Measuring Air−Water Interfacial Areas with X-ray Microtomography and Interfacial Partitioning Tracer Tests

Abstract

Air-water interfacial areas as a function of water saturation were measured for a sandy, natural porous medium using two methods, aqueous-phase interfacial partitioning tracer tests and synchrotron X-ray microtomography. In addition, interfacial areas measured in a prior study with the gas-phase interfacial partitioning tracer-test method for the same porous medium were included for comparison. For all three methods, total air-water interfacial areas increased with decreasing water saturation. The interfacial areas measured with the tracer-test methods were generally larger than those obtained from microtomography, and the disparity increased as water saturation decreased. The interfacial areas measured by microtomography extrapolated to a value (147 cm(-1)) very similar to the specific solid surface area (151 cm(-1)) calculated using the smooth-sphere assumption, indicating that the method does not characterize the area associated with microscopic surface heterogeneity (surface roughness, microporosity). This is consistent with the method resolution of approximately 12 microm. In contrast, the interfacial areas measured with the gas-phase tracer tests approached the N2/BET measured specific solid surface area (56000 cm(-1)), indicating that this method does characterize the interfacial area associated with microscopic surface heterogeneity. The largest interfacial area measured with the aqueous-phase tracer tests was 224 cm(-1), while the extrapolated maximum interfacial area was approximately 1100 cm(-1). Both of these values are larger than the smooth-sphere specific solid surface area but much smaller than the N2/BET specific solid surface area, which suggests that the method measures a limited portion of the interfacial area associated with microscopic surface heterogeneity. All three methods provide measures of total (capillary + film) interfacial area, a primary difference being that the film-associated area is a smooth-surface equivalent for the microtomography method. An advantage of the microtomography method is the ability to determine explicitly both total and capillary-associated interfacial areas, which is problematic for the tracer-test methods.

Three-dimensional distribution of water and air in soil pores: Comparison of two-phase two-relaxation-times lattice-Boltzmann and morphological model outputs with synchrotron X-ray computed tomography data

“…Another option is to work with porous media that do not contain any organic matter. For example, Brusseau et al [10] and Culligan et al [12] show air-water interfaces in 3D computed 2 tomography (CT) images of repacked sand and glass beads, respectively, at a resolution of about 12 µm using synchrotron X-ray CT. More recently, Andrew et al [4] show detailed air-water interfaces and are able to successfully measure contact angle of CO 2 -brine interfaces onto the solid surface of limestone at a small resolution of 2 µm. Working with a real soil material, Carminati et al [11] adopt yet another approach, in that they focus on the water that occupies part of the volume in larger pores, located between aggregates.…”

Image analysis algorithms for estimating porous media multiphase flow variables from computed microtomography data: a validation study

“…Advances in experimental and analytical techniques have made it possible to characterize and distinguish microscale characteristics such as pore geometry, pore network connectivity, fluid phase distributions in porous media, interfacial properties, and solute transport variables. Computed microtomographic (CMT) imaging studies have been presented in the fields of: (1) petroleum engineering, focusing on the extraction of pore morphology, network information, and relative permeability estimates for use in pore network simulators (e.g., [4,13,28,33,36,39,40,49,53]); (2) environmental engineering where the focus has been on describing nonaqueous phase liquid (NAPL) characteristics such as blob morphology (e.g., [1,2,44,45]) and fluid-fluid-specific interfacial area (e.g., [6,7,[14][15][16]); (3) geology and geochemistry [3,5,8,19,25,50]; (4) vadose zone and root zone processes (e.g., [11,12,22,43,54,55]); (5) and microbiology (e.g., [51]). …”

Using Synchrotron-Based X-Ray Microtomography and Functional Contrast Agents in Environmental Applications

“…We refer to Taina et al (2008) for an extensive review of tomography applications in soil science, and to Werth et al (2010) for contaminant hydrology-type applications. In environmental engineering, synchrotron-based microtomography has been widely used to describe multiphase variables such as nonaqueous phase liquid (NAPL) characteristics (blob morphology, e.g., Willson, 2005a, 2005b;Brusseau, 2005, 2006) and on measuring multiphase variables such as fluid saturations and distribution (e.g., Wildenschild et al, 2005), fluid-fluid specific interfacial area (e.g., Culligan et al, 2004Culligan et al, , 2006Brusseau et al, 2006Brusseau et al, , 2007Costanza-Robinson et al, 2008;Porter et al, , 2010 and curvatures .…”