Fine Structure Characterization of Representative Coal-Bearing Rocks of the Late Carboniferous Taiyuan Formation in Huainan Coalfield: Combined SEM, FESEM, and μCT Techniques

Abstract

Pores and fractures are important channels for coalbed methane (CBM) storage, seepage, and production, and accurate characterization of the microstructure of coal-bearing rock strata is of great significance for CBM exploration and development. Taking the coal-bearing rocks of the Late Carboniferous Taiyuan Formation in the Huainan coalfield as the research object, accurate characterization of the organic macerals, microstructure, and mineral distribution of sandstone, coal, and sandy mudstone was achieved using a multiscale combination of polarization microscopy (POM), X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), and X-ray computed tomography (μCT). The thin section identification results indicated that the organic matter in the coal measures rocks of the Taiyuan Formation was well developed and mainly composed of vitrinite, followed by fusinite and exinite, and in addition, there was a distribution of bituminite and sapropelite. The mineral composition of the rocks was dominated by quartz, calcite, siderite, and clay minerals, in addition to plagioclase and ankerite in the fine sandstone. In terms of pore and fracture development, all types of rocks were highly developed with nanoscale and micrometer-scale pores and of mostly irregular shapes, and all types of rocks had fracture development except for medium sandstone. The above-mentioned results show that the Late Carboniferous Taiyuan Formation in the Huainan coalfield has good space for CBM storage and transportation and has certain potential for CBM development. This study provides theoretical guidance for unconventional oil and gas exploration and development in the Huainan coalfield.