HR: 0830h
AN: NS41B-11    [Abstracts]
TI: Saturation Profiles from Lab-scale Permittivity Measurements and 2-Phase Flow Models.
AU: * Gorriti, A G
EM: a.g.gorriti@citg.tudelft.nl
AF: TUDelft Department of Geotechnology, P.O. Box 5028, Delft, 2600 GA Netherlands
AB: Laboratory fluid-flow experiments through soils are important to study the different fluid-flow processes that occur in the subsurface of the Earth. Most of them, measure the flow conditions at the entry and exit points of the sample, while, the saturation profile in the sample, and its change with time, is unknown. Until now, only very expensive and time-consuming techniques, such as CT or MRI scans, could provide information about the flow in the sample. Now, for the first time, we have developed a technique to measure the saturation profile of soil samples that is cheap and easy. With this technique, we obtain the saturation profiles from the inversion of permittivity measurements. The experimental set-up consists of a coaxial transmission line with a large sample holder (3 cm of diameter and 10 cm long) that allows for fluid-flow through the sample. The complex electric permittivity is reconstructed, per frequency, from the electromagnetic reflection and transmission responses of the line. Relative changes in the permittivity in the order of 1% can be detected over a wide frequency band up to 3 GHz, while the lowest usable frequency depends on the permittivity of the material filling the sample holder. The accurate measurements of permittivity performed with the described tool assume that the measured quantity is an effective property. The assumption then is that the sample is homogeneous. Under non-flowing conditions this can be a reasonable assumption, but during a flow experiment it cannot. This is clear from the fact that the reconstruction of the permittivity of these samples is not successful. The model of the sample must be modified to include the resulting heterogeneity. This is done by assuming a multilayered sample, each layer considered to be homogeneous with a constant permittivity and a known frequency dependence. Minimizing a cost function involving the measured reflection and transmission coefficients and the modelled response of the multilayered sample, we obtain the permittivity profile. The permittivity is mainly determined by the saturation, then, the permittivity profile within the sample is equivalent to the saturation profile. One can be obtained from the other using the Complex Refractive Index Model (CRIM). The saturation profile can also be obtained with traditional 2-phase flow modelling. Preliminary results show that the saturation profile obtained from the permittivity is more close to reality than the one inferred from 2-phase flow modelling.
DE: 0624 Guided waves
DE: 1866 Soil moisture
DE: 1894 Instruments and techniques
DE: 5109 Magnetic and electrical properties
DE: 5194 Instruments and techniques
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly