Analysis of RTM extended images for VTI media

Li, Vladimir; Tsvankin, Ilya; Alkhalifah, Tariq

doi:10.1190/segam2015-5930996.1

Cited by 3 publications

(2 citation statements)

References 19 publications

(11 reference statements)

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“…The acoustic assumption could be applied in reverse time migration (RTM) in TI media (Alkhalifah, 2000) resulting a large reduction in computational cost. The acoustic concept is commonly adopted by our Geophysical community and widely applied for almost all seismic data process methods like seismic modeling (Finkelstein and Kastner, 2007;Liu and Sen, 2010), underground imaging (Alkhalifah and Fomel, 2011;Li et al, 2016;Xu et al, 2016), full waveform inversion (FWI) (Gholami et al, 2013;Alkhalifah and Plessix, 2014) and traveltime tomography Tsvankin, 2013, Li et al, 2017). However, mitigating the accompanying S-wave artifacts often requires additional processing or limiting assumptions.…”

Section: Introductionmentioning

confidence: 99%

New acoustic approximation for transversely isotropic media with a vertical symmetry axis

Stovas

Alkhalifah

et al. 2020

GEOPHYSICS

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Seismic data processing in the elastic anisotropic model is complicated due to multiparameter dependency. Approximations to the P-wave kinematics are necessary for practical purposes. The acoustic approximation for P-waves in a transversely isotropic medium with a vertical symmetry axis (VTI) simplifies the description of wave propagation in elastic media, and as a result, it is widely adopted in seismic data processing and analysis. However, finite-difference implementations of that approximation are plagued with S-wave artifacts. Specifically, the resulting wavefield also includes artificial diamond-shaped S-waves resulting in a redundant signal for many applications that require pure P-wave data. To derive a totally S-wave-free acoustic approximation, we have developed a new acoustic approximation for pure P-waves that is totally free of S-wave artifacts in the homogeneous VTI model. To keep the S-wave velocity equal to zero, we formulate the vertical S-wave velocity to be a function of the model parameters, rather than setting it to zero. Then, the corresponding P-wave phase and group velocities for the new acoustic approximation are derived. For this new acoustic approximation, the kinematics is described by a new eikonal equation for pure P-wave propagation, which defines the new vertical slowness for the P-waves. The corresponding perturbation-based approximation for our new eikonal equation is used to compare the new equation with the original acoustic eikonal. The accuracy of our new P-wave acoustic approximation is tested on numerical examples for homogeneous and multilayered VTI models. We find that the accuracy of our new acoustic approximation is as good as the original one for the phase velocity, group velocity, and the kinematic parameters such as vertical slowness, traveltime, and relative geometric spreading. Therefore, the S-wave-free acoustic approximation could be further applied in seismic processing that requires pure P-wave data.

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Section: Introductionmentioning

confidence: 99%

New acoustic approximation for transversely isotropic media with a vertical symmetry axis

Stovas

Alkhalifah

et al. 2020

GEOPHYSICS

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“…The extended-domain signatures of the zero-dip normal-moveout (NMO) velocity V nmo (0), δ and η are related to their influence on the conventional-spread and non-hyperbolic moveout. Sava and Alkhalifah (2012) and Li, Tsvankin and Alkhalifah (2016) demonstrate that for VTI media the contribution of η increases with reflector dip (because η influences the NMO velocity of dipping events) and that energy focusing in the extended domain is sensitive to the lateral variation of δ (but not to δ itself). However, in TTI media with the symmetry axis orthogonal to interfaces, the NMO velocity is determined by V nmo (0) and δ, with no contribution of η (Tsvankin and Grechka 2011).…”

Section: Introductionmentioning

confidence: 99%

Image‐domain wavefield tomography for tilted transversely isotropic media

Tsvankin

Guitton

et al. 2019

Geophysical Prospecting

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Transversely isotropic models with a tilted symmetry axis have become standard for imaging beneath dipping shale formations and in active tectonic areas. Here, we develop a methodology of wave‐equation‐based image‐domain tomography for acoustic tilted transversely isotropic media. We obtain the gradients of the objective function using an integral wave‐equation operator based on a separable dispersion relation that takes the symmetry‐axis tilt into account. In contrast to the more conventional differential solutions, the integral operator produces only the P‐wavefield without shear‐wave artefacts, which facilitates both imaging and velocity analysis. The model is parameterized by the P‐wave zero‐dip normal‐moveout velocity, the Thomsen parameter δ, anellipticity coefficient η and the symmetry‐axis tilt θ. Assuming that the symmetry axis is orthogonal to reflectors, we study the influence of parameter errors on energy focusing in extended (space‐lag) common‐image gathers. Distortions in the anellipticity coefficient η introduce weak linear defocusing regardless of reflector dip, whereas δ influences both the energy focusing and depth scale of the migrated section. These results, which are consistent with the properties of the P‐wave time‐domain reflection moveout in tilted transversely isotropic media, provide important insights for implementation of velocity model‐building in the image‐domain. Then the algorithm is tested on a modified anticline section of the BP 2007 benchmark model.

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Gradient computation for VTI acoustic wavefield tomography

Wang

Tsvankin

et al. 2016

SEG Technical Program Expanded Abstracts 2016

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SUMMARYWavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a pseudospectral operator that employes a separable approximation of the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified stack-power objective functions. We also obtain the gradient expressions for the data-domain objective function, which can incorporate borehole information necessary for stable VTI velocity analysis. These gradients are compared to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations. Whereas the kernels computed with the two wave-equation operators are similar, the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show that the modified stack-power objective function produces cleaner gradients than the more conventional DSO operator.

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Analysis of RTM extended images for VTI media

Cited by 3 publications

References 19 publications

New acoustic approximation for transversely isotropic media with a vertical symmetry axis

New acoustic approximation for transversely isotropic media with a vertical symmetry axis

Image‐domain wavefield tomography for tilted transversely isotropic media

Gradient computation for VTI acoustic wavefield tomography

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