Pore-scale characteristics of multiphase flow in porous media: A comparison of air-water and oil-water experiments

Studies of NAPL dissolution in porous media have demonstrated that measurement of saturation alone is insufficient to describe the rate of dissolution. Quantification of the NAPL-water interfacial area provides a measure of the expected area available for mass transfer and will likely be a primary determinant of NAPL removal efficiency. To measure the interfacial area, we have used a synchrotron-based CMT technique to obtain high-resolution 3D images of flow in a Soltrol-water glass bead system. The interfacial area is found to increase as the wetting phase saturation decreases, reach a maximum, and then decrease as the wetting phase saturation goes to zero. These results are compared to previous findings for an air-water-glass bead study; The Soltrol-water interfacial areas were found to peak at similar saturations as those measured for the air-water system (20-35% saturation range), however, the peak values were in some cases almost twice Lis high for the oil-water system. We believe that the observed differences between the air-water and oil-water systems to a large degree can be explained by the differences in interfacial tensions for the two systems.