Vzj50063 641..648

The objective of this study was to examine the pore-scale distribution and morphology of organic immiscible liquid in natural porous media containing three immiscible fluids. High-resolution, threedimensional images of an organic liquid (tetrachloroethene) in both three-phase (water–air–organic liquid) and two-phase (water–organic liquid) systems were obtained using synchrotron X-ray microtomography. These data were used to quantitatively characterize the morphology of the organic liquid residing within columns packed with one of three natural, sandy porous media. Organic-liquid blobs varied greatly in both size and shape, ranging from small, single spheres ($0.03mm in diameter) to large, amorphous gangliawithmean lengths of 4 to 5 mm. Singlets comprised the greatest number of blobs, whereas the large ganglia, while much fewer in number, comprised the majority of the organic-liquid surface area and volume. A significant portion of the organic liquid in the three-phase systems was observed to exist as lenses and films in contact with air. These features were not observed in the two-phase water–organic liquid systems. The median of the blobfrequency distributions was smaller and the variance larger for the three-phase systems. In addition, the global specific surface areas of the organic liquid were greater for the three-phase systems. These differences are attributed to the presence of the organic-liquid lenses and films for the three-phase systems. CHARACTERIZING and predicting multiphase flow phenomena in subsurface systems are critical to fields such as contaminant hydrology, petroleum engineering, and soil physics, and a large body of literature has been developed on this topic. One area that has received increased attention lately is that of pore-scale multiphase processes. Recent advances in experimental and computational methods have allowed investigation of fundamental mechanisms controlling the displacement and distribution of immiscible fluids in porous media. Various imaging methods have been used for many years to examine fluid displacement and distribution in porous media. However, until recently, the visualization and quantification of fluid distributions at the pore scale in three-dimensional porous-medium samples was generally not feasible (e.g., Berkowitz and Hansen, 2001). The development of methods allowing high resolution, pore-scale imaging of immiscible fluids in three-dimensional systems of porousmedia has been central to recent advances in multiphase flow by providing a means to directly and quantitatively test theoretical and mathematical models. These methods include photoimaging of refractive-index matched systems, magnetic resonance imaging or nuclear magnetic resonance methods, and X-ray microtomography. They have been used, for example, to investigate the distribution and configuration of immiscible fluids in porous media for two-phase systems (Montemagno and Gray, 1995; Johns and Gladden, 1998, 1999, 2000, 2001; Pervizpour et al., 1999; Okamoto et al., 2001; Sederman and Gladden, 2001; Fontenot and Vigil, 2002; Zhang et al., 2002; Wildenschild et al., 2002; Becker et al., 2003; Stohr et al., 2003; Culligan et al., 2004; AlRaoush and Willson, 2005; Schnaar and Brusseau, 2005; Brusseau et al., 2006). To date, most of these studies have focused on model porous media such as well-sorted silica particles. In addition, three-phase systems comprising water, air, and organic liquid have not been examined. The objective of this study was to examine the porescale distribution and morphology of organic immiscible liquid in natural porous media containing three immiscible fluid phases. High-resolution, three-dimensional images of organic liquid in both three-phase (water–air– organic liquid) and two-phase (water–organic liquid) systems were obtained using synchrotron X-ray microtomography. These data were used to quantitatively characterize the configuration of the organic liquid. MATERIALS AND METHODS