| Shale's fine-grained texture, content of diverse organic matter types, and heterogeneous mineralogical composition create analytical challenges that can be met only by using high-resolution analytical and imaging techniques. In this study, non-destructive, high-resolution micro-Fourier Transform Infrared spectroscopy (FTIR) was employed in the investigation of chemical heterogeneity in coals and shales. Specifically, the investigation (i) centered on the chemical evolution of macerals in coals across thermal maturity at the micrometer level, and demonstrated that the increase in coal aromaticity during coalification is largely attributed to the accumulation of condensed aromatic structures in more mature coals; (ii) applied reflectance micro-FTIR mapping techniques and provided direct evidence of the inter-maceral interactions occurring during the peat forming and/or later coalification stage. It was demonstrated that small aliphatic components from resinite could diffuse over short distances into adjacent vitrinite, while no influence of funginite on the chemistry of adjacent vitrinite was observed; (iii) developed a micro-FTIR quantification methodology, and offered a fast and accurate quantification of the contents of clay minerals, quartz, and carbonates, as well as organic matter in shale on a micrometer-scale; (iv) demonstrated the evolutionary characteristics of organic matter in New Albany Shale samples (NAS, Upper Devonian/Lower Mississippian in age) along maturation by using micro-FTIR mapping. In situ micro-FTIR, in combination with complementary porosimetric techniques, can strengthen our understanding of porosity networks in shales. In addition to the chemical and mineralogical heterogeneity of coals and shales, the pore characteristics in NAS samples were synoptically investigated by employing multiple porosimetric techniques. The evolution of porosity with increasing maturity is largely associated with the organic matter transformation due to hydrocarbon generation and migration. Particle size has a significant influence on low-pressure gas adsorption measurements. |
