GEOCHEMICAL ANALYSES OF EOCENE OILS IN DEEPLY BURIED SANDSTONE RESERVOIRS IN THE DONGYING DEPRESSION, BOHAI BAY BASIN, NE CHINA

IF 1.8 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Journal of Petroleum Geology Pub Date : 2024-09-23 DOI:10.1111/jpg.12872
Xiaoxiao Zhou, Xiaojun Li, Xu Song, Yuzhi Li, Xuejun Wang, Ke Han, Haiqing Yan
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Abstract

We report the results of organic geochemical analyses of 19 crude oil samples from reservoir sandstones in the 4th Member of the Eocene Shahejie Formation from wells in the Minfeng Sag, Dongying Depression, Bohai Bay Basin (NE China). In addition, 42 Shahejie Formation core samples of dark-coloured mudstones, including 28 extracts, were analysed. Geochemical data included Rock-Eval measurements, gas chromatography, GC-MS and diamondoid analyses.

Maceral analyses showed that mudstones in the 4th Member of the Shahejie Formation (“Es4”) contain Types I and II1 kerogen. The member can be divided into upper (Es4s) and lower (Es4x) intervals. Oil-prone Es4s rock samples have good to excellent hydrocarbon-generating potential based on calculated initial TOC values; Rock-Eval Tmax values indicate that they are sufficiently mature for hydrocarbon generation. Analytical results suggest that both Es4s and Es4x mudrocks are potential source rocks for oils produced at fields in the Minfeng Sag.

Analysed crude oils from the Minfeng Sag were classified into three genetic groups. Group I oils are mature to highly mature and have undergone a moderate degree of thermal cracking. They are characterized by a low β-carotane/nC25 ratio and C30 4-methylsterane index (4MI); high values of oleanane index (oleanane /C30-hopane), C27 diasterane/C27 regular sterane (C27Dia/C27), regular sterane/17α hopane and gammacerane/C30 hopane (G/H); and medium pristane/phytane ratios (Pr/Ph). This suggests that Group I oils are mostly derived from source rocks in the upper part of the Es4x unit which are interbedded with evaporites. Group II oils are mature and have high 4MI and Pr/Ph ratios, low oleanane index, regular sterane/17α hopane and C27Dia/C27 ratios, and mediumβ-carotane/nC25 and G/H. These features are similar to those of Es4s source rocks, indicating their genetic correlation. Group III oils show the lowest maturity and highβ-carotane/nC25 and regular sterane/17α hopane, and low oleanane index, Pr/Ph and 4MI. Previously-published data indicates that oils similar to those in Group III were mainly sourced by Es4s mudstones.

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中国东北渤海湾盆地东营凹陷深埋砂岩储层中始新世石油的地球化学分析
我们报告了对渤海湾盆地东营凹陷民丰下陷油井中始新世沙河街地层第四系储层砂岩中 19 个原油样品的有机地球化学分析结果。此外,还分析了 42 个沙河街地层深色泥岩岩心样品,包括 28 个提取物。地球化学数据包括岩石评价测量、气相色谱、气相色谱-质谱和钻石样分析。宏观分析表明,沙河街地层第四系("Es4")泥岩含有 I 类和 II1 类角质。该层可分为上层(Es4s)和下层(Es4x)。根据计算得出的初始总有机碳值,易生油的 Es4s 岩石样本具有良好至卓越的碳氢化合物生成潜力;岩石-评价 Tmax 值表明,它们已足够成熟,可以生成碳氢化合物。分析结果表明,Es4s 和 Es4x 泥岩都是民丰沙格油田生产石油的潜在源岩。第一组为成熟至高度成熟的石油,经历了中等程度的热裂解。它们的特点是:β-胡萝卜烷/nC25 比率和 C30 4-甲基甾烷指数(4MI)较低;齐墩果烷指数(齐墩果烷/C30-桧烷)、C27 二甾烷/C27 普通甾烷(C27Dia/C27)、普通甾烷/17α 桧烷和加玛烷/C30 桧烷(G/H)的值较高;壬烷/phytane 比率(Pr/Ph)中等。这表明,I 组油主要来自 Es4x 单元上部与蒸发岩互层的源岩。第二组油成熟,具有较高的 4MI 和 Pr/Ph 比值、较低的齐墩果烷指数、规则的甾烷/17α 藿烷和 C27Dia/C27 比值以及中等的β-胡萝卜素/nC25 和 G/H。这些特征与 Es4s 源岩相似,表明它们之间存在遗传相关性。第 III 组油类的成熟度最低,β-胡萝卜素/nC25 和常规甾烷/17α 藿烷比率较高,齐墩果烷指数、Pr/Ph 和 4MI 较低。以前发表的数据表明,与第三组类似的油类主要来自 Es4s 泥岩。
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来源期刊
Journal of Petroleum Geology
Journal of Petroleum Geology 地学-地球科学综合
CiteScore
3.40
自引率
11.10%
发文量
22
审稿时长
6 months
期刊介绍: Journal of Petroleum Geology is a quarterly journal devoted to the geology of oil and natural gas. Editorial preference is given to original papers on oilfield regions of the world outside North America and on topics of general application in petroleum exploration and development operations, including geochemical and geophysical studies, basin modelling and reservoir evaluation.
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