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Sensibilité et inversion de formes d'ondes complètes en milieu poreux stratifié.

Abstract : Characterization of the porous media parameters, and particularly the porosity, the permeability and the fluid properties is very useful in many applications (hydrologic, natuarl hazards or oil industry). The aim of my research is to evaluate the possibility to determine these properties from the full seismic wave fields.
First, I am interested in the useful parameters and the specific properties of the seismic waves in the poro-elastic theory, often called Biot (1956) theory. I then compute seismic waves propagation in fluid saturated stratified porous media with a reflectivity method coupled with the discrete wavenumber integration method. I first used this modeling to study the possibilities to determine the carbon dioxid concentration and localization thanks to the reflected P-waves in the case of the deep geological storage of Sleipner (North Sea). The sensitivity of the seismic response to the poro-elastic parameters are then generalized by the analytical computation of the Fréchet derivatives which are expressed with the Green's functions of the unperturbed medium. The numerical tests show that the the porosity and the consolidation are the main parameters to invert.
The sensitivity operators are then introduced in a inversion algorithm based on iterative modeling of the full waveform. The classical algorithm of generalized least-square inverse problem is solved by the quasi-Newton technique (Tarantola, 1984). The inversion of synthetic data shows that we can invert for the porosity and the fluid and solid parameters (densities and mechanical modulus, or volumic rate of fluid and mineral) if the other parameters are well known.
However, the strong seismic coupling of the porous parameters leads to difficulties to invert simultaneously for several parameters. One way to get round these difficulties is to use additional information and invert for one single parameter for the fluid properties (saturating rate) or for the lithology. An other way is to realize differential inversion, to estimate the model variations.
Finally, I apply this algorithm on real data recorded on a Mediterranean coastal site. I can reconstruct a lithological model if I use additional informations from drilling measure.
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Submitted on : Tuesday, January 15, 2008 - 5:37:53 PM
Last modification on : Thursday, November 19, 2020 - 3:54:27 PM
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Louis de Barros. Sensibilité et inversion de formes d'ondes complètes en milieu poreux stratifié.. Géophysique [physics.geo-ph]. Université Joseph-Fourier - Grenoble I, 2007. Français. ⟨tel-00204917⟩

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