DEPOSITIONAL CONTROLS OF A GUELPH FORMATION PINNACLE REEF DEBRIS APRON AND THEIR EFFECT ON RESERVOIR QUALITY: A CASE STUDY FROM NORTHERN MICHIGAN Zachary M.K. Cotter A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 2020 Committee: James Evans , Advisor Margaret Yacobucci Yuning Fu © 2020 Zachary Cotter All Rights Reserved iii ABSTRACT James Evans, Advisor The Middle Silurian-aged Guelph Formation pinnacle reefs and associated deposits of the Michigan basin (U.S.A.) are a prolific hydrocarbon play, valued for its potential for enhanced oil recovery (EOR) and carbon sequestration. Recent work has aided in resolving reef growth models and complex architecture, however previous studies have been focused on reef development, largely overlooking depositional controls of the leeward debris apron development and implications for reservoir development. This study hypothesizes that the leeward debris apron of Guelph Formation pinnacle reefs accumulated with depositional controls and architectural elements like those of larger, line-fed slope apron systems of carbonate platform margins. This study utilizes a case study well, which was laterally deviated leeward of the reef pinnacle and captured the leeward slope profile of a Guelph Formation pinnacle reef. This study uses 70 m of whole core, 117 core plugs, 16 mercury injection capillary pressure (MICP) curves, 21 thin sections, in addition to a suite of geophysical wireline logs, including borehole image logs, to build a depositional model for the leeward debris apron and evaluate controls on reservoir quality. Core analysis of sedimentary deposits recovered from the well identified 16 lithofacies, interpreted to have been deposited within six facies associations including reef zone, tempestite, debrite-turbidite, subtidal back-reef, intertidal, and supratidal. Stratigraphic analysis revealed that the leeward debris apron developed within two distinct growth stages: (1) a stage correlative to active reef growth and accumulation of the debris apron and (2) a peritidal stage of deposition. Reef growth deposits (stage one) consisted of deepening upward sedimentary successions comprised of skeletal framestones, floatstones, rudstones, grainstones, wackestones iv and intraclastic conglomerates. The vertical succession of these deposits was interpreted to represent the lateral shift of environments downslope from active carbonate factory settings to more distal segments of the leeward slope. Sediment gravity flows, partial Bouma sequences (Ta and Tde), and well-preserved tempestite successions were present in a significant volume of recovered core, interpreted to suggest that off-bank transport via storm-wave resuspension and sediment gravity flows triggered by events of slope destabilization were the primary sediment transport mechanisms feeding development of the leeward debris apron. The vertical succession of deposits of the leeward debris apron of Guelph Formation reefs was found to resemble those of larger, line-fed slope apron systems associated with carbonate platform margins. Guelph Formation peritidal successions (stage 2) were observed to unconformably overlie subaerially- exposed reef stage deposits and the bottommost contact was interpreted as transgressive surface of erosion. Guelph Formation peritidal deposits consisted of mudstones, cryptalgal bindstones, and skeletal packstones which were interpreted to represent a shallowing-upward transition from subtidal-to-supratidal environments. The contact between the Guelph Formation and Ruff Formation was observed as a sharp, erosive unconformity interpreted to be a second transgressive surface of erosion with evidence of micro-karsting occurring just below the contact, suggesting the leeward slope underwent a second period of subaerial exposure. A generalized reservoir characterization effort was conducted on Guelph Formation sediments to characterize reservoir quality. Reservoir characterization revealed capillary behavior that can be generalized by three type curves, and the primary pore architecture and textures of sampled Guelph Formation sediments were overprinted by diagenetic processes including dolomitization, recrystallization, dissolution, stylolitization and fracturing. Tempestites were found to exhibit the best petrophysical character and highest degrees of petrophysical predictability, interpreted to be v a result of high initial bioclastic content and well-sorted textures generated by wave-suspension processes. vi I would like to dedicate this text to all of those who have helped me get to the point that I am in life. To my family, professors, colleagues, mentors, friends, and acquittances… Thank you for the inspiration in my life. vii ACKNOWLEDGMENTS I would like to thank my adviser Dr. James Evans for his guidance, teachings, patience and continuing support throughout this study and my greater term at Bowling Green. I would like to thank my undergraduate adviser Frank Schwartz for his continued mentoring, friendship, and for continuously pushing me to be the best scientist that I can be. I would like to thank Battelle’s energy group for giving me the opportunity to grow and learn as an intern. I would like to thank Autumn Haagsma, Amber Conner, Valarie Smith, Joel Main, Neeraj Gupta, Bill Harrison, Wayne Goodman, Charlotte Sullivan, Matt Rine, and the Core Energy LLC. team for their input and assistance in completing this project. I would also like to thank my committee members Peg Yacobucci and Yuning Fu for their assistance in completing this study. This project was lucky enough to obtain funding from several supporters including the Midwest Carbon Sequestration Partnership (MRCSP), the Geological Society of America (GSA), the American Association of Petroleum Geologists (AAPG) under the Fred Dix Memorial grant, and the Bowling Green State University Geology Department under the Richard Fox Practical Geophysics Grant. A special thank you to the family of Fred Dix and Richard Fox, memorial grants such as these fund so much great science; thank you! vi TABLE OF CONTENTS Page CHAPTER I: INTRODUCTION….…………………………………………………..... ..... 1 Carbonate Reefs ……………………………………………………………………..……… 4 Silurian Carbonate Reefs……………………………………………………………. 5 Leeward Reef Margins………………………………………………………………. 6 Peritidal Carbonates……..…………………………………………………………..……… 8 Carbonate Slope Systems………..…………………………………………………..……… 10 Debris Apron Models ………………………………………………………………. 11 Bioclastic Submarine Fan Models …………………………………………………. 13 Differentiating Debris Aprons from Calciclastic Submarine Fan……..……………. 16 Bioclastic Sedimentation ………..…………………………………………………..……… 17 Tempestites …………………………………………………………………………. 17 Subaqueous Gravity Flows …………………………………………………………. 18 Carbonate Reservoir Characterization .……………………………………………..……… 21 CHAPTER II: GEOLOGICAL BACKGROUND …….………………………………....... 25 Basin History ………….………..…………………………………………………..……… 25 Silurian Stratigraphy ………..…..…………………………………………………..……… 25 Paleogeography and Environment …………………………………………………..……… 26 Guelph Pinnacle Reef Depositional Models….……………………………………..……… 27 CHAPTER III: METHODOLOGY ……………………………….……………………..... 33 Case Study Field History ………..…………………………………………………..……… 33 Whole Core Analysis ………..…….………………………………………………..……… 33 vii Thin Section Petrography………..…………………………………………………..……… 34 Geophysical Well Log Analysis……………………………………………………..……… 34 Gamma-Ray Logs …….……………………………………………………………. 35 Bulk-Density Logs …………………………………………………………………. 35 Neutron Porosity Logs ……..………………………………………………………. 36 Resistivity Borehole Image Logs……………………………………………………. 37 Constructing the Geophysical Log Model ……….…………………………………..……… 38 Core Plug Analysis ….….………..…………………………………………………..……… 39 Mercury Intrusion Capillary Pressure (MICP) Analysis ….………………………..……… 41 CHAPTER IV: RESULTS …. ............................................................................................... 46 Lithofacies Analysis ……………..…………………………………………………..……… 46 Dolomitic Mottled Mudstone (Mm) ….……………………………………………. 46 Laminated Dolomitic Mudstone (Ml) ………………………………………………. 47 Pale Grey Mudstone (Mpg) ……..…………………………………………………. 48 Dolomitic Skeletal Wackestone (Sw)………………………………………………. 50 Dolomitic Skeletal Packstone (Sp)…….……………………………………………. 51 Dolomitic Skeletal Grainstone (Sg) …..……………………………………………. 52 Dolomitic Mottled Skeletal Floatstone (Sfm)………………………………………. 53 Dolomitic Cryptalgal Intraclastic Floatstone (Ifcr)…………………………………. 55 Dolomitic Intraclastic Boulder Floatstone (IFb) ……………………………………. 56 Coated Grain Dolomitic Rudstone (Rcg)……………………………………………. 58 Massive Amalgamated Skeletal Rudstone (Ram)……………………………………. 59 viii Cross-bedded Skeletal Rudstone (Rcb) ………..……………………………………. 60 Heterolithic Crypt-Algal Bindstone and Clotted Mudstone (Hcr)….………………. 61 Heterolithic Disturbed Crypt-Algal Bindstone and Skeletal Packstone (Hcrd)..…… 63 Wrinkled Algal Bindstone (Bcr)……………………………………………………. 64 Dolomitic Coral-Stromatoporoid Framestone (Fr)…………………………………. 65 Lithofacies Associations ………..…………………………………………………..……… 66 Supratidal Facies Association (FA1) ……..…………………………………………. 66 Intertidal Facies Association (FA2) ……...…………………………………………. 67 Subtidal Back-Reef (FA3) ………..……...…………………………………………. 68 Debrite-Turbidite Facies Association (FA4) …….…………………………………. 69 Tempestite Facies Association (FA5) …....…………………………………………. 71 Skeletal Reef Facies Association (FA6) …....………………………………………. 72 Depositional Environments ………..………………………………………………..……… 73 Reef Depositional Stage …………..……...………………………………………….