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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
41 - 60 of 330 results
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El Uso de los Atributos Respuesta en la Evaluación de la Traza Sísmica y el Reconocimiento Automático de Patrones
Authors J.A. Tovar, M. Caicedo and J. SierraSe evalúa la posibilidad de utilización de los atributos respuesta como herramientas de interpretación sísmica de detalle, conjuntamente con las tecnicas de reconocimiento automático de patrones en secciones post-apilamiento. Los resultados del modelaje sintético y de su posterior interpretación indican que los atributos respuesta son bastante estables y que permiten definir contactos de fluidos y delimitación de los mismos para la caracterización de yacimientos. Como parte del estudio se desarrolló un conjunto de programas que permiten tanto el modelaje unidimensional simple como la generación de los atributos respuesta de una sección completa. Finalmente se aplicaron las técnicas del reconocimiento de patrones para los atributos instantáneos y los atributos respuesta encontrando mejores patrones de identificación con estos últimos atributos.
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From seismic surface measurements to pseudo VSP data: a new tool in 3-D seismic interpretation
Authors R. Alá, W.E.A. Rietveld, C.P.A. Wapenaar and A.J. BerkhoutThe method of pseudo VSP generation is a method for transforming the seismic surface data into Vertical Seismic Profiles (VSP) in a numerical way. The main objective of this paper is to present some examples of the pseudo VSP method and its value in interpretation aspects on 3-D seismic data using 3-D wave field extrapolation operators. It is shown that the pseudo VSP allows insight and recognition of waves propagating through a 3-D subsurface.
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Solving the Fault Shadow Problem in the Wilcox Trend of South Texas
By S.W. FaginImaging distortions in the footwall of faults in the Wilcox trend of South Texas are shown to be caused by velocity effects associated with the truncation of overlying high-velocity Queen City Sandstone and low-velocity Reklaw. The thinning of these units across the fault give rise to appreciable velocity sags and pull-ups. Moreover, this variability in the thickness of velocity bodies gives rise to nonhyperbolic reflections which create apparent disruptions in footwall reflections. The only imaging solution which is free of these artifacts is prestack depth migration. A synthetic example is used to demonstrate fault shadow Imaging artifacts and their elimination by depth imaging. Identical artifacts are identified on a real data set and the imaging Improvements from prestack depth imaging are demonstrated.
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Robustness in Ray Reflection Tomography for Laterally Varying Media
Authors D. Manoel Soares Filho and S. Valilevich GoldinIn this paper we show that when we work with a basis of Bsplines defined by a convenient set of knots, for laterally velocity functions, large offsets and with soft constraints imposed in the Tikhonov's sense [Tikhonov, 1963], we can get excellent results applying Ray Reflection Tomography for kinematic interpretation of seismic records. We propose a method whose robustness is well illustrated by a synthetic application where a geological model described by fifty-four B-splines coefficients is reconstructed in up to three iterations from very different initial guesses, which are defined through the application of the Dix type approach [Goldin, 1986J for several sets of CMP gathers. The regularization matrices are defined by analysing the level curves of the resolution matrix elements interpolation [Soares, 1994].
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3D Numerical Modeling of Listric Faults as a Tool in Sesmic Interpretation
More LessThrough Three·Dimensional numerical modeling of listric fault surfaces, this paper discusses hanging wall rollover geometry as seen on seismic reflection date and 3D cubes. One of the major assumptions of 2D cross section restoration and balancing techniques is that the direction of the section has to be parallel to the direction of extension, which is not always known. Kinematics analysis based solely on fault trends are common, particularly in extensional submerged basins, but not always corroborated by kinematic and dynamic graphical methods of fault slip analysis in emerged basins. This work describes key 3D aspects of listric fault surfaces in orthogonal and oblique·slip deformation, where the strained hanging wall is adequately described by a process of simple shear during hanging wall collapse, incorporating inclined simple shear to dip·slip end oblique·slip extensional fault surfaces. This technique helps to constrain seismic interpretation of faults, as well as helps to constrain tectonic kinematics and the process of internal daformation mechanisms associated to 3D variations in fault geometry.
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Hierarchical decomposition and its application in seismic inversion and migration
Authors J.T. Fokkema and C.P.A. WapenaarHierarchical decomposition is the process of decomposing the actual wave field into a set of scattered wave fields which account for an increase of the complexity of the scattering domain with respect to the embedding. Unlike the linearization process in iterative Born-type inversion methods (like the distorted-wave Born method), hierarchical decomposition is data-driven, that is, the decomposition process is guided by the information that is available in the data. This paper discusses the consequences for seismic inversion and migration.
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Arctan Aa I Ro: a different seismic AVO attribute for fluid-lithology identification.
Authors J.P. Regueiro and E. González San MiguelA different AVO attribute, obtained from calculating the arctan of flo / Ro, two commonly used byproducts of AVO inversion (Ro = normal incidence reflectivity; flo = pseudo Poisson reflectivity), has been used to generate seismic sections which clearly indicate the presence of hydrocarbons. This technique is based on the existence of a preferred "background fluid-angle" in a Ro versus flo crossplot. In such crossplot, hydrocarbon bearing reservoirs show as anomalous angular values away from this trend. Well log and seismic data were analyzed for two actual cases: (1) a typical bright spot, gas reservoir (class 3 AVO response); and (2) a low impedance contrast, condensate reservoir (class 2 AVO response), and an interpretative-display scheme developed for the generation of the "arctan flo I Ro sections". For both cases, the final "arctan flo I Ro sections" directly indicate those events related to the hydrocarbon bearing reservoirs. This technique provides a new attribute to be examine when discriminating seismic data in the search for such reservoirs, primarily those hard-to-find low impedance contrast sandstones.
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The Vibrosels Method for Physical Modelling Systems
By M. SemanPhysical modelling systems are used in several institutions to record data over complex geological models. The dynamic range is limited due to the high frequencies involved. If the dynamic range were improved, physical modelling could be applied to a wider range of studies, e.g. deeper models, or use smaller transducers. The Vibroseis method offers a substantial improvement in signal to noise ratio (of the order of 24 dB) over the conventional method of driving transducers with a pulse. Such an improvement would be difficult to achieve by other means. Furthermore, the sweep signal may be convolved with a filter to correct for the ringy transducer response and obtain a result close to zero-phase Klauder wavelets
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Effect of Strain Amplitude and Frequency on Compressional Amplitudes in Sandstones
Authors A.N. Tutuncu, A.L. Podio and M.M. SharmaA series of experiments have been carried out on sandstone samples with wide range of porosities and permeabilities in order to investigate the influence of strain amplitude and frequency on compressional and shear velocities and attenuation of sedimentary granular rocks. Low frequency velocity data was obtained from uniaxial stress cycling measurements that were conducted at a frequency of 10-2 Hz at different levels of strain amplitude from 10-5 to 10-2. Attenuation information was obtained at 10-2 Hz from the stress-strain hysteresis observed in the cycling measurements. Compressional velocity data was collected at various stresses using four different transducer/receiver sets with frequencies 50 KHz, 100KHz, 180 KHz and I MHz. The strain amplitudes for all four types of ultrasonic measurements are in the range of 10-7 - 10-6. Shear velocities were simultaneously recorded at 1 MHz. Compressional wave amplitude data were collected at a few selected stresses in order to obtain attenuation at ultrasonic frequencies. Velocities calculated from the static moduli (10-2) increase as average stress is increased. The dry velocities are very sensitive to strain amplitude. As strain amplitude increases, both compressional and shear velocities decrease. When the velocities calculated from the static moduli are plotted together with the velocities measured using the 50 KHz, 100 KHz, 180 KHz and I MHz transducers, velocity dispersion is clearly observed. However, differences between static velocities and velocities measured from 50 KHz to 1 MHz can not be explained on the basis of the frequency dependence alone. Differences between the strain amplitudes of the measurement techniques is believed to be one of the major causes of dispersion observed in the dry rocks used in this study.
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Uso de Inversăo Sísmica e AVO na Estimativa de Parâmetros Petrofísicos
Authors S.L. Moura Freire and A. de Pinto BragaO principal objetivo deste trabalho é sugerir uma metodologia de estimativa da variaçăo de parâmetros petrofísicos de rochas reservatório e encaixantes através do uso combinado de inversăo e modelagem pré-stack de amplitudes sísmicas. O método é suportado e calibrado por perfis elétricos de um poço existente sobre a linha sísmica e consiste fundamentalmente na inversăo linear das amplitudes com base em um modelo de camadas planas e horizontais. A metodologia de inversăo/modelagem é aplicada em dados sísmicos adquiridos na costa do Estado da Bahia-Brasil. Os resultados encontrados após a inversăo, sugerem uma maior definiçăo de topos e bases dos principais pacotes litológicos, na seçăo de velocidade intervalar. Por outre lado, o uso da modelagem AVO iterativa permitu a estimativa da razăo de Poisson de um arenito turbidítico, mesmo nas porçőes da linha sísmica năo suportadas por poços.
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The Organization and Recent Scientific Achievements of the Ocean Drilling Program (ODP)
Authors D.A. Falvey and E.S. KappelThe Ocean Drilling Program (ODP) is an international partnership of scientists and research institutions organized to explore the history of the Earth beneath the ocean basins. ODP provides core samples from the ocean basins and shipboard and shore-based facilities for the study of these samples, and downhole measurements (i.e., wireline logging) and opportunities for special experiments to determine in situ conditions beneath the seafloor. These studies lead to a better understanding of plate tectonic processes, of the Earth's crustal structure and composition, of environmental conditions in ancient oceans, and of changes in climate through time. Such systematic advances in knowledge in turn lead to a fuller comprehension of the evolution of the Earth.
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Perfuraçőes do DSDP na Elevaçăo de Rio Grande - Implicaçőes para o Entendimento da Evoluçăo do Atlântico Sul
More LessAs linhas de costa da America do Sul e da África tém suscitado questionamentos desde os primeiros mapeamentos cartográficos inspirando suposiçőes quanto aos processos de formaçăo dos oceanos e de suas margens. Em meados da decada de 60, a evoluçăo cientifica e tecnológica já permitia a proposiçăo da Teoria da Tectónica de Placas, entăo sustentada principalmente por evidęncias sísmológicas, magnetométricas e batimétricas.
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OOP and Rifted Continental Margins
More LessRifted (also known as divergent or passive) continental margins are those characterized by a fused join or boundary between continental and oceanic crustal types, as opposed to convergent margins, where subduction or underthrusting of oceanic crust beneath continental material is occurring. The Ocean Drilling Program's approach to the study of these margins has to date concentrated in the North Atlantic, where the best examples of conjugate (paired) passive margins of various ages occur. ODP has drilled both non-volcanic and volcanic examples; recent research suggests that the absence or presence of massive volcanic outpourings accompanying continental breakup may be the Single most important distinguishing feature of rifted margins.
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Transform Margin Development: Preliminary logging results from ODP Leg 159 on the Côte D'Ivorie-Ghana margin
Authors C.A. Gonçalves, E. Ewert and C. BasileODP Leg 159 studied the Côte d'lvoire-Ghana transform margin in the eastern equatorial Atlantic during January and February 1995. Thirteen holes were drilled at four sites, recovering sediments from Late Albian to Pleistocene age. The margin has been created by major transform motion between the African and South America plates and is one of the best known examples of a former transform boundary between continental and oceanic crust (Masele and Blarez, 1987). Logging data were collected at three of the sites. and despite bad hole conditions. logging runs were obtained in four boles. This paper shows the preliminary logging results which cover the full sedimentary sequence cored. Together with the standard tools used by the oil industry. The Geochemical Logging Tool (GLrn') and the Formation MicroScanner (FMS1V) tool were also used.
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Cenozoic Evolution of Carbonate Platforms on the Northeastern Australian Margin: Synthesis of ODP Leg 133 Drilling Results
Authors J.A. McKenzie and P.J. DaviesDrilling during ODP Leg 133 was designed to study factors controlling both isolated and attached carbonateplatform evolution using sedimentary sequences that were deposited at varying water depths on the platform margins and slopes and in the adjoining basins. Shipboard and post-cruise data provide an integrated picture of the conditions promoting platform initiation and growth, as well as the environmental changes that can lead to platform demise. Results indicate that the Cenozoic evolution of the Queensland Plateau, Marion Plateau, and Great Barrier Reef was controlled by a complex interaction of variations in eustatic sea level,subsidence pulses, and paleoceanographic changes. In most cases, not a single factor, but a combination of factors was in operation at any specific time. Long-term platform development was strongly influenced by thenorthward drift of the Australian Plate throughout the Cenozoic. Plate motion resulted in a ransition from temperate to tropical surface-water temperatures, with a corresponding change in the type of carbonate sedimentation. Yet, short-term, rapid changes in paleoceanography seem to have dominated the system. Abrupt increases in surface-water temperatures led to the sudden development of extensive tropical reefal complexes in the early Miocene, whereas a decrease in late Miocene surface-water temperatures resulted in a change from tropical fauna and flora to a bioassemblage more compatible with a non-tropical environment. Together with the paleoceanographic changes, variations in relative sea level, whether eustatically or tectonically controlled, either helped maintain carbonate production or facilitated its decrease, sometimes resulting ultimately in the shutdown of the shallow-water carbonate factors. During specific time periods, the thermally driven circulation of seawater through the buried carbonate platform sediments apparently caused selective dolomitization. This process may be ongoing within the Queensland Plateau, possibly providing new clues for understanding massive carbonate platform dolomitization.
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REEVALUACION DE LA EXPLORACION DEL AREA NUTRIAS-BRUZUAL, Cuenca de Barinas-Apure, Venezuela
Authors L. Hernandez and A. PortillaEl estudio y la identificación de las características geológicas presentes en el área, con el soporte de la información geológica-geofísica existente es de gran importancia para el futuro de la exploraci6n petrolífera de esta parte de la cuenca. Se utiliza la metodología de interpretación sismosecuencial y sismotectónica para los 2100 Km de líneas sísmicas digitales. En el área, la columna estratigráfica está conformada por un basamento Igneo-Metamórfico, sobre el cual se encuentran las formaciones sedimentarias del cretáceo al reciente. La calibración sísmica y bioestratigráfica definen cuatro secuencias sísmicas de segundo orden: Cretáceo, Eoceno Medio, 0ligoceno (1)-Mioceno Inferior (?) y Mioceno Medio (?)-Plioceno (1).La secuencia Cretácea es principalmente arenosa, engrosa hacia el norte y adelgaza hacia el sur por efecto de sedimentación y erosión. La secuencia Eoceno Medio desaparece por truncamiento erosional en la parte media del área y es principalmente arenosa, y las secuencias del Oligoceno (?) Mioceno Inferior (?), y Mioceno Medio (?) -Plioceno (?), son molásicas. Estructuralmente únicamente las secuencias sísmicas cretácicas y Eoceno Medio están afectadas por fallas inversas y fallas normales de edad Cretáceo tardío - Eoceno Temprano, posteriormente reactivadas durante el Mioceno Temprano. Las secuencias del Oligoceno (?) al Plioceno (?) no están falladas. Los resultados resultados obtenidos hasta el momento indican que el área es de interés prospectivo aún cuando la mayoría de los pozos perforados no resultaron exitosos.
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ODP Drilling: Establishing Methane Sources and Migration Pathways Associated with Marine Gas Hydrates
Authors C. Paull, W. Ussler and W. BorowskiGeophysical models indicate that some continental margin sediments, like those of the Blake Ridge off southeastem North America, contain several percent gas hydrate. The amount of microbial methane required to fill a significant fraction of the sediment pore pace [i.e., > 5%] with gas hydrate is too large to be produced.by only in situ microbial processes. Thus, fluid migration and other gas-concentrating mechanisms are required to develop these gas hydrate accumulations. Testing models of fluid and gas migration in sediments associated with marine gas hydrates is one objective of Ocean Drilling Program (ODP) Leg 164 (October - December, 1995).
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High Resolution Seismic Surveying for Pleistocene Sequence Stratigraphy, New Jersey Continental Shelf and Upper Slope, In Support of the Ocean Drilling Program's Global Sea Level Objectives
Authors J.A. Austin Jr., C.S. Fulthorpe, G.S. Mountain, J. Diebold, P. Buhl and K.G. MillerOne of ODP's long-standing goals has been to understand amplitudes and timing of global sea-level fluctuations. Past drilling expeditions have examined the sea-level record on carbonate platforms (e.g.• Legs 101. 115 and 133) and on atolls and guyots (e.g.• Legs 143 and 144). Passive margin transects have also been targeted for study, most recently a shelf/slope corridor offshore the Mid-Atlantic region of the eastern United States (slope drilled as Leg 150).
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Estratigrafia de Alta Resoluçăo do Cone do Amazonas: Resultados do Oceari Drilling Program
Authors R.O. Kowsmann and C. PirmezO Cone do Amazonas e um dos maiores leques submarinos do Mundo e uma das feiçőes mais marcantes do Atlântico SuI. Possui 700 km de comprimento a partir da quebra da plataforma continental e até 400 km de largura (Damuth e Kumar, 1975; Damuth e Flood, 1985). Cerca de 4 km de sedimentos foram acumulados na porçăo central do Cone desde o Mioceno Superior (Silva et al., no prelo) pelo empilhamento de complexos de canais de passagem de correntes de turbidez encarapitados sobre cunhas de transbordamento destas correntes (levees).
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Polarizaçăo Induzida Espectral no Alvo M16 - Santaluz - BA
Authors E.E. Starteri Sampaio and C.E. Teixeira CardosoO método geofísico de polarizaçăo induzida espectral (SIP) é importante para a' prospecçăo de minerais metálicos e de argila disseminados nas rochas da crosta terrestre, tendo como objetivos a exploraçăo de minérios e água subterrânea.
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