Correlation Between Chang-9 Crude Oil and Potential Source Rocks, Upper Triassic Yan-Chang Formation, Middle Area of Ordos Basin: Correlation Between Crude Oil in the Chang-9 Member and Potential Source Rocks

IF 1.2 4区地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS

Geofluids Pub Date : 2024-09-24 DOI:10.1155/2024/4861384

Yan Liu, Han Yue, Rongxi Li, Xuefeng Liu

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Abstract

The Chang 9 oil layer deposits within Ansai District, Ordos Basin, yield considerable reserves of crude oil, yet their source remains ambiguous. This research endeavor was designed to characterize the Chang 9 crude oil and the Chang 7 and Chang 9 source rocks (SRs) of the Yan-Chang Formation via organic geochemical analysis. The results indicate that the Chang 9 crude oil exhibits a Pr/Ph ratio of 0.84–2.29 and Ga/C₃₀H less than 0.1, implying formed in a weak reduction to weak oxidation freshwater environment. The regular sterane C₂₇-C₂₈-C₂₉ configuration assumes an inversed “L” type, reflecting mixed sources and dominant terrestrial plant input. Ratios such as C₂₉20S/(20S + 20R) (0.54–0.6) and C₂₉ββ/(ββ + αα) (0.44–0.58) indicate a mature oil stage. The depositional environment of the C7 and C9 SRs is similar, with weak oxidation to reduction conditions, and consists mainly of Type I and II organics, with a relatively higher maturity of the C9 SRs. A difference in C₁₉/C₂₃TT and C₃₀D/C₃₀H was found between the C7 and C9 SRs. The results show that the C9 crude oils have a similar C₁₉/C₂₃TT with the C9 SRs and similar diahopanes distribution with Class II SRs (C7 and part of the C9 SRs). Thus, the C9 crude oils most likely originate from the C9 SR mixed with the C7 SRs.

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鄂尔多斯盆地中段上三叠统延长构造长-9原油与潜在源岩的相关性：长-9油层原油与潜在源岩的相关性

鄂尔多斯盆地安塞区的长九油层矿藏蕴藏着大量原油，但其来源仍然不明确。这项研究工作旨在通过有机地球化学分析，确定长 9 原油以及延长地层长 7 和长 9 源岩（SR）的特征。结果表明，长 9 原油的 Pr/Ph 比值为 0.84-2.29，Ga/C30H 小于 0.1，这意味着长 9 原油是在弱还原到弱氧化的淡水环境中形成的。常规甾烷 C27-C28-C29 构型为倒置的 "L "型，反映了混合来源和主要的陆生植物输入。C2920S/(20S + 20R) (0.54-0.6) 和 C29ββ/(ββ + αα) (0.44-0.58) 等比率表明石油处于成熟阶段。C7 和 C9 SR 的沉积环境相似，都是弱氧化到还原条件，主要由 I 类和 II 类有机物组成，C9 SR 的成熟度相对较高。C7 和 C9 SR 的 C19/C23TT 和 C30D/C30H 存在差异。结果表明，C9 原油的 C19/C23TT 与 C9 脂肪醇相似，重油烷烃的分布与二类脂肪醇（C7 和部分 C9 脂肪醇）相似。因此，C9 原油很可能来自于 C9 天然气与 C7 天然气的混合。

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来源期刊

Geofluids 地学-地球化学与地球物理

CiteScore

2.80

自引率

17.60%

发文量

835

期刊介绍： Geofluids is a peer-reviewed, Open Access journal that provides a forum for original research and reviews relating to the role of fluids in mineralogical, chemical, and structural evolution of the Earth’s crust. Its explicit aim is to disseminate ideas across the range of sub-disciplines in which Geofluids research is carried out. To this end, authors are encouraged to stress the transdisciplinary relevance and international ramifications of their research. Authors are also encouraged to make their work as accessible as possible to readers from other sub-disciplines. Geofluids emphasizes chemical, microbial, and physical aspects of subsurface fluids throughout the Earth’s crust. Geofluids spans studies of groundwater, terrestrial or submarine geothermal fluids, basinal brines, petroleum, metamorphic waters or magmatic fluids.