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The Oligocene age Boom Clay is a potential host material for radioactive waste disposal in Belgium. To better understand the physical basis of transport mechanisms of radionuclides, we aim to characterize the pore space and its connectivity at nm-scale in 3D. In the present study, X-ray μ-CT and FIB-SEM (focused ion beam scanning electron microscopy) tomography were combined, to investigate the 3D pore space of a Boom Clay sample from the Mol-1 borehole (depth corresponding to the level of the HADES-URF – ‘high activity disposal experimental site underground research facility’) at the Mol–Dessel research site for radioactive waste disposal (Belgium). BIB-SEM (broad ion beam scanning electron microscopy) was used to bridge the gap in resolutions between X-ray μ-CT and FIB-SEM and to optimize the selection of a relevant spot for FIB-SEM. Pore network extraction (PNE) modeling (Dong and Blunt, 2009 [1]) was used to simplify the results into a set of pore bodies and pore throats, which are suitable for a statistical description. Resulting pore-size distributions are interpreted to be power-law distributed over ∼6 orders of magnitude, showing the scale-invariance of the pore space. We present a conceptual model of the 3D pore network in Boom Clay. The extracted 3D pore network model can be used to estimate transport properties – in digital rock models. [ABSTRACT FROM AUTHOR]

We present a multi-scale 3D analysis of the pore network in a Rotliegend reservoir sandstone, both at the scale of the sand grains and the scale of the diagenetic clay cements that grow in the intragranular volume (IGV). For this we combine optical microscopy, micro-CT, Broad Ion Beam polishing, Scanning Electron Microscopy, Woods Metal Porosimetry and Focussed Ion Beam–SEM tomography. In cm-scale layers the samples show differences in IGV and sand fabric. In the layers where IGV is higher, there is less diagenetic cement and the IGV forms a connected network; in the layers where the sand fabric is more compacted, larger pores are connected via the pore network in the diagenetic clay cements with pore throat size down to 20 nm in diameter. We show that the pore network in all types of diagenetic clay is connected and conclude that the total gas volume that can be produced from such a reservoir sandstone includes the pore volume in the diagenetic clay cements. We predict a major change in transport properties when the diagenetic clay fill renders the IGV disconnected. [ABSTRACT FROM AUTHOR]