# P-wave seismic attenuation by slow-wave diffusion: Numerical experiments in partially saturated rocks

## Détails

ID Serval

serval:BIB_35A2B6F4561C

Type

**Article**: article d'un périodique ou d'un magazine.

Collection

Publications

Institution

Titre

P-wave seismic attenuation by slow-wave diffusion: Numerical experiments in partially saturated rocks

Périodique

Geophysics

ISSN-L

0016-8033

Statut éditorial

Publié

Date de publication

2007

Peer-reviewed

Oui

Volume

72

Pages

N11-N21

Langue

anglais

Résumé

P-wave attenuation by slow-wave diffusion is a significant loss mechanism

at seismic frequencies. This effect is known as mesoscopic loss,

because it is a consequence of fluid flow at mesoscopic- scale inhomogeneities.

These are larger than the pore size but smaller than the wavelength,

typically tens of centimeters, and are due to local variations in

lithological properties or to patches of immiscible fluids. Basically,

a P-wave traveling in a porous medium induces a fluid-pressure gradient

in regions of different properties, such as patches saturated with

different fluids, generating slow P-waves, which diffuse away from

the interfaces separating the fluids. This mechanism can be explained

by the combined effect of mesoscopic-scale inhomogeneities and mode

conversion at interfaces. We consider a periodically stratified medium

and perform numerical experiments to determine the P-wave quality

factor in partially saturated rocks. The modeling method is an iterative

domain-decomposition 2D finite-element algorithm for solving Biot

equations of motion in a parallel computer, which is a requirement

to run the numerical experiments at seismic frequencies. The simulated

pulses show evidence of the mesoscopic-loss mechanism, and the quality

factors estimated with the spectral-ratio and frequency-shift methods

are in good agreement with the theoretical values predicted by the

White theory. Errors in the estimation of the quality factor are

less than 5% (spectral ratio) and 3% (frequency shift).

at seismic frequencies. This effect is known as mesoscopic loss,

because it is a consequence of fluid flow at mesoscopic- scale inhomogeneities.

These are larger than the pore size but smaller than the wavelength,

typically tens of centimeters, and are due to local variations in

lithological properties or to patches of immiscible fluids. Basically,

a P-wave traveling in a porous medium induces a fluid-pressure gradient

in regions of different properties, such as patches saturated with

different fluids, generating slow P-waves, which diffuse away from

the interfaces separating the fluids. This mechanism can be explained

by the combined effect of mesoscopic-scale inhomogeneities and mode

conversion at interfaces. We consider a periodically stratified medium

and perform numerical experiments to determine the P-wave quality

factor in partially saturated rocks. The modeling method is an iterative

domain-decomposition 2D finite-element algorithm for solving Biot

equations of motion in a parallel computer, which is a requirement

to run the numerical experiments at seismic frequencies. The simulated

pulses show evidence of the mesoscopic-loss mechanism, and the quality

factors estimated with the spectral-ratio and frequency-shift methods

are in good agreement with the theoretical values predicted by the

White theory. Errors in the estimation of the quality factor are

less than 5% (spectral ratio) and 3% (frequency shift).

Mots-clé

PARTIAL GAS SATURATION, NONCONFORMING GALERKIN METHODS, FINITE-ELEMENT, METHODS, LAYERED POROUS ROCKS, ELASTIC-WAVES, COMPRESSIONAL WAVES, , WHITE MODEL, FREQUENCY RANGE, FLUID-FLOW, PROPAGATION

Création de la notice

25/11/2013 20:05

Dernière modification de la notice

20/08/2019 14:23