Permeant-induced changes in the permeability, microtexture, and pore structure of unconsolidated water-sensitive sediments

Permeameter experiments were conducted to determine the permeability response of a sand/clay aggregate mixture to changes in fluid composition. One series examined the effects of cation type and concentration using NaCI and CaCl2 solutions. Two series examined freshwater flushing of sediments equilibrated with seawater. The fourth series examined changes in permeability resulting from large versus small stepwise reductions in NaCI concentration. The major goals of the study were to determine the active mechanism of permeability change, and to correlate measured variations in pore structure with changes in permeability. To accomplish these goals, samples from the tested columns were examined by SEM, BET, and EGME surface area methods, and image analysis. Calcium was found to have a stabilizing effect on permeability and pore structure. However, drastic reductions in NaCI concentration or freshwater flushing led to clay dispersion. Once dispersed, clay particles were either flushed from the system or rearranged to form a clay-gel structure. Particle migration did not lead to permeability reduction, due to the presence of relatively large pore throats. The formation of a clay-gel structure resulted in drastic reductions in permeability.Raffensperger J.P., Ferrell Jr. Ray E. Permeant-induced changes in the permeability, microtexture, and pore structure of unconsolidated water-sensitive sediments. In: Proceedings of the 9th international Clay Conference, Strasbourg, 1989. Vol III : Geochemistry of clays. Nuclear waste disposal. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1990. pp. 75-83. (Sciences Géologiques. Mémoire, 87