Wave‐equation tomography using image‐space phase encoded data

Guerra, Claudio; Tang, Yaxun; Biondi, Biondo

doi:10.1190/1.3255696

Cited by 13 publications

(18 citation statements)

References 7 publications

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“…While several successful applications of DSO-MVA have been reported (Shen, et al, 2003, 2005, Fei and Williamson, 2009, Albertin et al, 2006, Guerra et al, 2009, the velocity updates calculated as the gradient of the DSO objective function commonly contain strong artifacts in the form of near-vertical stripes. These can dominate the gradient especially when velocity model is far from the true one, making convergence slow or even stopping it altogether.…”

Section: Introductionmentioning

confidence: 98%

On the gradient artifacts in migration velocity analysis based on differential semblance optimization

Fei

Williamson

2010

SEG Technical Program Expanded Abstracts 2010

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Differential Semblance Optimization (DSO) has been shown to be a stable and robust formalism for a number of seismic inverse problems. It has been shown to work well for Wave-Equation migration velocity analysis (MVA), which may overcome some of the problems of ray-based methods. However, velocity updates calculated from the DSO-MVA gradient suffer from artifacts in the form of strong near-vertical stripes, which are not seen in ray tomography or some other formulations of wave-equation MVA. We analyze the source of these artifacts and propose a modification to the update search direction to avoid them. Numerical tests confirm our approach, which eliminates this kind of artifact and speeds up convergence.

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Section: Introductionmentioning

confidence: 98%

On the gradient artifacts in migration velocity analysis based on differential semblance optimization

Fei

Williamson

2010

SEG Technical Program Expanded Abstracts 2010

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“…with ( x, j, q, ω) usually being a uniformly distributed pseudo-random sequence with zero mean, and q is the vector of random realizations .Other sequences, Gold codes for instance, used in third-and fourth-generation cellphones, can also be used to phase-encode the modeling (Guerra and Biondi, 2008). Phase-encoding the modeling experiments mitigates crosstalk between wavefields modeled from different reflectors as well as crosstalk between wavefields modeled from different SOCIGs.…”

Section: The Prestack Exploding-reflector Modelmentioning

confidence: 99%

“…Despite its theoretical superiority to ray methods, this relatively new technology has been rarely used in 3D projects (Fei et al, 2009) because of its higher cost and because it is less flexible than its ray-based counterpart in parameterizing the velocity model and in solving velocity problems in a target-oriented fashion. We overcome these limitations by using image-space generalized wavefields (Tang et al, 2008a;Guerra et al, 2009;Guerra, 2010). These wavefields are initiated in the image space, having as the initial condition key reflectors selected from a prestack image obtained with a wavefield-extrapolation migration.…”

Section: Introductionmentioning

confidence: 99%

Fast 3D migration-velocity analysis by wavefield extrapolation using the prestack exploding-reflector model

Guerra

Biondi

2011

GEOPHYSICS

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In areas of complex geology, migration-velocity estimation should use methods that describe the complexity of wavefield propagation, such as focusing and defocusing, multipathing, and frequency-dependent velocity sensitivity. Migration-velocity analysis by wavefield extrapolation has the ability to address these issues because, in contrast to ray-based methods, it uses wavefields as carriers of information. However, its high cost and lack of flexibility with respect to model parametrization and to target-oriented analysis have prevented its routine industrial use. We overcome those limitations by using new types of wavefield as carriers of information: the image-space generalized wavefields. These wavefields are synthesized from a prestack image computed with wavefield-extrapolation methods, using the pre-stack exploding-reflector model. Cost of migration-velocity analysis by wavefield extrapolation 1 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 because modeling these wavefields has as the initial conditions selected reflectors, which allow use of a horizon-based parametrization of the model space. In a 3D example of the North Sea, we show that using wavefields synthesized by the prestack exploding-reflector model greatly improves efficiency of migration-velocity analysis by wavefield extrapolation, while yielding a final migration-velocity model that is accurate as evidenced by well focused and structurally reasonable reflectors.2

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“…Biondi (2006,2007), Guerra et al (2009) andGuerra (2010) approach this problem in a completely different way. They synthesize a new data set based on the initial image using the concept of prestack-exploding-reflector modeling.…”

Section: Introductionmentioning

confidence: 99%

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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Wave‐equation tomography using image‐space phase encoded data

Cited by 13 publications

References 7 publications

On the gradient artifacts in migration velocity analysis based on differential semblance optimization

On the gradient artifacts in migration velocity analysis based on differential semblance optimization

Fast 3D migration-velocity analysis by wavefield extrapolation using the prestack exploding-reflector model

Imaging and velocity analysis by target-oriented wavefield inversion

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