Abstract 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 Beamâ€“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.