Analysis of RTM extended images for VTI media

Li, Vladimir; Tsvankin, Ilya; Alkhalifah, Tariq

doi:10.1190/geo2015-0384.1

Cited by 13 publications

(4 citation statements)

References 48 publications

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“…) that has a linear (V‐like) shape that was also observed in extended images generated with inaccurate η‐values for near‐horizontal interfaces in VTI media (Sava and Alkhalifah ; Li et al . ). This is explained by the fact that in both cases η influences only non‐hyperbolic (long‐spread) moveout.…”

Section: Signatures Of Medium Parametersmentioning

confidence: 97%

“…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 () and Li, Tsvankin and Alkhalifah () 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 ).…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Signatures Of Medium Parametersmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Image‐domain wavefield tomography for tilted transversely isotropic media

Tsvankin

Guitton

et al. 2019

Geophysical Prospecting

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“…We generate horizontal-space-lag extended images (Figure 3) and obtain the η-gradients for understated and overstated values of η. The η-errors induce residual energy in extended images (Figure 3) that has a linear ("V"-like) shape, which is typical for near-horizontal interfaces (Sava and Alkhalifah, 2012;Li et al, 2015). For both extrapolators, the extended images computed with the understated and even actual η-fields also contain considerable residual energy that spreads from the image point up to the surface.…”

Section: Modelmentioning

confidence: 99%

“…Weibull and Arntsen (2014) and Li et al (2016) attempt to estimate the VTI parameters using different image-domain tomographic algorithms. Li et al (2015) study the defocusing in the extended domain caused by errors in the VTI parameters. Here, we derive and test the wavefield-tomography gradients in the image and data domains using a wave-equation operator based on a separable P-mode approximation for VTI media.…”

Section: Introductionmentioning

confidence: 99%

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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