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Quantitative Analysis of Flow Processes in a Sand Using Synchrotron-Based X-ray Microtomography

^a Department of Geosciences, Oregon State University, Corvallis, OR 97331
^b Environment and Resources, Technical University of Denmark, DK-2800 Lyngby, Denmark
^c Hydrology, Department of Land, Air and Water Resources, University of California, Davis, CA 95616
^d Consortium for Advanced Radiation Sources and Department of Geophysical Sciences, University of Chicago, IL 60637

View larger version (37K): [in a new window]   Fig. 1. (a) Sample holder with porous nylon membrane. The centerpiece is screwed into the bottom piece, sealing the O-ring against the semipermeable nylon membrane. The inside diameter is 6.0 mm. (b) Alternative centerpiece for higher resolution imaging. Height and membrane configuration is identical to Fig. 1a. The inside diameter is 1.5 mm.

View larger version (14K): [in a new window]   Fig. 2. Typical histogram for a horizontal slice of one of the partially saturated volumes.

View larger version (25K): [in a new window]   Fig. 3. Sensitivity of saturation estimate to threshold of the gray-scale image. The saturation was estimated from the (mass and volume based) porosity. The analysis was performed using a gray-scale intensity of (a) 7300 as the threshold for fast drainage and (b) 6150 for slow drainage. The same axis length is used in both plots to ease comparison.

View larger version (164K): [in a new window]   Fig. 4. Drainage of APS-6.0 sample during multistep experiment (a) p = 0 cm; (b) p = 24 cm; (c) p = 79 cm; (d) p = 490 cm. Horizontal slice at 13.73 mm from the bottom. In these and all other gray-scale images the white or light areas represent the water phase, black is air, and the gray areas are sand grains.

View larger version (71K): [in a new window]   Fig. 5. Comparison of multistep (slow) and one-step (fast) drainage for the same 3.6-mm vertical slice of the APS-6.0 sample. The section shown is located at the bottom of the imaged stack of volumes. Multi-step: (a) p = 0 cm; (b) p = 24 cm; (c) p = 79 cm; (d) p = 490 cm. One-step: (e) p = 490 cm.

View larger version (129K): [in a new window]   Fig. 6. Difference in water and air distribution over the entire imaged section (15.5 mm) of the sample for (a) fast and (b) slow drainage (APS-6.0) to a capillary pressure of 490 cm. Fig. 6c. Cut-out of a small section of the sample illustrating in more detail the difference in fluid distribution between the fast (left) and slow (right) drainage processes.

View larger version (78K): [in a new window]   Fig. 7. Three-dimensional distribution of the air phase for slow (yellow) and fast (blue) drainage for APS-6.0.

View larger version (26K): [in a new window]   Fig. 8. Linear attenuation coefficient profiles for APS-6.0 sample. The initial "saturation" is the primary saturation of the dry sand; its measurement was limited to the top section only. The "satiated" profile is the secondary saturation following the slow primary drainage. Both were obtained by raising the water level to the top the sample (no vacuum or CO2 venting was used).

View larger version (90K): [in a new window]   Fig. 9. Linear attenuation profiles for (a) fast drainage (one-step) and (b) slow drainage (multistep) for the APS-1.5 sample.

View larger version (66K): [in a new window]   Fig. 10. Three-dimensional distribution of the air phase for slow (yellow) and fast (blue) drainage for APS-1.5.

View larger version (13K): [in a new window]   Fig. 11. Representative elementary volume analysis for linear attenuation coefficient of the two different samples.

View larger version (100K): [in a new window]   Fig. 12. Gray-scale images and corresponding binary representation of the air-phase distribution for a horizontal slice of APS-6.0 following (a) fast and (b) slow drainage. The analyzed sections are 230 by 230 pixels corresponding to 3.91 by 3.91 mm2.

View larger version (22K): [in a new window]   Fig. 13. Nearest neighbor distances for three slices (40, 110, and 160) for the two drainage conditions for APS-6.0.