Molecular and Carbon Isotopic Compositions of Crude Oils from the Kekeya Area of the Southwest Depression, Tarim Basin: Implications for Oil Groups and Effective Sources

Xiaojie Gao, Qilin Xiao (), Zhushi Ge, Suyang Cai, Haizhu Zhang, Xiang Wang, Zhenping Xu, Zhanghu Wang, Xiaomin Xie and Qiang Meng
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Xiaojie Gao: Key Laboratory of Oil and Gas Resources and Exploration Technology, College of Resources and Environment, Yangtze University, Wuhan 430100, China
Qilin Xiao: Key Laboratory of Oil and Gas Resources and Exploration Technology, College of Resources and Environment, Yangtze University, Wuhan 430100, China
Zhushi Ge: Key Laboratory of Oil and Gas Resources and Exploration Technology, College of Resources and Environment, Yangtze University, Wuhan 430100, China
Suyang Cai: Key Laboratory of Oil and Gas Resources and Exploration Technology, College of Resources and Environment, Yangtze University, Wuhan 430100, China
Haizhu Zhang: Research Institute of Exploration and Development, PetroChina Tarim Oilfield Branch, Korla 841000, China
Xiang Wang: Research Institute of Exploration and Development, PetroChina Tarim Oilfield Branch, Korla 841000, China
Zhenping Xu: Research Institute of Exploration and Development, PetroChina Tarim Oilfield Branch, Korla 841000, China
Zhanghu Wang: Key Laboratory of Oil and Gas Resources and Exploration Technology, College of Resources and Environment, Yangtze University, Wuhan 430100, China
Xiaomin Xie: Key Laboratory of Oil and Gas Resources and Exploration Technology, College of Resources and Environment, Yangtze University, Wuhan 430100, China
Qiang Meng: Key Laboratory of Oil and Gas Resources and Exploration Technology, College of Resources and Environment, Yangtze University, Wuhan 430100, China

Energies, 2024, vol. 17, issue 3, 1-23

Abstract: Molecular and stable carbon isotopic compositions of 32 crude oils from the Kekeya area of the Southwest Depression, Tarim Basin, were analyzed comprehensively to clarify oil groups and trace oil sources. The results indicate that lacustrine shale sequences within the Upper-Middle Permian Pusige Formation (P 3–2 p) are the major effective oil sources; the thermal maturation effects exert the crucial impact on geochemical compositions of crude oils. In the Kekeya structural belt, crude oils produced from the Lower-Neogene, Middle-Paleogene and Middle-Cretaceous sandstone reservoirs were generated mainly from deeply buried P 3–2 p at the late-to-high maturity stage. These condensates are depleted in terpanes, steranes and triaromatic steranes and enriched in adamantanes and diamantanes. The evaluated thermal maturity levels of crude oils by terpanoids and steranes are generally lower than that of diamondoids, implying at least two phases of oil charging. In the Fusha structural belt, oils produced from the Lower-Jurassic reservoirs (J 1 s) of Well FS8 were generated from the local P 3–2 p at the middle to late mature stage. On the contrary, these oils are relatively rich in molecular biomarkers such as terpanes and steranes and depleted in diamondoids with only adamantanes detectable. The P 3–2 p-associated oils can migrate laterally from the Kekeya to Fusha structural belt, but not to the location of Well FS8. The Middle-Lower Jurassic (J 1–2 ) lacustrine shales as the major oil sources are limited to the area around Well KS101 in the Kekeya structural belt. Crude oils originated from J 1–2 and P 3–2 p can mix together within the Cretaceous reservoirs of Well KS101 by presenting the concurrence of high concentrations of terpane and sterane biomarkers and diamondoids as well as 2–4% 13 C-enriched n -alkanes than those of P 3–2 p derived oils. This study provides a better understanding of hydrocarbon sources and accumulation mechanisms and hence petroleum exploration in this region.

Keywords: Tarim Basin; Kekeya area; biomarkers; diamondoids; carbon isotope; oil sources (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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