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4th International Congress of the Brazilian Geophysical Society
- Conference date: 20 Aug 1995 - 24 Aug 1995
- Location: Rio de Janero, Brazil
- Published: 20 August 1995
281 - 300 of 330 results
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Parallel Computing in Seismic Research
By B. BiondiImaging seismic data is an extremely computational intensive activity; some of the tasks, such as accurate 3-D velocity estimation and imaging of complex structures, are still beyond the reach of the most powerful computers available today. The computational power available for processing imposes a hard constraint on the methods that can be applied to analyze seismic data for exploration and development projects. Consequently, the evolution of computer technologies is one of the driving forces in the development of new seismic technologies. Because of this strong link between computer and seismic technologies, research in seismic processing needs to effectively exploit the available computational tools in order to be capable of fulfilling its mission to solve problems that applied geophysicists will encounter in the future. Parallel processing is at the core of the performance gains in today's high-performance computers. Parallel computers hold the irresistible promise of delivering high-computational power at affordable prices thanks to the leveraging of mass-produced hardware components such as micro-processors, memory, networks, and disk drives. However, the effective use of parallel computers is more difficult than the use of traditional serial/vector computers. These additional difficulties present several challenges to the adoption of parallel computers for seismic research.
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Practical, Scalable 3-D Seismic Processing
More LessThere are two reasons for the strong interest in the scalable parallel computers that have become available from several vendors over the past few years: (1) to save money on the types of seismic computing that have traditionally been done on expensive vector supercomputers and (2) to effectively exploit important new types of seismic imaging such as 3-D prestack depth migration and migration velocity analysis. Scalable parallel computers do both jobs very well because they use powerful superscalar RISC systems assembled with a scalable, "share nothing" philosophy. As such, this new class of machines is more practical than the massively parallel computers that appeared in the 1980's. The key to their practical use has been the simultaneous exploitation of two natural types of parallelism in 3-D seismic: "batch parallel" and "monolithic parallel."
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Practical Parallel Geopbysical Processing
Authors R. Zoll and M. BrzostowskiWe introduce some general concepts associated with using a parallel processing environment for geophysical applications. These concepts are based upon our experiences in writing software for a multi-node hardware system over the past five years. Each node has its own memory and may be integrated into a parallel processing system composed of I to 192 nodes. The later reflects the largest system we have experience with but is by no means an upper limit. The ideas we present here are applicable to any hardware platform fitting this general classification. The greater degree of freedom a parallel hardware system affords translates into more degrees of freedom in which an algorithm, or a job running such an algorithm, may be constructed. Having multiple CPU nodes in which to compute or contribute in terms of memory has given rise to a number of procedures to take advantage of this scalability. These concepts include the obvious procedure of using more than one node to those more complicated procedures of chainparallel, sweep-parallel, chain-sweep, cloning and partial Cloning. We introduce this nomenclature and explain the procedures with geophysical applications.
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Parallel Processing: Practical Experience
By S. FreitasDifferent types of parallel architectures present different types of trade-offs for the users. In this paper we will review common problems in implementing and using these systems and present our practical experience for solving them.
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Enabling Low-Cost 3-D Prestack Depth Migration
By S.A. Morton3-D prestack depth migration is proving itself useful and even critical for imaging in geologically complex areas, and hence is moving into the mainstream of seismic processing. While this movement has been fueled in large part by the relative affordability of modern parallel computers, the costs associated with large-scale 3-D prestack depth migration still prevent its routine and fully effective use. In this abstract, we summarize the state and costs of the predominant hardware and software technologies associated with prestack depth migration, and then present an approach which can dramatically reduce these costs and simultaneously improve the quality of the resulting image. In my presentation, I will describe the status of our implemention of affordable 3-D prestack depth migration.
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Estudio en el Sureste de Mexico Mediante dos Transectos
More LessEn este estudio se presentan dos modelos corticales del Sureste de México mediante dos Transectos que representan el comportamiento regional de la Anomalía de Bouguer. A los datos gravimétricos se integran los de magnetometría, geología de subsuelo y superficial, los cuales analizados separadamente y en conjunto, proporcionaron los medios para construir modelos geológicos regionales en los que se define una clara correspondencia con los diferentes estilos estructurales de las provincias geológicas por las que atravieza; ademas se identifican estructuras dentro del basamento magnetico, las cuales por sus características fisicas es probable que estén relacionadas con la apertura del Golfo de Mexico. Por otra parte, se hizo una evaluación del efecto Isostásico en el área de estudio, en la que se encontró que debido a la ubicación y a la orientación de los Transectos es despreciable en gran parte de los modelos.
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3-D DE BAJA COBERTURA, UN EJEMPLO
By H. CerquoneEn el diseńo de sismica 3-D, uno de los parametres que determina la calidad final es la cobertura. Sin embargo, en areas especificas la relación seńal/ruido es alta, 1lo que permite obtener secciones sismicas 2-D y 3-D de muy baja cobertura y mantener una calidad alta. La idea basica es mostrar que diseiiando 3-D de baja cobertura en areas determinadas se pueden obtener perfiles verticales y "time slices" de buena relación seńal/ruido a bajos costos.
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Estudio Geofisico de la Cuenca Sedimentaria Triasica en Mendoza
Authors E. Bibiana Castiglione, M. Mamaní and C. MoyanoEl estudio magnetotelúrico se realizó en una linea N-S, de 40 km de extensión, al este de la Cuenca Sedimentaria Triásica de Mendoza, frecuentemente denominada "Cuenca Cuyana" (Fernando Bettini, 1960) . El perfil se encuentra ubicado entre los paralelos de 32°15' - 32°45', Lat Sur, y entre entre los meridianos de 68°30W, figura N°1.
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Improvements with Amorphous and Nanocrystalline Ribbons to be Applied as Fluxgate Sensor Cores
More LessNew nominal compositions alloys have made available magnetic materials well suited for fluxgate sensors. This paper shows the magnetic properties evolution, of a near-zero magnetostrictive CoFeSiB ribbon as-quenched and after a convenient stress-annealing procedure. A ring-core fluxgate sensor was built applying this stress-annealed ribbon and its noise evaluation is compared with another ring-core sensor (of the same diameter) built using a FeCuNbSiB nanocrystalline ribbon.
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Regional Gravity Interpretation of Parnaiba Basin (Northern Brazil)
More LessGravity data have been collected mainly along tractorable roads crossing Pamafba basin and merged to already existent data bases of the Observatorio Nacional (ON), the Brazilian oil company [Petrobras), the national mineral production department (DNPM/CPRM) and Universidade Federal do Para (UFPa). Although the distribution of gravity stations is still inadequate, Bouguer and Free-Air maps have been produced and these are believed to be the first gravity maps for the whole basin. Contrary to the basin physiography, the Bouguer map shows elongated gravity lows with NE-SW and N-S directions parallel to the Transbrasiliano lineament and the Araguaia fold belt, respectively. A first attempt at interpreting the regional gravity anomalies resulted in the proposal of an anomalous, denser, material at middle-lower crustal depths.
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Gravity Interpretation of Recôncavo Basin: Apparent Density Contrast Map of Residual Anomalies
Authors P. de Tarso Luiz Menezes and J. Batista Corręa de SilvaWe present a gravity modeling of Recôncavo Basin. We apply a robust regional-residual separation method to the gravity data which minimizes the influence of observations having a great residual contribution in fitting the regional component. The resulting residual component is transformed into an apparent density contrast map by applying a linear inversion to produce estimates of the physical property of prismatic sources confined within a horizontal slab. The physical property is assumed to vary along the horizontal directions only. The method allowed to identify the major structural basement features. In addition, a new northwest-southeast trending transfer fault is evidenced by the residual gravity anomaly.
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Gravity Interpretation of Recdncavo Basin :The Bouguer Corrected Map
Authors P. de Tarso Luiz Menezes and J. Batista Corręa de SilvaWe present a Bouguer Corrected Map of Recôncavo Basin that is closed related to the Basin features. To obtain this anomaly, we compute a robust fourth-order polynomial representing the gravity effect of the Moho topography and then subtract it from the original Bouguer data. The Bouguer Corrected Map shows features that were hidden or poorly defined in the original map due to the Moho influence. These features are in agreement with the geological knowledge of the Basin. Thereforer, the Corrected Map is more suited to interpretation of the Basin framework than the original map.
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Spatially Smooth Magnetization Mapping
Authors W.E. Medeiros and J. Batista Corręa de SilvaApparent susceptibility and magnetization mappings are traditionally obtained with the ridge regression, or generalized inverse (GI) estimators. These estimators constrain the solutions to have minimum Euclidian norms, which is equivalent to require that all parameters composing the solutions be as close as possible to zero. As a result, the ridge and GI solutions are almost always in conflict with the actual geological information. We present a stable inversion method to estimate the spatial distribution of magnetization which does not bias the solution against the known geological information. In addition, at points where there is no geological information, the proposed method assumes continuity of the spatial variation of magnetization. The continuity constraint obeys a general linear relationship stablished by the interpreter; smoothness is an important particular case. The utility of the particular estimator imposing smoothness on the spatial variation of magnetization is illustrated and compared with the ridge and GI estimators in a simulated magnetization mapping of a complex geologic area. We found that this particular estimator is more versatile, effective, and operationally simpler than either the ridge or the GI estimator.
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Fractal Mapping of Digitized Topography
More LessFractal geometry is increasingly becoming a useful tool for modeling natural phenomena. The Earth's topography is one of this phenomenon that generally obeys fractal statistics. Measurements of the surface area display a power law dependence on unity of measure. The slope gives the fractal dimension (D). Inthe present work. the topography of atarget area of 100 lan2 of the Teresopolis (RJ) quadrangle topographic sheet was digitized (10 points per kilometer).Tben the digitized topography bas been used to obtain maps offractal dimension and roughness (coefficient of variation). Such detailed computer mapping was integrated with geologic and geomorphologic information. The main objective ot this work is the digital characterization of geologic and geomorphologic sites. The results show that fractal maps and roughness maps can be used to indicate the consection oflandfonns with tectonic,lithology, and climatic influence. The fractal map makes clear the tectonic lineaments not always evident in topographic maps. The roughness map showed difference oflitbology and distinguished structural lines of weakness in material.
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Interdisciplinary Interpretation of Borehole Magnetics and Helicopter Geophysics at the German Continental Deep Drilling Site (KTB)
Authors W. Bosum and B. RöttgerBorehole magnetometer measurements were carried out with a gyro oriented 3-axis borehole magnetometer in the Continental Deep Drilling Borehole (KTB), a helicopter survey delivered magnetic, radiometric and electromagnetic data in the KTB area. The borehole magnetic log provided a continuous record of the magnetic characteristics of penetrated rocks, locating boundaries of different rock types, mainly gneisses and metabasites, by short wavelength anomalies. 3-D-stationary measurements indicated magnetic source bodies in the environment of the drillhole and proved of tectonic evidence. From the magnetic log and the 3-D-measurements a detailed model was constructed, which was the basis for the interpretation of the helicopter magnetic anomalies. After a 2-dimensional interpretation a 3-D-model was constructed which gives valuable contributions to the identification of the geological structure. It enlarged the geological knowledge of the area considerably.
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Gravity Modelling of the Ramados Caldera (Argentinean Puna, Central Andes)
Authors A. Casas, E. Hernández, J. Martí and I. PetrinovicIn order to identify and characterize the vent area of abundant Upper Miocene proximal rhyolitic pyroclastic deposits and extrusive domes which concentrate in the Ramadas area, near Sant Antonio de los Cobres (Salta) at the Puna Altiplano (Central Andes), a detailed gravity survey has been carried out. Regional Bouguer gavity data were augmented with new 173 gravity observations measured sufficiently close-spaced to resolve the short wavelegth produced by the structure of interest. Besides, the geophysical survey was done in conjuction with geologic and geochemical studies which were critically important to our interpretation. After the separation of the regional trend, the residual anomaly map displays a circular gravity low reaching -80 mGal centered over scarce outcrops of rhyolitic and pyroclastic. This gravity low is interpreted as produced by block subsidence along ring fractures during eruption and/or deflation of the chamber. As the accumulation of thick, low density rock types in the zone of collapse is responsible of the prominent negative gravity anomalies, them has been used to estimated the thickness of caldera infill.
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Inércia Térmica no Infravermelho Termal : Porosidade e Componentes Químicos de Rochas
Authors A.P. Pachęco, Í. Vitorello and R. Sandes EhlersO efeito da porosidade e o relacionamento entre os valores de inércia térmica e os componentes químicos foram determinados para diversos tipos de rochas ígneas, metamórficas, e sedimentares. As determinaçőes de inércia térmica foram realizadas a partir de observaçőes radiométricas, na faixa de 8 a 14 m, das variaçőes de temperatura superficial da amostra, induzidas por om fluxo de calor incidente. Os resultados indicam que o aumento da porosidade tende a diminuir, acentuadamente, os valores de inércia térmica, quando a rocha se encontra em estado "seco". Por exemplo, rochas siliciclásticas, com 30% de porosidade, apresentam um decréscimo de aproximadamente 25% em seus valores de inércia térmica, quando medidas em estado "seco", em comparaçăo aos valores obtidos com o mesmo tipo de amostra, sem porosidade. No estado "saturado" em água, a mercia também tende a ter valores menores, sómente para rochas porosas com valores de iaercia termica superiores aos da agua. Entretanto, em rochas porosas com valores de inércia térmica menores do que aos da água, o efeito da porosidade e o inverso do caso anterior. Em rochas vulcânicas da Bacia do Paraná, a inércia térmica correlaciona-se negativamente com os teores de Si02, o que produz uma distinta separayiio entre litotipos basicos e acidos. As acidas apresentam valores de mercia termica menores do que as basicas, Entretanto, quando analizadas separadamente por litotipos, as rochas bilsicas e intermediilrias apresentam acentuadas correlacoes positivas entre valores de inercia tennica e Si02.
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Heavy Oil-Exploration and Development: A Case History from Alberta, Canada
Authors D. Misril, J. Livingstone and N. HarrisA crossfunctional team effort through an environment of innovation and continuous improvement using basic exploration techniques is presented to develop a significant oil field in the heavy oil region of Western Canada.
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Airborne Gravimetric Survey of Switzerland
Authors E. Klingele, M. Halliday and M. CocardThe Institute of Geodesy and Photogrammetry (IGP) of the ETH Zurich has acquired airborne gravity data in a joint project with LaCoste and Romberg Gravity Meters, Inc. The survey covering the entire country of Switzerland was flown in a Twin-Otter aircraft owned by the Swiss Federal Office of Cadastral Measwements. The aircraft was outfitted with three GPS receivers, one for navigational purpose and two for positioning and monitoring of aircraft accelerations. A modified LaCoste and Romberg marine gravimeter recorded data at a sampling rate of one second. Modifications included anti-alias filters and an absolute encoder for the measuring screw. Flights were performed during November and December 1992 at barometric altitude of 5200 m above sea level. A preliminary airborne Bouguer anomaly map. computed at flight altitude with topographic corrections up to 167kmwith density of 2670 kg/m3 is presented and qualitatively compared to the existing ground Bouguer anomaly map. Computation of the g values at crossing points between lines flown at comparable altitudes shows differences of the order of 25 mgal (10-5 m/s2). Computation of the RMS difference between upward continued ground data (extracted from the Bouguer gravity map of Switzerland) and the airborne Bouguer anomaly data gives differences of the order of 6.3 mgal.
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Sedimentary AeroMagnetics (SAM). An evaluation of Geological mapping capabilities
Authors T.J. McConnell and Z. BergerSedimentary AeroMagnetics (SAM) is the application of very high resolution aeromagnetic data to the exploration for hydrocarbons in the sedimentary section of a basin. Basically SAM provides very high spatial resolution of very low amplitude « 1 nT) anomalies originating from structures within the weakly magnetic sedimentary column. These sedimentary anomalies are superimposed upon the conventional high amplitude magnetic anomalies created by the crystalline basement. These low intensity anomalies generated from within the sediments are related to changes in the magnetic composition of the rocks. This can occur when rocks of differing magnetic intensities are juxtaposed across a fault, or at a stratigraphic truncation. Fluid flowalong faults and fracture zones can also produce magnetization effects which can allow direct delineament of the fault or fracture zone (McConnell and Phillips, 1994). Stratigraphic units of weakly magnetic shale and sandstone also create subtle plateau effects in the magnetic amplitude maps. SAM data is a result of combining improvements in aeromagnetic data acquisition technology with new ideas on the design of the survey parameters. SAM surveys are generally flown at 200 - 800 meter line spacings with a terrain clearance of 60 - 150 meters. Data processing techniques are used which preserve the broad band frequency spectrum of the acquired data thereby allowing interpretation of the separate and distinct anomaly sources of the sedimentary column and of the crystalline basement.
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