Key points:

  • The Opalinus Clay in the siting regions is characterised by a porosity of 10 – 13 vol.‑% with low variability and only minor differences with depth.
  • The mean pore size of the Opalinus Clay is in the range of a few nanometres.
  • A general increase of porosity with increasing clay-mineral content is observed for most clayrocks.
  • Clay-mineral-poor sections of the confining units are typically characterised by low porosity and larger pore sizes than in the Opalinus Clay.