Geologically constrained migration velocity analysis: Field example

Clapp, Robert G.

doi:10.1190/1.1816567

Cited by 38 publications

(37 citation statements)

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“…The use of horizons that represent major velocity changes and present good signalto-noise ratio, a common practice in MVA by ray-based methods (Stork, 1992;Kosloff et al, 1996Kosloff et al, , 1997Billette et al, 1997;Clapp, 2003), defines two main strategies for velocity update: grid-based tomography and horizon-based tomography. A residual moveout parameter defined along horizons is back-projected through the entire velocity model for both strategies or, alternatively, can be restricted to certain layers in the horizon-based strategy.…”

Section: Discussionmentioning

confidence: 99%

“…For instance, regarding to the intermediate migration of the nonlinear iterations, Kirchhoff migration is the most commonly used. However, images obtained with wave-extrapolation can also be used (Clapp, 2003), which yields more reliable moveout information in areas of geological complexity.…”

Section: Pre-stack-exploding-reflector Modelmentioning

confidence: 99%

“…Instead, to prevent these amplitude variations we apply a B-spline smoothing to the gradient, which consists of representing the gradient as B-spline basis functions, using the adjoint operator B , and transforming it back to the Cartesian space, using the forward operator B. Other smoothing schemes could also be applied, such as smoothing along geological dips (Clapp, 2003) computed on the migrated image using the original shot-profiles.…”

Section: Velocity Optimization Using Image-space Generalized Wavefieldsmentioning

confidence: 99%

“…Instead Kirchoff migration and ray-based methods are still the industry standards. In addition to the lower cost, ray-based methods are very flexible with respect to strategies for defining the velocity model using selected reflectors (Stork, 1992;Kosloff et al, 1996Kosloff et al, , 1997Billette et al, 1997;Clapp, 2003), which is not possible using the conventional migrationvelocity analysis with wave-extrapolation methods. But despite their advantages, ray methods do not satisfactorily describe complex wave propagation in the presence of large lateral velocity contrasts.…”

Section: Introductionmentioning

confidence: 99%

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Migration-velocity analysis using image-space generalized wavefields

Guerra

2013

13th International Congress of the Brazilian Geophysical Society &Amp; EXPOGEF, Rio De Janeiro, Brazil, 26–29 August 2013

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An accurate depth-velocity model is the key for obtaining good quality and reliable depth images in areas of complex geology. In such areas, velocity-model definition should use methods that describe the complexity of wavefield propagation, such as focusing and defocusing, multiple arrivals, and frequency-dependent velocity sensitivity. Wave-equation tomography in the image space has the ability to handle these issues because it uses wavefields as carriers of information. However, its high cost and low flexibility for parametrizing the model space has prevented its routine industrial use.This thesis aims at overcoming those limitations by using new wavefields as carriers of information: the image-space generalized wavefields. These wavefields are synthesized by using a pre-stack generalization of the exploding-reflector model. Cost of wave-equation tomography in the image space is decreased because only a small number of image-space generalized wavefields are necessary to accurately describe the kinematics of velocity errors and because these wavefields can be easily used in a target-oriented way. Flexibility is naturally incorporated into wave-equation tomography in the image space by using these wavefields because their modeling have as the initial conditions some key selected reflectors, allowing a layer-based parametrization of the model space.To use the image-space generalized wavefields in wave-equation tomography in the image space, the method is extended from the shot-profile domain to the image-space generalized-sources domain. In this new domain, the velocity updates are very fast. ER denotes Easily Reproducible and are the results of processing described in the paper. The author claims that you can reproduce such a figure from the programs, parameters, and makefiles included in the electronic document. The data must either be included in the electronic distribution, be easily available to all researchers (e.g., SEG-EAGE data sets), or be available in the SEP data library 2 . We assume you have a UNIX workstation with Fortran, Fortran90, C, X-Windows system and the software downloadable from our website (SEP synthetic data examples associated with this report are classified as NR because they were generated externally to SEP and only the results were released by agreement.Our testing is currently limited to LINUX 2.6 (using the Intel Fortran90 I thank Biondo Biondi, my adviser, for always being a source of encouragement and a reference on academic honesty. His attitude made clearer to me both the importance of obtaining good results and the usefulness of the bad ones, which deserve to be brought to light. I thank Jon Claerbout for initiating us students into the mysteries of inverse problems and for sharing his contagious enthusiasm for doing research. I admire his energy, curiosity, and serendipity. Bob Clapp has constantly been steps ahead of everyone in looking for computational solutions that best fit the type and size of geophysical problems we propose to solve. Also, his knowledge about ...

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Section: Discussionmentioning

confidence: 99%

Section: Pre-stack-exploding-reflector Modelmentioning

confidence: 99%

Section: Velocity Optimization Using Image-space Generalized Wavefieldsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Migration-velocity analysis using image-space generalized wavefields

Guerra

2013

13th International Congress of the Brazilian Geophysical Society &Amp; EXPOGEF, Rio De Janeiro, Brazil, 26–29 August 2013

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“…Therefore, different regularization parameters or schemes can be easily tested at little cost. I show inversion results with different regularizations, and demonstrate that regularization with nonstationary dip filters (Clapp, 2003(Clapp, , 2005Hale, 2007) …”

Section: Inversionmentioning

confidence: 91%

Imaging and velocity analysis by target-oriented wavefield inversion

Tang

2011

GEOPHYSICS

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This thesis develops a novel target-oriented inversion framework that uses wavefields as carriers of information to image both low-and high-wavenumber components of the earth model in complex geological settings, such as subsalt regions. The lowwavenumber component of the earth model is often known as background velocity, whereas the high-wavenumber component of the earth model is often known as reflectivity. I address the problem of reflectivity imaging with target-oriented wavefield least-squares migration, and the problem of velocity estimation with target-oriented wavefield tomography.Reflectivity images of the subsurface are commonly produced by prestack depth migration. When the overburden is complex and the reflectors are unevenly or insufficiently illuminated, the migration operator alone is inadequate to provide an optimal image.I tackle the problem of distorted illumination in reflectivity imaging by wavefield least-squares migration. I formulate least-squares migration in the image domain and solve it in a target-oriented fashion. In the image-domain formulation, explicit computation of the Hessian operator (the resolution function that measures the illumination deficiency of the imaging system) is the most important and challenging step. I develop a novel method based on phase encoding to efficiently and accurately compute the target-oriented Hessian operator. By design, the phase-encoded Hessian converges to the exact Hessian either deterministically (for plane-wave phase encoding) or statistically (for random phase encoding), while having the important advantages that no Green's functions need to be stored during computation and that v the number of wavefield propagations is also drastically reduced. The target-oriented Hessian operator is then used to recover the reflectivity by iterative inverse filtering. I regularize the inversion with dip constraints, which naturally incorporate interpreted geological information into the inversion.Accurate imaging of the reflectivity also requires an accurate background velocity model. High-quality velocity model-building in complex geology requires wavefieldbased velocity analysis to properly model band-limited wave phenomena. However, the high cost and lack of flexibility of target-oriented model-building prevent this method from being widely used in practice.I overcome the cost and flexibility issues of wavefield-based migration velocity analysis by developing target-oriented wavefield tomography. Target-oriented wavefield tomography is achieved by synthesizing a new data set specifically for velocity analysis. The new data set is generated based on an initial unfocused target image and by a novel application of generalized Born wavefield modeling, which correctly preserves velocity kinematics by modeling both zero and non-zero subsurface-offset-

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