HR: 16:00h
AN: H22J-01 INVITED     [PDF]
TI: Fingering and Intermittent Flow in Unsaturated Fractured Porous Media
AU: * Or, D
EM: dani@engr.uconn.edu
AF: University of Connecticut, Dept. of Civil and Environmental Engineering 261 Glenbrook Rd., Unit 2037, Storrs, CT 06269 United States
AU: Ghezzehei, T A
EM: TAGhezzehei@lbl.gov
AF: Lawrence Berkeley National Lab - Earth Sciences Division, Earth Sciences Division, Lawrence Berkeley National Lab 1 Cyclotron Rd., MS 90R1116, Berkeley, CA 94720 United States
AB: Because of the dominance of gravitational forces over capillary and viscous forces in relatively large fracture apertures, flow processes in unsaturated fractures are considerably different from flow in rock matrix or in unsaturated soils. Additionally, variations in fracture geometry and properties perturb the delicate balance between gravitational, capillary, and viscous forces, leading to liquid fragmentation, fingering and intermittent flows. We developed a quantitative framework for modeling fluid fragmentation and the subsequent flow behavior of discrete fluid elements (slugs). The transition from a slowly growing but stationary liquid cluster to a finger-forming mobile slug in a non horizontal fracture is estimated from the force balance between retarding capillary forces dominated by contact angle hysteresis, and the weight and shape of the cluster. For a steady flux we developed a model for liquid fragmentation within the fracture plane that gives rise to intermittent discharge, as has been observed experimentally. Intermittency is shown to be a result of interplay between capillary, viscous, and gravitational forces, much like internal dripping. Liquid slug size, detachment interval, and travel velocity are dependent primarily on the local fracture-aperture geometry shaping the seed cluster, rock-surface roughness and wetness, and liquid flux feeding the bridge (either by film flow or from the rock matrix). We show that the presence of even a few irregularities in a vertical fracture surface could affect liquid cluster formation and growth, resulting in complicated flux patterns at the fracture bottom. Such chaotic-like behavior has been observed in previous studies involving gravity-driven unsaturated flow. Inferences based on statistical description of fracture-aperture variations and simplified representation of the fragmentation processes yield insights regarding magnitude and frequency of liquid avalanches. The study illustrates that attempts at describing intermittent and preferential flow behavior by adjustment of macroscopic continuum approaches are destined to failure at most local scales. In accordance with recent observations, flow behavior in partially saturated fractures tends to produce highly localize pathways that focus otherwise diffusive fluxes (film flow or matrix seepage).
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
DE: 5104 Fracture and flow
SC: Hydrology [H]
MN: 2003 Fall Meeting