CONSTRUCTING A GEOMECHANICAL MODEL OF THE WOODFORD SHALE, CHEROKEE PLATFORM, OKLAHOMA, USA EFFECTS OF CONFINING STRESS AND ROCK STRENGTH ON FLUID FLOW By TYLER J. HAIR Bachelor of Science, 2010 Brigham Young University Provo, Utah Submitted to the Graduate Faculty of The College of Science and Engineering Texas Christian University In partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August, 2012 CONSTRUCTING A GEOMECHANICAL MODEL OF THE WOODFORD SHALE, CHEROKEE PLATFORM, OKLAHOMA, USA EFFECTS OF CONFINING STRESS AND ROCK STRENGTH ON FLUID FLOW By TYLER J. HAIR Thesis approved: Major Professor For The College of Science and Engineering Copyright by Tyler James Hair 2012 ii ACKNOWLEDGEMENTS I gratefully acknowledge my advisor and committee chairman, Dr. Helge Alsleben, for aligning me with this project and refining my writing and critical thinking through his tireless editing and guidance. I am also very grateful to Milton Enderlin for providing invaluable foundational knowledge and technical expertise. It was Milt’s passion for rock mechanics inspired me to pursue this project. Thank you to Dr. Nowell Donovan for our discussions of Oklahoma geology and the Woodford Shale, which helped me to connect what I’ve learned from other regions to this study. The hard work and cooperation of employees at the Oklahoma Geological Survey and the Oklahoma Petroleum Information Center helped to provide some of the most critical data for my study. In particular I’d like to thank Brian Cardott and Austin Holland of the OGS for providing valuable information through phone calls, emails and personal interviews. I want to thank Mr. Gary Burch, Manager of Geology – Arkoma Group, XTO Energy, for allowing me the opportunity to work on and learn about the Woodford Shale as a part of my internship. The interest he has shown in my career and his follow-up throughout the process has helped me to keep my end goal in mind. Bryan Sralla and Michael Sweatt, coworkers at XTO, were dedicated mentors throughout the process, allowing me to shadow them and support their exploration of the Woodford Shale. The unique experiences and training I received at XTO not only improved the quality of this study, but also made an immense impact on my future career. Lastly, I would like to thank my two boys, Austin and Blake, for keeping life in perspective and fun. My wife Rachel has been an optimist all along, and I am very grateful for her love, patience and encouragement. I dedicate this thesis to them. iii LIST OF FIGURES 1. Location map .......................................................................................................................3 2. Generalized pre-Mesozoic geologic map of southern United States ...................................5 3. Paleogeography of the Late Devonian .................................................................................6 4. Major Geologic Provinces of Oklahoma Map .....................................................................8 5. Restored strata thickness cross sections, Silurian to Mississippian, Oklahoma ..................9 6. Stratigraphic Column, Central Oklahoma..........................................................................12 7. Elemental Capture Spectroscopy log, Wyche#1 ................................................................14 8. Vitrinite reflectance analysis of the EOG Smith B. #31 3 SWD .......................................16 9. Characteristic Woodford Shale well log signatures, Permian and Anadarko Basins ........18 10. Triaxial compression test geometry and a plot of axial stress at failure ............................21 11. Graphic Correlation between dimple diameter and the UCS of the sample in psi ............22 12. Correlation between bulk density (Rhob), compressional slowness (DTc), and shear slowness (DTs) with the unconfined compressive strength (UCS in psi) of clean sandstones, with matrix density of 2.65 g/cm3, fully saturated with brine at normal pressure conditions.............................................................................................................24 13. Generic Stress Polygon Plot of SH versus Sh with fault boundaries displayed ...................26 14. A: Historical seismicity of Lincoln County, Oklahoma. ...................................................29 14. B: Synthesis of USGS earthquake summaries for three major events that occurred nearby the EOG Smith, B. 31 #3 SWD from 2010 to present ...........................................30 15. Stereonets comparing Woodford Shale fractures from two locations: the Cherokee Platform and the Arkoma Basin .........................................................................................35 16. World Stress Map Borehole Breakout data from 18 locations ..........................................37 17. World Stress Map for Oklahoma .......................................................................................38 18. Stress Polygon printed on Transparent Plastic...................................................................40 19. EOG Smith, B. #31-3 SWD core description ....................................................................43 20. Dynamic Stress Polygon for the EOG Smith, B. #31-3 SWD ...........................................47 21. Graphical correlation between UCS and Coefficient of Sliding Friction (µ) ....................49 22. Reactivation Map for EOG Smith, B. #31-3 SWD ............................................................51 iv LIST OF TABLES 1. Various rock strength values, UCS in psi ..........................................................................23 2. Summary of major earthquakes near the EOG Smith, B. #31-3 SWD ..............................31 3. Borehole breakout data from the World Stress Map database ...........................................39 4. Record of precise depth, grainsize, Munsell rock-color (for a dry sample), dimple diameter (measured in ticks) and whole core photographs for each sampling event ........49 v TABLE OF CONTENTS Acknowledgements .......................................................................................................... ii List of Figures ................................................................................................................. iii List of Tables .................................................................................................................. iv Introduction ...................................................................................................................... 1 Geological Background .................................................................................................... 4 Depositional History and Environment ........................................................................ 4 Structural History of the Nemaha Trend .................................................................... 10 Central Oklahoma Stratigraphy ................................................................................. 11 Source Rock Properties ............................................................................................ 15 General Well Log Characteristics .............................................................................. 17 Approach ....................................................................................................................... 20 Rock Strength Characterization from Core ................................................................ 20 Stress Magnitudes and Directions ............................................................................. 25 Principal (S1, S2, S3) and Component Stresses (SV, SH, Sh).................................... 25 Earthquake Focal Mechanisms and Local Faults .................................................... 28 Building a Stress Polygon ....................................................................................... 32 Determining the Orientation of SHaz ......................................................................... 33 Example 1 – EOG Smith, B. #31-3 SWD .................................................................. 42 Workflow ................................................................................................................. 46 Conclusions ................................................................................................................... 52 Appendices .................................................................................................................... 53 References .................................................................................................................... 64 vi Vita Abstract 1 INTRODUCTION A better understanding of the mechanical properties of drilled rock formations can alleviate many of the problems associated with drilling for and producing oil and gas from wells. Potential drilling and production problems include wellbore stability, sand production, changes in porosity and permeability due to compaction during reservoir depletion, closure of fracture apertures as a result of fluid production and lost circulation associated with the reactivation of planar mechanical discontinuities (Weingarten and Perkins, 1995; Khaksar et al., 2009; Enderlin and Alsleben, in press). One important mechanical property to understand in order to avoid these drilling problems is rock strength, which is defined herein as the level of stress at which failure occurs. Rock strength is a function of many components, including lithology, porosity, permeability,