Quantitative evaluation of pore structures within micron-scale laminae of lacustrine shales from the Second Member of the Kongdian Formation in Cangdong Sag, Bohai Bay Basin, China. (October 2022)

• Record Type: Journal Article
• Authors: Xin, Bixiao; Hao, Fang; Liu, Xuefeng; Han, Wenzhong; Xu, Qilu; Guo, Pengfei; Tian, Jinqiang
• Is Part Of: Marine and petroleum geology. Volume 144(2022)
• Publication Date: 2022-10
• Subjects: Micron-scale lamina -- Lacustrine shale -- Image segmentation -- Pore structures -- Diagenetic process; 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.2022.105827
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: Lamina is the basic and typical "building block" of organic-rich shales, which has significant impact on the generation, migrition, and accumulation of hydrocarbon. Integrated methods, including X-ray diffraction (XRD), scanning electron microscopes (SEM), and image processing technology, were applied to explore the pore type, pore size, and pore morphology of laminae in shales selected from the Second Member of the Kongdian Formation in Bohai Bay Basin. The application of image stitching and processing technology intuitively and accurately obtained the pore structure among different types of laminae including siliceous laminae, mixed laminae, dolomite laminae, and calcite laminae. The results showed that the average SEM-based surface porosity of laminae was in the following order: siliceous laminae > calcite laminae > dolomite laminae > mixed laminae. The siliceous lamina was dominated by interparticle pores between rigid grains, and was characterized by high volume of macropore. In addition to the pores between rigid grains, pores between clay platelets resulted in a large volume of nano-scale pores. Therefore, mixed lamina was characterized by the smallest average pore diameter and the lowest SEM-based surface porosity. The SEM-based surface porosity of calcite lamina and dolomite lamina was between that of siliceous lamina and mixed lamina, and abundant interparticle pores between grains and intraparticle pores within carbonate minerals were observed in calcite lamina and dolomite lamina. The porosity and pore type of calcite laminae are similar with that of dolomite laminae in certain aspects, while the pore size distribution range of dolomite lamina was wider than that of calcite lamina and the dissolution pores of the calcite lamina contributed more pore volume than that of dolomite lamina. Diverse pore structures among different laminae may be attribute to the synergistic effect of different mineral compositions and diagenetic processes. Graphical abstract: Laminae identification and evaluation. Image 1 Highlights: Different compositions and pore properties among laminae were revealed. Shale laminae containing favorable pore structures are in the order of siliceous laminae > calcite laminae > dolomite laminae > clay-rich siliceous laminae. The differences in mineral compositions and diagenetic processes are the main reasons for the variations in pore properties between laminae.