Skip Nav Destination
Filter
Filter
Filter
Filter
Filter

Search Results for
3-D common-offset depth migration

Update search

Filter

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

### NARROW

Peer Reviewed

Format

Subjects

Journal

Publisher

Conference Series

Date

Availability

1-20 of 4787 Search Results for

#### 3-D common-offset depth migration

**Follow your search**

Access your saved searches in your account

Would you like to receive an alert when new items match your search?

*Close Modal*

Sort by

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2000 SEG Annual Meeting, August 6–11, 2000

Paper Number: SEG-2000-0858

... Summary Exploiting the assumed regularity and symmetry of marine towed streamer data leads to an efficient workflow for 3D prestack

**depth****migration**and velocity model estimation. We decompose 3D marine towed streamer data into a set of**common**-**offset****common**-azimuth volumes. We perform our...
Abstract

Summary Exploiting the assumed regularity and symmetry of marine towed streamer data leads to an efficient workflow for 3D prestack depth migration and velocity model estimation. We decompose 3D marine towed streamer data into a set of common-offset common-azimuth volumes. We perform our initial migration with a high-quality ?-k V(z) prestack migration. The initial prestack V(z) migration is also used in lieu of prestack time migration to do AVO analysis or imaging of targets not affected by strong later velocity contrast.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2000 SEG Annual Meeting, August 6–11, 2000

Paper Number: SEG-2000-0842

... Summary The double square root (DSR) equation for laterally varying media in midpoint-

**offset**coordinates provides a convenient framework for developing efficient**3**-**D**prestack wave equation**depth****migrations**with screen propagators.**Common****offset**pseudo-screen**depth****migration**is a fast...
Abstract

Summary The double square root (DSR) equation for laterally varying media in midpoint-offset coordinates provides a convenient framework for developing efficient 3-D prestack wave equation depth migrations with screen propagators. Common offset pseudo-screen depth migration is a fast and accurate method for migrating common offset, common azimuth seismic data. The common offset pseudo-screen propagator down-ward contuiens the source and receiver wave fields simultaneously based on the DSR equation.

Proceedings Papers

Publisher: Offshore Technology Conference

Paper presented at the Offshore Technology Conference, May 2–5, 1994

Paper Number: OTC-7399-MS

... poststack

**migration**providing the initial field for prestack**migration**. Some important processing of the unstacked data preceded the**3**-**D**prestack**depth****migration**, including editing of noisy data, deconvolution, and sorting to**common****offset****3**-**D**data volumes. The sort to**common****offset**volumes allowed us...
Abstract

INTRODUCTION Subsalt imaging and subsalt trap identification have been recognized for years as important but difficult exploration objectives. By using subsalt imaging technology the explorationist hopes to determine the depth of the subsalt structures and the presence or absence of structural closure associated with the subsalt prospect, thereby obtaining a realistic assessment of the risks involved with drilling a subsalt well. Target-oriented 3-D prestack depth migration is the most powerful tool currently available to assist the explorationist in the quest for hydrocarbons below salt. In this paper we present a geophysical case study describing the steps taken to produce a useful subsalt image. POSTSTACK DEPTH MIGRATION, PRESTACK PROCESSING, AND 3-D PRESTACK IMAGING The first step of the 3-D prestack depth migration sequence involved several iterations of 3-D poststack depth migration. 3-D poststack migration allowed us to image sediments and faulting above salt, top of salt, and base of salt (assuming the base of salt has survived the stacking process). Iterative 3-D poststack depth migration was also essential in deriving the 3-D velocity field required in the 3-D prestack migration, but it was considerably less expensive than 3-D prestack depth migration. Imaging the subsalt target, which was considerably smaller in base area than the original survey, was accomplished by 3-D prestack depth migration. In brief, the process of iterative 3-D poststack depth migration is as follows: Before the first migration, we generated a 3-D sediment velocity field using a number of standard velocity analysis techniques. Poststack depth migration, using this velocity field, produced a correct image of the sediments above salt (including faults), and the top of salt, but it incorrectly imaged the base of salt and any subsalt reflectors. Interpreting the top of salt in 3-D from the first iteration yielded an updated velocity field, with salt velocity inserted everywhere below the top of salt. The second poststack migration, using this velocity field, now showed a correct image of the base of salt, but not below the base of salt. Interpreting the base of salt in 3-D from the second iteration yielded a new update for the velocity field, which should allow correct imaging of any subsalt reflectors which survived the stacking process. Poststack migration using this velocity field, by imaging very few subsalt reflectors, confirmed the need for 3-D prestack migration, with the final velocity field from poststack migration providing the initial field for prestack migration. Some important processing of the unstacked data preceded the 3-D prestack depth migration, including editing of noisy data, deconvolution, and sorting to common offset 3-D data volumes. The sort to common offset volumes allowed us to migrate manageable data sets on a Cray-2 computer in a relatively short time. Separate migration of the common offset volumes also allowed us to see how each volume contributes to the subsalt image (optionally editing poor images from the final stack), and to perform a migration velocity analysis which validates or invalidates our choice of 3-D velocity field. The prestack imaging was done by Kirchhoff migration, with traveltimes obtained by raytracing.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2007 SEG Annual Meeting, September 23–28, 2007

Paper Number: SEG-2007-2270

... Summary We present a new implementation of 3D Fourier finite-difference (FFD)

**depth****migration**method based on survey sinking (DSR) operator in source-geophone and midpoint-**offset**hybrid domain. The**3**-**D**DSR downwardcontinuation operator is decomposed into two orthogonal downward-continuation...
Abstract

Summary We present a new implementation of 3D Fourier finite-difference (FFD) depth migration method based on survey sinking (DSR) operator in source-geophone and midpoint-offset hybrid domain. The 3-D DSR downwardcontinuation operator is decomposed into two orthogonal downward-continuation operators: a 2-D inline prestack operator which is implemented in source-geophone coordinates and a 2-D crossline poststack operator which is implemented in midpoint-offset coordinates. This new implementation has much higher accuracy compared to the conventional FFD-based DSR implementation in midpoint-offset domain only. Numerical tests show that the new implementation is very efficient and provides much better migrated images than conventional implementation and the image quality from the new implementation is almost the same as that from shot profile migration. Introduction Two categories exist in the classification of one-way wave equation based depth migration: shot profile migration and survey sinking (DSR) migration (Claerbout, 1985) . In shot profile migration, source and receiver wave fields are extrapolated independently in depth and an imaging condition, such as the cross correlation of source/receiver wavefields, is applied to get the migrated image; In survey sinking migration, source and receiver wave fields are downward continued simultaneously and the zero-time and zero-offset imaging condition is applied to obtain the migrated image. Conventional survey sinking migration works in midpoint-offset domain to avoid sorting seismic data from common shot gathers to common receiver gathers. It has the advantage of unlimited apertures, contrast to limited apertures as in shot profile migration for the purpose of limiting computation time and memory requirements. In survey sinking migration, preprocessing of seismic data is required: The field recorded common shot gathers are first sorted into midpoint-offset domain (CMP bins) and then are regularized along offset. The input data for full DSR are 5-D, including arrival time; inline/crossline midpoints; and inline/crossline offsets. Taking advantages of the limited azimuthal range of conventional marine survey, a 5-D DSR extrapolation problem is reduced into a 4-D computation problem by making common azimuth assumption and applying stationary phase condition in cross line offset direction. This is the widely used common azimuth migration (CAM). (Biondi and Palacharia, 1996). In case of wide azimuth marine data, it is possible to group the wide azimuth data into different azimuth subsections and each subsection is then applied with CAM. Over years, different algorithms have been developed for DSR migration. Popovici (1996) developed a split-step DSR method and Biondi and Palacharia (1996) used phase shift plus interpolation (PSPI) approach. To achieve higher accuracy for strong lateral velocity variations, the generalized screen propagators (GSP) and Fourier finite difference (FFD) method (Zhang et al., 2005) have been proposed. All these methods work in midpoint-offset domain. However, detailed mathematical analysis shows that GSP/FFD implementation in midpoint-offset domain alone neglects the coupling term between midpoint wave number and offset wave number which has hugh compact on image quality when there are strong lateral velocity variations. In this paper, we present a new implementation of FFD based DSR depth migration in source-geophone and midpoint-offset hybrid domain.

Proceedings Papers

Publisher: Offshore Technology Conference

Paper presented at the Offshore Technology Conference, May 4–7, 1998

Paper Number: OTC-8681-MS

... on a downward-continuation operator derived from the full

**3**-**D**prestack downward-continuation operator.**Common**-azimuth data sets are recursively evaluated at increasing**depth**levels, starting from the**common**-azimuth data set recorded at the surface.**Common**-azimuth data has zero cross-line**offset**, and thus...
Abstract

Abstract Common-azimuth imaging can significantly reduce the cost of full-volume 3-D prestack depth imaging of marine data sets. The common-azimuth imaging procedure comprises of two steps: first, transformation of the prestack data to common azimuth data by azimuth moveout (AMO); second, imaging the transformed data by common-azimuth migration. Both these steps are computationally efficient. AMO is a partial migration operator and thus it has narrow spatial aperture. Common-azimuth migration is based on downward continuation of the wavefield; therefore, its computational cost increases only as the square of the image depth. In contrast, the cost of conventional Kirchhoff migration is proportional to the cube of the image depth. Because it is a wavefield-continuation method, common-azimuth migration does not require the computation of asymptotic Green functions. Therefore, common-azimuth imaging is likely to overcome some of the accuracy problems encountered by Kirchhoff migration in the presence of complex wave-propagation phenomena. The proposed common-azimuth imaging procedure successfully depth imaged a marine data set recorded in the North Sea. These positive results suggest the application of common-azimuth imaging to velocity estimation based on wavefield focusing. Introduction Computational cost is a main obstacle to the widespread use 3D prestack depth migration for full-volume imaging. Currently, 3-D prestack migration is almost exclusively performed by Kirchhoff methods because they effectively handle the irregular and sparse geometries of 3-D prestack data. However, the computational cost of full-volume imaging by Kirchhoff migration increases by a factor proportional to the cube of the depth extent of the image, making the imaging of deeper targets extremely expensive. In contrast, the cost of migration methods based on the downward continuation of the wavefield increases only with the square of depth. But 3-D prestack data cannot be efficiently downward-continued by standard methods because of their irregular and sparse sampling. Here I present a procedure for full-volume prestack imaging of marine data sets that takes advantage of the limited azimuthal range of 3-D marine data to reduce significantly the computational cost. The procedure comprises two steps. The first step transforms the recorded data into effective common-azimuth data, where the common-azimuth is the direction of the acquisition sail line. The second step images the synthesized common-azimuth data set by prestack migration based of the downward continuation of the wavefield. To transform marine data into effective common-azimuth data, I "rotate" the prestack data using a partial-prestack migration operator called azimuth moveout 3 (AMO). The AMO operator is defined in the time-space domain, and it can be applied as an integral operator to 3-D marine data with geometry irregularities caused by cable feather and multistreamer recording. The spatial aperture, and consequently the computational cost, of the AMO operator is approximately proportional to the azimuth rotation between the input offset vector and the output offset vector, and it is small when the azimuth rotation is small. Since the azimuths of most of the traces recorded during a marine acquisition are close to the nominal common azimuth, the cost of the AMO transformation is low. Common -azimuth migration is based on a downward-continuation operator derived from the full 3-D prestack operator 2 .

Proceedings Papers

Publisher: Offshore Technology Conference

Paper presented at the Offshore Technology Conference, May 4–7, 1998

Paper Number: OTC-8815-MS

... reflection point gathers, and

**depth**slices from prestack**migrated**synthetic data. Multiples produce strong coherent noise in all of these types of**migrated**images. However, stacking of the**common**-**offset**images effectively discriminates against these effects in 2-**D**, and we can produce a high-quality...
Abstract

Abstract One of the common techniques used to form depth images of subsalt structure from seismic data is Kirchhoff migration based on first-arrival traveltimes, Three of the most common factors blamed for poor results using this approach are limitations in the first-arrival traveltime approximation, multiples, and migration velocity model errors 1,2 . A 2-D seismic model study was conducted to assess the impact of each of these factors on our ability to form structural images from a realistic 2-D synthetic dataset. This work demonstrates that, even in the presence of these factors, Kirchhoff migration is capable of generating useful images of subsalt structure. Introduction In this study, I show that the use of first-arrival traveltimes, the presence of multiples, and the presence of reasonable errors in the migration velocity model do not appear sufficient to impair our ability to form useful images of subsalt structure using Kirchhoff prestack depth migration. The impact of each of these factors was analyzed individually by applying 2-D Kirchhoff prestack depth migration to a realistic synthetic dataset generated using 2-D acoustic finite-difference modeling. This study did not investigate the combined effects of velocity model errors and the presence of strong noise such as surface-related multiples in the input data. There are recognizable artifacts due to the first-arrival approximation on common-offset images, common reflection point gathers, and depth slices extracted from the prestack migrated synthetic data volume. Multiples also produce strong coherent noise in all of these types of migrated images. However, both the first-arrival artifacts and multiples vary strongly with offset, and stacking the individual common offset images produced a high-quality structural image of the subsalt section. One of the more interesting aspects of this work is the analysis of the effect of velocity errors on prestack depth migrated images. This work shows that typical velocity errors (those that do not significantly degrade the focus at the top of salt) do not significantly degrade subsalt images, and, in fact, that prestack depth migration is relatively robust with respect to the velocity errors one would typically expect to make. There are several important limitations of the methodology used in this study. Because the analysis 2-D, it cannot address the effects of limited azimuth or 3-D effects in the data. Also, since seismic energy decays more rapidly with propagation distance in 3-D than in 2-D, one would expect the multiples in real data to be stronger relative to subsalt primaries than predicted by 2-D modeling. Finally, since the data is acoustic, the relative amplitude of the signal versus source generated noise is only crudely approximated. Further work should be done to include these effects in the analysis. Modeling This model study was designed to test the hypothesis that first arrival travel times are insufficient to produced useful structural images for an actual Gulf of Mexico salt body. To test this hypothesis, a velocity model that preserved the kinematic properties of the migration velocity field used to image the salt body was generated (Fig. I). To produce artifacts in the model images representative of those in field data, it was also important that the model generate a realistic set of reflections.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2009 SEG Annual Meeting, October 25–30, 2009

Paper Number: SEG-2009-2939

...

**common**binning parameter choices in**3**-**D**NMO correction and prestack**migration**:**offset**, measured as the surface distance between source and receiver, and azimuth, similarly taken as the direction of the line connecting the source and receiver. Conventionally, at least two kinds of numerically efficient...
Abstract

Summary A key step in amplitude variation with offset (AVO) and with azimuth (AVOZ) analysis is transformation the seismic data from offset to incident angle domain. Conventional binning approaches according to source-receiver offset and azimuth on the surface smear the energy from different directions at the image point in the subsurface. The widely used offset-to-angle mapping cannot be directly used in prestack time migration because it neglects asymmetry of the ray paths. The up-to-date common-angle time migration fails to take ray bending and anisotropy into account. We present a table-driven and a data-driven 3-D angle-domain imaging approach in Kirchhoff prestack time migration (KPSTM) through more accurate evaluation of average azimuth and local incident angle of the rays at the reflector. The effects are illustrated on 2-D and 3-D synthetic data sets. Introduction AVO is used to infer the elastic properties of the rock. Its equation is generally expressed in terms of average angle of incidence rather than offset. However, seismic data are recorded as a function of offset, so a mapping must be found to relate offset to incident angle. Plane-wave or common-angle prestack migrations implicitly perform this mapping (Wapenaar and Berkhout, 1989; Rickett and Sava, 2001; Brandsberg-Dahl et al., 2003). This is the preferred methodology for structurally complex geology. Now, angle-domain imaging is gradually replacing offset-domain imaging in prestack depth migration. In AVO study, however, offset-to-angle mapping is routinely performed on the seismic data preconditioned by NMO correction or prestack time migration. Common-angle prestack time migration is seldom studied at this time of day (Perez and Marfurt, 2007). The black arrow in Figure 1a illustrates two common binning parameter choices in 3-D NMO correction and prestack migration: offset, measured as the surface distance between source and receiver, and azimuth, similarly taken as the direction of the line connecting the source and receiver. Conventionally, at least two kinds of numerically efficient methods are used to evaluate the relationship between offset and incident angle. One is based on the classical ray theory while the other is following Walden (1991) using the hyperbolic moveout of the reflected waves. In both cases, it is assumed that the earth is composed of a series of flat, homogenous, isotropic layers, and the down-going ray paths are symmetrical with the up-going ray paths. To take ray bending and VTI media into account, Bale et al. (2001) suggested to determine ray parameters and thus angles for the computation of AVO attributes using non-hyperbolic moveout. The preconditional processing for AVO study mentioned here has a few shortages. First of all, conventional binning approaches according to source-receiver offset and azimuth on the surface smear the energy from different directions at the image point in the subsurface. Once this happens, offset-to- angle mapping cannot be expected to tackle this problem any more. Second, the oversimplified definition of the azimuth is a poor representation for the wave propagating in the subsurface, particularly if a significant component of side-scattered energy exists. Therefore, Perez and Marfurt (2008) have proposed a new azimuthal binning to improve delineation of faults and fractures.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2005 SEG Annual Meeting, November 6–11, 2005

Paper Number: SEG-2005-2542

... veloc- ity updates for each CRP gather. The traveltime picking is limited to only a stacked or

**common**-**offset**volume, and it needs to be done only once; there is no need to do intensive**3**-**D**prestack**depth****migration**. Hence, the computation is much faster than other**migration**-based velocity analyses.**3**-**D**...
Abstract

ABSTRACT 3-D prestack depth migration and residual picking in common image gathers (CIGs) are the most timeconsuming part in 3-D migration velocity analysis. We propose a new algorithm that provides 3-D velocity analysis quickly and accurately. Spatial coordinates and orientations of reflection points are provided by 3-D poststack or prestack parsimonious migration; the migration involves only time samples that are picked from the salient reflection events on a poststack volume or on one common-offset volume. Ray tracing from the reflection points to the surface provides a common-reflection point (CRP) gather for each reflection point. Predicted moveouts for local velocity perturbations, based on the maximizing stacked amplitude, gives the estimated velocity updates for each CRP gather. The traveltime picking is limited to only a stacked or common-offset volume, and it needs to be done only once; there is no need to do intensive 3-D prestack depth migration. Hence, the computation is much faster than other migration-based velocity analyses. 3-D synthetic data tests show the algorithm works effectively and efficiently.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2009 SEG Annual Meeting, October 25–30, 2009

Paper Number: SEG-2009-2283

... Summary We present a

**3**-**D**automatic**migration**velocity analysis (MVA) algorithm based on**common**-azimuth**migration**(CAM) in the source-geophone implementation, and using differential semblance optimization (DSO). We have successfully tested the algorithm on the**3**-**D**SEG/EAGE overthrust model...
Abstract

Summary We present a 3-D automatic migration velocity analysis (MVA) algorithm based on common-azimuth migration (CAM) in the source-geophone implementation, and using differential semblance optimization (DSO). We have successfully tested the algorithm on the 3-D SEG/EAGE overthrust model and a 3D field dataset using a simple 1D velocity model as a starting point in each case. We conclude that wave-equation-based MVA may be a good alternative to ray-based tomography for velocity model-building in complex regions of the earth. Introduction An accurate velocity model is a prerequisite for satisfactory depth migration. Although ray-based tomography (e.g. Bishop et al., 1985, Sexton and Williamson, 1998) is still the workhorse for velocity model-building in the industry, interest has been growing in band-limited methods which more accurately represent the underlying physics, such as one-way wave equation-based MVA (Sava and Biondi, 2004; Shen et at 2003; Xie and Yang 2008; Fliedner et al, 2007; Albertin et al, 2006), and full waveform inversion (Tarantola, 1984: Pratt, 1999; Hadj-Ali et al., 2007). These methods offer improved stability in complex geology compared to ray-based ones (Sava and Biondo, 2004), and may also provide better resolution by taking advantage of the different information at different frequencies. The one-way wave equation-based MVA formulation is independent of the choice of propagator and data organization (Shen et al, 2003; Biondi and Sava, 2004; Khoury et al, 2006; Sava and Vlad, 2008). However, while shot-profile migration is now routine for depth imaging, the iterative nature of MVA makes a 3D shot-profile based inversion tremendously computationally intensive. On the other hand, CAM (Biondi and Palacharla, 1996), while potentially of limited applicability because of its assumptions, offers a very quick wave-equation based migration. For areas of moderate geological complexity, CAM provides as accurate an image as shot profile migration, but much more economically. So CAM provides an attractive framework for wave-equation based MVA. Khoury et al., 2006, presented a 2D DSRbased MVA tool in which the wave equation propagator is a GSP implemented in the mid-point offset domain. Hua et al., 2007, proposed a modified CAM, implementing the ffd wide-angle term in the source-geophone domain, which provides much better images in complex areas. In this paper, we present a 3D implementation of DSO-based MVA based on the CAM of Hua et al, 2007; the adjoint state method is used to calculate the velocity gradient. The method is applied to 3-D synthetic and field data, validating the feasibility of the algorithm. Theory In this part, we briefly review the theory of FFD source geophone implementation of CAM, DSO principle, and adjoint state method. The FFD source-geophone implementation of CAM was proposed by Hua, et al 2007. The common-azimuth DSR dispersion relation can be written as (Biondi and Palacharla, 1996): equation (1) amounts to a 2-D inline prestack depth migration using equation (2), followed by a 2-D crossline poststack migration. The wide-angle term in the mid-point offset implementation of CAM uses the standard Padé approximation for the square roots in equation (2), but discards the relatively computationally expensive operator arising from the cross-term between Km x and Kh x .

Proceedings Papers

Publisher: Offshore Technology Conference

Paper presented at the Offshore Technology Conference, May 4–7, 1992

Paper Number: OTC-6826-MS

... candidates for MZO. Here, reflected incnwing throughput by a factor equal to the number of node energy off of a salt dome appears nearly ftat on

**common**- sets. At the end of the entire process, all output fdes are**offset**sections taken along a concentric circle. Hence,**3**-**D**properly merged into one single fde...
Abstract

Abstract For 3-D pre-stack imaging to be a viable process, computer power must be sufficient to efficiently work with data sizes on the order of one TeraByte (one triltion bytes). Massively parallel computers provide a platform whereby such data volumes can be migrated with reasonable run times. 3-D DMO, 3-D MZO (migration-to-zem offset) and 3-D pre-stack depth migration are computationally intensive algorithms that easily fit into the paradigm of parallel computation. In this paper, we discuss the implementation of these algorithms on a 128-node parallel computer. Run-time speedups for these algorithms, compared with conventional non-parallel computers, are consistently well over an order of magnitude. Introduction As an industry, we have been performing iterative 2-D prestack time and depth migrations for the past several years. To date, 3-D pre-stack imaging has not been common practice (if practiced at all). Computer run times have been prohibitively long to even try 3-D pre-stack imaging, except in limited circumstances. In that interpretation is usually requiti to estimate and refine velocity-field information, many iterations of migration processes are needed to converge on an accurate representation of the velocity field. This only exacerbates the long rim-time problem. Massively parallel computers offer a solution to the heavy demands of 3-D prestack imaging. These algorithms and, indeed, most seismic data-processing algorithms are easily parallelized. In fact, in many cases, algorithm coding is simplifkd because the programmer need not spend as much time coding around machine limitations. To facilitate the writing of seismic-data processing algorithms and simplify their use for processors, we have written a seismic-processing operation system for massively parallel MIMD (multipleinstruction, multiple-data) computer architecture. We are currently using the software in a production environment on a 128-node Intel i860 supercomputer with the following parameters: Peak computational 10 Gflops (at 32-bit power preeision) Distributed memory 2 GBytes Disk storage 96 GBytes On-line tape storage 1.5 TBytes Because the computational power, memory, disk storage, and on-line tape storage are all independently configured using parallel arehiteetum, they can each be expanded indefinitely; and the software contains no hardware limits. In the following sections, we describe the implementation and the results of two heavy number-crunching algorithms: 3-D MZO and 3-D prestack depth migration. Migration to Zero Offset In practice, seismic-reflection data are reeorded using source and receiver pairs that are separated by some distance. In processing, DMO is applied to move recorded data from the source-receiver midpoint to the surface location where a coincident (zero-offset) source-receiver pair would have recorded a reflection from the same subsurface point. For a constant-velocity model, 3-D DMO moves refkxtions along the line connecting the source to the receiver. l%usj N operations are applied to a given input trace where N is the number of desired stacked traces located on a line between the source and receiver.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2002 SEG Annual Meeting, October 6–11, 2002

Paper Number: SEG-2002-1316

..., Prestack

**depth****migration**with acoustic screen propagators, 66th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, 415-418. Jin, S., Mosher, C.C., and Wu, R.S., 2000,**3**-**D**prestack wave equation**common****offset**pseudo-screen**depth****migration**, 70th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded...
Abstract

Summary Generalized screen propagator (GSP) is a wave-equation based, wide-angle wavefield continuation operator and has been applied to both poststack and prestack depth migrations for imaging complex structures. Offset domain GSP migration provides a fast and accurate 3-D wavefield extrapolation. Downward continuation of the wavefields is performed with a phase shift in a background medium followed by a wide-angle correction that accommodates strong lateral velocity variations. Using common angle imaging (CAI) condition, prestack GSP migration produces high quality images at a number of angles for velocity updating and amplitude-vesus-angle (AVA) analysis. A real dataset from deep-water Gulf of Mexico (GOM) is migrated by this method and is compared with the split-step Fourier DSR migration.

Proceedings Papers

Publisher: Society of Underwater Technology

Paper presented at the Safety in Offshore Engineering: Proceedings of an international conference, April 25–26, 1990

Paper Number: SUT-AUTOE-v25-075

... horlzontal profiles ~t 1s of course necessary to acquire selsmlc data over a closely sampled area, such as 1s regularly accomplished for conventlonal

**3**-**D**selsmlc surveys For shallow objectives, however, long streamers and large fold of**common**mld-polnt (CMP) stack are unnecessary and much of the complexity...
Abstract

ABSTRACT Using results obtained from existing 3-D marine seismic surveys acquired with a compact recording geometry we show how true-amplitude migration processing can yield remarkably well-defined images of the shallow geology in plan view. Examples of such images are presented showing features of small physical dimensions, as well as a number of responses that are presumed to represent gas hazards. The pictorial quality of intensity-modulated time slice displays is particularly striking. In many cases small yet potentially important targets could remain unsampled by the customary grid of 2-D survey lines, or would be virtually uninterpretable without the benefit of 3-D migration. Even when 3-D methods have been applied, conventional seismic cross sections are inappropriate for displaying responses resulting from fractures or channels that have a small spatial footprint. Commonly, these will remain unnoticed or be dismissed as noise in a vertical seismic profile. The Short-Offset field technique that we propose for this work can be economically applied to hazard surveys. Results suggest that the temporal bandwidth commonly specified for shallow profiling can probably be relaxed when areal data recording methods are applied Routine application would reasonably be expected to reduce drilling costs whilst significantly improving safety. INTRODUCTION Seismic techniques as applied to hazard surveys are essentially the same as those used for deep exploration, differing primarily in scale. The seismic source, record length, and sample rates both spatial and temporal, are adjusted to suit the shallower depths of investigation and the broader signal bandwidth that is expected to apply Recording instrumentation, processing, and final display methods also follow those employed for conventional surveys, resulting in a grid of intersecting 2-dlmenslonal vertical profiles. An immediate question concerns the suitability of the conventional seismic cross section display for site survey applications. Of principle interest in these studies is the detection of amplitude anomalies and determination of them spatial extent A further aim is to establish the competence or otherwise of shallow formations, as may be indicated for instance by evidence of faults or fractures. We hope to demonstrate that these objectives are better realised using sequences of horizontal seismic profiles displayed in variable intensity mode. In order to generate horizontal profiles it is of course necessary to acquire seismic data over a closely sampled area, such as is regularly accomplished for conventional 3-D seismic surveys For shallow objectives, however, long streamers and large fold of common mid-point (CMP) stack are unnecessary and much of the complexity associated with 3-D marine seismic surveys is thus avoided. Indeed, the hazard survey appears to be an ideal application for the so-called Short-Offset 3-D method described by Newman (1984, 1985, 1988, 1989.) A key requirement of the Short-Offset method is to approximate normal-incidence reflection responses, as nearly as is practicable, by operating with the minimum source-receiver separation that is consistent with tow noise and recording dynamic range considerations Data that are recorded in this way are well conditioned for predictive deconvolution and for a modified Kirchhoff migration process that simultaneously compensates the amplitude decay that accompanies geometrical spreading.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2003 SEG Annual Meeting, October 26–31, 2003

Paper Number: SEG-2003-1755

... using EOM prestack time

**migrated**images from Line 1 of the LITHOPROBE SNORCLE transect. 0 (**3**) (**3**) (**3**) ( ) / ( ) ( , , ) ( ) ( , , ) Gs gG G G s g S g s**D****D**Dtraces t r r c R W f t p t t ? ? ? ? ? ? ? ? ? ?? ?? ? ? ? ?x x x x x x (4) The optimal**common**-**offset**weight is given by (**3**) 0 0 ( ) 2cos...
Abstract

Summary In a ‘Kirchhoff’ (i.e. weighted diffraction stack) prestack migration, the summation over a complete diffraction surface can be thought of as an average of reflectivity estimates from migrated common-shot, common-receiver or common-offset gathers. The optimal weight for averaged reflectivity should be based on Bleistein et al’s (2001) ß common-offset weight. In comparison, the ß common-shot and common-receiver weights, although correct for individual gathers, produce average reflectivity estimates with a dip- and depth-dependent bias. Bleistein et al’s (2001) ß 1 common-offset weight is more suitable as a basis for practical weights because it downweights by the cosine of the ray half-opening or obliquity angle at the reflector and hence accounts for the corresponding reduced spatial resolution as obliquity angle increases.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2002 SEG Annual Meeting, October 6–11, 2002

Paper Number: SEG-2002-1220

.... Unfortunately, there is no equivalent simple remedy in

**3**-**D**, other than applying the**common**-**offset**weight (equation 4) to the shot gathers. Fortunately, the bias is less pronounced in**3**-**D**. SEG Int'l Exposition and 72nd Annual Meeting * Salt Lake City, Utah * October 6-11, 2002 Time**Migration**Weights Conclusions...
Abstract

Summary In a "Kirchhoff" (i.e. weighted diffraction stack) prestack migration, the summation over a complete diffraction surface can be thought of as an average of reflectivity estimates from migrated common-shot, common-receiver or common-offset gathers. The optimal weight for averaged reflectivity should be based on Bleistein et al''s (2001) ? common-offset weight. In comparison, the ? common-shot and common-receiver weights, although correct for individual gathers, produce average reflectivity estimates with a dip- and depth-dependent bias. Bleistein et al''s (2001) ?1 common-offset weight is more suitable as a basis for practical weights because it downweights by the cosine of the ray half-opening or obliquity angle at the reflector and hence accounts for the corresponding reducedspatial resolution as obliquity angle increases.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2002 SEG Annual Meeting, October 6–11, 2002

Paper Number: SEG-2002-1152

... to the midpoint ray parameter ( p ? ) domain. The

**common****offset**data are**3**-**D**Fourier transformed to frequency and wavenumber. For each**depth**slice in the output image, the appropriate phase shift and**migration**weight can be applied to each frequency-wavenumber component of the data using the relationship given...
Abstract

Summary 3-D prestack migration of constant-offset data can be formulated in the frequency-wavenumber domain as a stationary phase approximation to equivalent Kirchhoff expressions. This formulation constitutes a proof of Dubrulle''s (1983) heuristic algorithm. Numerical implementations are 3-D extensions of his algorithms and lead to very efficient migration under the assumption of lateral invariance in velocity and acquisition geometry. Introduction Dubrulle (1983) presented a method for migrating 2-D common-offset data in the frequency-wavenumber domain. His algorithm for finite offset data is based on a heuristic extension of an algorithm devised for zero offset data. The phase shifts required to migrate the data are computed by the numerical solution of a pair of algebraic equations relating the traveltime and midpoint ray parameter of a diffraction event to the offset and migration displacement.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2006 SEG Annual Meeting, October 1–6, 2006

Paper Number: SEG-2006-2604

... recorded by streamer. These problems usually hamper the practical applications of full

**3**-**D**DSR-based prestack**migration**.**Common**-azimuth prestack tau**migration**The data after Fourier transform along the cross-line**offset**axis becomes = i yh hk yhh hkuedhkku x yyh yx mm . (6) Inserting equation (6...
Abstract

ABSTRACT Prestack migration methods based on the double-square-root (DSR) equation are modified to operate in the two-way vertical traveltime (tau) domain in this paper. Unlike the traditional time imaging algorithms in which at most mild lateral variations of velocity are treated, the DSR equation tau migration approach includes reasonable treatment for media with strong lateral inhomogeneity. To address the problems that the full 3-D DSR equation prestack tau migration could meet in practical applications, we present a method for downward continuing common-azimuth data in the theoretical frame of cross-line common-offset migration. Migration of the Marmousi model proves that it works well in strong contrast media. The real data example illustrates the validity of common-azimuth prestack tau migration in production applications.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 1995 SEG Annual Meeting, October 8–13, 1995

Paper Number: SEG-1995-1197

... continuation because of their flexibility in handling

**3**-**D**data geometries. Kirchhoff methods can be employed to efficiently**migrate**data sets with uneven spatial sampling and data sets that are subsets of the complete prestack data, such as**common**-**offset**cubes and**common**-azimuth cubes. However, in principle...
Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2017 SEG International Exposition and Annual Meeting, September 24–29, 2017

Paper Number: SEG-2017-17777036

... added to the conventional framework of the land data processing. Presentation Date: Tuesday, September 26, 2017 Start Time:

**3**:30 PM Location: Exhibit Hall C/**D**Presentation Type: POSTER datum imaging**common**-**offset**panel input data**migration**modification**migrated**image upstream oil...
Abstract

ABSTRACT The beam PSDM (pre-stack depth migration) is a quite powerful method in terms of structural imaging and velocity model building, but it has difficulty on the treatment of topographic changes since the local slant stacking in this process implicitly requires flat observation surface. We firstly investigate the effect on the image of beam PSDM via the numerical simulation where the observation surface is strongly rugged, and confirm significant error in the image. We then propose a convenient solution for overcoming this problem in which the floating datum changes with the migration offsets. For the short offset data, the floating datum is not changed from the original floating datum. On the other hand, for far offset data, the floating datum is flattened since the incident angles of reflections from deep subsurface is close to zero. For the intermediate offset data, the smoothing is applied to the floating datum of the input data where the length of smoothing is increased with the migration offset. As the result of this modification of floating datum, the image by the common-offset beam PSDM is dramatically improved. This modification is quite simple and can be readily added to the conventional framework of the land data processing. Presentation Date: Tuesday, September 26, 2017 Start Time: 3:30 PM Location: Exhibit Hall C/D Presentation Type: POSTER

Proceedings Papers

Publisher: Offshore Technology Conference

Paper presented at the Offshore Technology Conference, May 3–6, 1999

Paper Number: OTC-10984-MS

... prestack

**migration**. Using a**3**-**D**PSPI**depth****migration**of**common**-receiver gathers, we obtained an image volume that compares favorably to that obtained from conventional CMP stack and**3**-**D**poststack time**migration**. Since irregularities in the source grid can affect amplitudes in the output image, we devised...
Abstract

Abstract A recent 3-D, 4-C seismic survey at Teal South in the Gulf of Mexico poses a number of challenges for AVO analysis, some which are not normally encountered in conventional marine streamer surveys. Among these, some are associated with the use of a sparse grid of ocean-bottom receivers. Before embarking on AVO analysis, therefore, we believe that it is necessary to demonstrate whether the survey sufficiently samples the AVO response of the subsurface and also to determine how best to process the survey so as to preserve that response. The former question is related to how evenly the subsurface is illuminated and also to how evenly the upcoming reflected wavefield is sampled at the seafloor. Ideally, both sources and receivers would be finely spaced on regular grids. Since this is certainly not the case for our receiver grid, we have less flexibility in dealing with azimuthal variations. That is, the distribution of azimuths and offsets in CMP bins will not only be limited, but will exhibit significant changes spatially. Regarding the processing question, tests support applying a conventional AVO-preprocessing sequence. Further, they indicate that AVO analysis of this survey might better be conducted after prestack migration. Using a 3-D PSPI depth migration of common-receiver gathers, we obtained an image volume that compares favorably to that obtained from conventional CMP stack and 3-D poststack time migration. Since irregularities in the source grid can affect amplitudes in the output image, we devised a regridding procedure as an alternative to binning. Our next step is to evaluate whether the proposed processing strategy outperforms conventional processing in conditioning prestack P-P and P-S reflection data for AVO analysis. Introduction Teal South is located in the Gulf of Mexico, 160 miles southwest of New Orleans, where the water depth is about 270 ft. Oil is produced from unconsolidated Tertiary sands at depths in the 4000-8000-ft range. Small reservoir volumes and high flow rates result in rapid depletion, hence possible rapid changes in seismic response over time. Texaco's 1997 ocean-bottom survey at Teal South (Ebrom, et al., 1998) was, to our knowledge, the first 3-D, 4-Ccommercial seismic survey recorded offshore in the Gulf of Mexico. It was designed as a vehicle for learning (1) how to acquire and process useful multicomponent data in a shallow, soft-seafloor area and (2) how to conduct cost-effective timelapse reservoir monitoring in such an environment. The 1997 survey will serve as a baseline for the time-lapse study; the first repeat survey is expected to be complete in the spring of 1999. (The repeat survey is funded by a consortium of companies, facilitated by the Energy Research Clearing House.) Although the 1997 survey was recorded after the start of production, poststack amplitude comparisons to an earlier pre-production streamer survey demonstrated large changes in the seismic response of some reservoirs that appear to be related to production-induced water intrusion. This paper describes progress in developing tools and a methodology for conducting time-lapse AVO analysis of the 4-C data set at Teal South. These are needed as a consequence of the significant differences between this type of survey and others (marine streamer surveys and land multicomponent surveys). Initial questions included: In view of the sparse receiver grid, will it be possible to exploit static AVO information in a single 3-D survey? If so, will time-lapse comparisons of repeated 3-D surveys be useful? Will we have to modify or abandon our current processing approach in order to exploit AVO effects? Can we exploit converted-wave (P-S) AVO using the OBC horizontal com

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2005 SEG Annual Meeting, November 6–11, 2005

Paper Number: SEG-2005-2021

... model building. Han and Wu (2005) have successfully applied this algorithm to 2-

**D**isotropic**migration**model building. Method The Gaussian beam approximation of a plane wave can be obtained in both the**common**-**offset**domain and**common**- shot domain. In the**common**-**offset**domain (Hill, 2001), the plane wave...
Abstract

ABSTRACT Prestack depth migration is a popular tool for velocity updating. A good migration method usually improves the performance of a velocity update. Gaussian beam migration is a desirable alternative to Kirchhoff migration due to its ability to image complicated geologic structures without loss of either accuracy or efficiency. Gaussian beam migration is often used in depth imaging, and is a potential tool for model building. In this paper we present a prestack plane-wave Gaussian beam depth migration algorithm which provides common image gathers for velocity analysis in the plane-wave domain. The algorithm may be performed with either common-offset gathers or common-shot gathers. Applying the imaging condition in the time-domain is more efficient than in the frequency domain. Common-offset migration is more efficient and accurate than common-shot migration with a time-domain imaging condition. Computational efficiency is an important factor in depth-migration based model building since velocity updating requires iterative migration processing. To speed up the algorithm with common-shot data, we ignore the amplitude of the shot field to efficiently apply the imaging condition in the time domain. With synthetic data sets, we test the proposed algorithm and illustrate its potential use for velocity updating with complex media. Our results are consistent with the expectation that in the plane-wave domain, the events in a common-image gather are sensitive to model velocity and interface inclination, while the imaged event contours are flat when the true velocity is used.

Advertisement