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9th International Congress of the Brazilian Geophysical Society
- Conference date: 11 Sep 2005 - 14 Sep 2005
- Location: Salvador, Bahia, Brazil
- Published: 11 September 2005
101 - 200 of 462 results
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Estratigrafia sísmica de alta resolução no lago Juparanã, Linhares (ES) - Brasil
Authors R.S. Hatushika, C.L. Mello and C.G. SilvaThe high-resolution seismic stratigraphy into the Juparanã lake, on Espírito Santo state, Brazil, allowed the preliminary acknowledgement of the Quaternary sedimentation in Doce river lower course lake system. It was possible identify two seismic sequences limited by well defined stratigraphic surfaces. The older Quaternary eposits were attributed to arenaceous alluvial sediments, while that overlying deposits had been associated to tabular argillaceous sediments, formed in a lacustrine phase after the damming of the Juparanã lake.
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Influence of Caribbean tectonics across the Eastern Venezuela petroleum basins
Authors M.G. Castillo Vincentelli and H.D. EbertVenezuelan industrial oil exploration has been improving our knowledge of the petroleum systems in the septentrional region of the South American plate.
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Investigações Geofísicas nos Sambaquis Fluviais de Moraes (Miracatu-SP) e Estreito (Itaoca-SP)
Authors M.D. Watanabe, E.B. Rocha and A. RugenskiThis work presents results obtended with application of radiometric geophysical method on the Moraes and Estreito fluvial sambaqui (shellmound), both localizated in Ribeira de Iguape Valley, SP – Brazil.
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Aplicação dos Métodos de Empilhamento CMP e SRC na Seção 50-RL-90 da Bacia do Tacutu
Authors G. Garabito, J. Eiras, M.G. da Silva and M. PorsaniThe Takutu basin, located astride the Brazil-Guyana border, was explored in Brazil by PETROBRAS in the eighties, where was performed seismic surveys of refraction and reflection, and also was perforated two wells. With the development of modern seismic
processing techniques, there is the possibility of reprocessing the old seismic data with the objective to contribute for an improved evaluation of hydrocarbons potential of the Takutu basin.
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Tectonosseqüências da bacia de Taubaté: Uma interpretação Sismoestratigráfica
Authors L. Molinari and L. BorghiThe Taubaté basin is a Cenozoic basin located in the Southeastern part of Brazil, and its evolution has been associated to the process of the South Atlantic opening. Although many studies have been done in this basin several uncertainties remains. Most of the studies is about surface geology resulting in a lack of knowledge about subsurface environment.
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The Joaquim Tavora case study, Parana basin, Brazil : From live oil show to upside potential estimate in a frontier exploration basin
Authors E.M. Meister and C. Edwal VassãoOil exploration efforts in the huge Paleozoic Parana basin of Brazil waxed and waned since 1892 without a commercial discovery. The recent serendipitous find of live oil in a water well at a basin-flank position does demand explorationists´ attention, however. In the Joaquim Tavora area, surface geology, magnetotelluric and airmag surveys point to the existence of large, untested structural traps for the Devonian to Permian section present.
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Análise Quantitativa dos Efeitos Mecanicos de Rifteamento e Sedimentaçao da Bacia do Reconcavo
Authors D.F. Freitas and J.J.C. PalmaIn this study it was developed a tectonophysic modeling program to simulate the mechanical effects related to the rifting and sedimentary infilling of a rift-type basin along its evolution. The program is based on extension models of Kusznir & Egan (1990) and Weissel & Karner (1989).
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Atributos Sísmicos e Interpretação Volumétrica na Identificação de Corpos Carbonáticos na Bacia de Santos - Brasil
More LessSeismic attributes were used in the volumetric interpretation of carbonatic reservoirs in Santos Basin. As a result, it was possible to visualize, map and characterize a series of carbonate bodies, what was not possible in conventional seismic data. The parametrization for the attributes extraction is a very sensitive step in this process and can determine the success of the interpretation.
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A practical and integrated depth migration approach to prospect identification in BMES-11
Authors M. Rhodes, M. Frismanis and B. DalstrømStatoil took over operatorship of block BM-ES-11 in March 2004 with the objective of identifying new exploration prospects near and under salt bodies. An integrated geological and geophysical project was initiated to provide reliable data for prospect generation in the salt flank and sub-salt areas in the southern part of block BM-ES-11, c.f.
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Seismic and magnetic characterization of Varge˜ao Dome Astrobleme, Southern of Brazil
Authors C. Kazzuo-Vieira, A. Penteado Crósta, A. Moreira Silva, A. Schrank, F. Gamboa and M. TygelVarge˜ao Dome is one of the few examples of eroded impact craters (astroblemes) in the South America. This conspicuous circular depression, located at 26 490S and 52 100W, was formed by the collision of a meteorite against the Earth’s surface and has
a diameter of 12.4 km, depicting sharp topographic gradients of up to 150 meters between its outer borders and inner portions.
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Brasil MegaSurvey – A Regional Study of the Campos Basin
Authors H. Edwards, J. Magalhaes Macedo, L. Groves, N. Humpheys, T. Jarratt, A. Smith, C. Lopez and G.A. BattilaniIn the frontier, deepwater province of the Campos Basin, finding hydrocarbon resources proves challenging due to a poor understanding of the stratigraphy, subsurface structure and depositional systems. All of which must be understood in a regional as well as a local context.
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Use of gammaspectrometric airborne data as tool in regional geologic mapping in the Parana State – Brazil
Authors J.H. Boniatti and F.J. Fonseca FerreiraThis paper presents results of the processing of gammaspectrometric data (TC, K, eU, and eTh) from a 300 km2 area to the North of Curitiba, PR. Samples are separated 67 m from each other along 1,000 m spaced, 120 m high flight lines.
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Avaliaçao Geotécnica - Geofísica das Subestruturas da Ferrovia Vitória - Minas (EFVM) Usando o Radar de Penetraçao no Solo (GPR)
Authors M.A. Barsottelli Botelho and C.G. JorgeThe application of Ground Penetrating Radar (GPR) as a Non Destructive Test (NDT) technique for the assessment of railway track bed ballast is presented in this paper. The GPR was applied on Vitória – Minas railroad (EFVM) and it allowed us to detect changes on geometry and composition of the ballast and sub-ballast which were revealed by amplitude and geometry variations of the reflectors corresponding to the air-ballast and ballast-sub-ballast interfaces.
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Modelagem Numérica Espectral Associada a Migraçoes Pré e Pós Empilhamento para Imagear as Estruturas Internas de um Arenito Análogo de Reservatório da Formaçao Água Grande, Bacia do Reconcavo (BA)
Authors O. Neumann and M.A. Barsottelli BotelhoO método geofísico eletromagnético designado por Radar de Penetração no Solo (GPR) é usado para investigar as estruturas internas de um afloramento de arenito pertencente à Formação Água Grande, na Bacia do Recôncavo. O arenito estudado é um afloramento representativo de uma das rochas reservatório de hidrocarbonetos da Bacia do Recôncavo, constituindo assim um chamado análogo de reservatório. A aquisição dos dados de GPR usou antenas de 200 MHz com a configuração de afastamento constante.
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Elements of Electromagnetic Theory for GPR Applications
Authors J.M. Carcione and M.A. Barsottelli BotelhoWe develop some aspects of the electromagnetic theory regarding the application of the ground-penetrating radar (GPR), namely, a model for the composite dielectric constant, the amplitude variations with offset (AVO), the concept of exploding reflector and Backus averaging to obtain the properties of finely-layered media. The electromagnetic properties are obtained by using a generalization of the Hanai-Bruggeman (HB) equation. The HB exponent (1/3 for spherical particles) is used as a fitting parameter for a sand-clay mixture saturated with water.
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Localização de Manilhas de Concreto Instaladas no Sítio Controlado de Geofísica Rasa do IAG-USP Através de Multi-Configurações das Antenas GPR: Resultados Preliminares
Authors R.S. Lima and J.L. PorsaniThis article shows the preliminary results of multi-configurations GPR antennas in order to locate concrete tubes installed in the Shallow Geophysical Test Site or Sítio Controlado de Geofísica Rasa-SCGR of IAG/USP. Four arrays of antennas were used: TE mode (Transversal Electric), TM mode (Transversal Magnetic), and the TE and TM Cross-Polarizations, according to definitions of Radzevicius & Daniels (2000). The results showed that the TE mode was excellent to detect concrete tubes that presented clear reflections, followed by TM mode.
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Polarization Issues in a Recent Sedimentation Environment
Authors J.M. Travassos and S.S. AndréThis work presents the preliminary results of a GPR survey done at Marambaia, RJ. Part of data acquisition gotten in the region will be presented, and will show to the result of multi polarization of a GPR section.
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Simulações Numéricas GPR para Arqueologia: Exemplos de Sambaquis e Urnas Funerárias
Authors S.I. Rodrigues and J.L. PorsaniIn this article, numerical simulation of GPR results are presented in order to detect human bones and funerary urns inside of carbonate shell layers (sambaquis), as well as to locate structures of dunes and water table. The results showed that human bones and funerary urns can be detected, however, they presented the same reflection pattern, not being possible to differentiate them. The structures of dunes and the water table also are identified, but depend on the electrical conductivity of sambaquis layer, which is underlying dunes. The obtained results are significant and will serve of base for future field works. Moreover, it shows the importance of numerical modeling as an auxiliary tool in interpretation of data, decreasing the uncertainties in interpetation process.
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Processamento de dados GPR registrados na Lagoa do Abaeté pelo método de empilhamento CRS
Authors G. Garabito, M.A. Barsottelli Botelho and T. DouradoThe Common Reflection Surface (CRS) stack method is suite to simulate a zero-offset section with high quality and high signal-to-noise ratio from multi-coverage reflection seismic data. This seismic imaging method is fully automatic and it may be applied to irregular geometry data. We present the first results of the application of the Common Reflection Surface (CRS) method based on global optimization to simulate a zero offset stacked section from multi-coverage Ground Penetrating Radar (GPR) real data. We lso present a comparison of the results of the CRS processing with the conventional NMO processing. The results show that the CRS processing provided a zero-offset stacked section with better resolution.
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Utilização do Geo-Radar nos trabalhos de escavação do Sítio Teixeira Lopes, Juiz de Fora, Minas Gerais, Brasil
Authors P.R.A. Aranha, A.P. de Paula Loures de Oliveira and C.H.B. RochaThis paper shows the GPR's results of its application on the study of the Teixeira Lopes Archeological Site, Juiz de Fora, Minas Gerais, Brazil. The excavation works took place in October 2004, in an attempt to verify archeological evidences that resisted the destruction of the site during the opening of two silos, in 1982. The material remains, as ceramic fragments and quartz chips, were quite deteriorated. In order to dinamize the work the area was profiled with the GPR (Ramac) through parallel lines 1 m apart, with 400 MHz antenna set, and interval acquisition at 0,05m. The radargrams detected some anomalies that were checked in loco and identified as wires, plastic, garbage, and others. This demonstrates that the Site is being even more disturbed since the 1982. Afterall, the GPR showed success in the application in this research.
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Finite difference modeling of 2D GPR data considering attenuation
Authors M. Heimer, M.A. Barsottelli Botelho and S. Pomponet OliveiraWe use a finite-difference scheme to simulate 2D ground penetrating radar data by solving the damped wave equation. We show that the stability condition for the damped scalar wave equation does not depend on the damping factor. As an example application of our modeling tool we investigate a typical situation in granite prospecting, where a conductive clay overburden masks the real position of the fractures in the granite. The results of the modeling have a good agreement with the actual data. Also, the algorithm shows well the increase in attenuation with the increase of the frequency. The algorithm shows to be a good basic modeling tool that can be used for further applications and for comparisons with other modeling methods like pseudospectral or finite elements.
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Utilização do GPR 3D bi-polarizado na localização de um BOP soterrado devido a colapso de terreno no Campo de Fazenda Belém, Bacia Potiguar
Authors P.X. Neto and W.E. de MedeirosO GPR utiliza antenas para irradiar a energia eletromagnética para o meio geológico. Esta energia, ao se propagar no meio geológico, sofre reflexão quando encontra interfaces com contrastes de impedância eletromagnética (interface litológica, objetos enterrados, etc) e é recebida pela antena receptora. A energia refletida por um alvo é função da amplitude e da direção de vibração (polarização) do campo eletromagnético incidente. Isso implica que o receptor é sensível à direção de vibração do campo eletromagnético e, portanto, sensível à morfologia ou disposição espacial do alvo.
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Interpretação em 3D de Dados de GPR em Estação de Interpretação de Dados Sísmicos
Authors A.J. Pereira, L.A.P. Gambôa, M.A.M. da Silva, A.R. Rodrigues and A. da CostaCom a conversão dos dados de GPR adquiridos em formato próprio, para um formato seg-y genérico passível de carregamento em estação de interpretação sísmica, foi possível a visualização em 3D de feições representativas da estratigrafia de um trecho da praia de Itaipuaçú, município de Maricá, Estado do Rio de Janeiro. Essa possibilidade permitiu a identificação nos perfis de feições correspondentes a canais que alimentavam uma paleolaguna, hoje colmatada, no reverso do cordão arenoso externo, além de estruturas análogas às feições observadas atualmente no pós-praia da referida praia, como por exemplo paleoescarpas de tempestades. Outra constatação foi verificar, ao longo de toda a planície mapeada, o lençol freático que ocorre em torno de 5 m de profundidade.
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Monitoramento da umidade de campo empregando a técnica de radar GPR
Authors N.S. Amparo, S.L. Machado, T.C. Dourado and M.A.B. BotelhoThis paper intends to evaluate the GPR potential of use aimed to obtention of water contente profiles in the vadose zone. In order to do that, a laboratory mechanical apparatus was developed in way that constant mid point tests can be perfomed, allowing the obtention of precise CMP radagrams. The apparatus, a sand box wit nominal dimensions of 1 x 0,7 x 0,7 m, had a mechanical device that assures equal displacements from central point. Laboratory tests were performed in order to calibrate equipament and obtain experimental data correlating soil water content and pulse travel velocities theoretical equation, develop inside the scope of the research program, was used in order to predict the relative amounts of water and air in the soil voids.
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Towards cost-effective 3D imaging with GPR
More LessThere are two situations that can motivate a GPR user to perform the investigation in a 3D mode rather than in the conventional 2D mode. The first case is when the 2D approach is not enough to achieve a reliable answer to a specific problem while 3D imaging has the potential for solving the problem correctly.
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Experimentos em Laboratório (1 GHz) e Trabalhos de Campo (200 MHz) com GPR Usando Corpos arenosos para Avaliar a Influência da água e de Hidrocarbonetos na Velocidade e na Amplitude da Onda Eletromagnética
Authors T.C. Dourado, M.A. Barsottelli Botelho, S.L. Machado and N.S. AmparoWe analyse GPR measurements (1 GHz) which were carried out on a well sorted, clean sand in a laboratory experimental site and we also executed AVO field experiments, both using TE and TM- mode configurations,. The AVO works were conducted on a sand dune field around the Lagoa do Abaeté (Salvador, Brazil).
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Detecting cavities and archaeological remains with GPR
Authors E.U. Ulugergerli and S. KadiogluTwo examples were considered in this presentation; detection of cavities in limestone, delineation of boundaries of an archeological remain using Ground Penetrating Radar (GPR) method and affect of the trees on the GPR data. The GPR method has been successfully applied to detect and map underground cavities in Limestone in a reservoir area of a dam being built in southeast Turkey.
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Multi-offset GPR surveys for complex targets
Authors L. Baradello, J.M. Carcione and D. Nieto YabarDuring the last twenty years Ground Penetrating Radar (GPR, georadar) has been successfully used to discover and map several subsurface structures. The mono-static georadar (one single antenna) is fast and inexpensive for these surveys. Often, in archaeological and geological investigations the structures can be very complex: ancient walls and debris in chaotic mixtures of sediments or fractures in rocks. These cases are difficult to interpret with conventional single-offset (SO) records because there is scattering and poor signal-to-noise (SN) ratio. The present paper shows how the GPR multi-offset (MO) technique can provide more information about complex targets and enhance weak reflections. We compare the multi-fold (MF) stack and the MO section to investigate which method gives the best performance.
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Imaging an hyperpicnal turbidite outcrop in Almada Basin (Brazil)
Authors M.A.R. Ceia, A.A.G. Carrasquilla and J.M. TravassosIn onshore Almada Basin, northeast Brazil, sandy and/or conglomeratic turbidites and shales outcrops of Urucutuca Formation occur. These rocks are part of an exhumed portion of the filling-section of the Almada Canyon, which is well mapped by seismic studies in offshore part.
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GPR simulations for pipeline oil drainage detection
Authors M.A.R. Ceia and A.A.G. CarrasquillaPipeline detection and investigation of leakage and fluid drainage play a major part in geophysics applied to downstream problems. Oil drainage may have impact in contaminating subsurface environment, and by consequence, affect socially and economically the nearby population. When that hazard occurs, it could be mapped by geophysical techniques. The strong contrast in electrical properties between oil (or gas), metallic pipes and sediments, makes GPR (ground penetrating radar) one of the best techniques to be used for mapping oil drainage and for pipeline detection.
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Estratigrafia de Alta Resolução da Formação Coqueiro Seco (Bacia de Sergipe-Alagoas) Através da Interpretação de Dados GPR
Authors P.T.L. Menezes, J.M. Travassos and L.S. FrancoA major problem related to carbonates reservoirs is the heterogeneity of porosity and permeability systems. Reservoir analogues can provide valuable definitions of geometric and petrophysical heterogeneities at inter well scales. Integration of ground-penetrating radar (GPR) surveys with sedimentological and stratigraphic data provides information on the internal heterogeneities of sedimentary sequences.
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GPR aplicado ao estudo de Reservatórios Análogos. Estudo de caso em Cordões Litorâneos do Delta do Rio Itapemirim (ES), Resultados Preliminares
Authors G.M. Sousa, P.T.L..J.C. Della Fávera and M.A.M. MedeirosClastic reservoirs analogues based on the interpretation of GPR data provide valuable definitions of geometric and petrophysical heterogeneities of sedimentary sequences at scales that allow dissection of the 3-D anatomy of clastic depositional systems.
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Discussão do conceito de Skin Depth e estimativa de parâmetros elétricos considerando os efeitos de polarização envolvidos a partir de medidas com GPR
The authors analyze, in this work, the polemic question of the signal, being measured by GPR, coming from depth greater than the plane wave skin depth. They conclude that signals are being measured, reflected from depths of the order of five times the skin depth for the 100 MHz frequency being used. They also estimate the dielectric constant for the mapped geologic formations using GPR.
More realistic values of K are obtained, for considering: a) the squared index of refraction, (c/v)2, as due to the electronic polarization, associated to the rock matrix, KM; b) the orientational polarization for the saline water, equal to 78, being considered for the water saturated pore spaces of the rocks, Kf. The mixed relation for a two components material was then used for the finalestimation.
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Aquisição e Processamento em Dados de Ground-Penetrating Radar (GPR) COS e Split-Spread
More LessAquisições de dados de GPR common offset (COS) (monocanal) e split spread (multicanal), com antena de 100 MHz foram realizadas em um afloramento com uma seção geológica que é marcada por variações estruturais na forma de um graben. Os dados de radar foram processados com o pacote Vista 2D/3D seguindo um fluxo de processamento de pré-empilhamento com edição dos dados, correção estática, escalonamento, filtro variável com o tempo, análise de velocidade, correção NMO, mute, e pós-empilhamento com escalonamento, filtro variável com o tempo, filtro multi-canal e migração. As seções finais são apresentadas em profundidade com os dados split-spread fornecendo uma maior representação das feições estruturais e litológicas do afloramento em comparação aos dados COS. A análise das técnicas de processamento de dados sísmicos para os dados de GPR em afloramentos vem a colaborar para o estudo de reservatórios em grandes profundidades, auxiliando em ajuste de parâmetros e verificando a eficácia dos processamentos sísmicos.
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Emprego do GPR para a Caracterização da Morfologia do Fundo e Espessura dos Depósitos da Represa de Guarapiranga, São Paulo / SP
Authors Renato Hochgreb Frazão, Jorge Luís Porsani and Renato Luiz PradoGuarapiranga reservoir is one of most important raw water reservoir for the city of São Paulo locate in an area of high population density in SE Brazil. It is responsible for 20% of potable distribution water. During the last decades the reservoir is experiencing a growing eutrophication process due to untreated sewage discharge. Preliminaries Ground Penetrating Radar (GPR) investigations were carried out in area of Guarapiranga reservoir by determine water depth and perform sub-bottom sediment profiling. Accurate periodic information on the elevations the top of sediment and top of original reservoir bottom is important to calculate the volume of sediment to be removed and to establish the reference elevations for the proposed dredging activities. The measurements are non-intrusive and non-destructive, and were conducted along survey lines. Compared with other geophysical methods, GPR profiles have a very high resolution. The selection of the optimum radar frequency is essential to obtain a good resolution and sufficient depth penetration. The obtained results are very interesting.
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Geologia Estrutural da Bacia Potiguar com base em dados aeromagnéticos
Authors Marcos de Barros Munis and Renato Lopes SilveiraThe E&P Data Bank - BDEP - is the trustee depositary of all geophysical project concerned with E&P activities in Brazil. Especulative data and proprietary data has a confidentially term of 10 or 5 years, respectively. After that, they became public and can be acquired by companies, universities, and others interested by a small price, aiming the further development of oil prospecting knowledge or either production.These public data are available for all the mineral and oil community in CD media. With the development of softwares on processing and filtering geophysical data, good opportunities are open to all. This paper deals with a fast treatment of aeromagnetic data from Bacia Potiguar, NE Brazil, with an improvement on signal / noise ratio giving new ways on structural geologic interpretations using upward continuation, first derivatives and pole reduced maps.
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Modelagem numérica de dados tensoriais de aerogradiometria gravimétrica 3D
More LessAir-FTG is nowadays the only existing airborne full tensor gradiometer technology that is flown for both detailed and regional surveys. The system takes real-time measurements of the differences in the gravity gradient field in three orthogonal directions and at me time compensates for bias in the orientation and movement of the aircraft. Each one of these measurements is related to either density contrasts or geometry of discrete bodies. In this work we elaborate a numerical algorithm to compute the five synthetic gxx, gxy, gxz, gyy and gyz independent tensor components. Results show that gradiometer depict a more observable advantage for identification of nearsurface targets, revealing structures such as lineaments, edges, corners and as a consequence body hapes and thickness. It is also shown that the best images of the subsurface rocks acquired by the air-FTG platform can provide more realistic information than the conventional vertical ground gravity field instruments when interpreting lateral density contrasts.
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Modelamento do sinal gravimétrico e aeromagnético das Alcalinas de Morro do Engenho, sudoeste de Goiás
Authors Alanna C. Dutra and Yára R. MarangoniA Província Alcalina Rio Verde – Iporá, na borda norte da Bacia do Paraná é caracterizada pela presença de intrusões alcalinas com forte assinatura aeromagnética e gravimétrica, apresentando-se como anomalias quase circulares. O Complexo Morro do Engenho (ME) está ao norte da província e constitui uma intrusão circular zonada de cerca de 5 km de diâmetro em superfície. As anomalias gravimétricas variam de +15 a +30 mGal com relação ao campo gravimétrico regional, enquanto que as anomalias aeromagneticas são da ordem de ±3000nT. O modelamento usando a técnica de inversão indica espessura variando de 10 a 12 km, com circunferência média em torno de 10 km. No modelamento conjunto 2,5D, o sinal aeromagnético parece ser gerado por um corpo de geometria cilíndrica vertical. Este corpo geométrico apresenta-se homogêneo e com profundidade compatível com os modelos gravimétricos.
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Interpretação geológico-geofísica de estruturas continentais e sua continuação em águas rasas na Bacia de Campos, Estado do Rio de Janeiro
More LessThis work presents the preliminary comparative analysis of the regional structures observed in onshore satellite images and their continuation toward the Campos Basin shallow water platform. These results were obtained by integration of aeromagnetic and gravimetric data, satellite images, topographic, and regional structural maps, combined with structural analysis from fieldwork.
The southern portion of the Campos Basin is located over gneissic rocks of the Cabo Frio Tectonic Domain (CFTD), a Cambrian-Ordovician tectonic unit formed during the agglutination of the Gondwana Paleocontinent. All the CFTD lithotypes are tectonically intercalated throughout thrust zones, dipping between 5º and 30º to the south. These units were deformed during D1 and D2 deformation stages, at c.a. 520 Ma (Schmitt et al., 2004). The CFTD was juxtaposed to the tectonic units of the Ribeira Belt during D3 phase. The contact is marked by a thrust fault striking NE-SW that dips 30º to the south, with a vergence towards the NW. This regional structure is present in the Macaé region, from where, supposedly, it inflects in an ENE-WSW direction towards the continental platform, with a predominant NE-SW strike related to Early Cretaceous syn-rift fault trends.
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Interpretação de Dados Aeromagnetométricos na Região do Gráben de São João, Rio<br>de Janeiro, Brasil
More LessSeveral anomaly-enhancement techniques were applied to high-resolution airborne magnetic data of the São João Graben, offshore Cabo Frio platform. That approach allowed the identification of several subtle basement faults and the definition of the tectonic framework.
We idendifiyed new NW-SE faults associated to Early Cretaceous transfer zones that segment the obliquely rifted Atlantic margin. That segmentation has important implications for risk factor of deep-water petroleum systems of Campos Basin.
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Estimating basement faults with vertical slips using gravity inversion in onshore Almada Basin, Brazil
More LessWe illustrate that the depth imaging of the fault plane may be obtained using gravity data. Our approach is based on a method that enhances the estimated relief resolution as compared with methods incorporating smoothness constraints. Our results using gravity data from Almada Basin, Brazil, produced an interpretative depth image of the faults compatible with the available seismic data interpretation.
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Radial inversion of 2D potential field data
Authors Valeria C. F. Barbosa and João B. C. SilvaWe propose a new 2D method for inverting potential field data with model constraints designed by the interpreter. Our method uses an interpretation model consisting of a source with polygonal cross section whose vertices are described by polar coordinates with an origin inside the source. With this coordinate system, constraints in an inversion are easier to develop and apply. Our inversion method assumes a known physical property contrast for the source and estimates the radii associated with the polygon vertices for a fixed number of equally spaced angles from 0o to 360o. A wide variety of constraints may be used to stabilize the solutions by introducing information about the source shape. The method recovers stable solutions whose shapes range from almost circular or pear-shaped to elongated in one or more directions.
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Gravity inversion in a user-friendly environment
Authors João B. C. Silva and Valeria C. F. BarbosaIn a user-friendly environment we present a method for inverting gravity data produced by multiple, complex and interfering 2D gravity sources having arbitrary shapes and arbitrary, but known density contrast. Our method is stable and is suitable to recover a complex 2D density distribution, leading to a reliable delineation of sectionally homogeneous sources with complex shapes. It is a method similar to interactive modeling but differs from it in automatically fitting the observations and in requiring from the interpreter only the knowledge of the outlines of the sources expressed by simple geometric elements such as points and line segments. Each geometric element operates as a skeletal outline of a particular homogeneous section of the gravity source to be
reconstructed. Also, the interpreter can define the geometric elements in an interactive way without worrying about the data fitting because it is automatically done. The examples with synthetic data illustrate the good performance of the method in mapping the complex geometry of gravity sources. The solution sensitivity to uncertainties in the prior information shows that to produce good results, the uncertainty on the contrast density of each homogeneous extent of the source should be smaller than 40 percent. The method was also applied to two sets of real data. The first one consists of several positive anomalies produced by metabasalts and metagabbros from a greenstone belt located in Rio Maria region, in Pará state, Brazil. The second one is a negative gravity anomaly produced by the Bodmin Moor Granite, which is part of the Cornubian Batholith in southwestern England. The estimated density contrast distribution in all tests demonstrates a good correlation of the estimated gravity sources with corresponding known geological features.
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Inversão gravimétrica usando regularização entrópica
More LessWe present a new gravity inversion method, which produces an apparent density contrast mapping on the horizontal plane, based on the combination of the minimization of the first-order entropy with the maximization of the zeroth-order entropy. The interpretation model consists of a horizontal grid of 3D vertical prisms, and the parameters to be estimated are the prisms density contrasts. The maximization of the
zeroth-order entropy is equivalent to the global smoothness constraint whereas the minimization of the first-order entropy favors solutions presenting abrupt borders, so a judicious combination of both constraints may lead to solutions characterized by regions where the estimated density contrasts are virtually constant, separated by abrupt discontinuities. The method has been applied to synthetic data simulating the presence of intrusive bodies in sediments. The comparison of the results with those obtained with the global smoothness constraint applied to the same data, showed that that both methods locate the sources with good precision, but the entropic regularization delineates the contour of the bodies with greater resolution, even in the case of 100 m wide bodies separated by a distance as small as 50 m.
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Crustal and tectonic features of northeast of São Paulo State and southwest of Minas Gerais State based on gravimetric studies in southeast Brazil
More LessThis paper presents the results of a geophysical study carried out at Northeast of São Paulo State and Southwest of Minas Gerais State (an area 80 km wide and 97,5 km long) in SE Brazil. The Bouguer anomaly map, geological and structural data allowed to identify three different gravity domains related to the structural pattern (crustal blocks limited by major discontinuities) in the area. These discontinuities were interpreted as geosuture zones lying under the Paraná Basin sediments and have their extends in the Pré-Cambrian Basement. The crustal discontinuities named Alterosa and Ribeirão Preto may be seen as A - type collision sutures with triple junction arrays. Two linear proeminent anomalies are recognized in the Bouguer anomaly map, the limit between the Brasília and São Paulo crustal blocks or paleoplates, the Alterosa suture is deduced in a NW-SE trend, and in a NE-SW trend is the Ribeirão Preto suture. The produced Bouguer anomaly map provides subsidies and information to new concepts and theories to the refinement of tectonic models.
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Gravimetric study in the northeast portion of Paraná Sedimentary Basin – Southeast Brazil. A preliminary Bouguer anomaly map
This paper presents the results of a geophysical study carried out at Northeast of Paraná Sedimentary Basin. Since the first geological surveys and studies with the aim objective to discover oil reserves the structural highs named Pitanga and Pau D’Alho were at the time the principal targets in subsurface and surface studies and prospecting. Such structural highs are evidences from the tectonic and geological evolution from the Paraná sedimentary basin and its related oil occurences. Potential geophysical methods such as gravimetry is a valuable tool in the understanding this structural domes and its evolution through the basin evolutionary story. This study is currently in its inittial phase but a preliminary Bouguer anomaly map provides a better visualisation and allows new concepts and theories of the polyphasic basin story.
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Aquisição e interpretação preliminar de dados gravimétricos do SE do Craton S.Francisco
Authors Luiz Gustavo Rodrigues Pinto, Naomi Ussami and Nelsi Côgo de SáA total of 176 gravity data was acquired, between coordinates 39° to 49°W and 17° to 23°S situated in SE São Francisco Craton. The position of each gravity station was obtained using GPS relative positioning method. The new data was added to the gravity data-bank of IAG/USP. A total of 12,339 stations were processed and preliminarily interpreted. The geology of this area is represented by Archean and Proterozoic metamorphic terrains of SE São Francisco Craton, including the Araçuai and Ribeira fold/thrust belts.
In order to separate shallow from deep sources of gravity field, a 50 km upward continued regional field was removed from Bouguer anomaly map. The residual gravity field from the Quadrilátero Ferrífero was correlated with the exposed geological units. Two main sources were mapped, the Archean metamorphic complex and Rio das Velhas Supergroup.
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A Superfície de Curie na Região Bahia Sul – Análise Espectral sobre dados<br>Aeromagnéticos de Alta Resolução
Authors Glauco Bragança and Luiz F.S. BragaIn this study we used spectral analyses over the High Resolution Airborne Magnetic (HRAM) data, acquired by Fugro-Lasa over the offshore Brazilian basins located in southern region of Bahia State. Depths do the Curie Surface were estimated and they allowed an investigation on the present thermal state of the various compartment of the studied area. Special care was taken on the investigation of the minimum size of the data window that may be used without compromising the reliability of the estimates. Additionally, we compared the regional behavior of the depths to the Curie Surface with the known structural setting of the Camamu-Almada, Cumuruxatiba and Jequitinhonha basins which brought insights on the correlation between the present thermal gradients and the Oil and gas potential in those basins.
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Airborne geophysical data as an aid to geological mapping and target selection in the<br>Tapajós Gold Province, Brazil
More LessAirborne geophysical data acquired over the Tapajós Gold Province (TGP) in west Central Amazon Province display different patterns previously not identified in geological field mapping. Integrated analysis of airborne magnetic and gamma-ray spectrometric data plus available geological data was conducted to map and analyze these patterns, and to obtain insight in their regional significance. Enhancement of the airborne magnetic and gamma-ray spectrometric data have resulted in better definition of both geological structure and lithological boundaries than indicated on previous maps. Comparison of multiple geophysical signatures and known mining occurrences were particularly valuable for defining old targets and direct new ways for gold prospecting in the area. Areas with high to moderate favorableness encompass wellknown gold deposits, as well as new signatures that may have economic importance. Geophysical data were successfully used to highlight relationships between main crustal domains, as well as their internal structures and boundaries. The northeast domain bears the signature of older crustal material covered by rocks of the Uatumã Supergroup generated through partial crustal melting. The western limit of this domain is close to the supposed limit that divides the Central Amazon and Ventuari-Tapajós provinces. A large structure marked by high amplitude in the western part may record oceanic crust subduction and formation of the Cuiú-Cuiú arc.
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Expressão gravimétrica e aeromagnética dos compartimentos e limites tectônicos da Província Borborema, Nordeste do Brasil
Borborema Province (BP) has a very complex history, but up to now, few geophysical data have been used to constrain its evolution history. This paper presents the first integrated gravity/magnetic/geological data interpretation of the tectonic framework of the province. BP is a Proterozoic fold belt extended between the São Luis - West Africa and São Francisco - Congo/Kasai cratons. Currently, as a result of an increase in geochronologic data, there is growing evidence that its evolution has occurred by a mechanism of terrane collage. This evolution model suggests that large crustal blocks were put together during Meso and Late-Proterozoic events, resulting in crust growing by the arrival of pieces of crust or by the addition of new crusts. Interpretation of regional magnetic and gravity maps revealed the boundaries between crust blocks or compartiments inside BP. As result of the integrated interpretation, it is proposed that BP is formed by the union of at least 11 crust blocks. Boundaries between these blocks form long lineaments in NE-SE direction, in some cases showing vergences to E-W direction. The major block to the south of BP is the São Francisco Craton. The boundary between BP and the craton is still a controversial question, but the geophysical data suggest that N-S lineaments, which occur inside the craton, prolong below Riacho do Pontal and Sergipano hrust fold belts, which are part of BP. In this way, the plate associated to the craton lies beyond its geologically mapped north limit.
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DADOS AEROMAGNÉTICOS APLICADOS NA INTERPRETAÇÃO DO ARCABOUÇO ESTRUTURAL DA PORÇÃO NORDESTE DA PROVÍNICA BORBOREMA, NE BRASIL
This paper reports processing techniques applied to airborne magnetic data to generate themes that could be used as a tool do delimitate the boundaries and the tectonic framework in the northeastern portion of the Borborema Province in NE Brazil. Data processing result in the generation of anomalous magnetic map, residual magnetic field, allowing to generate the horizontal gradient zero order, amplitude and inclination of the analytical signal (zero order), and Euler deconvolution for different structural index. Preliminary results show enhancement of main tectonic structures and boundaries of crustal blocks present in the region. Also, was able to quantify the major shear zones that define the framework of the Borborema Province, and to identify important features not present on actual maps. Magnetic anomalies correlated to different crustal blocks indicate the depth extension of the archean nuclei São José do Campestre to S-SW. Also, it was shown different magnetic signature as for the paleoproterozoic rocks, low magnetic response for the Seridó Belt and also distinct signatures for the pre- and syn-brasiliano granites compared to the pos-tectonic granites.
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DECONVOLUÇÃO DE EULER: NOVA PERSPECTIVA PARA A INTERPRETAÇÃO 3D DE ESTRUTURAS GEOLÓGICAS
This paper deals with a 3D magnetic data (Seridó Project, 1973) interpretation of regional geologic structures (Patos Lineament and João Câmara-Picuí Shear Zone) in Northeast Brazil based on horizontal position and depth for magnetic sources given by Euler deconvolution. Best parameters for Euler deconvolutions were found from different combinations of structural index, window sizes, and error tolerances. Best product yelded solutions for the structural trends with depth through 5 km. The Patos Lineament (E-W) and João Câmara-Picuí Shear Zone (NE-SW) showed maximum depth in the order of 3 km and 2 km, respectively. Deeper magnetic sources (> 5 km) were found under supracrustal sequence of the Seridó Belt, in the portions Southwest of Currais Novos city. 3D plots proved to be useful to get a glimpse on the geometry and distribution of magnetic material within these structures.
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Contribuição da Aerogeofísica nos Levantamentos Geológicos Regionais
More LessThis work consists of a qualitative airborne geophysical interpretation (magnetometry and gammaspectrometry) of an area of 35,450 km² of the Trombetas Aerogeophysical Project, which is located in the north portion of the the State of Pará, Brazil. The study aims at stressing the importance of the aerogeophysical surveys to the planning of the geological mapping, mainly in the regions of difficult access like this project area, whose geology is not well known but of great metalogenetic importance to the country.
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Gravity inversion of a complex interface in the presence of interfering sources
More LessWe present a new semi-automatic gravity interpretation method for estimating a complex interface separating two media containing heterogeneities produced by the existence of interfering sources. The method combines a robust fitting procedure and the constraint that the interface is very smooth near the interfering sources whose approximate horizontal coordinates are defined by the user. The proposed method differs from the regionalresidual techniques by using no spectral content assumption about the interface to be estimated, i.e., the interface can produce a gravity response containing both low- and high-wavenumber features. As a result, it may be applied to map the relief of a complex interface in a geological setting containing either shallow- or deepseated interfering sources. Tests with synthetic data have shown that the method can be of utility in estimating the basement relief of a sedimentary basin in the presence of salt layers and domes or in the presence of mafic intrusions in the basement and/or in both basement and sediments. The method was applied to real gravity data from two geological setting having different kind of interfering sources and interface to be interpreted: 1) the anorthositie-tonalite interface over the outcrop East Bull gabbro anorthosite complex, Ontario, Canada; and 2) the sediments-basement interface over Algarve Basin, south Portugal. The results showed good agreement with the corresponding known geological features, even when the estimated interface and the interfering sources present highly overlapping spectral contents.
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Delineamento crosta continental-crosta oceânica através da magnetometria
More LessWe present a method to delineate the boundary separating the oceanic and continent crusts using magnetic data. The method maps magnetic lineaments, which happen to occur solely in the continental crust. To this end, the magnetic signal is amplified by downward continuing the magnetic anomaly to a surface defined by the bathymetry of the continental shelf, continental slope, and part of the continental rise. The purpose is to locate the seaward end of the lineaments. The downward continuation if formulated using the equivalent layer principle, leading to a large-scale system of linear equations, that was solved via a conjugate gradient method. To stabilize the solutions we used the first-order Tikhonov regularization functional (global smoothness constraint). Examples with synthetic data showed that, in contrast with the plain visual inspection of the original aeromagnetic data, which leads to an erroneous delineation of the boundary separating the oceanic and continent crusts, the continued magnetic anomaly delineates this boundary with excellent resolution. The method has also been applied to real aeromagnetic data from a Brazilian coastal area, evidencing that the data window is located above the continental shelf, or, possibly
above a transitional crust.
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Towards evidences of a threshold system as the source for magnetic storms detected on Earth’s surface
Authors Ney A. B. Seixas, Luiz M. Barreto and Andrés R. R. PapaIn this work we present evidences that point to a threshold system as the source for magnetic storms detected on the Earth. We based our analysis on series of data acquired during many years in the network of magnetic observatories of the National Observatory (Brazil). In particular we focused our attention on October 2000 month of the Vassouras Observatory, which have been active since 1915. The data was appropriately processed using classical Fourier formalisms. The analysis of statistical distribution of amplitudes, periods of calm and storms was implemented on the difference resulting from the processed and unprocessed data.
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Integração de métodos geofísicos na modelagem crustal na Bacia de Santos
Authors Eduardo de Mio and Hung K. Chang e Fernando S. CorrêaThe Santos Basin is a passive margin basin generated during the Neocominian, associated with Gondwana breakup event. The thickness of the sedimentary package reach 15 km, including rift sequence deposited over a thinned crust which originally was 35 km thick. Crustal modeling was performed over 8 lines aiming to recognize the rift phase geometry and estimate the amount of crustal stretching. The database used was: four depth converted seismic horizons, magnetic and gravimetric grids and depth to magnetic basement data. The modeling results demand thick and widespreading volcanic layers to fit the model. These wedge shaped volcanic fill, bordered with normal faults, are a common feature in rift basins. Four volcanic provinces have been defined, based on structural compartmentalization and regional occurrence of the basal rift layer, so called Sin-Rift I phase.
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Evaluación del estado isostático del valle de La Rioja, La Rioja - Argentina
Authors Mario Gimenez, Gabriela Bustos, P. Martínez, A. Introcaso and T. JordanWe carry out a study isostatic 3D in the Valley of the east of La Rioja city in Argentina, considering a system of compensation isostática of the type Airy in stretched crustal.
The chart of Bouguer anomalies of gravimetric effects of the sedimentary column and of isostatic corrections, was used to prepare a chart of isostatic anomalies (or of residual isostatic anomaly) including the whole extension of the studied basin.
Our results point out that the isostatic anomalies are negative in the domain of the basin, with an evident deficit of antiroot. These values indicate us that in the future; 1) the crust underlying this basin, will ascend to reach the hydrostatic balance or 2) the strong crust could support the sedimentary deposit, without deformation.
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Análise de feições anômalas do modelo EGM96 na América do Sul utilizando dados da<br>missão GRACE
Authors Marcelo Augusto de V. Lopes and Eder Cassola Molinaof the Earth’s gravity field obtained by the EGM96 geopotential model in the brazilian territory, in order to evaluate if these features reveal the reality of the gravity field in the region or if they are result of the imprecision of the models used to elaborated the EGM96 model. To calculate the EGM96 coefficients, several types of data were used, such as satellite altimetry, land gravity observations, and the JGP95E topographic model. The fact that the gravity data in some regions of Brazil were not available when the coefficients of EGM96 were calculated, and that the topographic model over these regions were unavailable in that occasion, led to the possibility that the detected structures of the gravity field in such regions may be generated by the lack of data. These features were investigated by the analysis of the topographic model JGP95E compared with the topographic data obtained of the new highly precise model of SRTM, and the gravity anomaly of the EGM96 in comparison with a recent gravity field model calculated by GRACE mission and land gravity data. This analysis showed that there is no evidence that the investigated features have been originated by the filling up process of the areas where no gravity data was available to calculate the EGM96.
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Geoelectrical characterization of the Hydrogeological System in the part west of the Potiguar Basin applying the Vertical Electric Sounding method
More LessThis work presents a the results of a research project that it had as motivation to obtain a better knowledge of the Hydrogeological System of the Chapada do Apodi, which is an area in the which the federal and state governments are implementing important irrigation projects whose the viability and success are directly related with the considerable volumes exploitation warranty of physicalchemistry good quality groundwater. It has been intensive the increasing of drinking water supply coming from the regional aquifers Alluvium, Jandaira and Açu, This continuous withdraw has resulted in such problems as the decline of the groundwater levels in the regional aquifers. It is known based on previous hydrogeological studies in the Potiguar Basin that the Açu Formation presents outstanding lithologic and hydrologic heterogeneities that should be taken in account in groundwater exploitation for domestic, agricultural or industrial uses. Previous geophysical studies in others areas of the Potiguar Basin used the Electrical Resistivity method, however in the area studied in this work that corresponds to the Medio-Baixo Jaguaribe where the Açu Formation recovers an area of 1.100 km2 they were not still accomplished geophysical studies and consequently one doesn't know your thickness. Due to this fact the research project had as objective to obtain a geoelectrical model of the subsurface that describes in depth the stratigraphic sequence and its lateral variation along some profiles, identifying the Açu and Jandaira Formation’s thickness in the Medio-Baixo Jaguaribe's central portion that is localized in the west part of the Potiguar Basin. As it intended to map in depth the stratigraphic sequence the electrical resistivity survey was carried out using the Schlumberger configuration array. In the study area the crystalline basement is at the depth that varies from -100 m to –300 m in relation to the sea level, consequently the 23 vertical electric soundings (VES) stations were made and interpreted using the array of current electrode up to a maximum spacing AB/2 of 1 km. For the computational processing of the field data it was applied “ridge regression” inversion outline and used as priore information a lithostratigraphic log profile of a 250 m deep well. The results obtained by the geophysical investigation are analyzed and interpreted in terms of a hydrogeologic model of the deep regional Açu Aquifer.
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Análise Geofísica das Características Hidráulicas da Falha de Salvador na Região de Arembepe - Bahia
More LessThe hydraulic characteristics of the Salvador fault zone along the eastern boundary of the Recôncavo basin were inferred from sub-surface geologic and geophysical data. This fault put in direct contact the shaly sandstones of the São Sebastião Formation and the metamorphics rocks of the crystalline basement. The studied area is part the coastal zone of Salvador, included in the Camaçari country and extending from the Jauá beach to the Arembepe village.
Two geophysical methods were employed to evaluate the waters resources of the area. A total field magnetic map allows to recognize the underground fresh crystalline basement, whereas resistivity soundings were used to define a geo-structural model for the whole area. Sixteen magnetometric profiles and fifty two vertical electrical soundings were distributed in the area. The results allows to map the aquifer geometry and to infer some of their hydraulic characteristics, as well as to define the depth of the water level, and the presence of a fresh water - salt water interface close to the beach.
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Composição Isotópica e Hidroquímica de águas superficiais e subterrâneas da bacia do rio Salitre - Bahia
Hydrogen isotopes and major ion chemistry of waters from 24 wells and 5 superficial samples were used to study the recharge and flux of the aquifer system in the Salitre River Basin. Deuterium compositions varied in a range of 26‰, with the samples from wells varying from -19 to -36‰ (VSMOW). The more negative samples in the range of –36 to -31‰ are located in the southwestern border and characterize precipitations from the Morro do Chapéu region. The groundwaters samples in the range –24 to -19‰ are located in the eastern border of the basin, and characterize precipitations from the Jacobina região. These compositons were used to identify the trend of flux of groundwater in the basin. The hidrochemical data showed the enrichment in dissolved salts of groundwaters along the flux. Water from the Ourolândia Reservoir showed a big enrichment in deuterium and dissolved salts due to losses by evaporation. There was no conection between the reservoir and the sampled wells.
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O método eletromagnético HLEM na prospecção de água subterrânea em terrenos cristalinos
More LessO município de São Raimundo Nonato está localizado no estado do Piauí, Brasil. Em uma região denominada de polígono da seca, por ser dominada fundamentalmente por secas contínuas, e seu arcabouço geológico é constituído na sua maioria (cerca de 70%) por rochas cristalinas (granitos , gnaisses). Estruturalmente verificam-se algumas feições do tipo grabem, estruturas circulares, sistemas de fendas, fraturas interconectadas, descontínuas e com extensão limitada, além de lineamentos favoráveis a ocorrência de água subterrânea.
Uma conjugação de métodos foi utilizada pelo Observatório Nacional com o intuito de obter a localização mais provável de água subterrâneo. Os levantamentos geofísicos se caracterizaram por métodos eletromagnéticos, em particular o método eletromagnético HLEM (horizontal loop eletromagnetic).
Os dados gerados pelo método HLEM foram interpretados para identificação e localização de prováveis pontos de ocorrência de água subterrânea. Apresentando um bom resultado, da ordem de 90 %. Entretanto, a inversão unidimensional destes dados utilizando o programa EM1DFM mostrou-se uma ferramenta ainda mais poderosa para a indicação de água subterrânea.
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Teófilo A. R. Chifunga e Irineu Figueiredo
More LessGeophysical methods, particularlyelectroresistivity, are becoming a major tool in subsurface water exploration as their use diminishes costs by detecting precisely the exitence of water-prone structures and thus optimizing well location. This paper brings some technical and theoretical aspects of the electroresistivity method and details the procedures for the acquisition, processing and interpretation of data from crystalline basement aquifers. Results of a real case study are presented, from an area in the municipality of Sao José do Rio Pardo/SP.
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A sísmica de refração e o GPR no mapeamento do nível freático de aqüífero não<br>confinado. Uma análise comparativa a partir de um estudo na cidade de São<br>Paulo/Brasil
Authors Manuelle Santos Góis Paixão and Renato Luiz PradoThe work had as objective the water table mapping with GPR (Ground Penetrating Radar) method, and seismic refraction with a comparative analysis between both results, once both answers to the presence of interstitial water of vadosa zone are distinct. Geophysical data were acquired in São Paulo city, in
Brazil. Both methods revealed uncertainties in the determination of water table, but for the studied case, the most common errors were associated to the results of seismic refraction due to the uncertainty in the seismic wave velocity determination in the first layer. Considering the studied case, we find out the integration of the worked methods, always possible, can give rise to decrease related to inversion ambiguities of the data, and contribute to better accuracy in water table mapping.
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Prospecção Geoelétrica em Aqüíferos Fissurais, Estudo de Caso em São José do Ubá<br>(RJ)
In the crystalline system groundwater circulate through fractures and fissures. Geophysical methods are commonly used to investigate. In this paper we present the preliminary results of a geoelectrical survey conducted at Barro Branco sub basin, São José do Ubá county. We collected geoelectrical data at 3 profiles. Data were processed and interpreted with a 1D inversion scheme. Two main aquifer system were identified: sedimentary and cristalline.
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Prospecção de água subterrânea no Novo Repartimemto-Pa aplicando métodos elétricos e eletromagnéticos
Authors Lair da silva Freitas Filho and Om Prakash VermaThis geophysical study was carried out in the municipility of Novo Repatimento,localized in SW of the Pará state, with the objetive to detect fracture zones in the Pre-Cambrian basement to exploit groundwater. For this purpose were employed Vertical Eletrical Soundings (VES), Radial Soundings (RVES), Eletrical profiling, Very Low Frequency EM(VLF) and Horizontal Loop Eletromagnetic (HLEM) methods. Two types of aquifers were identified as a result of this study. (1) the fracture zones in the crystaline basement and, (2) the unconfined aquifer in the overbunden sediments. This unconfined aquifer is very limited in groundwater resounces due to its limited thickness, generally less than 4m. The fracture directions in the crystalline basement were inicially determined by RSEV and subsequently the condutor axes were localized by the HLEM profilings. Three of these HLEM profililes were run by VLF and eletric profilings. Eight conductor axes are identified which are probabely related to the fracture zones.The fracture zones are potentially a good groundwater supplier zones in this geological context.
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Aeromagnetic and Magnetotelluric Studies in Guaribas Region of Parnaiba Basin in North East Brazil for Groundwater Assessment
Authors E. Chandrasekhar, Mita Rajaram, S.P. Anand, Sergio L. Fontes and Jean Marie FlexorAeromagnetic and Magnetotelluric (MT) surveys have been conducted over the intra cratonic sedimentary Parnaiba basin located in the semi-arid northeastern part of Brazil for sub-surface structural mapping and ground water resource investigation. From aeromagnetic data several faults in the sub-surface have been identified that are conducive to be potential groundwater resource regions. Broad band (0.001sec – 1000sec) MT soundings along a profile within the area surveyed aeromagnetically, mapped two localized high conductivity zones (of resistivities <10 Ω-m) representing sedimentary aquifer zones. These zones lie close to the faults identified from the aeromagnetic survey whose top lies at depth of 150m.
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Sprites and the influence of the atmospheric density on their initiation mechanism
More LessSprites are transient optical signatures of mesospheric electrical breakdown in response to lightning discharges. Multiple sprites are often observed to occur simultaneously, laterally displaced from the underlying causative cloud-to-ground (CG) lightning discharge. The causes of this lateral displacement are presently not understood. We investigated the role of neutral density perturbations in determining the locations of sprite initiation by performing Computer simulations of the temporal-spatial evolution of lightning-induced electric fields in a turbulent upper atmosphere were performed. The modeled turbulence in the simulations spanned the amplitude range 10% to 40% of the ambient background neutral density, with characteristic scale sizes of 2 km and 5 km, respectively. The results indicate that neutral density spatial structure, similar to observed turbulence in the mesosphere, facilitates electrical breakdown in isolated regions of density depletions at sprite initiation altitudes. These spatially distributed breakdown regions provide the seed electrons necessary for sprite generation, and may account for the observed sprite offsets.
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2.5 - D Finite Element Algorithm for MCSEM Modeling
By Luiz RijoRecently a new and very important geophysical method for detection of oil-filled reservoir in deep-water areas has been introducing in the petroleum industry. The method, called Marine Controlled Source Electromagnetic (MCSEM), also known as Sea Bed Logging (SBL), maps the contrast between the electrical resistivity of an oilfilled reservoir and that of the sedimentary host strata. Usually the resistivity of the former is greater than that of the latter. The MCSEM method is based on the diffusion of electromagnetic energy at low frequency generated by a mobile horizontal electrical dipole and detected by an array of receivers distributed on seafloor. In this paper we present a finite element algorithm for 2.5-D MCSEM modeling. The performance of the algorithm is illustrated by means of some selected examples.
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Constrained 1-D inversion of MCSEM data on resistive oil reservoir
Authors Luiz Rijo and Frayzer L. AlmeidaRecently a new and very important geophysical method for detection of oil-filled layers in deep-water areas has been introduced to the petroleum industry. The method, called Marine Controlled Source Electromagnetic (MCSEM) maps the contrast of electrical resistivity between the reservoir and the host sedimentary layers. Usually the resistivity of the former is greater than that of the latter. The method is based on the diffusion of electromagnetic energy at low frequency generated by a mobile horizontal electrical dipole and detected by an array of receivers distributed on seafloor. In this paper an efficient algorithm is proposed for inversion of 1-D MCSEM in-line electrical field data. The bathymetry and the seawater resistivity, usually knowing a priori, are used as constrains for regularization of the algorithm. The efficiency of the algorithm was tested with three models with good results. The resolution of the inversion scheme improves greatly if one uses normalized data. The information of the background resistivity distribution for the normalization process can be obtained via well logging or through MMT surveys.
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High resolution geophysical survey performed at submarine slope area in Jubarte Field, Espírito Santo Basin
Authors Glória S. Cezar, Paola O. Pellizzari and Mário Ricardo CwikThe article presents partial result of high resolution geophysical survey, performed to provide information to support the design of marine installations, by the Engineering group of Petrobras.
The study area is located in Jubarte Field, Espírito Santo Basin and the survey comprised the acquisition of bathymetric data, sub-bottom profile (SBP) and sonar data. CTD’s profile were also performed in order to obtain sound velocity propagation in sea water and thus correct the depth values obtained from bathymetry. Only the sonar and SBP data will be discussed in this article.
The acquired data was processed and interpreted. The result consists of a map of submarine local features. The main features identified are presented in this article. A better characterization of the sea bottom features and sediments will be completed after the acquisition of sediments samples, which will be performed in a next phase of the survey.
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Caracterização dos Processos Sedimentares no cânion Almirante Câmara, Bacia de Campos
More LessThe Almirante Câmara canyon was first identify by Brehme (1984) and this is located on the slope at the northeast of the Campos Basin. This paper is a study of the main sedimentary processes identified on the Almirante Câmara canyon to contribute for a better understanding of its mechanisms of formation. The metodology apllied in the study of the canyon was: analysis of the local bathymetry, analysis of the 24 seismic profiles and correlations with the papers of Viana (1998) and the Site 515 of the Deep-Sea Drilling Project (DSDP). In this were identified five seismic units on the Campos slope. A major erosional unconformity was identified at the upper Mioceno, recognized as the Grey Marker of the basin.
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MAJOR TECTONIC FEATURES IN THE SOUTHEASTERN BRAZILIAN MARGIN
Authors Mohriak U. Webster and Paula B. OsniA regional geophysical and geological dataset has been integrated to analyse the major tectonic elements along the southeastern Brazilian margin, from the Espírito Santo towards the Santos basins, the most prolific oil provinces offshore Brazil. The diverse tectono-sedimentary domains identified along the continental margin are related to the Mesozoic-Cenozoic tectonic reactivations, particularly the syn-rift extensional processes associated with the separation of the West African and South American plates in the Late Jurassic – Early Cretaceous. These processes are responsible for synthetic and antithetic normal faults that formed half-grabens and grabens within the mainland and offshore, which were filled by continental volcanics and siliciclastic rocks in the Neocomian - Barremian. Subsequent to this syn-rift phase, the transitional phase (Aptian age) is associated with siliciclastic and carbonate sediments deposited above a regional unconformity (breakup unconformity) that heralds the continental drift phase and forms a sag basin that underlies the Aptian evaporites. The regionally extensive, thick evaporite layers that occur both along the Eastern Brazilian and West African margins suggest the occurrence of an elongated and shallow gulf that was periodically invaded by sea waters during the first marine ingressions of the nascent Atlantic Ocean. The presence of a highly mobile evaporite layer resulted in the development of a characteristic tectonic style marked by salt diapirs and salt walls associated with extensional and compressional structures. The outermost boundary of the salt layers seem to correlate with the feather edge of seaward-dipping reflectors that correspond to volcanic wedges formed during the inception of oceanic crust, which is related to propagators that advanced northwards by rupturing the crust and upper mantle. Several major tectonic features are associated with syn-rift and post-rift magmatic episodes, particularly in the southern Santos Basin (Florianópolis platform), in the northern Santos and southern Campos basins (Cabo Frio region), and in the Abrolhos region of the Espirito Santo Basin.
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Morfologia da calha principal do estuário Curimataú/RN, Nordeste, Brasil
O estuário do rio Curimataú é o mais proeminente da porção sul do litoral oriental do Rio Grande do Norte. Em suas margens se dá o desenvolvimento de importantes atividades econômicas como a carcinicultura e a indústria canavieira. A batimetria é uma das ferramentas básicas para compreensão de muitos processos estuarinos. Objetivando analisar a geometria e a morfologia da calha principal do estuário Curimataú, foram realizados perfis batimétricos longitudinais e tranversais à calha. A eco-sonda utilizada foi a da marca Odom modelo Hydrotrac, operando na freqüência de 200 kHz. A geração do Modelo Digital Batimétrico (MDB) foi obtida através de interpolação pelo método de krigagem. A malha de pontos interpolados ainda sofreu prévia correção da variação de maré. Com o fim de realçar a morfologia da calha do estuário produziram-se blocos-diagramas permitindo assim a compartimentação geomorfológica a partir do MDB gerado. A calha principal do estuário Curimataú possui largura entre 250 m e 500 m e profundidade média de 7 m. As principais morfologias encontradas consistiram em bancos, barras, canais de marés e franjas.
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Behavior of Martim Vaz Fracture Zone, from Mid Atlantic Ridge to Brazilian Coast
Authors Eliane da Costa Alves, Marcia Maia and Susanna Eleonora SichelMartim Vaz Fracture Zone (MVFZ), located at 20°10'S in the Mid-Atlantic Ridge (MAR), was defined by seismic register, gravity and magnetic isochrones. Today, this FZ show a second-order discontinuity, with offset 15 km corresponding to 1 My. However, in both sides of MAR, the MVFZ, two fossils FZ can be observed. If these fossils FZs were part of MVFZ, then MV was a double FZ during 5-20 My, and triple FZ between 20-80 My, with a width of 130km. Prior this time the tectonic network seemed to be more complex. The MVFZ was tectonic active, observed in seismic data set, with reactivations of old faults, strikeslip tectonics which has up lift the sedimentary column (Medium Oligocene), and beyond structure related the lithospheric flexure. All of these observation attested by a rich fractured oceanic crust and the overlaying sedimentation, with alternations of comprehensive and distensile stress associated with volcanism and normal faulting. Geological and geophysical studies, in addition earthquake epicenters, suggest that the continuation of ZFMV is related to the Cabo Frio High and to the tectonic and volcanic activity, which is express by the Poços de Caldas / Cabo Frio / Montes Submarinos Almirante Saldanha e São Tomé Alkalic Magmatic Seismic Lineament. All these observation let us to believe that MVFZ acts as a path way for the magma generated in the Tristão da Cunha Mantle Plume.
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Fatores condicionantes do arcabouço estrutural da tectônica gravitacional do Cone do Amazonas
More LessThe Amazon Cone, part of the Amazon Mouth Basin, is intensely affected by gravity-driven tectonics. In this work, approximately 9000 km of multichannel seismic reflection lines were analysed, which enabled us to create a structural map, as well as a map of the the morphology of detachment surface and isopach of Neomiocen–Recen sedimentary covert. Three main structural domains were identified in the region: a proximal extensive domain, which extends since the edge of the shelf to the depth of 500 m, an intermediate domain that translate in a rigid way and a contractional domain which covers an area of approximately 1000 m to 1500 m in depth. The extensive domain is characterised as having synthetic listric faults and rollovers. On the other hand, the contractional domain is characterised as having thrust faults. The Amazon Cone thin-skinned extension system, whose detachment surface is located at the base of the Neomiocene sequence, is divided in two main compartments, which are: the South-eastern
Compartment and the North-western Compartment. The South-eastern Compartment is characterised as a narrow gravitational system (115 km wide), geographically limited to the continental slope and its extension can reach up to 1500 m in depth. However, the North-western Compartment is characterised as a wider gravitational system (152 km wide), which reaches up to 2500 m in depth. The morphology of the surface detachment (base of the shale layer under pressure) seems to represent an important role in the development of the structural framework of the area. Extensional faults are located in the region of higher gradient of the detachment surface, while the thrust faults are in the region of lower gradient. The mechanism of differential sedimentary overload is another important factor of development of the structural framework in the region, because the extensive structures are located in the thickest part of the depocentres and the thrust faults are located on the boarders of the depocentres.
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Arquitetura sedimentar dos principais depocentros da seqüência pliocênica da Margem Catalano-Languedociana, Golfo de Lion, Mediterrâneo Ocidental
More LessOur study aims to assess the role of salt tectonics on the architecture of Pliocene sequence of the Catalano- Languedocian margin. The study is based on seismic and chronostratigraphic interpretation of multichannel seismic profiling and boreholes. Sediment thickness distribution illustrated by an isopach map reveals at how salt deformation has influenced the development of the identified depocenters. Subsidence of the Pliocene cover into the salt evacuation horizon and diapirisms are the mechanisms of salt tectonics that influenced the sedimentary architecture of the Pliocene sequence along the Catalano-Languedocian margin. The abrupt thickening of the Pliocene series along the present-day - 2200 isobath reflects the influence of the subsidence mechanism in creating depocenters in this region. In the south portion of the deep margin, halocknetic deformations create local accommodation space between salt pillows, with implications on the organization of the turbidite deposition in the area. Seismic facies analysis shows no evidence of canyons activity along the proximal Catalano-Languedocian margin during the Pliocene. Facies analysis suggests, on the other hand, that the source of siliciclastic input to the adjacent margin comes from the rhodanian canyons (Marti and Petit-Rhône Canyons), located to the east, on the Rhodanian margin.
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Análise da propagação das ondas compressionais (P) em sedimentos marinhos e sua aplicação na caracterização das propriedades acústicas do ambiente
The physical properties of marine sediments have been systematically acquired and studied in various parts of the world. However, several theories have proved that sedimentological parameters such as grain size, bulk density, porosity and water content cause relevant dispersion in models of measuring wave propagation. The aim of this study is the investigation of the relationship between a relative broad spectrum of these physical properties and geoacustic parameters. Two different physical properties have been investigated: velocity and the attenuation of compressional waves. An apparatus was constructed to measure these physical properties using ultrasonic waves (2,25 MHz). Some experiments have demonstrated good results with this approach in terms of resolution and penetration rate. The first laboratory results were performed in cores collected on the continental shelf offshore the city of Arraial do Cabo, in Rio de Janeiro state. The preliminary experiments indicate that fine-grain sediments display distinguishable properties in terms of acoustic wave speed. More measures are being done in those cores. The propagation and dispersion will be also compared with extensive data sets taken from literature. The results obtained are encouraging and indicate a feasible method to analyze the relationships between compressional wave propagation and sedimentological parameters.
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Qualitative Slope Stability Evaluation for a Pipeline Route Off Espirito Santo State, SE Brazil
Authors P.O. Pellizzari, P.O. Pellizzari, A. Ayres, C.G. Gallea, C. Gallea, G.X.O. Castańos, G. Castańos and P.O.V. PiauilinoIn order to select a pipeline route a geophysical, geological and geotechnical survey has been conducted at the continental slope off Espirito Santo state. The survey comprised an area of approximately 470 km² between the 60 m and 1.380 m isobath with a total of more than 5.700 km of geophysical data and 70 geological and geotechnical piston-cores. An integrated interpretation of the data showed the presence of several obstacles that should be avoided allowing the selection of an optimal route to the planned 12” export gas pipeline determining areas associated to erosional and depositional events. Moreover, a qualitative stability analysis showed that the area is stable under the actual geological conditions and that the instability features observed were generated during the pleistocene when the area was dominated by a shelf-edge delta associated to the Doce river.
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NW-trending lineaments across Brazilian margin: a discussion upon their origin and implications for the Albian-Maastrichtian paleobiogeography and paleoecology of the South Atlantic
Authors Claudio Lima and Dimas Dias-BritoSince the eighties, several groups of NW-trending lineaments running from the coast up to the Mid Ocean Ridge have been recognized across the South Atlantic Brazilian margin from analyses of gravity SEASAT data (Bostrom, 1989). The direction of sea floor spreading has remained remarkably constant around a ENE-trending since 84 m.y B.P. (Nurnberg & Muller, 1991; Mello & Dias, 1996). Therefore, at least for the time elapsed between the Upper Cretaceous and the Present, these features can not be straightly attributed to the divergence between South America and Africa plate since they show remarkable cross cutting relation with the EW- trending fractures zones. In this paper we briefly discuss some ideas concerning the origin of such features and some implications for the Upper Cretaceous paleobiogeography and paleoecology of the South Atlantic.
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Bacia Dove [Mar de Scotia – Antártica]. Processamento e Interpretação de Novos Dados de Sísmica 2D.
The structure of the transcurrent limit between the Scotia and Antarctica plates, and the development of small oceanic basins along the South Scotia Ridge is poorly known. New 2D reflection seismic data from the Dove Basin in the southeastern portion of the Scotia Sea, acquired during SCAN 2004 cruise, has being processed and interpreted. A preliminary interpretation suggests that the tectonic development of the Dove basin agrees with the others small oceanic basin near round and show particular asymmetric development of the spreading axis, indicating a complex setting of stress, displacement and rotation of the continental blocks.
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ASSOCIAÇÃO ENTRE A ANÁLISE PALEOAMBIENTAL DA FORMAÇÃO MACACU, GRÁBEN DA GUANABARA (RJ), E A SEDIMENTAÇÃO CENOZÓICA NA MARGEM CONTINENTAL ADJACENTE (PARTE NOTE DA BACIA DE SANTOS)
Authors Fábio de O. Costa and André L. FerrariThis paper aims to analyze the relationship between Paleogene offshore sedimentation from Macacu Basin (Guanabara Graben, RJ - Brazil) and the intense synchronous progradation at offshore Santos Basin. Guanabara Graben system is divided in three main environments: distal alluvial fan (facies association I); debris flow influenced braided river (facies association II); and braided river with episodic over flow (facies association III) in the axial of this system. The analyze of ten multichannel 2D seismic section (6 dip, 4 strike) from contiguous continental margin at the southwester-most Macacu Basin edge shows the development of three depositonal sequences since Paloegene. The second sequence is characterized by an oblique progradational prism near the continental border related to the onshore graben. This correlation is supported by paleocurrent data from faices association III.
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Seaward dipping reflectors na Margem Continental Brasileira
More LessThis study displays the occurrence of seaward dipping reflectors (SDRs) along the Brazilian Continental Margin, which were probably formed during the initiation of the margin. It is based on the interpretation of multichannel seismic lines collected during the Leplac Project, developed to establish the limits of the Brazilian Extended Legal Continental Shelf. The occurrence of the SDRs is quite extensive along the southern Brazilian Margin from Pelotas to Espírito Santo basins. But, apparently, the SDRs are not related to the oceanic-continental crust boundary at the Brazilian Margin, since earlier studies locate this boundary to the west of the SDRs.
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Sidney Luiz de Matos Mello e Cleverson Guizan Silva
Authors Maitê F. de Medeiros, Gilberto T. M. Dias and Marcelo SperleIlha Grande bay is located in the southern coast of Rio de Janeiro state, Brazil, and is characterized by a rocky coast with numerous islands, being Ilha Grande the main one with 193km2 of area. This region represents nowadays an important and strategic economic area both because of its touristic attractive and its position in the oil and gas scenario because of its proximity of the Santos Basin. In this work the west portion on the Ilha Grande Bay was priorized. The mean depth in this area is 20m with shallower areas occurring inside small bays and enseadas. Baía da Ribeira and Enseada de Parati, for example, show depths of less than 10m. A recent shallow seismic survey has been made in the area, with the acquisition of over 130km of high resolution seismic data in the frequency of 10 kHz, totalizing 6 profiles. The goal of this paper is to present the preliminary results of a project that has as the main objective the study of the holocenic sedimentary evolution of this area.
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Space-Time Evolution of the Marine Depocenters at the Pelotas Basin, Southern Brazilian Continental Margin
Authors Thiago B. S. Corrêa, Cleverson G. Silva and A. T. dos ReisThis study aims to investigate space and time evolution of the marine sequences at the Pelotas basin - southern Brazilian margin, based on interpretation of about 10.000 Km of multichannel seismic lines. This work was based on the association of depth to basement map and a series of isopach maps of marine sequences (Lower Cretaceous -Recent). It revealed that the sedimentary distribution pattern changed radically from the Lower Cretaceous to the Oligocene. Through time the main depocenters shifted seawards and backwards again under the influence of a series of processes. The configuration of depocenters was primarily conditioned by basement topographic features, while depocenter segmentation occurred under the influence of dynamic processes.
Since the end of the Oligocene a high sedimentary accumulation rate took place, giving rise to the onset of the Rio Grande Cone. This depos ition feature corresponds to the main depocenter at the south Brazilian Margin and its evolution is not related only to thermal-mechanical but also to dynamic processes such as bottom currents.
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Analysis of seafloor depth anomalies arround the south Ascension Island, South Atlantic
Authors Marisa Makler and Sidney L. M. MelloObserved seafloor depths from 12 kHz bathymetry coupled with seafloor spreading magnetic anomalies are used to derive depth anomalies across the Mid-Atlantic ridge axis between 2oS and 18oS. Theoretical seafloor depths are based on the plate cooling model and crustal ages depicted from magnetic anomalies between the zero age to 25 Ma. The magnetic anomalies are symmetric with respect to the ridge axis in the region, but the depth anomalies are quite asymmetric. The east side of the ridge axis is shallower (~ 1,000 meters) than the west side, probably as a result of an upwelling of thermal structure of the lithosphere. This type of thermal anomaly may be caused by a mantle plume located on the African Plate, which could well represent a larger swell linked to St. Helena Island and Fernando Pó-Annobon Volcanic Lineament as well.
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Radial gliding evinced by subsalt relief and salt-related structures: the example of the Gulf of Lions, Western Mediterranean
Authors A.T. Reis, C. Gorini, A. Mauffret, W.W. Weibul, M. Mepen and Di Lello M. and Stratievsky C.The young Messinian salt offshore the Gulf of Lions is a shallow décollement layer that permits direct correlation of gravity-driven structures with those predicted by analogue models. Sub-salt relief is cleary depicted by high resolution seismic data. Subsalt relief and salt isopach maps indicate the occurrence of radial gliding at the scale of the entire Gulf of Lions. This pattern of gravity gliding is also indicated by the occurrence of salt-related structures of smaller scale (families of transverse faults). Transverse faults strike parallel to the regional dip direction, indicating strike-parallel extension. As well as that, our results also permit correlation between categories of residual subsalt relief (local irregularities) and rooting of faults along with, depending on their directions, there has been either strike-slip mouvement or weld-parallel slip.
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Taxa de produção do calor radiogênico do embasamento cristalino das bacias de Camamu e Almada
More LessThe crystalline bedrock of the Camamu and Almada basins is characterized preferentially by metamorphic rocks of granulites facies and amphibolite, with archean and paleoproterozoics ages. The main litho logic units of this context are: (i) the metatonalites associates to basic granulites and metamonzonites; (ii) the granite of Teolândia and the granodiorite of Moenda associated with amphibolites;e (iii) the mafic dikes and the neoproterozoics sienites. Among these rocks, the metamonzonites, the granite of Teolândia, the granodiorite of Moenda and the sienitos are those ones that present greaters values of radiogenic heat volumetric production rates; the metatonalites present intermediate values and the basic granulites very low values. For the Camamu basin, the metatonalites are the rocks that probably more contribute for the radiogenic heat production rate in the area. Already for the Almada basin, the contribution includes also the neoproterozoics sienites.
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Estudo acerca das variações sazonais da condutividade térmica
More LessThe conductivity study was monitored in the period of un year. In order to do that, the measurements were performed on samples collected monthly, at 5,0cm depth. The selected site is representative of sandy. The moisture content of the collected samples changed significantly, that may be attributed to the seasonal variation of the local pluviometric precipitation. The thermal conductivities of the sandy samples varied from 0,12 to 2,38 W/m.oC, with an average value of 0,78 ± 0,57 W/m.oC. The variability observed from the above results indicates that the thermal conductivity values of materials existing in the aeration zone were significantly altered by physical variables. The thermal conductivity changes significantly between its extreme values, measured on field samples at natural conditions. The precautions should be taken when uses thermal conductivity values, for estimates in shallow geothermics.
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Gradiente e Fluxo Geotérmico do Estado de Santa Catarina
Authors Antonio Jorge de Lima Gomes and Valiya M. HamzaEste trabalho apresenta uma análise quantitativa de dados geotérmicos de 49 localidades do Estado de Santa Catarina distribuídos em 34 municípios. Os resultados obtidos indicam que a maior parte do Estado é caracterizada por gradientes geotérmicos no intervalo de 26 a 400C/km sendo que o valor médio é de 32 ± 8,6 ºC/km. Foram efetuadas medições de condutividade térmica em 19 amostras de rochas da Serra da Cambirela, Pântano do Sul e Ilha de Santa Catarina e uma reavaliação dos dados de condutividade térmica já existentes. As formações sedimentares de Estrada Nova, Serra Alta e Tatuí apresentaram valores de condutividade térmica relativamente baixa (menor que 2 W/m.K). Os valores mais altos (maior que 3,5 W/m.K) foram encontrados em amostras de arenitos da formação Botucatu e de rochas do embasamento (metamórficas e granitos porfíriticos da Serra da Cambirela). As demais formações sedimentares da bacia do Paraná apresentarem valores intermediários. As estimativas de fluxo geotérmico se encontram na faixa de 50 a 95 mW/m2 com valor médio de 75 ± 15 mW/m2. A elaboração de mapas geotermais permitiu avaliações de gradiente e de fluxo geotérmico em escala regional. Os mapas indicam fluxo geotérmico relativamente baixo (na faixa de 50 a 80mW/m2) na parte oeste do Estado. Contudo, a presença de aqüíferos confinados de grande porte, em profundidades entre 500 e 3000 metros, permite que várias regiões desta parte do Estado contenham recursos de energia geotérmica de baixa entalpia, passíveis de explotação econômica. Por outro lado, há indícios da existência de uma região de fluxo geotérmico elevado (valores superiores a 80 mW/m2) na parte leste, que compreende os municípios situados entre Gravatal, Águas Mornas e Caldas da Imperatriz. As características geológicas estruturais e ocorrências das fontes termais apontam para a existência de reservatórios geotermais também nesta região. Contudo, aquisição de dados de perfurações com profundidades maiores que mil metros são necessários para determinar a natureza de circulação hidrotermal e avaliação de potencial geotérmico das camadas profundas.
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Gradientes Geotérmicos nas Bacias Tafrogênicas da Região Sudeste
Authors Iran Ferreira Rodrigues and Valiya M. HamzaResultados de estudos geotérmicos realizados a partir da década de 1970 foram utilizados numa avaliação detalhada dos gradientes geotérmicos das bacias tafrogênicas da região sudeste do Brasil. O estágio atual da compilação engloba medidas experimentais em 28 locais distribuídos em 15 municípios. Os gradientes térmicos ficaram distribuídos no intervalo compreendido entre 16 a 57 ºC/km com valores médios de 23 ± 2,1 ºC/km para a bacia de Taubaté, de 20 ± 1,2 ºC/km para a bacia de São Paulo e de 38 ± 2,6 ºC/km para Resende. Esta faixa é típica de áreas continentais, tectonicamente estáveis. Contudo, foram encontradas áreas com gradientes térmicos acima de 35 ºC/km ao longo da borda norte, na parte central da bacia Taubaté, na região próxima de Jacareí e também na Bacia de Resende.
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Um critério para escolha da direção de linhas de vôo em aeromagnetometria no Brasil
More LessO presente trabalho visa estabelecer um critério para a escolha da direção de linhas de vôo em baixas latitudes magnéticas (como as do Brasil). Parte-se do princípio que, considerando apenas a componente induzida do campo, as anomalias alinham-se
paralelamente à declinação magnética. Desta forma, aplicamos o critério em simulações com linhas paralelas e perpendiculares à direção da declinação magnética, respectivamente as supostas melhores e piores direções de vôo possíveis, e comparamos os
resultados. Conclui-se que para o método magnetométrico, segundo os critérios adotados, a escolha pela direção de linhas de vôo paralelas à declinação magnética é significantemente melhor do que a escolha de linhas de vôo com direção perpendicular à declinação magnética.
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On the use of geothermal data for climate studies: a case study from Portugal
Authors António Correia and Jan SafandaPortugal using geothermal data has started in 1996. Reconstruction of ground surface temperature (GST) history from temperature logs measured in a 200 m deep borehole (TGQC-1), located near the town of Evora in Portugal, indicates warming of 1K since the second half of the nineteenth century to the middle of the 90s of the twentieth century, increasing considerably in the last 10 years. Results of the reconstruction (based on the functional space inversion (FSI) method) are compared with air temperatures recorded at the Lisbon meteorological station since 1856. The series display a warming trend with the amplitude about 1K for the same period. The coupling of the air and ground temperature changes and their downward propagation by heat conduction was confirmed by repeated logging in November 2003, 6.7 years after obtaining the first temperature log.
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A Reappraisal of Global Heat Flow Data
More Lessin an attempt to understand the characteristic features of global thermal field. The initial effort was directed at verifying the overall structure, quality and internal consistency of the database. Thus the present system of intercalating tables and references was transformed into a coherent and organized database that is amenable for scientific analysis. Subsequently, the format employed for geographic coordinates has been replaced by a consistent decimal degree system that allows implementation of automatic computer based processing facilities. At present, a detailed verification of the entire data set is being carried out to minimize problems arising from typographic errors.
The restructured database has been used in calculating mean values of heat flow for a regular grid system composed of 50 x 50 surface area elements. Spherical harmonic analysis of this system of regular grid values have allowed calculation of a new set of fully normalized Legendre coefficients (169 coefficients for a 12 degree expansion). Maps based on the new set of coefficients have lead to identification of several new features in the conductive component of global heat flow. Comparison with results of previous studies indicates discrepancies in several regions. There are indications that some of the major high heat flow anomalies identified in previous studies are artifacts of interpolation procedures. The reason appears to be widespread use of synthetic values instead of experimental data.
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Evolução Termotectônica da Parte Oeste da Bacia de Campos
Authors Roberta A. Cardoso and Valiya M. HamzaApresenta-se neste trabalho resultados de estudos sobre a evolução termotectônica da parte oeste da Bacia de Campos, na região Sudeste. Na primeira etapa deste estudo os dados de temperatura do fundo do mar e de temperaturas de poços de exploração foram utilizados na determinação do campo térmico atual da bacia, em 97 localidades. Na segunda etapa os perfis litológicos de seis poços e as idades das principais formações geológicas foram utilizados na reconstrução das seqüências evolutivas da bacia (subsidência tectônica) desde a sua formação, há 130 Ma. A elaboração das curvas de subsidência termal foi efetuada com base no procedimento conhecido como “backstripping”, no qual foi incorporado o processo de descompactação seqüencial dos sedimentos. Os resultados desta etapa foram ajustados aos modelos térmicos de subsidência, permitindo a determinação das condições paleotermais e o grau de estiramento da litosfera local. Há indícios de que a evolução da bacia ocorreu em duas fases distintas: a primeira entre 130 a 68 Ma e a segunda entre 68 Ma e o presente. Os graus de estiramento da litosfera variam de 1,4 a 1.9 para o primeiro estágio de subsidência e de 1,2 a 1,5 para o segundo estágio. Os resultados indicam fluxo térmico na faixa de 75 a 95mW/m2 no primeiro estágio, que é cerca de 30 a 50% superior aos valores atuais. As variações no fluxo geotérmico foram menos significativas no segundo estágio. Contudo, as avaliações da maturação térmica indicam que a geração de petróleo e gás ocorreu na fase final do segundo estágio, como conseqüência de soterramentos progressivos maiores.
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Um exemplo da utilização de gradiente transversal medido no aumento da resolução de imagens aeromagnéticas em baixas latitudes magnéticas
More LessThe present work was designed to evaluate if it is possible to observe an increase on the resolution of airborne magnetometry images when using measured lateral gradient during interpolation of total magnetic field data. Images were enhanced using pseudo-line method. The used sample dataset was collected at low magnetic latitudes, specifically in the Brazilian territory. The result for the specific dataset was clear, the enhanced image has a resolution much superior than the original image. Furthermore, its resolution can be compared with a resolution of a single sensor survey with half of line spacing of the original gradiometer survey.
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Análisis térmico de la Cuenca Oriental de Venezuela a partir de información de pozos
More LessThe Guárico Sub-basin, located within the Eastern Venezuelan Basin, forms an important region for oil exploitation, with an important number of oil producing wells and significant gas reserves. The geochemical well data and bore hole temperature values clearly shows an anomalous thermic behaviour in the northern region of the Guárico Sub-basin, represented by a high heat follow zone. The well selection and the quality control of their temperature data, allowed the elaboration of a series of thermal sections across the northern zone of the Subbasin where the data is concentrated. With these profiles it is possible to identify high temperature characteristics in the thick layer of the Miocene sediments and elaborate a series of heat flow maps corresponding to different geologic times. With these maps, a high heat flow has been recognized in the northern region of the Eastern Basin, with values between 60 and 75 mW/m2. The high temperature gradients to the north of the Guárico Subbasin and in the proximities of the Maturín Sub-basin are associated to Miocene sediments located between 2000 and 3500 meters depth. This high temperature gradient may be caused locally by the adiabatic compression of gases due to the compressive process associated with the Guárico Deformation Front. The regional cause of the high heat flow values in north-western Venezuela may be related to the subduction of the Caribbean Plate under the South American Plate. Under subduction melted material forms an asthenospheric wedge that erodes thermally the base of the Southamerican lithosphere producing a temperature high in the northwest and northcentral areas of Venezuela.
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Modelo de Circulação Hidrotermal em Meios Fraturados: Aplicação para Estudo do Intercâmbio Térmico das Áreas Geotermais
Authors Carlos H. Alexandrino and Valiya M. HamzaIn the present work we consider a simple semi-analytic model of heat transfer in fluid flow through subsurface conduits with impermeable walls as a means of investigating the temperature fields in geothermal areas. Results of numerical simulations based on finite difference methods are compared with results of generalized integral transform methods. The model is sufficiently flexible allowing determination of temperatures along the conduits in recharge and discharge zones as well as the intermediate zone of hydrothermal reservoirs. The success of the model however depends on the availability of complementary information on the structural and hydrogeological characteristics of the geothermal area. A number of tests were carried out for evaluating the effects of critical parameters such as temperature gradient, flow rate, dip angle of the fault zone and depth of the aquifer. As an example of application the model was employed for calculating the temperature field in the geothermal area of Cachoeira Dourada (GO). The model is also potentially useful in investigating paleothermal conditions of hydrothermal ore deposits.
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Gradiometria fluxgate no sítio Guarani Piracanjuba, Piraju-SP
We present fluxgate gradiometric maps obtained at the Piracanjuba archaeological site. Our geophysical study allowed the identification of an ancient fire hearth place that was important to site understanding and coal sampling for C14 dating.
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