Effects of clay-water interactions on water retention in porous media

Graduation date: 1984Capillary pressure-saturation data obtained for unconsolidated porous media with different liquids are examined to investigate the effects of clay-liquid interactions on liquid retention. Liquid retention functions are assumed to reflect the effective pore-size distributions. The hydraulic variables, capillary pressure and saturation, are transformed to account for changes in liquid retention that could be attributed to differences in contact angle, density, and surface tension of the liquids. The non-linear Su-Brooks (1976) retention function was linearized so that standard statistical programs can be used on the experimental capillary pressure-saturation data to obtain the retention parameters. The method developed is more rapid than the original method and takes all of the data into consideration. Capillary pressure-saturation data were collected on samples containing 40% montmorillonite as a function of total electrolyte concentration and sodium adsorption ratio. The latter affects measured values only at electrolyte concentrations below 0.5N̲. Three empirical retention functions were fit to the experimental data to determine the respective retention parameters. The retention functions fit the experimental data very well, with an average of R² of 0.9961. The average R² obtained from a multivariate regression model of retention parameters as a function of electrolyte concentration and sodium adsorption ratio was 0.948. The changes in capillary pressure-saturation relationships are explained by swelling. Retention curves for different clay minerals are compared when the wetting fluids are polar (water) or non-polar (soltrol) liquids. The retention curves for water in illite can be accurately predicted from the soltrol curves by assuming an adsorbed water layer up to 1580 molecular layers in thickness. This correction does not predict the measured curves for montmorillonite, apparently because of swelling of the clays in water