Thiadiamondoids as proxies for the extent of thermochemical sulfate reduction |
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| Institution: | 1. ExxonMobil Upstream Research Company, P.O. Box 2189, Houston, TX 77252-2189, USA;2. ExxonMobil Research and Engineering Company, Annandale, NJ 08801-0998, USA;3. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA;4. ExxonMobil Exploration Company, 233 Benmar, Houston, TX 77060, USA;5. Schlumberger Information Solutions, Mill Valley, CA 94941, USA;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;2. Institute of Earth Sciences, The Hebrew University, Jerusalem 91904, Israel;3. Tarim Oilfield Company, PetroChina, Korla, Xinjiang 841000, China;1. Key Lab of Petroleum Geochemistry, CNPC, Beijing 100083, China;2. State Key Lab for Enhancing Oil Recovery, Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China;3. Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada;4. School of Energy Resource, China University of Geosciences, Beijing 100083, China;1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA;2. Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260, USA;3. Department of Earth Sciences, University of California, Riverside, CA 92521, USA;1. Key Lab of Petroleum Resources Research, Institute of Geology and Geophysics, CAS, Beijing 100029, China;2. Key Lab of Exploration Technologies for Oil and Gas Resources of Ministry of Education, Yangtze University, Wuhan 430100, China;3. College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;4. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China;1. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China;2. Western Australia Organic and Isotope Geochemistry Centre, Department of Chemistry, Curtin University, GPO Box U1987, Perth, WA 6845, Australia;3. Tarim Oilfield Research Institute of Exploration and Development, PetroChina, Korla 841000, Xinjiang, China;4. Centre for Exploration Targeting, School of Earth Sciences, University of Western Australia, Crawley, WA 6009, Australia |
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| Abstract: | Thiadiamondoids have been analyzed in a suite of Smackover-derived oils from the US Gulf Coast to determine whether their abundance and distribution reflect alteration by thermochemical sulfate reduction (TSR). The sample suite includes oils and condensates having various thermal maturities that are characterized as being unaltered by TSR, altered by TSR, or of uncertain affinities due to inconsistencies between conventional geochemical indicators of TSR. Nearly all samples contain thiadiamondoids, indicating that small amounts of these compounds can be generated from sulfur rich kerogen. TSR results in the generation of H2S, sulfides and thiophenic aromatic hydrocarbons, either by reaction with sulfate or by back reactions with the evolved H2S. Evidence shows that thiadiamondoids originate exclusively from reactions involving TSR. Once generated, their high thermal stability permits thiadiamondoids to accumulate with little further reaction and their abundance reflects not only the occurrence of TSR, but the extent of the alteration. The abundance of thiaadamantanes (1-cage structures) is particularly diagnostic of the onset of TSR. Examination of condensates from reservoirs >180 °C indicates that the thiadiamondoids can be thermally degraded. They are more thermally stable than the dibenzothiophenes, but are less stable than diamondoid hydrocarbons. Their stability appears to increase with increasing cage number, suggesting that the thiatriamantanes are the best proxy for the extent of TSR alteration in very high temperature reservoirs. Polythiadiamondoids (diamondoids with multiple sulfur substitutions) were detected in trace amounts and are also indicators of TSR. |
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