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5th International Congress of the Brazilian Geophysical Society
- Conference date: 28 Sep 1997 - 03 Oct 1997
- Location: São Paulo, Brazil
- Published: 07 November 1997
21 - 40 of 416 results
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Vertical Geometric Factor of a Two-Coplanar Coils Sonde
Authors Paulo Roberto de Carvalho, Om Prakash Verma and Luiz RijoA vertical geometric factor of an unconventional two coplanar coils sonde (2C40-Coplanar) is determined and compared with that of the Shlumberger's conventional two coaxial coils sonde (2C40-Coaxial) and the coaxial focusing sonde (6FF40). We recommend the use of 2C40-Coplanar as an auxiliary electromagnetic induction tool in thin bed reservoirs because of its very low shoulder effects permits a good vertical resolution. Besides, presence of a hom in the log profile of a 2C40-Coplanar system against an interface between thick beds help in demarcating accurately the bed-boundaries.
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Potencial em Torno de urna Fonte Pontual de Corrente Elétrica em um Semi-Espaco cuja Resistividade É Funçăo Exponencial da Profundidade
More LessEste trabalho mostra a expressao do potencial em tomo de uma fonte pontual de corrente eletrica constante localizada no interior de urn serni-espaço, cuja condutividade varia exponencialmente com a profundidade, e aplica os resultados para modelar perfilagens elétricas de poço. Quando a resistividade cresce com a profundidade, 0 potencial tern uma componente logarítmica, divergindo no infinito.
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Russian Resistivity Log Interpretation Using Inversion
Authors R.K. Chundru, R. Busch, M.A. Jervis, M. Frenkel, A. Mezzatesta and K.-M. StrackRussian log interpretation has become an important and integral part of well log interpretation for major oil companies in search of oil in the former Soviet Union (FSU). In this work we address some of the major characteristics of common Russian resistivity logs especially BKZ logs and the difficulties associated with Russian log interpretation. Russian resisitivity log data primarily consist of focused (BK) and unfocused (BKZ) galvanic responses and induction tool responses. Russian log interpretation poses different kinds of problems compared to conventional western log interpretation due to the asymmetric and nonlinear nature of the tool responses. Traditionally, conventional resistivity interpretation is performed using charts. Chart interpretation is accomplished point by point and does not take into account asymmetric tool responses and bed-thickness effects. Other chart interpretation tools for Russian logs such as EKAR take into account layering effects, but require extensive interaction from the user, and do not provide uncertainty estimation for the results. Recent advances in computer hardware and development of fast forward modeling algorithms have allowed for the application of inversion algorithms in the interpretation of such well logs. We performed a 1-D and 2-D resistivity inversion on a Russian data set simulated for a benchmark Oklahoma formation model with conductive invasion in resistive layers. A joint inversion was performed using three unfocused galvanic curves (GZl, GZ2, and GZ3), a focused galvanic BK log (LL3-type device), and an induction (IK) curve using a Levenberg-Marquardt algorithm to estimate formation resistivity (R), invaded zone resistivity (Rxo) and invaded zone length (Lxo) for each layer. The mean squared difference between the simulated and synthetic data was used as the cost function. The inversion algorithm was successful in estimating the true model parameters from the Russian resistivity logs, including BKZ data.
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Geology and Petroleum Potential of the Rio Muni Basin, Offshore Equatorial Guinea
More LessThe Rio Muni Basin of Equatorial Guinea constitutes part of a series of Early Cretaceous rift segments, which underlie the eastern passive margin of the South Atlantic. Six wells have been drilled in the basin; three encountered oil and gas shows and two encountered gas shows. More than 6000 km of post-1979 seismic data have been acquired by a number of previous operators and by contractors. The Rio Muni basin shows strong similarities in stratigraphy and play possibilities with the adjacent hydrocarbon bearing basins of West Africa but is very lightly explored by comparison.
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In Search of Rt: Limits and Possibilities
Authors A.G. Mezzatesta, M.A. Frenkel and K.-M. StrackIn locating hydrocarbon, electrical logging techniques play a key role in distinguishing between oil and water saturated rocks. Among the electrical techniques, two classes of devices, induction and current injection (galvanic), are of significant importance in determining movable and residual hydrocarbons. In the past, the borehole electrical logs have been mostly interpreted using curve matching or approximate modeling techniques. This often resulted in underestimating the hydrocarbon and/or in false distinction between water- and oil-bearing zones. Here, we present an automated interpretation technique which has become feasible to the oil industry with the advancement in geophysical inversion and modeling and the advent of small parallel computers. In addition to an automated and more reliable interpretation, one can combine numerous different electrical measurements to avoid the inherent bias of the individual logging tools. Further, a thorough analysis of the interpretation methodologies used (namely inversion) allows us to provide uncertainty estimates for the interpretation results which can be translated directly into minimum and maximum pay values. The benefits of this technology are presented using case histories from different environments.
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Correlaçăo Estratigráfica de Perfis de Poço através de uma Rede Neuronal Direta Multicamadas
Authors André J.N. Andrade and Stefan M. LuthiA correlaçăo estratigráfica de perfis petrofísicos de poço aberto e uma das mais importantes aplicaçőes da geofísica de poço. Nesse processo, as curvas registradas no perfil constituem-se em uma importante ferramenta de trabalho para o intérprete, propiciando o correto mapeamento das estruturas de subsuperffcie, a caracterizaçăo dos sistemas deposicionais e numa escala de maior detalhe, a reconstituiçăo da morfologia das unidades de fluxo e das descontinuidades hidráulicas de um reservatório (DOVETON, 1986).
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Perfilagens de Temperatura em Poços Profundos: Instrumentaçăo e Aplicaçőes
O objetivo do trabalho foi o desenvolvimento de urn sistema de perfilagem de temperatura de baixo custo, com resoluçăo de centésimos de °C, podendo operar em profundidades da ordern de 1000m. Um rnedidor digital vinculado mecanicamente ao cabo multifio de descida permite medidas de profundidade, simultâneas as da temperatura. Os poços utilizados para testar o equipamento localizarn-se na cidade de Nuporanga-SP (20°44'S, 47°55'W) e já haviam sido perfilados anteriormente.
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Igneous Rocks Identification on Well-Log Data: An Interpretation Tool
An attempt to discriminate and characterise igneous rocks on well-log data is made in a well drilled on the Cabo Sub-basin (JG-1 well), situated on the northeastern coast of Brazil. This sub-basin is to date considered as a northern extension of the Sergipe-Alagoas Basin and like others brazilian marginal basins has its history closely related to the South Atlantic opening.
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Integration of Core-log Data: An Example from ODP Hole 959D
Authors Carlos A. Gonçalves and L. EwertCore and log measurements provide crucial information about subsurface formations. Their usage, is complicated by the different measurement methods employed, different volumes of formation analysed and the heterogeneity of the formations. While the problems of comparing core and log data are well known, the way in which these data can be most efficiently combined is not all clear in most cases. This paper shows an example from Ocean Drilling Program (ODP) Hole 959D, drilled in the Cote d' Ivoire-Ghana (CIG) margin. The integration of core and wireline log data helps to interpret the different stages observed as a result from the continental break-up and related transform tectonism associated with the motion between South America and Africa. The main objectives are to evaluate (1) the reliability of both types of measurements and (2) the extent to which the physical properties of the sediments are controlled by the tectonism. The effect of the transform deformation is seen in physical properties data derived from index properties measurements. Major breaks in porosity are associated to the tectoni zed lower Cretaceous and Cenozoic boundary, a trend also reflected in the P-wave velocity measurements. Core and well log data show the presence of a major unconformity between Cretaceous and Cenozoic, marked by an offset in porosity, density and P-wave data. The physical properties an log data are also heterogeneous, reflecting variations in consolidation, age and lithology.
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Multi-Scale Analysis of Well-Logs and of Seismic Reflection Data
Authors C.P.A. Wapenaar, J.C.M. Goudswaard, W.J.F. van Geloven and J.T. FokkemaIn well-logs we often encounter sharp outliers, or singularities, that are responsible for strong reflections. However, these reflectors are different from step-functions, in the sense that step-functions are scale-invariant whereas these singularities are not. In this paper a multi-scale analysis is performed on synthetic and real well-logs, as well as on their reflection responses, in order to test a method that can distinguish between scale-invariant and scale-variant reflectors. We will show that it is possible to extract a stable local singularity exponent exfrom a well-log, and that we can obtain the same exponent from seismic reflection data.
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Electric Resistivity of Near Surface Marine Sediments of the German Coast at the North Sea
Authors A. Ayres, F. Theilen and K. SchwarzerElectrical prospecting of soils and rocks is far more diversified than other geophysical methods. Some techniques use natural electrochemically-generated currents, the so called self-potential method. Other techniques make use of electric currents or fields that are introduced into the ground. The resistivity method has been traditionally used for differentiating oil and gas bearing from water saturated rocks. The main scope of this paper is to investigate the applicability of using electrical methods to evaluate some geological and geotechnical parameters of marine sediments concerning engineering and environmental problems.
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Stacking of Electrical Potential Gradient (EPG): A New Technique to Detect Abandoned Mining Galeries
More LessPast mining activities, specially in coal mines of southern Brazil have been recognised as problematic due to the risk they represent for areas in development (construction sites, roads, etc). The lack of precise location of abandoned galleries represents a serious risk of accident by inundation or gas leakage, where intercepted by new galleries. It is also important when there is a need to re-evaluate the re-opening of a mine. Although it is possible to detect the presence of sub-surface empty spaces by drilling, the high prices and technical problems of procedures such as these are not economically viable. Geophysical methods are the best alternative and have been applyed with considerable success. In general terms electroresistivity with variable arrangements present the best results. However, dificulties increase with the progressive depth of the empty spaces. Peters and Burdick (1983) have shown that it is possible to detect with confidence empty space with rates of depth/diameter of 10:1, with the use of the pole-dipole array together with special techniques of correction of values obtained.
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Avaliaçăo do Impacto Gerado por uma Fonte Impulsiva P
More LessA Tensăo Normal que incide em um ponto qualquer de urn meio sólido ideal, uma vez conhecida a localizaçăo da origem onde está aplicada uma Força, pode ser avaliada pela fórmula de Boussinesq (Bib. V.1), deduzida conforme os princípios da Teoria da Elasticidade, mas que tern amplo uso e aceitaçăo para projetos e investigaçőes em Geotecnia.
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Métodos Geoelétricos Aplicados na Correlaçăo com Ensaios de SPT nas Formaçőes Rio Claro e Corumbataí noMunicípio de Rio Claro-SP
More LessForam executados ensaios geofísicos pelos métodos da eletrorresistividade e polarizaçăo induzida (SUMNER, 1976), técnica da sondagem elétrica vertical - arranjo Schlumberger, no município de Rio Claro-SP. Os ensaios visaram obter uma correlaçăo dos parâmetres geoelétricos com a geologia e os índices de resistęncia a penetraçăo (N) de ensaios geotécnicos Standard Penetration Test - SPT.
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Slope Tectonics - Comparisons and Contrasts of Structural Styles of Salt and Shale Tectonics of the Northern Gulf of Mexico with Shale Tectonics of Niger Delta
Authors S. Wu and A. W. BallyThe northern Gulf of Mexico and the Niger Delta are both dominated by large deltaic depocenters situated on passive continental margins. Both areas are characterized by widespread growth faulting, a substratum of over-pressured shale and deep-water contractional folded belts. The main difference is that the Gulf of Mexico is additionally characterized by extensive and complex salt tectonics. Figure I summarizes the structural styles of both the northern Gulf of Mexico and the Gulf of Guinea.
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Ensaios de Sísmica de Reflexăo de Alta Resoluçăo na Planície AIuviaI do Rio Paraíba do SuI
Authors Joăo Carlos Dourado, Chang Hung Kiang and Walter Malagutti FilhoCom a finalidade de testar váras técnicas sísmicas no ambiente da planície aluvial (Dourado, 1996), foram executados cerca de 8100 m de sísmica de reflexăo de alta resoluçăo na planície aluvial do Rio Paraíba do SuI, nas proximidades do distrito de Eugęnio de Melo, Município de Săo José dos Campos (Figura 1).
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Environmental Radiation Pattern of the Lagoa Real Uranium District, Bahia, Brazil
Authors Elisabete M. Pascholati, Gilberto Amaral and Liliana Sayuri OsakoNatural or environmental radiation is the main source of radiation that affect man, comprising more than 70% of the total (natural plus man made). Man made radiation is originated from several sources, such as x-rays, nuclear weapons fallout, radioactive waste disposal, potassium in smokes of vegetal origin (cigarrettes, etc.), building materials, fertilizers with high U content, etc. Due to that it is important to know precisely the natural dose in order to monitor the man made sources. Natural radiation is composed of two parts, indoor and outdoor. Indoor radiation is mainly due to radon gas emanating from soil or rocks arid trapped inside houses. Outdoor radiation is manily due to gamma radiation, resulting from the decay of 40K, 238U and 2310, and high energy cosmic radiation. Radioactive isotopes (40K, 14C, 87Rb and 222Rn) within the body also contribute to the total dose.
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Estudo Cornparativo entre os Fluxos de Calor em uma Área de Plantaçăo de Cana de Acúcar e Outra corn Vegetaçăo Costeira Nativa
Authors Alberto Brum Novaes and F.C. Pataro de QuierozMedidas precisas da evaporaçăo em regiőes contrastantes da superfície natural, săo necessárias para estabelecer as reservas de água da regiăo e tentar predizer os efeitos de possíveis mudanças no uso do solo nestas regiőes, Um dos fatores de maior interesse ŕ agricultura é o transporte da urnidade de uma superfície natural para a atmosfera. Esta transferęncia de umidade da superfície vegetada, inclui a perda de água do solo nu bern como a transpiraçăo da planta. Atualmente, vários métodos estăo disponíveis para a medida destes fluxos, dentre eles um dos mais utilizados é o método do balanço de energia, que avalia os fluxos verticais de calor sensível e calor latente.
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Dosimetria Alfa-Gama de Rochas Usadas como Revestimento na Construçăo Civil
As migraçőes características de isótopes radiogęnicos nas camadas superficiais da Terra, nas águas e na atmosfera tęm sido, nos meios cientfíicos, mais uma das fontes de preocupaçăo, por sua conseqüente contaminaçăo do ambiente humano. Essa preocupaçăo, mais recentemente, pas sou a envolver tambęm os materiais geológicos, porque, apesar de sua baixa atividade em relaçăo a radioatividade artificial, seus efeitos podem ser prejudiciais ŕ saúde, porque săo cumulativos com o tempo.
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Monitoramento Sismográfico da Estaçăo de Tratamento de Água -eta e Elevatoria do Sistema Adutor Pedra do Cavalo
More LessEste trabalho apresenia os resultados do monitoramento de vibrarçőes transmitidas as instolaçőes da Estacçăo de Traiamento de Água - ETA e elevatória do Sistema Adutor Pedra do Cavalo, responsável pelo suprimento d'água na regiăo metropolitana de Salvador, Bahia, durante o levantamento sísmico 3-D no campo de CEXIS e adjacęncias, na Bacia do Recôncavo, a fim de prevenir danos e definir parâmetros de quatidade de carga versus distância para a sequrança das obras de engenharia existentes neste prospecto . No monitoramento foi utilizado um sismógrafo com 24 canais e geofones triaxiais, num projeto conjunto entre a PETROBRAS, CEPED E UFBA. Os resultados mostram que os níveis de vibraçőes induzidas pelas detonaçőes săo baixos e incapazes de causar qualquer dano ŕs instolaçőes, segundo os critérios de H125 quantidade de carga e distância mínima de segurança utilizados neste prospecto, pela equipe sísmica ES-26.
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