Spatial Dynamics of Tertiary Igneous Intrusion in Raton Basin, Southern Colorado Charles Lee Cavness III Submitted in partial fulfillment of the requirements for the degree of Bachelor of Arts Department of Geology Middlebury College Middlebury, Vermont May 2009 Spatial Dynamics of Tertiary Igneous Intrusion in Raton Basin, Southern Colorado Charles Cavness, Department of Geology Middlebury College, Middlebury, Vermont 05753 Between 33Ma and 20Ma, over 500 dikes intruded the Raton Basin in Southern Colorado. Dikes extend radially from the Spanish Peaks double volcano located on the northwest margin of the basin. In addition to dikes, sills permeate the basin, often intruding bituminous rank coal beds used by oil and gas companies to extract Coal Bed Methane (CBM). Previous research focusing on the geothermal and intrusive history of the basin suggests that the pervasive sill complexes are directly related to “feeder dikes.” This report combines 89 CBM well logs and an aeromagnetic survey to test this feeder dike hypothesis. Sills are identified in well logs by dual induction resistivity (DIR) log spikes exceeding 200 ohm(m). Dikes are identified by rotated to poll (RTP) vertical magnetic gradients exceeding 65 nT/m and dikes are mapped by tracing anomalous gradient ridges on aeromagnetic maps. Sill abundance is quantified for five stratigraphic categories in each well. Abundance is compared to (a) the proximity of the nearest dike to a given well and (b) the number of dikes within ten proximity ranges (500 meter intervals from 500 meters to 5 kilometers). Results show that sill abundance is significantly controlled by the number of dikes within 500 meters from a well, but that dikes outside of the 500 meter range have an insignificant effect on sill abundance in a well. Furthermore, the proximity of the single closest dike has a negligible effect on sill abundance. Results are presented in a series of scatter and bar graphs with accompanying regression analysis. Isopach mapping of sills supports statistical results by showing sill “hotspots” coinciding with areas of dike convergence. Given the quantitative and qualitative evidence that dike frequency within close proximity to a well affects sill abundance, the feeder dike hypothesis can be confirmed. These results may be useful to geothermal energy companies and CMB companies. Previous research suggests that sills control the movement of hydrothermal fluids, so drilling in areas where dikes converge on the surface will increase the probability of intercepting sills and the connected hydrothermal resources. Furthermore, CBM producers may avoid areas where sills have intruded and destroyed coals by drilling in areas removed from dikes. ii Acknowledgements I owe many thanks to those who made this project possible. Certainly the place to start will be my family. I owe you the most. Without you I would never have the opportunities that I enjoy so cavalierly today. Thank you mom and dad especially for all the support, love, encouragement, and advice. I can never repay you for all that you’ve given; I only hope that I’ve made you proud. Dad, you have been a guide and a motivator through my entire life – you always show me the way and push me to improve and excel. Mom, you have been my emotional support and nurturer – I don’t know how I could have survived without you. Frazier, you’ve been a great brother and friend, and I’m so proud of everything that you’ve accomplished. Thanks for keeping me in check. Thank you to the Middlebury Geology department. The department’s culture fueled me academically and socially during the long nights and challenging problem sets. That special culture would be impossible without the amazing faculty. Thank you Ray Coish, Pat Manley, Tom Manley, Jeff Munroe, Pete Ryan (thanks for a great senior seminar), and Eileen Fahey for making the fourth floor so lively. I also want to thank the other geology seniors for making our seminar one of the most enjoyable class I’ve taken at Middlebury. The closeness of our major made my thesis feel more like a group project than a solo mission. I’d like to give special thanks to Dave West for his tremendous advising on this project and throughout my career at Middlebury. Dave, you introduced me to geology and sparked my excitement in the subject. It was a privilege and honor to speak at your reception of the Perkins Award, which could not have been awarded to a more deserving professor. I sincerely appreciate all the opportunities afforded to me by Middlebury College. You surrounded me with great people and great ideas. Thank you for the Senior Research Fellowship, Palen ’40 Travel Conference Grant, Sustainable Study Abroad Grant, Old Stone Mill office and creative space, ACE grant, and countless other opportunities. Thank you Midd for helping me become the person that I am proud to be. Thanks to Pioneer Natural Resources and all its employees. Hal Macartney deserves special accolades; he was instrumental in facilitating this project, delivering the required data, and securing a license of PETRA software for Middlebury. Furthermore, Hal was a tremendous mentor and advisor during my summer working at Pioneer. Thank you Hadi Soetrisno, Karyn Powell, Neal Dannemiller, Paul Wilson, Sarah Hawkins, and Paul Clarke for answering so many of my questions and providing important information for this project. Thank you Bill Hegman and Chris Rodgers for your assistance in the stunningly complicated PETRA installation and data upload process. I may not have made it past square one without you. Last but certainly not least I must thank all my friends who always kept my work in check with my life. Some would say you’ve been a horrible influence, but I wouldn’t have it any other way. Thank you for so many memories – you are the greatest piece of my college experience, and you are who I will remember most fondly. You are fascinating, caring, genuine, and so much fun, and I am lucky to have each one of you in my life. iii TABLE OF CONTENTS TEXT PAGE Abstract ii Acknowledgements iii Table of Contents iv List of Figures vi Chapters: I. Introduction 1 II. Background on Geothermal Energy 3 III. Geology of Raton Basin 9 Introduction 11 Basin History and Stratigraphy 13 Structure 13 Igneous and Intrusive Geology 14 Coal and Coal Bed Methane 16 Geothermal Gradients 18 Previous Research in Raton Basin 19 IV. Data and Sources 20 Data and Sources 20 Well Data 22 Magnetic Data 24 Coal Data 24 V. Methods 26 Sill Measurements 26 Complex Identification 27 Sill Measurement Error 29 Dike Proximity Measurements 29 Dike Measurement Error 30 iv VI. Results 32 Nearest Dike Proximity 32 Frequency of Dikes Within Varying Proximity Ranges 36 Sill Isopach Mapping 40 Coal Isopach Mapping 43 VII. Discussion 47 Nearest Dike Proximity 47 Frequency of Dikes Within Varying Proximity Ranges 50 Positive Correlation between Sill Thickness and 500 m Dikes 51 Sill Isopach Mapping 53 Coal Isopach Mapping 54 Additional Controls 55 Recommendations for Future Studies 56 VIII. Conclusions 58 IX. References Cited 60 X. Appendix A 63 XI. Appendix B 66 XII. Appendix C 68 v LIST OF FIGURES FIGURE PAGE 1. Locator Map 2 2. Diagram of Geothermal Energy Facility 4 3. Diagram of Binary Cycle Turbine 4 4. Diagram of Heat Exchanger 5 5. Well Cost Curve 7 6. Structural Map of Raton Basin 10 7. Generalized Stratigraphic Column of Raton Basin 11 8. Photograph of the Stone Wall dike 15 9. Photograph of Vertical Dikes 16 10. Photograph of Intruded Coal Seam 18 11. Map of Well Points 21 12. Well Log Example 23 13. Aeromagnetic Map 25 14. Sill Induced DIR Log Spike 26 15. Sill Complex Identification and Highlighting 28 16. Scatter Plot: Total Sill Thickness vs. Nearest Dike Proximity 33 17. Scatter Plot: Raton Sill Thickness vs. Nearest Dike Proximity 33 18. Scatter Plot: Vermejo Sill Thickness vs. Nearest Dike Proximity 34 vi 19. Scatter Plot: Lower Raton Complex vs. Nearest Dike Proximity 34 20. Scatter Plot: Upper Raton Complex vs. Nearest Dike Proximity 35 21. Scatter Plot: Average Sill Thickness vs. 500m Dikes 37 22. Bar Graph: Average Sill Thickness vs. 1000m Dikes 37 23. Bar Graph: Average Sill Thickness vs. 2500m Dikes 38 24. Bar Graph: Average Sill Thickness vs. 5000m Dikes 38 25. Isopach Map of Sill Thickness in the Raton Formation 41 26. Isopach Map of Sill Thickness in the Vermejo Formation 42 27. Isopach Map of Coal Thickness in the Raton Formation 45 28. Isopach Map of Coal Thickness in the Vermejo Formation 46 29. Diagrammatic Cross Section of Intrusion Situation 49 vii I. Introduction Geothermal energy presents an economical, low emission, renewable alternative to hydrocarbon energy sources. The potential for geothermal energy production in the United States, particularly Enhanced Geothermal Systems (EGS), is on the scale of Terawatts (Tester et al., 2006). Furthermore, huge opportunities are offered by partnerships between geothermal energy producers and the oil and gas industry, and the coal bed methane field in the Raton Basin of Southern Colorado (Fig. 1) represents one such partnership opportunity. Geologically, the Raton Basin’s high geothermal gradients present a prime target for geothermal energy production. The basin also offers economic incentives beyond geology and heat potential - existing wells, proximal energy markets, and accessible land leases would reduce the cost of exploration, production, transmission, and land negotiation for geothermal energy companies partnered with gas producers. Geothermal energy producers must understand the sources of heat and the behavior of hydrothermal fluids within a prospect – this research addresses those issues by studying potential heat sources and controls on hydrothermal fluid movement. Previous studies of hydrothermal alteration in the Raton Basin have shown that intrusive bodies within the basin have acted as both heat sources and conduits of hydrothermal fluid in the past (Cooper et al., 2007).