Constraining tectonic compression processes by reservoir pressure evolution: Overpressure generation and evolution in the Kelasu Thrust Belt of Kuqa Foreland Basin,NW China |
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| Institution: | 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;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;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. Institute of Tarim Oilfield Company, PetroChina, Korla, 841000, Xinjiang, China;2. College of Geoscience, China University of Petroleum, Beijing 102249, China;3. State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, 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 |
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| Abstract: | The Kuqa Foreland Basin (KFB) immediately south of the South Tianshan Mountains is a major hydrocarbon producing basin in west China. The Kelasu Thrust Belt in the basin is the most favorable zone for hydrocarbon accumulations. Widespread overpressures are present in both the Cretaceous and Paleogene reservoirs with pressure coefficients up to 2.1. The tectonic compression process in KFB resulted from the South Tianshan Mountains uplift is examined from the viewpoint of the overpressure generation and evolution in the Kelasu Thrust Belt. The overpressure evolution in the reservoir sandstones were reconstructed through fluid inclusion analysis combined with PVT and basin modeling. Overpressures at present day in the mudstone units in the Kelasu Thrust Belt and reservoir sandstones of the Dabei Gas Field and the Keshen zone are believed to have been generated by horizontal tectonic compression. Both disequilibrium compaction and horizontal tectonic compression are thought to contribute to the overpressure development at present day in the reservoir of the Kela-2 Gas Field with the reservoir sandstones showing anomalously high primary porosities and low densities from wireline log and core data. The overpressure evolution for the Cretaceous reservoir sandstone in the Kelasu Thrust Belt evolved through four stages: a normal hydrostatic pressure (>12–5 Ma), a rapidly increasing overpressure (～5–3 Ma), an overpressure release (～3–1.64 Ma) and overpressure preservation (～1.64–0 Ma). Overpressure developed in the second stage (～5–3 Ma) was generated by disequilibrium compaction as tectonic compression due to the uplift of the Tianshan Mountains acted at the northern monocline of KFB from 5 Ma to 3 Ma, which provided abundant sediments for the KFB and caused the anomalously high sedimentation rate during the N2k deposition. From 3 Ma to 1.64 Ma, the action of tectonic compression extended from the northern monocline to the Kelasu Thrust Belt and returned to the northern monocline of KFB from 1.64 Ma to present day. Therefore, the horizontal tectonic compression was the dominant overpressure mechanism for the overpressure generation in the third stage (～3–1.64 Ma) and overpressure caused by disequilibrium compaction from 5 Ma to 3 Ma was only preserved in the Kela-2 Gas Field until present day. |
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| Keywords: | Tectonic compression Overpressure mechanism Overpressure evolution Fluid inclusions Kuqa foreland basin |
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