Tesi: "Full wavefrom inversion"

1

Guo, Gaoshan. "Inversion de la forme d'onde complète à source étendue dans le domaine temporel : théorie, algorithme et application". Electronic Thesis or Diss., Université Côte d'Azur, 2024. http://www.theses.fr/2024COAZ5014.

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Abstract (sommario):

La Full waveform inversion (FWI) est devenue la méthode d'imagerie de référence en exploration géophysique. FWI utilise les formes d'ondes complètes pour imager le sous-sol avec une résolution d'un demi longueur d'onde. Etant donné la dimension de l'espace des données et des modèles, la FWI est implémentée avec des méthodes d'optimisation locale sur un espace de recherche réduit où l'équation d'onde est résolue exactement à chaque itération. Cela requiert des modèles initiaux précis pour que les données simulées prédisent les données enregistrées sans saut de phase. Pour relâcher cette condition, plusieurs variantes de la FWI ont été proposées telles que les approches sur des espaces de recherche étendus. Parmi ces approches, la 'Wavefield Reconstruction Inversion (WRI)' implémente l'équation d'onde comme une contrainte faible pour ajuster les observables avec des champs d'onde calculées avec des sources étendues. Les extensions de sources sont estimées en ajustant au sens des moindres carrés la différence entre les données enregistrées et simulées traitées comme les données diffractées enregistrées. Il en résulte que ces sources volumiques sont calculées par renversement temporel (retro-propagation) des résidus déconvolués par le Hessien dans l'espace des données. Cette approche est nommée 'extended-source' FWI (ES-FWI).Dans cette thèse, je développe un algorithme opérationnel pour la ES-FWI. Le premier problème est le calcul des sources volumiques où la déconvolution des résidus par le Hessien est coûteuse. Des études précédentes approximent ce Hessien avec une matrice diagonale ce qui peut suffire dans des contextes favorables mais sujet à des minimums secondaires dans des milieux complexes. Je propose d'approximer l'inverse du Hessien par des filtres de Wiener/Gabor. Des tests numériques sur le modèle Marmousi II démontrent les améliorations apportées par ces filtres comparativement à l'approximation diagonale. Les champs d'ondes calculés avec l'assimilation des données ont une précision qui diminue loin des points de mesure ce qui peut piéger l'inversion dans des minimums secondaires. Pour améliorer la robustesse de la méthode, j'ai implémenté des opérateurs de pondération dans l'espace des données pour injecter progressivement des donnés plus complexes dans l'inversion et reconstruire le milieu de la surface vers les niveaux profonds. Cette approche de 'layer stripping' est illustrée avec les géomodèles complexes 2004 BP Salt et GO3DOBS.La ES-FWI est une forme généralisée de la FWI où l'inverse du Hessien du problème de source est utilisé comme une matrice de pondération dans l'espace des données. Cela engendre une décomposition du Hessien en un opérateur diagonal dans le domaine des sources et un opérateur par source dans l'espace des données représentant le Hessien du problème de source évoqué ci dessus. Je montre comment ré-utiliser cette décomposition dans la FWI pour développer une approximation du Hessien Gauss-Newton qui puisse être calculée efficacement tout en accélérant la convergence de la FWI. Alternativement, l'approximation proposée peut être utilisée comme préconditioneur pour des algorithmes de quasi-Newton.Finalement, j'étends l'application de la reconstruction des champs d'onde avec assimilation des données au problème de ‘redatuming'. Cette application requiert des champs d'ondes de haute précision si bien que j'implémente la déconvolution des données diffractées avec le solveur itératif MINRES plutôt qu'avec des filtres de Gabor. L'approche consiste simplement à calculer les champs d'onde avec l'assimilation des données et à les échantillonner sur la surface d'acquisition virtuelle. Cette approche est précise lorsqu'on connaît le milieu situé entre les surfaces définies par les acquisitions réelle et virtuelle. Le ‘redatuming' des sources et des capteurs peuvent être couplés. Cette approche est illustrée avec des géomodèles marins et terrestres et avec un jeu de données réels de fond de mer
Full waveform inversion (FWI) has emerged as the baseline seismic imaging method in exploration geophysics. Given the size of the data and model spaces, FWI relies on iterative local optimization methods and reduced search space where the wave equation is strictly satisfied at each iteration. This framework requires an accurate initial model allowing for the simulated data to match the recorded data with kinematic errors less than half the period to avoid cycle skipping. To mitigate cycle skipping, several variants of FWI have been developed over the last decade such as extended-space FWI where degrees of freedom are added to the forward problem. Among them, the wavefield reconstruction inversion (WRI) implements the wave equation as a soft constraint to match the data by combining a wave-equation relaxation with data assimilation. While WRI has been initially implemented in the frequency domain where the data-assimilated wavefields can be computed with linear algebra methods, the time-domain implementation with explicit time-marching schemes has proven challenging. It was recently recognized that the source extensions generated by the wave-equation relaxation are the least-squares solutions of the scattered-data fitting problem. As such, they are computed by backward modeling of deconvolved FWI data residuals by the data-domain Hessian. This reformulation of the wavefield reconstruction as a scattering source reconstruction has led to the extended-source FWI (ES-FWI).In this thesis, I develop a practical algorithm for ES-FWI. Firstly, I focus on the efficient computation of the source extensions where the deconvolution of the data residuals by the data-domain Hessian is the main computational bottleneck. Previous studies implement the Hessian with a scaled identity matrix, which is acceptable in certain favorable scenarios but prone to failure in complex media. I propose a more accurate approximation of the inverse Hessian with various matching filters such as 1D/2D Wiener and Gabor filters. Numerical tests conducted on the Marmousi II model show the relevance of these approximations. Moreover, the data-assimilated wavefields primarily consist of the ‘migration/demigration' of the recorded data. Accordingly, their accuracy diminishes away from the receivers, which can drive the inversion towards spurious minima in particular when surface multiples are involved in the inversion. To address this issue, I design a weighting operator based on time-offset windowing in the data misfit function to inject progressively more complex data in the inversion and reconstruct the medium from the shallow parts to the deep ones. The application of the BPsalt model illustrates the relevance of this layer-stripping scheme in a very challenging context.ES-FWI can be recast as a generalized FWI, where the data misfit function is weighted by the inverse data-domain Hessian of the source extension problem. This leads to a decomposition of the Gauss-Newton (GN) Hessian into a diagonal source-side Hessian and source-dependent receiver-side data-domain Hessians. I use this decomposition to propose a computationally efficient approximation of the GN Hessian. I approximate the inverse Hessian with 2D Gabor matching filters, which can be readily used as an approximation of the GN Hessian or as a preconditioner for the quasi-Newton method. Numerical tests demonstrate the improved convergence speed of FWI provided by this Hessian.Finally, I extend the application of the data-assimilated wavefield reconstruction towards seismic redatuming, where highly-accurate wavefield reconstruction is necessary. This prompts me to use the iterative solver to perform the deconvolution of the scattered data. Using reciprocity, I can chain source and receiver redatuming. Numerical tests and application to ocean-bottom seismic data validate the effectiveness of the proposed method

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2

Thomassen, Espen. "Full-waveform inversion studies". Thesis, Norwegian University of Science and Technology, Department of Electronics and Telecommunications, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9722.

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In this master thesis, full-waveform inversion (FWI) was applied to a synthetic, and very complex, geological structure containing a salt body. The main objective was to evaluate the capabilities of FWI to estimate velocities in this context, and more specially below the salt. Seismic depth imaging is now the preferred seismic imaging tool for today's most challenging exploration projects. Seismic depth imaging problem usually requires the definition of a smooth background velocity model before determining the short wavelength component of the structure by pre-stack depth migration. It is well established that success of pre-stack depth migration in complex geological media strongly depends from the definition of the background velocity model. Standard tools for building velocity models generally fail to reconstruct the correct sub-salt velocities. Sub-salt imaging is a very challenging problem and a lot of resources are spent trying to solve this problem, since salt bodies in the sub-surface are known to be very good hydrocarbon traps. In this master thesis, the work have been performed on a modified version of the 2004 BP velocity benchmark model. This model represents a very interesting salt context, where conventional imaging methods can not provide any good results. After describing the seismic inversion problem, and the FWI theory and code used in this work, the application to the 2004 BP benchmark model is described. FWI was first applied to the synthetic data using a starting model derived by smoothing the true velocity model. This is an easy way to ensure an adequate starting model, as the method is very dependent on a good starting model. In the inversion process 17 frequency components were used, ranging between 1 and 15 Hz. This resulted in a velocity model that accurately recovered both the salt body and the sub-salt velocities. The average deviation between the true and estimated sub-salt velocities was found to be approximately 6 %. A more realistic starting model was then derived using first-arrival traveltime tomography, a well known method for obtaining velocity models. FWI was applied to this starting model, and the result was also positive when using this starting model. The salt body was well delineated, whereas the sub-salt velocities were generally more inaccurate than for the previous application. The sub-salt velocity difference was increased to roughly 10 %. However, if more effort had been spent on reconstructing a more accurate starting model, the results might have improved. When fewer frequency components are used in the inversion, the result declined. A test using only 6 frequency components showed that the final reconstructed model suffered from a lack of recovered wavenumbers, especially at the deeper and more complex parts of the model. In such a complex medium as the 2004 BP benchmark model, it is hence necessary to introduce wavenumbers by including a sufficient number of frequency components in the inversion process. Other tests that were conducted showed that, in this particular case, the non-linearity of the inversion problem increased with higher frequencies, and was reduced by larger offset ranges included in the seismic data. The inversion is hence sensitive to the starting frequency as well as the starting model. The results in this master thesis demonstrate that FWI has a great potential in reconstructing sub-salt velocities in salt media. For the future, both applying the method to real data from a salt basin area, and develop a migration tool and test the effect of FWI on a migrated image, are interesting challenges.

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3

Irabor, Kenneth Otabor. "Reflection full waveform inversion". Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/60594.

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Abstract (sommario):

The Full Waveform Inversion (FWI) gradient is composed of a low wavenumber tomographic component and a high wavenumber migration component. A successful application of FWI requires that the low wavenumber parts of the model be recovered before the high wavenumbers. This process becomes difficult in datasets dominated by pre-critical angle reflection energies. Reflection waveform inversion (RWI) has been proposed as an alternative to help bootstrap the FWI method for reflection data. In this thesis, I have made a novel contribution to RWI using Finite Di fference Explicit Wavefi eld Decomposition (FDEWD). This method improves the wavefi eld decomposition process by cleanly decomposing the wavefi elds into four components using fi nite diff erence method and Fourier transform. Four component wavefi elds travelling left, right, up and down are simultaneously derived in this method compared to just opposite directions possible with most other methods. FDEWD also lacks the evanescent energy present in traditional Fourier based separation. The extra layer of separation introduced by FDEWD ensures that the tomographic component of the gradient is formed by energies propagating within and close to the first Fresnel zone, hence yielding a cleaner tomographic update. The FDEWD method developed here was then used in an RWI context to successfully invert a synthetic dataset and a blind dataset. The scheme involved a migration update step with an exaggerated step length and a tomographic update step with true step length computation. The results obtained shows that the new method produces superior results compared to the method based on direct separation of the total wavefi elds. FDEWD also allows for transmission FWI to be performed without the need to mute the data in any way. We have implemented the scheme here in a 2-D constant density acoustic wave equation. It is, however, possible to extend this method to 3-D, anisotropic and elastic problems.

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4

Guasch, Lluis. "3D elastic full-waveform inversion". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9974.

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Full Waveform Inversion (FWI) is a depth imaging technique that takes advantage of the full information contained in recorded seismic data. FWI provide high resolution images of subsurface properties, usually seismic velocities or related parameters, although in theory it could image any property used to formulate the wave equation. The computational cost of the methodology has historically limited its application to 3D acoustic approximations but recent developments in hardware capabilities have increased computer power to the point that more realistic approximations are viable. In this work the traditional acoustic approximation is extended to include elastic effects by introducing the elastic wave equation as the governing law that describes wave propagation. I have developed a software based on finite-differences to solve the elastic wave equation in 3D, which I applied in the development of a full-waveform inversion algorithm. The software is fully parallelised for both distributed and shared-memory systems. The first level of parallelisation distributes seismic sources across cluster nodes. Each node solves the 3D elastic wave equation in the whole computational domain. The second level of parallelisation takes advantage of present multi-core computer processor units (CPU) to decompose the computational domain into different volumes that are solved independently by each core. Such parallel design allows the algorithm to handle models of realistic sizes, increasing the computational times only a factor of two compared to those of 3D acoustic full-waveform inversion on the same mesh. I have also implemented a perfectly matched layer absorbing boundary condition to reproduce a semi-infinite model geometry and prevent spurious reflections from the model boundaries from contaminating the modelled wavefields. The inversion algorithm is based upon the adjoint-state method, which I reformulated for the wave equation that I implemented, which was based on particle-velocities and stresses, providing a comparison and demonstration of equivalence with previous developments. To examine the performance of the code, I have inverted several synthetic problems of increasing realism. I have principally used only pressure sources and receivers to assess the potential of the method's application to the most common industry surveys: streamer data for offshore and vertical geophones (only one component) for onshore exploration surveys. The results show that the imaged properties increase with the heterogeneity of the models, due to the increase in P-S-P conversions which provides the main source of information to invert shear-wave velocity models from pressure sources and receivers. It remains to demonstrate the inversion of field datasets and my future research project will focused on achieving this goal.

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5

Debens, Henry Alexander. "Three-dimensional anisotropic full-waveform inversion". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/32407.

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Full-waveform inversion (FWI) is a powerful nonlinear tool for quantitative estimation of high-resolution high-fidelity models of subsurface seismic parameters, typically P-wave velocity. A solution is obtained via a series of iterative local linearised updates to a start model, requiring this model to lie within the basin of attraction of the solution space's global minimum. The consideration of seismic anisotropy during FWI is vital, as it holds influence over both the kinematics and dynamics of seismic waveforms. If not appropriately taken into account, then inadequacies in the anisotropy model are likely to manifest as significant error in the recovered velocity model. Conventionally, anisotropic FWI either employs an a priori anisotropy model, held fixed during FWI, or uses a local inversion scheme to recover anisotropy as part of FWI; both of these methods can be problematic. Constructing an anisotropy model prior to FWI often involves intensive (and hence expensive) iterative procedures. On the other hand, introducing multiple parameters to FWI itself increases the complexity of what is already an underdetermined problem. As an alternative I propose here a novel approach referred to as combined FWI. This uses a global inversion for long-wavelength acoustic anisotropy, involving no start model, while simultaneously updating P-wave velocity using mono-parameter local FWI. Combined FWI is then followed by multi-parameter local FWI to recover the detailed final model. To validate the combined FWI scheme, I evaluate its performance with several 2D synthetic datasets, and apply it to a full 3D field dataset. The synthetic results establish the combined FWI, as part of a two-stage workflow, as more accurate than an equivalent conventional workflow. The solution obtained from the field data reconciles well with in situ borehole measurements. Although combined FWI includes a global inversion, I demonstrate that it is nonetheless affordable and commercially practical for 3D field data.

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6

Kamath, Nishant. "Full-waveform inversion in 2D VTI media". Thesis, Colorado School of Mines, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10116167.

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Full-waveform inversion (FWI) is a technique designed to produce a high-resolution model of the subsurface by using information contained in entire seismic waveforms. This thesis presents a methodology for FWI in elastic VTI (transversely isotropic with a vertical axis of symmetry) media and discusses synthetic results for heterogeneous VTI models.

First, I develop FWI for multicomponent data from a horizontally layered VTI model. The reflectivity method, which permits computation of only PP reflections or a combination of PP and PSV events, is employed to model the data. The Gauss-Newton technique is used to invert for the interval Thomsen parameters, while keeping the densities fixed at the correct values. Eigenvalue/eigenvector decompostion of the Hessian matrix helps analyze the sensitivity of the objective function to the model parameters. Whereas PP data alone are generally sufficient to constrain all four Thomsen parameters even for conventional spreads, including PS reflections provides better constraints, especially for the deeper part of the model.

Next, I derive the gradients of the FWI objective function with respect to the stiffness coefficients of arbitrarily anisotropic media by employing the adjoint-state method. From these expressions, it is straightforward to compute the gradients for parameters of 2D heterogeneous VTI media. FWI is implemented in the time domain with the steepest-descent method used to iteratively update the model. The algorithm is tested on transmitted multicomponent data generated for Gaussian anomalies in Thomsen parameters embedded in homogeneous VTI media.

To test the sensitivity of the objective function to different model parameters, I derive an an- alytic expression for the Fréchet kernel of FWI for arbitrary anisotropic symmetry by using the Born approximation and asymptotic Green’s functions. The amplitude of the kernel, which represents the radiation pattern of a secondary source (that source describes a perturbation in a model parameter), yields the angle-dependent energy scattered by the perturbation. Then the radiation patterns are obtained for anomalies in VTI parameters embedded in isotropic homogeneous media and employed to analyze the inversion results for the transmission FWI experiments.

To understand some of the challenges posed by data recorded in surface surveys, I generate the multicomponent wavefield for a model based on a geologic section of the Valhall Field in the North Sea. A multiscale approach is adopted to perform FWI in the time domain. For the available offset range, diving-wave energy illuminates the top 1.5 km of the section, with the updates in the deeper regions due primarily to the reflections. FWI is tested for three model parameterizations and the results are explained in terms of the P- and SV-radiation patterns described above. These parameterizations lead to different trade-offs, and the choice of parameterization for a given data set depends on the recorded offset range, the quality of the initial model, and the parameter that needs to be recovered most accurately.

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7

Li, Xiang. "Sparsity promoting seismic imaging and full-waveform inversion". Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54255.

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This thesis will address the large computational costs of solving least-squares migration and full-waveform inversion problems. Least-squares seismic imaging and full-waveform inversion are seismic inversion techniques that require iterative minimizations of large least-squares misfit functions. Each iteration requires an evaluation of the Jacobian operator and its adjoint, both of which require two wave-equation solves for all sources, creating prohibitive computational costs. In order to reduce costs, we utilize randomized dimensionality reduction techniques, reducing the number of sources used during inversion. The randomized dimensionality reduction techniques create subsampling related artifacts, which we mitigate by using curvelet-domain sparsity-promoting inversion techniques. Our method conducts least-squares imaging at the approximate cost of one reverse-time migration with all sources, and computes the Gauss-Newton full-waveform inversion update at roughly the cost of one gradient update with all sources. Finally, during our research of the full-waveform inversion problem, we discovered that we can utilize our method as an alternative approach to add sparse constraints on the entire velocity model by imposing sparsity constraints on each model update separately, rather than regularizing the total velocity model as typically practiced. We also observed this alternative approach yields a faster decay of the residual and model error as a function of iterations. We provided empirical arguments why and when imposing sparsity on the updates can lead to improved full-waveform inversion results.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

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8

Roberts, Mark Alvin. "Full waveform inversion of walk-away VSP data". Paris, Institut de physique du globe, 2007. http://www.theses.fr/2007GLOB0020.

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Du fait de l’épuisement des réserves de pétrole, l’exploration et la production sont réalisées dans des environnements de plus en plus complexes. Faire de l’imagerie sismique sous le sel allochtone (par exemple dômes de sel) demeure une tâche difficile à cause du fait contraste de vitesse dentre le sel et les sédiments voisins et les structures très complexes produites par les déplacements de sel. Les nappes de sel allochtone couvrent de nombreuses régions potentiellement productives dans l’offshore profond du Golfe du Mexique. Forer la base du sel est une tâche extrêmement difficile en raison des pressions de pore fortement variables que l’on recontre dans les sédiments sous le sel. Des méthodes sismiques pour estimer la vitesse des ondes sismiques peuvent être employées en même temps que des formules empiriques pour prévoir la pression de pore. Cependant, il est souvent impossible de mesures précises depuis la surface, et nous avons donc employé des données VSP (Vertical Seismic Profile) “walk-away” cela implique d’effectuer plusieurs tirs sismique à diverses distances du forage (géneralement avec un dispositif de canons á air) tout en enregistrement les vitesses mesurees par des geophones placés à des profondeurs appropriées dans le forage. Avant cette thèse, les données étaient traitées en utilisant l’information d’amplitude en fonction de l’angle dans un simple approximation 1D ou en utilisant l’information de temps de parcours (également avec une approximation 1D). Dans cette thèse, j’ai effectué une inversion 2D de forme d’onde pour résoudre le problème d’estimation des vitesses. Cela a l’avantage d’inverser simultanément l’ensemble des données (comprenant les ondes transmises, les ondes refléchies et les ondes converties) et la méthode inclut l’information de temps de parcours et d’amplitude. L’inversion a été exécute avec des méthodes locales d’inversion du fait de la taille du problème inverse et de la difficulté du problème direct. Les problèmes liés aux grandes variations de le sensibilité inhérents à l’acquisition de données, ont conduit à un examen de la méthode de Gauss- Newton et à des matrices, de préconditionnement possibles pour la méthode du gradient conjugué. En raison de la nature mal contrainte du problème inverse, une régularisation a été appliquée avec une méthode de préconditionnement innovatrice. La méthodologie a été appliquée à des données réelles et la pression de pore a été prédite en utilisant l’équation bien établie de Eaton. En outre, les structures sous le sel ont été déterminées, confirment ainsi l’efficacité de cette technique
Depletion of the earth’s hydrocarbon reserves has led to exploration and production in increasingly complex environments. Imaging beneath allochthonous salt (e. G. Salt domes) remains a challenging task for seismic techniques due to the large velocity contrast of the salt with neighbouring sediments and the very complex structures generated by salt movement. Extensive allochthonous salt sheets cover many potentially productive regions in the deep-water Gulf of Mexico. Drilling through the base of salt is an extremely challenging task due to widely varying pore-pressure found in the sediments beneath. Seismic methods to estimate the seismic velocity can be used in conjunction with empirical formula to predict the pore pressure. However, accurate measurements are often not possible from surface reflection seismic data, so walk-away Vertical Seismic Profile (VSP) data has been used. This involves repeatedly firing a seismic source at various distances from the borehole (usually an airgun array) while recording the velocities measured by geophones in the borehole placed at appropriate depths near the base of the salt. Before this thesis, the data had been processed using the amplitude versus angle information in a simple one-dimension approximation or using travel time information (also using a 1D assumption). In this thesis, I have used 2D full waveform inversion to tackle the problem of velocity estimation. This has the advantage of simultaneously inverting the whole dataset (including transmitted waves, reflected waves, converted waves) and the method includes traveltime and amplitude information. The inversion was performed using local inversion methods due to the size of the inverse problem and the cost of the forward problem. Concerns over large sensitivity variations, that are inherent in the data acquisition, have lead to an examination of the Gauss-Newton method and possible preconditioning matrices for the conjugate gradient method. Due to the poorly constrained nature of the inverse problem, a smoothness constraint has been applied with an innovative preconditioning method. The methodology has been applied to real data and the pore pressure has been predicted using the well established Eaton equation. In addition, the sub-salt structure was recovered, further demonstrating the value of this technique

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9

Al-Yaqoobi, Ahmed Musallam Ali. "Full-waveform inversion to 3D seismic land data". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/10927.

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Abstract (sommario):

Full-waveform inversion (FWI) is a technique that seeks to find a high-resolution high-fidelity model of the Earth's subsurface that is capable of matching individual seismic waveforms, within an original raw field dataset, trace by trace. The method begins from a best-guess starting model, which is then iteratively improved using a sequence of linearized local inversions to solve a fully non-linear problem. In principle, FWI can be used to recover any physical property that has an influence upon the seismic wavefield, but in practice the technique has been used predominantly to recover P-wave velocity, and this is the route that is followed here. Full-waveform tomographic techniques seek to determine a highly resolved quantitative model of the sub-surface that will ultimately be able to explain the entire seismic wavefield including those phases that conventional processing and migration seek to remove such as refracted arrivals. Although the underlying theory of FWI is well established, its practical application to 3D land data, and especially to seismic data that have been acquired using vibrators, in a form that is effective and robust, is still a subject of intense research. In this study, 2D and 3D FWI techniques have been applied to a vibrator dataset from onshore Oman. Both the raw dataset and the subsurface model cause difficulties for FWI. In particular, the data are noisy, have weak early arrivals, are strongly elastic, and especially are lacking in low-frequency content. The Earth model appears to contain shallow low-velocity layers, and these compromise the use of first-arrival travel-time tomography for the generation of a starting velocity model. The 2D results show good recovery of the shallow part of the velocity models. The results show a low-velocity layer that extends across the velocity model, but lacking in a high-resolution image due to the absence of the third dimension. The seismograms of the final inversion models give a good comparison with the field data and produce a reasonably high correlation coefficient compared to the starting model. An inversion scheme has been developed in this study in which only data from the shorter offsets are initially inverted since these represent the subset of the data that is not cycle skipped. The offset range is then gradually extended as the model improves. The final 3D model contains a strongly developed low-velocity layer in the shallow section. The results from this inversion appear to match p-wave logs from a shallow drill hole, better flatten the gathers, and better stack and migrate the reflection data. The inversion scheme is generic, and should have applications to other similar difficult datasets.

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10

Egorov, Anton. "Full waveform inversion of time-lapse VSP data". Thesis, Curtin University, 2018. http://hdl.handle.net/20.500.11937/79285.

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Abstract (sommario):

Vertical seismic profile (VSP) is one of the technologies for monitoring hydrocarbon production and CO2 geosequestration. However, quantitative interpretation of time-lapse VSP is challenging due to its irregular distribution of source-receiver offsets. One way to overcome this challenge is to use full waveform inversion (FWI), which does not require regular offsets. We present a workflow of elastic FWI applied to offset vertical seismic profile data for the purpose of identification and estimation of time-lapse changes introduced by injection of 15,000 t of CO2-rich gas mixture at 1.5 km depth. Application of this workflow to both synthetic and field data shows that elastic FWI is able to detect and quantify the time-lapse anomaly in P wave velocity with the magnitude of 100–150 m/s.

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11

Fichtner, Andreas. "Full seismic waveform inversion for structural and source parameters". Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-114940.

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12

Calderon, Agudo Oscar. "Acoustic full-waveform inversion in geophysical and medical imaging". Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/62620.

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Abstract (sommario):

Imaging methods are employed in multiple scientific disciplines to obtain properties of targets that are otherwise invisible to the human eye, such as for imaging the earth’s interior or the human body. In geophysics, the full-waveform inversion (FWI) method is often used to recover high-quality high-fidelity models of the subsurface by recording seismic data in the field, and modelling wave propagation with a wave equation. But the visco-elastic nature of the subsurface is typically ignored, and the acoustic approximation of the wave equation is utilised to reduce the compute costs. This results in less well-resolved and inaccurate models, as accurate physics of wave propagation is not considered. On the contrary, the application of FWI to medical imaging is still in its infancy, especially in 3D. Instead, ray-based tomographic methods are used, which do not ac- count for the physics of finite-frequency wave propagation, leading to poorer recovered models of physical properties. Here, I first propose a method to address elastic and viscous effects in FWI of seismic data, which is based on the use of matching filters and modelling elastic or viscous wave propagation prior to the inversion, while using the acoustic wave equation during the inversion. This represents a considerable time reduction over full elastic or viscous inversions. I show that the proposed method leads to more accurate and detailed P-wave velocity subsurface models, both on synthetic and field datasets. Then, I investigate the feasibility of 3D FWI for breast cancer diagnosis and analyse, for the first time, its implementation to obtain 3D images of the human brain with ultrasound through the skull. The results demonstrate FWI is now ready to be applied to these datasets, and could result in more accurate images and faster and safer acquisitions than with current methods.

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13

Thurin, Julien. "Uncertainties estimation in Full Waveform Inversion using Ensemble methods". Thesis, Université Grenoble Alpes, 2020. https://tel.archives-ouvertes.fr/tel-02570602.

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L'inversion de forme d'onde complète (FWI) est une méthode d'inversion non-linéaire qui a pour but l'obtention de modèles précis des propriétés physiques du sous-sol terrestre. Ces modèles, véritables cartes de propriétés physiques, sont indispensables pour l'exploration et l'étude des structures internes de la Terre.Généralement formulée sous la forme d'un schéma d'optimisation par la méthode des moindres carrés, la FWI compare des enregistrements sismiques observés en surface, avec des données synthétiques calculées à partir d'un modèle numérique de sous-sol. Alors qu'une infinité de modèles peut potentiellement expliquer les observations, la FWI, du fait de sa formulation, ne permet d'obtenir qu'un seul modèle du sous-sol fortement conditionné par le choix de modèle de départ. À cette ambiguïté s'ajoute la difficulté d'estimer l'incertitude de la solution, à cause du coût de calcul prohibitif de la FWI. La non-unicité de la solution et le manque de moyens d'estimation d'incertitude rend l'exploitation des modèles de FWI compliquée.Dans cette thèse, nous proposons une méthode non conventionnelle et abordable, intégrant l’estimation d’incertitude au coeur de la solution de FWI. Notre méthode combine la FWI conventionnelle et l’assimilation de données par méthodes d’ensemble. De ce fait, elle tire avantage de la vitesse de convergence de la FWI conventionnelle, ainsi que des capacités d'estimation d'incertitude du Filtre de Kálmán d'Ensemble dit "Transform" (ETKF). Cette combinaison est permise par les fondements théoriques communs aux problèmes d'optimisation en FWI conventionnelle et au filtrage bayésien de l'ETKF. Nous utilisons ce schéma, l’ETKF-FWI, afin de transposer le problème de FWI dans le cadre de l'inférence Bayésienne locale. Au lieu d’une unique solution, l’ETKF-FWI retourne un ensemble de modèles qui permet à la fois de calculer la meilleure solution au sens des moindres carrés, mais aussi l'information d’incertitude et de résolution associée à chaque paramètre. Cette estimation d’incertitude est rendue possible par l’approximation de bas-rang de la matrice de covariance a posteriori, calculée à partir de l’ensemble. Les valeurs de variance permettent d’évaluer le degré de variabilité de la solution au sein de l’ensemble. La résolution est quant à elle, donnée par les termes hors diagonaux de la matrice de corrélation, qui est préférée à la matrice de covariance pour sa nature adimensionnelle.L'application de l'ETKF-FWI à deux cas d'études (un test synthétique et une application sur données de terrain) nous permet d'évaluer la faisabilité, ainsi que les limites de notre technique. Malgré le coût de calcul important lié à la représentation d’ensemble, cette stratégie permet une implémentation complètement parallèle, la rendant avantageuse au regard des solutions existant dans la littérature.Ces tests nous permettent d’évaluer l’influence de la taille de l’ensemble sur l’estimation de la variance, en caractérisant le biais de sous-échantillonnage associé aux petits ensembles. Bien que ce biais soit classiquement corrigé grâce aux méthodes d’inflation d’ensemble, celles-ci ne semblent pas adaptées à l’ETKF-FWI, limitant l’estimation d’incertitude à des évaluations qualitatives. De plus, la complexité de l’application sur données de terrain impacte la création de l’ensemble initial, ce qui influence directement les capacités de l’ETKF-FWI à produire une estimation quantitative de l’incertitude.Nous terminons par l’application de l'ETKF-FWI à une inversion de plusieurs paramètres physique (vitesse des ondes P et densité), considéré comme un défi majeur en FWI conventionnelle. Ce test nous permet d’évaluer qualitativement les liens de corrélation et d'ambiguïté entre vitesse et densité, ainsi que leurs incertitude et résolution respectives. De plus, le modèle moyen issu de l’ETKF-FWI semble être de qualité supérieure, ce qui laisse supposer d’un possible effet de préconditionnement fourni par la covariance
Full Waveform Inversion (FWI) is an ill-posed non-linear inverse problem, aiming at recovering detailed pictures of subsurface physical properties, which are crucial to explore and understand Earth structures.Classically formulated as a least-squares optimization scheme, FWI yields a single subsurface model amongst an infinite possibility of solutions. With the general lack of systematic and scalable uncertainty estimation, this formulation makes interpretation of FWI's outcomes complex.In this thesis, we propose an unconventional, scalable way of tackling the lack of uncertainty estimation in FWI, thanks to data assimilation ensemble methods. We develop a scheme combining both classical FWI and the Ensemble Transform Kalman Filter, that we call ETKF-FWI, and which is successfully applied on two 2-D test cases. This scheme takes advantage of the theoretical common-ground between least-squares optimization problems and Bayesian filtering. We use it to recast FWI in a local Bayesian inference framework, thanks to the ensemble representation. The ETKF-FWI provides high-resolution subsurface tomographic models and yields a low-rank approximation of the posterior covariance, holding the uncertainty and resolution information of the proposed solution. We show how the ETKF-FWI can be applied to qualitatively evaluate uncertainty and resolution of the solution. Instead of providing a single solution, the filter yields an ensemble of models, from which statistical information can be inferred.Uncertainty is evaluated from the ensemble's variance, which relates to the diversity of solution amongst the ensemble members for each parameter. We show that lines of the correlation matrix are ideal to evaluate qualitatively parameters resolution, thanks to their adimentionality. While the methodology is computationally intensive, it has the benefit of being fully scalable. Its applicability is demonstrated on a synthetic benchmark. This preliminary test allows us to assess the sensitivity of the ensemble representation to the common undersampling bias encountered in ensemble data assimilation. While undersampling does not affect the image reconstruction in any way, it results in variance underestimation, which makes the whole exercise of quantitative uncertainty assessment complicated. Ensemble inflation has been used to mitigate this bias, but does not seems to be a practical solution.A field data experiment is also discussed in this thesis. It makes it possible to test the sensitivity of the ETKF-FWI to complex noise structure and realistic physics. As it stands, the complexity of the problem reduces flexibility in the ensemble generation, and hence on the uncertainty estimate. Despite these limitations, results are consistent with the synthetic benchmark, and we are able to provide a qualitative uncertainty assessment. The field data case also allows us to evaluate the possibilities to use the ETKF-FWI on multiparameter inversion, which is still regarded as a challenging topic in FWI. The ETKF-FWI multiparameter inversion yields improved models compared with conventional ones. More importantly, it makes it possible to assess the uncertainty associated with parameters cross-talks

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Shah, Nikhil. "Seismic 'Full Waveform Inversion' of wrapped and unwrapped phase". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24849.

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Full Waveform Inversion (FWI) is a highly promising but far from robust and stable optimisation for computing the subsurface velocity model from seismic data acquired with long offsets and low frequencies. Mathematically, it solves the non-linear problem of matching model-predicted data to observed data with an iterative localised minimisation of the misfit. Therefore it is necessarily restricted by the need for an accurate starting model. In this thesis, we look at being able to relax the constraints on the starting model in FWI, obtain lower wavenumber updates from FWI, and in the process distinguish between adequate and inadequate starting models. Our approach here is to precede the conventional Born-based iterations with Rytov-based iterations which isolate discrete frequency phase. Here the misfit function being minimised is the norm of the phase residual which measures the difference in phase between observed and predicted data. Our treatment of the phase residual differs from previous work in two specific ways: i) we define the time-weighted phase residual, ii) we unwrap the residual thereby accounting for errors greater than half a cycle or 'cycle-skipped'. Previous work did (i) using the Laplace-Fourier domain i.e. using an exponential function. Here we use a more versatile time window which prepares the residual for (ii). Previous work in the context of FWI did not attempt (ii) at all. We find it is the combination of (i) and (ii) that provides the solution we are looking for. In this thesis we formulate the theory for inverting the time-weighted phase residual. We find this mismatch measure meets the requirement of being able to distinguish between adequate and inadequate starting models. Finally, we demonstrate that an 'unwrapped' solution deals with the latter. The unwrapped solution is shown to correctly invert cycle-skipped data and successfully update longer wavelengths than possible with conventional inversion when wide-angle data is available. This leads to a multi-scale approach which ends with conventional inversion but begins with phase-unwrapped inversion at the lowest useable frequency. It finds the global minimum solution to the full wavefield inverse problem down to a depth governed by the offset range of the survey using only a simple starting model.

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Ben, Hadj Ali Hafedh. "Three dimensional visco-acoustic frequency domain full waveform inversion". Nice, 2009. http://www.theses.fr/2009NICE4111.

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En exploration sismique, il est primordial d’extraire des données enregistrées les paramètres physiques étudiés du sous-sol afin de localiser correctement les réservoirs potentiels. Dans ce cas, l’imagerie sismique est l’une des plus importantes étapes dans cette quête. Le processus d’imagerie a reposé pendant longtemps sur une décomposition par échelles : la première étape consiste à construire un modèle de vitesse des bas nombres d’ondes qui explique correctement la cinématique du signal enregistré et la seconde à prendre en compte l’amplitude par migration afin de détecter les contrastes de réflectivité. Dans les années 80, une méthode d’imagerie quantitative, nommée inversion des formes d’ondes, a été proposée pour rassembler les deux étapes du processus d’imagerie au sein d’une approche intégrée. L’objectif de l’inversion des formes d’ondes est de construire simultanément tout le spectre des nombres d’ondes en exploitant l’ensemble des arrivées enregistrées par des dispositifs d’acquisition fournissant un large éclairage angulaire du milieu. La méthode est formulée sous la forme d’un problème d’optimisation pour lequel les différences entre les données enregistrées aux récepteurs et les données modélisées sont minimisées au sens des moindres carrés. Dans ce contexte scientifique, l’objectif de cette thèse est de développer et d’évaluer une méthode d’inversion des formes d’ondes en domaine fréquentiel pour la reconstruction de modèles du sous-sol 3-D dans le cadre de l’approximation visco-acoustique ou le milieu est paramétré par la vitesse de propagation des ondes de compression, la densité et l’atténuation
In seismic exploration, it is crucial to extract from the recorded data the physical of the subsurface in order to correctly locate the potential reservoirs. In this context, seismic imaging is an important step in this quest. The imaging process has been for a long time based on a two-scale strategy : the first step consists in building a smooth velocity model, which correctly explains the kinematics, and the second step in taking into account the dynamics through a migration process to detect reflectivity contrasts. In the eighties, a quantitative imaging method, called waveform inversion, has been proposed to bring together the two stages in an integrated approach. The objective of waveform inversion is to build the whole spectrum of wavenumbers by exploiting all the recorded arrivals acquired by wide aperture acquisitions. The method is formulated as a least squares optimization problem which aims to minimize the differences between the recorded and the modelled data. During the last few years, the waveform inversion method has been a main research topic in the academic and industrial communities. Many issues related to the starting anisotropy and elasticity, and the transition from 2-D to 3-D have been investigated. In this context, the objective of this thesis is to investigate and to develop a waveform inversion approach in the frequency domain and within the visco-acoustic approximation for the reconstruction of a 3-D subsurface model where the model is parametrized by the P-waves velocity, density and attenuation

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Brown, Vanessa. "Integration of seismic full waveform and controlle-source marine electromagnetic inversion". Institut de physique du globe (Paris), 2012. http://www.theses.fr/2012GLOB1201.

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17

Van, Vorst Daryl. "Cross-hole GPR imaging : traveltime and frequency-domain full-waveform inversion". Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/51664.

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Ground-penetrating radar (GPR) has the potential for high-resolution imaging of near-surface material properties, including electrical conductivity and permittivity, which can be used for geological interpretation of the near subsurface. This thesis presents ray-based traveltime inversion and frequency-domain full-waveform inversion (FWI) techniques for application to borehole GPR surveys. Ray-based traveltime inversion is attractive for its speed, reliability, and ability to work in 3D, but the ray approximation involved limits recoverable detail to greater than one wavelength. The traveltime method presented here uses an efficient and easily programmed fast-sweeping eikonal solver to compute traveltimes. The inversion method also incorporates the unknown time offset between signal transmission and start of recording at the receiver as a model parameter that is recovered simultaneously with the material slowness. The resolution of FWI approaches the diffraction limit of one half wavelength, but at a substantial computational cost. The FWI inversion scheme presented here works in 2D and is unique in its simultaneous recovery of the source wavelet, conductivity, and permittivity. Its frequency-domain formulation allows for efficient factorization of the forward modeling operator and its subsequent application to multiple right-hand sides in order to quickly construct the forward model Jacobian. Efficient calculation of the Jacobian allows the use of the Gauss-Newton technique rather than the gradient descent method that is common for other GPR FWI inversions. Measured data must be converted from 3D to 2D before use with this 2D FWI technique. I present a graphical derivation of the perpendicular ray Jacobian, which is an essential part of 3D to 2D transformation. The graphical derivation provides the reader with an intuitive understanding of the Jacobian that is difficult to obtain from traditional mathematical treatments. I also illustrate that 3D to 2D transfer functions previously derived for the acoustic case are applicable to borehole GPR.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

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18

Knaute, Philip Horst. "Full-waveform inversion for near-surface characterisation using land-seismic data". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708885.

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Silverton, Akela Tian Theresa. "Applied 3D full-waveform inversion : increasing the resolution and depth penetration". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/44733.

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High-resolution velocity models, at near surface and deeper reservoir depths are produced with three-dimensional, acoustic, anisotropic, full-waveform inversion. Industry experts show eager interest in the development of this technology with a drive to push its application to reflection-dominated streamer datasets as well as ocean-bottom-node datasets in geologically complex environments. Here, a robust methodology employing the use of key strategies to address the inversion of such datasets, attaining increased resolution and depth penetration, is explored. Synthetic tests were undertaken to exploit the use of reflected energy. Key strategies: muting of direct arrivals, time windowing, and layer-stripping, all produced highly resolved, full waveform inversion models. These strategies have been incorporated into inversion schemes focusing solely on reflection targets. Strategies to further improve model resolution for field datasets were then investigated. Close examination of a full-waveform inversion model for a shallow-water ocean-bottom-node dataset, revealed a systematic mismatch between the observed and predicted data. After conducting a series of tests, it was illustrated that systematic errors in the starting model, source wavelet, incomplete convergence, or an inadequate finite-difference mesh did not cause the mismatch. Instead, inadequacies in the physics used during inversion are believed to be the cause. The introduction of an offsetvariable density scheme during inversion, compensated efficiently and heuristically for these inaccuracies, removing the mismatch and increasing the model resolution. The sensitivity of full-waveform inversion to local minima, where the computed model is stuck away from the real global-minimum solution and further iterations of the optimisation bring no reward, was kept in mind during the inversion of two deep-water ocean-bottom node datasets. Thus, full-waveform inversion was undertaken using conditioned data obtained through adaptive matching, incorporating higher frequencies and a greater weight on reflected energy, valuably pushing the limits of resolution and depth penetration of the update. The use of all these robust methodologies improved the travel-time match; better flattened common-image gathers giving a closer fit to well logs and an improvement in the pre-stack depth-migrated image. Effectively, the reflectivity was non-linearly migrated into the velocity model via the inversion acting on raw unprocessed waveforms. Thus, full waveform inversion can eventually replace conventional processing and migration - all that is needed, is a full-bandwidth velocity model.

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Jazayeri, Sajad. "Full-waveform Inversion of Common-Offset Ground Penetrating Radar (GPR) data". Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7815.

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Maintenance of aging buried infrastructure and reinforced concrete are critical issues in the United States. Inexpensive non-destructive techniques for mapping and imaging infrastructure and defects are an integral component of maintenance. Ground penetrating radar (GPR) is a widely-used non-destructive tool for locating buried infrastructure and for imaging rebar and other features of interest to civil engineers. Conventional acquisition and interpretation of GPR profiles is based on the arrival times of strong reflected/diffracted returns, and qualitative interpretation of return amplitudes. Features are thereby generally well located, but their material properties are only qualitatively assessed. For example, in the typical imaging of buried pipes, the average radar wave velocity through the overlying soil is estimated, but the properties of the pipe itself are not quantitatively resolved. For pipes on the order of the radar wavelength (<5-35 cm), pipe dimensions and infilling material remain ambiguous. Full waveform inversion (FWI) methods exploit the entire radar return rather than the time and peak amplitude. FWI can generate better quantitative estimates of subsurface properties. In recent decades FWI methods, developed for seismic oil exploration, have been adapted and advanced for GPR with encouraging results. To date, however, FWI methods for GPR data have not been specifically tuned and applied on surface collected common offset GPR data, which are the most common type of GPR data for engineering applications. I present an effective FWI method specifically tailored for common-offset GPR data. This method is composed of three main components, the forward modeling, wavelet estimation and inversion tools. For the forward modeling and iterative data inversion I use two open-source software packages, gprMax and PEST. The source wavelet, which is the most challenging component that guarantees the success of the method, is estimated with a novel Sparse Blind Deconvolution (SBD) algorithm that I have developed. The present dissertation indicates that with FWI, GPR can yield better quantitative estimates, for example, of both the diameters of small pipes and rebar and their electromagnetic properties (permittivity, conductivity). Also better estimates of electrical properties of the surrounding media (i.e. soil or concrete) are achieved with FWI.

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Gholami, Yaser. "Two-dimensional seismic imaging of anisotropic media by full waveform inversion". Nice, 2012. http://www.theses.fr/2012NICE4048.

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L’utilisation du formalisme TG43 est courante dans la plupart des Systèmes de planification de Traitement (SPT) dédiés à la curiethérapie. Les grandeurs physiques issues de ce formalisme sont généralement obtenues à partir de simulation Monte Carlo et présentées sous forme d’abaques servant de référence. L’utilisation du code PENELOPE en curiethérapie est très récente ; Sa jeunesse a justifié autant notre choix que son absence de la littérature. Notre choix s’est porté sur PENELOPE pour différentes raisons. La première est que sa physique est plus récente assurant une meilleure précision des résultats. La deuxième, quant à elle, s’appuie sur l’ouverture du code permettant la maîtrise de l’ensemble des processus de la simulation. Ainsi, un des objectifs de nos travaux a consisté à montrer le potentiel que peut avoir ce code afin d’enrichir des données caractérisant les sources de rayonnement de curiethérapie. Le code MCNPX a été utilisé en parallèle afin de valider les résultats des simulations avec PENELOPE. Les géométries de deux modèles de sources d’IR 192 utilisés en curiethérapie, Microselectron HDR v2 et Flexisource, Haut Débit de Dose (HDD) ont été modélisées avec les deux codes de calcul. Pour les deux modèles de source, les résultats de nos simulations ont été comparés à ceux obtenus dans les travaux antérieurs. Une bonne concordance des résultats à proximité des sources jusqu’à des distances inférieures à 4 cm est montrée. Les écarts entre les résultats observés au-delà de 4 cm résident dans les différences concernant les fonctions de dose radiale et d’anisotropie
Exploring the solid Earth for hydrocarbons, as social needs, is one of the main tasks of seismic imaging. As a domain of the modern geophysics, the seismic imaging by full waveform inversion (FWI) aims to improve and refine imaging of shallow and deep structures. Theoretically, the FWI method takes into account all the data gathered from subsurface in order to extract information about the physical parameter of the Earth. The kernel of the FWI is the full wave equation, which is considered in the heart of forward modeling engine. The FWI problem is represented as a least-squares local optimisation problem that retrieved the quantitative values of subsurface physical parameters. The seismic images are affected by the manifested anisotropy in the seismic data as anomalies in travel time, amplitude and waveform. In order to circumvent mis-focusing and mis-positioning events in seismic imaging and to obtain accurate model parameters, as valuable lithology indicators, the anisotropy needs to integrated in propagation-inversion workflows. In this context, the aim of this work is to develop two dimensional FWI for vertically transverse isotropic media (VTI). The physical parameters describing the Earth are elastic moduli or wave speeds and Thomsen parameter(s). The forward modeling and the inversion are performed entirely in frequency domain. The frequency-domain anisotropic P-SV waves propagation modelling is discretized by the finite element discontinuous Galerkin method. The full waveform modelling (FWM) is performed for VTI and titled transverse isotropic (TTI) media by various synthetic examples. The gradient of the misfit function is computed by adjoint-state method. The linearized inverse problem is solved with the quasi-Newton l-BFGS algorithm, which is able to compute an estimated Hessian matrix from a preconditionner and few gradients of previous iterations. Three categories of parametrization type are proposed in order to parametrize the model space of the inverse problem. The sensitivity analysis on acoustic VTI FWI method is preformed by studying the partial derivative of pressure wave field and the grid analysis of least-squares misfit functional. The conclusions inferred from the sensitivity analysis of least-squares misfit functional. The conclusions inferred from the sensitivity analysis are verified by FWI experimental on a simple synthetic model. The anisotropic parameter classes that can be well retrieved by VTI FWI are recognized. Furthermore, the acoustic VTI FWI is applied on the realistic synthetic Valhall benchmark for a wide-aperture surface acquisition survey. The anisotropic acoustic and elastic FWI are performed on the three components of ocean bottom cable (OBC) data sets from Valhall oil/gas field that is located in North Sea

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Krischer, Lion [Verfasser], e Heiner [Akademischer Betreuer] Igel. "Scaling full seismic waveform inversions / Lion Krischer ; Betreuer: Heiner Igel". München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2017. http://d-nb.info/1137835230/34.

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Butzer, Simone [Verfasser], e T. [Akademischer Betreuer] Bohlen. "3D elastic time-frequency full-waveform inversion / Simone Butzer. Betreuer: T. Bohlen". Karlsruhe : KIT-Bibliothek, 2015. http://d-nb.info/107189403X/34.

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24

Trinh, Phuong-Thu. "3D Multi-parameters Full Waveform Inversion for challenging 3D elastic land targets". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAU033/document.

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L’imagerie sismique du sous-sol à partir de données terrestres est très difficile à effectuer due à la complexité 3D de la proche surface. Dans cette zone, les ondes sismiques sous forme d’un paquet compact de phases souvent imbriquées sont dominées par des effets élastiques et viscoélastiques, couplés aux effets dus à la surface libre qui génèrent des ondes de surface de grande amplitude et dispersives.L’interaction des ondes sismiques avec une topographie plus ou moins complexe dans un contexte de fortes hétérogénéités de la proche surface induit d’importantes conversions des ondes avec de fortes dispersions d’énergie. Il est donc nécessaire de prendre en compte à la fois une représentation tridimensionnelle précise de la topographie et une physique correcte qui rend compte de la propagation du champ d’onde dans le sous-sol au niveau de précision réclamé par l’imagerie sismique. Dans ce manuscrit, nous présentons une stratégie d’inversion des formes d’onde complètes (FWI en anglais) efficace, autonome et donc flexible, pour la construction de modèles de vitesse à partir de données sismiques terrestres, plus particulièrement dans les environnements dits de chevauchements d’arrière pays(foothills en anglais) aux variations de vitesse importantes.Nous proposons une formulation efficace de cette problématique basée sur une méthode d’éléments spectraux en domaine temporel sur une grille cartésienne déformée, dans laquelle les variations de topographie sont représentées par une description détaillée de sa géométrie via une interpolation d’ordre élevé. La propagation du champ d’onde est caractérisée par une élasticité linéaire anisotrope et par une atténuation isotrope du milieu: cette deuxième approximation semble suffisante pour l’imagerie crustale considérée dans ce travail. L’implémentation numérique du problème direct inclut des produits matricevecteurefficaces pour résoudre des équations élastodynamiques composant un système différentielhyperbolique du second ordre, pour les géométries tridimensionnelles rencontrées dans l’exploration sismique. Les expressions explicites des gradients de la fonction écart entre les données et les prédictions sont fournies et inclut les contributions de la densité, des paramètres élastiques et des coefficients d’atténuation. Ces expressions réclament le champ incident venant de la source au même temps de propagation que le champ adjoint. Pour ce faire, lors du calcul du champ adjoint à partir de l’instant final, le champ incident est recalculé au vol à partir de son état final, de conditions aux bords préalablement sauvegardées et de certains états intermédiaires sans stockage sur disques durs. Le gradient est donc estimé à partir de quantités sauvegardées en mémoire vive. Deux niveaux de parallélisme sont implémentés, l’un sur les sources et l’autre sur la décomposition du domaine pour chaque source, cequi est nécessaire pour aborder des configurations tridimensionnelles réalistes. Le préconditionnement de ce gradient est réalisé par un filtre dit de Bessel, utilisant une implémentation différentielle efficace fondée sur la même discrétisation de l’espace du problème direct et formulée par une approche d’éléments spectraux composant un système linéaire symétrique résolu par une technique itérative de gradient conjugué. De plus, une contrainte non-linéaire sur le rapport des vitesses de compression et de cisaillement est introduite dans le processus d’optimisation sans coût supplémentaire: cette introductions’avére nécessaire pour traiter les données en présence de faibles valeurs de vitesse proche de la surface libre.L’inversion élastique multi-paramètres en contexte de chevauchement est illustrée à travers des exemples de données synthétiques dans un premier temps, ce qui met en évidence les difficultés d’une telle reconstruction…
Seismic imaging of onshore targets is very challenging due to the 3D complex near-surface-related effects. In such areas, the seismic wavefield is dominated by elastic and visco-elastic effects such as highly energetic and dispersive surface waves. The interaction of elastic waves with the rough topography and shallow heterogeneities leads to significant converted and scattering energies, implying that both accurate 3D geometry representation and correct physics of the wave propagation are required for a reliable structured imaging. In this manuscript, we present an efficient and flexible full waveform inversion (FWI) strategy for velocity model building in land, specifically in foothill areas.Viscoelastic FWI is a challenging task for current acquisition deployment at the crustal scale. We propose an efficient formulation based on a time-domain spectral element method (SEM) on a flexible Cartesian-based mesh, in which the topography variation is represented by an accurate high-order geometry interpolation. The wave propagation is described by the anisotropic elasticity and isotropic attenuation physics. The numerical implementation of the forward problem includes efficient matrix-vector products for solving second-order elastodynamic equations, even for completely deformed 3D geometries. Complete misfit gradient expressions including attenuation contribution spread into density, elastic parameters and attenuation factors are given in a consistent way. Combined adjoint and forward fields recomputation from final state and previously saved boundary values allows the estimation of gradients with no I/O efforts. Two-levels parallelism is implemented over sources and domain decomposition, which is necessary for 3D realistic configuration. The gradient preconditioning is performed by a so-called Bessel filter using an efficient differential implementation based on the SEM discretization on the forward mesh instead of the costly convolution often-used approach. A non-linear model constraint on the ratio of compressional and shear velocities is introduced into the optimization process at no extra cost.The challenges of the elastic multi-parameter FWI in complex land areas are highlighted through synthetic and real data applications. A 3D synthetic inverse-crime illustration is considered on a subset of the SEAM phase II Foothills model with 4 lines of 20 sources, providing a complete 3D illumination. As the data is dominated by surface waves, it is mainly sensitive to the S-wave velocity. We propose a two-steps data-windowing strategy, focusing on early body waves before considering the entire wavefield, including surface waves. The use of this data hierarchy together with the structurally-based Bessel preconditioning make possible to reconstruct accurately both P- and S-wavespeeds. The designed inversion strategy is combined with a low-to-high frequency hierarchy, successfully applied to the pseudo-2D dip-line survey of the SEAM II Foothill dataset. Under the limited illumination of a 2D acquisition, the model constraint on the ratio of P- and S-wavespeeds plays an important role to mitigate the ill-posedness of the multi-parameter inversion process. By also considering surface waves, we manage to exploit the maximum amount of information in the observed data to get a reliable model parameters estimation, both in the near-surface and in deeper part.The developed FWI frame and workflow are finally applied on a real foothill dataset. The application is challenging due to sparse acquisition design, especially noisy recording and complex underneath structures. Additional prior information such as the logs data is considered to assist the FWI design. The preliminary results, only relying on body waves, are shown to improve the kinematic fit and follow the expected geological interpretation. Model quality control through data-fit analysis and uncertainty studies help to identify artifacts in the inverted models

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25

Sears, Timothy John. "Elastic full waveform inversion of multi-component ocean-bottom cable seismic data". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613186.

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26

GALUZZI, BRUNO GIOVANNI. "MODELLING AND OPTIMIZATION TECHNIQUES FOR ACOUSTIC FULL WAVEFORM INVERSION IN SEISMIC EXPLORATION". Doctoral thesis, Università degli Studi di Milano, 2018. http://hdl.handle.net/2434/545844.

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Abstract (sommario):

Full Waveform Inversion has become an important research field in the context of seismic exploration, due to the possibility to estimate a high-resolution model of the subsurface in terms of acoustic and elastic parameters. To this aim, issues such as an efficient implementation of wave equation solution for the forward problem, and optimization algorithms, both local and global, for this high non-linear inverse problem must be tackled. In this thesis, in the framework of 2D acoustic approximation, I implemented an efficient numerical solution of the wave equation based on a local order of approximation of the spatial derivatives to reduce the computational time and the approximation error. Moreover, for what concerns the inversion, I studied two different global optimization algorithms (Simulated Annealing and Genetic Algorithms) on analytic functions that represent different possible scenarios of the misfit function to estimate an initial model for local optimization algorithm in the basin of attraction of the global minimum. Due to the high number of unknowns in seismic exploration context, of the order of some thousands or more, different strategies based on the adjoint method must be used to compute the gradient of the misfit function. By this procedure, only three wave equation solutions are required to compute the gradient instead of a number of solutions proportional to the unknown parameters. The FWI approach developed in this thesis has been applied first on a synthetic inverse problem on the Marmousi model to validate the whole procedure, then on two real seismic datasets. The first is a land profile with two expanding spread experiments and is characterized by a low S/N ratio. In this case, the main variations of the estimated P-wave velocity model well correspond to the shallow events observed on the post-stack depth migrated section. The second is a marine profile extracted from a 3D volume where the local optimization, based on the adjoint method, allows to estimate a high-resolution velocity model whose reliability has been checked by the alignment of the CIGs computed by pre-stack depth migration.

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27

GALUZZI, BRUNO GIOVANNI. "Modelling and Optimization Techniques for Acoustic Full Waveform Inversion in Seismic Exploration". Doctoral thesis, Università degli Studi di Milano, 2018. http://hdl.handle.net/10281/204387.

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Abstract (sommario):

Full Waveform Inversion has become an important research field in the context of seismic exploration, due to the possibility to estimate a high-resolution model of the subsurface in terms of acoustic and elastic parameters. To this aim, issues such as an efficient implementation of wave equation solution for the forward problem, and optimization algorithms, both local and global, for this high non-linear inverse problem must be tackled. In this thesis, in the framework of 2D acoustic approximation, I implemented an efficient numerical solution of the wave equation based on a local order of approximation of the spatial derivatives to reduce the computational time and the approximation error. Moreover, for what concerns the inversion, I studied two different global optimization algorithms (Simulated Annealing and Genetic Algorithms) on analytic functions that represent different possible scenarios of the misfit function to estimate an initial model for local optimization algorithm in the basin of attraction of the global minimum. Due to the high number of unknowns in seismic exploration context, of the order of some thousands or more, different strategies based on the adjoint method must be used to compute the gradient of the misfit function. By this procedure, only three wave equation solutions are required to compute the gradient instead of a number of solutions proportional to the unknown parameters. The FWI approach developed in this thesis has been applied first on a synthetic inverse problem on the Marmousi model to validate the whole procedure, then on two real seismic datasets. The first is a land profile with two expanding spread experiments and is characterized by a low S/N ratio. In this case, the main variations of the estimated P-wave velocity model well correspond to the shallow events observed on the post-stack depth migrated section. The second is a marine profile extracted from a 3D volume where the local optimization, based on the adjoint method, allows to estimate a high-resolution velocity model whose reliability has been checked by the alignment of the CIGs computed by pre-stack depth migration.

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28

Zhang, Fengjiao. "Quantifying the Seismic Response of Underground Structures via Seismic Full Waveform Inversion : Experiences from Case Studies and Synthetic Benchmarks". Doctoral thesis, Uppsala universitet, Geofysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-187142.

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Seismic full waveform inversion (waveform tomography) is a method to reconstruct the underground velocity field in high resolution using seismic data. The method was first introduced during the 1980’s and became computationally feasible during the late 1990’s when the method was implemented in the frequency domain. This work presents three case studies and one synthetic benchmark of full waveform inversion applications. Two of the case studies are focused on time-lapse cross-well and 2D reflection seismic data sets acquired at the Ketzin CO2 geological storage site. These studies are parts of the CO2SINK and CO2MAN projects. The results show that waveform tomography is more effective than traveltime tomography for the CO2 injection monitoring at the Ketzin site for the cross-well geometry. For the surface data sets we find it is difficult to recover the true value of the velocity anomaly due to the injection using the waveform inversion method, but it is possible to qualitatively locate the distribution of the injected CO2. The results agree well with expectations based upon conventional 2D CDP processing methods and more extensive 3D CDP processing methods in the area. A further investigation was done to study the feasibility and efficiency of seismic full waveform inversion for time-lapse monitoring of onshore CO2 geological storage sites using a reflection seismic geometry with synthetic data sets. The results show that waveform inversion may be a good complement to standard CDP processing when monitoring CO2 injection. The choice of method and strategy for waveform inversion is quite dependent on the goals of the time-lapse monitoring of the CO2 injection. The last case study is an application of the full waveform inversion method to two crooked profiles at the Forsmark site in eastern central Sweden. The main goal of this study was to help determine if the observed reflections are mainly due to fluid filled fracture zones or mafic sills. One main difficulty here is that the profiles have a crooked line geometry which corresponds to 3D seismic geometry, but a 2D based inversion method is being used. This is partly handled by a 3D to 2D coordinate projection method from traveltime inversion. The results show that these reflections are primarily due to zones of lower velocity, consistent with them being generated at water filled fracture zones.

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Ernst, Jacques Robert. "2-D finite-difference time-domain full-waveform inversion of crosshole georadar data /". Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17105.

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30

Wellington, Paul John. "Efficient 1D, 2D and 3D Geostatistical constraints and their application to Full Waveform Inversion". Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAU032/document.

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Abstract (sommario):

L'inversion de forme d'onde complète (FWI) est un processus non-linéaire et mal posé d’ajustement de données, dans notre cas, issues d’acquisitions simiques. Cette technique cherche à reconstruire, à partir d’un modèle initial obtenu à faible nombre d’onde (faible résolution), des paramètres constitutifs contrôlant la propagation des ondes à grands nombres d’ondes (forte résolution). Durant ce processus itératif, certains artéfacts peuvent altérer la qualité du modèle reconstruit. Afin de diminuer ces artéfacts et d’assurer une reconstruction des paramètres qui soit cohérente d’un point de vue géologique, différentes techniques de pré-conditionnement ou de régularisation peuvent être proposées.Cette thèse se focalise sur le potentiel de nouveaux filtres multi-dimensionnels construits dans l’espace des nombres d’ondes et orientés suivant les structures géologiques. Une stratégie de pré-conditionnement a été mise au point à l’aide de ces filtres et a été appliquée avec succès à la problématique FWI. La formulation analytique 1D de l’opérateur inverse de covariance laplacienne (Tarantola, 2005) constitue la base de la formulation d’opérateurs de dimension supérieure qui sont validés ici en les comparants avec l’opérateur analytique de covariance laplacienne 1D. Nous avons utilisé cette fonction analytique inverse 1D comme la base de filtrage de dimension supérieure, via l’addition de multiples fonctions inverses orientées orthogonalement. Ces fonctions laplaciennes inverses additionnelles (AIL) sont obtenues pour des configurations 2D et 3D après discrétisation par des techniques de différences finies. Nous montrons que l’on peut calculer un filtre en nombre d’onde de manière rapide et robuste en résolvant le système linéaire associé à ces opérateurs inverses. Lorsque des pentes sont inclues à l’étape de discrétisation par différences finies, il est alors possible d’utiliser ces opérateurs comme des filtres en nombre d’ondes orientés vers les structures géologiques, ceci avec une grande efficacité.Ce filtre (AIL) montre des propriétés rapides de convergence et des performances indépendantes du vecteur à filtrer. Nous montrons notamment comment ce filtre peut être utilisé comme un opérateur utile pour le gradient associé à la FWI. Le pré-conditionnement du gradient peut atténuer les effets du problème mal-posé qui vont s’étendre dans l’espace des modèles. Deux exemples synthétiques (Valhall et Marmousi) calculés dans l’espace des fréquences sont proposés dans cette thèse. Le pré-conditionnement AIL s’avère efficace pour atténuer d’une part la signature mal-posée provenant de la présence de bruit ambient dans les données observées et d’autre part d’artéfacts liés aux effets de repliement spatial liés aux conditions d’imagerie par FWI. La possibilité d’inclure des pentes permet de filtrer de manière préférentielle en considérant des pendages géologiques. Cette stratégie de filtrage permet l’atténuation d’artéfacts, tout en préservant le contenu en nombre d’ondes de la stratigraphie orthogonale au pendage.Un cas réel d’inversion 2D FWI est finalement abordé permettant tout d’abord d’illustrer la sensibilité des résultats d’inversion au modèle initial. Celui-ci est d’importance majeure, particulièrement dans les régions profondes dépassant la pénétration maximale des ondes transmises. L’application de la technique FWI à cette acquisition sismique a permis d’améliorer de manière significative la cohérence sur une image migrée par renversement du temps (RTM). Nous montrons également que le pré-conditionneur AIL permet une décroissance significative du nombre de tirs requis à modéliser dans la boucle d’inversion, sans pour autant dégrader le contenu en nombre d’onde des structures géologiques principales dans les résultats finaux obtenus après inversion
Full waveform inversion (FWI) is a non-linear, ill-posed, local data fitting technique. FWI looks to moves from an initial, low-wavenumber representation of the earth parameters to a broadband representation. During this iterative process a number of undesirable artifacts can map into our model parameter reconstruction. To mitigate these artifacts and to ensure a geologically consistent model parameter reconstruction, various preconditioning and/or regularization strategies have been proposed.This thesis details the construction of new, efficient, multi-dimensional, structurally-orientated wavenumber filters. A preconditioning strategy has been devised using these filters that we have successfully applied to FWI. The 1D analytical inverse Laplacian covariance operator (Tarantola, 2005) forms the basis of higher dimensional operators and is initially validated by comparing to the 1D analytical Laplacian covariance operator. We use this analytical 1D inverse function as the basis for higher dimensional filtering via the addition of multiple, orthogonally orientated inverse functions. These additive inverse laplacian functions (AIL) are shown in 2D and 3D configurations and are discretized using finite-difference techniques. We show that one can calculate, a rapid and robust wavenumber filter, by solving the linear system associated with these inverse operators. When dip is included at the finite difference discretization stage, it is possible to use these operators as highly efficient, structurally orientated wavenumber filters.The AIL filter is shown to be rapid to converge and its performance is independent of the vector to be filtered. We show, that the filter can be a useful preconditioning operator for the FWI gradient. Preconditioning the gradient can mitigate against ill-posed effects mapping into the model-space. Two synthetic (Valhall and Marmousi) frequency domain FWI example are shown in this thesis. The AIL preconditioner has success at mitigating the ill-posed imprint coming from ambient noise in the observed data and also artifacts from spatial aliasing effects in the FWI imaging condition. The ability to include dip, allows one to preferentially filter along geological dip. This filtering strategy allows the mitigation of artifacts, while simultaneously preserving the stratigraphic based wavenumber content that is orthogonal to dip.A 2D, real data FWI case-study is also shown and we highlight the sensitivity of the inversion result to the initial model. The initial model is of key importance, this especially true in the areas deeper than the maximum penetration of transmitted waves. The application of FWI on this line is able to significantly improve gather alignment on a RTM, migrated image. We also see that the AIL preconditioner can allows us to significantly decrease the number of shot records we are required to model in our inversion workflow without degrading the key geological wavenumber content in the final inversion result

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31

Gras, Andreu Clàudia. "Inversion of multichannel seismic data by combination of travel-time and full-waveform tomography". Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/668456.

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This thesis presents the implementation and application of a procedure combining different geophysical techniques to extract high-resolution information that helps characterizing the structure and properties (p-wave velocity, Vp) of the subsurface by using marine multichannel seismic (MCS) data alone. The challenge is overcoming the inherent non-linearity and non-uniqueness of inverse methods, in general, and of full-waveform inversion (FWI), in particular, which are especially critical for short-offset, band-limited seismic data. I have designed and applied a modelling sequence consisting of: (1) data re-datuming or downward continuation (DC) by back-propagation of the recorded seismograms to the seafloor; (2) travel-time tomography (TTT) using especially the first arrivals of the re-datumed shot gathers, and (3) FWI of the original shot gathers using the model obtained by TTT as initial reference. This workflow is first tested with synthetic data, and then applied to field data acquired in the Alboran Sea (SE Iberia). Due to the short source-receiver offset and the depth of the water column, refractions are hardly identified as first arrivals. To solve this problem, I changed the reference datum of the data set from the sea surface to the seafloor, by implementing a DC code that uses a solver of the acoustic wave equation developed at Barcelona-CSI [Dagnino et al., 2016]. By modifying the MCS records to simulate a seafloor-type acquisition it is possible to recover refracted phases, crucial in Vp modelling, as first arrivals. Then, I performed TTT using the travel times of the DC first arrivals to obtain a coarse, but kinematically correct, Vp model. This TTT Vp model has the correct low-wavenumber information because the waveforms simulated with the inverted model and the recorded ones are not cycle-skipped. To better constrain the result, particularly in the deep parts of the model, I have incorporated the seismic phases corresponding to a major reflecting interface (top of the basement, TOB) and performed a joint refraction and reflection TTT combining the original and the DC field data. Finally, finer structural details are progressively introduced in the initial model by applying iterative, multi-scale FWI to the original MCS data. The results confirm that the combination of data re-datuming and TTT provides reference models that are accurate enough to apply FWI to relatively short offset streamer data in deep-water settings as the ones used, even if records lack low frequencies (< 4 Hz). I also show that, when the initial model is not kinematically correct, the FWI falls into a local minimum. The application of the workflow to the Alboran field data reveals a number of geological structures in the FWI Vp model that cannot be appreciated in the TTT Vp model, nor easily interpreted based on MCS images alone. A sharp strong velocity contrast defines the geometry of an irregular TOB that includes high velocity volcano-like structures. The model clearly images steeply dipping Vp changes at the flanks of the basin that may correspond to faults. Moreover, it displays a 200–300 m thick high-velocity layer that could probably correspond to evaporites deposited during the Messinian crisis in the Mediterranean. The result is validated by comparing the two-way time-transformed Vp model and the time-migrated MCS image, showing that velocity changes coincide with major reflectivity contrasts. Overall, this study shows that by using an appropriate workflow, in our case including DC of MCS data to the seafloor, joint refraction and reflection TTT, and FWI, accurate, geologically meaningful Vp models can be obtained even for non-optimal data sets. In particular, our results provide information that improves the geological characterization and interpretation of the subsurface of the Alboran Basin. The main results have recently been published in Solid Earth [https://doi.org/10.5194/se-2019-46].
Aquesta tesi presenta el desenvolupament, implementació i aplicació d'un procediment que combina diferents tècniques d'inversió tomogràfica per extreure informació d'alta resolució que permeti caracteritzar l'estructura i propietats (velocitat d'ona p, Vp) del subsòl marí, utilitzant exclusivament dades de sísmica de reflexió multicanal (MCS). El repte principal és el de superar els problemes inherents de no-linealitat i no-unicitat dels mètodes d'inversió, en general, i de la inversió de forma d’ona completa (FWI), en particular, especialment crítics en registres sísmics que manquen de baixes freqüències (<4 Hz) i han estat adquirits amb un abast experimental relativament curt (~6 km). Per afrontar el problema, l’estudi proposa i segueix un flux de treball que primer es posa a prova amb dades sintètiques, i després s'aplica a dades de camp adquirides al mar d’Alboran. Primerament es va desenvolupar un codi que modifica les dades sísmiques retro-propagant-les a la superfície del fons marí, simulant així una adquisició virtual en aquesta superfície. Els registres resultants permeten identificar les refraccions com a primeres arribades, que aporten informació robusta i essencial per modelar la Vp. Posteriorment, amb els temps d'aquestes arribades es va dur a terme la tomografia de temps de trajecte (TTT). En l'aplicació amb dades de camp, es va afegir la reflexió del sostre del basament (TOB) per acotar millor el resultat. Els models obtinguts mostren la variació de Vp correcta del subsòl, ja que els sismogrames simulats amb aquests models i els que es pretenen reproduir no mostren desfasaments importants. Aquest fet possibilita la correcta aplicació de tècniques més complexes com la FWI utilitzant el model de TTT com a inicial. La FWI proporciona un model de Vp d’alta resolució del medi utilitzant tot el camp d'ones de les dades originals. Aquesta tesi és la primera aplicació pràctica de FWI amb dades de camp a nivell nacional, i s’han utilitzat essencialment codis desenvolupats al BCSI. Els resultats revelen diverses formes geològiques d'interès, la geometria irregular del TOB, causada per possibles estructures volcàniques, i falles; a més d'una capa d'alta Vp que pot correspondre a evaporites dipositades durant el Messinià. Els resultats principals s’han publicat recentment a Solid Earth [https://doi.org/10.5194/se-2019-46].

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32

Przebindowska, Anna [Verfasser], e T. [Akademischer Betreuer] Bohlen. "Acoustic Full Waveform Inversion of Marine Reflection Seismic Data / Anna Przebindowska. Betreuer: T. Bohlen". Karlsruhe : KIT-Bibliothek, 2013. http://d-nb.info/1037776216/34.

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33

Groos, Lisa [Verfasser], e T. [Akademischer Betreuer] Bohlen. "2D full waveform inversion of shallow seismic Rayleigh waves / Lisa Groos. Betreuer: T. Bohlen". Karlsruhe : KIT-Bibliothek, 2013. http://d-nb.info/1044956208/34.

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34

Zheng, York Yao. "Time-lapse seismic imaging using elastic full waveform inversion of ocean-bottom cable data". Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648657.

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35

Zhou, Wei. "Velocity model building by full waveform inversion of early arrivals & reflections and case study with gas cloud effect". Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAU024/document.

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L'inversion des formes d'onde (full waveform inversion, FWI) a suscité un intérêt dans le monde entier pour sa capacité à estimer de manière précise et détaillée les propriétés physiques du sous-sol. La FWI est généralement formulée sous la forme d'un problème d'ajustement des données par moindres carrés et résolus par une approche linéarisée utilisant des méthodes d'optimisation locales. Cependant, la FWI est bien connue de souffrir du problème de saut de phase rendant les résultats fortement dépendant de la qualité des modèles initiaux. L'inversion des formes d'ondes des arrivées réfléchies (reflection waveform inversion, RWI) a récemment été proposée pour atténuer ce problème en supposant une séparation d'échelle entre le modèle de vitesse lisse et le modèle de réflectivité à haut nombre d'onde. La formulation de RWI considère explicitement les ondes réfléchies afin d'extraire de ces ondes une information sur les variations lisses de vitesse des zones profondes. Cependant, la méthode néglige les ondes transmises qui contraignant les informations lisses de vitesse en proche surface.Dans cette thèse, une étude de la sensibilité en nombre d'ondes des méthodes de FWI et RWI a d'abord été revisitée dans le cadre de la tomographie en diffraction et des décompositions orthogonales. A partir de cette analyse, je propose une nouvelle méthode, à savoir l'inversion jointe des formes d'ondes transmises et réfléchies (joint full waveform inversion, JFWI). La méthode propose une formulation unifiée pour combiner la FWI des transmissions et la RWI pour les réflexions, donnant naturellement une sensibilité commune aux petits nombres d'onde venant des arrivées grand-angle et réfléchies. Les composantes à hauts nombres d'onde sont naturellement atténuées par la formulation. Pour satisfaire l'hypothèse de séparation d'échelle, j'utilise une paramétrisation du sous-sol basée sur la vitesse des ondes de compression et l'impédance acoustique. La complexité temporelle de cette approche est le double de la méthode de FWI classique et la requête mémoire reste la même.Une procédure d'inversion est ensuite proposée, permettant d'estimer alternativement le modèle de la vitesse du sous-sol par JFWI et l'impédance inversion de formes d'ondes réfléchies. Un exemple synthétique réaliste du modèle de Valhall est d'abord utilisé avec des données de streamer et à partir d'un modèle initial très lisse. Dans ce cadre, alors que la FWI converge vers un minimum local, la JFWI réussit à reconstruire un modèle de vitesse lisse de bonne qualité. La prise en compte des ondes tournante par la JFWI montre un fort intérêt pour la qualité de reconstruction superficielle, comparée à la méthode RWI seule. Cela se traduit ensuite par une reconstruction améliorée en profondeur. Le modèle de vitesse lisse construit par JFWI peut ensuite être considéré comme modèle initial pour la FWI classique, afin d'injecter le contenu en haut nombres d'onde tout en évitant le problème de saut de phase.Les avantages et limites de l'approche de JFWI sont ensuite étudiés dans une application sur données réelles, venant d'un profil 2D de données de fond de mer (OBC) recoupant un nuage de gaz au dessus d'un réservoir. Plusieurs modèles initiaux et stratégies d'inversion sont testés afin de minimiser le problème de saut de phase, tout en construisant des modèles de sous-sol avec une résolution suffisante. Sous réserve de mettre en œuvre des stratégies limitant le problème de saut de phase, la JFWI montre qu'elle peut produire un modèle de vitesse acceptable, injectant les bas nombres d'onde dans le modèle de vitesse. L'amélioration de l'éclairage en angles de diffraction fournie par des acquisitions 3D devrait permettre de pouvoir commencer l'inversion par JFWI à partir de modèle encore moins bien définis
Full waveform inversion (FWI) has attracted worldwide interest for its capacity to estimate the physical properties of the subsurface in details. It is often formulated as a least-squares data-fitting procedure and routinely solved by linearized optimization methods. However, FWI is well known to suffer from cycle skipping problem making the final estimations strongly depend on the user-defined initial models. Reflection waveform inversion (RWI) is recently proposed to mitigate such cycle skipping problem by assuming a scale separation between the background velocity and high-wavenumber reflectivity. It explicitly considers reflected waves such that large-wavelength variations of deep zones can be extracted at the early stage of inversion. Yet, the large-wavelength information of the near surface carried by transmitted waves is neglected.In this thesis, the sensitivity of FWI and RWI to subsurface wavenumbers is revisited in the frame of diffraction tomography and orthogonal decompositions. Based on this analysis, I propose a new method, namely joint full waveform inversion (JFWI), which combines the transmission-oriented FWI and RWI in a unified formulation for a joint sensitivity to low wavenumbers from wide-angle arrivals and short-spread reflections. High-wavenumber components are naturally attenuated during the computation of model updates. To meet the scale separation assumption, I also use a subsurface parameterization based on compressional velocity and acoustic impedance. The temporal complexity of this approach is twice of FWI and the memory requirement is the same.An integrated workflow is then proposed to build the subsurface velocity and impedance models in an alternate way by JFWI and waveform inversion of the reflection data, respectively. In the synthetic example, JFWI is applied to a streamer seismic data set computed in the synthetic Valhall model, the large-wavelength characteristics of which are missing in the initial 1D model. While FWI converges to a local minimum, JFWI succeeds in building a reliable velocity macromodel. Compared with RWI, the involvement of diving waves in JFWI improves the reconstruction of shallow velocities, which translates into an improved imaging at greater depths. The smooth velocity model built by JFWI can be subsequently taken as the initial model for conventional FWI to inject high-wavenumber content without obvious cycle skipping problems.The main promises and limitations of the approach are also reviewed in the real-data application on the 2D OBC profile cross-cutting gas cloud.Several initial models and offset-driven strategies are tested with the aim to manage cycle skipping while building subsurface models with sufficient resolution. JFWI can produce an acceptable velocity model provided that the cycle skipping problem is mitigated and sufficient low-wavenumber content is recovered at the early stage of inversion. Improved scattering-angle illumination provided by 3D acquisitions would allow me to start from cruder initial models

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36

Klimm, Bernd [Verfasser], Axel [Akademischer Betreuer] Klar e Thomas [Akademischer Betreuer] Bohlen. "Time Domain Full Waveform Inversion Using ADI Modeling / Bernd Klimm. Betreuer: Axel Klar ; Thomas Bohlen". Kaiserslautern : Technische Universität Kaiserslautern, 2013. http://d-nb.info/1041255543/34.

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37

Nangoo, Tenice Peaches. "Seismic full-waveform inversion of 3D field data : from the near surface to the reservoir". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/18898.

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Abstract (sommario):

The theory of FWI is well-established. However its practical application to 3D seismic datasets is still a subject of intense research. This technique has shown spectacular results in quantitatively extracting P-wave velocities in the shallow near surface at depths of less than 1 km, using wide-angle OBC datasets. This study deals with establishing a robust methodology for the application of FWI that can be routinely applied to analogous field datasets, both in the shallow near surface and at deeper reservoir depths. A practical strategy for anisotropic 3D acoustic FWI was developed and implemented. The stratergy is tested on a series of 3D datasets: (1) a synthetic Marmousi dataset, (2) an OBC field data and (3) a streamer data. A 3D synthetic Marmousi data is used to compare FWI implementations in both the time domain and the frequency domain. In both domains, it was possible to recover an almost ‘perfect’ model with complete data coverage, no noise, and few iterations. Both approaches were useful and competitive, and ideally both should be available within a comprehensive suite of inversion tools. The anisotropic time-domain FWI strategy was successfully implemented to complex OBC field data set with long offsets, full-azimuthal coverage and low frequencies. The FWI quantitatively recovered p-wave velocities in the shallow near surface, at intermediate depths where the sediments are gas bearing, and at deeper reservoir depths. The velocities are indeed realistic and are consistent with an independent reflection PSDM volume, well data and pressure data. The synthetic FWI data better match the field data, with the phase residuals between the two datasets significantly reduced to low values. The gathers are flatter and the depth-migrated images are more resolved and focused. The strategy was also successfully implemented to complex streamer field data set with short offsets, narrow-azimuthal coverage and reduced signal at the low frequencies. The FWI quantitatively recovered P-wave velocities down to depths of 750 m. A complex series of high and low velocity channels are recovered. These are consistent with an independent reflection PSTM volume. The synthetic FWI data better match the field data, with the phase residuals between the two datasets significantly reduced to low values. The depth-migrated images are more resolved and focused in the shallow section.

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38

Irnaka, Theodosius Marwan. "3D elastic full waveform inversion for subsurface characterization.Study of a shallow seismic multicomponent field data". Thesis, Université Grenoble Alpes, 2021. http://www.theses.fr/2021GRALU004.

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L'inversion de forme d'onde complète (FWI) est une procédure d'ajustement itératif des données entre les données observées et les données synthétiques. Les données synthétiques sont calculées en résolvant une équation d'onde. La FWI vise à reconstruire les informations détaillées des propriétés physiques du sous-sol. La méthode FWI a été développée au cours des dernières décennies, grâce à l'augmentation de la capacité de calcul et au développement de la technologie d'acquisition. La FWI a également été appliquée à à des échelles variées, allant de l'échelle globale, lithosphérique, crustale, jusqu'à la proche surface, c'est à dire quelques mètres de profondeur.Dans ce manuscrit, nous étudions l'inversion d'un jeu de données de source et de récepteur multicomposantes en utilisant un algorithme d'inversion de forme d'onde complète viscoélastique pour une cible sismique peu profonde. La cible est une ligne de tranchée enterrée à environ 1 m de profondeur. Nous présentons le pré-traitement des données, y compris une correction par déconvolution pour compenser les différentes conditions de couplage de la source et du récepteur pendant l'acquisition, ainsi qu'un procédé d'inversion en plusieurs étape pour la reconstruction des vitesses des ondes P et S. Notre mise en œuvre est basée sur une modélisation viscoélastique utilisant une discrétisation par éléments spectraux pour rendre compte avec précision de la complexité de la propagation des ondes dans cette région peu profonde. Nous illustrons la stabilité de l'inversion en partant de différents modèles initiaux, soit basés sur l'analyse des courbes de dispersion, soit des modèles homogènes cohérents avec les premières arrivées. Nous obtenons des résultats similaires dans les deux cas. Nous illustrons également l'importance de la prise en compte de l'atténuation en comparant les résultats élastiques et viscoélastiques. Les résultats 3D permettent de localiser précisément la ligne de tranchée en termes d'interprétation. Ils montrent également une autre structure de ligne de tranchée, dans une direction formant un angle de 45 degrés avec la direction de la ligne de tranchée ciblée. Cette nouvelle structure avait été précédemment interprétée comme un artefact dans les anciens résultats d'inversion 2D. L'interprétation archéologique de cette nouvelle structure est actuellement en discussion.Nous réalisons également trois expériences différentes pour comprendre l'effet des données à composantes multiples sur la FWI. La première expérience est une analyse de sensibilité de plusieurs paquets d'ondes (onde P, onde S et onde de surface) sur un modèle 3D simple basé sur une direction cartésienne de la source et du récepteur. La seconde expérience est une inversion élastique 3D basée sur des données synthétiques (utilisant la source de direction cartésienne) et de champ (utilisant la source Galperin) avec diverses combinaisons de composants. Seize combinaisons de composantes sont analysées pour chaque cas. Dans la troisième expérience, nous effectuons la décimation de l'acquisition sur la base de la deuxième expérience. Nous démontrons un avantage significatif des données multicomposantes FWI grâce à ces expériences. Dans une échelle sismique peu profonde, les inversions avec les composantes horizontales donnent une meilleure reconstruction en profondeur. En se basant sur la décimation de l'acquisition, l'inversion utilisant des données sismiques 9C fortement décimées produit des résultats similaires à l'inversion utilisant des données sismiques 1C sur l'acquisition complète
Full Waveform Inversion (FWI) is an iterative data fitting procedure between the observed data and the synthetic data. The synthetic data is calculated by solving the wave equation. FWI aims at reconstructing the detailed information of the subsurface physical properties. FWI has been rapidly developed in the past decades, thanks to the increase of the computational capability and the development of the acquisition technology. FWI also has been applied in a broad scales including the global, lithospheric, crustal, and near surface scale.In this manuscript, we investigate the inversion of a multicomponent source and receiver near-surface field dataset using a viscoelastic full waveform inversion algorithm for a shallow seismic target. The target is a trench line buried at approximately 1 m depth. We present the pre-processing of the data, including a matching filter correction to compensate for different source and receiver coupling conditions during the acquisition, as well as a dedicated multi-step workflow for the reconstruction of both P-wave and S-wave velocities. Our implementation is based on viscoelastic modeling using a spectral element discretization to accurately account for the wave propagation's complexity in this shallow region. We illustrate the inversion stability by starting from different initial models, either based on dispersion curve analysis or homogeneous models consistent with first arrivals. We recover similar results in both cases. We also illustrate the importance of taking into account the attenuation by comparing elastic and viscoelastic results. The 3D results make it possible to recover and locate precisely the trench line in terms of interpretation. They also exhibit another trench line structure, in a direction forming an angle at 45 degrees with the direction of the targeted trench line. This new structure had been previously interpreted as an artifact in former 2D inversion results. The archaeological interpretation of this new structure is still a matter of discussion.We also perform three different experiments to study the effect of multicomponent data on this FWI application. The first experiment is a sensitivity kernel analysis of several wave packets (P-wave, S-wave, and surface wave) on a simple 3D model based on a Cartesian based direction of source and receiver. The second experiment is 3D elastic inversion based on synthetic (using cartesian direction's source) and field data (using Galperin source) with various component combinations. Sixteen component combinations are analyzed for each case. In the third experiment, we perform the acquisition's decimation based on the second experiment. We demonstrate a significant benefit of multicomponent data FWI in terms of model and data misfit through those experiments. In a shallow seismic scale, the inversions with the horizontal components give a better depth reconstruction. Based on the acquisition's decimation, inversion using heavily decimated 9C seismic data still produce similar results compared to the inversion using 1C seismic of a dense acquisition

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39

Baron, Julie <1987&gt. "Seismic tomographic full-waveform inversion for the Vrancea sinking lithosphere structure using the adjoint method". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6540/1/Baron_Julie_tesi.pdf.

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The Vrancea region, at the south-eastern bend of the Carpathian Mountains in Romania, represents one of the most puzzling seismically active zones of Europe. Beside some shallow seismicity spread across the whole Romanian territory, Vrancea is the place of an intense seismicity with the presence of a cluster of intermediate-depth foci placed in a narrow nearly vertical volume. Although large-scale mantle seismic tomographic studies have revealed the presence of a narrow, almost vertical, high-velocity body in the upper mantle, the nature and the geodynamic of this deep intra-continental seismicity is still questioned. High-resolution seismic tomography could help to reveal more details in the subcrustal structure of Vrancea. Recent developments in computational seismology as well as the availability of parallel computing now allow to potentially retrieve more information out of seismic waveforms and to reach such high-resolution models. This study was aimed to evaluate the application of a full waveform inversion tomography at regional scale for the Vrancea lithosphere using data from the 1999 six months temporary local network CALIXTO. Starting from a detailed 3D Vp, Vs and density model, built on classical travel-time tomography together with gravity data, I evaluated the improvements obtained with the full waveform inversion approach. The latter proved to be highly problem dependent and highly computational expensive. The model retrieved after the first two iterations does not show large variations with respect to the initial model but remains in agreement with previous tomographic models. It presents a well-defined downgoing slab shape high velocity anomaly, composed of a N-S horizontal anomaly in the depths between 40 and 70km linked to a nearly vertical NE-SW anomaly from 70 to 180km.

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40

Baron, Julie <1987&gt. "Seismic tomographic full-waveform inversion for the Vrancea sinking lithosphere structure using the adjoint method". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6540/.

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Abstract (sommario):

The Vrancea region, at the south-eastern bend of the Carpathian Mountains in Romania, represents one of the most puzzling seismically active zones of Europe. Beside some shallow seismicity spread across the whole Romanian territory, Vrancea is the place of an intense seismicity with the presence of a cluster of intermediate-depth foci placed in a narrow nearly vertical volume. Although large-scale mantle seismic tomographic studies have revealed the presence of a narrow, almost vertical, high-velocity body in the upper mantle, the nature and the geodynamic of this deep intra-continental seismicity is still questioned. High-resolution seismic tomography could help to reveal more details in the subcrustal structure of Vrancea. Recent developments in computational seismology as well as the availability of parallel computing now allow to potentially retrieve more information out of seismic waveforms and to reach such high-resolution models. This study was aimed to evaluate the application of a full waveform inversion tomography at regional scale for the Vrancea lithosphere using data from the 1999 six months temporary local network CALIXTO. Starting from a detailed 3D Vp, Vs and density model, built on classical travel-time tomography together with gravity data, I evaluated the improvements obtained with the full waveform inversion approach. The latter proved to be highly problem dependent and highly computational expensive. The model retrieved after the first two iterations does not show large variations with respect to the initial model but remains in agreement with previous tomographic models. It presents a well-defined downgoing slab shape high velocity anomaly, composed of a N-S horizontal anomaly in the depths between 40 and 70km linked to a nearly vertical NE-SW anomaly from 70 to 180km.

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41

Macedo, Daniel Leal 1975. "Scattering-based decomposition of sensitivity kernels of acoustic full waveform inversion = Decomposição baseada em teoria de espalhamento dos núcleos de sensibilidade da inversão de onda completa acústica". [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265785.

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Abstract (sommario):

Orientador: Dietrich Wilhelm Schleicher
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica, Instituto de Geociências
Made available in DSpace on 2018-08-26T05:18:51Z (GMT). No. of bitstreams: 1 Macedo_DanielLeal_D.pdf: 16481305 bytes, checksum: 3d47b0427882ec03cc38bd035feee293 (MD5) Previous issue date: 2014
Resumo: A inversão de onda completa (FWI, do inglês ''full waveform inversion'') nãolinear baseada em gradientes (métodos de descida) é, a princípio, capaz de levar em conta todos os aspectos da propagação de onda contida nos dados síismicos. Porém, FWI baseada em gradientes é limitada pela sua bem conhecida sensibilidade no que diz respeito à escolha do modelo inicial. Com o intuito de melhor entender algumas questões relacionadas à convergência do modelo na FWI, nós estudamos uma decomposição baseada na teoria de espalhamento que permite dividir os núcleos de sensibilidade dos campos de onda acústica em função dos parâmetros do modelo em duas partes: uma relativa ao componente de fundo, outra relativa à componente singular do modelo. Estimativas para a perturbação de fundo, bem como para a perturbação da parte singular do modelo obtidas com os adjuntos destes subnúcleos são componentes da estimativa obtida com o adjunto do núcleo total de sensibilidade. Os experimentos numéricos suportam a tese de que a decomposiçao em subnúcleos permite que se retroprojete somente os resíduos do campo de onda espalhado de modo a obter estimativas razoáveis da perturbação de fundo do modelo. Em um experimento com geometria de aquisição restrita (dados de reflexão com afastamento curto), os subnúcleos baseados em espalhamento múltiplo se aproveitam da autoiluminacão do meio devido às ondas multiplamente espalhadas. A autoiluminação fornece estimativas melhores com conteúdo espectral mais rico nas baixas frequências
Abstract: While in principle nonlinear gradient-based full-waveform inversion (FWI) is capable of handling all aspects of wave propagation contained in the data, including full nonlinearity, in practice, it is limited due to its notorious sensitivity to the choice of the starting model. To help addressing model-convergence issues in FWI, we study a decomposition based on the scattering theory that allows to break the acoustic-wavefield sensitivity kernels with respect to model parameters into background and singular parts. The estimates for both background perturbation and/or singular-part perturbation obtained with the subkernels' adjoints are components of the estimate obtained with the total kernel's adjoint. Our numerical experiments shows the feasibility of our main claim: the decomposition into subkernels allows to backproject the scattered-wavefield residuals only so as to obtain reasonable background-model perturbation estimates. In an experiment with restricted acquisition geometry (reflection data, narrow offset), the multiple-scattering subkernels take advantage of medium self-illumination provided by the scattered wavefields. This self-illumination provides better estimates, with longer wavelengh content
Doutorado
Reservatórios e Gestão
Doutor em Ciências e Engenharia de Petróleo

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42

Athanasopoulos, Nikolaos [Verfasser], e T. [Akademischer Betreuer] Bohlen. "Challenges in near-surface seismic full-waveform inversion of field data / Nikolaos Athanasopoulos ; Betreuer: T. Bohlen". Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/122302797X/34.

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43

Zhou, Zhen Verfasser], Klaus [Akademischer Betreuer] [Reicherter e Harry [Akademischer Betreuer] Vereecken. "Enhanced crosshole GPR full-waveform inversion to improve aquifer characterization / Zhen Zhou ; Klaus Reicherter, Harry Vereecken". Aachen : Universitätsbibliothek der RWTH Aachen, 2020. http://d-nb.info/123131754X/34.

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44

Ehsan, Jamali Hondori. "Full waveform inversion of supershot-gathered data for optimization of turnaround time in seismic reflection survey". Kyoto University, 2016. http://hdl.handle.net/2433/217744.

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45

Musayev, Khayal [Verfasser], Klaus [Gutachter] Hackl e Wolfgang [Gutachter] Friederich. "Seismic reconnaissance in a tunnel environment using full waveform inversion / Khayal Musayev ; Gutachter: Klaus Hackl, Wolfgang Friederich". Bochum : Ruhr-Universität Bochum, 2017. http://d-nb.info/1123283494/34.

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46

Ernesti, Johannes [Verfasser], e C. [Akademischer Betreuer] Wieners. "Space-Time Methods for Acoustic Waves with Applications to Full Waveform Inversion / Johannes Ernesti ; Betreuer: C. Wieners". Karlsruhe : KIT-Bibliothek, 2018. http://d-nb.info/1160303525/34.

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47

Schäfer, Martin [Verfasser], e T. [Akademischer Betreuer] Bohlen. "Application of full-waveform inversion to shallow-seismic Rayleigh waves on 2D structures / Martin Schäfer. Betreuer: T. Bohlen". Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1054396957/34.

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48

Seidl, Robert [Verfasser], Ernst [Akademischer Betreuer] Rank, Hans-Joachim [Gutachter] Bungartz e Ernst [Gutachter] Rank. "Full Waveform Inversion for Ultrasonic Nondestructive Testing / Robert Seidl ; Gutachter: Hans-Joachim Bungartz, Ernst Rank ; Betreuer: Ernst Rank". München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1151638668/34.

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49

Jiang, Hao. "Imagerie sismique˸ stratégies d’inversion des formes d’onde visco-acoustique". Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEM013/document.

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Abstract (sommario):

L’atténuation sismique est un paramètre physique très utile pour décrire et imager les propriétés du sous-sol, et tout particulièrement les roches saturées et les nuages de gaz. Les approches classiques analysent l’amplitude du spectre des données ou bien la distorsion de ce spectre, avec des méthodes asymptotiques. L’inversion des formes d’onde (Full Waveform Inversion en anglais, FWI) est une approche alternative qui prend en compte les aspects de fréquences finies. En pratique, à la fois les vitesses et l’atténuation doivent être déterminées. Il est connu que l’inversion multi-paramètre ne conduit pas à un résultat unique.Ce travail se focalise sur la détermination des vitesses et de l’atténuation. La dispersion liée à l’atténuation produit des modèles de vitesse équivalents en termes de cinématique. Je propose une inversion hybride : la « relation cinématique » est un moyen de guider l’inversion des formes d’onde non-linéaire. Elle se décompose en deux étapes. Dans un premier temps, l’information cinématique est remise à jour, et ensuite les vitesses et l’atténuation sont modifiées, pour une cinématique donnée. Différentes approches sont proposées et discutées au travers d’applications sur des données synthétiques 2D, en particulier sur les modèles Midlle-East et Marmousi
Seismic attenuation is a useful physical parameter to describe and to image the properties of specific geological bodies, e.g., saturated rocks and gas clouds. Classical approaches consist of analyzing seismic spectrum amplitudes or spectrum distortions based on ray methods. Full waveform inversion is an alternative approach that takes into account the finite frequency aspect of seismic waves. In practice, both seismic velocities and attenuation have to be determined. It is known that the multi-parameter inversion suffers from cross-talks.This thesis focuses on retrieving velocity and attenuation. Attenuation dispersion leads to equivalent kinematic velocity models, as different combinations of velocity and attenuation have the same kinematic effects. I propose a hybrid inversion strategy: the kinematic relationship is a way to guide the non-linear full waveform inversion. The hybrid inversion strategy includes two steps. It first updates the kinematic velocity, and then retrieves the velocity and attenuation models for a fixed kinematic velocity. The different approaches are discussed through applications on 2D synthetic data sets, including the Midlle-East and Marmousi models

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50

Jiang, Hao. "Imagerie sismique˸ stratégies d’inversion des formes d’onde visco-acoustique". Electronic Thesis or Diss., Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEM013.

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Abstract (sommario):

L’atténuation sismique est un paramètre physique très utile pour décrire et imager les propriétés du sous-sol, et tout particulièrement les roches saturées et les nuages de gaz. Les approches classiques analysent l’amplitude du spectre des données ou bien la distorsion de ce spectre, avec des méthodes asymptotiques. L’inversion des formes d’onde (Full Waveform Inversion en anglais, FWI) est une approche alternative qui prend en compte les aspects de fréquences finies. En pratique, à la fois les vitesses et l’atténuation doivent être déterminées. Il est connu que l’inversion multi-paramètre ne conduit pas à un résultat unique.Ce travail se focalise sur la détermination des vitesses et de l’atténuation. La dispersion liée à l’atténuation produit des modèles de vitesse équivalents en termes de cinématique. Je propose une inversion hybride : la « relation cinématique » est un moyen de guider l’inversion des formes d’onde non-linéaire. Elle se décompose en deux étapes. Dans un premier temps, l’information cinématique est remise à jour, et ensuite les vitesses et l’atténuation sont modifiées, pour une cinématique donnée. Différentes approches sont proposées et discutées au travers d’applications sur des données synthétiques 2D, en particulier sur les modèles Midlle-East et Marmousi
Seismic attenuation is a useful physical parameter to describe and to image the properties of specific geological bodies, e.g., saturated rocks and gas clouds. Classical approaches consist of analyzing seismic spectrum amplitudes or spectrum distortions based on ray methods. Full waveform inversion is an alternative approach that takes into account the finite frequency aspect of seismic waves. In practice, both seismic velocities and attenuation have to be determined. It is known that the multi-parameter inversion suffers from cross-talks.This thesis focuses on retrieving velocity and attenuation. Attenuation dispersion leads to equivalent kinematic velocity models, as different combinations of velocity and attenuation have the same kinematic effects. I propose a hybrid inversion strategy: the kinematic relationship is a way to guide the non-linear full waveform inversion. The hybrid inversion strategy includes two steps. It first updates the kinematic velocity, and then retrieves the velocity and attenuation models for a fixed kinematic velocity. The different approaches are discussed through applications on 2D synthetic data sets, including the Midlle-East and Marmousi models

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Tesi sul tema "Full wavefrom inversion"

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