STRUCTURAL INTERPRETATION OF THE CHEROKEE ARCH, SOUTH CENTRAL WYOMING, USING 3-D SEISMIC DATA AND WELL LOGS by Joel Ysaccis B. ABSTRACT The purpose of this study is to use 3-D seismic data and well logs to map the structural evolution of the Cherokee Arch, a major east-west trending basement high along the Colorado-Wyoming state line. The Cherokee Arch lies along the Cheyenne lineament, a major discontinuity or suture zone in the basement. Recurrent, oblique-slip offset is interpreted to have occurred along faults that make up the arch. Gas fields along the Cherokee Arch produce from structural and structural-stratigraphic traps, mainly in Cretaceous rocks. Some of these fields, like the South Baggs – West Side Canal fields, have gas production from multiple pays. The tectonic evolution of the Cherokee Arch has not been previously studied in detail. About 315 mi2 (815 km2) of 3-D seismic data were analyzed in this study to better understand the kinematic evolution of the area. The interpretation involved mapping the Madison, Shinarump, Above Frontier, Mancos, Almond, Lance/Fox Hills and Fort Union horizons, as well as defining fault geometries. Structure maps on these horizons show the general tendency of the structure to dip towards the west. The Cherokee Arch is an asymmetrical anticline in the hanging wall, which is mainly transected by a south-dipping series of east-west striking thrust faults. The interpreted thrust faults generally terminate within the Mancos to Above Frontier interval, and their vertical offset increases in magnitude down to the basement. Post-Mancos iii intervals are dominated by near-vertical faults with apparent normal offset. They seem to extend up to the near the surface and affect rocks as young as Eocene in age. From the analyzed data, two possible episodes of deformation are indicated: early thrusting and subsequent dip-slip and/or wrench movement. The main thrusting occurred during the Upper Cretaceous (between Mancos and Above Frontier interval). The wrenching and dip slip offset occurred during deposition of the Tertiary section. The thrust-fold system of the Cherokee Arch correlates in time with the Laramide Orogeny (Late Cretaceous through mid-Eocene). iv TABLE OF CONTENTS ABSTRACT …………………………………………………………………………… iii TABLE OF CONTENTS ……………………………………………………..……….. v LIST OF FIGURES …………………………………………………………….…….. vii LIST OF TABLES ……………………………………………………………….……. xi ACKNOWLEDGEMENTS ………………………………………………….………. xii 1. INTRODUCTION ………………………………………………………..………… 1 1.1 Research Objectives .……………………………………………..………….. 1 1.2 Previous Work ………………………………………………………………. 2 1.2.1 Regional Tectonics …………………………………………...……. 2 1.2.2 Local Tectonics ……………………………………………………. 5 1.3 Study Area and Data Set ………………………………………………...…. 12 1.3.1 3-D Seismic Data Set …………………………..………………… 17 1.3.2 Digital Well Logs ………………………………………...………. 17 1.4 Research Contributions …………………………………………….………. 19 2. GEOLOGIC SETTING …………………………………………………..………. 20 2.1 Stratigraphy ………………………………………………………...………. 20 2.2 Important Structural Conceptual Models ………………………...………… 29 v 2.3 Structural Geology …………………………………………………………. 29 2.3.1 Regional Structure ……………………………………..………… 29 2.3.2 Local Structure …………………………………………………… 35 2.4 Petroleum Geology ……………………………………...…………………. 37 3. SEISMIC DATA ANALYSIS ………………………………..…………………… 39 3.1 Methods ……………………………………………………………….……. 39 3.2 Results ……………………………………………………………...………. 41 3.2.1 Synthetic Seismograms ……………………………...…………… 41 3.2.2 Horizons …………………………………………………..……… 48 3.2.3 Faults ………………………………………………………...…… 65 3.2.4 Time Structure Maps ……………………………………...……… 66 3.2.5 Time Slices …………………………………………………..…… 74 3.2.6 Isochron Maps ………………………………………….………… 74 3.3 Discussion …………………………………………………………..……… 90 4. CONCLUSIONS AND RECOMMENDATIONS ……………………………….. 98 4.1 Conclusions ……………………………………………………..………….. 98 4.2 Recommendations ………………………………………………………….. 99 REFERENCES ………………..……………………….…………………………..… 100 CD ROOM …………………………………………….……………………. Back Pocket vi LIST OF FIGURES Figure 1.1. Structural orientation of the thrust belt orogen, arches and basins of the Laramide foreland …..……………..………………..…………………………… 4 Figure 1.2. Geologic map of Precambrian rocks of southern Wyoming and northern Colorado ……………………………………………………………...……………. 6 Figure 1.3 Structure map: Cherokee Ridge Arch ……………………………………….. 7 Figure 1.4 Tectonic features of the Greater Green River Basin ……………...…..…….. 8 Figure 1.5 Deepest wells used for calibration purposes, South Baggs- West Side Canal field ….……………………………………………………..…….. 10 Figure 1.6 Location of the study area, and other Lewis Shale Consortium studies ..…... 11 Figure 1.7 Seismic base map on the top of the Almond for the South Baggs- West Side Canal field ………..…………………………………………………….. 13 Figure 1.8 Seismic line showing significant horizons picked on South Baggs-West Side Canal survey………………………………………………….….. 14 Figure 1.9 Seismic line B-B’ showing a flower structure observed by Hull (2001)…… 15 Figure 1.10 Shaded relief map showing location of study area…..…….…………..…... 16 Figure 1.11 Index map of northwestern Colorado and south-central Wyoming showing study area and gas fields …………….…………………………...….……. 18 Figure 2.1 Stratigraphic chart showing Phanerozoic nomenclature for the state of Wyoming ..…..………………………..………………………............................. 21 Figure 2.2 Chronostratigraphic column and type log.…..…………..…..…….….…….. 27 Figure 2.3 Structure map of southwestern Wyoming and adjacent areas …....……........ 30 Figure 2.4. The location of the study area is shown in relation to the Interior Cretaceous Seaway ………………………………………………..……………….. 32 vii Figure 2.5. Contractional amalgamation boundaries indicating major northeast-striking tectonic provinces. …………………………..…………… 33 Figure 2.6 Interpreted Landsat image of the Cherokee Ridge Arch ……...……………. 36 Figure 3.1 Seismic base map showing the location of seismic lines …..……....………. 40 Figure 3.2 Synthetic seismogram for the Celsius Bogey Draw 1 well ……………........ 44 Figure 3.3 Synthetic seismogram for the Haystack Unit 4 well …………….…………. 45 Figure 3.4 Synthetic seismogram for the South Baggs Unit 26 well …………………... 47 Figure 3.5 Interpreted seismic line L-L’ …………………………...…………………... 49 Figure 3.6 Horizon calibration: comparison of Cherokee Arch survey vs. South Baggs survey ………………………………………………………………… 51 Figure 3.7 Horizon calibration: comparison of Cherokee Arch survey vs. Powder Mountain survey ………………………………………………….……….. 52 Figure 3.8 Interpreted seismic line K-K’ ………………………………….…………… 54 Figure 3.9 Interpreted seismic line A-A’ ………………………………………………. 55 Figure 3.10 Interpreted seismic line B-B’ ………………………..………….…………. 56 Figure 3.11 Interpreted seismic line C-C’ ..……...………………..……………………. 57 Figure 3.12 Interpreted seismic line D-D’ …………………………..…………………. 58 Figure 3.13 Interpreted seismic line E-E’ …………...…………………………………. 59 Figure 3.14 Interpreted seismic line F-F’ …………...…………………………………. 60 Figure 3.15 Interpreted seismic line G-G’ …………..…………………………………. 61 Figure 3.16 Interpreted seismic line H-H’ …………..…………………………………. 62 Figure 3.17 Interpreted seismic line I-I’ …………….…………………………………. 63 viii Figure 3.18 Interpreted seismic line J-J’ …………….…………………………………. 64 Figure 3.19 Time structure map of the Madison horizon ………………..…………….. 67 Figure 3.20 Time structure map of the Shinarump horizon …………….……………… 68 Figure 3.21 Time structure map of the Above Frontier horizon …...……….…..……… 69 Figure 3.22 Time structure map of the Mancos horizon …………………..…………… 70 Figure 3.23 Time structure map of the Almond horizon ………………………………. 71 Figure 3.24 Time structure map of the Lance/Fox Hills horizon ………………...……. 72 Figure 3.25 Time structure map of the Fort Union horizon ………………..…………... 73 Figure 3.26 Time slice map at 3608 ms (two way travel time) ……………...………… 75 Figure 3.27 Time slice map at 2352 ms (two way travel time) ……………...………… 76 Figure 3.28 Time slice map at 1848 ms (two way travel time) …………..…….……… 77 Figure 3.29 Time slice map at 1624 ms (two way travel time) …….……….….……… 78 Figure 3.30 Time slice map at 1504 ms (two way travel time) …………....….……….. 79 Figure 3.31 Isochron map from Shinarump – Madison ………..………………………. 82 Figure 3.32 Isochron map from Above Frontier – Shinarump ………..……………….. 83 Figure 3.33 Isochron map from Mancos – Above Frontier ……………………...…….. 84 Figure 3.34 Interpreted seismic line E-E’ showing intervals of major thickness change……………………………………………………………... 86 Figure 3.35 Isochron map from Almond – Mancos ……………………………………. 88 Figure 3.36 Isochron map from Lance/Fox Hills – Almond ………………..…………. 89 Figure 3.37 Isochron map from Fort Union – Lance/Fox Hills ………………...……… 91 ix Figure 3.38 Percentage of thickening vs. time (Ma) …………..……………………….. 95 x LIST OF TABLES Table 3.1 Average interval velocity based on the South Baggs Unit 26 synthetic seismogram ………………………..………………………………...….... 81 xi ACKNOWLEDGEMENTS A project such as this could not have been completed without the help, consideration and understanding of many people: ¾ I thank Dr. Neil Hurley, my advisor, for his endless help and technical guidance in this research and throughout my studies at CSM. His comments helped to focus my thinking and made me critically evaluate the ideas presented here. ¾ My gratitude goes to Drs. Charles Kluth and Robert Benson for their valuable collaboration. They provided important input, advice and suggestions at different stages of the project that allowed me to make this product better. ¾ I acknowledge PDVSA for providing financial support. ¾ John Young, Ed Blott and Joel Scoville kindly provided data and advice for use