Dissertations / Theses on the topic 'Migration amplitudes'

Two- (2D) and three- (3D) dimensional pre-stack and post-stack seismic reflection data are used to investigate the processes which have led to the development of amplitude anomalies on reflections in the faulted, Cenozoic overburden on the Laminaria High, Northwest Shelf of Australia. The integration of amplitude and seismic attribute maps for four key horizons (the seabed, Horizon H9, Horizon H10 and Horizon H13) with the corresponding two-way time (TWT) structure maps has identified the structural controls on the distribution of seismic anomalies. On the seabed, the main anomaly is located on the up-dip side of the fault trace, and is elongated parallel to the local time structure contours. These observations are consistent with the anomalies having developed in response to structurally-controlled fluid seepage along, and up-dip migration away from the fault trace. Amplitude anomalies associated with the deeper H9 reflector are also located adjacent to fault traces but are discordant to the local time structure contours. This observation suggests that the anomalies may be due to cemented hardgrounds that formed due to seepage when the faults intersected the palaeo-seafloor but were subsequently buried and deformed during ongoing sedimentation and fault growth/linkage. Reprocessing of the 2D and 3D seismic pre-stack data supports the seismic interpretation of amplitude anomalies at the seabed. It is concluded that these anomalies are robust – that is, they are likely to reflect geological processes and are not simply a function of the chosen seismic processing workflow – and are caused by localised changes in acoustic impedence in the subsurface. More important is that using processed data without the knowledge of the background processing sequence for the data could be an issue in any 2D or 3D seismic interpretation. For this reason the veracity of processing of any seismic data needs to be questioned, and should not be taken for granted especially if different surveys produce conflicting interpretations. 2D hydrocarbon migration modelling combined with fault slip- and dilation-tendency analyses were undertaken in order to investigate the impact of faults and host-rock lithologies on hydrocarbon seepage at the present-day sea floor. Results show that some active faults associated with amplitude anomalies (e.g. Fault F10) are critically stressed, assuming a static, and spatially homogeneous regional stress field. However, other faults associated with amplitude anomalies (e.g. Fault F11) appear not to be critically stressed. These results suggests that the “regional” stress field could, in fact, vary spatially and temporally allowing faults in different parts of the study area to become critically stressed – hence act as fluid migration pathways – at different times. The migration models show that hydrocarbon migration pathways are strongly influenced by fault-zone properties, specifically the capillary entry pressure (CEP) along faults. The dip of the sediment layers also influences hydrocarbon leakage from the subsurface to the seabed. In general, the migration models show vertical hydrocarbon migration along faults coupled with lateral migration below the seal layers and between faults. Fluids migrate along faults with two patterns of flow based on the CEP values along the faults: 1) focused – fluids migrate as a linear pattern along faults when the capillary entry pressure along the fault is within the lower range of the “background” CEP values; 2) diffuse – fluids are guided by faults when the capillary entry pressure along the fault is within the higher range of the “background” CEP values.

In this abstract, we present a nonlinear curvelet-based sparsity-promoting formulation of a seismic processing flow, consisting of the following steps: seismic data regularization and the restoration of migration amplitudes. We show that the curvelet's wavefront detection capability and invariance under the migration-demigration operator lead to a formulation that is stable under noise and missing data.

Migration can accurately locate reflectors in the earth but in most cases fails to correctly resolve their amplitude. This might lead to mis-interpretation of the nature of reflector. In this thesis, I introduced a method to accurately recover the amplitude of the seismic reflector. This method relies on a new transform-based recovery that exploits the expression of seismic images by the recently developed curvelet transform. The elements of this transform, called curvelets, are multi-dimensional, multi-scale, and multi-directional. They also remain approximately invariant under the imaging operator. I exploit these properties of the curvelets to introduce a method called Curvelet Match Filtering (CMF) for recovering the seismic amplitude in presence of noise in both migrated image and data. I detail the method and illustrate its performance on synthetic dataset. I also extend CMF formulation to other geophysical applications and present results on multiple removal. In addition of that, I investigate preconditioning of the migration which results to rapid convergence rate of the iterative method using migration.

La migration est une étape clé de la chaîne de traitement des données de sismique réflexion. Intervenant après les phases de pré-traitement, et d'estimation du modèle de vitesse, elle peut servir de base à la caractérisation litho-sismique du réservoir. En effet lorsqu'elle est faîte avant sommation, en profondeur et en amplitude préservée, elle permet d'obtenir les réflectivités du sous-sol en fonction de l'angle d'incidence de l'onde sismique. Une inversion stratigraphique des paramètres élastiques du réservoir est alors possible permettant une caractérisation sismique plus détaillée du réservoir. Jusqu'à présent la migration en amplitude préservée était essentiellement basée sur des techniques de traçé de rayons, qui hélas présentent de réelles limitations pour les milieux géologiques complexes caractérisés par de fortes variations latérales de vitesse. L'utilisation d'approximations n one-way z paraxiales de l'équation d'onde permet de s'affranchir de ces limitations puisque, dans le cadre de la migration profondeur, elles fournissent des solutions précises et robustes pour l'ensemble de la bande de fréquences sismiques. En outre elles prennent en compte naturellement les trajectoires multiples induites par des modèles de vitesse complexes (en particulier dans le cas des structures salifères ). Longtemps pénalisées par leur coût numérique dans les applications 3D ces méthodes peuvent actuellement être appliquées sur données réelles. Elles portent le nom de migration par équation d'onde. Sur le plan de la préservation des amplitudes l'étude de la migration par équation d'onde n'a pas débouché jusqu'à présent sur une formulation aussi aboutie qu'avec l'utilisation de la théorie des raies. Dans ce domaine les efforts doivent porter tant sur la propagation numérique du champs d'onde, que sur la condition d'imagerie. Mon travail de thèse porte sur la définition et le développement numérique d'une méthode de migration par équation d'onde quantitative à 2D. Dans un premier temps, j'ai abordé l'étude de la préservation des amplitudes par l'approximation "one-way" paraxiale de l'équation des ondes. Je me suis familiarisé avec la technique en m'appuyant sur les travaux et les algorithmes développés à l'Institut Français du Pétrole. Dans un second temps, j'ai modifié le principe d'imagerie classique, de façon à constituer des collections migrées en fonction de l'angle de réflexion, et à retrouver l'information sur la dépendance angulaire de la réflectivité ou de la perturbation d'impédance. Cela devrait nous permettre de mieux caractériser le sous-sol dans le cas de milieux complexes ou les analyses classiques (AVO) ne donnent pas de résultats satisfaisants.

In this paper, we recover the amplitude of a seismic image by approximating the normal (demigrationmigration)operator. In this approximation, we make use of the property that curvelets remain invariant under the action of the normal operator. We propose a seismic amplitude recovery method that employs an eigenvalue like decomposition for the normal operator using curvelets as eigen-vectors. Subsequently, we propose an approximate non-linear singularity-preserving solution to the least-squares seismic imaging problem with sparseness in the curvelet domain and spatial continuity constraints. Our method is tested with a reverse-time ’wave-equation’ migration code simulating the acoustic wave equation on the SEG-AA salt model.

L'obtention d'images tri-dimensionnelles du sous-sol est actuellement l'un des enjeux les plus importants en sismique petroliere. A l'aide d'ondes emises et propagees dans le sous-sol, et en se basant sur la physique de la propagation, on extrait des informations sur le milieu traverse pour en obtenir une image. Compte tenu des moyens de calculs actuels, on utilise des methodes de resolution qui ne tiennent pas ou tres peu compte de la complexite du milieu. En particulier, elles se basent sur l'hypothese d'une invariance laterale qui n'est pas acceptable dans les cas geologiquement complexes. Il devient alors indispensable d'utiliser un formalisme tri-dimensionnel. Au cours des dernieres annees, des travaux theoriques ont montre qu'il etait possible d'obtenir des images quantitatives en profondeur et avant sommation des donnees, par inversion linearisee au sens de born et avec l'approximation haute frequence (theorie des rais). Le principal but de cette these est donc l'etude et le developpement des aspects theoriques et pratiques d'une methode susceptible : ? de prendre en compte les variations tri-dimensionnelles du milieu ; ? d'utiliser toutes les donnees avant sommation ; ? de quantifier les contrastes d'un parametre physique caracterisant le sous-sol ; ? et de fournir des images 3d en fonction de la profondeur. Jusqu'a tres recemment, ce type de methodes semblait irrealisable avec les moyens de calculs actuels. Bien qu'il existe deja de nombreux algorithmes d'imagerie profondeur, aucun ne donne actuellement d'information quantitative. Nous montrons ici qu'il est en fait possible de developper, avec des ressources informatiques limitees, des algorithmes respectant la geometrie effective de la propagation d'ondes dans le milieu. Deux appplications sur donnees reelles de mer du nord fournies par la compagnie norsk hydro sont presentees pour tester les strategies de programmation et prouver la faisabilite d'une migration 3d en profondeur, a amplitude preservee et avant sommation des donnees (3d papsdm). Ces tests demontrent ainsi clairement que des applications realistes de la methode proposee sont possibles et qu'elles ameliorent grandement les resultats obtenus dans une meme zone avec l'approximation 2d.

A frequência com que trabalhadores migrantes encontram-se submetidos a condições indignas de moradia despertou o interesse na investigação da existência e da extensão de obrigação jurídica do empregador em relação a seu correspondente direito. Como deixa entrever a jurisprudência a respeito, à exceção das ocasiões em que o empregador expressamente assume obrigação de tal natureza, o problema não encontra resposta normativa enunciada de forma específica. À vista dos direitos fundamentais, normas jurídicas nacionais e internacionais convergem no sentido de que o conteúdo do direito à moradia não se preenche com a simples existência de um abrigo ou alojamento; tem deveras maior alcance e abrange a concepção da moradia adequada. A inserção do direito à moradia do trabalhador migrante no âmbito do contrato de emprego pode suscitar colisão entre aquele direito fundamental e o de proteção à propriedade do empregador. A solução apresentada pretende oferecer uma resposta plausível e fundamentada à indagação central da pesquisa, dentre os possíveis encaminhamentos do problema.
The frequency with which migrant workers are subjected to degrading housing conditions has aroused the interest in investigating the existence and extent of the employer\'s legal obligation in relation to his/her corresponding right. As jurisprudence about it allows us to glimpse, except for occasions where the employer expressly assumes an obligation of such nature, the problem finds no normative response specifically set out. In view of fundamental rights, national and international legal standards converge in the sense that the content of the right to housing is not filled with the mere existence of a shelter; indeed has greater range and covers the conception of a dignifying housing. The insertion of the housing rights of migrant workers under the scope of the labor agreement may raise collision between that fundamental right and that of protecting the employer\'s property. The solution presented aims to provide a plausible answer and reasoned to the research central question, among the possible referrals of the problem.

Orientador: Martin Tygel
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica e Instituto de Geociencias
Made available in DSpace on 2018-08-04T20:27:31Z (GMT). No. of bitstreams: 1 Santiago_TaniaMariaGodinho_M.pdf: 6170921 bytes, checksum: fb1caa1410e2409aa2455f02c3c86e58 (MD5) Previous issue date: 2004
Resumo: Atualmente, a indústria do petróleo, tanto na área de caracterização de reservatórios quanto na de exploração, tem feito cada vez mais uso do estudo da variação da amplitude sísmica com o afastamento fonte-receptor, ou com o ângulo de reflexão, como ferramenta auxiliar na previsão da existência de hidrocarbonetos nos reservatórios. Como o método, rotineiramente utilizado, de transformação de afastamento para ângulo de reflexão, em dados migrados na configuração afastamento comum, envolve erros que podem diminuir a confiabilidade deste estudo, toma-se necessário uma nova maneira para a obtenção de dados que produzam curvas mais acuradas da variação da amplitude com o ângulo de reflexão (AVA). Neste sentido, apresenta-se nesta dissertação a migração Kirchhoff no domínio de ângulo comum 2,5D por empilhamento em tempo e em amplitude verdadeira, e os resultados de sua aplicação em dados sísmicos sintéticos de três modelos geológicos. Discute-se a influência, nos resultados, dos parâmetros de aquisição dos dados sísmicos e a parametrização da migração, especificamente a abertura e intervalo entre os ângulos de mergulho da migração. São feitas comparações das curvas de amplitude versus o ângulo de reflexão oriundas dos conjuntos de dados migrados no domínio de ângulo comum e no domínio de afastamento comum, e mostra-se a maior eficiência da primeira migração em obter curvas de AVA que se aproximam mais das curvas teóricas
Abstract: The analysis of amplitude variation with offset or reflection angle is of great importance in the oil industry to predict hydrocarbon presence in the reservoir. This analysis is applied to both reservoir and exploration areas. The usual transformation method from offset to reflection angle, for common-offset migrated data, involves errors that may produce unreliable results. Thus, it becomes necessary to find altemative procedures to obtain appropriate data to provide more reliable curves of amplitude versus reflection angle (AVA). This work considers 2.5D true amplitude Kirchhoff-time migration in the common-angle domain, and its application to synthetic seismic data. It also examines the influence of seismic acquisition and migration parameters, aperture and migration dip-angle increment, on the migration results. Comparison between AVA curves obtained from common-angle and common-offset migrated data confirms that the former is a more reliable procedure
Mestrado
Mestre em Ciências e Engenharia de Petróleo

This thesis embodies a mathematical, physical, and quantitative investigation into the imaging and amplitude estimation of subsurface earth reflectivity structure within the framework of pre stack wave-equation depth migration of multi-offset seismic reflection data. Analysis is performed on five prestack depth migration reflectivity "imaging conditions" with respect to image quality and quantitative accuracy of recovered reflectivity amplitudes. A new computationally efficient and stable prestack depth migration imaging method is proposed which is based upon a geometric approximation to the theoretically correct, but unstable, "dynamic" imaging condition. The "geometric" imaging condition has the desirable property of true-amplitude reflectivity recovery in regions of both 1-D and 2-D velocity variation, while fully retaining and optimizing the favorable imaging characteristics of current, non-true amplitude formulations. The currently predominant "crosscorrelation" and "excitation-time" migration imaging methods are shown to possess significantly less accurate imaging and amplitude-recovery characteristics relative to the proposed geometric migration. The respective signal-to-noise recovery of their imaged amplitudes deteriorates approximately linearly (excitation-time) and quadratically (crosscorrelation) with depth. As a necessary prerequisite to the imaging analysis, a true-amplitude prestack depth migration equation is derived which appears to be new to the literature. This result is obtained in the form of a 2.5-D farfield Kirchhoff integral solution to the acoustic wave equation, after the application of a dynamic imaging condition to the reconstructed upgoing and downgoing wavefields. This solution is in harmony with zeroth order asymptotic ray theory (ART) assumptions, and depends upon WKBJ Green's functions which can be numerically evaluated for arbitrary migration models by raytracing methods. A new and "generalized" Kirchhoff prestack depth migration equation is subsequently obtained by the introduction of a weighting function into the true-amplitude migration integral. The weight is a function of both the reconstructed upgoing and downgoing wavefields, and is determined analytically by a mathematical application of each specific reflectivity imaging condition. This generalized equation is significant in that it provides a common mathematical, physical and computational basis for the comparative analytical and quantitative analysis of reflectivity image quality and amplitude recovery among current prestack migration philosophies and variants of those migration themes. In addition, three ancillary research objectives are achieved. The first achievement is the development of a Kirchhoff prestack depth migration computer algorithm to implement the generalized imaging of surface-recorded seismic reflection data. This algorithm can be readily modified to perform seismic wavefield imaging for other recording geometries such as cross-borehole or vertical seismic profiling, and may be suitable to non-seismic applications such as the imaging of electromagnetic wavefields and satellite-acquired synthetic aperture radar data. The second result is the development of a fast two-point raytracing computer algorithm which provides accurate computation of a subsurface grid of traveltimes and 1.5-D zeroth order ART amplitudes in a 1-D acoustic medium. This algorithm is useful for subsurface wavefield reconstruction and imaging, and for inversion applications such as geotomography. The third objective is the detailed quantitative examination of migration imaging quality and true relative-amplitude normal-incidence reflectivity recovery from numerically migrated depth images. This is achieved successfully in an extensive 2.5-D synthetic data analysis, using a challenging 2-D structural model, synthetic multifold reflection seismogram shot gathers, and the numerical imaging and modelling algorithms developed as part of this thesis research.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

O objetivo deste trabalho foi estudar a composição da avifauna aquática, a diversidade, suas abundâncias, a variação mensal e sazonal das populações e entender a relação desses fatores com a variação de maré na Laguna da Ilha Comprida. Ocorreram 6193 indivíduos referentes a 54 espécies, a diversidade de acordo com o Índice de Shannon foi 2,7036. Não houve diferença estatística no número total de indivíduos entre os meses e estações. Já a riqueza variou, sendo o maior valor na primavera, explicada pela ocorrência de espécies visitantes do hemisfério norte durante a migração para o sul. Houve correlação negativa entre a riqueza de espécies, número de indivíduos e diversidade, com a oscilação da maré, pois conforme a maré diminuía, aumentava a área disponível para descanso e forrageio. A Família Ardeidae apresentou correlação negativa mais forte em relação à amplitude de maré ao ser comparada as Famílias Scolopacidae e Charadriidae. Este fato ocorreu pela presença de Egreta caerulea que depende da maré baixa para forragear. A Laguna é uma importante área para avifauna aquática utilizada para alimentação e descanso, principalmente na maré baixa, além de ponto de parada para aves costeiras na migração para o sul durante a primavera.
The objectives of this work was to study the composition of aquatic bird, its diversity, abundance, monthly and seasonal variation of the bird populations and understand the relation of these factors with tidal variation at Laguna da Ilha Comprida Island. We registered 6193 individuals of bird referring to 54 species, being that the Shannon diversity index was 2,7036. There were not statistics difference between total number of individuals, the months and seasons. However there was variation of the species richness, being the biggest valor in the spring, explained for the occurrence of visiting species of north hemisphere during the migration for the south. There were negative correlation enters the species richness, individual number and diversity with the tidal oscillation. Because when the tide was low, increase the area available for rest and foraging. The Ardeidae family presented stronger negative correlation in relation of tidal variation when comparative being the Families Scolopacidae and Charadriidae. This fact occurred for the presence of Egreta caerulea that depends on the low tide to foraging. The Laguna is an important aquatic area for bird, used for feeding and rest, during the low tide and stopover for coastal birds in the migration for the south during the spring

In this paper, we present a nonlinear curvelet-based sparsity-promoting formulation for three problems in seismic processing and imaging namely, seismic data regularization from data with large percentages of traces missing; seismic amplitude recovery for subsalt images obtained by reverse-time migration and primary-multiple separation, given an inaccurate multiple prediction. We argue why these nonlinear formulations are beneficial.

Mon travail de thèse se propose d'étudier la structure, les propriétés physiques et les processus géodynamiques de la zone de subduction d'Equateur-Colombie grâce à l'adaptation et le développement d'outils d'imagerie sismique (inversion de formes d'ondes 'alias' tomographie en diffraction) et à leur application aux données de sismique marine multitrace (MCS) et grand-angle OBS (WA) acquises en Equateur-Colombie pendant les campagnes SISTEUR et SALIERI. Ces outils m'ont permis de réaliser une imagerie fine et quantitative à trois niveaux : l'imagerie superficielle (~ 0-3 km), l'imagerie à profondeur intermédiaire (~ 3-10 km) et l'imagerie profonde (~ 10-30 km). Dans le domaine superficiel, j'ai effectué une cartographie fine et quantitative des propriétés physiques des sédiments au voisinage du BSR (Bottom Simulating Reflector), interpreté comme la base de stabilité des hydrates de gaz. Sur le profil SIS-40 situé sur la marge sud de la Colombie, j'ai pu identifier la présence de failles qui perturbent localement le BSR. Les résultats présentés sous la forme d' une série de logs adjacents de l'image migrée en profondeur, montrent que certaines régions du BSR sont caractérisées par une augmentation de la vitesse (1470-1650 m/s), indiquant la présence d'une faible quantité d'hydrates de gaz au dessus du BSR; d'autres zones situées immédiatement sous le BSR sont caractérisées par une diminution de la vitesse (~1200 m/s), liée à la présence de gaz libres piégés sous la couche d'hydrate de gaz. A des profondeurs moyennes j'ai étudié la structure du chenal de subduction (profil SIS-72). Le chenal constitue la limite mécanique entre la plaque chevauchante et la plaque plongeante. Il est délimité à son toit par un fort réflecteur interprété comme le décollement interplaque et à sa base par le toit très réflectif de la croûte océanique en subduction. L'imagerie fine et quantitative des propriétés physiques du décollement interplaque permet de mieux comprendre le rôle de la circulation des fluides et des variations lithologiques et physiques, sur le couplage mécanique inter-plaque. En raison de la sensibilité de la méthode de tomographie en diffraction au macro-modèle de vitesse, un code de correction de ce modèle a été implémenté, afin d'obtenir des images tomographiques fiables (i.e. géométrie et amplitudes correctes). Du fait de la bande passante limitée de la source et de la longueur du dispositif d'acquisition limitée à 4.5 km, les images tomographiques ont une résolution spatiale limitée : l'image tomographique présente un déficit des petits et grands nombre d'onde (fréquences spatiales) limitant ainsi l' interprétation géologique des paramètres physiques cartographiés. Un traitement spécifique basé sur la modélisation des traces sismiques a été implémenté. L'image tomographique, traitée comme une série de traces verticales, constitue la donnée observée. L'espace des modèles est constitué par un ensemble de modèles impulsionnels et unidimensionnels de Terre construits aléatoirement. Ces modèles sont dégradés par convolution avec une estimation de l'ondelette source afin de fournir une représentation synthétique de l'image tomographique « observée ». La minimisation de la fonction coût entre les traces migrées et les traces synthétiques est effectuée dans le cadre d'une inversion globale par recuit simulé (VFSA= « Very Fast Simulated Annealing »). Le modèle moyen issu de cette procédure fournit un modèle 2D fin de vitesse, fonction de la profondeur et comparable à la limite de la résolution théorique de la source. A l'issue de ce traitement, des perturbations de vitesse positives sont mises en évidence au toit de la croûte, et d'autres négatives accompagnent certains segments du niveau du décollement. Ces dernières sont probablement associées à la présence de fluides. Le domaine plus profond a été étudié à partir des données MCS et WA dans le double but (1) d'améliorer la résolution spatiale des images sismiques du Moho et du contact interplaque en relation avec la zone sismogène, et (2) de détecter la présence d'anomalies crustales de vitesse et d'analyser leur relation avec les zones d'aspérité sismologiques. L'utilisation conjointe des données de sismique MCS et WA a été mise en oeuvre pour prolonger vers le bas les images de sismique verticale et tenter ainsi d'établir une relation entre les processus profonds et les manifestations en surface. L'application de la chaîne de traitement au profil SIS-44 a permis d'obtenir un modèle de vitesse bien contraint jusqu'à 25 km de profondeur. Ce modèle met en évidence des réflecteurs profonds (Moho et contact interplaque ) et des réflecteurs plus superficiels (splay fault), dont l'interprétation était initialement incertaine sur les images migrées en temps.