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11th International Congress of the Brazilian Geophysical Society
- Conference date: 24 Aug 2009 - 28 Aug 2009
- Location: Salvador, Brazil
- Published: 24 August 2009
81 - 100 of 418 results
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Geometric Theory Of Seismic Imaging
More LessIn this paper I provide an overview of main concepts and results by S.V.Goldin in the field of geometric theory of seismic imaging. Then I present some recent results on velocity continuation of seismic images developing his ideas.
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Inversão Sísmica Em Três Dimensões A Partir De Dados De Reflexão Sísmica Por Algoritmos Genéticos Híbridos
Authors Samuel G. Huamán Bustamante and Marco Aurélio C. PachecoThe objective of the present work is to investigate a
method to help in the quantification of seismic
characteristics underground. The two-dimensional
seismic model of reflection employs the equation Normal
Move Out (NMO) to calculate the travel times of P waves
reflected on inclined and isotropic layers. This equation
uses the root mean square velocity as a representative
value of the joined layers velocities. At the inversion
process, for multiple layers, the root mean square
velocities are the main problem to estimate the layer
velocities. Consequently, to solve that problem, the
proposed method estimates sequentially the parameters
of the seismic model using travel times and the Hybrid
Genetic Algorithms (Genetic algorithm and the Nelder
Mead Simplex algorithm). The travel times are synthetic
and the estimation of parameters is treated as a
minimization problem. With proposed method was
obtained high grade of accurate, and the reduction of
85.23% of computing time when the method uses only
Genetic Algorithms. For decreasing the complexity and
the delay to generate the models in three dimensions is
proposed the construction of a three-dimensional seismic
model formed with two-dimensional models, under every
rectangular cell of the mesh of receptors of the seismic
survey, for curved isotropic layers with soft variations in
the gradient and without discontinuities. The twodimensional
models form polygons that represent the
surfaces of interfaces that are designed under the
rectangles of the surface or soil. Two sets of polygonal
surfaces are generated to help at the geometric
localization of layers.
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Adaptive Method For Swell Noise Attenuation In The Time-Frequency Domain
Authors Julio Valença Tavares and Luiz Geraldo LouresCoherent noises are those that appear through a systematic way and swell noise is a kind of coherent seismic noise. This happens during the marine seismic acquisition and is generated basically by the motion of the ship, cable depth controllers, or sea surface waves. For the swell noise analysis and attenuation we used a one dimensional wavelet transform, in the sense that it operates on single traces, to apply a time-frequency domain filter. The shifting (time) and level (frequency) dependent soft-threshold is estimated using a method based on Bayes’ Rules. Using this proposed methodology for synthetic data analysis the results were satisfactory. When real seismic data is used the results show good agreement due to the algorithm adaptive structure. The noise is removed considerably and the signal doesn't loose the interesting information, validating the proposed model. As the algorithm makes the threshold estimation in function of the scale and for each trace time interval, nine threshold values are calculated for each trace. Therefore, it is possible to reduce the noise for different signal-to-noise ratios (SNR) along each trace. The noise free traces don't change, because in those cases the threshold tends to be zero making possible the perfect signal reconstruction. However, when the SNR tends to be one or the noise and signal amplitude and frequency are similar their coefficient variances tend to be close causing a threshold estimation enough to mute the signal. In agreement with the increasing demand for offshore exploration, also driven by 4D seismic acquisitions, the swell noise will be a frequent problem, because in order to achieve a good geologic model all the distortions generated by the data acquisition should be attenuated.
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Anomalias Magnéticas Da Província Alcalina Rio Verde - Iporá, Sudoeste De Goiás
Authors Alanna C. Dutra and Yára R. MarangoniThe Rio Verde - Iporá Province is a suite of alkaline rocks
predominantly mafic-ultramafic, in central Brazil. These
alkaline complexes are characterized by a series of small
bodies with strong aeromagnetic signal presenting
themselves as almost circular anomalies. The
aeromagnetic anomaly varies from +6000 to -3000 nT.
The anomaly magnetic field was used in the 3D inversion
to model the magnetic susceptibility distribution. The
model has a maximum value for magnetic susceptibility
0.1 (SI) in prisms that reaches up to 10 km depth under
the alkaline anomalies. The bodies resemble magmatic
chambers emplaced in the upper crust in a NW-SE
direction.
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Eletrorresistividade Aplicada No Sítio Arqueológico Ap-Ma-05, Macapá-Ap: Resultados Preliminares
In this article we present preliminary results of resistivity
measurements that were carried out at the archaeological
site AP-MA-05 to find remains buried by ancient people
that could have lived in the area. Archaeological
excavation on places indicated by resistivity anomalies
revealed concentration of lateritic rocks fragments and
fragmented pottery.
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Aplicação Das Técnicas De Medição De Gás Radônio E De Imageamento Elétrico 3D E 2D Em Áreas Sob Contaminação De Hidrocarboneto
Authors Sérgio Luiz Da Silva Quintão, Andresa Oliva, Ciências Exatas, Mathias Du Puits, Axel Schmidt, Holger Weiβ, Jorge Ibirajara Coelho, Marcus Paulus Martins Baessa, Fátima Do Rosário, José Ribamar Silveira Da Silva, Carlos Silva Rosa, Flávia Castro, Marco Aurélio Zequim Pede, Chang Hung Kiang and Márcio Costa AlbertoA contaminação do solo por NAPL (contaminantes não-voláteis) oriundo de vazamentos de combustíveis, óleo mineral e solventes orgânicos é considerada um problema mundial. Para a realização de uma remediação adequada em áreas impactadas é fundamental o conhecimento da distribuição do NAPL no subsolo. Para se estabelecer um plano de remediação adequado, geralmente são coletadas amostras de solo que posteriormente serão enviadas ao laboratório para as análises pertinentes. Entretanto, o número de amostras pode ser limitado, impedindo assim a delimitação adequada da pluma de contaminação. Além disso, a análise das amostras em laboratório pode levar algum tempo, causando atraso no trabalho de investigação. Dessa maneira, técnicas que permitam tanto um aumento no número de pontos de investigação, como rapidez na obtenção de dados, vêm sendo cada vez mais utilizadas com sucesso na identificação de áreas impactadas. Neste trabalho utilizou-se as técnicas de imageamento elétrico 3D e 2D e uma nova técnica envolvendo a medição de gás Radônio 222 em solos/sedimentos, para identificar e delimitar as áreas impactadas em subsuperfície.
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Diurnal Variation Of The Occurrence Of Plasma Irregularities In The Equatorial Electrojet Over Brazilian Sector
Authors L.M. Guizelli, C.M. Denardini, H.C. Aveiro, P.D.S.C. Almeida and L.C.A. ResendeEquatorial electrojet (EEJ) observations using VHF radars show backscattered echoes from two types of electron density irregularities, Type 1 and Type 2. In this paper, we present an statistics of occurrence irregularities in the ionospheric plasma at the e-region hight, observed by a 50 MHz coherent backscatter radar installed in Brazil. This radar detects small-scale irregularities (3 meters) between approximately 90 to 130 km heights in the equatorial ionosphere.
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Global 4-D Seismic Inversion And Time-Lapse Fluid Prediction
Authors Y. Lafet, B. Roure, P.M. Doyen, R. Bornard and H. BuranIndependent inversion of base and monitor seismic surveys can yield estimates of elastic properties that are inconsistent with expected production effects. We therefore propose a global time-lapse inversion scheme, involving joint inversion of base and monitor data. All vintages and input angle stacks are combined in a single objective function, which is optimized using simulated annealing to estimate the time-variant distribution of elastic attributes that best matches all available data. The multi-vintage nature of the optimization allows us to incorporate flexible, user-defined rock physics constraints on the evolution of Vp, Vs and density between consecutive surveys. There are no restrictions on the number of input angle stacks or number of monitor surveys. The constrained, global inversion solution can therefore be easily updated as new data become available. We apply the global 4-D inversion with rock physics coupling to data from the Brage Field and compare results with a workflow involving separate inversion of base and monitor data. The global 4-D inversion results are combined with a time-lapse Bayesian fluid classification scheme to map production-induced fluid movement and quantify associated uncertainty.
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Relevo Do Embasamento E Da Moho Na Borda Norte Da Bacia Do Paraná Através De Dados Gravimétricos
Authors Vanderlei C. Oliveira Jr. and Yára R. MarangoniThis paper presents the results from an iterative inversion
that considers all Bouguer anomaly signal and different
mass sources at each step. Results are compared with
independent geophysical and geological information.
Relief from mantle-crust and basement interfaces are
provided. The study area shows Moho going deeper
towards E, with depths from 38 to 42 km. Basement has
two grabens of 4 and 3 km deep with a horst in between.
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Undershooting In The Recovery Of The Coverage Affected By Operational Obstacles In A 3D Seismic Survey
More LessThere is a great difference between the developed (preplot)
and the executed (post-plot) projects in seismic data
acquisition processes. There are many possible causes
for these differences: cities, buildings, roads, oil pipelines,
etc. One way to minimize the negative effects of the
impossibility to perform a recording at a shot point is to
use the Undershooting method. This method enables the
acquisition of information regarding the common midpoint
(CMP), and can be used depending on the relation
between the offset and the objective depth at that point.
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Estrutura Da Plataforma Continental Do Sudeste Com Ondas De Superfície Do Sismo De S. Vicente De 2008: Primeiros Resultados
Authors Paula Gomes De Carvalho and Marcelo AssumpçãoWe present the first results of a study about the structure
of the continental shelf in SE Brazil. We use records of
the earthquake occurred in 2008 near São Vicente, São
Paulo’s southern coast. The surface waves (Love and
Rayleigh) show variation of velocity with the period
(dispersion) that is being analyzed using five
seismographic stations located in Brazilian SE. The
preliminary results shown in this paper are compared with
velocities found by Feng et. al., 2007 et. al. (2007) for the
periods of 10, 20 and 30s. We also obtained the velocity
profile for the ESAR station (Angra dos Reis, RJ - Brazil)
using the velocity inversion (Herrmann & Ammon,
2002).The velocities in the continental crust are larger
than the oceanic crust velocities and also indicates that
the Santos Basin’s basement is about 12 kilometers
deep. The velocity inversion of the others stations will be
made in the future, as well as the study of the focal
mechanism of the earthquake.
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Soa Based Data And Application Integration An Enabler For Creative Interpretative Workflows
By Clay HarterVirtually all geologic and geophysical interpretation
upon the use of computer software to retrieve
data and provide analytic and interpretive tools to
the subsurface. Most companies use a diverse set of
software applications and data to perform these tasks.
This paper describes some of the technical challenges
faced when integrating these applications and data and
describes an integration solution based upon
oriented architecture (SOA). Several example workflows
are then described that leverage a SOA integration
framework.
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Shear-Wave Coupling In Inhomogeneous Weakly Anisotropic Media
Authors Ivan Pšençík and Véronique FarraWe present an approximate procedure for computing coupled
S waves in inhomogeneous weakly anisotropic media.
The procedure can be used to compute S waves propagating
in smooth inhomogeneous isotropic or anisotropic
media. In anisotropic media, it can describe behaviour
of coupled as well as decoupled S waves. Basic part of
the procedure is an approximate computation of the common
S-wave ray, a trajectory, along which properties of
both S waves propagating in anisotropic media are computed.
For computation of the common ray and of the
approximate geometrical spreading along it, we use the
first-order ray tracing and dynamic ray tracing concept, developed
for computations of P waves in inhomogeneous
weakly anisotropic media. The amplitude coefficients of the
coupled S waves are computed by solving a coupled system
of ordinary differential equations - the coupling equations
- along the common S-wave ray. The performance
of the procedure is illustrated on several models of varying
strength of anisotropy. Its accuracy is tested by comparing
its results with results of the standard ray theory.
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Geofísica Aplicada À Arqueologia No Estado Do Pará, Brasil
More LessThe first geophysical experiments applied to Archaeology
in Pará were performed in 1977. Since then, the
application of geophysical methodologies to Archaeology
has allowed to the indication of excavations where
archaeologists found mainly ceramic artifacts (pottery,
burial urns, cooking hearts, sherds, pipes, and ax heads).
Experiments were also made to map the archaeological
black earth layer (TPA). Examples that show the success
of the geophysical methodologies as applied to
Archaeology in Pará are presented.
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Psdm Applications In Albacora Field, Campos Basin
Albacora field has a seismic survey acquired in 2002 whose area is 720 square kilometers. This extension and the variety of reservoirs, which contains since Cretaceous until Tertiary turbidite sandstones along ring fence area, required a velocity model building for prestack depth migration (PSDM) using regional horizons: Sea bottom, gray marker, blue marker, seismic cretaceous and top salt. During interpretation of PSDM data some improvements have been observed: better lateral positioning of geologic events (e.g. faults, sloping beds, channels) and enhancement of image in the vicinity of regions with lateral velocity variations (canyons, fault slips) northern of ring fence area. Attribute analysis in PSDM data have confirmed these benefits, which have resulted in change of the spatial positioning anomalies in relation to time maps.
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Estudo Time-Lapse E Análise De Avo Para Reservatórios Carbonáticos
More LessThe use of time-lapse technique has been a challenge for
the seismic monitoring of carbonate reservoirs, despite
great success for use in siliciclastic reservoirs. The oil
carbonate reserves increasingly gaining importance due
to the discovery and recovery fields already in production.
Thus, studies are necessary to understand anomalies in
seismic data through application of analysis AVO / AVA
(amplitude versus offset and amplitude versus angle) for
various saturations of fluids such as brine, oil and gas,
and the establishment of methodologies that allow timelapse
studies in carbonates, and promotion of more
efficient tests for fluids detection.
This work proposed a methodology to the time-lapse
study in carbonates, based on data synthetic idealized
second references and use of rock physics models, such
Gassmann (1951) and Batzle & Wang (1992). The tests
in dolostones and limestones cases showed trends of
variation in their elastic and petrophysical parameters in a
similar way, but with limited sensitivity to the stages of
saturation. The density parameter of the rock has good
distinction of fluids in saturation, even when combined
with other petrophysical attributes. Parameters such as
shear modulus, S velocity and S impedance are used for
lithological distinction between the dolostones and
limestones carbonates for the examples studied. The
analysis AVO / AVA allowed lithological differentiation and
fluid phases differentiation.
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Análise Preliminar De Estruturas Geotectônicas No Amapá, Borda Oriental Do Escudo Das Guianas, Através De Métodos Geofísicos
Authors Saulo Siqueira Martins and José Gouvêa LuizSeveral structures are observed in Paleozoic, Mesozoic,
and Cenozoic of Guiana Shield. The structures have a
NW-SE trend, representing shear belts. Many of the
structures suffered reactivation during those periods. In
this study we applied two geophysical methods,
gravimetry and ground penetrating radar, in order to
understand the dynamic of the structures and how they
can influence the formation of local Tertiary sedimentary
basins.
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The Early January Coronal Mass Ejection And The Estimate Of Its Arrival To Venus
Authors Alisson Dal Lago, Bern Inhester and Luis Eduardo Antunes VieiraOn January 8th, 2007, at 14:54UT, a coronal mass ejection (CME) was observed by LASCO C2, onboard SOHO. Latter on the same day, LASCO C3 also observed this CME, which continued moving outward during most of January 9th. SOHO/EIT did not detect any activity on the solar disk during this period, suggesting that the CME was ejected behind the East limb, towards planet Venus. Thus, we expect the CME to reach Venus some few days after its launch. STEREO/SECCHI COR1 and COR2, A & B, coronagraphs also observed the same CME event. Because STEREO was in the early beginning of its mission, both spacecrafts A and B were near the Earth, and it was possible to combine observations from their instruments and SOHO/LASCO. We estimate the travel time of the Jan. 8th-9th (2007) CME from the Sun to Venus using 3 approaches. In the near-future, our estimates should be confirmed when data from Venus Express mission is available.
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Geoelectrical Behavior Of Miocene And Quaternary Strata In Eastern Marajó Island/Pa
More LessThe use of VES in E Marajó Island had discriminated the
presence of an interval with anomalous high resistivity,
attributed to the presence of the concretionary horizon,
this was crucial to define the top of the Barreiras
Formation. The lateral occurrence of the Barreiras Fm
and the Quaternary deposits and the abrupt passage
between these units are consistent with the presence of a
tectonic fault. This information supports previous studies
that have claimed reactivation along tectonic faults as the
responsible for renewing sediment deposition during the
Quaternary in island.
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Processamento E Interpretação De Dados Eletromagnéticos Aéreos Do Sistema Vtem No Brasil
More LessSince 2005, there have been several VTEM surveys in
the Brazilian territory. There is no doubt of the success
and popularity of this system in Brazil. However,
frequently, VTEM contractors still do not understand the
basic concepts of processing and interpretation of such
data. This paper reviews the important aspects of the
processing and interpretation of VTEM from a perspective
of a geophysicist that has been intensely working with
Brazilian VTEM datasets as an interpreter and as a data
processing manager.
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