The utility of high-resolution micro-CT for characterising the structure of unconventionals on length scales from millimetres down to microns was advanced by implementation of a sample preparation and scanning workflow to selectively increase the X-ray attenuation of pores or organic matter (OM) and thus enhance their contrast and resolution in tomographic images. Subsamples (of 2–3 mm diameter) of a siliceous and a calcareous shale, both organic-rich, were scanned in the following four states:
infiltrated with diiodomethane,
stained with iodine.
All four tomograms were spatially registered to align perfectly, from which their differences highlighted either the pore space (with diiodomethane) or the OM (with iodine). These 3D digitised maps provided unprecedented insight into the forms of the resolvable pore and OM features and their distribution in relation to the background of sub-resolution porosity and OM. Segmentation of the pore and OM phases yielded total contents in reasonable quantitative agreement with helium porosity and TOC measurements on neighbouring material. Further statistical methods were applied to quantify the co-location of porosity and OM within the tomograms, as a basis for classifying their main feature types and the frequency of their occurrence.