HR: 17:45h
AN: H34A-08    [Abstracts]
TI: Numerical modeling of surface and water phase contributions to the electrical properties of partially saturated sandstones
AU: Brovelli, A
EM: alessandro.brovelli@unimib.it
AF: Universita' di Milano - Bicocca, Dipartimento di Scienze dell'Ambiente e del Territorio, Piazza della Scienza, 1, Milan, I-20126 Italy
AU: * Cassiani, G
EM: giorgio.cassiani@unimib.it
AF: Universita' di Milano - Bicocca, Dipartimento di Scienze Geologiche e Geotecnologie, Piazza della Scienza, 4, Milan, I-20126 Italy
AU: Dalla, E
EM: elisa.dalla@unimib.it
AF: Universita' di Milano - Bicocca, Dipartimento di Scienze dell'Ambiente e del Territorio, Piazza della Scienza, 1, Milan, I-20126 Italy
AU: Bergamini, F
EM: francesca.bergamini@unimib.it
AF: Universita' di Milano - Bicocca, Dipartimento di Scienze dell'Ambiente e del Territorio, Piazza della Scienza, 1, Milan, I-20126 Italy
AU: Pitea, D
EM: demetrio.pitea@unimib.it
AF: Universita' di Milano - Bicocca, Dipartimento di Scienze dell'Ambiente e del Territorio, Piazza della Scienza, 1, Milan, I-20126 Italy
AU: Binley, A M
EM: a.binley@lancaster.ac.uk
AF: Lancaster University, Department of Environmental Science, Bailrigg, Lancaster, LA1 4YQ United Kingdom
AB: Non-invasive techniques, such as ground penetrating radar, electrical resistivity tomography, and spectral induced polarization have found increasing application for the (time-lapse) monitoring of vadose zone dynamics. Critical to the usefulness of such techniques is the capability to link hydrological quantities of interest, such as moisture content, to the geophysical properties measured by non-invasive methods. Existing relationships are invariably empirical in nature, and should be calibrated on a site-by-site basis. Fundamental investigation of the electrical response of partially saturated natural porous media appears to be necessary to improve on the reliability of the hydro-geophysical relationships. We investigated the electrical response of a partially saturated, weakly consolidated sandstone via pore scale modelling, based on a digital representation of the porous medium. We created this representation purely on the basis of experimental grain-size distribution and porosity data, by using a synthetic, non-overlapping and gravitationally stable packing of spheres. Then we generated a digital representation of this medium by discretizing it in voxels. We simulated primary drainage by preforming a morphological analysis of the digital pore space. The pore-scale distribution of the phases at discrete pressure steps is computed using Laplace equation for a spherical interface and zero contact angle. Then we simulated the direct current response and the dielectric response of the multiphase system at each degree of saturation by means of finite-difference and finite-element solutions to the relevant partial differential equations. Both volume and surface pathways were taken into account. We compared the model results with laboratory data on DC resistivity and electrical permittivity of the studied sandstone. Three different approaches to model surface conductivity in simulating the DC response have been implemented and tested, reaching the conclusion that surface and volume conduction through the bulk of the aqueous phase do not act in parallel, but significant interaction of the two pathways may occur at low water saturation and/or in presence of a significant clay fraction. It is notable that the same pore-scale model is capable of reproducing both the DC response and the dielectric response of the same medium, on the basis of the same elementary principles.
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting