The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Biondo Biondi - One of the best experts on this subject based on the ideXlab platform.
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wave equation Migration Velocity analysis for vti models
Geophysics, 2014Co-Authors: Biondo Biondi, Robert G Clapp, Dave NicholsAbstract:ABSTRACTAnisotropic models are needed for wave simulation and inversion where a complex geologic environment exists. We extended the theory of wave equation Migration Velocity analysis to build vertical transverse isotropic models. Because of the ambiguity between depth and δ in the acoustic regime, we assumed δ can be accurately obtained from other sources of information, and inverted for the NMO slowness and the anellipticity parameter η. We combined the differential semblance optimization objective function with the stacking power maximization to evaluate the focusing of the prestack image in the subsurface-offset domain. To regularize the multiparameter inversion, we built a framework to adapt the geologic and the rock physics information to guide the updates in NMO slowness and η. This regularization step was crucial to stabilize the inversion and to produce geologically meaningful results. We tested the proposed approach on a synthetic data set and a 2D Gulf of Mexico data set starting with a fairly...
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tomographic full waveform inversion tfwi by combining fwi and wave equation Migration Velocity analysis
Geophysics, 2013Co-Authors: Biondo Biondi, Ali AlmominAbstract:Convergence of full waveform inversion can be improved by extending the Velocity model along either the subsurface-offset axis or the time-lag axis. The extension of the Velocity model along the time-lag axis enables us to linearly model large time shifts caused by Velocity perturbations. The extension is based on a new linearization of the scalar wave equation where the extended-Velocity perturbation is convolved in time with the Laplacian of the background wavefield. This linearization is accurate for both reflected events and transmitted events and, in particular, for diving waves recorded at large offsets. The modeling capabilities of the proposed linearization enable the simultaneous inversion of reflections and diving waves even when the starting Velocity model is far from being accurate. We solve the resulting optimization problem with a nested algorithm. The inner iterations are based on the proposed linearization and on a mixing of scales between the short- and long-wavelength components of the v...
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moveout based wave equation Migration Velocity analysis
Geophysics, 2013Co-Authors: Yang Zhang, Biondo BiondiAbstract:ABSTRACTCurrent wave-equation Migration Velocity analysis schemes suffer from problems such as severe nonlinearity (which causes the issue of cycle skipping) and imprecise objective functions (which can accrue Velocity errors by honoring residuals caused by model complexity and incomplete acquisition). To provide an improvement, we developed an alternative method to perform wave-equation Migration Velocity analysis by maximizing the flatness of the angle-domain common image gathers. We replaced the ray-based tomographic operator with the wave-equation-based one, although keeping the conventional moveout-based tomography work flow. Instead of maximizing the image-stack-power objective function directly with respect to the slowness, we linked the objective function to the slowness indirectly through an intermediate moveout parameter. By focusing on the common image gather kinematics, this approach greatly reduced the risk of cycle skipping in the absence of low-frequency data, and it produced high-quality g...
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subsalt Velocity estimation by target oriented wave equation Migration Velocity analysis a 3d field data example
Geophysics, 2013Co-Authors: Yaxun Tang, Biondo BiondiAbstract:ABSTRACTWe apply target-oriented wave-equation Migration Velocity analysis to a 3D field data set acquired from the Gulf of Mexico. Instead of using the original surface-recorded data set, we use a new data set synthesized specifically for Velocity analysis to update subsalt velocities. The new data set is generated based on an initial unfocused target image and by a novel application of 3D generalized Born wavefield modeling, which correctly preserves Velocity kinematics by modeling zero and nonzero subsurface-offset-domain images. The target-oriented inversion strategy drastically reduces the data size and the computation domain for 3D wave-equation Migration Velocity analysis, greatly improving its efficiency and flexibility. We apply differential semblance optimization (DSO) using the synthesized new data set to optimize subsalt velocities. The updated Velocity model significantly improves the continuity of subsalt reflectors and yields flattened angle-domain common-image gathers.
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residual moveout based wave equation Migration Velocity analysis
Seg Technical Program Expanded Abstracts, 2012Co-Authors: Yang Zhang, Biondo Biondi, Yaxun TangAbstract:We propose a new method to perform wave-equation Migration Velocity analysis by maximizing the flatness of the angledomain common image gathers. Instead of maximizing the image-stack-power objective function directly with respect to the slowness, we link the objective function to the slowness indirectly through an intermediate moveout parameter. This approach is immune to the cycle-skipping problem, and it produces high-quality gradients. In addition, the proposed method does not require explicit picking of the moveout parameters. Our numerical examples demonstrate the great potential of this method: in the first example where there is a Gaussian-shaped anomaly slowness error, our method produces well-behaved gradient; from our test on the Marmousi models, the proposed method converges to a high-quality model that uniformly flattens the angle-domain common image gathers.
Fumio Takemura - One of the best experts on this subject based on the ideXlab platform.
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on the lateral Migration of a slightly deformed bubble rising near a vertical plane wall
Journal of Fluid Mechanics, 2010Co-Authors: Kazuyasu Sugiyama, Fumio TakemuraAbstract:Deformation-induced lateral Migration of a bubble slowly rising near a vertical plane wall in a stagnant liquid is numerically and theoretically investigated. In particular, our focus is set on a situation with a short clearance c between the bubble interface and the wall. Motivated by the fact that numerically and experimentally measured Migration velocities are considerably higher than the Velocity estimated by the available analytical solution using the Faxen mirror image technique for a/(a +c) ≪ 1 (here a is the bubble radius), when the clearance parameter e(=c/a) is comparable to or smaller than unity, the numerical analysis based on the boundary-fitted finite-difference approach solving the Stokes equation is performed to complement the experiment. The Migration Velocity is found to be more affected by the high-order deformation modes with decreasing e. The numerical simulations are compared with a theoretical Migration Velocity obtained from a lubrication study of a nearly spherical drop, which describes the role of the squeezing flow within the bubble―wall gap. The numerical and lubrication analyses consistently demonstrate that when e ≤ 1, the lubrication effect makes the Migration Velocity asymptotically μ V 2 B1 /(25eγ) (here, V B1 , μ and γ denote the rising Velocity, the dynamic viscosity of liquid and the surface tension, respectively).
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on the lateral Migration of a slightly deformed bubble rising near a vertical plane wall
arXiv: Fluid Dynamics, 2010Co-Authors: Kazuyasu Sugiyama, Fumio TakemuraAbstract:Deformation-induced lateral Migration of a bubble slowly rising near a vertical plane wall in a stagnant liquid is numerically and theoretically investigated. In particular, our focus is set on a situation with a short clearance $c$ between the bubble interface and the wall. Motivated by the fact that numerically and experimentally measured Migration velocities are considerably higher than the Velocity estimated by the available analytical solution using the Fax\'{e}n mirror image technique for $a/(a+c)\ll 1$ (here $a$ is the bubble radius), when the clearance parameter $\varepsilon(= c/a)$ is comparable to or smaller than unity, the numerical analysis based on the boundary-fitted finite-difference approach solving the Stokes equation is performed to complement the experiment. The Migration Velocity is found to be more affected by the high-order deformation modes with decreasing $\varepsilon$. The numerical simulations are compared with a theoretical Migration Velocity obtained from a lubrication study of a nearly spherical drop, which describes the role of the squeezing flow within the bubble-wall gap. The numerical and lubrication analyses consistently demonstrate that when $\varepsilon\leq 1$, the lubrication effect makes the Migration Velocity asymptotically $\mu V_{B1}^2/(25\varepsilon \gamma)$ (here, $V_{B1}$, $\mu$, and $\gamma$ denote the rising Velocity, the dynamic viscosity of liquid, and the surface tension, respectively).
William W. Symes - One of the best experts on this subject based on the ideXlab platform.
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Migration Velocity analysis and waveform inversion
Geophysical Prospecting, 2008Co-Authors: William W. SymesAbstract:Least-squares inversion of seismic reflection waveform data can reconstruct remarkably detailed models of subsurface structure and take into account essentially any physics of seismic wave propagation that can be modelled. However, the waveform inversion objective has many spurious local minima, hence convergence of descent methods (mandatory because of problem size) to useful Earth models requires accurate initial estimates of long-scale Velocity structure. Migration Velocity analysis, on the other hand, is capable of correcting substantially erroneous initial estimates of Velocity at long scales. Migration Velocity analysis is based on prestack depth Migration, which is in turn based on linearized acoustic modelling (Born or single-scattering approximation). Two major variants of prestack depth Migration, using binning of surface data and Claerbout's survey-sinking concept respectively, are in widespread use. Each type of prestack Migration produces an image volume depending on redundant parameters and supplies a condition on the image volume, which expresses consistency between data and Velocity model and is hence a basis for Velocity analysis. The survey-sinking (depth-oriented) approach to prestack Migration is less subject to kinematic artefacts than is the binning-based (surface-oriented) approach. Because kinematic artefacts strongly violate the consistency or semblance conditions, this observation suggests that Velocity analysis based on depth-oriented prestack Migration may be more appropriate in kinematically complex areas. Appropriate choice of objective (differential semblance) turns either form of Migration Velocity analysis into an optimization problem, for which Newton-like methods exhibit little tendency to stagnate at nonglobal minima. The extended modelling concept links Migration Velocity analysis to the apparently unrelated waveform inversion approach to estimation of Earth structure: from this point of view, Migration Velocity analysis is a solution method for the linearized waveform inversion problem. Extended modelling also provides a basis for a nonlinear generalization of Migration Velocity analysis. Preliminary numerical evidence suggests a new approach to nonlinear waveform inversion, which may combine the global convergence of Velocity analysis with the physical fidelity of model-based data fitting.
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Migration Velocity analysis and waveform inversion
Geophysical Prospecting, 2008Co-Authors: William W. SymesAbstract:Least-squares inversion of seismic reflection waveform data can reconstruct remarkably detailed models of subsurface structure and take into account essentially any physics of seismic wave propagation that can be modelled. However, the waveform inversion objective has many spurious local minima, hence convergence of descent methods (mandatory because of problem size) to useful Earth models requires accurate initial estimates of long-scale Velocity structure. Migration Velocity analysis, on the other hand, is capable of correcting substantially erroneous initial estimates of Velocity at long scales. Migration Velocity analysis is based on prestack depth Migration, which is in turn based on linearized acoustic modelling (Born or single-scattering approximation). Two major variants of prestack depth Migration, using binning of surface data and Claerbout's survey-sinking concept respectively, are in widespread use. Each type of prestack Migration produces an image volume depending on redundant parameters and supplies a condition on the image volume, which expresses consistency between data and Velocity model and is hence a basis for Velocity analysis. The survey-sinking (depth-oriented) approach to prestack Migration is less subject to kinematic artefacts than is the binning-based (surface-oriented) approach. Because kinematic artefacts strongly violate the consistency or semblance conditions, this observation suggests that Velocity analysis based on depth-oriented prestack Migration may be more appropriate in kinematically complex areas. Appropriate choice of objective (differential semblance) turns either form of Migration Velocity analysis into an optimization problem, for which Newton-like methods exhibit little tendency to stagnate at nonglobal minima. The extended modelling concept links Migration Velocity analysis to the apparently unrelated waveform inversion approach to estimation of Earth structure: from this point of view, Migration Velocity analysis is a solution method for the linearized waveform inversion problem. Extended modelling also provides a basis for a nonlinear generalization of Migration Velocity analysis. Preliminary numerical evidence suggests a new approach to nonlinear waveform inversion, which may combine the global convergence of Velocity analysis with the physical fidelity of model-based data fitting.
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wave equation Migration Velocity analysis by differential semblance optimization
2005Co-Authors: William W. Symes, Peng ShenAbstract:Differential semblance measures the deviation from flatness or focus of image gathers. The differential semblance objective function posed on the sub-surface offset domain responds smoothly to Velocity changes. Therefore gradient descent methods are uniquely attractive for Velocity updating by differential semblance optimization. Because of their kinematic fidelity, wave equation (depth extrapolation) Migration methods are natural platforms for Velocity analysis in complex structures. The gradient of the objective function with respect to Velocity is fomulated through the adjoint of differential Migration. Limited memory BFGS algorithm is used for the Velocity optimization. The method for wave equation Velocity analysis developed in this thesis study is applied to both synthetic and real data examples.
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angle domain common image gathers for Migration Velocity analysis by wavefield continuation imaging
Geophysics, 2004Co-Authors: Biondo Biondi, William W. SymesAbstract:We analyze the kinematic properties of offset‐domain common image gathers (CIGs) and angle‐domain CIGs (ADCIGs) computed by wavefield‐continuation Migration. Our results are valid regardless of whether the CIGs were obtained by using the correct Migration Velocity. They thus can be used as a theoretical basis for developing Migration Velocity analysis (MVA) methods that exploit the Velocity information contained in ADCIGs.We demonstrate that in an ADCIG cube, the image point lies on the normal to the apparent reflector dip that passes through the point where the source ray intersects the receiver ray. The image‐point position on the normal depends on the Velocity error; when the Velocity is correct, the image point coincides with the point where the source ray intersects the receiver ray. Starting from this geometric result, we derive an analytical expression for the expected movements of the image points in ADCIGs as functions of the traveltime perturbation caused by Velocity errors. By applying this ana...
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kinematic artifacts in prestack depth Migration
Geophysics, 2004Co-Authors: Christiaa C Stolk, William W. SymesAbstract:Strong refraction of waves in the Migration Velocity model introduces kinematic artifacts?coherent events not corresponding to actual reflectors?into the image volumes produced by prestack depth Migration applied to individual data bins. Because individual bins are migrated independently, the Migration has no access to the bin component of slowness. This loss of slowness information permits events to migrate along multiple incident-reflected ray pairs, thus introducing spurious coherent events into the image volume. This pathology occurs for all common binning strategies, including common-source, common-offset, and common-scattering angle. Since the artifacts move out with bin parameter, their effect on the final stacked image is minimal, provided that the Migration Velocity model is kinematically correct. However, common-image gathers may exhibit energetic primary events with substantial residual moveout, even with the kinematically accurate Migration Velocity model.
Paul Sava - One of the best experts on this subject based on the ideXlab platform.
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anisotropy signature in extended images from reverse time Migration
Seg Technical Program Expanded Abstracts, 2012Co-Authors: Paul Sava, Tariq AlkhalifahAbstract:Reverse-time Migration can accurately image complex geologic structures in anisotropic media. Extended images at selected locations in the earth, i.e. at commonimage-point gathers (CIPs), carry enough information to characterize the angle-dependent illumination and to provide measurements for Migration Velocity analysis. Furthermore, inaccurate anisotropy leaves a distinctive signature in CIPs, which can be used to evaluate anisotropy through techniques similar to the ones used in conventional wavefield tomography.
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wave equation Migration Velocity analysis with time shift imaging
Geophysical Prospecting, 2011Co-Authors: Tongning Yang, Paul SavaAbstract:Wave-equation Migration Velocity analysis is a technique designed to extract and update Velocity information from migrated images. The Velocity model is updated through the process of optimizing the coherence of images migrated with the known background Velocity model. The capacity for handling multi-pathing of the technique makes it appropriate in complex subsurface regions characterized by strong Velocity variation. Wave-equation Migration Velocity analysis operates by establishing a linear relation between a slowness perturbation and a corresponding image perturbation. The linear relationship and the corresponding linearized operator are derived from conventional extrapolation operators and the linearized operator inherits the main properties of frequency-domain wavefield extrapolation. A key step in the implementation is to design an appropriate procedure for constructing an image perturbation relative to a reference image that represents the difference between the current image and a true, or more correct image of the subsurface geology. The target of the inversion is to minimize such an image perturbation by optimizing the Velocity model. Using time-shift common-image gathers, one can characterize the imperfections of migrated images by defining the focusing error as the shift of the focus of reflections along the time-shift axis. The focusing error is then transformed into an image perturbation by focusing analysis under the linear approximation. As the focusing error is caused by the incorrect Velocity model, the resulting image perturbation can be considered as a mapping of the Velocity model error in the image space. Such an approach for constructing the image perturbation is computationally efficient and simple to implement. The technique also provides a new alternative for using focusing information in wavefield-based Velocity model building. Synthetic examples demonstrate the successful application of our method to a layered model and a subsalt Velocity update problem.
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numeric implementation of wave equation Migration Velocity analysis operators
Geophysics, 2008Co-Authors: Paul Sava, Ioan VladAbstract:Wave-equation Migration Velocity analysis MVA is a technique similar to wave-equation tomography because it is designedtoupdateVelocitymodelsusinginformationderivedfrom full seismic wavefields. On the other hand, wave-equation MVA is similar to conventional, traveltime-based MVAbecause it derives the information used for model updates from properties of migrated images, e.g., focusing and moveout. The main motivation for using wave-equation MVAis derived from its consistency with the corresponding wave-equation Migration, which makes this technique robust and capable of handling multipathing characterizing media with large and sharp Velocity contrasts. The wave-equation MVAoperators are constructed using linearizations of conventional wavefield extrapolation operators, assuming small perturbations relative to the background Velocity model. Similar to typical wavefield extrapolation operators, the wave-equation MVAoperators can be implemented in the mixed space-wavenumber domain using approximations of different orders of accuracy.As for wave-equation Migration, wave-equation MVA can be formulated in different imaging frameworks, dependingonthetypeofdatausedandimageoptimizationcriteria. Examples of imaging frameworks correspond to zero-offset Migrationdesigned for imaging based on focusing properties of the image, survey-sinking Migration designed for imaging based on moveout analysis using narrow-azimuth data, and shot-record Migration also designed for imaging based on moveout analysis, but using wide-azimuth data. The wave-equation MVA operators formulated for the various imaging frameworks are similar because they share elements derived from linearizations of the single square-root equation. Such operators represent the core of iterative Velocity estimation based on diffractionfocusingorsemblanceanalysis,andtheirapplicabilityin practice requires efficient and accurate implementation. This tutorial concentrates strictly on the numeric implementation of thoseoperatorsandnotontheiruseforiterativeMigrationVelocityanalysis.
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wave equation Migration Velocity analysis i theory
Geophysical Prospecting, 2004Co-Authors: Paul Sava, Biondo BiondiAbstract:We present a Migration Velocity analysis (MVA) method based on wavefield extrapolation. Similarly to conventional MVA, our method aims at iteratively improving the quality of the migrated image, as measured by the flatness of angle-domain common-image gathers (ADCIGs) over the aperture-angle axis. However, instead of inverting the depth errors measured in ADCIGs using ray-based tomography, we invert ‘image perturbations’ using a linearized wave-equation operator. This operator relates perturbations of the migrated image to perturbations of the Migration Velocity. We use prestack Stolt residual Migration to define the image perturbations that maximize the focusing and flatness of ADCIGs. Our linearized operator relates slowness perturbations to image perturbations, based on a truncation of the Born scattering series to the first-order term. To avoid divergence of the inversion procedure when the Velocity perturbations are too large for Born linearization of the wave equation, we do not invert directly the image perturbations obtained by residual Migration, but a linearized version of the image perturbations. The linearized image perturbations are computed by a linearized prestack residual Migration operator applied to the background image. We use numerical examples to illustrate how the backprojection of the linearized image perturbations, i.e. the gradient of our objective function, is well behaved, even in cases when backprojection of the original image perturbations would mislead the inversion and take it in the wrong direction. We demonstrate with simple synthetic examples that our method converges even when the initial Velocity model is far from correct. In a companion paper, we illustrate the full potential of our method for estimating Velocity anomalies under complex salt bodies.
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wave equation Migration Velocity analysis ii subsalt imaging examples
Geophysical Prospecting, 2004Co-Authors: Paul Sava, Biondo BiondiAbstract:Subsalt imaging is strongly dependent on the quality of the Velocity model. However, rugose salt bodies complicate wavefield propagation and lead to subsalt multipathing, illumination gaps and shadow zones, which cannot be handled correctly by conventional traveltime-based Migration Velocity analysis (MVA). We overcome these limitations by the wave-equation MVA technique, introduced in a companion paper, and demonstrate the methodology on a realistic synthetic data set simulating a salt-dome environment and a Gulf of Mexico data set. We model subsalt propagation using wave paths created by one-way wavefield extrapolation. Those wave paths are much more accurate and robust than broadband rays, since they inherit the frequency dependence and multipathing of the underlying wavefield. We formulate an objective function for optimization in the image space by relating an image perturbation to a perturbation of the Velocity model. The image perturbations are defined using linearized prestack residual Migration, thus ensuring stability, relative to the first-order Born approximation assumptions. Synthetic and real data examples demonstrate that wave-equation MVA is an effective tool for subsalt Velocity analysis, even when shadows and illumination gaps are present.
Ali Almomin - One of the best experts on this subject based on the ideXlab platform.
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tomographic full waveform inversion tfwi by combining fwi and wave equation Migration Velocity analysis
Geophysics, 2013Co-Authors: Biondo Biondi, Ali AlmominAbstract:Convergence of full waveform inversion can be improved by extending the Velocity model along either the subsurface-offset axis or the time-lag axis. The extension of the Velocity model along the time-lag axis enables us to linearly model large time shifts caused by Velocity perturbations. The extension is based on a new linearization of the scalar wave equation where the extended-Velocity perturbation is convolved in time with the Laplacian of the background wavefield. This linearization is accurate for both reflected events and transmitted events and, in particular, for diving waves recorded at large offsets. The modeling capabilities of the proposed linearization enable the simultaneous inversion of reflections and diving waves even when the starting Velocity model is far from being accurate. We solve the resulting optimization problem with a nested algorithm. The inner iterations are based on the proposed linearization and on a mixing of scales between the short- and long-wavelength components of the v...
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Tomographic full waveform inversion (TFWI) by combining full waveform inversion with wave-equation Migration Velocity anaylisis
SEG Technical Program Expanded Abstracts 2012, 2012Co-Authors: Biondo L. Biondi, Ali AlmominAbstract:The extension of the Velocity-model domain to subsurface offsets solves the local-minima problem of data-fitting waveform inversion. By regularizing the extended-model data-fitting inversion with the addition of an image-focusing term to the objective function, we achieve robust global convergence of the waveform inversion problem. The method shares with full waveform inversion the advantage of simultaneously solving for all the wavelengths of the model, but it also has the global convergence characteristics of wave-equation Migration Velocity analysis. The numerical implementation of the proposed inversion method requires the solution of an extended wave-equation where Velocity is a convolutional, instead of scalar, operator. The resulting method is therefore computationally intensive, and more computationally efficient approximations would be beneficial. Numerical tests performed on synthetic data modeled assuming a modified Marmousi model demonstrate the global convergence as well the high-resolution potential of the method.
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correlation based wave equation Migration Velocity analysis
Seg Technical Program Expanded Abstracts, 2011Co-Authors: Ali AlmominAbstract:Wave equation Migration Velocity analysis (WEMVA) is a family of techniques that aims to improve the subsurface Velocity model by minimizing the residual in image space. However, since the true image unknown, measuring the residual in image space is a challenge for WEMVA techniques. In his paper, I present a new method of measuring the image perturbation that is based on the cross-correlation of the observed image with a reference image in reflection angle gathers. I derive the gradient of this technique and show that it does not have the problem of cycle skipping and could be easily automated. I then show some synthetic examples and compare its gradient to the optimum WEMVA gradient.