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

Abstract

A new experimental method was developed to determine 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 estimate air‐water interfacial 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 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 nonmonotonic relation to the saturation. The interfacial area data are then compared with existing network models.