Explicit 3D depth migration with a constrained operator

Geophysics ◽  
2006 ◽  
Vol 71 (2) ◽  
pp. S63-S71 ◽  
Author(s):  
Rune Mittet
Keyword(s):  
Wave Equation ◽  
Outer Part ◽  
Floating Point ◽  
Acoustic Wave Equation ◽  
Impulse Responses ◽  
Lateral Velocity ◽  
Alternative Scheme ◽  
Depth Migration ◽  
Complex Multiplications ◽  
Extrapolation Operator

Numerical anisotropy is one of the main problems in the design of explicit 3D depth-extrapolation operators. This paper introduces a new method based on constraining the number of independent coefficients for the full 3D extrapolation operator. The extrapolation operator is divided into two regions. The coefficients for the inner part of the extrapolation operator are treated the same as the full 3D extrapolation operator. The coefficients for the outer part of the extrapolation operator are constrained to be constant as a function of azimuth for a given radius. This strategy reduces the number of floating-point operations because, for each extrapolation step, the number of complex multiplications are reduced and replaced by complex additions. The numerical workload of this alternative scheme is comparable to the Hale-McClellan scheme. Impulse responses are compared with finite-difference solutions for the two-way acoustic-wave equation. It is demonstrated that the numerical anisotropy for the proposed scheme is negligible and that the constrained-depth-extrapolation operator can be used in media with large lateral velocity contrasts. The design of constrained-depth-extrapolation operators with different maximum propagation angles in inline and crossline directions is explained and exemplified. These types of operators can be used to suppress the propagation of aliased energy in the crossline direction during depth extrapolation while reducing numerical cost.

Hybrid Fourier finite-difference 3D depth migration for anisotropic media

Geophysics ◽  
2008 ◽  
Vol 73 (2) ◽  
pp. S27-S34 ◽  
Author(s):  
Tong W. Fei ◽  
Christopher L. Liner
Keyword(s):  
Wave Equation ◽  
Finite Difference ◽  
Acoustic Wave ◽  
Seismic Data ◽  
Transversely Isotropic ◽  
Acoustic Wave Equation ◽  
Near Surface ◽  
Depth Migration ◽  
Surface Distortions ◽  
Vti Media

When a subsurface is anisotropic, migration based on the assumption of isotropy will not produce accurate migration images. We develop a hybrid wave-equation migration algorithm for vertical transversely isotropic (VTI) media based on a one-way acoustic wave equation, using a combination of Fourier finite-difference (FFD) and finite-difference (FD) approaches. The hybrid method can suppress an additional solution that exists in the VTI acoustic wave equation, and it offers speed and other advantages over conventional FFD or FD methods alone. The algorithm is tested on a synthetic model involving log data from onshore eastern Saudi Arabia, including estimates of both intrinsic and layer-induced VTI parameters. Results indicate that VTI imaging in this region offers some improvement over isotropic imaging, primarily with respect to subtle structure and stratigraphy and to image continuity. These benefits probably will be overshadowed by perennial land seismic data issues such as near-surface distortions and multiples.

scholarly journals Wave-equation time migration

Geophysics ◽  
2020 ◽  
pp. 1-58
Author(s):  
Sergey Fomel ◽  
Harpreet Kaur
Keyword(s):  
Wave Equation ◽  
Time Domain ◽  
Field Data ◽  
Model Building ◽  
Lateral Velocity ◽  
Depth Migration ◽  
Time Migration ◽  
Expensive Model ◽  
Approximate Equations ◽  
Ray Coordinates

Time migration, as opposed to depth migration, suffers from two well-known shortcomings: (1)approximate equations are used for computing Green’s functions inside the imaging operator; (2) in case of lateral velocity variations, the transformation between the image ray coordinates andthe Cartesian coordinates is undefined in places where the image rays cross. We show that thefirst limitation can be removed entirely by formulating time migration through wave propagationin image-ray coordinates. The proposed approach constructs a time-migrated image without relyingon any kind of traveltime approximation by formulating an appropriate geometrically accurateacoustic wave equation in the time-migration domain. The advantage of this approach is that thepropagation velocity in image-ray coordinates does not require expensive model building and canbe approximated by quantities that are estimated in conventional time-domain processing. Synthetic and field data examples demonstrate the effectiveness of the proposed approach and show that theproposed imaging workflow leads to a significant uplift in terms of image quality and can bridge thegap between time and depth migrations. The image obtained by the proposed algorithm is correctlyfocused and mapped to depth coordinates it is comparable to the image obtained by depth migration.

Migration with the full acoustic wave equation

Geophysics ◽  
1983 ◽  
Vol 48 (6) ◽  
pp. 677-687 ◽  
Author(s):  
Dan D. Kosloff ◽  
Edip Baysal
Keyword(s):  
Wave Equation ◽  
Finite Difference ◽  
Acoustic Wave ◽  
Physical Model ◽  
Wave Equations ◽  
Synthetic Data ◽  
Acoustic Wave Equation ◽  
Model Data ◽  
Lateral Velocity ◽  
Alternative Approach

Conventional finite‐difference migration has relied on one‐way wave equations which allow energy to propagate only downward. Although generally reliable, such equations may not give accurate migration when the structures have strong lateral velocity variations or steep dips. The present study examined an alternative approach based on the full acoustic wave equation. The migration algorithm which developed from this equation was tested against synthetic data and against physical model data. The results indicated that such a scheme gives accurate migration for complicated structures.

Two-way wave equation-based depth migration using one-way propagators on a bilayer sensor seismic acquisition system

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. S271-S278
Author(s):  
Jiachun You ◽  
Ru-Shan Wu ◽  
Xuewei Liu ◽  
Pan Zhang ◽  
Wengong Han ◽  
...  
Keyword(s):  
Wave Equation ◽  
Acoustic Wave ◽  
Seismic Data ◽  
Second Order ◽  
Acquisition System ◽  
Initial Condition ◽  
Acoustic Wave Equation ◽  
Data Set ◽  
Depth Migration ◽  
Migration Method

Conventional migration uses the seismic data set recorded at a given depth as one initial condition from which to implement wavefield extrapolation in the depth domain. In using only one initial condition to solve the second-order acoustic wave equation, some approximations are used, resulting in the limitation of imaging angles and inaccurate imaging amplitudes. We use an over/under bilayer sensor seismic data acquisition system that can provide the two initial conditions required to make the second-order acoustic wave equation solvable in the depth domain, and we develop a two-way wave equation depth migration algorithm by adopting concepts from one-way propagators, called bilayer sensor migration. In this new migration method, two-way wave depth extrapolation can be achieved with two one-way propagators by combining the wavefields at two different depths. It makes it possible to integrate the advantages of one-way migration methods into the bilayer sensor system. More detailed bilayer sensor migration methods are proposed to demonstrate the feasibility. In the impulse response tests, the propagating angle of the bilayer sensor migration method can reach up to 90°, which is superior to those of the corresponding one-way propagators. To test the performance, several migration methods are used to image the salt model, including the one-way generalized screen propagator, reverse time migration (RTM), and our bilayer sensor migration methods. Bilayer sensor migration methods are capable of imaging steeply dipping structures, unlike one-way propagators; meanwhile, bilayer sensor migration methods can greatly reduce the numbers of artifacts generated by salt multiples in RTM.

Tomographic velocity analysis and wave-equation depth migration in an overthrust terrain: A case study from the Tuha Basin, China

2018 ◽  
Vol 6 (1) ◽  
pp. T1-T13
Author(s):  
Bin Lyu ◽  
Qin Su ◽  
Kurt J. Marfurt
Keyword(s):  
Wave Equation ◽  
Data Quality ◽  
Model Building ◽  
Velocity Model ◽  
Lateral Velocity ◽  
Near Surface ◽  
Depth Migration ◽  
Time Migration ◽  
Head Waves ◽  
Velocity Variations

Although the structures associated with overthrust terrains form important targets in many basins, accurately imaging remains challenging. Steep dips and strong lateral velocity variations associated with these complex structures require prestack depth migration instead of simpler time migration. The associated rough topography, coupled with older, more indurated, and thus high-velocity rocks near or outcropping at the surface often lead to seismic data that suffer from severe statics problems, strong head waves, and backscattered energy from the shallow section, giving rise to a low signal-to-noise ratio that increases the difficulties in building an accurate velocity model for subsequent depth migration. We applied a multidomain cascaded noise attenuation workflow to suppress much of the linear noise. Strong lateral velocity variations occur not only at depth but near the surface as well, distorting the reflections and degrading all deeper images. Conventional elevation corrections followed by refraction statics methods fail in these areas due to poor data quality and the absence of a continuous refracting surface. Although a seismically derived tomographic solution provides an improved image, constraining the solution to the near-surface depth-domain interval velocities measured along the surface outcrop data provides further improvement. Although a one-way wave-equation migration algorithm accounts for the strong lateral velocity variations and complicated structures at depth, modifying the algorithm to account for lateral variation in illumination caused by the irregular topography significantly improves the image, preserving the subsurface amplitude variations. We believe that our step-by-step workflow of addressing the data quality, velocity model building, and seismic imaging developed for the Tuha Basin of China can be applied to other overthrust plays in other parts of the world.

Illumination‐based normalization for wave‐equation depth migration

Geophysics ◽  
2003 ◽  
Vol 68 (4) ◽  
pp. 1371-1379 ◽  
Author(s):  
James E. Rickett
Keyword(s):  
Wave Equation ◽  
Reference Model ◽  
Synthetic Data ◽  
Data Migration ◽  
Synthetic Image ◽  
Lateral Velocity ◽  
Depth Migration ◽  
True Model ◽  
The Cost ◽  
Normalization Scheme

Illumination problems caused by finite‐recording aperture and lateral velocity lensing can bias amplitudes in migration results. In this paper, I develop a normalization scheme appropriate for wave‐equation migration algorithms that compensates for irregular illumination. I generate synthetic seismic data over a reference reflectivity model, using the adjoint of wave‐equation shot‐profile migration as the forward modeling operator. I then migrate the synthetic data with the same shot‐profile algorithm. The ratio between the synthetic migration result and the initial reference model is a measure of seismic illumination. Dividing the true data migration result by this illumination function mitigates the illumination problems. The methodology can take into account reflector dip as well as both shot and receiver geometries, and, because it is based on wave‐equation migration, it naturally models the finite‐frequency effects of wave propagation. The reference model should be as close to the true model as possible; good choices include the migrated image, or a synthetic image with a single known dip that corresponds to the expected dip of a reflector of interest. Computational shortcuts allow the illumination functions to be computed at about the cost of a single migration. Results indicate that normalization can significantly reduce amplitude distortions due to irregular subsurface illumination.

Reducing two-way splitting error of FFD method in dual domains

Geophysics ◽  
2011 ◽  
Vol 76 (4) ◽  
pp. S165-S175 ◽  
Author(s):  
Jin-Hai Zhang ◽  
Zhen-Xing Yao
Keyword(s):  
Fourier Transform ◽  
Finite Difference ◽  
Impulse Responses ◽  
Lateral Velocity ◽  
Depth Migration ◽  
Computational Costs ◽  
Cross Terms ◽  
Implicit Finite Difference ◽  
Seismic Depth Migration ◽  
Root Operator

The Fourier finite-difference (FFD) method is very popular in seismic depth migration. But its straightforward 3D extension creates two-way splitting error due to ignoring the cross terms of spatial partial derivatives. Traditional correction schemes, either in the spatial domain by the implicit finite-difference method or in the wavenumber domain by phase compensation, lead to substantially increased computational costs or numerical difficulties for strong velocity contrasts. We propose compensating the two-way splitting error in dual domains, alternately in the spatial and wavenumber domains via Fourier transform. First, we organize the expanded square-root operator in terms of two-way splitting FFD plus the usually ignored cross terms. Second, we select a group of optimized coefficients to maximize the accuracy of propagation in both inline and crossline directions without yet considering the diagonal directions. Finally, we further optimize the constant coefficient of the compensation part to further improve the overall accuracy of the operator. In implementation, the compensation terms are similar to the high-order corrections of the generalized-screen method, but their functions are to compensate the two-way splitting error rather than the expansion error. Numerical experiments show that optimized one-term compensation can achieve nearly perfect circular impulse responses and the propagation angle with less than 1% error for all azimuths is improved up to 60° from 35°. Compared with traditional single-domain methods, our scheme can handle lateral velocity variations (even for strong velocity contrasts) much more easily with only one additional Fourier transform based on the two-way splitting FFD method, which helps retain the computational efficiency.

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