scholarly journals DETERMINATION OF THE STACKING VELOCITY FIELD VIA OPTIMIZATION METHODS

2015 ◽  
Vol 33 (3) ◽  
pp. 503
Author(s):  
Danian Steinkirch De Oliveira ◽  
Milton José Porsani ◽  
Paulo Eduardo Miranda Cunha
Keyword(s):  
Genetic Algorithm ◽  
Velocity Field ◽  
Seismic Velocity ◽  
A Priori ◽  
Time Interval ◽  
Velocity Analysis ◽  
Seismic Processing ◽  
Velocity Models ◽  
Good Imaging ◽  
Seismic Image

ABSTRACT. We developed a strategy for automatic Semblance panels pick, that uses Genetic Algorithm optimization method. In conjunction with restrictions and penalties set from a priori information it’s obtained as a result a nonlinear fit of time interval velocities, that when converted at root mean square (RMS) velocity, better maximizes the sum of the Common Mid Point (CMP) group, corrected with normal moveout (NMO). Currently, a good imaging of deep reflectors, especially in Brazilian basins, below the salt layer, has proved to be a major challenge. Obtaining a seismic velocity field corresponding to the subsurface geology and resulting in a focused seismic image is the main target of seismic processing. In the last decade, the reflection tomography has established itself as one of the main methods of velocity model construction for seismic data migration. On the other hand the full waveform inversion (FWI), taken forward due to recent advances in computing, become feasible in inversion of 2D and 3D velocity models. Despite the stacking velocity analysis be, among these, the less accurate method for generating velocity fields, it is still used on a large scale by the oil and seismic processing companies, because of its low cost and can provide a good initial velocity field for tomography and FWI.Keywords: Genetic Algorithm, velocity analysis, Semblance.RESUMO. Foi desenvolvida uma estratégia de pick automático dos painéis de Semblance , que usa o método de otimização Algoritmo Genético. Em conjunto com restrições e sanções estabelecidas a partir de uma informação a priori, foi obtido como resultado um ajuste não-linear de velocidades intervalares em tempo, que quando convertidas em velocidade RMS, melhor maximiza a soma do grupo CMP, corrigida de NMO. Atualmente, provou ser um grande desafio a geração de uma boa imagem de refletores profundos, especialmente em bacias brasileiras abaixo da camada de sal. A obtenção de um campo de velocidades sísmica correspondente à geologia do subsolo, resultando em uma imagem sísmica focada é o principal alvo de processamento sísmico. Na última década, a tomografia de reflexão estabeleceu-se como um dos principais métodos de construção de modelo de velocidade de migração de dados sísmicos. Por outro lado, a inversão de onda completa (FWI) tomou a frente, devido aos seus excelentes resultados de inversão de modelos de velocidade 2D e 3D, que se tornaram viáveis somente pelos recentes avanços na computação. Apesar da análise de velocidade de empilhamento ser, entre estes, o método menos preciso para gerar campos de velocidade, ainda é utilizada em larga escala pelas companhias de petróleo e processamento sísmico, por causa do seu baixo custo e por poder proporcionar um bom campo de velocidade inicial para tomografia e FWI.Palavras-chave: Algoritmo Genético, análise de velocidade, Semblance.

High-resolution seismic velocity analysis by sign-based weighted semblance

Geophysics ◽  
2021 ◽  
pp. 1-35
Author(s):  
M. Javad Khoshnavaz
Keyword(s):  
Seismic Velocity ◽  
Resolution Enhancement ◽  
Synthetic Data ◽  
Correlation Coefficients ◽  
Velocity Model ◽  
Seismic Attenuation ◽  
Velocity Analysis ◽  
Velocity Models ◽  
Amplitude Versus Offset ◽  
Amplitude Versus

Building an accurate velocity model plays a vital role in routine seismic imaging workflows. Normal-moveout-based seismic velocity analysis is a popular method to make the velocity models. However, traditional velocity analysis methodologies are not generally capable of handling amplitude variations across moveout curves, specifically polarity reversals caused by amplitude-versus-offset anomalies. I present a normal-moveout-based velocity analysis approach that circumvents this shortcoming by modifying the conventional semblance function to include polarity and amplitude correction terms computed using correlation coefficients of seismic traces in the velocity analysis scanning window with a reference trace. Thus, the proposed workflow is suitable for any class of amplitude-versus-offset effects. The approach is demonstrated to four synthetic data examples of different conditions and a field data consisting a common-midpoint gather. Lateral resolution enhancement using the proposed workflow is evaluated by comparison between the results from the workflow and the results obtained by the application of conventional semblance and three semblance-based velocity analysis algorithms developed to circumvent the challenges associated with amplitude variations across moveout curves, caused by seismic attenuation and class II amplitude-versus-offset anomalies. According to the obtained results, the proposed workflow is superior to all the presented workflows in handling such anomalies.

Migration moveout analysis and depth focusing

Geophysics ◽  
1993 ◽  
Vol 58 (1) ◽  
pp. 91-100 ◽  
Author(s):  
Claude F. Lafond ◽  
Alan R. Levander
Keyword(s):  
Heterogeneous Media ◽  
A Priori ◽  
Complex Structure ◽  
Tomographic Reconstruction ◽  
Synthetic Data ◽  
Real Data ◽  
Velocity Model ◽  
Velocity Analysis ◽  
Data Set ◽  
Velocity Models

Prestack depth migration still suffers from the problems associated with building appropriate velocity models. The two main after‐migration, before‐stack velocity analysis techniques currently used, depth focusing and residual moveout correction, have found good use in many applications but have also shown their limitations in the case of very complex structures. To address this issue, we have extended the residual moveout analysis technique to the general case of heterogeneous velocity fields and steep dips, while keeping the algorithm robust enough to be of practical use on real data. Our method is not based on analytic expressions for the moveouts and requires no a priori knowledge of the model, but instead uses geometrical ray tracing in heterogeneous media, layer‐stripping migration, and local wavefront analysis to compute residual velocity corrections. These corrections are back projected into the velocity model along raypaths in a way that is similar to tomographic reconstruction. While this approach is more general than existing migration velocity analysis implementations, it is also much more computer intensive and is best used locally around a particularly complex structure. We demonstrate the technique using synthetic data from a model with strong velocity gradients and then apply it to a marine data set to improve the positioning of a major fault.

CSEM-regularized seismic velocity inversion: A multiscale, hierarchical workflow for subsalt imaging

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. B241-B252 ◽  
Author(s):  
Daniele Colombo ◽  
Diego Rovetta ◽  
Ersan Turkoglu
Keyword(s):  
Seismic Velocity ◽  
Fundamental Problem ◽  
Velocity Model ◽  
Seismic Inversion ◽  
Velocity Fields ◽  
Coupling Mechanism ◽  
Correct Result ◽  
Velocity Analysis ◽  
Velocity Inversion ◽  
Velocity Models

Seismic imaging in salt geology is complicated by highly contrasted velocity fields and irregular salt geometries, which cause complex seismic wavefield scattering. Although the imaging challenges can be addressed by advanced imaging algorithms, a fundamental problem remains in the determination of robust velocity fields in high-noise conditions. Conventional migration velocity analysis is often ineffective, and even the most advanced methods for depth-domain velocity analysis, such as full-waveform inversion, require starting from a good initial estimate of the velocity model to converge to a correct result. Nonseismic methods, such as electromagnetics, can help guide the generation of robust velocity models to be used for further processing. Using the multiphysics data acquired in the deepwater section of the Red Sea, we apply a controlled-source electromagnetic (CSEM) resistivity-regularized seismic velocity inversion for enhancing the velocity model in a complex area dominated by nappe-style salt tectonics. The integration is achieved by a rigorous approach of multiscaled inversions looping over model dimensions (1D first, followed by 3D), variable offsets and increasing frequencies, data-driven and interpretation-supported approaches, leading to a hierarchical inversion guided by a parameter sensitivity analysis. The final step of the integration consists of the inversion of seismic traveltimes subject to CSEM model constraints in which a common-structure coupling mechanism is used. Minimization is performed over the seismic data residuals and cross-gradient objective functions without inverting for the resistivity model, which is used as a reference for the seismic inversion (hierarchical approach). Results are demonstrated through depth imaging in which the velocity model derived through CSEM-regularized hierarchical inversion outperforms the results of a seismic-only derived velocity model.

High-resolution seismic velocity analysis as a tool for exploring gas hydrate systems: An example from New Zealand’s southern Hikurangi margin

2016 ◽  
Vol 4 (1) ◽  
pp. SA1-SA12 ◽  
Author(s):  
Gareth J. Crutchley ◽  
Guy Maslen ◽  
Ingo A. Pecher ◽  
Joshu J. Mountjoy
Keyword(s):  
High Resolution ◽  
Marine Sediments ◽  
Gas Hydrate ◽  
Seismic Data ◽  
Seismic Velocity ◽  
Coarse Grained ◽  
Velocity Analysis ◽  
Low Velocity ◽  
Free Gas ◽  
Velocity Models

The existence of free gas and gas hydrate in the pore spaces of marine sediments causes changes in acoustic velocities that overprint the background lithological velocities of the sediments themselves. Much previous work has determined that such velocity overprinting, if sufficiently pronounced, can be resolved with conventional velocity analysis from long-offset, multichannel seismic data. We used 2D seismic data from a gas hydrate province at the southern end of New Zealand’s Hikurangi subduction margin to describe a workflow for high-resolution velocity analysis that delivered detailed velocity models of shallow marine sediments and their coincident gas hydrate systems. The results showed examples of pronounced low-velocity zones caused by free gas ponding beneath the hydrate layer, as well as high-velocity zones related to gas hydrate deposits. For the seismic interpreter of a gas hydrate system, the velocity results represent an extra “layer” for interpretation that provides important information about the distribution of free gas and gas hydrate. By combining the velocity information from the seismic transect with geologic samples of the seafloor and an understanding of sedimentary processes, we have determined that high gas hydrate concentrations preferentially form within coarse-grained sediments at the proximal end of the Hikurangi Channel. Finer grained sediments expected elsewhere along the seismic transect might preclude the deposition of similarly high gas hydrate concentrations away from the channel.

DETERMINATION OF THE STACKING VELOCITY FIELD VIA OPTIMIZATION METHODS

2016 ◽  
Vol 33 (3) ◽  
Author(s):  
Danian Steinkirch de Oliveira ◽  
Milton José Porsani ◽  
Paulo Eduardo Miranda Cunha
Keyword(s):  
Genetic Algorithm ◽  
Velocity Field ◽  
A Priori ◽  
Optimization Methods ◽  
Optimization Method ◽  
A Priori Information ◽  
Algorithm Optimization ◽  
Genetic Algorithm Optimization ◽  
Priori Information

ABSTRACT. We developed a strategy for automatic Semblance panels pick, that uses Genetic Algorithm optimization method. In conjunction with restrictions and penalties set from a priori information... RESUMO. Foi desenvolvida uma estratégia de pick automático dos painéis de Semblance , que usa método de otimização Algorítmo Genético. Em conjunto com restrições...

scholarly journals Challenges and opportunities from large volume, multi-offset Ground Penetrating Radar data

2021 ◽  
Author(s):  
Dimitrios Angelis ◽  
Craig Warren ◽  
Nectaria Diamanti ◽  
James Martin ◽  
Peter Annan
Keyword(s):  
Wave Propagation ◽  
Electromagnetic Wave ◽  
Ground Penetrating Radar ◽  
Electromagnetic Wave Propagation ◽  
Survey Methods ◽  
Velocity Analysis ◽  
Seismic Processing ◽  
Velocity Models ◽  
Challenges And Opportunities ◽  
Ground Penetrating

<p>The most frequently used survey mode for acquiring Ground Penetrating Radar (GPR) data is common offset (CO) – where a single transmitter and receiver pair move along a survey line at a constant (offset) separation distance. This allows rapid and dense data acquisition, and therefore high-resolution large-scale investigations, to be carried out with relative ease, and at relatively low cost. However, it has long been known that multi-offset survey methods, such as common mid-point (CMP) and wide-angle reflection-refraction (WARR), can offer many benefits over CO: detailed subsurface EM wave velocity models; enhanced reflection sections with higher signal-to-noise ratio (SNR); the potential to adapt well-established advanced seismic processing schemes for GPR data [1-2].</p><p>Despite the advantages of multi-offset GPR data, these methods have seen limited adoption as, in the past, they required significantly more time, effort, and hence cost, to collect. However, recent advances in GPR hardware, particularly in timing and control technology, have enabled the development of multi-concurrent sampling receiver GPR systems such as the “WARR Machine” manufactured by Sensors & Software Inc. [3-4]. These newly developed GPR systems have the potential to provide all the aforementioned benefits with considerably less effort and therefore reduced survey cost, as they allow for the fast acquisition of multi-offset WARR soundings.</p><p>In this work, we look at the challenges and opportunities from collecting and processing multi-offset GPR data. We demonstrate a processing workflow that combines standard GPR processing approaches, with methods adapted from seismic processing, as well as our own algorithms. This processing framework has been implemented into a GUI-based software written in MATLAB [5], and has been tested using both synthetic [6] and real multi-offset GPR data. Some of the specific challenges with multi-offset GPR that we investigate are time zero misalignments, CMP balancing, velocity analysis, and automated velocity picking. We show how addressing these issues can result in improved velocity analysis, and ultimately in improved subsurface velocity models, and stacked sections.</p><p><strong>References</strong></p><p>[1] Ursin, B., 1983. Review of elastic and electromagnetic wave propagation in horizontally layered media. Geophysics, 48(8), pp.1063-1081.</p><p>[2] Carcione, J. and Cavallini, F., 1995. On the acoustic-electromagnetic analogy. Wave Motion, 21(2), 149-162.</p><p>[3] Annan, A. P., and Jackson, S., 2017. The WARR machine. 2017 9th International Workshop on Advanced Ground Penetrating Radar (IWAGPR).</p><p>[4] Diamanti, N., Elliott, J., Jackson, R. and Annan, A. P., 2018, The WARR Machine: System Design, Implementation and Data: Journal of Environmental & Engineering Geophysics, 23, pp.469-487.</p><p>[5] Angelis, D., Warren, C. and Diamanti, N., 2020. A software toolset for processing and visualization of single and multi-offset GPR data. 18th International Conference on Ground Penetrating Radar.</p><p>[6] Warren, C., Giannopoulos, A. and Giannakis, I., 2016. gprMax: Open source software to simulate electromagnetic wave propagation for Ground Penetrating Radar. Computer Physics Communications, 209, pp.163-170.</p>

Image-ray tracing for joint 3D seismic velocity estimation and time-to-depth conversion

Geophysics ◽  
2008 ◽  
Vol 73 (3) ◽  
pp. S99-S114 ◽  
Author(s):  
Einar Iversen ◽  
Martin Tygel
Keyword(s):  
Velocity Field ◽  
Seismic Velocity ◽  
A Priori ◽  
Velocity Model ◽  
Migration Velocity ◽  
Velocity Estimation ◽  
P Waves ◽  
Data Set ◽  
Time Migration ◽  
Elementary Waves

Seismic time migration is known for its ability to generate well-focused and interpretable images, based on a velocity field specified in the time domain. A fundamental requirement of this time-migration velocity field is that lateral variations are small. In the case of 3D time migration for symmetric elementary waves (e.g., primary PP reflections/diffractions, for which the incident and departing elementary waves at the reflection/diffraction point are pressure [P] waves), the time-migration velocity is a function depending on four variables: three coordinates specifying a trace point location in the time-migration domain and one angle, the so-called migration azimuth. Based on a time-migration velocity field available for a single azimuth, we have developed a method providing an image-ray transformation between the time-migration domain and the depth domain. The transformation is obtained by a process in which image rays and isotropic depth-domain velocity parameters for their propagation are esti-mated simultaneously. The depth-domain velocity field and image-ray transformation generated by the process have useful applications. The estimated velocity field can be used, for example, as an initial macrovelocity model for depth migration and tomographic inversion. The image-ray transformation provides a basis for time-to-depth conversion of a complete time-migrated seismic data set or horizons interpreted in the time-migration domain. This time-to-depth conversion can be performed without the need of an a priori known velocity model in the depth domain. Our approach has similarities as well as differences compared with a recently published method based on knowledge of time-migration velocity fields for at least three migration azimuths. We show that it is sufficient, as a minimum, to give as input a time-migration velocity field for one azimuth only. A practical consequence of this simplified input is that the image-ray transformation and its corresponding depth-domain velocity field can be generated more easily.

Nonlinear 3-D traveltime inversion of crosshole data with an application in the area of the Middle Ural Mountains

Geophysics ◽  
2001 ◽  
Vol 66 (2) ◽  
pp. 627-636 ◽  
Author(s):  
Pantelis M. Soupios ◽  
Constantinos B. Papazachos ◽  
Christopher Juhlin ◽  
Gregory N. Tsokas
Keyword(s):  
Seismic Velocity ◽  
Null Space ◽  
Fresnel Zone ◽  
A Priori ◽  
Synthetic Data ◽  
Real Data ◽  
Velocity Estimation ◽  
Three Dimensions ◽  
Ural Mountains ◽  
Velocity Models

This paper deals with the problem of nonlinear seismic velocity estimation from first‐arrival traveltimes obtained from crosshole and downhole experiments in three dimensions. A standard tomographic procedure is applied, based on the representation of the crosshole area into a number of cells which have an initial slowness assigned. For the forward modeling, the raypath matrix is computed using the revisited ray bending method, supplemented by an approximate computation of the first Fresnel zone at each point of the ray, hence using physical and not only mathematical rays. Since 3-D ray tracing is incorporated, the inversion technique is nonlinear. Velocity images are obtained by a constrained least‐squares inversion scheme using both “damping” and “smoothing” factors. The appropriate choice of these factors is defined by the use of appropriate criteria such as the L-curve. The tomographic approach is improved by incorporating a priori information about the media to be imaged into our inversion scheme. This improvement in imaging is achieved by projecting a desirable solution onto the null space of the inversion, and including this null‐space contribution with the standard non‐null‐space inversion solution. The efficiency of the inversion scheme is tested through a series of tests with synthetic data. Moreover, application in the area of the Ural Mountains using real data demonstrates that the proposed technique produces more realistic velocity models than those obtained by other standard approaches.

Linear aspects of tomographic velocity analysis

Geophysics ◽  
1991 ◽  
Vol 56 (4) ◽  
pp. 483-495 ◽  
Author(s):  
C. Stork ◽  
R. W. Clayton
Keyword(s):  
Inverse Problem ◽  
Velocity Field ◽  
A Priori ◽  
Complex Structure ◽  
Velocity Analysis ◽  
Inversion Problem ◽  
Reflection Seismology ◽  
Conceptual Tool ◽  
Wide Range ◽  
Ray Trace

Prestack velocity analysis in areas of complex structure is a coupled migration and transmission inversion problem that can be analyzed from a tomographic perspective. By making as few a priori assumptions about the solution as possible in parameterizing the inverse problem, generalized tomographic velocity analysis is applicable to a wide range of geologic cases. Constraints modify the method to the unique characteristics of each application. The ray trace/traveltime formulation for tomography, as proposed by Bishop et al. (1985), provides a conceptual tool for presenting features that are important to automated prestack velocity analysis in complex structure, such as (1) the coupling of the velocity field to the reflector positions, (2) the nonuniform coverage of the model by the data, (3) the ability to perform a controlled inversion of large matrices over a wide eigenvalue range, and (4) the implementation of constraints in the inversion. These features may impact other automated prestack velocity analysis methods for reflection seismology.

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