Method and algorithm for using surface waves

• US 7,330,799 B2
• Filed: 10/28/2004
• Issued: 02/12/2008
• Est. Priority Date: 12/21/2001
• Status: Expired due to Term

• Current Assignee: Geowave Inc.
• Original Assignee: Societe de Commercialisation de Produits de La Recherche Appliquee-Socpra-Sciences et Genie SEC
• Inventors: Lefebvre, Guy, Benhassen, Mourad Karray
• Primary Examiner(s): NGHIEM, MICHAEL P
• Application Number:
  US10/974,974
• Publication Number:
  US 20050143924A1
• Time in Patent Office: 1,202 Days
• Field of Search: 702/2, 702/5, 702/14, 702/16, 702/18, 702/66, 702/75, 703/5, 367/57, 367/73, 735/96, 735/97
• US Class Current: 702/75
• CPC Class Codes: G01V 1/284 Application of the shear wave component and/or several components of the seismic signal

Abstract

A method and an algorithm allowing the use of surface waves. In particular, the method uses separation of the modes and, by the dispersion curve of more than one mode in the inversion process, it allows a determination of a shear wave propagation velocity profile that, with the aid of the Poisson ratio, constitutes a unique solution and a complete characterization of a medium on the point of view of its elastic properties.

Claims

1. A method, using a Rayleigh wave, for establishing a set of dispersion curves characterizing a medium, wherein each dispersion curve is associated to a propagation mode of said Rayleigh wave, the method comprising:

deploying on a surface of the medium a plurality of sensors;

generating a surface wave in the medium;

monitoring with said sensors a propagation of the surface wave for providing a plurality of signals in the time domain, wherein said signals comprise a spectrum of frequencies;

determining, from said plurality of signals, and for each of said frequencies, an energy distribution as a function of phase travel time and group travel time, wherein said determining an energy distribution comprises computing a wavelet transform of said signals as a function of said phase travel time and group travel time for providing said energy distribution;

identifying a set of said propagation modes of the Rayleigh wave using said energy distribution;

establishing, for each identified propagation mode, a dispersion curve using said energy distribution, thereby providing said set of dispersion curves characterizing said medium; and

further comprising at least one of;

inverting said dispersion curves for determining a profile of shear velocity as a function of a depth in said medium, said inversion comprising reconstituting the shear wave velocity profile that corresponds to at least two of said dispersion curves, wherein said reconstituting comprises adjusting said shear velocity profile such as to minimize an error between a calculated dispersion curve and an experimental dispersion curve, wherein said calculated dispersion curve is calculated with the shear velocity profile and wherein said experimental curve is one of said dispersion curves;

inverting said dispersion curves for determining a profile of a Poisson ratio as a function of a depth in said medium, said inversion comprising reconstituting the profile of the Poisson ratio that corresponds to at least two of said dispersion curves; and

inverting said dispersion curves for determining a profile of a Poisson ratio and a shear wave velocity profile, both profiles being characteristics of the medium, as a function of a depth in said medium, said inversion comprising reconstituting the profile of the Poisson ratio and the profile of the shear wave velocity that will simultaneously correspond to at least two dispersion curves.

2. The method of claim 1, wherein said determining an energy distribution comprises weighting said signals prior to computing the wavelet transform.

3. The method of claim 1 wherein said computing, determining, identifying and establishing are performed automatically.

4. The method as claimed in claim 1, wherein said reconstituting the shear wave velocity profile further comprises adjusting said shear velocity profile such as to minimize a difference between a shape of the calculated dispersion curve and a shape of the experimental dispersion curve.

5. The method as claimed in claim 1, wherein said reconstituting the profile of the Poisson ratio comprises adjusting said profile of the Poisson ratio such as to minimize an error between a calculated dispersion curve and an experimental dispersion curve, wherein said calculated dispersion curve is calculated with the profile of the Poisson ratio and wherein said experimental curve is one of said dispersion curves.