Neste trabalho apresentamos um novo método de compressão, com perda controlada de dados, que tem a vantagem de ter uma taxa significativa de compressão sem introduzir nenhuma perda superior a um parâmetro escolhido pelo usuário. Esta abordagem é uma abordagem mista, pois usa técnicas de compactação de dados tanto com perda quanto sem perda. Isto quer dizer que conseguimos um método que alia as vantagens da alta compressão, sem introduzir distorções indesejáveis nos dados. Mostramos como a massa de dados utilizada nos nossos estudos é obtida e a sua importância na prospecção de depósitos de hidrocarbonetos. É apresentado um levantamento bibliográfico com técnicas de compressão aplicadas a dados sísmicos tipicamente utilizadas em aplicações comerciais. Por fim, apresentamos os resultados da compressão utilizando o método em conjuntos de dados sísmicos reais. Para 1% de erro, os arquivos de dados sísmicos compactados passaram a ter algo próximo a 25% de seus tamanhos originais, o que representa um fator de compressão de aproximadamente 4 / This work presents a new compression method with controlled loss of data, which has the advantage of having a significant compression ratio without introducing to the data a loss higher than a parameter chosen by the user. This approach is a mixed approach, as it uses lossy and lossless data compression techniques. This means that we have achieved a method that combines the advantages of high compression without introducing undesirable distortions in the data. We show how the mass of data used in our studies is obtained and its importance in the exploration of hydrocarbon deposits. A literature review is presented with compression techniques applied to seismic data typically used in commercial applications. Finally, we present the results of compression using the method on real seismic data sets. For 1% error, the archives of seismic data now have close to 25% of their original size, which represents a compression factor of about 4

[pt] A interpretação de dados sísmicos é de fundamental importância para a industria de óleo e gás. Uma vez que esses tipos de dados possuem um caráter volumétrico, não é tão simples se identificar e selecionar atributos presentes em sua estrutura 3D. Além disso, a grande presença de ruídos e concavidades acentuadas nesse tipo de dado aumenta a complexidade de sua manipulação e visualização. Devido a essas características, a geometria do dado é muito complexa, sendo necessários modelos de iluminação mais realísticos para realizar a iluminação do volume sísmico. Este trabalho consiste em realizar a visualização volumétrica de dados sísmicos baseada no algoritmo de traçado de raios, utilizando um modelo de iluminação por oclusão direcional, calculando a contribuição de luz ambiente que chega a cada elemento do volume. Desta forma, conseguimos realçar a geometria do dado sísmico, sobretudo onde as concavidades e falhas são mais acentuadas. O algoritmo proposto foi inteiramente implementado em placa gráfica, permitindo manipulação a taxas interativas, sem a necessidade de pré-processamento. / [en] The interpretation of seismic volumetric data has a major importance for the oil and gas industry. Since these data types have a volumetric character mode, identify and select attributes present in this struct become a difficult task. Furthemore, the high-frequecy noise and depth information typically found in this type of data, increasesthe complexity of their manipulation and visualization. Due to these characteristics, the geometry of 3D sismic data is very complexy and is necessary more realistic light model to perfom the illumnination of the seismic volume. This work consists of performing a volumetric visualization of seismic data based on ray tracing algorithm, using an illumination model by directional occlusion, computing the ambiente light attenuated by the elements in the light trajetory for all elements in the volume. Thus, we emphasize the geometry of the seismic data, especially the depth cues and spatial relationship. The proposed algorithm was fully implemented on graphics card, allowing at interactive rates, without any pre-processing.

The primary focus of this thesis is to examine the detailed seismic structure of the northern Cascadia margin, including the Cascadia basin, the deformation front and the continental shelf. The results of this study are contributing towards understanding sediment deformation and tectonics on this margin. They also have important implications for exploration of hydrocarbons (oil and gas) and natural hazards (submarine landslides, earthquakes, tsunamis, and climate change). The first part of this thesis focuses on the role of gas hydrate in slope failure observed from multibeam bathymetry data on a frontal ridge near the deformation front off Vancouver Island margin using active-source ocean bottom seismometer (OBS) data collected in 2010. Volume estimates (∼ 0.33 km^3) of the slides observed on this margin indicate that these are capable of generating large (∼ 1 − 2 m) tsunamis. Velocity models from travel time inversion of wide angle reflections and refractions recorded on OBSs and vertical incidence single channel seismic (SCS) data were used to estimate gas hydrate concentrations using effective medium modeling. Results indicate a shallow high velocity hydrate layer with a velocity of 2.0 − 2.1 km/s that corresponds to a hydrate concentration of 40% at a depth of 100 m, and a bottom simulating reflector (BSR) at a depth of 265 − 275 m beneath the seafloor (mbsf). These are comparable to drilling results on an adjacent frontal ridge. Margin perpendicular normal faults that extend down to BSR depth were also observed on SCS and bathymetric data, two of which coincide with the sidewalls of the slump indicating that the lateral extent of the slump is controlled by these faults. Analysis of bathymetric data indicates, for the first time, that the glide plane occurs at the same depth as the shallow high velocity layer (100±10 mbsf). In contrast, the glide plane coincides with the depth of the BSR on an adjacent frontal ridge. In either case, our results suggest that the contrast in sediments strengthened by hydrates and overlying or underlying sediments where there is no hydrate is what causing the slope failure on this margin. The second part of this dissertation focuses on obtaining the detailed structure of the Cascadia basin and frontal ridge region using mirror imaging of few widely spaced OBS data. Using only a small airgun source (120 cu. in.), our results indicate structures that were previously not observed on the northern Cascadia margin. Specifically, OBS migration results show dual-vergence structure, which could be related to horizontal compression associated with subduction and low basal shear stress resulting from over-pressure. Understanding the physical and mechanical properties of the basal layer has important implications for understanding earthquakes on this margin. The OBS migrated image also clearly shows the continuity of reflectors which enabled the identification of thrust faults, and also shows the top of the igneous oceanic crust at 5−6 km beneath the seafloor, which were not possible to identify in single-channel and low-fold multi-channel seismic (MCS) data. The last part of this thesis focuses on obtaining detailed seismic structure of the Vancouver Island continental shelf from MCS data using frequency domain viscoacoustic full waveform inversion, which is first of its kind on this margin. Anelastic velocity and attenuation models, derived in this study to subseafloor depths of ∼ 2 km, are useful in understanding the deformation within the Tofino basin sediments, the nature of basement structures and their relationship with underlying accreted terranes such as the Crescent and the Pacific Rim terranes. Specifically, our results indicate a low-velocity zone (LVZ) with a contrast of 200 m/s within the Tofino basin sediment section at a depth 600 − 1000 mbsf over a lateral distance of 10 km. This LVZ is associated with high attenuation values (0.015 − 0.02) and could be a result of over pressured sediments or lithology changes associated with a high porosity layer in this potential hydrocarbon environment. Shallow high velocities of 4 − 5 km/s are observed in the mid-shelf region at depths > 1.5 km, which is interpreted as the shallowest occurrence of the Eocene volcanic Crescent terrane. The sediment velocities sharply increase about 10 km west of Vancouver Island, which probably corresponds to the underlying transition to the Mesozoic marine sedimentary Pacific Rim terrane. High attenuation values of 0.03 − 0.06 are observed at depths > 1 km, which probably corresponds to increased clay content and the presence of mineralized fluids. / Graduate / 0373 / 0372 / 0605 / subbarao@uvic.ca

Multicomponent seismic imaging techniques improve geological interpretation by providing crucial information about subsurface characteristics. These techniques deliver different images of the same subsurface using multiple waveforms. Compressional (P) and shear (S) waves respond to lithology and fluid variations differently, providing independent measurements of rock and fluid properties. Joint interpretation of multicomponent images requires P-wave and S-wave events to be aligned in depth. The process of identifying P and S events from the same reflector is called depth-registration. The purpose of this investigation is to illustrate procedures for depth-registering P and S seismic data when the most fundamental information needed for depth-registration – reliable velocity data – are not available. This work will focus on the depth-registration of a 9-component 3-dimensional seismic dataset targeting the Sycamore formation in Stephens County, Oklahoma. The survey area – 16 square miles – is located in Sho-Vel-Tum oilfield. Processed P-P, SV-SV, and SH-SH wave data are available for post-stack analysis. However, the SV-data volume will not be interpreted because of its inferior data-quality compared to the SH-data volume. Velocity data are essential in most depth-registration techniques: they can be used to convert the seismic data from the time domain to the depth domain. However, velocity data are not available within the boundaries of the 9C/3D seismic survey. The data are located in a complex area that is folded and faulted in the northwest part of the Ardmore basin, between the eastern Arbuckle Mountains and the western Wichita Mountains. Large hydrocarbon volumes are produced from stratigraphic traps, fault closures, anticlines, and combination traps. Sho-Vel-Tum was ranked 31st in terms of proved oil reserves among U.S. oil fields by a 2009 survey. I will interpret different depth-registered horizons on the P-wave and S-wave seismic data volumes. Then, I will present several methods to verify the accuracy of event-registration. Seven depth-registered horizons are mapped through the P-P and SH-SH seismic data. These horizons show the structural complexity that imposes serious challenges on well drilling within the Sho-Vel-Tum oil field. Interval Vp/Vs – a seismic attribute often used as lithological indicator – was mapped to constrain horizon picking and to characterize lateral stratigraphic variations. / text

Afin de réaliser des traitements locaux sur des données de diverses natures (volumes, images ou signaux) contenant des éléments informatifs dans certaines bandes de fréquence, nous nous intéressons dans cette thèse à l’étude de bancs de filtres (BdF). Plus précisément, nous étudions l’existence et la synthèse de BdF de réponses impulsionnelles finies (RIF) inverses d’un BdF d’analyse RIF redondant complexe fixé. Nous proposons en particulier des méthodes testant l’inversibilité de la matrice d’analyse et la construction d’un inverse explicite à l’aide de la formulation polyphase. À partir de ce dernier, nous proposons une paramétrisation réduite de l’ensemble des BdF de synthèse permettant d’optimiser leurs réponses selon différents critères. Cette étude est étendue au cas multidimensionnel notamment par l’utilisation de la notion de résultant. Ces outils permettant de représenter efficacement certaines informations structurées dans des données, il devient possible de les préserver tout en rejetant d’éventuelles perturbations. Le premier cadre considéré est celui du bruit gaussien. Nous avons utilisé le principe de Stein pour proposer deux méthodes de débruitage : FB-SURELET-E et FBSURELET-C. Elles sont comparées à des méthodes récentes de débruitage conduisant à de bons résultats en particulier pour des images texturées. Un autre type d’application est ensuite considéré : la séparation des structures orientées. Afin de traiter ce problème, nous avons développé une méthode de filtrage anisotrope. Les algorithmes réalisés sont finalement testés sur des données issues de différents domaines applicatifs (sismique, microscopie, vibrations) / Our main purpose in this PhD thesis is to perform local frequential (or directional) processing in different kind of data (volumes, images or signals). To this end, filter banks (FBs) are studied. More precisely, we first investigate the existence and the construction of synthesis FBs inverse to a given FIR complex analysis FB. Through the study of the polyphase analysis matrix, we are able to propose methods to test the invertibility and to build one inverse FB. Using this inverse, we provide a parametrization of the set of synthesis FB, with which we optimize filter responses with different criteria. The same study is performed in the multidimensional case. Since FBs provide an efficient representation of structured information in data, it is then possible to preserve them while rejecting unwanted perturbations. By associating Stein’s principle and those FB, we proposed two methods to denoise signals and images corrupted by Gaussian noise. These methods, named FB-SURELET-E and FB-SURELET-C, are compared to recent denoising methods and are found to offer good results, especially for textured images. Another type of application is then investigated : separation of oriented structures. To this end, we have developed an anisotropic filtering method. The different proposed methods are finally applied on images and signals from various fields : seismic images and cubes, transmission electron microscopy (TEM) images of catalysts and vibration signals from car engines

[pt] A melhoria nas técnicas de obtenção de dados sísmicos fez com que estes dados sejam da ordem de até terabytes, o que gera um grande problema no armazenamento e transmissão dos mesmos. No que se refere ao problema de armazenamento em disco, apesar da queda no preço do disco rígido, o avanço das técnicas de obtenção do dado sísmico e o barateamento destas técnicas de obtenção do dado fazem com que a demanda por espaço em disco cresça mais rápido do que a queda no preço do hardware. Outro fator importante é a limitação de espaço físico para armazenar todos os discos rígidos de forma a garantir a segurança da informação destes discos. Este trabalho tem como objetivo apresentar uma nova técnica de compactação para dados sísmicos utilizando a transformada wavelet 3D. É feito um comparativo com as técnicas de compressão atuais, que utilizam a transformada 2D. / [en] Improvements made in techniques for seismic data acquisition have led to data that are of the order of terabytes, which in turn creates the problem of data storage and transmission of them through the network. In regards to the problem of disk storage, despite the hard disk decreasing price, the improvement and reduction cost in seismic data acquisition techniques has pushed the demand for disk space to grow faster than the reduction of the hardware cost. Another important factor is the space necessary to store all hard drives, to provide security for information from these records. In order to tackle these problems this thesis presents a new technique for seismic data compression using 3D wavelet transform. It is also presented in comparison with current compression techniques which use the 2D transform.

The study area, Dhurnal oil field, is located 74 km southwest of Islamabad in the Potwar basin of Pakistan. Discovered in March 1984, the field was developed with four producing wells and three water injection wells. Three main limestone reservoirs of Eocene and Paleocene ages are present in this field. These limestone reservoirs are tectonically fractured and all the production is derived from these fractures. The overlying claystone formation of Miocene age provides vertical and lateral seal to the Paleocene and Permian carbonates. The field started production in May 1984, reaching a maximum rate of 19370 BOPD in November 1989. Currently Dhurnal‐1 (D-1) and Dhurnal‐6 (D-6) wells are producing 135 BOPD and 0.65 MMCF/D gas. The field has depleted after producing over 50 million Bbls of oil and 130 BCF of gas from naturally fractured low energy shelf carbonates of the Eocene, Paleocene and Permian reservoirs. Preliminary geological and geophysical data evaluation of Dhurnal field revealed the presence of an up-dip anticlinal structure between D-1 and D-6 wells, seen on new 2003 reprocessed data. However, this structural impression is not observed on old 1987 processed data. The aim of this research is to compare and evaluate old and new reprocessed data in order to identify possible factors affecting the structural configuration. For this purpose, a detailed interpretation of old and new reprocessed data is carried out and results clearly demonstrate that structural compartmentalization exists in Dhurnal field (based on 2003 data). Therefore, to further analyse the available data sets, processing sequences pertaining to both vintages have been examined. After great effort and detailed investigation, it is concluded that the major parameter giving rise to this data discrepancy is the velocity analysis done with different gridding intervals. The detailed and dense velocity analysis carried out on the data in 2003 was able to image the subtle anticlinal feature, which was missed on the 1987 processed seismic data due to sparse gridding. In addition to this, about 105 sq.km 3D seismic data recently (2009) acquired by Ocean Pakistan Limited (OPL) is also interpreted in this project to gain greater confidence on the results. The 3D geophysical interpretation confirmed the findings and aided in accurately mapping the remaining hydrocarbon potential of Dhurnal field.

This research investigates the character and significance of shelf-edge deltas within the sedimentary source-to-sink system, and how variability at the shelf edge leads to different styles of deep-water deposition. Because the shelf-edge represents one of the key entry points for terrigenous sediment to be delivered into the deep water, understanding of the sedimentary processes in operation at these locations, and the character of sediment transported through these deltas is critical to understanding of deep-water sedimentary systems. The research was carried out using three datasets: an outcrop dataset of 6000 m of measured sections from the Permian-Triassic Karoo Basin, South Africa, a 3D seismic data volume from the Eocene Northern Santos Basin, offshore Brazil and a dataset of 29 previously published descriptions of shelf-edge deltas from a variety of locations and data types. The data presented highlight the importance of sediment instability in the progradation of basin margins, and deep-water transport of sediment. The strata of the Karoo Basin shelf margin represent river-dominated delta deposits that become more deformed as the shelf-edge position is approached. At the shelf edge, basinward dipping, offlapping packages of soft-sediment-deformed and undeformed strata record repetitive collapse and re-establishment of shelf-edge mouth bar packages. The offlapping strata of the Karoo outcrops record progradation of the shelf margin through accretion of the shelf-edge delta, for over 1 km before subsequent transgression. The Eocene Northern Santos Basin shelf margin, in contrast, exhibits instability features which remove kilometers-wide wedges of the outer shelf that are transported to the basin floor to be deposited as mass-transport packages. In this example, shelf-edge progradation is achieved through „stable. accretion of mixed turbidites and contourites. The data also emphasize the importance of the role of shelf-edge delta processes in the delivery of sediment to the basin floor. A global dataset of 29 examples of shelf-edge systems strongly indicates that river domination of the shelf-edge system (as read from cores, well logs or isopach maps) serves as a more reliable predictor of deep-water sediment delivery and deposition than relative sea level fall as traditionally read in shelf-edge trajectories or sequence boundaries. / text

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.

This thesis work is directed at estimating gas hydrate and free gas distribution and saturation in local structures in the Ulleung Basin, East Sea offshore Korea. The estimates are obtained from a 2-D multi-channel seismic (MCS) reflection profile from the basin. Firstly, structures of locally focused upwelling fluid and gas flow were imaged using time-migrated sections and seismic attributes, and secondly seismic velocities were obtained to estimate gas hydrate and free gas saturations. The structures investigated are up to 1 km across, and are characterized by reduced reflectivity (‘blank zones’) and pulled-up sediment reflectors on the seismic sections. Throughout the study, a comparison is made between the blank zones and areas outside them where not much gas hydrate or gas is expected, to examine their peculiar characteristics as related to the formation of gas hydrate and underlying free gas. The regional depth of possible occurrence of gas hydrate and free gas is determined by predicting the base of the gas hydrate stability zone (BGHSZ) from sediment properties and heat flow estimates calibrated by a few bottom-simulating reflectors (BSRs) from outside the analyzed seismic section. A large number of normal moveout (stacking) velocity profiles were obtained within and outside the blank zones. Interval velocities were then derived by applying the commonly used unconstrained Dix equation as well as by applying constraints to inversion using regularized linear inversion and non-linear Bayesian inversion. The latter method fully explores the uncertainty of the interval velocity estimates. Compared to areas outside the blank zones, the velocities within the blank zones are up to 30% larger at about 30 m above the BGHSZ and up to 65% smaller immediately below the BGHSZ. The velocity increase implies a gas hydrate saturation of 10-40% of the pore space. The velocity decrease implies a free gas saturation of 1-4% of the pore space. Their detailed distribution within individual structures cannot be resolved. Reflector pull-up in time sections in the hydrate zone allows an independent velocity estimate, assuming the pull-up is solely a velocity effect. The implied velocity is much higher than the interval velocity estimates, so there also must be physical deformation. The heat flow estimated depth of the BGHSZ is in good agreement with the transition from gas hydrate to free gas as inferred from seismic velocities. The general conclusion of the thesis work is that a variety of careful analyses of MCS data that characterize the seismic signal and estimate the seismic velocity structure can provide insight into gas hydrate and free gas occurrences. The large amounts of gas hydrate and free gas associated with the blank zones inferred by this study should draw special attention to future energy and climate effects in this area and other similar regions.