HR: 1340h
AN: H33A-0454    [Abstracts]
TI: X-ray CMT Study Shows that Drainage Boundary Condition is Responsible for Dynamic Effect in Sandy Material
AU: * Wildenschild, D
EM: wildend@geo.oregonstate.edu
AF: Dept. of Geosciences, Oregon State University, Corvallis, OR 97330 United States
AU: * Wildenschild, D
EM: wildend@geo.oregonstate.edu
AF: Environment and Resources, Danish Technical University, Lyngby, 2800 Denmark
AU: Hopmans, J W
EM: jwhopmans@ucdavis.edu
AF: Hydrology Program, University of California, Davis, CA 95616 United States
AU: Rivers, M L
EM: rivers@cars.uchicago.edu
AF: CARS / Dept. of Geophysical Sciences, University of Chicago, Chicago, IL 60637 United States
AB: To address some unanswered questions regarding the cause of observed `dynamic' flow phenomena in porous media, minute pore-scale multi-phase flow experiments were developed to non-destructively visualize the flow process in a sample of porous material. The flow experiments were performed concurrently with collection of high resolution tomographic images. The samples were exposed to similar pressure boundary conditions as in a previous experiment; one-step and multi-step drainage experiments where the water was drained from the sample using either one large or several small pressure steps, respectively. Qualitative examination of the obtained microtomographic images shows that the difference in drainage pattern, and resulting residual water phase saturation, for the two drainage conditions is quite dramatic. For the high initial flow rates, drainage tends to take place in the most well-connected and largest pores first, meaning that subsequent drainage of the finer pores is unlikely because they are no longer hydraulically connected to the main flowing continuum. To support this observation we also performed quantitative analyses on the microtomographic data. A nearest neighbor analysis was performed on the air phase distribution found in the images and showed characteristic differences between fast and slow drainage. Under fast drainage the air bubbles tend to be few and far apart, whereas a larger number of closely spaced and smaller bubbles are obtained under slow flow conditions.
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting