Interval velocity estimation using iterative prestack depth migration in the constant angle domain

We propose a method for estimating interval velocity using the kinematic information in defocused diffractions and reflections. We extract velocity information from defocused migrated events by analyzing their residual focusing in physical space (depth and midpoint) using prestack residual migration. The results of this residual-focusing analysis are fed to a linearized inversion procedure that produces interval velocity updates. Our inversion procedure uses a wavefield-continuation operator linking perturbations of interval velocities to perturbations of migrated images, based on the principles of wave-equation migration velocity analysis introduced in recent years. We measure the accuracy of the migration velocity using a diffraction-focusing criterion instead of the criterion of flatness of migrated common-image gathers that is commonly used in migration velocity analysis. This new criterion enables us to extract velocity information from events that would be challenging to use with conventional velocity analysis methods; thus, our method is a powerful complement to those conventional techniques. We demonstrate the effectiveness of the proposed methodology using two examples. In the first example, we estimate interval velocity above a rugose salt top interface by using only the information contained in defocused diffracted and reflected events present in zero-offset data. By comparing the results of full prestack depth migration before and after the velocity updating, we confirm that our analysis of the diffracted events improves the velocity model. In the second example, we estimate the migration velocity function for a 2D, zero-offset, ground-penetrating radar data set. Depth migration after the velocity estimation improves the continuity of reflectors while focusing the diffracted energy.

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Influence of structural dip angles on interval velocity analysis

Geophysics ◽

10.1190/1.2918741 ◽

2008 ◽

Vol 73 (4) ◽

pp. U13-U18 ◽

Cited By ~ 15

Author(s):

Moshe Reshef ◽

Andreas Rüger

Keyword(s):

Velocity Analysis ◽

Prestack Depth Migration ◽

Scattering Angle ◽

Depth Migration ◽

Interval Velocity ◽

Important Input ◽

The Common ◽

Summation Process

Common scattering-angle and traditional common-offset gathers can be of limited use for interval velocity analysis in regions with complex geologic structures. In the summation process, which occurs when generating each trace in the common-image gather, vital information about structural dip is lost during prestack depth migration. This inadvertently lost data can provide important input to moveout-based velocity-updating algorithms. Maintaining this crucial dip information can improve the quality of the velocity analysis and imaging processes.

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Interval velocity analysis for prestack depth migration

10.1190/1.1889525 ◽

1989 ◽

Author(s):

John MacBain

Keyword(s):

Velocity Analysis ◽

Prestack Depth Migration ◽

Depth Migration ◽

Interval Velocity

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Incorporating geologic information into reflection tomography

Geophysics ◽

10.1190/1.1707073 ◽

2004 ◽

Vol 69 (2) ◽

pp. 533-546 ◽

Cited By ~ 98

Author(s):

Robert G. Clapp ◽

Biondo L. Biondi ◽

Jon F. Claerbout

Keyword(s):

Velocity Structure ◽

Null Space ◽

Velocity Model ◽

Prestack Depth Migration ◽

Depth Migration ◽

Interval Velocity ◽

Velocity Models ◽

Regularized Inversion ◽

Symmetric Operators ◽

Reflection Tomography

In areas of complex geology, prestack depth migration is often necessary if we are to produce an accurate image of the subsurface. Prestack depth migration requires an accurate interval velocity model. With few exceptions, the subsurface velocities are not known beforehand and should be estimated. When the velocity structure is complex, with significant lateral variations, reflection‐tomography methods are often an effective tool for improving the velocity estimate. Unfortunately, reflection tomography often converges slowly, to a model that is geologically unreasonable, or it does not converge at all. The large null space of reflection‐tomography problems often forces us to add a sparse parameterization of the model and/or regularization criteria to the estimation. Standard tomography schemes tend to create isotropic features in velocity models that are inconsistent with geology. These isotropic features result, in large part, from using symmetric regularization operators or from choosing a poor model parameterization. If we replace the symmetric operators with nonstationary operators that tend to spread information along structural dips, the tomography will produce velocity models that are geologically more reasonable. In addition, by forming the operators in helical 1D space and performing polynomial division, we apply the inverse of these space‐varying anisotropic operators. The inverse operators can be used as a preconditioner to a standard tomography problem, thereby significantly improving the speed of convergence compared with the typical regularized inversion problem. Results from 2D synthetic and 2D field data are shown. In each case, the velocity obtained improves the focusing of the migrated image.

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Unified imaging of multichannel seismic data: Combining traveltime inversion and prestack depth migration

Geophysics ◽

10.1190/1.2957761 ◽

2008 ◽

Vol 73 (5) ◽

pp. VE269-VE280 ◽

Cited By ~ 7

Author(s):

Priyank Jaiswal ◽

Colin A. Zelt

Keyword(s):

Seismic Data ◽

Joint Inversion ◽

Velocity Model ◽

Depth Image ◽

Prestack Depth Migration ◽

Traveltime Inversion ◽

Depth Migration ◽

Interval Velocity ◽

Wide Aperture ◽

Zero Offset

Imaging 2D multichannel land seismic data can be accomplished effectively by a combination of traveltime inversion and prestack depth migration (PSDM), referred to as unified imaging. Unified imaging begins by inverting the direct-arrival times to estimate a velocity model that is used in static corrections and stacking velocity analysis. The interval velocity model (from stacking velocities) is used for PSDM. The stacked data and the PSDM image are interpreted for common horizons, and the corresponding wide-aperture reflections are identified in the shot gathers. Using the interval velocity model, the stack interpretations are inverted as zero-offset reflections to constrain the corresponding interfaces in depth; the interval velocity model remains stationary. We define a coefficient of congruence [Formula: see text] that measures the discrepancy between horizons from the PSDM image andtheir counterparts from the zero-offset inversion. A value of unity for [Formula: see text] implies that the interpreted and inverted horizons are consistent to within the interpretational uncertainties, and the unified imaging is said to have converged. For [Formula: see text] greater than unity, the interval velocity model and the horizon depths are updated by jointly inverting the direct arrivals with the zero-offset and wide-aperture reflections. The updated interval velocity model is used again for both PSDM and a zero-offset inversion. Interpretations of the new PSDM image are the updated horizon depths. The unified imaging is applied to seismic data from the Naga Thrust and Fold Belt in India. Wide-aperture and zero-offset data from three geologically significant horizons are used. Three runs of joint inversion and PSDM are required in a cyclic manner for [Formula: see text] to converge to unity. A joint interpretation of the final velocity model and depth image reveals the presence of a triangle zone that could be promising for exploration.

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Vertical seismic profiling depth migration of a salt dome flank

Geophysics ◽

10.1190/1.1442164 ◽

1986 ◽

Vol 51 (5) ◽

pp. 1087-1109 ◽

Cited By ~ 35

Author(s):

N. D. Whitmore ◽

Larry R. Lines

Keyword(s):

Data Processing ◽

Survey Design ◽

Velocity Model ◽

Salt Dome ◽

Velocity Estimation ◽

Seismic Profiles ◽

Depth Migration ◽

Vertical Seismic Profiles ◽

Interval Velocity ◽

Vsp Data

Vertical seismic profiles (VSPs) can supply information about both velocity and subsurface interface locations. Properly designed VSPs can be used to map steeply dipping interfaces such as salt dome flanks. Mapping subsurface interfaces with VSP data requires careful survey design, appropriate data processing, interval velocity estimation, and reflector mapping. The first of these four ingredients is satisfied, in most cases, by preacquisition modeling. The second is accomplished by careful data processing. Initial velocity estimates are provided by seismic tomography. Velocity‐model refinement is accomplished by a combination of iterative modeling and iterative least‐squares inversion. Finally, the resultant interval velocities are used in depth migration of the processed VSP. These four ingredients have been combined to map a salt dome flank.

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Imaging and velocity estimation with depth‐focusing analysis

Geophysics ◽

10.1190/1.1443228 ◽

1992 ◽

Vol 57 (12) ◽

pp. 1608-1622 ◽

Cited By ~ 76

Author(s):

Scott MacKay ◽

Ray Abma

Keyword(s):

Velocity Estimation ◽

Prestack Depth Migration ◽

Depth Migration ◽

Focal Surface ◽

Seismic Image ◽

Surface Image ◽

Zero Offset ◽

Imaging Conditions ◽

Zero Time ◽

Migration Velocities

Prestack depth migration uses two imaging conditions, zero time and zero offset, during downward continuation to form a migrated depth section. When the migration velocities are exact, the two imaging conditions act in a complementary fashion to yield a focused image. When the migration velocities are in error, reflected energy collapses to zero offset at depths that are inconsistent with the zero‐time imaging condition. The result is a deteriorated seismic image. However, by interpreting the nonzero times at which focusing actually occurs, the migration velocities can be updated iteratively in a process called depth‐focusing analysis. To produce a well‐focused seismic image, the goal of depth‐focusing analysis must be the elimination of focusing errors; however, practical considerations can prevent this goal from being achieved. Therefore, to relax the sensitivity of the migrated image to focusing errors, we introduce a nonzero‐time imaging condition by extracting the data along the interpreted surface of focusing from the depth‐focusing analysis volume. This method, called focal‐surface imaging, estimates the results of prestack depth migration using the updated velocities. Depth‐focusing analysis is shown to be a robust approach to velocity estimation and imaging. Limitations arising from constant‐velocity and low‐dip approximations are reduced in the presence of increasing velocities with depth. Lateral velocity errors, sources of exaggerated focusing errors and diverging velocity solutions, can also be addressed by applying a damping factor to the interpreted depth errors. Velocity estimation and focal‐surface imgaging, using iterative prestack depth migration, were applied to a southern North Sea data set. Starting with a regional velocity function, the first iteration provided an updated velocity field that more accurately conformed to the known lithologies. The focal‐surface image, formed from the same iteration, contained significantly more focused energy than the conventional section formed by prestack depth migration. However, structural differences between the two sections indicated the need for another iteration of migration using the updated velocities. The second iteration indicated smaller velocity errors and enough similarity between the migrated section and the new focal‐surface image to indicate that further iterations were unnecessary.

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2D Seismic Imaging Improvement through Prestack Depth Migration (PSDM) Method

Indonesian Journal of Physics ◽

10.5614/itb.ijp.2019.30.1.5 ◽

2019 ◽

Vol 30 (1) ◽

pp. 23-26

Author(s):

Iyod Suherman ◽

Taufan Wiguna ◽

Rahadian Rahadian ◽

Djunaedi Muljawan ◽

Omar Moefti

Keyword(s):

Seismic Imaging ◽

Geological Structure ◽

Prestack Depth Migration ◽

Depth Migration ◽

Velocity Modeling ◽

Interval Velocity ◽

Time Migration ◽

Prestack Time Migration ◽

Seismic Reflector

The quality of seismic is important for interpretation. Prestack Depth Migration produce better quality of seismic imaging. The seismic generated through PSDM method has better seismic reflector and geological structure appearance compared to Prestack Time Migration (PSTM) method. Accurate interval velocity modeling is a key in PSDM process, involving dix transformation, coherency inversion, and tomography. Comparison between PSTM and PSDM show that PSDM offer better imaging for interpretation because PSDM has better seismic reflector continuity and good geological appearance.

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