Kliknij ten link, aby zobaczyć inne rodzaje publikacji na ten temat: Migration amplitudes.
Artykuły w czasopismach na temat „Migration amplitudes”
Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych
Sprawdź 50 najlepszych artykułów w czasopismach naukowych na temat „Migration amplitudes”.
Przycisk „Dodaj do bibliografii” jest dostępny obok każdej pracy w bibliografii. Użyj go – a my automatycznie utworzymy odniesienie bibliograficzne do wybranej pracy w stylu cytowania, którego potrzebujesz: APA, MLA, Harvard, Chicago, Vancouver itp.
Możesz również pobrać pełny tekst publikacji naukowej w formacie „.pdf” i przeczytać adnotację do pracy online, jeśli odpowiednie parametry są dostępne w metadanych.
Przeglądaj artykuły w czasopismach z różnych dziedzin i twórz odpowiednie bibliografie.
1
Amazonas, Daniela, Rafael Aleixo, Gabriela Melo, Jörg Schleicher, Amélia Novais i Jessé C. Costa. "Including lateral velocity variations into true-amplitude common-shot wave-equation migration". GEOPHYSICS 75, nr 5 (wrzesień 2010): S175—S186. http://dx.doi.org/10.1190/1.3481469.
Pełny tekst źródłaStreszczenie:
In heterogeneous media, standard one-way wave equations describe only the kinematic part of one-way wave propagation correctly. For a correct description of amplitudes, the one-way wave equations must be modified. In media with vertical velocity variations only, the resulting true-amplitude one-way wave equations can be solved analytically. In media with lateral velocity variations, these equations are much harder to solve and require sophisticated numerical techniques. We present an approach to circumvent these problems by implementing approximate solutions based on the one-dimensional analytic amplitude modifications. We use these approximations to show how to modify conventional migration methods such as split-step and Fourier finite-difference migrations in such a way that they more accurately handle migration amplitudes. Simple synthetic data examples in media with a constant vertical gradient demonstrate that the correction achieves the recovery of true migration amplitudes. Applications to the SEG/EAGE salt model and the Marmousi data show that the technique improves amplitude recovery in the migrated images in more realistic situations.
2
Gray, Samuel H. "Spatial sampling, migration aliasing, and migrated amplitudes". GEOPHYSICS 78, nr 3 (1.05.2013): S157—S164. http://dx.doi.org/10.1190/geo2012-0451.1.
Pełny tekst źródłaStreszczenie:
Seismic migration is a multichannel process, in which some of the properties depend on various grid spacings. First, there is the acquisition grid, which actually consists of two grids: a grid of source locations and, for each source location, a grid of receiver locations. In addition, there is a third grid, the migration grid, whose spacings also affect properties of the migration. Sampling theory imposes restrictions on migration, limiting the frequency content that can be migrated reliably given the grid spacings. The presence of three grids complicates the application of sampling theory except in unusual situations (e.g., the isolated migration of a single shot record). I analyzed the effects of the grids on different types of migration (Kirchhoff, wavefield extrapolation migration, and slant-stack migration), specifically in the context of migration operator antialiasing. I evaluated general antialiasing criteria for the different types of migration; my examples placed particular emphasis on one style of data acquisition, orthogonal source and receiver lines, which is commonly used on land and which presents particular challenges for the analysis. It is known that migration artifacts caused by inadequate antialiasing can interfere with velocity and amplitude analyses. I found, in addition, that even migrations with adequate antialiasing protection can have the side effect of inaccurate amplitudes resulting from a given acquisition, and I tested how this effect can be compensated.
3
Vivas, Flor A., i Reynam C. Pestana. "True-amplitude one-way wave equation migration in the mixed domain". GEOPHYSICS 75, nr 5 (wrzesień 2010): S199—S209. http://dx.doi.org/10.1190/1.3478574.
Pełny tekst źródłaStreszczenie:
One-way wave equation migration is a powerful imaging tool for locating accurately reflectors in complex geologic structures; however, the classical formulation of one-way wave equations does not provide accurate amplitudes for the reflectors. When dynamic information is required after migration, such as studies for amplitude variation with angle or when the correct amplitudes of the reflectors in the zero-offset images are needed, some modifications to the one-way wave equations are required. The new equations, which are called “true-amplitude one-way wave equations,” provide amplitudes that are equivalent to those provided by the leading order of the ray-theoretical approximation through the modification of the transverse Laplacian operator with dependence of lateral velocity variations, the introduction of a new term associated with the amplitudes, and the modification of the source representation. In a smoothly varying vertical medium,the extrapolation of the wavefields with the true-amplitude one-way wave equations simplifies to the product of two separable and commutative factors: one associated with the phase and equal to the phase-shift migration conventional and the other associated with the amplitude. To take advantage of this true-amplitude phase-shift migration, we developed the extension of conventional migration algorithms in a mixed domain, such as phase shift plus interpolation, split step, and Fourier finite difference. Two-dimensional numerical experiments that used a single-shot data set showed that the proposed mixed-domain true-amplitude algorithms combined with a deconvolution-type imaging condition recover the amplitudes of the reflectors better than conventional mixed-domain algorithms. Numerical experiments with multiple-shot Marmousi data showed improvement in the amplitudes of the deepest structures and preservation of higher frequency content in the migrated images.
4
BORTFELD, R., i M. KIEHN. "REFLECTION AMPLITUDES AND MIGRATION AMPLITUDES (ZERO-OFFSET SITUATION)1". Geophysical Prospecting 40, nr 8 (listopad 1992): 873–84. http://dx.doi.org/10.1111/j.1365-2478.1992.tb00557.x.
Pełny tekst źródła
5
Hanitzsch, Christian. "Comparison of weights in prestack amplitude‐preserving Kirchhoff depth migration". GEOPHYSICS 62, nr 6 (listopad 1997): 1812–16. http://dx.doi.org/10.1190/1.1444282.
Pełny tekst źródłaStreszczenie:
Three different theoretical approaches to amplitude‐preserving Kirchhoff depth migration are compared. Each of them suggests applying weights in the diffraction stack migration to correct for amplitude loss resulting from geometric spreading. The weight functions are given in different notations, but as is shown, all of these expressions are similar. A notation that is well suited for implementation is suggested: entirely in terms of Green's function quantities (amplitudes or point‐source propagators). For the most common prestack configurations (common‐shot and common‐offset) and 3-D, 2.5-D, and 2-D migrations, expressions of the weights are given in this notation. The quantities needed for calculation of the weights can be computed easily, e.g., by dynamic ray tracing.
6
Nguyen, Bao D., i George A. McMechan. "Excitation amplitude imaging condition for prestack reverse-time migration". GEOPHYSICS 78, nr 1 (1.01.2013): S37—S46. http://dx.doi.org/10.1190/geo2012-0079.1.
Pełny tekst źródłaStreszczenie:
An implicitly stable ratio imaging condition for prestack reverse-time migration (RTM) was defined using excitation criteria. Amplitude maxima and their corresponding occurrence times were saved at each grid point during forward source wavefield extrapolation. Application of the imaging condition involves dividing the amplitudes of the back-propagated receiver wavefield by the precomputed maximum source wavefield amplitude only at the grid points that satisfy the image time at each time step. The division normalizes by the source amplitude, so only the highest signal-to-noise ratio portion of the data is used. Provided that the source and receiver wavefield amplitudes are accurate at the reflection points, the peak wavelet amplitudes in the migrated image are the angle-dependent reflection coefficients and low wavenumber artifacts are significantly reduced compared to those in images calculated by crosscorrelation. Using excitation information and time-binning for the imaging condition improves computational and storage efficiency by three or more orders of magnitude when compared to crosscorrelation with the full source wavefield. Numerical tests with synthetic data for the Marmousi2 model have shown this method to be a cost-effective and practical imaging condition for use in prestack RTM.
7
Dellinger, Joe A., Samuel H. Gray, Gary E. Murphy i John T. Etgen. "Efficient 2.5-D true‐amplitude migration". GEOPHYSICS 65, nr 3 (maj 2000): 943–50. http://dx.doi.org/10.1190/1.1444790.
Pełny tekst źródłaStreszczenie:
Kirchhoff depth migration is a widely used algorithm for imaging seismic data in both two and three dimensions. To perform the summation at the heart of the algorithm, standard Kirchhoff migration requires a traveltime map for each source and receiver. True‐amplitude Kirchhoff migration in 2.5-D υ(x, z) media additionally requires maps of amplitudes, out‐of‐plane spreading factors, and takeoff angles; these quantities are necessary for calculating the true‐amplitude weight term in the summation. The increased input/output (I/O) and computational expense of including the true‐amplitude weight term is often not justified by significant improvement in the final muted and stacked image. For this reason, some authors advocate neglecting the weight term in the Kirchhoff summation entirely for most everyday imaging purposes. We demonstrate that for nearly the same expense as ignoring the weight term, a much better solution is possible. We first approximate the true‐amplitude weight term by the weight term for constant‐velocity media; this eliminates the need for additional source and receiver maps. With one small additional approximation, the weight term can then be moved entirely outside the innermost loop of the summation. The resulting Kirchhoff method produces images that are almost as good as for exact true‐amplitude Kirchhoff migration and at almost the same cost as standard methods that do not attempt to preserve amplitudes.
8
Yang, Jizhong, Yuzhu Liu i Liangguo Dong. "Least-squares reverse time migration in the presence of density variations". GEOPHYSICS 81, nr 6 (1.11.2016): S497—S509. http://dx.doi.org/10.1190/geo2016-0075.1.
Pełny tekst źródłaStreszczenie:
Least-squares migration (LSM) is commonly regarded as an amplitude-preserving or true amplitude migration algorithm that, compared with conventional migration, can provide migrated images with reduced migration artifacts, balanced amplitudes, and enhanced spatial resolution. Most applications of LSM are based on the constant-density assumption, which is not the case in the real earth. Consequently, the amplitude performance of LSM is not appropriate. To partially remedy this problem, we have developed a least-squares reverse time migration (LSRTM) scheme suitable for density variations in the acoustic approximation. An improved scattering-integral approach is adopted for implementation of LSRTM in the frequency domain. LSRTM images associated with velocity and density perturbations are simultaneously used to generate the simulated data, which better matches the recorded data in amplitudes. Summation of these two images provides a reflectivity model related to impedance perturbation that is in better accordance with the true one, than are the velocity and density images separately. Numerical examples based on a two-layer model and a small part of the Sigsbee2A model verify the effectiveness of our method.
9
Chavent, Guy, i René‐Edouard Plessix. "An optimal true‐amplitude least‐squares prestack depth‐migration operator". GEOPHYSICS 64, nr 2 (marzec 1999): 508–15. http://dx.doi.org/10.1190/1.1444557.
Pełny tekst źródłaStreszczenie:
In order to define an optimal true‐amplitude prestack depth migration for multishot and multitrace data, we develop a general methodology based on the least‐squares data misfit function associated with a forward model. The amplitude of the migrated events are restored at best for any given geometry and any given preliminary filtering and amplitude correction of the data. The migrated section is then the gradient of the cost function multiplied by a weight matrix. A study of the Hessian associated with this data misfit shows how efficiently to find a good weight matrix via the computation of only few elements of this Hessian. Thanks to this matrix, the resulting migration operator is optimal in the sense that it ensures the best possible restoration of the amplitudes among the large class of least‐squares migrations. Applied to a forward model based on Born, ray tracing, and diffracting points approximation, this optimal migration outperforms or at least equals the classic Kirchhoff formula, since the latter belongs to the class of least‐squares migrations and is only optimal for one shot and an infinite aperture. Numerical results illustrate this construction and confirm the above expectations.
10
Yue, Yubo, Yujin Liu, Yaonan Li i Yunyan Shi. "Least-squares Gaussian beam migration in viscoacoustic media". GEOPHYSICS 86, nr 1 (16.12.2020): S17—S28. http://dx.doi.org/10.1190/geo2020-0129.1.
Pełny tekst źródłaStreszczenie:
Because of amplitude decay and phase dispersion of seismic waves, conventional migrations are insufficient to produce satisfactory images using data observed in highly attenuative geologic environments. We have developed a least-squares Gaussian beam migration method for viscoacoustic data imaging, which can not only compensate for amplitude decay and phase dispersion caused by attenuation, but it can also improve image resolution and amplitude fidelity through linearized least-squares inversion. We represent the viscoacoustic Green’s function by a summation of Gaussian beams, in which an attenuation traveltime is incorporated to simulate or compensate for attenuation effects. Based on the beam representation of the Green’s function, we construct the viscoacoustic Born forward modeling and adjoint migration operators, which can be effectively evaluated by a time-domain approach based on a filter-bank technique. With the constructed operators, we formulate a least-squares migration scheme to iteratively solve for the optimal image. Numerical tests on synthetic and field data sets demonstrate that our method can effectively compensate for the attenuation effects and produce images with higher resolution and more balanced amplitudes than images from acoustic least-squares Gaussian beam migration.
11
Gray, Samuel H., i Norman Bleistein. "True-amplitude Gaussian-beam migration". GEOPHYSICS 74, nr 2 (marzec 2009): S11—S23. http://dx.doi.org/10.1190/1.3052116.
Pełny tekst źródłaStreszczenie:
Gaussian-beam depth migration and related beam migration methods can image multiple arrivals, so they provide an accurate, flexible alternative to conventional single-arrival Kirchhoff migration. Also, they are not subject to the steep-dip limitations of many (so-called wave-equation) methods that use a one-way wave equation in depth to downward-continue wavefields. Previous presentations of Gaussian-beam migration have emphasized its kinematic imaging capabilities without addressing its amplitude fidelity. We offer two true-amplitude versions of Gaussian-beam migration. The first version combines aspects of the classic derivation of prestack Gaussian-beam migration with recent results on true-amplitude wave-equation migration, yields an expression involving a crosscorrelation imaging condition. To provide amplitude-versus-angle (AVA) information, true-amplitude wave-equation migration requires postmigration mapping from lateral distance (between image location and source location) to subsurface opening angle. However, Gaussian-beam migration does not require postmigration mapping to provide AVA data. Instead, the amplitudes and directions of the Gaussian beams provide information that the migration can use to produce AVA gathers as part of the migration process. The second version of true-amplitude Gaussian-beam migration is an expression involving a deconvolution imaging condition, yielding amplitude-variation-with-offset (AVO) information on migrated shot-domain common-image gathers.
12
Deng, Feng, i George A. McMechan. "True-amplitude prestack depth migration". GEOPHYSICS 72, nr 3 (maj 2007): S155—S166. http://dx.doi.org/10.1190/1.2714334.
Pełny tekst źródłaStreszczenie:
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.
13
Vivas-Mejía, Flor-A., Herling González-Alvarez, Ligia-E. Jaimes-Osorio i Nancy Espindola-López. "Deconvolution-type imaging condition effects on shot-profile migration amplitudes". CT&F - Ciencia, Tecnología y Futuro 5, nr 1 (30.11.2012): 05–18. http://dx.doi.org/10.29047/01225383.217.
Pełny tekst źródłaStreszczenie:
Amplitude preservation in Pre-Stack Depth Migration (PSDM) processes that use wavefield extrapolation must be ensured – first, in the operators used to continue the wavefield in time or depth, and second, in the imaging condition used to estimate the reflectivity function. In the later point, the conventional correlation-type imaging condition must be replaced by a deconvolution-type imaging condition. Migration performed in common-shot profile domain obtains the final migrated image as the superposition of images resulting of migrate each shot separately. The amplitude obtained in a point of the migrated image corresponds to the sum of the reflectivities for each shot which has illuminated such point, along the angles determined by the velocity model and the positions of the source and the receiver. The deeper the reflector, the lower the amplitude of the illumination field will be. As result, the correlation-type imaging condition produces images with an unbalanced amplitude decrease with depth. A deconvolution-type imaging condition scales the amplitudes through a correlation, using the weighting function dependent on the spectral density or the illumination of the downgoing wave field. In this article, two possible scaling functions have been used in the case of a single shot. In the case of data with multiple shots, five scaling possibilities are presented with the spectral density or the illumination function. The results of applying these imaging conditions to synthetic data with multiple shots show that the values of the amplitude in the migrated images are influenced by the coverage of the common midpoint, compensating this effect only in one of the imaging conditions described. Numerical experiments with synthetic data generated using Seismic Unix and the Sigsbee2a data are presented, highlighting that in velocity fields with strong vertical and lateral velocity variations, the balance of the amplitudes of the deep reflectors relative to the shallow reflectors is strongly influenced by the imaging condition applied.
14
da Silva Neto, Francisco A., Jessé C. Costa, Jörg Schleicher i Amélia Novais. "2.5D reverse-time migration". GEOPHYSICS 76, nr 4 (lipiec 2011): S143—S149. http://dx.doi.org/10.1190/1.3571272.
Pełny tekst źródłaStreszczenie:
Reverse-time migration (RTM) in 2.5D offers an alternative to improve resolution and amplitude when imaging 2D seismic data. Wave propagation in 2.5D assumes translational invariance of the velocity model. Under this assumption, we implement a finite-difference (FD) modeling algorithm in the mixed time-space/wavenumber domain to simulate the velocity and pressure fields for acoustic wave propagation and apply it in RTM. The 2.5D FD algorithm is truly parallel, allowing an efficient implementation in clusters. Storage and computing time requirements are strongly reduced compared to a full 3D FD simulation of the wave propagation. This feature makes 2.5D RTM much more efficient than 3D RTM, while achieving improved modeling of 3D geometrical spreading and phase properties of the seismic waveform in comparison to 2D RTM. Together with an imaging condition that compensates for uneven illumination and/or the obliquity factor, this allows recover of amplitudes proportional to the earth’s reflectivity. Numerical experiments using synthetic data demonstrate the better resolution and improved amplitude recovery of 2.5D RTM relative to 2D RTM.
15
Chen, Yuqing, Bowen Guo i Gerard T. Schuster. "Migration of viscoacoustic data using acoustic reverse time migration with hybrid deblurring filters". GEOPHYSICS 84, nr 3 (1.05.2019): S127—S136. http://dx.doi.org/10.1190/geo2018-0256.1.
Pełny tekst źródłaStreszczenie:
Viscoacoustic migration can significantly compensate for the amplitude loss and phase distortion in migration images computed from highly attenuated data. However, solving the viscoacoustic wave equation requires a significant amount of storage space and computation time, especially for least-squares migration methods. To mitigate this problem, we used acoustic reverse time migration (RTM) instead of viscoacoustic migration to migrate the viscoacoustic data and then we correct the amplitude and phase distortion by hybrid deblurring filters in the image domain. Numerical tests on synthetic and field data demonstrate that acoustic RTM combined with hybrid deblurring filters can compensate for the attenuation effects and produce images with high resolution and balanced amplitudes. This procedure requires less than one-third of the storage space and is [Formula: see text] times faster compared with the viscoacoustic migration, but at the cost of mildly reduced accuracy. Here, [Formula: see text] represents the number of iterations used for least-squares migration method. This method can be extended to 3D migration at even a greater cost saving.
16
Schleicher, Jörg, Jessé C. Costa i Amélia Novais. "A comparison of imaging conditions for wave-equation shot-profile migration". GEOPHYSICS 73, nr 6 (listopad 2008): S219—S227. http://dx.doi.org/10.1190/1.2976776.
Pełny tekst źródłaStreszczenie:
The application of a deconvolution imaging condition in wave-equation shot-profile migration is important to provide illumination compensation and amplitude recovery. Particularly if the aim is to successfully recover a measure of the medium reflectivity, an imaging condition that destroys amplitudes is unacceptable. We study a set of imaging conditions with illumination compensation. The imaging conditions are evaluated by the quality of the output amplitudes and artifacts produced. In numerical experiments using a vertically inhomogeneous velocity model, the best of all imaging conditions we tested is the one that divides the crosscorrelation of upgoing and downgoing wavefields by the autocorrelation of the downgoing wavefield, also known as the illumination map. In an application to Marmousi data, unconditional division by autocorrelation turned out to be unstable. Effective stabilization was achieved by smoothing the illumination map.
17
Chattopadhyay, Sandip, i George A. McMechan. "Imaging conditions for prestack reverse-time migration". GEOPHYSICS 73, nr 3 (maj 2008): S81—S89. http://dx.doi.org/10.1190/1.2903822.
Pełny tekst źródłaStreszczenie:
Numerical implementations of six imaging conditions for prestack reverse-time migration show widely differing ability to provide accurate, angle-dependent estimates of reflection coefficients. Evaluation is in the context of a simple, one-interface acoustic model. Only reflection coefficients estimated by normalization of a crosscorrelation image by source illumination or by receiver-/source-wavefield amplitude ratio have the correct angle dependence, scale factor, and sign and the required (dimensionless) units; thus, these are the preferred imaging-condition algorithms. To obtain accurate image amplitudes, source- and receiver-wavefield extrapolations must be able to accurately reconstruct their respective wavefields at the target reflector.
18
Yu, Zhou, George A. McMechan, Phil D. Anno i John F. Ferguson. "Wavelet‐transform‐based prestack multiscale Kirchhoff migration". GEOPHYSICS 69, nr 6 (listopad 2004): 1505–12. http://dx.doi.org/10.1190/1.1836823.
Pełny tekst źródłaStreszczenie:
We propose a Kirchhoff‐style algorithm that migrates coefficients obtained by wavelet decomposition of seismic traces over time. Wavelet‐based prestack multiscale Kirchhoff migration involves four steps: wavelet decomposition of the seismic data, thresholding of the resulting wavelet coefficients, multiscale Kirchhoff migration, and image reconstruction from the multiscale images. The migration procedure applied to each wavelet scale is the same as conventional Kirchhoff migration but operates on wavelet coefficients. Since only the wavelet coefficients are migrated, the cost of wavelet‐based migration is reduced compared to that of conventional Kirchhoff migration. Kirchhoff migration of wavelet‐decomposed data, followed by wavelet reconstruction, is kinematically equivalent to and yields similar migrated signal shapes and amplitudes as conventional Kirchhoff migration when data at all wavelet scales are included. The decimation in the conventional discrete pyramid wavelet decomposition introduces a translation‐variant phase distortion in the wavelet domain. This phase distortion is overcome by using a stationary wavelet‐transform rather than the conventional discrete wavelet‐transform of the data to be migrated. A wavelet reconstruction operator produces a single composite broadband migrated space‐domain image from multiscale images. Multiscale images correspond to responses in different frequency windows, and migrating the data at each scale has a different cost. Migrating some, or only one, of the individual scale data sets considerably reduces the computational cost of the migration. Successful 2D tests are shown for migrations of synthetic data for a point‐diffractor model, a multilayer model, and the Marmousi model.
19
Wapenaar, C. P. A. "3-D migration of cross‐spread data: Resolution and amplitude aspects". GEOPHYSICS 62, nr 4 (lipiec 1997): 1220–25. http://dx.doi.org/10.1190/1.1444223.
Pełny tekst źródłaStreszczenie:
Ideally, full prestack migration involves a 4-D integration along the source and receiver coordinates. Obviously, for cross‐spread data (typical for land acquisition) this 4-D integration cannot be effectuated. An analysis is presented of the resolution and amplitude behavior of full prestack migration, applied to cross‐spread data. Moreover, a proposal is made to modify operators that partly compensate for the diminishing effects of the cross‐spread aquisition geometry on amplitudes and resolution.
20
Mosher, Charles C., Timothy H. Keho, Arthur B. Weglein i Douglas J. Foster. "The impact of migration on AVO". GEOPHYSICS 61, nr 6 (listopad 1996): 1603–15. http://dx.doi.org/10.1190/1.1444079.
Pełny tekst źródłaStreszczenie:
Amplitude variation with offset (AVO) analysis is often limited to areas where multidimensional propagation effects such as reflector dip and diffractions from faults can be ignored. Migration‐inversion provides a framework for extending the use of seismic amplitudes to areas where structural or stratigraphic effects are important. In this procedure, sources and receivers are downward continued into the earth using uncollapsed prestack migration. Instead of stacking the data as in normal migration, the prestack migrated data are used in AVO analysis or other inversion techniques to infer local earth properties. The prestack migration can take many forms. In particular, prestack time migration of common‐angle sections provides a convenient tool for improving the lateral resolution and spatial positioning of AVO anomalies. In this approach, a plane‐wave decomposition is first applied in the offset direction, separating the wavefield into different propagating angles. The data are then gathered into common‐angle sections and migrated one angle at a time. The common‐angle migrations have a simple form and are shown to adequately preserve amplitude as a function of angle. Normal AVO analysis is then applied to the prestack migrated data. Examples using seismic lines from the Gulf of Mexico show how migration improves AVO analysis. In the first set of examples, migration is shown to improve imaging of subtle spatial variations in bright spots. Subsequent AVO analysis reveals dim spots associated with dry‐hole locations that were not resolvable using traditional processing techniques, including both conventional AVO and poststack migration. A second set of examples shows improvements in AVO response after migration is used to reduce interference from coherent noise and diffractions. A final example shows the impact of migration on the spatial location of dipping AVO anomalies. In all cases, migration improves both the signal‐to‐noise ratio and spatial resolution of AVO anomalies.
21
Vanelle, Claudia, Miriam Spinner, Thomas Hertweck, Christoph Jäger i Dirk Gajewski. "Traveltime-based true-amplitude migration". GEOPHYSICS 71, nr 6 (listopad 2006): S251—S259. http://dx.doi.org/10.1190/1.2356091.
Pełny tekst źródłaStreszczenie:
True-amplitude Kirchhoff migration (TAKM) is an important tool in seismic-reflection imaging. In addition to a structural image, it leads to reflectivity maps of the subsurface. TAKM is carried out in terms of a weighted diffraction stack where the weight functions are computed with dynamic ray tracing (DRT) in addition to the diffraction traveltimes. DRT, however, is time-consuming and imposes restrictions on the velocity models, which are not always acceptable. An alternative approach to TAKM is proposed in which the weight functions are directly determined from the diffraction traveltimes. Because other methods exist for the generation of traveltimes, this approach is not limited by the requirements for DRT. Applications to a complex synthetic model and real data demonstrate that the image quality and accuracy of the reconstructed amplitudes are equivalent to those obtained from TAKM with DRT-generated weight functions.
22
Schleicher, Jörg, i Claudio Bagaini. "Controlling amplitudes in 2.5D common‐shot migration to zero offset". GEOPHYSICS 69, nr 5 (wrzesień 2004): 1299–310. http://dx.doi.org/10.1190/1.1801946.
Pełny tekst źródłaStreszczenie:
Configuration transform operations such as dip moveout, migration to zero offset, and shot and offset continuation use seismic data recorded with a certain measurement configuration to simulate data as if recorded with other configurations. Common‐shot migration to zero offset (CS‐MZO), analyzed in this paper, transforms a common‐shot section into a zero‐offset section. It can be realized as a Kirchhoff‐type stacking operation for 3D wave propagation in a 2D laterally inhomogeneous medium. By application of suitable weight functions, amplitudes of the data are either preserved or transformed by replacing the geometrical‐spreading factor of the input reflections by the correct one of the output zero‐offset reflections. The necessary weight function can be computed via 2D dynamic ray tracing in a given macrovelocity model without any a priori knowledge regarding the dip or curvature of the reflectors. We derive the general expression of the weight function in the general 2.5D situation and specify its form for the particular case of constant velocity. A numerical example validates this expression and highlights the differences between amplitude preserving and true‐amplitude CS‐MZO.
23
Whitcombe, David N., i Randall J. Carroll. "The application of map migration to 2-D migrated data". GEOPHYSICS 59, nr 7 (lipiec 1994): 1121–32. http://dx.doi.org/10.1190/1.1443668.
Pełny tekst źródłaStreszczenie:
Two‐dimensional migrated time interpretations are used in a novel application of map migration. This is done by following the seismic migration along the 2-D lines by a map migration in a direction orthogonal to the lines, thus achieving a fully 3-D migrated representation of the subsurface. In addition to modifying the 2-D times and positions, this approach corrects the amplitudes of the 2-D migrated data, which suffer from being corrupted by focusing or defocusing because of the reflector curvature orthogonal to the line direction. A Gulf of Mexico case study illustrates how this map migration technique simplifies the time structure map and explains anomalous amplitude variations.
24
Docherty, Paul. "A brief comparison of some Kirchhoff integral formulas for migration and inversion". GEOPHYSICS 56, nr 8 (sierpień 1991): 1164–69. http://dx.doi.org/10.1190/1.1443136.
Pełny tekst źródłaStreszczenie:
Kirchhoff migration has traditionally been viewed as an imaging procedure. Usually, few claims are made regarding the amplitudes in the imaged section. In recent years, a number of inversion formulas, similar in form to those of Kirchhoff migration, have been proposed. A Kirchhoff‐type inversion produces not only an image but also an estimate of velocity variations, or perhaps reflection coefficients. The estimate is obtained from the peak amplitudes in the image. In this paper prestack Kirchhoff migration and inversion formulas for the one‐parameter acoustic wave equation are compared. Following a heuristic approach based on the imaging principle, a migration formula is derived which turns out to be identical to one proposed by Bleistein for inversion. Prestack Kirchhoff migration and inversion are, thus, seen to be the same—both in terms of the image produced and the peak amplitudes of the output.
25
Wang, Yanghua. "Inverse- Q filtered migration". GEOPHYSICS 73, nr 1 (styczeń 2008): S1—S6. http://dx.doi.org/10.1190/1.2806924.
Pełny tekst źródłaStreszczenie:
An inverse-[Formula: see text] filtered migration algorithm performs seismic migration and inverse-[Formula: see text] filtering simultaneously, in which the latter compensates for the amplitudes and corrects the phase distortions resulting from the earth attenuation effect. However, the amplitudes of high-frequency components grow rapidly in the extrapolation procedure, so numerical instability is a concern when including the inverse-[Formula: see text] filter in the migration. The instability for each frequency component is independent of data and is affected only by migration models. The stabilization problem may be treated separately from the wavefield-extrapolation scheme. The proposed strategy is to construct supersedent of attenuation coefficients, based on given velocity and [Formula: see text] models, before performing wavefield extrapolation in the space-frequency domain. This stabilized algorithm for inverse-[Formula: see text] filtered migration is applicable to subsurface media with vertical and lateral variations in velocity and [Formula: see text] functions. It produces a seismic image with enhanced resolution and corrected timing, comparable to an ideal image without the earth attenuation effect.
26
Dutta, Gaurav, i Gerard T. Schuster. "Attenuation compensation for least-squares reverse time migration using the viscoacoustic-wave equation". GEOPHYSICS 79, nr 6 (1.11.2014): S251—S262. http://dx.doi.org/10.1190/geo2013-0414.1.
Pełny tekst źródłaStreszczenie:
Strong subsurface attenuation leads to distortion of amplitudes and phases of seismic waves propagating inside the earth. Conventional acoustic reverse time migration (RTM) and least-squares reverse time migration (LSRTM) do not account for this distortion, which can lead to defocusing of migration images in highly attenuative geologic environments. To correct for this distortion, we used a linearized inversion method, denoted as [Formula: see text]-LSRTM. During the least-squares iterations, we used a linearized viscoacoustic modeling operator for forward modeling. The adjoint equations were derived using the adjoint-state method for back propagating the residual wavefields. The merit of this approach compared with conventional RTM and LSRTM was that [Formula: see text]-LSRTM compensated for the amplitude loss due to attenuation and could produce images with better balanced amplitudes and more resolution below highly attenuative layers. Numerical tests on synthetic and field data illustrated the advantages of [Formula: see text]-LSRTM over RTM and LSRTM when the recorded data had strong attenuation effects. Similar to standard LSRTM, the sensitivity tests for background velocity and [Formula: see text] errors revealed that the liability of this method is the requirement for smooth and accurate migration velocity and attenuation models.
27
Herrmann, Felix J., Cody R. Brown, Yogi A. Erlangga i Peyman P. Moghaddam. "Curvelet-based migration preconditioning and scaling". GEOPHYSICS 74, nr 4 (lipiec 2009): A41—A46. http://dx.doi.org/10.1190/1.3124753.
Pełny tekst źródłaStreszczenie:
The extremely large size of typical seismic imaging problems has been a major stumbling block for iterative techniques to attain accurate migration amplitudes. These iterative methods are important because they complement theoretical approaches hampered by difficulties controlling problems such as finite-acquisition aperture, source-receiver frequency response, and directivity. To solve these problems, we apply preconditioning, which significantly improves convergence of least-squares migration. We discuss different levels of preconditioning: corrections for the order of the migration operator, corrections for spherical spreading, and position- and reflector-dip-dependent amplitude errors. Although the first two corrections correspond to simple scalings in the Fourier and physical domain, the third correction requires phase-space (space spanned by location and dip) scaling, which we carry out with curvelets. Our combined preconditioner significantly improves the convergence of least-squares wave-equation migration on a line from the SEG/EAGE [Formula: see text] salt model.
28
Ekren, B. O., i Bjørn Ursin. "True‐amplitude frequency‐wavenumber constant‐offset migration". GEOPHYSICS 64, nr 3 (maj 1999): 915–24. http://dx.doi.org/10.1190/1.1444599.
Pełny tekst źródłaStreszczenie:
Low S/N ratios, interfering diffractions, and dip‐related problems (e.g., reflector point dispersal, dip‐dependent NMO, and reflection angle) make reliable amplitude versus offset (AVO) analysis a difficult task. Prestack time migration (PSTM) collapses diffractions, increases the S/N ratio, and reduces dip‐related problems. Therefore, PSTM is usually required before offset dependent information can be extracted from seismic data, and PSTM is mandatory before comparing real seismic data with 1-D earth model synthetic data. We present a 2-D frequency‐wavenumber common‐offset prestack time migration algorithm. To treat the amplitudes correctly, a 3-D to 2-D transform of the data is required before doing the migration. This is done by correcting the data for out‐of‐plane geometrical spreading. Migration artifacts are attenuated, exploiting the fact that the maximum dip to be migrated decreases with increasing traveltime and offset. The final processing steps before further processing are 2-D geometrical spreading correction and removal of the implicit NMO correction inherent in the migration. Two marine data examples show improved data quality after prestack time migration, making subsequent amplitude analysis more reliable.
29
Dutta, Gaurav, i Gerard T. Schuster. "Wave-equation Q tomography". GEOPHYSICS 81, nr 6 (listopad 2016): R471—R484. http://dx.doi.org/10.1190/geo2016-0081.1.
Pełny tekst źródłaStreszczenie:
Strong subsurface attenuation leads to distortion of amplitudes and phases of seismic waves propagating inside the earth. The amplitude and the dispersion losses from attenuation are often compensated for during prestack depth migration. However, most attenuation compensation or [Formula: see text]-compensation migration algorithms require an estimate of the background [Formula: see text] model. We have developed a wave-equation gradient optimization method that inverts for the subsurface [Formula: see text] distribution by minimizing a skeletonized misfit function [Formula: see text], where [Formula: see text] is the sum of the squared differences between the observed and the predicted peak/centroid-frequency shifts of the early arrivals. The gradient is computed by migrating the observed traces weighted by the frequency shift residuals. The background [Formula: see text] model is perturbed until the predicted and the observed traces have the same peak frequencies or the same centroid frequencies. Numerical tests determined that an improved accuracy of the [Formula: see text] model by wave-equation [Formula: see text] tomography leads to a noticeable improvement in migration image quality.
30
Angus, D. A. "True amplitude corrections for a narrow-angle one-way elastic wave equation". GEOPHYSICS 72, nr 2 (marzec 2007): T19—T26. http://dx.doi.org/10.1190/1.2430694.
Pełny tekst źródłaStreszczenie:
Wavefield extrapolators using one-way wave equations are computationally efficient methods for accurate traveltime modeling in laterally heterogeneous media, and have been used extensively in many seismic forward modeling and migration problems. However, most leading-order, one-way wave equations do not simulate waveform amplitudes accurately and this is primarily because energy flux is not accounted for correctly. I review the derivation of a leading-order, narrow-angle, one-way elastic wave equation for 3D media. I derive correction terms that enable energy-flux normalization and introduce a new higher-order, narrow-angle, one-way elastic wave extrapolator. By implementing these correction terms, the new true amplitude wave extrapolator allows accurate amplitude estimates in the presence of strong gradients. I present numerical examples for 1D velocity transition models to show that (1) the leading-order, narrow-angle propagator accurately models traveltimes, but overestimates transmitted- or primary-wave amplitudes and (2) the new amplitude corrected narrow-angle propagator accurately models both the traveltimes and amplitudes of all forward-traveling waves.
31
Vidale, John E., i Heidi Houston. "Rapid calculation of seismic amplitudes". GEOPHYSICS 55, nr 11 (listopad 1990): 1504–7. http://dx.doi.org/10.1190/1.1442798.
Pełny tekst źródłaStreszczenie:
The ability to calculate traveltimes and amplitudes of seismic waves is useful for many reflection seismology applications such as migration and tomography. Traditionally, ray tracing (C⁁erveny et al., 1977; Julian, 1977), paraxial methods (Claerbout, 1971), or full‐wave methods (Alterman and Karal, 1968) are used for such calculations. These methods have in common considerable computational expense. Recently, Vidale (1988, 1990a) presented two‐dimensional and three‐dimensional methods to efficiently compute traveltimes of the first arrivals to every point in a regularly spaced grid of points, given an arbitrary velocity field sampled at these points. The computational cost of finding each traveltime is roughly one square root operation.
32
Symes, William W. "Approximate linearized inversion by optimal scaling of prestack depth migration". GEOPHYSICS 73, nr 2 (marzec 2008): R23—R35. http://dx.doi.org/10.1190/1.2836323.
Pełny tekst źródłaStreszczenie:
Linearized inversion provides one possible sense of image amplitude correctness. An image or bandlimited model perturbation has correct amplitudes if it is an approximate inversion, that is, if linearized modeling (demigration), with the image as input, reproduces the data approximately. The theory of linearized acoustic inverse scattering with slowly varying background or macromodel shows that an approximate inversion may be recovered from the output of prestack depth migration by a combination of scaling and filtering. The necessary filter is completely specified by the theory, and the scale factor may be estimated via filtering, linearized modeling, a second migration, and the solution of a small auxiliary inverse problem.
33
Fischer, Robert S., Xiaoyu Sun, Michelle A. Baird, Matt J. Hourwitz, Bo Ri Seo, Ana M. Pasapera, Shalin B. Mehta i in. "Contractility, focal adhesion orientation, and stress fiber orientation drive cancer cell polarity and migration along wavy ECM substrates". Proceedings of the National Academy of Sciences 118, nr 22 (24.05.2021): e2021135118. http://dx.doi.org/10.1073/pnas.2021135118.
Pełny tekst źródłaStreszczenie:
Contact guidance is a powerful topographical cue that induces persistent directional cell migration. Healthy tissue stroma is characterized by a meshwork of wavy extracellular matrix (ECM) fiber bundles, whereas metastasis-prone stroma exhibit less wavy, more linear fibers. The latter topography correlates with poor prognosis, whereas more wavy bundles correlate with benign tumors. We designed nanotopographic ECM-coated substrates that mimic collagen fibril waveforms seen in tumors and healthy tissues to determine how these nanotopographies may regulate cancer cell polarization and migration machineries. Cell polarization and directional migration were inhibited by fibril-like wave substrates above a threshold amplitude. Although polarity signals and actin nucleation factors were required for polarization and migration on low-amplitude wave substrates, they did not localize to cell leading edges. Instead, these factors localized to wave peaks, creating multiple “cryptic leading edges” within cells. On high-amplitude wave substrates, retrograde flow from large cryptic leading edges depolarized stress fibers and focal adhesions and inhibited cell migration. On low-amplitude wave substrates, actomyosin contractility overrode the small cryptic leading edges and drove stress fiber and focal adhesion orientation along the wave axis to mediate directional migration. Cancer cells of different intrinsic contractility depolarized at different wave amplitudes, and cell polarization response to wavy substrates could be tuned by manipulating contractility. We propose that ECM fibril waveforms with sufficiently high amplitude around tumors may serve as “cell polarization barriers,” decreasing directional migration of tumor cells, which could be overcome by up-regulation of tumor cell contractility.
34
Ursin, Bjørn, i Martin Tygel. "Zero-offset seismic amplitude decomposition and migration". GEOPHYSICS 72, nr 4 (lipiec 2007): S187—S193. http://dx.doi.org/10.1190/1.2741366.
Pełny tekst źródłaStreszczenie:
In an anisotropic medium, a normal-incidence wave is multiply transmitted and reflected down to a reflector where the phase-velocity vector is parallel to the interface normal. The ray code of the upgoing wave is equal to the ray code of the downgoing wave in reverse order. The geometric spreading, KMAH index, and transmission and reflection coefficients of the normal-incidence ray can be expressed in terms of products or sums of the corresponding quantities of the one-way normal and normal-incidence-point (NIP) waves. Here, we show that the amplitude of the ray-theoretic Green’s function for the reflected wave also follows a similar decomposition in terms of the amplitude of the Green’s function of the NIP wave and the normal wave. We use this property to propose three schemes for true-amplitude poststack depth migration in anisotropic media where the image represents an estimate of the zero-offset reflection coefficient. The first is a map migration procedure in which selected primary zero-offset reflections are converted into depth with attached true amplitudes. The second is a ray-based, Kirchhoff-type full migration. The third is a wave equation continuation algorithm to reverse-propagate the recorded wavefield in a half-velocity model with half the elastic constants and double the density. The image is formed by taking the reverse-propagated wavefield at time equal to zero followed by a geometric spreading correction.
35
Osorio, Luana Nobre, Bruno Pereira-Dias, André Bulcão i Luiz Landau. "Migration deconvolution using domain decomposition". GEOPHYSICS 86, nr 3 (21.04.2021): S247—S256. http://dx.doi.org/10.1190/geo2020-0352.1.
Pełny tekst źródłaStreszczenie:
Least-squares migration (LSM) is an effective technique for mitigating blurring effects and migration artifacts generated by limited data frequency bandwidth, incomplete coverage of geometry, source signature, and unbalanced amplitudes caused by complex wavefield propagation in the subsurface. Migration deconvolution (MD) is an image-domain approach for LSM that approximates the Hessian operator using a set of precomputed point spread functions. We have developed a new workflow by integrating the MD and domain decomposition (DD) methods. DD techniques aim to solve large and complex linear systems by splitting problems into smaller parts, facilitating parallel computing, and providing a higher convergence in iterative algorithms. We suggest that instead of solving the problem in a unique domain, as conventionally performed, splitting the problem into subdomains that overlap and solve each of them independently. We accelerate the convergence rate of the conjugate-gradient solver by applying the DD methods to retrieve better reflectivity, which is mainly visible in regions with low amplitudes. Moreover, using the pseudo-Hessian operator, the convergence of the algorithm is accelerated, suggesting that the inverse problem becomes better conditioned. Experiments using the synthetic Pluto model demonstrate that our algorithm dramatically reduces the required number of iterations while providing a considerable enhancement in image resolution and better continuity of poorly illuminated events.
36
Yang, Jidong, i Hejun Zhu. "Viscoacoustic reverse time migration using a time-domain complex-valued wave equation". GEOPHYSICS 83, nr 6 (1.11.2018): S505—S519. http://dx.doi.org/10.1190/geo2018-0050.1.
Pełny tekst źródłaStreszczenie:
During seismic wave propagation, intrinsic attenuation inside the earth gives rise to amplitude loss and phase dispersion. Without appropriate correction strategies in migration, these effects degrade the amplitudes and resolution of migrated images. Based on a new time-domain viscoacoustic wave equation, we have developed a viscoacoustic reverse time migration (RTM) approach to correct attenuation-associated dispersion and dissipation effects. A time-reverse wave equation is derived to extrapolate the receiver wavefields, in which the sign of the dissipation term is reversed, whereas the dispersion term remains unchanged. The difference between the forward and time-reverse wave equations is consistent with the physical insights of attenuation compensation during wavefield backpropagation. Due to the introduction of an imaginary unit in the dispersion term, the forward and time-reverse wave equations are complex valued. They are similar to the time-dependent Schrödinger equation, whose real and imaginary parts are coupled during wavefield extrapolation. The analytic property of the extrapolated source and receiver wavefields allows us to explicitly separate up- and downgoing waves. A causal imaging condition is implemented by crosscorrelating downgoing source and upgoing receiver wavefields to remove low-wavenumber artifacts in migrated images. Numerical examples demonstrate that our viscoacoustic RTM approach is capable of producing subsurface reflectivity images with correct spatial locations as well as amplitudes.
37
Hua, Biaolong, i George A. McMechan. "Parsimonious 2D prestack Kirchhoff depth migration". GEOPHYSICS 68, nr 3 (maj 2003): 1043–51. http://dx.doi.org/10.1190/1.1581075.
Pełny tekst źródłaStreszczenie:
The efficiency of prestack Kirchhoff depth migration is much improved by using ray parameter information measured from prestack common‐source and common‐receiver gathers. Ray tracing is performed only back along the emitted and emergent wave directions, and so is much reduced. The position of the intersection of the source and receiver rays is adjusted to satisfy the image time condition. The imaged amplitudes are spread along the local reflector surface only within the first Fresnel zone. There is no need to build traveltime tables before migration because the traveltime calculation is embedded into the migration. To further reduce the computation time, the input data are decimated by applying an amplitude threshold before the estimation of ray parameters, and only peak and trough points on each trace are searched for ray parameters. Numerical results show that the proposed implementation is typically 50–80 times faster than traditional Kirchhoff migration for synthetic 2D prestack data. The migration speed improvement is obtained at the expense of some reduction in migration quality; the optimal compromise is implemented by the choice of migration parameters. The main uses of the algorithm will be to get a fast first look at the main structural features and for iterative migration velocity analysis.
38
Shin, Changsoo, Kurt J. Marfurt, Kwon Gyu Park, Dong‐Joo Min, Kwangjin Yoon, Dongwoo Yang, Taeyoung Ha, Seungwon Ko, Wonsik Kim i Soonduk Hong. "Traveltime and amplitude calculation using a perturbation approach". GEOPHYSICS 67, nr 5 (wrzesień 2002): 1648–55. http://dx.doi.org/10.1190/1.1512812.
Pełny tekst źródłaStreszczenie:
Accurate amplitudes and correct traveltimes are critical factors that govern the quality of prestack migration images. Because we never know the correct velocity initially, recomputing traveltimes and amplitudes of updated velocity models can dominate the iterative prestack migration procedure. Most tomographic velocity updating techniques require the calculation of the change of traveltime due to local changes in velocity. For such locally updated velocity models, perturbation techniques can be a significantly more economic way of calculating traveltimes and amplitudes than recalculating the entire solutions from scratch. In this paper, we implement an iterative Born perturbation theory applied to the damped wave equation algorithm. Our iterative Born perturbation algorithm yields stable solutions for models having velocity contrasts of 30% about the initial velocity estimate, which is significantly more economic than recalculating the entire solution.
39
Grubb, H., A. Tura i C. Hanitzsch. "Estimating and interpreting velocity uncertainty in migrated images and AVO attributes". GEOPHYSICS 66, nr 4 (lipiec 2001): 1208–16. http://dx.doi.org/10.1190/1.1487067.
Pełny tekst źródłaStreszczenie:
Estimating a suitable velocity field for use in prestack depth migration is inherently uncertain because of limitations on the available data and estimation techniques. This uncertainty affects both the migrated depth of structures and their amplitudes in the inverted images. These effects can be estimated by performing multiple migrations with a set of velocity fields and colocating features in the migrated images. This lets us examine the imaging procedure’s sensitivity to changes in the velocity field so we can assess both structural and amplitude uncertainties in migrated images. These two types of uncertainties affect interpretation in different ways. For instance, with structural uncertainty interpretation we consider the change in migrated location of structures when deciding on drilling locations, optimizing well trajectories, or computing uncertainty in volumetric calculations. With amplitude uncertainty or amplitude versus offset (AVO) uncertainty interpretation, we consider (1) uncertainty in crossplots of pairs of AVO attributes at a point of interest or (2) uncertainty of the attribute values along identified structures. For any interpretation informing a decision, the uncertainty can help estimate risk. Our data processing approach is based on amplitude‐preserving prestack depth migration followed by AVO inversion, or AVO migration/inversion. It is valid for estimating AVO attributes in simple to moderately complex structural settings. Our methods of assessing the effect of velocity uncertainty can also be applied when obtaining structural uncertainties for a complex overburden geology or amplitude uncertainties in conventional NMO‐based AVO analysis. They may also be applied straightforwardly to any poststack attribute analysis. Key to the approach is the availability of multiple velocity fields to generate multiple migrated images. In our application, an automatic algorithm samples possible fields, but the set of fields to consider could be generated from another source, such as interpretation.
40
Li, Qihua, i Xiaofeng Jia. "Generalized staining algorithm for seismic modeling and migration". GEOPHYSICS 82, nr 1 (1.01.2017): T17—T26. http://dx.doi.org/10.1190/geo2015-0652.1.
Pełny tekst źródłaStreszczenie:
The staining algorithm is introduced to improve the signal-to-noise ratio (S/N) of poorly illuminated subsurface structures in seismic imaging. However, the amplitudes of the original and the stained wavefield, i.e., the real and the imaginary wavefields, differ by several orders of magnitude, and the waveform of the stained wavefield may be greatly distorted. We have developed a generalized staining algorithm (GSA) to achieve amplitude preservation in the stained wavefield. The real wavefield and the stained wavefield propagate in the same velocity model. A source wavelet is used as the source of the real wavefield; however, the real wavefield is extracted from the stained area as the source of the stained wavefield. The GSA maintains some properties of the original staining algorithm. The stained wavefield is synchronized with the real wavefield, and it contains only information relevant to the target region. By imaging with the stained wavefield, we obtain higher S/Ns in images of target structures. The most significant advantage of our method is the amplitude preservation of the stained wavefield, which means that this method could potentially be used in quantitative illumination analysis and velocity model building. The GSA could be adopted easily for frequency-domain wavefield propagators and time-domain propagators. Furthermore, the GSA can generate any number of stained wavefields. Numerical experiments demonstrate these features of the GSA, and we apply this method in target-oriented modeling and imaging as well as obtaining amplitude-preserved stained wavefields and higher S/Ns in images of target structures.
41
Schleicher, Jorg, Martin Tygel i Peter Hubral. "3-D true‐amplitude finite‐offset migration". GEOPHYSICS 58, nr 8 (sierpień 1993): 1112–26. http://dx.doi.org/10.1190/1.1443495.
Pełny tekst źródłaStreszczenie:
Compressional primary nonzero offset reflections can be imaged into three‐dimensional (3-D) time or depth‐migrated reflections so that the migrated wavefield amplitudes are a measure of angle‐dependent reflection coefficients. Various migration/inversion algorithms involving weighted diffraction stacks recently proposed are based on Born or Kirchhoff approximations. Here a 3-D Kirchhoff‐type prestack migration approach is proposed where the primary reflections of the wavefields to be imaged are a priori described by the zero‐order ray approximation. As a result, the principal issue in the attempt to recover angle‐dependent reflection coefficients becomes the removal of the geometrical spreading factor of the primary reflections. The weight function that achieves this aim is independent of the unknown reflector and correctly accounts for the recovery of the source pulse in the migrated image irrespective of the source‐receiver configurations employed and the caustics occurring in the wavefield. Our weight function, which is computed using paraxial ray theory, is compared with the one of the inversion integral based on the Beylkin determinant. It differs by a factor that can be easily explained.
42
Verma, Sumit, Shiguang Guo i Kurt J. Marfurt. "Data conditioning of legacy seismic using migration-driven 5D interpolation". Interpretation 4, nr 2 (1.05.2016): SG31—SG40. http://dx.doi.org/10.1190/int-2015-0157.1.
Pełny tekst źródłaStreszczenie:
Legacy seismic surveys cover much of the midcontinent USA and Texas, with almost all 3D surveys acquired in the 1990s considered today to be low fold. Fortunately, recent advances in 5D interpolation have not only enhanced the quality of structural and stratigraphic images, but they have also improved the data sufficiently to allow more quantitative interpretation, such as impedance inversion. Although normal-moveout-corrected, common-midpoint-based 5D interpolation does an excellent job of amplitude balancing and the suppression of acquisition footprint, it appears to misinterpolate undercorrected diffractions, thus smearing fault and stratigraphic edges. We described a least-squares migration-driven 5D interpolation workflow, in which data were interpolated by demigrating the current subsurface image to the missing offsets and azimuths. Such demigration accurately interpolates fault edges and other diffractors, thereby preserving lateral discontinuities, while suppressing footprint and balancing the amplitudes. We have applied this workflow to a highly aliased low-fold survey acquired in the early 1990s now of use in mapping the newly reinvigorated Mississippi Lime play. This workflow improves reflector continuity, preserves faults delineated by coherence, balances the amplitude, and provides improved well ties.
43
Rickett, James E. "Illumination‐based normalization for wave‐equation depth migration". GEOPHYSICS 68, nr 4 (lipiec 2003): 1371–79. http://dx.doi.org/10.1190/1.1598130.
Pełny tekst źródłaStreszczenie:
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.
44
Ayeni, Gboyega, i Biondo Biondi. "Target-oriented joint least-squares migration/inversion of time-lapse seismic data sets". GEOPHYSICS 75, nr 3 (maj 2010): R61—R73. http://dx.doi.org/10.1190/1.3427635.
Pełny tekst źródłaStreszczenie:
Two related formulations are proposed for target-oriented joint least-squares migration/inversion of time-lapse seismic data sets. Time-lapse seismic images can be degraded when reservoir overburden is complex or when acquisition geometries significantly differ, because the migration operator does not compensate for the resulting amplitude and phase distortions. Under these circumstances, time-lapse amplitudes are poor indicators of production-related changes in reservoir properties. To correct for such image degradation, time-lapse imaging is posed as joint inverse problems that utilize concatenations of target-oriented approximations to the linear least-squares imaging Hessian. In both formulations, spatial and temporal constraints ensure inversion stability and geologically consistent time-lapse images. Using two numerical time-lapse data sets, we confirmed that these formulations can attenuate illumination artifacts caused by complex overburden or geometry differences, and that they yield better-quality images than obtainable with migration.
45
Liu, Xuejian, Yike Liu, Huiyi Lu, Hao Hu i Majid Khan. "Prestack correlative least-squares reverse time migration". GEOPHYSICS 82, nr 2 (1.03.2017): S159—S172. http://dx.doi.org/10.1190/geo2016-0416.1.
Pełny tekst źródłaStreszczenie:
In the correlative least-squares reverse time migration (CLSRTM) scheme, a stacked image is updated using a gradient-based inversion algorithm. However, CLSRTM experiences the incoherent stacking of different shots during each iteration due to the use of an imperfect velocity, which leads to image smearing. To reduce the sensitivity to velocity errors, we have developed prestack correlative least-squares reverse time migration (PCLSRTM), in which a gradient descent algorithm using a newly defined initial image and an efficiently defined analytical step length is developed to separately seek the optimal image for each shot gather before the final stacking. Furthermore, a weighted objective function is also designed for PCLSRTM, so that the data-domain gradient can avoid a strong truncation effect. Numerical experiments on a three-layer model as well as a marine synthetic and a field data set reveal the merits of PCLSRTM. In the presence of velocity errors, PCLSRTM shows better convergence and provides higher quality images as compared with CLSRTM. With the newly defined initial image, PCLSRTM can effectively handle observed data with unbalanced amplitudes. By using a weighted objective function, PCLSRTM can provide an image with enhanced resolution and balanced amplitude while avoiding many imaging artifacts.
46
Deng, Feng, i George A. McMechan. "Viscoelastic true-amplitude prestack reverse-time depth migration". GEOPHYSICS 73, nr 4 (lipiec 2008): S143—S155. http://dx.doi.org/10.1190/1.2938083.
Pełny tekst źródłaStreszczenie:
A new true-amplitude prestack elastic depth-migration algorithm includes compensation for transmission and anelastic attenuation losses in an isotropic medium. Geometric spreading and its compensation are incorporated by extrapolating up- and downgoing waves using a full two-way wave equation. Intrinsic attenuation is simulated and compensated for using composite memory variables derived from standard linear solid relaxation mechanisms. Zoeppritz equations and their approximations are used to compute and analyze the angle-dependent reflection/transmission coefficients; converted energy is included at each interface. Transmission losses for compressional waves are compensated, based on estimation of angle-dependent elastic reflectivity using a two-pass recursive procedure. The image condition is the ratio of the compressional receiver/source wavefield amplitudes. Application to synthetic data from a dipping-layer model and a salt model accurately extracts P-velocity, S-velocity, density, and P-wave impedance beneath the target reflector, even under a salt overhang. Factors not explicitly considered include building of the smooth background velocity and attenuation models, estimates of the source time function, directivity and coupling, multipathing arrivals, and effects of attenuation and anisotropy on the reflection/transmission coefficients.
47
Gray, Samuel H., Chester A. Jacewitz i Michael E. Epton. "Analytic synthetic seismograms for depth migration testing". GEOPHYSICS 56, nr 5 (maj 1991): 697–700. http://dx.doi.org/10.1190/1.1443087.
Pełny tekst źródłaStreszczenie:
By using the fact that raypaths in a linear acoustic velocity field are circular arcs, we analytically generate a number of distinct nontrivial synthetic seismograms. The seismograms yield accurate traveltimes from reflection events, but they do not give reflection amplitudes. The seismograms are useful for testing seismic migration programs for both speed and accuracy, in settings where lateral velocity variations can be arbitrarily high and dipping reflectors arbitrarily steep. Two specific examples are presented as illustrations.
48
Duveneck, Eric, Michael Kiehn, Anu Chandran i Thomas Kühnel. "Reflection angle/azimuth-dependent least-squares reverse time migration". GEOPHYSICS 86, nr 5 (30.08.2021): S325—S338. http://dx.doi.org/10.1190/geo2020-0701.1.
Pełny tekst źródłaStreszczenie:
Seismic images under complex overburdens such as salt are strongly affected by illumination variations due to overburden velocity variations and imperfect acquisition geometries, making it difficult to obtain reliable image amplitudes. Least-squares reverse time migration (LSRTM) addresses these issues by formulating full wave-equation imaging as a linear inverse problem and solving for a reflectivity model that explains the recorded seismic data. Because subsurface reflection coefficients depend on the incident angle, and possibly on the azimuth, quantitative interpretation under complex overburdens requires LSRTM with output in terms of image gathers, e.g., as a function of the reflection angle or angle and azimuth. We have developed a reflection angle- or angle/azimuth-dependent LSRTM method aimed at obtaining physically meaningful image amplitudes interpretable in terms of angle- or angle/azimuth-dependent reflection coefficients. The method is formulated as a linear inverse problem solved iteratively with the conjugate gradient method. It requires an adjoint pair of linear operators for reflection angle/azimuth-dependent migration and demigration based on full wave-equation propagation. We implement these operators in an efficient way by using a mapping approach between migrated shot gathers and subsurface reflection angle/azimuth gathers. To accelerate convergence of the iterative inversion, we apply image-domain preconditioning operators computed from a single de-remigration step. An angle continuity constraint and a structural dip constraint, implemented via shaping regularization, are used to stabilize the solution in the presence of limited illumination and to control the effects of coherent noise. We examine the method on a synthetic data example and on a wide-azimuth streamer data set from the Gulf of Mexico, where we find that angle/azimuth-dependent LSRTM can achieve significant uplift in subsalt image quality, with overburden- and acquisition-related illumination variation effects on angle/azimuth-dependent image amplitudes largely removed.
49
Keho, T. H., i W. B. Beydoun. "Paraxial ray Kirchhoff migration". GEOPHYSICS 53, nr 12 (grudzień 1988): 1540–46. http://dx.doi.org/10.1190/1.1442435.
Pełny tekst źródłaStreszczenie:
A rapid nonrecursive prestack Kirchhoff migration is implemented (for 2-D or 2.5-D media) by computing the Green’s functions (both traveltimes and amplitudes) in variable velocity media with the paraxial ray method. Since the paraxial ray method allows the Green’s functions to be determined at points which do not lie on the ray, two‐point ray tracing is not required. The Green’s functions between a source or receiver location and a dense grid of thousands of image points can be estimated to a desired accuracy by shooting a sufficiently dense fan of rays. For a given grid of image points, the paraxial ray method reduces computation time by one order of magnitude compared with interpolation schemes. The method is illustrated using synthetic data generated by acoustic ray tracing. Application to VSP data collected in a borehole adjacent to a reef in Michigan produces an image that clearly shows the location of the reef.
50
Mulder, W. A., i R. ‐E Plessix. "A comparison between one‐way and two‐way wave‐equation migration". GEOPHYSICS 69, nr 6 (listopad 2004): 1491–504. http://dx.doi.org/10.1190/1.1836822.
Pełny tekst źródłaStreszczenie:
Results for wave‐equation migration in the frequency domain using the constant‐density acoustic two‐way wave equation have been compared to images obtained by its one‐way approximation. The two‐way approach produces more accurate reflector amplitudes and provides superior imaging of steep flanks. However, migration with the two‐way wave equation is sensitive to diving waves, leading to low‐frequency artifacts in the images. These can be removed by surgical muting of the input data or iterative migration or high‐pass spatial filtering. The last is the most effective. Iterative migration based on a least‐squares approximation of the seismic data can improve the amplitudes and resolution of the imaged reflectors. Two approaches are considered, one based on the linearized constant‐density acoustic wave equation and one on the full acoustic wave equation with variable density. The first converges quickly. However, with our choice of migration weights and high‐pass spatial filtering for the linearized case, a real‐data migration result shows little improvement after the first iteration. The second, nonlinear iterative migration method is considerably more difficult to apply. A real‐data example shows only marginal improvement over the linearized case. In two dimensions, the computational cost of the two‐way approach has the same order of magnitude as that for the one‐way method. With our implementation, the two‐way method requires about twice the computer time needed for one‐way wave‐equation migration.