Oil Content and Its Occurrence State of Lower Member of Shahejie Formation Shale in Dongying Sag
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摘要: 渤海湾盆地东营凹陷沙河街组页岩是当前页岩油勘探开发的重点层系之一，但其矿物组分复杂、纹层类型多样，导致页岩油有利区分布非均质性强、难预测，油气开发效果差异显著.以东营凹陷沙河街组三段下亚段（沙三下段）陆相富有机质页岩为例，结合岩心观察、薄片观测、矿物成分分析、分步热解、低温氮气吸附和场发射扫描电镜等技术，明确了不同类型页岩储集性和含油性差异，厘清了页岩油赋存的孔隙大小、可动油下限，探讨了页岩油含量影响因素.结果表明沙河街组页岩油赋存孔隙空间类型多样，包括纹层缝和多种类型粒间孔隙，在常温常压条件下，滞留油在纳米尺度范围内主要储集在15~100 nm范围内的孔隙中，游离油赋存的孔径下限约为3 nm.有机质丰度是页岩油形成和富集的物质基础，足够大的储集空间则为保持充足的滞留烃数量提供了有效保障.因此，具有高TOC含量、高孔隙度的富有机质纹层状灰质页岩和富有机质纹层状混合质页岩含油性好、游离油含量高，是研究区最有利的页岩岩相类型.研究结果为进一步深化陆相页岩油富集机制与优化开发策略提供了重要依据.Abstract: The Shahejie Formation shale in Dongying sag is one of the key formations in shale oil exploration and development. However, its complex mineral composition and diverse laminae types result in strong heterogeneity in the distribution of favorable shale oil zones, posing significant challenges for prediction and leading to highly variable development outcomes. In this study it focuses on the organic-rich lacustrine shale of the lower third member of the Shahejie Formation (Sha-3 lower member) as a case study. By employing techniques such as core observation, thin section analysis, mineral composition testing, stepwise pyrolysis, low-temperature nitrogen adsorption, and field emission scanning electron microscopy (FE-SEM), the study characterizes variations in reservoir quality and oil-bearing potential among different shale types. The analysis clarifies the pore size distribution for shale oil occurrence and identifies the lower pore size limit for movable oil, while exploring factors influencing shale oil content. The Shahejie Formation shale features diverse pore types, including laminar fractures and various intergranular pores. Under ambient temperature and pressure, residual shale oil is mainly stored in the pores of 15-100 nm in the nanoscale range, with a lower pore size limit of approximately 3 nm for free oil occurrence. Organic matter abundance (TOC) provides the material foundation for shale oil generation and enrichment, while sufficiently large reservoir spaces ensure the retention of significant hydrocarbon quantities. Among the studied shale lithofacies, organic-rich laminated calcareous shale and laminated mixed shale with high TOC content and high porosity demonstrate superior oil-bearing potential and higher free oil content, making them the most favorable lithofacies in the study area. These findings offer critical insights for advancing the understanding of lacustrine shale oil enrichment mechanisms and optimizing development strategies.
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Key words:
- shale oil /
- reservoir quality /
- oil-bearing potential /
- movable oil threshold /
- Jiyang depression /
- petroleum geology
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图 1 渤海湾盆地东营凹陷区域位置图和综合柱状图
Fig. 1. Location map and comprehensive stratigraphic column of the Dongying sag in the Bohai Bay basin
图 2 东营凹陷沙三下亚段页岩矿物组成特征
Fig. 2. Mineral composition of the lower submember of Sha-3 in the Dongying sag
图 3 东营凹陷沙河街组页岩主要岩相类型及特征
Fig. 3. Main lithofacies types and characteristics of Shahejie Formation shale in Dongying sag
图 4 东营凹陷沙河街组页岩孔隙度和含油性特征
Fig. 4. Shale porosity and oil bearing characteristics of Shahejie Formation in Dongying sag
图 5 SEM图像揭示页岩油主要的赋存位置
a~c.富有机质纹层状灰质页岩；d.富有机质块状灰质页岩；e，f.富有机质层状混合质页岩
Fig. 5. SEM images reveal the main locations of shale oil
图 6 不同岩相页岩典型样品的洗油前后低温N2吸附表征的孔体积分布特征
Fig. 6. Pore volume distribution characteristics characterized by N2 adsorption before and after oil washing in typical shale samples with different lithofacies
图 7 东营凹陷沙河街组页岩油主要赋存空间
Fig. 7. Main occurrence space of shale oil in Shahejie Formation in Dongying sag
图 8 孔隙度和TOC对页岩油含量的控制作用
Fig. 8. The controlling effect of porosity and TOC on shale oil content
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