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7th International Congress of the Brazilian Geophysical Society
- Conference date: 28 Oct 2001 - 31 Oct 2001
- Location: Salvador, Bahia, Brazil
- Published: 28 October 2001
1 - 100 of 465 results
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Aproximações Quadráticas Para Análise De Avo De Ondas Convertidas
Linearized approximations for reflections coefficients
used for AVO analysis are not suitable to determine
density contrasts. Second order approximations of
converted waves reflected amplitudes are necessary to
estimate density and the lithological indicators associated
to it. We present explicit second order expression
for reflected and transmitted amplitudes of converted
waves in isotropic media which can be used to
extend AVO analysis accurately to converted waves.
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Combining P-P And P-Sv Avo To Improve Estimation Of Elastic Parameters
More LessCompressional wave amplitude-versus-offset analysis
(AVO) is being widely used in different geological
settings as a lithology indicator and also as a direct
hydrocarbon indicator. Ambiguities associated to
elastic parameters estimation from AVO is
commonplace in most inversion procedures used up
today. Basic approaches to determine elastic
parameters directly from the coefficients of the P-P
reflectivity approximation (Rpp) fail because of the
uncertainties associated to the third coefficient, which
depend on larger incidence angles than intercept (A)
and gradient (B) estimates. One way to get around
this problem is to use the reflectivity information
from P-SV AVO (Rps) in addition to the traditional PP
AVO. This procedure can potentially reduce the
uncertainties and improve estimation of elastic parameters.
In this paper I demonstrate how to extract elastic
parameters from P-SV AVO and the way to combine
these parameters with those extracted from P-P AVO.
A simple low-contrast approximation is derived and
is compared with a more accurate, yet more complex,
high-contrast approximation. This procedure makes
possible to access the uncertainties associated with
the parameters estimated from P-SV AVO.
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Determination Of Reservoir Characteristics By Multiple Diffraction Stacking (Mds)
Authors J.C.R. Cruz, G. Garabito and K. ObaidullahAmplitude-versus-offset or (AVO) analysis is usually
carried out by using linear approximations of the
Knott-Zoeppritz equation. For comprehensive
analysis, a detailed knowledge of velocity model is
essential to determine incidence angles using ray
tracing. The angular reflection coefficients and the
incidence angles are determined by means of doublediffraction
stack of common-offset seismic data. For
determining zero-offset reflection coefficients is used
a true amplitude Kirchhoff migration operator. The
two resulting sets are then used in Hilterman's linear
approximation of Zoepritz Equations to determine NI
and PR. As long as we are within the bounds of
assumptions involved, a reasonable estimate of the
zero-offset reflection coefficient or the Poisson
reflectivity can be made. The data sets of the two
parameters are then available for attribute
determination and reservoir characterization.
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Interpretation Of Long Offset Avo Attributes
Authors Douglas Foster, Jeff Malloy, Bill Beck and Marc SbarAVO effects in large offset P-wave data (up to 60°) is
investigated. In addition to conventional P-wave
AVO attributes (A and B) a third term (C) is exa mined.
Background trends for crossplots of the attributes
are related to rock property relationships. Exact
expressions are given for the first 3 terms, (A, B, C),
of the expansion of Knott-Zoeppritz equations of the
reflected P-wave energy. These exact expressions are
compared to the commonly used linearized (first
order contrasts of rock properties) attributes. The
effect of variation in water saturation and porosity in
a sandstone embedded in shale is investigated in a
numerical example, based on rock physics models of
a well log. The AVO attributes show promise to distinguish
so-called fizz-gas (low saturated gas sands)
from commercial gas and differentiate porosity in
reservoir rocks.
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Quantifying Avo Attributes And Their Effectiveness
More LessQuantifying the effectiveness of any AVO technique
has always been a concern for progressive
geoscientists assessing and modeling reservoirs. This
paper compares three major AVO-based attributes
and their applications. Elastic impedance, lambdamu-
rho, and conventional intercept-gradient AVO
techniques are compared for various angular
apertures and well availability using a 3D prestack
seismic model. The effectiveness of each technique
is determined by comparing the apparent reservoir
extent to the known reservoir extent.
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Reflection Impedance
Authors Lúcio T. Santos, Martin Tygel and Antonio C. Buginga RamosAVO is now an established technology and has been
widely deployed as a lithology indicator and also as a
direct hydrocarbon indicator. In recent years this
technology has become a routine processing and its
application to large 3D volumes has relied on the use
of near- and far-offset stack volumes. These volumes
greatly reduce the amount of pre-stack information
that needs to be stored for standard AVO processing.
Additionally, these volumes are easily converted into
usual AVO attributes, like intercept and gradient,
which can then be interpreted in terms of anomalies
and calibrated with well logs. Reservoir
characterization studies make use not only of these
traditional AVO attributes but also impedance
volumes. The near-offset, or the intercept, stack
volume offers a natural way of obtaining acoustic
impedance volume through the use of post-stack
inversion algorithms. However, to invert far-stack
volume one needs an approach capable of estimating
impedances for a variable incidence angle. This
approach has been described in the elastic impedance
function presented by Connolly (1999). In this work
we propose an approach called reflection impedance,
which is based on constant ray parameter and a power
relationship between density and S-wave velocity.
This new method proved to be of better accuracy for
angular impedance estimation and reflection
coefficient recovery when compared with the elastic
impedance approach.
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Shear Waves Avo Azimuthal Analysis In Vacuum Field, New Mexico
More LessShear wave amplitude versus offset (AVO)
analysis was used in Phase VII Reservoir
Characterization Project in Vacuum Field, New
Mexico, for porosity and permeability estimation and
time-lapse investigation of the Upper San Andres reservoir.
DeVault (1998) pointed out that plane-wave
reflection coefficients for shear waves can be
inverted for density contrast, fracture density
contrast and shear velocity contrast.
The interpretation of the AVO attributes can
help to estimate the porosity and permeability of the
reservoir. The result obtained for porosity agrees with
the data from well logs, especially in the center of the
reservoir area, around the producers and injector
wells. Upper San Andres reservoir is a dolomite
where most of the permeability is provided by
vertical fractures. The fracture density was
particularly efficient in portraying the intense
fracturing between CVU-97 and CVU-200,
confirmed by the oil production increase after CO2 injection.
The time-lapse analysis showed variation in the
density between the pre and the post CO2 injection in
the northern part of the reservoir, with agreement
with the production wells in this area.
AVO attributes inversion proved to be a reliable
method for reservoir attribute determination and
time-lapse analysis, and provides an important link
between seismic data and rock properties.
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The Generation Of A Rock And Fluid Properties Volume Via The Integration Of Multiple Seismic Attributes And Log Data
Authors Matthew Carr, Richard Cooper, Maggie Smith, M. Turhan Taner and Gareth TaylorWe present a systematic seismic reservoir characterization
workflow that integrates log and seismic data using an artificial neural network.
Seismic attributes are examined both qualitatively and
quantitatively to determine the best discriminators of rock
and fluid properties. These attributes are systematically
classified using an artificial neural network, the Kohonen
self-organizing map (K-SOM) algorithm. Ultimately the
classified litho-facies volume is calibrated to available well
control by applying the K-SOM technology to well-derived data.
The product is a seismic-scale rock and fluid properties reservoir model that is consistent with borehole and surface seismic data.
The workflow is applied to the characterization of a Vicksburg-age reservoir in South Texas.
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The Rock Physics Of Seismic Fluid Attributes
Authors Vaughn L. Ball, Kevin Northey and Doug FosterThe tendency for a rock to change its bulk properties
upon fluid substitution is its "Fluid Sensitivity", and
is an intrinsic property of the rock. The magnitude of
the change in bulk rock properties is predictably
related to changes in seismic reflection attributes.
These changes are often called the "fluid effect". We
can speak of a fluid effect in relation to the classic
"A", "B", and "C" coefficients of the Aki & Richards
linearization. Fluid sensitivity and fluid effect are
often qualitatively related to porosity and P-wave
velocity, but can be more precisely related to an
important property of porous rocks called the "Biot
Coefficient". For most seismic attributes, the fluid
effect is independent of the surrounding lithology.
Only the fluid effect for the "B" attribute has a
component that depends on surrounding rocks. The
fluid effect for seismic attributes are separable in
relation to properties of the rock, and properties of
the fluid, and can be expressed as the product of rock
properties and fluid properties.
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3D Wavefield Imaging In The Deepwater Gulf Of Mexico
Authors Paul Valasek, Kay Dautenhahn Wyatt, Dan Whitmore, Yunqing Shen, Zhaobo Meng and Keith L. BranhamWhen complex structures with large velocity contrasts are present, wavefield techniques can provide improved imaging (structure, amplitude, and phase) over the more traditional Kirchhoff integral methods. Wavefield techniques rely on two elements: firstly, an advanced acquisition design with complete azimuthal coverage; and, secondly, wave equation based prestack
imaging methods. Together, these two elements offer improved seismic imaging in complex structural environments by better handling of multipathing, amplitudes and phase. A wavefield
experiment was conducted last year in a complex subsalt area of the deepwater Gulf of Mexico using a full-azimuth vertical cable acquisition strategy. Here, we discuss some of the unique
challenges associated with wavefield imaging such as velocity analysis and residuals correction. Finally, comparisons will be shown between conventional Kirchhoff imaging and wavefield imaging.
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A Deepwater Pore Pressure Risk Management Case In Offshore Brazil
Authors William L. Abriel, Dieter Letsch, Mike Luken, Stan Teerman and Jay BrutonA well was planned as the first in the deepwater
Cumuraxitiba basin offshore Brasil. The well casing
and the mud program were designed for abnormal
pressure based on risk from offset wells on the shelf
and a seismic velocity model. Interval probability
analysis illustrated an opportunity to decrease the
uncertainty of this risk.
Basin modeling and seismic tomography were
performed and uncertainty was reduced, pointing to
the probability of a normally pressured well. The well
design was altered reducing cost, and the subsequent
drilling of the well has confirmed the normal pressure prediction.
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Mantle-Plume-Generated Triple Junction Between Ne Brazil And West Africa?
More LessThis paper has three purposes. First, it offers an overview
of the nature and history of the interior and
offshore basins of Northeast Brazil and West Africa,
and their relationship to the development of the
Southern and Equatorial branches of the Atlantic.
Second, it places emphasis on the differences of the
rift systems and the control exercised by basement
structures on the conjugate margins of West Africa
and Northeast Brazil. Third, as the most important, it
challenges the idea of a mantle-plume-generated
triple junction between Northeast Brazil and West
Africa.The Benue Trough is very often cited as one of
the best examples of a failed arm of an RRR triple
junction (Burke and Wilson, 1976), formed through
the activation of a mantle plume. This would imply
in: (1) early crustal doming, warping and flexure over
a plume with crestal alkaline volcanoes; (2) formation
of three simultaneous rift arms, symmetrically orientated
at 1200 to each other; (3) if one rift arm is
aborted, the other two develop into a single ridge
(new margin) and drift begin; and (4) growth of delta
at the mouth of a failed arm. Among them, just the
last one is corroborated by the data set. Voluminous
magmatism clearly post-dated the opening of the
Equatorial Atlantic. Rifting and drifting were diachronous
among the African - Brazilian basins and the
rift arms are not symmetrically orientated, and finally,
instead of one, there are two failed arms: Benue
Trough and the onshore Potiguar basin.
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Sequence Stratigraphy, Facies Analysis And Paleoceanographic Events Of The Neogene Deep-Water Section In The Campos Basin, Offshore Brazil
More LessThe Campos Basin, situated offshore Rio de
Janeiro State, around 23 degrees latitude south,
has a total area around 100,000 Km2. It is the
most prolific basin in Brazil, with more than five
giant oil fields, of which at least four produce in
Neogene reservoirs.
This work was carried out in a thick deep-water
sedimentary section developed on the basin slope
during the Neogene and Upper Oligocene, using
3D seismic sections, well log correlations, cored
facies analyses, nanofossil biozones and
paleoecology (fig. 1).
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Offshore Brazil Santos Basin Exploration Potential From Recently Acquired Seismic Data
Authors Roberto Fainstein, George Jamieson, Andrew Hannan, Norman Biles, Ana Krueger and Dianna ShelanderThe deep and ultradeep water regions offshore east Brazil is
increasingly attracting attention from exploration and
production companies. Brazil hydrocarbon production is
derived mainly from the giant deepwater fields of the
Campos Basin. By contrast, the deepwater regions of the,
adjacent to the south, Santos Basin have remained largely
under-explored. In actuality, Santos Basin is one of the
largest under-explored basins of the world. In the last two
decades, there have been several significant discoveries in the
southern portion of Santos Basin mainly on carbonate
reservoirs. Recently in 1999 a significant discovery occurred
on Upper Cretaceous turbidite reservoirs in deepwater. This
paper outlines the encouraging hydrocarbon potential of the
deepwater realm of Santos Basin by utilizing a recently
acquired, processed and interpreted 2D dataset which has
revealed numerous, largely untested, play types. These plays
include both structural and stratigraphic components. Saltrelated
large 4-way closures, including faulted and unfaulted
turtle structures and drapes over salt have been identified
along with sub-unconformity traps. All these identified play
types have examples with associated amplitude anomalies,
which are widespread throughout the basin, at varying
stratigraphic and structural levels.
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A Multi-Frequency Inductive 5Th Generation Em System For Geophysical Exploration
The multi-frequency inductive electromagnetic systems had their origin in the work by Dias (1968; 1973) and five generations of these equipments appeared in the market since then. The system discussed here belongs to the last generation. It consists of a loop-loop minimum coupling system operating at 54 values of frequency in the interval 1.125 Hz to 10.473 KHz, with transmitterreceiver separation spreading up to 1 km on a terrain of 100 Ωm resistivity background. A scheme is also presented here for processing the field data and constructing
2D pseudo-sections for resistivity and polarization parameter. The area test for this experiment is situated on a gnaissic basement covered by intemperized basement rock and quaternary beach sediments on the Farm São João in Rio das Ostras/RJ. This system was capable to discriminate and map a zone of washed sand, probably more indicated for groundwater taking, and a zone where clay minerals are present.
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An Easy Windows Graphic Interface For 3-D Electrical Geophysics Modeling
Authors Humberto Deodato M. Monteiro and Luiz RijoThe finite element method is a very powerful tool
for modeling complex problems in physical science,
engineering and geophysics. However, for three
dimensional analysis, the arduous pre-processing
stage which consists of supplying the data for the
mesh and the physical properties for each element is,
certainly, a weakness of the method. In order to
handle this disadvantage, we developed a simple
Windows graphic interface for entering the
information of the physical properties across the mesh
at no great pains. We use the 3-D Resistivity and IP
modeling problem to show how the proposed graphic
interface facilitates the access of finite element data.
Apparent resistivy and PFE pseudo-sections at 10
parallel survey lines, one dipole unit apart, are
displayed graphically to exhibit the output graphic
interface that was also developed for presentation of
the modeling results.
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Analysis Of Georadar Reflection Responses
Authors Jacob Fokkema, Emile Fokkema, Sicco Beekman and Evert SlobUnderstanding the nature of the georadar reflection
response in terms of the dielectric permittivity and
conductivity contrast is important in the realm of
interpretation. This motivates the present study,
which has the aim to carry out an experiment in a
controlled fashion such that the relation can be established
between the measurement and the relevant
physical parameters. In the present paper we present
the results of such a measurement and an interpretation
based upon a 1D model, which is realistic enough
to accommodate sophisticated physical parameter models.
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Coast Effects On Magnetotelluric Data From The Brazilian Southeastern Region
Authors Antonio L. Padilha, Ícaro Vitorello and Marcelo B. PáduaThe coast effect on magnetotelluric (MT) data acquired
near the Brazilian SE coast in the state of São
Paulo is investigated using two-dimensional (2D)
modeling. The Atlantic ocean was modeled as a layer
of constant resistivity (0.3 ohm.m) and thicknesses up
to 2.0 km at 160 km from the coast, according to
bathymetry. Offshore Santos Basin was also included
in the model using parameters derived from boreholes
and seismic lines. The continental resistivity model
was constructed based on the electrical structure inferred
from previous MT studies. The modeling exercise
shows that the ocean-coast effects are very important
for periods greater than some seconds at distances
of tens of kilometers from the coast. Synthetic
data from the model are compared with a MT sounding
carried out in the Serra da Mantiqueira plateau.
Splitting between TE and TM modes observed at a
period of 30 s in the MT data can be explained as
being generated by electric currents induced in the
highly conductive Atlantic ocean (coast effect), about 90 km away.
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Crosswell Electromagnetic Tomography: Some Results Using Born Approximation
Authors Licurgo Peixoto de Brito and José Felipe Souza de AlmeidaA method of crosswell electromagnetic imaging is
presented and used to analyze the relevant parameters
for electromagnetic tomography. The influence of a
punctual inhomogeneity on the magnetic field is
calculated through the Sensitivity function based on
Born approximation. The analysis of the extremals of
that function is applied to generate crosswell images.
The method showed that the resolution is very good
vertically and very poor horizontally. Images are not
affected by increasing the number of receivers and
their horizontal alignment with the scatter, but local
maxima occur if transmitter and scatter are not
horizontally aligned. Furthermore, vertical resolution
is improved for increasing number of transmitters and
the aperture. These results are in agreement with
those well known in electromagnetic tomography literature.
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Desenvolvimento De Um Sistema Hlem De Campo Magnético Induzido, No Domínio Da Freqüência, Para Prospecção Mineral
More LessAn electromagnetic system was developed
using some parts of an old Slingram ABEM EM35/88
as transmitter and receiver coils and matching
transformers. Modern circuits with low noise lock-in
amplifiers and analog multiplier were used to detect
signal from a high magnetic permeability receiver
coil. In phase and quadrature voltage of lock-in
amplifiers outputs were achieved using square
waveform reference from the transmitter coil circuit.
Comparison of these voltage by a precise analog
multiplier give us the electrical apparent conductive
of the overburden layer (conductor). One third lock-in
circuit was used to adjust the spacing intercoil by
nulling the total field component.
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Dual-Mode Mt Static Shift Correction Using In-Loop And Single-Loop Tem Data
By Max A. MejuAccurate removal of static shifts caused by nearsurface
heterogeneities in dual-mode magnetotelluric (MT) apparent resistivity
sounding curves in complex geological terrains is
an outstanding problem in MT data analysis.
Using field examples, it is shown that the in-loop
and single-loop TEM curves vary in the same
manner as transverse electric and transverse
magnetic mode MT apparent resistivity curves
over 2D geological terrains. This suggests that
dual-mode TEM data can be used to effectively
remove static shift in MT sounding curves
leaving only those signatures due to
electromagnetic induction in larger local and
regional structures that may then be reliably
modelled using existing multi-dimensional
interpretation schemes.
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Electromagnetic Tomography With Absolute Constrains
Authors Victor Cezar T. de Souza, Luiz Rijo and João J. BaptistaAn iterative inversion process is employed to analyze
the incorporation of absolute constrains to obtain high
resolution image of cross-well electromagnetic (EM)
tomography. The image scheme assumes a cylindrical
symmetry about vertical magnetic dipole sources and
employs the finite element method to solve the
scattered EM fields by anomalous conductivity
imbedded in an homogeneous background. Images of
illustrative models show that to obtain relevant results
of inversion process, we have to incorporate absolute
constrains for the first guess and also on the borders
of model, to guarantee the convergence to
experimental model. The resolution of method is
examined through changing of frequency and
conductivity contrast between the targets and the
background. Reconstructed models show that, at low
conductivity contrasts, the resolution improves with
increasing frequency. On the other hand, for one
given frequency, large contrasts make the resolution
deteriorates. However when the frequency is
decreased, the quality of image improves.
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Electromagnetic Tomography With Derivative Constraints
Authors João J. Baptista, Luiz Rijo and João J. BaptistaIn this paper about electromagnetic tomography we
test the use of smoothings constraints implemented by
derivative operators of first, second and third order
calculated by the regularization method proposed by
Tihkonov. To get this, we use the same model
published by Alumbaugh & Morrison (1995). During
the inversion of the data we adopted the Maquardt
algorithm. The finite elements method was used to
calculated de forward model The knowledge of the
true conductivity of host is sufficient to guarantee the
recuperation of the image at any frequency between
10 to 1000 kHz. In this case no other constraint is
necessary. When the conductivity of the host is
partially known, within 20%, the use of derivative
constraints permits the achievement of good results in
range of 50 and 500 kHz.
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Geoeletroestratigrafia Bi-Dimensional Da Parte Central Da Bacia Do São Francisco (Mg)
Authors Ana Lucia Rodrigues and Sergio Luiz FontesNo âmbito de um programa de exploração realizado
no início da década de 90, o Observatório Nacional
realizou 43 sondagens magnetotelúricas (MT),
perfazendo um total de 7 perfis geoelétricos, ao
longo de linhas sísmicas previamente levantadas,
cobrindo uma área de 11.000 km2, ao norte do
estado de MG, na Bacia Proterozóica do São
Francisco (ou Bacia do Bambuí). A variação de
freqüência utilizada foi de 0,001 a 400 Hz. A
região localiza-se entre as latitudes 46º e 45º e
longitudes 16º e 17º, próximo da zona de
confluência dos rios S. Francisco e Paracatu,
estendendo-se até as margens do Rio Urucuia
(região transversal ao Rio S. Francisco). As
cidades mais próximas são Santa Fé de Minas e São
Romão. Os dados MT obtidos no levantamento
geofísico foram interpretados anteriormente a partir
de inversão 1D (Porsani e Fontes, 1992; Porsani,
1993), que supõe a variação da resistividade
elétrica apenas com a profundidade, não se
admitindo variação lateral ao longo dos perfis.
Tendo em vista o potencial para hidrocarbonetos da
bacia, objetivou-se, neste trabalho, reinterpretar os
perfis MT obtidos anteriormente, utilizando-se um
algoritmo de inversão bi-dimensional (Mackie et
al., 1997), que permite observar as mudanças
laterais da resistividade elétrica, fornecendo
informações que possibilitam a obtenção de
interpretações mais precisas em sub-superfície.
Os resultados preliminares das inversões 2-D de
quatro perfis MT apresentam estruturas de falhas
não observadas nos estudos de inversão 1D.
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Geração De Campo Magnético Direcional E Focalização Por Combinações De Dipolos Magnéticos
Authors Antonio V.C. Barbosa and Om P. VermaAn enhanced resolution is required in
electromagnetic investigation of the “low Induction
Number – LIN” targets. This could be obtained by
creating a directional magnetic field flux and focusing
it at in a predetermine depth zone. This is achieved by
combining the field of two magnetic dipoles in
different configurations to obtain vertically and
horizontally directed fields in the central portion of
the dipole configuration. Focalization of the field in
depth is controlled by the separation between the
dipoles. Results in the forms of directional magnetic
fields maps and the curves of the variations in the
intensity of these magnetic field components with
depth are presented. This study suggests an
innovative way to create directional and focalized
magnetic fields; consequently opens a new horizon in
electromagnetic exploration methods.
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Imageamento Geoelétrico De Colunas E Secções De Modelos 1–D Utilizando Técnicas Geoestatísticas
More LessO método do imageamento geoelétrico é uma importante
ferramenta no mapeamento de estruturas 2-D,
tendo sido propostas muitas técnicas de inversão com
esta finalidade. No entanto, quando a estrutura em
sub-superficie é próxima de camadas horizontais, a
hipótese 1-D deve ser considerada como a mais efetiva
para uma solução precisa. A combinação da técnica
da sondagem elétrica convencional com técnicas
geoestatísticas de imageamento, para investigação em
áreas de geologia não complexa, foi aqui desenvolvida.
As técnicas geoestatísticas, que incluem a krigagem
associada a uma forte “anisotropia” horizontal,
foram usadas primeiramente na elaboração de colunas
geoelétricas de SEVs individualmente. Posteriormente,
foram estendidas para o imageamento de secções
eoelétricas. As secções imageadas em dois levantamentos
são consistentes com as informações
geológicas/hidrogeológicas disponíveis e com um
levantamento anterior de eletrorresistividade realizado
pela Universidade Federal do Ceará. A metodologia
Geoestatística aqui estabelecida pode ser utilizada
na representação de variáveis da perfilagem geofísica,
assim como no imageamento bidimensional de propriedades
físicas com distribuição em camadas horizontais.
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Inversão Bidimentsional De Sondagens Elétricas Verticais Com Algoritmos Genéticos
Authors Niraldo R. Ferreira, Milton J. Porsani and Olivar A.L. LimaThis work investigates the two-dimensional (2D) resistivity inversion using genetic algorithm combined with Gauss-Newton method.
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Investigações Eletromagnéticas (Mt/Tem) Na Porção Continental Da Bacia Do Espírito Santo: Primeiros Resultados
A 200 Km geophysical transect crossing both on
shore terrains of the Espirito Santo basin and the
contiguous crystalline region has recently been
established. It includes magnetotellurics - MT,
transient electromagnetics – TEM, potential field -
magnetic and gravimetric mesurements as part of a
multi-institutional project involving UENF, UnB,
Petrobras and Observatório Nacional aiming at the
regional characterization of the basin. The objectives
of the study comprehend better knowledge of the
basement structure, continental crust – oceanic crust
contact, crust- mantle contact, lateral variations of
crustal structures, etc. This paper is concerned with
the very first results obtained with the MT and TEM
methods along the transect. Main results to date are
the geoelectrical signatures of the on shore basin
limits and the Colatina Vitoria fault.
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Metamorphoses Of Maxwell’S Equations
By Luiz RijoMaxwell’s equations are the starting-point of
electrical geophysics. From Magnetotelluric method
(low frequencies) to GPR (high frequencies) they are
behind of every electric geophysics techniques.
Since their origin, more than one hundred years
ago, Maxwell’s equations have been redressed in
many different manners. Maxwell started with a set of
twenty equations. Heaviside purified them to four
vector equations. With the contribution of Einstein’s
special theory of relativity the four vector equations
are recast into two tensor equations. Now, with the
aid of Clifford geometric algebra Cl3 they have been
reduced to just one single equation.
The saga of Maxwell’s equations helps to clarify
the physics of electromagnetism and simultaneously
gives us more confidence to work with them.
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Modelagem Bidimentsional De Resistividade Por Diferenças Finitas Para Um Caso De Modelo Primário Heterogêneo
Authors Frederico A.F. de Oliveira and Hédison K. SatoThe Choise of suitable boundary conditions plays an important role on two-dimensional resistivity modelling by finite differences.
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Modelagem Matemática E Numérica Da Propagação De Ondas Eletromagnéticas Acopladas A Ondas Elásticas, Considerando-Se O Efeito Sismomagnético
More LessInteraction of electromagnetic fields with elastic bodies is
the subject of many theoretical investigations in
mechanics of continua for the last decades. Some variants
of direct and inverse problems have been studied leading
into the determination of some characteristics of medium.
It is very interesting to study this phenomenon due to the
possibility of applying this theory to geophysical
prospecting and study of earthquake sources. Olsen [6]
has represented some experimental results of interactions
of power-line electromagnetic field with the Earth crust.
He has showed that high harmonic fields are produced by
basic harmonic field of frequency ωo = 60 Hz. One
possible explanation of this effect is a nonlinear
interaction of electromagnetic field with seismic field.
Our work is dedicated to the investigation of this
interaction. We form the basic equations for the
description of some variant of this coupling and consider
a simple mathematical model of this process. It is possible
to construct in linear approximation the solution of
corresponding problem, showing that higher harmonic
fields’ generation process can be described for that model.
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Modeling Of Geomagnetic B Field Under The Electrojet
Authors Marcos W.C. Silva and Luiz RijoOne of the traditional geophysical methods employed
in the determination of conductivity distribution of
subsurface in regional scale is the Magnetotelluric
Method (MT). It uses both electric and magnetic
fields at ground surface and is based on the
hypothesis that these fields propagate as plane waves.
In the equatorial region this hypothesis is not always
valid for low frequencies in resistive terrain due to
the presence of the equatorial electrojet.
Instead of using the electric and magnetic fields,
as MT, here we employ the vertical component of the
magnetic field normalized by the horizontal
component to analyse the influence of a 2-D structure
which is parallel to the electrojet upon the
geomagnetic field scattered by a 2-D structure. The
finite elements method was used for numerical
modeling. The electrojet was modeled as infinite
current line and as a planar gaussian distribution of
current. The effects of the two electrojets on the
response of the 2-D heterogeneity were compared
against the plane waves results.
We concluded that at frequencies higher than 10-2
Hz there is no observable discrepancy between the
plane wave and electrojet responses. Between 10-2
and 10-3 Hz the difference is very small. At these
frequencies the lateral edges of the 2-D heterogeneity
is easily detected. At 10-4 Hz the signature of the
buried structure is no longer delineated, showing thus
the influence of geometry of the equatorial electrojet
source on the low frequency response.
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Multicomponent Induction Logging Response In A 3-D Borehole Environment
Authors Tsili Wang, Liming Yu, Otto Fanini and Berthold KriegshäuserA multicomponent induction tool has the capability of resolving formation's resistivity anisotropy properties.
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Processing And Inversion Techniques For Multicomponent Induction Log Data
Authors Berthold F. Kriegshäuser, Otto N. Fanini and L. YuIn this paper we present advanced processing and
inversion techniques to derive horizontal and vertical
formation resistivities from multicomponent
induction log data. This newly developed induction
logging tool (3DEXSM) is designed to identify and to
delineate productive low-resistivity reservoirs
frequently encountered in hydrocarbon exploration.
An example of such a reservoir is a finely laminated
sand/shale sequence of which the sand laminae can
contain hydrocarbons found in deep water
environments. These reservoirs exhibit electrical
anisotropy, i.e., the resistivities parallel and
perpendicular to bedding are different and cannot be
accurately delineated by conventional induction
instruments with their transmitter and receiver
orientation parallel to the borehole axis. However, the
new multicomponent transmitter-receiver
configuration provides direct measurements to derive
both horizontal and vertical resistivity that allows
evaluation of the hydrocarbon bearing sand laminae.
The tool is comprised of three mutually orthogonal
induction transmitter-receiver configurations yielding
all necessary data to derive the horizontal and vertical
resistivities of the formation.
In this paper, we introduce various processing and
inversion techniques such as real-time data
processing, shoulder bed and borehole correction
schemes, an automatic ‘thin-layer’ inversion scheme,
and an efficient ‘pseudo 2-D’ inversion algorithm.
We demonstrate the performance of these
interpretation techniques on synthetic and field data sets.
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Projeto De Um Sistema Semi-Automatizado De Medidas De Potencial Elétrico Natural Ou Induzido Do Solo Para Aplicações Geoelétricas
More LessThe devices were developed to realize
spontaneous and induce voltage measurement on the
ground. In both case we used a multiwire cable with
multiple voltage inputs along the length that becomes
possible to conect it in six stainless electrodes fixed in
the ground at same time. An automatic sequence
digital system controlled by pushbutton touch allows
to couple electrodes sequentially to a electronic DC
voltmeter with autozeroing circuit based in PID
servocontrol circuit. A 60 Hz notch filter and a roll-off
low pass filter with time constant of 1s are used to
minimize line and spheric noises. Electronic control
system becomes too possible to couple cable with
receiver datalogger of SYSCAL R-2 in dipole- dipole
sounding array.
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Resistivity Imaging From Mt And Seismic Data In The Tucuman Plain, Argentina
Authors A. Favetto, M.C. Pomposiello and E. RosselloMT data along two traverses in the Tucumán Plain
were analyzed and it was found that basin sediments
are formed mainly by two layers. Then, seismic
reflection data coincident to the traverses have been
used to constrain the geometry between the basement
and the sedimentary rocks. The models obtained
from data inversion show a sharp resistivity contrast at the interfaces.
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Scattering Of Electromagnetic Plane Waves By A Vertical Dike Under A Conductive Overburden: Implications Fo Gpr And Tdem
Authors Lurimar Smera Batista and Edson Emanoel Starteri SampaioThe expressions for the exact solution of the scattering of a TE mode electromagnetic plane wave in the time domain, by a vertical dike under a conductive horizontal layer, have been established.
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Tem Survey At Sergipe-Alagoas Basin
Authors Paulo de Tar so L. Menezes, Eutair R. De Morais and Alan S. CunhaCarbonates make up about 20% of the
sedimentary rocks record, but they account for more
than 50% of the world’s proven oil reserves (Palaz &
Marfut, 1997). Carbonates differ from siliciclastics in
generation, geomorphology, and diagenesis, all of
which modify the mineralogy, porosity and
permeability so important to reservoir quality.
Recent discoveries of high porosity’s layers
in deeply seated carbonate sediments have pointed
out that deep hydrocarbon carbonate reservoirs are an
important Brazilian exploration frontier (Brunh,
1990). Among the most impressive deep reservoirs in
Brazil are the fields of Badejo, Pampo e Linguado at
Campos Basin (reservoir is located 2500-3100 m
depth - Lagoa Feia Formation), and Tubarªo at
Santos Basin (reservoir at 4600-4850 m depth -
GuarujÆ Formation).
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The Effect Of Air In The Numerical Solution Of The Te Mode Of The Magnetotelluric Method
Authors Michael Heimer and Luiz RijoWe present the numerical solution of the model of
an infinite fault for the TE mode using the finite
elements method to investigate the effect of the air in
the TE solution. We compare our solution for the
normalized electric field with one approximated
analytic solution, which neglects the effect of the air,
and with another exact semi-analytic solution. The
latter comparison shows a difference that cannot be
explained by numerical errors. Examining the effect
of the air on apparent resistivity, we compare three
profiles of apparent resistivity obtained with our FE
solution with the profiles obtained using the
approximated solution. The discrepancy between the
apparent resistivities shows to be small, figuring in
the range of the instrumental field error.
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The Use Of Telluric And Magnetotelluric Methods In Graben Studies
In past years telluric measurements have been used on
sedimentary basins to explore lateral variation of
electrical resistivity. Magnetotellurics is currently
used in investigation both, vertical and lateral
changes in electrical conductivity of earth subsurface.
This paper concerns the application of both methods
to the study of a graben in NE Portugal and shows
that the complementary of the methods can be used in
order to infer information concerning the threedimensionality
of geological structures.
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Two-Step Inversion Scheme For Complex Magnetotelluric Apparent Resistivity Data
Authors Atahebson B. Santos, Edson E.S. Sampaio and Milton J. PorsaniInterpretation of magnetotelluric data under the assumption of isotropic and one-dimentsional structures is a valuable procedure for exploration and solid earth geophysics investigation.
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Estimativa Das Direções Principais De Tensão In Situ Por Anisotropia De Velocidades
Authors Raquel Velloso, Guilherme Vasquez and Lucia Duarte DillonNeste trabalho estimam-se as direções principais de tensão in situ pelo método denominado VELAN (Velocity Anisotropy), que consiste na medida da velocidade de propagação de ondas ultra-sônicas em diversas direções radiais numa amostra proveniente de um testemunho orientado. Estas medidas permitem determinar as direções de máxima e mínima velocidades
que por sua vez se relacionam com as direções principais de tensões in situ. Realizaram-se ensaios de VELAN com duas amostras que apresentaram resultados bastantes coerentes
entre si. A observação das amplitudes das ondas registradas e a análise de imagens de tomografia computadorizada foram importantes no mapeamento de heterogeneidades, permitindo uma melhor definição das direções de máxima e mínima velocidade. A utilização do método VELAN para a estimativa de direções das tensões in situ mostrou-se bastante vantajosa por se tratar de um método simples, rápido e eficiente.
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Fracture System Analysis Aided By Gpr: Applications On Dimension Stone Quarries Modelling
Authors Adelir José Strieder and Sérgio Alfredo BuffonFracture system analysis is the subject of structural
geology and its methods can be applied in dimension
stone quarries. The dimension stone modelling
through fracture system access can be aided by GPR
(ground penetrating radar) technique in different
ways. The fracture map of a dimension stone massif
demands lateral interpolation of a discontinuous
vector and the extrapolation (projection) of each
fracture set into depth. Controlled GPR scanning
profiles can enable fracture continuation into depth,
even under soil cover, as well as determination of a
large number of fracture features. Modelling
dimension stone deposits requires a well-defined
analysis of disjunctive structures and an adequate
GPR profiling program based on fracture set
characterization. An appropriate GPR data processing
program can be valuable for engineering purposes
(rock massif characterization), placing aside again
structural geology and rock mechanics disciplines.
Key words: dimension stone modelling, structural
analysis, GPR exploration
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Geophysical Tomography In Engineering Geology: An Overview
More LessAn overview of the tomographic interpretation
method in engineering geophysics is presented,
considering the two approaches of the deterministic
tomography inversion, developed for rock elasticity
analysis, and the probabilistic tomography imaging
developed in the potential fields domain. The
theoretical basis of both approaches is shortly
outlined before showing a laboratory and a field
application.
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Magnetômetro Fluxgate, De Circuito Aberto, Para Análise De Ruídos Em Sensores
More LessDescription of the development of a system to
evaluate noises and alignment for fluxgate sensors
of different sizes and geometries is presented. The
first circuit was built for 7 KHz sensors cores
excitation and a second one is being developed for
16.625 KHz sensors core excitation.
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Mapeamento Dos Dutos Na Baía De Guanabara
Com o grande vazamento de óleo ocorrido em
Janeiro de 2000 na Baía de Guanabara, a Petrobrás
foi solicitada em curto prazo, a apresentar perante
aos órgãos governamentais, um mapeamento
detalhado e atualizado de todos os dutos que
compõem sua malha de transporte de derivados entre
a Refinaria Duque de Caxias (REDUC) e os
terminais da Ilha D’Água. Isto implicou em
determinar a posição espacial inicialmente de 9
dutos ao longo de 13 km de trajeto, confirmando
através de inspeção por mergulho, pontos onde o
assentamento não estivesse em posição ideal. Para
tal fim, foram contratadas empresas de
levantamentos geofísicos, geotécnicos e de
mergulho. Os dados geofísicos oriundos dos vários
métodos utilizados perfizeram 2400 km de dados e
para absorver este grande fluxo respondendo
imediatamente aos vários questionamentos surgidos,
foram montadas equipes de processamento e
interpretação que possibilitaram executar
intervenções para detalhamento de interesses
específicos (inspeções submarinas, coletas de
testemunhos, etc.). Como resultado foram
produzidas plantas com a posição espacial de cada
um dos dutos, desde sua partida da refinaria até a
chegada aos terminais marítimos de escoamento
situados na Baia de Guanabara.
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Monitoração Sismográfica De Edifícos Adjacentes Aos Túneis Da Av. Luiz Eduardo Magalhães
More LessIn this paper I present the result of studies with respect to vibrations in surrounding building due to blasting carried out to build large tunnels (400m long) in urban areas.
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O Emprego Das Técnicas Sísmica E De Radar Entre Furos (Crosshole) Em Estudo Para Fundação De Obra Subterrânea Na Cidade De São Paulo-Sp
Authors Renato Luiz Prado, Rubens Paschoal Cordeiro and Vicente Luiz GalliAiming for the use of the geophysical crosshole
techniques for studies of the deformability and
resistance of soil mass and its geological
characterization, it was carried out a seismic and radar
crosshole tests in na underground work in São Paulo city, Brazil.
It is discussed the main acquisition procedures of the
both techniques and some empirical relationships
between the elastic and the electromagnetic waves
relating to the mechanic properties and the
sedimentologic characteristics of the soil mass. It is
also presented a tomographic section derived from the radar data.
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O Uso Do Potencial Espontâneo (Sp) Em Caso De Infiltração Em Barragem
Authors José Domingos Faraco Gallas and Walter Malagutti FilhoThis paper presents the application of the self
potential method (SP) for leaking in an earth’s dam.
The tests were carried out in part of the embankment
which was submitted to a partial failure originated by
a leakage. It was employed the gradients technique in
this survey. The results showed the efficiency of the
SP method to detect the anomalous flow from the
reservoir and to indicate the leaking area.
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Utilização Do Gpr No Projeto Executivo Da Barragem De Pindobaçu, Rio Itapicuru-Açu (Ba)
This study shows the results of a geophysical survey
conducted with GPR to support the study of a dam in
Itapicuru-Açu River. The objective of the study was
to identify geologic structures found in the
underground surface (rock mass discontinuity, geologic contacts).
The information available from rotative drillings and
the geologic knowledge of the area enabled a good
correlation between data during result interpretation,
and three different types of lithologies were identified in the area.
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Velocidade De Propagação Sísmica De Ondas Love Em Argila De Pântano
More LessDos ensaios sísmicos realizados in-situ no
terreno pantanoso da futura Fábrica RIO
POLÍMEROS, no Município de Duque de
Caxias/RJ, o qual é caracterizado por uma capa de
argila orgânica saturada, muito mole, de espessura
da ordem de 6 metros, estão focalizados neste
trabalho os resultados das medições da velocidade
de propagação à superfície do terreno, de ondas SH,
ou Love. Os valores obtidos para essas, entre 31 m/s
e 37 m/s, se situam significativamente abaixo dos
indicados na literatura técnica. Como os ensaios
produziram sismogramas confiáveis,
repetitivamente, decidiram os autores divulgar essa
informação para a comunidade geofísica.
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An Interdisciplinary Geophysical Approach To Detect Cavities In A Karst Region
More LessThe aim of this research carried out by Istituto Nazionale di Oceanografia e di Geofisica Sperimentale-OGS Trieste, was to apply several geophysical methodologies such as ERT (Earth
Resistivity Tomography), GPR, and microgravity survey to detect cavities in karst area. A well-known cavity system was chosen as the test site, in order to verify geophysical data with a real situation. The results was really satisfactory, since the methods had a very good power of investigation and they has been complementary which other. The surveying lines location was carried out in collaboration with the “Civico Museo di Storia Naturale” of Trieste.
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Aplicação De Ensaios Elétricos E Eletromagnéticos Em Problema De Poluição Ambiental
This work aims at the detection of the contamination
caused by a waste disposal area, through
the electric geophysical methods of resistivity, induced
electromagnetics. Field measurements had been
carried out in Ribeirão Preto, São Paulo, Brazil, in a
deactivated waste disposal area. The obtained data
had been dealt with appropriate softwares that enabled
the distinction of the anomalies which help the
characterization of the environmental pollution problem.
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Caracterização De Paleoambiente Submarino Com Side Scan Sonar, Ecobatímetro E Amostras De Fundo – Bacia De Campos - Rj
Authors Anídio C.T. Corrêa, Luiz A.P. Gamboa and Georgina O. CastañosSide scan sonar images acquired by Petrobrás in
Campos Basin during the year of 1998, presented
large linear features which lay down on the sea floor,
at a water depth of 110m. The features were also
registered in bathymetric profiles and have been
operationally described as beachrocks.
In this study, specially designed softwares for digital
image processing allowed a better view of one of
these occurrences, in the central portion of Campos
Basin, in an area close to the shelf brake.
Based on the studies conducted on the sonographic
images, regarding the submarine environment and the
information provided by samples, which were
collected directly from the sea floor, the features were
assumed to be old sand ridges which laid down along
the shoreline. Afterwards, the ridges were cemented,
in a period of time during which the relative sea level
was stabilized, which is thought to have happened
15.800 years BP. When the sea level re-start to rise
up, the morphologies were drowned, becoming a rigid
substract for the instalation of thick algal banks.
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Characterisation Of Three Different Waste Disposals Using Resistivity And Ip Methods
Authors A. Bratus and D. Nieto YabarThis is the report of an integrated geophysical survey
on a landfill system, composed of three urban solid
waste disposals located in three different old quarries
of sand and gravel.
The landfills have different ages and different isolation
systems. The oldest one (called A) was closed in the
eighties and doesn’t have any isolation, the second one
(called B) was closed in the nineties and has a clay
isolation layer as prescribed by the Italian law of 1982,
the third one (called C) is open and has HDPE isolation.
In all the case studies, the depth of the body waste is
about 20 m and the water table is located at 70 m from
the surface.
To investigate the area, earth resistivity and induced
polarisation tomography have been used.
Two N-S lines of 630 m and one E-W line of 310 m
have been done in different periods of the year in order
to define:
• The most proper measurement array geometry
• The landfills geometry
• The waste resistivity and chargeability features
• Contamination in the surrounding geological strata
due to leachate movement
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Clima De Ondas Na Bacia De Campos: Fundamentos E Análise Dos Dados
More LessEste trabalho tem como principal objetivo o estudo do
clima de ondas na Bacia de Campos. Para realizá-lo foi
utilizada uma bóia oceanográfica do tipo “pitch and
roll”, operada pela Petrobras, no período 91/95, na região
dos campos de Marlim e Barracuda, ambos com mais
de 1000 metros de profundidade. Tal iniciativa foi, até
agora, a mais ampla e detalhada campanha de coleta de
dados de onda feita no Brasil. Os resultados deste estudo
revelaram características desconhecidas do clima de
ondas da região. Mais de 60 parâmetros de onda foram
obtidos, a partir do processamento das medições instrumentais
e da modelagem de algumas grandezas físicas
das ondas. Os resultados possuem aplicação direta em
várias áreas como engenharias oceânica, naval e costeira,
além de meio ambiente e novas pesquisas.
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Climate Changes Of The Recent Past In Southern Parts Of Brazil
Authors Andrei S.B. Cavalcanti and Valiya M. HamzaBore-hole temperature data from 23 localities in
southern Brazil were examined for identifying thermal
signals related to climate changes of the historic
past. Both forward and inverse modeling methods
were employed in the analysis of vertical distribution
of temperatures. The forward modeling approach is
based on the classical method of least square fits to
theoretical curves, with a priori assumption as to the
form of temperature variation. The inverse method
can handle non-linear problems and allows convenient
trade-off between model and data.
The data set examined so far reveal the following
information about recent climate changes in southern Brazil:
- the form of temperature variation is indicative of a
warming trend in all of the 23 localities;
- the magnitudes of temperature variations are in the
range of 1 to 40C while the time elapsed vary from
20 to 200 years;
- the climate change seem to be more pronounced in
coastal areas compared to that in inland and semiarid
zones;
- there is a progressive increase in the age of climatic
perturbation, as one moves from the coastal area
towards the interior of the continent;
- changes in vegetation cover have marked effects on
surface temperatures in southern parts of Brazil;
- the changes found in semi-arid zones, being unaffected
by changes in vegetation cover, appears to be
indicative of global climate changes.
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Cronologia De Sedimentação Recente Na Baía De Todos Os Santos Usando Pb210 E Cs137
Authors Roberto Max de Argollo and Antônio Expedito G. de AzevedoThree sediment cores from Todos os Santos Bay were
analysed for 210Pb, 137Cs and 226Ra. The core BTS-7,
collected alongside a channel, had predominance of
fine sand followed by mud; the cores BTS-8 and BTS-
9, coming from a low energy area, had predominance
of mud. The recent mass and linear sedimentation rates
determined in these cores were, respectively, for the
BTS-7, 3.8 kg m–2 a–1 and 4.5 mm a–1; for the BTS-8
7.6 kg m–2 a–1 and 9.5 mm a–1 and for the BTS-9 8.6 kg
m–2 a–1 and 9.9 mm a–1. For the core BTS-9 was noted
an increase in the sedimentation rate from 2.9 mm a–1
in the lower part to 9.9 mm a–1 in the upper 33 cm,
probably due to changes induced by the deforestation
of the margin of the Bay on that place. The activity
levels of 137Cs do not exceed 5 Bq kg-1, which
correspond to 20 % of those found in sediments of
nothern hemisphere. In the core BTS-9, 137Cs had its
activity peak (4.90 Bq kg-1) in the depth of 32.5 cm,
corresponding to the year of 1965 and was detected up
to 40.5 cm, year of 1958. , suggesting that 137Cs did not
migrate to the lower layers after its deposition.
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Delimitação Da Pluma De Contaminação Dos Resíduos Sólidos Do Lixão Do Aurá (Ananindeua/Pa) Por Imageamento Elétrico
Na área de abrangência do lixão do Aurá foi realizado
imageamento elétrico ao longo de nove perfis, usando
arranjo Wenner. Os resultados obtidos com essa
metodologia confirmam trabalhos realizados
anteriormente na área, indicando que a água
subterrânea está sendo atingida pelo deslocamento da
pluma de contaminação provocada pelo chorume
produzido pela degradação dos resíduos sólidos da área.
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Environmental Gamma Radiation Dose In Municipalities, Eastern São Paulo State, Brazil
Authors Rodrigo O. Bastos and Elisabete M. PascholatiAerial gamma spectrometric data were reprocessed
aiming to estimate outdoor gamma radiation dose for
an area of about 11500 Km2 in eastern of São Paulo
state, Brazil, which covers fifty municipalities.
To evaluate the reliability of these
reprocessed data, a residual analysis was carried out
for grids constructed by different methods of
interpolation, and results for the Itu Intrusive Suite
obtained from the aerial data were compared with
published values estimated from terrestrial survey.
This comparison shows up attenuation regarding
probably to soil moisture and vegetal recovery of at least 20%.
A map of average radiation dose per
municipality is presented. The averages varied from
665 μSv. year -1 in Engenheiro Coelho to 1276 μSv.
year -1, in Votorantim. Median values were estimated
for Campinas, Itu and Paulínia (924 μSv. year -1,
900 μSv. year -1 e 847 μSv. year–1 , respectively). The
population-weighted average dose for the area was 888 μSv. year -1.
The municipalities situated over sediments
of Paraná Basin presented lowers averages. The
higher ones were estimated in municipalities where
part of the area covers granite intrusive suites.
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Estatística Básica Com Grandezas Do Clima De Ondas Da Bacia De Campos
More LessEste trabalho apresenta alguns resultados do estudo do
Clima de Ondas da Bacia de Campos: Fundamentos e
Análise dos Dados (Seixas, 2001). Os resultados constituem
a base para o entendimento das características do
clima desta região ou de qualquer outra.
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Estudos Geofísicos Integrados No Lixão De Cuiabá, Mt, Brasil – Resultados Preliminares
One of the major concerns in geoenvironmental
projects is the soil and water contamination caused by
the waste disposal. The geophysical methods applied
are a good way to get some information required in a
site characterization program. This work shows some
results obtained through resistivity, EM inductive and
GPR surveys in the search of informations about the
impact caused by a waste disposal area in Cuiabá,
State of Mato Grosso, Brazil.
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Five Years Of Ozone Measurements At La Paz, Bolivia
Authors Francesco Zaratti, Ricardo N. Forno and Eduardo R. PalenqueWe present main results of a 5 years ozone
measurements program at La Paz, Bolivia, where
a Brewer spectrophotometer is in operation since
July 1996. We also show interesting comparisons
with “overpassing” satellite data, taken by the
TOMS (Total Ozone Mapping Spectrophotometer).
Finally, results of an ozone sonde
campaign, carried out in order to explore a
possibly ozone anomaly over the Andean
Highland, are reported.
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Groundwater And Contaminated Land Geophysics: Pressing Problems And The Way Forward
By Max A. MejuEnvironmental geophysics is enjoying rapid growth in
the present socio-political climate of increasing
awareness of the effect of man’s past activities on the
environment. It deals with pressing issues attracting
public attention ranging from local-scale fluid-rock
changes to large-scale climatic changes caused by
natural processes and anthropogenic activities.
Realistic multi-dimensional imaging of contaminated
land, understanding fluid-rock interactions, optimal
data integration and remote prediction of flow and
subsoil composition are the pressing scientific issues
at the present time. Some suggestions are offered in
this paper for handling these challenging problems.
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Imageamento Elétrico 2-D Aplicado À Avaliação Ambiental De Posto De Combustíveis
More LessAn study including geoelectrical
methods, drilling and chemical water analysis
was carried out in an area to determine the
extent of oil contamination in groundwater.
Resistivity method was applied using a high
resolution 2-D electrical imaging technique.
The origin of a well defined high
resistivity anomaly was proved to be due a
hydrocarbon contamination at the top of the
saturated zone, showing the importance of the
geophysical technique to this kind of problem.
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Investigações Geofísicas Na Avaliação De Risco Geológico Em Áreas Cársticas Urbanas - Exemplos Da Região Metropolitana De Curitiba , Pr, Brasil
Authors Marcio J. Silva, Augustinho Rigoti, Eduardo de Mio and Fernando Santos CorrêaColapsos e acomodações da superfície são comuns
em terrenos calcários e têm geralmente pequena
importância quando ocorrem em áreas não povoadas,
mas podem ser desastrosos quando ocorrem em áreas
urbanas. Nos municípios localizados ao norte de
Curitiba, região objeto do presente estudo, já foram
registradas muitas ocorrências deste tipo de fenômeno
mas, felizmente, sem conseqüências desastrosas até o
momento. Contudo, o risco existe, é real. É muito
importante poder-se contar com técnicas de
reconhecimento de subsuperfície para demarcar as
áreas de maior risco ou investigar as condições em
áreas onde ocorrem grandes concentrações de pessoas
como escolas e outros locais que causam
aglomerações. Investigações diretas, com furos de
sondagem, são muito caras para serem utilizadas
sistematicamente. Por outro lado, métodos geofísicos
podem auxiliar muito neste reconhecimento, com
vantagens de custo e rapidez.
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Levantamento Geofiísico No Depósito De Lixo De Bangu Na Zona Oeste Da Cidade Do Rio De Janeiro
Authors Alexandre C. Monteiro and Rozanda G. da S. CostaThere is a program of decontamination of Guanabara bay in Rio de Janeiro state, Brazil. The Sarapuí river which has its estuary on this bay, pass by the east boundary of the waste disposal studied by this work.
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Método Eletromagnético Indutivo E Gpr Aplicados À Detecção De Contaminação Do Solo E Água Subterrânea Por Resíduos Industriais
Authors Wagner França Aquino and Marco Antonio B. BotelhoIn the study presented, geophysical surveys were
applied in the assessment of soil and groundwater
contamination of an abandoned industrial area, where
the hazardous wastes were infiltrated directly into the
soil. The proposed goals were to detect and map the
presence of the contaminants on the subsurface
through the use of frequency domain electromagnetic
method (FDEM) and ground penetrating radar (GPR).
The FDEM method was carried out to obtain apparent
electrical conductivity of the terrain in different
investigated depths, what allowed to map contaminant
plume related to the inorganic compounds
disseminated in the soil and dissolved in the
groundwater. The GPR data provided the imaging of
the contaminants present in the vadose and saturated
zones, besides to confirm the indications of the
contamination flow as pointed by the FDEM survey.
Also, it was verified that the low frequency antenna
(25MHz) is able tool to determine the extension of the
inorganic contamination plume.
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Modelagem De Pseudo-Seções De Resistividade E Polarizabilidade Aparentes – Estudo Em Uma Área De Disposição De Resíduos Urbanos
More LessThis work shows the results of quantitative
interpretations of pseudosections of resistivity and
apparent polarity. These pseudosections were
obtained using the electric profiling , in dipole-dipole
arrangement, at a sanitary landfill near the city of Rio
Claro, São Paulo. The modeled pseudosections, using
algorithm based on finite element numerical modeling
methods, permitted the determination of the limits
and depths of the waste pile and the surrounding
zone contaminated by percolation of leachate derived
from the landfill.
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Programa Pax-Vóbis
More LessThe Program PAX-VÓBIS, proposed by the Department
of Geophysics of University Federal of Pará
(UFPA) to the municipal government of Belém, has 4
new objectives to exercise of Geophysics: 1) environmental
studies of cemetery of Tapanã, 2) monitoring
Bengui cemetery, 3) revision of the law of implantation
of cemiteries, 4) course about study impacts
of cemiteries with geophysics. The project was
demanded by the City hall, due to the repercussion
obtained with the use of Geophysics in the investigation
of cemeteries, that helped in the decision of the
definitive closing of Bengui cemetery due to the inappropriate
groundwater level in the region. The Program
PAX-VÓBIS was hampered by the cut of resources
because of the new law of fiscal responsability.
But nevertheless the first results already obtained
with electroresistivity proved again that the Geophysics
can give a very important contribution in the
study of cemeteries.
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Prospecção Do Contaminante (Bhc) Através Da Eletrorresistividade
Authors Eduardo Moraes and Patricia GrazinoliThis paper presents a case study in which the
Resistivity method was used at a site known as
Cidade dos Meninos, in the Municipality of Duque de
Caxias, Rio de Janeiro, where the subsoil was
contaminated by an organochlorine pesticide called
HCH – Hexaclorocyclehexane, and by metabolites. A
comparison between preliminary evaluation of this
method and the Ground Penetrating Radar (GPR) has
been presented elsewhere (Grazinoli et al., 1999). The
contamination occurred by the disposal of a great
quantity of HCH directly above the soil, without any
protection. The Resistivity survey was carried out in
order to help the determination of the site
stratigraphy, and the detection of contamination
processes that were taking place. Detailed geological
and hydrogeological informations, as well as Ground
Penetrating Radar (GPR) data were used to help the
interpretation (Barreto, 1998; Grazinoli, 1997).
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Tópicos Sobre Metodologias Passíveis Para A Determinação Do Pé Do Talude Continental Conforme A Convenção Das Nações Unidas Sobre O Direito Do Mar
More LessThis work aims at presenting some topics about the methodology employed by Brazil in order to determine
the foot of the continental slope and another one that would be developed from stratigraphical studies for the
same intention in accordance to United Nations Convention on the Law of the Sea (UNCLOS). Just to
exemplify, the method was applied in the Brazilian Southern Margin. The Brazilian’s methodology was
developed as established on 76 article, line b, UNCLOS: “…the foot of continental slope (FCS) is the point of
the maximum change in gradient in its base”. In the same area were carried out data from core samples and
their results may be considered as an alternative method to FCS determination, in terms of: “In the absence of
evidence in contrary, ….”, as establishes the same convention. When both results were plotted, it could be
noticed that Brazilian’s methodological results presents a reasonable coherence and consistence, and even,
may not be considered “aggressive” in terms of territorial demands.
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Utilização Integrada De Métodos Elétricos E Do Gpr Na Análise Ambiental Do Aterro Sanitário De Jundiaí – Sp
This paper reports the results of a geophysical
research in the waste disposal located at Jundiaí-SP.
This site is typified by waste cells, which have
significant quantities of material above the water
table. The main objectives were: to characterize the
structure of the waste disposal in subsurface, to
determine the depth of the water table, the direction
of the groundwater flow and to map the
contamination plume. Vertical electrical sounding
(VES), electrical profiling and ground penetrating
radar (GPR) were used in an integrated way. Based
on the VES resistivity values, it was possible to
identify the contaminants in the sediments and the
depth to the water table. The results of the electrical
profiling integrated to the GPR allowed for the
mapping of conductivity lateral variation, with higher
condutivity zones interpreted as more contaminated
sites or fractured zones in the bedrock. As a final
product, a potentiometric map indicates the
preferential groundwater flow.
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Valores De Resistividade Elétrica Em Um Latossolo Do Distrito Federal
The electrical resistivity geophysical method
is fairly used in geological and groundwater studies,
as well as environmental monitoring activities. This
method has high sensibility for moisture variations,
and in the soils, this kind of variation can be
correlated with structural and textural aspects.
Therefore, seems to be possible to use electrical
resistivity measurements to estimate variations in
physical properties of soils. In this work, electrical
resistivity measurements were used for evaluate the
lateral variation of texture in a latosoil. The study area
is located at Distrito Federal, in the central region of Brazil.
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Aplicação De Gpr (Ground Penetrating Radar) Como Ferramenta No Diagnóstico Ambiental Em Área Industrial
This paper presents the results of an investigation carried out by the Universidade Federal do Rio de Janeiro (UFRJ) with the cooperation of the Petroflex Indústria e Comércio S.A., a petrochemical industry. This research is part of the company Social Project (2000-2005), titled: “Conheça seu Manguezal” (Knowing your mangrove). The company is located on the borders of the Guanabara Bay, Rio de Janeiro State, Brazil. In the study, Geophysical survey was applied in two areas located within the industrial park in order to identify solid waste contamination (rubber and plastic and metal brass). It was used the Ground Penetrating Radar (GPR) technique with equipment RAMAC/MALA, which provides high resolution images of the underground. The study area consists of clay landfills on clay and sands deposited in marine conditions, which are presently contaminated by brackish water.
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Avaliação Do Potencial Arqueológico Da Pedra Da Gávea: “Desmistificando Um Mito Com O Auxílio Do Gpr”
A ocorrência de vazios rochosos, comumente
chamado de cavernas, está condicionada à ação
geológica no tempo em formações específicas
(calcárea por exemplo) e/ou à atividade humana.
Através da observação geológica direta e de
procedimentos de investigações indiretas (geofísica),
verificou–se a impossibilidade da ocorrência destas
estruturas no maciço rochoso da Pedra da Gávea. Um
levantamento do tipo reflexão, com seis linhas de
caminhamento foi suficiente para constatar a
inexistência de contrastes de propriedades elétricas.
Um total de aproximadamente 850 m3 de rocha sólida
foi investigado.
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Avaliação Do Radar De Penetração No Solo (Gpr) Em Uma Investigação Do Subsolo
Authors Patricia L. Grazinoli and Henrique Lorenzo CimadevilaThis paper presents a stratigraphy study carried out
with the Ground Penetrating Radar (GPR). This study
was made at the construction site of a building in the
campus of the Federal University of Rio de Janeiro.
The site was investigated by conventional percussion
borings (SPT - Standard Penetration Test), and the
two methods were evaluated for the capacity to detect
the interfaces between different layers, in particular
the soil-rock interface. In the GPR investigation three
antennae were used: 50, 100 and 200 MHz. The
penetration of the GPR method was restricted by the
presence of a fill layer, about 3m thick, and by the
possibility that the pore-water contains salt. The data
obtained with the various antennae, after processing,
revealed the most relevant ground features, the data
obtained with the 50 MHz antenna being specially
revealing with respect to the soil-rock interface.
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Emprego Do Gpr Na Investigação Morfológica Dos Solos Dos Tabuleiros Costeiros No Litoral Norte Do Estado Da Bahia
More LessExperimental employ of Ground-penetrating radar to
investigation of tablelands of north coastal at Bahia, Brazil
Nine profiles were studied along a catena developed
on Barreiras Group sediments, in Fazenda Rio Negro,
Entre Rios town (Bahia - Brasil). It was used, besides
the analysis traditionally maid, the search
electromagnetic through GPR - Ground-penetrating
radar. The objective of such a study was it of
analyzing the level of answer of that tool in the
acquisition of information about the features that
happen in the underground, by means of comparisons
of the radargramas and pedologic descriptions
obtained in the area. The used equipment was a
Geophysical Survey model, with antenna of 80 MHz.
The results of the radargramas indicate that the
antenna maid is not the ideal for risings that demand
larger detail of the most superficial layers, up to 1,0
depth meter. For the deepest layers it showed an
excellent answer, mainly in the investigation in the
occurrence of hardened layers, as the hardpan. The
radargrametric analysis confirmed the existence of a
process of transformation in Podzoils, that happens
accompanied by the hardpan and fragipan in depth.
Index terms: soil prospection, Ground-penetrating
radar, soil genesis, coastal tablelands, Barreiras Group.
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Gpr Technique Applied To Mineral Exploration Of Geodes In Basalts: Agate Geode Deposits (Rs, Brazil)
Authors Angelo M. Hirakata and Adelir José StriederThe agate geode deposits occurring in the Salto do
Jacuí Mining District (RS, Brazil) are considered to
be the world largest ones. They are hosted in
tholeiitic basalts of Serra Geral Fm. (Paraná Flood
Basalts). The agate geodes occur in highly vesiculated
basalts, that are variably weathered. Agate geodes
vary in size from 0,10 to 1,0 m, but usually show a
mean diameter in the range of 0,25 – 0,40 m. Agate
geodes are often completely massive, fulfilled by
chalcedony, or by chalcedony and quartz. GPR
technique was applied agate geode exploration.
Key words: GPR technique, agate geodes, basalts,
mineral exploration, geophysic
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Gpr Technique Applied To Mineral Exploration Of Geodes In Basalts: Amethyst Geode Deposits (Rs, Brazil)
More LessGeodes in basalts are not simply a void problem. The
amethyst geodes are hosted by a massive, poorly
fractured basalt. Amethyst geodes range from 0,1 to
1,0 m in diameter, and are variably filled with
different paragenesis. GPR technique does permit
imaging amethyst geodes and other structural features
based on contrasting electrical properties of materials.
GPR imaging resolution, penetration and wave
propagation image features depend on EM wave
frequency. High frequency EM wave (800 and 1000
MHz) has low penetration and high resolution, and
they are suitable for amethyst geode detection, even
the reflection and diffraction pattern produced. Low
frequency EM imaging (250 MHz) imaging for
amethyst geode can display reflection and diffraction
pattern similar to that defined for high frequency
ones, but can also image fracture systems crosscutting
host basalts. These radargrams patterns can be used
mainly for amethyst exploration and extraction planning.
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Imageamento Com Gpr De Fraturas Em Aqüíferos Fissurais: O Caso De Equador/Rn
O trabalho aqui apresentado visa indicar o
GPR (Ground Penetrating Radar) como método de
prospecção de feições geológicas em alguns terrenos
cristalinos capeados por coberturas sedimentares. Em
diversas porções da região NE do Brasil, a exemplo
de Equador-RN, as características geológicas e
climáticas favorecem o uso do GPR. Estas
características se refletem basicamente sob a forma de
um capeamento sedimentar pouco espesso e
relativamente resistivo, o qual não interfere
efetivamente na propagação das ondas
eletromagnéticas geradas pelo equipamento.
Com base no truncamento de refletores
subhorizontais referentes ao bandamento local, pôdese
identificar diversos sistemas de fraturas. Estes
fraturamentos diferem entre si basicamente com
respeito ao mergulho (desde baixo ângulo a
subverticalizado) e ao tipo de conectividade.
A consistência dos resultados com GPR é
atestada pelos dados dos levantamentos de
eletroresistividade e VLF elaborados no mesmo local.
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Levantamento Experimental Gpr No Rio Taquari, Bacia Do Pantanal Matogrossense
An experimental investigation has been carried out
using GPR - Ground Penetrating Radar methods in
Taquari River, located in Pantanal Matogrossense
Basin - Brazil, in order to understand the silting
process on the river and also to map the channels
along the river, that is essential to local navigation.
Many GPR profiles have been carried out in Lower
Taquari river, near Santa Maria and Porto Santa Luzia
farms. Preliminary interpretations were encouraging,
allowing to locate the channels of the river and the
occurrence of very big sand deposits, showing the
viability of GPR application to Taquari river
sedimentation process studies. All data collected are
now been analysing in order to understand the local
dynamic sedimentation process, as part of a MSc.
Dissertation in progress by an IAG-USP student.
Results from these geophysical investigations are
going to serve as guidance to multidisciplinary
studies of Pantanal Program, by government of Mato
Grosso do Sul State.
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Levantamento Geofísico Utilizando O Método Gpr Na Mineração Millennium (Pb)
This paper show the results of a GPR survey carried
out in a excellent geological environment, allowed
penetration exceeding 60 meters with 25 MHz antenna.
Several boreholes in the survey line show that the
GPR data agree closely with the depth of Fm.
Barreiras sediments covered by sand dunes.
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Levantamento Gpr Em Afloramentos Turbidíticos Da Bacia De Almada-Ba
Authors Marco Ceia, Abel Carrasquilla and Jandyr TravassosIn onshore Almada Basin, northeast of Brazil, sandy
and/or conglomeratic turbidites and shales outcrops of
Urucutuca Formation occurs. These rocks are part of
an exhumed portion of the filling-section of the
Almada Canyon. Such outcrops are unique examples
of passive margin transgressive marine sequence
turbidites in Brazil, which were sedimented during
the Maastritchian/Campanian. They are analogues to
some important turbidite reservoirs of Campos Basin,
which is the most productive oil basin in Brazil. To
aid studies of internal geometry and facies association
which will help to improve the knowledge of the
properties of such kind of rocks, a GPR (Ground
Penetrating Radar) survey was performed in this
region. This work aims to show the first results
obtained at one of the outcrops.
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Localização De Fraturas Em Rochas Graníticas, No Município De Capão Bonito-Sp, Brasil
Authors Abad Oliveira Souza Júnior and Jorge Luís PorsaniGround Penetrating Radar - GPR and Resistivity
methods were used with the objective to detect
fracture zones and the top of fresh rock, in
ornamental granite mine, located near Capão
Bonito City, São Paulo State, Brazil. Eight profiles
of reflections GPR and 19 WARR’s Soundings
were acquired using antennas of 25, 50, 100 and
200 MHz. Two vertical electrical sounding were
acquired too. Analysis of GPR’s profiles allowed to
locate stronger dipping and sub horizontal
reflectors, probably related with the fractures zones
filled with water. Besides, were identified two
shadow zones that can be related with intrusions of
diabase’s dike, and one hyperbolic reflector with a
boulder. The fresh rock was identified about 23m of
depth. The results obtained probably will go help
the project of mine engineering looking forward to
advancing of work front.
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Mapeamento De Pluma Contaminante De Hidrocarbonetos A Partir De Seções Gpr Em Um Posto De Abastecimento Em Fortaleza - Ceará
The Ground Penetrating Radar (GPR) technique
can be helpful in mapping sites of shallow hydrocarbon
contamination (LNAPL). The radar signals are
severely attenuated above LNAPL contaminated zones,
allowing its detection and monitoring. During the
remediation procedure of a contaminated gas station
in Fortaleza, Ceará State, GPR surveys were carried
out to delineate the LNAPL plume in the subsurface.
The dispersion characteristics of this hydrocarbon
contamination could be identified throughout the
unsaturated zone above the water table.
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Resultados Da Utilização De Gpr Na Localização De Cavidades (Pockets) No Pegmatito De Morro Redondo, Coronel Murta, Mg
More LessThe GPR method was used to identify pockets
inside an underground mine, which was mined before
by artisan miners, at Morro Redondo, pegmatite
deposit in Minas Gerais State (Brazil). This work
points out the difficulties to interpret the GPR data
due to the presence of tunnels and the irregularities of
walls, and by the use of unshield antennas. The
method was able to show the contacts between the
pegmatite vein and surrounding rocks (schist), and
also had a marginal results, which was the
localization of previously unknown tunnels and
galleries placed in the lower parts of the pegmatite body.
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Uso Do Gpr Na Caracterização Interna De Feições Geológicas Cenozóicas No Litoral Centrooeste Do Ceará, Brasil
Ground Penetrating Radar (GPR) profiles have
been recorded in the coastal region of Lagoinha, in Ceará
State, NE Brazil, to investigate internal structures and
facies of the partially buried sedimentary units. GPR
profiles show reflection patterns which can be assigned
to the lithified sandstones of Barreiras Formation
(Tertiary) and beach rocks (Quaternary). Furthermore,
vibra-cores were collected to correlate GPR reflections
with changes in subsurface lithologies.
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Utilização De Gpr E Eletrorresistividade Para Mapeamento De Dutos Decorrentes De Piping, Gouveia, Mg
A piping system was recognized using different
geophysical methodologies to access the subsurficial
distribution of its channels. The responses of three
antennas (100, 200, and 400 MHz) of the groundpenetrating
radar (GPR) method were compared, as
well as resistivity profiles obtained with different
electrode arrays (Cacau, Wenner, and dipole-dipole).
The best GPR results were obtained with the 100
MHz antennas, which was used to achieve five
profiles to demarcate the path of the pipe. The pipe
was well identified by using the Cacau (with fixed
electrodes with offset of 40 meters) and Wenner
arrays, and all the other profiles has indicated a
second pipe unrelated to the main pipe.
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Utilização Do Gpr Na Investigação Da Estratigrafia Da Região Costeira De Itaipuaçú – Maricá (Rj)
O principal objetivo deste estudo é o de investigar
a estratigrafia Quaternária costeira, num trecho da
região da praia de Itaipuaçú, município de Maricá,
Estado do Rio de Janeiro, utilizando como
ferramenta básica o GPR (Radar de Penetração no
Solo). A praia de Itaipuaçú possui um arco praial
de aproximadamente 10 Km de extensão, e é
caracterizada por um perfil refletivo, com ondas
de alta energia e principalmente pela característica
textural das areias (muito grossas, arredondadas)
formadas por quartzo puro transparente, o que
destoa do padrão das outras praias que formam o
litoral leste do Estado do Rio de Janeiro.
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Abordagem Geofísica Em Terrenos Sedimentares Costeiros Baseada Em Técnicas De Eletrorresistividade, Eletromagnético Indutivo E Inversões E Sua Aplicação À Prospecção De Água Subterrânea (Região De Cascavel – Estado Do Ceará)
More LessResistivity methods (lateral profile and vertical soundings) were integrated with eletromagnetic data derived from EM-34. Also, the combined data inversion (ER+EM) were carry out showing the potentiality of the integrated geophysical techniques to the study of groundwater in coastal regions of the State of Ceará, NE Brazil. A joint interpretation of the above techniques, show that the crystalline structure under the sedimentary cover were the most important zone to the water contribution in several wells in Cascavel region. Several anomalies related to low conductivity zones represent good places for groundwater prospecting.
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Caracterização Isotópica Do Aqüífero São Sebastião Na Região Do Pólo Petroquímico De Camaçari – Ba
The groundwater reservoirs from the São Sebastião
Formation in the region of Camaçari – Dias D´Ávila
are intensively exploited through deep well pumping
for industrial and urban uses. The geometry of the
reservoirs is defined by sandstones blocks
interlayered by shale-siltstone sequences in a geologic
context separated by faults. The exit temperature of
the water of the production wells allowed to identify
the capture zone of water that varied from the
superficial part of the aquifer to more than 300 m of
depth. The isotopíc composition of the groundwater
was found very homogeneous and close to the
average composition of precipitation in the nearby
region of Salvador, indicating a local recharge of
these aquifers without participation of transported
water from long distance by a regional flow system in
the deep layers. The difference between the isotopic
composition of surface water (rivers and dams) and
monitoring wells with the groundwater indicated no
direct connection between these water bodies.
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Comparação Do Desempenho Dos Métodos Eletroresistivo E Transiente Eletromagnético Num Caso Especifico De Prospecção De Águas Subterrâneas
Authors Alfredo Moisés Vallejos Carrasco and Luis RijoThe resistivity method is the most used geophysical
prospecting technique for groundwater exploration.
However, it is not easy to use it in inhabited areas due
to the necessity to spread electrical wires for more
than one kilometer, depending on the desired
investigation depth. The time domain electromagnetic
(TEM) method, also used for groundwater
exploration, does not have this disadvantage, because
this inductive method uses a square loop whose
dimension is not an obstacle to be used in inhabited
places. On the other hand, TEM is more sensible to
cultural electrical noises.
To compare the performance of these techniques in an
urban area, we simulated and interpreted vertical
electric and TEM soundings through programs
developed by Rijo (1994ab,1996). In this comparison
we considered the 21 vertical electric soundings
models using an arrangement type Schlumberger and
synthetic curves for TEM.
As a result, from the apparent resistivity values
obtained of these methods, we derive a linear
relationship, in bilogaritmic scale, between the
spacing (meters) and the time (miliseconds). Thus, it
is possible to estimate a desired investigation depth in
urban areas using the TEM when the application of
the resistivity method is limitated by the accessibility.
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Contribuição Da Sondagem Elétrica Vertical À Hidrogeologia Da Bacia Do Paraná No Município De Juscimeira-Mt
More LessThis study was done in four areas of Juscimeira’s
municipal (MT) Brazil and it was used the
Vertical Electrical Sounding method to determine
the vertical dimensions of the geologic units that
form the Parana’s Basin. The study allowed to
know the depth of the top and the thickness of
Furnas/Ponta Grossa Formations and
Furnas/Ponta Grossa Transition. Theses
information will guide the drilling of deep wells
whose objective is the exploitation of Furnas’
aquifer. The knowledge of the thickness of
Furnas’ aquifer is an important prerequisite to the
determination of the reserves of water at this
aquifer, while the thickness of the others units
have a relevant role at the studies of the
vulnerability to the contamination of Furnas’ aquifer.
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Correlation Of Electrical And Hydraulic Conductivities Of Porous Aquifer – A Critique
Authors Sri Niwas and O.A.L. de LimaThis paper recollects the most important existing
equations derived for electrical and hydraulic effects
by considering simple aquifer models – non-shaly
and shaly sands. A critique about the possible
correlation between electrical and hydraulic
conductivity is presented, vis-à-vis estimation of the
later from the former with a requisite confidence.
Only the relations developed mathematically are
chosen for discussion and empirical relations are left
out. A more plausible general aquifer model based
equations are presented to show that the relationship
is direct only in electrolyte (conductance) dominated
aquifer case and inverse in matrix (resistance)
dominated aquifer. Few data points published already
are analyzed to show the efficacy of the equations.
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Deep Electromagnetic Mapping Of The Serra Grande Aquifer For Optimum Groundwater Development On The Eastern Margin Of Parnaiba Basin, Piaui State, Brazil
Authors A.K. Mohamed, P.M. Abreu, M.A. Meju, S.L. Fontes, E.F. La Terra and C.R. GermanoA combined TEM -AMT survey was recently
carried out along three east-west transects at
the eastern margin of Parnaíba basin for
hydrogeological purposes. The MT data have
been processed using conventional tensorial
analysis technique and corrected for static shift
using dual-mode TEM data. Two-dimensional
regularis ed inversion of the TE and TM MT
data revealed distinct geoelectric patterns for
the three profiles. The contact between the
sedimentary and crystalline basement rocks
was clearly imaged in all the profiles. Grabenlike
structures are present in all cases and are
best developed about 20-30 km away from the
basin margin in the Monsenhor Hipólito and
Itainópolis transects. The graben structures are
considered to be the best places for drilling for
groundwater in this region. The 2-D resistivity
model for the Monsenhor Hipólito profile also
appears to define the position of a major fault
herein interpreted as the Picos fault, which
may have implications for groundwater
development in the area.
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Desempenho Do Método Vlf Na Locação De Poços Em Terrenos Cristalinos De Uma Área Do Agreste Do Estado De Pernambuco, Brasil
Este trabalho trata da aplicação do método geofísico
VLF à prospecção de água subterrânea em terrenos
cristalinos do Agreste Meridional do Estado
de Pernambuco, Brasil, totalizando uma superfície
de 323km2, compreendendo parte dos municípios
de Jupi, Lajedo e Calçado, sendo a área delimitada
pelas coordenadas geográficas 8o38’52” e 8o48’09”
de latitude sul ; 36o16’27” e 36o26’45” W. Gr. O
equipamento utilizado foi o Wadi, fabricado pela
ABEM. Foram executados cerca de 75km de perfis
VLF transversais às estruturas fraturadas, normalmente
orientadas NW-SE, tendo sido locados e
perfurados 146 poços profundos durante o período
compreendido entre 1998 e meados de 2000. Os
resultados das locações através da técnica VLF
comparados com 91 locações usando critérios variados,
na mesma área e período desta pesquisa,
mostraram um melhor desempenho da metodologia
aqui utilizada no que se refere às vazões médias
obtidas. A vazão média obtida com a metodologia
VLF foi de 3635L/h, enquanto que com outros
critérios foi de 1595L/h. Além do mais, a percentagem
de poços secos (vazão inferior a 500L/h) foi de
4% para a locação com a ferramenta VLF, enquanto
que com outras ferramentas foi de 17%.
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Efeito De Pequenas Distâncias Entre Os Eletrodos De Corrente Em Perfis Elétricos Com Arranjo Gradiente
More LessOver the years Gradient Arrays have been used in
resistivity profiling surveys over hard rocks in order
to locate fracture zones in both efficient and
inefficient ways, for groundwater prospecting. Many
of the unsuccessful applications are due to small
current electrode distance (AB). In this paper we
study the depth of investigation for the gradient array
and perform some numerical examples to show the
effect of the use of such small distance in the obtained
profiles. We see that when a small AB distance is
used, as soon as the location of the potential
electrodes changes, the depth of investigation of the
array is also changed, and so, a profile/sounding
curve is obtained, leading many times, in a
misinterpretation of the profile curves.
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Electromagnetic Studies Of The Região Dos Lagos In Rio De Janeiro State - Brazil: Tectonic Framework And Groundwater Prospects
This work presents results of a geophysical survey
employing electromagnetic (magnetotelluric -MT and
time domain electromagnetics-TEM) techniques to
probe the upper crustal geoelectric structure aiming at
contributing to the geophysical knowledge of a poorly
understood area in southeastern Brazil. The survey
was carried out in Região dos Lagos - “The Lakes
Region” of Rio de Janeiro State, Brazil. A total of 34
MT-TEM soundings were located along two profiles
18 Km and 27 Km long both in the SE-NW direction
crossing orthogonally the observed regional faults
known from surface geology, aeromagnetic and
remote sensing images of the area.
The region is characterized by rocks predominantly of
pre-Cambrian age, fractured and altered gneisses and
sedimentary covers of quaternary age, described as
current and sub current sediments deposited in flood
plains and close to the coastal region. Twodimensional
geoelectrical models of the two profiles
evidenced some groundwater prospects at shallow
depths associated with quaternary sediments and
fracture zones. Anomalously conductive block at
depths between 3 and 6 Km may be related to
magmatic materials.
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Ensaios De Resistividade Aplicados Em Estudos Hidrogeológicos Em Maceió, Alagoas - Brasil
More LessThe characterization of Barreiras/Marituba
Aquifer System, major source of water supply of
Maceió City, Alagoas State, Brasil, is an important
way to subsidy a sustainable usage and management
of groundwater. The tectonic and stratigraphycal
framework that was built using well logs and surface
geological information propose a model with a series
of grabens and horsts structures. To check and
calibrate this geological model were applied
geoelectrical surveys. Based on data obtained from
dipole-dipole electrical profiling and vertical
electrical souding it was possible to identify fault
zones and important stratigraphycal characteristics,
that confirms the proposed geological model.
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