Orientational mapping of minerals in Pierre shale using X-ray diffraction tensor tomography

Abstract

Shales have a complex mineralogy with structural features spanning several length scales, making them notoriously difficult to fully understand. Conventional attenuation-based X-ray computed tomography (CT) measures density differences, which, owing to the heterogeneity and sub-resolution features in shales, makes reliable interpretation of shale images a challenging task. CT based on X-ray diffraction (XRD-CT), rather than intensity attenuation, is becoming a well established technique for non-destructive 3D imaging, and is especially suited for heterogeneous and hierarchical materials. XRD patterns contain information about the mineral crystal structure, and crucially also crystallite orientation. Here, we report on the use of orientational imaging using XRD-CT to study crystallite-orientation distributions in a sample of Pierre shale. Diffraction-contrast CT data for a shale sample measured with its bedding-plane normal aligned parallel to a single tomographic axis perpendicular to the incoming X-ray beam are discussed, and the spatial density and orientation distribution of clay minerals in the sample are described. Finally, the scattering properties of highly attenuating inclusions in the shale bulk are studied, which are identified to contain pyrite and clinochlore. A path forward is then outlined for systematically improving the structural description of shales.

4D Imaging of Two‐Phase Flow in Porous Media Using Laboratory‐Based Micro‐Computed Tomography

“…Limiting the scope to CT, we find it natural to expect that future experimental setups with dedicated software will be capable of retrieving information that is currently not accessible without lengthy post-analysis, like detailed local mineralogy, pore surface roughness, and power law exponents related to self-organized critical dynamics (Bak et al, 1987). We note that with diffraction contrast, additional features can be extracted, as recently demonstrated both with X-rays (Mürer et al, 2021) and neutrons (Woracek et al, 2018).…”

X-ray tensor tomography for small-grained polycrystals with strong texture

“…The existing implementation of the ZH algorithm used for a number of publications (Liebi et al, 2015(Liebi et al, , 2018Gru ¨newald et al, 2020;Mu ¨rer et al, 2021) is only implemented up to ' = 6, which is not sufficient for this paper. In attempting to extend this algorithm, we found that a great simplification of the implementation could be achieved by utilizing the approach of Wigner's D matrices to carry out the rotations rather that the explicit rotations of polar coordinates used in the existing implementation.…”

“…This method, known as small-angle X-ray scattering tensor tomography (SASTT), has been successfully applied to study a wide range of phenomena in mineralized organic tissue, ranging from bioinspired synthetic materials (Rajasekharan et al, 2018) to axon orientations in brains (Georgiadis et al, 2021) and healing around bone implants (Liebi et al, 2021). This method has been extended to wide-angle X-ray scattering (WAXS) from crystalline systems including hydroxyapatite in bone (Gru ¨newald et al, 2020(Gru ¨newald et al, , 2023 and clay minerals in Pierre shale (Mu ¨rer et al, 2021). Yet studies so far have been limited to materials that display weak axially symmetric texture similar to that commonly observed in SAXS.…”

Recent developments in X-ray diffraction/scattering computed tomography for materials science

“…XRD-TT is a useful method for evaluating the scattering tensor of a sample's microstructure. Mürer et al studied Pierre shale using XRD-TT to show the nanostructure orientation of clay minerals at ID15A, ESRF [79]. Shale is comprised of various mineral phases with different shaped flakes and grains that give rise to anisotropic small-and wide-angle…”