Microscopic characteristics of pore-fracture system in lacustrine shale from Dongying Sag, Bohai Bay Basin, China: Evidence from scanning electron microscopy. (April 2023)

• Record Type: Journal Article
• Authors: Zhang, Pengfei; Lu, Shuangfang; Li, Junqian; Wang, Junjie; Zhang, Junjian; Chen, Guo; Huang, Hongsheng; Zhi, Qi; Yin, Yajie
• Is Part Of: Marine and petroleum geology. Volume 150(2023)
• Publication Date: 2023-04
• Subjects: Pore type -- Pore morphology -- Pore size -- Lacustrine shale -- Shahejie formation -- Dongying sag; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2023.106156
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: The occurrence and mobility of oil obtained from shales are primarily controlled by the pore–fracture networks of the shales. To clarify the distributions and characteristics of the type, morphology, and size in lacustrine shale pores, shale samples obtained from the Shahejie Formation, Dongying Sag, Bohai Bay Basin in China were examined using argon ion milling and scanning electron microscopy. In this study, pores were mainly classified as interparticle pores, intraparticle pores, and fractures and further classified into 14 types, comprising intraparticle pores (7 types), interparticle pores (6 types), and fractures, based on the differences in their components. Interparticle pores have more complex morphologies than intraparticle pores and fractures. Complex shapes characterize the interparticle pores between quartz granules and at the edges of feldspar granules. Intraparticle pores mainly contribute to mesopores and then to macropores, while interparticle pores behave in the opposite manner. Micropores are primarily derived from the intraparticle pores present in clay aggregates and dissolution pores present in calcite or dolomite granules. However, macropores mainly come from the interparticle pores present within or at the edges of quartz granules; consequently, siliceous-rich shales may be the favorable shale oil reservoirs called interlayer shale oil. Moreover, organic-rich calcareous shales with numerous large dissolution pores can become optimal self-generation and self-storage shale oil reservoirs. This study gives insight into the evaluation of shale oil exploration and development in the Dongying Sag in the Bohai Bay Basin. Highlights: Fracture, 7 types of intra- and 6 types of interparticle pores were observed. The morphology and size of each type of pore were well revealed. Micropores mainly come from intraparticle pores in clay and carbonate minerals. Macropores primarily come from interparticle pores associated with quartz granules.