Origin of the hydrocarbon gases carbon dioxide and hydrogen sulfide in Dodan Field (SE-Turkey) |
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| Institution: | 1. Istanbul University, Engineering Faculty, Geology Department, TR-34850, Avc?lar, Istanbul, Turkey;2. TPAO International Projects Department, Sö?ütözü Mah. 2180 Cad. No: 86, 06100, Çankaya, Ankara, Turkey;3. TPAO Exploration Department, Sö?ütözü Mah. 2180 Cad. No: 86, 06100, Çankaya, Ankara, Turkey;1. Université de Lorraine, CNRS, GeoRessources, UMR 7359, BP 70239, F-54506 Vand?uvre-lès-Nancy, France;2. Institute of Geology of Ore Deposits, Mineralogy, Petrography and Geochemistry, Russian Academy of Sciences, IGEM RAS, Staromonetny per. 35, 119017 Moscow, Russia;3. CNRS, CRPG, UMR 7359, 15 rue Notre Dame des Pauvres, F-54500 Vand?uvre-lès-Nancy, France;4. CNRS, IRAP, UMR 5277, 14 avenue Edouard Belin, F-31400 Toulouse, France;1. Petroleum Exploration & Production Research Institute, SINOPEC, Beijing 100083, China;2. Department of Geology and Geophysics, School of Environmental Sciences, University of Liverpool, Liverpool L69 3GP, UK;3. Hangzhou Branch of Research Institute of Petroleum Exploration and Development, PetroChina, Hangzhou 310023, China;4. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China;1. Institute of Earth Sciences, Hebrew University, Jerusalem 91904, Israel;2. US Geological Survey, Denver, CO 80225, USA;3. EOG Resources, Denver, CO 80202, USA;4. Biomarker Technologies, Rohnert Park, CA 94928, USA;5. ExxonMobil Upstream Research Company, Houston, TX 77389, USA;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Changping District, Beijing, 102249, China;2. College of Geosciences, China University of Petroleum, Beijing, 102249, China;3. Research Institute of Exploration and Development, Tarim Oilfield Company, PetroChina, Korla, Xinjiang, 841000, China;1. Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Science, Peking University, Beijing 100871, China;2. Institute of Geophysics, Research Institute of Exploration and Development, PetroChina Xinjiang Oilfield Company, Xinjiang 830013, China;3. PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, Changping, Beijing 102249, China;2. Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences, Wuhan, Hubei 430074, China;3. SINOPEC Exploration Company, Chengdu, Sichuan 610041, China;4. Department of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027, China |
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| Abstract: | Gas occurrences consisting of carbon dioxide (CO2), hydrogen sulfide (H2S), and hydrocarbon (HC) gases and oil within the Dodan Field in southeastern Turkey are located in Cretaceous carbonate reservoir rocks in the Garzan and Mardin Formations. The aim of this study was to determine gas composition and to define the origin of gases in Dodan Field. For this purpose, gas samples were analyzed for their molecular and isotopic composition. The isotopic composition of CO2, with values of ?1.5‰ and ?2.8‰, suggested abiogenic origin from limestone. δ34S values of H2S ranged from +11.9 to +13.4‰. H2S is most likely formed from thermochemical sulfate reduction (TSR) and bacterial sulfate reduction (BSR) within the Bakuk Formation. The Bakuk Formation is composed of a dolomite dominated carbonate succession also containing anhydrite. TSR may occur within an evaporitic environment at temperatures of approximately 120–145 °C. Basin modeling revealed that these temperatures were reached within the Bakuk Formation at 10 Ma. Furthermore, sulfate reducing bacteria were found in oil–water phase samples from Dodan Field. As a result, the H2S in Dodan Field can be considered to have formed by BSR and TSR.As indicated by their isotopic composition, HC gases are of thermogenic origin and were generated within the Upper Permian Kas and Gomaniibrik Formations. As indicated by the heavier isotopic composition of methane and ethane, HC gases were later altered by TSR. Based on our results, the Dodan gas field may have formed as a result of the interaction of the following processes during the last 7–8 Ma: 1) thermogenic gas generation in Permian source rocks, 2) the formation of thrust faults, 3) the lateral-up dip migration of HC-gases due to thrust faults from the Kas Formation into the Bakuk Formation, 4) the formation of H2S and CO2 by TSR within the Bakuk Formation, 5) the vertical migration of gases into reservoirs through the thrust fault, and 6) lateral-up dip migration within reservoir rocks toward the Dodan structure. |
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| Keywords: | Origin of gases Hydrocarbon gases Thermochemical sulfate reduction BSR Basin modeling Southeastern Turkey |
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