Abstract: Dongpu sag in Bohai Bay Basin is a faulted saline lacustrine basin, where the shale is characterized by “multiple thin layers”, leading to complex shale oil enrichment patterns and significant difficulties in sweet spot identification. Based on core testing data of the Member 3 of Shahejie Formation, combined with exploration practices and retrospective evaluation of old wells, this study investigates the enrichment characteristics of thin interbedded shale oil in the saline lacustrine basin of Dongpu sag. The research results indicate as follows. (1) The shale in the Member 3 of Shahejie Formation of Dongpu sag primarily consists of lithofacies assemblages composed of laminated calcareous shale, siltstone, carbonate rock, and mixed rock, exhibiting “box-type” accumulation characteristics. The laminated carbonate shale acts as both source rock and reservoir, characterized by thin single-layer thickness and “four high” (high total organic carbon content, high oil content, high porosity, and high mobility) attributes. Oil and gas in adjacent siltstones, carbonate rocks, and mixed rocks display micro-migration and near-source accumulation characteristics. (2) Overpressure serves as the external manifestation of thin interbedded shale oil enrichment in saline lacustrine basins, and the degree of overpressure development is positively correlated with hydrocarbon mobility. The development depth of overpressure is basically consistent with the initial threshold of shale oil retained hydrocarbons, and the cause of overpressure is closely related to the massive hydrocarbon generation of source rocks. The overpressure development areas in saline lacustrine basins are significantly influenced by salt rocks, locally forming self-sealing systems. (3) Rapid logging and mud logging identification and sweet spot prediction technologies for the thin-interbedded shale oil in saline lacustrine basins have been developed. The technical features show the large overlapping envelope areas both resistivity versus acoustic time difference curves and natural gamma versus acoustic time difference curves, moderate-to-strong seismic event amplitudes, and vertical lithofacies differentiation via P-wave velocity and elastic modulus. (4) A selection criterion for thin interbedded shale oil in saline lacustrine basins was established. Based on three key factors, i.e., favorable lithofacies unit distribution, overpressure development zones, and thermal maturity (vitrinite reflectance ranging from 0.65% to 1.25%), six sweet spots of shale oil intervals in Dongpu sag were delineated. Exploration practice confirms that the thin interbedded shale oil in the Member 3 of Shahejie Formation of Dongpu sag exhibits a box-type accumulation pattern. Diverse shale assemblages developed in high-frequency oscillatory saline lacustrine basins in Dongpu sag possess exploration potential, with the estimated shale oil resources exceeding 4×10⁸t. The research results provide important theoretical guidance for exploration evaluation and sweet spot prediction of thin interbedded shale oil in faulted saline lacustrine basins.

Key words: Dongpu sag, saline lacustrine basin, thin interbedded shale oil, lithofacies unit, overpressure, sweet spot

摘要： 渤海湾盆地东濮凹陷为断陷咸化湖盆，其泥页岩具有“多层薄层”的特征，页岩油富集规律复杂，甜点识别难度大。基于沙河街组三段（沙三段）的取心测试资料，结合勘探实践及老井的回顾性评价成果，研究了东濮凹陷咸化湖盆薄互层页岩油富集特征。研究结果表明：①东濮凹陷沙三段页岩主要为纹层状碳酸盐质页岩与粉砂岩、碳酸盐岩、混积岩等组成的岩相组合，具有“箱体”成藏特征；纹层状碳酸盐质页岩为生油岩兼储集体，具有单层厚度薄及“四高”（高总有机碳含量、高含油性、高孔隙度、高可动性）的特征，而油气在与之毗邻的粉砂岩、碳酸盐岩和混积岩中则具有微运移的近源成藏特征。②超压是咸化湖盆薄互层页岩油富集的外在表现形式，超压的发育程度与油气流动性的强弱呈正相关关系；超压的发育深度与页岩油滞留烃的起始界限基本一致，其成因与烃源岩大量生烃关系密切；咸化湖盆超压发育区受盐岩影响显著，局部可形成自封闭系统。③针对咸化湖盆薄互层页岩油形成的测井/录井快速识别与甜点预测技术，其技术特征为电阻率与声波时差、自然伽马与声波时差测井曲线的包络面积“双大”，地震同相轴呈中—强振幅，可根据纵波速度与弹性模量在纵向上区分岩相。④建立了咸化湖盆薄互层页岩油的选层选区标准，依据优势岩相体分布+超压发育区+热演化程度（镜质体反射率为0.65%～1.25 %）3个关键要素，明晰了东濮凹陷6套页岩油甜点层系。勘探实践证实，东濮凹陷沙三段薄互层页岩油具有“箱体式”成藏模式。东濮凹陷高频振荡咸化湖盆中发育的多类型页岩组合均具备勘探潜力，其页岩油的评价资源量超过4×10⁸t。研究成果对断陷咸化湖盆薄互层页岩油的勘探评价与甜点预测具有重要理论指导作用。

关键词: 东濮凹陷, 咸化湖盆, 薄互层页岩油, 岩相体, 超压, 甜点