- Home
- Conferences
- Conference Proceedings
- Conferences
6th International Congress of the Brazilian Geophysical Society
- Conference date: 15 Aug 1999 - 19 Aug 1999
- Location: Rio de Janeiro, Brazil
- Published: 15 August 1999
301 - 320 of 399 results
-
-
Reflection And Transmission Properties Of Self-Similar Interfaces
Authors Kees Wapenaar and Jacob FokkemaWe represent an interface by a self-similar singularity, embedded between two homogeneous half-spaces and
we evaluate its frequency-dependent normal incidence reflection and transmission coefficients. For ƒ → () the
expressions for the coefficients reduce to those for a discrete boundary between two homogeneous half-spaces;
for ƒ → the effect of the embedding half-spaces vanishes. These asymptotic expressions have a relatively
simple form and depend on the singularity exponent .
-
-
-
Reciprocity Theorems For Time-Lae Seismics Based On The Full And One-Way Wave Equations
Authors Jacob Fokkema, Kees Wapenaar and Menno DillenIn this paper we present acoustic reciprocity theorems for the full and one-way wave equations and we discuss their application in time-lapse seismics.
-
-
-
Enhanced 3D Seismic Surveys Using A New Airborne Pipeline Mapping System
Authors Terence J. McConnell, Bob Lo, Alastair Ryder-Turner and James A. MusserThe need to accurately locate pipelines and other cultural features is of paramount importance to the safety,
planning and quality of 3D seismic data.
With the current industry trend being to maximize production from known reserves, there is an increased practice
of shooting 3D seismic surveys over mature and previously abandoned oil and gas fields. In many instances, the
infrastructure in the abandoned, and even the active oil and gas fields is poorly documented, and hazard locations are inaccurate.
This lack of knowledge about the location of pipelines, well heads and other oil field infrastructure poses a danger
to the seismic crews drilling shot holes within the boundaries of the oil field. It can also cause degradation of the
quality of the seismic data; gaps in the shot point positions, created by safety requirements to avoid areas of
uncertain pipeline location, result in poor, or zero, seismic fold coverage in the areas of most interest; the oil field itself.
The purpose of this paper is to present a new airborne technology for the detection and mapping of oil field
infrastructure, and to review how this technology, when used in conjunction with modern 3D seismic planning
software, can result in cost savings, enhanced safety and higher quality 3D seismic surveys.
-
-
-
Three Dimensional Gradient Magnetics - Geologic Applications
Authors Terence J. McConnell, Bob Lo, Alastair Ryder-Turner and Zeev BergerAirborne magnetic mapping has been in use for petroleum exploration for decades, with the last 5 years having seen a
renaissance in the use of the magnetic technique. Newer surveys have focused on measuring the weakly magnetic
faults and lithologies of the sedimentary sequence, near surface paleo-channels, and the size and shape of salt
intrusions, all in addition to the basement structure.
Hood ( 1965) was the first to describe and quantify the benefits of acquiring magnetic gradient data from an airborne
platform. Since that time, magnetometer sensor technology has developed significantly, and new attempts are being
made to usefully acquire and interpret the additional information held within the three dimensional magnetic gradients of
the magnetic field. Gravity data acquisition, the other potential field method, has also recently seen a move towards use
of gradient arrays (Pawlowski 1998). In the systems currently operational, the full gravity gradient tensor is measured.
The increased amount of information gathered about the gravitational field within the sedimentary sequence has been
used very successfully to enhance the exploration process.
Three dimensional magnetic gradient systems are currently in use for the detection and detailed mapping of oil field
infrastructure (pipelines, well heads and other hazards), thereby assisting in the safety and planning of 3D Seismic
surveying. At the same time that these operations are under way, the systems have been observed as well to provide an
impressive amount of information about the background geology of the oil field.
This helicopter-borne three dimensional magnetic gradient technology has recently been used to collect 50 meter line
spacing data in several key exploration areas in both the plains and fold belt regions of the Western Canada
Sedimentary Basin. The purpose of this paper is to describe the technology and geologic applications of the system.
Case histories will be presented to show the increased information content of the gradients versus the total field.
-
-
-
Interpretação De Dados De Magnetometria Do Projeto Aerogeofísico Uraricoera (Estado De Roraima, Brasil) E Sua Aplicação No Mapeamento Geológico Regional
Authors Cláudio Couto Reis and Luiz Fernando Santana BragaEsse trabalho refere-se ao processamento e interpretação de dados aerogeofísicos de magnetometria do levantamento
intitulado Projeto Uraricoera (Prospec, 1978), fornecidos pela CPRM (Serviço Geológico do Brasil) na forma de arquivos digitais.
O levantamento foi realizado no ano de 1977, totalizando 31.138 km de perfis de magnetometria e gamaespectrometria,
adquiridos com intervalo de amostragem de 2 s e com uma altura de vôo média em relação ao terreno de 158 m. As
linhas de vôo têm direção N-S e estão espaçadas de 2 km. Já as linhas de controle são E-W e possuem um
espaçamento de 20 km.
A área pesquisada tem 49.500 km2 e situa-se entre os paralelos 1o e 4o de latitude norte e 62o e 64o de longitude oeste.
Abrange principalmente a porção noroeste do Estado de Roraima, além de parte adjacente do Estado do Amazonas –
Brasil (Figura 1). Devido à sua posição geográfica afastada dos centros urbanos, bem como pelas dificuldades de
acesso e pela cobertura de floresta equatorial densa, trata-se de uma das regiões do território nacional mais
desconhecidas geologicamente, fato que justifica o presente estudo.
-
-
-
The Continental Shelf Of Brazil: Going Beyond The 200 Nautical Miles…
More LessO Plano de Levantamento da Plataforma Continental Brasileira (LEPLAC) tem por objetivo estender o limite da
Plataforma Continental, no seu enfoque jurídico (PCJ), além do limite das 200 milhas náuticas da Zona Econômica
Exclusiva (ZEE), de acordo com o que preceitua a Convenção das Nações Unidas sobre o Direito do Mar (UNCLOS).
Na região da PCJ além das 200 milhas, o Brasil exercerá direitos exclusivos de soberania para fins de exploração e
aproveitamento dos recursos naturais (vivos e não-vivos) do leito do mar e do subsolo. As atividades do LEPLAC –
iniciadas em 1987, com a aquisição de dados de sísmica de reflexão multicanal (46.000 km), batimetria (100.000 km),
gravimetria (94.000 km) e magnetometria (88.000 km) – vêm sendo conjuntamente executadas pela PETROBRAS e
MARINHA DO BRASIL, apoiadas por pesquisadores do Programa de Geologia e Geofísca Marinha (PGGM) e do
Departamento Nacional da Produção Mineral (DNPM), sob a coordenação e diretrizes da Comissão Interministerial para
os Recursos do Mar (CIRM). Os resultados do LEPLAC devem ser submetidos à Comissão de Limites da Plataforma
Continental, da ONU, até novembro de 2.004.
-
-
-
Correlação Entre As Distribuições De T2 (Rmn) E Dos Tamanhos De Poros Observados Em Análises De Imagens Petrográficas (Aip)
More LessThe relaxation time (T2) distibution curve, from nuclear magnetic resonance (NMR) analysis, is related to pore
size distribution within the rock, factor that controls fluids volume that will be produce. Small pores correspond
to low T2 values. A cutoff value of T2 is used to distinguish immobile fluid in small pores from mobile fluid in
larger pores. T2 cutoff corresponds to a fixed pore size.
The petrographic image analysis (PIA) directly provides a pore size distribution curve observed in thin section.
In this work, pore size distribution curves obtained from these two methods, NMR and PIA, in sandstone and
conglomerate samples was correlated. The surface relaxivity (ρ), constant of proporcionality between PIA pore
size distribution and MNR pore size distribution, was calculate to each sample.
-
-
-
Seismic Acquisition Metadata - Storing, Managing And Mining
Authors John Archer and Todd PorterLogistics and planning play an ever more important role in determining the efficiency and profitability of a seismic
operation as surveys continue to grow in size and complexity. The seismic metadata (information describing the seismic
data) associated with these surveys is increasing at an even greater rate, yet is still stored in disparate locations such as
trace headers, coordinate files, paper and electronic observer logs, ledgers, maps and various spreadsheets and
databases. Efficient management, analysis and archival of metadata is both fundamental to acquisition logistics and
quality control, and prevents 'metadata smear' associated with grouping temporally or spatially varying information during
data processing. Furthermore, with the recent increase in popularity of time lapse seismic, the archived metadata from
one survey becomes the pre-plan information for a repeat seismic survey, and it is consequently more important than
ever that it be efficiently gathered, stored, analysed and archived.
By combining previously autonomous metadata sources with GIS layers (such s digital orthophotos and CAD files of
pipelines or wells) into a single data warehouse, real inter-dependencies can be established through spatial, attribute,
and temporal analysis, and proper cause and effect examination performed.
This paper present the issues critical to building such a system will look at one particular implementation and will
examine case studies illustrating some of the benefits that can be derived therefrom.
-
-
-
Safety For The Use Of Explosives In Petroleum Prospection
Authors Roberto Breves Vianna and Nélio Waldomiro OstjenDuring the exploratory phase of the petroleum industry, explosives are being largely employed. Up until
some years ago, SAFETY in their use had very little consideration, in Brasil as well as abroad. As a result,
there were a number of accidents involving inhabitants of the regions where there had been oil prospection,
causing deaths and mutiliation.
In Brasil, investigation of a tragedy caused by the finding of a charge left over from seismic work, showed
that the explosive with its electric cap, had been left buried in a swampy area for various years, and had
maintained all of its physical/chemical properties. When inadvertently handled, it exploded, causing death
and destruction.
Our company is specialized in seismic prospection and have instituted strict safety procedures, in order to
eliminate all possibilities of similar accidents happening.
However, we should call attention to the fact that many years still constitute potential risks, which are being
aggravated by the incrase of demographic density. Special attention by the authorities is recommended, so
that accidents can be avoided. Areas under risk should be cheched over by specialized personnel, to
eliminate abandonned charges, which certainly constitute a major risk in many regions where explorations
was intense.
-
-
-
Modelo Cualitativo Del Desarrollo Mesozoico Del Sistema De Cuenca De Antepais Cubano
More LessThe Cuban orogenic belt, is a key in the geological evolution of the Caribbean. We centered the study in the AEF of the
basins of collision; developed from the Upper Cretaceous Campanian-Maastrichtian in which began the collision of the
volcanic island arc with the southern passive margin of the North American Plate and continuous obduction and over
thrust until ends of the Middle Eocene.
In this work, we propose the foreland basin system for occidental and central Cuba, with age beginning from the Upper
Campanian-Maastrichtian. Reaffirming the importance of these sequences like collectors of petroleum. These meet
within the group of depozones that develop from the beginning of the foreland basins system, and by oligo-miecene
movements and recent have been distinguished in the basins recognized as Central, Saramaguacán (California), Vertientes and another of great importance for petroleum prospecting.
-
-
-
Optimization-Based Reservoir Modeling: Example On A Million-Cell Model
Authors Wenceslau Peres Gouveia Jr., A.S. Cullick and Clayton V. Deutsch3-D reservoir characterization procedures aim at achieving a spatial distribution of reservoir properties that is
consistent with the available reservoir data. Geostatistical algorithms, probably the most popular approach for
reservoir characterization, have indeed provided a practical methodology to this problem. These techniques,
however, have been somewhat limited on the number of data sets they can account for and on the propagation
of data uncertainties and data resolution on reservoir properties to the final model.
We have proposed an optimization-based approach for reservoir modeling (Gouveia et al., 1998) that can
overcome some of these limitations. This algorithm provides a framework to integrate a broad spectrum of data
sets (well, seismic, production and geological data) in such a way that the respective degrees of data
uncertainty and resolution are taken into consideration. These features come at a considerable computational
cost when compared to geostatistical techniques. However, via a modified Monte Carlo sampling procedure, we
were able to reduce the computational cost to the point that the proposed methodology can be applicable to
more realistic reservoir modeling situations. Here, we report results that illustrate the performance of the
optimization algorithm on the modeling of a synthetic reservoir parameterized by a one-million-cell model
defined on a Cartesian grid.
-
-
-
Seismic Modeling Of Experimental Stratigraphy
Authors Lincoln F. Pratson and Wenceslau Peres GouveiaSeismic modeling of experimental stratigraphy provides a far more realistic framework for studying the seismic
response of stratigraphy through synthetic modeling than has previously been available. The XS basin, a unique
facility developed at the University of Minnesota, paves the way for a detailed study of the evolution of
stratigraphy under controlled rates of sea-level changes, sediment supply and subsidence. The stratigraphy
generated by this experimental basin approaches the appearance and complexity found in sedimentary bodies
ranging in scale from bedforms to continental margins. We describe a preliminary methodology to map digital
photographs of the resulting stratigraphy into acoustic models that are then used as input to seismic modeling
algorithms.
-
-
-
Geoelectric Structure Of Central Part Of Ribeira Belt - Cruzeiro Region (Sp)
A Magnetotelluric study realized at Serra do Mar Plateu (Figueiredo et.al., 1997) identified the major tectonic blocks of
the region and a crustal conductor at 10 km depth. This conductor was associated to a brittle-ductile transition zone
delineating the upper-midlle crust boundary in the region. That interesting results motivated new studies along the
Ribeira Belt (Brito et.al., 1997). In this work we present the preliminary results of a MT campaign realized at the central
portion of the Ribeira Belt, Cruzeiro (SP) region.
-
-
-
Seismic Modeling With Complex Geology And Topography
Complex geology, due to folding and faulting, implying in strong lateral velocity variations and the rough
topographic relief are the principal constraints that may be faced in order to obtain a reliable subsurface seismic
image. Several physical investigations to support acquisition parameters and processing are on demand before
any new seismic acquisition in such area, in order to establish the best strategy to get a better subsurface
image. To perform this strategy we got information from several sources: geology, geophysics and modeling, in
the former we used finite difference acoustic and elastic wave propagation with topographic effects included
and ray tracing modeling, considering isotropic or smoothly inhomogeneous media. As a result of such
integration, we could investigate some acquisition parameters and processing steps which to have greater
impact on seismic data quality.
-
-
-
Optimization Of Subsalt Imaging
Authors Uwe Albertin, S. Kapoor, Wenfong Chang, Nigel Purnell and Tom LearySuccessful subsalt imaging in the Gulf of Mexico depends critically on three aspects of the imaging
process; the building of an accurate sediment velocity model, defining the geometry of the salt body or
bodies, and successful application of 3D poststack and prestack depth migration algorithms. Even if the
target subsalt dips are moderate, steep dip imaging is often necessary for defining the geometry of the
salt bodies, parts of which may have significant dip. In addition, even though energy that propagates
through salt may be dip-limited because of the sharp velocity contrast between sediment and salt, energy
that propagates laterally from outside salt may also contribute to the flanks of subsalt reflectors with
steep dip. In such areas careful processing to preserve dips is necessary, with the ultimate goal being a
subsalt image that is as interpretable subsalt as it is outboard of salt. Here we discuss several
techniques for optimizing steep-dip salt and subsalt imaging, including iterative prestack depth migration
and velocity updating for sediment velocities, iterative prestack and poststack depth migrations for salt
boundary definition, proper interpretation of the salt boundary, and optimal application of a Kirchhoff
algorithm for final imaging. These techniques are illustrated with examples from an area of significant
complexity in the Gulf of Mexico.
-
-
-
Velocity Resolution And Salt Boundary Placement In Subsalt Imaging
Authors Uwe Albertin, S. Kapoor, Wenfong Chang, Richard Beals and Jeff CurtisThe interpretation of salt geometry is a critical aspect of velocity model building for 3D salt and subsalt
imaging. Here we investigate the effect of salt boundary placement error in the velocity model building
process. Using an example from deep water Gulf of Mexico, we first illustrate how velocity resolution
drops beneath salt . We then show how an error in salt boundary placement can produce significant
residual moveout in prestack migrated gathers. If this residual moveout is interpreted as arising from a
velocity anomaly in the sediment, a velocity update of the sediment will introduce error into the sediment
velocity model that in turn introduces false structure into the depth image. We show for this example that
the correct placement of salt both flattens gathers and eliminates the false depth structure. Techniques
for distinguishing between sediment errors and salt boundary placement errors are discussed.
-
-
-
Determinação Do Controle Estrutural De Fontes De Água Mineral: Estudo De Caso Em Santo Antônio De Pádua (Rj)
A cidade de Santo Antônio de Pádua localiza-se no extremo noroeste do Estado do Rio de Janeiro, próxima à divisa com Minas Gerais (Fig. 1). Grande parte de sua economia encontra-se baseada na produção de pedra ornamental e na atividade agro-pastoril. A exploração de águas minerais dos tipos magnesiana e carbogasosa, incluindo-se algumas com íons raros classificadas como iodada e litinada, é bem incipiente, quase que só atendendo a demanda local. Mesmo essa pequena produção de águas minerais vem, nos últimos anos, decrescendo inclusive com o fechamento de várias fontes. Os principais motivos para tal declínio correspondem às baixas vazões dos aqüíferos e a contaminação de alguns deles, principalmente daqueles situados dentro do perímetro.
Numa tentativa de estimular a economia da região, a Prefeitura da cidade estabeleceu um convênio com o Departamento de Geologia Aplicada da Faculdade de Geologia UERJ (DGAP/FGEL/UERJ) visando a realização de estudos que permitissem viabilizar a produção de água mineral. Para tal o DGAP estabeleceu um plano de ações onde buscou-se determinar, em uma primeira instância, os controles das diversas ocorrências de águas minerais, de modo a verificar a possibilidade do aumento das vazões das fontes conhecidas e, posteriormente, estabelecer um modelo que pudesse ser extrapolado para a identificação de novas ocorrências. Para a formulação de um modelo prospectivo foi estudada uma fonte Pádua localizada (Fonte Pádua) dentro da cidade.
A fonte Pádua (iodada) se encontra em produção, mas por possuir uma baixa vazão, 11000 l/24h (Falcão, 1978) a comercialização da água é restrita somente ao município.
-
-
-
Transfer Function Estimation For Electromagnetic Induction Studies: Evolution And State Of The Art
More LessTo use magnetotelluric (MT) data to image crustal structure one must first reduce long time series of electric
and magnetic fields to transfer functions (TFs) or impedance tensors which vary smoothly with frequency. In
many cases neither the natural source signal, nor the dominant noise sources are well modeled as stationary
Gaussian processes, so the most obvious least squares approach to MT impedance estimation often fails
catastrophically. Developments over the past two decades have improved the situation considerably, and with
proper care modern MT surveys can routinely produce stable and repeatable impedance estimates, with
meaningful estimates of statistical precision. Two develoments have been key to these improvements: adaptive
schemes which automatically downweight or eliminate poor quality data, and the remote reference method, in
which data from a second site is used to cancel local noise and improve data weighting. Initial developments in
both of these areas largely involved ad-hoc schemes, such as coherency sorting for data screening, or simple
analogues to least squares for remote reference processing. Subsequently more rigorously justifiable (but
operationally quite similar) statistical schemes were introduced. Here I review some important aspects of these
developments, including the regression M-estimate for single station impedance estimation, and its extension to
the case of remote reference data. I will also consider the application of multivariate statistical methods to
analysis of data from small (2-5 station) arrays of MT (or EM profiling) instruments. These methods allow a more
full use of all data channels, and can ion some cases lead to significant improvements over estimates based on
standard robust remote reference approaches. Finally, I consider jackknife methods for error bar estimation,
presenting a comparison of error bars computed by several methods for a series of replicated MT impedance
estimates from a pair of semi-permanent MT sites.
-
-
-
Geophysical And Imaging Processing Techniques Applied To Regional Geological Correlation: The Case Of Paranoá Group, Goiás State, Brazil
More LessThe Paranoá Group has a high economic potential for base metals and gold; however, the geologic knowledge is far from being satisfactory. It is still necessary that the tectono-lithostratigraphic subdivisions be better understood. That Group is part of the Brasília Folded Belt, which is represented by, meso to neoproterozoic metasediments between the São Francisco Craton at east and the Goiás Median Massive at west (Marini et al., 1984 - Fig1).
The area covered by the geophysical survey outcrops basement and supercrustal rocks. Basement is represented by Granit-gnaissic Complex (GGC), the Niquelândia (NC) and Barro-Alto (BAC) complexes. The supracrustal rocks (Brasília Folded Belt) are constituted by Serra da Mesa (SM), Araí (A) and Paranoá Groups (Marini, op cit.). Some important questions remain, as it was not possible yet to correlate the local geologic information of the northeastern part of the area (which contain 10 sub-units for Paranoá group (Fuck et. al., 1988) with the regional knowledge. The available geologic map (CPRM, 1987) has only two major sequences Pelitic-psamo-carbonate (Ppc) and Pelitic-psamitic (Pp). In order to answer these questions, we have used a combination of geophysical and image processing techniques, involving joint processing, integration and interpretation of aerogamaspectrometric and Landsat data on the software ER Mapper 5.5. After the pre-processing corrections, data was processed using pseudocolor, intensity layer, rgb composite, band rationing, principal component analysis, spatial frequency filtering and sun shading features. The processed images were integrated by joining them with a pseudocolor and intensity layer, together or by applying the combination (RGB)) and fusion (IHS) techniques. At the Total Counts image (CT in Fig. 2) the higher intensities can be associated to the Granit-gnaissic Complex, bordering the Niquelândia Complex (northeastern corner of the image). The lower counts are associated to the mafic-ultramafic Complexes (Niquelândia e Barro Alto). At the thorium channel (Th – Fig. 2) the higher counts are associated to the Serra da Mesa Group (northwestern part of the image) and Paranoá Group (southeastern part of the image). At the potassium channel (K – Fig. 2) the higher counts are probably associated to feldspatic quartzite's. We show in Figure 2 the geologic map (CPRM, 1987), comparing with the radiometric data, especially the ternary image, it can be seen the major contacts
between the units are easily identified. The best results of digital processing were a [(5/4)x(3/4)]R, 5/1G, 5/7B and Pc1] (Souza Filho & Drury, 1997) and principal components 1R 2 G and 3B (6 bands) images. In these image (Fig. 3) is possible to subdivide the
sequence (Ppc) into several sub-units. For instance, carbonate rocks appear in green-brown tons (Fig. 3a) and the blue tons (Fig. 3b). The psamitic rocks (alluminous material) appear in red tons (Fig. 3a). The interpretation of the integrated images has shed some new light into the geologic knowledge of the area by identifying the sub-units in the sequence Pelitic-psamo-carbonate and determining their relationship with the regional structures along the Brasilia Belt.
-
-
-
Integração De Dados Batimétricos No Cone Do Amazonas
More LessA bibliography research was conducted in order to know previous works carried out in the Amazon Fan’s area
with indication about its delineation extension. It was verified that a great number of researchers has proposed
similar points of view about Amazon Fan’s with respect to this subject. The isobath line was the main tool used
in order to reach this deal and was perfect to delineate Amazon Fan’s length. On the other hand, the transversal
Amazon Fan’s was not clearly documented and the use of isobath line does not seem so helpful in this case.
This work intends to integrate the pieces of information carried out in this previous works that have had with
subject Amazon Fan’s delineation extension with information obtained from bathymetric data set composed by
measurements collected by Brazilian Government Program to Delineation of Its Continental Margin (LEPLAC)
and other bathymetric measurements from public domain like (GEODAS – GEOphysical Data System for Marine
Geophysical Data – NGDC/NOAA, versão 3) and then to propose a light of the interpretation of the results a
current Amazon Fan’s geomorphologic delineation extension.
-