Skip to Main content Skip to Navigation
Theses

QUANTIFICATION DES PARAMETRES DE TRANSPORT DES SOLUTES EN MILIEUX POREUX PAR TOMOGRAPHIE DE RESISTIVITE ELECTRIQUE : DEVELOPPEMENTS METHODOLOGIQUES ET EXPERIMENTAUX

Abstract : Electrical resistivity tomography is a common geophysical method often used to detect and follow plume pollutants in aquifers. However ERT is an integrative method whose reliability of the models is faced to the non-unicity of the inverse problem solutions. These constraints limit the interpretation to a qualitative view of the resistivity contrast distribution modelled in 2D or 3D, being the result of the choice of the inverse parameters and the combination of several hydrody- namic paramaters related to the poral network. The purpose of this thesis is to test the abilities of the ERT imaging to quantify solute transport parameters in miscible displacement occurred in groundwater and the sensitivity of the inverse parameters most influencing the modelling of the dispersion front. Tests are conducted from laboratory experiments led on glass bead packs poured into a transpar- ent plexiglas container. Two vertical lines of 21 stainless steel electrodes are fixed on the lateral sides of the container to perform the ERT monitoring, of the NaCl dissolved in the tracer, from a sequence of 210 quadripole measurements acquired in transverse dipole-dipole each 5 minutes. A light panel is placed behind the experimental device and a video follow up of the dyed part of the tracer is done from the other side. Video analysis reveal a faster propagation of the dye in contact of the vertical edge, which is neg- ligible for the lowest flow rates imposed by the pump. In contrast, ERT mesurements are strongly disturbed by the resistant edges of the plexiglas container that affect the resulting models. Nor- malisation of the apparent resisitivity measurements from a set aquired at the experimental stage and by the Archies law strongly tones down these resistive artefacts. ERT modelling is here particularly sensitive to the grid mesh, the norm (L1 or L2) applied on data and parameters, and the damping factor . High values of and the cutoff factor tend to smooth the resistivity constrasts in the area of the mixing front and increase the weight of the horizontal edge effects on D and . While results from inverse modelling constraint by low and cutoff factors are much closer to the video analysis but with enhanced side slope effects at the rear and the front of the mixing area. The interstitial velocity u is independant of the choice of the inverse parameters. For both meth- ods u is always inferior to the flow rate provided by the pump, whose the gap is expressed as a retardation factor Rf . This retardation is due to adsorption of Na+ on the beads surfaces, which contributes to delay the dispersion front followed by ERT. The retardation expressed by the video analysis can be due to the important size of the molecule of the dye which is easily slowed down in lower permeability areas, added to an eventual affinity to the solid surface. The ranges of fluid conductivity contrasts and stability of the interfaces tested here have no influ- ences on the dispersion which is dominated by the flow velocity u. Estimations of the dispersion coefficient D as function of the Péclet is consistent with the theoretical curve of Bachmat (1968) and Bijeljic & al (2004). First field experiments are conducted in 2D on homogeneous unsaturated sand where measure- ments are free of all kind of edge effects. However, data normalisation is much more complicated since the saturation state and the initial fluid conductivities need to be estimated to calibrate the Archies law. Moreover, the RMS error of the ERT models highlights that the inversion process is not enough constraint by the data which does not allow to quantify the transport parameters.
Document type :
Theses
Complete list of metadatas

Cited literature [128 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-00682952
Contributor : Gregory Lekmine <>
Submitted on : Tuesday, March 27, 2012 - 3:00:12 PM
Last modification on : Monday, December 14, 2020 - 9:51:25 AM
Long-term archiving on: : Thursday, June 28, 2012 - 2:33:11 AM

Identifiers

  • HAL Id : tel-00682952, version 1

Collections

Citation

Grégory Lekmine. QUANTIFICATION DES PARAMETRES DE TRANSPORT DES SOLUTES EN MILIEUX POREUX PAR TOMOGRAPHIE DE RESISTIVITE ELECTRIQUE : DEVELOPPEMENTS METHODOLOGIQUES ET EXPERIMENTAUX. Sciences de la Terre. Université Paris Sud - Paris XI, 2011. Français. ⟨tel-00682952⟩

Share

Metrics

Record views

591

Files downloads

1456