AVO analysis for converted waves

Alvarez, K. Arana; Donati, M.; Aldana, Milagrosa

doi:10.1190/1.1821196

Cited by 6 publications

(2 citation statements)

References 2 publications

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“…Kelly and Ford (2000) derived another approximation using generalized density and shear wave velocity. Alvarez and Donati (1999) systemically carried out contrast research and proposed a different approximation formula. Vant and Brown (2001) expressed a small-angle approximation as a function of a first-order power series expansion of trigonometric functions.…”

Section: Introductionmentioning

confidence: 99%

Converted wave AVO inversion for average velocity ratio and shear wave reflection coefficient

Wei

Chen

2008

Appl. Geophys.

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Based on the empirical Gardner equation describing the relationship between density and compressional wave velocity, the converted wave reflection coefficient extrema attributes for AVO analysis are proposed and the relations between the extrema position and amplitude, average velocity ratio across the interface, and shear wave reflection coefficient are derived. The extrema position is a monotonically decreasing function of average velocity ratio, and the extrema amplitude is a function of average velocity ratio and shear wave reflection coefficient. For theoretical models, the average velocity ratio and shear wave reflection coefficient are inverted from the extrema position and amplitude obtained from fitting a power function to converted wave AVO curves. Shear wave reflection coefficient sections have clearer physical meaning than conventional converted wave stacked sections and establish the theoretical foundation for geological structural interpretation and event correlation. The method of inverting average velocity ratio and shear wave reflection coefficient from the extrema position and amplitude obtained from fitting a power function is applied to real CCP gathers. The inverted average velocity ratios are consistent with those computed from compressional and shear wave well logs.

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Section: Introductionmentioning

confidence: 99%

Converted wave AVO inversion for average velocity ratio and shear wave reflection coefficient

Wei

Chen

2008

Appl. Geophys.

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“…Closed-form solutions for the reflection coefficients of PS-waves in isotropic media can be found in Donati (1998), Larsen et al (1999), Alvarez et al (1999) and Nefedkina and Buzlukov (1999). Rüger (1996) developed approximate expressions for the PS-wave reflection coefficients in VTI media and the symmetry planes of HTI media.…”

Section: Introductionmentioning

confidence: 99%

Small‐angle AVO response of PS‐waves in tilted TI media

Behura

Tsvankin

2005

SEG Technical Program Expanded Abstracts 2005

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Field records for small source-receiver offsets often contain intensive converted PS-waves that cannot be generated in laterally homogeneous isotropic models. Among the most likely physical reasons for this converted energy is the presence of anisotropy on either side of the reflector. Here, we study the small-angle reflection coefficients of the split converted PS 1-and PS 2-waves (R P S1 and R P S2) for a horizontal interface separating two transversely isotropic media with arbitrary orientations of the symmetry axis. The normal-incidence reflection coefficients R P S1 (0) and R P S2 (0) vanish when both halfspaces have a horizontal symmetry plane, which happens if the symmetry axis is vertical or horizontal (i.e., if the medium is VTI or HTI). For a tilted symmetry axis in either medium, however, the magnitude of the reflection coefficients can reach substantial values close to 0.1, even if the strength of anisotropy is moderate. To study the influence of the orientation of the symmetry axis and the anisotropy parameters, we develop concise weak-contrast, weak-anisotropy approximations for the reflection coefficients and compare them with exact numerical results. In particular, the analytic solutions show that the contributions of the Thomsen parameters and δ to the coefficients R P S1 (0) and R P S2 (0) are governed by simple functions of the symmetry-axis tilt ν, which have the same form for both halfspaces. If the symmetry-axis orientation and anisotropy parameters do not change across the interface, the normal-incidence reflection coefficients are insignificant, regardless of the strength of the velocity and density contrast. The AVO (amplitude variation with offset) gradients of the PS-waves are mostly influenced by the anisotropy of the incidence medium that causes shear-wave splitting and determines the partitioning of energy between the PS 1 and PS 2 modes. Because of their substantial amplitude, small-angle PS reflections in TI media contain valuable information for anisotropic AVO inversion of multicomponent data. Our analytic solutions provide a foundation for linear AVO-inversion algorithms and can be used to guide nonlinear inversion based on the exact reflection coefficients.

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Small-angle AVO response of PS-waves in tilted transversely isotropic media

Behura

Tsvankin

2006

GEOPHYSICS

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Field records for small source-receiver offsets often contain intensive converted PS-waves that may be caused by the influence of anisotropy on either side of the reflector. Here, we study the small-angle reflection coefficients of the split converted [Formula: see text]- and [Formula: see text]-waves ([Formula: see text] and [Formula: see text]) for a horizontal interface separating two transversely isotropic (TI) media with arbitrary orientations of the symmetry axis. The normal-incidence reflection coefficients [Formula: see text] and [Formula: see text] vanish when both half-spaces have a horizontal symmetry plane, which happens if the symmetry axis is vertical or horizontal (i.e., if the medium is VTI or HTI). For a tilted symmetry axis in either medium, however, the magnitude of the reflection coefficients can reach substantial values that exceed 0.1, even if the anisotropy strength is moderate. To study the influence exerted by the orientation of the symmetry axis and the anisotropy parameters, we develop concise weak-contrast, weak-anisotropyapproximations for the PS-wave reflection coefficients and com-pare them with exact numerical results. In particular, the analytic solutions show that the contributions made by the Thomsen parameters [Formula: see text] and [Formula: see text] and the symmetry-axis tilt [Formula: see text] to the coefficients [Formula: see text] and [Formula: see text] can be expressed through the first derivative of the P-wave phase velocity at normal incidence. If the symmetry-axis orientation and anisotropy parameters do not change across the interface, the normal-incidence reflection coefficients are insignificant, regardless of the strength of the velocity and density contrast. The AVO (amplitude variation with offset) gradients of the PS-waves are influenced primarily by the anisotropy of the incidence medium that causes shear-wave splitting and determines the partitioning of energy between the [Formula: see text] and [Formula: see text] modes. Because of their substantial amplitude, small-angle PS reflections in TI media contain valuable information for anisotropic AVO inversion of multicomponent data. Our analytic solutions provide a foundation for linear AVO-inversion algorithms and can be used to guide nonlinear inversion that is based on the exact reflection coefficients.

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AVO analysis for converted waves

Cited by 6 publications

References 2 publications

Converted wave AVO inversion for average velocity ratio and shear wave reflection coefficient

Converted wave AVO inversion for average velocity ratio and shear wave reflection coefficient

Small‐angle AVO response of PS‐waves in tilted TI media

Small-angle AVO response of PS-waves in tilted transversely isotropic media

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