A well-preserved 250 million-year-old oil accumulation in the Tarim Basin,western China: Implications for hydrocarbon exploration in old and deep basins |
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| Institution: | 1. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China;2. CSIRO Division of Earth Science and Resource Engineering, P.O. Box 1130, Bentley, WA 6102, Australia;3. Tarim Oilfield Research Institute of Exploration and Development, PetroChina, Xinjiang, Korla 841000, China;1. Key Lab of Petroleum Geochemistry, CNPC, Beijing 100083, China;2. State Key Lab for Enhancing Oil Recovery, Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China;3. School of Energy Resource, China University of Geosciences, Beijing 100083, China;4. Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;2. Institute of Earth Sciences, The Hebrew University, Jerusalem 91904, Israel;3. Tarim Oilfield Company, PetroChina, Korla, Xinjiang 841000, China;1. School of Geosciences, China University of Petroleum, Qingdao, 266580, China;2. Institute of Energy, Peking University, Beijing, 100871, China;3. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266071, China;4. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 10083, China;2. Beijing Research Institute of Uranium Geology, Beijing 100029, China |
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| Abstract: | A giant oilfield (YM-2) with an estimated reserve of close to one billion bbl was recently discovered in an Ordovician carbonate reservoir at a burial depth of 5800–6200 m in the northern Tarim Basin, western China. Biomarker and isotope geochemistry of the hydrocarbons indicate that the oil was derived from Ordovician marine source rocks at early to peak oil generation. Authigenic illite (K–Ar) dating, fluid inclusion analysis, fluid inclusion PVTx and thermal history modeling indicate that the accumulation is of primary in origin, and the original charge occurred in the Permian during the Late Hercynian Orogenic Stage, approximately 290–250 million years ago. The physiochemical compositions of the hydrocarbons and formation water remained largely unchanged since the initial accumulation. The excellent preservation of such an old accumulation at such a great depth is due to continuous burial of the YM-2 structure since the Triassic, a thick effective seal, and a relatively low geothermal gradient with a current reservoir temperature of 127–130 °C. This finding suggests that under suitable conditions old petroleum accumulations can be well-preserved, and some old and deep basins may be prospective frontiers for future exploration. |
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