llthotype observed In the cores examined In this study.

~~2 8 1 0~~

SKELETAL-PELOIPAL GRAINSTONE - These sediments aro very similar to those above. The top oI this unit is marked by a skelstal-peloldal gralnstone about 7 feet thick with good Interparticle porosity and permeability. This gralnstono Is correlative In wells A-4 through A-9 (Cross Section A-A", Plate llf-1).

______Very good interparticle porosity and permeability. Coarse grained crinold ossicles are the dominant grain type present. Crinold and other skeletal grains present do not show signs of abrasion or early marlnB cementation. This unit thickens to tho NW and thins to tho SE and is correlative In wells A-1 through A-20 (Cross Section A-A", Plates 111-1 and ill-2).

~~SKELETAL y/ACKESTONE TO PACKSTONE - Dark, micrlte-rich limestone. Very tight.~~

KEY RESERVOIR GEOLOGY OF THE DUNDEE LIMESTONE, TEXTURE LITHOLQGY m w p a WEST BRANCH FIELD, MICHIGAN DOLOMITE ______by Brendan C. Curran ______LIMESTONE “CHERTY LIMESTONE Operator: Marathon Oil Company Well Name: Heintz #9 COAJWEHHaf/' fttSTFICTED UPWARD / UPWARD UEUlCYCLE County: Ogemaw ri c m ic v c u Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UJ -0.03_AP_0.45 R(ILM |n-m “ 1 _?L_C5jGNS)__o_ JO n (IL D )n -m 2_____ ftp) 3

~~BQTIQ i CORE~~

~~OEEF INC UCT10M~~

~~LATE TOLOG'~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.1 0.01 0.1 0.01~~

GENERALIZED CORE DESCRIPTION PgUQMillZSB-MUCSIOME • Fair to poor Intercrystalllno porosity ond pormoabltlly. Contains 2760 ------a tovi dlvorslty ot tossll types. Very corrolatlvo In alt field cross sections (Plates lll-t through 111-5).

______- Fair to good Intorpartlclo porosity and permeability. Contains many coarsening upward homlcyclos. Bases of these 2790 homlcyclos aro usually low porosity, polold-rlch packstones. Better sorted, coarser grained skeletal packstones and gralnstonos with good Intorpartlclo porosity are common near the top of Ihe homlcyclos. A wide range of fossil types are represented, although medium gralnod crinold ossicles are tho most common grain type. Most skolotol groins show signs of abrasion and muny show signs of early marine 2800 cementation, This Is the most common lilhotypo observod in tho cores examined In this study.

~~2010~~

2620 SKELETAL-PELOID AL GRAINSTONE These sediments aro very similar to those above. The top of this unit Is marked by a skeletal-peloldal. .gralnstone . . gra|nstonB about a(j0ut 7 feet 7 f o o t thick with good Interpartlcle porosity and permeability. This gralnstone Is correlative in wells A-4 through A-9 (Cross Socllon A-A", Plate 111-1). 2830

~~2840~~

~~2850~~

2860 ______Vory good Interpartlcle porosity and permeability. Coarse grained crinold ossicles are tho dominant grain typo present. Crinold and other skeletal grains present do not show signs of abrasion or oarly marine cementation. This unit thickens to tho NW and thins to the SE and Is correlative in wells A-1 thro u g h A-20 (C ross Soction A-A", P la te s 111-1 a n d 111-2). 2870

~~, - Dark, mlcrlte-rlch limestone. Very tight.~~

RESERVOIR GEOLOGY KEY OF THE DUNDEE LIMESTONE, TEXTURE UTHOIOGV M W P G WEST BRANCH FIELD, MICHIGAN / 1 ~ DOLOMITE ______by Brendan C. Curran ______LIMESTONE “CHERTY W LIMESTONE Operator: Marathon Oil Company Well Name: Heintz #9 COMCEHWaf?I resmCTSD r IIPWAAD / upwaao HEMicrac hem cy a n County: Ogemaw Location: Sec. 24-T22N-R2E Permit No.: 38054 Plate 11-1

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE:~~

~~Oversize maps and charts are filmed in sections in the following manner:~~

~~LEFT TO RIGHT, TOP TO BOTTOM, WITH SMALL OVERLAPS~~

~~The following map or chart has been refilmed in its entirety at the end of this dissertation~~

~~(not available on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover.~~

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~~CAl (INI LLS jOHMM) _LLp_(OHM_MJ_~~

~~POROSITY~~

~~—* , 1 ■ VI'"" ” jfi< ’ ■ ■ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission k 90 So /Sw oS 1 0.1 O.Q1:10 1 0.1 0,01 o~~

~~GENERALIZED CORE DESCRIPTION~~

...... I • Skeletal-poloidal packstono. Very tight with a thin zono with fair Interparticle porosity and permeability. From logs and limited core coverage, the top of this unit appears to have the best reservoir properties In the Rogers City 2 6 2 0 - Limestone. Porosity distribution appears irregular In core and may be secondary due to leaching. Skeletal grains are dominated by poorly sorted crinold ossicles to <0.5mm).

~~2630~~

~~BOTTOM CORE 1~~

DOLOMITIZED MUDSTONE - Fair to poor Intercrystalline porosity and permeability. Contains a low diversity of fossil typos. This unit marks the topof the Dundee and Is very correlative In all field cross sections (Plates HT-t through IK-5). ______

PELOIDAL-SKELETAL PftCKSTONE - Poor to fair interpartlcle porosity nnd permeability. Those sedimonts aro dominated by pelolds and generally contain o low amount of skeletal material. A wide diversity ot fossil types are represented. Tho best porosity and permeability occurs at the top of coarsening upward hemlcyclos where coarser-grained, better sorted skeletal packstones and grainstones are present.

~~2710 -~~

PFIOIDAL-SKELETAL GRAINSTONE • Fair to good Interpartlcle porosity and permeability. The tops of hemlcycles In this unit are represented by grainstones made up ot fine-grained pelolds and a limited amount of skeletal material. Tills unit Is part of a porosity zone correlative in wells A-4 to A-9 (Cross Section A-A'", Plato III- 1 ). SKEl-U I AC'-VEfimPAL GRAIRmoNfc - uooa interpartlcle porosity ano pormeannnV. Skeletal material Is dominated by medium grained crinold ossicles and abraded brachiopod tragmonts. This unit Is corrolatlve In wells A-6 to A-14 (Ctose Section A- BOTTOM A'". Plate lll-fi------CORE 2

~~TEXTURE j y F LITHQLQGY DOLOMITE LIMESTONE CHERTY LIMESTONE~~

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 r , ,*rfc* >«BfBWH5OT^VW>t«B5sP*.- iSlSaSSH...... _ . . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ZED MUDSTONE - Fair to poor intercrystalllns porosity and permeability, contains a low diversity of fossil types. This unit marks the top ol the Dundee and Is very correlative In all lleld cross sections (Plates HT-1 through r o - 5 ) . ______

PELOIDAL-SKELETAL PACKSTONE - Poor to fair Intorparllclo porosity and permeability. Theso sediments are domlnatod by pelolds and generally contain a low amount of sknlotcl material. A wide diversity of fossil types are represented. Tho beat porosity and permeability occurs at tho top of coarsening upward homlcycles where coarser-grained, better sorted skeletal pacltslones and grainstones are present.

PELOIDAL-SKELETAL GRAINSTONE • Fair to good Interpartlcle porosity and permeability. The tops of hemlcycles In this unit are represented by grainstones mado up of fine-grained pelolds and a limited amount of skeletal material. This unit Is part of a porosity zone correlative in wells A-4 to A-9 (Cross Section A-A‘", Pli.o lu l l .

bKfcLEi Al- h e l u iu a l GHAtws Ilittfc - utioo inierpamciB porosity anb pormcSbnliv. Skeletal material Is dominated by medium grained crinold ossicles and abraded brachiopod fragmonts. This unit Is correlative In wells A-6 to A-14 (Cross Section A- BOTTOM A '". P late 111-1).______CORE 2

~~KEY W& u a q t o a y . DOLOMITE LIMESTONE ' CHERTY . LIMESTONE~~

~~COARSEMNO I / RESTWCTED UPWARD I UPWARD I HEM ICYCU / HEMICYOE~~

~~RESERVOIR GEOLOGY OF THE DUNDEE LIMESTONE, WEST BRANCH FIELD, MICHIGAN by Brendan C. Curran~~

~~Operator: Marathon Oil Company Well Name' Donovan #6 County: Ogemaw Location: Sec. 19-T22N-R2E Permit No. 40484~~

~~Plate H-2~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. L'j~~

~~PLEASE NOTE:~~

~~Oversize maps and charts are filmed in sections in the following manner:~~

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______Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ♦0.05 4P 0.45 POROSITY k90

~~0 0 PEF 10.0 TENS (LO) 500 PO) GR ■120 30 150~~

~~100 10 0.1 0 .01*1010 2700~~

~~2750~~

~~GAMUt\ RAT 2600 BOTTOM CORE~~

~~CAL~~

~~SFL~~

~~MEDIUM INDUCTION~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. It90 So / Sw~~

~~o 1 0.1 0.0110 1 0.1 0.01 (J I !~~

GENERALIZED CORE DESCRIPTION RQGERS C1TY ZONE 1 - Dark, nodular mlcritic limestone. Vary tight. DQLOMITIZED MUDSTONE « Very poor Intorcrystollinp porosity and permeability. Contains a low diversity of fossil typos. Capped by a pyritizod hurdgruund that marks the top of tho Dundee Limestone. This unit is very correlative in all field cross s e c tio n s (P lates UI-1 th ro u g h tii-5).______

E5LQJPAIi“SKEI-..^TAii—PACKSTONE - Poor Interpartlcle porosity and permeability. Coro permeabilities aro very high due to numerous small-scale fracture sets associated with styloiites. Coarsening upward hemlcyclos are Incomplete and are dominated by poorly sorted, peloid and mlcrlte-rich packstones. Many fossil types are a p re s e n t. r 2740

SKELETAL-PELOIDAL GR A INSTONE - A higher energy zone with fair to good interparticle porosity and permeability. Medium-grained crinold ossicles and abraded brachlopod fragments are the most common skeletal grains. This unit is correlative in wells A-6 to A-14 (Cross Section A-A', Plate 111-1).

______PELOIPAL-SKELE1AL PACKSTONE - Poor to good Interpartlcle porosity and permeability. Contains a wide range of fauna. Porosity distribution is largely controlled by coarsening upward hcmicycles (poor near the base, fair to good near the top). This unit is an example of tho most common lithotype observed in tho cores examined in this study.

CRINOID ORAINSTONE - Good Interpartlcle porosity and permeability, well-sorted, coarse-grained crinold ossicles are the dominant allochem typo. This unit is nan of o porosity zone that can bo correlated between walls A-1 and A-19 (cross sec tio n A-A", P la te s ill-1 and III-2). B etw een this well a n d the E stey E-8 (A-10 and A-18 on tho cross section A-A”), this unit becomes finer grained, more cyclic, and less porous and permeable.

~~KEY TEXTURE UTHOLQGY M W P G 7 DOLOMITE LIMESTONE CHERTY LIMESTONE~~

~~■ COARSEMMG RESTHCTED W UPWARD UPWARO S HEMCYCU 7HEMGrCU~~

~~RESERVOIR GEOLOGY OF THE DUNDEE LIMESTONE, WEST BRANCH FIELD, MICHIGAN by Brendan C. Curran~~

~~Operator: Marathon Oil Company Well Name Cox #2 County: Ogemaw Location: Sec. 20-T22N-R2E Permit No. : 37325 Plate 11-3~~

~~m. *------—^ — .—...... Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE:~~

~~Oversize maps and charts are filmed in sections in the following manner:~~

~~LEFT TO RIG HT, TOP TO BOTTOM , W ITH SM ALL OVERLAPS~~

~~The following map or chart has been refilmed in its entirety at the end of this dissertation~~

~~(not available on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover.~~

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I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IHHHB Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DEEP INDUCTION LOG

~~— sm u m .— MEDUIM INDUCTION LOG GAMMA RAY NEUTRON POROSITY 150 (PLUG) POROSITY (PLUG) k CALIPER LATEROLOG~~

~~-2650~~

~~2700~~

~~DEEP INDICTION~~

~~BOTTOM CORE~~

~~(SNP)~~

~~EROLO~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. •a(PLUG) k So / sw~~

~~0.1 0.01 0 1 . 0.01~~

GENERALIZED CORE DESCRIPTION ______Fair IntoreryatBlllne porosity end poor pormeoblllty. Contains a low diversity of fossil typos. Streaks of unaltered lime mudstone are Interbedded with dolomite. Some small-scale fractures are prosont, creeling local permeability highs. This unit is prosont at the top of the Dundee and Is very correlative In all flold cross sections.

______Poor Intorportlclo porosity and pormoablllty. Small tidCturs sr.ts are prosont associated with stylolltos, creating local pormoablllty hlgh3. Contains tho okolotai grains of many f03sll typos and some fine-grained pololds. Soma chort nodulos nro also prosont. Tills unit 13 vary correlative In tho SE and thlcltono toward tho contor of tho field (correlative In wollo A-12 to A-34, B-3 to B- 12, end C-1 to C-12, crons ooctlons /--A", B-B', and C-C', Pintos 111-1 through llt-5). This unit grados Into loos muddy, more porous pololdal-aliolotal packstonos to tho

~~______,______~~

Thla unit represents tho most common lithotypo obsorved In tha cores oxamlnod In thl3 study and probably accounts for much of tho rosorvolr porosity In this flold. Tho high Intorpartlclo porosity zonos created at tho top of homlcycles are too thin and iatarally variable to bo correlated Individually.

______Fair to good Intorpartlclo porosity and pormoablllty. Contains modlum-gralnod crlnold osslclos, abraded brachlopod fragmonts, and llne-grslnod pololds. This unit Is part of a corrolatlvo porosity zono Idontlflod In wolls A-1 to A-19 and B-1 to B-12 (Cross Sections A-A" and B-B', Platos llf-1, III-2, a n d III-4).

~~SKELETAL WACKE5TQNE - Tight, mlcrlto-rlch llmostono. Contains a wldo diversity of fossil typos.~~

~COA4L-STH W A fgPQ RCTP~ fLOATSTOTCE- Vory good Intra- and Interpartlcle ooronity. Not cnrrolntlvn on cress snrttnna. FENF.STRAL PACKSTONF. - Good fonostral and Intorpartlclo porosity and 2750 pormoablllty. Not Idontlflod In other cores and not corrolatlvo on avallnblo logs.

KEY UIHQlQgy RESERVOIR GEOLOGY M W M OF THE DUNDEE LIMESTONE, DOLOMITE WEST BRANCH FIELD, MICHIGAN LIMESTONE “ C H ER TY by Brendan C. Curran LIMESTONE Operator: Marathon Oil Company COARSEN NO / RESTRICTED UPWARD / UPWARD Well Name HEW (CYCLE U ICW CYCLE Estey E-8 I County: Ogemaw Location: Sec. 28-T22N-R2E Permit No. 32190 Plate II-4

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~~Oversize maps and charts are filmed in sections in the following manner:~~

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SIDEWALL NEUTRON (PLUG) POROSITY tu (PLUG) k S o / Sw . _Qf£P lNBU(}TLQy_ T. POROSITY

~~MEDUJHJNDUCTION_ r . C A LJPERio~~

~~200! 0.1 0.01 0.1 0.01 -10 100 10 0.2 1.0 100 1000 20 10~~

~~- 2700-~~

~~BOTTOM COtTE~~

~~ME DUIM - INDl CTION~~

~~DEEP — INDUCTION~~

~~CAL (SNP)~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLUG) k So/Sw~~

~~______GENERALIZED CORE DESCRIPTION ROGERS CITY ZONE 1 - Dark nodular mlcrlllc llmostono. Vory tight.~~

______- Fair to good Intercrystalllno porosity and poor pormoablllty. Contains a low diversity of fobsll typos. This unit Is vory corrolatlvo In oil field cross soctlons (Platos HI-1 through HT-5). ______c h e r t v SKELETAL WACKESTONE - Poor Intorgranular porosity and pormoablllty. Lorgo chart nodulos aro common. Tho top 4 foot of this unit aro dolomltlzod arid contain fair to good Intcrcrystallino porosity and pormoablllty. This unit Is corrolatlvo In tho SE and thlclions toward tho contor of tho flold. This unit latornlly grndos Into pololdnl-sltolotnl pachslonos to tho NW. Corrolatlvo In wolls A-12 to A-34, B-3 to B- 12. nnd C-1 to C-12 (Cross Soctlons A-A'._B:B'. and C-C. Platos ffl.-2 through M-S). ____ SKELETAL-PELOIDAI- PACKSTOffE - Poor to good Intorpartlclo porosity and pormoablllty. Main skeletal constituents aro modlum-gralnod crlnold osslclos nnd brachlopod shall frngmonts. Bottor porosity and pormoablllty zonoo o c c u r n e a r tho tops of coarsening upward homlcyclos. This unit In corrolatlvo In wolls A-22 to A-34 and C-4 to C-12 (Cross Soctlons A-A" and C-C', Platos m-2, HI-3, and IH-5).

PELOIDAL-SKELETAL PACKSTONE - Tho top 3 foot of this unit oro a mlcrlte-rich packstono/wackostono with vory poor porosity and pormoablllty. This tight zono is corrolatlvo In wolls A-22 to A-34, nnd C-4 to C-12 (Cross Sbctions A-/C and C-C', Plates m-2, m-3, an d HI-5).

Tho rost of this unit is n pololdal-skolatal packstono containing numerous coarsening upward hcmlcyclas with fair to good Intorpartlclo porosity ond pormoablllty. This zono Is largoly undifferentiated in flold cross soctlons. This represents tho most common llthotypo observed In tho coros examined In this study.

~~KEY TEXTUBE L|TH0L0Gy~~

~~DOLOMITE LIMESTONE~~

~~CHERTY ‘ LIM ESTONE~~

~~COARSEHNO RESTRICTED RESERVOIR GEOLOGY UPWARD UPWARD HEMICYOf HEMICY&E OF THE DUNDEE LIMESTONE, fi WEST BRANCH FIELD, MICHIGAN J j by Brendan C. Curran~~

~~Operator: Marathon Oil Company Well Name Doran #5 County: Ogemaw Location: Sec. 27-T22N-R2E Permit No. : 32143 Plate H-5~~

~~— p—• „ \ ' a ' « ■"— Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE:~~

~~Oversize maps and charts are filmed in sections in the following manner:~~

~~LEFT TO RIG HT, TOP TO BO TTO M , W ITH SM ALL OVERLAPS~~

~~The following map or chart has been refilmed in its entirety at the end of this dissertation~~

~~(not available on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover.~~

~~Black and white photographic prints (17" x 23") are available for an additional charge.~~

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~~LATSROLOG~~

~~MEDIUM JNOUCTION.~~

~~DEEP INDUCTION~~

~~100 1000 2.5 2.6 2.0 3.0~~

~~(PLUG) POROSITY (PLUG) k~~

~~loo io 0.1 0.01 2600~~

~~=EP^ INDU :tion~~

~~- 2650 - MEOII INDUCTI~~

~~PTO~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LUa o~~

~~o o~~

~~______GENERALIZED CORE DESCRIPTION 2510- ROGERS CITY ZONE 3 - Dark nodular wackestono. Very light, tow visible skeletal grains. Highly stylolltlzed.~~

~~(core romovod prior to study)~~

ROGERS CITY ZONE 2 - Skeletal wackostono to packstono. The top 8 foot ol this unit Is a packstono with poor to fair Intorpartlcle porosity and permeability (visual 2530 estimate). Tho main skolotal constituents are poorly sortod crlnold osslclos (>20mm to

~~Tho rest of this unit la a vary tight nodular wackostone. 2540 ]~~

~~2550-~~

~~ROGERS CITY ZONE 1 • Dark nodular mlcrltlc limestone. Very tight. The top of t this 2560- unit Is marked by a packstone with very poor porosity that often Is recognizable on well logs.~~

~~2570-~~

~~2580-~~

(PLUG) k 2590*

~~0.1 0.01 2600-~~

DOLOMITI2EP MUDSTONE • ■ Poor to fair Intercrystalllno porosity and poor iermeabillty. Contains a low diversity of fossil typos. Very tight streaks due to fntorcry8talflne calclto cement aro common. This unit occurs at the top of the Dundoo 2610’ and Is very correlative In all field cross sections (Platos nr-1 th ro u g h uT-S), ______.

______- Poor Intorpartlcle porosity and pormoablllty. Tho top 5 fOGt of this unit aro dolomltizod and have fair Intercrystalllno porosity and pormoablllty. Chort nodulos aro common. This unit Is corrolativp in wolls A-12 to A- 2620- 34, B-3 to B-12, and C-1 toto C-12 (Cross Soctlons A-A", B-B', and C-C’, Platos HI-2 through JE-5).

2630*I I SKELETAL-PELOIDAL PACKSTONE • Poor to good Intorpartlclo porosity and permeability. Main skeletal constituonis aro modlum-gralnod crlnold osslclos and abraded brachlopod shells. Contains many coarsening upward hamlcycloa which largely control porosity distribution. Lowor porosity occurs noar tho base and higher 2640- porosity occurs noar tho top of thoso cycles. This unit Is corrolatlvo In wolls A-22 nnd A-34 and C-4 to G-12 (Cross Soctlons A-A" and C-C', platos m-2, ffl-3, an d UT-S). ¥

PELOIPAL-5KELETAL PACKSTONE - Thd top 3 foot of thl3 zono Is a mlcrlto-rlch 2650- packstono with vory poor porosity end pormoablllty. This tight zono l3 corrolatlvo In wolls A-22 to A-34 and C-4 to C-12 (Cross Soctlons A-A" and C-C’, Platos HT-2, m-3, and ffl-5).

Tho romalndor of this unit Is dominated by pololdal-skolotal packstonos with poor to 2660 fair intorpartlclo porosity and pormoablllty. Somo thin bods of porous Skolotal- poloidol gralnstono oxlst noar tho top of coarsening upward homlcyclos In this unit. This Is tho most common llthotypo recognized In the cores examined In this study.

~~2 670-] r~~

~~2680-~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (PLUG) POROSITY (PLUG) k~~

~~MEDIUM'*'; INDUCTION (~~

~~-ATEROl OG~~

~~^ $2** **• mi- • ------Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. t»u lu J f o i1 ifiHiHs'if VurMuuUlliV \vutlidst'6no.~ '~~

~~2550~~

~~______• Dark nodular mlcrlllc llmaslono. Vory tight. Tho top of this 2550' unit la marked by a packstono with very poor porosity that olten Is recognizable on well lo g s.~~

~~2 57 0 ’~~

~~(PLUG) k 2590-~~

~~2600-~~

______HQLQMtHZEB. MUDSTONE - Poor to fair Intercrvatalllne porosity and poor pormoablllty. Contains a low divorslty of fossil types. Very tight streaks duo to Intercrystalllno calclto cement are common. This unit occurs at the top of the Dundee and Is very correlative In all field cross sections (Plates HI-1 through iS-5). ______■

CHERTY SKELETAL WACKESTONE - Poor Intorpartlclo porosity and permeability. The top 5 foot of this unit aro dolomttlzed and have fair Intercrystalllno porosity and permeability. Chort nodules aro common. This unit Is corrolatlvo In wolls A-12 to A- 34, B-3 to B-12, and C-1 to C-12 (Cross Sections A-A", B-B', and C-C', Platos 3H-2 through UI-5).

2630 SKELETAL-PELOIDAL PACKSTONE - Poor to good Intorpartlclo porosity and pormoablllty. Main skolotal constituents are modlum-gralnod crlnold osslclos and abraded brachlopod shells. Contains many coarsening upward homicycles which largely control poiosiiy distribution. Lower porosity occurs near the base and higher porosity occurs near the tap of thoso cyclos. This unit is correlative in wolls A-22 and A-34 and C-4 to G-12 (Cross Soctlons A-A" and C-C', plates 1112, E-3, and 1H-5).

PELOIDAL-SKELETAI. PACKSTONE - Tho top 3 foot of this zono Is u mlcrlta-rlch packstono with very poor porosity and pormoablllty. This tight zono Is corrolatlvo in wolls A-22 to A-34 and C-4 to C-12 (Cross Sections A-A" and C-C', Platos DI-2, H-3, a n d m -5).

Tho remainder of this unit Is dominated by peloldal-skelotal packstonos with poor to fair Intorpartlclo porosity and permeability. Some thin beds of porous skeletal- ?olo!da! gralnstono exist near tho top of coarsening upward homicycles In this unit, his Is the most common llthotype recognized In the cores examined In this study.

2670*

~~2680-~~

~~BOTTOM KELETAL-PELQIDAL PACKSTONE - Mlcrlte-rlch packstone with very poor porosity. CORE~~

T » » LITHOLQGY RESERVOIR GEOLOGY DOLOMITE OF THE DUNDEE LIMESTONE, LIMESTONE WEST BRANCH FIELD. MICHIGAN CHERTY LIMESTONE by Brendan C. Curran i COARSEMMO RESTRICTED Operator: Marathon Oil Company UPWARD UPWARD HEM CYCLE / HEMICYCLE Well Name Hart #2 County: Ogemaw Location: Sec. 34-T22N-R2E Permit No. 26245 ^ Plate H-6

~~■fk S i-!1! ff. ^~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE:~~

~~Oversize maps and charts are filmed in sections in the following manner:~~

~~LEFT TO RIGHT, TOP TO BOTTOM, WITH SMALL OVERLAPS~~

~~The following map or chart has been refilmed in its entirety at the end of this dissertation~~

~~(not available on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover.~~

~~Black and white photographic prints (17" x 23") are available for an additional charge.~~

~~University Microfilms International~~

~~MEDIUM INDUCTION LOG CALIPER G 1G (PLUG) POROSITY (PLUG) k So /sw LATEROLOG -0 30 30~~

~~100 100 1 0.01 0 1 0.0~~

~~BOTTOM CORE 1~~

~~BOTTOM COfflE 2~~

~~)IUM DUCTIO~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ______'J____ J 1 *______■>______V 1 T___ < t L <~~

~~So/Sw~~

~~0,1 0.01 GENERALIZED CORE DESCRIPTION~~

~~. - Dark, nodular mlcrltlc llmostone. Vory tight.~~

Good Intorcrystalllno porosity and fair to poor pormoablllly. This unit occurs at thotho top top of ftho'Dundeo ■' - - and — Is corrolatlvo■ In all’Hold ... c ro s s s e■" c tio ...... n s (P lain s DT-1 th ro u g h DI-S). HI-5). ______Poor Intorpartlclo poro3lty and pormoablllty. Tho mlcrltlc matrlK of Iho top 4 foot of tljls unit hsvo boon aolomlllzod ana havo fair to good Intorcrystnlllno porosity and pormoablllty. This unit is corrolatlvo In tho SE and centra! area of tho Hold (Cross Suctions A-A, B-B1, and C-C', Platos M-2 through IH-5).

~~(CORE NOT RECOVERED)~~

/ SKELETrtL-PELQIDAL PACKSTONE - Poor to good intorpartlcle porosity , and permeability. Skeletal ararains dominated by moduim-gralnsd crlnold ossicles And brachlopod fragmonts. This '~ unit Is corrolatlvo In wolls A-22 to A-34 and C-4 to 12 (C ro ss S ectio n s A-A” an d C-C').

PEI.OIDAL-SKEI.ETAL PACKSTONE - Tho top 6 foot ol this unit Is a mlcrlte-rlch packstono with vory-poor porosity and pormoablllty. This tight zono is correlative In w olls A-22 to A-34 a n d C-4 to C-12 (C ro ss S o ctlo n s A-A" a n d C-C', P lato s III-2, III-3, an d III-5).

Tho rest of this unit Is dominated by pololdal-skelotnl , with poor to fair Intorpartlcle porosity and pormoablllty. Somo porous, thin bods of g raln sto n o oxlat noar tho top of coorsonlng upward homicycles.

KEY RESERVOIR GEOLOGY LUMOIOOY OF THE DUNDEE LIMESTONE, t / < , J D O LO M ITE WEST BRANCH FIELD. MICHIGAN LIMESTONE by Brendan C. Curran CHERTY LIMESTONE O perator: Marathon Oil Company A IfcOAftSEMNa I RESTRICTED Well Name Hart #7 M UPWARD / UFWAftO W HEM I CYCLE I lHFMfCYCL* County: Ogemaw Location: Sec. 34-T22N-R2E Permit No.: 32145 Plate 11-7

~~r r~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE:~~

~~Oversize maps and charts are filmed in sections in the following manner:~~

~~LEFT TO RIG HT, TOP TO BO TTO M , W ITH SM ALL OVERLAPS~~

~~The following map or chart has been refilmed in its entirety at the end of this dissertation~~

~~(not available on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover.~~

~~Black and white photographic prints (17" x 23") are available for an additional charge.~~

~~University Microfilms International~~

~~MEDIUM INDUCTION~~

~~CALIPER LATEROLOG -I (PLUG) POROSITY (PLUG) k S o I Sw ' 0.2 1.0 •10~~

~~100 10 0.1 0.01 0.1 0.0: 2600~~

* 2650 -

~~111 _~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ■ S a a M ...... - M .~~

~~So / Sw~~

GENERALIZED CORE DESCRIPTION DOLOMITIZED MUDSTONE Poor to good intercrystalllno porosity and poor to fair permeability. Some mudstone > streaks streaks remain remain unreplaced unreplaced by by dolomite. This unit is very corrolatlvo In all flold cross soctlons (Platos 111-1 through III-5). ______CHERTY SKELETAL WACKESTONE - Poor to fair Intorpartlclo porosity and pormoablllty. Tho top 3 foot ot thl3 unit have boon dolomitized and have Inlr mtorcrystallina porosity and pormoablllty. Largo chort nodules aro common. This unit |3 corrolatlvo In well3 A-12 to A-34, B-3 to B-12, and C-1 to C-12 (Cross Soctlons A- A", B-B', an d C-C').

______- Poor to good Intorpartlclo porosity and pormoablllty. Mlcrlto-rlch tight zonos are common at tho baso of coarsonlng upward homicycles. Modlum-gralnod skolotal-peloidal packstonos with fair to good interpartlcle porosity and pormoablllty are common near tho top of tho homicycles. Crlnold and brachlopod parts aro the main skeletal grain typos and show less abrasion and fragmontatlon noar the base of coarsonlng upward homicycles than at tho top. This unit is corrolatlvo in wolls A-22 to A-34 and C-4 to C-12 (Cross Sections A-A" an d C-C', P latos III-2, HI-3, and III-5).

PELOIDAL-SKELETAL PACKSTONE - The top 3 foot of this unit are mlcrlto-rlch packstonos with vory poor porosity and pormoablllty. This tight unit Is corrolatlvo In w olls A-22 to A-34 an d C-4 to C-12 (Cro3S S ectio n A-A” a n d C-C', P lato s III-2, III-3, an d lll-S). Tho rest of this unit contains many coarsening upward homicycles and Is dominated by poloidal-skolotal packstonos with poor to loir Intorpartlclo porosity nnd pormoablllty. Thin grainstono3 aro present at tho top of some homlcyclos and create thin zonos of good intorpartlclo porosity.

SKELETAL-PELOIPAL GRAINSTONE - Fair to good intorpartlclo porosity nnd permeability. Tho medium to fine-grained skeletal material Is made up of crlnold — \03slcles and abraded brachlopod, bryozoan, and other fossil hard parts. Many grains show evidence of early marine cementation. This unit Is correlative In wells s A-25 to A-34 (C ro ss S octlon A-A". Plate III-3). ______

~~KEY TEXTURE LITHOLOGY M wp a _ J lDOLOMITE RESERVOIR GEOLOGY LIMESTONE OF THE DUNDEE LIMESTONE, CHERTY WEST BRANCH FIELD, MICHIGAN LIMESTONE ______by Brendan C. Curran ______~~

~~COAftSEMMQ R£5TTflCTEO UTWARD UPWARD HEM1CYCLE Operator: Marathon Oil Company t- 7FCMICYCLE Well Marne: Reinhardt #3 County: Ogemaw Location: Sec. 35-T22N-R2E Permit No.: 32144 Plate II-8~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE:~~

~~Oversize maps and charts are filmed in sections in the following manner:~~

~~LEFT TO RIGHT, TOP TO BOTTOM, WITH SMALL OVERLAPS~~

~~The following map or chart has been refilmed in its entirety at the end of this dissertation~~

~~(not available on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover.~~

~~Black and white photographic prints (17" x 23") are available for an additional charge.~~

~~University Microfilms International~~

~~(PLUG) POROSITY (PLUG) k So /sw~~

~~GAMMA I1AY POROSITY INDEX (%)~~

~~250 20 10 10 100 10 0.1 0.01 0.01~~

~~2570~~

~~2590 cur The: pore p ro l 2 60 0- 2600 2600- o r t to o tho |~~

~~SKF 2610 porn obra that: high and. 2620~~

~~2630~~

~~The pac grr.~~

~~•GR 2650 - 2650~~

~~2660 -~~

~~'CAL (SNP) 2670 sL<~~

~~CORE~~

~~KEY LUUOL^Y~~

~~J y, /".J D O LO M ITE~~

~~L IM E ST O N E C H E R T Y , .LIMESTONE~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UG) l( So /Sw~~

~~ocUi o~~

~~GENERALIZED CORE DESCRIPTION 2570 I - Dark, nodular mlcrltlc limestone. Very tight.~~

~~2580~~

iJumMIH/bl) MUETSTONE - halr io oooa iniorcrvstaillno porosity and poor pormoablllty. This unit is cappod by an extonstvcly bio-orodod hardground and is 2590 7 vary rnrrntntivn In nil flold cross gnrtlnn.a. CHERTY SKELETAL WflCKESTONE - Poor Intorpartlclo porosity and pormoablllty. Tho top 5 feet ol this unit havo boon dolomitized and hovo fair Intorcrystalllno porosity and pormoablllty. Pormoablllty highs In coro analysos in this unit aro probably rotated to small scalo fractures associated v/ith compaction of chart nodulos 2600 or stylolltlzatlon. This unit Is correlative In tho SE and thickens toward the centor of tho flold (C ro ss S ectio n s A-A", B-B', an d C-C', P latos III-2 th ro u g h III-5).

SKELETAL-PELOIPAL PACKSTONE - Poor to fair intorpartlclo porosity and 2610 permeability. Main skoletol constituents are modlum-gralnod crlnold ossicles and abraded brachlopod shells. This unit contains many coarsonlng upward hemlcyclos that largely control porosity distribution. Lower porosity occurs near tho base, and higher porosity occurs near tho top of hemlcyclos. Corrolatlvo In wolls A-22 lo A-34 an d C-4 to C-12 (C ro ss S o ctlo n s A-A" an d C-C', P latos llf-2, III-3, an d III-5). 2620 - L. PELOIDAL-SKEt.ETAl. PACKSTONE - The top 6 foot of this unit aro a mlcrite-rlch packstono with very poor porosity and permeability. This tight zono is correlative in 2630 w ells A-22 to A-34 a n d C-4 to C-12 (C ro ss S ec tio n s A-A" a n d C-C', P lato s III-2, III-3, and III-5). Tho rest of this largely undifferentiated unit Is dominated by pololdal-skoletal packstones with poor porosity and pormoablllty. Thin bods of skelotal-peloidal 2640 gralnstono exist near the top ol many coarsonlng upward homicycles ana create zones of fair to good interpartlclo porosity and permeability.

~~2650~~

~~2660~~

~~2670 ■ Very poor porosity and permeability.~~

~~KEY RESERVOIR GEOLOGY UTHOLOGV OF THE DUNDEE LIMESTONE, D O LO M ITE WEST BRANCH FIELD, MICHIGAN LIM E ST O N E ______by Brendan C. Curran ______C H E R T Y , LIMESTONE Operator: Marathon Oil Company~~

~~COARSEMNO / R REStnCTEO Well Name: Buckingham #4 I County: Ogemaw Location: Sec. 35-T22N-R2E Permit No.: 29775 Plate II-9~~

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE:~~

~~Oversize maps and charts are filmed in sections in the following manner:~~

~~LEFT TO RIGHT, TOP TO BOTTOM, WITH SMALL OVERLAPS~~

~~The following map or chart has been refilmed in its entirety at the end of this dissertation~~

~~(not available on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover.~~

~~Black and white photographic prints (17" x 23") are available for an additional charge.~~

~~University Microfilms International~~

~~0.2 1.0 in 100 250~~

~~- 2600~~

~~• 2650 -~~

~~CAL~~

~~BOTTOM CORE~~

~~Reproduced with p e rm issio n ^co p yrig h t owner. Further reproduction prohibited without permission. G) PERM k~~

~~GENERALIZED CORE DESCRIPTION i - Dark, nodular inlet!',Is limestone. Very light.~~

DOLOMITIZED MUDSTONE - Fair to good Intorcrystalllno porosity and poor permeability. Capped by a pyrltlzod hordground that marks tho top of tho Dundee Limestone. This unit Is very correlative In all field cross sections (Plates 111-1 - III-5). CHERTY SKELETAL WACKESTONE - Poor Intorpnrtlclo porosity and pormoablllty. Tho top 4 foot of this unit have been dolomltlzed and have fair Intorcrystalllne porosity and permeability. Large chert nodules aro common. A variety ol fossil typos are also common. This unit Is corrolatlve In tho SE between wells A-12 and A-34, B-3 and B-12, and C-1 and C-12 (Cross Sections A-A", B-B', and C-C', Plates III-2 through III-5).

SKELETAL-PELQIDAL PACKSTONE ■ Fair to good Intorpnrtlclo porosity and pormoablllty. Mlcrito-rich tight zono3 nro common at the base of hemlcyclos. Tho main skeletal constituents are modlum-grnincd crlnold ossicles and brachiopod shells (usually fragmented). This unit Is correlative In wells A-22 to A-34, and C-4 to C-12 (C ross S ectio n s A-A" and C-C', P lates III-2, III-3, an d III-5).

2620- PELOIDAL-SKELETAL PACKSTONE - Tho top 5 feet of this unit Is a mlcrlte-rlch packstono with vory poor porosi! :y and pormoebillty. This tlf ht packstono Is corrolntlvo In wells A-22 to A-34, and iC-4 to C-12 (C ro ss S ectio n A-f ’ and C-C; Pintos III-2, HI-3, a n d III-5).

2630“ The rest of this unit contains many coarsening upward hemlcyclos with poor to good Intorpartlclo porosity and permoabillty. Low porosity palcldal-skolotal packstonos to wackcstones aro common at tho base of tho hemlcyclos, and higher porosity skelotal-poloidal packstonos and gralnstoncs arc common near tho top of tho hemlcyclos. This Is tho moat common lithotype represented in tho cores examined In this study and mpkos up many of tho largoly undifforontlatod areas In tho field cross s e c tio n s .

26 5 0 - SKELETAL-PELQIDAL GRAINSTONE - Fair to good Intorpartlclo porosity and pormoablllty. Dominant allochoms are medium to fino-gralnod crlnold and brachiopod skeletal pans and flno-gralnod peloids. Skeletal grains shew signs of abrasion and marine cementation. Tms unit Is corrolatlvo In wells A-22 to A-34 and C-6 to C-12 2 6 6 0 - (Cros3 Sections A-A" and C-C', Plates 111-2, 111-3, and 111-5).

~~SKELETAL WACKESTONE - Tight, dark grey limootono. Contains many fossil typos, usually dominated by crlnold 03slclos and brachiopod sholls. Many brachiopods aro 2 6 7 0 - still ortlculatod.~~

~~268~~

MUDSTONE - Vory tight, light brown iimostcno. Fossils include ostracods, forams, gastropods, and unidentiflod dark organic spheres (spores?). Many cemonMllled vortical tubes aro present as well as what oppeor to be largo (>2 cm in diameter) 2 7 1 0 - vertical burrows or borings. This unit has not been correlated in < i cross sections in this stu d y .

~~KEY TEXTURE LiTHOLOGV RESERVOIR GEOLOGY DOLOMITE OF THE DUNDEE LIMESTONE, LIMESTONE C H E R T Y WEST BRANCH FIELD, MICHIGAN LIMESTONE ______by Brendan C. Curran ______~~

r/cOATOEM Iwl / f’XSTrnjcrco \ j UFWAfiD \ j U.’W.’iWJ) Operator: Marathon Oil Company iillRfiiBIlB Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BOTTOM CORE T-GR

~~-z* r Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oco o GENERALIZED CORE DESCRIPTION . - Dark, nodular mlcrltlc llmostono. Vory light.~~

2580 ...... Fair to good Intorcryntnlllno porosity and poor pormoablllty. Cappod by a pyrltlzod hardground that marks tho top of tho Dundoo llmostono. This unit Is vary corrolatlvo In all Hold cross sections (Pintos llt-1 ■ III-5). __ CHERTY SKELETAL WACKESTONE - Poor Intorpartlclo porosity and pormoablllty. 2590 Tho top 4 foot of this unit havo boon dolomltlzod and havo fair Intorcrystalllno porosity and pormoablllty. Largo chort nodulo3 urc common. A vorloly ot fossil typos aro also common. Thl3 unit Is corrolatlvo In tho SE botwoon wolls A-12 and A-34, B-3 and 8-12, and C-1 and C-12 (Cross Soctlon3 A-A”, B-B\ and C-C', Pintos ltl-2 through llt-5). 2 6 0 0 -

SKELETAL-PELQIDAL PACKSTONE - Fair to good Intorpartlclo porosity and pormoablllty. Mlcrito-rlch tight zonos aro common at tho booo of homicyclos, Tho main skolotal constltuonts aro mcdium-grnlnod crlnold osslclos and brachiopod 26 1 0 - sholls (usually fragmontod). This unit Is corrolatlvo In v/olls A-22 to A-34, and C-4 to C-12 (C ro ss S o ctio n s A-A" an d C-C', P la te s ll!-2, III-3, and III-5).

2 6 2 0 -7 PELPIPAL-SKELETAL.. PACKSTONE - Tho top 5 feat of this unit Is a mlcrlto-rlch packstono with vory poor porosity and permeability. This tight packstono Is corrolatlvo In wolls A-22 to A-34, and C-4 to C-12 (Cross Section A-A" and C-C: Platos III-2, III-3, an d lll-S). Tho rest of this unit contains many coarsening upward homicyclos with poor to good 2630--, intorpartlclo porosity and pormoablllty. Low porosity peloidal-skolotal packstonos to Us wackostonos aro common at tho baso ot tho homicyclos, and hlghor porosity skolotal-pololdal packstonos and grainstonos aro common noar tho top of tho homicyclos. This is tho most common llthotypo roprosontod In tho coros oxomlnod In this study and makes up many of tho largely undltlorontlatod areas In tho Hold cross 2*«0-i s o c tio n s.

-2 6 5 0 - SKELETAL-PELQIDAL GRAINSTONE - Fair to good Intorpartlclo porosity and permeability. Dominant allochems aro medium to flno-gralnod crlnold and brachiopod skolotal parts and flno-gralnod pelolds. Skolotal grains show signs of abrasion and marine comontatlon. This unit Is correlative In v/olls A-22 to A-34 and C-6 to C-12 2 6 6 0 - ■ r (C ro ss S ectio n s A-A” an d C-C', P tatos llt-2, III-3, an d HI-5). SKELETAL WACKESTONE - Tight, dark gray llmostono. Contains many fossn typos, r usually dominated by crlnold osslclos and brachiopod sholl3. Many brachlopods are 2670- 1. ZX7 still articulated.

______- Very good intorpartlclo and IntrapartlcJb 2680 porosity and pcrmooDimy. The top half of this zone Is a crlnold gralnstono, tho lowor half Is a corol-stromotonorold flootstone. Not corrolatlvo in cross sections, ______MUDSTONE TO..SKELETAL PACKSTONE - Tight, dork gray llmostono. Skolotol groin typos aro dominated by crlnold ossicles, corals, and stromatoporoids. Somo delicato 2690 corals appear to bo preserved in growth position. This unit was not corrolatfvo on cross soctions with tho woll logs available during this study.

~~2 7 0 0 -~~

MUDSTONE • Very tight, light brown limestone. Fossils include ostracods, forams, gastropods, and unidentified dark organic spheres (spores?). Many cement-fillod vortical tubes aro present as well as what appear to be largo (>2 cm In diameter) 2710 vertical burrows or borings. This unit has not been correlated in cross soctions In this study.

~~KEY TEXTURE RESERVOIR GEOLOGY DOLOMITE OF THE DUNDEE LIMESTONE. L M E ST O N E WEST BRANCH FIELD, MICHIGAN CHERTY LIMESTONE by brendan C. Curran~~

~~B y COAR3P.MMO /I RESTRICTED Marathon Oil Company Hr upward / UPWARO Operator: V HOUCVCLE HFJJICYCLE Well Name Grow it4 County: Ogemaw Location: Sec. 35-T22N-R2E Permit No. 28399 Plate 11-10~~

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GAM M A RAY DEEP INDUCTION LOG 0______150 IIDEWALL NEUTRON POROSITY CALIPER MEDIUM INDUCTION LOG (PLUG) POROSITY (PLUG) k So /Sw LATEROLOG -8

~~,1 0.01~~

~~2 6 0 0 -~~

~~? O T Ig COHEl~~

~~CAUPER~~

~~:E P " CTION MEDU INDUCT~~

~~TEROL~~

^Scout tickets & core analysos suggest that core depths are mislabeled. Porosity■> .... streaks at 2623-2636(1. and 2739-2742(1. (reported ^reported corecore depth) apparently corrolato to porosity stroaks at 2570-2584(t. and 2633-2636(1. (log depth), respectively. Also, a 52(t. gap in reported core dODth botween 2674 and 2726(1. does not ovist

~~Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ’LUG) k So /Sw~~

~~• crUJ uO~~

GENERALIZED CORE DESCRIPTION UULPMITIZEU TOrnTSiuNfc • h o p r to pood imorcrvataTllne poroanv ana poSi1 Agy \6\ iBir permeability. Contains a low diversity of fossil typos. Vory corrolatlvo In all field cro ss aflpVlftRtt (Ptalfln 111.1 throuqh_iU.5) ______2630 ' ______STONE • Poor Intorpartlclo porosity ond pormoablllty. Tho top 4 teot of this unit havo boon doiomitlzcd ond hove poor to fair Intorcrystallmo pcroslty ond pormoablllty. Largo chort nodulos aro common throughout this unit. Crlnold, brachiopod, bryozoan, trlloblto, and ostracod skolotal parts are common. This unit Is corrolatlvo In tho contra! and SE aroos of tho flold. This unit grades laterally Into loss* 2640 muddy pcloidal-skeletal packstonos to tho NW. Corrolatlvo In wolls A-12 to A-34, B-4 to B-12, and C-1 to C-12 (Cross Soctions A-A", B-B\ and C-C').

SKELETAL-PELQIDAL PACKSTONE - Poor to fair intorpartlclo porosity and 2650 pormoablllty. Main skolotal constituents aro fino to modium-gralnod crlnold ossicles and abradod and rounded brachiopod sholls. Coarsening upward homicyclos aro present but poorly developed. This unit is corrolatlvo In tho SE In wollo A-22 to A-34 a n d C-4 to C-12 (C ro ss S o ctio n s A-A" an d C-C', Plat03 III-2, III-3, a n d IH-5).

2660 PELOIPAL-SKELETAL PACKSTONE - Tho top 3 foot of this unit Is a mlcrlto-rlch packstono with vory poor porosity and permeability. Tnls tight unit Is corrolatlvo In w olls A-22 to A-34 an d C-4 to C-12 (C ro ss S e c tio n s A-A" a n d C -C \ P latos III-2, III-3, o nd IIf-5). 2670 Tho rost of this unit is a poloidal-skolotal packstono that contains many coarsening upward homicyclos with poor to good intorpartlclo porosity and permeability. This zono 13 largely undifferentiated In field cross sections. Tnls reproaents tho most common llthotype observed In tho cores examined in this study. f rzx 2740

PELOIPAL-SKELETALPACKSTONE • This is the very top ot a unit that occurs as a 2750 skelotai-peloidal gralnstono in other wells with good Interparticle porosity and ibillty. Although tho coro that Is present is o low porosity packstono, core .sis suggests that core that Is now missing had bettor porosity and pormoablllty similar to othor cored wells.

~~KEY~~

~~d o l o m i t e RESERVOIR GEOLOGY LIMESTONE~~

~~CHERTY OF THE DUNDEE LIMESTONE. LIMESTONE WEST BRANCH FIELD, MICHIGAN by Brendan C. Curran ______~~

Operator: Marathon Oil Company Well Name: Grow #9 County: Ogemaw Location: Sec. 35-T22N-R2E that core depths aro mislabeled, d 2739-2742ft. (reported core Permit No.: 321 65 ty streaks at 2570-25C4ft. and Also, a 52ft. gap in reported Plate 11-11 )os not oxlst.

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~~u s 0 2000 . . 2000 0 riPHi uo 0.4500 - • -0 '50 0 2000 ------2000 o RMOB M 5 R 150 0 3 0 — — 0 2000 1— 2000.0~~

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2700*

~~2Q00 2600~~

~~RESERVOIR GEOLOd DUNDEE LIMES) WEST BRANCH FIELD, ; PLATE 111-1, STRA CROSS SECTIC~~

~~(Wells A-1 th rough i~~

~~by Brondon C. Curr~~

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~~150.0 .3 0 0 0 0 - — - — - - - - - —— -.1000 30090 — aooo o 0 3000 2QGO 0 NPHI 2 6 0 0 - 0 3000 ______-o 100 0 3000 2000 0 F1H00 1 500 20000 1 0000 0 2000 2000.0~~

~~R1 DATUM~~

~~7700 - 7 7 0 3 -~~

~~RESERVOIR GEOLOGY OF THE DUNDEE LIMESTONE WEST BRANCH FIELD, MICHIGAN PLATE 111-1, STRATIGRAPHIC CROSS SECTION A-A~~

~~(Wells A-1 th rough A-11)~~

~~by Brendan C. Curran~~

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~~150 I |?0 RHOP______301 1000 |~~

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~~RESERVOIR GEOLOGY OF THE DUNDEE LIMESTONE WEST BRANCH FIELD, MICHIGAN PLATE m-2, STRATIGRAPHIC CROSS SECTION A'-A"~~

~~(Wells A-12 through A-23)~~

~~by B rondan C. Curran~~

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~~1 RESERVOIR GEOLOGY OF THE DUNDEE LIMESTONE WEST BRANCH FIELD, MICHIGAN PLATE m-3, STRATIGRAPHIC CROSS SECTION A"-A"’~~

~~{Wells A-24 th ro u g h A-34}~~

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~~RESERVOIR GEOLOGY OF THE DUNDEE LIMESTONE~~

~~WEST BRANCH FIELD, MICHIGAN PLATE m-4, STRATIGRAPHIC CROSS SECTION B-B'~~

~~by Brondon C. Curran~~

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~~C-1 C-2 C-3~~

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~~R SERVOIR GEOLO ; y o f the EZ> SJNDEE LIFW? ^ 1 TONE~~

~~■ W E S T BRANCH F I E L S MICHIGAN SEE A ll-5, S T FR? TIGRAPHIC = ?O S S SECTI fM C -C' by Brondan C .~~

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