THE JOURNAL OF THE OKLAHOMA CITY GEOLOGICAL SOCIETY VOLUME 71 Number 1 ~ January | February 2020 ~
Carbonate Diagenesis Of The Arbuckle Group North Central Oklahoma To Southeastern Missouri Completions-Induced Seismicity in the STACK-SCCOP area of central Oklahoma: Alpha SE, My Favorite Earthquake Swarm
Some interesting articles in the second first half of 2019
And Much More
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The Journal of the Oklahoma City Geological Society Volume 71 Number 1
The Shale Shaker The Shale Shaker is published under the oversight of members of the OCGS Publications Committee, who are responsible for all of the editorial and technical content. Publication production assistance provided by: ART DIRECTOR, PRODUCTION AND DESIGN Theresa Andrews, Visual Concepts and Design, Inc. firstname.lastname@example.org
OCGS Board Officers President – Patrick Kamann email@example.com Vice President – Mallory Zelawski firstname.lastname@example.org Treasurer – Drew Dressler email@example.com Secretary – Cole Hinds firstname.lastname@example.org Education Chair – Rosie Gilbert email@example.com Social Chair – Galen Miller firstname.lastname@example.org Social Media Chair – Britni Watson email@example.com Website Chair – Julian Michaels firstname.lastname@example.org Publications Chair – Dan Costello email@example.com Past President – Steve Ladner firstname.lastname@example.org Councilor – Doug Bellis doug.bellis@warwick-energy Membership Chair – Mark Oerkerman email@example.com
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January ~ February 2020 | Page 1
The Journal of the Oklahoma City Geological Society Table of Contents
Shale Shaker Features
3 2020 Centennial Sponsorship Announcement
32 Some Interesting Articles In The Second First Half Of 2019; Andrew Cullen, Warwick Energy
4 Letter from the OCGS President: Welcome to 2020; Patrick Kamann, President, OCGS Board of Directors
36 My Favorite Earthquake Swarm:
Completions-Induced Seismicity in the STACK-SCCOP area of central Oklahoma: Alpha SE; Andrew Cullen, Warwick Energy
5 Letter from the Editor: The Next Step; Dan Costello, Editor
45 2020 Budget
OCGS Membership & New Members
46 State of the Industry; Dan Costello
10 Carbonate Diagenesis Of The Arbuckle Group North Central Oklahoma To Southeastern Missouri; Britney J.Temple, Chesapeake Energy Corporation; Phillip A. Bailey, Crawley PetroleumCorporation; and Jay M. Gregg, Boone Pickens School of Geology
About the Cover
Theresa Andrews created the cover of the Shale Shaker. COVER PHOTO: Photomicrograph from the St. Joe 66W84 core (featured in this month’s technial article), upper part of the Eminence Fm. This section contains a vug partially filled by coarse crystalline dolomite cement displaying compositional zoning. The replacive dolomite surrounding the zoned cement displays coarse crystalline planar to nonplanar texture. The horizontal field is 1.7mm
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Letter from the OCGS President
By: Patrick Kamann, President, OCGS Board of Directors
met, I would like to introduce myself. My name is Patrick Kamann and I have been a member of the OCGS board for the last two years. Most recently, I served as the Vice-President. I came to Oklahoma a little over 15 years ago to attend graduate school at Oklaho- ma State University. From there, I soon found myself working as a young geolo- gist at Devon Energy. One of the first things I was introduced to in Oklahoma City was our Society. Former leaders at Devon, such as Jeff Hall, Dale Fritz, and Bill Coffey, were strong supporters of the Society. I quickly learned the Society pro- vides great social events to connect with local geologists and opportunities to grow my geologic knowledge through training. Recently, I was visiting with a geologist who attended our January luncheon. They remarked they enjoyed the talk, but that it was the first OCGS event they had attend- ed in 5 years. Sometimes the demands at work or home can make it difficult to set aside time to network. However, I believe the time spent networking or training will help one achieve their long-term career
goals. I encouraged them to set aside time to reengage with the OCGS. I would like to invite each of you to reach out to a geo- scientist in your network and invite them to the next OCGS event. Encourage them to be an active member of our society, just as Jeff, Dale, and Bill encouraged me to be active. As you may know, and will see in this publication, the Board worked hard to form partnerships with local companies in 2020 through our Centennial Sponsor- ship Program. These sponsors are helping us provide world class luncheon talks and training courses this year. In return, we provide their staff access to the training and social events. Additionally, our spon- sors receive recognition at our events and advertising space in our publications. I would like to extend a sincere thank you to our sponsors for their generous support. As sponsors, you are helping us build a relevant Society for the future. Regards, Patrick OCGS President
I would like to welcome the members of our society to a new year. As the new president of the OCGS, I am excited about the future of our organization and proud to be your president for the next two years. For those of you I have not Patrick Kamann Welcome to 2020
Weston Resources, Inc. Michael Weston Smith Geologist 2500 South Broadway, Suite 220 Edmond, Oklahoma 73013 (405) 203 6866 email@example.com
DICK HOWELL Sales Manager 405.315.4206 Dick.Howell@columbinelogging.com www.columbinelogging.com
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Letter from the Editor
By: Dan Costello, Editor
When horizontal drilling and multi-stage completions evolved to the point where it was viable to directly drill the source rock, our methods for evaluating plays needed to change. Is the concept of net pay still viable in nanodarcy-type rock? How do we evaluate geological risk when the con- ventional aspects of trap and seal do not apply? What is the best way to consis- tently define the drainage dimensions of a horizontal well? These questions have real impacts to prospect development and project economics. These changes required the industry to think different about shales and our ap- proach towards understanding them. There have been many great papers pub- lished here in the Shale Shaker and else- where about the Woodford and Springer formations, two of Oklahoma’s world- class source rocks. In addition, local uni- versities and the state survey have hosted workshops and consortia to further our understanding of these resources. In the past couple years, innovations have shifted towards completions and our engi- neer peers work on the most efficient way to stimulate the rock. Geologists are still
needed, of course – reservoir quality is the starting point for everything. The most powerful completion in a thin, immature reservoir cannot outproduce a thick, ma- ture, high-TOC area. More recently as commodity prices have slipped, the need to focus on economics has required the in- dustry to focus on the highest return areas. While this has resulted in a significant rig drop in Oklahoma, the rock here has not changed. There are still plenty of opportu- nities in Oklahoma. After a decade of focusing on resource plays, the industry is seemingly “moving on” from focusing on large acreage po- sitions that cover multiple counties. The majors have renewed their interests in offshore drilling. As the onshore industry moves forward, I am curious what the next revolution will be. Demand continues to rise, and hydrocarbons will be necessary for decades into the future. As with past cycles in the oil and gas industry, I imag- ine the starting point will be in the geosci- ences. The same holds true for mining, environmental, and other industries – it all starts with the rock.
Dan Costello The Next Step
It has now been over ten years since the “Shale Revolution” that brought me and many others into the oil and gas industry. This industry change required a combina- tion of geological analysis and techno- logical advances to successfully drill and unlock the hydrocarbons from the rock. We’d always known the oil and gas was there – the shales were the “kitchen” of the hydrocarbon factory; an important step in the petroleum system analysis, but not the focus.
January ~ February 2020 | Page 5
OCGS Membership & New Members
SOCIETY MEMBERSHIP _____________________________________________________________________________ As of 2/7/20 OCGS 318 Active 52 Associate 13 Emeritus 10 Honorary 4 Student _____ 397 TOTAL NEW MEMBERS _____________________________________________________________________________
SANIAGO FLORES CHESAPEAKE ENERGY
JOHN RAMSEY STRATEGIC RESOURCES CORPORATION
APRIL MORENO-WARD ROSE STATE COLLEGE
SHA GRANT SANDRIDGE RESOURCES
DAVID HULL DEVON ENERGY
JAMES HAMILTON HAMPTON OIL
BRIAN MOSS CONTINENTAL RESOURCES
SARAH ALLEN CHESAPEAKE ENERGY
AARON JANIEC PALADIN
BRYANT REASNOR CHESAPEAKE ENERGY
AARON VRBENEC CHESAPEAKE ENERGY
DAVE CLUPPER CLUPPER COMPANY
ZACHARY WILLIAMS DEVON ENERGY
DREW SEYMOUR SAMSON RESOURCE
R. TAYLOR R.C TAYLOR
IAN COX UNIVERSITY OF OKLAHOMA
DREW KREMAN CHESAPEAKE ENERGY
WAKIL BUNU BALUMI OKLAHOMA STATE UNIVERSITY
AMANDA HILLS ARNOLD PROPERTIES, LLC
HUGH PEACE DEGOLYER & MACNAUGHTON
MITCHELL SIGLER CHESAPEAKE ENERGY
JOSH ZIMMER ZIMMER RESOURCES, LLC
JOE FOSTER FOSTER COMPANY
Page 6 | Volume 71 Number 1
January ~ February 2020 | Page 7
C R A W L E Y P E T R O L E U M
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By: Britney J.Temple, Chesapeake Energy Corporation, Oklahoma City, OK; Phillip A. Bailey, Crawley Petroleum Corporation, Oklahoma City, OK; and Jay M. Gregg, Boone Pickens School of Geology, Oklahoma State University, Stillwater OK Oil and Gas Exploration Carbonate Diagenesis Of The Arbuckle Group North Central Oklahoma To Southeastern Missouri ABSTRACT The Arbuckle Group (Upper Cambrian and Lower Ordovician) carbonates of the southern Midcontinent are an important petroleum reservoir and also are used to store petroleum waste-water. Additionally, the Arbuckle likely has been a major source and conduit for petroleum and metalliferous fluids that sourced large economic ore deposits in the Ozark region. The Arbuckle section is comprised of cyclic, cherty dolomites, interbedded, occasionally, with thin, quartzic sandstone. Depositional fabrics observed range from shallow subtidal to peritidal facies. Dolomites interpreted as early replacement, observed in all facies, exhibit a range of very fine to medium crystal size and planar textures. Carbon and oxygen isotope values of early diagenetic do- lomite indicate equilibrium with evaporated early Ordovician seawater. Dolomite interpreted as late diagenetic replacement exhibits medium to coarse planar to nonplanar textures likely resulting from recrystallization of early diagenetic dolomites. Analysis of fluid inclusions in void filling rhombic and saddle dolomite cements indicate the presence of warm (90° to 155°C), saline (10 to 27 wt.% NaCl equivalent) basinal fluids. Late diagenetic replacive and void filling dolomite cements display more negative δ 18 O values compared with early diagenetic replacement dolomite. Reconstruction of the iso- topic composition of these fluids indicate an evolved water that has interacted with continental basement or sediments derived from basement rocks. These fluids likely are sourced from the Arkoma and/or Anadarko basins and driven by a gravity fluid flow mechanism initiated during the Ouachita orogeny.
INTRODUCTION TheArbuckle Group carbonates are an im- portant petroleum reservoir and are used to store wastewater emplaced through injec- tion wells in Oklahoma (Murray, 2014). Additionally the Arbuckle may have been a major conduit for metalliferous fluids affecting the Ozark region and contribut- ing to the Tri-State Mississippi Valley- type (MVT) mineral district of Oklahoma, Kansas and Missouri as well as the MVT deposits of the Ozark region of Missouri and Arkansas (Leach and Rowan, 1986; Gregg and Shelton, 2012; Mohammadi et al., 2019a). Most previous studies of the Arbuckle have focused on characterizing the stratig- raphy and lithology of the Arbuckle strata in the southern portions of Missouri and Oklahoma (He et al., 1987; Overstreet et al., 2003; Palmer et al., 2012; Lucia, 2012). Some studies have addressed the diagenesis of the Arbuckle (Lynch and Al-Shaieb, 1991; Gao et al., 1995; Leach et al., 1975). Yet little is known about the petrology of these units in the north- central portion of Oklahoma where recent petroleum exploration activity has led to
increased wastewater injection into the Arbuckle. In addition, there have been no studies conducted on the Ordovician rocks underlying the Tri-State MVT district. This study integrates petrology and geo- chemistry to illustrate how both early dolomitization and late diagenetic events affected Arbuckle carbonate strata in southwestern Missouri and northeastern Oklahoma. It provides insight into the evolution of porosity and permeability in the Arbuckle, as well as the influence of these diagenetic events on overlying units. Furthermore it enhances our knowledge of the origins, compositions, and pathways of basinal fluids throughout the southern Midcontinent. Northern Oklahoma and southwestern Missouri are part of the stable cratonic interior of North America. The Ozark Uplift is the primary tectonic feature in this region and is bound by the Illinois Basin to the northeast, For- est City Basin to the northwest, Arkoma Basin to the south, and Reelfoot Rift to the southeast (He et al., 1997; Shelton et GEOLOGICAL SETTING Regional tectonic setting:
al., 2009). Major tectonic features in the north-central Oklahoma region include the Nemaha Fault Zone with the Anadar- ko Basin and Oklahoma aulacogen to the south (Campbell et al., 1991). Heterogene- ities in Proterozoic continental basement indicate multiple igneous and metamor- phic terranes underlying the Midcontinent sedimentary cover (Denison, 1981; Che- noweth, 1968; Reeder, 1974). Subsurface faulting in Oklahoma occurs throughout the sedimentary cover and these faults ex- tend into Precambrian basement (Marsh and Holland, 2016). During the Ordovician, the Ozark Uplift was located on the Laurentian continent between 10° and 25°S (Palmer, 2012; Fritz et al., 2012). The Arbuckle compris- es part of the Sauk megasequence and was deposited under epeiric sea conditions on a shallow water platform as a series of 3rd to 5th order depositional cycles. These strata are further defined by regional and sub-regional unconformities (He et al., 1997; Overstreet et al., 2003; Palmer et al., 2012). Depositional environments ranged from supratidal to shallow subtidal and transitioned to an off-platform set- ting southward into the Arkoma Basin and
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Oklahoma aulacogen (Gatewood, 1976; Perry, 1989). Paleotopography of the eroded, ‘high relief’ (10’s of meters) Pro- terozoic basement indicate a ‘pock mark’ landscape (Tulsa Mountains) in northeast- ern Oklahoma (Chenoweth, 1968; Reeder, 1974). Consequently, deposition of basal siliciclastic and carbonate units during the earliest Ordovician transgression may have resulted in locally thick deposits or non-deposition depending on the relief of the paleo-terrane. There are three documented stratigraphic naming systems used for Upper Cambrian and Lower Ordovician strata of Okla- homa, Missouri, Arkansas, and Kansas (McQueen, 1931; McCracken, 1955; Che- noweth, 1968; Overstreet et al., 2003). Cambrian-Lower Ordovician strata in southwestern Missouri (and northeastern Oklahoma) do not retain the “group” des- ignation and are indicated by formational names. For convenience the term “Ar- buckle” will be used throughout the study area for Cambrian-Ordovician strata in the subsurface below the Simpson Group (Fig. 1). Strata included in the Arbuckle Group are temporally equivalent to the El- lenburger Group in Texas, Knox Group of the Appalachian Basin and other “Great American Carbonate Bank” carbonate units of North America and elsewhere (Derby et al., 2012). Late Paleozoic tectonism along the Ouachita Thrust Belt is believed to have resulted in northward flow of basinal flu- ids through lower Paleozoic sediments including the Arbuckle (Bethke and Mar- shak, 1990; Leach and Rowan, 1986; Viets and Leach 1990; Appold and Gar- ven, 1999). Petrographic and geochemical evidence for late diagenetic alteration of Arbuckle age carbonates exists through- out the Midcontinent (Gregg, 1985; Gregg and Shelton, 1989; Lynch and Al-Shaieb, 1991; Shelton et al, 1992; Gao et al., 1995; Gentry, 2012; Gregg et al., 2015).
Figure 1 Stratigraphic Column showing Cambrian through Devonian strata in the study area.
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Carbonate Diagenesis OfThe Arbuckle Group North Central OklahomaTo Southeastern Missouri, cont. Oil and Gas Exploration
METHODS Seven subsurface cores penetrating the Arbuckle Group were described and sam- pled at the Oklahoma Geological Survey Petroleum Information Center (OPIC) in Norman, OK and the Missouri Geological Survey McCracken Core Library in Rolla, MO. The cores range from 16m to 422m in length and lie along a section from near Springfield in southwestern Missouri to near Fairview in north-central Oklahoma (Fig. 2). Original copies of wireline logs were obtained for several wells in the study from the Oklahoma City Geological Society Mid-Continent Log Library. Petrographic analysis was conducted on ninety-eight thin sections made from samples taken from the cores. Cathodolu- minescence (CL) petrography was carried out using a CITL CL8200 MK5-1 cold cathode optical CL system mounted on an Olympus BX 41 microscope equipped with a “Q-imaging” 5-megapixel cooled, low-light, digital camera system.
Fluid inclusion microthermometric mea- surements were performed on doubly polished thick sections that were prepared using techniques designed to avoid exten- sive heating of samples (Goldstein and Reynolds, 1994). Measurements were made using a Linkam THMSG 600 heat- ing and cooling stage. Errors of homog- enization (T h ) and last ice melting (T m ) temperatures were ±1.0°C and ±0.3°C, respectively based on analysis of synthet- ic fluid inclusions (Shelton and Orville, 1980). Inclusions analyzed in this study were aqueous, two-phase, primary inclu- sions (classification of Roedder, 1984). T m measurements were used to calculate sa- linities using equations of Bodner (1993). Carbon and oxygen isotope composi- tions were measured at the University of Miami Stable Isotope Laboratory using a Finnigan-MAT 251 mass spectrometer. Standard error was reported relative to the Vienna Pee Dee Belemnite (VPDB) stan- dard for δ 13 C and δ 18 O and was less than ±0.08‰ based on replicate measurements
(Swart and Eberli, 2005). Ratios of 87 Sr/ 86 Sr were measured using a Thermal Ionisation Mass Spectrometry (TIMS) at the University of Kansas Radiogenic Isotope Laboratory and have errors of 0.000014 at 95% confidence level. RESULTS Lithology: Core sections (whole and discontinuous slabs) of Arbuckle strata in southwestern Missouri and northern Okla- homa were studied including: SCU CO2, St. Joe 55W84, Amoco SHADS No. 4 (SHADS 4), Williams American Airlines 2 (WAA 2), Osage C-1, MH Meisner 2, and HC Wichert 1 (Figs. 2 and 3). These cores lie on an east to west section extend- ing from just west of Springfield, MO to just west of Fairview in central Major Co., OK. Emphasis was placed on the St. Joe 66W84 and SHADS 4 locations as these cores both extend from the surface to Pre- cambrian basement (Fig. 3). Descriptions of the St. Joe 66W84 core are available in Overstreet et al. (2003; see also Over-
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Figure 2. Map showing locations of cores used in this study. The location of Arbuckle oil production is shown.
Figure 3. Stratigraphic fence showing cores used for this study.
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Carbonate Diagenesis OfThe Arbuckle Group North Central OklahomaTo Southeastern Missouri, cont. Oil and Gas Exploration
street, 2000) and an unpublished St. Joe Minerals Corp. core description by Hol- land available at the Missouri Geological Survey. A lithology log of the SHADS 4 core with a full description is available in Derby et al. (1991). Additional descrip- tions of all of the cores used in this study are available in Temple (2013) and Bailey (2018).
The Cambrian-Ordovician Arbuckle sec- tion can be characterized as a series of third order sequences made up of meter- scale 4 th and 5 th order cycles (Overstreet et al., 2003). The 4 th and 5 th order cycles typically include subtidal burrowed mud- stones and oolitic grainstones overlain by peritidal lithologies consisting of throm- bolite boundstones, cyanobacterial stro-
matolites, microbial laminites (Fig. 4A & B), and frequently, in the Roubidoux Formation, quartz sandstones. The cycles typically are capped by desiccation cracks and chert pebble breccias (Fig. 4A), which have been interpreted as evidence of sub- aerial exposure (He et al., 1997; Over- street et al., 2003).
Figure 4. Arbuckle lithologies observed in cores. A. St. Joe 66W84 core, Cotter Dolomite, top core section is dolomitized oolitic grainstone. Lower core section contains a sedimentary breccia (left) at the top of a cycle, microbial laminates, and chert pseudomorphic after gypsum (right). B. SHADS 4 core, Cotter-Powell Dolomite, core section through a dolomitized microbial stromatolite. C. SHADS 4 core, Gasconade Dolomite, solution enlarged vugs in a dolomitized microbial laminate lined with coarse crystalline saddle dolomite cement. D. SHADS 4 core, Jefferson City Dolomite, dolomitized grainstone containing isolated solution enlarged vugs lined with cm scale saddle dolomite crystals.
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Petrology: All of the cores examined in this study are completely dolomitized ex- cept for those lithologies that have been replaced by chert. Chert frequently replac- es oolitic grainstones in these units (Fig. 5A), preserving the original limestone depositional texture. Chert nodules, are observed mostly in the Cotter, Jefferson City, and Gasconade dolomites, and fre-
quently have a similar shape and texture as gypsum and anhydrite nodules (Fig. 4A and 5B). Visually estimated porosities in dolomite lithologies range from 5 to 10% intercrystal with moldic, fenestral, frac- ture, vug, and occasionally, breccia poros- ity ranging up to 20%. Open space poros- ity frequently is filled by coarse (>0.2mm) crystalline rhombic and saddle dolomite
cement (Fig. 4C & D) that is occasion- ally followed by calcite cement. Less frequently void space is lined by druzy quartz crystals, particularly in the lower part of the Arbuckle. Occasionally sulfide minerals (pyrite, sphalerite, and galena) are observed either as open space filling crystals or replacing carbonate lithologies.
Figure 5. Photomicrographs of host lithologies. A. St. Joe 66W84 Core, Jefferson City Dolomite, chert replacing oolitic limestone. Plane polarized light. B. St. Joe 66W84 Core, Cotter-Jefferson City Dolomite. Fine to medium crystalline planar dolomite replacing a brecciated microbial laminate with heavy stylolites. Chert, pseudomorphic after gypsum, is visible in the upper left quadrant of the photomicrograph. Plane polarized light. C. HC Wichert 1 Core, near top of the Arbuckle (≈ Cotter Dolomite). Very fine crystalline planar-s dolomite replacing microbial laminates. A vertical fracture filled by dolomite cement is visible in the center. Plane polarized light. D. Osage C-1 Core, (≈ lower Roubidoux – upper Gasconade dolomite. Coarse crystalline nonplanar dolomite replacing burrowed mudstone. Red arrows indicate quartz sand grains. Cross polarized light.
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Carbonate Diagenesis OfThe Arbuckle Group North Central OklahomaTo Southeastern Missouri, cont. Oil and Gas Exploration
Figure 6. Open space filling cement in Arbuckle carbonates in southwestern Missouri. A. SCU-CO2 Core, Cotter Dolomite. Dolomite cement lining a vug. Cross polarized light. B. CL image of (A). Note the four distinct compositional zones of Voss et al. (1989). C. St. Joe 66W84 Core, Eminence- Potosi formation. Dolomite cement lining a vug. Cross polarized light. D. CL image of (C), three of the four compositional zones of Voss et al. (1989) are visible. Zone 2 is represented by a thin non-CL zone occasionally visible between Zone 1 and the multi-banded Zone 3. E. SCU-CO2 Core, Cotter Dolomite. Open space filling dolomite and calcite cement filling a vug. Cross polarized light. F. CL image of (E) showing bright yellow and dull orange, banded, calcite cement.
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Replacement dolomite in subtidal, bur- rowed mudstones is typically unimodal, very fine to fine crystalline (<0.01 mm) planar-s dolomite (dolomite textural clas- sification of Sibley and Gregg, 1987) (Fig. 5C). Replacement dolomite in sedi- mentary breccias and subtidal to inter- tidal burrowed-skeletal wackestones and pelletal-skeletal packstones display poly- modal, fine to medium crystalline (<0.05 to 0.2 mm) planar-e to planar-s dolomite, occasionally with mimically replaced ooids and skeletal grains. Occasionally replacement dolomite is characterized by medium to coarse crystalline (0.1 to >0.2 mm), planar to nonplanar dolomite crystals (Fig. 5D). Typically the planar to nonplanar dolomite replacement texture is observed replacing oolitic and pelletal- skeletal packstones, dolomitic sandstones and microbial laminates. It most frequent- ly is observed with void filling rhombic and saddle dolomite cements as described below. Cathodoluminescence (CL) response of carbonates results from excitation by an electron beam incident on a polished thin section. The color and brightness of CL response is a result of the trace and mi- nor element composition of the carbonate mineral. These trace and minor elements
principally are Mn 2+ (an activator) and Fe 2+ (a quencher). Typically CL is used to reveal subtle changes in composition, and thus fluid chemistry during crystal growth, resulting in a compositional “microstratig- raphy” in the carbonate crystal (Machel and Burton, 1991). The CL response ob- served in fine to medium crystalline (0.05 to 0.2 mm), planar-e to planar-s replace- ment dolomites typically consists of either dull to moderately bright CL with no com- positional zonation or dull to moderately bright CL displaying up to 2 to 3 compo- sitional zones. Replacement dolomite ob- served in dolomitic sandstones and replac- ing microbial stromatolites display similar CL characteristics. Nonplanar dolomite typically displays a mottled uniform to multi-zoned CL response. Replacive chert displays no CL response. Fenestral, vug, and moldic porosity fre- quently is observed in dolomite litholo- gies. Fracture and breccia porosity is ob- served throughout the cores and frequently appears to be enhanced by dissolution (Fig. 4 C & D). Porosity is predominantly filled by coarse crystalline (>0.2mm up to 4.0mm) rhombic and saddle dolomite ce- ment (Figs. 6 & 7) followed occasionally by coarse crystalline, open space filling, blocky calcite (Fig. 6E & F). Less fre-
quently dolomite cement is interspersed with quartz cement (Fig. 7C & D). Do- lomite cements in southwestern Missouri display a distinctive CL zonation pattern consisting of four major compositional zones frequently subdivided by second- ary alternating bright, dull, to dark bands (Fig. 6 B). The compositional cement zonation is similar to the 4-zone CL stra- tigraphy observed northeast of the study area in the Bonneterre Dolomite (Gregg, 1985; Voss et al., 1989). Occasionally one or more of the compositional zones will be missing, typically zones 2 and 3, re- sulting in an incomplete CL stratigraphy (Fig. 6 D). Calcite cement displays bright to less bright CL as thin multiple zones (Fig. 6 F). Quartz cement displays no CL response (Fig. 7 D). In the lower part of the SHADS 4 cores in eastern Oklahoma the CL compositional zonation observed in dolomite cements from the lower part of the Arbuckle is similar to that observed in southern Missouri (Fig. 7A& B). In the upper part of the Arbuckle section in the SHADS 4 and in the WAA 2, MH Meisner 2 and HC Wichert cores dolomite cements occupying open pore spaces (fractures, vugs, molds) display a complex zonation of up to six compositional zones alternat- ing from dull to bright CL response (Fig. 7 C, D, E & F).
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January ~ February 2020 | Page 17
Figure 7. Open space filling cement in Arbuckle carbonates in northern Oklahoma. A. SHADS 4 Core, near the bottom of the Gasconade Dolomite. Dolomite cement filling a vug. Cross polarized light. B. CL image of (A) displaying the four compositional zones of Voss et al. (1989). C. SHADS 4 Core, lower Jefferson City Dolomite. Saddle dolomite cement lining a vug. Cross polarized light. D. CL image of (C) displaying a series of dull to bright compositional zones. Note the quartz cement (Q), displaying no CL response, precipitated after initial dolomite cementation but prior to the main stage of saddle dolomite precipitation. E. Meisner MH 2 Core. upper Arbuckle (Cotter-Powell formations). Dolomite cement lining a vug. Cross polarized light. CL image of (E) displaying several bright and dark compositional bands followed by a prominent non-CL zone filling most of the vug.
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Fluid inclusion microthermometry: Two-phase (liquid plus vapor) aqueous inclusions were observed in dolomite and calcite cements. Measured inclusions range in size from 2 to 10 μm with an av- erage of about 6 μm. Smaller inclusions were observed but due to poor optical res- olutions were not measured. No petroleum inclusions were observed in the study area. The inclusions typically contain ~2-10% vapor volume at room tempera- ture (21°C) and vapor bubble movement at room temperature was common. Mea-
surements were made for vapor homog- enization temperature (T h ), ice melting temperature (T m ) and eutectic temperature (T e ) where possible. Two hundred fourteen fluid inclusions were analyzed either for T h , T m or both. Out of those, one hundred twenty-seven fluid inclusions, for which both the T h and T m values were obtained, were grouped as assemblages and plotted (Table 1, Fig. 8). Tables with individual fluid inclusion measurements are avail- able in Temple (2016) and Bailey (2019).
Homogenization temperatures (T h ) of pri- mary fluid inclusions in dolomite range from 80° to 169°C. Final ice-melting temperatures (T m ) range from -3.7 in the St. Joe 66W84 core to -35.7°C in the MH Meisner 2 core with calculated salini- ties of 6.0 and 32.6 wt. % NaCl equiva- lent respectively. All of the cores studied display two fluid end members: a lower temperature (80 to120°C) fluid with mod- erate to high salinity (17-33 wt. % NaCl equivalent) and a higher temperature (120 to162°C) fluid with a moderate salinity
Figure 8. Fluid inclusion assemblages measured for this study plotted as homogenization temperatures (T h
) vs. wt.% NaCl equivalent calculated
from final ice melting temperatures (T m
). Assemblages are calculated from the average T h
and salinity of a group of fluid inclusions proximal to one
another that are interpreted to have formed at the approximately the same time from the same fluid. Only inclusions where both T h and T m are measured are used to calculate averages for assemblages. Three fluid end members (labeled) are apparent from the distribution of these data.
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Table 1. Fluid inclusion assemblages. Only inclusions where both T h and T m are measured are used to calculate averages for assemblages. For values of all 214 fluid inclusions analyzed see Temple (2016) and Bailey (2019).
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(18 to 26 wt. % NaCl equivalent). A third fluid end member was observed in samples from the St. Joe 66W84 core comprised of a higher temperature (122 to 169°C) low salinity (6 to 17 wt. % NaCl equivalent) fluid. Eutectic (first melting) temperatures in dolomite hosted fluid inclusions, where they were measured, range from -43.4° to -34.5° C. Only three calcite hosted fluid inclusions (belonging to the same assemblage) were measured in this study (SCU CO2 core). Calcite T h values range from 107.4 to 115.6° C and T m values range from -23.1 to -27.8°C with calculated salinities of 24.4 to 27.29 wt. % NaCl equivalent re- spectively. Isotope Geochemistry: Very fine to me- dium (<0.05 to 0.2mm) crystalline planar dolomites replacing microbial laminate, burrowed mudstone, and grainstone lithol- ogies display carbon and oxygen isotope values ranging from δ 13 C = -4.7 to -0.5‰ and δ 18 O = -6.4 to -3.0‰ (Table 2, Fig. 9A). Medium to coarse (0.1 to >0.2mm) crystalline planar to nonplanar dolomite replacing these lithologies display carbon and oxygen isotope values ranging from δ 13 C = -3.8 to -1.1‰ and δ 18 O = -8.0 to -5.3‰. These values are generally more depleted with respect to δ 13 C and slightly enriched with respect to δ 18 O when com- pared to those of He et al. (1997) for the Upper Cambrian – Lower Ordovician sec- tion in the Ozark region of Missouri to the northeast of the study area. However, the data of He et al. (1997) was weighted by heavier sampling of the Upper Cambrian part of the section, which was responsible for the more enriched carbon and depleted oxygen values in that study. A weak, but significant, trend of more depleted oxygen values downward in the section was ob- served in this study for the St. Joe 66W84 core. However, a similar trend was not ob- served in the SHADS 4 core, where data also was collected covering the entire sec- tion. No other trends in carbon and oxy- gen isotope values were observed in the cores sampled for this study.
Dolomite cements display δ 13 C values ranging from -3.5 to -0.6‰ and δ 18 O val- ues ranging from -10.5 to -4.2‰ (Fig. 9A). Values of δ 13 C or δ 18 O in dolomite cements displayed no significant trends in the vertical section when compared with depth. These values are largely similar to carbon and oxygen isotope values mea- sured for dolomite cements by He et al. (1997). Data was obtained for a single calcite cement sample from the upper part of the Arbuckle section in the SCU CO2 core: δ 13 C = -3.2 and δ 18 O = -9.0. Fine crystalline planar replacement do- lomite displays values of 87 Sr/ 86 Sr rang- ing from 0.7099 to 0.71909. Values of 87 Sr/ 86 Sr measured for medium to coarse (0.1 to >0.2mm) crystalline planar-non- planar replacement dolomite range from 0.7095 to 0.7097. Values of 87 Sr/ 86 Sr for coarse crystalline saddle dolomite cement range from 0.7090 to 0.7103 (Fig. 9B). All of these values, except for two dolomite cement samples, are higher than would be expected for dolomite precipitated in equilibrium with Lower Ordovician sea- water (Veizer et al., 1999; Shields et al., 2003). DISCUSSION The development of carbonate petro- graphic textures observed in this study over paragenetic time is shown in Figure 10. The diagenetic events resulting in the observed carbonate textures are catego- rized as early and late (burial) and are dis- cussed in depth below. Early Diagenesis: Sedimentation in the Arbuckle Group in southwestern Missouri and northern Oklahoma was dominated by limestone deposition, with periods of increased siliciclastic input in response to meter-scale sea level changes (He et al., 1997; Overstreet et al., 2003). Repeated sea level change likely resulted in alternat- ing marine and fresh water cementation, dissolution of limestone and resultant for- mation of mold, vug, and breccia porosity. Evidence for extensive karst development
has been documented in the Arbuckle, especially associated with third order sea level falls (He et al., 1997; Overstreet et al., 2003). This resulted in dissolution along fractures, large scale brecciation associated with sink holes, and unconfor- mity related breccias (Lucia, 2012; Fritz et al., 2012). Early diagenesis of the original Arbuckle limestone sediments involved both silici- fication and dolomitization (Fig. 10). The timing of silica replacement likely was prior to dolomitization, in most cases, as the micro texture of allochems, such as ooids are preserved (Fig. 5A). Dolomiti- zation largely destroyed micro textures and much of the depositional textures in the original Arbuckle limestones. Fre- quently, however, many of the larger scale sedimentological features such as microbial laminations, stromatolites, bur- rows, and occasionally, ooids and skeletal grains, were partially preserved by mim- ic replacement by dolomite (Sibley and Gregg, 1987). Planar dolomite textures (Fig. 5B) replacing Arbuckle limestones are interpreted as syndepositional in the case of very fine to fine (<0.05 to 0.1mm) crystalline dolomite replacing microbial laminates to early diagenetic in the case of fine to medium (0.05 to 0.2mm) crys- talline dolomite replacing subtidal grain- stones and mudstones. These textures are typical of dolomites that have formed un- der relatively low temperature and pres- sure conditions (Sibley and Gregg, 1987). Carbon and oxygen isotope analyses of fine crystalline planar dolomite in the Ar- buckle displays relatively enriched d 18 O values (Fig. 9A). Assuming an early dia- genetic temperature of 30°C, reasonable considering the tropical location of the re- gion during the Ordovician (Derby et al., 2012), and the dolomite-water fraction- ation factor of Woronick & Land (1985), water in equilibrium with early diagenetic dolomite sampled in this study should range from d 18 O ≈ -7.0 to -4.0‰ VSMOW . This is enriched with respect to the calcu- lated d 18 O values of Early Ordovician sea-
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Table 2. Isotope data. All δ 18 O and δ 13 C values are expressed as ‰ VPDB. Textural terms are from Sibley and Gregg (1987). Planar and nonplanar dolomites all replace preexisting limestone or are recrystallization products of preexisting dolomite. Dolo- mite and calcite cement are void filling. Crystal sizes range from: very fine = <0.05mm, fine = 0.05 to 0.1mm, medium = 0.1 to 0.2mm, and coarse = >0.2mm. Very fine to medium crystalline planar dolomites were typically regarded as early diagenetic and medium to coarse planar and nonplanar dolomites were inter- preted as late diagenetic replace- ments of limestone or recrystal- lized early diagenetic dolomite.
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Figure 9. A. Carbon and oxygen isotope data for early replacive dolomite (very fine to fine crystalline planar), late replacive dolomite (medium to coarse crystalline planar to nonplanar), and late (void filling rhombic and saddle) dolomite cement. One value for late calcite cement also is shown. B. Oxygen isotope values plotted against 87 Sr/ 86 Sr values. Fields for calcite in equilibrium with early Ordovician seawater (Shields et al., 2003) are shown in blue in both A and B.
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Oil and Gas Exploration Carbonate Diagenesis OfThe Arbuckle Group North Central OklahomaTo Southeastern Missouri, cont.
water (Shields et al. 2003) by 1 to 4‰ and is precisely the values expected for sea- water evaporated up to the point of gyp- sum precipitation. Depleted d 13 C values observed in some of the samples analyzed (Fig. 9A) are consistent with oxidation of organic matter in the restrictive peritidal setting (Oehlert and Swart, 2014) and ear- ly diagenetic recrystallization of syndepo- sitional dolomite in the zone of microbial sulfate reduction (Hudson, 1977). Given the evidence for evaporites through- out the Arbuckle section, such as chert nodules that mimic gypsum (Figs. 4A & 5B), gypsum and halite casts, and solution collapse features at the top of cycles (He et al., 1997; Overstreet et al., 2003; Fritz
et al., 2012; Palmer et al., 2012), early dolomitization likely occurred through an evaporative pumping mechanism (Hsü and Siegenthaler, 1970) in the peritidal sections. In the case of subtidal sediments, refluxing brines that were generated in the overlying peritidal sections likely dolomi- tized the limestones (Adams and Rhodes, 1960). Holocene dolomitization by evap- orated seawater in sabhka environments has been observed in the Persian Gulf region (McKenzie et al., 1980; Patterson and Kinsman, 1982) and produce litholo- gies that are similar to the Ordovician rocks studied here. Late Diagenesis: Dolomites exhibiting medium to coarse (0.1 to >0.2mm) crys-
talline planar to nonplanar textures in the Arbuckle section are interpreted as later diagenetic in origin (Fig. 5D; Fig. 10). Nonplanar dolomite observed in this study likely is the product of recrystallization of early replacive dolomite or, possibly in some cases, dolomitization of previously undolomitized limestone at temperatures greater than 60°C (Sibley andGregg, 1987; Gregg and Shelton, 1990). These late dia- genetic textures frequently are associated with solution-enlarged vugs, fractures, breccias, and other megaporosity (Fig. 4C & D) that is filled by large rhombic and saddle dolomite cement and occasionally followed by coarse blocky calcite cement (Figs. 6, 7, & 10). The megaporosity like- ly provided pathways for late diagenetic
Figure 10. Paragenesis of replacement lithologies and void filling cements. Late diagenetic quartz cement (not shown) occasionally is observed either predating or postdating dolomite cement.
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fluid flow. CL zonation observed in void- filling dolomite cements (Figs. 6 & 7) re- sult from changing chemical composition (Fe 2+ and Mn 2+ ) of the precipitating fluids indicating geochemically evolving flu- ids moving through the rock (Gregg and Shelton, 2012). The consistency of the CL zoning patterns observed, especially in the Ozark (southwestern Missouri and north- eastern Oklahoma) portions of the study area indicates the regional nature of these fluids (Voss et al. 1989). The distribution of fluid temperatures and salinities observed in this study (Fig. 8) are remarkably similar to those observed by Shelton et al. (1992) for the Bonne- terre Dolomite to the northeast and the re-
sults obtained in this study are interpreted similarly. Low eutectic temperatures (T e = -43.4° to -34.5° C) measured indicate that these fluids were not simple NaCl brines but complex saline brines consist- ing of Ca, Mg, Na chlorides and sulfates. The fluid inclusion data indicates three geochemically distinct fluid end-members with a range of intermediate fluid com- positions (Fig. 8). These fluid end mem- bers can be interpreted to indicate either mixing of two end-member saline fluids, shown as Fluids 1 and 2 in Figure 8. Inter- mediate fluid temperatures and salinities in that interpretation formed from a mix- ing of the fluids as they moved through the study area. Alternately, the data may be interpreted as a cooling trend of one
fluid. A third high temperature, low salin- ity fluid was observed in the lower part of the Arbuckle section only in southwestern Missouri (Fig. 8). This fluid also was ob- served by Shelton et al. (1992) at the base of the Bonneterre Dolomite to the east of the study area. This fluid may have origi- nated in the Reelfoot Rift (Keller et al., 2000) and did not migrate westward into the Oklahoma portion of the study area. Carbon and oxygen isotope geochemis- try of the void filling dolomite cements (Fig. 9A) can be interpreted in light of the fluid inclusion data discussed above. Us- ing a temperature range of 90° to 150°C for the precipitating basinal water and the dolomite-water fractionation factor of
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Oil and Gas Exploration Carbonate Diagenesis OfThe Arbuckle Group North Central OklahomaTo Southeastern Missouri, cont.
Woronick & Land (1985), water in equi- librium with void filling dolomite cements sampled in this study ranges from d 18 O ≈ -1.0 to +13.0‰ VSMOW . These values are not consistent with any Paleozoic seawa- ter and likely represent an evolved basinal fluid with a possible seawater origin ( e.g. Shelton et al. 2009). Carbon and oxygen values for planar to nonplanar replacive dolomite, interpreted to be late diage- netic, are generally intermediate between void filling dolomite cements and early replacive dolomite. As coarse (>0.2mm) planar to nonplanar textures likely rep- resent a recrystallization texture they are expected to display the late diagenetic iso- tope signature buffered by the early diage- netic signature. Strontium isotope data for the study area is more problematic. A majority of the 87 Sr/ 86 Sr ratio values of void filling dolo- mite cements as well as values for replacive dolomite indicate a continental basement or basement-derived sedimentary rock signature ( 87 Sr/ 86 Sr ratios > 0.7095) and is higher than would be expected for carbon- ates precipitated in equilibrium with early Ordovician seawater (Veizer et al., 1999; Shields et al., 2003). An Ordovician sea- water signature would be expected for the early replacive dolomites. An explanation that can be offered for these observations is that all of the dolomite studied are re- set with respect to evolved basinal fluids that derived their 87 Sr/ 86 Sr composition from continental basement or sedimentary rocks derived from continental basement. The findings of this study are consistent with previous research suggesting basin fluid flow events on the Midcontinent of North America corresponding with Ouachita (Alleghenian coeval) orogeny tectonism during the Late Pennsylva- nian and Permian Periods (Bethke and Marshak, 1990; Viets and Leach, 1990; Shelton et al. 1992; Appold and Garven, 1999). Basinal brines are thought to have migrated northward from the Arkoma and/or the Anadarko basins by means of
a gravity (topographical) driven fluid flow system (Appold and Garven, 1999). Saline fluid inclusions observed in open space filling calcite and dolomite cements in overlying Mississippian strata in south- western Missouri and in northern Okla- homa (including the STACK play of north central Oklahoma) bear a striking resem- blance in both temperature and salinity to fluid inclusions observed in this study (Mohammadi et al., 2019a; 2019b; Jaisw- al et al., 2019). It is very likely that the saline Mississippian fluids were sourced from the underlyingArbuckle section. The MVT deposits in the overlying Mississip- pian strata and in Cambrian – Ordovician strata northeast of the study area likely were precipitated by saline fluids that mi- grated from the Arkoma basin and through the study area as a result of the Allegha- nian-Ouachita tectonism during the Late Pennsylvanian to Permian (Leach, 1994; Appold and Nunn, 2005; Stoffell et al., 2008). This tectonic activity also led to the doming of the Ozark Uplift in flexural response to thickening of the Ouachitas, causing downwarping in the Arkoma ba- sin, setting the stage for gravity-driven fluid flow from the basin to the study area (Stoffell et al., 2008). Since the MVT de- posits are relatively close to the study area and have similar mineralogy, isotopic, and fluid inclusion compositions it is inferred that the fluids that precipitated carbonate cements in the study area have a similar origin. Later strike-slip faulting and re- activation of basement faults during the Laramide orogeny may have allowed for additional migration of high salinity and highly radiogenic fluids to be pumped from the underlying formations into the Arbuckle Group and possibly into the overlying strata (King, 2013). Petroleum fluid inclusions are rare in the Arbuckle Group. Neither Shelton et al. (1992) or this study observed petroleum fluid inclusions in southern Missouri or northeastern Oklahoma. King (2013) ob- served primary, pseudosecondary, and
secondary petroleum fluid inclusions in the Arbuckle in saddle dolomite cements in southern Kansas. That study postulated the migration of petroleum during and after saddle dolomite precipitation. Al- though the evidence is not widespread, the explanation of King (2013) may offer in- sight into the timing of petroleum migra- tion in the Arbuckle Group. CONCLUSIONS The Arbuckle Group was deposited as a series of meter-scale carbonate cycles on a shallow water platform, typically con- sisting of subtidal facies overlain by peri- tidal facies. Early dolomitization likely occurred through an evaporative pump- ing mechanism in the peritidal sections as indicated by evidence for evaporites and enriched δ 18 O values in early replacive do- lomites. Refluxing brines that were gener- ated in the peritidal sections likely dolo- mitized the underlying subtidal facies. During burial, basinal fluids migrated through porosity created by dissolution during sea level falls and fractures created during burial. These fluids recrystallized early replacement dolomite and precipi- tated void filling rhombic and saddle dolo- mite cements, authigenic quartz cements, and calcite cement. Fluid inclusion and isotope data from re- crystallized replacive dolomite and dolo- mite cement is consistent with an evolved basinal fluid that interacted with continen- tal basement or sediments derived from basement. These fluids are similar to in- cluded fluids observed in overlying Mis- sissippian strata and MVT ore deposits in the Ozark region. The data presented in this study are con- sistent with the prevailing hypotheses of migration of basinal fluids by means of a gravity driven flow system originating in the Arkoma and/or Anadarko basins dur- ing the Ouachita orogeny.
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