Nanometer-scale pore fluid distribution and drying damage in preserved clay cores from Belgian clay formations inferred by BIB-cryo-SEM

This paper reports on the distribution of in-situ porewater in clay cores from Boom Clay and Pittem Clay (Gent Formation) and identification of typical pore-scale damage induced by drying. BIB-cryo-SEM shows that the majority of pores visible at SEM resolution (> 50 nm) does not contain water, suggesting that the water content measured by weight loss is located in clay aggregates, in pores <50 nm. Because water-free pores are not expecting in-situ clay formation, we conclude that the procedure used to preserve the original clay cores is not fully efficient. Observations of evolution of microstructures before and after drying by sublimation of water point to four types of typical drying damage driven by the shrinkage of clay particles. On the one hand, quantification of pore size and pore morphologies before and after drying indicates no significant change in statistical pore characterization, suggesting that quantitative pore morphology studies on large number of pores performed on dried samples are representative of the preserved core samples. On the other hand, the observed drying damage is proposed to be responsible of the changes of fluid flow properties typically measured by other authors on preserved and dried specimens of clays.