Shi Xukai, Xie Xiaomin
Hubei Key Laboratory of Petroleum and Environmental Geochemistry (School of Resources and Environment, Yangtze University) Wuhan 430100 China
RSC Adv. 2025 Jun 25;15(27):21715-21730. doi: 10.1039/d5ra01740h. eCollection 2025 Jun 23.
The Paleogene Shahejie Formation, including the first (Es) and third (Es) members of the Shahejie Formation, and the third member of Dongying Formation (Ed) are important source rocks in the Qinnan Sag, Bohai Bay Basin. In order to uncover the source of oil and gas in this sag, basic geochemical, molecular geochemical, organic petrological, and -alkane monomer carbon isotopic characteristics of source rocks and oils were analyzed in detail. In combination with the geological settings, the percentage contribution of these three sets of source rocks was assessed in the Qinnan Sag. Results obtained from the source rocks offered the following insights: (1) total organic carbon (TOC) ranged from 1.0% to 3.0%, and the S-TOC indicated that the qualities of source rocks followed the order of Es > Es > Ed. (2) Organic matter (OM) of the Ed source rock belonged to Type II, while those of Es and Es belonged to Type II. The molecular geochemical parameters (CPI, CTeT/CTT, C-C regular steranes, and 4-MSI) also revealed that the organic matter in the source rocks mainly originated from mixtures of algae and terrestrial higher plants. (3) The % values of Ed, Es, and Es were 0.61%, 0.80%, and 0.88%, respectively. These results were consistent with the maturity molecular parameters (including -max, Ts/Tm, C-ααα20/(20 + 20) and C-ββ/(ββ + αα)). (4) Pr/Ph, Pr/C, and Ph/C values indicated that the three sets of source rocks were deposited in a reduced lacustrine environment with different salinities (analyzed with G/CH), and the salinities of Ed and Es indicated a freshwater brackish water environment, while that of Es suggested a brackish semi-saline water environment. (5) combining the geological settings with the geochemical results of oil-source correlations, it was found that the contribution of Es source rock dominated (>50%) in the sag. Overall, this study provides more accurate data of oil source formation and is significant for oil exploration in the Qinan Sag, Bohai Bay Basin.
古近系沙河街组，包括沙河街组一段（Es₁）和三段（Es₃）以及东营组三段（Ed）是渤海湾盆地歧南凹陷重要的烃源岩。为揭示该凹陷油气来源，对烃源岩和原油的基础地球化学、分子地球化学、有机岩石学以及正构烷烃单体碳同位素特征进行了详细分析。结合地质背景，评估了歧南凹陷这三套烃源岩的贡献率。烃源岩分析结果如下：（1）总有机碳（TOC）含量在1.0%至3.0%之间，S-TOC表明烃源岩质量顺序为Es₃＞Es₁＞Ed。（2）Ed烃源岩的有机质属于Ⅱ型，而Es₁和Es₃的有机质属于Ⅱ型。分子地球化学参数（CPI、CTeT/CTT、C-C规则甾烷和4-MSI）也表明烃源岩中的有机质主要来源于藻类和陆生高等植物的混合物。（3）Ed、Es₁和Es₃的%β值分别为0.61%、0.80%和0.88%。这些结果与成熟度分子参数（包括β-max、Ts/Tm、C-ααα20/(20 + 20)和C-ββ/(ββ + αα)）一致。（4）Pr/Ph、Pr/C和Ph/C值表明这三套烃源岩沉积于不同盐度的还原湖相环境（用G/CH分析），Ed和Es₁的盐度表明为淡水-微咸水环境，而Es₃的盐度表明为微咸-半咸水环境。（5）结合地质背景与油源对比的地球化学结果，发现Es₃烃源岩在凹陷中的贡献率占主导（＞50%）。总体而言，本研究提供了更准确的油源形成数据，对渤海湾盆地歧南凹陷的石油勘探具有重要意义。
