Geochemical and Microstructural Characteristics of Clay Minerals and Their Effects on the Pore Structure of Coal-Measure Shale: A Case Study in Qinshui Basin, China

• Main Authors: Ali, M. (Author), Kong, S. (Author), Li, K. (Author), Liang, Y. (Author), Zhang, Y. (Author), Zhao, Y. (Author)
• Format: Article
• Language: English
• Published: MDPI 2023
• Subjects: Case-studies; clay minerals; Coal; coal-measure shale; Coal-measure shale; compaction; Compaction; Compositional characteristics; Crystallinity; Enamels; Field emission microscopes; Fluorescence spectroscopy; Fourier transform infrared spectroscopy; Gas content; Geochemical characteristic; kaolinite; Kaolinite; Microstructural characteristics; Morphological forms; Physicochemical properties; pore structure; Pore structure; Pores structure; Qinshui basin; Scanning electron microscopy; Sedimentology; Shale; Structure of coal; Textures; X ray powder diffraction
• Online Access: View Fulltext in Publisher

 As the essential component of shale, clay minerals have a vital influence on the pore structure and the gas content of reservoirs. To investigate the compositional characteristics of coal-measure shale and its effects on pore structure, a total of thirteen Taiyuan formation shale samples were collected from the Qinshui Basin and were analyzed using a combination of X-ray diffraction analysis, X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy (FE-SEM), polarized optical microscopy, and field emission scanning electron microscopy. The results show that the principal minerals of the samples are quartz, kaolinite, and illite. Most of the kaolinite was an original terrigenous detrital material with low crystallinity and a low degree of ordering, whereas the illite was mainly composed of 1Md resulting from diagenesis. Clay minerals developed slits, irregularly-shaped or multisized pores during diagenesis, which can be classed into interlayered pores, intergranular pores, and microfractures. Eight micro-morphological forms of clay minerals were summarized based on FE-SEM observations, such as compacted, parallel, bent, tilted, mutually supporting structures, etc., which are mainly formed by the mechanical compaction of clay minerals with different sizes, shapes, and contact relationships. The diversity and complexity of the micro-morphological forms of clay minerals contribute to the strong heterogeneity, low porosity and high permeability anisotropy of shale. © 2023 by the authors.