- Home
- Conferences
- Conference Proceedings
- Conferences
10th International Congress of the Brazilian Geophysical Society
- Conference date: 19 Nov 2007 - 23 Nov 2007
- Location: Rio de Janeiro, Brazil
- Published: 19 November 2007
101 - 150 of 484 results
-
-
O estudo de interferências e estruturas geológicas em subsuperfície através do Radar de Penetração no Solo (GPR), no município de Rio Claro – SP
Authors André Felipe Gonçalves De Mario and João Carlos DouradoEste estudo foi realizado no Município de Rio Claro-SP durante o ano de 2006, com o objetivo de estudar interferências e estruturas geológicas em subsuperfície através do método “GPR”. Para a realização deste estudo foram escolhidas duas localidades distintas, sendo que uma apresentava situação propicia para o estudo de interferências em subsuperfície (canos, dutos, túneis) e outra possuía rochas basálticas próximas à superfície (profundidade de até 5 metros), sendo assim possível estudar como estes
corpos estão em subsuperfície.
-
-
-
Uso do GPR para a localização de sítios arqueológicos no Uruguai
Authors Ariovaldo da Costa, Amilson Rodrigues and Carlos A. CostaTwo GPR (Ground Penetrating Radar) surveys were acquired in Colonia del Sacramento y Montevideo, Uruguay, aimed at the identification of archeological sites. After data processing, it was possible to identify various subsurface anomalies related to
ancient ruins corresponding to the Spanish colonialism time.
-
-
-
A UHF step frequency GPR for the ESA EXOMARS mission
The WISDOM (Water Ice and Subsurface Deposit Observations on Mars) Ground Penetrating Radar has been selected in accordance with the primary objectives of the PASTEUR payload of the EXOMARS exobiology mission. The investigation of the nature of
the Martian subsurface by orbital instruments (MARSIS and SHARAD HF radar sounders) concerns large areas at substantial depths. In contrast WISDOM will be used to probe the first meters of the shallow underground. This paper presents the operational mode as well as the instrument design and some simulation and measurements results.
-
-
-
The long range HF mono and bi-static GPR TAPIR story
An impulse polarimetric monostatic HF Ground Penetrating Radar (GPR) has been developed in the frame of the NetLander mission in order to investigate the geological features of the Martian subsurface and search for potential water reservoirs. Then to improve the performances, the instrument has been upgraded to be able to operate either in a moncstatic mode or a bistatic mode. The concept, operation modes and performances of the radar are presented as well as some results from field campaigns.
-
-
-
Imageamento com GPR de análogos de reservatórios de hidrocarbonetos da fase prérifte da Bacia do Recôncavo, Brasil
Authors Moisés Vieira Pinto and Marco Antônio Barsottelli BotelhoThis work focuses the GPR application to stratigrafic geology, since the GPR can gives excellent detail about internal structure of a resistive rock. The hidrocarbon reservoir analogous rocks usually are electrically resistive sandstones which allows the GPR obtain excellent radargrams with high ratio signal/noise and low attenuation. So, the GPR can give precious information about the structural and stratigrafic pattern of the sandstones bodies. This work presents the results of GPR surveys over sandstones outcrops of Boipeba Member, Agua Grande Formation, and Maracangalha Formation, both in pre-rift stratigraphy sequence of Recôncavo Basin, northeast of Brazil. The data acquisition over the outcrops was carried using 200 MHz antennas with constant offset configuration. The GPR data processing consisted of application of frequency filters, mute off, lateral cross-correlation, automatics and linear gains, deconvolution, and time migration. After the data processing, the obtained radargrams reveal internal structures of the studied outcrops. The obtained results, such as the sigmoid reflectors of Água Grande Formation and the cross-stratification of Aliança Formation (Boipeba Member) confirm the great applicability of the GPR method for imaging internal structures of sedimentary rocks analogous of hydrocarbons reservoirs.
-
-
-
1-D Analysis of EM Wave Velocity between two boreholes
More LessThis work presents preliminary results of borehole and surface GPR data. We analyzed cross-hole and level-run data. The resulting 1-D velocity model was compared with the CMP derived one in order to reveal the subsurface structure and variation in saturation. In spite of the differences between the surface and the borehole velocity estimates it appears that they may play a complimentary role.
-
-
-
Avaliação Sobre a Eficiência do Radar de Penetração no Solo (GPR) na Detecção de Dutos em Travessias de Rios
More LessThis work presents same results about the use of Ground Penetrating Radar (GPR) to locate buried tubes at areas where the tubes cross different rivers located on northeast of Brazil. The main objective was to verify the efficiency of the method to map ducts buried on areas where they cross rivers. To help this work , it is also used the Pipeline Current Mapper (PCM) to help define the real position of the tubes and helpping the interpretation of the radargrans, mainly at areas where the GPR does not get good results (shally areas). The radargrans presented here have good quality and the granulometric histograms from the soil where they were acquired reveals that the sands dominates over silt and clay.
-
-
-
Caracterização Tridimensional dos Depósitos Sedimentares da Restinga da Marambaia
Authors Maria C. Pessoa and Jandyr M. TravassosO presente trabalho apresenta resultados do levantamento de GPR 3-D realizado nos depósitos sedimentares do Quaternário que constituem a Restinga de Marambaia. As amostragens espaciais inline e cross-line são iguais, não havendo interpolação de perfis. As antenas foram mantidas na configuração fixed-offset, mantendo as antenas paralelas entre si e perpendiculares aos perfis GPR nas duas direções de medida, evitando-se assim a mistura de polarizações. A amostragem especial nas duas direções da mesma ordem de grandeza corrobora para imagemaneto de alta qualidade das estruturas sedimentares.
-
-
-
High–resolution radar mapping of the Cierva Peninsula
Authors Jandyr M. Travassos, Jorge E. Musa and Luis PecheThis work deals with the stratigraphy of the ice cover of the Cierva Point, Antarctic Peninsula. The topography is limited by gentle slope towards the South; a more abrupt one to the north and two abrupt rocks outcrops to the West and East. Twenty-five GPR profiles revealed the structure of the ice and bed topography.
-
-
-
Migração Reversa no Tempo por Diferenças Finitas (MRTDF) de Dados de GPR, Aplicada em Análogos de Rocha-Reservatório
Authors Gleide A. N. Dias, Paula F. da Rocha and Carlos E. M. FernandesA tertiary sediment deposit composed by a layered sequence of intermingled sands. silts and clays, about 10 m thick, was select as an analogue geologic model of a true oil/gas reservoir rock. The use of such analogues is an accepted approach to emulate the interior if an oil/gas deposit. GPR’s radargrams from split-spread set-us at the site surface, were then reprocessed to enhance data quality as detailed in the article. Stacking did not enhance the radargrams’ visual clearness whereas corrections with velocity values considered closer to the sub-soils’ reality offered the best response, exposing clearly not only the trough-like geometry of the deposit, but also the lateral faults that border it. The steps that had to be followed in applying the finite differencials came from an algorithm recently developed reversed time migration using finite differencials applied to GPR collected data from a reservoir rock analogue.
-
-
-
Utilização de imageamento de GPR 2D para adequação de malha de sondagem, com base na detecção de interferências em sub-superfície
Authors Vitor Pimenta and Fábio José MirandaA perfuração de sondagem para fins ambientais em áreas industriais requer um planejamento que considere possíveis interferências em sub-superfície. Em muitos casos essas interferências, tais como cabos elétricos, tubulações de transferência de produtos, água ou esgoto, não possuem as built, dificultando sua localização e consequentemente aumentando o risco das sondagens interceptarem as mesmas. O GPR (Ground Penetrating Radar), ferramenta muito utilizada atualmente para investigação rasa de
subsuperfície, possibilita, dentre sua vasta gama de aplicações, suporte para a locação de investigações diretas. O mapeamento de possíveis artefatos enterrados nos dados de GPR possibilita indicações das interferências subterrâneas, evitando que as perfurações interceptem interferências indesejadas em sub-superfície.
-
-
-
Atenuações do Signal GPR 3D Aplicadas a Identificação de Solo Contaminado por Hidrocarbonetos - Estudo de Caso
This paper presents the results of an electromagnetic GPR method application to identify low reflectivity zones associated to hydrocarbon soil contaminations. The survey was performed around diesel tank areas placed over weathered granite zones six meters thick. These areas show a strong attenuation for the GPR signal which are correlated to the gas measurement anomaly in the Photon Ionization Detector – PID – as well as hydrocarbon geochemistry anomaly. It confirms how this methodology can be extend to such cases.
-
-
-
Influência de heterogeneidades crustais na evolução estrutural da bacia de Iguatu (CE) com base em modelagem gravimétrica 3-D
More LessThe tectonic configuration of northeastern Brazil is dominated by a continental scale, Cretaceous extensional system superimposed upon intensively deformed Precambrian basement rocks of the Borborema Province. Through 3D gravity modeling it is possible to estimate therelationship between the extensional tectonic efforts and the role of preexisting structural framework inserted in final rift geometry. The 3D gravity modeling procedure incorporates the presence of interfering sources of a heterogeneous structural framework and reveals an up to 1600 m thick asymmetric half-graben located at the bend of reactivated sigmoidal-shaped shear zones. The internal rift geometry suggests a fully separated growth of the fault segments by rift initiation, forming two independent depocenters. The overlapping fault segments have been linked by relay ramps. Release faults were identified nearly perpendicular or oblique to master faults, forming marginal strike ramps and horst structures in all sub-basins. The emplacement mechanism of Brasiliano granites around the Iguatu basin was also partially oriented by the same structural framework, which is indicated by the gravity signature of the granitic bodies after removal of gravity effect of the basin-filling deposits.
-
-
-
Perfil magnetométrico sobre estrutura em graben no Escudo das Guianas, que suporta sedimentos proterozóicos da Formação Prosperança, na bacia do Amazonas
This work presents the results of a carried through magnetic survey in a segment of highway BR-174, in Presidente Figueiredo districtal, where it occurs expositions of the Prosperança Formation, joined basal of the Basin Sedimentary of Amazon, occupying grabens developed on rocks of Uatumã Supergroup, in the Shield of the Guianas. The work consisted of a profile of total magnetic intensity, with measures effected to each 100m of distance, whose resulted they show narrow relations with the local geologics features, allowing to the identification of litologies and geologic structures.
-
-
-
Integração de métodos potenciais com dados de poços e sísmica para a caracterização geológica e estrutural da Bacia de Cumuruxatiba
The Cumuruxatiba Basin has an extensional area around of 20.200 km², located in the brazilian east margin, in the south of Bahia state. Although important hydrocarbon reserves haven’t been found, it presents a series of geological features that indicate the potential of production pole of oil. Based on the interpretation of the gravity and aeromagnetic maps, joint with the seismic lines interpretation, it was observed important faults trends and structural traps in both maps (gravity and magnetic). Some of these lineaments were extracted from the potential maps, mainly of the gravimetric map, and this features were correlated with de fault system interpreted from the seismic lines and, atypical features were observed in the seismic lines in the South portion of the basin that would be related to salt domes, but the anomaly observe on the magnetic map suggested that the lithology shows by the seismic line would be basalt intrusion.
-
-
-
3D gravity inversion incorporating prior information via an adaptive learning procedure
Authors J.S. Fernando, J. S. Silva Dias, Valéria C.F. Barbosa and João B.C. SilvaWe develop a 3D gravity anomaly inversion to estimate a 3D density-contrast distribution that gives rise to a complex, interfering gravity field. Our approach estimates the 3D density-contrast distribution that fits the observed anomaly within the measurement errors and favors compact gravity sources closest to pre-specified geometric elements such as lines and points. This method retrieves the geometry of multiple gravity sources with prescribed density contrasts (positive and negative values) assigned to each geometric element. In this way, each geometric element operates as the first-guess skeletal outline of a particular, homogeneous section of the gravity source to be reconstructed. Based on an iterative learning scheme, the number of parameters, the number of geometric elements, their spatial positions and the associated target density contrasts may increase automatically. Tests on synthetic data from geometrically complex bodies and on field data collected over a granitic pluton, located in the Carajás province of the eastern Amazonian Craton, Brazil, illustrate that our method makes its possible to reconstruct a sharp image of multiple and closely located gravity sources.
-
-
-
Delineamento simultâneo do relevo do embasamento e de diápiros salinos em pacotes sedimentares com densidade variando com a profundidade através da gravimetria
We present a new gravity interpretation method to delineate the basement relief and the shape of homogeneous salt domes and salt sills within sediments whose densities increase with depth. The interpretation model consists of juxtaposed 2D vertical prisms for thebasement, and 2D prisms with polygonal cross sections for the domes and sills. We presume that the physical properties of all sources are known a priori. The estimation of the basement relief is stabilized by the global and weighted smoothness constraints whereas the estimation of the domes and sills is stabilized by concentrating the estimated anomalous mass about known directions. We applied the method to synthetic data to demonstrate its utility in delineating salt structures in marginal basins, whose basement is formed by horsts, grabens, and step faults. We also applied the method to a real gravity profile perpendicular to the coast line in the Campos Basin, Brazil.
-
-
-
Gravimetria da porção nordeste da Bacia Sedimentar do Paraná –Mapa Bouguer preliminar
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 method 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 data acquisition but a preliminary Bouguer anomaly map provides a better visualisation and allows new concepts and theories of the polyphasic basin story.
-
-
-
Magnetometria da porção nordeste da Bacia Sedimentar do Paraná – Mapa magnetométrico preliminar
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 occurrences. Potential geophysical method such as magnetometry is a valuable tool in the understanding this structural domes and its evolution through the basin evolutionary story. This study is currently in data acquisition but a preliminary total field magnetometric map provides a better visualization and allows new concepts and theories of the polyphasic basin story.
-
-
-
Inversão de anomalia gravimétrica na borda norte da Bacia do Paraná
More LessThe Bouguer anomaly map of the north part of Paraná Basin displays two elongated NS negative anomalies. These anomalies were inverted using an algorithm to determine the basement relief. The maximum depth expected was controlled by values from receiver function in the area. Inversion confirms the initial hypothesis of grabens at the basement as responsible for the low anomalies. These grabens have varying relief but can be 2 km deeper than the surrounding basement. Inversion failed in the central part of profile and a font of positive density may be necessary to account for the observed anomaly.
-
-
-
Interpretação Qualitativa do Projeto Aerogeofísico Sudeste de Rondônia e a sua Contribuição para o Mapeamento Geológico Regional
This work consists of a qualitative airborne geophysical interpretation (magnetometry and gammaspectrometry) of an area of 43,019 km² of the Sudeste de Rondônia Aerogeophysical Project, which is located in the southeast portion of the the State of Rondônia and northwest of Mato Grosso, 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.
-
-
-
Mapeamento de Magnetização Aparente Usando Regularização Entrópica
Authors João B. C. Silva, Suzan S. de Vasconcelos and Valéria C.F. BarbosaWe present a new apparent-magnetization mapping method on the horizontal plane that combines the minimization of the first-order entropy with the maximization of the zeroth-order entropy of the estimated magnetization contrasts. The interpretation model is a grid of vertical, juxtaposed prisms in both horizontal directions. We assume that the top and the bottom of the magnetic sources are flat and horizontal and estimate the prisms’ magnetization contrasts. The minimization of the first-order entropy favors solutions presenting sharp borders, and the maximization of the zeroth-order entropy prevents the tendency of the source estimate to become a single prism. Thus, a judicious combination of both constraints may lead to solutions characterized by regions with virtually constant estimated magnetization contrasts separated by sharp discontinuities. We apply our method to synthetic data from simulated intrusive bodies in sediments that present flat and horizontal tops. By comparing our results with those obtained with the smoothness constraint, we show that both methods produce good and equivalent locations of the sources’ central positions. However, the entropic regularization delineates the boundaries of the bodies with greater resolution. Both the proposed and the smoothness constraints are applied to a real anomaly over a magnetic skarn in Butte Valley, Nevada. The entropic regularization produced an estimated magnetization distribution with sharper boundaries, smaller volume, and higher apparent magnetization as compared with the results produced by the smoothness constraint.
-
-
-
Radiometria e Gravimetria associadas a estruturas geológicas da Bacia Paraíba, limite sul
More LessGeological studies associated to Geophysics were developed and consolidated in this work as a safe source of information, allowing us to identify, locate and characterize features that exist in part of the Paraíba Basin. The Bouguer, Regional and Residual
Gravimetric Maps backgrounded enough information for the development of a structural contour map, which allowed the discovery of existing structures in the studied region. The Radiometric Survey did not register anomalous scintillometric values, helping,
however, in the identification of lithological elements in that area, which in turn show a soft value heightening to the west of that region associated to the presence of altered rocks in the basement. Seismicity was registered around the borders of the Goiana Graben, strong indicative of “block accommodation” possibly related to that Graben.
-
-
-
Interpretação de Anomalia Magnética no Alto de Cabo Frio Utilizando Inversão Compacta Generalizada
More LessThe Cabo Frio Island alkaline suite in Arraial do Cabo (RJ) is an important onshore feature associated to the Cabo Frio High tectonic activity. In this article, we deal with the conspicuous aeromagnetic anomaly occurring at the Southwestern area of this island by applying a processing workflow based on a modified approach of the generalized compact inversion in order to simulate and test several interpretive hypotheses about the magnetization distribution and its relation with the geologic scenario. This approach allows dealing with the complex interactions of multiple magnetic sources in close area distribution. Using a grid composed by several bi-dimensional prisms with singular magnetization amplitudes, the geologic features can be represented in a realistic background. In this study, the a priori constraining parameters for the anomalies sources location were derived from the application of the Euler’s Deconvolution. Several a priori different magnetic inclinations were tested with the model of prisms in order to simulate remanent or non induced magnetization. An interactive procedure based on the interpreter’s evaluation of results of the inversion for different a priori inclinations is implemented in order to attain an interpretive hypothesis that is consistent with geological information. This procedure allow us to develop a consistent model for the Arraial do Cabo anomaly based on two sources located at different depths and opposed magnetization, one of them with a reverse magnetization compared to present day magnetic field.
-
-
-
Modelo gravimétrico-magnético do Gráben de Paranaguá-PR
More LessThis study presents a 2D gravimetric-magnetic model of the continental portion of the Paraná state coastal plain which is related with the Ponta Grossa Arch central region. Through simultaneous inversion of the gravimetric and magnetic data it was generated a model of the top of the basement underlying the sediments of this region. The model includes the density and magnetic susceptibility of the Cenozoic sediments, basement rocks and diabase dykes, and shows the variations of deep to the top of the basement, that reaches 148 meters in the deepest point. Using the thickness of the dykes calculated from this model it was possible estimate a crustal extension of 22% and a frequency about 2 dykes/km.
-
-
-
Inversão gravimétrica do relevo do embasamento usando regularização entrópica
Authors João B.C. Silva, Alexandre S. Oliveira and Valéria C. F. BarbosaWe present a new gravity inversion method, which estimates the basement relief of a sedimentary basin, whose sediments may present a constant or a decreasing density contrast with depth relative to the basement. The method combines the minimization of
the first-order entropy measure with the maximization of the zeroth-order entropy measure of the solution vector. The interpretation model consists of a set of rectangular juxtaposed vertical prisms with known density contrasts and whose thicknesses represent
the depths to the basement relief and are the parameters to be estimated. 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 discontinuities. We applied our method to synthetic data from a simulated sedimentary basin with steep borders and flat bottom. Compared with the global smoothness inversion of the same data, the entropic regularization delineated the basement relief with greater precision. By comparing our results with those obtained with the weighted smoothness inversion, the results were similar, but the entropic regularization does not require the knowledge of the basin’s maximum depth. We applied our method to the Bouguer anomaly from the northern portion of Steptoe Valley, Nevada, delineating a discontinuous basement relief in accordance with the known geological setting of the area.
-
-
-
Tietê Airborne Gravity Test Area
Authors Henrique A.P. Dal Pozzo, Wladimir Shukowsky and Eder C. MolinaThis paper presents the conception and the characteristics of the airborne gravity systems testing area established in the vicinity of Tietê, SP, as integrating part of the procedures of Parnaíba Basin Airborne Geophysical Survey
-
-
-
Mapa magnético parcial do Fanerozóico do estado do Paraná, sul do Brasil
More LessThe improvement of old aeromagnetic data base using classic, recent and modern processing techniques is one of the objectives of this paper. The 80`s aeromagnetics surveyings that covered partial area of Paraná State, southern Brazil, have been used to outline and to confirm the structural framework of the Parana Basin. Results obtained from processing methods like upward continuation, total horizontal gradient, analytic signal, analytic signal tilt and total horizontal gradient of analytic signal tilt will be discussed as best results for this present research.
-
-
-
Levantamento gravimétrico da Bacia do Paraná na região de Osório, Rio Grande do Sul. Implicações das estruturas do embasamento e do magmatismo Serra Geral na exploração dos carvões da Jazida Santa Terezinha
More LessStratigraphic analysis is a great tool to evaluate the potential of a basin as fossils fuel reservoir, extremely important in our society. In the same way, geophysics is essential for many areas of geology, mainly in preliminary researches of sedimentary basins. The present project had as main motivation the integration of these different techniques, in the Jazida Santa Terezinha, formed during the Early Permian and located inside of the Paraná Basin, where it is believed that its extensive layers of coal in depth have great potential for CBM (Coal Bed Metane) accumulation. The coal deposit is locates in the coast north of the State of the Rio Grande do Sul, more precisely, in the cities of Osório, Tramandaí, Imbé and Xangri-lá. The principal goal of this Project is to contribute on the characterization of the tectnostratigraphic of the study area through the application of stratigraphic and gravimetric techniques. More specifically, the objective is to delimitate the coal bed geometry, the basement structures and mapping of the diabase placed on subsurface related to the Eopermian rocks of Rio Bonito Formation (coal bed).
-
-
-
Interpretação de dados magnéticos do Projeto Rio do Sangue, Mato Grosso
This paper presents some results of an extensive processing, interpretation and geological integration campaign of airborne magnetic field data. It comprised data from the sampling of 30.360 linear kilometers of profiles, spaced 2 km apart, covering an area of 54.000 km2 in northwest Mato Grosso State (Rio do Sangue Project, DNPM/DGM/CPRM). Transformed and interpretation products allowed the mapping of magnetic structures and domains. The integration of geophysical and geological information leads to the get a better picture of the spatial structural framework present in the surveyed area.
-
-
-
Geophysical modeling of geode in basalts type deposit in the Santana do Livramento region, southwestern Rio Grande do Sul, Brazil
More LessThe occurrence of amethyst and/or agate bearing geodes in the volcanic rocks of the Serra Geral Formation has been recently studied in more details. The Santana do Livramento region (southwestern Rio Grande do Sul, Brazil) shows small occurrences of this type of ore deposit. Such occurrences are hosted by basalts or by colluviums, and are, however, poorly studied. The geology of this region is made up by volcanic rocks of the Serra Geral Formation, and by sedimentary rocks of the Botucatu Formation. The
present study shows the results of a local geophysical survey and a geophysical model for such an ore deposit.
-
-
-
Absolute gravimetry on the Observatório Nacional – Agulhas Negras Calibration Line
Authors Mauro Andrade de Sousa and Alcides Antonio dos SantosThe Observatório Nacional – Agulhas Negras Gravity Calibration Line was established in the 1980s using LaCoste & Romberg gravimeters model “G” only. Five gravity stations were irregularly positioned along its 230km spanning a total range of 627 mGal. The new absolute gravimeter Micro-g Solutions A-10 #011 of Observatório Nacional was taken to each calibration station and new measurements were made. Vertical gravity gradients were also measured. This report shows the results found and a comparison with previous values based solely on relative gravimetry.
-
-
-
Processamento, nivelamento e integração de levantamentos aerogeofísicos magnetométricos na porção sul do Cráton São Francisco, Minas Gerais
The main purposes of this study were focused to the processing, leveling and integration of several magnetic airborne geophysical surveys, acquired in the southern part of São Francisco Craton, State of Minas Gerais. To the leveling and integration of the several blocks of data from the Brazil-Germany Geophysical Agreement (CGBA), flown during the 70’s, a series of techniques were applied in order to achieve an adequate result. The task revealed laborious due to the lack of continuity among 59 data blocks, obtained with different flight heights, 2 km line spacing and east-west direction. This mosaic allows for the study of the major magnetic structures on another integration done in this work from four high density airborne surveys (250 m / 500 m line spacing) flown in the center-southeastern portion of the State of Minas Gerais. These four detailed surveys encompass the Rio das Velhas Project (RV), the Gems of Minas Gerais – Itabira/Ferros Project (IF), and the Áreas 2 and 3 of Minas Gerais Airborne Geophysics Survey Program (PLAMG) Integration used available procedures of gridding techniques such as knitting (suture, trend removal, and shared points). The evaluation and analysis of parameters and edge relationships among airborne surveys were used to define the best approach to join each pair of data block.
-
-
-
Imagens magnetométricas e sua aplicação na definição do arcabouço magnéticoestrutural da porção sul do Cráton São Francisco, Minas Gerais
The mosaic of five aerogeophysical surveys flown in the State of Minas Gerais were correlated with the available geological data to define the magnetic-structural framework of southern portion of São Francisco Craton (Figure 1). The data processing consisted in leveling and integration of the blocks from the Brazil-Germany Geophysical Agreement -CGBA (1971, 2 km line spacing) and four high density airborne surveys (250 m / 500 m line spacing). These four detailed surveys encompass the Rio das Velhas Project -RV (1992), the Gems of Minas Gerais – Itabira/Ferros Project –IF (1996), and the Áreas 2 and 3 of Minas Gerais Airborne Geophysics Survey Program – PLAMG (2000/2001) (Figure 1). Linear transformations of the magnetic total field (amplitude and inclination of the analytical signal, vertical derivative, and horizontal gradient) were efficient in helping with the definition of geophysical discontinuities and magnetic sources associated with geological units. Regarding CGBA, magnetic domains were interpreted as large regional blocks. These units were correlated with the mapped regional geology, allowing nomination of domains. The integration of the other surveys, more modern and with higher data density, allowed a more detailed correlation with mapped regional geology. The obtained results showed an excellent correlation between geophysical units and known geology. The interpretation of magnetic linear features revealed a large amount of structures not recorded in the present geological cartography. This happened with a swarm of mafic dikes, as well. The magnetic framework when integrated with the mapped geology lead to the visualization of regional tectonic blocks and the main shear zones present in the area. The main results are associated with the tectonic compartimentation of the south portion of São Francisco Craton, with the limits of Mineiro Belt and Araçuaí Belt.
-
-
-
Bacia do Parnaíba – Arcabouço tectônico estrutural baseado em dados aeromagnéticos regionais
More LessAn aeromagnetic and aerogravimetric survey covering all Parnaíba Sedimentary Basin was flown from Feb., 2005 to Aug., 2006 and is now available to all geological community by ANP. The area covers 746182 km2 with 183877 km of gravimetric and magnetic profiles. The flight lines directions are E-W with 6 km spacing and the control lines are N-S with 24 km spacing. Three sub-areas with detailed surveys including aeromagnetic and aerogamaspectrometric profiles with 0.5 km spacing flight lines was followed up and are now under analysis by ANP. This paper deals with the aeromagnetic regional data and gives a new approach to better understanding the basin structures looking for the best places for deposition of oil and gas source rocks. First derivative, reduction to the pole and Euler deconvolution were the main skills used to get the results.
-
-
-
Inversão gravimétrica 3D de bacia sedimentar com variação do contraste de densidade com a profundidade segundo uma lei parabólica
More LessWe present a gravity inversion method for estimating the 3D basement relief of a sedimentary basin. We assume that the density contrast between the basement and the sediments decreases with depth according to a parabolic law. We discretize the sedimentary section into a grid of 3D vertical, juxtaposed prisms in both horizontal directions. The prisms’ thicknesses represent the depths to the basement relief and are the parameters to be estimated from the gravity data. To produce a stable solution we maximize the smoothness of the estimated relief using the overall smoothness regularization. We apply our method to synthetic data from simulated complex 3D basement relief and the results show well-resolved estimated relief, starting at different initial guesses. These results are obtained if the values defining the parabolic decay of the density contrast with depth are known. We conducted a numerical analysis to investigate the solution sensitivity to the effects caused by: (1) random noise in data, (2) the depth to the true basement relief, and (3) the density-contrast decay with depth according to the parabolic law. We show that, if the density contrast in the deepest portion of the basin is above a threshold, our method retrieves the 3D geometry of the basement relief regardless of the true basement depths and regardless of the pseudorandom noise sequences.
-
-
-
Structural And Lithological Inversion Using Gravity And Magnetic Data Integrated With Geological Infomation
Authors Mark E. Odegard, William G. Dickson, Janice M. Christ and James GanathThis paper presents the techniques and results of a depth to basement inversion effort over the South China Sea area of Southeast Asia. Integrating the results of the inversions with geoseismic, well and geological data results in an accurate and informative description of the tectonics and structure of the area. Results show that significant packages of sediments of exploration interest exist that have not been exploited. Basin geometry and structure can be derived from the inversion of gravity and magnetic data. Using some newly developed techniques these inversions can also discriminate between different lithologies. Magnetic data can be inverted for magnetic basement and for intermediate layers of volcanic material. Gravity data can be inverted for structures which produce density contrasts in basins. Combining these results, basin structure can be explored to determine depth to basement, to high density structures such as carbonates, and to high susceptibility structures such as volcanics. New high resolution data sets for gravity and magnetic data have been merged and now cover all of greater Southeast Asia. These data allow us to extend our interpretation to all offshore basins and some onshore as well. We use the structural interpretations described above along with enhancements of gravity, magnetic and digital elevation model data. Combining these interpretations and enhancements with published data in a GIS environment allows us to constrain additional interpretations of tectonic development, and sedimentary facies and structures in basins. Examples are shown for basins around the South China Sea. Early results from offshore South America will also be presented.
-
-
-
Comportamento de Perfis Geofísicos na Determinação de Zonas de Aquíferos
Métodos geofísicos são comumente usados para mapear e identificar zonas aquíferas, otimizando a elaboração de projetos de poços tubulares que tem como escopo a explotação de água subterrânea. Dentre os diversos métodos existentes, a resistividade elétrica, a radiometria e o potencial eletroquímico das formações rochosas são classicamente utilizados na determinação das seções filtrantes de poços tubulares semi-artesianos. Esta pesquisa teve por objetivo efetuar estudos comparativos dos traços dos perfis geofísicos de resistividade, potencial espontâneo e raios gama, com o escopo principal de pesquisar a(s) causa(s) que justificasse(m) o fato de que, em praticamente todas as perfilagens geofísicas que utilizam estes três métodos, há fatores desconhecidos operantes que mascaram o traço do perfil geofísico, de maneira tal que a configuração deste traço, representando as características litológicas atravessadas, diferem dos resultados esperados, tendo como base a conceituação teórica. Foram utilizadas amostragens de componentes e fluidos, os quais foram analisados por difratometria de raios X e os resultados obtidos comprovaram a influência do fluido utilizado na perfuração de poços no comportamento dos perfis geofísicos de eletroresistividade e potencial espontâneo.
-
-
-
Real-time multiparameter analysis of groundwater by optical detection
Authors Pauline Amez-Droz and Pierre-Andre SchneggSimultaneous detection of physical and chemical parameters is applied to real-time analysis of groundwater from an Alpine karst spring. Continuous sampling of the spring water was carried out during a half year. Following parameters were recorded by the instrument : groundwater temperature, electrical conductivity and turbidity, dissolved organic matter and concentration of injected artificial dye tracers (uranine, sulforhodamine and Tinopal during 3 tracer tests). This study permitted the identification of sources of contamination of the spring.
-
-
-
Estrutura Geoelétrica e Reservas Hídricas dos Aqüíferos Cristalinos da Bacia do Alto Curaçá Usando Multi-perfilagens de IP-Resistividade
The well locations within crystalline aquifers of Bahia are dominantly made using hydrogeological criteria, based on images of the earth surface and on outcrop analysis of brittle structures in the rocks. The statistics of water production wells drilled to an average depth of 80m shows a large proportion of dry wells (32%). Specific discharge are normally low, ranging from 0.08 to 1.72 m3/h/m, with average of 0.15 m3/h/m. Hydrochemically there is a direct correlation between water salinity, the depth of the water entrances and the density of vegetal cover. In general salinity changes from 120 to 26,900 mg/l of dissolved salts, with average of 5,990 mg/l. In this work we discuss a geophysical strategy proposed to explore rationally the groundwater stored in the semi-arid terrains of the upper Curaçá basin, Bahia. Three main subjects were considered to be solved. The first one was to develop a conceptual geohydrological model to represent the water storage and transmission within the fractured aquifer systems of the area. The second was to optimize a geoelectrical procedure capable of imaging, with good spatial resolution, these complexes underground reservoirs. The third was to search the mechanisms and processes responsible for the high water salinization in the studied aquifers.
-
-
-
Caracterização Hidrogeofísica do Aqüífero Urucuia na Sub-bacia dos Rios Arrojado e Formoso, Bahia
Authors Emerson S. M. dos Santos and Olivar A.L. de LimaThe hydrogeological characteristics of the Urucuia aquifer system within the Arrojado-Formoso river basin were studied using geoelectrical soundings and gravimetric maps. Sixty five Schlumberger IP-resistivity soundings, expanded to a maximum current AB/2 spacing of 1.000 m, were used to define the aquifer geometry and the structure of its substratum within the depth range from 0 to 500 m. The jointly inversion of the time-domain chargeability and the apparent resistivity data were useful to better define the depth to the top of the aquifer system. These results allow to infer the general unconfined nature of the groundwater flow within the aquifer and to map a groundwater divide in the occidental portion of the basin. In some places there is a local confinement caused by intense silicification of some sandstone horizons. A regional Bouguer gravity map essentially confirms the block faulting structure inferred from the sounding data.
-
-
-
Aplicação do método eletromagnético na determinação da interface água doce-água salgada na Vila do Bonifácio, Bragança-PA
An study including conductivity measurements and groundwater flux determination was carried out in a Village located close to the northeast coast of Pará. The objective of the study was to provide orientation for the location of tubular wells in places where the
saline intrusion of the ocean is deeper. The measurements involved ground apparent conductivity using EM inductive techniques and water conductivity of samples obtained in the shallow excavated wells that are actually used for water supply in the village. The results indicate the central portion of the village as the best place for the location of the tubular wells.
-
-
-
Modelagem Geofísica Para Água Subterrânea nos Aqüíferos Fissurais da Sub-Bacia do Barro Branco, Município de São José de Ubá (RJ)
More LessThis paper show a successful case history on groundwater geophysical modeling of fissured aquifers in São José de Ubá (RJ). Three resistivity profiles were acquired over a faulting zone, the main idea behind the survey was to determine the depth continuity of the faults. Data were interpreted through 2D smooth inversion scheme. Two main aquifers systems were identified in the studied area. A sedimentary cover with depths varying from 2 to 12 meters; and sub-vertical fissured aquifers characterized by low resistivity zones. The occurrence of these zones in all three profiles indicate the continuity of these fractures along the studied area.
-
-
-
Estudo de contaminação de águas subterrâneas em Ji-Paraná- Rondônia pelo método da eletrorresistividade
More LessThe study of quality of groundwater of the urban zone of the city of Ji-Paraná, State of Rondônia, accomplished by Silva, 2001, showed anomalous concentrations of nitrate in wells, in reason of the great amount of existent sewages in the place. Face to the results obtained in that work, the present study had as objective, to determine the extension of the contamination through the use of applied geophysical method of dipolo-dipolo electric profiling survey. It was then accomplished a geophysical rehearsal in the
Neighborhood Nova Brasília in november of 2006 and after the processing of the geoeletric profile, it was possible to evaluate the characteristics of the soil, as the depth of the water level, the rocky top and the extension of the contamination for nitrate originating from of the countless sewages of the area, characterized by zones of low resistividades. The good correlation among high concentrations of nitrate in wells with the zones of low resistividade in the eletric profiling lines, it allows to affirm that the employed geophysical method was shown efficient to assist the objectives of this work.
-
-
-
Utilização Do GPR e Eletrorresistividade (SEV) Na Localizaçào de Aquíferos Razos na Região dos Lagos - Parque Ecológico Municipal do Mico Leão Dourado - Município de Cabo Frio - RJ (Estudos Preliminares)
This work presents the results of an investigation carried out by the Universidade do Estado do Rio de Janeiro (UERJ) with the cooperation of the Prefeitura de Cabo Frio. The area is located on the borders of the Cabo Frio city, Rio de Janeiro State, Brazil. In the study, Geophysical survey was applied in Parque Ecológico Municipal do Mico Leão Dourado area located within the Tamoios District in order to identify the basement and local sites for fresh water. It was used the Ground Penetrating Radar (GPR) technique with RAMAC/MALA equipment, which provides high resolution images of the underground and Resistivity methods. The study area consists of sands deposited in marine conditions, which are presently surrounded by beach and local population with poor fresh water conditions.
-
-
-
Compartimentação magnética-estrutural e conectividade dos sistemas aqüíferos Serra Geral e Guarani na região central do estado do Paraná, sul do Brasil
More LessThe present research has been discuss a structured area in central Paraná State, southern Brazil, delimited by coordinates 24º00’ - 25º00’ S and 51º00 - 53º00’ W with just about 23,000 km2. The study involves GIS integration of aerogeophysical, geological, structural lineaments (DEM and Landsat imagery), hydrogeological and hydrochemical data. Basalts flows and diabase dykes (NW-SE) of the Serra Geral Formation (Lower Cretaceous) predominate in the studied area. These rocks correspond to the overlying Serra Geral Aquifer System (SGAS-fractured). The purpose of the study is processing and interpretation aeromagnetic data from various techniques, useful for enhance shallow and deep sources. The integration with others remote sensing and geological data to make possible to outline the regional structural framework. Finally, the study investigated the structural control of both flow and chemistry of SGAS groundwater and also to identify fractures that might represent hydraulic connection zones to the underlying
Guarani Aquifer System (GAS-granular).
-
-
-
Hidrogeofísica com o uso do Método CSAMT em Caracol, Estado do Piauí, Brasil
The municipal district of Caracol is located in the south of Piauí state. This work describes the integration of geological and geophysical data for construction and recoverery of wells for human provisioning. The methodology embraced fotointerpretation of CBERS images, elaboration of maps of lineaments, morphostructures, and terrestrial geophysics to determine the directions of the faults and fractures responsible for percolation and storage of groundwater in the area. In the area of Caracol two prominent directions were identified: one parallel to the main shear zone, direction N60E and the other N50W. The geophysical profiles of conductivity using the CSAMT (Controlled Source Audiomagnetotelluric) method indicated that the fractures N50W are distensive and more promising for storage of groundwater. Using this result four localities were marked for construction and two for recovery.
-
-
-
Estudo Geofísico dos aqüíferos subterrâneos da região de Tamoios, Cabo Frio-RJ. Resultados Preliminares com Magnetometria e Sísmica de Refração
The work presents results and initial pespective of the campaign of geophysical search using magnetics survey and seismic refraction for groundwater search. The survey was done in the region of the Lakes, in the municipal districts of Cabo Frio – Reserva Ecológica do Mico Leão Dourado- RJ-Brazil. Site average spacing was 1 -10 m in line covered a distance of 900 m trending in the NW-SE direction. The area lies the tropical climate region (hot with summer rains) with a mean temperature of 23ºC with a predominating Northeast wind exists with a very high evaporation rate along the coastal region. The annual rainfall index is 791 mm/yr. This is adduced to the phenomenon called resurgence thereby affecting the recharge of the existing aquifers. There is the existence oh high saline water intrusion in the Coastal region which incur into the aquifers in the region, this is worst during the summer and thereby necessitating the need for good groundwater supply. We have interpreted in the area presents a group of faults
trending in the SE-NW direction. Most of the study area is on crystalline lands, so that the largest concentration of water resources in subsurface is confined within the faults and fractures. Locally no faulting was observed. In the area of the coastal slopes lands with low topographical and low plain is filled with the sediments of Quaternary age, described as being current sediments and ancient deposits close to the flood plains at the coast.
-
-
-
A correlação entre parâmetros geoelétricos e hidrodinâmicos de aquíferos: Resistência Transversal versus Transmissividade
More LessEstimates of hydrodynamic parameters from geoelectrics data settings play an important role in hydrogeology studies. In such context, correlation between transversal resistence (RT) and transmissivity (T) has been considered as an useful tool for evaluation of aquifer hydrodynamic characteristics. Fourteen Vertical Electrical Soundings (VES) using Schlumberger configuration close to tubular wells were carried out in Bebedouro´s region (state of São Paulo, Brazil) aiming to get RT. Through a representative average value of hydraulical condutivity (K) obtained from Adamantina Formation, it was possible to estimate T parameter, that in turn allowed a RT x T relationship, which was analyzed by linear regression, and the results had been considered satisfatory validating the applicability of the method.
-
-
-
Seismic Activity Induced by Water Wells, Paraná Basin, Brazil
Shallow seismic activity has been observed in the Bebedouro rural area, Northeast of São Paulo State, Brazil, since 2004. A 6-station seismographic network, installed in March 2005, has recorded around 2,200 micro-earthquakes. The events with magnitudes
up to 2.9 and intensities V MM (March-April 2005) are located near some groundwater wells (120-200m deep) drilled in early 2003 to extract water from a basalt fractured aquifer. The activity occurs as swarms of events mostly during the rainy season when the wells are not pumped. The third swarm occurred in April 2006 one month after four new wells were drilled. Migration of the epicenters away from the wells with the largest water flow, more than 150m3/h, was clearly observed in 2005 with a “seismic diffusivity” of about 0.3 to 0.6m2/s. The spatio-temporal evolution of the seismicity shows it was triggered by the drilling and operation of the waterwells.
-