HR: 0800h
AN: V11B-1421    [Abstracts]
TI: Experiments on Porous Flow With Cooling Boundary
AU: * Watanabe, T
EM: twatnabe@sci.toyama-u.ac.jp
AF: Toyama University, Dept. Earth Sci., Gofuku 3190, Toyama, 930-8555 Japan
AB: Fluid migrations in geological problems (hydrothermal systems, magma migration, etc.) are not purely mechanical problems. They involve heat transfer and/or chemical reactions, which may cause the structural change of fluid paths. When the fluid flows into cooler regions, it may precipitate dissolved materials along its paths. Such a structural change affects the fluid flow and leads to a temporal change in flux. In order to understand the fluid migration with thermal and chemical processes, we have conducted experiments of porous flow with a cooling boundary. We employ packed nylon beads (D=0.4 mm, L=0.4 mm) and NH$_{4}$Cl aqueous solution as a porous matrix and a fluid, respectively. The solubility of NH$_{4}$Cl is very sensitive to the temperature. A small temperature drop makes a considerable amount of precipitation. Undersaturated NH$_{4}$Cl solution is injected at a constant rate from the column of beads. The top part of the column is cooled from the outside, where NH$_{4}$Cl can precipitate in pores to reduce the permeability. We change the temperature of the cooling boundary, the fluid injection rate, and the concentration of NH$_{4}$Cl, and study the temporal change of the temperature of the fluid, the outflow rate, and the fluid pressure. We have observed three different types of temporal change. When the cooling of the fluid is not effective, the fluid does not precipitate dissolved NH$_{4}$Cl. The outflow rate and the fluid pressure are kept constant. On the other hand, when the cooling is effective, the fluid precipitates NH$_{4}$Cl. The fluid pressure increases to keep the outflow rate constant. The second case is subdivided into two types. When the cooling effect is strong, the precipitation makes a strong lid at the cooling boundary. The fluid pressure increases steadily. When the cooling effect is moderate, the elevated fluid pressure breaks the low permeability lid. The fluctuation of the fluid pressure is observed.
DE: 8424 Hydrothermal systems (8135)
DE: 8434 Magma migration
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting