Information Circular 39A DFF-OG-OU-011 Structural and Stratigraphic Analysis of the Shell Rex Timber No. 1-9 Well, Southern Ouachita Fold and Thrust Belt, Clark County, Arkansas Ted Godo1, Peng Li2, and M. Ed Ratchford2 1 Shell Exploration & Production Company, Houston, Texas 2 Arkansas Geological Survey, Little Rock, Arkansas Bekki White, Director and State Geologist Arkansas Geological Survey December 2008 STATE OF ARKANSAS Mike Beebe, Governor ARKANSAS GEOLOGICAL SURVEY Bekki White, Director and State Geologist COMMISSIONERS Dr. Richard Cohoon, Chairman………………………………………………..Russellville William Willis, Vice Chairman………………………………………………..Hot Springs David J. Baumgardner.........................................................................................Little Rock Brad DeVazier…………………………………………………………………Forrest City Keith DuPriest……………………………………………………………………Magnolia Becky Keogh……………………………………………………………………Little Rock David Lumbert………………………………………………………………….Little Rock i Table of Contents Table of Contents………………………………………………………………………….ii List of Figures and Table……………………………………………………....................iii List of Plates and Appendices……………………………………………………………..v Acknowledgments ............................................................................................................. vi Introduction......................................................................................................................... 1 Regional Geologic Setting.................................................................................................. 3 Well Evaluation .................................................................................................................. 6 Geochemistry.................................................................................................................... 11 Depositional Environment ................................................................................................ 16 Deepwater Elements and Terminology......................................................................... 16 Outcrop Analogs and Well Log Interpretation ............................................................. 17 Structural Evaluation ........................................................................................................ 19 Borehole Televiewer Analysis...................................................................................... 23 Sandstone Petrology ......................................................................................................... 33 General Discussion ....................................................................................................... 33 Petrographic Analysis of Well Samples ....................................................................... 34 Diagenesis......................................................................................................................... 38 Discussion......................................................................................................................... 54 References Cited............................................................................................................... 55 ii List of Figures and Table Figure 1. Surface and subcrop geology of the Rex Timber 1-9 Well, Clark County, Arkansas.............................................................................................................................. 2 Figure 2. Partial stratigraphic section from the Ouachita Mountains region, Arkansas and Oklahoma............................................................................................................................ 4 Figure 3. Structural contour map of the top of the Stanley Formation near the Rex Timber No. 1-9 well……………………………………………………………………….8 Figure 4. Stratigraphic and thermal maturity evaluation of Rex Timber No. 1-9 well ... 10 Figure 5. The conversion relationship between level of maturity (LOM) and vitrinite reflectance (Ro)................................................................................................................. 12 Figure 6. Total Organic Carbon (TOC) values of samples in the Rex Timber No. 1-9 well……………………………………………………………………………………….14 Figure 7A. Interpreted electrical log shapes from the Rex Timber No. 1-9 well (1,700 – 2,000 ft)………………………………………………………………………...19 Figure 7B. Interpreted electrical log shapes from the Rex Timber No. 1-9 well (2,640 – 3,200 ft)……………………………………………………………………… 20 Figure 7C. Interpreted electrical log shapes from the Rex Timber No. 1-9 well (5,250 – 5,950 ft)……………………………………………………………………… 21 Figure 8. Seismic Line 83-506-2334 (migrated stack) displaying a dip section of the Moccasin prospect……………………………………………………………………….24 Figure 9A. Low-angle fractures (LAF) and bedding (B)………………………………..26 Figure 9B. Low-angle fractures (LAF) and high-angle fractures (HAF) ........................ 27 Figure 9C. Fracture cluster (FC) with undeformed sandstone above and below ............ 28 Figure 9D. Lines drawn parallel to the direction of maximum compressive stress σ1 during folding.................................................................................................................... 29 Figure 9E. Interval of 2,299-2,397 ft (701-731 m) showing folds above a thrust fault (F) ........................................................................................................................................... 53 Figure 9F. Lenses (L) of Jackfork sandstone in shale ..................................................... 55 iii Figure 10. Classification of sandstone examined by point counting methods using twenty-two (22) thin sections from the Rex Timber No. 1-9 well. Classification scheme is from Folk (1968)………………………………………………………………………36 Figure 11. Constituents of sandstones examined in the Rex Timber No. 1-9 well. Results based on point counts of thin sections from ditch cuttings (300 points per thin section). 37 Figure 12. EDAX elemental analysis spectrums of selected carbonates in the Rex Timber No. 1-9. Spectrums displayed from thin sections shown on Plate 4B and Plate 7D…….53 Table 1. Thermal maturity level and visual kerogen type analysis for Rex Timber No. 1-9 well……...……………………………………………….…………………………..15 iv List of Plates and Appendices Plate 1. Location map and surface geology of the southern Ouachita Mountain region, Arkansas……………………………….At the end of manuscript and separate file on disk Plate 2. Photomicrographs and petrographic descriptions. A) 5,040 – 5,050 ft; B) 5,040 – 5,050 ft; C) 2,370 – 2,380 ft; D) 2,370 – 2,380 ft……………………………………...39 Plate 3. Photomicrographs and petrographic descriptions. A) 1,530 – 1,540 ft; B) 2,370 – 2,380 ft; B) 5,210 – 5,220 ft; C) 4,670 – 4,680 ft; D) 2,620 – 2,630 ft………………..41 Plate 4. Photomicrographs and petrographic descriptions. A) 3,790 – 3,800 ft; B) 3,508 ft; C) 1,480 – 1,490 ft; D) 1,480 – 1,490 ft………………………………………………42 Plate 5. Photomicrographs and petrographic descriptions. A) 1,480 – 1490 ft; B) 5,210 – 5,220 ft; C) 3,860 – 3,870 ft; D) 5,300 – 5,310 ft………………………………………..44 Plate 6. Photomicrographs and petrographic descriptions. A) 4,570 – 4,580 ft; B) 4,570 – 4,580 ft; C) 4,670 – 4,680 ft; D) 4,670 – 4,680 ft……………………………………...45 Plate 7. Photomicrographs and petrographic descriptions. A) 1,530 – 1,540 ft; B) 3,100 – 3,110 ft; C) 1,460 – 1,470 ft; D) 1,460 – 1,470 ft……………………………………...47 Plate 8. Photomicrographs and petrographic descriptions. A) 3,860 – 3,870 ft; B) 3,860 – 3,870 ft; C) 5,520 – 5,530 ft; D) 5,510 – 5,520 ft……………………………………...48 Plate 9. Photomicrographs and petrographic descriptions. A) 3,370 – 3,385 ft; B) 1,210 – 1,220 ft; C) 1,160 – 1,170 ft; D) 3,370 – 3,385 ft……………………………………...49 Plate 10. Photomicrographs and petrographic descriptions. A) 5,110 – 5,120 ft; B) 5,110 – 5,120 ft; C) 3,790 – 3,800 ft; D) 3,790 – 3,800 ft……………………………………...50 Plate 11. Photomicrographs and petrographic descriptions. A) 5,520 – 5,530 ft; B) 5,520 – 5,530 ft; C) 1,460 – 1,470 ft; D) 5,110 – 5,120 ft……………………………………...51 Plate 12. Photomicrographs and petrographic descriptions. A) 3,515.3 ft; B) 6,150 – 6,160 ft; C) 5,110 – 5,120 ft; D) 5,110 – 5,120 ft………………………………………..53 Appendix 1. Total organic carbon (TOC) analysis for Rex Timber No. 1-9 well………60 Appendix 2. Thin section point counts from Rex Timber No. 1-9 well………………...65 v Acknowledgments The authors express their gratitude to Shell Exploration & Production Company (SEPCO) for sharing their data, technical advice, and subsurface knowledge of the Ouachita Mountains region in Arkansas for this publication. We are also thankful to the geology staff of the Arkansas Geological Survey (AGS) for reviewing the technical aspects of the manuscript and providing supplemental geologic information that is germane to this report. Finally, we would like thank Nathan Taylor and Jerry Clark, GIS specialists at the AGS for preparing the graphics and plates in this report. vi Structural and Stratigraphic Analysis of the Shell Rex Timber No. 1-9 Well, Southern Ouachita Fold and Thrust Belt, Clark County, Arkansas Ted Godo1, Peng Li2, and M. Ed Ratchford2 1 Shell Exploration & Production Company, Houston, Texas 2 Arkansas Geological Survey, Little Rock, Arkansas Introduction A joint research project between the Arkansas Geological Survey (AGS) and Shell Exploration & Production Company (SEPCO) was undertaken to report the findings of three exploration wells drilled by Shell in the 1980’s in the Arkansas portion of the Ouachita Mountains. Shell had recognized three exploration targets in the Ouachita fold and thrust belt of