Subsalt imaging via target‐oriented 3-D prestack depth migration

Ratcliff, Davis W.; Jacewitz, Chester A.; Gray, Samuel H.

doi:10.1190/1.1437009

Cited by 15 publications

(4 citation statements)

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“…In practice sub-salt imaging in the Gulf of Mexico is relatively simple, since the velocity of the salt (constant) and of the clastic sediments (a linear function, V = V o + k x Z, where Z is depth) are well known. The model building task involves the definition of the complex shape of the allochtonous salt body (Ratcliff et al, 1994) within a relatively undeformed post-rift Neogene sedimentary pile (Figure 5). New approaches in the Gulf of Mexico include the use of Shear Waves, converted at the salt interface (PSS Waves), to image the sub-salt geometry from three-component geophones lying on the sea floor (Kendall et al, 1998).…”

Section: Time Migrationmentioning

confidence: 99%

Depth Imaging Sub-salt Structures: A Case Study in the Midyan Peninsula (Red Sea)

Mougenot¹,

Al-Shakhis²

1999

GeoArabia

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In the Midyan Peninsula (onshore northern Red Sea, Saudi Arabia), the current prospective oil and gas exploration targets are sub-salt structures. In this region, conventional time-migrated seismic sections are distorted due to the presence of salt diapirs, faults, and related lateral velocity variations. As demonstrated in other sub-salt prospects (North Sea, Gulf of Suez, and Gulf of Mexico), pre-stack depth migration can remove these distortions and accurately focus the structural image. Depth migration, however, requires a model which includes both lateral and vertical velocity variations to compensate for ray bending. Building such a velocity model is an iterative process which involves integration of various time/depth processing and interpretation skills. A 2-D seismic line, crossing various extensional structures in the dip direction, is used to illustrate these depth-imaging techniques. At the location of the sub-salt prospect, the depth image is improved and the lateral position of the main fault is shifted by 345 meters. The resulting structural model has refined the target definition and well position. This imaging approach is compared with the different steps of the seismic processing/interpretation flow.

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Section: Time Migrationmentioning

confidence: 99%

Depth Imaging Sub-salt Structures: A Case Study in the Midyan Peninsula (Red Sea)

Mougenot¹,

Al-Shakhis²

1999

GeoArabia

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“…Also, since these wave algorithms involve Fourier transforms of the input data and/or the finite‐difference solution of the wave equation, they can handle only regularly spaced input data. On the other hand, the Kirchhoff integral method can easily accommodate an irregular data geometry, and can image subsurface structures of any dip, including turned waves (Ratcliff, Gray and Whitmore 1992; Ratcliff, Jacewitz and Gray 1994). Although 3D wave‐equation‐based migration algorithms have existed for many years, 3D Kirchhoff depth migration is still the most popular, flexible, and cost‐effective method for imaging of subsurface structures.…”

Section: Introductionmentioning

confidence: 99%

Parsimonious 3D post‐stack Kirchhoff depth migration

Bao

McMechan

2005

Geophysical Prospecting

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A B S T R A C TParsimonious post-stack migration is extended to three dimensions. By tracing single rays back along each incident wave direction (as determined by a local slant stack at the receivers), the ray tracing can be embedded in the migration. This approach significantly reduces the computer time and disk space needed because it is not necessary to build and save image time maps; 3D migration can be performed on a workstation or personal computer rather than using a supercomputer or cluster.The location of a reflector in the output image is defined by tracing a zero-offset ray to the one-way traveltime (the image condition); the orientation of the reflector is defined as a surface perpendicular to the raypath. The migration impulse response operator is confined to the first Fresnel zone around the estimated reflection point, which is much smaller than the large isochronic surface in traditional Kirchhoff depth migration. Additional efficiency is obtained by applying an amplitude threshold to reduce the amount of data to be migrated. Tests on synthetic data show that the proposed implementation of parsimonious 3D post-stack Kirchhoff depth migration is at least two orders of magnitude faster than traditional Kirchhoff migration, at the expense of slightly degraded migration image coherence. The proposed migration is expected to be a useful complement to conventional time migrations for fast initial imaging of subsurface structures and for real-time imaging of near-offset sections during data acquisition for quality control.

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“…Many standard methods, which work well in weak-contrast media, often fail in strong-contrast media. Ray-based Kirchhoff migration is the most commonly used method for 3-D prestack depth migration due to its high efficiency and flexibility in handling 3-D prestack data geometry (Ratcliff et al, 1994;Audebert et al, 1997). Migration accuracy of this approach, however, relies on the high-frequency asymptotic ray approximation.…”

Section: Introductionmentioning

confidence: 99%

Offset‐domain pseudoscreen prestack depth migration

Jin

Mosher

2002

GEOPHYSICS

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The double square root 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. Offset‐domain pseudoscreen prestack depth migration downward continues the source and receiver wavefields simultaneously in midpoint‐offset coordinates. Wavefield extrapolation is performed with a wavenumber‐domain phase shift in a constant background medium followed by a phase correction in the space domain that accommodates smooth lateral velocity variations. An extra wide‐angle compensation term is also applied to enhance steep dips in the presence of strong velocity contrasts. The algorithm is implemented using fast Fourier transforms and tri‐diagonal matrix solvers, resulting in a computationally efficient implementation. Combined with the common‐azimuth approximation, 3‐D pseudoscreen migration provides a fast wavefield extrapolation for 3‐D marine streamer data. Migration of the 2‐D Marmousi model shows that offset domain pseudoscreen migration provides a significant improvement over first‐arrival Kirchhoff migration for steeply dipping events in strong contrast heterogeneous media. For the 3‐D SEG‐EAGE C3 Narrow Angle synthetic dataset, image quality from offset‐domain pseudoscreen migration is comparable to shot‐record finite‐difference migration results, but with computation times more than 100 times faster for full aperture imaging of the same data volume.

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Subsalt imaging via target‐oriented 3-D prestack depth migration

Cited by 15 publications

References 0 publications

Depth Imaging Sub-salt Structures: A Case Study in the Midyan Peninsula (Red Sea)

Depth Imaging Sub-salt Structures: A Case Study in the Midyan Peninsula (Red Sea)

Parsimonious 3D post‐stack Kirchhoff depth migration

Offset‐domain pseudoscreen prestack depth migration

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