Shale Shaker Vol 70, No 3 May-June 2019

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Tectonic joint size, abundance, and connectivity: Examples from Woodford Shale and Hunton Limestone and Much More

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The Journal of the Oklahoma City Geological Society Volume 70 Number 3

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. OCGS Board Officers President – Stephen Ladner Vice President /Membership Chair – Patrick Kamann Secretary – Cole Hinds Treasurer & Finance Committee Chair – Drew Dressler Councilor & Governance Chair – Herb Martin Social Committee Chair – Galen Miller Education Committee Chair – Rosie Gilbert Website Chair – Julian Michaels Shale Shaker Editor/Publications Chair – Dan Costello

Directors Doug Bellis Lesley Evans Eric Kvale Britni Watson Mallory Zelawski OCGS OFFICES 10 NW 6th St. Oklahoma City, OK 73102 Phone: (405) 235-3648 | Fax: (405) 235-1766 Website:

AAPG Mid-Continent Section Representative H.W. (Dub) Peace, Geologist and AAPG Mid-Continent Section Past President Past President – John Brett

May ~ June 2019 | Page 95

The Journal of the Oklahoma City Geological Society Table of Contents

Shale Shaker Features

98 Letter from the President OCGS: Happy Birthday OCGS ; Steve Ladner, President, OCGS Board of Directors


What You Missed: OSU York Donation 2019 MCGL Recipients

112 Tectonic joint size, abundance, and

99 Letter from the Editor: What’s on Your Bookshelf?; Dan Costello, Editor

connectivity: Examples from Woodford Shale and Hunton Limestone; Sayantan Ghosh, University of Oklahoma; Roger M. Slatt, University of Oklahoma 138 Discussion of: My Favorite Outcrop(s): The Woodford Shale SH-77D: Le Couer de Arbuckle Mountains, O.K. ; Sayantan Ghosh, University of Oklahoma; Daniela Becerra, University of Calgary; Roger M. Slatt, University of Oklahoma


Upcoming Events


OCGS Membership & New Members


OCGS Financial Statements


Memorial: Herbert G. Davis


Memorial: William Vernon York

144 State of the Industry; Dan Costello

108 Memorial: Robert W. Allen; Joel Alberts; Bob Newman


Advertisers Index


What You Missed: Clay Shoot 2019

About the Cover

Theresa Andrews created the cover of the Shale Shaker. COVER PHOTO: Fractures in the Hunton Limestone exposed in the Jennings Quarry near Fittstown, Oklahoma. Photo credit: Sayantan Ghosh.

Page 96 | Volume 70 Number 3

ISSN: 0037-3257 Shale Shaker is the registered trademark of the Journal of the Oklahoma City Geological Society. The Shale Shaker (USPS 000- 771) is published bi-monthly from January through December by the Oklahoma City Geological Society, 10 NW 6th Street, Okla- homa City, OK 73102. Annual membership dues for the Oklahoma City Geological Society are $100.00 and a subscription to the Shale Shaker is included with each membership. For non-members, the subscription rate is $60.00 in the U.S.A. and $80.00 for- eign per year. Layout and typesetting by Theresa Andrews, Visual Concepts and Design Inc., Oklahoma City. Send email address changes to: Shale Shaker , 10 NW 6 th Street, Oklahoma City, OK 73102 or All materials herein are copyrighted by the Oklahoma City Geological Society. The purpose of the Shale Shaker is two-fold: To keep members informed of the activities of the Society and to encourage the ex- change and dissemination of technical information related to the geological profession. The Shale Shaker welcomes contributions from all sources, but does not intend to adopt any position nor endorse any specific policies through this publication; instead, it endeavors to provide a neutral forum for exchange of ideas and technical discussions amongst professionals serving the geosci- ences. It is committed to serve the geoscience community with scientific, technical and other related information, so to encourage professional development while not endorsing specific policies. DISCLOSURE AND DISCLAIMER: The views, comments, and opinions expressed in the articles and columns of the Shale Shaker are those of the respective authors and not necessarily those of the OCGS or the staff of the Shale Shaker . Neither the OCGS, nor the staff of the Shale Shaker , make any representation as to the accuracy or correctness of the material presented within the Shale Shaker .

May ~ June 2019 | Page 97

Letter from the OCGS President

By: Steve Ladner, President, OCGS Board of Directors

Board has been planning a strategy for the next 100 years. We believe that the soci- ety serves its members with networking opportunities, technical education oppor- tunities, and a superb technical journal. Networking is so important in our indus- try, it is a chance to compare notes, make new friendships and to hear about job or consulting opportunities. OCGS offers a shrimp boil, clay shoots, a golf tourna- ment, a Christmas party and luncheons to make new friends and business connec- tions. The technical education program offers many chances to grow in your pro- fession. The Board believes that as we ap- proach our next 100 years, we believe to advance our profession, continuing edu- cation is the defining element and that we should offer 6 to 8 courses per year. This creates a niche for smaller companies and companies on budgets to get great quality continuing education without travel ex- penses and at competitive prices. What issues are ahead of us as we approach our 100 th birthday? Well Membership has taken a big hit since 2015. We have lost 573 members since 2015, basically a 50% hit. We struggle with retaining members under 40, with 61% of our members com- ing from two groups: the 30-39 and the 60-69 age group. We are looking at ways to increase membership. We are offering courses with a more general appeal to at- tract membership outside of OKC, we will be doing a welcome back in the fall and open house with Board members and will encourage you to come and bring a non-

member, we are looking at an auto pay on website, and going to both OSU and OU to meet students and get them signed up early. We also believe a mentoring program will be a much needed element to help pass the torch and to not lose the experience base as they retire, 44% of our members are close to retirement age. Another area in mentoring is to do mock interviews in the fall for students at OU and OSU. We did them for OU last year at their request and had a very good response. We will also offer a Panel Discussion this fall, “Stump the Chump”, an opportunity to ask experi- enced people on subjects from geology to leadership. As we gear up for our next 100 years, we do face challenges but there are so many opportunities to grow, readjust and be in position to pass the baton to the next gen- eration of geologists in OKC for the next 100 years. In the interim, don’t miss out on the Jeff Dravis Austin Chalk course in July, and Mudrocks course by Jeff May in October. Also, come and see old friends and make some new ones at the Shrimp Boil in September. As always, we could use your help and please consider volunteering and help us prepare and be ready for the next 100 years. Feel free to contact me at slad- if you would like to talk about the society or have ideas for the next 100.

AAPG was established in 1917, and just celebrated their 100 th birthday. As part of their newly formed mission AAPG started advocating the formation of small local groups to step forward in the growth of the profession, and not many years after that, in 1921, the OCGS was founded. Dr. Irving Perrine was the first president, and contrary to popular belief, I was not Vice President. So over the course of the past 98.5 years, we have seen several gen- erations contribute to the society and gain from the society. In 18 short months, we will be celebrating our 100 th birthday. As we approach that landmark, the OCGS Steve Ladner Happy Birthday OCGS

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Page 98 | Volume 70 Number 3

Letter from the Editor

By: Dan Costello, Editor

geology, Oklahoma, and the oil industry. If you have other books you’d like to sug- gest, I’m always adding to my list – send me a note at! In my Geology 101 class we read excerpts from John McPhee’s Annals of the Former World, based on his travels with geolo- gists across the US along the 40 th parallel, documenting the fascinating geologic his- tories and varied terranes that make up our country. This was enough to intrigue me to read the full book and eventually switch to a geology major. Later in college I read A Short History of Nearly Everything by Bill Bryson, a humorous history of sci- ence stretching from Newton to current day. I was surprised by how many early scientists – the literal “Renaissance Men” – did not let any one label define them but practiced geology as well as botany, math- ematics, and wrote poetry. This makes all scientists today seem pretty pigeon-holed! When I moved to Oklahoma to start a ca- reer in oil and gas, I received a copy of The Prize: The Epic Quest for Oil, Money and Power as part of my orientation at my first job. Written by Daniel Yergin, this is a history of the oil and gas industry deserving of the word “Epic” in its title. The thick size of the book put me off at first, but eventually I picked it up and was subsumed by the wide breadth of stories contained. It is really not a history of the petroleum industry, but a world history told through the lens of oil and how it in- fluences countries, wars, and companies.

This book was great at putting individual events that I’d heard of (the Drake well, the 1973 oil crisis, Spindletop) into a larger context. Published in 1990, it does not capture more recent history. For that, I read The Frackers by Gregory Zucker- man which follows the rise of horizontal drilling and the shale revolution. This was an enjoyable read, especially since it cap- tured a story that I was actively participat- ing in. One of my more recent reads is only tan- gentially related to the oil business – one with the lengthy title of Boom Town: The Fantastical Saga of Oklahoma City, Its Chaotic Founding, Its Apocalyptic Weather, Its Purloined Basketball Team, and the Dream of Becoming a World- class Metropolis by Sam Anderson. This book has no coherent timeline, jumping back and forth between the founding of Oklahoma City and its ongoing revival, both interspersed with pieces on the OKC Thunder’s appearance in the NBAfinals in 2014. Many of the stories from the capi- tal’s early days are comical, and difficult to imagine that such events occurred only 120 years ago – only a few generations. The sections focused on the past 20-30 years were illuminating as well, telling of a city tied to the ups and downs of the oil industry and reflecting the highs and lows over time. So many books, not enough time….

Dan Costello

What’s on Your Bookshelf?

“Books have a unique way of stopping time in a particular moment and saying: Let’s not forget this.” -Dave Eggers It is a rare day when I do not spend some amount of time with my nose in my Kindle e-reader. A bulk of my time spent reading is with science fiction or fantasy sagas, but every now in then I throw in some non- fiction for a change of pace. Not being native to Oklahoma, I’ve done quite a bit of reading into the history of my adopted state and the stories of those who brought the oil and gas industry forward to today. Below are a few of my favorite books on

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May ~ June 2019 | Page 99

Crab Eyes Outcrop on Charon Gardens trail, Witchita Mountains Wildlife Refuge. Accessed from: photo/106563289/charon-gardens-wichita-mountains-wildlife-refuge-crab-eyes. Photo credit: Roger Fritz

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OCGS Events




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OCGS Membership & New Members

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May ~ June 2019 | Page 103

OCGS Financial Statements

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May ~ June 2019 | Page 105


AMemorial to Herbert G. (Herb) Davis

June 23, 1930 - April 21, 2019 Herb was a petroleum geologist who devoted his life to his family, education, science and the energy industry. He was born on June 23, 1930 in Buffalo, New York to George & Pearl Davis. After high school graduation, Herb moved to his mother's home town in Perry, Oklahoma in 1948. He enrolled at Oklahoma A&M College, (Oklahoma State University), where he earned his B.S. in Geology in 1953. During college he was a member of the Sigma Phi Epsilon Fraternity, Men's Honor Society, Sigma Gamma Epsilon, Geology Honor Society, ROTC Honor Society, Society of American Military Engineers and the ROTC Officers Club.  Herb met Shirley Etheredge at Oklahoma A&M in 1952 and they married in 1953 in Fort Belvoir, Virginia. They lived in Heidelberg, Germany while he served his tour of duty as a military geologist and intelligence officer in the U.S. Army Corp of Engineers from 1953-1955. He retired a Captain in the U.S. Army Reserve in 1962.

Herbert G. Davis

Upon returning to the U.S. in 1955, he began his career as a petroleum geologist with Stanolind Oil & Gas Co. in Wichita, Kansas. He later worked in Liberal, Kansas and Oklahoma City, Oklahoma with the same company, then Pan American Petroleum Corpora- tion, which became AMOCO.  He resigned in 1967 and became a consulting petroleum geologist. Herb and his long-time friend, Bob Northcutt of Ponca City, formed "Davis & Northcutt" Consulting Geologists in 1968. They also operated as Westside Service Company, then D-N-C Exploration Company, and Davis - Northcutt & CochraneConsulting Geologists from 1968-1972. Herb and Shirley formed "Herbert G. Davis Inc.", an oil and gas exploration company in 1973, which they operated until 1988 with oil & gas production in Okla- homa, Kansas, Texas, Kentucky, Louisiana, & Mississippi.  Herb was a people person and enjoyed friends and colleagues throughout his life. He was networking before it was in vogue, truly a man of vision before his time. He believed in and loved participating in his profession and became a member of the American Association of Petroleum Geologists in 1956. He served as Chairman House of Delegates, President of the Division of Professional Affairs, Chairman of the Trustee Associates, and was a Director of the AAPG Corporation and Trustee of the AAPG Foundation for 13 years. He received the Distinguished Service Award in 1982, Honorary Membership in 1986, DPA Life Membership in 1995 and was elected a Trustee Emeritus in 1999 and received the Foundation "Chairman's Award" in 2012. In his dedication to support the needs of students who desire to further their studies in the field of geology, Herb and Shirley established the first Presidents Distinguished Scholarship in 1980 for a geology student at O.S.U. In 2006, they established the Herbert G. and Shirley A. Davis Named Grant for a geology student at O.S.U. with the AAPG Foundation.  They also established a scholarship for a geology student at O.S.U. with the Oklahoma Geological Foundation in 2007. These noteworthy actions of "Giving Back" will be the legacy of Herbert G. Davis. In 2009 Herb was honored with the Living Legend Award by the Oklahoma Geological Foundation and in 2019 awarded the Oklahoma State University Boone Pickens School of Geology Super Cowboy Legacy Award in recognition & appreciation for consistent dedica- tion, generosity, and significant contributions to the School.  Herb was a life member of the OSU Alumni Association, and received the Distinguished Alumni Award and Arts & Science Distin- guished Alumni Award in 1990. He served the OSU Foundation Board of Governors twelve years and as a trustee for ten years, serving as Chairman in 1985 and 1991. He also served on the OSUAthletic Council and as an Adjunct Professor in the Arts & Science School of Geology.  Herb & Shirley were members of the First Christian Church of Oklahoma City and moved their membership to Edmond First Christian Church in 2008. In 2015 they relocated to be near family and transferred their membership to First Christian Church in Norman. Herb is survived by his wife, and best friend Shirley of almost 66 years. (June 2019). He is also survived by his daughters and their families. Linda Dorfman & husband Jan of Littleton, Colorado and Teresa Pope & husband Don of Norman. Grandchildren Joe Davis Cobb & wife Hannah of Edmond, George Cobb & wife Courtney of OKC, Karen Dorfman of Littleton, Colorado and Jason Dorfman, wife Claire & great-granddaughter Evelyn of Vancouver, Washington. He is also survived by many life-long friends in the oil industry, Oklahoma State University, and his many affiliations through his interests. In lieu of flowers donations may be made to the Oklahoma Geological Foundation or Oklahoma State University Foundation.

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AMemorial to William (Bill) Vernon York

July 22, 1931 - April 28, 2019  William Vernon York, 87, died April 28, 2019 in Oklahoma City, OK. Bill was born July 22, 1931 in Mountain View, Oklahoma to Everett York and Era Roxie Willis York. Bill graduated high school in Roff, OK as Valedictorian of his class in May 1949. He went on to study at East Central in 1949 to 1950, and was in the Army National Reserves before he mobilized to Camp Polk, LA. Bill was a Ko- rean War Veteran who served his Country between 1950 to 1952 with the 45th Infantry and the 171st Field Artillery as a supply Sergeant, Sergeant York. Bill married Geleeta Kirk his last year of college and graduated from Oklahoma State University with a Bachelor's Geology Degree.  After graduating they moved to Fort Smith, AR where Bill worked for Carter Oil in Fort Smith, AR for 2 years, and then moved to Shawnee, OK to work for Humble Petroleum, which later changed to Exxon. He transferred to Enid, Oklahoma for 3 years, then toAmarillo, TX and back to Oklahoma City, and continued to work for Humble Petroleum for a total of 17 years. In 1972 Bill began to work for Ar-


nold Oil and retired from there in 1996. Bill continued to visit his office for many years and brought doughnuts to his former co-workers.  Bill was an avid vintage car collector and like to restore vehicles. He and other friends started the Central Oklahoma Jaguar Association of which he was a member, along with various other car clubs. Bill is preceded in death by his parents, 4 sisters, Jessie Earl York, Dora Alice Daiker, Nova Dimples Ivy, Dorothy Carmen Etchison.  Bill is survived by his wife of 64 years, Geleeta York, daughter and son-in-law, Missy Tomlinson and Chris Tomlinson, grandson, Cory Tomlinson, his brother and sister-in-law Raymond Peyton and Yvonne Jo York, and many nieces and nephews.  Bill was a member of AAPG and OCGS. Donations can be made to Oklahoma Geological Foundation, or to Oklahoma State University Geological Scholarship Fund.

May ~ June 2019 | Page 107

By: Joel Alberts and Bob Neman Memorial

ATribute to Robert W. (Bob) Allen, 1923-2019

Robert W. Allen was born on April 16, 1923. He was the second of three sons of Dr. and Mrs. Edward P. Allen of Oklahoma City. His older brother, Phil, is deceased and brother Paul lives in Oklahoma City. In 1941, he graduated from Classen High School in Oklahoma City and in September of that year, Bob was one of two from Oklahoma to attend VMI, Virginia Military Institute. On December 8, 1941 he enlisted in the Reserve Corps of the U.S. Army Active Combat Battalion. He was first assigned to the University of Pennsylvania and was then assigned to the 138th Engineer Combat Battalion. They crossed the Rhine and went into Central Germany. After being discharged in 1946, he attended the University of Oklahoma and received his BS Degree in both Zoology and Geology. He was a member of Beta Theta Pi fraternity.

RobertW. Allen

On August 21, 1948, he married Barbara Smith of Oklahoma City. They had three children, Katherine Carr, Robert W. Allen Jr., both of Ardmore OK, and Diane Fuller of Apple Valley, California. There are six grandchildren, four great granddaughters and one great grandson. Bob lost Barbara on January 24, 2007. He later married Francis (Fran) Graffham on November 7, 2010. He is survived by his wife, Fran, and his children, grandchildren, and greatgrandchildren. From 1949 until 1954, Bob worked a a geologist for the Globe Oil and Refining Company in Oklahoma City. In 1954, the family moved to Ardmore where he became Division Geologist for Southern Oklahoma for Continental Oil. In 1962, he opened his office in Ardmore as an independent consulting Petroleum Geologist. Over his long career, Bob received numerous awards: In 1988 he became the 17th Honorary Life Member of the Ardmore Geological Society, an affiliate of the AAPG that has been active in Ardmore since 1921. In 1997, the Mid-Continent section of AAPG gave Bob the Certificate of Merit Award for 55 years of membership. In 2003 Bob received the “Rotarian of the Year” award from the Ardmore Rotary Club. In 2005, The Mid-Continent section of AAPG awarded him the Robey H. Clark Award. and in 2010, the AAPG Special Award was presented to him at the National Meeting in New Orleans. He has also been named an Oklahoma Legend by the Oklahoma Geological Foundation and has received the Distinguished Service Award from the Mewbourne College of Earth and Energy at the University of Oklahoma. Bob served as an officer on many boards including the First Presbyterian Church of Ardmore, the Ardmore Higher Education Center, The Southern Oklahoma Blood Institute, and the Alumni Advisory Council for the School of Geology and Geophysics at the University of Oklahoma. Bob Allen adored the Arbuckle Mountains. He also would rather lead a good field trip than almost anything except drilling a new well. An authority on the Arbuckle Mountains, Bob loved to teach field geology to anyone willing to listen and over about a span of 40 years, he led hundreds of field trips for audiences ranging from scout troops to AAPG past-presidents. One of the highlights of his field-tripping experiences was the day we took Jim Gibbs, Marlan Downey, and John Lorentz to the Lazy S Ranch north of Ardmore. For 25 years, Bob led Halliburton’s new classes of engineers into the Arbuckle Mountains. For 9 hours Bob would take them to the Basal Oil Creek and Woodford Formations, a “dead” Viola quarry, a “live” quarry in the West Spring Creek Formation worked by Mar- tin-Marietta, the Washita Valley fault, Turner Falls, angular unconformaties, and the Goddard Youth Camp Museum south of Sulphur, Oklahoma.

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At this museum, Bob would show the class his magnum opus – his diorama depicting a cross section beneath the East Davis Oil Field. Bob loved to teach people “what is beneath your feet” and was in the process of writing a monograph on the subject at the time of his death on April 29, 2019.. The Summer, 2018, issue of the Sooner Magazine, published by the University of Oklahoma, featured Bob in an article titled “Technol- ogy Rebel and Early-day Wildcatter Stands on Solid Ground.” This statement accurately summarizes his long and illustrious scientific career, as his favorite quote was “You have to look at the rocks to know where you’re drilling.”

The quintessential petroleum geologist and educator, he will be missed by many.

Bob’s passion for the geology of southern Oklahoma and his love for teaching others is best put in his own words. “Rocks are beautiful, and geology is important for everyone to understand, not just geologists.” Andrew Cullen Below is a cross-section by Bob Allen & Bob Neman from an OGS workshop in 2012.

May ~ June 2019 | Page 109

WhatYou Missed

Clay Shoot 2019

Page 110 | Volume 70 Number 3

OSU York Donation 2019 MCGL Recipients

The 2019 MCGL York Donation received by OSU Students Michael Mullen, Travis Boxford and Katelyn Clark are the recipients of the 2019 Mid Continent Geological Library Geleeta & Bill York Scholarship. The $10,000 award was equally divided between these geology students in anticipation of their upcoming OSU Geological Field Camp, a required course in Colorado. The members of the MCGL congratulate you!

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May ~ June 2019 | Page 111

By: Sayantan Ghosh and Roger M. Slatt (University of Oklahoma) Oil and Gas Exploration

Tectonic joint size, abundance, and connectivity: Examples from Woodford Shale and Hunton Limestone

Measuring joint sizes in three dimensions is a challenge, as they are not concurrently exposed in all directions in the outcrops. More often than not, a single fracture's trace (vertical or horizontal or both) or face is partly obscured. Using limited observations to develop discrete fracture network (DFN) models is challenging because the estimation of the invisible or partially visible lengths or heights neces- sitates intelligent approximations. We studied three outcrops/quarries at the western edge of the Arkoma Basin to quantify natural fracture attributes in the

Woodford Shale and Hunton Limestone. Quarry-measured fracture height and ap- erture values were plotted against their cumulative numbers to obtain best-fit ap- erture and height distributions. The frac- ture height distributions were then used as inputs for respective length-height corre- lation equations to obtain fracture lengths. We used the "window sampling method" on fracture height traces to calculate fracture intensities. Fracture connected volumes were then examined using DFN models in FracMan TM Software. Compared to the Hunton Limestone,

Woodford Shale has relatively long and continuous bed-normal joints. The Wood- ford Shale has two predominant joint/frac- ture sets (E-W and NE-SW); the Hunton Limestone has three to four (E-W, NE-SW to N-S, and NW-SE). Woodford Shale E-W average fracture height is roughly twice and aperture roughly half that of the NE-SW fractures, considering fractures with height > 1 m. Unlike the Woodford Shale, the Hunton Limestone has lower dimensional variability among joint/frac- ture sets. Apertures and heights in both formations primarily exhibit exponential or lognormal best fits. Length-height re-

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Figure 1: Location of the outcrop/quarry study areas and a horizontal well used for joint connectivity analysis. Structural features of the field study areas are shown within the dash-outlined box.

lationships exhibit a power law or linear fit. Woodford and Hunton fracture inten- sities range 0.256-0.282 and 0.279-0.344 fractures/m, respectively. Field-measured fracture intensities as simulator input result in fully connected DFNs in both Woodford and Hunton. Half the measured intensities result in a fully connected DFN in the Hunton Limestone but not Woodford Shale. 1. Introduction The Woodford Shale is a prolific hydro-

carbon producing formation in Oklahoma. It is a silica and TOC rich, fractured reser- voir and source rock. The natural fractures present within this formation, even though vital for fluid transport, have not been rig- orously investigated in terms of size and connectivity. The Arkoma Basin ( Figure 1 ) is a prolific petroleum (mainly gas)-producing basin in North America (Suneson, 2012). His- torically, conventional production in this basin has taken place from several for- mations such as the Red Oak Sandstone, the Shapiro Sandstone, the Wapanuchka

Limestone, and the Bigfork Chert (Sune- son, 2012). However, with advanced hori- zontal drilling technology, the Woodford Shale, which is both the source and res- ervoir rock, emerged as one of the main targets (Vulgamore et al., 2007; Keller, 2010). As of 2016, the Woodford Shale in the Arkoma Basin in Oklahoma has pro- duced 1.3 million barrels of oil and ~ 2.5 TCF of gas. Mode I (opening mode) fracture size (ap- ertures, length, and height) manifest great variability which may sometimes traverse several orders of magnitude within a giv-

May ~ June 2019 | Page 113

Oil and Gas Exploration Tectonic joint size, abundance, and connectivity: Examples from Woodford Shale and Hunton Limestone, cont.



Figure 2: Geologic map of the eastern Arbuckle Mountains and the Lawrence Uplift. A) The Wyche Shale Pit, Jennings Quarry, and the Clarita Shale Pit locations are marked both in the geologic map and on the map of Oklahoma in black, red, and green stars respectively. Notice the general NW-SE bed strike trends near the Wyche Shale Pit (dip < 10 o NE) and Jennings Quarry (variable dips), and N-S strike near the Clarita Shale Pit (dip < 10 o E). B) Cross sections along lines DD’, EE’, and FF’. Wyche Shale Pit, indicated by a black star, is situated close to the DD’ section.

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en array (Odling et al., 1999; Gillespie et al., 2001). Fractures may have a central size, with smaller or larger fractures in lesser quantities. This type of size restric- tion is termed a "characteristic size distri- bution" (Gillespie et al.,1993; Hooker et al., 2012). Alternatively, fractures may be devoid of a characteristic distribution and exhibit a distribution such as a power-law size distribution (Gillespie et al., 2001; Ortega et al., 2006) We performed the DFN modeling in Frac- Man TM Software which was previously employed by Shuttle et al. (2000), Der- showitz (2006), Dershowitz et al. (2010), and Rogers et al. (2014). Solely outcrop data was used in this study because core, image log, and seismic data are not avail- able. Even if other datasets were available, outcrop studies must be included as con- straints on joint sizes. According to Ah- madhadi et al (2008), Fischer et al (2009), Barbier et al. (2012), and Beaudoin et al. (2012), due to limited visibility of frac- tures in core and image logs, outcrops are valuable in the study of natural fractures. Joint length-height relationship has not been the focus of substantial joint-relat- ed literature. Therefore, our first focus is to shed light on this geometric aspect of joints, in addition to quantifying natural fracture aperture and intensity using out- crop observations in a contiguous shale and carbonate rock sequence. In this study, we have also demonstrated the use of pho- tographs acquired from quarry walls to build natural fracture models without re- sorting to the use of equipment such as LI- DAR scanners, which are expensive and require substantial data processing times. Additionally, scarce literature is avail- able on joint connectivity using software modeling on data derived from the field. Therefore, our second focus is to use the outcrop-derived information to build DFN models to realize natural fracture con- nectivity levels at different fracture in- tensities. These two relatively unexplored parameters related to geometry and con-

nectivity will further our understanding of joints in shales and carbonates. Finally, in the future, our DFN model may be used as a geologic model for hy- draulic fracturing simulation. Figure 1 (map of Oklahoma), shows the location of a horizontal treatment well drilled within the Woodford Shale in the Arkoma Basin. It is situated 20-25 miles (32-40 km) east of the outcrop/quarry measurement ar- eas. In this particular treatment well, the geologic formations confining the field microseismic cloud, i.e., the Caney Shale, Sycamore Limestone, Woodford Shale, Hunton Group Limestone, Sylvan Shale, Viola Group Limestone, and Bromide Formation are shown in Figure 2A. The details on microseismic cloud geometries associated with this treatment well may be found in Neuhaus (2011). Hydraulic frac- turing simulation is beyond the scope of this study. However, sequential steps lead- ing up to geologic/DFN models (usable for hydraulic fracturing simulations) is the focus of this study. These sequential steps are significant in their own right as they reveal important information about the na- ture of natural fractures in the Woodford Shale and surrounding formation. In summary, this study includes outcrop/ quarry fracture data acquisition, building the DFN models, and performing joint/ fracture connectivity analysis aided by the modeled version of an actual horizontal treatment well. 2. Geology As subsurface analogs for the fracture model, we investigated three quarries located on the eastern edge of the Ar- buckle Mountains, i.e., the Wyche Shale Pit (exposes the Woodford and the Mayes Shales), the Jennings Quarry (exposes the Hunton Group Limestone), and the Clarita Shale Pit (exposes the Woodford Shale) marked by stars in Figures 1 and 2 . The Wyche Shale Pit (34°40'22.7"N, 96°38'34.8"W) is located south of the city

of Ada. The structural position is east of the Arbuckle Mountains and west of the Arkoma Basin on a structure identified as the Lawrence Uplift/Horst. The Franks Graben is positioned south of the Law- rence Horst. The rocks in the Lawrence Horst dip gently east, while those in the Franks Graben possess mild westward dip, indicating Mode III or scissor type movement in the Stonewall Fault (Sune- son, 1997). The structure along the line DD’ ( Figure 2A ) resembles a gently dip- ping monocline at the Woodford Shale ex- posure ( Figure 2B ). The Jennings Quarry (34°35'39.3"N, 96°39'01.2"W) is located in the city of Fittstown, OK. The structural position is a faulted area known as the Franks fault zone (Suneson, 1997). To the east of the Franks fault zone is the Franks Graben (which gradually merges with the Arkoma Basin further east), where mostly Middle- Upper Pennsylvanian rocks are exposed. To the west of the fault zone is the Hunton Anticline, which bears a nearly rectangu- lar shape and exposes Lower-Middle Or- dovician age rocks (Suneson, 1997). The Clarita Shale Pit (34°27'45.1"N, 96°27'21.8"W) is located south of the city of Clarita and north of Bromide, Oklaho- ma. The structural position is the Clarita Horst, which is bounded on the north by the Clarita Fault and on the south by the Bromide Fault (structure map in Figure 1 ). The Clarita Horst also dips slightly to the east, similar to that of the Lawrence Horst, exposing the older rocks to the west. Section FF' ( Figure 2B ) shows the cross-section line located near the Clarita Shale Pit. After Woodford Shale deposition, a ma- jor tectonic event, the Ouachita Orogeny, began roughly 350-330 mya (Middle to Late Mississippian) (Suneson, 1997). This was a major period of faulting and moun- tain building in southern Oklahoma and western Arkansas. The driving force be- hind this orogeny was the collision of the North American and Gondwanan plates

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Oil and Gas Exploration

Tectonic joint size, abundance, and connectivity: Examples from Woodford Shale and Hunton Limestone, cont.

(Suneson, 2012). The Ouachita Orogeny also initiated the formation of the Arkoma Basin, which is an arcuate foreland basin (Byrnes and Lawyer, 1999). However, this area, including the Hunton Anticline is also thought to have been affected by the Arbuckle Orogeny (Suneson, 1997) that followed said events. The Cherokee Platform and the Ozark Uplift to the north, and the Ouachita and the Arbuckle Uplifts to the south surround the Arkoma Basin in Oklahoma. 3. Methods for quantifying outcrop fracture size and intensity Joints may be elliptical, circular (penny- shaped), or carry other geometries. In this study, they were modeled as rectangu- lar because the visible traces on the out- crop were linear and therefore easier to model as such. Fracture orientations were measured on the quarry floor and quarry walls. Definitions of fracture length,

height, spacing, and kinematic aperture are shown in Figure 3 . We studied the quarries/outcrops ( Figures 4 - 6 ) for both fracture intensities and dimensions. For fracture length vs. height correlations, several fracture faces were photographed (i.e., camera oriented perpendicular to the strike of a particular set). For exam- ple, we captured photographs in the N-S direction for the E-W length vs. height interpretation of each fracture ( Figure 4A ). For fracture height distribution only, photographs were captured parallel to the strikes of the particular fracture sets ( Fig- ure 4B ). Figure 4C illustrates the height interpretations in the Woodford Shale in the Wyche Shale Pit. Figure 5 shows the Woodford Shale fracture traces (lengths) in the Clarita Shale Pit. Photograph of the quarry wall exposing NW-SE traces in the Hunton Group is shown in Figure 6A as an example. Figure 6B illustrates the vertical trace (fracture height) interpretations of the NW-SE sets. Figures 6C and 6D show

the termination and crosscutting relation- ships between different fracture sets in the Hunton Group. Several fracture abundance measurement methods exist- scanline sampling, win- dow sampling, and circular window sam- pling (Zeeb et al., 2013). The "scanline sampling" method requires bed-by-bed fracture linear intensity (P10) measure- ments along scanlines. The fracture linear intensity (P10) is the number of fractures along a scanline divided by the scanline length (e.g., Hooker et al., 2013). Maul- don et al. (2001) and Rohrbaugh et al. (2002) described the "circular window sampling" method. In this method, the number of fracture intersections with a circle is divided by four times the circle radius to find the fracture areal intensity (P21) (Zeeb et al., 2013). Researchers such as Pahl (1981) and Priest (1993) have described the "window sampling" method. This method gives the fracture

Figure 3: Cartoon depicting joint (Mode I or opening mode) aperture, length, height, and spacing.

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areal intensity (P21) in fractures/m by di- viding the total length (m) of the fracture traces in an observed area (m 2 ) by the ob- served area (Zeeb et al., 2013). Mauldon and Dershowitz (2000) devised P10, P21, and other terminologies (mentioned later) describing fracture abundance. We used the window sampling method for measuring fracture intensities in the Wyche Shale Pit ( Figure 4 ) and the Jen- nings Quarry ( Figure 6 ). The window sampling method was chosen for several reasons. First, the quarries only expose the top 30-40 feet of Woodford Shale and the Hunton Group Limestone. Therefore, the layer-by-layer scanline measurement of the entire formations was unsuitable. An area method was required, which meant either the circular window sampling or the window sampling method could be applied. However, the exposures in either Woodford Shale or Hunton Group Lime- stone are not big enough to draw enough circles with several intersecting fractures for statistical analysis. Therefore, we preferred the window method amongst the two area methods. Examples of pho- tographs used for the window sampling method of the Woodford Shale at the Wyche Shale Pit are shown in Figure 4C . The same for the Hunton Group Lime- stone at the Jennings Quarry is illustrated in Figure 6B . In each of these figures, dividing the total fracture trace lengths by the area in the respective photographs (excluding the debris) gives the areal frac- ture intensity (P21) values. Priest (1993) also used this method of fracture intensity determination on a mine wall. In addition, Manda and Mabee (2010) suggested a higher accuracy of the window sampling method compared to other sampling meth- ods. In spite of our best efforts for maintain- ing accuracy, there are some limitations to these measurements. A hierarchical pattern of fracture bed boundedness (e.g., Hooker et al., 2013, p. 58) exists at several locations. The most obvious measurement limitation in a hierarchical pattern is the

vertical truncation due to the removal of rock matrix itself or the obscurity of some of the longer fractures into the quarry floor. Hierarchical pattern of fracture bed boundedness has been witnessed in many carbonate and clastic rocks (Cooke et al., 2006, Bertotti et al., 2007; Zahm and Hen- nings, 2009). Compared to the shorter, bed-bounded fractures, the ones with large heights are more effective, in carry- ing fluids across several beds; therefore, the latter dominates the overall vertical permeability. The quarry floor surfaces are generally covered with rock debris. However, cer- tain spots in the Wyche Shale Pit, the Jen- nings Quarry, and the Clarita Shale Pit of- fer relatively clean surfaces for recording fracture lengths and kinematic apertures (opening displacements). The Clarita Shale Pit allowed E-W fracture lengths and apertures measurements in the Wood- ford Shale. The Wyche Shale Pit allowed measurements of the NE-SW apertures on the quarry floor. The Jennings Quarry al- lowed measurements of N-S and the E-W Hunton Group Limestone fracture aper- tures on the quarry floor. The fracture ki- nematic apertures were interpreted to have been unaffected, or minimally influenced by shear, indicating they are overwhelm- ingly opening mode fractures. 4. Results of outcrop fracture size and intensity measurements 4.1 Shale The fracture length vs. height values of all sets in the Woodford Shale were plotted jointly (i.e., not for each set individually) as not many well-exposed faces with sub- stantial length and height were available ( Figure 7H ). Fracture length vs. height relations were tested for best fit against a linear and a power-law regression. Other distributions did not fit the data as strongly as these two did. In the Woodford Shale, the R 2 values for the linear and power-law equations are virtually identical.

For the Woodford Shale, the length vs. height relation derived from Eq. 1 ob- tained from measurements in the Wyche Shale Pit walls, underpredicts the lengths based on the heights. For example, the maximum and average measured lengths of E-W fractures measured at the Clarita Shale Pit were 27.5 m and 15.5 m respec- tively. However, based on the measured heights at the Wyche Shale Pit, Eq. 1 yields a maximum length of 11.3 m and an average length of 5.5 m. Therefore, in this equation, the length axis (y-axis in Figure 7H ) was scaled up by a factor of two to render the calculated lengths comparable to those measured in Clarita Shale Pit. Therefore, the old linear equation ( Eq. 1 ) transforms into Eq. 2 . L = 2.83H 0.8533 .................................. Eq. 1 L = 5.65H 0.8533 ................................ Eq. 2 Where: L =length; H =height Except for the E-W set apertures in the Woodford Shale, which show a power-law best fit ( Table 1, Figure 7E ), all other siz- es fit either an exponential ( Table 1 , Fig- ures 7B, 7D, 7F ) or a lognormal ( Table 1 , Figures 7A, 7C, 7G ) distribution, which are both categorized as "characteristic" size distributions (Hooker et al., 2014). All measured spacing coefficient of varia- tion (C v = σ spacing /µ spacing ) values are < 1, which is defined by Gillespie et al. (1999) as lower clustering compared to that in randomly spaced fractures (i.e., joints in the study areas are evenly spaced). The measured heights of the E-W and NE-SW fractures in the Woodford Shale exhibit significant differences. Consequently, the calculated lengths from Eq. 2 also exhibit significant differences ( Table 1 ). 4.2 Carbonate The Jennings Quarry was studied for the carbonates (Hunton Group Limestone). Excluding NW-SE set height distribution in the Hunton Group Limestone, which exhibits both power-law and exponential

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Oil and Gas Exploration Tectonic joint size, abundance, and connectivity: Examples from Woodford Shale and Hunton Limestone, cont. A


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Figure 4: A) An example of length vs. height interpretation on the E-W fracture (opening mode) faces in the Woodford Shale. Double-headed vertical and horizontal arrows represent the height and length of each face respectively. B) E-W fracture (opening mode) traces. C) E-W fracture trace interpretation from B. Note: 5ft high Jacob’s staff in all figures.

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