Abstract. Computer X-ray microtomography (µXCT) represents a powerful tool for
investigating the physical properties of porous rocks. While calculated
porosities determined by this method typically match experimental
measurements, computed permeabilities are often overestimated by more than
1 order of magnitude. This effect increases towards smaller pore sizes, as
shown in this study, in which nanostructural features related to clay
minerals reduce the permeability of tight reservoir sandstone samples.
Focussed ion beam scanning
electron microscopy (FIB-SEM) tomography was applied to determine the permeability effects of
illites at the nanometre scale, and Navier–Stokes equations were applied to
calculate the permeability of these domains. With these data, microporous
domains (porous voxels) were defined using microtomography images of a tight
reservoir sample. The distribution of these domains could be extrapolated by
calibration against size distributions measured in FIB-SEM images. For this,
we assumed a mean permeability for the dominant clay mineral (illite) in the
rock and assigned it to the microporous domains within the structure. The
results prove the applicability of our novel approach by combining FIB-SEM
with X-ray tomographic rock core scans to achieve a good correspondence
between measured and simulated permeabilities. This methodology results in a
more accurate representation of reservoir rock permeability in comparison to
that estimated purely based on µXCT images.
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