Geochemical characteristics and isotopic reversal of natural gases in eastern Kopeh-Dagh,NE Iran |
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| Institution: | 1. Department of Geology, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Iran;2. Petroleum Geology and Geochemistry Research Centre (PGGRC), Shahid Chamran University of Ahvaz, Iran;3. National Iranian Oil Company, Exploration Directorate, Tehran, Iran;1. A.P. Karpinsky Russian Geological Research Institute (VSEGEI), Sredny Av. 74, 199106, St. Petersburg, Russia;2. Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655, Hannover, Germany;3. Institute of Geology, Leibniz University Hannover, Callinstraße, 30, 30167, Hannover, Germany;4. TOTAL EXPLO EAC /PN, 2 Place Jean Millier, 92069, Paris La Defense, France;1. Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, Wuhan 430074, China;2. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;3. Shenzhen Branch of China National Offshore Oil Corporation Ltd., Shenzhen 510240, China;1. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China;2. Department of Geochemistry, Yangtze University, Jingzhou, Hubei 434023, PR China;3. The School of Earth Science and Resources, China University of Geosciences, Beijing 100083, PR China;4. Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China;1. Department of Geology, School of Science, University of Sulaimani, Kurdistan, Iraq;2. Geology Department, Faculty of Applied Science, Taiz University, 6803 Taiz, Yemen;1. Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Wuhan 430074, China;2. School of Petroleum Engineering, University of New South Wales, Sydney, NSW 2052, Australia;1. Department of Geology, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Iran;2. Petroleum Geology and Geochemistry Research Centre, (PGGRC), Shahid Chamran University of Ahvaz, Iran;3. National Iranian Oil Company, Exploration Directorate, Tehran, Iran |
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| Abstract: | Natural gas samples from two gas fields located in Eastern Kopeh-Dagh area were analyzed for molecular and stable isotope compositions. The gaseous hydrocarbons in both Lower Cretaceous clastic reservoir and Upper Jurassic carbonate reservoir are coal-type gases mainly derived from type III kerogen, however enriched δD values of methane implies presence of type II kerogen related material in the source rock. In comparison Upper Jurassic carbonate reservoir gases show higher dryness coefficient resulted through TSR, while presence of C1 C5 gases in Lower Cretaceous clastic reservoir exhibit no TSR phenomenon. Carbon isotopic values indicate gas to gas cracking and TSR occurrence in the Upper Jurassic carbonate reservoir, as the result of elevated temperature experienced, prior to the following uplifts in last 33–37 million years. The δ13C of carbon dioxide and δ34S of hydrogen sulfide in Upper Jurassic carbonate reservoir do not primarily reflect TSR, as uplift related carbonate rock dissolution by acidic gases and reaction/precipitation of light H2S have changed these values severely. Gaseous hydrocarbons in both reservoirs exhibit enrichment in C2 gas member, with the carbonate reservoir having higher values resulted through mixing with highly-mature-completely-reversed shale gases. It is likely that the uplifts have lifted off the pressure on shale gases, therefore facilitated the migration of the gases into overlying horizons. However it appears that the released gases during the first major uplift (33–37 million years ago) have migrated to both reservoirs, while the second migrated gases have only mixed with Upper Jurassic carbonate reservoir gases. The studied data suggesting that economic accumulations of natural gas/shale gases deeper than Upper Jurassic carbonate reservoir would be unlikely. |
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| Keywords: | Carbon isotope Eastern Kopeh-Dagh TSR Mixing |
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