Effects of oil cracking on fluorescence color,homogenization temperature and trapping pressure reconstruction of oil inclusions from deeply buried reservoirs in the northern Dongying Depression,Bohai Bay Basin,China |
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| Institution: | 1. Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences, Wuhan 430074, China;2. Department of Earth and Planetary Sciences and Macquarie University Marine Research Centre, Macquarie University, North Ryde, Sydney, NSW 2109, Australia;3. UMR 6524 ‘Magmas et Volcans’, Universite Blaise Pascal, 5, Rue Kessler, F-63038 Clermont-Ferrand Cedex, France;1. Department of Earth Science, Zhejiang University, Hangzhou 310027, China;2. School of Geosciences, China University of Petroleum, Qingdao 266580, China;3. Research Institute of Unconventional Petroleum and Renewable Energy, China University of Petroleum, Qingdao 266580, China;4. State Key Laboratory of Organic Geochemistry (SKLOG), Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;5. State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China;6. Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing 100083, China;1. Faculty of Engineering, University of Nottingham, The Energy Technologies Building, Innovation Park, Jubilee Campus, Triumph Road, Nottingham NG7 2TU, UK;2. Advanced Geochemical Systems Ltd., 1 Towles Fields, Burton-on-the-Wolds, Leicestershire LE12 5TD, UK;3. Centre for Environmental Geochemistry, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK;1. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China;2. Colorado School of Mines, Golden, CO 80401, USA;3. Tarim Oilfield Research Institute of Exploration and Development, PetroChina, Xinjiang, Korla 841000, China;4. China University of Petroleum, Qingdao, Shandong 266580, China;1. School of Geosciences, China University of Petroleum, Qingdao, Shandong 266580, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266071, China;3. Dept. of Geosciences, The University of Arizona, 1040 E 4th St., Tucson, AZ 85721, USA;4. Research Institute of Yanchang Petroleum (GROUP) Co., Ltd, Xi’an, Shanxi 710075, China;5. College of Geological Science and Engineering, Shandong University of Science and Technology, Qingdao, Shandong 266590, China |
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| Abstract: | The effects of oil cracking on fluorescence color, homogenization temperature (Tho) and trapping pressure (Pt) of oil inclusions from deeply buried reservoirs (DBRs) (3672–4359 m) in the northern Dongying Depression were determined based on fluorescence spectroscopy and homogenization temperatures of oil inclusions, kinetic modeling of crude oil cracking, and petroleum inclusion thermodynamics modeling.The modeling results demonstrate that fluorescence color, Tho and predicted Pt have strong relationships with the transformation rate via cracking of oil to gas (Tr), and the formation temperature (Tf) that the inclusions experienced. The fluorescence color is hardly influenced at all during the initial stages of oil cracking (Tr < 13%, Tf < 160 °C), but fluorescence color begins to shift toward shorter wavelengths (blue shift) during progressive oil cracking (Tr < 24%, Tf < 190 °C). With further oil cracking, the fluorescence color may either experience no change or continue its blue shift. Eventually the fluorescence color will disappear as the aromatic compounds are completely cracked. The Tho increases at first (Tr < 24%, Tf < 190 °C), but then decreases or even becomes negative during major oil cracking. The reconstructed Pt values show a corresponding reverse trend.Oil inclusions from DBRs and other shallow reservoirs in the Dongying Depression show an obvious blue shift in fluorescence color at a depth of approximate 4000 m (Tf = 160 °C) and generally contain solid bitumen below 4000 m, supporting the effect of oil cracking on fluorescence variation, consistent with the modeling result. The Tho from DBRs in the Minfeng area increases with increasing burial depth (Tf < 190 °C), which is also consistent with the modeling results. However, the Tho of oil inclusions with blue-white fluorescence from DBRs in the Shengtuo area did not show such a trend. Recent trapping, high trapping pressure and higher-maturity oil may have led to a low-degree of oil cracking, and thus less modification of Tho in the Shengtuo area.Oil cracking results in consistent volume ratios of pyrobitumen to oil inclusions (Fvpy) in the same fluid inclusion assemblage, and the Fvpy value increases with oil cracking level, which can be used to recognize if oil cracking has occurred in oil inclusions and what level of oil cracking they have experienced.As the oil cracking model used in this study did not account for the role of pressure, it is more applicable for oil inclusions that were trapped under normally pressured conditions. Oil inclusions trapped under overpressured conditions will be less influenced by oil cracking. |
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| Keywords: | Petroleum inclusion Fluorescence spectroscopy Homogenization temperature Trapping pressure Overpressure Pyrobitumen Oil cracking kinetics Petroleum inclusion thermodynamics modeling |
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