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Theses and Dissertations
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Stratigraphic Interpretation and ReservoirImplications of the Arbuckle Group (Cambrian-Ordovician) using 3D Seismic, Osage County,OklahomaRyan Marc KeelingUniversity of Arkansas, Fayetteville
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Recommended CitationKeeling, Ryan Marc, "Stratigraphic Interpretation and Reservoir Implications of the Arbuckle Group (Cambrian-Ordovician) using3D Seismic, Osage County, Oklahoma" (2016). Theses and Dissertations. 1557.http://scholarworks.uark.edu/etd/1557
Stratigraphic Interpretation and Reservoir Implications of the Arbuckle Group (Cambrian-
Ordovician) using 3D Seismic, Osage County, Oklahoma
A thesis submitted in partial fulfillment
of the requirements for the degree of
Master of Science in Geology
By
Ryan Marc Keeling
University of Arkansas
Bachelor of Science in Geology, 2014
May 2016
University of Arkansas
This thesis is approved for recommendation to the Graduate Council
Dr. Christopher Liner
Thesis Advisor
Dr. Walter Manger
Committee Member
Mr. Chris Moyer
Committee Member
Abstract
The Arbuckle Group in northeastern Oklahoma consists of multiple carbonate
formations, along with several relatively thin sandstone units. The group is a part of the “Great
American Carbonate Bank” of the mid-continent and can be found regionally as far east as the
Arkoma Basin in Arkansas, and as far west as the Anadarko Basin in Oklahoma. The Arbuckle is
part of the craton-wide Sauk sequence, which is both underlain and overlain by regional
unconformities.
Arbuckle is not deposited directly on top of a source rock. In order for reservoirs within the
Arbuckle to become charged with hydrocarbons, they must be juxtaposed against source rocks or
along migration pathways. Inspired by the petroleum potential of proximal Arbuckle reservoirs
and the lack of local stratigraphic understanding, this study aims to subdivide Arbuckle
stratigraphy and identify porosity networks using 3D seismic within the study area of western
Osage County, Oklahoma. These methods and findings can then be applied to petroleum
exploration in Cambro-Ordovician carbonates in other localities.
My research question is: Can the Arbuckle in SW Osage County be stratigraphically
subdivided based on 3D seismic characteristics?
This paper outlines the depositional environment of the Arbuckle, synthesizes previous
studies and examines the Arbuckle as a petroleum system in Northeastern Oklahoma. The
investigation includes an interpretation of intra-Arbuckle unconformities, areas of secondary
porosity (specifically, sequence boundaries), and hydrocarbon potential of the Arbuckle Group
using 3D seismic data interpretation with a cursory analysis of cored intervals.
Acknowledgments
This study was made possible by the generous donation of data from Spyglass Energy
Group, LLC and the Osage Nation Minerals Council, Oklahoma. I would like to give a special
thanks to my advisor, Dr. Christopher Liner, for bringing me on-board and providing me with
everything I needed to be successful in this endeavor. Dr. Liner’s geophysical knowledge
allowed me to learn so much in an area I was not as knowledgeable in previously. In addition, I
would also like to observe my other committee members, Dr. Walt Manger and Mr. Chris
Moyer. I chose this committee for the extremely diverse wealth of knowledge each individual
possesses in his own right, and I am extremely grateful that they each accepted to be a part of it. I
have to thank Dr. Walt Manger for his everlasting, adamant thoughts on nearly every geological
concept. It is his continued passion for geology that amazes me and helped realize my own. My
third and final committee member I did not know until I was a graduate student at the University
of Arkansas. Mr. Chris Moyer had previously worked at ExxonMobil with both of my parents,
and Southwestern Energy, which will be my place of employment. I do not believe this to be
coincidental, but believe this to be part of someone’s plan. I would like to thank him for helping
me find the focus of my thesis and his constant availability and willingness to assist me in my
research.
I would like to thank the University of Arkansas for providing the ideal academic
environment in which to earn both my Bachelor’s and Master’s degree. This area and institution
is a hidden gem, and I can honestly say that I only hope it remains this way.
My most sincere thanks goes to my parents, Ted and Maryanne Keeling. Without
their continued support I would not be where I am today. They are my role models and the
reason I chose to study geology, and I aspire to one day be as great as them.
Table of Contents
I. Introduction……………………………………………………………………………1
a. Data………………………………………………………………………………..5
b. Karst Formation…………………………………………………………………...6
c. Seismic Sequence Stratigraphy……………………………………………………8
II. Geologic History……………………………………………………………………....9
a. Arbuckle Group………………………………………………………………….10
b. Simpson Group…………………………………………………………………..12
c. Previous Work…………………………………………………………………...12
III. Methods……………………………………………………………………………....14
IV. Results and Interpretations…………………………………………………………...35
V. Conclusions…………………………………………………………………………..41
VI. Future Work………………………………………………………………………….42
VII. References……………………………………………………………………………44
VIII. Appendix: Seismic Grid……………………………………………………………...48
IX. Appendix: Core Discussion………………………………………………………….52
X. Appendix: Seismic Horizons in Google Earth……………………………………….55
List of Figures
Figure 1 - Geologic Provinces of Oklahoma (OGS)………………………………………………3
Figure 2 - Osage County, Oklahoma Stratigraphic Chart………………………………………....4
Figure 3 - Osage County, Oklahoma...…………………………………………………………….5
Figure 4 - Location of Wild Creek 3D seismic survey…………………………………………….6
Figure 5 - Block diagrams showing depositional setting………………………………………...11
Figure 6 - Paleogeographic map of the Late Cambrian Period………………………………......11
Figure 7 - Histogram of frequency spectrum from OpendTect………………………………......14
Figure 8 - Synthetic seismogram…………………………………………………………………16
Figure 9 - Well-A synthetic projected on Wild Creek in-line 3915……………………………...17
Figure 10 – Cross line 11581 with superimposed Well-A……………………………….……....17
Figure 11 – Cross line 11336 view of Simpson-Arbuckle unconformable contact…………..….19
Figure 12 - Top Arbuckle contoured time structure map………………………………………...19
Figure 13 - Top Arbuckle contoured subsea depth structure map……………………………......20
Figure 14 - Top Arbuckle horizon amplitude map with time structure contours………………...20
Figure 15 - Top Arbuckle 3D time structure map……………………………………………......21
Figure 16 - PoSTM data flattened on Oswego LS……………………………………………......23
Figure 17 - UMC demonstrated. Note green arrows signifying onlap…………………………...24
Figure 18 - UMC contoured time structure map…………………………………………………24
Figure 19 - UMC contoured subsea depth-structure map…………………………………….......25
Figure 20 - UMC 3D time structure map………………………………………………………...25
Figure 21 - MLC demonstrated. Note green arrows signifying paleokarst………………………26
Figure 22 - MLC contoured time structure map………………………………………………….27
Figure 23 - MLC contoured subsea depth-structure map………………………………………...27
Figure 24 - UMC 3D time structure map………………………………………………………...28
Figure 25 - Seismic subdivisions of the Arbuckle in the Wild Creek survey area……………….29
Figure 26 - Arbuckle porosity zone (PHI-1)……………………………………………………..30
Figure 27 - Time structure map of the PHI-1 zone……………………………………………….31
Figure 28 - Horizon amplitude map of the PHI-1 zone…………………………………………..32
Figure 29 - 3D view of PHI-1 zone horizon amplitude map……………………………………..32
Figure 30 – PHI-2 zone vertical section and horizon amplitude map……....................................34
Figure 31 – Cross line 11001 demonstrating the tracked (white) paleokarst horizon…………..38
Figure 32 – Cross line 11001 showing distinct sinkhole features………………………………38
Figure 33 – Cross line 11336 with Lower Arbuckle paleokarst horizon………………………...39
Figure 34 - Amplitude map of Lower Arbuckle paleokarst horizon……………………………..40
Figure 35 – Width of Lower Arbuckle paleokarst feature…………………………………….....40
Figure 36 - Base map with 6 corresponding inlines and cross lines (Figures 38-43)………….....48
Figure 37 - IL3690……………………………………………………………………………......49
Figure 38 - IL3830……………………………………………………………………………......49
Figure 39 - IL3970………………………………………………………………………………..50
Figure 40 - XL10920……………………………………………………………………………..50
Figure 41 - XL11230…………………………………………………………………………......51
Figure 42 - XL11550…………………………………………………………………………......51
Figure 43 - Google Earth image with wells displayed that were used for core observation…......52
Figure 44 - Core from Texaco Kohpay well………………………………………………….......53
Figure 45 - Core from Oliphant LaFortune #3 well……………………………………………...53
Figure 46 - Core from Oliphant Nate #1 well…………………………………………………….54
Figure 47 - Core from Texaco Osage C-1 well…………………………………………………..54
Figure 48 - Google Earth image of Wild Creek survey bounds with observed well localities…..56
Figure 49 - MLC depth structure map overlaid on Wild Creek survey outline…………………..56
Figure 50 - Paleokarst horizon amplitude map overlaid on Wild Creek survey outline………....57
Figure 51 - Coastal onlap curve for Late Cambrian and Ordovician time……………………….57
List of Tables
Table 1…………………………………………………………………………………………15
1
I. Introduction
The Arbuckle Group (hereafter Arbuckle) was deposited during late Cambrian-middle
Ordovician time, when the continental interior was covered by a shallow sea. Arbuckle is a
carbonate formation, comprised mostly of dolomite. Carbonate sediment was deposited in
present day northeastern Oklahoma on a shallow-shelf setting. Equivalent lithostratigraphic units
are the El Paso Group of southwestern Texas, the Ellenburger Group of central and north Texas,
the Knox group of the eastern United States, and the Beekmantown Group in the northeastern
United States. In southern Oklahoma, stratigraphic units of the Arbuckle are the Fort Sill
Limestone, Royer Dolomite, Signal Mountain Formation, Butterfly Dolomite, McKenie Hill
Formation, Cool Creek Formation, Kindblade Formation, and West Spring Creek Formation
(Ham, 1973). However, based on previous investigations, the Arbuckle formation in northern
Oklahoma, specifically my study area, is more comparable to the Arbuckle facies of the Ozarks.
Therefore, I will proceed with the following Arbuckle stratigraphy from oldest to youngest:
Potolsi Dolomite, Eminence Dolomite, Gasconade Dolomite, Roubidoux Formation, Jefferson
City Dolomite, Cotter Dolomite, Powell Dolomite, and the Everton formation. The nearest
Arbuckle outcrop expressing these divisions is in North central Arkansas (McFarland, 1998).
There has been no attempt to correlate these formations from outcrop into the subsurface in
Osage County, Oklahoma. However, we do seek to subdivide the subsurface Arbuckle in the
study area into outcrop-recognized units.
The environment of deposition (EOD) reflects sea level cyclicity, therefore forming
multiple third and fourth order unconformable surfaces within the Arbuckle Group itself.
Identification of intra-Arbuckle unconformities by way of seismic interpretation can prove
2
difficult due to the subtle nature of such surfaces, caused by the Arbuckle peritidal EOD (Derby
et al., 2012). Intra-Arbuckle unconformities may be associated with porosity development due to
the subaerial exposure of the carbonate surface. Reservoir development within the Arbuckle is
commonly along sequence boundaries, especially where facies “have strong diagenetic
overprints from dolomitization and dissolution associated with paleokarstic events” (Fritz et al.,
2012). Therefore, the petroleum industry will commonly target unconformable surfaces as
possible localities for petroleum reservoirs. I argue here that high-quality 3D seismic data can
identify intra-Arbuckle unconformities and associated porosity zones as an indicator of
petroleum reservoir potential in the study area and, perhaps, across the Cherokee Platform.
Being deposited on the stable craton, the Arbuckle Group did not undergo any
contemporary significant orogenic events. The subsurface structure, however, is affected by the
Ozark Uplift to the east, and the Nemaha Uplift to the west. Another catalyst in forming
Arbuckle structure was the Mid-Continent Rift System, a failed rift system that extends from
present day Minnesota to southern Kansas (Figure 1).
3
Figure 1 - Geologic Provinces of Oklahoma (OGS) from Northcutt and Campbell (1995).
Petroleum potential of the Arbuckle Group is enhanced when it is juxtaposed against the
younger Woodford Shale or is along hydrocarbon migration pathways, and expresses enhanced
zones of porosity (Fritz, 2012). Rock layers that have been dolomitized are widespread and
important because they are targeted as a reservoir for petroleum. Dolomitization pertains to the
process by which limestone is converted to dolomite; when limestone encounters magnesium-
rich water, the mineral dolomite, CaMg(CO3)2, replaces the calcite in the rock, volume for
volume.
Areas of widespread dolomite are targeted by the petroleum industry because the
conversion of limestone to dolomite induces the development of secondary porosity, which
4
allows the rock to retain a larger amount of hydrocarbons than the surrounding rock (Northcutt
and Johnson, 1997).
This study is based on a 45 square mile 3D seismic survey to map and analyze intra-
Arbuckle sequence boundaries and associated porosity zones. The study area is located in
western Osage County, Oklahoma (highlighted in Figure 2).
Figure 2 - Osage County, Oklahoma Stratigraphic Chart (Liner et al., 2013)
5
Figure 3 - Osage County, Oklahoma (modified from World Atlas, 2015)
a. Data
The Wild Creek survey area (Figure 4) consists of 45 square miles of 3D seismic data
that was imported into OpendTect for an open source seismic interpretation. The data
set was acquired by Chevron in the mid 1990’s and processed through a post-stack
time migration (PoSTM). The data bin size is 66 ft x 66 ft with a datum of +1200 SS,
time sample rate of 2 milliseconds, and a trace length of 2 seconds. Well data and
core taken in and around the surveys was provided by the Oklahoma Geological
Survey (OGS) in Oklahoma City, OK. All wells that penetrated the Arbuckle that are
proximal to the study area are vertical and only one of these wells, herein called Well-
A, had a sonic log and penetrated the complete Arbuckle section. The Well-A sonic
log allowed us to correlate formation tops in the well log to corresponding horizons in
6
the seismic survey. Well-A is 1.5 miles east of the seismic survey area requiring a
jump correlation; however, we are confident of formation correlations due to the lack
of structural complexity in the area.
Figure 4 - Location of Wild Creek 3D seismic survey, and approximate location of Well-A, in
Osage Co., OK (modified from Google Earth, 2015)
b. Karst Formation
Karst refers to a landscape that is formed by specific diagenetic processes occurring in
carbonate or evaporitic rocks. Karst is primarily caused by acidic meteoric waters permeating
and leaching through the predominantly soluble rocks, creating surface and subsurface
underground drainage features. (Sykes, 1995). Franseen et al. (2003) notes that the most
7
common karst forms associated with the Arbuckle group are caves, sinkholes, joint-controlled
solution features, and collapse breccias.
The driving factor in karst formation is the chemical imbalance of C02 and calcium
carbonate, the CO2 contained in the atmosphere and the calcium carbonate contained within
the rock. As rainfall (H2O) descends through the troposphere, it comes in contact with
atmospheric carbon dioxide (CO2), forming the weak carbonic acid (H2CO3). When this
carbonic acid comes into contact with limestone, it begins to dissolve it. As long as there is
CO2 within the system it will continue to dissolve carbonates (Sykes, 1995).
Karst is important to this research because it serves as evidence for intra-Arbuckle
unconformities. If paleokarst can be identified with seismic data, we can validate the surface
at which it originates as a seismic unconformity. Karst that “has been buried by younger
sediments or sedimentary rocks or otherwise removed from the sphere of active meteoric
diagenesis” is known as paleokarst. (Matthews, 1994). Due to enhanced porosity, paleokarst
features are important to the petroleum industry. In Kansas, erosion and karst of the upper
Arbuckle surface drive petroleum production associated with the unconformity surface
(Franseen et al., 2003).
The Tarim Basin, arguably China’s most prolific oil province, contains Ordovician
paleokarst deposits that have been specifically targeted for hydrocarbon production (Zhao et
al, 2014). With the use of 3D seismic surveys and seismic attribute techniques, the mapping
and characterization of paleokarst features are possible. With better imaging and
characterization techniques, geologists have been able to classify which paleokarst features
are favorable as potential hydrocarbon reservoirs.
8
c. Seismic Sequence Stratigraphy
A seismic unconformity is an unconformable surface or sequence boundary that can be
identified by seismic interpretation. The approach taken in this study to identify sequences
within the Arbuckle parallels well-known methodology of identifying reflection terminations
(truncation, onlap) to identify disconformable surfaces (Mitchum, 1977; Vail et al., 1977).
Since intra-Arbuckle unconformities are low-angle surfaces and very subtle, it is difficult to
distinguish such surfaces with seismic. However, karst features, truncation, and onlap/offlap
relationships are the most visible unconformable contacts when being viewed with seismic
that may be able to help distinguish seismic sequence boundaries. Divergent stratigraphic
relationships occurring at the sequence boundaries resulted from; 1) subhorizontal erosional
disconformities that truncate underlying platform deposits (Figure 18), or 2) angular
unconformities created by onlap of Arbuckle sediment onto basement granitic bodies,
referred to as granitic hills (Figure 18). As Vail (1987) noted, systems tracts provide a seismic
target that is thicker than an individual reservoir unit, but has a genetic relationship to that
reservoir unit. This genetic relation between systems tracts and reservoir units makes the
seismic prediction of reservoirs more dependable.
9
II. Geologic History
The study area is denoted by the red dot in Figure 1, located in northeastern Oklahoma
within the Cherokee Platform. As described by Charpentier (1997), “The Cherokee Platform
Province extends from southeastern Kansas and part of southwestern Missouri to northeastern
Oklahoma” and “is 235 miles long (north-south) by 210 miles wide (east-west) and has an area
of 26,500 sq. mi”. This area experienced at least one major tectonic event: the subsequent uplift
of the Nemaha Ridge and Ozark Dome. These local uplifts that bound the Cherokee Platform on
the western and eastern edge, respectively, are thought to be the result of multiple orogenies
during the Pennsylvanian period. During this time, a broad, north-south trending arch rose above
sea level from central Oklahoma to Kansas (Nemaha Uplift or Ridge). The Nemaha Ridge
became a notable positive feature during later significant Early Pennsylvanian deformation likely
associated with similarly-aged plate convergence along the Ouachita Mountain orogenic belt in
Arkansas (Newell et al., 1989). This uplift and erosion locally affected the Arbuckle strata,
especially on structural highs (Franseen et al., 2003). Concurrently, a broad uplift also formed to
the east in the Ozark region of Oklahoma, Missouri, and Arkansas, termed the Ozark Uplift
(Johnson, 2008).
Near the end of the Early Ordovician, falling sea level left the craton void of seawater
and exposed predominantly Cambro-Ordovician carbonates and Precambrian basement rocks
(Franseen, 2003). Weathering and erosion produced a regional unconformity and associated karst
system over most of the North American craton, deemed the Arbuckle-Ellenburger-Knox-Prairie
du Chien-Beekmantown-St. George karst plain (Kerans, 1988).
10
a. Arbuckle Group
Arbuckle Group rocks are part of the craton-wide Sauk Sequence, which is bound at its top
and at its base by major interregional unconformities (Sloss, 1963). Arbuckle strata are part
of the “Great American Carbonate Bank” that stretched along the present southern and
eastern flanks of the North American craton (Wilson et al., 1991). The bank is composed of
hundreds of meters of mostly dolomitized intertidal to shallow subtidal cyclic carbonates
overlain by a regional unconformity (Wilson et al., 1991). This EOD persisted throughout the
Arbuckle time of deposition and is reflected in a suite of highly heterogeneous rocks
(Franseen, 2003). The Arbuckle and equivalent lithostratigraphic units, the El Paso Group of
southwestern Texas, the Ellenburger Group of central and north Texas, the Knox group of the
eastern United States, and the Beekmantown Group in the northeastern United States
comprise or partially comprise the Sauk III supersequence, which began to form with the late
Dresbachian – early Franconian transgression and terminated with a major regression in the
Middle Ordovician (Fritz, 2012). The Arbuckle group is a cyclic carbonate that is dominated
by both intertidal and shallow subtidal facies (Figure 5 and 6). The present depositional
model is an extensive, dominantly regressive tidal flat with persistent peritidal facies (Fritz,
2012). The unconformity resting on top of the Arbuckle group is recognized as proof of an
eustatic sea-level drop and has been used to delineate between the Sauk and Tippecanoe
depositional megasequences. In addition, the Arbuckle contains multiple unconformities at
major sequence boundaries (Fritz, 2012).
11
Figure 5 - Block diagrams showing (A) regional depositional setting (approximate scale in
hundreds of miles) and (B) hypothetical depositional model showing tidal currents (modified from
Pratt and James, 1986).
Figure 6 - Paleogeographic map of the Late Cambrian Period; study area denoted by red dot
(Blakey, 2011)
12
b. Simpson Group
This group represents a significant change in the depositional environment compared to the
preceding Arbuckle Group. The Simpson Group in the study area is a series of predominantly
sandstones and shales, with several limestone beds. In northeastern Oklahoma, the Simpson
Group is composed of 3 formations which are in ascending order, the Burgen Sandstone,
Tyner Shale, and the Fite Limestone. These formations were formed in a shallow marine
environment over a period of 25 million years, concluding with the withdrawal of the sea
(Denison, 1997). The local thickness of the Simpson Group as reported by Clark (1963)
ranges from 71-310 feet.
c. Previous Work
Several industry and academic studies have examined the identification of Arbuckle
stratigraphy and porosity zones. However, the majority of these studies have focused on
reservoir characterization or outcrop analysis with little work done in regard to 3D seismic
interpretation of intra-Arbuckle stratigraphic sequences and porosity networks.
Seismic mapping of the Arbuckle Group in Oklahoma has been aimed mostly at exploration
for the Arbuckle-Simpson aquifer in southern Oklahoma. Publications such as Smith et al.
(2010) and Kennedy et al. (2009) discuss epikarst and fault occurrences within the aquifer,
both playing a significant role in groundwater recharge.
The most relevant work concerning identifying sequence boundaries and porosity zones
within the Arbuckle has been performed in Kansas. Perhaps the most notable study was
conducted by Nissen et al. (2005) and focused on paleokarst features along the
Arbuckle/Simpson unconformity surface. Volumetric seismic attributes, such as coherence,
maximum positive curvature, and maximum negative curvature were extracted to analyze
karst features and geometry along the unconformity. The authors concluded that preferred
13
lineament directions appear to be related to regional structure, as well as geomorphic features
such as polygonal karst (Nissen et al, 2005).
There are no previous 3D seismic studies of the Arbuckle Group in Osage County to
identify intra-Arbuckle sequence boundaries and porosity zones. Therefore, methodologies
were developed from seismic studies in other areas. Abad (2013) used coherency and
curvature attributes to identify paleokarst along unconformities in the Ellenburger Group of
Texas, the lateral equivalent of the Arbuckle Group of the Midcontinent. Similarly, Zhao et
al. (2014) seismically identified karst features along unconformable boundaries within the
middle Ordovician of the Tarim Basin, China.
The Wild Creek 3D seismic survey has previously been interpreted for basement
fractures (Liner, 2015), upper Mississippian tripolitic chert (Benson, 2014), geomechanical
properties of Mississippian limestone (Jennings, 2014), and Pennsylvanian clinoforms (West,
2015).
14
III. Methods
The Wild Creek 3D is a 45 square mile survey located in Osage County, Oklahoma
(Figure 4). It was acquired and processed by Chevron Corporation in the mid 1990’s, has a bin
size of 66 x 66 feet and a 2 ms time sample rate. Figure 7 displays the frequency spectrum
indicating a -20dB bandwidth of 10 Hz – 105 Hz, giving it a dominant frequency (fdom) of 62.5
Hz.
Figure 7 - Histogram of frequency spectrum from OpendTect, taken from Wild Creek 3D survey
Well-A is approximately 1 mile east of the Wild Creek survey and includes digital well
logs and formation tops. Well-A digital logs were used to correlate depths and thicknesses of the
formations in the survey area. The interval velocity for the Arbuckle in the survey area is 20,000
feet/second. This value is used to determine the wavelength, vertical resolution, and lateral
resolution of the Arbuckle Group.
Using the equation for wavelength,
15
λ= V/fdom (1)
where V is the interval velocity calculated from sonic and fdom is the dominant frequency. The
wavelength, vertical and lateral resolution in the Arbuckle section are estimated as
λ= 20,000 (ft/s) / 62.5 Hz = 320 ft (2)
Vertical Resolution = λ/4 = 80 ft (3)
Lateral Resolution = max (bin size, λ/2) = 160 ft (4)
This yields a wavelength of 320 feet, meaning that the vertical resolution of the data is 80 feet.
Lateral resolution is limited by the maximum of either the bin size or the half-wavelength (Liner,
2004). The maximum between the two values and therefore the lateral resolution is 160 feet. The
survey acquisition parameters are shown in Table 1.
Table 1 - Wild Creek 3D survey parameters, calculated using equations from (Liner, 2004)
16
A synthetic seismogram was generated for Well-A on the Wild Creek 3D seismic survey (Figure
8). Figure 10 shows the Well-A synthetic projected on in-line 3915 of the Wild Creek post-stack
(PoSTM) data, along with the corresponding stratigraphic column and formation tops. Once the
well was brought into the PoSTM data, the acoustic impedance (AI) log was displayed adjacent
to the well bore, colored in with gamma ray (GR) (Figure 10). This action was performed in
order to more clearly observe formation boundaries. From the synthetic seismogram, the top of
the Arbuckle Group was identified, tracked using OpendTect seismic software and mapped over
the survey area.
Figure 8 - Synthetic seismogram created from sonic and density logs in Well-A, shown with
correlated formation tops
17
Figure 9 - Well-A synthetic projected on Wild Creek in-line 3915, along with the corresponding
stratigraphic column and formation tops
Figure 10 – Cross line 11581 with superimposed Well-Al. Well display settings are AI curve
colored with GR; blue is carbonate section, brown is clastics. The red box on the stratigraphic
column demonstrates the approximate amount of time represented on the cross line shown
(Precambrian - Lower Pennsylvanian).
18
The first seismic interpretation step is to observe and track the Simpson-Arbuckle
unconformable contact (Figure 11). This contact is present throughout the survey and fairly easy
to track due to the sharp impedance contrast at the unconformity surface. A series of maps have
been generated to show structural and amplitude (post-stack time migration, or PoSTM) variance
at this contact and can be viewed here (Figures 12, 13, 14, 15). A velocity model was applied to
the Arbuckle to convert two-way time to depth using
V = 2 * ( MD - KB + SRD ) / T, (5)
where MD is measured depth, KB is Kelley bushing, SRD is seismic reference datum, T is
reflection time and all depths are in feet. Inserting Arbuckle data for Well-A on the Wild Creek
3D survey, the depth conversion velocity is found to be 11345 ft/s. This will be used as a
constant velocity for depth conversion to scale horizon times to depth from SRD (C. Liner, 2016,
Personal Comm.).
19
Figure 11 – Cross line 11336 view of Simpson-Arbuckle unconformity contact and Arbuckle-
Basement unconformity contact.
Figure 12 - Top Arbuckle contoured time structure map.
20
Figure 13 - Top Arbuckle contoured subsea depth structure map.
Figure 14 - Top Arbuckle horizon amplitude map with time structure contours.
21
Figure 15 - Top Arbuckle 3D time structure map.
The Simpson Group has a diagnostic low amplitude reflector caused by clastics in the
section, as opposed to the dominantly dolomitic underlying Arbuckle Group. At the contact with
the Arbuckle dolomite, a sharp increase in velocity is observed in the form of a positive
amplitude reflection (Figure 11). The Simpson-Arbuckle contact is a highly irregular surface.
Although no distinct paleokarst features are observed at this contact in our data, based on
previous work, we believe that they may be present (Fritz et al., 2012). Once the Arbuckle
surface is mapped, the basement can be tracked in order to constrain the Arbuckle Group (Figure
11). The basement was also fairly easy to track due to its constant reflector at the base of the
Arbuckle, caused by a change in velocity from dolomite to granite. It must be noted that in some
areas the Reagan Sandstone is present at the basal Arbuckle succeeding granitic basement. This
22
causes a different impedance change at this boundary and can make it difficult in some areas to
distinguish between horizons. Without sufficient well control to make interpretations a certainty,
a lower amplitude signature occurring at this contact can be interpreted to be either the Reagan
Sandstone or a porosity zone within the lower Arbuckle, most likely paleokarst. However, when
distinguished, this contact can be seen on-lapping the granitic hills of the basement and adds to
the stratigraphy we are trying to delineate in the area.
The most useful technique in identifying intra-Arbuckle sequence boundaries was
flattening the seismic data cube on the Middle Pennsylvanian Oswego Limestone (refer to
stratigraphic column in Figure 2). The Oswego Limestone is the most consistent, widespread
reflector in the survey area, therefore it was chosen for this process. An example of this flattened
cube can be seen in Figure 16. The horizontal black reflector at the top of the image is the
Oswego Limestone. The purpose of this technique is to demonstrate structure in the Middle
Pennsylvanian time, which effectively eliminates any structural deformation from the Middle
Pennsylvanian time to present. This provided a more structurally simplified view of the Arbuckle
Group, allowing internal features to not be as obscured by structure. An attribute known as
“Velocity Fan” was also applied to the seismic data. This smooths reflection signatures in the
data, effectively decreasing the amount of noise visually observed. This allows for a simplified
inline (IL) and cross line (XL) view of the data, and reflection continuity can be more easily
discerned. This proved to be a less complicated approach to image and interpret stratigraphy,
especially within a unit such as the Arbuckle. The first intra-Arbuckle unconformity observed is
the Upper-Middle Arbuckle seismic sequence boundary (UMC) (Figure 17). Cross line 11336
demonstrates the UMC. Note the onlap (green arrows in figure) of Lower Arbuckle onto the
23
basement high, assuming uniform anticlinal structure. The UMC can be seen overlapping these
cycles almost horizontally. A porosity zone also exists under the UMC, further providing
evidence that this is in fact an exposure surface (Fritz, 2012). This contact may onlap or just
overcome the peak of the most prominent anticline in the survey area, demonstrated in Figures
18, 19, and 20 by the structural high in the northeastern portion of the survey.
Figure 16 – XL 11336 PoSTM data flattened on Oswego LS
24
Figure 17 - UMC demonstrated. Note green arrows signifying onlap.
Figure 18 - UMC contoured time structure map
25
Figure 19 - UMC contoured subsea depth-structure map
Figure 20 - UMC 3D time structure map
26
The second identifiable intra-Arbuckle unconformity is the middle-lower Arbuckle
seismic sequence boundary (MLC) (Figure 21). This contact was discovered with evidence of
paleokarst features along its base, indicating that it is an exposure surface. The first and perhaps
most distinct features noticed are on cross line 11001 shown in Figure 21, the paleokarst features
denoted by the green arrows. The MLC also is affected by the structural regime of the area,
demonstrating structural highs in the northeastern area of the survey (Figures 22, 23, 24).
Figure 21 – Arbuckle MLC and associated paleokarst features (green arrows).
27
Figure 22 - MLC contoured time structure map
Figure 23 - MLC contoured subsea depth-structure map
28
Figure 24 - UMC 3D time structure map
By tracking the UMC and MLC horizons within the seismic survey, the Arbuckle was
subdivided into upper, middle, and lower sections. Figure 25 show the final subdivisions of the
Arbuckle in the Wild Creek survey area based on the seismic sequence stratigraphy performed.
29
Figure 25 - Seismic subdivisions of the Arbuckle in the Wild Creek survey area shown on cross
line 11336.
Fritz (2012) notes that porosity zones and/or reservoir development within the Arbuckle
Group are often associated with sequence boundaries. Here we infer internal Arbuckle porosity
zones by the appearance of negative amplitude anomalies, implying a vertical decrease in
acoustic impedance. It is well-established that carbonate impedance declines with increasing
porosity (Rasolofosaon and Zinszner, 2014). This association depends on knowledge that the
Wild Creek data polarity is USA standard (impedance decrease is a negative reflection
coefficient), which is known to be true because of the strong negative amplitude anomaly
associated with low-impedance tripolitic chert that develops locally at the
Mississippian/Pennsylvanian unconformity (Benson, 2014; Jennings, 2014).
30
The Arbuckle amplitude anomaly shown on Figure 26 is interpreted as a widespread
porosity zone within the survey area. It exists just below the UMC and can be auto-tracked in the
northeastern portion of the survey. This is a weak, yet persistent, negative amplitude anomaly
with strongest development on the crests and flanks of anticlinal structures (Figures 27, 28, 29).
This may be due to extensive weathering and dissolution associated with paleokarst associated
with basement structural highs. Although not distinctly imaged in our data, sub-resolution
paleokarst features may occur in this zone. It is also possible that basement-associated
hydrothermal fluids (Liner, 2015) caused or enhanced the inferred porosity zone.
Figure 26 - Negative amplitude anomaly (white arrows) interpreted as an Arbuckle porosity zone
(PHI-1). This PHI-1 zone is persistent throughout the survey area, and can also be seen in Figure
18 as the bright negative amplitude just below the UMC.
31
Figure 27 - Time structure map of the PHI-1 zone in the Wild Creek survey area. Note structural
high in central to northeast portion of survey.
32
Figure 28 - Horizon amplitude map of the PHI-1 zone. Areas of most negative amplitude,
indicating best and/or thickest porosity development, are seen in the central portion of the
survey.
Figure 29 - 3D view of PHI-1 zone horizon amplitude map. Note most negative amplitude values
occurring on or proximal to structural highs.
33
An additional Arbuckle porosity zone (PHI-2) has been mapped in the Wild Creed survey area
(Figure 30). In addition to the PHI zones imaged in this thesis, there were 6 similar zones
discovered in the data.
34
Figure 30 – Arbuckle PHI-2 interpreted porosity zone. A) XL 11541 showing porosity zone (white
arrows). B) PHI-2 horizon amplitude map.
35
IV. Results and Interpretation
From the seismic mapping methods used in OpendTect software, two sequence boundaries
were identified and mapped within the Arbuckle Group in Osage County, Oklahoma. Perhaps the
most significant result is evidence for paleokarst along the middle-lower Arbuckle sequence
boundary within the study area. This is observed in the seismic data as a negative amplitude
“bright spot” near the Arbuckle-Basement contact. While several of these events can be observed
on the crest or flanks of current and paleo-structural highs, they do not appear to be structurally
dependent within the lower Arbuckle, since these features occur also in areas of low structural
relief (Figure 21). Seismic evidence cannot determine if these paleokarst features contain
hydrocarbons, but similar features seen in other areas of the world are high-priority drilling
targets (Zhao, 2014). According to Fritz (2012), paleokarst features have been observed in
outcrop along the southern Ozark uplift within the Arbuckle Group in northeastern Oklahoma.
They are observed as collapse breccias interpreted to have formed in response to karst
conditions. Syndepositional karst development along sequence and/or parasequence boundaries,
especially at the top of sub-tidally dominated, third-order cycle, sequence boundaries, is a
prominent reservoir type within the Arbuckle Group of Oklahoma (Fritz, 2012) indicating that
sequence boundaries within the lower zones of the Arbuckle Group should be examined for
untapped production.
Like all seismic data, the Wild Creek survey is subject to resolution limits (Table 1). Within
the Arbuckle, the lateral resolution limit is 160 feet, meaning that features with lateral scales less
than 160 are not independently resolved by the seismic data. It is likely that smaller, sub-
resolution paleokarst features other than those described here are present in the data.
36
Features that are diagnostic of the ~500 ft thick upper Arbuckle, above the UMC (Figure 17),
are a karsted, irregular Arbuckle-Simpson contact, and more numerous areas of negative
amplitude anomalies (PHI zones) compared with the middle and lower Arbuckle. These PHI
zones appear to not be directly linked to a paleo-structural influence. They are instead most
likely linked to exposure surfaces. However, the strongest negative amplitude areas within these
PHI zones occur near these structural highs. This is likely due to enhanced dissolution on paleo-
structural highs due to extended amounts of time the rock endured subaerial exposure.
These comments also apply to the middle Arbuckle. Within this upper sequence, PHI zones
are most evident in the central to eastern parts of the survey, decreasing in occurrence towards
the western boundary of the survey. The most prominent porosity zone occurs along the UMC
just within the top of the middle Arbuckle (Figure 17, 26).
The middle Arbuckle within the Wild Creek survey does not contain as many negative
amplitude anomaly zones as the upper Arbuckle. This may be related to middle Arbuckle
thickness as defined here, the middle Arbuckle being about 400 feet thick, 100 feet thinner than
the upper Arbuckle. In addition to being thinner, the middle Arbuckle might consist of different
facies that are not as conducive for porosity development, or might not have been exposed to the
sea level variation that effected the upper Arbuckle (see Appendix; Figure 51). This may be a
good topic for further work.
PHI-1 that is tracked in the middle Arbuckle is shown here in several different views
(Figures 26, 27, 28, 29), and it is noted that areas of most negative amplitude (Figures 28, 29) are
on the crests or flanks of structures. The areas in which PHI-1 is most continuous does not seem
limited to the areas of most structural relief, therefore most likely not directly controlled by
37
structural influence. Based on observation, this zone and its porosity development was most
likely induced by exposure, enhanced in certain areas by paleo-structure. PHI-2 (Figure 30)
occurs in the upper Arbuckle and is concentrated in the central to eastern parts of the survey.
The lower Arbuckle in the study area is about 300 ft thick, considerably thinner than the
upper and middle cycles. This section is constrained by a continuous, positive amplitude event at
its upper bound that marks an unconformable surface and bounded below by Arbuckle-basement
contact. An interesting feature within the lower Arbuckle is the occurrence of paleokarst features
(Figures 31-35). These were identified too late in the study (Liner, pers. comm.) for detailed
analysis, but a cursory introduction can be given here. Paleokarst along the lower Arbuckle
sequence boundary, could be an area of future investigation (see future work).
Reflections seem discontinuous and prove difficult to trace within the lower Arbuckle,
implying internal stratigraphy may be highly variable. Based on paleokarst evidence within the
lower section, this variability could possibly be attributed to dramatic sea level cyclicity. The
Arbuckle Group is known to have been deposited in a peritidal dominated setting, but evidence
of paleokarst implies that (in the study area) the craton must have been subaerially exposed for a
significant amount of time during early Arbuckle deposition. This is required in order for
paleokarst features to achieve the observed scale and lateral extent (Figure 35). These features
formed along an exposure surface, but are observed penetrating half of the lower Arbuckle, or
approximately 100 feet vertical extent. To image the lower Arbuckle paleokarst system, two
cross lines are shown in Figures 31-33 with and without interpretation. An amplitude map was
then generated on this horizon (Figure 34, 35) to demonstrate lateral extent and approximate
width of the karst feature.
38
Figure 31 – Cross line 11001 demonstrating the tracked (white) paleokarst horizon below the
MLC.
Figure 32 – Cross line 11001 without horizon showing paleokarst horizon with distinct sinkhole
features
39
Figure 33 – Cross line 11336 with lower Arbuckle paleokarst horizon.
40
Figure 34 - Amplitude map of lower Arbuckle paleokarst horizon. Note two cross lines
displayed.
Figure 35 - Detail view of lower Arbuckle negative amplitude anomaly showing approximate
width of paleokarst feature. Width of feature at measured location is 683 ft.
41
V. Conclusions
The goal of this study was to determine if Arbuckle stratigraphy in SW Osage County,
OK could be subdivided using 3D seismic techniques. Careful interpretation of the Wild Creek
3D seismic survey reveals evidence of two unconformity surfaces within the Arbuckle.
Arbuckle subdivision was accomplished by seismic mapping techniques that highlight
evidence of intra-Arbuckle unconformities, including as onlap, seismic layering characteristics
and karst indicators. Approximately 50 interpreted paleokarst sinkholes are observed within the
Arbuckle Group of the study area, and the seismic lateral resolution (166 ft) limited the ability to
observe paleokarst features smaller than 160 feet. All observed paleokarst features occur along
the middle-lower Arbuckle seismic sequence boundary (MLC) and are recognized by their
corresponding negative amplitude and geometry. Tracking the lower Arbuckle throughout the
survey area, zones of negative amplitude similar to those seen in the paleokarst forms can be
observed. These may indicate additional unresolved paleokarst areas or the discontinuous basal
Reagan Sandstone.
The upper-middle Arbuckle contact (UMC) is observed as a subtle disconformity with a
basal negative amplitude anomaly interpreted as a porosity zone. No paleokarst features are
observed along this surface, however, it is possible that they may present but not be resolvable.
As stated earlier, reservoir development and porosity enhancement take place along sequence
boundaries. Therefore, not only does the evidence of a disconformity solidify this feature as an
intra-Arbuckle unconformable surface, but the most widespread porosity zone in the survey area
occurs at its base (Figure 17, 26).
42
VI. Future Work
To the author’s knowledge, this is the first investigation of the Arbuckle Formation using
the Wild Creek 3D seismic survey data. Paleokarst features were observed along the middle-
lower Arbuckle seismic sequence boundary (MLC) and should be further analyzed to identify
and map them using seismic. If modern digital well logs could be obtained in the survey are, the
paleokarst features could be further confirmed and a petrophysical study conducted. Paleokarst
features are known to be petroleum reservoirs worldwide, providing reason to further investigate
these features in the survey area.
Within the study area the middle Arbuckle contains few porosity zones, but it does
possess the most prominent one. This can possibly be attributed to less-favorable depositional
facies and/or lack of exposure surfaces, questions that could be addressed by drilling cores
located in, or adjacent to, the study area. If seismic sequence boundaries can be correlated to
core, factors that contribute to the formation of porosity zones can then be discerned.
A petrophysical study of Arbuckle sequence boundaries and facies would be possible if
modern digital well logs can be obtained that have penetrated the entire Arbuckle at several
points in the study area. The digital logs necessary for such a study are NPHI (neutron porosity),
RHOB (bulk density), resistivity, PhiT (total porosity), and geomechanical logs from full wave
sonic (Young’s Modulus, Poisson’s Ratio). In addition, the Arbuckle is historically known as a
saltwater disposal unit because of its under-pressured nature. If pressure data from mud logs or
well logs can be obtained, this would help identify a pressure regime for the Arbuckle in this
locality.
43
In this study, I have shown that 3D seismic data in Southwestern Osage County,
Oklahoma can be used to stratigraphically subdivide the Arbuckle Formation into three
unconformity-bounded units. If the intra-Arbuckle unconformities are in fact second or third-
order sequence boundaries, it is likely they can be extended throughout northern Oklahoma. The
attempt to extend such surfaces can be applied to other seismic surveys throughout the area as
well.
44
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48
VIII. Appendix: Seismic Grid
A total of 6 representative lines (Figures 37-42) from the Wild Creek survey are
presented here, along with the corresponding base map (Figure 36). Three inlines are shown in
the E-W direction, as well as three cross lines in the N-S direction. Well-A is denoted by the red
circle on Figure 36, as projected from approximately 1.5 miles east of the seismic survey. In each
figure the top of the Arbuckle is denoted by the blue line and the top of the basement is denoted
by the red line.
Figure 36 - Base map with 6 corresponding inlines and cross lines (Figures 37-42) denoted by red
lines
49
Figure 37 - IL3690
Figure 38 - IL3830
50
Figure 39 - IL3970
Figure 40 - XL10920
51
Figure 41 - XL11230
Figure 42 - XL11550
52
IX Appendix: Core Discussion
A cursory analysis of core was performed with the intent to describe rock type and
distinguish porosity zones, if any. Core was observed at the Oklahoma Geological Society
(OGS) Oklahoma Petroleum Information Center (OPIC) facility in Norman, OK. All photos
were taken and used with permission from OPIC. A total of 4 cores from Osage County (Figure
43) were viewed and the following figures demonstrate representative features of all cores
(Figures 44-47). Note the red dot denoting well location on the base map in Figures 44-47.
Figure 43 - Google Earth image with wells displayed that were used for core observation. Note
Wild Creek survey area.
53
Figure 44 - Vugular porosity in Arbuckle at approx. 2365’ M (Texaco Kohpay well)
Figure 45 - Interpreted Arbuckle algal facies at approx. 3356’ MD (Oliphant LaFortune #3 well)
54
Figure 46 - Interpreted Arbuckle solution channel following fracture, coated with bitumen at
approx. 2863’ MD; pictured also in a light box under UV light to show fluorescence (Oliphant
Nate #1 well)
Figure 47 - Vugular porosity zone at approx. 3436’ MD (Texaco Osage C-1 well)
55
X Appendix: Seismic Horizons in Google Earth
The Arbuckle MLC and paleokarst horizons were tracked and mapped, and the
OpendTect map view images of these surfaces were brought into Google Earth and overlaid to
scale onto the Wild Creek survey outline. As a possible petroleum reservoir horizon, it is
important to consider where these zones are located in relation to surface features. Figure 48
shows the Wild Creek survey area denoted by the red box, along with visually observed well
pads seen on Google Earth. Due to time constraints, steps were not taken to investigate these
wells and their corresponding data (date drilled, TD, productive horizon(s), etc.). Figures 49 and
50 demonstrate the MLC depth-structure map and the paleokarst horizon amplitude map overlain
on the Wild Creek survey bounds.
This task was performed to assess potential land issues if an operator was to drill what we
interpret as a paleokarst feature. In figure 49, note the well furthest to the southwest and its
location with respect to the subsurface structural high. The MLC is interpreted as an
unconformity surface, however, it is increasingly difficult to interpret near the structural high due
to seismic reflection obscurity caused by the basement. The most southwestern well shown in
Figure 50 may still prove a viable candidate for a workover operation to investigate the MLC and
possible paleokarst horizon, if it has not already penetrated the Arbuckle. No well pads were
observed in Figure 50, where the paleokarst horizon has its strongest negative amplitude and is
most laterally continuous. However, an in-depth investigation on Google Earth and the OGS
website would prove helpful in finding any additional well information for this area of interest.
56
Figure 48 - Google Earth image of Wild Creek survey bounds with observed well localities
Figure 49 - MLC depth structure map overlaid on Wild Creek survey outline
57
Figure 50 - Paleokarst horizon amplitude map overlaid on Wild Creek survey outline
Figure 51 - Coastal onlap curve for Late Cambrian and Ordovician time based on Ross and Ross
(1988). Arbuckle Group highlighted with red box (Modified from Franseen, 2004).
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