Clay swelling and formation permeability reductions induced by a nonionic surfactant

A major concern with the use of surfactant flushing to mobilize nonaqueous phase liquids in aquifers is specific mineral-surfactant interactions that may effect significant permeability changes in the soil formation. Soils comprised of Ottawa sand mixed with small percentages of bentonite (0-5%) that had moderate initial hydraulic conductivity (>10(-6) m/s) were investigated for loss of permeability upon flushing with solution containing a nonionic surfactant (polyoxyethylene sorbitan monooleate). Columns containing 0, 1, 2, 3, 4, and 5% clay had permeability reductions of 1, 5, 13, 44, 49, and 69%, respectively. The surfactant-clay interactions were further investigated as the cause of the permeability reductions. Some transport of clay through the column was apparent from a small amount of release measured. A permeability change was correlated with the colloid transport in the column with the highest clay concentration, although its effect was transient. Clay swelling was postulated as the primary mechanism for the permeability reductions. It was determined through X-ray diffraction that the surfactant was spreading the silica layer spacings of the clay from a hydration spacing of 15.23 Angstrom to a surfactant-swelled spacing of 18.02 Angstrom. A model was formulated to describe the reduced permeability by the increase in clay volume due to swelling measured by X-ray diffraction and was capable of describing the observed data well with an average error of approximately 10%.