The use of layered or smoothed velocity models for prestack Kirchhoff depth migration

Mispel, J.; Hanitzsch, C.

doi:10.1190/1.1826690

Cited by 4 publications

(3 citation statements)

References 1 publication

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“…1996). Moreover, several studies have shown that using smooth velocity macro‐models does not significantly alter imaging quality (Versteeg 1993; Mispel & Hanitzsch 1996). Consequently, there is a need for methods that directly estimate smooth heterogeneous velocity fields, and one of the central benefits of stereotomography is being able to provide such models.…”

Section: Practical Aspectsmentioning

confidence: 99%

“…The background model, or so‐called velocity macro‐model (Berkhout 1984), must contain all the long wavelengths of the model. Generally, it may be assumed smooth (Versteeg 1993; Lailly & Sinoquet 1996; Mispel & Hanitzsch 1996), and the corresponding wave propagation may be reasonably simulated by ray theory. In tomographic methods, a reflected/diffracted event can be represented by a ray connecting source → reflecting/diffracting point → receiver (see Fig.…”

Section: From Controlled Directional Reception To Stereotomographymentioning

confidence: 99%

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Velocity macro-model estimation from seismic reflection data by stereotomography

Billette¹,

Lambaré²

1998

Geophys. J. Int.

238

126

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We introduce a new tomographic method for estimating velocity macro‐models from seismic reflection data. In addition to traveltimes picked on locally coherent reflected events, the method requires that the associated local slopes of the events be picked simultaneously in the common‐shot and common‐receiver trace gathers. The data then consist of a discrete collection of traveltimes, positions and slopes for selected reflected events. Unlike traveltime tomography, picked events are only required to be locally coherent. It is not necessary to follow continuous arrivals all over the trace gathers. Indeed, the method does not require the introduction of interfaces in the model description. Several approaches of tomography using the slope have already been proposed. We present a unified formulation for slope tomography methods, in which the model is described by the velocity field and a set of ray‐segment pairs associated with the reflected/diffracted events. We propose a new robust slope tomography method, which we call ‘stereotomography’. It consists of fitting all observed data (positions, slopes and traveltimes) to data calculated by ray tracing. There are no theoretical limitations in stereotomography for laterally heterogeneous velocity macro‐models. Practically, traveltimes and slopes are picked on local slant stack panels. Ray multipathing can be accounted for since paths are discriminated by their associated slopes. The non‐linear inverse problem is iteratively resolved by a local optimization. The Fréchet derivatives are estimated by paraxial ray tracing. Validation tests on 1‐D and 2‐D synthetic data are analysed. In the first 1‐D example, we study the sensitivity of the method to model parameters (using a singular‐value decomposition). The second 1‐D example evaluates picking precision and shows that it is sufficient for constraining the velocity field. The last example is a 2‐D application in which data are calculated directly by ray tracing. It shows the performance of the method in the presence of strong lateral velocity variations.

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Section: Practical Aspectsmentioning

confidence: 99%

Section: From Controlled Directional Reception To Stereotomographymentioning

confidence: 99%

Velocity macro-model estimation from seismic reflection data by stereotomography

Billette¹,

Lambaré²

1998

Geophys. J. Int.

238

126

View full text Add to dashboard Cite

show abstract

“…For CPU efficiency, we decided to stick to smooth reference velocity fields. This is still a highly debated question, but we believe that, in many cases of practical interest, the introduction of interfaces in the reference model ("blocky" model), while inducing a huge computational overload, will not improve the imaging results significantly (Versteeg, 1991;Clar et al, 1996;Mispel and Hanitzsch, 1996). On the contrary, refining the quality of the smooth model itself and accounting in detail for the real acquisition geometry can definitely yield appreciable improvements.…”

Section: Ray Tracing For Imagingmentioning

confidence: 99%

Fast 2-D ray+Born migration/inversion in complex media

1999

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In this paper, we evaluate the capacity of a fast 2-D ray+Born migration/inversion algorithm to recover the true amplitude of the model parameters in 2-D complex media. The method is based on a quasi-Newtonian linearized inversion of the scattered wavefield. Asymptotic Green's functions are computed in a smooth reference model with a dynamic ray tracing based on the wavefront construction method. The model is described by velocity perturbations associated with diffractor points. Both the first traveltime and the strongest arrivals can be inverted. The algorithm is implemented with several numerical approximations such as interpolations and aperture limitation around common midpoints to speed the algorithm. Both theoritical and numerical aspects of the algorithm are assessed with three synthetic and real data examples including the 2-D Marmousi example. Comparison between logs extracted from the exact Marmousi perturbation model and the computed images shows that the amplitude of the velocity perturbations are recovered accurately in the regions of the model where the ray field is single valued. In the presence of caustics, neither the first traveltime nor the most energetic arrival inversion allow for a full recovery of the amplitudes although the latter improves the results. We conclude that all the arrivals associated with multipathing through transmission caustics must be taken into account if the true amplitude of the perturbations is to be found. Only 22 minutes of CPU time is required to migrate the full 2-D Marmousi data set on a Sun SPARC 20 workstation. The amplitude loss induced by the numerical approximations on the first traveltime and the most energetic migrated images are evaluated quantitatively and do not exceed 8% of the energy of the image computed without numerical approximation. Computational evaluation shows that extension to a 3-D ray+Born migration/inversion algorithm is realistic.

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Practical aspects and applications of 2D stereotomography

Billette¹,

et al. 2003

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Stereotomography is a new velocity estimation method. This tomographic approach aims at retrieving subsurface velocities from prestack seismic data. In addition to traveltimes, the slope of locally coherent events are picked simultaneously in common offset, common source, common receiver, and common midpoint gathers. As the picking is realized on locally coherent events, they do not need to be interpreted in terms of reflection on given interfaces, but may represent diffractions or reflections from anywhere in the image. In the high‐frequency approximation, each one of these events corresponds to a ray trajectory in the subsurface. Stereotomography consists of picking and analyzing these events to update both the associated ray paths and velocity model. In this paper, we describe the implementation of two critical features needed to put stereotomography into practice: an automatic picking tool and a robust multiscale iterative inversion technique. Applications to 2D reflection seismic are presented on synthetic data and on a 2D line extracted from a 3D towed streamer survey shot in West Africa for TotalFinaElf. The examples demonstrate that the method requires only minor human intervention and rapidly converges to a geologically plausible velocity model in these two very different and complex velocity regimes. The quality of the velocity models is verified by prestack depth migration results.

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The use of layered or smoothed velocity models for prestack Kirchhoff depth migration

Cited by 4 publications

References 1 publication

Velocity macro-model estimation from seismic reflection data by stereotomography

Velocity macro-model estimation from seismic reflection data by stereotomography

Fast 2-D ray+Born migration/inversion in complex media

Practical aspects and applications of 2D stereotomography

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