WEB Nanoindentation of gas shales – analytical potential and limitationsWednesday (01.01.2020) 02:45 - 03:00 Part of:
Shales are in the focus of geological studies for various reasons. They are important energy carriers and natural barriers (e.g., for nuclear waste storage), but also of great relevance for drilling stability in geothermal energy projects. Shales are fine-grained rocks and typically highly inhomogeneous, consisting of inorganic (minerals) and finely dispersed organic constituents. The proportion of organic matter is of particular importance, as it has a great impact on the gas storage and retention behavior, as well as on geomechanical properties. Due to the inherent complexity of these rocks, the determination of representative material parameters remains challenging. Frequent macro- and microfractures inhibit the determination of matrix properties at the macroscale, which highlights the necessity for small-volume testing methods such as nanoindentation. Furthermore, the correct identification of individual constituents at the micrometer-scale, as well as the preparation of unaltered specimens, are often problematic. Here we use nanoindentation as a viable tool for local micromechanical shale characterization, and a series of potential economical gas shales from a deep research borehole in the Songliao Basin (NE China) were examined. Nanoindentation was complemented by optical and scanning electron microscopy to determine mineralogy and organic matter compositions. This comprehensive approach allowed to evaluate the influence of burial temperature and stress, as well as related structural modifications (e.g., porosity changes) on micromechanical properties. The results clearly highlight the potential of nanoindentation for shale characterization, but also point to the importance of a tailored investigation approach.