Application of the monoterpane ratio (MTR) to distinguish marine oils from terrigenous oils and infer depositional environment in northern Tarim Basin,China |
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| Institution: | 1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, 18 Fuxue Road, Beijing 102249, China;2. Department of Organic Geochemistry and Environmental Science, College of Geosciences, China University of Petroleum, 18 Fuxue Road, Beijing 102249, China;3. Department of Geoscience, University of Calgary, 2500 University Drive, NW, Calgary, Alberta T2N 1N4, Canada;4. School of Energy Resource, China University of Geosciences, Beijing 100083, China;1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 511 Kehua Street, Guangzhou, Guangdong 510640, China;2. Xi''an AMS Center and State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an 710075, China;3. Tarim Oilfield Company, PetroChina, Kuerle 841000, China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;2. Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences, Wuhan 430074, 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. 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. Institute of Earth Sciences, Hebrew University, Jerusalem 91904, Israel;4. Liverpool University, Department of Earth, Ocean and Ecological Sciences, Liverpool, Merseyside L69 3GP, UK;1. Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences), Ministry of Education, Wuhan, 430074, China;2. China University of Petroleum (Huadong), Qingdao, Shandong, 266580, China;3. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing, 100083, China;4. China University of Petroleum, Changping, Beijing 102249, China |
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| Abstract: | Six monoterpenoid hydrocarbons including two acyclic, two monocyclic and two aromatic components were identified and quantified in 49 oil and condensate samples using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC–TOFMS). Among them, 2,6-dimethyloctane (2,6-DMO) and 2-methyl-3-ethylheptane (2-M-3-EH) are the most abundant compounds and geochemically significant. Used in conjunction with other geochemical parameters such as pristane/phytane (Pr/Ph) and dibenzothiophene/phenanthrene (DBT/P) ratios, the 2-M-3-EH/2,6-DMO ratio (monoterpane ratio, MTR) provides a useful tool for distinguishing marine oils and condensates from those of terrigenous origin. Oils and condensates derived from marine source rocks have high MTR (> 0.4), low Pr/Ph and high DBT/P values, whereas those generated from terrigenous source rocks have lower MTR (< 0.3), higher Pr/Ph and lower DBT/P values. Differences in MTR values are mainly caused by variations in the concentrations of 2-M-3-EH as the concentrations of 2,6-DMO are in the same range in different sample groups. The 2-M-3-EH is enriched in marine oils and condensates from highly anoxic depositional environments, but depleted in terrigenous oils and condensates from oxic/sub-oxic depositional environments. The MTR may serve as a new parameter for assigning the source rock depositional environment. MTR values higher than 0.4 may indicate reducing conditions while MTR values lower than 0.3 may suggest an oxic/sub-oxic condition. |
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| Keywords: | Monoterpenoid hydrocarbons 2-Methyl-3-ethylheptane 2 6-Dimethyloctane Depositional environment Tarim Basin |
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