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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
241 - 260 of 330 results
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Mudanças Temporais da Temperatura Subsuperficial
More LessForam realizadas medidas diárias dos valores da temperatura no período compreendido do ano de 1992 ao ano de 1994, no horário das 08h, nos meses de junho a dezembro, ŕs profundidades de 0.0m , 0.5m e 1.0m. Os resultados mostram que as magnitudes das variaçőes dos valores da temperatura, ŕ profundidade de 1.0m, năo podem ser consideradas como desprezíveis, ou saja; as diferenças mínimas entre os valores médios mensais da temperatura foram de 1,63 °c a 2,04°C, enquanto que as variaçőes diárias da temperatura atingiram até 0,41 °C. No período relativo a este trabalho, ocorreu um decréscimo sistemático dos valores médios mensais da temperatura, ŕ profundidade de 1,0m. Tal decréscimo é causado por fonte externa sendo, ainda, imprevisível seu comportamento futuro.
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Modelo Termomecânico de Cisalhamento Puro Aplicado a Registros Estratigráficos da Bacia do Paraná
Authors M.C. Lopes Quintas and M.S.M. MantovaniO presente trabalho tem por objetivo fornecer subsídio geofísico para o estudo de processos envolvidos na evoluçăo mecánica da bacia do Paraná. Apresenta-se aqui um estudo termomecânico baseado em registros de 81 poços exploratórios para hidrocarbonetos, perfurados através da Petrobrás e Paulipetro, e analisados através de modelos distensivos de cisalhamento puro (McKenzie. 1978; Royden & Keen. 1980).
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Avaliaçăo Paleomagnética e Tectono-Sedimentar das Formaçőes Poti e Pastos Bons na Regiăo de Floriano-Nazaré do Piaui
Authors B. Vieira de Alencar, M. Silva Borges and A.M. GoésOs dados paleomagnéticos provenientes das formaçőes Poti e Pastos Bons, na regiăo entre Floriano e Nazaré do Piauí, foram reavaliados sob o ponto de vista estratigráfico e tectónico . Esta análise ratificou a nova proposta de revisăo estratigráfica nesta área. A partir de dados paleomagnéticos foram definidos dois conjuntos estatísticos, um ligado ao topo e a base da Formaçăo Poti, e o outro relacionado ŕ Formaçăo Pastos Bons. As dispersőes das direçőes de magnetizaçăo podem também estar relacionadas com processos tectónicos atuantes na regiăo.
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Application of the Petroleum System Concept in the Assessment of Explor. Risk: The Camamu Basin Example, Offshore Brazil
Authors M.R. Mello, F.T.T. Goncalves, A.S.T. Netto, J.L. Amorim and R.E. WitzkeIn the last years, a multidisciplinary approach involving geochemical, geological, geophysical and microbiostratigraphic research, has greatly enhanced the level of understanding of some of the most representative petroleum systems in the Brazilian sedimentary basins (Mello et al., 1994). After 35 years of exploration, the application of the petroleum system concept (Magoon, 1988) in the Camamu basin, offshore Bahia (Fig. 1), NE Brazil allowed the identification of a new exploration target, which after drilled resulted in a 157 M bbl discovery. The petroleum system postulated for the area, emphasized the genetic relationship between a Lower Neocomian lacustrine fresh to brackish water source rock associated with Barremian lacustrine sandstones turbidities reservoir (Morro do Barro-Rio de Contas (!) petroleum system).
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Lithosphere Structure of the South American Plate From Dispersion of Surface Waves
More LessA total of 48 group velocity dispersion curves were computed in order to study shear velocity structure within South American Plate. It was applied single station method and moving window analysis technique to periods ranging from 17s to 85s. Based on their azimuthal distribution and shape similarities, the group velocity dispersion curves were grouped and the results inverted, using differential inversion method to yield shear-velocity models for the Mid- Atlantic Ridge and Andes Ridge. The result of the inversion process applied to the data from oceanic paths has shown 4 consistent interfaces at average depths of 14km, 40km, 74km and 110km. The crustupper mantle transition is verified at 40km, shown by an increase of shear velocities values up to 4.40km/s. The structural interfaces of the continental paths have resulted in average depths of 6km, 20km, 50km and 120km. The shear velocities values are lower than those found for oceanic paths with values around 3.60 krn/s in the upper 20km. The transition between crust and upper mantle is found around 50km with shear velocity values of about 4.36km/s. Lithosphere bottom is shown around 120km as a low velocity zone is observed.
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Expresion de Magnitud Basada en la Duración para Sismos del Centro-Oeste Argentino
Authors C.A. Puigdomenech, M.H. Millán and M.A. AraujoUna expresión para estimar la magnitud, basada en la distancia hipocentral (en km.) y en la duración (en segundos) del registro, se obtuvo para sismos localizados en el centro-oeste argentino (25° - 37° latitud Sur y 62° - 70° longitud Oeste). La determinación se realizó con la información de 125 registros de componente vertical de la estación Coronel Fontana (CFA), ubicada a los 31° 36' 25.12" de latitud Sur y a los 68° 14' 21.4" de longitud Oeste. Las magnitudes muestras utilizadas para calcular el modelo, fueron determinadas por el Servicio Geológico de los Estados Unidos. Para el calculo de la expresión de magnitud, se utilizó una Regresión Múltiple entre las variables candidatas (logaritmo en base 10 de la duración del registro de un sismo, log t; y la distancia hipocentral, D) que fueron seleccionadas al aplicar la técnica de Regresión por Pasos.
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Migration of Stresses and Highfrequency Seismic Noice in the Earth Crust
Authors B.P. Dyakonov and A.K. TroyanovRegistration of geoacoustic noises was carried out within the band of frequences 30-2500 Hz by a number of instruments that included a borehole probe with three inducers-accelerometers, preamplifier, commutator, calibration apparatus and also a surface block with amplifier, control device and recording instruments. Borehole 470, wherein measurements within an interval of depth 100-1000 m were repeated annually beginning from 1984, is situated in the area of iron-ore-deposits of the Turgai deflection in Northern Kazakhstan at a distance of 200 m from a tectonic disturbance. Similar research was carried out in the engeosynclinal complex of rocks opened by the Urals superdeep borehole (USDB), situated approximately 600 km to the north of borehole 470.It is established that the Urals superdeep borehole observes the same temporal trend in noise intensity as borehole 470 but with a delay of 2-3 years.The completed work offered an opportunity to expose slow dynamic processes of a regoinal scale, to obtain quantitative evaluations of such most important parameters as an amplitude of stresses'fault, the magnitude and direction of epicentral velocity of stresses' migration.
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Frequency-dependent attenuation of Love waves and its estimation
By X.-P. LiAbsorption analysis of Love channel waves plays an important role in in-seam seismic exploration, because the usefulness of this method in a particular locality depends on the rate at which Love-type channel waves are attenuated during their passage through the coal seam. In the absence of any evidence of reflections, it is always important to know at what range such features would have been detected in case of their presence. Obviously this is determined by a number of factors, for example, the distance and especially the absorption. By introducing the complex propagation functions into the known dispersion relation of Love waves for a simple symmetric homogenous three-layered linear elastic model, the frequency-dependent attenuation relation can be explicitly given assuming that the quality factor of the coal (Qp,) and the country rock (Qp,) is constant. The attenuation coefficient of the Love waves becomes a non-linear function of the frequency because of the velocity dispersion. In this case the spectral ratio method can not be applied since it can only estimate the frequency-independent component Q. Therefore, a modification of the spectral ratio method is presented to inverse the frequency-dependent Q of Love-waves.
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Estimation of Apparent Seismic Attenuation of Crystalline Rocks in the German KTB Area Using VSP Data
By X.-P. LiIn this paper, an attenuation function which depends on the quality factor Q and the velocity V of the medium is used to describe the attenuation of seismic waves. With this attenuation function one can then easily derive the spectral ratio method to estimate the spatial cumulative attenuation. What important is that a similar derivation as given in the literature can be made to estimate a cumulative attenuation in the frequency domain, whose slope gives direct estimates of the inverse quality factor (Q-I) without any assumption about the medium. This derivation has been applied sucessfully to investigate the apparent seismic attenuation of crystalline rocks from the VSP measurements recorded in the German KTB (Continental Deep Drilling Program)-Oberpfalz. The investigations demonstrate that the seismic Q of the crystalline rocks in the KTB-area is frequency-dependent.
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Tomographic Images of P Wave Velocity Distribution at the Central and Southern Aegean Sea Area, Greece.
Authors I.F. Louis, G.A. Karantonis, K.C. Makropoulos and D. HatzfeldIn this study, an investigation of the P-wave velocity distribution beneath the Aegean region with application of seismic tomography techniques is presented. The data set used for this purpose was collected during the two month operation of a local seismological network of analogue and digital stations operated in the area during the summer of 1988. From the total of 828 recorded events, a selection of 205 accurately located and equally distributed earthquakes was used. A particular technique was developed for the selection in order to conserve the larger and deeper events. Several tests were performed for the determination of the appropriate initial velocity model, and the model parametrisation was carefully designed. The data set used, and the limited extension of the study area allow for increased resolution in the investigation of the velocity structure of the crust. The results presented by means of contour maps and cross sections, reveal the velocity structure of the crust and are in good general agreement with the results of other geophysical studies.
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Gauss-Newton vs. Newton Method for the Estimation of Changing Reflector Slopes
Authors W. Mouzer Figueiró and S. Valilevich GoldinThe slope (or the varying dip) of a seismic curved reflector has a very important physical meaning. It does not influence the operator defined by the Gauss-Newton method because the linear part of this operator does not depend on the slope of the reflector. The non-linear nature of the slope, when it is not sufficiently small, can make the Gauss-Newton method diverge in presence of noise (Goldin, 1999). In addition, it was observed (numerically) that, for a determined range of values for the signal-noise ratio, the Gauss-Newton method diverges when we wish to invert the slope of the reflector and this divergence is not observed when Newton method is used regarding the same range of signal-noise ratio values. More specifically speaking, three well defined intervals of behavior of these two methods were observed in a range of low signal-noise ratio values: in the first (the highest ratio values within this range) both methods converge, in the second (intermediary values) Gauss-Newton diverges and Newton converges and in third (lowest values) both diverge (Gauss-Newton more dramaticaly). In short terms, the substitution of the traditional Gauss-Newton by Newton algorithm improves significantly the convergence of the procedure of the estimation of the slope.
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EI Meacanismo de Flexión Viscoelástica en las Sierras de Córdoba Rep. Argentina; Analysis Preliminar en 31°30' Sur
Authors S. Miranda and A. IntrocasoLa litosfera es la región de corteza y parte del manto superior que soporta significativos esfuerzos desviatorios. Su espesor puede definirse sobre las bases de sus propiedades sísmicas, termales. composioionales o mecánicas. La litosfera mecánica es la porción de corteza y manto superior con una resistencia para soportar esfuerzo de largo periodo. Se define entonces isostasia como la condición en la cual todos los esfuerzos son hidrostáticos bajo la profundidad de compensación.
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Nuevos Cambios Temporales de "G" y "H" en la Región Sismotectónica de la Sierra Pampeana Argentina de Pie de Palo
Authors A. Introcaso, J.A. Robles, S. Miranda, P. Martinez and M.E. GimenezLa Sierra de Pie de Palo (San Juan - Argentina), perteneciente a la provincia geológica de las Sierras Pampeanas (figura 1) se localiza en el antepais Andino sobre la zona de subduoción subhorizontal de la Placa de Nazca en una región sísmicamente activa y de fuerte acortamiento cortical caracterizada por bloques de basamento precámbricos ascendidos. con un estilo de deformación análogo al de la estructura Larámica de Estados Unidos (Jordan et al., 1983). El 23 de Noviembre de 1977, se produjo un evento sísmico compresivo (Hs=7.4), con epicentro en el borde oriental de la sierra de Pie de Palo. que ocasionó un ascenso de más de 1.2 metros sobre el bloque de Niquizanga. Este movimiento vertical se pudo detectar a través de sucesivas remediciones altimétricas y gravimétricas en las etapas pre y post sísmicas, Ilevadas a cabo sobre la línea N23 (San Juan-Chepes), de una longitud aproximada de 230 Km (amojonada en promedio cada 4 Km), bordeando en su recorrido el sector sur de Pie de Palo cruzando la zona epicentral. Se analiza el comportamiento de las variaciones temporales de gravedad con apoyo en nivelaciones de precisión simultáneas, con énfasis en la etapa postsísmica.
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Mecanismos Alternativos que Explican el Levantamiento Andino, en una Sección Gravimétrica en 36° Sur
Authors M.P. Martinez, M.E. Gimenez and A. IntrocasoSe preparó la sección gravimétrica centrada en la latitud aproximada de 36°S (Introcaso, 1976), que se extiende desde el Océano Pacífico, atraviesa la República de Chile, la Cordillera de los Andes (Chilena y Argentina), luego se interna en la República Argentina y llega hasta el Océano Atlántico (figura 1, ubicación y figura 2 perfil gravi-altimétrico). Para determinar los acortamientos cordilleranos, se separó la porción correspondiente a la gran masa andina, resultando en consecuencia un ancho de 340 Km en estas latitudes, así, se incluye la Cordillera Principal (Argentino- Chilena) y la Cordillera Frontal en la Argentina, infiriendo que a ambos lados de ésta existen "excesos de masas". De esta manera, siguiendo entre otros las ideas de Introoaso et al, (1992), el acortamiento se define como: SH = (ST + SR) / Tn (1) donde: SH=acortamiento cortical; ST=área topográfica; SR=área de la raíz cortical; Tn=espesor normal de corteza, 33 Km (Woollard, 1969). Se tomó 300 m como el nivel base no afectado por deformación (Isacks, 1988), y se computó el área topográfica (ST) mediante suma de paralelepípedos de 10 Km de base y altura correspondiente con la asumida para cada estación, el área de la raíz cortical se determinó a travésdel resultado de la invesión de la anomalía de Bouguer, así: ST= 450,4 Km2; SR=3679.6 Km2 y SH=125,15 Km, siendo en este caso el acortamiento. el único proceso interviniente en la elevación de los andes.
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High Resolution Seismic Profiling of Paleochannels
More LessSeismic reflection profiling is used mainly to explore for fossil fuels in sedimentary basins. It has been less successful when applied to other mineral resources, perhaps due to the complexity of the targets. Paleochannels are of interest to the mining industry s they may contain minerals or groundwater, and these paleochannels may be easier to map by the seismic method than other targets. A seismic line was shot over a paleochannel using high-resolution techniques and was successful in showing reflections in and below the paleochannel.
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Reengenharia e Qualidade Total Aplicadas ao Processo Sísmica
Authors F.M. Roxo da Motta, J. Acúrcio Cánario de Moraes and J.C. CorręaNos últimos anos, a industria do petróleo tem se preocupado com o avanço tecnológico, no sentido de produzir instrumentos cada vez mais sensíveis ŕs variaçőes das propriedades fisicas das rochas. Outra preocupaçăo tem sido o incremento no grau de automaçăo do processo de registro. Entretanto percebe-se que mesmo dispondo desses recursos năo se tem a garantia de total confiabilidade dos dados de posicionamento. Acrescente-se a falta de pronta interaçăo entre os equipamentos de campo e os pacotes de processamento sísmico. Este trabalho procura mostrar um projeto realizado pela Petrobrás, com conceitos de qualidade total e reengenharia de processos, para garantir: total confiabilidade dos dados de posicionamento e automaçăo do processamento de geometria de dados sísmicos. No estágio atual, o tempo de processamento da geometria reduziu-se para cerca de 2% do tempo original, com total confiabilidade dos resultados.
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Repensando os Processos de Negócios da Organizaçăo em Busca de Vantagens Competitivas: Uma Proposta Para a Reengenharia de Processos
More LessMuitas Organizaçőes vivem, hoje, um tipo particular de "Revoluçăo Industrial", mais intenso e profundo que aqueles ocorridos anteriormente, onde as grandes questőes năo săo de ordem técnica ou politica, mas, em sua maioria, econômica e social. Práticas de gestăo empresarial mais modernas, como: "Total Quality Management", "Just-in-Time" e "Business Process Reengineering", entre outras, questionam fortemente os paradigmas estabelecidos por uma visăo tradicionalista de administraçăo e advogam a extinçăo das pesadas estruturas verticalizadas e hierarquizadoras, em prol de uma formavăo mais horizontalizada e transfuncional, consequentemente, mais flexível, ágil e participativa. Num cenário de crescente globalizaçăo de atividades e de constante preocupaçăo com as impressőes manifestadas pelos clientes, analisar e compreender claramente quais săo as forças que impulsionam ou restringem a açăo organizacional, passa a ser o caminho quase obrigatório ŕ obtençăo de um certo diferencial mercadológico e/ou tecnológico. O presente trabalho, embasado em pesquisas sobre uma dessas novas abordagens: a Reengenharia de Processos, apresenta uma proposta de roteiro metodológico para a reformulaçăo de processos que caracterizam áreas detentoras de conhecimentos especializados, como é o caso do segmento geocientifico.
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A Reorganizaçăo do Segmento E & P da Petrobras Através das Técnicas da GQT e Reengenharia
Authors S. Possato, G.J.F. Fernandes and L.G. de F. AranhaO modelo de organizaçăo do segmento Exploraçăo, Produçăo e Perfuraçăo da Petrobras (EXPROPER) era constituido, ao final de 1994, por tręs Departamentos, com uma Sede na cidade do Rio de Janeiro - RJ e mais sete órgăos operacionais, que reuniam cerca de 21.700 empregados, contendo 860 funçőes geręnciais.
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Hydrocarbon Exploration By Integrated Geophysics Methods in the Barents and Pechora Seas. Experiments and Results
More LessIn 1991 • 1993 MAGE carried out high resolution marine gravity and gradient hydromagnetic survey on three oil perspective fields in the Pechora Sea (Prirazlomnoe, Medynskoe, Alexeevskoe) as well as two gas perspective fields in the Barents Sea (Sbtokmanskoe and Ludlovskoe). The purpose of the exploration was to define the possibility of the marine gravity and gradient magnetic survey in the area of high latitude to solve problems of geological mapping and hydrocaJbon deposits prognosis. The study has been fulfilled by the Russian equipment. Accuracy of the gravity anomaly·is less than :1;0,15·0,25 mGal. Magnetic measurements precision is less than :tl • 2 nT. The distance between lines is 0,5 Ian in the Pechora Sea and 1 • 2 Ian in the Barents Sea. The study of the sea bottom relief structure plays an important role for the exploration of the field tectonic structure on the sbelf of the Barents and Pechora seas. Interpretation potential fields data with regional seismic, log analysis and relief help to receive the new information for geological structure of the hydrocarbon deposits.
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Postsunset F-Region Airglow Disturbances Associated with Gravity Waves
Authors J.H.A. Sobral, G.L. Borba, M.A. Abdu, I.S. Batista, C.J. Zamlutti, H. Takahashi and Y. NakamuraWe report observations of airglow (OI 630 nm) intensity perturbations which are possibly caused by thermospheric gravity waves. Those perturbations are not very frequently observed during the year, as discussed below. Two photometers scanned approximately 75 degrees around zenith in the magnetic meridional and zonal p1lanes at Caçhoeira Paulista (CP, Geogr. 22 41 S, 45000 W, dip 28 S).
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