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6th International Congress of the Brazilian Geophysical Society
- Conference date: 15 Aug 1999 - 19 Aug 1999
- Location: Rio de Janeiro, Brazil
- Published: 15 August 1999
61 - 80 of 399 results
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Inversão Gravimétrica Do Relevo Não Suave De Uma Bacia Sedimentar Com Variação Do Contraste De Densidade
More LessWe present a new stable method for interpreting the basement relief of a sedimentary basin which delineates
sharp discontinuities in the basement relief and incorporates any law known a priori for the spatial variation of
the density contrast. The subsurface region containing the basin is discretized into a grid of juxtaposed
elementary prisms whose density contrasts are the parameters to be estimated. It is imposed that any vertical
line intersect the basement relief only once and that the mass deficiency be concentrated near the Earth's
surface, subject to the observed gravity anomaly being fitted within the experimental errors. In addition, upper
and lower bounds on the density contrast of each prism are introduced a priori (one of the bounds being zero)
and the method assigns to each elementary prism a density contrast which is close to either bound. The
basement relief is, therefore, delineated by the contact between the prisms with null and nonnull estimated
density contrasts, the latter occupying the upper part of the discretized region. Thus, the method is stabilized by
introducing constraints favoring solutions having the attributes (shared by most sedimentary basins) of being
an isolated compact source with lateral borders dipping either vertically or toward the basin center and having
horizontal dimensions much greater than its largest vertical dimension. Arbitrary laws of spatial variations of
the density contrast, if known a priori, may be incorporated to the problem by assigning suitable values to the
nonnull bound of each prism. The proposed method differs from previous stable methods by using no
smoothness constraint on the interface to be estimated. As a result, it may be applied not only to intracratonic
sag basins where the basement relief is essentially smooth, but also to rift basins whose basements present
discontinuities caused by faults. The method's utility in mapping such basements were demonstrated in tests
using synthetic data produced by simulated rift basins. The method mapped with good precision a sequence
of step faults which are close to each other and present small vertical slips, a feature particularly difficult to
detect from gravity data only. The method was also able to map isolated discontinuities with large vertical
throw. The method was applied to the gravity data from Recôncavo Basin, Brazil. The results showed close
agreement with known geological structures of the basin. It also demonstrated the method's ability to map a
sequence of alternating terraces and structural lows, which could not be detected just from the inspection of
the gravity anomaly.
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Hidrologia Subterranea Da Area De Um Aterro Sanitario Utilizando Geofisica Eletrica
More LessElectrical sounding measurements of resistivity and induced polarization parameters combined with a selfpotencial surveywere used for mapping the sub-surface geology and hidrology around the new Salvador sanitary landfill. This landfill is located within the Rio Joanes basin, close to a surface reservoir used for water supply in the Salvador Metropolitan Area. The main aquifer
zone is represented by sandstones of Barreiras Formation and the wheathered basement. The geophysical results are presented as structural sections and maps showing the geometry and the lithologic variability of this aquifer. They may serve as a geophysical reference for monitoring the eventual groundwater changes caused by the landfill operation.
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Detecção De Refletores Sísmicos Por Rede Neural Discreta
Authors Alexandre Beltrão Ferreira and André AndradeThe artificial neural networks have proven to be a powerful tool to solving a wide variety of optimization
problems. In this work we develop a recurrent network with no self-feedback loops and no hidden neurons for
seismic signal processing where this neural network gives us reflectivity location and reflectivity magnitude
estimation. The most important advantage of this neural network is the use a type of activation function which
permits three possible states of neuron to estimate the position of the seismic reflectors in such way to
reproduce its true polarities. The operational evaluation of this neural network architecture is accomplished in
synthetic data obtained through the ray theory.
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Automatic Lithologies Identification From Well Log
Authors André Andrade and Anna Ilcéa FischettiThe complex mineralogical constitution of reservoir rocks and the need of correct lithology identification in a borehole
from well log data, makes lithologic identification of a rock possible, not by means of a complete mineralogical
description, but through the identification of its main mineral constituents or essential mineral.
For identification of essential mineral, through the well log data, several numeric methods were developed, like the
compositional analysis and graphical methods, such as the M-N plot (BURKE et al,1969).
We show here, the mineral essential determination method from well log data, by means of a simulation of interpretation
performed by log analyst utilization of the M-N plot, through an artificial neural network architecture with competitive
layer, intending to simulate the decision problem of log analyst, when the M-N plot is used.
In the enviroment of artificial neural network computations, the log analyst decision problem simulation, when
M-N plot is used, can be understood as a decision problem with an alternative finite number or as non-linear
classification of stimulus group in the patterns set.
The perfomance of this approach is shown over real data from PETROBRAS obtained at Amazon Basin.
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Wireline Logs Restoration Through Self-Adjustable F
Authors Carlos Eduardo Guerra and André AndradeThe lack of a good vertical resolution of deep investigation wireline tools is the main cause of difficulties in the
log interpretation, mainly in the cases where the layers reservoirs have thickness less than the vertical
resolution of the tool. The combined measurement of shallow and deep resistivities, for instant, enable the
parameters determination like Rt( true resistivity), Rxo (resistivity of invaded zone) and di (diameter of invasion).
But in complex reservoirs we have difficulty in obtaining a confident reading of Rt due the low vertical resolution
of deep reading tools. In this work, we present a methodology that outlines this problem, using image
processing techniques, which allow to incorporate information from high-resolution log into the low-resolution
log. This information is generated by the shallow investigation tool, whose measurements do not relate directly
with the reservoir parameters. The final result is an improvement in the vertical resolution of logs got from
deep investigation tools.
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Automatic First Break Picking In Seismic Traces By Neural Network
Authors Anna Ilcéa Fischetti and André AndradeThe first break picking is a manual task of seismic interpreters performed before many computational
seismic processing, based in their geological and geophysical experience and interpretative criterions.
In this paper we propose an automatic approaches to this task, based in the apresentation of an artificial neural
network architecture, that quest simulate the human visual system behavior in a decision problem form. The
applicability, efficiency and limitations of this approach will be appraised in synthetic data obtained starting out
from the ray theory.
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South Central Andes Gravity,New Data Base
Authors M. Araneda, M.S. Avendaño, S. Schmidt, H.J. Götze, J. Muñoz and M. SchmitzFrom 1993 to 1998 approximately 3.927 gravity stations were taken in the Central Southen Andes, comprising the
southern central zone of Chile and the central western part of Argentina, between latitudes 37.50ºS to 42.5ºS and
69ºW as far as the coast of the Pacific Ocean. To this information, 9.123 old stations were included, which were
reprocessed and when in some doubt, were remeasured. Now the the database contains 13.050 gravity stations
available which can be used along with other geophysical and geological information for an interdisciplinary
interpretation to be able to understand some structural aspects and evolution of the Southern Central Andes. In
this paper, we present the new data base by means of maps of Bouguer anomaly and isistatic anomaly, together
with a very preliminary interpretation.
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Efeitos Das Tempestades Magnéticas Na Ionosfera De Baixa Latitude
Authors Cristina Sayuri Yamashita, J.H.A. Sobral and M.A. AbduAs tempestades magnéticas e os seus efeitos na ionosfera terrestre constituem atualmente um dos temas de
maior interesse da comunidade científica especializada no campo de estudos da climatologia espacial cujo
conteúdo versa sobre o estudo integrado do sistema ionosfera/termosfera/magnetosfera/meio interplanetário.
As tempestades magnéticas são caracterizadas basicamente por fortes depleções na variação temporal do
parâmetro geomagnético Dst e também por valores elevados do índice Kp. Durante a ocorrência delas, a
ionosfera sofre perturbações em nível global. O objetivo deste estudo é analisar em detalhe os efeitos de uma
grande tempestade magnética na ionosfera sobre a região de Fortaleza. Os principais efeitos ionosféricos a
serem aqui investigados são os seguintes: 1) Penetração de campos elétricos zonais (direção leste-oeste) na
região de baixa e média latitude; 2) Efeitos dos ventos termosféricos perturbados (Disturbance Dynamo). A
metodologia a ser empregada para o estudo dos efeitos ionosféricos das tempestades magnéticas consiste
basicamente na comparação dos parâmetros ionosféricos dos dias magneticamente perturbados com o valor
médio dos mesmos parâmetros dos dias magneticamente quietos.
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Mt Studies At Sedimentary Basin Of Sierras Pampeanas, Argentina
Authors Cristina Pomposiello, Ana Osella, Alicia Favetto and Claudia SainatoMT data from profiles located over intermontane sedimentary basins of Sierras Pampeanas in North-West of
Argentina are analyzed through 2D inversion methods.
These basins are very deep and have an important deposit of Tertiary sediments. Sediments contain Miocene to
recent sequences of volcanic or continental detrial origin. Lithological variations occur from one intermontane
basin to another and they lie on a basement peneplain surface formed after the middle Paleozoic and frequently
exhumed on the range.
The resulting electrical models show sedimentary sequences with variable thickness (between 3 to 9 km). In all
cases, a very conductive layer beneath the basement are detected.
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Condicionamento Estrutural Sobre O Aqüífero Barreiras E Sistema Lacustre Do Bonfim-Nísia Floresta-Rn
Authors Leandson R.F. Lucena, Sebastião K. Oliveira and Walter E. MedeirosA cenozoic sedimentar region, localized near the eastern coastline of Rio Grande do Norte state, Brazil, was studied. This region contains the Bonfim lake that is an importante source of potable water to supply the cities in the region, including Natal (capital of the state). A joint study of morphotectonic, geologic, gravimetric and resistivity data revealed that the shallow structural trends are aproximately paralel to the deep structural trends. Based on this concordance, it is suggested that the shallow structures were formed, at least in part, activating the older and deeper structures. The Bonfim lake is localized on the crossing of two regional trends; these structures define a graben, which is resposible for the local increase in the saturated thickness of the Barreiras aquifer. The refered graben conditionates the groundwater flow from the Barreiras aquifer to the Bonfim lake.
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Estudio Geofísico De La Cuenca De Grenada
Authors Nuris Orihuela Guevara and Daniel LoureiroThe results of a combined gravimetric-magnetic study of the Grenada Basin are presented. Two domains migth
be recognized based on the map patterns of the anomalies in the area. South of parallel 15.5° regional gravity
shows a steep and steady gradient, presumably associated to the development of a relatively thick sedimentary
basin. Modeling of a gravimetric profile suggests that the thickness of the crust varies from a maximun of
about 25 km under the Aves Ridge, to less than 8km beneath the Grenada Basin, where it might be covered by
as much as 7 km od sediments. This architecture is interpreted as a result of the development of the Grenada
Basin in an extensional back-arc setting. Furthermore, the high frequency magnetic anomalies along the profile
have been successfully matched using a madel where the uppermost oceanic crust was divided into alternately
normally and reversely magnetized blocks. The fact that no major uplift or ridge trace is actually present in the
basin is regarded as a result of thermal subsidence enhanced by sediment loading postdating the sea floor
spreading event.
The second domain, north of parallel 15,5°, is characterized by high frequency residuals probably indicating a
shallow and strongly faulted basement.
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First Mesopause Temperature Profiles From A Fixed Lidar Station At 23º S
Authors B.R. Clemesha, P.P. Batista, P.P.M. Jorge, D.M. Simonich, H. Takahashi and I. VeselovskiiThe INPE sodium lidar, which has been in operation since 1972, was recently modified so as to enable
measurements to be made of the Doppler temperature of the Na atoms in the atmospheric sodium layer. A
relatively simple modification to the dye laser transmitter causes it to produce a multi-line output with 1.98 pm
spacing between individual lines, each of which has a bandwidth of less than 0.05 pm. By changing the gas
pressure in the Fabry-Perot interferometer which produces this line structure, it is possible to switch between a
laser output where the lines exactly coincide in wavelength with the Na D2 hyperfine lines, and one where the
central laser line is exactly equidistant from the D2 lines. Doppler temperature is measured by determining the
change in the effective backscattering cross-section of atmospheric Na atoms when the laser is switched
between these two positions. Measurements were made on a total of 15 nights from July to October, 1998,
providing temperature profiles between heights of about 83 and 105 km. Almost all measurements showed a
mesopause temperature structure strongly perturbed by tides and gravity waves, with peaks in sodium density
occurring at almost the same height as the temperature maxima on the bottom side of the sodium layer. The
lowest temperatures, between 170 and 200 K, typically occur above 100 km, and the average profile for all our
measurements is similar to the winter profile seen at mid-latitudes, with a mesopause temperature of 190 K at
103 km.
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Migración De Solutos En Formaciones Porosas Saturadas
Authors Jacqueline Köhn, Eduardo E. Kruse and Juan E. SantosEste trabajo se refiere al modelado del flujo subterráneo y la simulación del transporte de contaminantes en
formaciones porosas saturadas. La elaboración de un modelo matemático que describa esta situación no sólo
es útil para representar el estado actual de contaminación sino para realizar un pronóstico hacia el futuro. La
metodología utilizada se basa en la observación, teorización y simulación que se puede obtener en geofísica
vinculando las distintas posibilidades que brinda la interrelación de respuestas reales del comportamiento
hidrológico y la matemática aplicada que proporciona la estructura lógica para descifrar los efectos individuales
de los fenómenos físicos generales. La técnica numérica TVD y el método iterativo mixto de características
fueron empleados para la simulación de transporte bidimensional de contaminantes. Con el objetivo de
comparar ambos métodos se planteó un caso sintético de migración de contaminante conservativo (cloruro) a
partir de una fuente continua y puntual ubicada en la zona saturada.
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Rooted Structuring As Key For Southern Apennine Oil Exploration
Authors Anna Del Ben and Icilio FinettiIt is Authors’ opinion that a key point for the evaluation of the prospect in Southern Apennine, having as target
the top of the Apulian Platform, is constituted by the type of the structure involved. That is, if the explored
feature is formed by a block rooted with its own basement and practically not or not much displaced, in that
case the preservation of the integrity of the reservoir and its oil trapping is possible. But when the explored
structure consists of thrust-blocks, disrooted from their basement and prominently displaced, than the resulting
reservoir/cover conditions don not allow oil trapping or preservation of oil accumulation. Examples of both
types of features are examined.
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Multiple Attenuation In The Plane Wave Domain By Matching Filter
Authors Reynam Pestana, Paul L. Stoffa and Mrinal SenIn this paper we present a method of multiple attenuation
in the plane wave domain that uses a filter estimation
procedure to match the angle dependent primaries
to predict the observed multiples. The filter is obtained
through the solution of an optimization problem. Instead
of using a source function estimate we use the primaries
from the shallow part of the data (reflectivity) to estimate
the multiples associated with these events that are correct
in traveltime, but not necessarily in amplitude. Using
this filter the amplitude and phase of the multiples
are estimated and the predictedmultiples are subtracted
from the data to obtain multiple free data. The application
of this method is illustrated on synthetic and real
data and the results demonstrate its effectiveness in attenuating
multiples. The proposed method is computationally
very efficient.
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Seismic Sedimentology Of Mioceno Deposits In The Mioceno Norte Area,Lake Maracaibo,Venezuela
Authors Hongliu Zeng, William A. Ambrose, Edgar Villalta, Roger Tyler and Noel TylerThis study provides a case history in which the reservoir-level facies interpretation in a densely drilled, but spatially
restricted, area containing 240 wells is extended to a ‘bigger, 3-D-survey area’ by means of seismic sedimentology. In
turn, seismic facies images verify and improve upon the existing facies interpretation by adding control between and
beyond wells.
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Application Of Rms Amplitude Anomaly Mapping In Inferring Controls On Fluid Saturation And Fault-Bound Reservoir Compartments In The C4 Member (Lower Misoa Formation), Phase Iii Area, Bloque I Area , Lake Maracaibo, Venezuela
Three-dimensional seismic data are increasingly being used in reservoir characterization studies as an aid in
detecting and delineating structural and lithologic features as well as changes in fluid distribution that may not
be resolvable with log data at wide well spacings. Amplitude maps, in addition to displaying distribution of
lithology, can also be effective in inferring subtle faults associated with changes in reservoir fluid content.
In a IZmonth reservoir characterization study of tide-dominated deltaic and shelf reservoirs of the Lower
Eocene Misoa Formation in a 4-mi*(10.4-km*) rectangular area (Phase III Area) in the Bloque I Area,
3-D seismic data were used in conjunction with logs from approximately 50 wells to detect and delineate faults
and to infer interwell sand-body distribution. The goal of this reservoir analysis was to construct an improved
geological model of oil- and gas-productive reservoirs in the Lower Eocene to better understand controls on
reservoir compartmentalization and to identify areas of unswept hydrocarbons. This paper provides examples
from the C4 Member and demonstrates how 3-D seismic data were used to infer the presence of faults not
previously detected in earlier studies of these reservoirs with conventional log data and to illustrate their control
on fluid distribution.
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3D Seismic Stratal-Surface Concepts Applied To The Interpretation Of A Fluvial Chanell System Deposited In A High-Accommodation Environment
Authors Bob A. Hardage and Randy L. RemingtonA fundamental thesis of seismic stratigraphy is that seismic reflections follow impedance contrasts that coincide with
strata1 surfaces. which are surfaces where depositional processes occur at a fixed moment in geologic time. This stratalsurface
concept IS used herein to image a narrow (width -300 ft). thin, fluvial channel system that is embedded within a
seismic reflection peak. The peak reflects from a large (about 2. X 2.mi) area of nonchannel facies that dominate its waveshape.
The targeted channel facies are confined to an interval that vertically spans less than 30 ft According to principles of
seismic stratigraphy, four conformable seismic strata1 surfaces that pass through the interior of this channel sequence
were constructed across the 3-D seismic-data volume. The channel images portrayed on these seismic horizons, which
were spaced at vertical increments of 2 ms. illustrate the principle that seismic altributes viewed on seismic strata1
surfaces provide valuable images offacies distributions within thin-bed sequences and help seismic interpreters segregate
channel facies from nonchannel facie? Acomparison is made between channel images on seismic strata1 surfaces that
are conformable to two different reference surfaces, one reference surface being positioned below the targeled fluvial
system and the second reference surface being above the thin-bed channels This comparison supports the premise
that seismic interpreters should extrapolate strata1 surfaces both upward and downward across a thin-bed target to
optimize the image of that target.
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Emprego Do Gpr Para Estudos Geológicos Na Mineração Jundu, Descalvado-Sp
Authors Jorge Luís Porsani and Walter Malaqutti FilhoThe GPR method was used in the Jundu mines, located in Descalvado-SP, to subsided geological detail studies.
For such, it was carried out several profiles with the antennas of 50 and 100 MHz, being used the Ramac-Mala
equipment. The obtained data were processed and presented in the form of profiles. The interpretation of the
results allowed to detail the stratigraphy, and determine the depth of the water table. It was determined the
influence area provoked by the collapse of the top of the cave. The results present na excelent concordance
with the information given by drilling holes and geological outcrop studies.
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A New Approach To Map Host Rock For Gold Exploration In The Rio Das Velhas Greenstone Belt, Quadrilátero Ferrível, Minas Gerais, Brazil
Authors Adelene M. da Silva, Anne E. McCarfertt and Augusto C.B. PiresAn empirical modeling approach was used to locate zones that are favorable for gold mineralization in Rio das Velhas Greenstone Belt, Quadrilátero Ferrífero (QF). A known spatial coincidence exists between banded iron formation (BIF) host lithology, structures and mineralogy type that are indicative of gold. Quantitative relationships between airborne geophysical and geological data sets with known gold occurrences were determined using probability ratio analysis. Spatial associations between geophysical data and host lithology were combined to produce predictive models to explore for Archean oxide-BIF-hosted deposits. This approach has shown great capability for linking geological and geophysical interpretation. The results of this modeling map areas of exposed and subsurface geologic units that are important to gold exploration in the area.
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