Organic geochemistry of marine source rocks and pyrobitumen-containing reservoir rocks of the Sichuan Basin and neighbouring areas,SW China |
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| Institution: | 1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou 510640, China;2. Wuxi Institute of Petroleum Geology, Sinopec, Wuxi, Jiangsu 214151, China;3. Research Institute of Petroleum Exploration and Development-Langfang Branch, PetroChina Ltd, Langfang, Hebei 065007, China;4. Southwest Oil and Gas Field Company, PetroChina, Chengdu, Sichuan 610051, China;5. Research Institute of Petroleum Exploration and Development, PetroChina Ltd, Beijing 100083, China;6. Zhongyuan Oilfield Company, Sinopec, Puyang, Henan 457001, China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China;2. University of Geosciences, Beijing 100083, China;3. Xinjiang Petroleum Institute, PetroChina, Karamay 83400, China;4. Exploration & Production Research Institute, Sinopec, Beijing 100083, China;1. Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland;2. Oil and Gas Institute, ul. Lubicz 25a, 31-503 Kraków, Poland;1. School of Geosciences, China University of Petroleum, 66 Changjiang West Road, Huangdao District, Qingdao, Shandong, 266580, China;2. College of Geosciences, China University of Petroleum, 18 Fuxue Road, Changping District, Beijing, 102249, China;3. College of Geological Science and Engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Huangdao District, Qingdao, Shandong, 266510, China;1. Research Institute of Exploration and Development, China National Petroleum Corporation, Beijing 100083, China;2. Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China;3. Institute of Earthguake Science, China Seismological Bureau, Beijing 100036, China;1. PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China;2. Geophysical Exploration Company, CNPC Chuanqing Drilling Engineering Limited Company, Chengdu, Sichuan 610210, China |
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| Abstract: | Three bitumen fractions were obtained and systematically analysed for the terpane and sterane composition from 30 Paleozoic source rocks and 64 bitumen-containing reservoir rocks within the Upper Sinian, Lower Cambrian, Lower Silurian, Middle Carboniferous, Upper Permian and Lower Triassic strata in the Sichuan Basin and neighbouring areas, China. These bitumen fractions include extractable oils (bitumen I), oil-bearing fluid inclusions and/or closely associated components with the kerogen or pyrobitumen/mineral matrix, released during kerogen or pyrobitumen isolation and demineralization (bitumen II), and bound compounds within the kerogen or pyrobitumen released by confined pyrolysis (bitumen III). In addition, atomic H/C and O/C ratios and carbon isotopic compositions of kerogen and pyrobitumen from some of the samples were measured. Geochemical results and geological information suggest that: (1) in the Central Sichuan Basin, hydrocarbon gases in reservoirs within the fourth section of the Upper Sinian Dengying Formation were derived from both the Lower Cambrian and Upper Sinian source rocks; and (2) in the Eastern Sichuan Basin, hydrocarbon gases in Middle Carboniferous Huanglong Formation reservoirs were mainly derived from Lower Silurian source rocks, while those in Upper Permian and Lower Triassic reservoirs were mainly derived from both Upper Permian and Lower Silurian marine source rocks. For both the source and reservoir rocks, bitumen III fractions generally show relatively lower maturity near the peak oil generation stage, while the other two bitumen fractions show very high maturities based on terpane and sterane distributions. Tricyclic terpanes evolved from the distribution pattern C20 < C21 < C23, through C20 < C21 > C23, finally to C20 > C21 > C23 during severe thermal stress. The concentration of C30 diahopane in bitumen III (the bound components released from confined pyrolysis) is substantially lower than in the other two bitumen fractions for four terrigenous Upper Permian source rocks, demonstrating that this compound originated from free hopanoid precursors, rather than hopanoids bound to the kerogen. |
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| Keywords: | Sichuan basin Sequential extraction Kerogen and pyrobitumen pyrolysis Terpanes and steranes Carbon isotope |
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