DUNDEE FIELDS IN THE CENTRAL MICHIGAN BASIN Thesis for the Degree of M. S. \ MICHIGAN STATE UNIVERSITY CHARLES VINCENT BUSH 1983 -3". ‘lr—‘i-lil*’4vw.!j.l‘ 5:. y: yd-r -.~ I). a 4*" , I . ‘ ii I. 3‘ ~ 1- .. , “r ' I r ' H‘ r I. awn '{ ; I‘ I 1.! ‘ r ( f I." J.‘ ‘ ." “-3 I “ I ’I l .9 ‘ 'i ‘ l . ‘ ‘ ‘ ‘ I x -. m' ‘r 1:, l I ‘ .2? .. i l A '_ ;. ' ’ “ u. ‘I' I‘ ‘ r ’ ’ I . I g' .x I l: E n - i w \n j!“ ‘5' 'h -1 L.‘ a (I 0‘ I . 'Q .. .- . . .‘. r : ~~ ; w g _ w J . K ,. r 3 pg I/Vma/ if“ r V‘ ' ‘1,” 3 i‘ .3 l '6 I ~ In -. x. r .lu, 3 \. d 4;)" '7. H. \\ I: " l D ' J I c .4! ' II. v.4" "' ‘ .. x J ' WARM» £‘-.~A. .\ This is to certify that the thesis entitled Dundee Fields in the Central Michigan Basin presented by Charles Vincent Bush has been accepted towards fulfillment of the requirements for Masters degree in Geology vars/{£4,417 Major professor Date I // 0-7639 MS U is an Afiman've Action/Equal Opportunity Institution RETURNING MATERIALS: IV1€31_J Place in book drop to LIBRARIES remove this checkout from aggggggggl_ your record. FINES will be charged if book is returned after the date stamped below. ABSTRACT DUNDEE FIELDS IN THE CENTRAL MICHIGAN BASIN By Charles Vincent Bush The Dundee Formation of the Michigan Basin has been studied since the late 1800's. The purpose of this study includes the determination of relationships between structural, lithologic and production trends. Within the basin, the Dundee exhibits dominant northwest-southeast lineaments which create positive trends and control the distribution of ‘ structures. The shape of these structures are determined by this trend and subordinate east-west cross-folding. The Dundee varies in thickness from 200 feet to #40 feet in the study area. Reefing, increased carbonate buildup on positive areas, yields thick intervals on positive structures. A The Dundee is a brown, locally dolomitized, wackestone or packstone. Fossils include brachiopods, corals, and stromatoporoids. A strong relationship exists between structure and dolomitization. Systems of fractures developed during folding provided pathways for dolomitizing fluids. Much of the production comes from epigenetic dolomites along these fractures. Primary porosity on the flanks of these structures may also create traps. DUNDEE FIELDS IN THE CENTRAL MICHIGAN BASIN by Charles Vincent Bush A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Geology 1983 ACKNOWLEDGEMENTS Many people have contributed to the completion of this study. I am especially indebted to Dr. J. H. Fisher, Chairman of the Advisory Committee, for his time, patience and friendship. Our informal discussions of geology and the oil industry were particularly rewarding. Appreciation is extended to the other members of the Committee, Dr. C. E. Prouty and Dr. J. W. Trow, for their constructive criticism and suggestions. Gratitude is extended to the Tenneco Oil Company for supplying financial aid which allowed continuation of this study. I would also like to thank Loretta Knutson for her expert typing and editing of this text. I wish to thank my friends and acquaintances at Michigan State. Each in their own way provided avenues of escape from the rigors and tedium of graduate school. A special thanks goes to my entire family, especially my mother and father. Their continued love, support and gentle prodding through what seemed to them an endless college career helped me finally finish my days at MSU. I would also like to thank Dana Blakley, someone very special who provided me with love, understanding and friendship throughout my graduate studies. TABLE OF CONTENTS LIST OF FIGURES O O O O O O O O O O O INTRODUCTION ........................ General........ ........ ....... Area of Study ....................... Method of Study ..... . .......... . ..... STRUCTURE O O O O O O O O OOOOOOOOOOOOOOOOOO General O O O O O O O O O O O O O O Central Michigan Basin Structure STRATIGRAPHY O O O O O O O O OOOOOOOOOOOOOOOO General. . . ..... . ................. Traverse Group ...................... Dundee Formation . . ........ . .......... Detroit River Group . . . . . . LITHOLOGY OF THE DUNDEE ........... . . . . . . . POROSITY DEVELOPMENT . . . . PrimaryPorosity...... ...... Secondary Porosity. . . . . . Dolomitization and Porosity ....... . . . . . . . . . . Porosity in the Dundee . . . . PRODUCTION IN THE DUNDEE . . . . RECENT ACTIVITY ....... . . CONCLUSIONS O O O O O O O O O O 'SUGGESTIONS FOR FURTHER STUDY REFE REN CBS O O O O O O O O OOOOO O O O O O O O O O O O O APPENDIXI ........ . . . APPENDIX 11 O O O O O O O OOOOOOOO O OOOOOOO O O O APPENDIX III ......... . .— O‘V \I MN.— 20 20 25 29 31 37 37 #2 47 55 63 67 7O 75 76 82 91 Figure I. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. LIST OF FIGURES Areaofstudy.......... Typicalwelllog. . . . . . . . . Major structural features . . . . Gravity anomaly map . . . ...... Devonian depocenter location . . Rectilinear pattern of faulting . . Structural trends in the Basin . . . Structural trends in oil fields . . . Stratigraphic column . . . . . . Devonian subsurface nomenclature Mechanics of structural inversion . CNL-FDC lithology determination. Dunham's classification scheme . . Depositional processes vs. primary porosity . Chemical zones in sedimentary carbonates Diagenetic realms. . . . . . . . . . . Porosity vs. pressure solution . . . . . . Correction nomograph for porosity values CNL-FDC crossplot . . . . . . . CNL-sonic crossplot . . . . . . . Dundee oil and gas fields. . . . . Township location map (Appendix I) 11 13 14 15 19 21 23 28 34 38 40 III #5 as 57 59 so 64 82 INTRODUCTION General The Dundee Formation in Michigan has been the subject of study since the late 1800's. Since the discovery of oil in the Dundee in 1928, the studies have taken an economic turn. To date, the Dundee is the most prolific oil producer in the state. Studies have been conducted on a variety of aspects of the formation in different areas of the state. Most of the investigations have concentrated on the conditions present in known producing structures (Tinklepaugh, 1957; Jackson, 1958; Paris, 1977; Ten Have, 1979; Richey, 1980; and others). A few studies have addressed the problems involving the Dundee from a regional view (Bloomer, 1969; Landes, 1946). The purpose of this study includes the determination of the factors and mechanisms that control petroleum accumulation in the Dundee. The formations in the central Michigan Basin show distinct structural, lithologic, and production trends. The relationship of these trends to controls on the Dundee will be examined. Utilizing well logs, drillers' records, and literature, the Dundee Formation is delineated. This is accomplished by the construction of maps depicting porosity, thickness, structure, and lithology in the area of study. The mechanisms controlling the formation of primary and secondary porosity are considered. This allows the prediction of favorable conditions for the occurrence of porosity in the Dundee. The relationship between secondary porosity and dolomitization in the basin has been the subject of various studies involving several formations including the Dundee. The conditions and restrictions concerning secondary porosity are outlined and related to the Dundee in the area of study. This study represents the first regional investigation of the Dundee Formation in the central Michigan Basin in some time. Radical changes have taken place recently in the understanding of dolomitization, diagenesis, porosity formation and preservation, and well treatment. Analysis of the completed data and maps indicates the relationships between lithology, porosity, structure, and production. It is the hope and purpose of this writer that the results of this study will provide comprehensive and current information regarding the geological characteristics of the Dundee and the related production trends. It is also hoped that this study will serve as a useful basic framework for study and exploration in the central Michigan Basin, as well as outlining areas in need of further study. Area of Study The area of study is a four county region in central Michigan consisting of Clare, Midland, Isabella, and Gladwin Counties (Figure 1). This region of the Michigan Basin encompasses a large percentage of the current Dundee oil and gas production. Although many of the fields date back to the 1930's, recent activity has yielded substantial new data and spurred interest in the area. Method of Study Data for the subsurface maps prepared for this project were obtained by the correlation of approximately 400 well logs from the Michigan State Geological Survey files and the Michigan State University collection. Well locations were chosen to yield the best control pattern. Preference was given to recent, more sophisticated well logs over those with older surveys. Where well logs were not available, drillers' logs on file at the Michigan Geological Survey were used to obtain formation taps and lithologic descriptions. aruzn MICHIGAN DEPARTMENT OF CONSERVATION PIESOUEISLE 0T3 £00 I I IALPENA GRAND TRAVERSE KALKASKA CIAIFDRD‘ OSCODA ALCDNA ISTEE 'EXFORD LISSAUKEZIMSCOW 055W IOSCD UASON LAKE OSCEOLA OCEANA NEWAYGD MECOSTA ISABELLA I \ GLADWIN MIDLAND \\ r—I HON TCALU GAATIOT SAGINAW ARENAC HURON DAY A TUSCDL ‘ SAN IL Ac KENT EDNA CLINTON LAP!!! GENESEE ALLEGAN GARRY EATON INGHAU LNIKBJON UACOIBA OAKLAND I VAN SURE" IALAHAZOO CALHOUN JACKSON wASHTENAw VAvut BERRIEII CASS SI JOSE“! BRANCH HILLSDALE LENAOCE I‘HDNRDE I I Figure 1. Area of study. The quality of the drillers' logs varied. Those logs which appeared accurate and well recorded generally agreed with nearby well control and were included in the data base. Others which seemed poorly documented or which were significantly different from surrounding information were omitted. Formation tops were recorded for the Bell Shale, the Dundee Formation, and the Detroit River Group. The top of the Bell .Shale and the Dundee Formation top are distinctive markers on logs in the area of study (Figure 2). The log signature of the Bell and Dundee carried extremely well from log to log. The tops of these two formations can be picked consistently and accurately. The top of the Detroit River Group has been the subject of debate for many years in the Michigan Basin. Landes (1951) studied the information available and summarized the controversy surrounding the top of the Detroit River Group as follows: "Because the basal part of the Dundee Formation is a limestone or a dolomite and the upper part of the Lucas Formation is also a limestone or a dolomite in most places, it is not always possible to ascertain the exact position of the contact of the two formations. Furthermore, the task is complicated by an erosional unconformity at the top of the Detroit River Group that cuts out certain beds within a relatively short distance due to different levels of erosion. As fossils are not available in most cuttings, the determination of the contact in wells must be based on lithologic differences. The following criteria are useful in various parts of the basin: sand in the basal part of the Dundee, chert in the lower part of the Dundee, limestone in the Dundee, darker color of carbonate rocks in the basal part of the Dundee, dolomite in the Lucas, and anhydrite in the Lucas. Calcium sulfate, present mainly as anhydrite, occurs in the top few feet of the Lucas over much of the Basin. Lilienthal (1978) denotes a radioactive marker called "DR-l" and a porosity zone used in various combinations to represent the top of the Detroit River Group: 1) at the marker "DR-l" only, 2) below the marker "DR-l" and Bell Dundee File untrue-55373;“ frwg ”EH"! J'Illflmlflf‘ vww- ’9:- r7 #3:.) 7<~Yf~ '-J:9y:002: Detroit River Figure 2. Typical well log. above the porosity zone, 3) below the marker "DR-l" and in the porosity zone. The character and extent of the marker and the porosity zone are not consistent enough in the area of study to allow regional correlation. For the purpose of this study, the top of the Detroit River Group will be placed at the first anhydrite observed on well logs, commonly called the "Detroit River Anhydrite". STRUCTURE General The Michigan Basin is a roughly circular, asymmetrical, autogeosyncline or intracratonic basin, located in the Central Interior Platform (Figure 3). It covers the entire southern peninsula and part of the northern peninsula of Michigan, eastern Wisconsin, portions of Ontario, northern Indiana, northeastern Illinois, and northwestern Ohio. The basin is surrounded by major tectonic features: the Wisconsin Arch to the west, the Canadian Shield to the north, the Algonquin Arch to the east, the Findlay Arch to the southeast, and by the Kankakee Platform on the southwest. Many theories on the mechanisms responsible for the formation and the structure of the Michigan Basin region have been proposed. Pirtle (1932) ' described the structure in the basin in relation to the surrounding positive features. He believed the structures within the basin were controlled by trends of folding or lines of structural weakness which originated in the basement rock and that the basin originated in Precambrian time. Deposition was controlled by the Wisconsin Arch, the Cincinnati Arch, and the Kankakee Platform. He suggested the Wisconsin Arch of today represents the remnant of a Precambrian mountain range that once bordered an ancestral geosyncline in the Michigan area. The subsequent erosion of the mountain range supplied sediment to the embryonic basin. Many of Pirtle's interpretations were based on his recognition of dominant northwest-southeast trends in the basin, as well as subordinate trends running northeast-southwest. Newcombe (1933) also cited the structural trends in the basin. Newcombe‘s report on the geology of the Michigan Basin is an excellent reference and an aid LAKE SUPER/0R \~ . . CANADA UPPER MICHIGAN ' I \ MICHIGAN BASIN HOWELL ANTICUNE LAKE ‘ \ géi. aucwc 1“; ALBION- scmo -’ memo LUCAS- A :BNROE - ULT a H ENflON lw ILL. .. .. . u . 1 l‘ u. u .- .. -- OI . .. n .- D”’ ”"0 an ‘ OI . .. DO. .- .0 a .. . a ......... vi. .l. . ...-a¢-:D': “to.” . c- ' fin“"‘"’ .t . - g in the studying of the basin. Several theories on the structural and geological aspects of the basin proposed by Newcombe have since been supported by evidence gathered since 1933. Newcombe believed zones of weakness in the basement rock controlled the formation of the Michigan Basin in Precambrian time. These zones of weakness were thought to be related to the Keweenawan disturbance. The principle folding of the anticlinal trends in the basin occurred in the Late Devonian. Subsequent movements during the Late Mississippian accentuated the structures already present and created new structures as well. Kirkham (1937) proposed that the shifting of large bodies of magma from one area of the crust to another created a downwarping and not a true basin. He did not believe that horizontal and tangential forces played a role in the origin of the basin. He did believe, however, that during the movement of the magma, the Precambrian surface became marked by faults, rifts, and joints. These features caused zones of weakness along which forces could later act. Lockett (1947) took the same approach as Pirtle. Lockett related the surrounding positive features to the origin of the basin. These dominant features are the remnants of Precambrian mountain ranges. Erosion of these mountains supplied sediment, and the weight of the sediment initiated subsidence. He states that the zones of weakness were present in the Precambrian surface, but that the differential subsidence along the zones was in response to sediment loading, not orogenic forces. The layering of sediments over the Precambrian surface created the basis for the anticlinal and the synclinal features observed in the basin. Cohee (1944-1949) prepared numerous maps and texts on the Michigan Basin, in particular, the Traverse, Dundee, and Rogers City Formations. This series of isopachs, structure contour, and lithology maps aided the exploration effort in the basin. Cohee depicts the dominant trends in the basin. Cohee and 10 Landes (1958) consider the basin to first show closure in Late Silurian time. Intermittant folding and subsidence occurred throughout the Paleozoic, with the major folding event in the Late Mississippian. Gravity and magnetic studies have also been used as a basis for theories of the basin origin. Hinze and Merritt (1963, 1969) conducted regional gravity and magnetic surveys in the Michigan Basin. A gravity and magnetic anomaly was observed which runs northwest-southeast through the basin (Figure 4). They suggested the anomaly represents an ancestral rift zone, and that the rift zone had a dominating effect on the development of the basin. High density mafic rocks of Keweenawan age were being emplaced along the rift. These dense rocks may have initiated subsidence in the basin. Ells (1969) published a summary of much of the previous work done in the Michigan Basin. He presented the important theories concerning the origin of the basin and discussed the major structures. 'Ells cited the dominant northwest- southeast anticlinal trend. These trends, he suggests, record the periods of intermittant activity throughout the Paleozoic. J. H. Fisher (1969) constructed isopach maps on a number of Paleozoic intervals. He suggested that an embryonic Michigan Basin was present during Cambrian time. In Trenton time, the Michigan Basin evolved into a true basin in the shape and size as we know it today. During the Mohawkian and Cincinnatian, periods of significant subsidence took place. Thin layers of shales and carbonates accumulated in Early Silurian time, and during the Middle Silurian time a massive reef developed around the margin of the basin. These encircling reefs starved the interior of the basin during the Niagaran, as observed by the thinning of the sediments toward the center of the basin. The major sinking in the basin in Salina time is recorded by a thick accumulation of carbonates, shales, and evaporites in a depocenter near the southwest end of Saginaw Bay. In 11 ll ‘ ‘3" I l: w .fi ....... . . .. Ta , . .4 .1. .. . .., , EAQA... of the southern peninsula of Michigan. Merritt, 1969) (Hinze and one milligal Figure 4. Bouguer gravity anomaly map Contour interval 12 the Devonian, the depocenter was slightly northwest of Saginaw Bay (Figure 5). Several major unconformities were created by uplifts during the Early Devonian. A thicker Middle and Upper Devonian sequence of carbonates and black shales developed during a period of increased subsidence. Fisher believes the trends in the Michigan Basin may be in part controlled by a rectilinear pattern of faulting in the basement rocks. This pattern of faulting is reflected in the rectilinear faulting pattern observed in the Canadian Shield (Figure 6). The trends of the fault patterns may control the observed orientation of the Dundee oil fields present in the central Michigan Basin. Prouty (1976) suggested that lineaments observed in the LANDSAT imagery of the Michigan Basin are traces of faults. These lineaments reflect both the interior structures of the basin and the radial features around the perimeter of the basin (Figure 7). The orientation of the fault traces can be used to construct a model for the tectonic history of the basin (Ten Have, 1979). Prouty attributes the faults to a wrenching deformation model and related the folds present in the basin to the resultant movement on these faults. The stresses applied to the O region are due in part to the structural activity in the Appalachians throughout the Paleozoic. Evidence indicates many episodes of deformation and shearing. Although many orientations occur for fault lineaments, major trends can still be distinguished. Prouty believes the most intense period of folding occurred in Pre-Marshall Mississippian time. Lilienthal (1978) constructed a series of cross-sections of the basin. These cross-sections radiate from the Sparks deep test well in Gratiot County and are based on the correlation of gamma-ray and neutron logs. The cross-sections cover most of the lower peninsula of Michigan. These sections are useful in determining general geologic trends, position of depoCenters through time, and the presence or absence of particular horizons in a region of the basin. l3 {NWM‘S Figure 5. Devonian isopach depicting location of depocenter (Fisher, J. H., 1969). l4 E s I I I Scale 1:5.000.000 .\ / I I 88- ACHIUGD / oilF LAKE "\ who“ C1 Figure 6. Rectilinear pattern of faulting in the Canadian Shield (tectonic map of Canada, 1969; Fisher, J. A., 1981). '15 ' : : ..\ - I \ - 55.33.? m- ' I ->:°;::s,c..“'““T"‘ . a \‘2 - i A. \. ‘ . ,II .0 l I o «the... \. \' I -: i . k c ‘ " ‘ Iz/L reg-.003" T’\u\'07m.-,—-—‘s‘sru I out“ \ “OK-“M... °.‘ ~' h on. ”0.. .- . «can W --- 8;)..‘If3- "0.,[4‘5' k ;-_;‘ .’./ ‘l . (7'2". ’-.‘_,/,’:_4""‘/;/'. i /.’-r ’2" I’ll-"”- fl, ' I (.JJ'.I_£.L_‘-/.'_.. /_ Figure 7. Structural trends in the Michigan Basin (compiled by Prouty, 1976). 16 Central Michigan Basin Structure A structure contour map was constructed on the top of the Dundee Formation (Plate 1). Formation tops were picked from well logs and drillers' records. Locations of the key well logs used in the study are given in Appendix I. Tops obtained from drillers' logs were only recorded for map use and do not appear in the Appendix. While control was good in most areas, some areas lacked adequate coverage for detailed mapping. The contour patterns in these areas are inherently more interpretive, but were constructed in such a way as to honor all the data available. Township names and locations are given on Figure 22 in Appendix I. The central Michigan Basin area occupies the deepest part of the basin. Newcombe (1933) described the area as a single structural province. The region is characterized by broad anticlinal and synclinal folds in subparallel trends. These trends of folding roughly parallel the axis of the slightly ovate Michigan Basin. Relief on structures ranges from tens of feet to hundreds of feet. The age of the folding is not fully known, but the structures record multiple periods of tectonic activity. The configurations of the structures are thought to be controlled by vertical tectonics in the basement rocks of the basin. The regional dip of the area of study is difficult to establish because of the complexity of structure and the variability of dip values near local structures. The regional dip trends to the north and northeast toward the Devonian depocenter. In areas less affected by structures, dip values range from 25'lmile to 80'] mile along a line trending NltSOE. Distinct structural trends can be outlined in the area of study. A strong northwest-southeast lineament is observed in structures in this area, with a weaker northeast—southwest lineament. These lineaments may be reflections of fault patterns in the basement rocks. 17 Structural highs occur en echelon in the dominant northwest to southeast trend. 0n the map (Plate 1) three major structurally high trends are observed. The Broomfield trend runs from Sherman Township to Deerfield Township in Isabella County. The Freeman-Porter trend runs from Redding Township, Clare County, southeast to Porter Township, Midland County. The third major trend, the Headquarters-Bentley trend, runs from Franklin Township, Clare County, southeast through Bentley Township, Gladwin County. Several minor highs occur subparallel to these major trends. Two types of oil field structures occur along these high trends. Several of the larger fields in the area are of one type - arcuate structures with pistol-like outlines. Examples of this type are the Mount Pleasant, Porter, and Bentley fields. These structures are generally assymmetrical. The major structural axis is interrupted by subordinate cross folding and faulting. These fields can be several miles long, as shown by the Mount Pleasant field. Along these structures, cross-folding and saddles change the size, shape, and direction of the fields. The fields have numerous structural irregularities caused by these features which create traps for hydrocarbons. . Circular oil fields are the other type of structures. Newcombe (1933) and E115 (1969) suggested these fields were caused by cross buckling in the Dundee. The displacement in the folding is about the same in all directions, as opposed to the other type of fields which have major and minor directions of folding. These circular fields tend to be somewhat smaller than the Mount Pleasant type fields. Examples of the circular fields are the Grout, Edenville, Billings, and Leaton fields. Both types of oil field structures may be controlled by vertical tectonics. These relative movements originate in the Precambrian and effect the overlying l8 strata as well. Structural trends of faulting and zones of weakness in the Precambrian control the orientation of Devonian Dundee oil fields. An example of Dundee oil field orientations is shown in Figure 8. Two directions of structure are indicated by the field shapes. A dominant northwest- southeast trend controls the shape of the oil fields as well as the distribution. Oil fields in this area occur in sub-linear groups along this direction. The east- west trends create cross folding in the fields which changes the direction of the axes. The arcuate shapes of the fields and the irregularities in the outline of production result from cross folding. Many of the structures exhibit steep dips on one flank and gentler or shallower dips on the other flank. Most tend to have a steep clip on the southwest side of the structure and the lesser dip on the northeast side. The Mount Pleasant field and the Porter field show this well. The steep clips are generally l50'/mile to ZOO'Imile, and the gentler dips being approximately 35'] mile to 70'] mile. This configuration may be in part due to the regional dip in the area of study. Folding of the dipping beds occurs almost parallel to the strike of the beds. This could result in two different dip values on the flanks. Normal faulting movement at depth is another possibility for some structures. The upthrown side of the structure creates the steep dip, and the downthrown side creates the shallow dip. A more complete structural study of each field would be necessary to determine the dominant structural controls. The complex structural configuration in the central Michigan Basin lends itself to many different interpretations. Each of these interpretations may outline areas of economic interest. Many of the areas of the region have yet to be explored in detail. Along with the refinement of geophysical data in the area, determination of the structure in 'the central Michigan Basin may become increasingly more detailed. l9 Vernon \ Rosebush +— Lyeaton Pleasant Porter Figure 8. Structural trends in oil fields. STRATIGRAPHY General The Middle Devonian strata in the area of study is comprised of the Traverse Group, the Dundee Formation, and the Detroit River Group. Of particular interest in the study are the Bell Shale at the base of the Traverse Group, and the Dundee Formation (Figure 9). The tops of these formations were obtained from well logs and drillers' records on file at the Michigan Geological Survey. Where recent geophysical well logs were available, accurate formation tops could be determined. Some of the older electric and gamma-ray surveys did not distinguish the formations as clearly, and estimations of the contacts were required. Even in these cases, the tops can be assumed to be accurate to within a few feet. The characteristic well log tracks and my interpretations of the formation tops are depicted in Figure 2. In locations where well logs were not available, drillers' records were utilized. The quality and reliability of the drillers' records varied. In some instances, good drilling records were kept with careful sample analysis. These records generally yielded tops and thicknesses in line with surrounding well log data, and were included in the study. The records which appeared unreliable or that differed greatly with the surrounding data were omitted. Some subjective judgement and common sense was used in deciding which records were to be included in this study. Interpretation and contouring of the data is also a subjective process. Contouring is an individual interpretation of the data concerning the thickness and character of a rock unit. Variations in the control pattern, reliability of data, and the interpreter may lead to very different results. 2( 21 04mm STRATIGRAPHIC SUCCESSION IN MICHIGAN “W I“ IVSTIII 1 sum 31“! _______—-—E-—‘,—( momma-on u 0 z u U ~—--—.——--— .- .- —— —..——-—-——-_- -u---—.—v b—u— -- -———--—--.———-— b.._---— —-—.—_—.— mm _---—-—4——--- —-—-u¢~o—-o u.- -—l |~—|---— b—~u_- u—n—us‘ __~ '——— —~u. Figure 9. Stratigraphic succession in Michigan. 22 Traverse Group The Traverse Group of the Michigan Basin is commonly divided into three units for subsurface work. These three units are: the Traverse Formation, Traverse Limestone, and the Bell Shale (Figure 10). The Group varies in thickness, from about 800' in the north to less than 100' in the southwest corner of Michigan (Lilienthal, 1978). The Traverse Formation is a gray shale near the top of the interval. This gray shale gradually becomes lighter colored and calcareous lower in the interval. Near the base of the formation the shale grades into a light colored argillaceous limestone. This gradational lithology, from gray, pure shale to a lighter, argillaceous limestone, can make correlation in the subsurface difficult. The Traverse Limestone has a variable lithology as well. It is primarily a shale in eastern Michigan, with a progressive increase in limestone occurring to the west. In western Michigan, the Traverse Limestone is predominantly pure limestone and dolomitic limestone. The Traverse Limestone produces oil and gas in Michigan. Through 1979, the Geological Survey of Michigan reported 106,665,092 barrels of oil and 9,008,289 MCF of gas had been produced from Traverse pools. Most of the production occurs in southwestern Michigan. A variety of trap types have been encountered, bioherms, stratigraphic pinchouts, collapse features, and anticlines. The Bell Shale covers much of the central Michigan Basin. It is the lowermost formation of the Traverse Group, and is predominantly a shale (Lilienthal, 1978). It is generally 60' to 70' thick, but may locally exceed 100' in thickness. The Bell Shale thins toward the southwest corner of Michigan and eventually pinches out. Bloomer (1969) noted this trend of thickening and suggested a source to the north or northeast of the area of study for the Bell Shale. 23 System Group Formation Traverse Unit Traverse Traverse Limestone D Bell Shale E V 0 Rogers City Dundee N I A Lucas Detroit River Amherstburg Sylvania Sandstone Figure 10. Subsurface nomenclature common to the Michigan Basin Devonian System (Lilienthal, 1978; Tinklepaugh, 1957). 211 In the central Michigan Basin, the Bell Shale is typically a dark gray to black shale. It is often calcareous, and crinoids seem to be the dominant fossil types. These crinoid fragments usually occur in thin beds, somewhat size sorted, with partings parallel to bedding. An isopach map of the Bell Shale was constructed (Plate 2). Well coverage of the Bell was good, with many of the wells in the area targeted to the Dundee. Drillers' records were less accurate, a large number of which were recorded prior to 1950. Lithologic descriptions in these older records are often limited to shale or shale and shells. Thid 0359.355 1 0. on c. -o. : (moored) uogimos ainssald #9 There are certain conditions which are necessary for dolomitization to take place (Wilson, 1975); l) a fluid of the correct chemical composition to react with the sediment, capable of dissolving CaC03 and releasing Mg, 2) a carbonate sediment of sufficient porosity and permeability to act as a host during Mg replacement, 3) a long enduring supply of Mg, and 4) a hydrodynamic head to force large volumes of water through the sediment. Dolomite can be either primary or secondary. Primary dolomite is formed by the penecontemporaneous replacement of unconsolidated carbonate sediments (Bathurst, 1975). These types of dolomites are typical of the supratidal environment and are often associated with evaporites, mud cracks, and algal mats. Secondary dolomite forms by the replacement of pre-existing carbonates. These forms of dolomite include diagenetic and epigenetic dolomite. Both of these occur in the Dundee Formation. Diagenetic dolomite forms relatively early in the history of a sediment. Tinklepaugh (1957) describes this dolomite as "forming lenses .or layers with obscure stratification". Porosity in these dolomites is slight and they are generally fine grained. Fossils remain as molds and relict structures are common (Chilingar, 1958). Epigenetic dolomite is formed later in the sediment history by the alteration of completely lithified limestone. Replacement dolomite shows strong fabric selectivity (Sibley, 1980). A number of factors determine the response of a carbonate to replacement by dolomite. Grain size is an important control. Fine grained sediments are preferentially dolomitized, such as the mud based matrix in a packstone. Composition is also important, aragonite being replaced before low magnesium calcite. 50 Various mechanisms have been presented for the formation of diagenetic and epigenetic dolomite. Most models are based upon processes observed in Recent carbonate sediments. Some are, however, based on trends observed in ancient carbonate sequences, petrology, and chemistry of the dolomites in these sequences. The present concern with Recent dolomite formation and the difficulty in determining ancient processes is a problem which still lacks a solution. The effects of post burial processes are not yet understood. There may be an important relationship between burial history and dolomite occurrence, hydrocarbon generation, and entrapment (Landes, 19146). The Evaporative Reflux (Seepage Refluxion) model is based on evaporation of sea water in a restricted environment to produce a Mg-rich brine (Adams and Rhodes, 1960; Deffeyes, et al., 1965; llling, 1965). Precipitation of gypsum and anhydrite raises the Mg concentration relative to the Ca concentration. The evaporites are deposited on tidal flats in supratidal areas. The solution with the high Mg:Ca ratio moves downward through the carbonate sediment and dolomitization occurs. A similar model, called the Capillary Concentration model, relies on the simple concentration of the pore fluids by evaporation, the precipitation of gypsum, and the subsequent increase in the Mg:Ca ratio. Recharge of the system occurs during unusually high tides (Carpenter, 1980). Some studies conducted on the Michigan Basin have proposed dolomitization by Seepage Refluxion (Bloomer, 1969). Dolomite formed by this mechanism would be associated with evaporites in a supratidal environment, which may have existed on the west side of the state in Devonian Dundee time (Gardener, 1971+). These dolomites are of limited extent in the basin. Carbonate sequences exposed to seepage refluxion are generally heavily altered to dolomite. A high percentage of the original sediment is converted to 51 \ dolomite, with a much lesser amount remaining as the original material. These dolomites are associated with areas that were once emergent and which had a restricted marine environment. Mixed-water models have been proposed by Hanshaw (1971), Badiozamani (1973), Folk and Land (1975), and others. The model proposed by Badiozamani, termed the "Dorag" model has gained wide acceptance. The "Schizohaline" model presented by Folk and Land is very similar to the Dorag model. . Interaction of a lense of fresh water with an underlying mass of sea water is the basis for these models. The interface between the two water masses is gradational, with a zone of brackish water occurring. Badiozamani (1973) estimated that fresh water mixed with between 596 and 3096 sea water yielded a solution undersaturated with respect to calcite and many times supersaturated with respect to dolomite. It is in this zone of mixing that dolomitization occurs. Mixing in of the sea water supplies the necessary Mg. Fluctuation of this zone of mixing can happen for many reasons: change in the rate of recharge of the fresh water lense, seasonal changes in the level of waters, local evaporation of the fresh water at the surface, and tectonic activity in the area of the sediment. Fluctuation of the zone of mixing allows great thicknesses of the sediment to be exposed to dolomitization. This model is often used to explain regional dolomites that have no associated evaporites. Dolomitization of the Dundee Formation by the Dorag model would yield regional dolomites associated with areas that were emergent in Dundee time. These emergent areas would allow formation of a fresh water lense and a zone of mixing. Prediction of the areas that were emergent in Dundee time could be accomplished by observing erosion of the Dundee on positive structures. Emergent areas of the Dundee may have been present on the extreme west and southwest areas of the state. The Dorag model of dolomitization may in 52 fact have been active in these areas. In the area of study, the Bell Shale and the Dundee have been shown to be conformable. No areas of emergence existed during Devonian Dundee time in the central basin. The Dorag model of dolomitization is not applicable to the area of study. Shale dewatering has been presented as a mechanism for dolomite formation. Dolomitization of existing limestones by connate water expelled during compaction of shales adjacent to or within the Dundee has been proposed (Illing, 1959, 1965). Metals may be derived from the sediment during dewatering, serving as a source of magnesium from Mg-calcite muds. Illing suggests dolomitization may occur as progressive burial releases water from the shales. This water, he suggests, may be more or less saline than the water in the limestone. This aspect of the model has similarities to the Dorag model, with mixing of waters controlling dolomite formation. If this model is applied to the area of study, the Bell Shale would typify the source of the water. Connate waters derived from the Bell would move downward into porous horizons of the Dundee and dolomitization would ensue. No major studies have been conducted on the relationship of the Dundee to the Bell Shale in terms of dolomite percent and chemical similarities. Richey (1980) believes shale dewatering accounts for little of the dolomite present in the Dundee. Less than 596 dolomite is found in the 20 foot interval of the Dundee next to the Bell Shale. A greater iron content occurs in the top 5 feet of the Dundee, which may indicate some of the iron was derived from the Bell (Tinklepaugh, 1957). Ten Have (1979) also. found the largest iron content in the top 20 feet of the Dundee. This could mean waters moved downward from the Bell or that the Bell Shale acted as an impermeable horizon to upward moving fluids. Mudt more detailed work is necessary before a solution can be determined. 53 In many of the producing Dundee fields, dolomite percentage has been shown to vary greatly over short distances, both vertically and horizontally (Richey, 1980; Ten Have, 1979; Hyde, 1979; Hamrick, 1978; and Jackson, 1958). These studies have suggested structurally controlled dolomitization along fractures and joints which formed epigenetic dolomite. The highest occurrence of dolomite is generally along the axes of the fields and associated with minor cross faults. Richey (1980) believes the dolomitizing fluids originated in horizons below the Dundee. The non-ferroan character of the dolomite and the increasing dolomitization with depth support this. Hyde (1979), using core samples, showed dolomite occurrence followed natural porosity zones present in the Dundee. Ten Have (1979) and Hamrick (1979) also suggested dolomitization along the porous zones in the Dundee, somewhat parallel to bedding. Most likely, these zones of dolomite followed previously porous zones rather than creating the porosity through dolomitization as some have suggested. The resultant epigenetic dolomites are lower in dolomite percentages than those formed by evaporative reflux on the west side of the state. Ten Have (1979) found a maximum of I43% dolomite in his study of the West Branch Field. Averages of 10% to 30% are common in a 20 foot interval of a producing field. Unlike the dolomite on the west side of the state, the epigenetic dolomite controlled by structure lacks lateral continuity (Gardner, 1974). A close relationship exists between porosity and dolomite occurrence. 0f the carbonate hydrocarbon reservoirs in North America, nearly 80% are dolomite mineralogies (Blatt, et al., 1975). The location of porosity and the presence of dolomite are essential for successful exploration in carbonate sequences. 54 The relative proportion of lime mud and coarser grains in the original sediment affects the porosity development. Lucia (1962) showed sediments remaining as limestones had higher proportions of crinoidal material and less than 35% lime mud. Sediments that were dolomitized, however, had higher proportions of lime mud and less coarser material. In Devonian sediments that are limestones, the best porosity is in rocks that were originally 5-20% lime mud. These sediments has a supporting framework which resisted compaction, and the lime mud inhibited the formation of cement (Bathurst, 1975). As the amount of lime mud increased over 20%, the porosity decreased, probably through compaction of the sediment. Schmoker and Halley (1982) suggested limestones are less resistant to the effects of compaction, and the associated increase in temperature and pressure with burial. The relationship between porosity and dolomitized sediments is complex. The majority of carbonate petrologists agree that dolomite formation give rise to porosity providing a solid framework is present which will minimize the effects of compaction (Chilingar, 1972). Weyl (1960) suggested a local source for carbonates involved in dolomite formation. Dolomite formation took place at the expense of nearby dissolved carbonates. The resultant dolomite would occupy a 12-13% smaller volume than the limestone it replaced. The difference in volume is reduced by compaction of the sediment until a solid framework of the dolomite crystals is formed. Dolomites are generally more resistant to the porosity reducing effects of temperature and pressure than limestones. Ten Have (1979) showed that Dundee dolomites have an increased porosity. He did not conclude whether the dolomitization created the porosity or the dolomite formed where there was higher original porosity. He suggested'that much of the dolomite formed in zones of initial porosity which provided porous avenues for transport of the fluids. 55 Bloomer (1969) identified five types of porosity in the Dundee dolomites: l) angular vugs lined with white dolomite crystals formed by the solution of breccia clasts, 2) solution of clasts without the dolomite lining, 3) vugs formed by solution of fossil fragments, 4) voids formed by the solution of anhydrite nodules, and 5) solution of replacement anhydrite. Studies have been done which investigate the role of fabric and texture selectivity during dolomitization. It has been shown that a fine grained material is more susceptible to replacement by dolomite than coarser grained material. The porosity and permeability of a dolomitized sediment varies intensely with the degree of dolomitization. Murray (1960) conducted studies on a number of samples of various percent dolomite. He found that for between 0% and 50% dolomite, a slight decrease in porosity occurred. For dolomite percentages between 50% and 80%, the porosity values increased rapidly to a maximum value of 30% porosity at 80% dolomite percent. The pore size and porosity increased with the increasing dolomitization. Dolomitization is an important mechanism for the formation and preservation of porosity in carbonate sequences. Successful hydrocarbon exploration depends on the location and knowledge of porosity trends. Dolomitization in the Dundee Formation controls the distribution of most of the production. The studies conducted on Michigan oil and gas fields have shown Dundee production to be from predominantly dolomite reservoirs. In the next section, the porosity trends in the Dundee are outlined and related to production in the area of study. Porosity in the Dundee Porosity values were calculated for the Dundee interval in the area of study. Porosity data were collected from suites of neutron, sonic, and density logs run by Schlumberger. The readings of the sonic, neutron, and density logs 56 depend not only on porosity, but also on the formation lithology and the fluid content. These logs respond differently and independently to the different matrix compositions, and to the presence of light oils or gas. A limestone matrix is the basis for all calibration of log runs in the central Michigan Dundee Formation. The combination of these logs can furnish more accurate information than can be supplied by a single log. The most common neutron logs run by Schlumberger in Michigan are the Sidewall Neutron Porosity log (SNP) and the Compensated Neutron Log (CNL). The Borehole Compensated Sonic log (BHC-Sonic) is the most common sonic log. Crossplots of two porosity logs are convenient to display both porosity and lithology characteristics. These crossplots place the bulk density (pb) or sonic transit time (t) against a correlated porosity value “CNL or (DSNP). Corrections to the porosity value measured on the logs are required for lithology, mud cake thickness, borehole salinity, mud weight, depth of measurement, and borehole temperature. These corrections are accomplished by the use of a Schlumberger nomograph (Figure 18) by one of the two following methods: 1) Log run with automatic caliper. "Back out" the caliper correction to find the "chart base" porosity. Go down to Reference (*), Block A, and follow trend lines to "Borehole Size Minus Panel Setting". This value is the chart base porosity. Draw a vertical line through all chart blocks at this value, as the one on Figure 18.- If "Borehole Size Minus Panel Setting" is negative, as in the example, normally assume that it is caused by mud cake. Do not make both borehole size (Block A) and mud cake (Block B) corrections. Beginning at Block B, find corrections for each block and add the algebraic total to the chart base porosity. This is the environmentally corrected CNL porosity. 57 Schlumberger-- DUAL SPACING NEUTRON LOG (CNL*) CORRECTION NOMOGRAPH FOR OPEN HOLE’ loam I... Penalty lust «Hg. ....2.p.u. he!!!” CM!“ "Um” “can... 1.0.6.“) Gent-Osmlsdh (ambit) ”rehash-mks MM. ....uw.u “MRI-‘5... 'M-Cet'....+4in. Mall“; 1|. "Ml-bis. Dre-Who‘d. MW. ....9Jbl.sl finds-Incision”- t. "um" pumps.) t. ....m‘r . (tun-en) MM)....lmhfil “Mosh-w ”Minnflbm WI—wvo-IJ9 “(illumlflhfl no-+2.o¢o.:-u+ “(Injunlflhm 0.7?0-251-13.-L0 m ....O lJ-M‘LJ‘J.‘ W ....O A.,-N“L0-26:u. M ....2|m0 ~‘274‘31-ma 01pm ....lmh 'Mdm . '97445 Figure 18. Correction nomograph for porosity value adjustment (Schlumberger, 1979). llllllllllll.[lll|l t ’lllllll til {I} 58 If "Borehole Size Minus Panel Setting" is positive, normally assume that the hole is washed out and mud cake thickness, if any, is indeterminate. Beginning with Block A, but skipping Block B, find corrections and proceed as above. 2) Log not run with automatic caliper. Draw a vertical line through all the blocks at the corrected CNL reading. If "Borehole Size Minus Panel Setting" is positive, begin at Block A and find corrected CNL porosity as above. Do not use both Block A and B. If "Borehole Size Minus Panel Setting" is negative, begin at Block B and find corrected CNL porosity as above. The value obtained after the nonograph corrections is an environmentally corrected porosity value. These values can now be used in any one of the proper crossplots. Neutron-Density crossplots are one type used. Figure 19 is an example of the crossplot. A Compensated Formation Density log (F DC) measures the bulk density of the rock (ob). This is plotted against a corrected porosity value MCNL) cor or (¢SNP)cor' The location of the crossplotted points determines the porosity value. In the example shown on Figure 19, oh = 2.62 and (¢CNL)c or = 13.5%. This defines point P, lying between the limestone and dolomite curves and falling near a line connecting the 10% porosity gradations on the two curves. Assuming the matrix is limestone and dolomite, by proportioning the distance between the two curves, the point is found to correspond to about l15% dolomite and 55% limestone. Sonic-Neutron crossplots are another type of plot used (Figure 20). The procedure is the same as for the Neutron-Density crossplot, but sonic transit time (t) is used instead of bulk density. 59 I———I POROSITY AND UTHOLOGY DETERMINATION FROM FORMATION DENSITY LOG AND ' SIDEWALL NEUTRON POROSITY LOG (SNP‘) MAYALSOBEUSEWWHGNTF.G.«HNEUTRONLOGS SALT WATER. LIQUID-FILLED HOLES n 0““-.. ’ L 2::m:-——‘"_- .7— Foce-SNP“ J Pf 3 LI ' I__ -."9""'"4 -.’.‘.""“ -.-..+.__”Sm ' . - 4‘ T“ 02’"... .-.... ._--- a.» P. sou: DENSITY. Nolm' . -_- -?—.-_. - hog ocusmt mnosm. ”Jpn-an. m-IJI («99.91" NEUTRON POROSITY INDEX. p.u. WENT uuss'rous mom . CP-Ib 'MdM Figure 19. Crossplot of CNL porosity and FDC bulk density for a corrected porosity determination (Schlumberger, 1979). 60 POROSITY AND LITHOLOGY DETERMINATION FROM SONIC LOG AND COMPENSATED NEUTRON LOG (CNL‘) '. ‘ A L A! I L I ' ' I L j r i L T Y I 7 cm O... - .n- - 517:2: 22.3mm can»; ..... ._.. . ,. 2:7: :7: -- 1,. I39 jig/fl;"“:;_:;::z:: 3‘. In”... _._....-....--.Eng:lhh -.._.._.._.. ..._ .- '_."' -o---l--— iw ~>oWfl--—o Cu. .- - b.-.-—-..vl :22; ':.:':::;s ééf- ._ A‘ n.-—.—---... a“--- an--- .—-.. o.-.“ ”— mneCA-u a. -9.-. I some TRAusIT TIIIIE. psi" ' 3 .— 4—.-.....J 4 "'©W°::::T:“ 7 , y "” ----... - - -- .——-—————-. u 1 . o .- - o I . I I . ‘ - e . ' v - o——-.- Qu-.. g;..-o—- Os--’.-.- -7 o.-. ~ . - -L’. _ V i ‘ - -I- O O u - J .-—— v— . J i r I t u—scoc—éou-V ' +- —_b.. u. -o — o oo- .-. .oo— ‘ ' . - r ‘ _—._.......--.~ g - -—.>~-.... fi_ quu-w-Qvfi--tO—Ow-Q . -—--o- -- ~- p. - A—A - —---\--‘.1----. o-.---. o no 20 co we“)... NEUTRON POROSITY INDEX. 9.0. (APPAREIIT LIMESTONE POROSITY) “tut-0m a.» Figure 20. Crossplot of sonic transit time (t) and CNL porosity for a correCted porosity determination (Schlumberger, 1979). 61 These crossplotted porosity values were placed on a map (Plate 5). Even though the number of wells useful in the crossplot method were limited, enough were available to develop some distinct trends. Zones of highest average porosity correlated well with areas which were structurally positive. Examples of this are found in the Winterfield and Cranberry Lake fields in Clare County, and along the Porter field in Midland County. The association of high porosity zones with positive structures has been determined in a number of field studies conducted on the Dundee in Michigan. These positive features are generally also associated with a higher dolomite percentage. Porosity in these zones may be in part due to faulting and fracturing, but it is primarily due to the effects of dolomitization. Murray (1960), and others, have found that increased porosity is related to the degree of dolomitization. The greatest increase in porosity occurs in the range between 50% and 80%. A decrease or redistribution of initial porosity occurs along with the process. This is more than compensated for by the replacement or dissolution of other fragments in the sediment which creates porosity. The high degree of lateral and vertical dolomite variability suggests that dolomites associated with positive structures are predominantly epigenetic. As one moves off structures in the area, dolomites and limestones which represent a more general regional Dundee Formation are encountered. This has been supported by previous studies as well (Powell, 1959; Jodry, 1954; Tinklepaugh, 1957; Egleston, 1957; Jackson; 1958; Paris, '1977; Dastanpour, 1977; Hamrick, 1978; Ten Have, 1979;Iand Richey, 1980). A large area of low porosity occurs in the northern half of Midland County. This area corresponds with the area of low dolomite percentage (Plate ’4). This indicates that at least in this location, preservation of primary porosity in the Dundee as a whole is not common. Zones and patches of higher porosity do occur 62 within the interval, but as a whole, the interval has very low porosity. These more porous zones are the avenues along which dolomitizing fluids would more should the proper structural and chemical environment develop. In general, a strong correlation exists between porosity, dolomite content, and structure. Recurring associations of porosity with high dolomite percentages and positive structures make these types of conditions most desirable as a prospective hydrocarbon reservoir. The association of these characteristics are the typical fields studied in the previous work in the Michigan Basin. Other types of reservoir conditions may exist which may be just as important. Detailed mapping of the porosity zones over smaller areas may locate porosity traps not located directly over positive relief structures. Some of the zones of porosity may be primary or early diagenetic, which were present in the rock before folding. The coincidental location near a forming positive structure can create a porosity trap on the flanks of the structure. Dolomitization need not occur in order for porosity to be present. The idea of initial zones of porosity not associated with dolomitization has important uses in exploration of the Dundee. In order to delineate these porous zones and trace them across an area, careful log to log correlation of various zones would be required, which is beyond the scope of this study. Such a study would yield important information regarding the type and distribution of porosity in the Dundee. Detailed petrographic work needs yet to be conducted on the Dundee interval where it is not associated with structures. Studies of the Dundee off structure could determine regional textural and lithologic characteristics. These regional characteristics in turn control the response of the Dundee to dolomitization. A composite of these studies would form a detailed history of porosity in the Dundee and allow prediction of possible economic reserves. PRODUCTION IN THE DUNDEE The Dundee Formation is the most prolific oil producing zone in Michigan. Production was first established in the Muskegon field on the west side of the state. Large scale production in the central Michigan Basin began with the discovery of the Mount Pleasant field in 1928. Since that time, over 200 oil and gas fields have been discovered in Michigan. The Dundee Formation reached maximum production in the late 1940's and has been steadily declining since then. According to figures published by the Michigan Geological Survey, the Dundee has produced 341,229,283 barrels of oil and 41,527,206 MCF of gas through 1979 (Ann. Stat. Summary 32). Many of the fields lie in a broad sweeping band that runs from west to east across the central lower peninsula, including the central basin area (Figure 21). Dundee fields, with the exception of a few, occur in a small central portion of the basin. A number of factors may contribute to this pattern. Ten I-lave (1979) suggests a correlation between the occurrence of the Bell Shale and production in the Dundee. The Bell Shale is fairly continuous over the basin and pinches out in the southwest corner of the state (Figure 21). Most areas in which the Bell Shale is absent represent shallow depths to the Dundee Formation, usually less than 1300' (Bloomer, 1969). Hydrocarbon loss can occur easily as this shallow depth and large accumulations are rarely found. Even at greater depths, in the absence of the Bell Shale, no cap rock existed, and hydrocarbons were probably lost to upper horizons. The source of the hydrocarbons may be the organic rich beds in the Dundee or deeper horizons in the stratigraphic column. The dynamic bottom drive ‘1 64 V gun-gtvoll A 'W ' «uvunv‘v ‘ C j spec's-s, ‘5‘°" gag-slne 00‘006 s .g..... lessen-On ‘ ’ “ use-009:; unified-Cl 1 2.4%-: '— '="' - .Fn .a—Il ‘8 . I it ". . cusses-‘8' .__ $55 bO'Cb- .‘ but! . ~.'| .‘.'°" 0 . r r H o . s a s ‘ k ‘ W"‘.'."-.1 4' . I I I . i , i 40~OUII~ cog-Gun Sh!aeieenr¢~sa less-OIOO i I If JOSID- IissIOAsC Figure 21. Dundee oil and gas fields in the Michigan Basin. 65 hydrologic systems prevalent in the Dundee fields suggests that the hydrocarbons or the hydrocarbon precursors were moved upward into porous zones of the Dundee in much the same way as as the hydrothermal brines moves upward. The movement of brines and hydrocarbons into the Dundee determines the regional extent of production. A study of the oil field waters and hydrocarbon characteristics may determine a correlation between the chemical environment and the occurrence of oil and gas. Specific chemical environments may be found to occur only in the central Michigan Basin which limit the development and movement of hydrocarbons into the Dundee. These chemical environments will not only depend on the Dundee, but on deeper horizons as well. Prouty (personal communication) has suggested brines present in the Dundee originate in the Prairie du Chien Group. These upwelling Prairie du Chien brines may control the location of hydrocarbon occurrence. A detailed study of the central Michigan Basin crudes and oil field waters could yield data for predictions of favorable conditions for hydrocarbon accumulation. The crude present in the Dundee is generally high gravity and paraffin based. Gravities range from 35° API to 45° API and average around 40° API (Newcombe, 1933). Variation in the sulfur content occurs, typically increasing downdip, as does the API gravity of the oil. The Dundee crudes are found in two major types of traps. Bell, Witherspoon, and Hautau (1956) categorized the type of traps on the basis of the structure, the location, and the type of porosity in the pay section. One type is anticlinal fields with localized sheet porosity. This sheet porosity may occur on several zones, but is normally best developed near the top of the pay. In several other fields, almost vertical lenses of well developed secondary porosity exist. The porosity development and hydrocarbon accumulation are controlled by a complex fracture porosity system, such as in 66 the Deep River field in Arenac County. Most of the fields have efficient bottom water drives and show high potential. Both of these trap types are found in the Dundee in the area of study. RECENT ACTIVITY Dundee exploration has been primarily limited to development of known structures. Of the wells drilled in Michigan, 7% are targeted to the Dundee. In the area of study, about 6% of the permits issued are for wells targeted to the Dundee. Permit locations have been issued for a number of well sites, but not all of these locations will actually be drilled. Permitting patterns can help to identify the areas of interest. In a recent State of Michigan oil and gas lease sale, tracts of land were offered in Clare County. Bidding on the parcels ranged from the minimum of $4 per acre to $220 per acre. The highest bids were for tracts close to known producing oil fields. Several tracts within or adjacent to the Headquarters and Skeels fields in Clare County brought bids of over $150 per acre. Both of these fields have more than one pay horizon, including the Dundee and Richfield. Dundee discoveries have been limited in the past few years. In 1979, Don Yohe Enterprises made a Dundee pool discovery, the Lake Isabella Corporation #1-9, in the Broomfield field. The well was good for an initial production of 15 BOPD and 15 BWPD. Production is from approximately a 3 foot section of dolomite at a depth of 3752 feet. Also in 1979, the Chase Oil- Company discovered a Dundee pay with the Wonsey ill-24 in Rolland Township, Isabella County. Initial production was 25 BOPD and 25 BWPD from 6 feet of dolomite. These two discoveries are the latest in the area of study. Drilling activity in the four county area has concentrated on development of the two new Dundee pools and extensions of existing pools. The Dundee completions for 1981 and the first quarter of 1982 are given in Appendix 111. A7 68 Only one well, the Muskegon Development Company Pohl #1-36 was classified as exploratory, with all other Dundee wells classified as development. The most active area is in Isabella County. The Broomfield Dundee discovery kicked off a series of wells in the area. In all, 7 wells were completed in 1981, and 9 have been completed so far in 1982. Of these 16 wells, 12 have produced Dundee oil and 4 have been dry. The combined production in the new Broomfield field is about 300 BOPD. Other existing fields in Isabella County experienced continued development, notably the Rolland field. This field had 4 development wells drilled during 1981, with 3 finding oil. Development wells were also completed in the Vernon, Leaton, and Mount Pleasant fields. Clare County did not have any wells completed in the Dundee Formation during 1981. A number of wells were completed to deeper horizons and will be discussed later. Drilling activity was also low in Midland County, centering on the Porter field. Development drilling in Gladwin County centered on the North and South Buckeye fields. The Wiser Oil Company drilled all of the wells in these fields during 1981 and 1982. In the South Buckeye field, 4 wells were completed for oil in the Dundee, and one oil producer was completed in the North Buckeye field. Horizon Oil and Gas struck oil in the Beaverton field with the Cingano #1-36. In all, 23 wells were drilled to the Dundee during 1981 in the area of study. In the first 5 months of 1982,“ wells were drilled to the Dundee. Of these 34 wells, 25 have produced oil for a success ration of 73.5%. The Dundee well depths range from 3600 feet to about 3800 feet. Average production from these Dundee wells is about 25 BOPD. The Dundee Formation is nonprorated in Michigan, with no limit placed on the 69 maximum daily production. As of August 1, 1982, oil produced from the Dundee yielded $31 per barrel. Figures published recently outlined the cost of drilling and completing a Dundee well in the central Michigan Basin during 1981. Drilling a 3900' well costs an average of $160,875, and completion costs an additional $151,875, for a total cost of $312,750 per well. On a per foot basis, drilling and completion .in the Dundee costs about $80.19 per foot. These costs have increased drastically in the last few years. The values given above represent a 37% increase in drilling costs and a 14% increase in completion costs of 1979 prices (Oil and Gas News, 1982). Drilling activity to other horizons continued in the area of study. A Prairie du Chien test, the Hunt Winterfield Unit A-l, struck gas in commercial quantities in Clare County. Other deep tests to the Prairie du Chien have proven dry, and interest in the horizon is dwindling in the area of study. To the west, activity in the Prairie Du Chien is somewhat more stable. Many of the Richfield development wells drilled during 1981 were located over Dundee structures. A common practice of locating deeper tests over known Dundee structures has had great success in the basin. The possibility of striking oil may exist in more than one horizon. Most of the Richfield wells were confined to development. A discovery in the Richfield occurred in the Leaton field in Isabella County. The Traverse Lime and the Berea continued to be targets in the area, with 5 wells to the Traverse and 7 to the Berea. Two Berea discoveries occurred in 1981, the Burgess Traverso #1, and the Union Mary Narmore #46, both in Midland County. CONCLUSIONS From the maps prepared and from data obtained from various sources, certain conclusions may be made concerning the Middle Devonian Dundee in the central Michigan Basin. Distinct structural trends exist in the central basin. A strong northwest- southeast lineament is observed, with a weaker northeast-southwest lineament. Configuration of these structures is controlled by vertical tectonics. The Precambrian rock surface is believed to be heavily faulted and fractured, with relief created by the relative vertical movement of adjacent blocks. The faulting observed in the Canadian Shield to the north may continue into the Michigan Basin and control the structural trends in the central basin. These structures occur en echelon and create oil field traps by folding and crossfolding of the overlying strata. Two types of Dundee fields are commonly created in the area of study: circular fields and linear, somewhat arcuate fields. Both of these field types are normally asymmetrical The Bell Shale thickens to the northeast in the central basin. This thickening corresponds to the position of the Devonian depocenter northwest of Saginaw Bay. The Bell Shale is a transgressive shale which onlapped the Dundee surface from the east and northeast. A source for the shale would also be to the east or northeast. . The isopach map of the Bell (Plate 2) shows some areas of minor thinning or thickening in subparallel trends to the Dundee structures. This suggests that the surface of the Dundee had at least some relief as the Bell was being deposited. A gently undulating submarine surface may have been present at the close of Dundee time. 7n 71 Local areas of variable thickness are also observed in the Dundee interval (Plate 3). A variety of mechanisms may control the thickness of the Dundee. The configuration of the Detroit River surface created areas more favorable to carbonate buildup. These slightly positive Detroit River structures shallowed the water and effectively promoted reef growth. Carbonate buildup occurs more rapidly on these areas relative to the deeper water areas. This process of "reefing" best explains the location of thick Dundee intervals on the top of structural highs. Later structural activity can accentuate the positive structures. Studies conducted on the central Michigan Basin suggests a major period of deformation occurred in Pre-Marshall Mississippian time. The Dundee in the area of study is typically a brown to gray biocalcarenitic wackestone or packstone. Fossil types include corals, brachiopods, stromatoporoids, and crinoidal debris. Scattered groups of stylolites are found, many containing a black residue, and they occur roughly parallel to bedding. In some areas the Dundee becomes heavily brecciated and fractured. The Dundee is locally dolomitized in the basin, and distribution of the dolomite follows distinct trends. The highest percent dolomite in the Dundee interval is typically over or directly adjacent to the positive structure. The wide variation in the dolomite percentages over these structures indicates epigenetic dolomite. This dolomite is strongly associated with the structure, usually decreasing rapidly off structure. Epigenetic dolomitization occurs along faults, fractures, and porous zones within the Dundee. These porous zones in the Dundee may be a primary porosity zone in the carbonate or porosity formed during an earlier diagenetic process. When dolomitization does occur, these porous horizons are preferentially dolomitized. This creates the strong association of dolomite with porosity zones. 72 Dolomite can form in the Dundee without an associated structure. Dolomite that is not associated with a positive structure may be an early diagenetic dolomite. This diagenetic dolomite forms lenses or layers with obscure stratification. Porosity in these dolomites is generally slight and they are fine grained. Location of these diagenetic dolomites can be off structure or over structure, since they were formed before the folding of the strata. Dolomite formation in the area of study proceeded by one of three mechanisms. The dolomite associated with structures, epigenetic dolomite, formed by fluids moving through the rock along fractures and faults, and porous zones as stated earlier. These types of dolomites are associated with much of the Dundee production in Michigan. Diagenetic dolomite, was formed much earlier in the history of the Dundee strata. These patches of dolomite are controlled by both primary porosity and textural characteristics. Shale dewatering, to a minor extent, may be responsible for a small percentage of the dolomite formed in the Dundee. Dolomite formed in this way is normally confined to the upper horizons of the Dundee. More detailed petrographic and geochemical work is needed to determine the importance of this mechanism. Porosity and increasing dolomite percentages in the Dundee follows many of the same trends. Dolomitization of a carbonate creates porosity when the rock is altered to greater than 50% dolomite. This trend is observed in the central basin, with areas of greatest porosity often corresponding to areas of high dolomite percent and structure. This trend has been outlined in a number of previous studies of carbonate sequences. Dolomites not located over structures are representative of the regional dolomites in the Dundee. These dolomites are typically low in porosity and have 73 a lower percent dolomite content. The low porosity values normally obtained for these regional dolomites suggest that porosity is not well preserved in the Dundee. Northern Midland County is an example of an area of regional diagenetic dolomite. While it is true that the regional dolomites do not have as high an overall porosity value as epigenetic dolomites, porosity zones can exist within the interval. Diagenetic dolomites that have had later structural activity may create hydrocarbon traps. . The best reservoirs are positive structures, faulted and fractured, with associated high dolomitization and increased porosity. Cranberry Lake and Winterfield fields are good examples of this type. Dolomite distribution in these fields is strongly controlled by structure and production will be from these horizons. Porosity which is not related to structure, formed prior to the folding, may create traps off structures or on the flanks of structures. This concept has interesting applications in the central basin. Positive structures which have been tested on the axis and have proven nonproductive may in fact produce from diagenetic porosity traps on the flanks. Production from the Dundee interval will continue exploration interest in the area. While it is believed few large fields remain to be discovered, many small fields likely await discovery. The lower cost of Dundee wells and the shallower drilling depth make Dundee wells a way to establish regular production in the area. The drilling of development wells and the deeper drilling of known structures will dominate the Dundee exploration programs in the Michigan Basin. Another, interest will lie in the exploration of older fields and previous tests which were considered noncommercial. Advances in recovery techniques, and knowledge of the productions trends, may create new interest. in horizons 74 once thought nonproductive. Many of the older Dundee tests drilled only a few feet into the formation and stopped after production was not obtained at the Dundee-Bell contact. These areas represent locations in which deeper testing may find hydrocarbons. SUGGESTIONS FOR FURTHER STUDY Information is far from complete concerning the Middle Devonian formation in the central basin. In order to clarify the relationships that exist between dolomitization, porosity, structure, lithology, and production the following suggestions are made: 1. A study of the Bell Shale to determine the chemical, structural, and physical relationship to the Dundee. The relationship of the Bell shale to production in the Dundee may be determined, as well as the relationship of dolomite percent in the Dundee. 2. A detailed petrographic study of the Dundee Formation, primarily the intervals present off structure. This may yield a typical regional dolomite and aid in the exploration for traps not associated with epigenetic dolomites on structure. 3. A study of the oil fields brines and hydrocarbons may allow the determination of the source of the fluids and oils. This would shed light on the controls and mechanisms of dolomite formation. 4. Detailed mapping of the porosity zones present in the Dundee interval. These patchy, noncontinuous zones are related to initial porosity and porosity developed much later in the diagenetic history. Mapping of the units on cross-sections may determine porosity traps off structure. 7‘ REFERENCES REFERENCES Adams, J. E. and Rhodes, M. L., 1960. Dolomitization by seepage refluxion: Amer. Assoc. Petrol. Geol. Bull., v. 44, p. 1912-1940. Back, W. and Hanshaw, B., 1970. Comparison of chemical hydrology of carbonate Peninsula of Florida and Yucatan: Jour. Hydrology, v.10, p. 330-368. Badiozamani, K., 1973. The Dorag dolomitization model — application to the Middle Ordovician of Wisconsin: Jour. Sed. Petrol., v. 43, p. 965-984. Bathurst, R. G. C. (ed.), 1976. Carbonate sediments and their diagenesis: Developments in Sedimentology, v. 12, Elsevier, Amsterdam, 658p. Beales, F. w. and Oldershaw, A. E., 1969. Brecciation and Devonian carbonate reservoir porosity in western Canada: A.A.P.G. Bull, v. 53, no. 3, p. 503-512. Bebout, D. G. and Pendexter, C., 1975. 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Illing, L. V.; Wells, A. J. and Taylor, J. C., 1965. Penecontemporaneous dolomite in the Persian Gulf: Soc. Econ. Paleont. Mineral., Spec. Publ., no. 13, p0 89-1110 Jackson, R. P., 1958. Dolomitization and structural relations of the Deep River, North Adams, and Pinconning Oil Fields, Michigan: Unpub. Masters Thesis, Michigan State Univ. Kirkham, V. R. D., 1937. Theory of origin of oil and gas bearing folds in Michigan and theory of origin of oil and gas: Mich. Oil and Gas News, May 15. Knapp, T. S., 1979. Devonian oil fields in Michigan (abst.), i_n The Hydrocarbon Potential; the Michigan Basin; The Way Ahead (anonymous): Mich. Basin Geol. Soc., Lansing, Michigan, U.S.A., p. 14. Krauskopf, K. B., 1967. Introduction to Geochemism, p. 85-88. Krumbein, W. C. and Sloss, L. 0., 1963. Stratigraphy and sedimentation: 2nd ed., Freeman and Co., San Francisco, p. 71-74. Land, L. S., 1973a. Contemporaneous dolomitization of Middle Pleistocene reefs by meteoric water, north Jamaica: Bull. 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The origin of common dolomite textures: clues from the Pliocene: Unpublished. Schmoker, J. W. and Halley, R. B., 1982. Carbonate porosity versus depth: "compaction" curves for south Florida: In press. , 1982. High porosity Cenozoic carbonate rocks of south Florida: progressive loss of porosity with depth: In press. Schlumberger, 1979. Log interpretation charts: Schlumberger Limited, Inc., New York, 97p. Syrjamaki, R., 1977. Stratigraphy of the Prairie du Chien Group of the Michigan Basin: Unpub. Masters Thesis, Michigan State Univ. Ten Have, L. E., 1979. Relationship of dolomite/limestone ratios to the structure of the West Branch Oil Field, Ogemaw County, Michigan: Unpub. Masters Thesis, Michigan State Univ. Thomas, G. E., 1962. Grouping of carbonate rocks into textural and porosity units for mapping purposes, i_n Classification of Carbonate Rocks: Amer. Assoc. Petrol. Geol., Mem., no. 1, p. 193-223. Tinklepaugh, B. M., 1957. A chemical, statistical, and structural analysis of secondary dolomitization in the Rogers City Dundee Formation of the central Michigan Basin: Unpub. Masters Thesis, Michigan State Univ. Wanless, H. R., 1979. Limestone response to stress: presure solution and dolomitization: Jour. Sed. Petrol., v. 49, no. 2, p. 437-462. ‘ (Weyl, P. K., 1960.' Porosity through dolomitization: conservation of mass requirements: Jour. Sed. Petrol., v. 30, p. 85-90. APPENDIX I 82 'P-—-- . a. s '34:" i‘fiW‘fi'ITi'i 2 0‘ ”In.“ 1‘ I: u- “a.“ sures. ELI‘HJI m I 19 «egg. WK. not sum Hues» mm ' ,_. —. 31....-.” G n, A 1% '18 C EA'DTN union an M 0L::: sucxflt M' “:- ' .- I I mun 1 hum sentry ' mu: Y 3“" stunt» routed 7._E': _ -_._____--I--—-J. annual sen-oar m- uou unus- (use: tutu I 'suumu I“- stun duo-c tumour uni:- IL15 I” :7" I, Ll: ”Jim. ; 1svrm: V at l—s-Aff‘ii—E-L-L-A' m" ' . ' a... II: ii:- @431- Figure 22. Index map of township names and locations. 83 ooun oaon o: No. .n saw 9:20 95.0%.. mezmz .. 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Z... .00 000000 :00 .000. 000052 000052 0:0". 00.000000 00.00000 000.com . $000. 00... 00... 00... .>0.m. 0.800.. :03 \n..0m.030... 000005000. . 0000000.. APPENDIX 11 Tribal Oil Company Appendix 11. Sample well descrifiion. Exploratory Dry Hole TD 4081 in Detroit River 22-19N-1W Gladwin Twp. (Gladwin Co.) Permit No. 29065 James S. Graver No. l-22 Location: Elevations: 3577-3738 3738-3741 374 l-3742.3 3742.3-3742.95 3742.95-3745.0 3745.0-3756.0 37 56.0-3772.66 3772.66-3798 3798-3803 3803-3816 NW K NW K NW K Section 22, T.l9N., R.lW. 330 feet from North and 330 feet from West line of quarter section. 803.7 Kelly Bushing BELL SHALE Shale: gray, soft, fossiliferous CORE NO. l 13738-3798 Recovered 31.66/60.0' (3741-3801 drillers measure) Lost on connection Shale: dark gray Shale: dark gray, calcareous, hard, crinoidal DUNDEE Limestone: dark gray, fine crystalline, argillaceous, crinoidal, some horizontal banding Limestone: dark gray-brown to brown-gray, fine crystalline, mottled, churned, slightly crinoidal, dense, some medium irregular, dolomite filled voids, stylolite at 3746.7, crinoidal band at 3745.2, numerous corals 3748-3750 (Core droped on rig floor from 3751-3772.66, pieces out of order) Limestone: as above becoming gray-brown, less mottled on surface Lost in hole. Drilled with rock bit 3708-TD No samples Limestone: brown, fine crystalline, slightly porous, no show. Poor samples to 3820-30 sample 3816-3874 3874-3901 3901-3930 3930-3946 3946-3952 3952-3985 3985-4033 4033-4050 4050-4055 4055-4065 4065-4076 4076-4081 4081 92 Appendix II (Continued). Limestone: light brown to buff, fine to very fine crystalline matrix, occasional coarse crystal, partly fragmental "reworked", some small vugs, pyritic, trace limestone: brown, fine crystalline, tight, some medium-coarse, white dolomite crystals, some scattered, "dead" carbonaceous stain 3837- 3843, no fluorescence, no gas show Limestone: as above, fragmental, spotted porous, no show and Dolomite: light brown to brown, fine-medium crystalling to partly sucrosic Limestone: brown and dark brown, fine crystalline, slightly argillaceous, some white dolomite infilling, some vugy porosity, some Dolomite: light brown, fine-medium crystalline, spotted porosity, no show Dolomite: brown and dark brown, fine-medium crystalline to partly coarse crystalline, partly calcareous, porous Limestone: dark brown to gray-brown, fine crystalline, argillaceous, tight and Dolomite: brown, fine-medium crystalline, some white dolomite infilling Dolomite: brown to dark brown, fine-medium crystalline, occasional dead stain, slightly argillaceous in part Dolomite: brown with some light brown to buff, fine-medium crystalline, partly argillaceous, some white dolomite infilling, spotted vugy porosity Limestone: brown to slightly gray-brown, fine crystalline, partly dolomitic, some Dolomite: as above, some white dolomite infilling, some Dolomite: dark brown, fine crystalline, argillaceous Dolomite: brown, very fine sucrosic, porous Dolomite: as above, trace Limestone: gray-brown, fine crystalline, tight, with Anhydrite: white to light brown DETROIT RIVER ANHYDRITE Dolomite: brown, very fine sucrosic, Dolomite: light brown, very fine sucrosic, anhydritic, with Anhydrite: white to light brown Limestone: light brown and light gray-brown, fine crystalline, tight, some Dolomite: as above Total Depth Schlumberger - 4092 TD Driller APPENDIX III 93 2:222... 2% ..0 558.28 59.8... a: 02026 , 0. 5.5.022 Sm ~02 £5 ..0 558.050 22.58... 3.3% 35.2... 9. 533...... .0 23> NR... 3% :0 5058.28 23.58... £029.. .362... 3 .533 :8 «RR «Sn <5 5058.28 23.585 3323... 226.2... <0.-. «:38. .0... 5:: 39.... 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