The effect of temperature on capillary pressure-saturation relationships for air-water and perchloroethylene-water systems

The temperature dependence of capillary pressure-saturation relationships was measured for air-water and perchloroethylene-water systems in silica sand. Changes in capillary pressures, irreducible water phase saturations, and residual nonwetting saturations with temperature were determined. Relationships for temperature dependence of contact angle and interfacial tension were incorporated into the van Genuchten [1980] model and fitted to the data. Capillary pressures a constant degrees of saturation decreased as temperature increased. Hysteresis decreased, irreducible water saturations increased, and residual nonwetting saturations decreased as temperature increased. The magnitude of the change in capillary pressures could not be explained by the temperature dependence of wetting-nonwetting interfacial tensions alone. Derived parameters for the temperature dependence of the contact angle predicted an increase of contact angle of roughly 45 degrees-50 degrees for air-water and perchloroethylene systems with a temperature increase from 20 degrees to 80 degrees C, while literature studies suggest that contact angles should decrease with increasing temperature. It was concluded that the parametric relationship for temperature effects incorporated into the van Genuchten [1980] model fit the data well, but other effects in addition to changes in interfacial tension and contact angle played a role in the temperature dependence of capillary pressure-saturation relationships.