Multicomponent prestack depth migration using the elastic screen method

Geophysics ◽  
2005 ◽  
Vol 70 (1) ◽  
pp. S30-S37 ◽  
Author(s):  
Xiao-Bi Xie ◽  
Ru-Shan Wu
Keyword(s):  
Synthetic Data ◽  
Data Sets ◽  
Converted Wave ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
S Waves ◽  
Angle Correction ◽  
Scattering Effects ◽  
Wave Imaging ◽  
Migration Method

A 3D multicomponent prestack depth-migration method is presented. An elastic-screen propagator based on one-way wave propagation with a wide-angle correction is used to extrapolate both source and receiver wavefields. The elastic-screen propagator neglects backscattered waves but can handle forward multiple-scattering effects, such as focusing/defocusing, diffraction, interference, and conversions between P- and S-waves. Vector-imaging conditions are used to generate a P-P image and a P-S converted-wave image. The application of the multicomponent elastic propagator and vector-imaging condition preserves more information carried by the elastic waves. It also solves the polarization problem of converted-wave imaging. Partial images from different sources with correct polarizations can be stacked to generate a final image. Numerical examples using 2D synthetic data sets are presented to show the feasibility of this method.

Identifying, removing, and imaging P‐S conversions at salt‐sediment interfaces

Geophysics ◽  
2003 ◽  
Vol 68 (3) ◽  
pp. 1052-1059 ◽  
Author(s):  
Richard S. Lu ◽  
Dennis E. Willen ◽  
Ian A. Watson
Keyword(s):  
P Wave ◽  
Time Interval ◽  
S Wave ◽  
Converted Wave ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Time Migration ◽  
Wave Imaging ◽  
Wave Image ◽  
Converted Waves

The large velocity contrast between salt and the surrounding sediments generates strong conversions between P‐ and S‐wave energy. The resulting converted events can be noise on P‐wave migrated images and should be identified and removed to facilitate interpretation. On the other hand, they can also be used to image a salt body and its adjacent sediments when the P‐wave image is inadequate. The converted waves with smaller reflection and transmission angles and much larger critical angles generate substantially different illumination than does the P‐wave. In areas where time migration is valid, the ratio between salt thickness in time and the time interval between the P‐wave and the converted‐wave salt base on a time‐migrated image is about 2.6 or 1.3, depending upon whether the seismic wave propagates along one or both of the downgoing and upcoming raypaths in salt as the S‐wave, respectively. These ratios can be used together with forward seismic modeling and 2D prestack depth migration to identify the converted‐wave base‐of‐salt (BOS) events in time and depth and to correctly interpret the subsalt sediments. It is possible to mute converted‐wave events from prestack traces according to their computed arrival times. Prestack depth migration of the muted data extends the updip continuation of subsalt sedimentary beds, and improves the salt–sediment terminations in the P‐wave image. Prestack and poststack depth‐migrated examples illustrate that the P‐wave and the three modes of converted waves preferentially image different parts of the base of salt. In some areas, the P‐wave BOS can be very weak, obscured by noise, or completely absent. Converted‐wave imaging complements P‐wave imaging in delineating the BOS for velocity model building.

Reverse time migration

Geophysics ◽  
1983 ◽  
Vol 48 (11) ◽  
pp. 1514-1524 ◽  
Author(s):  
Edip Baysal ◽  
Dan D. Kosloff ◽  
John W. C. Sherwood
Keyword(s):  
Wave Amplitude ◽  
Synthetic Data ◽  
Data Sets ◽  
Field Observations ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Migration Method ◽  
Zero Offset ◽  
Time Extrapolation

Migration of stacked or zero‐offset sections is based on deriving the wave amplitude in space from wave field observations at the surface. Conventionally this calculation has been carried out through a depth extrapolation. We examine the alternative of carrying out the migration through a reverse time extrapolation. This approach may offer improvements over existing migration methods, especially in cases of steeply dipping structures with strong velocity contrasts. This migration method is tested using appropriate synthetic data sets.

Converted-Wave Prestack Depth Migration of North Sea Salt Domes

1999 ◽  
Author(s):  
X. Zhu ◽  
J. Langhammer ◽  
D. King ◽  
E. Madtson ◽  
H. K. Helgesen ◽  
...  
Keyword(s):  
North Sea ◽  
Sea Salt ◽  
Converted Wave ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Salt Domes

An improved plane wave prestack depth migration method

2001 ◽  
Author(s):  
Peiyong Sun ◽  
Shulun Zhang ◽  
Jingxia Zhao
Keyword(s):  
Plane Wave ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Migration Method

MULTI-COMPONENT SEISMIC—THE TOOL FOR ALL REASONS

2002 ◽  
Vol 42 (1) ◽  
pp. 587
Author(s):  
F.L. Engelmark
Keyword(s):  
Fractured Reservoirs ◽  
Time Lapse ◽  
P Wave ◽  
Converted Wave ◽  
S Waves ◽  
The North ◽  
Impedance Contrast ◽  
Seismic Sensors ◽  
Wave Imaging ◽  
Wave Modes

Marine multi-component seismic, known as 4C, is an emerging seismic technology providing improved and sometimes unique solutions to many common problems. In the marine environment the seismic sensors have to be placed on the sea-floor to capture converted or shear wave modes that cannot propagate through liquid media. Although this means increased acquisition cost, the improved information content makes it money well spent to better image and characterise reservoirs.The 4C solutions fall into two major groups of five. First there are the imaging solutions:Improved standard P-wave imaging. Improved converted wave (P-S) resolution in the shallow sediments. Converted wave imaging through gas clouds. Converted wave imaging of low impedance contrast reservoirs. Improved sub-salt and sub-basalt imaging with converted waves. The second group consists of the five characterisation solutions:Improved fracture characterisation by means of P-S waves. Qualitative 4D or time-lapse characterisation of fractured reservoirs with low intrinsic permeability. Improved lithology and fluid characterisation by combining the information in the two wave modes. Improved quantitative time-lapse evaluation of pressure and saturation changes. Improved characterisation of drilling hazards by combined evaluation of the two wave modes. So far the most popular 4C solutions are imaging through gas and improved P-wave imaging of Jurassic reservoirs in the North Sea, for example the Statfjord, Brent and Beryl fields. However, as the technology is developing and maturing, the characterisation solutions will probably be the most common applications of 4C in the near future.

scholarly journals Imaging near-surface heterogeneities by natural migration of backscattered surface waves: Field data test

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. S197-S205 ◽  
Author(s):  
Zhaolun Liu ◽  
Abdullah AlTheyab ◽  
Sherif M. Hanafy ◽  
Gerard Schuster
Keyword(s):  
Surface Waves ◽  
Field Data ◽  
Synthetic Data ◽  
Data Sets ◽  
Data Set ◽  
Near Surface ◽  
3D Data ◽  
Strong Surface ◽  
Migration Method ◽  
Recorded Data

We have developed a methodology for detecting the presence of near-surface heterogeneities by naturally migrating backscattered surface waves in controlled-source data. The near-surface heterogeneities must be located within a depth of approximately one-third the dominant wavelength [Formula: see text] of the strong surface-wave arrivals. This natural migration method does not require knowledge of the near-surface phase-velocity distribution because it uses the recorded data to approximate the Green’s functions for migration. Prior to migration, the backscattered data are separated from the original records, and the band-passed filtered data are migrated to give an estimate of the migration image at a depth of approximately one-third [Formula: see text]. Each band-passed data set gives a migration image at a different depth. Results with synthetic data and field data recorded over known faults validate the effectiveness of this method. Migrating the surface waves in recorded 2D and 3D data sets accurately reveals the locations of known faults. The limitation of this method is that it requires a dense array of receivers with a geophone interval less than approximately one-half [Formula: see text].

True-amplitude prestack depth migration

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. S155-S166 ◽  
Author(s):  
Feng Deng ◽  
George A. McMechan
Keyword(s):  
Velocity Ratio ◽  
Synthetic Data ◽  
Transmission Losses ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Prestack Migration ◽  
Time Migration ◽  
Geometric Spreading

Most current true-amplitude migrations correct only for geometric spreading. We present a new prestack depth-migration method that uses the framework of reverse-time migration to compensate for geometric spreading, intrinsic [Formula: see text] losses, and transmission losses. Geometric spreading is implicitly compensated by full two-way wave propagation. Intrinsic [Formula: see text] losses are handled by including a [Formula: see text]-dependent term in the wave equation. Transmission losses are compensated based on an estimation of angle-dependent reflectivity using a two-pass recursive reverse-time prestack migration. The image condition used is the ratio of receiver/source wavefield amplitudes. Two-dimensional tests using synthetic data for a dipping-layer model and a salt model show that loss-compensating prestack depth migration can produce reliable angle-dependent reflection coefficients at the target. The reflection coefficient curves are fitted to give least-squares estimates of the velocity ratio at the target. The main new result is a procedure for transmission compensation when extrapolating the receiver wavefield. There are still a number of limitations (e.g., we use only scalar extrapolation for illustration), but these limitations are now better defined.

Anisotropic parsimonious prestack depth migration

Geophysics ◽  
2013 ◽  
Vol 78 (1) ◽  
pp. S25-S36 ◽  
Author(s):  
Ernesto V. Oropeza ◽  
George A. McMechan
Keyword(s):  
Model Building ◽  
Computing Time ◽  
Synthetic Data ◽  
Transversely Isotropic ◽  
Velocity Model ◽  
P Wave ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Tti Media ◽  
Map Migration

An efficient Kirchhoff-style prestack depth migration, called “parsimonious” migration, was developed a decade ago for isotropic 2D and 3D media by using measured slownesses to reduce the amount of ray tracing by orders of magnitude. It is conceptually similar to “map” migration, but its implementation has some differences. We have extended this approach to 2D tilted transversely isotropic (TTI) media and illustrated it with synthetic P-wave data. Although the framework of isotropic parsimonious may be retained, the extension to TTI media requires redevelopment of each of the numerical components, calculation of the phase and group velocity for TTI media, development of a new two-point anisotropic ray tracer, and substitution of an initial-angle isotropic shooting ray-trace algorithm for an anisotropic one. The model parameterization consists of Thomsen’s parameters ([Formula: see text], [Formula: see text], [Formula: see text]) and the tilt angle of the symmetry axis of the TI medium. The parsimonious anisotropic migration algorithm is successfully applied to synthetic data from a TTI version of the Marmousi2 model. The quality of the image improves by weighting the impulse response by the calculation of the anisotropic Fresnel radius. The accuracy and speed of this migration makes it useful for anisotropic velocity model building. The elapsed computing time for 101 shots for the Marmousi2 TTI model is 35 s per shot (each with 501 traces) in 32 Opteron cores.

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