Homogeneity vs. heterogeneity of porosity in Boom Clay

Microstructural investigations at the nm-µm scale on three Boom Clay samples from the Mol site, result in porosity characterization of Boom Clay and its different mineral phases. More than 33000 pores were detected, segmented manually and analysed for their size, shape and orientation. Two main pore classes were defined: Small pores (<500nm) within the clay matrices of samples, and big pores (> 500nm) at the interfaces between clay and non-clay mineral (NCM) grains. Samples investigated show similar porosities in the clay-matrix of all samples, but differences occur at the interfaces between clay-matrix and NCM-grains. Pore morphologies and porosities were found to be characteristic of different mineral phases present in the samples. Visible porosities measured on 2D representative areas are 15-17% for all samples investigated. Pore-size distributions were calculated for pores within the clay-matrices and are similar between all samples. They show log-normal distributions with a peaks around 60nm. Power-laws were used for extrapolation of pore-size distributions below the limit of pore detection resolution (pdr) (~ 50nm), which resulted in total estimated porosities of 20-30%. These values are in good agreement with data from Mercury Injection Porosimetry (porosities 35-40%) and water content porosity measurements (~ 36% porosity), both Boisson (2005).