PETROPHYSICAL PROPERTIES OF THE TENSLEEP SANDSTONE AT SAGE CREEK FIELD, BIGHORN BASIN, WYOMING by Ricky Adi Wibowo A thesis submitted to the Faculty and Board of Trustees of Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Geology). Golden, Colorado Date_________________ Signed:______________________ Ricky Adi Wibowo Approved:______________________ Dr. Neil F. Hurley Thesis Advisor Golden, Colorado Date_________________ Dr. Murray Hitzman Professor and Interim Head, Department of Geology and Geological Engineering ii ABSTRACT The Tensleep Sandstone of Middle Pennsylvanian to Lower Permian age occurs throughout central and north-central Wyoming. Eolian deposits dominate the upper half of the 120 ft (37 m) thick formation. The lower half consists of mixed marine and eolian sediments. Sedimentary structures, petrophysical properties, and genetic units are the keys to define facies within the eolian system. Grain flow strata with loose grain packing have better reservoir characteristics than more tightly packed wind ripple facies. Both rock types are commonly found in porous and permeable eolian cross-stratified facies. Related deposits, such as interdune, dolomitic sandstone, and marine facies, are lower quality reservoirs when compared to the eolian cross-stratified sediments. Bounding surfaces of the first-, second- and third-order define compartmentalization in eolian dune deposits. The study objectives are: (1) describe facies of the eolian and other associated deposits within the Tensleep Sandstone, including the signatures of eolian bounding surfaces, (2) describe small-scale heterogeneity within eolian deposits using petrophysical analyses based on capillary pressure, minipermeameter, laboratory nuclear magnetic resonance (NMR), and petrography, and (3) relate petrophysical analysis results iii from one cored well to another non-cored well that has FMI (Formation Micro Imager) and CMR (Combinable Magnetic Resonance) logs. The Sage Creek field area in the northern Bighorn basin, Wyoming, provides three different Tensleep data sets. Bear Canyon is a nearby excellent outcrop located about 7 mi (11 km) northeast of the field. A cored interval of the Tensleep Sandstone is available from the Fox #1 well and a complete log suite, including FMI and CMR logs, is available from the SCU #21 well. The measured section at Bear Canyon suggests that the Tensleep Sandstone is divided into the eolian-dominated Upper Tensleep and mixed eolian-marine sediments of the Lower Tensleep. A detailed core description and petrophysical analyses of 18 samples from the Fox #1 well suggest that facies controls permeability and porosity. Minipermeameter measurements sampled every 0.5 ft (15 cm), combined with mercury injection capillary pressure (MICP), nuclear magnetic resonance (NMR) tests, and petrographic analysis demonstrate the various facies within the Tensleep Sandstone. T2 is a measure of the relaxation time of hydrogen protons subjected to NMR testing. Fast decay T2 distributions are related to wind ripples and commonly show bimodal curves in the CMR logs. The grain flow facies has longer T2 times and a unimodal distribution. Interdune, dolomitic sandstone and marine facies commonly show similar T2 distributions, which involve fast decay times. Petrophysical properties from the core relate to the same eolian intervals from a different well with a CMR log. The combination of the FMI and CMR logs can be used iv to define the eolian facies within the Tensleep Sandstone interval. The T2 distributions from the CMR log are used to define the grain flow and wind ripple strata, while the FMI log is used to determine bounding surfaces and facies within the eolian system. v TABLE OF CONTENTS Page ABSTRACT……………………………………………………………………………iii LIST OF FIGURES…………………………………………………………………....x LIST OF TABLES…………………………………………………………………...xvi ACKNOWLEDGMENTS…………………………………………………………..xvii Chapter 1 INTRODUCTION…………………………………………………….… 1 1.2. Research Objectives…………………………………….…………..… 4 1.3. Previous Investigations…………………………………………….… 5 1.4. Research Contributions……………………………….…..………….. 8 Chapter 2 GEOLOGICAL SETTING……………………………….……………. 9 2.1. Study Area…………………………………………………………… 9 2.2. Stratigraphy and Sedimentology………………………………….… 10 2.2.1. Regional Stratigraphy………………………………………... 10 2.2.2. Tensleep Sandstone………………………………………….. 16 2.2.2.1. Paleogeographic Setting……………………………. 20 2.2.2.2. Eolian Processes………………………………….…. 24 2.2.2.3. Lithofacies…………………………………………… 29 2.2.2.4. Parasequences and Bounding Surfaces………….…... 33 2.2.2.5. Reservoir Heterogeneity…………………………….. 39 2.2.3. Local Stratigraphy……………………………………………. 44 2.3. Structural Geology…………….………………………………….… 46 2.3.1. Regional Structural Geology…………………………………. 46 2.3.2. Local Structural Geology…………………………………….. 48 vi Page 2.4. Petroleum Geology………….………………………………….…… 49 Chapter 3 OUTCROP STUDY: BEAR CANYON, PRYOR MOUNTAINS…… 57 3.1. Introduction.…….………….………………………………….……. 57 3.2. Location……….. …………………………………………..…….…. 59 3.3. Lithofacies Types…………………………………………..…….…. 60 3.4. Description of Measured Section…………………………..…….…. 63 3.5. Bounding Surfaces………………….….…………………………….. 70 3.6. Discussion…………………………………………………………… 72 Chapter 4 SAGE CREEK CREEK FIELD CORRELATION …….……………. 75 4.1. Index Map……….………..….……………………………..….……. 75 4.2. Correlation Framework……………………………………….……... 77 4.2.1. Well Log Signatures………..………………………………… 78 4.2.2. Comparison to Outcrop………………………………….…… 84 4.3. Discussion……………………………………………………..…….. 88 Chapter 5 SAGE CREEK FIELD: CORE DESCRIPTION, FOX #1….……….. 90 5.1. Introduction……………………………………………………….…..90 5.2. Location………………………………………………………….….. 91 5.3. Lithofacies Types……………….…………..………………….……. 91 5.3.1. Marine Sandstone...……………………………………….…. 96 5.3.1.1. Physical Description ………………………………... 96 5.3.1.2. Discussion – Marine Sandstone……….……………. 102 5.3.2. Eolian Sandstone……………………………………………. 103 5.3.2.1. Physical Description………………….……………. 104 5.3.2.2. Wind Ripple Facies………………………………… 107 5.3.2.3. Grainflow Facies…………………….……………... 109 5.3.2.4. Grainfall Facies…………………….……………... 110 5.4. Bounding Surfaces……………………………………….………… 111 5.5. Core Analyses………………………………………………….…... 112 5.5.1. Conventional…………………………………………….….. 113 vii Page 5.5.2. Minipermeameter…………………………………………… 116 5.5.3. Capillary Pressure Analysis………………………………… 123 5.5.4. Nuclear Magnetic Resonance (NMR) Analysis…………….. 153 5.5.4.1 NMR T2 Distribution….……………………………. 155 5.5.4.2 NMR Porosity……....………………………………. 158 5.5.4.3 NMR T2 Cutoff…………..…………………………. 159 5.5.4.4 NMR Permeability ….……………………………… 163 5.5.4.5 NMR Pore Size Distribution..……….……………… 169 5.5.5 Dykstra-Parson Coefficient....……………………………….. 175 5.5.6 Petrography…………………....……………………………... 180 5.6. Discussion…………………………………………………………... 186 Chapter 6 SAGE CREEK FIELD: PETROPHYSICAL ANALYSIS, SAGE CREEK UNIT (SCU) #21……….…………………………………….. 188 6.1. Location………………………………….…………………………. 188 6.2. Borehole Images Analysis……………………………………..…... 189 6.2.1. Introduction to Borehole Image Logs…………………….… 191 6.2.1.1 Dip Determination…………………………………... 192 6.2.1.2 Lithology Determination………………………….… 194 6.2.1.3 Removal of Structural Dip…………………………... 199 6.2.2. Description of Stratification……………………………….... 202 6.2.3. Bounding Surfaces……….………………………………..… 204 6.3. Combinable Magnetic Resonance (CMR) Analysis………………. 219 6.3.1. Introduction to NMR logging..……………………………… 220 6.3.2. Porosity……………………………………………………… 226 6.3.3. Porosity Result from the SCU #21 well…………………...… 229 6.3.4. Permeability…………………………………………………. 238 6.4. Discussion…………………………….…………………………….. 247 Chapter 7 DISCUSSION……………………………………………………..……. 250 Chapter 8 CONCLUSIONS AND RECOMMENDATIONS……………..…….. 260 viii Page REFERENCES……………………………………….…………………………….. 263 Appendix A Measured Section at Bear Canyon Appendix B Fox #1 Well Core Description and Photographs Appendix C Fox #1 Well Data Appendix D Core Analysis Report Appendix E Sage Creek Unit #21 Well Data (All appendices are in CD at the back of this dissertation) ix LIST OF FIGURES Page Figure 1.1 Location map Sage Creek field………………………………………….... 3 Figure 2.1 Bighorn basin map ………..…………………………………………....... 11 Figure 2.2 Asymmetrical synclinal cross section……………..……………………... 12 Figure 2.3 Stratigraphic column of Bighorn basin …….………………………..…... 13 Figure 2.4 Stratigraphic chart of Bighorn, Wind River, and Powder River basins..… 17 Figure 2.5 Columnar section of stratigraphy at Tensleep Canyon………………….... 19 Figure 2.6 Pennsylvanian to Early Permian paleogeographic map………………….. 21 Figure 2.7 Eolian paleodispersal patterns in Bighorn basin…………………………. 22 Figure 2.8 Schematic air flow diagram over dunes……….…………………………. 25 Figure 2.9 Transgressive strata by climbing bedforms.…………………..………...... 28 Figure 2.10 Lithofacies of the Tensleep Sandstone with their interrelations…………. 30 Figure 2.11 Eolian bedforms of different hierarchy ……………….…………………. 35 Figure 2.12 Three orders of bounding surfaces ………………………………………. 35 Figure 2.13 Bounding surfaces in the Tensleep Sandstone ………..…………………. 36 Figure 2.14 Scales of reservoir heterogeneity ………………….……..………………. 40 Figure 2.15 Permeability heterogeneity due to stratification …………………………. 42 Figure 2.16 Permeability heterogeneity at bounding surfaces …………………..……. 43 Figure 2.17 Tensleep Sandstone type log at SCU #21 ……………….………………. 45 x Page Figure 2.18 Structural map top of Dinwoody at Sage Creek ………………………… 49 Figure 2.19 Burial history of the Bighorn basin…………….………………………… 51 Figure 2.20 Structural contour map of Sage Creek……………………………………. 55 Figure 2.21 Origin