Evaluation of sedimentary features and biomarkers in the Paleogene Niubao formation in the Lunpola basin, Tibetan platea
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ORIGINAL PAPER
Evaluation of sedimentary features and biomarkers in the Paleogene Niubao formation in the Lunpola basin, Tibetan plateau: implications for the oil source rocks and exploration Hao Liu1,2,4 · Chan Wang3,4 · Jianghong Deng3 · Bin Deng3 · Yong Li1,2 · Yunlong Xu1,2 Received: 18 May 2020 / Accepted: 28 October 2020 © Geologische Vereinigung e.V. (GV) 2020
Abstract The Paleogene Niubao formation is mainly exposed in the central part of the Lunpola basin in the hinterland of the Tibetan Plateau and has high potential for oil and gas exploration and development. The biomarkers of source rocks are systematically studied by selecting representative samples. The middle and upper Niubao formation contain rhythmically inter-bedded mudstone and sandstone that show periodic variations characteristic of the lake water environment. Additionally, the large volumes of muddy dolomite in the upper Niubao formation (UNF) are associated with high salinity in the lake environment under a hot and arid climate. The organic geochemical analysis shows that the middle Niubao formation (MNF) and UNF have high organic abundance (total organic carbon (TOC) contents of 1.48–8.96% in the MNF and 1.52–12.83% in the UNF) and type I–II kerogen. The analysis shows that the UNF was deposited in a persistent, anoxic, stratified and highly saline paleo-lake environment, which was beneficial to the preservation of organic matter. The high phytoalkane and γ-paraffin contents in the UNF indicate a strongly reducing and highly saline lacustrine depositional environment. The high pregnane contents and ascending sterane in the source rocks in the MNF indicate high maturity, and the distribution of n-alkanes and regular sterane indicates the input of some terrestrial organic matter. The high maturity indicates that the source rock in the MNF may represent the main hydrocarbon-generating layer in the basin. Keywords Biomarkers · Source rocks · Oil and gas basins · Paleogene · Tibetan plateau
Introduction Oil shale is one of the most important large-scale recoverable fossil fuels. The total reserves in China exceed 7199.37 × 108 t, among which the Tibetan Plateau, which is virgin land for energy exploration and development in China, has considerable energy reserves, with proven reserves reaching * Chan Wang [email protected] 1
College of Energy, Chengdu University of Technology, Chengdu, Sichuan, China
2
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan, China
3
College of Earth Science, Chengdu University of Technology, Chengdu, Sichuan, China
4
School of Environment and Earth Science, The University of Queensland, Brisbane, QLD, Australia
1200 × 108 t (Zhang et al. 2011). As the first reserve in the lacustrine basin of the Tibetan Plateau, the Lunpola basin has proven reserves of 60 × 108 t, which indicates that the Lunpola basin has considerable reserves and prospects for oil and gas production (Zhao et al. 2006). Historically, oil and gas exploration
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