Determination of the Air−Water Interfacial Area in Wet “Unsaturated” Porous Media

Abstract

A method is proposed for determining the area of the air−water interface in wet but unsaturated porous media. The method depends on determining the critical concentration of surfactant necessary to achieve water movement within the system. Effective surfactants are insoluble in water, are spread as monolayers at the air−water interface, and form solid monolayers which have little or no effect on the surface tension of water until surface concentration of surfactant molecules reaches a known critical value. At this critical concentration, capillary pressure gradients are established within the system, and water moves. Studies of the effects of different water concentrations on air−water interfacial areas show the correct trends and trend toward the correct limits. Advantages and limitations of the technique are discussed. The air−water interfacial area in wet unsaturated porous media has not previously been experimentally accessible.

Insights into the Relationships Among Capillary Pressure, Saturation, Interfacial Area and Relative Permeability Using Pore-Network Modeling

“…These techniques are mostly categorized under two main groups; tracers or imaging techniques. Aqueous tracers have been used by Karkare and Fort (1996), Brusseau et al (1997), Kim et al (1997), Saripalli et al (1998), Anwar (2000), Schaefer et al (2000), and Chen and Kibbey (2006), and gas tracers have been used in some other studies such as Kim et al (1999), Costanza-Robinson and Brusseau (2002), and Brusseau et al (2006). Imaging techniques have been used by Montemagno and Gray (1995), Wildenschild et al (2002), Cheng et al (2004), Culligan et al (2004), Al-Raoush and Willson (2005a,b), and Brusseau (2005, 2006).…”

Capillary pressure driven water movement in wet unsaturated porous media: effect of particle electric charge

“…Notwithstanding, further studies performed by Henry et al 4 found that the resultant moisture content distribution in the column was different when the low-solubility alcohol as butanol was used. In the literature, sand was almost always used to simulate the wet unsaturated porous medium, 1,[5][6][7][8][9][10] and similar results indicate that the surfactant causes differences in capillary pressure within the system and water moves to re-establish equilibrium. [7][8] The amount of water that moves depends 7 on all the factors that influence capillary pressure -particle wettability, size, size distribution, packing, etc., as well as the character of the surfactant monolayer that establishes the capillary pressure gradient within the system.…”

Partitioning Tracers for In-Situ Measurement of Nonaqueous Phase Liquids in the Subsurface - Final Report - 09/15/1996 - 09/14/2000

“…A recent surge in interest in this topic, however, has led to several potentially viable approaches. Static column methods based on the use of water-insoluble surfactants have recently been proposed as a means to measure interfacial areas (42)(43)(44)(45). In addition, experimental methods based on visualization techniques have been proposed (e.g., 46).…”