- Home
- Conferences
- Conference Proceedings
- Conferences
4th International Congress of the Brazilian Geophysical Society
- Conference date: 20 Aug 1995 - 24 Aug 1995
- Location: Rio de Janero, Brazil
- Published: 20 August 1995
51 - 100 of 330 results
-
-
The Organization and Recent Scientific Achievements of the Ocean Drilling Program (ODP)
Authors D.A. Falvey and E.S. KappelThe Ocean Drilling Program (ODP) is an international partnership of scientists and research institutions organized to explore the history of the Earth beneath the ocean basins. ODP provides core samples from the ocean basins and shipboard and shore-based facilities for the study of these samples, and downhole measurements (i.e., wireline logging) and opportunities for special experiments to determine in situ conditions beneath the seafloor. These studies lead to a better understanding of plate tectonic processes, of the Earth's crustal structure and composition, of environmental conditions in ancient oceans, and of changes in climate through time. Such systematic advances in knowledge in turn lead to a fuller comprehension of the evolution of the Earth.
-
-
-
Perfuraçőes do DSDP na Elevaçăo de Rio Grande - Implicaçőes para o Entendimento da Evoluçăo do Atlântico Sul
More LessAs linhas de costa da America do Sul e da África tém suscitado questionamentos desde os primeiros mapeamentos cartográficos inspirando suposiçőes quanto aos processos de formaçăo dos oceanos e de suas margens. Em meados da decada de 60, a evoluçăo cientifica e tecnológica já permitia a proposiçăo da Teoria da Tectónica de Placas, entăo sustentada principalmente por evidęncias sísmológicas, magnetométricas e batimétricas.
-
-
-
OOP and Rifted Continental Margins
More LessRifted (also known as divergent or passive) continental margins are those characterized by a fused join or boundary between continental and oceanic crustal types, as opposed to convergent margins, where subduction or underthrusting of oceanic crust beneath continental material is occurring. The Ocean Drilling Program's approach to the study of these margins has to date concentrated in the North Atlantic, where the best examples of conjugate (paired) passive margins of various ages occur. ODP has drilled both non-volcanic and volcanic examples; recent research suggests that the absence or presence of massive volcanic outpourings accompanying continental breakup may be the Single most important distinguishing feature of rifted margins.
-
-
-
Transform Margin Development: Preliminary logging results from ODP Leg 159 on the Côte D'Ivorie-Ghana margin
Authors C.A. Gonçalves, E. Ewert and C. BasileODP Leg 159 studied the Côte d'lvoire-Ghana transform margin in the eastern equatorial Atlantic during January and February 1995. Thirteen holes were drilled at four sites, recovering sediments from Late Albian to Pleistocene age. The margin has been created by major transform motion between the African and South America plates and is one of the best known examples of a former transform boundary between continental and oceanic crust (Masele and Blarez, 1987). Logging data were collected at three of the sites. and despite bad hole conditions. logging runs were obtained in four boles. This paper shows the preliminary logging results which cover the full sedimentary sequence cored. Together with the standard tools used by the oil industry. The Geochemical Logging Tool (GLrn') and the Formation MicroScanner (FMS1V) tool were also used.
-
-
-
Cenozoic Evolution of Carbonate Platforms on the Northeastern Australian Margin: Synthesis of ODP Leg 133 Drilling Results
Authors J.A. McKenzie and P.J. DaviesDrilling during ODP Leg 133 was designed to study factors controlling both isolated and attached carbonateplatform evolution using sedimentary sequences that were deposited at varying water depths on the platform margins and slopes and in the adjoining basins. Shipboard and post-cruise data provide an integrated picture of the conditions promoting platform initiation and growth, as well as the environmental changes that can lead to platform demise. Results indicate that the Cenozoic evolution of the Queensland Plateau, Marion Plateau, and Great Barrier Reef was controlled by a complex interaction of variations in eustatic sea level,subsidence pulses, and paleoceanographic changes. In most cases, not a single factor, but a combination of factors was in operation at any specific time. Long-term platform development was strongly influenced by thenorthward drift of the Australian Plate throughout the Cenozoic. Plate motion resulted in a ransition from temperate to tropical surface-water temperatures, with a corresponding change in the type of carbonate sedimentation. Yet, short-term, rapid changes in paleoceanography seem to have dominated the system. Abrupt increases in surface-water temperatures led to the sudden development of extensive tropical reefal complexes in the early Miocene, whereas a decrease in late Miocene surface-water temperatures resulted in a change from tropical fauna and flora to a bioassemblage more compatible with a non-tropical environment. Together with the paleoceanographic changes, variations in relative sea level, whether eustatically or tectonically controlled, either helped maintain carbonate production or facilitated its decrease, sometimes resulting ultimately in the shutdown of the shallow-water carbonate factors. During specific time periods, the thermally driven circulation of seawater through the buried carbonate platform sediments apparently caused selective dolomitization. This process may be ongoing within the Queensland Plateau, possibly providing new clues for understanding massive carbonate platform dolomitization.
-
-
-
REEVALUACION DE LA EXPLORACION DEL AREA NUTRIAS-BRUZUAL, Cuenca de Barinas-Apure, Venezuela
Authors L. Hernandez and A. PortillaEl estudio y la identificación de las características geológicas presentes en el área, con el soporte de la información geológica-geofísica existente es de gran importancia para el futuro de la exploraci6n petrolífera de esta parte de la cuenca. Se utiliza la metodología de interpretación sismosecuencial y sismotectónica para los 2100 Km de líneas sísmicas digitales. En el área, la columna estratigráfica está conformada por un basamento Igneo-Metamórfico, sobre el cual se encuentran las formaciones sedimentarias del cretáceo al reciente. La calibración sísmica y bioestratigráfica definen cuatro secuencias sísmicas de segundo orden: Cretáceo, Eoceno Medio, 0ligoceno (1)-Mioceno Inferior (?) y Mioceno Medio (?)-Plioceno (1).La secuencia Cretácea es principalmente arenosa, engrosa hacia el norte y adelgaza hacia el sur por efecto de sedimentación y erosión. La secuencia Eoceno Medio desaparece por truncamiento erosional en la parte media del área y es principalmente arenosa, y las secuencias del Oligoceno (?) Mioceno Inferior (?), y Mioceno Medio (?) -Plioceno (?), son molásicas. Estructuralmente únicamente las secuencias sísmicas cretácicas y Eoceno Medio están afectadas por fallas inversas y fallas normales de edad Cretáceo tardío - Eoceno Temprano, posteriormente reactivadas durante el Mioceno Temprano. Las secuencias del Oligoceno (?) al Plioceno (?) no están falladas. Los resultados resultados obtenidos hasta el momento indican que el área es de interés prospectivo aún cuando la mayoría de los pozos perforados no resultaron exitosos.
-
-
-
ODP Drilling: Establishing Methane Sources and Migration Pathways Associated with Marine Gas Hydrates
Authors C. Paull, W. Ussler and W. BorowskiGeophysical models indicate that some continental margin sediments, like those of the Blake Ridge off southeastem North America, contain several percent gas hydrate. The amount of microbial methane required to fill a significant fraction of the sediment pore pace [i.e., > 5%] with gas hydrate is too large to be produced.by only in situ microbial processes. Thus, fluid migration and other gas-concentrating mechanisms are required to develop these gas hydrate accumulations. Testing models of fluid and gas migration in sediments associated with marine gas hydrates is one objective of Ocean Drilling Program (ODP) Leg 164 (October - December, 1995).
-
-
-
High Resolution Seismic Surveying for Pleistocene Sequence Stratigraphy, New Jersey Continental Shelf and Upper Slope, In Support of the Ocean Drilling Program's Global Sea Level Objectives
Authors J.A. Austin Jr., C.S. Fulthorpe, G.S. Mountain, J. Diebold, P. Buhl and K.G. MillerOne of ODP's long-standing goals has been to understand amplitudes and timing of global sea-level fluctuations. Past drilling expeditions have examined the sea-level record on carbonate platforms (e.g.• Legs 101. 115 and 133) and on atolls and guyots (e.g.• Legs 143 and 144). Passive margin transects have also been targeted for study, most recently a shelf/slope corridor offshore the Mid-Atlantic region of the eastern United States (slope drilled as Leg 150).
-
-
-
Estratigrafia de Alta Resoluçăo do Cone do Amazonas: Resultados do Oceari Drilling Program
Authors R.O. Kowsmann and C. PirmezO Cone do Amazonas e um dos maiores leques submarinos do Mundo e uma das feiçőes mais marcantes do Atlântico SuI. Possui 700 km de comprimento a partir da quebra da plataforma continental e até 400 km de largura (Damuth e Kumar, 1975; Damuth e Flood, 1985). Cerca de 4 km de sedimentos foram acumulados na porçăo central do Cone desde o Mioceno Superior (Silva et al., no prelo) pelo empilhamento de complexos de canais de passagem de correntes de turbidez encarapitados sobre cunhas de transbordamento destas correntes (levees).
-
-
-
Polarizaçăo Induzida Espectral no Alvo M16 - Santaluz - BA
Authors E.E. Starteri Sampaio and C.E. Teixeira CardosoO método geofísico de polarizaçăo induzida espectral (SIP) é importante para a' prospecçăo de minerais metálicos e de argila disseminados nas rochas da crosta terrestre, tendo como objetivos a exploraçăo de minérios e água subterrânea.
-
-
-
The Magnetic Signature of the San Gregorio Gold Mine Area, Uruguay
More LessThe San Gregorio gold mine lies on a northwesttrending shear structure in the Uruguay shield, southwest Minas de Corrales. Ground magnetic surveys in the vicinity of the gold deposit suggest several structures that appear to have controlled the gold mineralization. The analysis of magnetic susceptibility values allowed to concluded that the most important anomaly sources of the San Gregorio mine area are the non altered basic rocks, mainly the quartz diorites which generally occur in the hanging wall of the mineralized zone. Other lithologies shows low levels of magnetic susceptibility with weak contrast between mineralization and host rocks.
-
-
-
Caracterizaçăo de uma Área Escola na Regiăo de Presidente Figueiredo (Amazonas) Através do Emprego de Métodos Geoelétricos
More LessEste trabalho apresenta os resultados do levantamento geoelétrico (sondagens elétricas verticaís e perfilagens elétricas horizontais), utilizando as técnicas de Wenner e de Schlumberger, desenvolvidas em tręs áreas distintas (áreas 1, 2 e 3), localizadas no Município de Presidente Figueiredo, porçăo norte do Estado do Amazonas, ao longo da rodovia BR-174. Tem por objetivo principal a caracterizaçăo de uma alternativa para a realizaçăo dos trabalhos de campo da disciplina Geofísica do Departamento de Geocięncias da Universidade do Amazonas. As áreas pesquisadas, envolvendo partes representativas das unidades litológicas ocorrentes na área, apresentam valores de resistividade aparente distintos, compatíveis com as características litológicas observadas e ao grau de intemperizaçăo das mesmas. A área 1, abrangendo rochas areníticas da Formaçăo Trombetas, apresenta valores de resistividade aparente variando entre 5.005 a 9.797 ohm.m (configuraçăo de Wenner), cuja profundidade de investigaçăo foi da ordem de 1m, e de 7.337 a 15.904 ohm.m (configuraçăo de Schlumberger), com 4,5m de profundidade investigada, o que caracteriza urn evidente aurnento nos valores de resistividade aparente com a pro fundidade. A área 2, constituída de rochas efusivas, apresenta valores de resistividade aparente menores, alcançando 18.086 ohm.m ( Sch1umberger) a 24m de profundidade investigada, demonstrando urna maior condutividade elétrica dessas rochas. A área 3, compreende rochas graníticas fortemente intemperizadas. Mostra urna grande variaçăo nos valores de resistividade aparente, independente da profundidade investigada. O elevado grau de intemperismo nesta área, e responsavel pelas grandes alteraçőes nas características de condutividade elétrica desse material litológico.
-
-
-
Análise Integrada de Informaçőes Geofísicas, Morfológicas e Geológicas da Porçăo Centro-Nordeste do Estado de Roraima
Authors J. da Silva Carvalho and R.L. Castro de AraújoA área tema deste trabalho, localizada na regiăo centro-nordeste do Estado de Roraima, envolve parte da regiăo dos campos gerais, com feiçőes morfológicas típicas de area arrasada e peneplanizada, onde se destacam relevos residuais, representados pelas serras do Cauarane, Moça e Murupu com fortes evidęncias de controle estrutural pelos eventos tectônicos que incidiram na mesma. Compreende terrenos gnáissicos e graníticos da Suíte Metamórfica Urariquera (Arqueano/Proterozóico Inferior), além de quartzitos, anfibolitos, piroxenitos·· e xistos, pertencentes ao Grupo Cauarane (Proterozóico Inferior), riodacitos, dacitos e riolitos, pertencentes ao Grupo Surumu (Proterozóico Médio). Ocorrem ainda rochas cataclasadas e milonitizadas relacionadasao evento tectonotermal K'Mudku (Proterozóico Superior), diques básicos da Suíte Básica Apoteri (Mesozóico) além de sedimentos arenosos e argilosos pertencentes ŕ Formaçăo Boa Vista e ŕ unidade denominada Depósitos Recentes e Sub-Recentes, de ida desterciaria e quaternária, respectivamente. A análise das informaçőes geofísicas disponíveis (magnetométricas e radiométricas) se apresenta como importante subsídio para uma melhor compreensăo do comportamento litológico e estrutural da área. Da mesma forma, as correlaçőes dessas informaçőes com os aspectos morfológicos verificados, se apresentam como ferramentas indispensáveis para o melhor entendimento dos aspectos geologicos de uma área como essa.
-
-
-
Distribuiçăo Vertical das Concentraçőes de U,Th, e K nos Sedimentos do Grupo Bambuí na Regiăo de Pirapora (MG)
Authors A. Roque and F. Brenha RibeiroA distribuiçăo de temperaturas no interior de bacias sedimentares é determinada pela densidade de fluxo de calor no seu embasarnento, pela variaçăo da condutividade térmica no seu interior e pelo transporte advectivo de calor por fluidos, água principalmente, contidos nos seus sedimentos. O calor radiogęnico gerado em sedimentos e metassedimentos é, em geral, pequeno e tem pouca influęncia no estabelecimento do campo de temperatura de uma bacia. No entanto, a contribuiçăo do calor radiogęnico pode ser importante para processos que ocorrem nos sedimentos como, por exemplo, a maturaçăo de hidrocarbonetos. Pequenas diferenças de temperatura, passíveis de serem produzidas pela geraçăo de calor nos sedimentos, podem, dependendo das condiçőes existentes, ter efeito significativo sobre o processo de maturaçăo (Rybach, 1986).
-
-
-
Ensaios de Modelagens Geofisicas Aplicados a Regiőes Portadoras de Estruturas Circulares Kimberlíticas, Bacia do Parnaíba, NE do Brasil
More LessAlgumas regiőes da Bacia do Parnaíba (NE do Brasil) que apresentam anomalias aeromagnetométricas interessantes, associadas ŕ existęncia de Províncias Kimberlíticas, estăo sendo objeto de investigaçőes. A ocorręncia de estruturas circulares de natureza endógena e exógena, distribuídas dispersamente ou em grupos, pode ser notada por quase toda a superficie de 650000Km2 desta bacia (Castelo Branco, 1986). Métodos geofisicos (magnetometría, gravimetría, gama-spectrometria, sondagens elétricas verticais) foram utilizados. Ensaios de modelagem 2-D apontam, em alguns casos, para uma interpretaçăo condizente com a presença em subsuperficie de estruturas do tipo câmara magmática-« pipes », alojadas no substrato cristalino da bacia.
-
-
-
Caracterizaçăo Geológico-Geofísica do Greenstone Belt Rio das Velhas
Authors M. de Araújo Vieira and S. Lima da SilvaÉ do conhecimento geral que os levantamento geofisicos refletem de modo destacado as rochas e estruturas geológicas de uma regiăo, fomecendo informaçőes sobre as características petrográficas do subsolo, destacando certos tipos de depósitos minerais.
-
-
-
Prospecting in Depth: Examples from the Onshore Wilcox Play, Louisiana and Texas, U.S.A.
Authors C. E. Guzman, M. Ramaswamy, K. P. Lawler and B. K. WrightA methodology of depth conversion used in the liilcox Tertiary play in onshore Louisiana and Texas, U. S. A. is discussed. A time map and a map of maximum coherency seismic velocities are used to generate a depth map. Since depth conversion depends substantially on velocities, precision velocity measurements are made using an event oriented algorithm. The velocities are carefully analyzed for misties and then contoured within geologic boundaries. liell information, if any, is also incorporated into the velocity map, and then the time map is converted to a depth map. To calibrate the method, a couple of examples are presented. An example where the method was used to help locate a drill site and predict geologic horizon depth will also be discussed. lIith the availability of new processing techniques, greater confidence may be placed on this method to generate prospects directly. To illustrate, a structural prospect that is not apparent on a time map will be shown.
-
-
-
Radiometric and Sulphur Isotopic Studies on the Sulphide Bodies from the Singhbhum Cu-U Belt, Eastern India
Authors D. Sengupta, D.J. Dutta and A. BoyceDetailed studies have been carried out by us (Sengupta and Kalvey, 1992: Sengupta et al-, 1995; Boyce et al-, 1995) at vari_ ous locations in the Singhbhum Shear Zone, Bihar, India to understand the nature of uranium and copper mineralisations in this region. Based on our studies on the distribution of uranium and copper in the copper deposits in the Shear Zone, it has been found that the uranium and copper mineralisations are not necessarily closely associated. Though the uranium and copper bearing solutions proceeded along the same shear planes in the soda granites, there was a time gap between the mineralisation of uranium and copper· This is also supported by the geochronolgical data available at present (Rao et al·, 1979, Bhattacharyya, 1992). In the shear zone, uranium seems to be an important byproduct from the copper deposits with uranium in the range of 10- 250 ppm. The sulphur isotopic studies carried out on individual sulphide mineral pairs showed a narrow distribution of 6 S (+3-9 to +6·3 per mil)· This indicates that the Singhbhum copper ores conform well with the strata bound sulphide deposits in volcanic rocks which exhibit typically positive 6 S- Studies, carried so far, has helped in understanding the nature of the uranium and copper mineralisation (Sengupta et al-, 1995: Boyce et al-, 1995) as well as in assaying of the natural radiation background in the Shear Zone (Sengupta and Kalvey, 1992)- It would also be helpful in discovering higher grades of uranium deposits than those presently known in these region.
-
-
-
Petrophysical peculiarities or ores of skarn-magnetite deposits ( Russia, the Southern Urals)
Authors T.A. Sherendo, I.I. Gluchich, A.A. Garaeva and G.S. NechkinThe petrophysical investigations of ore magnetites from Magnitogorsk and Malyi Kuibas skarn-magnetite deposits were fulfilled. It was revealed essential difference between petrophysical properties of magnetites from various ore types : magnetites from disseminated are have the values of magnetic parameters, that are near to stoichometrical composition (as = 91 Am2/kg and Res = 1.0 kAlm), whereas these parameters for massive ore are equal to 82 Am2/kg and 3.9 kAlm, correspondingly. Thermal metamorphism and dynarnometamorphism exert a strong influence on grains' microstructure and magnetic properties of ore magnetite : as a result of recrystallization there are forming magnetite grains, more pure and less stressed and more "soft" in magnetic respect. It is confirmed by increase of specific saturation magnetization as up to 92 Am2/kg and by decrease of coercive force Hcs up to 0.1 kA/m.
-
-
-
The Study of Ore Field's Tectonics According to Measurements of Seismoacoustic Emission of Rocks and Helium Concentrations in Boreholes
Authors A.K. Troyanov and A.K. YurkovMeasurements of seismoacoustic emission (SAE) of rocks in borehole allow to receive essentially new information about modern dynamic processes in geological medium. Zones of rocks breaking and jointing are as a rule marked by anomalous level of SAE amplitudes. Dynamically active tectonic fractures in space around a borehole are also distinguished by the same SAE anomalies. Increased helium concentrations in subsurface water are connected with disjunctive disturbances in the Earth's crust, especially with deep faults. In this case there are marked only permeable disturbances, along which filtration of subsurface water may take place. Measurements of SAE and helium concentrations in boreholes of the Urals and Northern Kazakhstan are used to study the tectonics of ore fields. Interpretation of measurements of SAE and helium concentrations allows to characterize a tectonic disturbance according to its dynamic activity and its permeability.
-
-
-
Procesamiento de Datos Geofísicos y Geoquímicos de la Región de Santa Terezińa de Goiás - Brasil
Authors C.H. Tapia Calle and A.C.B. PiresImágenes aerogamaespectrométricas a colores fueron usadas, en el mapearniento de regiones rnineralizadas de uránio, (Duval, 1972), determinación de zonas con alta radiactividad, (IAEA, Viena 1991) e otros rninerales, como oro, tungsteno, molibdeno(IAEA, 1991, Hildemaro 1993). Los datos empleados en este trabajo fueron los de el Proyecto Geofisico Brasil-Canada (PGBC,1977), junto con datos geoquímicos (PGBC, 1977 Carmo 1978, Borges et al., 1990) y estos fueron tratados mediante el proceso de apeamiento temario de radioelementos (Brome et al., 1987) y el de potásio anómalo (Pires, 1995). Dichos datos geofísicos, geoquímicos pertenecen a la hoja topográfica de Santa Terezinha de Goiás , cuya Secuéncia Vulcano Sedimentaria del rnismo nombre (esquisto de cIorita muscovita cuarzo), es la roca portadora de la rnineralización de esmeralda. La generación de mapas de isovalores e imagenes a color fueron realizadas usando softwares de tratarniento de datos, para posteriormente efectuar la interpretación y correlación con sus alvos respectivamente.
-
-
-
Estudios Geofísicos en la Exploración de Yacimientos de Uranio-Aqua de Las Liebres - Mendoza-Argentina
Authors S.A. Pastore, G.F.E. Rocco and F.S. VolponiEn el ańo 1991, se planteó por parte de la Comisión Nacional de Energia Atómica de Argentina (CNEA), la necesidad de contar con una técnica geofisica que brindara óptimos resultados en el seguimiento de un horizonte de Areniscas mineralizadas con Uranio, en el sector Agua de Las Liebres, Distrito Uranitero Sierra Pintada, San Rafael, Mendoza (principal zona de explotación de Uranio en la República argentina).
-
-
-
Geophysical Case Studies of Two Kimberlites in Minas Gerais, Brazil
More LessIn the search for primary source rocks for economic deposits of diamonds in Minas Gerais, geophysical methods have become an important part of the exploration program. Prospective areas are covered with a high resolution airborne magnetometer survey. The results are processed, contoured, imaged and target anomalies are selected. The original magnetic profiles are reviewed for interpretation as a quality control and priorities assigned to the anomalies based on size estimation, depth of burial and location relative to corroborating data from Landsat ™ images and heavy mineral concentrate samples. Ground follow-up including magnetic surveys gravity surveys and resistivity soundings may then be carried out over the expected surface position of the aeromagnetic anomaly. Positive results would then prompt a drilling program to test the source of the geophysical anomaly. Modeling of the ground geophysical results would provide valuable information on the depth to target and the boundaries of the pipe in addition to the recommended drill hole position. In this paper the geophysical signatures of two large kimberlites from Minas Gerais State, Brazil are presented.
-
-
-
Integrated Geophysical Surveys for Searching of Podiform Chromite in Albania
Authors A. Kospiri and A. ZajmiThe purpose of this paper is to describe the application of geophysical methods to the search for chromite in Albania. Albania is well known for its chromite resources and ranks third amongst world producers of high-quality chromite. The ultramafic massif of Bulqiza, is the most important chromite bearing one. Surveying a surface of about 120 square kilometers (30% of massifs area) in that massif with integrated geophysical methods a considerable number of targets bas been discovered (more than 35), from which some are already objects under mine activity. In the integrated methods for chromite exploration in Bulqiza ultramafic massif are included: geological, gravity, magnetic and electrical mapping of the scale 1:2000 with survey grids 40x20m, 20x5m. Based on the interpretations of geophysical exploration were projected drillings which led to the discovery of some big ore deposits.
-
-
-
Deep Crustal Studies: An Aid to Diamond Exploration
More LessNew seismic vertical and wide-angIe reflection data collected by LITHOPROBE across the Trans-Hudson Orogen provide striking images of juvenile Paleoproterozoic arc rocks interposed between the deformed margins of the Archean Superior and Hearne cratons. Along the western half of this collisional tectonic belt the crustal architecture is roughly symmetric about a crustal-scale culmination within the accreted juvenile collage, which geologic and isotopic data suggest may be cored by Archean basement. West of the culmination, highly reflective packages dip consistently westward into the lower crust, beneath the straddling Wathaman batholith and reworked Archean continental margin of the Hearne craton. On the eastern flank, crustal imbrication, on a scale imaged in few other orogens, is observed within the juvenile Flin Flon belt, where a package of shallowly east-dipping reflections extends from the surface to 14 s. Sheets of middle to lower crustal arc rocks have been stacked below a major detachment that carries the upper crustal remnants of an island arc complex. The combined reflection data outline a spatially well-defined Moho subsurface. These high quality reflectors have over 500 km lateral continuity and show considerable relief (36-52 km depth), including a prominent root. beneath the crustal culmination. Surface projection of some of the Moho anomalies are associated with regions of more than 100 kimberlite pipe discoveries. A number of these diatremes are diamondiferous. Discovery of these anomalous targets are aided by the deep crustal anomalies.
-
-
-
Modelamento Analógico em Polarizaçăo Induzida
Authors J. Domingos Faraco Gallas and O. Prakash VermaO objetivo deste trabalho é o desenvolvimento de uma técnica e metodologia para modelamento analógico IP em laboratório. Foram usados modelos cilíndricos e tabulares (placas), construídos com cimento, areia quartzítica e grafita. Como a grafita apresenta um intenso fenômeno IP, variou-se o teor de grafita contido nos modelos. Assim, para diferentes formas e medidas dos modelos, variou- -se tambem o conteúdo de partículas polarizáveis, no sentido de verificar o comportamento da resposta IP quanto a forma, conteúdo de grafita, profundidade e direçăo do modelo estudado.
-
-
-
Inversăo Linearizada de Sondagem Elétrica Vertical Utilizando Norma Lp
Authors N.R. Ferreira and M.J. PorsaniA inversăo de dados geofísicos pode ser vista como um procedimento para obter modelos que descrevam adequadamente um conjunto de dados. As medidas de levantamentos geofísicos traduzem as variaçőes das propriedades físicas das rochas . A partir os dados geofísicos levantados podem ser obtidas informaçőes para construçăo de um modele geológico de subsuperfície.
-
-
-
MIGRACION KIRCHOFF EN PROFUNdIdAd PREAPILAMIENTO EN AREA COMPLEJA: Caso Historico en el Flanco Surandino
Authors J. Licheri, A. Gonzalez, J. Fuente, K. Ritchie and J. AndersonSe presentan en forma práctíca las experiencias y resultados de la migración en profundidad preapilamiento utilizando el algoritmo de Kirchoff para el procesamiento de la información de 200 km de línea sísmica de diferentes levantamientos que componen la exploración regional que Corpoven, S.A. ha realizado en el flanco sur de los Andes Venezolanos. EI objetivo fue ubicar las estructuras prospectivas en su verdadera posición en el subsuelo, reduciendo posibles efectos "pull up", y otras deformaciones de la imagen sísmica causadas por variaciones del campo de velocidades en zonas típicas del frente de montańas mayores al 20% dentro de la longitud del cable (3000 m).
-
-
-
Resposta Geofisica do Jazimento Antonio : Macico do Escambray, Cuba
More LessO jazimento de Antonio - situado no Maciço do Escambray, regiăo central de Cuba - é um depósito cupro-zincífero, associado com sulfetos maciços da formaçăo Los Pasos, de caráter vulcanógeno-sedimentar. Como parte do programa de exploraçăo que vem realizando em Cuba, a empresa Joutel Resources Ltd. tem utilizado intensamente técnicas geofisicas aéreas e terrestres, com ęnfase especial nos métodos eletromagnético e magnético. Os levantamentos conduzidos na regiăo do deposito de Antonio volveram os sistemas eletromagnéticos, em dominic de tempo e de frequęncia. O objetivo principal destes levantamentos foi o de identificar a real extensăo do corpo mineralizado, como forma de racionalizar o emprego de sondagem para avaliaçăo do potencial mineral do depósito. A análise da resposta geofisica do depósito de Antonio aos diferentes métodos utilizados, com ęnfase nos resultados do levantamento EM-MAG-RAD-VLF, executado em 1995, pela Scintrex Ltd., é o que trata o presente trabalho.
-
-
-
Geophysical Signatures of Australian Base Metal Deposits
By J.R. BishopThe geophysical signatures of Australia's base metal mines and important deposits are presented and evaluated. The results suggest that induced polarisation (IP) is probably the most effective method for directly detecting unmetamorphosed sediment-hosted deposits and carbonate-hosted deposits, whereas electromagnetics (EM) is probably the best for volcanogenic and metamorphosed sedimenthosted orebodies. Magnetics is best for skarns and Cobar-style deposits. However, for all targets, it is emphasised that usually more than one method is required.
-
-
-
Auscultaçâo Geodésica na Regiăo da Hidrelétrica Segredo (II)
Authors C. Gemael and P.L FaggionEm artigo anterior o autor (Gemael, 1993) descreveu a primeira parte dos trabalhos geodésicos desenvolvidos na regiăo da Hidrelé trica Segredo, implantada pela COPEL no Rio Iguaçu, na regiăo sudeste do Estado do Paraná. Objetivo: detetar eventuais subsidęncias do solo nas vizinhanças da barragem após o enchimento do reservatório.
-
-
-
Crosswell Seismic Profiling: A Tool for High Resolution Reservoir Characterization and Monitoring
By J.M. HarrisCrosswell seismic profiles provide a view of petroleum reservoirs that complements in resolution and coverage other geophysical data such as surface seismic, bore hole logs, and core data. See Figure 1. The technology is rapidly maturing and there are many applications in high resolution petroleum reservoir characterization, monitoring of steam recovery processes, monitoring of miscible gas floods, and in the delineation of gas storage fields. There are also numerous environmental applications. In this talk, I will review the state-of-the-art of the acquisition and processing technologies. New source technologies promise to deliver better data in less time and at lower cost. ew and improved processing methods, particularly of the reflections, are providing images capable of subtle qualitative and quantitative interpretations for reservoir properties. The integration of crosswell images through geostatistics and flow simulations is at the forefront of reservoir characterization science. While the continued development of the technology is being driven by applications, there are also many exciting research activities. I will identify some of this ongoing research and summarize the future needs.
-
-
-
How well can seismic anisotropy resolve natural fractures in hydrocarbon reservoirs, and is there room for improvement?
By C. MacBethThe influence that fractures have on seismic waves is controlled by the nature of the network formed by the fracture system. However. the relationship between natural fracture networks and the wavefield needs careful consideration to understand which factors consort to form . the overall seismic response. Dilute concentrations of smooth euclidian shapes fail to adequately represent nature's complexity when investigating seismic scattering from natural fracture networks. In spite of this drawback, theories based on such work have been successful at helping to resolve details of simple fractured targets in a wide variety of geological scenarios. For more complex reservoir settings and more widespread use of this technique. future work must address possible departures from such traditional approaches. to consider actual mapped measurements. Work is currently in progress to ·achieve this goal using a technique which permits the: definition of a numerical equivalent medium for an ·arbitrary input. This helps to investigate whether the directional behaviour of the transmitted wavefield has potential in defining these different network realization; and to isolate the most critical features of this response.
-
-
-
Issues in Rock Physics and Implications for DHI Interpretation
Authors J.P. Castagna and M.L. BatzleSeismic techniques for direct hydrocarbon indication rely on the changes in seismic character which accompany changes in pore fluid content. Interpretation and modeling of DHI's require an understanding of the factors affecting seismic velocities and reflection coefficients. which arc in tum dependent on pore fluid properties. rock frame properties. and fluid substitution within a given rock frame. Recent developments in rock physics have greatly increased our general understanding in these areas. but have also revealed complications that require further research.
-
-
-
3D Reservoir Characterization Pavuyacu Fleld Maranon basin, Peru
Authors J.L. Petroperu, W.S. Petroperu and J. SherwoodThe PAVUYACU field is situated in the Maranon basin in the oriente jungle of Peru. The field produces from sandstone reservoirs in the Upper Cretaceous. The sands are fluvial deltaic in the upper units and more marine deltaic in the lower units. The field had produced at a maximum rate of 9,500 SOPO from 14 wells in 1982. This production had declined to 2,500 BOPO in 1993. At this time it was declded to shoot a 3D seismic survey and carry out an integrated Interpretation to see if any upside potential remained in this field.
-
-
-
Geostatistical Inversion of Seismic Data
Authors O. Dubrule, M. Thibaut and A. HaasGeostatisical inversion of seismic data, a novel acoustic impedance inversion technique. Is presented. illustrated by an example and discussed. The method generates 3D acoustic impedance models at the reservoir scale. These models can then be used for predicting reservoir properties such as lithology or porosity. Nonuniqueness of the inversion process is quantified by generating possible 3D acoustic Impedance realisations", all compatible with the acoustic Impedance traces at the wells. and the 3D seismic block. Vertical and horizontal continuity of these realisations Is constrained by means of an input vartogram model. Different geological scenarios can be generated, satisfying a given vartogram, and systematic vertical variations in acoustic impedance can be controlled by a vertical trend in the mean and standard deviation of acoustic impedance. Compared to existing stratigraphic inversion techniques. the main characteristic of the method is that acoustic impedance traces are generated sequentially: an objective function is minimised on a trace by trace basis instead of being minimised over the whole seismic block. This feature provides speed and flexibillty to the geostatistical inversion technique.
-
-
-
4·0 SEISMIC: A POWERFUL NEW TECHNOLOGY FOR MONITORING STEAM MOVEMENTS IN DURI FIELD· CENTRAL SUMATRA
Authors M.F. Bee, S.D. Jenkins, J.H. Lyle and E. MurhantoroRepetitive (4-0) seismic surveys are able to monitor reservoir changes due to steam injection in Duri Field. Maps of reflection anomalies from the base of the injection interval show the spatial distribution in the 4-0 pattern can be made from seismic anomalies calibrated with the help of core and well temperature measurements. Some of the Duri oil reservoirs have minor gas saturation before steam injection due to pressure depletion, After steam injection, a high velocity annulus attributable to fluid pressures exceeding bubble point pressure is observed on themonitor data sets. Subsequent movement of this pressure front indicates areas of greatest permeability and is potential predictor of later thermal and steam front movements.
-
-
-
Crustal Structure of the Argentine Continental Margin and of the Argentine Basin from Seismic Reflection Data
Authors K. Hinz and J.D. GiordanoConstruction and structural elements of the volcanic margin of Argentine are discussed on the basisof deep reflection seismic data. Further, the results of seismic measurements along flow-line traverses across Cretaceous-aged oceanic crust of the South Atlantic. According to our studies most of the South Atlantic divergent margins are volcanic margins characterized by voluminous structures showing a distinct seaward dipping reflection pattern and prominent magnetic anomalies. The ephemeral emplacement of these voluminous constructions occurred during Hauterivian through Barremian in the South Atlantic. Episodes of an intensive production of oceanic crust have been recognized in the South Atlantic during the Albian through early Campanian.
-
-
-
Elusive Salt Tectonics in the Deep-Water Region of the Sergipe-Alagoas Basin: Evidence from Deep Seismic Reflection Profiles
More LessContrasting with the passive margin basins in Southeastern Brazil, which are characterized by voluminous volcanism during the rift phase and a characteristic, thick salt diaper province in deep waters, the Sergipe and Alagoas basins have been considered as paradigms of non-volcanic rifted margins lacking a deep-water salt dlapir province. However, a number of deep seismic reflection profiles In the Serglpe and Alagoas basins suggest: (1) the occurrence of thick wedges of seaward-dipping reflectors associated with emplacement of oceanic crust; (2) some elusive features might be associated with deep-water salt tectonics. Although subject to controversial interpretation, especially because of an apparent association with fracture zones and volcanic features, the structural styles In the deep-water region of the Serglpe and Alagoas basins have possible analogs in other salt provinces, particularly the North Sea and the western North Atlantic passive margins. Although untested, this model has profound Implications in deep-water petroleum exploration.
-
-
-
Geomorfologia do Grupo Sudeste de Cânions - Leque Submarino de Săo Tomé-Rl, com Base em Sísmica de Alta Resoluçao
More LessO Complexo do Leque Submarino de Săo Tomé e uma protuberância sedimentar localizada ao longo do talude e elevaçăo continental do Cabo Săo Tomé-Bacia de Campos/RJ. Seu mais notável dominio e representado pelo Leque Superior, que se desenvolve ao longo do talude continental da area (Figuras Ie 2).
-
-
-
Estratigrafia Acústica do Grupo Sudeste de Cânions - Leque Submarino de Săo Tomé - RJ
More LessO Leque Submarino Săo Tomé localiza-se ao longo do talude e elevaçăo continentais da Bacia de Campos - Rio de Janeiro. O seu mais notavel dominio fisiográfico e representado pelo Leque Superior, resultante da intensa progradaçăo terrígena Oligo-holocęnica que modelou morfologicamente o talude continental da bacia (Figs. 1 e 2).
-
-
-
Desenvolvimento Tectônico e Intrepretaçăo de Sequęncias Sedimentares das Cadeias Oceânicas Islândia-Faeroe e Aegir, no Mar da Noruega
Authors D.L. Castro and F. TheilenA cadeia oceânica que se estende da margem continental da Groelândia através da Islândia, das Ilhas Faeroe até as Ilhas Shetland representa a mais importante cadeia asísmica conhecida. Ela foi gerada a partir da abertura do Mar da Groelândia- Noruega no início do Terciário pelo deslocamento das placas oceânicas da America do Norte e da Eurasia sobre o "hot spot" que hoje se localiza sob a Islândia.
-
-
-
Refletores Intra-Água na Bacia de Campos
Authors G. Rodrigues de Lima, P.O.V. Piaullino and S. SchreinerO texto apresenta os resultados parciais de uma pesquisa em andamento sobre a utilizaçăo de dados da sismica de reflexăo na delimitaçăo das massas d'agua dos oceanos. O emprego de perfis de reflexăo sísmica em duas ou tręs dimensőes, tal qual na geologia, pode facilitar em muito a correlaçăo entre as rnediçőes pontuais de determinadas propriedades fisicas do meio aquoso. É apresentada a seqüęncia de processamento dos dados sísmicos e o seu resultado, bem como săo feitas comparaçőes com dados de mediçőes diretas da temperatura e velocidade do som na água.
-
-
-
Determinaçăo do Espectro Direcional de Ondas na Bacia de Campos
Authors N.A. Barbosa Seixas and C.E. ParenteOs diversos tipos de onda que se propagam no oceano (ondas superficiais, intemas, tsunamis, mares, ondas planetarias, etc ...) săo, em geral, classificadas por faixas de período, possuindo relaçăo com os processos que the deram origem. Neste trabalho serăo estudadas as ondas superficiais de gravidade geradas pelo vento, cujos periodos variam entre 2 e 20 s. A agităo maritima e entăo definida como a variaçăo irregular da interface atmosfera-oceano, resultante da transmissăo da energia proveniente dos ventos ŕ massa fluida dos mares, onde a gravidade atua como força restauradora, recuperando a condiçăo de equilibrio da superficie.
-
-
-
Reflexőes Sísmicas da Estratificaçăo da Água Oceânica Profunda da Costa Norte do Brasil
More LessUm processamento especial para os dados de sísmica de reflexăo multicanal da camada de água oceânica profunda da costa do Para, regiăo Norte do Brasil, mostrou uma diversidade de refletores nesse intervalo. Uma análise comparativa entre esses dados sísmicos e os dados ocenográficos da área conduziu a interessantes resultados: a estratificaçăo de temperaturas e salinidades das águas oceânicas apresenta uma razoável correlaçăo com os dados de velocidades sísmicas;os dados de velocidades do som na água, calculados a partir de informaçőes oceanográficas de temperatura e salinidade atraves da utilizaçăo de formulas rnaternaticas (Mackenzie,1959) apresentam-se similares ŕs velocidades sísmícas obtidas no processamento. Esse estudo sinaliza a possibilidade de uso da sísmica de reflexăo no mapeamento das massas e correntes oceânicas profundas.
-
-
-
Interpretaçăo Sismoestratigráfica da Plataforma do Amazonas
Authors T.C.M. Araújo and F. TheilenEm outubro de 1990, foram conduzidas investigaçőes sísmicas de alta resoluçăo na plataforma do Amazonas, dentro do Projeto MAR 3.1. Foram coletados, ao todo, 16 perfis de sísmica de reflexăo monocanal, na área que liga a plataforma intema com o cone profundo. As seçőes sísmicas obtidas foram analisadas, neste trabalho, com base nos conceitos da sismoestratigrafia, com o objetivo de se obter a história da evoluçăo sedimentar para a área em questăo. Duas discordâncias regionais foram mapeadas: a discordância I (Mioceno Médio) e a discordância II (Oligoceno Inferior). Uma grande mudança no regime sedimentar da área ocorreu após a formaçăo da discordancia I, marcada pela chegada do grande aporte dos clásticos carreados pelo Amazonas. Os clásticos săo representados, nas seçőes sísmicas, por uma zona transparente. Bacias sedimentares foram mapeadas, mostrando uma discordância localizada a 200 ms (tempo duplo) abaixo do fundo do mar. A presença de onlaps e downlaps confirmam os ciclos de transgressăo e regressăo ocorridos na área. A variabilidade espacial e temporal nas condiçőes sedimentares desta área, é marcada pela presença de feiçőes de corte e preenchimento, nas sequęncias sedimentares.
-
-
-
O Cânion Submarino do Amazonas: Uma Análise Baseada em Dados Sísmicos e Gravimétricos
More LessO Cânion Submarino do Amazonas está localizado na plataforma continental do Amazonas, na desembocadura do rio homônimo. Dados de sísmica de reflexăo oriundos do Projeto MAR 3.1, bem como dados de gravimetria (Projeto EQUANT II) foram usados para analisar o comportamento deste cânion sobre a plataforma continental. A análise dos perfis de sísmica de reflexăo monocanal permitiram mapear o curso do cânion sobre a plataforma. Na plataforma, o cânion chega a atingir 400 m de profundidade e 9 km de largura. Com base na direçăo e localizaçăo das estruturas de cânions encontradas nas seçőes sísmicas, e sugerido que o mesmo faz parte de um sistema meandrante submerso. O mapa de anomalia ar livre mostrou a complexidade da área. Na regiăo onde se encontra o cânion, as isolinhas mostram, na plataforma, uma curvatura para nordeste (NE). Essa curvatura também a visivel no mapa de anomalia Bouguer. Essa curvatura e atribuída a presença do eixo do gráben do Mexiana-Este, indicando um controle tectônico para o curso do Cânion Submarino do Amazonas sobre a plataforma continental.
-
-
-
Geometry of Five Submarine Slumps Complexes - Campos Basin, Brazil
Authors D.D. Castro, J.G. Rizzo, J. Heinerici and L.G.G. CaddahIn the Campos Basin, offshore Rio de Janeiro State, Brazil, between Săo Tome Canyon, to the north, and Grupo Sudeste de Cânions, to the south, the late Miocene to recent sediments of the continental slope comprise submarine slumps complexes. Seismic mapping of these slumps has provided some clues to its geometry and behaviour. The slumping processes were recurrent in the geologic time generating a series of six slumps here named Slump I (the oldest) to Slump VI (the youngest). The maximum thickness of these slumps ranges from 50 to 85 m and cover areas ranging from 875 to 1575 km>, The slump III was not completely traced due to its less regional significance. The submarine slumps IV, V and VI show a complete slump structure consisting of head, body and toe regions, while in the slumps I and II only body and toe regions are present. It was observed that extensional structures (normal faults) prevail at the head and the compressional ones (thrust faults and folds) in the toe region. Triggering mechanisms for slumping are not completely understood, Costa et al. (1994) and Viana et al. (1994), consider the lowering of the sea level the principal slumping factor.
-
-
-
Aquisiçăo de Dados Sonográficos, Batimétricos e de Perfis de Alta Freqüęncia na Bacia de Campos
Authors P. Orlando, V. Piauilino, P.R. Maldonado and L.E.N. FonsecaO avanço da exploraçăo para águas cada vez mais profundas na Bacia de Campos e o desafio de instalar equipamentos para a produçăo e escoamento do petróleo exigem um maior conhecimento do fundo marinho. O desenvolvimento do Programa de Inovaçăo Tecnológica e Desenvolvimento Avançado em Águas Profundas e Ultraprofundas, conhecido como PROCAP-2000, propiciou a integraçăo e o esforço necessário para a campanha de levantamento de dados sonográficos e batimétricos de varredura e de perfil sísmico de alta freqüęncia ( SBP). Pesquisou-se uma area de 42.869 Km2 ( 25.000 km lineares) situada entre as isóbatas de 150 a 3000 metros aproximadamente que correspondem a 40 % da Bacia de Campos (Figura I). O levantamento foi realizado em aproximadamente 100 dias, dividindo-se em sete embarques de 14 dias. As Iinhas foram orientadas no sentido leste-oeste e perpendiculares ŕs isóbatas( do cinion de S. Tome para norte) a oblíquas (do canion de Sao Tome para sui), cobrindo a área programada. Este texto visa apresentar dados sobre a campanha de levantamento, das rotinas de processamento e dos primeiros resultados e suas aplicaçőes.
-
-
-
THE EFFECTS OF SALT WITHDRAWAL ON TRAP EVOLUTION AND HYDROCARBON SYSTEMS IN THE GULF OF MEXICO BASIN
Authors C..J. Andol and C.A. DengoThe northern Gulf of Mexico basin margin exhibits a wide spectrum of hydrocarbon system elements from initial to mature stages that resulted from, or were influenced by salt withdrawal. In the past decade, improved seismic data quality and geological concepts developed by workers inside and outside the petroleum industry have led to a fundamentally new regional understanding of the distribution of structural styles and their evolution in the context of allochthonous, laterally displaced salt sheets with multi-phase emplacement histories.
-