Experimental measurement of air-water interfacial area during gravity drainage and secondary imbibition in porous media

A new experimental method was developed to determine air-water interfacial area as a function of capillary pressure and water saturation in unsaturate d porous media. The surfactant sodium dodecyl benzene sulfonate (SDBS) was used in equilibrium column adsorption experiments to estimate air-water int erfacial area for water saturations (milliliter water per milliliter void) 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 d rainage versus columns equilibrated under secondary imbibition. Gravity dra inage experiments showed the air-water interfacial area decreased linearly with saturation, while imbibition experiments showed a more complex nonmono tonic relation to the saturation. The interfacial area data are then compar ed with-existing network models.