Experimental study of electrical complex resistivity in a 2D multiphase porous medium under non-isothermal conditions: application to soil remediation monitoring
Résumé
In this decade, electro-geophysical methods are widely used in different environmental subjects. Study on soil remediation polluted by DNAPLs has become a certain need for all countries. Geoelectrical methods show their potential to facilitate evaluating decontamination processes. Our challenge in this study was to understand how coupled temperature and saturation changes affect electro-geophysical parameters in a contaminated 2D sample. The primary objective was to evaluate the efficiency and potential of spectral induced polarization (SIP) for monitoring the recovery of dense non-aqueous phase liquids in contaminated porous media. A set of 2D tank experiments investigated the impacts of temperature and saturation changes on the electrical complex resistivity of a saturated porous medium under non-isothermal conditions. The measurements were made with a coal-tar and water fluid pair in a porous medium that has been simulated by 1 mm glass beads. We circulated hot water around the tank and used an immersion heater to heat the porous medium in the tank at different stages. The SIP technique (also called complex resistivity) was used to measure the complex electrical resistivity of a medium in the frequency domain. The experimental results for a simple drainage case were validated using numerical modeling. The complex electrical resistivity was used to obtain the saturation field before and after imbibition. For this purpose, the generalized Archie’s law obtained for the same fluid pair with 1D cells (with a vertical flow) was used. Our results from electrical resistivity measurements for saturation fields are in accordance with 2D tank images and can illustrate the saturation change with pointwise resistivity measurements. The results show that saturation change has the main role in electrical resistivity variation compared to temperature (5 to 7%). We also studied the effects of temperature change on the Cole-Cole parameters and the results confirm our previous findings with the same variation trend in these parameters. The results from varying electrical complex resistivity from the 2D tank (with vertical and horizontal flow) in the laboratory conditions will help us to understand the coupled temperature and saturation effects on complex resistivity in a real polluted site case.
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