Salt-flank delineation by interferometric imaging of transmitted P- to S-waves

Geophysics ◽  
2006 ◽  
Vol 71 (4) ◽  
pp. SI197-SI207 ◽  
Author(s):  
Xiang Xiao ◽  
Min Zhou ◽  
Gerard T. Schuster
Keyword(s):  
Velocity Model ◽  
Seismic Profile ◽  
Migration Velocity ◽  
Interferometric Imaging ◽  
S Waves ◽  
Time Migration ◽  
Transmitted Waves ◽  
Imaging Results ◽  
Vsp Data ◽  
Migration Method

We describe how vertical seismic profile (VSP) interferometric imaging of transmitted P-to-S (PS) waves can be used to delineate the flanks of salt bodies. Unlike traditional migration methods, interferometric PS imaging does not require the migration velocity model of the salt and/or upper sediments in order to image the salt flank. Synthetic elastic examples show that PS interferometric imaging can clearly delineate the upper and lower boundaries of a realistic salt-body model. Results also show that PS interferometric imaging is noticeably more accurate than conventional migration methods in the presence of static shifts and/or migration velocity errors. However, the illumination area of the PS transmitted waves is limited by the width of the shot and geophone aperture, which means wide shot offsets and deeper receiver wells are needed for comprehensive salt-flank imaging. Interferometric imaging results for VSP data from the Gulf of Mexico demonstrate its superiority over the traditional migration method. We also discuss other arrivals that can be used for interferometric imaging of salt flanks. For comparison, reduced-time migration results are presented, which are similar in quality to those obtained for interferometric imaging. We conclude that PS interferometric imaging of VSP data provides the geophysicist with a new tool by which salt flanks can be viewed from both above and below VSP geophone locations.

Reduced‐time migration of transmitted PS waves

Geophysics ◽  
2003 ◽  
Vol 68 (5) ◽  
pp. 1695-1707 ◽  
Author(s):  
David Sheley ◽  
Gerard T. Schuster
Keyword(s):  
Velocity Model ◽  
Migration Velocity ◽  
P Wave ◽  
Data Set ◽  
Interferometric Method ◽  
Direct Wave ◽  
Time Migration ◽  
Transmitted Waves ◽  
Vsp Data ◽  
Reduced Time

We develop the novel theory of transmitted PS migration and show that PS transmitted arrivals in a Gulf of Mexico vertical seismic profile (VSP) data set can be migrated to accurately image a salt sheet even though the receiver array is below the transmitting boundary. We also show that migrating transmitted arrivals is effective in illuminating the base of an orebody invisible to PP reflections. In general, interfaces that bisect wavepath propagation (i.e., the source and receiver are on opposite sides of the interface and therefore invisible to PP reflections) can be imaged by migration of PS transmitted waves. These results suggest that migration of PS transmitted waves opens new opportunities in imaging nearly vertical impedance boundaries that are typically invisible to conventional reflection imaging of crosswell and VSP data. We also present a new interferometric method, denoted as reduced‐time migration, which uses the arrival‐time difference between the direct P‐wave and subsequent events to increase migration accuracy. Reduced‐time migration removes static time shifts in the data, decreases the focusing error due to an incorrect migration velocity model, and relocates reflection or PS transmission events to be closer to their true positions. Although limited to crosswell and VSP geometries, synthetic‐ and field‐data examples show that reduced‐time migration is noticeably more accurate than conventional migration in the presence of static shifts and/or migration velocity errors. The main assumption of reduced‐time migration is that the direct wave samples errors which are representative of errors in the migration aperture. Transmission wavepaths, in general, are subparallel to the direct wave and therefore the two modes encounter similar errors and, hence, reduced‐time migration is effective in improving the focusing of migration energy. For the PP reflection case, the direct wave and the reflected waves often traverse different parts of the earth, therefore, reduced‐time migration will remove static shifts but it is not expected to mitigate velocity errors if the errors are spatially variant. However, if there is a general and consistent bias in the velocity model, reduced‐time migration is expected to deliver improved results over conventional Kirchhoff migration.

scholarly journals Shot-gather time migration of planar reflectors without velocity model

Geophysics ◽  
2011 ◽  
Vol 76 (2) ◽  
pp. S93-S101 ◽  
Author(s):  
Andrej Bóna
Keyword(s):  
Synthetic Data ◽  
Velocity Model ◽  
Migration Velocity ◽  
Time Migration ◽  
Second Derivatives ◽  
Migration Method ◽  
Prestack Time Migration ◽  
Zero Offset ◽  
2D And 3D ◽  
Homogeneous Media

Standard migration techniques require a velocity model. A new and fast prestack time migration method is presented that does not require a velocity model as an input. The only input is a shot gather, unlike other velocity-independent migrations that also require input of data in other gathers. The output of the presented migration is a time-migrated image and the migration velocity model. The method uses the first and second derivatives of the traveltimes with respect to the location of the receiver. These attributes are estimated by computing the gradient of the amplitude in a shot gather. The assumptions of the approach are a laterally slowly changing velocity and reflectors with small curvatures; the dip of the reflector can be arbitrary. The migration velocity corresponds to the root mean square (rms) velocity for laterally homogeneous media for near offsets. The migration expressions for 2D and 3D cases are derived from a simple geometrical construction considering the image of the source. The strengths and weaknesses of the methods are demonstrated on synthetic data. At last, the applicability of the method is discussed by interpreting the migration velocity in terms of the Taylor expansion of the traveltime around the zero offset.

Frequency-dependent reflection wave-equation traveltime inversion from walkaway vertical seismic profile data

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. R947-R961
Author(s):  
Yikang Zheng ◽  
Yibo Wang ◽  
Qiang Luo ◽  
Xu Chang ◽  
Rongshu Zeng ◽  
...  
Keyword(s):  
Wave Equation ◽  
Calculated Data ◽  
Velocity Model ◽  
Seismic Profile ◽  
Initial Model ◽  
Vertical Seismic Profile ◽  
Frequency Dependent ◽  
Traveltime Inversion ◽  
Time Migration ◽  
Vsp Data

To accurately image the geologic structures from walkaway vertical seismic profile (VSP) data, it is necessary to estimate the subsurface velocity field with high resolution and enhanced illumination of deep reservoirs. Because full-waveform inversion (FWI) suffers from cycle skipping when the initial model is far from the true model, we have adopted frequency-dependent reflection wave-equation traveltime inversion (FRWT) to generate the background velocity model for VSP migration. The upgoing reflection data are separated from the original shot gathers, and dynamic warping is used to evaluate the traveltime differences between the observed data and the calculated data. Different frequency bands of the data are inverted in sequence to reconstruct the velocity model with higher resolution. We also implement wavefield decomposition on the gradient field to extract the contributions of reflection components and improve the updated model. The inverted results obtained from FRWT can be used as the initial model for conventional FWI or the velocity model for reverse time migration. The experiments on synthetic data and field data demonstrate that our approach can effectively recover the background velocity model from walkaway VSP data.

Automatic migration velocity estimation for prestack time migration

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. U1-U11 ◽  
Author(s):  
Chunhui Dong ◽  
Shangxu Wang ◽  
Jianfeng Zhang ◽  
Jingsheng Ma ◽  
Hao Zhang
Keyword(s):  
Computational Cost ◽  
Velocity Model ◽  
Migration Velocity ◽  
Velocity Estimation ◽  
Velocity Analysis ◽  
Data Set ◽  
Analysis Process ◽  
Time Migration ◽  
Imaging Results ◽  
Prestack Time Migration

Migration velocity analysis is a labor-intensive part of the iterative prestack time migration (PSTM) process. We have developed a velocity estimation scheme to improve the efficiency of the velocity analysis process using an automatic approach. Our scheme is the numerical implementation of the conventional velocity analysis process based on residual moveout analysis. The key aspect of this scheme is the automatic event picking in the common-reflection point (CRP) gathers, which is implemented by semblance scanning trace by trace. With the picked traveltime curves, we estimate the velocities at discrete grids in the velocity model using the least-squares method, and build the final root-mean-square (rms) velocity model by spatial interpolation. The main advantage of our method is that it can generate an appropriate rms velocity model for PSTM in just a few iterations without manual manipulations. In addition, using the fitting curves of the picked events in a range of offsets to estimate the velocity model, which is fitting to a normal moveout correction, can prevent our scheme from the local minima issue. The Sigsbee2B model and a field data set are used to verify the feasibility of our scheme. High-quality velocity model and imaging results are obtained. Compared with the computational cost to generate the CRP gathers, the cost of our scheme can be neglected, and the quality of the initial velocity is not critical.

Migration velocity analysis based on focusing diffractions generated using the CRS wavefront attributes: Application to real land data

Geophysics ◽  
2021 ◽  
pp. 1-50
Author(s):  
German Garabito ◽  
José Silas dos Santos Silva ◽  
Williams Lima
Keyword(s):  
Time Domain ◽  
Real Data ◽  
Normal Incidence ◽  
Velocity Model ◽  
Migration Velocity ◽  
Velocity Analysis ◽  
Velocity Models ◽  
Time Migration ◽  
Migration Velocity Analysis ◽  
The Time Domain

In land seismic data processing, the prestack time migration (PSTM) image remains the standard imaging output, but a reliable migrated image of the subsurface depends on the accuracy of the migration velocity model. We have adopted two new algorithms for time-domain migration velocity analysis based on wavefield attributes of the common-reflection-surface (CRS) stack method. These attributes, extracted from multicoverage data, were successfully applied to build the velocity model in the depth domain through tomographic inversion of the normal-incidence-point (NIP) wave. However, there is no practical and reliable method for determining an accurate and geologically consistent time-migration velocity model from these CRS attributes. We introduce an interactive method to determine the migration velocity model in the time domain based on the application of NIP wave attributes and the CRS stacking operator for diffractions, to generate synthetic diffractions on the reflection events of the zero-offset (ZO) CRS stacked section. In the ZO data with diffractions, the poststack time migration (post-STM) is applied with a set of constant velocities, and the migration velocities are then selected through a focusing analysis of the simulated diffractions. We also introduce an algorithm to automatically calculate the migration velocity model from the CRS attributes picked for the main reflection events in the ZO data. We determine the precision of our diffraction focusing velocity analysis and the automatic velocity calculation algorithms using two synthetic models. We also applied them to real 2D land data with low quality and low fold to estimate the time-domain migration velocity model. The velocity models obtained through our methods were validated by applying them in the Kirchhoff PSTM of real data, in which the velocity model from the diffraction focusing analysis provided significant improvements in the quality of the migrated image compared to the legacy image and to the migrated image obtained using the automatically calculated velocity model.

Imaging reflection-blind areas using transmitted PS-waves

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. S241-S250 ◽  
Author(s):  
Yi Luo ◽  
Qinglin Liu ◽  
Yuchun E. Wang ◽  
Mohammed N. AlFaraj
Keyword(s):  
Mode Conversion ◽  
Imaging Techniques ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Reflected Waves ◽  
Prestack Migration ◽  
Reflection Data ◽  
Time Migration ◽  
Transmitted Waves ◽  
Vsp Data

We illustrate the use of mode-converted transmitted (e.g., PS- or SP-) waves in vertical seismic profiling (VSP) data for imaging areas above receivers where reflected waves cannot illuminate. Three depth-domain imaging techniques — move-out correction, common-depth-point (CDP) mapping, and prestack migration — are described and used for imag-ing the transmitted waves. Moveout correction converts an offset VSP trace into a zero-offset trace. CDP mapping maps each sample on an input trace to the location where the mode conversion occurs. For complex media, prestack migration (e.g., reverse-time migration) is used. By using both synthetic and field VSP data, we demonstrate that images derived from transmissions complement those from reflections. As an important application, we show that transmitted waves can illuminate zones above highly de-viated or horizontal wells, a region not imaged by reflection data. Because all of these benefits are obtained without extra data acquisition cost, we believe transmission imag-ing techniques will become widely adopted by the oil in-dustry.

Time-migration velocity analysis by image-wave propagation of common-image gathers

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. VE161-VE171 ◽  
Author(s):  
J. Schleicher ◽  
J. C. Costa ◽  
A. Novais
Keyword(s):  
Wave Propagation ◽  
Seismic Event ◽  
Velocity Model ◽  
Migration Velocity ◽  
Velocity Analysis ◽  
Reference Velocity ◽  
Time Migration ◽  
Migration Velocity Analysis ◽  
Velocity Image ◽  
The Common

Image-wave propagation or velocity continuation describes the variation of the migrated position of a seismic event as a function of migration velocity. Image-wave propagation in the common-image gather (CIG) domain can be combined with residual-moveout analysis for iterative migration velocity analysis (MVA). Velocity continuation of CIGs leads to a detection of those velocities in which events flatten. Although image-wave continuation is based on the assumption of a constant migration velocity, the procedure can be applied in inhomogeneous media. For this purpose, CIGs obtained by migration with an inhomogeneous macrovelocity model are continued starting from a constant reference velocity. The interpretation of continued CIGs, as if they were obtained from residual migrations, leads to a correction formula that translates residual flattening velocities into absolute time-migration velocities. In this way, the migration velocity model can be improved iteratively until a satisfactory result is reached. With a numerical example, we found that MVA with iterative image continuation applied exclusively to selected CIGs can construct a reasonable migration velocity model from scratch, without the need to build an initial model from a previous conventional normal-moveout/dip-moveout velocity analysis.

Integrated prestack depth migration of vertical seismic profile and surface seismic data from the Rocky Mountain Foothills of southern Alberta, Canada

Geophysics ◽  
2003 ◽  
Vol 68 (6) ◽  
pp. 1782-1791 ◽  
Author(s):  
M. Graziella Kirtland Grech ◽  
Don C. Lawton ◽  
Scott Cheadle
Keyword(s):  
Seismic Data ◽  
Rocky Mountain ◽  
Velocity Model ◽  
Seismic Profile ◽  
Vertical Seismic Profile ◽  
Prestack Depth Migration ◽  
Data Set ◽  
Depth Migration ◽  
Southern Alberta ◽  
Vsp Data

We have developed an anisotropic prestack depth migration code that can migrate either vertical seismic profile (VSP) or surface seismic data. We use this migration code in a new method for integrated VSP and surface seismic depth imaging. Instead of splicing the VSP image into the section derived from surface seismic data, we use the same migration algorithm and a single velocity model to migrate both data sets to a common output grid. We then scale and sum the two images to yield one integrated depth‐migrated section. After testing this method on synthetic surface seismic and VSP data, we applied it to field data from a 2D surface seismic line and a multioffset VSP from the Rocky Mountain Foothills of southern Alberta, Canada. Our results show that the resulting integrated image exhibits significant improvement over that obtained from (a) the migration of either data set alone or (b) the conventional splicing approach. The integrated image uses the broader frequency bandwidth of the VSP data to provide higher vertical resolution than the migration of the surface seismic data. The integrated image also shows enhanced structural detail, since no part of the surface seismic section is eliminated, and good event continuity through the use of a single migration–velocity model, obtained by an integrated interpretation of borehole and surface seismic data. This enhanced migrated image enabled us to perform a more robust interpretation with good well ties.

Specular interferometric imaging of vertical seismic profile data

2015 ◽  
Vol 3 (3) ◽  
pp. SW57-SW62 ◽  
Author(s):  
Yunsong Huang ◽  
Ruiqing He ◽  
Chaiwoot Boonyasiriwat ◽  
Yi Luo ◽  
Gerard Schuster
Keyword(s):  
Ray Tracing ◽  
Field Data ◽  
Seismic Profile ◽  
The Other ◽  
Interferometric Imaging ◽  
Profile Data ◽  
Vertical Seismic Profile ◽  
Ghost Image ◽  
Primary Image ◽  
Vsp Data

We introduce the concept of seminatural migration of multiples in vertical seismic profile (VSP) data, denoted as specular interferometric migration, in which part of the kernel is computed by ray tracing and the other part is obtained from the data. It has the advantage over standard migration of ghost reflections, in that the well statics are eliminated and the migration image is no more sensitive to velocity errors than migration of VSP primaries. Moreover, the VSP ghost image has significantly more subsurface illumination than the VSP primary image. The synthetic and field data results validate the effectiveness of this method.

Migration of seismic data from inhomogeneous media

Geophysics ◽  
1981 ◽  
Vol 46 (5) ◽  
pp. 751-767 ◽  
Author(s):  
Les Hatton ◽  
Ken Larner ◽  
Bruce S. Gibson
Keyword(s):  
Theoretical Approach ◽  
Synthetic Data ◽  
Velocity Model ◽  
Implicit Assumption ◽  
Geologic Structure ◽  
Structural Shape ◽  
Depth Migration ◽  
Position Errors ◽  
Time Migration ◽  
Imaging Results

Because conventional time‐migration algorithms are founded on the implicit assumption of locally lateral homogeneity, they leave events mispositioned when overburden velocity varies laterally. The ray‐theoretical depth migration procedure of Hubral often can provide adequate first‐order corrections for such position errors. Complex geologic structure, however, can so severely distort wavefronts that resulting time‐migrated sections may be barely interpretable and thus not readily correctable. A more accurate, wave‐theoretical approach to depth migration then becomes essential to image the subsurface properly. This approach, which transforms an unmigrated time section directly into migrated depth, more completely honors the wave equation for a medium in which variations in interval velocity and details of structural shape govern wave propagation. Where geologic structure is complicated, however, we usually lack an accurate velocity model. It is important, therefore, to understand the sensitivity of depth migration to velocity errors and, in particular, to assess whether it is justified to go to the added effort of doing depth migration. We show a synthetic data example in which the wave‐theoretical approach to depth migration properly images deep reflections that are poorly resolved and left distorted by either time migration or ray‐theoretical depth migration. These imaging results are, moreover, surprisingly insensitive to errors introduced into the velocity model. Application to one field data example demonstrates the superior treatment of amplitude and waveform by wave‐theoretical depth migration. In a second data example, deep reflections are so influenced by anomalous overburden structure that the only valid alternative to performing wave‐theoretical depth migration is simply to convert the unmigrated data to depth. When the overburden is laterally variable, conventional time migration of unstacked data can be as destructive to steeply dipping reflections as is CDP stacking prior to migration. A schematic example illustrates that when migration of unstacked data is judged necessary, it should normally be performed as a depth migration.

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