Quantitative characteristics of microstructure of shale reservoirs with different lithofacies in Dongying Sag， Jiyang Depression
The Shahejie Formation in the Jiyang Depression develops multiple sets of thick organic-rich shale sequences with different lithofacies and has strong vertical heterogeneity. To clarify the pore-fracture development characteristics of shale reservoirs with different lithofacies and their impacts on...
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| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | zho |
| Published: |
Editorial Office of Petroleum Geology and Recovery Efficiency
2025-07-01
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| Series: | Youqi dizhi yu caishoulu |
| Subjects: | |
| Online Access: | https://yqcs.publish.founderss.cn/thesisDetails#10.13673/j.pgre.202504033&lang=en |
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| Summary: | The Shahejie Formation in the Jiyang Depression develops multiple sets of thick organic-rich shale sequences with different lithofacies and has strong vertical heterogeneity. To clarify the pore-fracture development characteristics of shale reservoirs with different lithofacies and their impacts on reservoir properties， this study focused on the shale intervals of Es4U （The Upper Submember of the 4th Member of the Eocene Shahejie Formation） and Es3L （The Lower Submember of the 3rd Member of the Eocene Shahejie Formation）in the Dongying Sag of the Jiyang Depression. Test methods including core observation， thin-section identification， whole-rock X-ray diffraction， argon ion polishing， and field-emission scanning electron microscopy （FE-SEM） were used， and the mineralogical and petrological characteristics of shale oil reservoirs were determined. The “high-magnification large-field quantitative analysis methods” combining argon ion polishing and FE-SEM imaging were employed to comparatively analyze reservoir space types and quantitative pore structure characteristics of different lithofacies. Research reveals that the shale minerals are characterized by “high carbonate content， medium feldspar content， and low clay content”. The Es4U and Es3L in Jiyang Depression develop matrix-type and interbedded-type shale facies. The matrix-type shales primarily consist of carbonate-rich shale facies and mixed shale facies， and the interbedded-type shales consist of sandstone-interbedded shale facies. The deep subsidence zones of the northern steep slopes in the Dongying Sag feature sandstone-interbedded layered calcareous mixed facies， whereas the depocenters exhibit matrix-type laminated or layered carbonate-rich shale facies. The reservoir spaces feature a “five-pore and five-fracture” system comprising intergranular pores， intragranular pores， calcite intercrystalline pores， clay mineral interlayer pores， pyrite intercrystalline pores， along with grain-edge fractures， calcite intercrystalline fractures， structural fractures， bedding fractures， and overpressure fractures， predominantly dominated by nano- and micro-nano pores. Significant differences exist in pore-fracture development characteristics and reservoir properties among different lithofacies. The development of micro-fractures， such as intercrystalline fractures， grain-edge fractures， and bedding fractures， determines the effectiveness of shale reservoir spaces. According to the differences in the connectivity efficiency and development of various micro-fractures， the matrix-type laminated shale exhibits a complex pore-fracture network connectivity pattern composed of bedding fractures， grain-edge fractures， intercrystalline fractures， intergranular pores， and intercrystalline pores （dissolution pores）， demonstrating high-efficiency storage spaces. In contrast， layered shales mainly rely on grain-edge fractures for micro-nano pore connectivity， showing relatively poorer effective storage capacity. |
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| ISSN: | 1009-9603 |