Pore Size and Permeability of Experimentally Compacted Smectire and Kaolinite Clay. Permeability and Elastic Moduli

Clay and shale sequences may constitute thick intervals with a gradual decrease in porosity and corresponding increase in velocity of elastic waves. This is seen also in intervals where clay and shale samples easily disintegrate in water, which would indicate that the porosity reduction is merely a consequence of mechanical compaction. Mondol et al. (2007, 2008) studied this phenomenon by laboratory experiments involving compaction of dry or sea-water saturated smectite and kaolonite powder. During these tests, velocity of elastic compressional waves and of elastic shear waves was measured; the volume of expelled water was monitored, and porosity () as well as bulk density, , could be calculated. From these data the authors could derive compressional modulus (M), shear modulus (G), and bulk modulus (K) as well as fluid permeability (k). From samples of the kaolinite and smectite used during these experiments, the specific surface could be measured by nitrogen adsorption (BET, Fabricius 2011). The BET data allow calculation of average pore radius. The present study addresses whether these data may be applied to derive a tool for estimating permeability from elastic moduli, bearing in mind that elastic moduli may be derived from logging data.