Formation and preservation of ultra-deep liquid petroleum in the Ordovician sedimentary succession in Tarim Basin during the neotectonic phase

• Published in: Journal of Asian earth sciences 2023-07, Vol.250, p.105645, Article 105645
• Main Authors: Li, Feng, Lü, Xiuxiang, Zhu, Guangyou, Chen, Jianfa, Wang, Rui, Wu, Zhenghui, He, Tao, Xue, Nan
• Format: Article
• Language: English
• Subjects: Diamondoids; Neotectonism; Oil–source correlation; Tarim Basin; Thermal cracking; Ultra-deep liquid petroleum
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/j.jseaes.2023.105645

[Display omitted] •Neotectonism led to abnormally rapid subsidence and high temperatures.•Insufficient time at high temperatures controls the preservation of liquid petroleum.•The concentration ratios and isomerization ratios of diamondoid can be used for oil-source correlation.•Gas invasion affects the effectiveness of diamondoid proxies for maturity evaluation. The transformation of liquid petroleum to natural gases is accelerated at increasing depths and temperatures. Natural gas exploration predominantly focuses on deep layers. However, the ultra-deep petroleum (maximum burial depth of ∼ 7110 m and reservoir temperature of ∼ 166℃) in the Ordovician sedimentary succession in Tarim Basin has been found to remain in a liquid phase without cracking, and their mechanisms of formation and preservation are unclear. This study performed integrated high-resolution comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC–TOFMS), gas chromatography-mass spectrometry (GC–MS), stable carbon isotopes, and fluid inclusions. The similar molecular compositions and low δ13C values of n-alkanes (−36.0 ‰ to − 33.0 ‰) suggest that the oils are derived from the Cambrian Yuertusi Formation, with moderate thermal maturity (0.8–0.9 %) without distinct cracking. The low variety and abundance of diamondoids, narrow distribution of diamondoid proxies (concentration ratios and isomerization ratios) as well as lack of thiadiamondoids and ethanodiamondoids support this interpretation. The main charging period was the Late Hercynian orogeny, as evidenced by fluid inclusions and the burial model. Abnormally rapid subsidence during the neotectonic phase (age