HR: 0800h
AN: H21B-1343    [Abstracts]
TI: Pore Size Distributions Inferred from Modified Inversion Percolation Modeling of Drainage Curves
AU: * Dralus, D E
EM: danica@geology.wisc.edu
AF: University of Wisconsin - Madison, 1215 W Dayton Street, Madison, WI 53706-1600 United States
AU: Wang, H F
EM: wang@geology.wisc.edu
AF: University of Wisconsin - Madison, 1215 W Dayton Street, Madison, WI 53706-1600 United States
AU: Strand, T E
EM: tyson.strand@tsi.com
AF: TSI, Inc., 500 Cardigan Road, Shoreview, MN 55126-3996 United States
AU: Glass, R J
EM: rjglass@sandia.gov
AF: Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-1138 United States
AU: Detwiler, R L
EM: detwiler1@llnl.gov
AF: Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-080 United States
AB: Experiments have been conducted of drainage in sand packs. At equilibrium, the interface between the fluids forms a saturation transition fringe where the saturation decreases monotonically with height. This behavior was observed in a 1-inch thick pack of 20-30 sand contained front and back within two thin, 12-inch-by-24-inch glass plates. The translucent chamber was illuminated from behind by a bank of fluorescent bulbs. Acquired data were in the form of images captured by a CCD camera with resolution on the grain scale. The measured intensity of the transmitted light was used to calculate the average saturation at each point in the chamber. This study used a modified invasion percolation (MIP) model to simulate the drainage experiments to evaluate the relationship between the saturation-versus-height curve at equilibrium and the pore size distribution associated with the granular medium. The simplest interpretation of a drainage curve is in terms of a distribution of capillary tubes whose radii reproduce the the observed distribution of rise heights. However, this apparent radius distribution obtained from direct inversion of the saturation profile did not yield the assumed radius distribution. Further investigation demonstrated that the equilibrium height distribution is controlled primarily by the Bond number (ratio of gravity to capillary forces) with some influence from the width of the pore radius distribution. The width of the equilibrium fringe is quantified in terms of the ratio of Bond number to the standard deviation of the pore throat distribution. The normalized saturation-vs-height curves exhibit a power-law scaling behavior consistent with both Brooks-Corey and Van Genuchten type curves. Fundamental tenets of percolation theory were used to quantify the relationship between the apparent and actual radius distributions as a function of the mean coordination number and of the ratio of Bond number to standard deviation, which was supported by both MIP simulations and corresponding drainage experiments.
DE: 1832 Groundwater transport
DE: 1866 Soil moisture
DE: 1875 Vadose zone
DE: 1894 Instruments and techniques: modeling
SC: Hydrology [H]
MN: Fall Meeting 2005