HR: 10:35h
AN: V51L-02    [PDF]
TI: The Permeability of Volcanic Rocks: Experimental Data, Modelling and Textural Influence
AU: * Mueller, S
EM: mueller@min.uni-muenchen.de
AF: Department of Earth and Environmental Sciences, LMU Munich, Theresienstr. 41, Munich, 80333 Germany
AU: Melnik, O
AF: Institute of Mechanics, Moscow State University, 1 Michurinsky Prospect, Moscow, 119192 Russian Federation
AU: Spieler, O
AF: Department of Earth and Environmental Sciences, LMU Munich, Theresienstr. 41, Munich, 80333 Germany
AU: Scheu, B
AF: Department of Earth and Environmental Sciences, LMU Munich, Theresienstr. 41, Munich, 80333 Germany
AU: Dingwell, D B
AF: Department of Earth and Environmental Sciences, LMU Munich, Theresienstr. 41, Munich, 80333 Germany
AB: The gas permeability of volcanic rocks may influence eruptive processes. The transition from a quiescent degassing dome to rock failure (fragmentation) is likely to be influenced by the rock's permeability, which affects the speed by which a gas overpressure in vesicles is reduced in response to decompression. Using a modified setup of the fragmentation bomb we measure unsteady-state gas flow through porous samples at a high initial pressure differential. After sudden decompression above the rock cylinder, pressurized gas flows through the sample. Two pressure transducers record the pressure signals above and below the sample, whereas the exponentially decreasing trend in the lower space delivers the basis for the permeability determination. To explain the pressure evolution in the high-pressure chamber we developed a transient filtration model that takes into account compressibility of the gas phase, non-linear friction law and gas removal from the chamber through the porous sample. The recorded pressure drop at the upper transducer was used as a boundary condition at the top of the sample. Using the lower end of the pressure curve the linear permeability of the sample was calculated to get the best fit to the data at low pressure drops. Then the non-linear term was added to get the best fit for the whole time interval of the experiment. It was found that the best non-linear fit for the data occurs when the friction coefficient is inversely proportional to the square root of the Reynolds number. The coefficient also depends on the porosity of the sample as a power law function. Measured permeability data show roughly a logarithmic relationship between porosity and permeability. An influence of the pore spaces texture on the degassing behavior of the rock is evident. Our preferred interpretation of the results is a combination of two different but overlapping effects; we propose that at low porosities, gas escape occurs predominantly through microcracks or elongated micropores, whereas at higher porosities, the influence of vesicles becomes progressively stronger as they form an increasingly connected network.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 5114 Permeability and porosity
DE: 8400 VOLCANOLOGY
DE: 8414 Eruption mechanisms
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting