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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).