RESERVOIR CHARACTERIZATION AND PETROLEUM POTENTIAL OF THE UPPER CRETACEOUS WALL CREEK MEMBER OF THE FRONTIER FORMATION, WESTERN POWDER RIVER BASIN, WYOMING by Joseph T. Dellenbach A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Geology). Golden, Colorado Date: ________________________ Signed: __________________________________ Joe Dellenbach Signed: ___________________________________ Dr. Stephen A. Sonnenberg Thesis Advisor Golden, Colorado Date: ________________________ Signed: ___________________________________ Dr. Stephen Enders Professor and Department Head Department of Geology and Geological Engineering ii ABSTRACT Upper Cretaceous Frontier Formation sandstone deposits in the Western Powder River Basin of Wyoming have proven to be prolific hydrocarbon producers, and show great potential for further exploration and development. The Frontier Formation is composed of tight sandstones (low permeability and porosity) with the upper Wall Creek Member serving as the main petroleum target. The Frontier Formation is commonly interpreted as a progradational clastic delta system resulting from the Sevier Orogeny in Cenomanian to Turonian time spreading over a large area of the present day Powder River Basin. Sediments were eroded from the Sevier Highlands and transported eastward into the Western Interior Cretaceous Basin. The aim of this research is to interpret facies, depositional environments, diagenetic processes, and to identify potential reservoir facies in the upper Wall Creek Member. Five upward coarsening sandstone packages were identified in the Wall Creek Member using core analysis and various well logs in the study area. Core analysis suggests the sediments of the Wall Creek Member were deposited in shallow marine delta front environments. Petrographic analysis indicates that early chlorite coating of silica grains prevented quartz overgrowth and preserved some of the initial porosity. Late dissolution of calcite cementation created secondary porosity in the Wall Creek sandstones. These two diagenetic features enhance porosity and permeability and allow hydrocarbons to migrate into the system. iii TABLE OF CONTENTS ABSTRACT ................................................................................................................................... iii LIST OF FIGURES ...................................................................................................................... vii LIST OF TABLES ....................................................................................................................... xiv ACKNOWLEDGEMENTS .......................................................................................................... xv CHAPTER 1 INTRODUCTION ................................................................................................ 1 1.1 Overview .............................................................................................................. 1 1.2 Study Objectives and Purpose ............................................................................. 5 1.3 Research Methods ................................................................................................ 5 1.4 Study Area ........................................................................................................... 6 1.5 Dataset.................................................................................................................. 8 CHAPTER 2 BACKGROUND GEOLOGY.............................................................................. 9 2.1 Regional Geology ................................................................................................ 9 2.2 Structural Setting ............................................................................................... 10 2.3 Stratigraphy ........................................................................................................ 12 2.4 Formation Equivalents ....................................................................................... 14 2.5 Petroleum System .............................................................................................. 15 2.6 Previous Work ................................................................................................... 16 2.7 History of Area .................................................................................................. 19 2.8 Current Production ............................................................................................. 21 CHAPTER 3 CORE ANALYSIS ............................................................................................. 23 3.1 Core Observation and Methodology .................................................................. 23 iv 3.1.1 Bioturbation and Ichnofacies .............................................................. 23 3.2 Key Stratigraphic Surfaces ................................................................................ 26 3.2.1 Transgressive Surface of Erosion ....................................................... 27 3.2.2 Flooding Surface ................................................................................. 28 3.2.3 Minor Flooding Surface ...................................................................... 29 3.2.4 Minor Erosional Surface ..................................................................... 30 3.2.5 Regressive Surface of Erosion ............................................................ 31 3.3 Facies Descriptions ............................................................................................ 32 3.3.1 Facies 1: Fine- to medium-grained sandstone with mud rip-up clasts ................................................................................................... 32 3.3.2 Facies 2: Coarse- to very coarse-grained sandstone ........................... 33 3.3.3 Facies 3: Medium- to lower coarse-grained sandstone ....................... 34 3.3.4 Facies 4: Fine- to lower medium-grained sandstone .......................... 35 3.3.5 Facies 5: Very fine- to lower fine-grained sandstone ......................... 36 3.3.6 Facies 6: Muddy to silty sandstone ..................................................... 37 3.3.7 Facies 7: Silty to sandy mudstone ....................................................... 38 3.3.8 Facies 8: Bioturbated silty- to very fine-grained sandstone................ 39 3.3.9 Facies 9: Bioturbated silty to sandy mudstone ................................... 40 3.4 Facies Distribution ............................................................................................. 42 3.5 Ichnology ........................................................................................................... 43 3.6 Sedimentary Structures ...................................................................................... 46 3.7 Facies Summary ................................................................................................. 48 3.8 Facies Associations ............................................................................................ 49 3.8.1 Facies Association 1: Reworked Transgressive Deposits ................... 49 3.8.2 Facies Association 2: Delta Front ....................................................... 50 v 3.8.3 Facies Association 3: Prodelta to Offshore Transition ....................... 50 3.9 Stratigraphic Correlations .................................................................................. 51 3.10 Log Correlations of Core Wells ......................................................................... 52 CHAPTER 4 PETROGRAPHIC ANALYSIS ......................................................................... 56 4.1 Petrographic Analysis ........................................................................................ 56 4.2 Previous Work ................................................................................................... 56 4.3 Thin Section Analysis ........................................................................................ 60 4.4 FE-SEM Analysis .............................................................................................. 69 4.5 Diagenesis Summary ......................................................................................... 77 CHAPTER 5 RESERVOIR CHARACTERIZATION ............................................................ 79 5.1 Reservoir Quality ............................................................................................... 79 5.2 Porosity and Permeability .................................................................................. 79 5.3 Reservoir Targets ............................................................................................... 80 5.4 Mowry Shale and Pressure................................................................................. 88 5.5 Mapping ............................................................................................................. 89 5.6 Production .......................................................................................................... 89 5.7 Discussion .......................................................................................................... 93 CHAPTER 6 CONCLUSIONS AND FUTURE WORK ......................................................... 94 6.1 Conclusions ........................................................................................................ 94 6.2 Future