Abstract
A new experimental method was developed to measure air-water interfacial area as a function of capillary pressure and water saturation in unsaturated porous media. The surfactant sodium dodecyl benzene sulfonate (SDBS) was used in equilibrium column adsorption experiments to determine the air-water interfacial area for water saturations (ml water/ml pore space) ranging from 0.05 to 1.0, and pressures ranging from 0 to 20 cm of water. A comparison was made between columns which were equilibrated under gravity drainage, versus columns equilibrated under secondary imbibition. Gravity drainage experiments showed the air-water interfacial area decreased linearly with saturation, while imbibition experiments showed a more complex non-monotonic relation to the saturation.
