Western Michigan University Western Michigan University ScholarWorks at WMU ScholarWorks at WMU Master's Theses Graduate College 8-2012 Reservoir Characterization and Enhanced Oil Recovery Potential in Reservoir Characterization and Enhanced Oil Recovery Potential in Middle Devonian Dundee Limestone Reservoirs, Michigan Basin, Middle Devonian Dundee Limestone Reservoirs, Michigan Basin, USA USA Abrahim Abduslam Follow this and additional works at: https://scholarworks.wmich.edu/masters_theses Part of the Geology Commons, and the Sedimentology Commons Recommended Citation Recommended Citation Abduslam, Abrahim, "Reservoir Characterization and Enhanced Oil Recovery Potential in Middle Devonian Dundee Limestone Reservoirs, Michigan Basin, USA" (2012). Master's Theses. 21. https://scholarworks.wmich.edu/masters_theses/21 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].
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Western Michigan University Western Michigan University
ScholarWorks at WMU ScholarWorks at WMU
Master's Theses Graduate College
8-2012
Reservoir Characterization and Enhanced Oil Recovery Potential in Reservoir Characterization and Enhanced Oil Recovery Potential in
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 Compartmentalization and Reservoir Distribution 77
Stratigraphic Correlations and Cross-sections 78
VI. DUNDEE HISTORIC PRODUCTION AND ENHANCED OIL
RECOVERY (EOR) POTENTIAL 87
Historic Production 89
West Branch Field 90
South Buckeye Field 92
Mount Pleasant Field 93
Enhanced Oil Recovery (EOR) 95
VII. CONCLUSIONS 100
BIBLIOGRAPHY 102
APPENDICES
A. Core Descriptions 108
B. Core Charts (Adobe® Illustrator) 148
C. Core Photographs 175
D. Conventional Core Analysis 183
E. Cross-sections 222
v
LIST OF TABLES
1. Stratigraphic section of the Rogers City Limestone, Dundee Limestoneand overlying Bell Shale from outcrop in northeast Michigan 15
2. Cores used in this study 26
3. Dunham classification of carbonate rocks 2
vi
LIST OF FIGURES
1. Location of the study area illustrating the targeted Middle DevonianDundee Oil Fields 4
2. The major structural features of the Michigan Basin 6
3. Basement province map of the southern Peninsula of Michigan 8
4. Structure map of North and South Buckeye oil fields in GladwinCounty, Michigan 9
5. Proposed paleogeography distribution map, showing that the MichiganBasin was located at 30° south latitude during the Middle Devonian 10
6. Stratigraphic column of the Michigan Basin with the Rogers City andDundee formations highlighted in red circle 13
7. Slabbed core and thin-section showing the Rogers City and Dundeecontact from Schember-Shears #3, South Buckeye Field 15
8. Cross-section showing the contact between Rogers City and Dundee:the contact is readily picked in the presence of anhydrite capping theDundee unit in the western part of the Basin (blue box) 17
9. Map of the Michigan Basin showing the spatial distribution of Dundeedepositional environments and cross-sectional (K-L) view of thetransitioning lithologies 19
26. Cross plot of porosity and permeability measurements from whole coreanalysis of fenestral, peloidal grainstone/packstone facies 51
27. The thin-section photomicrograph showing an example of fenestralvugs filled by fine grained micritic internal sediment (red arrow) andthe remnant pore spaces within the fenestrae filled with sparry calcite(yellow arrow) 51
28. The micrite envelopes of the outer part of the shell are a result ofmicrobial microboring and infilling of the holes by micrite 54
Vlll
List of Figures—Continued
29. (A) An example of predominantly intraparticle porosity in crinoid stemand stromatoporoid (yellow arrow) (B) Crinoid fragments and otherskeletal fragments, including mollusks, are dissolved leaving abundantmoldic porosity (yellow arrow) in relatively fine grain matrix 56
30. The open galleries of the stromatoporoids are extensively occluded bycalcite cement (yellow arrows) in facies 3 of the North Buckeye Field 56
31. Fenestral fabric in tidal flat facies showing fenestral porosity (Fs) inlight blue that is larger than the associated peloidal texture 57
32. Example of meteorically leached mollusk shells resulting in moldicporosity in the crinoidal grainstone facies 58
33. The syntaxial overgrowth on crinoid ossicles (Cri) has reduced most ofpre-existing interparticle porosity (yellow arrows) 59
34. The presence of fractures (when unhealed with calcite cement) in manycases, can greatly increase the permeability of the rock 61
35. Thin-section photomicrograph of large amplitude stylolites typical ofmany stylolite solutions seems in carbonate mud matrix 61
36. Depositional setting for the seven depositional facies of the Rogers Cityand Dundee Limestone 63
37. Idealized vertical stacking patterns of seven facies seen within the coresexamined in this study 68
38. Stacking pattern in different facies areas/fields observed in the RogersCity and Dundee interval from the six fields 69
39. Changes in sea level recorded in the Middle Devonian deposits inGivetian stage, red star shows the proposed Rogers City and Dundeecontact at approximately 390 Ma 70
40. All core measured porosity-permeability data with the three reservoirfacies highlighted 75
42. Modern analog from the Persian Gulf is used to demonstrateinterpretations of lateral continuity in peritidal facies 82
43. Stratigraphic cross section (A- A') across South Buckeye Field showinglateral variations in the stromatoporoid boundstone facies (marked inyellow) 85
44. Example ofmodern patch reef complex in the Belize coast 86
45. Average per well water production from representative fields with twodistinct trends of relatively high water production per well frominferred bottom water drive in Rogers City (RGRC) dolomite Fields(Fork, Vernon, Crystal, and Deep River Fields) vs. relatively low waterproduction from probable gas expansion drive in Dundee (DUND)Limestone Fields (West Branch and South Buckeye Fields 88
46. Performance history of the West Branch Dundee reservoir showing theoil production per year (green line) associated with primary andsecondary annual decline (pink line). In the West Branch Field, thewaterflood began in 1966 91
47. Performance history of the South Buckeye Dundee reservoir showingthe annual oil production (green curve) and annual water production(blue curve) associated with annual decline (pink line) 93
48. Performance history of the Mount Pleasant Dundee reservoir showingthe annual oil production (green curve) and annual water production(blue curve) associated with 4.5% annual decline (pink line) 94
49. Example of three wells of the fenestral facies showing the heterogeneity(porosity and permeability) within a single well 99
x
CHAPTER I
INTRODUCTION
Summary of the Problems
In carbonate reservoirs, the heterogeneity of reservoir rock properties is a
fundamental complexity that complicates the effective production of hydrocarbon.
Therefore, this research is focused on understanding the geological origin of
heterogeneity on the basis of detailed sedimentologic, petrophysical, and petrographic
study of Middle Devonian Dundee carbonate reservoirs.
Middle Devonian Dundee Limestone reservoir facies in the Michigan Basin
are very heterogeneous and have confounded reservoir quality prediction in most
important hydrocarbon targets. Generally, prediction of vertical and lateral geological
heterogeneity of Dundee Limestone reservoirs and the consequent variation in
petrophysical properties, including porosity and permeability remains a major
problem for exploration and especially, effective production practices. Furthermore, a
better understanding of the regional and in-field distribution of reservoir facies and
reservoir quality in the Dundee can be useful during the enhanced recovery stage of
production, when the detailed understanding of internal heterogeneity of reservoir
facies can be used to increase hydrocarbon recovery from remaining oil in the most
important producers in the Michigan Basin.
Preliminary Hypotheses
Addison (1940) and Curran and Hurley (1992) describe production in the
Dundee Limestone Formation from several pay zones with considerable variation in
thickness, lateral continuity and petrophysical properties. Syndepositional local
structures may have resulted in limited lateral continuity of some, but not all,
reservoir facies. For instance, the presence of patch reef facies may indicate isolated
and non-continuous facies that pinch out on a spatial scale of less than 100 meter
associated with local paleobathymetry highs. Elsewhere, in the absence of patch reef
reservoir facies, grainstone reservoir facies may have greater lateral continuity. The
geometry of facies distribution and reservoir properties are attributable to variable
depositional environments and diagenetic alteration in different Dundee Limestone
fields. In particular, it is uncertain if the key control on reservoir quality is
depositional facies, or syndepositional and postdepositional processes (physical-
chemical) of burial diagenesis.
This study undertakes a sub-regional study of the Dundee Limestone (i.e.
detailed geological and petrophysical characterization) in order to discriminate
between these hypotheses. This will provide a better understanding of reservoir
quality in order to better evaluate the most prospective EOR targets in Dundee
Limestone oil fields in the Michigan Basin.
Thefundamental questions addressed in this study are:
1. What are the important reservoir facies and petrophysical properties of
reservoir facies in the Dundee Limestone?
2. What is the spatial distribution and geometry of Dundee heterogeneity in
reservoirs?
3. What petrophysical and reservoir geometry properties are most prospective
for EOR in the Dundee?
Research Objective
The main objective of this study is to evaluate EOR potential with a focus on
reservoir petrophysics and geometry in several representative Dundee oil fields.
Previous studies have addressed individual reservoir facies, determining the
calcite/dolomite ratio, and production characteristics in Dundee oil fields. However, this
research is an attempt to determine sedimentary lithofacies in high resolution scale
through the development of reservoir characterization method for EOR, and to create a
robust depositional model. This integrated approach uses representative core
observations, petrophysical data, core to wire-line log correlations, and the comparison
of production history data to geological reservoir characterization data to understand
diverse Dundee Limestone reservoirs facies.
A better understanding of vertical and areal porosity and permeability
distribution is significant in planning and implementing waterflood, or CO2 Enhanced
Oil Recovery projects in different Dundee oil reservoirs. The petrophysical properties
are the key to prediction of reservoir quality and heterogeneity, and to the assessment of
potential reservoir, production, and ultimate recovery. Furthermore, EOR projects can
be better designed to take advantages of the discontinuous reservoir facies geometry
(i.e., patch reef).
This study has determined sedimentary lithofacies and the reservoir properties
in six large Dundee oil fields in which primary depositional facies dominate the
geological control on reservoir properties. These fields include Mt Pleasant, Wise,
South Buckeye, North Buckeye, Butman, and West Branch fields, which are located
3
in the central Michigan Basin within Isabella, Midland, Gladwin, and Ogemaw
Counties (Figure 1).
The intensive study of the petrophysical properties and spatial geometry of the
reservoir facies in several Dundee limestone reservoirs provide a better insight for the
assessment of EOR potential within different Dundee Limestone reservoirs in the
Michigan Basin.
CORE 15
O• Butman
GLADWINBuckeye North
iBuckeye South
MIDLAND
ARENAC
BAY
Figure 1. Location of the study area illustrating the targeted Middle Devonian DundeeOil Fields. The cores used in this study are marked by purple circle.
CHAPTER II
REGIONAL SETTING
Michigan Basin
The Michigan Basin is a large, nearly circular, intracratonic Basin in the North
America craton. The Basin is encircled by the Canadian Shield to the north, the
Kankakee arch to the south, Findlay-Algonquin arches to the east and southeast
(Figure 2), and to the west and northwest by the Wisconsin arch and Wisconsin
Highland (Cohee and Landes. 1958). The total area of the Basin is 80,000 mi2
(207,000 km2) which contains up to 16, 000 ft (4800 m) of the Paleozoic sedimentary
rocks. The Basin is predominantly Cambrian marine siliciclastics overlain by Early
Ordovician to Middle Devonian carbonates and evaporites (Cohee and Landes, 1958;
Catacosinos et al., 1990). It has been noted that carbonate rocks are the predominant
lithology in the Michigan Basin (Rullkotter et al., 1986). A Pre-Cambrian complex of
igneous and low grade meta-sedimentary rocks occurs within a major north-northwest
to south-southeast trend associated with a basement gravity anomaly located in the
central portion of the Michigan Basin. This anomaly is interpreted as a failed
Proterozoic rift system and a portion of the Mid-Continent Rift (Fowler and Kuenzi,
1978). Faults and fractures in the Basin mostly trend northwest to southeast and are
associated with the Paleozoic anticlines. These structures characterize the intrabasinal
structural grain of the Michigan Basin (Catacosinos et al., 1990).
Figure 2. The major structural features of the Michigan Basin. Black ring shows theapproximate extent of the Michigan Basin (Modified from Catacosinosetal., 1990).
Much work has been done on characterizing the structural geology of the
Michigan Basin (Pirtle, 1932; Cohee and Landes. 1958; Hinze and Merritt, 1969;
Hinze and Kellogg, 1975; Prouty, 1983; Catacosinos et al., 1990). The Michigan
Basin is characterized by a dominantly northwest to southeast structural trend. Hinze
6
and Kellogg (1975) concluded that the structural phenomenon is a reflection of the
northwest to southeast structural grain in the Precambrian basement and the influence
of subsequent Paleozoic horizontal stress.
Based on the lithologic data collected from drill holes and geophysical data,
Hinze and Kellogg (1975) divided the Precambrian basements province into four
major basement structures: 1- Grenville province in the southeast, 2- Keweenawan rift
zone which transects the Basin in a northwest-southeast trend, 3- Central province in
the southwest and 4- Penokean province in the north (Figure 3).
The general structure interpretations present in the study area are based on
mapping the top Rogers City, a distinctive boundary below the superjacent Bell Shale
in the gamma ray log. These formation tops were picked from wire-line log data. The
basement structural highs trend northwest-southeast and created a possible substrate
for patch reef buildups in the Devonian (Catacosinos et al., 1991). Montgomery
(1986) noted that the South Buckeye field is present on a positive structure
corresponding to the major northwest-southeast trend in the central Michigan Basin
(Figure4), whereas in the nearby North Buckeye field the axis of the anticlinal
structure is transverse to the regional trend. In the West Branch field, about 30 mi (48
km) northeast of North and South Buckeye fields (Figure 1), Curran (1990) described
an asymmetrical anticline with a northwest- southeast trend. The best example of the
larger structural northwest-southeast trend is the Mt Pleasant field, which is
conceivably related to the basement movements (Little, 1986).
MAFIC EXTRUSIVE
AND INTRUSIVE ROCKS
MAFIC VOLCANIC ROCKS
Penokean (1.6-1.8 BY}
Keweenawan{l.QS-1.1B.Y)
Grenville<0.8-1.1 B.Y)
entral(U-1.5B.Y
^^Predominant Structuraltrend
Figure 3. Basement province map of the southern Peninsula of Michigan (Modifiedfrom Hinze et al., 1975).
KEY
— — TowraNp boundariesContour interval: 20 feet
Contoured on the base of the Belt Shale
;Ki!OfTw?te r1.6
filW ft 11
R1W R1E
Figure 4. Structure map of North and South buckeye oil fields in Gladwin County,Michigan (McCloskey, 2012).
Devonian Stratigraphic Framework
Devonian strata represent the second most prolific oil producing units of the
Michigan Basin. Middle Devonian oil producing formations have several significant
reservoir and seal systems, and some of these formations are also EOR and CO2
sequestration targets.
The intracratonic Michigan Basin during the Devonian (385 million years)
was located 20-30 degrees south of the equator (Figure 5). The proposed
paleogeographic distribution map for the Middle Devonian suggest that the Michigan
Basin was located in shallow tropical marine environments, which promotes
carbonate sedimentation (Scotese, 1984 and Blakey, 2005).
Figure 5. Proposed paleogeography distribution map, showing that the MichiganBasin was located at 30° south latitude during the Middle Devonian.Brown and green is the land mass, dark blue is deeper water and lightblue is shallower water. Red square represents the location of theMichigan Basin (After Blakey, 2011).
10
Several regional stratigraphic studies have been conducted in the Michigan
Basin (Fisher, 1969; Gardner, 1974; Lilienthal, 1978; Catacosinos et al., 1990). The
Upper and Middle Devonian strata in the Michigan Basin are overlain by
Mississippian strata, while the lower Devonian is generally absent (Figure 6). The
only remaining portion of Lower Devonian beds are those of the deeply eroded
Garden Island Formation (Lilienthal, 1978). Devonian strata in the Michigan Basin
are underlain by the sequence-bounding base Kaskaskia unconformity, which
separates Silurian Bass Islands Group strata from superjacent Devonian rocks (Ehlers,
1945). The Middle Devonian Dundee Formation is a complex carbonate succession
that is stratigraphically underlain by the Detroit River Group and overlain by the
Traverse Group.
The Detroit River Group consists of mixed carbonate and evaporite strata with
an average thickness of 1100 feet (335m) in the central Basin (Addison, 1940). The
Detroit River Group contains three stratigraphic units: the Sylvania Sandstone at the
base, consisting predominately of well sorted, fine to medium-grained sandstone
interbeded with cherty carbonate sediments (Catacosinos et al., 1991). The
Amherstburg Formation in the middle primarily composed of limestone and varying
amounts of dolomite (Catacosinos et al., 1991), and the upper-most Lucas Formation
comprising mainly evaporite and dolomite sediments, which are interpreted as being
deposited in a mosaic of shallow water restricted environment (Catacosinos et al.,
1991). The Dundee Limestone is readily distinguished from anhydrite or other
restricted and evaporitic lithologies of the underlying Lucas Formation (Gardner,
1974).
The Middle Devonian Dundee Limestone formation is overlain by the Bell
Shale Formation. The Dundee carbonates (more than 400 ft thick in the eastern part of
11
the Basin) have been subdivided into two units in the eastern part of the Basin, the
Dundee Formation is subdivided into the Rogers City and Dundee Limestone units
(Ehlers and Radabaugh, 1938; Gardner, 1974), which will be discussed in more detail
in the following section.
Traverse Group in the subsurface of the Michigan Basin was subdivided into
three units: the Traverse Formation at the top, the Traverse Limestone in the middle,
and the Bell Shale Formation at the base. The Bell Shale, which is underlain by the
Rogers City Limestone, is fossilliferous grayish shale with variable thickness ranging
from 10ft- 80ft and pinches out toward the southwest (Lilienthal, 1978; Catacosinos
et.al, 1991). The Bell Shale is interpreted as being deposited on a shallow shelf with
muddy influx sources to the east (Gardner, 1974). The Bell Shale and the Rogers City
contact is one of the most distinctive log picks in the Michigan Basin (Figure 8).
Figure 6. Stratigraphic column of the Michigan Basin with the Rogers City andDundee formations highlighted in red circle (modified from Catacosinosetal., 1990).
13
Dundee Formation Stratigraphic Nomenclature
The stratigraphic nomenclature that is applied to the Dundee interval is based
upon the outcrop and subsurface investigations. The Dundee Limestone and the Rogers
City formations are the units of interest and are considered as two distinct formations,
the Rogers City and the Dundee Limestone formations throughout this study.
The term Dundee Limestone was first proposed by Lane (1893) to describe
outcrops in the southeastern Michigan near the town of Dundee. From the outcrop
studies in northeast Michigan, Ehlers and Radabaugh (1938) described that the upper
part of the Dundee Limestone is characterized by two distinct types of gastropods:
Omphalocirrus manitobensis and Buchelia tyrell (fauna not present in the upper
portion of the Dundee Limestone) which is different from the fauna in the lower part of
the Dundee. Based on these observations, the Dundee was subdivided into the upper
Rogers City and the lower Dundee units. The authors described the Rogers City as a
crystalline fine to medium-grained, gray limestone, with discontinuous alternating
bands of thinly bedded magnesium-rich limestone (Ehlers and Radabaugh, 1938, Table
1).
In the subsurface, Curran and Hurley, (1992) conducted a detailed study of
eleven cores at West Branch field in Ogemaw County. They differentiate between the
Rogers City (above) and the Dundee (below) units in the subsurface through the
recognition of a mineralized, bioeroded hardground surface (Figure 7), which places
open marine (Rogers City) on top of the shallow platform Dundee Limestone. This
bioeroded hardground surface is interpreted as a depositional hiatus or a platform
drowning event. The Dundee Limestone was partially lithified, before the deposition of
the overlying Rogers City Limestone. The Rogers City/Dundee contact was well
documented in the several studied cores in this project.
14
Table I. Stratigraphic section of the Rogers City Limestone, Dundee Limestone andoverlying Bell Shale from outcrop in northeast Michigan (After Ehlersand Radabaugh, 1938).
Unit Bed | Thickness (cm) j LithologyBellShale i
V
ZCDO
oa>
•ac3
Total
-i—
30.4
1493.5
121.9
259.0
243.8
195.5
60.9
1798.3
2194.5
6398.2
Shale, calcareous, bluish gray and abundantly fossiliferous
Limestone, buffgray to bull, medium grained, fairlythickbedded and porous, containing some fossilsLimestone,gray, finely crystalline,dense and thick bedded,containing some fossilsLimestone. Lower 2-3 feet mottled buff and bufl-gray,magnesian and thin-bedded, upper6 feet less mottled and lessmagnesian and thicker bedded than underlying beds,containing some fossilsDolomite, with discontinuous, alternating bulTand buff-graybands, fine-grained and thin-bedded, containing some fossilsLimestone, gray, weathering to a buffgray, composed ofnumerous shells ofbrachiopods and a smaller number of otherinvertebrates
Limestone, gray, weathering buff gray, with few chertnodules, containing some fossils
Limestone, buff gray to buff, weathering to brown, andthickbedded, containing some fossilsLimestone, buff gray to gray, mottled, dense and somewhatmagnesian in lowerpari,containing somefossils
Figure 7. Slabbed core and thin-section showing the Rogers City and Dundee contactfrom Schember-Shears #3, South Buckeye field. This hardground mayalso be present along a mineralized stylolite seam, Sty= Stylolite, Pel=Peloids (picture courtesy of McCloskey, 2012)
15
Kirschner and Barnes (2009) established three hierarchical procedures using
wire-line logs to distinguish between the Rogers City and Dundee units (Figure 8) in
the subsurface: in the presence of anhydrite capping the Dundee unit in the western
part of the Basin, the contact between these two units is readily picked. However, in
the absence of anhydrite in the central and eastern part of the Basin a distinct break
from essentially zero porosity in the Rogers City in the calibrated neutron porosity log
to a more porous section in the Dundee. And finally a distinct gamma ray spike when
porosity logs are unavailable or the Rogers City and Dundee are both dolomitized is
useful to separates the Rogers City and Dundee contact.
The Rogers City interval in the central and eastern part of the Basin is mainly
considered a nonproductive, low porosity limestone. The Dundee unit in the central
Basin is chiefly dolomitized, whereas to the east, the amount of dolomite is sharply
diminished or highly localized (Montgomery et al., 1998).
16
35311
BAKER
37672
DURKEE, B M
36839
1873Mb MCDONALD <4810MI:
34500
KRYSZAK
RGRC
DUND
LUCS
Figure 8. Cross-section showing the contact between Rogers City and Dundee: thecontact is readily picked in the presence of anhydrite capping the Dundeeunit in the western part of the Basin (blue box). GR (track 1 with shadedyellow to brown for increasing GR response), which makes a distinctseparation between Rogers City and Dundee unit (red box), and makes adistinct separation between Bell Shale and underlain Rogers City (redcircle). NPHI (track2) provides a distinct break from zero porosity in theupper Rogers City to more pores section in lower Dundee unit (blackbox). RHOB (track 2 green line) record the much higher density valuesfor the anhydrites in the Lucas Formation which separate Lucasformation from overlain Dundee Limestone (blue circle). NPHI-RHOBseparation in limestone (shaded blue) calibrated logs indicates dolomite(shaded pink) when associated with low GR readings and RHOB<2.9.
17
Previous Work
Gardner (1974) studied the stratigraphic relationships and the depositional
environments of the Middle Devonian stratigraphy in the Michigan Basin. His
interpretations of the depositional environments were based on lithofacies,
sedimentary structures determined from cores, and constructed isopach maps using
wire-line logs. Gardner determined that the depositional history of the Middle
Devonian strata can be related to stages one and two of the Kaskaskia Sequence.
Gardner described the Dundee as a biostromal shelf carbonate, with predominately
dark, fine grained offshore facies to the east and sabkha and lagoonal facies to the
west. In his model (Figure 9) Gardner interpreted the overall depositional setting of
the Dundee as an east to west transgressive system across the Michigan Basin with a
brief regressive stage, which results in the deposition of the Reed City anhydrite in the
western part of the Basin.
Montgomery (1986) studied the Dundee depositional facies and porosity
relationships in the South Buckeye Field. He noted that the distribution of the oil
producing zones in the Dundee Limestone was controlled by the primary depositional
facies and the structural influence. Montgomery also interpreted that the pay zones of
the South Buckeye Field were developed by organic buildups on top of preexisting
structure. These interpretations were based on his observations in 12 conventional
cores. The four major facies Montgomery identified in Buckeye Field were: 1)
wackestone/mudstone; and 4) fenestral pelletal packstone.
Lagoon ^P = 1.13-1.20
Laminated CaS04 precipitate,Dolomitization by seepage reflux-ion through porous, transgressive,
biostromal deposits
Biocalcarenites and calcisiltites
Decreasing grain size and increasingdark color seaward
Figure 9. Map of the Michigan Basin showing the spatial distribution of Dundeedepositional environments and cross-sectional (K-L) view of thetransitioning lithologies. Dundee facies were deposited in transgressivesequence that extended across the Michigan Basin with a brief regressivestage that allowed for the deposition of the Reed City anhydrite in thewestern part of the Basin (modified after Gardner, 1974).
19
Curran and Hurley (1992) studied the sedimentology, facies distribution, and
porosity development in the Dundee reservoir in West Branch Field. Based on data
collected from eleven cores and log correlations, six facies were recognized: 1)
crinoidal grainstones; 2) skeletal-peloidal grainstones and packstones; 3) skeletal
wackestones; 4) restricted-fauna mudstones and wackestones; and 5) stromatoporoid
coral rudstone, and 6) fenestral-cryptalgal laminites. This last facies was
volumetrically insignificant as it was located below the oil water contact. Curran and
Hurley suggested that the Dundee reservoir in the West Branch Field was deposited in
normal marine conditions and added that the most productive zone in the reservoir
originated from primary porosity in lenticular beds of skeletal grainstones and reef
related boundstones. They described the contact area between the Dundee Limestone
and the overlying Rogers City unit of the Dundee Formation as a disconformity
consisting of a pyritized bioeroded hardground. They also found that the top 10-15ft
(3-4.5 m) of the Dundee Formation below the Rogers City unit contains pervasive
amounts of dolomite, resulting in high porosity and low permeability facies. Curran
and Hurley concluded that the dolomitization in the Dundee occurred as an early
facies-related feature formed before the deposition of the Rogers City Limestone.
Wood et al. (1996) and Montgomery et al. (1998) stated that most of the wells
in the Dundee were drilled in 1930s and 1940s with initial production rates varying
from 2000-9000 bbl/day due to solution enhanced porosity in some areas (i.e. Rogers
City Dolomite). They observed that excellent primary interparticle porosity occurs in
other places, and high permeability fractures are also present. They also reported that,
wells in many of the Dundee Fields (producing from both Rogers City and Dundee
reservoirs) throughout the Basin were abandoned, due to the aggressive, early
development practices, coupled with the strong water drive which resulted in water
20
coning. This water coning caused a significant volume of oil (about 60-80% of
potentially producible oil) to be bypassed and considered unrecoverable between
wells in some fields (Montgomery et al., 1998). Based on information from the
Cronus Development Tow# 1-3 HD-1 well in Crystal Field (the first horizontal well
in this field), and supplemented with the preexisting field information, Montgomery
et al. (1998) concluded that horizontal drilling was a feasible technique to
significantly enhance production from Dundee reservoirs(i.e. Rogers City Dolomite)
in the Michigan Basin. They estimated that more than 200,000 bbl of recoverable
reserves can be extracted from the Tow #1-3 in Crystal Field. In addition, two
horizontal wells were drilled in another portion of Crystal Field, but those wells
produced mostly water with minute amounts of oil. Montgomery et al., (1998)
believed that these wells were drilled near the oil water contact or crossed fractures
that extended into the water saturated zone. Montgomery et al., (1998) reported that
by early 1998 the initial production from 15 horizontal wells drilled in various
Dundee reservoirs ranged from 5-127 bbl/day. Based on these results, they concluded
that successful horizontal drilling in the Rogers City dolomite and Dundee Limestone
reservoirs requires further study of the reservoir complexity, structure distribution,
and oil water contacts.
Luczaj et al., (2006) studied hydrothermal fractured dolomite distribution and
its characteristics in the Dundee reservoir rocks of the central Michigan Basin using
core description and fluid-inclusion microthermometric methods. Luczaj et al., (2006)
grouped the Rogers City and Dundee units together as the Dundee Formation,
whereas in this thesis the Rogers City and Dundee used as separate units. Luczaj et al.
stated that the Dundee Formation contained fracture-controlled and facies-controlled
reservoirs, and added that in the central Michigan the fractured dolomite reservoirs
21
had tremendous oil production in the Michigan Basin. These authors documented that
the saddle dolomite in the Dundee occurs as a result of hydrothermal fluid circulation
along the fractures and faults with temperature ranging from 120-150 degrees
centigrade. In addition, they concluded that the occurrence of the fractures and the
saddle dolomite precipitation in the Dundee Formation accounts for reservoir
development because both occurred prior to oil migration and reservoirs filling.
Consequently, they concluded that dolomitization in the Dundee Fields (Rogers City
dolomite) of the central Basin were related to deep-seated fault and fracture systems.
Kirschner and Barnes (2009) characterized the geology and the petrophysical
properties of the Dundee Limestone by using wire-line logs and conventional core
analysis including porosity and permeability data. They observed that the separation
of the Rogers City and the Dundee Limestone can b made by the wire-line log
signatures and added that the Dundee Limestone is characteristically porous while the
Rogers City typically has little to no porosity when found as limestone lithology.
Further, Kirschner and Barnes documented an estimated CO2 storage capacity of
0.13Gt in the Rogers City and 1.88Gt in the Dundee limestone. They concluded that
the Dundee Limestone is an important geological sequestration reservoir target
compared to the Rogers City.
22
CHAPTER III
METHODOLOGY
This study utilized several phases of sampling, analysis, and interpretation of
core for reservoir characterization. The core data was gathered from Michigan
Geological Repository for Research and Education (MGRRE) at the Western
Michigan University. There are fifteen cored wells within the selected study area
available at MGRRE core lab and these cores were studied in detail in this research
(Appendix A, B). Generally the core footages cover most of the producing interval of
the Dundee Limestone and part of the overlying Rogers City Limestone. However,
some of the slabbed cores contain a number of missing sections that were removed for
description and other testing. The conventional cores analysis (porosity and
permeability) and petrophysical wire-line logs were available at MGRRE.
Core Descriptions
In this research, fifteen cores were selected based upon the presence of
interval coverage, whole core analyses and an available suite of wire-line logs. A
detailed geologic description was performed on approximately 1100 feet (335 m) in
fifteen cores from six Dundee fields (Table2). Insights from core examination were
supplemented with inspection of 26 cores in South Buckeye field from McCloskey
(2012), and an additional 11 cores in West Branch field from Curran (1990). These
cores were selectively studied to sample each of the seven depositional facies and to
evaluate reservoir characteristics from field to pore scale in order to assess enhanced
oil recovery (EOR) potential in the Dundee Limestone in the Michigan Basin. Cores
that covered the Dundee limestone interval and part of the Roger City were present in
Isabella, Midland, Gladwin, and Ogemaw Counties. All cores are located in the east-
23
central part of the Michigan Basin (Figure 1) and were examined and described
thoroughly using a binocular microscope and hand lens. Core photographs were taken
after the core was polished to improve clarity and maximize the observation and
documentation of depositional features and rock fabric. The core photographs are
located in Appendix C.
Detailed observation of lithology, fossil content, cement type, pore types and
distribution, and primary sedimentary structure were conducted to document the
vertical lithologic succession, define distinct Dundee depositional facies, and develop
depositional environment interpretation and geological control on reservoirquality for
Dundee Limestone. The lithofacies distribution and pore geometry were described
using Dunham (1962) and Embry and Klovan (1971) classification for the
depositional facies and Choquette and Pray (1970) for porosity classifications (Table
3, Figure 10). Some wells have good subsurface data quality (core, core analysis,
wire-line logs) but lack modern wire-line logs or were missing key cored intervals.
The most notable wells that had all of the required data are located in Mount Pleasant,
North Buckeye, and South Buckeye and West Branch fields. Additionally, because of
lost core interval, an interpretation of some but not all cored depth normalized to the
depths used in the wire-line logs. When the shifted depths (i.e., between the core data
and the wire-line logs) are used, the position of a described or analyzed length of core
can be referenced directly to match the wire-line logs (Appendix B).
Petrographic Analyses
During a preliminary study of each core, samples were cut for petrographic
thin-sections analysis. Prior to detailed description of a core, it is desirable to have at
least a preliminary description of each sample in thin-section in order to identify grain
24
types and diagenetic fabrics accurately. Sixty thin-sections were made from selected
facies and supplemented with preexisting thin-section in the collection at the MGRRE
core lab. The thin-sections were impregnated with blue epoxy to highlight porosity,
and some thin-sections were partially stained with alizarin red and potassium
ferricyanide stain. Alizarin red stain allows for the discriminating between calcite and
dolomite. It has been noted by Tucker (2001) that Alizarin red stain changes non-
ferroan calcite to pink while non-ferroan dolomite remains unstained. The potassium
ferricyanide stain has a high sensitivity for ferrous iron, which allows for the rapid
identification of ferroan calcite and ferroan dolomite in carbonate rocks. Hatzman
(1999) stated that the ferroan calcite stains pale to deep blue and ferroan dolomite
stains a turquoise color with potassium ferricyanide. Thin-sections were examined
and photographed for detailed analysis using a Leica DC Camera petrographic
microscope. Petrographic analysis of thin-sections yielded qualitative petrophysical
characterization to identify primary depositional and diagenetic processes in order to
determine the geological controls on reservoir quality and pore geometry. Thin-
section data was compiled with wire-line log derived porosity and the conventional
core analysis data in order to make a comprehensive data set of reservoir quality
attributes.
25
Table 2. Cores used in this study.
Permit
#
Well Name Field
Name
County Production Total Field Production
19693 McNerney, BE3
Wise Isabella Dry Hole 4.2 MMbbl. Through2010
39770 Mt Pleasant
Unit Tract 55
Mt
Pleasant
Isabella Oil 30.4 MMbbl. Through2010
39771 Mt Pleasant
Unit Tract 46
Mt
Pleasant
Isabella Oil 30.4 MMbbl. Through2010
36367 McClintic-3 Mt
Pleasant
Isabella Oil 30.4 MMbbl. Through2010
36387 Miller, Viola1
Mt
Pleasant
Isabella Oil 30.4 MMbbl. Through2010
35461 Sierra Land
CO., INC 1,Mt
Pleasant
Midland Oil 30.4 MMbbl. Through2010
35764 Ames, C W 1 Mt
Pleasant
Midland Oil 30.4 MMbbl. Through2010
36227 Sokolowski,CT1
Mt
Pleasant
Midland Oil 30.4 MMbbl. Through2010
36259 Pfund-1 Mt
Pleasant
Midland Oil 30.4 MMbbl. Through2010
32780 State
Buckeye B-6North
BuckeyeGladwin Oil 21.5 MMbbl. Through
2011
52002 Salla, John 9-11 HD
North
BuckeyeGladwin Oil 21.5 MMbbl. Through
2011
43383 Nusbaum
Kern 3-W,South
BuckeyeGladwin Oil 7.5 MMbbl. Through
2010
36730 Fitzwater #6-
26
South
BuckeyeGladwin Oil 7.5 MMbbl. Through
2010
35720 Huston 1-2 Butman Gladwin Oil 39 Mbbl. Through 2001mostly from Lucas Fm
28399 Grow 4 West
Branch
Ogemaw Oil 14.2 MMbbl Through2011
26
Conventional Core Analyses
Conventional whole core analyses (porosity and permeability data) were
originally obtained from core measurements by the operators prior to the initiation of
this study. The data from conventional whole core analyses were obtained from
MGRRE core lab at Western Michigan University, which includes footage analyzed,
Crinoidal skeletal wackestone is the only facies recognized from the Rogers
City. Facies 1 constitutes approximately 16 % of the gross thickness of the fifteen
studied cores examined throughout the study area (Appendix B). This facies is a
uniformly facies in the Rogers City Limestone. Common skeletal components include
crinoids, gastropods, brachiopods, ostracods, trilobites, and forams. This facies is
occasionally interbedded with thin crinoidal packstone beds that range in thickness
from a centimeter to several centimeters, and also contains mud- rich nodular texture
generally of centimeter scale with rounded to elliptical outlines (i.e. Mt Pleasant Unit
Tract 55 and McNerney, B E3 wells, Figure 11). Low amplitude stylolites occur
within sediment packages and at package boundaries. The nodular fabric is often
enhanced by pressure solution, with stylolite sutures surrounding the nodular grains
(Figure 11).
The crinoidal skeletal wackestone facies is characterized as a very dense, low
porosity and permeability rock type that is an effective impermeable seal for the most
Dundee Limestone reservoirs. Limited whole core analysis for this facies indicates an
average porosity of 1 % and average permeability of 0.2md (Figure 12).
Interpretation: Crinoidal skeletal wackestone facies in the Rogers City was
deposited during a marine transgression period, which places deeper marine Rogers
City on top of the shallow marine Dundee Limestone (Curran and Hurly, 1992). The
33
most common textures observed in this facies are wackestone and mud-rich
packstone, which indicates low depositional energy conditions. This type of facies
indicates a low energy, open marine with normal salinity environment of deposition
(Scoffin, 1987). The composition of crinoid stems, bivalve, and gastropods fauna
(Flugel, 2004) suggests that the depositional environment was a low energy, well
oxygenated open marine. In core, the transition from shallow marine Dundee
limestone facies to open marine Rogers City facies is abrupt in most examples. This
facies has a sharp stylolitic contact (Figure 11) of the open marine Rogers City above
shallow carbonate facies of the Dundee Limestone.
MT Pleasant Unit tract 55, 3573' llMT Pleasant I
Sty ' . : .
I m '
0.1 mm
Figure 11. Crinoidal skeletal wackestone facies. (A) Core photograph, mud nodulartexture (Nod) ranging from 1-2 cm in diameter. (B) Slabbed corephotograph showing the contact between the upper Rogers City (RGRC)and the lower Dundee Limestone (DUND), separated by mineralizedstylolite (Sty). (C) Thin-section photomicrograph, showing stylolites inlow amplitude and crinoids-rich (Cri).
34
♦Crinoidal Skeletal Wackestone
2 4
Porosity {%)
Figure 12. Cross plot of porosity and permeability measurements from whole coreanalyses of crinoidal skeletal wackestone facies. Large triangle showsaverage.
Figure 14. (A) Slabbed core illustrating the crinoidal grainstone tempestites (outlinedin blue) interbedded with burrowed skeletal peloidal grainstone facies.(B) Core photograph, note the burrow structure (Bur) is surrounded bycrinoids-rich debris (Cri D).
37
100
£ 10
CO<u i
Ei_
Q.
0.1
♦ Burrowed Peloidal Grainstone/Packstone
♦ ♦
♦ ST *^oo o
<ms> ♦
♦♦
—1 r~♦-6 8 10
Porosity (%)12 14 16
Figure 15. Cross plot of porosity and permeability measurements from whole coreanalyses of burrowed peloidal grainstone/packstone facies. Largetriangle represents average.
Facies 3: Crinoidal grainstone (shoal)
The crinoidal grainstone facies was cored in South Buckeye and West Branch
Fields. Facies 4 constitutes approximately 8 % of the gross thickness of the fifteen
cores examined throughout the study area. In the South Buckeye Field this facies
occurs as thin (1-2 ft) interbeds with the stromatoproid boundstone facies but is found
as thicker (5-9 ft) beds in the Nusbaum Kern 3-W and Fitzwater #6-26 well.
However, the crinoidal grainstone facies does occur as significant thick separate units
in Grow # 4 well, West Branch Field with a thickness of 25 feet (7.6m) (Appendix B).
This facies is characterized by moderate to well sorted, fine to medium
grained carbonate sand. Facies 3 is primarily made up of fine grained crinoid ossicles
(Figure 16) with average of 0.1-0.2 mm in diameter and can comprise up to 80% of
38
the rock material. Other skeletal constituents within this facies include brachiopods,
bryozoans, rugose coral and some scattered peloids. Pressure solution associated with
this facies results in low amplitude swarm stylolites both within sediment packages
and at package boundaries.
Major porosity types of this facies include interparticle, intraparticle, and
limited vuggy and moldic porosity. Porosity ranges in this reservoir facies from 2% to
12%o, with average porosity of 7%, and permeability ranging from 0.1 md to 189md,
with an average of 14md from whole core analyses (Figure 17). This facies is the
primary reservoir facies in West Branch Field and a secondary reservoir facies in the
South Buckeye Field.
Interpretation: The crinoidal grainstone facies is interpreted to be deposited in
an inner to middle ramp setting (Figure 36), very high energy shoal, above fair
weather base. Well to moderately sorted grains are common in middle carbonate
ramp and lagoonal patch reef settings (Flugel, 2004), controlled by high energy
conditions, resulting from wave action and/or other shallow water currents. The wave
action winnowed out mud leaving well sorted grains, which suggests a shoal
environment. Sediment deposition and reworking probably occurred in shallow water
depths ranging from near sea level to 20 feet (6 m) below sea level. The major
accumulations of the grainstone occur surrounding the reef facies (i.e. South Buckeye
Field) or are not associated with reefs (i.e. West Branch Field). Pressure solution is
common in the form of stylolites throughout this facies due to chemical compaction.
Burial cement observed in this facies is intergranular calcite crystal as syntaxial rim
cement on crinoid ossicles (Figure 16 and 33).
39
0.3 mm
Figure 16. Crinoidal grainstone facies. (A) Slabbed core photograph of the crinoidalgrainstone facies. (B) Thin-section photomicrograph of crinoids-richsediment (Cri) with sparry calcite cement, porosity is in blue, porositytype is interparticle porosity (BP). Note cleavage extends throughcrinoidal grains and syntaxial cement overgrowth indicating syntaxialovergrowth formation (Sc).
1000
T? iooE
iE ioA03<D
£
Ql
0.1
♦Crinoidal Grainstone
♦f !
♦ *A
10
Porosity (%)12
-4—
14 16
Figure 17. Cross plot of porosity and permeability measurements from whole coreanalyses of crinoidal grainstone facies. Large triangle represents average.
Figure 20. Patch reef facies. (A) Core photograph of stromatoporoid boundstoneshowing pillar and lamina structure (yellow arrows). (B) Thin-sectionphotomicrograph, porosity is in blue, intraparticle porosity is dominant.
44
Note some of the intraparticle pores are partially filled with calcitecements, but most of the galleries are open pore spaces.
10000
E
1000
£» 100
JQ
Cl 1
0.1o
♦ Stromatoporoid.
•Ooo
o <x>
o~o o
op <$
4 6 8 10
Porosith(%)12
O
o o
14 16 18
Figure 21. Cross plot of porosity and permeability measurements from whole coreanalyses of stromatoporoid boundstone facies. Large triangle is average.
Facies 6: Skeletal wackestone (lagoon)
The skeletal wackestone facies forms approximately 17% of the gross
thickness of the fifteen studied cores examined throughout the study area (Appendix
B). This facies is found within repeated shallowing upward sequences with cycles
consisting of subtidal lagoonal wackestones grading upward to packstones and
grainstones facies. The skeletal wackestone facies is in sharp stylolitic contact with
the fenestral, peloidal grainstone/packstone facies (facies 7) when present in studied
cores (Figure 22).
The common allochems in this facies include gastropods, ostracods, bivalves,
trilobites, brachiopods, bryozoans, coral, and with minor stromatoporoid debris
present in a few places. These skeletal grains are scattered in carbonate mud (Figure
45
23). Minor intercalations of peloidal skeletal grainstone and wackestone are
occasionally associated with this facies in beds less than a foot thick when present.
Pressure solution of carbonate results in abundant wispy stylolitization.
The porosity types within this facies are vuggy and moldic with limited
fracture porosity. Porosity value ranges from 0.5%> to 10%, with average porosity of
4%, and permeability ranging from 0.0 lmd to 135md, with an average of 2md from
whole core analyses (Figure 24). This facies is interpreted as a non-reservoir facies
due to its generally low porosity and permeability value.
Interpretation: The skeletal wackestone facies was formed in a lagoonal
depositional environment of an inner ramp setting (Figure 36), low-energy with open
water circulation at or just below the fair weather wave base (Flugel, 2004). Limited
distribution of skeletal grains, lack of bioturbation and a muddy matrix suggest a low
energy environment of deposition.
There is little cement observed in this facies due to limited distribution of
primary porosity available for cementation. Other factors that affected this facies are
the dissolution of some calcite crystals and skeletal fragments to form vuggy and
moldic porosity. The minor primary porosity associated with coral and
stromatoporoid fragments, is commonly filled with calcite cement. However, the
secondary dissolution enhancement of porosity is pronounced in few places by the
presence of small amount of moldic porosity that occurs after mollusks shells (Figure
29). Fractures and stylolitization (large and swarm sutured styolites) are common in
this facies. Styolites result in increased permeability by connecting the isolated vugy
porosity in this facies (Figure 34). A sharp stylolitic contact of the skeletal
wackestone facies with the peritidal facies (facies #7) coincides with rapid fluctuation
in sea level.
46
Figure 22. Slabbed core showing a sharp stylolitic contact between the fenestralpeloidal grainstone/packstone facies and skeletal wackestone facies. Thewhite arrow indicating the "up" direction in the core.
Figure 23. Skeletal wackestone facies. (A) Core photograph of skeletal wackestonefacies associated with stylolites (Sty) and fractures (Fr). (B) Thin-sectionphotomicrograph, porosity is in blue, dominant moldic porosity (Mo),skeletal grains include gastropods (Gsp) and ostracod fragments. Notethe low-amplitude suture stylolites (Sty) and oil stain (Oil S).
47
100o Skeletal Wackestone
Figure 24. Cross plot of porosity and permeability measurements from whole coreanalyses of skeletal wackestone facies. Large triangle represents average.
The fenestral peloidal grainstone/packstone facies has produced the most oil
and gas from Dundee limestone reservoirs. It is observed in North Buckeye, Mt
Pleasant, and Wise Fields, which forms approximately 42%> of the gross thickness of
the fifteen studied cores examined throughout the study area (Appendix B). This
facies is commonly the upper most Dundee Limestone unit and is capped by more
open marine Rogers City facies when present. The geometry of this facies is typically
laterally extensive on a field scale. The fenestral reservoir unit is composed of several
shallowing upward, high-frequency cycles consisting of a lower skeletal wackestone
and an upper fenestral grain-dominated grainstone and packstone facies.
Facies 7 is buff to tan limestone with solution enhanced fenestral pores
(commonly ranging from 0.1-6mm long and 0.01-2mm wide). This facies is largely
48
made up of peloids, which can comprise up to 90% of the rock material. The peloids
are fine grained carbonate sand (generally less than 0.2 mm in size), moderately
sorted and spherical to subspherical-shaped and with uniform size. Skeletal grains
within this facies include brachiopods, bivalves, ostracods, gastropods, crinoids,
corals, and stromatoporoids debris. The sedimentary structures found in this facies
include small cyanobacterial mats, tidal laminations, and fenestral structure (Figure
25).
Porosity within this facies is dominantly fenestral, interparticle and
intraparticle with minor fracture porosity. Variable porosity ranges in this reservoir
facies from 1% to 14%, with average porosity of 9%, and permeability ranging from
0.1md to 5200md, with an average of 195md from whole core analyses (Figure 26).
Interpretation: Facies 7 was formed in a peritidal depositional environment in
an inner ramp setting (Figure 36). Shallow platform interior areas are typically
composed of protected shallow marine environments with moderate circulation.
Peloids commonly occurred in shallow marine subtidal and tidal flat settings as thick
graded laminae with fenestral fabric (Wilson, 1975). These tidal flat facies typically
occur as stacked cycles, each ideally containing internal shallowing upward
succession (Flugel, 2004). The formation of fenestral pores is a result of gas
production associated with the decay of organic material and the lateral migration of
water and/or gas, all occurring within peritidal environments (Shinn, 1983a). The
cyanobacteria laminations, buff color and the blocky calcite cement are notable and
observed in the Dundee Limestone peritidal facies. The presence of these features in
facies 7 indicates that the deposits were likely formed in a peritidal environment that
was intermittently exposed above sea level. The fenestral voids in facies 7 were filled
by fine grained micritic internal sediment and the remnant pore spaces within the
49
fenestrae were filled with sparry calcite cement (Figure 27) a further indication of
peritidal deposition. Such internal sediments present in the fenestral voids suggest
that this deposit was formed in peritidal environment and was subaerially exposed
(Scholle and Ulmer-Scholle, 2003). The allochemical components of this facies are
cemented by calcite crystals and some pores were completely occluded by blocky
calcite cement. When the fenestral voids are unfilled, fenestrae may enhance porosity
and permeability when partly connected. Shinn (1968) suggests that the peritidal
sediments resist compaction due to syndepositional cementation. The allochems in
this facies show few signs of physical compaction, whereas pressure solution is very
common in the form of stylolites.
hi
Mt Pleasant Unit Tract 55, 3594'
SybTFL •__
I
Figure 25. Fenestral peloidal grainstone/packstone facies . (A) The core photographdisplays an irregular tidal flat lamination (TFL), cyanobacterial mats(Syb), and fenestral structure (Fs). (B) Thin-section photomicrograph,porosity is in blue color, note fenestral fabric with irregular fenestrae(Fs) in relatively fine peloids grains (Pel). These fenestrae are partlyfilled with calcite cements (CC) and some of them are completelyoccluded in this peloidal peritidal deposit.
50
10000
^ 1000•a
E
7* 100
JQ
S 10Ec0)
Q. i --
o.i
♦ Fenestral Peloidal Grainstone/Packstone
6 8 10
Porosity (%)16
Figure 26. Cross plot of porosity and permeability measurements from whole coreanalysis of fenestral, peloidal grainstone/packstone facies. Large trianglerepresents average.
MtPleasant Unit Tract 55, 3575' |
•'fa i
P§ {
B8?5
Figure 27. The thin-section photomicrograph showing an example of fenestral vugsfilled by fine grained micritic internal sediment (red arrow) and theremnant pore spaces within the fenestrae filled with sparry calcite(yellow arrow).
51
Diagenesis
Introduction
The diagenesis of carbonates encompasses any physical and chemical
alterations that affect sediments after deposition until the realms of incipient
metamorphism (Tucker and Wright, 1990). Diagenesis often starts at the sea floor
(syngenetic or eogenetic alteration), continues through deep burial (mesogenetic
alteration), and extends to subsequent uplift (telogenetic alteration) (Scholle and
Ulmer-Scholle, 2003). Most carbonates are deposited and start their diagenetic history
in the marine phreatic zone (Longman, 1980).
Diagenesis includes not only distinct processes such as cementation that form
limestones and dissolution which produces caves, but also includes subtle processes
such as the formation of micro-porosity and changes in trace elements content
(Tucker and Wright, 1990). Furthermore, diagenetic processes can enhance, create
and/or destroy porosity in carbonate rocks. As depth increases, there is a general
decrease in porosity; however, there are late processes of dissolution and fractures
that can enhance porosity. Diagenetic processes affecting carbonate sediments and
rocks are micritization, dissolution and cementation, compaction, neomorphism,
dolomitization, and replacement of carbonates by non-carbonates (Flugel, 2004).
Marine carbonates consist of a mixture of aragonite, high-magnesium (Mg)
calcite and low-Mg calcite. Aragonite and high-Mg calcite are common in recent
carbonates and are metastable because they transform to calcite with time. Low-Mg
calcite is the most stable form of CaC03 and deposited from meteoric water (Tucker
and Wright, 1990).
52
Diagenetic alterations in the Dundee Limestone
A study of the diagenetic evolution of Dundee Limestone reservoirs in the
Michigan Basin was undertaken to better understand the controls on reservoir quality.
Core and petrographic analyses of the Dundee Limestone indicate that the original
fabric of most carbonate rocks has been altered by diagenetic processes. The major
syndepositional and diagenetic processes affecting the Dundee carbonate reservoirs
are microbial micritization, dissolution-cementation, burrowing, and physical and
chemical compaction. The most common diagenetic feature present in the Dundee
Limestone is pressure solution and stylolitization.
Microbial Micritization
This is a process whereby the bioclastics and other particles are altered by
endolithic algae, fungi and bacteria while on or just below the sea floor (Tucker and
Wright, 1990). Microbial micritization and micrite envelops formed around many of
the skeletal grains in grainstones and packstones (Bathurst, 1975). These envelopes
were created through the alteration of grains rather than precipitation of a new rind
around the grain. Algae, fungi, or bacteria bore into the grain, die, and the subsequent
alteration of the organic material provides a chemical environment conducive to
calcium carbonate precipitation during the filling of the voids (Bathurst, 1975; Tucker
and Wright, 1990).
Evidence of micritization in the form of micrite envelopes and completely
micritized grains are common in the bioturbated peloidal grainstone/packstone,
crinoidal grainstones, and reef flank facies (facies 2, 3, and 4). The micrite envelope
developed on echinoderm, trilobite, and brachiopod fragments, which were bored by
53
the action of endolithic algae. The pores are filled by surrounding micrite matrix
(Figure 28).
Figure 28. The micrite envelopes of the outer part of the shell are a result of microbialmicroboring and infilling of the holes by micrite. (A) Note the micriteenvelope surrounding the trilobite fragment (Yellow arrow). (B) Note athin coating of micrite envelopes is evident around brachiopodfragments (yellow arrow).
Burrowing
Biological processes, such as burrowing activities, are most widespread in
marine environments. Burrows are formed in relatively unconsolidated sediments by
the activity of animals during feeding, resting or migration, and also make an
important contribution to the structure of carbonate sediments. Burrowing and
bioturbation are more common in inner and mid-ramp environments (Flugel, 2004)
where biologic alteration of primary depositional fabric and grain reworking may
determine the distribution of porosity and permeability pathways.
In this study, evidence of pervasive bioturbation is very common in the
peloidal grainstone/packstone facies (facies 2). Burrows are more recognizable (i.e.,
South Buckeye Field) due to the difference in color between burrow and surrounding
54
sediment (Figure 13). Many burrows are filled by medium to fine sand sized bioclast
fragments and peloids, which affected the porosity and permeability and adds
additional complexity to reservoir quality.
Dissolution-cementation
Dissolution-precipitation processes suggest diagenesis in the meteoric
environment (Wallace et al., 1991). Undersaturated meteoric water in pores will
dissolve carbonate grains, sediments, and cements. Dissolution is more effective in
shallow near surface meteoric environments, in deep burial, cold water, and in the
deep sea (Flugel, 2004), where seawater becomes undersaturated with respect to
aragonite and high Mg-calcite. Mixing zones of marine and non-marine waters is also
considered an important site of major dissolution caused by mixing corrosion (Tucker
and Wright, 1990).
Dissolution and leaching of gastropod and some brachiopod fragments
resulted in the development of many types of secondary porosity including moldic,
intraparticle, and vuggy (Figure 29). The crinoidal grainstone and skeletal wackestone
facies (facies 3 and 6) show areas where dissolutions has occurred and removed
aragonitic skeletal grains. Meteoric dissolution also affects the crinoidal skeletal
wackestone and reef flank facies (facies 1 and 4) where moldic and vuggy porosity is
present.
The moldic, secondary porosity has been partially reduced through later
cementation with blocky calcite crystal cement. In patch reef facies some of the
intraparticle pores and the spaces between latilaminae are partially occluded with
calcite cements but some of the chambers are open pore space (Figure 20). However,
in North Buckeye Field, where the patch reef facies is not a primary reservoir due to
55 •
its low porosity and permeability, the open framework of stromatoporoids is
extensively occluded by calcite cements (Figure 30). One explanation for this contrast
may be related to the timing and intensity of cementation. The most significant
amount of cementation occurs in patch reef environment with higher rates of agitation
and/or lower sedimentation rates (Flugel, 2004).
Figure 29. (A) An example of predominantly intraparticle porosity in crinoid stem andstromatoporoid (yellow arrow) (B) Crinoid fragments and other skeletalfragments, including mollusks, are dissolved leaving abundant moldicporosity (yellow arrow) in relatively fine grain matrix.
State Bucke
Figure 30. The open galleries of the stromatoporoids are extensively occluded bycalcite cements (yellow arrows) in facies 3 of the North Buckeye Field.
56
The fenestral peloidal grainstone/packstone facies (facies 7) shows areas
where most of fenestral porosity is well preserved suggesting that the fenestrae
formed in an active diagenetic environment where early lithification is common
(Shinn, 1983b). Some of the voids are partially filled with blocky calcite spar cement
or internal sediment (Figure 31), however, the effect of this process on the reservoir is
relatively minor because of the large amount of preserved primary porosity.
Figure 31. Fenestral fabric in tidal flat facies showing fenestral porosity (Fs) in lightblue that is larger than the associated peloidal texture. Note some oflarge pores either partially or fully filled with blocky calcite (BC), andsome small pores are either partially or fully filled with sparry calcitecrystals (yellow arrow). This is the main reservoir facies.
The most common types of calcite cement encountered in most studied facies
are calcite crystals and blocky calcite cement. These cement types may indicate
diagenesis in meteoric regime (Longman, 1980). Calcite crystals replace mollusk
57
fragments (Figure 32) and line pore spaces (Figure 32). Calcite crystals range in size
from 0.1 to 0.3mm. All porous facies described here, contain some blocky and calcite
crystal cement. Further, most of the interparticle pore space is lost to cementation by
varying amounts of calcite crystal and blocky calcite cement rather than compaction
suggesting relatively early diagenetic cementation, consistent with early meteoric
processes.
Other observed cements are represented by syntaxial calcite overgrowth
cement. This type of cement is encountered most communally around the echinoderm
debris (Bathurst, 1975), which will be discussed in greater detail in the following.
Figure 32. Example of meteorically leached mollusk shells resulting in moldicporosity in the crinoidal grainstone facies. This moldic secondaryporosity has been partially or fully occluded by calcite crystal and blockycalcite cement (yellow arrows).
Syntaxial overgrowth cement is widespread in wackestones, packstones, and
grainstones. The origin of this cement on echinoderms is explained as a filling of
58
secondary pores produced by differential dissolution of carbonate mud in the vicinity
of echinoderms (Flugel, 2004). The presence of syntaxial overgrowth on echinoderms
is common in the meteoric phreatic zone (Scholle and Ulmer-Scholle, 2003).
However, syntaxial overgrowths are rare in the meteoric vadose zone and deep burial
environment (Longman, 1980). Syntaxial overgrowths were observed in crinoidal
skeletal wackestone and crinoidal grainstone facies (facies land 3) where crinoid
fragments are surrounded by syntaxial cement (Figure 33). In most cases, syntaxial
overgrowth initiates on echinoderm framework grains partially occludes interparticle
porosity (Figure 34).
Fwater # 6-26, 3624' —»• '•*"•; ^—~
Figure 33. The syntaxial overgrowth on crinoid ossicles (Cri) has reduced most ofpre-existing interparticle porosity (yellow arrows).
59
Fractures and Stylolitization
Much burial diagenesis of non-cemented carbonate sediments under an
overburden results in physical compaction, the reduction in porosity and grain
fracture. Physical compaction is commonly followed by chemical compaction, which
results in stylolites and solution seams formed under burial conditions (Flugel, 2004).
Physical compaction includes dewatering, grain reorientation and brittle or plastic
grain deformation reducing porosity in many carbonate deposits (Scholle and Ulmer-
Scholle, 2003).
The physical compaction features observed in this study are fractures and
shattering of relatively robust brachiopod shells. The fractures observed from core and
thin-section examination include small-scale fractures ranging from 0.1-6cm (Figure
22 and 23a), and fractures associated with sutured stylolites (Figure 23a and 34 a),
which generally occur in the open marine and lagoonal facies (facies land 6). Natural
opening-mode fractures are observed and locally abundant in core. In some cases
fractures have a wide range of sizes and most are filled with calcite cement. Some
fractures remain open in the crinoidal grainstone facies (Figure 34b).
Chemical compaction in carbonate rocks results in dissolution and
accumulation of insoluble residue along stylolite surfaces. Stylolitization, which is the
predominate phenomenon of chemical compaction, occurres in all facies in the form
of stylolites and solution seams. Stylolites in all facies are irregular, suture-like, and
have high and low amplitude (Figure 35). Concentrations of insoluble residues occur
along many suture grains contact (Figure 35). Microstylolites are common between
skeletal grains and carbonate mud matrix, implying that pressure solution came after
the matrix was lithified.
60
Figure 34. The presence of fractures (when unhealed with calcite cement) in manycases, can greatly increase the permeability of the rock. (A) A limestonewith multiple fractures associated with stylolites are partially lined upwith calcite cements (white arrows), and small fractures are completelyfilled with calcite cement (yellow arrows). (B) Note opening-mode fractures in crinoidal grainstone facies (yellow arrows).
[State Buckeye B-6, 3624' 1Ki K—#k.
- •**•*, ' V'
-•it
-:;'JLjII^ **#'••
1j
SsSPiiis• *3 '<kM
v*V-"---P^! 0.3mm
Figure 35. Thin-section photomicrograph of large amplitude stylolites typical of manypressure solutions in carbonate mud matrix. Note enrichment of darkinsoluble materials along irregular stylolite, in which case stylolites canbe recognized by change in texture of the rock (yellow arrows).
61
Depositional Environment Model
Carbonate Ramp
A carbonate ramp is very low gradient depositional slope from the shallow
water shoreline or lagoon to the Basin floor, with usually less than one degree slope
and has no slope break (Read, 1995). The carbonate ramp system contains tidal flat,
lagoonal, and shoal facies (Tucker and Wright, 1990). Primarily the carbonate ramp
facies are controlled by energy level (fair-weather wave base and storm wave base)
and also are controlled by sea level fluctuation, which simply shift facies belts up and
down the ramp (Flugel, 2004).
A conceptual model of the Middle Devonian Dundee Limestone is
summarized in Figure 36. This model was constructed based on the interpretation and
definition of depositional facies and their vertical stacking patterns derived from core
analysis. The depositional environment interpretations of the study area indicate that
the Dundee Limestone was deposited in an inner carbonate ramp setting while the
Rogers City was deposited in a mid carbonate ramp setting in the Michigan Basin.
The Rogers City and Dundee Limestone formations along this ramp consist of open
Figure 37. Idealized vertical stacking patterns of seven facies seen within the coresexamined in this study. The blue triangle represents the transgressivesystems tract and the red triangle represents the highstand systems tract.
68
Permit # 36730Permit # 32780
Figure 38. Stacking pattern in different facies areas/fields observed in the Rogers Cityand Dundee interval from six fields. The Dundee interval within the
cores examined in this study has one low frequency cycle and two tothree high frequency cycles. The blue triangle in the low frequencycycles column represents the transgressive systems tract and the red
69
<5
<LU
>-
380
390
triangle represents the highstand systems tract. These symbols representshoaling and flooding events in high frequency column. NPHI = neutronporosity, RHOB = bulk density, perm = permeability.
Figure 39. Changes in sea level recorded in the Middle Devonian deposits in Givetianstage, red star shows the proposed Rogers City and Dundee contact atapproximately 390 Ma (Modified after Haq and Schutter, 2008).
70
CHAPTER V
GEOLOGIC RESERVOIR CHARACTERIZATION
Reservoir characterization of the in six Dundee oil fields includes the
description of fifteen conventional cores (Table 2) and petrographic analysis.
Conventional core analyses for 21(Appendix D) wells and wire-line logs for 48 wells
were also studied and compared to core material. Reservoir properties were delineated
for different depositional facies observed in core compared to core analysis data. The
core data were calibrated to the well-log patterns to predict vertical and lateral
reservoir geometry. Correlations are presented in cross-sections that show
interpretations of structure, stratigraphy, and thickness of important reservoir units.
Subsurface correlation is based primarily on stratigraphic continuity, or the premise
that similar facies maintain similar stratigraphic thickness between closely spaced
wells.
The correlation of depositional facies observed in cores, through calibration of
log responses can be used to predict the likely facies in nearby wells in studied fields
on the basis of the similarity in log responses. Understanding the spatial distribution
and properties of reservoir facies is important for predicting reservoir quality and
reservoir continuity, which in turn supports implementation of more effective
waterflood or CO2 EOR in diverse Dundee oil fields in the Michigan Basin. This
chapter addresses the important task of populating the geologic framework with
petrophysical properties and well logs data from the three main reservoir facies,
including crinoidal grainstone, stromatoporoid boundstone, and fenestral peloidal
grainstone/packstone (facies 3, 5, and 7). The goal of this chapter is to examine in
71
depth the need of reservoir properties to implement waterflood or CO2 EOR in the
Dundee Limestone reservoirs.
Reservoir Quality
The quality of a reservoir is a function of petrophysical properties.
\Eetrophysical properties such as porosity and permeability are often highly variable in
carbonate strata and rarely show a regular relationship as in siliciclastics. Carbonate
reservoirs are characterized by the extreme heterogeneity of porosity and
permeability, as a result of depositional and diagenetic processes (Flugel, 2004).
Carbonate rocks have complex porosity distributions as a result of both their
biological genesis and subsequent diagenetic overprinting (Choquette and Pray,
1970). Characterization of carbonate reservoirs is therefore complicated due to the
inherent heterogeneity and complexity of carbonate geological systems. This study
defines three different reservoir types within the Dundee Limestone, which include: 1)
recovery of these Dundee reservoirs requires an understanding of fluid flow, which in
turn requires a detailed understanding of porosity and permeability within these
facies.
Porosity and Permeability
Porosity and permeability are two of the important fundamental properties that
control the storage and movement of fluids in reservoirs. Porosity is the ratio of the
pore volume to the bulk volume of material (Lucia, 1999). The porosity in the
sedimentary rocks split into two major categories; primary porosity forms during the
72
depositional phase (i.e., interparticle or framework growth porosity), and secondary
porosity (i.e., moldic or vuggy porosity), forms during diagenesis during all post-
depositional stages (Flugel, 2004). Schmoker et al. (1985) reported that the carbonate
reservoirs within the United States have porosities ranging from 1-35%, with average
values of 12% in limestone reservoirs and 10% in dolomite reservoirs.
Permeability is the ability of a fluid to pass through a sediment or rock.
Permeability is calculated according to Darcy's law (Eq 1) and commonly expressed
in millidarcy (Flugel, 2004). Permeability is important because it is a rock property
that relates to the rate at which hydrocarbons can be recovered. Additionally, the
viability of a carbonate reservoir is more dependent on its permeability rather than
porosity for hydrocarbon recovery (Tucker and Wright, 1990). Typically in carbonate
reservoirs, permeability values vary between 0.01 millidarcy (md) to well over 1
Darcy. A permeability of 0.1 md is generally considered minimum for oil production
(Lucia, 1999).
Equation 1 Darcy's Law:
Where Q is rate of flow, k is permeability, \i is fluid viscosity, (AP)/L is the potential
drop across a horizontal sample, and A is the cross-sectional area of the sample.
Dominant pore types in reservoir facies 3,5, and 7 are commonly interparticle,
intraparticle, and limited fracture and moldic porosity, with the exception of facies 7,
which contains predominately fenestral porosity. Comparisons of all Dundee porosity
vs. permeability show no distinct relationship in these reservoirs (Figure 40). The
73
results of conventional core analysis from studied cores show high contrast and
variation in core properties (porosity and permeability). Large differences in the
relationship between porosity and permeability support the complexity of Dundee
reservoirs. However, when porosity and permeability data for each depositional facies
are plotted individually, better correlation relationships became apparent (i.e., facies 3
and 5, Figure 15 and 19, respectively).
Porosity and permeability cross plots typically demonstrates that the crinoidal
grainstone facies has moderate porosity ranges in this reservoir facies from 2% to
12%, with average porosity of 7%, and permeability ranging from 0.1md to 189md,
with an average of 14md. Stromatoporoid boundstone facies has moderate to high
porosity and permeability with average of 7% and 123 md, respectively. Fenestral
peloidal grainstone/packstone facies has the highest porosity and permeability values
with average of 9% and 195md. The excellent reservoir quality in the fenestral facies
is clearly a result of a well-connected network of fenestral pores developed in the tidal
flat facies, which results in higher permeability values. Porosity and permeability
relationships in these three reservoir facies (facies 3, 5, and 7) are evidence of
generally good reservoir quality indicating that these reservoirs types should be good
candidates for effective waterflood or potential C02 EOR injection activity.
Porosity and permeability variations from well to well within the same field
and within the same facies are significant. Therefore, the facies are not the only
controls on the Dundee reservoir rock properties. There is clearly another factor that
controls on reservoir properties (diagenesis), which will be discussed in greater detail
in the following section.
74
10000
10 12Porosity (%)
Figure 40. All core measured porosity-permeability data with the three primaryreservoir facies highlighted. As shown, there are strong variationsbetween different types as well as within single types.
Diagenetic Controls on the Reservoir Quality
The substantial reduction of porosity with progressive burial has been well
documented in carbonates (Schmoker and Halley 1982; Halley and Schmoker 1983;
Scholle and Halley 1985; Amthor et al. 1994; Brown 1997; Goldhammer 1997),
however, it is not true for permeability with depth relations. In carbonate strata
primary pore types are highly variable in shape and size. Diagenetic alteration of
carbonate pore types adds additional complexity to pore geometry, distribution and
reservoir quality (Choquette and Pray, 1970).
Strata within the Dundee Limestone are buried to a range of at least 2600 to
3550 feet (780 to 1100 m). Core and petrographic analyses of the Dundee Limestone
75
indicates that the original fabric of most depositional facies was subjected to
diagenetic processes that substantially modified reservoir qualities. Diagenesis
typically reduces porosity, redistributes the pore space, and alters permeability
characteristics. Dundee porosity is commonly partially occluded by diagenetic
cements. The dominant pore-occluding cements are blocky/sparry calcite pore fill and
syntaxial overgrowth cement.
In most examples of the patch reef facies (facies 5) primary porosity is only
partially reduced by calcite cement. However, in the North Buckeye Field for
example, the pores in stromatoporoids are extensively occluded by calcite cement
(Figure 30) resulting in very low porosity and permeability, and poor reservoir quality
for this facies. In the grainstone facies (facies 3), interparticle porosity of primary
origin is dominant. Grainstone reservoir facies however, commonly contain
interparticle porosity-occluding sparry calcite or syntaxial overgrowths cement
(Figure 33), which reduces the size of the interparticle pores and decreases the
permeability (<14md average) relative to other reservoir facies. Crinoidal grains are
especially subject to development of syntaxial overgrowths that totally occlude
effective porosity. The fenestral peloidal grainstone/packstone facies (facies 7) has
some fenestral porosity partially filled with blocky calcite spar cement or internal
sediment (Figure 31). In the fenestral reservoir facies the effect of this process is
relatively minor resulting in the large amount of preserved primary porosity. As a
result of the combined influence of primary and secondary processes on the
formation, preservation and destruction of porosity, reservoir quality is higher in
facies 5 and 7 and lower in facies 3. The high degree of variation in reservoir
76
properties in these important reservoir facies is caused by diagenetic changes to
primary pore networks.
Reservoir Compartmentalization and Reservoir Distribution
Reservoir compartmentalization can have a significant impact on effective
field development and secondary and enhanced recovery activity.
Compartmentalization caused by vertical facies variations and fluid flow barriers or
lateral depositional discontinuities can have an adverse effect on oil or gas recovery
factors by reducing drainage and sweep efficiency. Understanding the nature and
geological origin of compartmentalization in Dundee reservoirs is a key to predicting
connected reserves, and effectively optimizing field development in order to increase
production rates and ultimate recovery. Reservoirs in Dundee oil fields are
compartmentalized at both an inter-well and reservoir-scale. In the studied fields the
reservoir facies are vertically compartmentalized by impermeable facies, which baffle
and inhibit vertical fluid flow (i.e., facies 2 and 6).
The patch reef and peritidal facies (facies 5 and 7) form important
hydrocarbon producing facies in most Dundee oil Fields. The patch reef facies forms
a potential reservoir when the open galleries of the stromatoporoids and the
interparticle and intraparticle pores are well connected and not cemented, resulting in
good reservoir quality. A detailed study of core in the stromatoporoid boundstone
facies (23 feet) of Havens-Denham #1; Permit #43382 well at the South Buckeye
Field revealed that the patch reef are likely highly compartmentalized growth
structure resulting in baffles and barriers to fluid flow in the reservoir unit
(McCloskey, 2012). This was documented by a high degree of variation of porosity
77
and permeability values (Appendix D). The fenestral reservoir unit (facies 7) is a
succession of interstratified peritidal and lagoonal facies. This interstratification
further compartmentalizes the reservoir (Figure 41). The lagoonal facies (facies 6)
varies in thickness from a foot to several feet, and appears to be laterally correlative
and relatively continuous (e.g., Mt Pleasant Field, Appendix B). Lagoonal facies have
high potential to act as baffles or flow barriers affecting the reservoir production
performance. Few of these impermeable beds (lagoonal facies) may vertically
compartmentalize the reservoir interval (Appendix B). The heterogeneous
characteristics of the reservoir are well demonstrated in the frequent vertical
variations of core derived porosity and permeability (Appendix D). The crinoidal
grainstone facies (facies 3) however, also contributes to reservoir volume. This facies
occurs as thin beds (1-2 ft) usually below the stromatoproid boundstone facies as
facies 2 and 6). In contrast, the crinoidal grainstone facies occurs as a significant,
thickly bedded and separate unit in the West Branch Field with a composite thickness
of 40 feet (12 m). This facies might have more enhanced recovery potential because
of its lower primary recovery, porosity and permeability values and greater lateral
extent compared to the stromatoporoid boundstone facies (see below).
Stratigraphic Correlations and Cross-sections
Wire-line logs respond to petrophysical properties and not to geologic
properties (i.e. rock lithology). Wire-line logs, for instance, may not be used to
differentiate between grainstone and wackestone or between grain types. However,
wire-line logs can distinguish different rock types based on the bulk densities/porosity
78
relationships (Lucia, 1999). Wire-line logs can be extremely valuable in inferring
several reservoir properties (e.g., porosity). In this study, on the basis of core to log
calibration, log response corresponds to core and core analysis data with reasonable
consistency.
The primary stratigraphic factors that influence recovery efficiency are
reservoir continuity and associated permeability heterogeneity. The depositional
model construction and vertical successions of facies and rock fabrics obtained from
core descriptions was extended to electric-log-facies correlation field-wide to expand
the coverage of one dimensional data. The stratigraphic correlation is based upon a
grid of regional wire-line log cross-sections, tied to cored wells. Wire-line logs that
have been used for this correlation method include gamma-ray (Gr), neutron porosity
(NPHI), and bulk density (RHOB). Prior to establishing the correlation between the
continuous well log data set and core measurements was performed, three steps were
considered: 1) Shifting the depth of core to match the depth of the wire-line log (±1-
10 feet). 2) Cross-sections were hung on the contact between the Rogers City and The
Dundee. 3) Picking distinct well log signature that could be directly related to distinct
facies types in the recovered core. Some depositional facies (i.e., facies 1, 6 and 7)
have similar log characteristics when discriminated by bulk density and neutron
porosity logs (Figure 41). This correlation work contributed to a better understanding
of the reservoir geometries and may help explain possible waterflood or C02
performance.
In North Buckeye, Wise, and Mt Pleasant fields production comes from one
uniform reservoir type, the fenestral reservoir facies. The cross-section of this
reservoir facies was constructed in the Mt Pleasant Field only because of better
79
available data control. It is inferred that this degree of lateral continuity can be applied
to both the Wise and North Buckeye fields. However, in these fields, due to lack of
modern wire-line logs, core data and conventional core analysis only few cross-
sections can be confidently established (Appendix E).
A field-wide cross-section (Figure 41) was constructed from well logs in the
Mt Pleasant Field in Isabella and Midland Counties. This cross-section was
constructed where conventional cores from wells located from the northwest to
southeast provide good indication of overall reservoir lateral continuity and
reasonable petrophysical homogeneity. In the Mt Pleasant Field the predominant
facies are fenestral peloidal grainstone/packstone and skeletal wackestone facies. It is
composed of several shallowing upward sedimentary cycles. These cycles consist of
shallow lagoonal wackestone that grade upward into fenestral grainstone/packstone
suggesting shallower water, intertidal to supratidal conditions. The stratigraphic cross-
section (Figure 41) demonstrates that these facies are correlative throughout the entire
field representing multiple regressive cycles. These regressive cycles are bounded at
the base by an interpreted flooding surface observed on Pfund #1; Permit #36259 well
(Figure 41). The flooding surface is observed as a crinoidal skeletal wackestone
representing an open marine depositional environment similar to the Rogers City
facies (Appendix B). This flooding surface is laterally traceable throughout the field
based on the distinctive gamma ray log response. The geometry and development of
the fenestral reservoir facies is quite extensive both vertically and laterally across
distances of up to 10 miles and creates a generally uniform producing zone
throughout the Mt Pleasant Field. The packages of the fenestral reservoir facies are
separated by a few inches to several feet of non-productive skeletal wackestone facies
80
(facies 6). The most continuous and highest porosity and permeability reservoir zones
are concentrated in the upper Dundee with an average thickness of 16 feet. Highest
confidence was placed on core data, where lateral relationships and significance of
reservoir unit could be determined through depositional facies correlation. The
interpretation of substantial lateral continuity of the peritidal fenestral reservoir facies
is also supported by modern analogs of Persian Gulf (Figure 42). This modern analog,
in terms of the facies distribution closely matches the fenestral reservoir facies of
portions of the Middle Devonian Dundee of the Michigan Basin.
MILLER. VIOLA
ISABELLA
Mount Pleasant
MT PLEASANT UNIT TRACT 55 SIERRA LAND CO , INC
MIDLAND
Mount Pleasant
MIDLAND
Mount Pleasant
Skeletal Crinoidal Wackestone B Fenestralpeloidal Grainstone/Packstone Skeletal Wackestone
Figure 41. Dip oriented stratigraphic cross-section showing inferred lateral continuity ofthe fenestral reservoir facies in the Mount Pleasant field. The stratigraphic datum for thecross-section is the major flooding surface at the top of the Dundee Limestone (RogersCity/ Dundee contact). A
1
laterally continuous, overall regressive cycle consisting of interbeddedfenestral peloidal grainstone/packstone and skeletal wackestone cycles islocated above an interpreted flooding surface marked with a red dashedline. The flooding surface is traceable throughout the field as shown inthis cross-section. The fenestral facies (light blue line and) skeletalwackestone (green line) are correlative throughout. RGRC = RogersCity, DUND = Dundee, GR = gamma-ray log, NPHI = neutron porositylog, RHOB - bulk density log.
LagoonsOffshore
Coral ReefShoal Tidal flat Sabkha
Tertiary Lsoutcrop
10 km
Figure 42. Modern analog from the Persian Gulf is used to demonstrateinterpretations of lateral continuity in peritidal facies (Modified fromNoel and Robert, 2010).
In the South Buckeye Field where the main reservoir type is the patch reef,
there is a limited lateral extent of the patch reef facies within the Dundee Limestone.
82
Insights from two cores (Nusbaum Kern 3-W and Fitzwater 6) examined in this field
were supplemented with inspection of several cores in South Buckeye Field by
McCloskey (2012). These cores were selectively correlated in strike well log cross
section, which shows the vertical and lateral variation of the patch reef facies. Due to
this spatial variability closely spaced wells (>1 mile) in this cross section, features
such as pinch-outs and gradual facies transitions are clearly documented (Figure 43).
An interesting observation from this cross-section is that in the Oard well, the
reservoir facies (facies 5) is completely absent. This relationship and the overall
variation in stratigraphic position and thickness of the boundstone reservoir facies
confidently supports the limited lateral continuity of the patch reef facies across the
South Buckeye Field within distances a little as 0.4 miles. The stromatoporoid
boundstone reservoir facies therefore has distinct petrophysical and reservoir
geometry properties compared to other reservoir facies in the Dundee Limestone.
The characterization of patch reef reservoirs is often aided by modern analogs
to infer the spatial distribution of facies. The distribution of modern patch reefs across
the Belize coast for example, shows significant variability of patch reefs within 0.25
mile (Figure 44) and helps explain the patch reef geometry in the South Buckeye
Field (McCloskey, 2012). In particular, modern environments are an important tool
for visualizing the spatial distribution of facies in a reservoir during a single slice
through time (Grammer et al., 2004).
The West Branch Field was extensively studied by Curran (1990) and Curran
and Hurley (1992). In this study only one cored well (Grow #4) was studied in detail
and this analysis was supplemented with inspection of 11 cores from Curran (1990).
Based on the observation from 11 cores, Curran concluded that most production
83
comes from primary porosity in the grainstone facies (facies 3). From three field-wide
cross-sections in the West Branch field, Curran has suggested that the reservoir facies
(facies 3) was correlative up to 2-3 mile.
As confirmed from core, conventional core analysis, wire-line log, and
production history in this study, the hydrocarbon production at West Branch Field has
occurred primarily from the shoal grainstone facies (facies 3)whereas with secondary
contributions from the shoal grainstone reservoir facies in the South Buckeye Field.
Total reservoir thickness in the producing wells ranges from 20 to 30 feet in West
Branch Field. The shoal reservoir facies has a grain-supported architecture with
minimal carbonate mud, and therefore, has the highest reservoir capacity. The pore
systems of the shoal reservoir facies consist of interparticle and limited moldic and
vuggy pore types. The correlation between porosity and permeability for crinoidal
grainstones is known to be very good in this reservoir (Figure 19). The geometry of
the grainstone reservoir facies is quite extensive both vertically (40 feet thick) and
laterally across distances of up to 3 miles and creates a uniform producing zone
throughout the West Branch Field. The shoal grainstone facies is associated with
impermeable bioturbated peloidal grainstone/packstone and skeletal wackestone
facies (Appendix B). In contrast, the shoal grainstone facies in the South Buckeye
Field is not well developed either vertically or laterally and results in limited lateral
continuity of the reservoir facies (Figure 43, red color).
WOODRING ESTATE
41014
GLADWINBuckeye South
(Skeletal Crinoidal
Wackestone
FITZWATER
36730
GLADWINBuckeye South
• Bioturbated Peloidal
Grainstone/Packstone
O. OARD
35697
GLADWINBuckeye South
•CrinoidalI Grainstone
NUSBAUM KERN STATE BUCKEYE D
43383 41122
GLADWINBuckeye South
I Coral-stromatoporoidFloatstone
RGRC
GLADWINBuckeye South
StromatoporoidBoundstone
Figure 43. Stratigraphic cross section (A A') across South Buckeye Field showinglateral variations in the stromatoporoid boundstone facies (marked inyellow). Note the absence of reservoir facies at O. Oard well indicatesthat the stromatoporoid boundstone facies is laterally discontinuous(blue line). This cross-section was constructed from well logs in theSouth Buckeye Field, and the datum for the cross-section is the majorflooding surface at the top of the Dundee Limestone (Rogers City andDundee contact). RGRC = Rogers City, DUND = Dundee, GR =gamma-ray log, NPHI= neutron porosity log, RHOB = bulk density log.
85
Figure 44. Example of modern patch reef complex in the Belize coast. Note the X-X'cross-section highlights and illustrates the discontinuous and irregulargeometries and sizes of patch reefs growing on this carbonate platform.
This chapter explored the detailed process of reservoir characterization. In
terms of the application of this study is to maximize the recovery of bypassed or
trapped hydrocarbons in these reservoir facies (Facies 3, 5, and 7), it is critically
important that the operator have access to scientifically predict the geometrical
distribution of the reservoir facies in the Dundee Limestone reservoirs. One of the
interesting results from this study is that in contrast to the layer-cake geology
characteristic of peritidal settings, the lateral relationships of peritidal facies, shown
in figure 41, demonstrate extensive continuity of this facies.
86
CHAPTER VI
DUNDEE HISTORIC PRODUCTION AND
ENHANCED OIL RECOVERY (EOR) POTENTIAL
The Middle Devonian Rogers City and the Dundee Limestone formations are
prolific hydrocarbon reservoirs that have produced in excess of 375 million bbl of oil
(MMBBL) from more thanl37 fields mostly in the central part of the Michigan Basin.
The majority of the Dundee oil Fields were discovered in 1930s and 1940s. However,
wells in many of the fields are now abandoned due to aggressive development during
the early stages of production resulting in overdrilling, pressure loss, or water coning
(Montgomery et al., 1998).
The Rogers City and Dundee reservoir types are characterized as fracture
controlled and/or facies controlled, respectively. The fracture controlled dolomite
reservoirs occur predominantly in the central Basin (Ten Have, 1979). The fractured
controlled reservoirs were generally more productive than facies controlled reservoirs,
although the facies controlled are complex, and often less understood in light of
deposition and diagenesis (Luczaj et.al. 2006). Wood et al., (1998) reported that the
most productive intervals in the Rogers City and Dundee come from the sucrosic
dolomite facies of the Rogers City in the central part of the Basin. However, in the
eastern part of the Basin, where the Dundee reservoir produces primarily from
sedimentary facies controlled limestone reservoirs, the most productive zones in the
Dundee reservoirs are related to primary porosity in lenticular beds of skeletal
grainstones and stromatoporoid and coral patch reef facies (Curran and Hurley, 1992;
Wood et.al, 1998). This study adds another important reservoir facies, the peritidal
facies, which forms a main producing unit in several Dundee Limestone fields (Mt
Pleasant, Wise and North Buckeye fields). This facies has high reservoir quality and
87
laterally (dip and strike oriented) extensive reservoir geometry. It extends up to 10
miles across the Mount Pleasant Field based on core to log correlation. On the basis
of cumulative oil production, the peritidal facies in the Dundee Limestone outweighs
all other producing facies in importance.
Field production characteristics in the Dundee Formation (Rogers City and
Dundee, Figure 45) fields indicate at least two distinct field drive mechanisms: 1)
bottom water and 2) gas expansion. These mechanisms have been interpreted based
on water production and pressure decline curves (personal communication, Harrison,
2012). Pressure decline is more pronounced in the gas expansion fields whereas the
initial pressures are generally preserved in the inferred bottom water drive, Rogers
City dolomite fields.
This chapter briefly compares Dundee Limestone production history along
with geologic framework and petrophysical properties to describe reservoir
performance and help predict the potential recoverable hydrocarbons in the patch reef,
shoal, and peritidal reservoirs.
Vernon Field
__^, Crystal Field
DUND
Figure 45. Average per well water production from representative fields with twodistinct trends of relatively high water production per well from inferred
88
bottom water drive in Rogers City (RGRC) dolomite Fields (Fork,Vernon, Crystal, and Deep River Fields) vs. relatively low waterproduction from probable gas expansion drive in Dundee (DUND)Limestone Fields (West Branch and South Buckeye Fields, fromHarrison, 2001).
Historic Production
There are a number of known limitations in the historic production data, for
Devonian carbonates including the Dundee Limestone formation. There is only
modest production since 1982 and the production is often grouped into multi well
leases. Usually there is no digital data before 1997. From 1934 to 1986 the State of
Michigan produced an annual statistical summary of oil and gas fields in paper
records. It is only annual and cumulative field production and does not contain
individual well or lease information. For many of the older fields, there is a gap in
annual field production data from 1986 to 1997. Additionally, some of these fields
have problems with combining data from different Devonian formations and it is
often not possible to determine whether production came from Lucas, Dundee or
Traverse formations. The three fields studied here however, do have reasonably
reliable production data availability. These fields include West Branch, South
Buckeye, and Mount Pleasant fields.
Many old producing fields in the Dundee are interpreted to have had less than
50% of the oil reserves recovered from the estimated original oil in place (OOIP).
Production rates from these reservoirs decreased because reservoir pressure from the
gas expansion drive is nearly depleted possibly due to extensive flaring of natural gas
early in the field history. Recovery from pressure-depleted zones can be increased by
repressurizing the reservoir. Therefore, the Dundee Limestone fields were selected as
89
the focus of this study because of the fundamentally greater enhanced oil recovery
(EOR) potential compared to bottom water drive, Rogers City reservoirs.
West Branch Field
West Branch oil field is an anticlinal trap with northwest-southeast trend that
is primarily located in T22N-R2E, (West Branch Township) in Ogemaw County,
Michigan. The field is approximately nine miles long and one mile wide (Ten Have,
1979). West Branch Field has produced hydrocarbon from several Middle Devonian
formations including the Dundee. However, the Dundee reservoir is by far the
dominant producing unit in the West Branch Field. The first Dundee production was
discovered on March 8, 1934 with the completion of Pure Oil Company's # 1 Fisk
well in Section 27 of West Branch Township, Ogemaw County. In this well the
Dundee oil reservoir occurs at a depth of 2625 ft (800m) with initial production (IP)
of 21 BOPD (barrels of oil per day). Average gravity of produced oil is 36.8° API
units (Mortl, 1991).
In January, 1966 development of the West Branch Field proceeded on ten-acre
spacing, with the wells located in the centers of governmental-surveyed quarter-
quarter-quarter sections. Drilling by several independent producers extended the field
to the southeast into Section 6, T.21N., R.3E., Mills Township, and to the northwest
into Sections 23 and 24, T.22N., R.1E., Ogemaw Township (Vugrinovich and
Matzkanin, 1981). In 1974, the Marathon Oil Company commenced a field-wide
secondary recovery program that water-flooded the Dundee reservoir using a five-spot
well pattern. Oil production reached its second-highest peak in 1981 (Figure 46),
when about 300,000 barrels was produced. A steep decline ensued after 1986 and is
sustained to date, averaging 5.5% per year (Figure 46).
90
The West Branch Field produces oil from grainstone reservoir facies with an
average porosity and permeability of 7% and 14md, respectively. Thickness of the pay
zone is 20-30 feet (Curran and Hurley, 1992). The reservoir unit in the field is thought
to extend over approximately 1870 acres. Since discovery, more than 325 wells have
been drilled producing an excess of 14 MMbbl. The estimated original oil in place
(OOIP) is 26.4 MMbbl, however, 9.5 MMbbl was produced through primary recovery
and 4.7 MMbbl from secondary recovery to date. The total percentage of estimated oil
recovery (primary and secondary) relative to OOIP is 53%. As of 2010, the field
produces approximately 51,400 barrels per year (Figure 46).
Figure 46. Performance history of the West Branch Dundee reservoir showing the oilproduction per year (green line) associated with primary and secondaryannual decline (pink line). In the West Branch Field, the waterfloodbegan in 1966 (from Harrison, 2012).
91
South Buckeye Field
South Buckeye oil field is located on a major anticline fold in T18N-R1W, of
Buckeye Township, in Gladwin County, Michigan, with a few wells located east of
the range line in Hay Township T18N-R1E (Addison, 1940; Harrison, 1991). The
South Buckeye oil field has produced oil and gas from several Middle and Late
Devonian formations including the Dundee. The Dundee reservoir, however, is the
primary unit in the South Buckeye Field and was discovered on July 20, 1936 with the
completion of the Oard No. 1. The Dundee oil reservoir occurs at depth of 3570 ft
(1,088 m) in this well, and the well flowed at rates (IP) greater than 135 BOPD
(Addison, 1940; Mortl, 1991). After production for more than fifty years, the Wiser
Oil Company started a secondary recovery program by water flooding portions of the
field using a five-spot well pattern (Harrison, 1991).
The South Buckeye Field produces oil from patch reef reservoir facies with an
average porosity and permeability of 7% and 123md, respectively. Average thickness
of the pay zone is about 11 feet. Since discovery, more than 240 wells have been
drilled producing an excess of 7.7Mbb through 2011. However, only 45 wells are
active to date, 21 currently water injection wells, and 177 wells were plugged and
abandoned. Average gravity of produced oil is 39° API units (personal
communication, Harrison, 2012). The estimated original oil in place (OOIP) is about
27 MMbbl, however, 5.4 MMbbl were produced through primary recovery and 2.3
MMbbl through secondary recovery. The total percentage (primary and secondary) of
the OOIP is 28%. As of 2011, the field produces approximately 12,000 barrels per
year (Figure 47). That suggested that the recovery efficiencies were only about 28% of
OOIP. In this field, however, original oil in place may be overestimated due to the
patchy distribution of reservoir facies (see below).
92
10,000South Buckeve Oil Field Dundee .Annual Production
Figure 47. Performance history of the South Buckeye Dundee reservoir showing theannual oil production (green curve) and annual water production (bluecurve) associated with annual decline (pink line). Pilot waterfloodingbegan in 1980 (from Harrison, 2012).
Mount Pleasant Field
The Mount Pleasant oil field was the first commercial Dundee field in
Michigan, and was discovered in 1928 in Mt Pleasant Township, Midland County,
Michigan. Mt Pleasant Field lies in both Isabella and Midland Counties (T18-14N-
2W), Michigan (Mortl, 1991).When the Mount Pleasant Field was discovered in the
central basin, serious attention from the petroleum industry became directed toward
the Michigan Basin (Addison, 1940). The depth of the Dundee reservoir is at 3,545 ft
(1,080 m). After fifty five years of production, several producers commenced a pilot
secondary recovery program that water-flooded portions of the field (personal
93
communication, Harrison, 2012). However, the size of these pilot projects is small,
and only limited data on the performances of these pilot projects is publicly available.
The Mount Pleasant Field produces oil from fenestral reservoir facies with an
average porosity and permeability of 9% and 195md, respectively. Average thickness
of the pay zone is approximately 40 feet. The reservoir unit of the field is thought to
extend over approximately 7310 acres. Since discovery, 589 wells have been drilled
in the field. Cumulative production from this reservoir exceeds 29 MMbbl of through
2011. There are currently only 10 producing wells, 4 water injection wells, 2
observation wells, and 573 wells were plugged and abandoned. Average gravity of
produced oil is 41.2° API units (personal communication, Harrison, 2012). The
estimated original oil in place (OOIP) is about 66.8 MMbbl, with 28.3 MMbbl
produced through primary recovery and 1.2 MMbbl produced through secondary
recovery. Only 44% of the original oil in place has been recovered from Mount
Pleasant Field during the primary and secondary production phase. As of 2011, the
field produces approximately 15000 barrels per year (Figure 48).
Mount Pleasant Oil Field Dundee Annual Production10000 1 600
1000
a 100
10
900l\HIO'J»(NICO<t(10lMlCO"J03•a-^LnLnkOicioi-^r^oooooociciOOOcicioiffidicifficriciiowmijiciooo•—I i—li-trHrHtHrHi-lr-lr-li-I (H r-l rH (M (N CM
Production Year
Figure 48. Performance history of the Mount Pleasant Dundee reservoir showing theannual oil production (green curve) and annual water production (blue
94
curve) associated with 4.5% annual decline (pink line). Pilotwaterflooding began in 1980 (from Harrison, 2012).
Enhanced Oil Recovery (EOR) Potential
Enhanced oil recovery (EOR) is a term used for a wide variety of techniques
for increasing the amount of crude oil that can be extracted from an oil field. Gas
injection (including CO2) and water injection for pressure maintenance is presently
the most commonly used approach to enhance recovery (Grammer et al., 2008).
Recovery efficiency, which is also called oil efficiency factor, is expressed as a ratio
of recovered oil to original oil in place (Larue, 2004, Eq. 1).
In this study, the Dundee Limestone produces oil predominately from three
different reservoir types; the stromatoporoid boundstone (patch reef), crinoidal
grainstone (shoal), and fenestral peloidal grainstone/packstone (peritidal). These
reservoir facies have an average thickness of the pay zone is 11 feet, 20-30 feet, and
40-60 feet, respectively. Cumulative production from a patch reef reservoir in South
Buckeye Field exceeds 7.7 MMbbl with primary recovery efficiencies of
approximately 20% (Eq.l). Production from the South Buckeye Field declined
significantly in the primary phase of production possibly due to either the reefs have
reached or are nearing their economic limit in the primary phase of hydrocarbon
production or reservoir pressure from the gas expansion drive is nearly depleted.
However, the South Buckeye Field has been converted to secondary recovery
operations, primarily through water injection for pressure maintenance, conducted in
95
the late 1980s (Figure 47), with additional recovery of approximately 45 % of the
primary recovery. Overall, the higher production from the patch reef facies indicates a
good response to secondary waterflood operations. The good response is attributed to
good overall reservoir quality and interconnectivity of the pore system in the patch
reef facies. Therefore, more recoverable oil can be extracted from the patch reef facies
based on the reservoir properties and estimated OOIP. However, the limited lateral
continuity of the patch reef facies and problematic OOIP estimates probably makes
this reservoir facies less efficient for EOR compared with other two facies (3 and 7).
The total recoverable oil reserves from shoal reservoir facies in the West
Branch Field are estimated to be about 26.4 MMbbl. The shoal reservoir facies has
produced in excess of 9 MMbbl in primary recovery and nearly 4.7 MMbbl from
secondary waterflood. The enhanced oil recovery pilot and field-wide waterflood
projects in the West Branch Field has achieved significant secondary waterflood oil
recovery. This facies generally produces from a uniform pore type (interparticle
porosity) and has high porosity and moderate permeability with an average of 7% and
14md, respectively. The good reservoir efficiency in the shoal facies is attributed to
the lateral continuity of the facies and good interconnectivity of this facies due to the
nature of the pore system (pore-throat size distribution) as well as of the amount of
porosity. Pore-throat size distribution is one of the important factors determining
permeability because the smallest pore throats are the bottlenecks that determine the
rate at which fluids pass through a rock (Kopaska-Merkel, 1991). The shoal reservoir
facies appears to possess good reservoir quality and good vertical and lateral
continuity on the basis of core analysis, production performance and core to log
correlation. Therefore, the shoal reservoir facies is a good candidate for enhanced oil
recovery to produce bypassed oil from shoal reservoir facies in the Dundee limestone.
96
Production in the Mount Pleasant Field started in the late twenties and the
field began experiencing steep production rate declines (Figure 48). After fifty years
of production, the field was converted to a pilot waterflood program. The field
production characteristics, including the heterogeneous nature of the field (i.e.,
especially porosity and permeability), may contribute to the different reservoir
performance. Distribution of porosity and permeability for three selected wells (
Pfund 1, permit # 36259; McClintic 3, permit # 36367; and Mt Pleasant Unit Tract
55, permit # 39770) demonstrate that (Figure 49) the fenestral reservoir (facies 7)
within the Dundee Limestone is thought to have a dual permeability system: a higher
permeability component consisting of interconnected vugs and solution-enhanced
fractures and stylolites seams, and a lower permeability component consisting of
microporosity and interparticle porosity. Through the primary production phase, fluids
move more easily through the higher permeability component. However, a large total
volume of hydrocarbons are stored in the lower permeability component. In light of
reservoir quality shown in porosity vs. permeability cross plot, the better production
probably resulted from the better reservoir quality zones (Figure 49). Additionally, the
estimated primary recovery efficiency in the Mount Pleasant Field is 42%, indicating
that the higher permeability component of the dual porosity system is being swept
very efficiently. The pilot waterflood program in the field resulted in low recovery
efficiency (<2% of OOIP) because the oil in the lower permeability reservoir type has
been ineffectively swept by the injected fluid.
Importantly, the remaining oil in the Mount Pleasant Field is concentrated in
the low permeability component and would be a target for waterflood or CO2
enhanced oil recovery (EOR). The injected fluid (water or CO2) flows at a faster rate
through the high-permeability grainstone intervals and at a lower rate in the low-
97
permeability of microporosity and interparticle porosity grainstone intervals,
effectively bypassing much of the oil in the lower permeability component. This
suggests that the microporosity and interparticle porosity are excellent targets for
waterflood or CO2 enhanced oil recovery because they have moderate porosity, low
permeability, and high initial oil saturation (Appendix D).
In North Buckeye, Wise, and Mt Pleasant fields production comes from one
uniform reservoir type, the fenestral reservoir facies. Analysis of this reservoir facies
was only documented in the Mt Pleasant Field because of better available data
control. It is inferred that this degree of the reservoir properties and reservoir
geometries can be applied to both the Wise and North Buckeye fields. The insights
from the geologic reservoir characterization and field production history provide an
understanding of the reservoir architecture, pore networks, and flow units within the
Dundee Limestone in six fields. It is this foundation that gives some context to areas
with better reservoir development and economic waterflood or CO2 EOR potential.
The geological framework, production performance, and operational understanding
should provide useful guidance for future waterflood or C02 EOR potential
expansion. Fundamentally the fenestral facies performance differently than grainstone
or patch reef. North Buckeye and Wise fields both perform like Mount Pleasant does.
98
10000Porosity vs. Permeability for Facies 7
4
6 8 10
Porosity %
♦Permit #36259
•Permit # 39770A Permit#36367
14 10
Figure 49. Example of three selected wells of the fenestral facies showing theheterogeneity (porosity and permeability) within a single well. Note thatthe fenestral reservoir facies has a dual permeability system, a higherpermeability component consisting of interconnected vugs and solution-enhanced fractures and stylolites seams (blue circle), and a lowerpermeability component consisting of microporosity and interparticleporosity (red circle).
99
CHAPTER VII
CONCLUSIONS
This study evaluates the depositional and diagenetic controls on reservoir
quality within several Dundee Limestone oil fields in order to identify reservoir-prone
facies and predict their distribution. The distribution of reservoir facies in the Dundee
Limestone is controlled by primary depositional processes in conjunction with a suite
of diagenetic processes. In the fifteen wells described in this study, seven distinct
depositional facies have been identified in the Dundee, as well as Rogers City. These
facies were placed into an idealized vertical succession in order to evaluate a
sequence stratigraphic model oh the basis of an inferred depositional model from
deepest/open marine to shallowest/tidal flat.
Oil production occurs from at least three different reservoir facies; 1)
Crinoidal grainstone; 2) Stromatoporoid boundstone; and 3) Fenestral peloidal
grainstone/packstone in different Dundee fields. The other four facies 1) Crinoidal
stromatoporoid rudstone; and 4) Skeletal wackestone, which most commonly form
seals and baffles. This is largely due to their disconnected pore space, consisting
primarily of limited distribution of interparticle, moldic and vuggy pores. Facies 3 and
5 very rarely have reservoir potential when molds are dissolved and the isolated vugy
porosity is interconnected by stylolitization and fracturing.
Examination of conventional core analysis data from the hydrocarbon
reservoir facies indicates that these facies have variable porosity and permeability
relationships. The correlation between porosity and permeability of the reservoir
facies are known to be poor in the Dundee limestone due to the varying connectivity
of different pore types. Reservoir quality in these fields is controlled by lithologic
100
variations and the spatial heterogeneity in diagenetic processes. Variations in
diagenetic alterations such as porosity, permeability and lithology, could produce
zones with different reservoir properties and so different petrophysical behaviors. The
combination of porosity and permeability data in terms of reservoir quality provides a
convenient starting point to address the differences between facies and between
reservoir zones.
This study provides additional information on the opportunities for
implementing water flooding or C02 enhanced oil recovery (C02-EOR). With similar
subsurface reservoirs, waterflood or enhanced recovery initiatives should understand
the reservoir quality and geometry to evaluate the potential of preferential sweep of
unrecovered hydrocarbon. The implementation of EOR in more laterally continuous
reservoir (i.e., fenestral peloidal grainstone/packstone facies) should be more efficient
and effective than typically spatially isolated reservoir facies such as patch reef facies
of the South Buckeye Field. For example, the patch reef reservoir (facies 2), has
distinct petrophysical reservoir properties and also has distinct reservoir geometry
properties, in particular laterally discontinuous patch reef facies. This characteristic
results in less efficient for EOR potential.
101
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Schmoker, J.W., Krystinik, K.B. and Halley, R.B., 1985, Selected Characteristics ofLimestone and Dolomite Reservoirs in the United States: AAPG Bulletin, v. 65,n. 5, p. 733-741. Scholle, P.A., And Halley, R.B., 1985, Burial diagenesis: outof sight, out of mind, in Schneidermann, N., and Harris, P.M., eds., CarbonateCements: SEPM, Special Publication 36, p. 309-334.
Scholle, P. A., and Ulmer-Scholle, D. S., 2003, A Color Guide to the PetrographyofCarbonate Rocks: Grains, Textures, Porosity, Diagenesis, American Associationof Petroleum Geologists Memoir 77, 474p.
Scotese, C. R., 1984 Paleozoic Paleomagnetism and the Assembly of Pangea, In Vander Voo, R., Scotese, C. R., and Bonhommet, N., eds., Paleozoic
106
Paleomagnetism: American Geophysical Union Geodynamic Series, v.12, p.l-10.
Shinn, E.A., 1968, Praticle Significance of Birdseyes structures in carbonate rocks:Journal of Sedimentary Petrology, v. 38, p. 215-223.
Shinn, E.A., 1983a, Birdseyes, fenestrae, shrinkage pores, and loferites: Areevaluation, Journal of Sedimentary Petrology, v. 53, n. 2, p. 619-628.
Strasser, A., Hillgartner, H., Hug, W. & Pittet, B., 2000, Third-order depositionalSequences Reflecting Milankovitch Cyclicity. - Terra Nova 12, 303-311
Ten Have, E. L., 1979, Relationship of Dolomite/Limestone Ratios to the Structureand Producing Zones of the West Branch Oil Field, Ogemaw County, Michigan:M.S. thesis, Michigan State University, East Lansing, lOOp.
Tucker, M.E. and Wright, V.P., 1990, Carbonate Sedimentology: Blackwell Science,Maiden, Massachusetts, 482 p.
Tucker, M., E., 2001, Sedimentary Petrology- an Introduction to the Origin ofSedimentary Rocks, 3rd ed., Blackwell Science Ltd., Oxford, p. 111.
Vugrinovich, R. G., and Matzkanin, A. D., 1981, Enhanced Oil & Gas Recovery inWest Branch Field Dundee Oil Pool in the Michigan Basin: SecondaryRecovery Report No.8.
Wallace, M. W., Kerans, C, Playford, P. E., and McManus, A., 1991, Burialdiagenesis in the Upper Devonian Reef Complexes of the Geike Gorge Region,Canning Basin, Western Australia. American Association of PetroleumGeologists, Bulletin., v. 75, p. 1018-1038.
Wilson, J. L, 1975, Carbonate Facies in Geologic History: Springer-Verlag Berlin,471p.
Wood, J. R., Allan, J. R., Harrison III, W. B., and Eric Taylor, 1996, Horizontal WellTaps Bypassed Dundee oil Crystal field, Michigan: oil and gas report.
107
Appendix ACore Descriptions
108
Permits 19693
Oxy USA Inc., Mcnerney, B E13. Wise FieldIsabella County Michigan
Depth Interval: 3678.5' - 3717'Rogers City:
The Rogers City facies is dense, low porosity and permeability. The boundarycontact between Rogers City and Dundee is marked by irregular surface (stylolite).
3678.5'-3683': Ls, dark gray, crinoidal/skeletal wackestone, Fl, occasionallyinterbedded with packstone, containing fossil fragments such as crinoids,gastropods, brachiopods, ostracods, and intraclasts. It has stylolite structure,has low porosity and permeability which acts as a cap rocks in the mostDundee intervals. Its contact with lower Dundee Limestone is marked byirregular surface. The depositional environment is interpreted as an openmarine.
Dundee Limestone:
3683'3684': Ls, gray buff, fenestral, peloidal grainstone/packstone, F7, this faciesmade up largely of peloids. The skeletal grains include casts of fossilfragments, gastropods, ostracods, bivalves. Stylolites are very common in thisfacies, oil stain. The only sedimentary structures are fenstrae, smalllaminations, and cyanobacterial mat. This interval is very pores. Thedepositional environment is high energy peritidal.
3684'-3687.5': Ls, brown- grey, skeletal wackestone, F6, with casts of gastropods,bivalves, forams, peloids, ooids, crinoids, ostracod fragments, and calcareoussponges. No visual porosity was observed. It has stylolites and some fractures.Partially dolomitization of carbonate mud was observed. The depositionalenvironment is low energy shallow lagoon.
3687.7' (Thin-section) Skeletal Wackestone it haspeloids, ooids,crinoids.
3687.5'-3692': Ls, grey buff, fenestral, peloidal grainstone/packstone, F7. Grainsinclude peloids, with casts of fossil fragments, gastropods, ostracods, bivalves.The sedimentary structures associated with this facies are fenstrae, smalllaminations, and cyanobacterial mat. Porosity within this facies is dominantlyfenestral and interparticle, high permeability and porosity, main reservoir in
109
this field. The vugs are partially filled with calcite crystals. Stylolites arecommon throughout this facies, oil stain, the depositional environment isperitidal.
3692'-3695.5': Ls, brown-gray, skeletal wackestone F6, skeletal grains includegastropods, bivalves, ostracod fragments, forams, and minor stromatoporoids.No visual porosity. The stylolites and some fractures are observed. Thedepositional environment is interpreted as a low energy lagoon.
3693.1' (Thin-section) Skeletal Wackestone.
3695.5'3698': Ls, grey buff, fenestral, peloidal grainstone/packstone, F7. Thisinterval is largely made of peloids, and with casts of fossil fragments,gastropods, ostracods, bivalves. The sedimentary structures associated withthis facies are fenstrae and small laminations, and cyanobacterial mat. Porositywithin this facies is dominantly fenestral and interparticle, main reservoir inthis field. The vugs are partially filled with calcite crystal cement. Stylolitesare common throughout this facies, oil stain and the depositional environmentis interpreted as peritidal
3698'-3700': Ls, brown-gray, very fined grain, skeletal wackestone, F6 with casts ofgastropods and ostracod fragments. No visual porosity, it has stylolites andsome vertical fracture (5-8cm). The depositional environment is low energylagoon.
3700'3709.5': Ls, gray buff, fenestral, peloidal grainstone/packstone, F7. Thisfacies consist of peloids, gastropods, ostracods, bivalves. This interval is veryporous. The sedimentary structures associated with this facies are fenstrae andsmall laminations, and cyanobacterial mat. Porosity within this facies isdominantly fenestral and interparticle porosity, main reservoir in this field.The vugs are partially filled with calcite crystal cement. Stylolites are commonthroughout this facies, oil stain, and the depositional environment is peritidal.
3700.8' (Thin-section) Peloidal grainstone
3709.5'-3711': Ls, gray buff, skeletal wackestone, F6, fined grained, fossilfragments, bivalves, gastropods, ostracods, forams and ooids??. The styloliteshave bladed dolomite along vertical lines. This interval has low permeabilityand porosity.
3709.3' (Thin-section) skeletal wackestone.
110
3711'-3714.5': Ls, grey buff, fenestral, peloidal grainstone/packstone, F7, mainlymade up of peloids, and with casts of fossil fragments, gastropods, ostracods,bivalves. The sedimentary structures associated with this facies are fenstraeand small laminations, and cyanobacterial mat. Porosity within this facies isdominantly fenestral and interparticle porosity, main reservoir in this field.Stylolites are common throughout this facies, oil stain, and the depositionalenvironment is peritidal.
3714.5'-3717': Ls, brownish gray, very fined grain, skeletal wackestone, F6, skeletalgarains include gastropods, ostracod fragments, forams very abundant. Sparsevugy and moldic porosity that partially filled with calcite cements, stylolitesare very common. The depositional environment is low energy lagoon.
3716.6' (Thin-section) Skeletal Wackestone.
Ill
Permit#35461
Oryx Energy Co., Sierra Land CO., INC 1, Mt PleasantMidland County Michigan
Depth Interval: 3530'-3615'
Rogers City:
3530'-3544': Ls dark gray, crinoidal/skeletal wackestone, Fl, consists of crinoids,and other fossil fragments, intraclasts, has stylolite structure and has very lowporosity and permeability, which act as cap rocks in the most Dundeeintervals. This facies representing open marine environment.
Dundee Limestone:
3544'-3554': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include tidallaminations, and fenestral structure. Porosity within this facies is dominantlyfenestral and moldic porosity, and forms a main reservoir in this field.
3554'-3556': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Novisual porosity, it has stylolites and some fractures. The depositionalenvironment is low energy shallow lagoon.
3560'-3563': Missing interval.
3563'-3565': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3565'-3569': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure observed in this facies is fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic porosity, high permeability and porosity, main reservoirin this field. The vugs are partially filled with calcite crystal cement, stylolitestructure, the depositional environment is peritidal.
3569'-3570.5': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Thisfacies is u interbedded with peloidal grainstone facies #7. It has low and highamplitude stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
112
3570.5'-3574': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral porosity, high permeabilityand porosity, main reservoir in this field. The vugs are partially filled withcalcite crystal cement, stylolite structure, the depositional environment isperitidal.
3574'-3577': Ls, light to brownish gray, skeletal wackestone, F6, it is highlybioturbated with casts of bivalves, ostracod fragments, and calcareous sponges(stromatoporoid) at 3680'. No Visual porosity, it has low and high amplitudestylolites and some fractures, oil stain. The depositional environment is lowenergy shallow lagoon.
3577'-3579': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and allochems grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. The vugs are partiallyfilled with calcite crystal cement, stylolite structure.
3579'-3581': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Novisual porosity, it has stylolites and some fractures. The depositionalenvironment is low energy shallow lagoon.
3581' -3584.5': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the skeletal grains include coral and sponges fragments. The mainsedimentary structures are tidal laminations, and fenestral structure. Very fineto fine sand grain, porosity within this facies is dominantly fenestral andmoldic porosity, high permeability and porosity, main reservoir in this field.The depositional environment is peritidal.
3584.5'-3585.5: Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3585.5-3588': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure observed in this facies is fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic porosity, high permeability and porosity, main reservoir
113
in this field. The vugs are partially filled with calcite crystal cement, stylolitestructure, the depositional environment is peritidal.
3588'-3590': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Thisfacies is u interbedded with peloidal grainstone facies #7. It has low and highamplitude stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3590'-3594': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure observed in this facies is fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic porosity, high permeability and porosity, main reservoirin this field. The vugs are partially filled with calcite crystal cement, stylolite.
3594'-3598': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Thisfacies is u interbedded with peloidal grainstone facies #7. It has low and highamplitude stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3598'-3607': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral porosity, high permeabilityand porosity, main reservoir in this field. The vugs are partially filled withcalcite crystal cement, stylolite structure, the depositional environment isperitidal.
3607'-3610': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). It haslow and high amplitude stylolites and some fractures, oil stain. Thedepositional environment is low energy shallow lagoon.
3610'-3615': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral porosity, high permeabilityand porosity, main reservoir in this field. The vugs are partially filled withcalcite crystal cement, the depositional environment is peritidal
♦ This core was depth-shifted up 5 feet to match the wire-line logs
114
Rogers City:
Permit#35764
Oryx Energy Co., Ames, C W 1, Mt PleasantMidland County Michigan
Depth Interval: 3530'-3595'
3530'-3534': Ls dark gray, crinoidal/skeletal wackestone, Fl, consists of crinoids,and other fossil fragments, intraclasts, has stylolite structure and has very lowporosity and permeability, which act as cap rocks in the most Dundeeintervals. This facies representing open marine environment.
Dundee Limestone:
3534'-3543': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include smallcyanobacterial mats, tidal laminations, and fenestral structure. Very fine tofine sand grain, porosity within this facies is dominantly fenestral and moldicporosity, and forms a main reservoir in this field. This facies has beendeposited in peritidal environment.
3543'-3545': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Novisual porosity, it has stylolites and some fractures. The depositionalenvironment is low energy shallow lagoon.
3545' -3548': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include smallcyanobacterial mats, tidal laminations, and fenestral structure. Very fine tofine sand grain, porosity within this facies is dominantly fenestral and moldicporosity, high permeability and porosity, main reservoir in this field. Thedepositional environment is peritidal.
3548'-3550': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3550'-3557': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure observed in this facies is fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic porosity, high permeability and porosity, main reservoir
115
in this field. The vugs are partially filled with calcite crystal cement, stylolitestructure, the depositional environment is peritidal.
3557'-3560': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures. The depositional environment is lowenergy shallow lagoon.
3560'-3568': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure found in this facies is fenestral structure.Very fine to fine sand grain, porosity within this facies is dominantly fenestraland moldic porosity, high permeability and porosity, main reservoir in thisfield. The depositional environment is peritidal.
3568'-3573': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Thisfacies is u interbedded with peloidal grainstone facies #7. It has low and highamplitude stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3573'-3577': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral porosity, high permeabilityand porosity, main reservoir in this field. The vugs are partially filled withcalcite crystal cement, stylolite structure, the depositional environment isperitidal.
3577'-3579': Ls, light to brownish gray, skeletal wackestone, F6, it is highlybioturbated with casts of bivalves, ostracod fragments, and calcareous sponges(stromatoporoid). No Visual porosity, it has low and high amplitude stylolitesand some fractures, oil stain. The depositional environment is low energyshallow lagoon.
3579'-3584': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. The vugs are partiallyfilled with calcite crystal cement, stylolite structure, the depositionalenvironment is peritidal.
116
3584'-3587': Ls, light to brownish gray, skeletal wackestone, F6, it is highlybioturbated with casts of bivalves, ostracod fragments, and calcareous sponges(stromatoporoid). No Visual porosity, it has low and high amplitude stylolitesand some fractures, oil stain. The depositional environment is low energyshallow lagoon.
3587'-3589': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral and moldic porosity. Thevugs are partially filled with calcite crystal cement, stylolite structure, thedepositional environment is peritidal.
3589'-3595': Ls, light to brownish gray, skeletal wackestone, F6, it is highlybioturbated with casts of bivalves, ostracod fragments, and calcareous sponges(stromatoporoid). No Visual porosity, it has low and high amplitude stylolitesand some fractures, oil stain. The depositional environment is low energyshallow lagoon.
117
Permit#36227
Oryx Energy Co., Sokolowski, C T 1, Mt PleasantMidland County Michigan
Depth Interval: 3544'-3609'Dundee Limestone:
3544'-3548': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include tidallaminations, and fenestral structure. Porosity within this facies is dominantlyfenestral and moldic porosity, and forms a main reservoir in this field.
3548'-3551': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Novisual porosity, it has stylolites and some fractures. The depositionalenvironment is low energy shallow lagoon.
3551' -3561': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the skeletal grains include coral and sponges fragments. The mainsedimentary structures are tidal laminations, and fenestral structure. Very fineto fine sand grain, porosity within this facies is dominantly fenestral andmoldic porosity, high permeability and porosity, main reservoir in this field.The depositional environment is peritidal.
3561'-3563': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3563'-3573': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure observed in this facies is fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic porosity, high permeability and porosity, main reservoirin this field. The vugs are partially filled with calcite crystal cement, stylolitestructure, the depositional environment is peritidal.
3573'-3574': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures. The depositional environment is lowenergy shallow lagoon.
3574'-3585': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure found in this facies is fenestral structure.
118
Very fine to fine sand grain, porosity within this facies is dominantly fenestraland moldic porosity, high permeability and porosity, main reservoir in thisfield. The depositional environment is peritidal.
3585'-3587': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Thisfacies is u interbedded with peloidal grainstone facies #7. It has low and highamplitude stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3587'-3591': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral porosity, high permeabilityand porosity, main reservoir in this field. The vugs are partially filled withcalcite crystal cement, stylolite structure, the depositional environment isperitidal.
3591'-3597': Ls, light to brownish gray, skeletal wackestone, F6, it is highlybioturbated with castsof bivalves, ostracod fragments, and calcareous sponges(stromatoporoid). No Visual porosity, it has low and high amplitude stylolitesand some fractures, oil stain. The depositional environment is low energyshallow lagoon.
3597'-3600: Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and allochems grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. The vugs are partiallyfilled with calcite crystal cement, stylolite structure.
3600'-3601': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Novisual porosity, it has stylolites and some fractures. The depositionalenvironment is low energy shallow lagoon.
3601' -3603': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the skeletal grains include coral and sponges fragments. The mainsedimentary structures are tidal laminations, and fenestral structure. Very fineto fine sand grain, porosity within this facies is dominantly fenestral andmoldic porosity, high permeability and porosity, main reservoir in this field.The depositional environment is peritidal.
119
3603'-3604': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3604'-3609': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure observed in this facies is fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic porosity, high permeability and porosity, main reservoirin this field. The vugs are partially filled with calcite crystal cement, stylolitestructure, the depositional environment is peritidal.
120
Rogers City:
Permit#36259
Oryx Energy Co., Pfund-1, Mt PleasantMidland County Michigan
Depth Interval: 3525'-3660'
3525'-3539': Ls dark gray, crinoidal/skeletal wackestone, Fl, consists of crinoids,and other fossil fragments, intraclasts, has stylolite structure and has very lowporosity and permeability, which act as cap rocks in the most Dundeeintervals. This facies representing open marine environment.
Dundee Limestone:
3539'-3553': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include tidallaminations, and fenestral structure. Very fine to fine sand grain, porositywithin this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. The vugs are partiallyfilled with calcite crystal cement, stylolite structure, the depositionalenvironment is peritidal.
3553'-3555': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures. The depositional environment is lowenergy shallow lagoon.
3555'-3563': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include tidallaminations, and fenestral structure. Very fine to fine sand grain, porositywithin this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. This facies wasdeposited in peritidal environment.
3563'-3565': Limestone, light to brownish gray Ls, skeletal wackestone, F6, withcasts of bivalves, ostracod fragments, coral and calcareous sponges(stromatoporoid). Wispy and suture stylolites and some fractures. Thedepositional environment is low energy shallow lagoon.
3565'-3569': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral brachiopods andsponges fragments. The sedimentary structures found in this facies includetidal laminations, and fenestral structure. Very fine to fine sand grain, porosity
121
within this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field3569'-3571': Ls, light tobrownish gray, skeletal wackestone, F6, with casts of bivalves, ostracodfragments, coral and calcareous sponges (stromatoporoid). Wispy and suturestylolites and some fractures. The depositional environment is low energyshallow lagoon.
3571'-3579' Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral brachiopods andsponges fragments. The sedimentary structures found in this facies includesmall cyanobacterial mats, tidal laminations, and fenestral structure. Very fineto fine sand grain, porosity within this facies is dominantly fenestral andmoldic with minor stylolitic porosity, high permeability and porosity, mainreservoir in this field. The vugs are partially filled with calcite crystal cement,stylolite structure, the depositional environment is peritidal
3579'-3581': Ls, light to brownish gray, skeletal wackestone, F6, very fine-grained,with casts of bivalves, ostracod fragments, coral and calcareous sponges(stromatoporoid). This facies interpreted as storm deposit. Stylolite structure iscommon, no visual porosity. Low porosity and permeability based on the coreanalysis date. The depositional environment is low energy shallow lagoon.
3581'-3583': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include brachiopods, coral,sponges fragments, stromatoporoid rich. The sedimentary structures found inthis facies include small cyanobacterial mats, tidal laminations, and fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic with minor stylolitic porosity, high permeability andporosity, main reservoir in this field. The vugs are partially filled with calcitecrystal cement, stylolite structure, the depositional environment is peritidal.
3583'-354.5: Limestone, light to brownish gray Ls, skeletal wackestone, F6, veryfine-grained, with casts of bivalves, ostracod fragments, coral and calcareoussponges (stromatoporoid it about 10 cm). This facies interpreted as stormdeposit. Wispy and suture stylolites is common, no visual porosity. Lowporosity and permeability based on the core analysis date. The depositionalenvironment is low energy shallow lagoon.
3584.5'-3587': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral brachiopods andsponges fragments, stromatoporoid. The sedimentary structures found in thisfacies include small cyanobacterial mats, tidal laminations, and fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral porosity, high permeability and porosity, main reservoir in this field.
122
The vugs are partially filled with calcite crystal cement, stylolite structure, thedepositional environment is peritidal.
3587'-3589': Limestone, light to brownish gray Ls, skeletal wackestone, F6, veryfine-grained, with casts of bivalves, ostracod fragments, coral and calcareoussponges (stromatoporoid it about 10 cm). This facies interpreted as stormdeposit. Stylolite structure is common, no visual porosity. Low porosity andpermeability based on the core analysis date. The depositional environment islow energy shallow lagoon.
3589'-3604': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral brachiopods andsponges fragments and stromatoporoid rich at 3598'-3600'. The sedimentarystructures found in this facies include small cyanobacterial mats, tidallaminations, and fenestral structure. Very fine to fine sand grain, porositywithin this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. The vugs are partiallyfilled with calcite crystal cement, stylolite structure, the depositionalenvironment is peritidal.
3604'-3606.5': Ls, light to brownish gray, skeletal wackestone, F6, very finegrained, with casts of bivalves, ostracod fragments, coral and calcareoussponges. This facies interpreted as storm deposit. Stylolite structure iscommon, no visual porosity. Low porosity and permeability based on the coreanalysis date. The depositional environment is low energy shallow lagoon.
3606.5'-3634': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral brachiopods andsponges fragments, stromatoporoid at 3642.5' (12cm). The sedimentarystructures found in this facies include small cyanobacterial mats, tidallaminations, and fenestral structure. Very fine to fine sand grain, porositywithin this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. The vugs are partiallyfilled with calcite crystal cement, stylolite structure, the depositionalenvironment is peritidal.
3634'-3636': Ls, light to brownish gray, skeletal wackestone, F6, very fine-grained,with casts of bivalves, ostracod fragments, coral and calcareous sponges. Thisfacies interpreted as storm deposit. Wispy and suture stylolites is common, novisual porosity. Low porosity and permeability based on the core analysis date.The depositional environment is low energy shallow lagoon.
3636-3639': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral brachiopods andsponges fragments. The sedimentary structures found in this facies include
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small cyanobacterial mats, tidal laminations, and fenestral structure. Very fineto fine sand grain, porosity within this facies is dominantly fenestral andmoldic porosity, high permeability and porosity, main reservoir in this field.The vugs are partially filled with calcite crystal cement, stylolite structure, thedepositional environment is peritidal.
3639'-3644': Ls, light to brownish gray, skeletal wackestone, F6, very fine-grained,with casts of bivalves, ostracod fragments, coral and calcareous sponges. Thisfacies interpreted as storm deposit. Wispy and suture stylolites is common, novisual porosity. Low porosity and permeability based on the core analysis date.The depositional environment is low energy shallow lagoon.
3644'-3650': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral brachiopods andsponges fragments. The sedimentary structures found in this facies includesmall cyanobacterial mats, tidal laminations, and fenestral structure. Very fineto fine sand grain, porosity within this facies is dominantly fenestral andmoldic with minor stylolitic porosity, high permeability and porosity, mainreservoir in this field. This facies interpreted as peritidal environment.
3650'-3652': Ls, light to brownish gray, skeletal wackestone, F6, very fine-grained,with casts of bivalves, ostracod fragments, coral and calcareous sponges. Thisfacies interpreted as storm deposit. Wispy and suture stylolites is common, novisual porosity. Low porosity and permeability based on the core analysis date.The depositional environment is low energy shallow lagoon.
3652'-3657': Ls dark gray, crinoidal/skeletal wackestone, Fl, consists of crinoids,and other fossil fragments, intraclasts, has stylolite structure and has very lowporosity and permeability, which act as cap rocks in the most Dundeeintervals. This facies representing open marine environment. Floodingsurface @3652.5-3654(diverse fauna include crinoids and finger coral,sponges, and stromatoporoid debris)
124
Rogers City:
Permit#36367
Oryx Energy Co., Mcclintic-3, Mt PleasantIsabella County Michigan
Depth Interval: 3570'-3640'
3570'-3576': Ls dark gray, crinoidal/skeletal wackestone, Fl, consists of crinoids,and other fossil fragments, intraclasts, has stylolite structure and has very lowporosity and permeability, which act as cap rocks in the most Dundeeintervals. This facies representing open marine environment.
Dundee Limestone:
3576'-3581': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include smallcyanobacterial mats, tidal laminations, and fenestral structure. Very fine tofine sand grain, porosity within this facies is dominantly fenestral and moldicporosity, and forms a main reservoir in this field. This facies has beendeposited in peritidal environment.
3581'-3583': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Novisual porosity, it has stylolites and some fractures. The depositionalenvironment is low energy shallow lagoon.
3583' -3593': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include smallcyanobacterial mats, tidal laminations, and fenestral structure. Very fine tofine sand grain, porosity within this facies is dominantly fenestral and moldicporosity, high permeability and porosity, main reservoir in this field. Thedepositional environment is peritidal.
3593'-3596': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3596'-3599': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure observed in this facies is fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic porosity, high permeability and porosity, main reservoir
125
in this field. The vugs are partially filled with calcite crystal cement, stylolitestructure, the depositional environment is peritidal.
3599'-3601': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures. The depositional environment is lowenergy shallow lagoon.
3601'-3603': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure found in this facies is fenestral structure.Very fine to fine sand grain, porosity within this facies is dominantly fenestraland moldic porosity, high permeability and porosity, main reservoir in thisfield. The depositional environment is peritidal.
3603'-3604': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Thisfacies is u interbedded with peloidal grainstone facies #7. It has low and highamplitude stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3604'-3607': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral porosity, high permeabilityand porosity, main reservoir in this field. The vugs are partially filled withcalcite crystal cement, stylolite structure, , the depositional environment isperitidal.
3607'-3609': Ls, light to brownish gray, skeletal wackestone, F6, it is highlybioturbated with casts of bivalves, ostracod fragments, and calcareous sponges(stromatoporoid). No Visual porosity, it has low and high amplitude stylolitesand some fractures, oil stain. The depositional environment is low energyshallow lagoon.
3609'-3614': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. The vugs are partiallyfilled with calcite crystal cement, stylolite structure, the depositionalenvironment is peritidal.
126
3614'-3617': Limestone, light to brownish gray Ls, skeletal wackestone, F6, it ishighly bioturbated with casts of bivalves, ostracod fragments, and calcareoussponges (stromatoporoid). No Visual porosity, it has low and high amplitudestylolites and some fractures, oil stain. The depositional environment is lowenergy shallow lagoon.
3617'-3625': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral and moldic porosity. Thevugs are partially filled with calcite crystal cement, stylolite structure, thedepositional environment is peritidal.
3625'-3627': Ls, light to brownish gray, skeletal wackestone, F6, it is highlybioturbated with casts of bivalves, ostracod fragments, and calcareous sponges(stromatoporoid). No Visual porosity, it has low and high amplitude stylolitesand some fractures, oil stain. The depositional environment is low energyshallow lagoon.
3627'-3631': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. The vugs are partiallyfilled with calcite crystal cement, stylolite structure, the depositionalenvironment is peritidal.
3631'-3636': Limestone, light to brownish gray Ls, skeletal wackestone, F6, it ishighly bioturbated with casts of bivalves, ostracod fragments, and calcareoussponges (stromatoporoid). No Visual porosity, it has low and high amplitudestylolites and some fractures, oil stain. The depositional environment is lowenergy shallow lagoon.
3636'-3640': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral and moldic porosity. Thevugs are partially filled with calcite crystal cement, stylolite structure, thedepositional environment is peritidal.
♦ This core was shifted up 5 feet.
127
Rogers City:
Permit#36387
Oryx Energy Co., Miller, Viola 1, Mt PleasantIsabella County Michigan
Depth Interval: 3560'-3630'
3560'-3588: Ls dark gray, crinoidal/skeletal wackestone, Fl, consists of crinoids,and other fossil fragments, intraclasts, has stylolite structure and has very lowporosity and permeability, which act as cap rocks in the most Dundeeintervals. This facies representing open marine environment.
Dundee Limestone:
3588'-3594': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include smallcyanobacterial mats, tidal laminations, and fenestral structure. Very fine tofine sand grain, porosity within this facies is dominantly fenestral and moldicporosity, and forms a main reservoir in this field. This facies has beendeposited in peritidal environment.
3594'-3598': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Novisual porosity, it has stylolites and some fractures. The depositionalenvironment is low energy shallow lagoon.
3598' -3606': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include smallcyanobacterial mats, tidal laminations, and fenestral structure. Very fine tofine sand grain, porosity within this facies is dominantly fenestral and moldicporosity, high permeability and porosity, main reservoir in this field. Thedepositional environment is peritidal.
3606'-3614': Missing interval.
3614'-3616': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3616'-3618': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure observed in this facies is fenestral
128
structure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic porosity, high permeability and porosity, main reservoirin this field. The vugs are partially filled with calcite crystal cement, stylolitestructure, the depositional environment is peritidal.
3618'-3620': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures. The depositional environment is lowenergy shallow lagoon.
3620'-3623': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure found in this facies is fenestral structure.Very fine to fine sand grain, porosity within this facies is dominantly fenestraland moldic porosity, high permeability and porosity, main reservoir in thisfield. The depositional environment is peritidal.
3623'-3626': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Thisfacies is u interbedded with peloidal grainstone facies #7. It has low and highamplitude stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3626'-3630': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure found in this facies is fenestral structure.Very fine to fine sand grain, porosity within this facies is dominantly fenestraland moldic porosity, high permeability and porosity, main reservoir in thisfield. The depositional environment is peritidal.
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Rogers City:
Permit#39770
Oryx Energy Co., Mt Pleasant Unit Tract 55Isabella County Michigan
Depth Interval: 3557' - 3617'
3557'-3572': Ls dark gray, crinoidal/skeletal wackestone, Fl, consists of crinoids,minor bivalves, trilobites, fossil fragments, intraclasts, has stylolite structureand has very low porosity and permeability, which act as cap rocks in the mostDundee intervals. This facies representing open marine environment.
3574.4' (Thin-section) Crinoidal wackestone.
Dundee Limestone:
3572'-3577': Ls, light to brownish gray, fenestral peloidal grainstone/ packstone,F7, and the grains within this facies includes peloids and sparsely gastropodsand bivalves, trilobites, and other fossil fragments. The sedimentary structuresfound in this facies include small cyanobacterial mats, tidal laminations, andfenestral structure. Very fine to fine sand grain, porosity within this facies isdominantly fenestral and moldic porosity, main reservoir in this field. Thedepositional environment is peritidal.
3575' (Thin-section) peloidalpackstone
3577'-3579': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofgastropods, bivalves, forams, peloids, crinoids, ostracod fragments, andcalcareous sponges (stromatoporoid) at 3578'. No Visual vugy porosity, it hasstylolites and some fractures. Partially dolomitization of carbonate mud. Thedepositional environment is interpreted as a low energy shallow lagoon.
3579' -3590': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, this interval occasionally interbedded with skeletal wackestone at 3584',grains within this facies includes mainly peloids and sparsely gastropods andbivalves, trilobites, and other fossil fragments. Porosity within this facies isdominantly fenestral, moldic and interparticle porosity, main reservoir in thisfield. The vugs are partially filled with calcite crystal cement, stylolitestructure common throughout the core. The sedimentary structures found inthis facies include small cyanobacterial mats, tidal laminations, and fenestralstructure, the depositional environment is peritidal.
3590'-3593': Ls, light to brownish gray, skeletal wackestone, F6, consist ofgastropods, ostracods, bivalves, trilobites. Low porosity and permeability,stylolites are very common throughout the core.
3592.2' (Thin-section) skeletal wackestone
3593'-3597': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, grains includes mainly peloids and sparsely gastropods and bivalves. Thesedimentary structures found in this facies include small cyanobacterial mats,tidal laminations, and fenestral structure. Very fine to fine sand grain, porositywithin this facies is dominantly fenestral and interparticle porosity, mainreservoir in this field. The vugs are partially filled with calcite crystal cement,stylolite structure, the depositional environment is peritidal.
3593.9' (Thin-section)peloidal grainstone
3597'-3600': Ls, light to brownish gray, skeletal wackestone, F6, consists ofgastropods, ostracods, bivalves, and trilobites and corals, stylolites, no visualporosity. The depositional environment is low energy shallow lagoon.
3597.9' (Thin-section) skeletal wackestone
3600'-3607': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, the grains present in this facies include mainly peloids and sparselygastropods and bivalves, ostracods, trilobites. Porosity within this facies isdominantly fenestral and moldic porosity, main reservoir in this field. Thevugs are partially filled with calcite crystal cement, stylolite structure commonthroughout the core. The sedimentary structures found in this facies includesmall cyanobacterial mats, tidal laminations, and fenestral structure, thedepositional environment is peritidal.
3607'-3610': Ls, light gray, skeletal wackestone, F6, consists of gastropods,ostracods, bivalves, trilobites, and peloids. Low porosity and permeability,calcite cements, it has stylolite and vertical fractures at 3609'. Thedepositional environment is low energy shallow lagoon.
3606' (Thin-section) skeletal wackestone
3610'-3616' Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and grains include mainly peloids and sparsely gastropods and bivalves,ostracods, trilobites. Porosity within this facies is dominantly fenestral andinterparticle, forms a main reservoir in this field. The vugs are partially filledwith calcite crystal cement, stylolite structure common throughout the core.The sedimentary structures found in this facies include small cyanobacterial
131
mats, tidal laminations, and fenestral structure, the depositional environmentis peritidal.
3610.5' (Thin-section) peloidalpackstone
3616'-3617': Ls, light to brownish gray, skeletal wackestone, F6, very fine-grained,consist of gastropods, ostracods, bivalves, peloids, and trilobites, stylolitestructure are common, no visual porosity. Low porosity and permeabilitybased on the core analysis date. The depositional environment is low energyshallow lagoon.
♦ This core was shifted up 3 feet
132
Permit#39771
Oryx Energy Co., Mt Pleasant Unit Tract 46, Mt PleasantIsabella County Michigan
Depth Interval: 3567'-3627'
Rogers City:
3567'-3582': Ls dark gray, crinoidal/skeletal wackestone, Fl, consists of crinoids,and other fossil fragments, intraclasts, has stylolite structure and has very lowporosity and permeability, which act as cap rocks in the most Dundeeintervals. This facies representing open marine environment.
Dundee Limestone:
3582'-3588': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include smallcyanobacterial mats, tidal laminations, and fenestral structure. Very fine tofine sand grain, porosity within this facies is dominantly fenestral and moldicporosity, and forms a main reservoir in this field. This facies has beendeposited in peritidal environment.
3588'-3590': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Novisual porosity, it has stylolites and some fractures. The depositionalenvironment is low energy shallow lagoon.
3590' -3595': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include smallcyanobacterial mats, tidal laminations, and fenestral structure. Very fine tofine sand grain, porosity within this facies is dominantly fenestral and moldicporosity, high permeability and porosity, main reservoir in this field. Thedepositional environment is peritidal.
3595'-3597': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3597'-3606': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure observed in this facies is fenestralstructure. Very fine to fine sand grain, porosity within this facies is dominantlyfenestral and moldic porosity, high permeability and porosity, main reservoirin this field. The vugs are partially filled with calcite crystal cement, stylolitestructure, the depositional environment is peritidal.
3606'-3608': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Wispyand suture stylolites and some fractures. The depositional environment is lowenergy shallow lagoon.
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3608'-3611': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structure found in this facies is fenestral structure.Very fine to fine sand grain, porosity within this facies is dominantly fenestraland moldic porosity, high permeability and porosity, main reservoir in thisfield. The depositional environment is peritidal.
3611'-3614': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, and calcareous sponges (stromatoporoid). Thisfacies is u interbedded with peloidal grainstone facies #7. It has low and highamplitude stylolites and some fractures, oil stain. The depositionalenvironment is low energy shallow lagoon.
3614'-3617': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral porosity, high permeabilityand porosity, main reservoir in this field. The vugs are partially filled withcalcite crystal cement, stylolite structure, , the depositional environment isperitidal.
3617'-3621': Ls, light to brownish gray, skeletal wackestone, F6, it is highlybioturbated with casts of bivalves, ostracod fragments, and calcareous sponges(stromatoporoid). No Visual porosity, it has low and high amplitude stylolitesand some fractures, oil stain. The depositional environment is low energyshallow lagoon.
3621'-3625': Ls, light to brownish gray, fenestral peloidal grainstone/packstone,F7, and the observed grains within this facies include coral and spongesfragments. The sedimentary structures found in this facies include, tidallaminations, and fenestral structure very limited. Very fine to fine sand grain,porosity within this facies is dominantly fenestral and moldic porosity, highpermeability and porosity, main reservoir in this field. The vugs are partiallyfilled with calcite crystal cement, stylolite structure, the depositionalenvironment is peritidal.
3625'-3627': Limestone, light to brownish gray Ls, skeletal wackestone, F6, it ishighly bioturbated with casts of bivalves, ostracod fragments, and calcareoussponges (stromatoporoid). No Visual porosity, it has low and high amplitudestylolites and some fractures, oil stain. The depositional environment is lowenergy shallow lagoon.
♦♦♦ This core was shifted up 8 feet.
134
Permit # 36730
Summit Petroleum Corp., Fitzwater 6. South buckeye FieldGladwin County Michigan
Depth Interval: 3560'-3624'Rogers City:
3560'-3562': Ls, dark gray, crinoidal/skeletal wackestone, Fl, contains crinoids,bryozoans, brachiopods, ostracods, undifferentiated fossils, intraclasts, smallfractures filled with calcite cement. It has stylolite structure and has very lowporosity and permeability according to the core analysis which acts as caprocks in the most Dundee intervals.
Dundee Limestone:
3562'-3564': Burrowed peloidal grainstone/packstone, F2. This facies is observedon top of the Dundee just below the Rogers City. The skeletal grains of thisfacies include brachiopods, crinoids, bivalves, ostracods, trilobites, bryozoans,corals, and phylloid algae. Burrows are the only sedimentary structure presentin the skeletal peloidal grainstone facies. Peloids are observed as majorcomponents of this facies. Wispy and suture stylolites are common throughoutthis facies. It is commonly fine to medium-grained and moderately sorted. Themajor porosity types include interparticle, intraparticle porosity. It is a non-reservoir facies due to its low porosity and permeability.
3563' (thin-section)peloidal grainstone/packstone
3564'-3670.5': Ls, gray-brownish gray, stromatoporoid boundstone, F5. Bioclastswithin this facies include massive and tabular stromatoporoids, corals,brachiopods, crinoids, bryozoans, and trilobites. Minor intercalations ofcrinoidal grainstone and skeletal peloidal grainstone are occasionallyassociated with this facies. Stylolites are common throughout this facies.Porosity of this facies includes growth framework, vuggy, and intraparticleporosity and also some interparticle porosity in the grainstone facies. It is themain reservoir in South Buckeye field.
3565' (thin-section) StromatoporoidBoundstone
3570.5'-3572.5: Ls, brownish gray, crinoidal grainstone, F3, consists of crinoids,peloids, bivalves, trilobites, ostracods, bryozoans, brachiopods. It is very finegrained and moderately sorted. The crinoidal grainstone facies is usually foundbelow the stromatoporoid boundstone facies and sometimes it is interbeddedwith burrowed skeletal peloidal grainstone facies. Wispy and suture stylolites.Porosity of this facies includes intraparticle and interparticle and moldicporosity (interpreted as a secondary reservoir facies).
135
3571' (thin-section) Crinoidal Grainstone
3572.5'-3590.5': Ls, gray-brownish gray, stromatoporoid boundstone, F5. Bioclastswithin this facies include massive and tabular stromatoporoids, corals,brachiopods, crinoids, bryozoans, and trilobites. Minor intercalations ofcrinoidal grainstone and skeletal peloidal grainstone are occasionallyassociated with this facies. Porosity of this facies includes growth framework,vuggy, and intraparticle porosity and also some interparticle porosity in thegrainstone facies.
3587' (thin-section) StromatoporoidBoundstone
3590.5'-3600': Burrowed peloidal grainstone/packstone F2. The skeletal grains ofthis facies include brachiopods, crinoids, bivalves, ostracods, trilobites,bryozoans, corals, and phylloid algae. Burrows are the only sedimentarystructure present in the skeletal peloidal grainstone facies. Peloids areobserved as major components of this facies. Stylolites are commonthroughout this facies. It is commonly fine to medium-grained and moderatelysorted. The major porosity types include interparticle, intraparticle porosity. Itis a non-reservoir facies due to its low porosity and permeability.
3600'-3602': Crinoidal grainstone, F3, consist of crinoids, peloids, bivalves,trilobites, ostracods. It is very fine-grained and moderately sorted. Wispy andsuture stylolites. The crinoidal grainstone facies is usually found below thestromatoporoid boundstone facies and sometimes it is interbedded withburrowed skeletal peloidal grainstone facies. Porosity of this facies includesintraparticle porosity and also some interparticle and moldic porosity(interpreted as a secondary reservoir facies).
3602'-3608.5': Burrowed peloidal grainstone/packstone, F2. The skeletal grains ofthis facies include brachiopods, crinoids, bivalves, ostracods, trilobites,bryozoans, corals, and phylloid algae. Burrows are the only sedimentarystructure present in the skeletal peloidal grainstone facies. Peloids areobserved as major components of this facies. It is commonly fine to medium-grained and moderately sorted. This facies is interbedded with thestromatoporoid boundstone facies at 3610' and also the crinoidal grainstonefacies. Stylolites are common throughout this facies. The major porosity typesinclude interparticle, intraparticle porosity. It is a non-reservoir facies due toits low porosity and permeability.
3608.5'-3610.5' Coral-stromatoporoid rudstone/rudstone, F4. This facies variesfrom fine to medium-grained, well sorted, with skeletal graindebris consistingof crinoids, bivalve, brachiopods, finger and tabulate corals, sponges, and
136
stromatoporoid fragments, were deposited in grainy or muddy matrix. Porositytype within this facies is predominantly intraparticle and interparticle.
3609' (thin-section) ReefFlank
3610.5'-3617': Burrowed peloidal grainstone/packstone, F2. The skeletal grains ofthis facies include brachiopods, crinoids, bivalves, ostracods, trilobites, bryozoans,corals, and phylloid algae. Burrows are the only sedimentary structure present in theskeletal peloidal grainstone facies. Peloids are observed as major components of thisfacies. It is commonly fine to medium-grained and moderately sorted. This facies isinterbedded with the stromatoporoid boundstone facies at 3610' and also the crinoidalgrainstone facies. Stylolites are common throughout this facies. The major porositytypes include interparticle, intraparticle porosity. It is a non-reservoir facies due to itslow porosity and permeability
3617'-3624': Crinoidal grainstone, F3, consists of crinoids, peloids, bivalves,trilobites, ostracods. It is very fine-grained and moderately sorted. Wispy andsuture stylolites. The crinoidal grainstone facies is usually found below thestromatoporoid boundstone facies and sometimes it is interbedded withburrowed skeletal peloidal grainstone facies. Stylolites are commonthroughout this facies. About foot or so there is fining up sediments whichindicate to a storm deposit (at 3620'). Porosity of this facies includesintraparticle, interparticle, intercrystalline porosity (interpreted as a secondaryreservoir facies).
Summit Petroleum Corp., Nusbaum Kern 3-W. South buckeye FieldGladwin County Michigan
Depth Interval: 3526'-3686'Rogers City:
3526'-3547': Ls, dark gray, crinoidal/skeletal wackestone, Fl, contains crinoids,bryozoans, brachiopods, ostracods, undifferentiated fossils, intraclasts, smallfractures filled with calcite cement. It has stylolite structure and has very lowporosity and permeability according to the core analysis which acts as caprocks in the most Dundee intervals.
353 7.4' (thin-section) Crinoidal wackestone
Dundee Limestone:
3547'-3552': Burrowed peloidal grainstone/packstone, F2, this facies is observedon top of the Dundee just below the Rogers city. The skeletal grains of thisfacies include brachiopods, crinoids, bivalves, ostracods, trilobites, bryozoans,corals, and phylloid algae. Burrows are the only sedimentary structure presentin the skeletal peloidal grainstone facies. Peloids are observed as majorcomponents of this facies. It is commonly fine to medium-grained andmoderately sorted. The major porosity types include interparticle, intraparticleporosity. It is a non-reservoir facies due to its low porosity and permeability.
3552'-3554' Coral-stromatoporoid rudstone/rudstone, F4. This facies varies fromfine to medium-grained, well sorted, with skeletal grain debris consisting ofcrinoids, bivalve, brachiopods, finger and tabulate corals, sponges, andstromatoporoid fragments, were deposited in grainy or muddy matrix. Porositytype within this facies is predominantly intraparticle and interparticle.
3554'-3662': Ls, gray - brownish gray, stromatoporoid boundstone, F5. Bioclastswithin this facies include massive and tabular stromatoporoids, corals,brachiopods, crinoids, bryozoans, and trilobites. Occasionally interbeddedwith crinoidal skeletal grainstone facies at 3570', 3571', and 3576'. Porosityof this facies includes growth framework, vuggy, and intraparticle porosityand also some interparticle porosity. It is the main reservoir facies.
3562'-3563: Ls, brownish gray, crinoidal grainstone, F3, consist of, crinoids,peloids, bivalves, trilobites, ostracods, bryozoans, brachiopods. Very finegrained and moderately sorted. The crinoidal grainstone facies is usually foundbelow the stromatoporoid boundstone facies and sometimes it is interbeddedwith burrowed skeletal peloidal grainstone facies. Wispy and suture stylolites
138
are common. Porosity of this facies includes intraparticle interparticleintercrystalline porosity (interpreted as a secondary reservoir facies).
3562' (thin-section) Crinoidal Grainstone
3563'-3667.3': Ls, gray - brownish gray, stromatoporoid boundstone, F5, theskeletal grains within this facies include massive and tabular stromatoporoids,corals, brachiopods, crinoids, bryozoans, and trilobites. Porosity of this faciesincludes growth framework, vuggy, and intraparticle porosity and also someinterparticle porosity.
3564.4' (thin-section) Stromatoporoid Boundstone.
3577.3'-3573': Burrowed peloidal grainstone/packstone, F2. This facies isobserved on top of the Dundee just below the Rogers City. The skeletal grainsof this facies include brachiopods, crinoids, bivalves, ostracods, trilobites,bryozoans, corals, and phylloid algae. Burrows are the only sedimentarystructure present in the skeletal peloidal grainstone facies. Peloids areobserved as major components of this facies. It is commonly fine to medium-grained and moderately sorted. The major porosity types include interparticle,intraparticle, limited distribution of vuggy, moldic, and intercrystallineporosity. It is a non-reservoir facies due to its low porosity and permeability.
3573'-3582': Crinoidal grainstone, F3, consist of crinoids, peloids, bivalves,trilobites, ostracods. It is very fine-grained and moderately sorted. Thecrinoidal grainstone facies is usually found below the stromatoporoidboundstone facies and sometimes it is interbedded with burrowed skeletal
peloidal grainstone facies. Porosity of this facies includes intraparticle, andinterparticle porosity (interpreted as a secondary reservoir facies).
3574.7' (thin-section) Crinoidal Grainstone
3582'-3586': Burrowed peloidal grainstone/packstone, F2. This facies is observedon top of the Dundee just below the Rogers City. The skeletal grains of thisfacies include brachiopods, crinoids, bivalves, ostracods, trilobites, bryozoans,corals, and phylloid algae. Burrows are the only sedimentary structure presentin the skeletal peloidal grainstone facies. Peloids are observed as majorcomponents of this facies. It is commonly fine to medium-grained andmoderately sorted. The major porosity types include interparticle, intraparticle,and intercrystalline porosity.
Summit Petroleum Corp., State Buckeye B-6, North Buckeye FieldGladwin County Michigan
Depth Interval: 3589' - 3667'Rogers City:
3589'-3609.5': Ls, dark grey, Crinoidal/ Skeletal wackestone Fl, contain fossilfragments such as crinoids, gastropods, brachiopods, ostracods, andintraclasts. Small fractures filled with calcite cements, the depositionalenvironment is open marine (subtidal). It has stylolite structure and has verylow porosity and permeability according to the core analysis which acts as caprocks in the most Dundee intervals.
3602.8' (Thin-section) crinoidal wackestone.
Dundee Limestone:
3609.5'-3643': Ls, buff to tan, fenestral peloidal grainstone/packstone, F7, veryfine grained, and moderately sorted, fenestrae dominant and oil stained. Thisfacies is largely made up of peloids. Skeletal grains within this facies includebrachiopods, bivalves, ostracods, gastropods, crinoids, stromatoporoids at3635, and corals rich at 3646.5. The sedimentary structures found in this faciesinclude small cyanobacterial mats, tidal laminations, and fenestral structure(vertical and horizontal fenestrae), stylolite structures. Porosity within thisfacies is dominantly fenestral porosity, high permeability and porosity, mainreservoir in this field.
3643'-3646': Ls, brown- gray, skeletal wackestone, F6, with casts of gastropods,bivalves, forams, peloids, ooids, crinoids, ostracod fragments, and calcareoussponges. No Visual porosity was observed. It has stylolites and some fractures.Partially dolomitization of carbonate mud was observed. The depositionalenvironment is low energy shallow lagoon.
3646'-3656': Coral-stromatoporoid rudstone/rudstone, F4. This facies variesfrom fine to medium-grained, well sorted, with skeletal grain debris consistingof crinoids, bivalve, brachiopods, finger and tabulate corals, andstromatoporoid fragments, were deposited in grainy or muddy matrix. Porositytype within this facies is predominantly intraparticle and interparticle with aminor intercrystalline component.
3656'-3666': Stromatoporoid boundstone, F5. Bioclasts within this facies includemassive and tabular stromatoporoids, corals, brachiopods, crinoids, bryozoans,and trilobites. Occasionally interbedded with crinoidal skeletal grainstonefacies. Porosity of this facies includes growth framework, vuggy, andintraparticle and also some interparticle porosity in the grainstone facies,fractures augment, moderate to high porosity/permeability. Main reservoir inSouth Buckeye field.
3666'-3667': Ls, very dark gray, Coral-stromatoporoid rudstone/rudstone, F4.This facies varies from fine to medium-grained, well sorted, with skeletalgrain debris consisting of crinoids, bivalve, brachiopods, finger and tabulatecorals, and stromatoporoid fragments, were deposited in grainy or muddymatrix. Porosity type within this facies is predominantly intraparticle andinterparticle with a minor intercrystalline component.
♦ This core was shifted up 6 feet
141
Permit#52002
Summit Petroleum Corp., Salla, John 9-11 HD, North Buckeye FieldGladwin County Michigan
Depth Interval: 3598' - 3658'Rogers City:
3598'-3599: Ls, dark grey, Crinoidal/ Skeletal wackestone Fl, contains fossilfragments such as crinoids, gastropods, brachiopods, ostracods, andintraclasts. Small fractures filled with calcite cements, the depositionalenvironment is open marine (subtidal). It has stylolite structure and has verylow porosity and permeability according to the core analysis which acts as caprocks in the most Dundee intervals.
Dundee Limestone:
3599'-3624': Ls, buff to tan, fenestral peloidal grainstone/packstone, F7, very finegrained, and moderately sorted, fenestrae dominant and oil stained. This faciesis largely made up of peloids. Skeletal grains within this facies includebrachiopods, bivalves, ostracods, gastropods, crinoids, and stromatoporoids.The sedimentary structures found in this facies include small cyanobacterialmats, tidal laminations, and fenestral structure (vertical and horizontalfenestrae), stylolite structures. Porosity within this facies is dominantlyfenestral porosity, high permeability and porosity, main reservoir in this field.
3624'-3625.5': Ls, brown- gray, skeletal wackestone, F6, with casts of gastropods,bivalves, forams, peloids, ooids, crinoids, ostracod fragments, and calcareoussponges. No Visual porosity was observed. It has stylolites and some fractures.Partially dolomitization of carbonate mud was observed. The depositionalenvironment is low energy shallow lagoon.
3625.5'-3633': Missing interval
3633'-3644': Ls, buff to tan, fenestral peloidal grainstone/packstone, F7, very finegrained, and moderately sorted, fenestrae dominant and oil stained. This faciesis largely made up of peloids. Skeletal grains within this facies includebrachiopods, bivalves, ostracods, gastropods, crinoids, and stromatoporoids.The sedimentary structures found in this facies include small cyanobacterialmats, tidal laminations, and fenestral structure (vertical and horizontalfenestrae), stylolite structures. Porosity within this facies is dominantlyfenestral porosity, high permeability and porosity, main reservoir in this field.
3644'-3646': Ls, brown- gray, skeletal wackestone, F6, with casts of gastropods,bivalves, forams, peloids, ooids, crinoids, ostracod fragments, and calcareoussponges. No Visual porosity was observed. It has stylolites and some fractures.
142
Partially dolomitization of carbonate mud was observed. The depositionalenvironment is low energy shallow lagoon.
3646'-3650': Coral-stromatoporoid rudstone/rudstone, F4. This facies variesfrom fine to medium-grained, well sorted, with skeletal grain debris consistingof crinoids, bivalve, brachiopods, finger and tabulate corals, andstromatoporoid fragments, were deposited in grainy or muddy matrix. Porositytype within this facies is predominantly intraparticle and interparticle with aminor intercrystalline component.
3650'-3656': Stromatoporoid boundstone, F5. Bioclasts within this facies includemassive and tabular stromatoporoids, corals, brachiopods, crinoids, bryozoans,and trilobites. Occasionally interbedded with crinoidal skeletal grainstonefacies. Porosity of this facies includes growth framework, vuggy, andintraparticle and also some interparticle porosity in the grainstone facies,fractures augment, moderate to high porosity/permeability. Main reservoir inSouth Buckeye field.
3656'-3658': Ls, buff to tan, fenestral peloidal grainstone/packstone, F7, very finegrained, and moderately sorted, fenestrae dominant and oil stained. This faciesis largely made up of peloids. Skeletal grains within this faciesstromatoporoids. The sedimentary structures found in this facies include smallcyanobacterial mats, tidal laminations, and fenestral structure (vertical andhorizontal fenestrae), stylolite structures. Porosity within this facies isdominantly fenestral porosity, high permeability and porosity, main reservoirin this field.
♦> This core was shifted up 5 feet
143
Permit#35720
Jordan Energy Exploration Co Lie, Hutsonl-2., ButmanGladwin County MI
Depth Interval: 3656'-3686'Rogers City:
The Rogers City facies is dens, grey-dark gray Ls, low porosity and permeability. Theboundary contacts between the Rogers City and Dundee is marked by irregularsurface (stylolite).
3656-3674.5 Limestone, gray-dark gray Ls, crinoidal/skeletal wackestone, Fl, fineto medium-grained muddy packstone with burrows, bivalves, corals,intraclasts, suture stylolites, chert nodules, no visual porosity. Intercalatedwith crinoidal bioturbated packstone at 3660.3-62, 3664-65. This faciesrepresenting open marine environments.
Dundee Limestone
3674.5-3686: Ls, gray-brownish gray, stromatoporoid boundstone, F5. Bioclastswithin this facies include massive and tabular stromatoporoids, corals,brachiopods, crinoids, bryozoans, and trilobites. Minor intercalations ofcrinoidal grainstone and skeletal peloidal grainstone are occasionallyassociated with this facies. Stylolites are common throughout this facies.Porosity of this facies includes growth framework, vuggy, and intraparticleporosity and also some interparticle porosity in the grainstone facies. It isrepresenting a good reservoir based on the Neutron porosity log.
144
Permit#28399
DEVELOPMENT CO., Grow 4, West BranchOgemaw CO, MI
Depth Interval: 2540' - 2716'Rogers City:
2540'-2573.5': Ls dark gray, crinoidal/skeletal wackestone, Fl, consists of crinoids,and other fossil fragments, intraclasts, has stylolite structure and has very lowporosity and permeability, which act as cap rocks in the most Dundeeintervals. This facies representing open marine environment.
Dundee Limestone:
2573.5'-2582': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, coral and calcareous sponges (stromatoporoid).Wispy and suture stylolites and some fractures. The depositional environmentis low energy shallow lagoon.
2582'-2591': Ls, light to brownish gray, burrowed peloidal grainstone/packstone,F2, this facies is observed on top of the Dundee just below the Rogers city.The skeletal grains of this facies include brachiopods, crinoids, bivalves,ostracods, trilobites, bryozoans, corals, and phylloid algae. Burrows are theonly sedimentary structure present. Peloids are observed as major componentsof this facies. It is commonly medium to fine-grained and moderately sorted.Wispy and suture stylolites, oil stained. This facies was deposited in protectedshallow marine environment.
2591'-2616': Ls, brownish gray, crinoidal grainstone, F3, consist of, crinoids,peloids, bivalves, trilobites, ostracods, bryozoans, brachiopods. Very finegrained and moderately sorted. The crinoidal grainstone facies is usually foundbelow the stromatoporoid boundstone facies and sometimes it is interbeddedwith burrowed skeletal peloidal grainstone facies. Porosity of this faciesincludes intraparticle, interparticle, and moldic porosity (interpreted as asecondary reservoir facies).
2616'-2625': Ls, light to brownish gray, burrowed peloidal grainstone/packstone,F2, this facies is observed on top of the Dundee just below the Rogers city.The skeletal grains of this facies include brachiopods, crinoids, bivalves,ostracods, trilobites, bryozoans, corals, and phylloid algae. Burrows are theonly sedimentary structure present. Peloids are observed as major componentsof this facies. It is commonly medium to fine-grained and moderately sorted.Wispy and suture stylolites, oil stained. This facies was deposited in protectedshallow marine environment.
145
2525'-2648': Ls, brownish gray, crinoidal grainstone, F3, consist of, crinoids,peloids, bivalves, trilobites, ostracods, bryozoans, brachiopods. Very finegrained and moderately sorted. The crinoidal grainstone facies is usually foundbelow the stromatoporoid boundstone facies and sometimes it is interbeddedwith burrowed skeletal peloidal grainstone facies. Porosity of this faciesincludes intraparticle, interparticle, and moldic porosity (interpreted as asecondary reservoir facies).
2648'-2652': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, coral and calcareous sponges (stromatoporoid).Wispy and suture stylolites and some fractures. The depositional environmentis low energy shallow lagoon.
2652'-2662': Ls, brownish gray, crinoidal grainstone, F3, consist of, crinoids,peloids, bivalves, trilobites, ostracods, bryozoans, brachiopods. Very finegrained and moderately sorted. The crinoidal grainstone facies is usually foundbelow the stromatoporoid boundstone facies and sometimes it is interbeddedwith burrowed skeletal peloidal grainstone facies. Porosity of this faciesincludes intraparticle, interparticle, and moldic porosity (interpreted as asecondary reservoir facies).
2662'-2670': Ls, light to brownish gray, burrowed peloidal grainstone/packstone,F2, this facies is observed on top of the Dundee just below the Rogers city.The skeletal grains of this facies include brachiopods, crinoids, bivalves,ostracods, trilobites, bryozoans, corals, and phylloid algae. Burrows are theonly sedimentary structure present. Peloids are observed as majorcomponentsof this facies. It is commonly medium to fine-grained and moderately sorted.Wispy and suture stylolites, oil stained. This facies was deposited in protectedshallow marine environment.
2670'-2682': Ls, brownish gray, crinoidal grainstone, F3, consist of, crinoids,peloids, bivalves, trilobites, ostracods, bryozoans, brachiopods. Very finegrained and moderately sorted. The crinoidal grainstone facies is usually foundbelow the stromatoporoid boundstone facies and sometimes it is interbeddedwith burrowed skeletal peloidal grainstone facies. Porosity of this faciesincludes intraparticle, interparticle, and moldic porosity (interpreted as asecondary reservoir facies).
2682'-2704': Ls, light to brownish gray, coral-stromatoporoid rudstone F4. Thisfacies varies from fine to medium-grained, well sorted, with skeletal graindebris consisting of crinoids, bivalve, brachiopods, finger and tabulate corals,sponges, and stromatoporoid fragments, were deposited in grainy or muddymatrix. Porosity type within this facies is predominantly intraparticle andinterparticle.
146
2704'-2716': Ls, light to brownish gray, skeletal wackestone, F6, with casts ofbivalves, ostracod fragments, coral and calcareous sponges (stromatoporoid).Wispy and suture stylolites and some fractures. The depositional environmentis low energy shallow lagoon.
147
Appendix B
Core Descriptions Charts and Graphics
148
LEGEND
Grain Types, sedimentaryStructures, and Porosity Typesfff Stylolitic
(| Burrowed
=00: Fenestral Textures
•r$fi/ Brachiopod
A Gastropod
/^J Stromatoporoid
\f Brvozoan
@ Coral
^^ Undifferentiated Fossils
000 Peloids
-^ Crinoids
BC Intercrystalline Porosity
BP Interparticle Porosity
WC Intracrystalline Porosity
\Yp Intraparticle Porosity
PW Framework Porosity
MO Moldic
VUG Vug
-Dundee-Rogers City contact
Total Depth
Thin Section
Limestone
Idealized Vertical Succession of Seven FaciesFenestral Peloidal Grainstone/Packstone (Peritidal)
F5
F3
Skeletal Wackestone (Lagoonal)
Stromatoporoid Boundstone (Patch reef)
Coral-stromatoporoid (loatstone to rudstone (Reef Flank)
Figure E. 1. A base map with three cross-section lines strike oriented (A-A' and B-B') and dip oriented cross-section (C-C).
to
MT PLEASANT UNIT TRACT 19 MT PLEASANT UNIT TRACT 46
39821 39771
ISABELLAMount Pleasant
ISABELLAMount Pleasant
Skeletal Crinoidal Wackestone
MCCLINTIC
36820
ISABELLAMount Pleasant
MCCLINTIC
36367
ISABELLAMount Pleasant
MAEDER GRACE L
36647
ISABELLAMount Pleasant
Fenestral peloidal Grainstone/Packstone
EMMONS BROTHERS
37069
A'
RGRC
DUND
Facies 6
Facies 7
ISABELLA
Mount Pleasant
Skeletal Wackestone
Figure E.2. Stratigraphic cross-section (A-A') showing inferred lateral continuity of the fenestral reservoir facies (Aboveblue line) and skeletal wackestone facies (green line). The stratigraphic datum for the cross-section is themajor flooding surface at the top of the Dundee Limestone (Rogers City/Dundee contact). The floodingsurface is marked with red dashed line (FS). RGRC = Rogers City, DUND = Dundee, GR = gamma-ray log,NPHI = neutron porosity log, RHOB = bulk density log.
toto
MT. PLEASANT UNIT TRACT 52 MT PLEASANT UNIT TRACT 55
39824 39770
B
ISABELLAMount Pleasant
ISABELLAMount Pleasant
BISHOP J
36854
ISABELLAMount Pleasant
Skeletal Crinoidal Wackestone
MCCLINTIC STATE CHIPPEWA STATE CHIPPEWA
36815 36884 36910
A <025MI> A <0.16MI> A
ISABELLAMount Pleasant
ISABELLAMount Pleasant
ISABELLAMount Pleasant
Fenestral peloidal Grainstone/Packstone
EMMONS BROTHERS
37069
B'
RGRC
DUND
Facies 6
Facies 7
ISABELLAMount Pleasant
Skeletal Wackestone
Figure E.3. Stratigraphic cross-section (B-B') showing inferred lateral continuity of the fenestral reservoir facies (Aboveblue line) and the skeletal wackestone (green line). The stratigraphic datum for the cross-section is the majorflooding surface at the top of the Dundee Limestone (Rogers City/Dundee contact). The flooding surface ismarked with red dashed line (FS). RGRC = Rogers City, DUND = Dundee, GR = gamma-ray log, NPHI =neutron porosity log, RHOB = bulk density log.
totoOs
MT. PLEASANT UNIT TRACT 21 MT PLEASANT UNIT TRACT 55 FISHER BROTHERS A SCHROT, JOHN J
Figure E.4. Stratigraphic cross-section (C-C) showing inferred lateral continuity of the fenestral reservoir facies(Aboveblue line) and skeletal wackestone (green line). The stratigraphic datum for the cross-section is the majorflooding surface at the top of the Dundee Limestone (Rogers City/Dundee contact). The flooding surface ismarked with red dashed line (FS). RGRC = Rogers City, DUND = Dundee, GR = gamma-ray log, NPHI =neutron porosity log, RHOB = bulk density log.
METHNER S MAXWELL
37290
ISABELLA
D'
RGRC
DUND
FloodingSurface?
LUCS
Figure E.5. Stratigraphic cross-section (D-D') showing the inferred flooding surface (FS markedwith red dashed line). The stratigraphic datum for the cross-section is the majorflooding surface at the top of the Dundee Limestone (Rogers City/Dundee contact).RGRC = Rogers City, DUND = Dundee, LUCS= Lucas Formation, GR = gamma-ray log, NPHI = neutron porosity log, RHOB = bulk density log.
227
STROHKIRCH. A
31979
GLADWINBuckeye North
• Skeletal Crinoidal
Wackestone
GLADWINBuckeye North
F5 Stromatoporoid Boundstone
GLADWINBuckeye North
• Coral-StromatoporoidFloatstone
GLADWINBuckeye North
• Skeletal Wackestone
GLADWINBuckeye North
• Fenestral peloidalGrainstone/Packstone
Figure E.6. Stratigraphic cross-section (E-E') showing inferred lateral continuity of the fenestralreservoir facies (Above blue line). The stratigraphic datum for the cross-section isthe majorflooding surface at the top of the Dundee Limestone (Rogers City/Dundeecontact). The flooding surface is marked with red dashed line (FS). RGRC =Rogers City, DUND = Dundee, GR = gamma-ray log, NPHI = neutronporosity log,RHOB = bulk density log.