The Geochemistry of Oils and Gases From the Cumberland Overthrust Sheet in Virginia and Tennessee By Kristin O. Dennen, Mark Deering, and Robert C. Burruss Chapter G.12 of Coal and Petroleum Resources in the Appalachian Basin: Distribution, Geologic Framework, and Geochemical Character Edited by Leslie F. Ruppert and Robert T. Ryder Professional Paper 1708 U.S. Department of the Interior U.S. Geological Survey Suggested citation: Dennen, K.O., Deering, Mark, and Burruss, R.C., 2014, The geochemistry of oils and gases from the Cumberland overthrust sheet in Virginia and Tennessee, chap. G.12 of Ruppert, L.F., and Ryder, R.T., eds., Coal and petroleum resources in the Appalachian basin; Distribution, geologic framework, and geochemical character: U.S. Geological Survey Professional Paper 1708, 38 p., http://dx.doi.org/10.3133/pp1708G.12. iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Petroleum Geology Overview ......................................................................................................................1 Regional Geology ..................................................................................................................................1 Structure of the Cumberland Overthrust Sheet ...............................................................................4 Reservoir Characteristics ....................................................................................................................4 Possible Source Rocks ........................................................................................................................4 The Gloeocapsomorpha Prisca Enigma ............................................................................................7 Methods...........................................................................................................................................................8 Sample Collection .................................................................................................................................8 Instrumental Analysis...........................................................................................................................8 Whole Crude Oil ...........................................................................................................................8 Elemental, Isotopic, and API Gravity Analysis ........................................................................8 Standard Biomarker Analysis ....................................................................................................9 Natural Gas Analysis ...................................................................................................................9 Results .............................................................................................................................................................9 Oil Geochemistry ...................................................................................................................................9 Elemental, Isotopic, and API Gravity Analysis ........................................................................9 Biomarker Profiles .......................................................................................................................9 Terpanes ...............................................................................................................................9 Steranes .............................................................................................................................11 Aromatic Fraction Biomarkers .......................................................................................11 Natural Gas Geochemistry ................................................................................................................11 Molecular Composition .............................................................................................................11 Isotopic Composition of Methane, Ethane, Deuterium, and Carbon Dioxide ..................11 Isotopic Composition of Gases With Higher Carbon Numbers ..........................................11 Discussion .....................................................................................................................................................16 Data Quality..........................................................................................................................................16 Compositional Trends in Oil From the Cumberland Overthrust Sheet ........................................16 Gas Chromatographic and Biomarker Profiles .....................................................................16 Light Hydrocarbon Parameters ...............................................................................................16 Isotopic Composition of Oil ......................................................................................................18 Evidence for Variations in the Depositional Environment of the Source Rocks .......................18 Pristane-to-Phytane Ratio and Carbon Preference Index ..................................................18 Carbon Preference Index .........................................................................................................18 Natural Gas Geochemistry ................................................................................................................22 Methane ......................................................................................................................................22 Ethane and Propane ..................................................................................................................22 Natural Gas Plots .......................................................................................................................22 Natural Gas From the Ben Hur and Rose Hill Fields ...................................................23 Natural Gas From the Swan Creek Field .......................................................................23 Conclusions...................................................................................................................................................24 iv Acknowledgments .......................................................................................................................................26 References Cited..........................................................................................................................................26 Appendix A.—Individual Gas Chromatographic Profiles of the Whole Crude Oils ..........................29 Appendix B.—Representative Biomarker Profiles ................................................................................37 Figures 1. Map showing the location of the study area ...........................................................................2 2. Generalized stratigraphic chart for the Cumberland overthrust sheet ...............................3 3. Generalized cross sections of the study area .........................................................................5 4. Bar charts showing percentage of each molecular component in the analyzed gas samples from the Cumberland overthrust sheet ............................................................15 5.–13. Graphs showing— 5. The n-heptane-to-methylcyclohexane ratio versus the toluene-to-n-heptane ratio of oil samples from the Cumberland overthrust sheet and from oil samples from other Paleozoic reservoirs in the United States and Canada ....................17 6. The iso-heptane values versus n-heptane values of oil samples from the Cumberland overthrust sheet and of oil samples from Ordovician to Tertiary reservoirs elsewhere in the United States and Canada ......................................................19 7. The isotopic compositon of carbon of the saturated fraction of the oil versus the isotopic composition of carbon of the aromatic fraction of the oil from the samples in this study, along with isotopic composition of carbon values from the saturated and aromatic fractions of oil samples from the Trenton Group in the Michigan basin for comparison ........................................................................20 8. The carbon preference index versus the pristane-to-phytane ratio for the oil samples in this study and for oil samples from other geographic areas for comparison ............................................................................................................................21 9. The ratio of gas wetness versus the average depth below well head of a gas-producing formation for gas samples from the Cumberland overthrust sheet ..........................................................................................................................22 10. The isotopic composition of carbon in methane relative to the Vienna Peedee belemnite standard versus the isotopic composition of hydrogen (deuterium) in methane relative to the Vienna standard mean ocean water standard for gas samples from the Cumberland overthrust sheet ............................................................23 11. The isotopic composition of carbon in propane versus that in ethane for the gas samples from the Cumberland overthrust