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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
151 - 200 of 330 results
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Caracterización Petrofisica de las Secuencias Productoras de Hidrocarburos en un Pozo de la Costa Norte de La Republica de Cuba Aplicando GEONUC
EI trabajo presenta una integración de la infomación geologo-geofísica obtenida durante la perforación del pozo PE4, con el objetivo de caracterizar su potencial gasopetrolifero. EI pozo PE4 alcanzó la profundidad de 1736m. atravesando los sedimentos de Ia Unidad Tectono Estratigráfica Placetas, productoras de petróleo en los yacimientos Boca de Jaruco y Varadero. Estas secuencias de rocas carbonatadas fueron sometidas a un intenso programa de investigaciones: registros geofísicos, investigaciones hidrodinómicas e incluso la recuperación de un testigo con el objetivo de establecer el tipo de reservorio, realizar la caracterización litológica y Ia evaluación de su potencialidad. EI sistema modular GEONUC nos permitió utilizar diferentes variantes para lograr los objetivos planteados, destacandose los resultados de los crossplot de Chandelier para Ia caracterización del reservorio. Además facilitó el análisis del complejo de métodos utilizados para realizar una recomendacion sobre Ia optimización de los métodos geofísicos a realizar en estas condiciones.
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Duas Aplicaçőes de Janelas de Filtragem em Problemas Geofísicos
Authors J. Marques Jr. and C.R. Teixeira RégisCom o advento do uso dos computadores a área de processamento de sinal experimentou urn acelerado desenvolvimento, onde a filtragem digital ocupa um lugar de fundamental importância. Dentro deste contexto, damos enfoque aos filtros lineares năo recursivos, particularizando-se o uso das janelas de filtragem, também referenciadas na literatura como funçőes de truncamento. Os filtros săo em geral usados para separar a informaçăo indesejável (ruído) da informaçăo desejável (sinal). Ná Geofísica, esta reparaçăo pode ser realizada com base na frequęncia, velocidade, polarizaçăo e amplitude. A filtragem com base na frequęncia é a mais comum. Serăo abordados aqui dois exemplos de filtragem baseada na frequęncia.
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3D AVO Analysis Applied to Characterization of Fractured Reservoirs
Authors A.C.B. Ramos and T.L. DavisOver the years amplitude VB offset (AVO) analysis has been sucessfully used to predic reservoir properties and fluids, in some caaes allowing the spatial location of gas-water and gaa-oil contacts. In this paper, we show that AVO technique can also be used to characterize fractured reservoirs, allowing spatial location of crack density variations. The Cedar Hill Field in the San Juan Basin, New Mexico, produces methane from fractured coal bed of the Fruitland Formation. The presence of fracturing is critical to methane production due to the absence of matrix permeability in the coals. To help characterize this coalbed reservoir a three-dimensional, multicomponent seismic survey was acquired in this field. Two modeling techniques (using ray tracing and reflectivity methods) predict the effects of fractured coalseam zones on non-normal P-wave reflectivity. Synthetic CMP gathers are generated for a horizontally layered earth model, which uses elastic parameters derived from sonic and density log measurements. Fracture density variations in the coalbeds are simulated by anisotropic modeling. The large a..cowtic impedance contrasts associated with the sandstone/ coal interfaces dominate the P-wave reflectivity response, They far outweigh the effects of contrasts in anisotropy parameters, for the computed models. Seismic AVO analysis of nine macrobins obtained from the 3-D volume confirms model predictions. Areas with large AVO products identify coal zones with large Pois- IOn's ratio contrast, therefore high fracture density in the coalbed methane reservoir. Source-receiver azimuth sorting i. used to detect preferential directions of azimuthal anisotropy caused by the coal's fracturing system.
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The Elastic Properties of Shales: Theoretical Modeling
By B.E. HornbyShales are complex porous materials, normally consisting of percolating and interpenetrating fluid and solid phases. The solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure. The shape, orientation, and connection of the two phases control the anisotropic elastic properties of the composite solid. I will show a theoretical framework that allows one to predict the effective elastic properties of shales. The theory is based on a combination of anisotropic formulations of the self consistent (SCA) and differential effective medium (DEM) approximations. This combination guarantees that both the fluid and solid phases percolate at all porosities.
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The Elastic Properties of Shales: Laboratory Experiments
By B.E. HornbyThe ultrasonic anisotropic elastic properties of shales were measured with control of both overburden and pore pressures. Previous measurements on shales are few and, with the exception of one study, (Tosaya, 1982) the shale properties are measured dry or under undrained or partially drained conditions. Measurement under undro.ined or partially drained conditions results in unknown high sample pore pressures and hence unrealistically low, unknown effective stresses. Relating such measurements to earth properties at known depths is questionable. Due to the low permeability of shales (e.g. Cook et al., 1990; Katsube et al., 1991) control of sample pore pressure is difficult, if not impossible, using standard ultrasonic laboratory equipment. Special equipment and techniques were employed in order to measure the elastic properties of shales at known overburden stress and pore pressures. Automatic, computer control of pressures were required, as well as special methods to increase the drainage of shale samples during the test. Even with the specialized equipment and techniques, a time period of more than one month, with the equipment continuously running, is needed to measure accurately the anisotropic properties of shale for a single core interval. Measurements of compressional and shear wave velocity were taken on a range of plugs cut from whole core and oriented at different angles with respect to the visual axis of symmetry. These measurements were then inverted for the anisotropic elastic properties of the shale and the reconstructed elastic stiffnesses were then analyzed in terms of their anisotropy and other properties.
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Pre-salt Source Rock Development on Brazil's Conjugate Margin: West African Examples
Authors S.G. Henry, W.M. Brumbaugh and N. CameronThe West Africa hydrocarbon provinces between Nigeria and Angola are conjugate to Brazil's rifted margin. With each new deep water exploration well, Africa's pre-salt source rock sequences show a remarkable similarity to those known in Brazil. Recently an entirely new West African pre-salt source rock, the Falcao, was discovered in the offshore Kwanza Basin of Angola. The Falcao source rock has geochemical affinities with the Lagoa Feia of the Campos Basin, Brazil and was similarly deposited above the syn-rift section in Sag Basins. The focus of this paper is on the seismic identification of pre-salt Sag Basins, syn-rift sequences and their relationships to the underlying crustal structure. Seismic facies analysis was critical for identifying paleodrainage, clastic shorelines, carbonate mounds and the depocenters in which the Sag Basin source rocks developed. Understanding the tectonic framework in which the Kwanza Basin syn-rift and Sag Basin successions developed is particularly applicable in view of the region's predrift proximity to Brazil and especially the Campos Basin.
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Reservoir Characterization Through an Integrated Approach at Auger Field, Deepwater, Gulf of Mexico
By D.T. McGeeShell Offshore Inc.'s Auger Field currently holds the record for deepest water production (2,862 ft. (872 m)) in the Gulf of Mexico and deepest water production from a TLP (Tension Leg Platform) in the world. Auger Field is located in the Garden Banks OCS area, 214 miles (344 km) southwest of New Orleans. LA. The current most likely recoverable reserve estimates are 220 MMBE. Production began April 15, 1994 from the first well and has exceeded expectations. Currently, six wells are on production from the deepest reservoir with an average cumulative daily production rate of more than 55,000 BOPD and 105 MMCFPD. The success of Auger Field has resulted from an integrated approach using geologic, geophysical, reservoir engineering and production engineering disciplines to reduce the planned well count from 27 to 11 wells resulting in a $US 180 MM capital savings. The integrated approach aided in understanding the turbidite reservoir geometries ranging from sheets to shingled, amalgamated channels with overlying levee and overbank deposits (Steffens, 1993; McGee et al, 1994). These differences in reservoir geometries dictated the placement and number of development wells including a horizontal well planned for a shingled reservoir. The desire for the horizontal well was defined by close examination of a high frequency 3D survey to interpret loop scale stratigraphy and seismic inversion for subseismic stratigraphy.
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The Use of 3D Seismic as a Tool to Increase Ultimate Recovery from the Yibal Shuaiba Reservoir, Oman
By D.K. SkaloudThe Yibal Field, located in northem Oman, is a highly mature oil field, with a current total of 436 wells, from which about half of the ultimately recoverable reserves have been produced. Some 100 Shuaiba reservoir production wells have been preselected using structural and amplitude interpretations of a 3D seismic survey acquired in 1988. The seismic data were integrated with petrophysical, geological and production models arrive at optimal well locations and trajectories. The results of these wells, many of which are horizontal, have been very encouraging in terms of production and recovery improvements and demonstrate the success of the approach. Top Shuaiba seismic attribute data are shown to have high predictive value for reservoir porosity, hydrocarbon distribution and production behavior. New 3D data were acquired in 1993 to improve the structural model, identify remaining unswept oil and enable real time reservoir visualization. Although not yet fully processed and evaluated, interpretations of time lapse effects in reservoir fluid distribution are presented.
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A Simple 3-Parameter TI Model for the Elastic Behavior of Shales
Authors M. Schoenberg, F. Muir and C.M. SayersA simple three-parameter transversely isotropic (TI) elastic model is presented which yields a reasonable first approximation for the elastic behavior of a wide variety of shales. A key feature of this model is that the zero-offset normal moveout velocity for qP-waves is constrained to equal the vertical qP speed. A simple but surprisingly effective approximation to the qP slowness surface is presented that allows for compressional wave velocity modeling and constrained tomography through shale regions with the specification of just two parameters.
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Seismic Attenuation and Dispersion in Oil and Gas Fields
Authors M.B. Rapoport and V.I. RyjkovAn effect of strong dissipation of seismic energy in oil and gas fields is experimentally established. Strong increasing of attenuation decrement and phase velocity dispersion was obtained from VSP and CMP data on productive intervals' depths. We have newer observed this effect outside fields even if reservoirs' properties are rather stable. This phenomenon could be explained as hydrocarbons influence. Noise-resistant methods with errors' corrections have been worked out to study the changes in frequency spectral due to absorption and dispersion. Experimental results of the study of inelastic properties of the real geological media are presented. Parameters of geological media inelasticity - seismic waves attenuation and phase velocity dispersion - are proposed for interpretation as hydrocarbons indicators.
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Estimating Rock Volumes from 2-D Seismic Usiug Constrained Conditional Simulation
Authors R.T. Houck, N.J. House-Finch and D.G. CarpenterAn interpreted 2-D seismic grid is used to estimate the probability distribution of gross rock volume, accounting for the mapping indeterminacy inherent in 2-D seismic. Because of sparse spatial sampling in the crossline direction and the possibility of sideswipe, there are a large number of subsurface structure maps that fit an interpretation of a 2-D seismic grid. This mapping indetenninacy is an inherent property of 2-D seismic, and is not present in 3-D seismic. Both 2-D and 3-D seismic are affected by additional uncertainties associated with picking and depth conversion. By treating an interpreted 2-D grid as a set of observations that constrain the possible subsurface structures rather than as a structure to be mapped, an ensemble of structure maps is generated using a modified form of geostatistical conditional simulation. Gross rock volumes computed from each one of these maps are used to construct a cumulative distribution function. Because this procedure compensates for the crossline imaging distortion that causes 2-D seismic to overestimate structural sizes, this distribution can be expected to yield more realistic estimates of hydrocarbon volumes.
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Quantifying the Benefits of Seismic Data for Reservoir Characterization: A Case Study
By S.B. GorellThe use of geophysical data for reservoir characterization has become a common practice. Advances in seismic processing and interpretation now routinely provide additional information which can be utilized for reservoir characterization. In addition to structural data, seismic attributes such as velocity, amplitude, energy, phase and travel time can be extracted over an interval being investigated. These seismic attributes can then be integrated with existing well data. In situations where correlations can be established between seismic and well attributes, the seismic data can be used to influence the interpolation of well attributes away from the wells. In contrast to using only well data, seismic data has the advantage that it provides information almost everywhere in the reservoir, not just at well locations. The techniques used to create such models are goestatistical algorithms based on kriging formalisms.
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Backus averaging generalized for poroelasticity
Authors S. Gelinsky and S.A. ShapiroTypical sedimentary rocks are not purely elastic materials but fluid saturated, porous composites. It seems natural to investigate the influence of porosity fluctuations and other fluid properties in the context of Backus averaging for thinly layered reservoir rock. By averaging over many thin layers consisting of materials with different bulk- and shear moduli the vertically heterogeneous, isotropic medium will be replaced by a homogeneous, anisotropic (TI) effective medium. The layer thicknesses must be small compared to the wavelength of seismic waves propagating in the medium. We determine the five resulting poroelastic constants Bi, Bi, B; of the TI effective medium in terms of the original Backus constants MB, BB, FB, CB and LB and of further terms describing the influence of fluid properties. Hereby we also determine the poroelastic Biot constants Bs, B; and Bs to describe the TI poroelastic medium completely. Further we generalize this approach to layers which are poroelastic and itself TI. These results can serve as a basis to study the influence of porosity fluctuations and fluid properties on the propagation of obliquely incident P-,SV- and SH- seismic plane waves in a poroelastic, fluid-saturated, and finely layered medium. Since the permeability of a porous medium will vary from layer to layer as the poroelastic constants do, we calculate the effective anisotropic permeability as a function of the fluctuations of porosity.
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Seismic Modelling and Amplitude Analysis For Reservoir Prediction -- Merluza Gas Development, Offshore Brazil
Authors T.W. Riddle, D.K. Purcell, J.E. Kruger and Y. ShohamReservoir porosity-thickness prediction from seismic data has contributed to the economic viability of the Merluza Gas discovery in the Santos Basin Offshore Brazil by increasing the reliability of gas volume estimates. The Merluza structure was formed by upward movement of Lower Cretaceous salt creating an elongated north-south treading anticline in the overlying Cretaceous sediments. Here Pecten discovered two gas bearing zones of Upper Cretaceous age at an average depth of about 4500m. Results of stratigraphic seismic studies along with well data and core studies indicate that the lower gas bearing zone consists of a turbidite channelized fan complex deposited during the Turonian age sea level low stand. The upper sands are seismically transparent, but !he lower sand unit presents itself as a single, Isolated, structurally uncomplicated seismic event believed to represent a single depositional lobe. The possibility of rapid lateral variation of porosity and thickness of this lobe poses obvious questions concerning recoverable gas volumes and the economic viability of the prospect. However, the excellent seismic data quality at depth, characterized by high Signal to Noise ratio and excellent ties to the well logs, coupled with a simple geologic model allows the use of the seismic amplitudes as a predictor of reservoir quality and extent.
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Estimativa dos Perfis de Constantes Elasticas em Carbonatos Pouco Permeaveis a Partir de Dados Laboratoriais
More LessEste trabalho visa a obtenção de perfis de módulos de Young (E), incompressibilidade (K) e cisalhamento (G) estáticos e dinâmicos, para calcários pouco permeáveis. Foram utilizados dados de velocidade compressional (Vp) e velocidade cisalhante (Vs) obtidos em laboratório a partir de 30 amostras secas e 7 amostras saturadas com água da formação. As amostras secas também foram modeladas por Biot (Biot et al., 1956). A partir dos resultados encontrados para Vp e Vs, juntamente com dados de petrofísica, foram obtidas relações entre Vp e Vs, e entre Vp, Vs e porosidade (Φ). Estas relações foram comparadas com relações já existentes na literatura. Com estas relações e com dados de perfil de Vp e Φ, foi possível a obtenção do perfil de Vs, fundamental para o cálculo dos módulos elásticos dinámicos. Relações entre os módulos elásticos dinâmicos e estáticos também foram obtidas a partir de medidas simultâneas (dinâmicas e estáticas) em laboratório, a partir das quais foi possível calcular os perfis de módulos elásticos estáticos para todo o intervalo de interesse.
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THREEDIMENSIONAL ALLAN FAULT PLANE ANALYSIS
Authors K.S. Hoffman, D. R. Taylor and R. T. SchnellAllan fault plane analysis is a useful tool for determining hydrocarbon migration paths and the location of possible traps. While initially developed for Gulf Coast deltaic and interdeltaic environments, fault plane analysis has been successfully applied in many other geologic settings. Where the geology involves several intersecting faults and greater complexity, many two-dimensional displays are required in the investigation and it becomes increasingly difficult to accurately visualize both fault relationships and migration routes. Threedimensional geospatial fault and structure modeling using new computer techniques, however, facilitates both visualization and understanding and extends fault plane analysis into much more complex situations. When a model is viewed in three dimensions, the strata on both sides of a fault can be seen simultaneously while the true structural character of one or more fault surfaces is preserved. Three-dimensional analysis improves the speed and accuracy of the fault plane methodology.
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Modelagem Sismica para Caracterizacao de Fraturamento
Authors C.E.B. de Salles and I. de Araújo SimőesA presença de fraturas em reservatórios de petróleo impőe ao meio um sistema adicional de porosidade, caracterizado por alta permeabilidade e baixa capacidade de armazenamento, conduzindo assim a uma permeabilidade anisotrópica. Sua caracterizaçăo é de fundamental importância para o desenvolvimento e a geręncia da Iavra em reservatórios fraturados. A abordagem de meio equivalente permite avaliar as respostas da propagaçăo de ondas em um meio isotrópico heterogęneo, substituindo-o por um anisotrópico homogęneo, reduzindo assim as complexidades da propagaçăo em meios heterogęneos. Para tanto, utilizou-se a metodologia proposta por Hudson (1980, 1981), que calcula os parâmetros elásticos do meio equivalente, quando o comprimento da onda usada no levantamento é muito maior que as dimeçőes das heterogeneidades. A modelagem sísmica foi conduzida em um modelo geológico de quatro camadas e utilizando metodologia de Perfil Sísmico Vertical (PSV) multicomponente. Esta odelagem permitiu determiner, além da geometria de aquisiçăo que fornecesse a máxima conversă da onda P em onda S, a inferęncia das direçőes principais de fraturamento, a partir da análise dos diagramas de polarizaçăo.
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Delimitaçăo de Depósitos de Leques Aluviais e Fluviais Através de Sismica 3D - Um Caso Historico
A interpretaçăo, em escala de detalhe, de dados sismicos 3D calibrados com sismogramas sintéticos, possibilitou a delimitaçăo da ocorręncia dos reservatórios profundos (3.700m) de gás do Campo de Arabaiana, Bacia Potiguar imersa, margem continental equatorial brasileira. O mapeamento indicou que o campo ocorre em um rollover de uma estrutura anticlinal associada ao bloco baixo de uma ampla falha Iístrica normal (Falha de Pescada), de direçăo E-W. Através de critérios sísmicos e geológicos foi possível individualizar dois tipos de reservatórios no campo: a) leques aluviais, sintectônicos ŕ Falha de Pescada, que ocorrem a até 2km desta; e b) depósitos fluviais, que contęm o principal play, presentes na porçăo setentrional do campo, dispostos perpendicularmente ao sistema de leques aluviais. O limite sul desta fácies é definido pela Falha de Arabaiana (sintética ŕ Falha de Pescada), de direçăo E-W. A fácies fluvial possui dois depocentros, aparentemente interligados, coincidentes com estruturas dômicas ao nível do topo do reservatório.
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Diferentes Abordagens na Utilizaçăo de Dados Sísmicos na Geraçăo de Modelos de Porosidade
Authors G. Schwedersky, A. Sampaio de Almeida and C. BettiniNeste trabalho, procurou-se mostrar a importancia da incorporaçăo da informaçăo sísmica na geraçăo de modelos de porosidade em campos de hidrocarbonetos onde a informaçăo obtida em peços é muito esparsa. Na integraçăo da informaçăo sísmica, foram utilizadas técnicas convencionais de estimativa a partir de fórmulas de regressăo assim como técnicas geoestatísticas de estimativa e simulaçăo. A utilizaçăo da geoestatistica mostrou-se mais adequada na geraçăo de modelos de porosidade, fornecendo modelos mais confiáveis, além de permitir uma análise da incerteza envolvida no processo.
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Influęncia da Temperatura na Dispersăo e Atenuaçăo em Arenitos Saturados
Authors G. Fernandes Vasquez, L. Duarte Dillon, A. Bastos and J.A. SoaresO estudo das propriedades elásticas das rochas, pelos métodos baseados na propagaçăo de ondas em subsuperfície (como a sísmica e perfilagem), tem sido aplicado ŕ delimitaçăo e caracterizaçăo de reservatórios de hidrocarbonetos, procurando um maior aproveitamento de jazidas já em exploraçăo. Na realidade, as rochas năo săo materiais perfeitamente elásticos. Ŕ medida que se propagam pelas rochas, as ondas tęm suas amplitudes reduzidas (atenuaçăo) e suas formas alteradas, sendo suas velocidades dependentes da freqüęncia (dispersăo). Estes fenômenos săo interligados, compreendendo o que define-se como absorçăo sísmica, causada pelo comportamento apenas parcialmente elástico das rochas. Dada a alta sensibilidade da absorçăo ŕ estrutura do espaço poroso e ao fluido saturante, seu conhecimento é importante para aplicaçőes como a detecçăo direta e identificaçăo de fluidos, delimitaçăo e caracterizaçăo de reservatórios e monitoramento da produçăo. A teoria de Biot descreve o comportamento das velocidades sísmicas de rochas saturadas, prevendo uma dispersăo de velocidades um tanto modesta se comparada ŕquela observada na prática, principalmente no caso de fluidos muito viscosos. Neste resumo descrevem-se resultados de medidas de absorçăo (fator Q) e dispersăo de velocidades para rochas saturadas com óleo em funçăo da temperatura, dados raramente encontrados na literatura. Observa-se que, com o decréscimo da viscosidade do óleo, a dispersăo observada aproxima-se daquela prevista por Biot, ocorrendo também decréscimo na atenuaçăo. Estes resultados evidenciam a ocorręncia do efeito de fluxo localizado de fluido na escala dos poros.
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Estimativa da Capacidade de Estocagem de Fluido de Reservatorio a Partir da Amplitude Sismica, Campo de Bonito, Bacia de Campos
Authors M. Blauth, J. Marcio da Silva and R. Marcio de OliveiraA sísmica de reflexăo tem um grande potencial para auxiliar no desenvolvimento dos campos de petróleo, podendo contribuir para: (1) delimitaçăo de jazidas; (2) identificaçăo de fluidos; (3) caracterizaçăo de reservatório e (4) monitoramento de reservatório. A utilizaçăo da mesma, no entanto, tem-se limitado basicamente a execuçăo dos dois primeiros propósitos. O penúltimo, objeto do presente trabalho e o último, de maior dificuldade, tęm sido alvo secundário. O presente trabalho abrange a porçăo superior de reservatório carbonático pertencente a Formaçăo Macaé do Campo de Bonito que se localiza no pólo sul da Bacia de Campos. Tem como objetivo principal definir um modelo quantitativo preditivo da capacidade de estocagem de fluido (Hphi) do reservatório através da análise da anomalia de amplitude sísmica. Os valores de anomalia de amplitude sísmica (nível do reservatório carbonático) foram extraídos dos dados de levantamento sismico 3D, cuja maIha é composta por linhas espaçadas de 53 m e traços com 26 m de distância entre si.
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O Método GPR Aplicado ŕ Caracterizaçăo de Reservatórios: Um Exemplo no Afloramento Açu - Bacia Potiguar - RN
Authors J.L. Porsani and A. Rangel RodriguesO método eletromagnético GPR (Ground Penetrating I Radar) foi utilizado no Afloramento Açu-Bacia Potiguar-RN. Visando obter uma imagem de muito alta resoluçăo da subsuperficie. Realizou-se tręs perfis de 100m com antenas de 25, 50 e 100 MHz, utilizando-se a técnica WARR (Wide Angle Reflection and Refraction). Após o processamento dos dados, obteve-se tręs seçőes verticais. Mapeou-se varies horizontes refletores até 30 metros de profundidade, do qual a feiçăo mais interessante é na forma de uma "cunha" se espessando para o final do perfil. Esta estrutura está em comum acordo com a geologia local. Resultados de tręs poços rasos deram suporte a interpretaçăo destas seçőes. Este trabalho mostra que o GPR e uma ferramenta útil aplicada ŕ geofisica de afloramentos, voltado principalmente para caracterizaçăo de reservatórios.
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Estimativa do Módulo de Cisalhamento Estático de Rochas via Perfis Geofísicos de Poços
Authors J.A. Soares, L. Duarte Dillon, A. Bastos and G.F. VasquesA avaliaçăo do módulo de cisalhamento estático das rochas, a partir dos perfis geofisicos de poços, é proposta neste trabalho baseada em urn conjunto de mediçőes feitas em laboratório. O módulo de cisalhamento elástico estatico de um folhelho pouco consolidado da Bacia de Campos (RJ - Brasil) foi obtido, in situ, por uma nova ferramenta disponível no mercado a qual mede as deformaçőes apresentadas pelo poço, a cada 30°, quando este é submetido a um teste de micro-fraturamento hidráulico. Por outro lado, os módulos elásticos dinâmicos do folhelho foram obtidos através dos perfis geofísicos de velocidades e de densidade total. A transformaçăo destes módulos dinâmicos nos seus correspondentes estáticos foi feita através de relaçőes lineares empíricas observadas em laboratório a partir de mediçőes simultaneas dos módulos elásticos dinâmicos e estáticos em um conjunto de amostras de rocha. Assim, foi possível a comparaçăo entre o módulo de cisalhamento estático medido in situ e o módulo de cisalhamento estático estimado a partir dos perfis geofísicos.
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Caracterizaçăo de Reservatório via Rede Neural
Authors J. Schmidt and M.S. dos SantosO presente trabalho investiga a possibilidade da aplicaçăo presente trabalho investiga a possibilidade da aplicaçăo das redes neurais como ferramenta auxiliar na caracterizaçăo de reservatórios utilizando dados sísmicos. As redes neurais năo săo programadas, mas treinadas com a apresentaçăo repetida de dados de entrada e respostas desejadas. Os dados de entrada săo os atributos sísmicos extraidos dos dados sísmicos, nos locals dos poços, e a resposta desejada săo as propriedades físicas medidas nos poços. No contexto da análise dos atributos sísmicos, treinar uma rede neural é equivalente a uma calibraçăo dos atributos sísmicos. Os resultados preliminares obtidos indicam que as redes neurais constituem uma ferramenta valiosa a ser utilizada no processo de caracterizaçăo de reservatórios. As redes neurais possibilitam o mapeamento de pequenas variaçőes nas propriedades físicas do reservatório que afetam a resposta sísmica, mas que săo visualmente imperceptíveis no dado sísmico.
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Influęncia de Parâmetros Térmicos e Petrofísicos na Resistividade Aparente da Formaçăo
Authors K. Cozzolino and A.Q. Howard Jr.O processo de invasăo ocorre em formaçőes permeáveis onde a pressăo dentro do poço e superior a pressăo do fluído da formçăo. A simulaçăo do processo de invasăo năo e uma tarefa fácil, pois depende de inúmeros fatores como saturaçőes, molhabilidade, pressăo e pressăo capilar, permeabilidades e viscosidades dos fluidos existentes. Cozzolino e Howard (1995) revizaram a equaçăo de Buckley-Leverett adaptando o fenômeno de invasăo para o caso de simetria cilíndrica (Figura 1). Tal processo permite a obtençăo da distribuiçăo radial de resistividade da formaçăo se acoplado, por exemplo, ŕ Lei de Archie, que relaciona as propriedades elétricas e petrofísicas da formaçăo em uma equaçăo simples. Havendo uma diferença de temperatura entre a lama e a formaçăo adjacente, os efeitos transientes da temperatura sobre tal distribuiçăo de resistividade podem ser avaliados. Finalmente, a resistividade aparente da formaçăo é obtida. pela convoluçăo da distribuiçăo de resistividade da formaçăo com o fator geométrico radial da ferramenta de induçăo. Desta forma, os efeitos de parâmetros térmicos e petrofísicos na resistividade aparente săo obtidos.
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Modelagem Petrofísica Integrada: Uma Ferramenta de Apoio ŕ Interpretaçăo
Authors L. Duarte Dillon, G. Fernandes Vasquez, J.A. Soares and A. da Costa BastosA modelagem petrofísica é uma importante ferramenta para o processo de interpretavăo do dado geofisico. Sua contribuiçăo permite uma melhor visualizaçăo de como a resposta elástica do sistema rocha-fluido está conectada ŕs demais propriedades petrofísicas tais como: cimentaçăo, porosidade, tipo de fluidos saturantes, entre outros. Apresentamos, neste trabalho, uma proposta de modelagem petrofísica integrada como uma importante ferramenta na estimativa do comportamento elástico de rochas saturadas em condiçőes de subsuperficie. Este processo combina de forma recursiva e interativa, a obtençăo das propriedades elásticas de rochas e fluidos sob condiçőes controladas em laboratório ŕs modelagens teóricas e ou empíricas. Serăo apresentados alguns casos brasileiros que ilustram a utilizaçăo deste tipo de modelagem. O objetivo e exemplificar como esta técnica pode auxiliar o processo de interpretaçăo do dado geofísico.
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The HC Generative Subsystems of Productive Mexican Basins
Authors N. Holguin, F. Galindo, E. Serrano, A. Romero, A. Sosa and G. MartinezBetter understanding and greater new insight into the petroleum systems of Mexico have been gained from extensive field research - more than 40,000 samples have been analyzed by Rock-Eval pyrolysis and, then the data interpreted; added to the information obtained from chromatography and, to a lesser degree from carbon isotope testing, biological marker and other types of analytical testing - made it possible not only to characterize the source rocks, but also determine with a high degree of exactness the origins of many of the hydrocarbons HC in Mexico, and also allowed a better understanging of the petroleum systems in Mexico.
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Estimativas de porosidade e argilosidade usando técnicas petrofísicas e geostatísticas
Authors A.L.O. Gomes and J.M. HarrisUma grande enfase tem sido dada hoje ao estudo das roches reservatórios de hidrocarbonetos, pois uma melhor caracterizaçăo das mesmas implica num melhor dimensionamento das reservas e um aperfeiçoamento do processo de produçăo com uma grande economia de recursos (Sheriff, 1992). Os reservatórios săo em geral heterogęneos e anisotrópicos e na sua avaliaçăo é preciso conhecer uma grande variedade de parâmetros que os caracterizam, como por exemplo litologia, porosidade, cimentaçăo, tipo de fluido intersticial e permeabilidade, que săo influenciados por fatores do tipo idade da rocha, pressăo e temperatura.
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Some Applications of the Walkaway VSP Survey at Mars and Auger, Deepwater Gulf of Mexico, U.S.A.
Authors C.E. Guzman, M. Ramaswamy, C.L. West, S.D. McIninch, L.B. Franceware and N.W. KimDuring 1989 - 1991 Shell Ottshore Inc. acquired several lfalkaway VSP surveys as part of the evaluation program tor development wells in the deepwater Gult ot Mexico. VSP design, data and interpretation from the MARS and AUGER fields are presented (Figure 1). At MARS, first arrival walkaway VSP data allowed discrimination between two salt models (Figure 2) and revealed the presence of lateral velocity gradients in the sedimentary section. The walkaway geometry was then used to acquire a Multioffset VSP (Figure 3). First arrival data from the Multioffset allowed the estimation of the sediment velocity gradients; reflection data from this Multioffset was used to validate results from 3D surface seismic. At AUGER understanding salt geometry was critical to explore for attic reserves. By careful design of areal walkaway VSP surveys and analysis of 3-component data, it was possible to infer the salt geometry aiding the interpretation ot 3D surface seismic (Figure 4). The walkaway VSP geometry proved to be a powerful tool; data acquired enabled better calibration of surface seismic, validation ot geologic salt models and supplied information used to build velocity models for depth migration ot surface seismic.
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.3-D Acquisition Realities and Processing Strategies in Mountainous Thrust Areas
Authors S. MacKay, S. Wright, J. Gaiser, A. Jackson, C. Beasley and R.D. WisecupThe inherent structural complexity of thrust plays makes them ideal candidates for 3-D seismic imaging. However, there are many practical constraints placed on the acquisition of 3-D data in the mountainous terrains typically associated with thrust regimes. Financial considerations can result in tradeoffs between a desired acquisition geometry and that which is practical. Topographic relief can also impose irregular geometries and shortened receiver arrays. Such factors create challenges to the formation of a valid 3-D seismic image. Therefore, the realities of acquiring data in mountainous areas must be coupled to the appropriate processing strategies to yield an optimal result.
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Seismic Processing Issues In the Design of 3D Surveys
More LessThe seismic data collected during a 3D survey is typically subjected to a series of processing steps. Principal amongst these are: Statics - both refraction and reflection, NMO, DMO, Stack and Migration. The success or failure of each processing step depends on how the data were sampled. In other words, the layout of shots and associated receivers can critically affect the outcome of seismic data processing.
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Experimental Comparison between Single and Multi-Channel Telemetry Systems in Harsh and Mountainous Areas
Authors P. Burger, J.J. Postel and A. MartinezA review of the last decades of land seismic acquisition shows that, in the 80s, cable telemetry acquisition systems gradually replaced conventional systems. Over a period more than ten years, singlechannel telemetry systems dominated the market and became the standard of the industry for land operations. Two important improvements, better quality (no crosstalk and no ElectroMagnetic Interference noise pick-up) and higher productivity, have been shown with the introduction of telemetry techniques, in comparison with conventional systems. With the extension of large 3-D surveys, multi-channel telemetry systems have been introduced showing that the cost-per-channel factor outweighs the advantage in seismic data quality of the single-channel. Besides improved data quality, are there operational advantages for the single-channel versus multi-channel systems which could counterbalance the price per channel increase? An example taken from a portable crew operating in a jungle and mountainous area illustrates the fact that single-channel operational superiority compensates for the increase in capital expenditures.
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3-D Design with DMO Modelling
Authors D.L. Connelly and M. GalbraithThe seismic industry applies dip moveout (DMO) processing increasingly often to correct for the up-dip reflection point smear inherent in common midpoint (CMP) 3-D seismic surveys. Successful DMO application requires a complete reconstruction of a wave field by shifting and summing energy along sourcereceiver azimuths dependent upon the 3-D survey geometry. In order to design 3-D surveys for successful application of DMO, we require knowledge of the interaction between 3-D geometry and the effect of DMO on recorded seismic data.
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Uses of GIS Data in 3D Seismic Designs and Acquisition
Authors G. Elkington, M. Lansley, F. Martin and R. UtechTraditionally, the designer for 3D seismic acquisition attempts to maximize the geophysical attributes while minimizing the field effort and environmental impact. It was difficult to incorporate real world information such as terrain, existing access, production facilities etc. into the design. Today however, Geographical Information Systems (GIS) and 3D seismic survey design can be integrated. Several practical applications are presented to illustrate how this information can be analyzed and subsequently incorporated to provide an optimum solution. In particular, the use of aerial photos, satellite images and digital elevation models superimposed on the theoretical designs lead to more refined and practical shooting technique, by simply taking into account all the interpreted features. With the aid of computer software, the geophysicist can quantify more realistically: - traditional fold, azimuth and offset distribution - DMO attributes (Beasley, 1993) - economics - environmental impact - operation logistics The examples presented will show 3D prospects from several areas in Latin America, where the design stage was greatly aided by the GIS data provided by our clients and/or other service companies. The use of GIS data, along with the classical sampling and data processing considerations, can help the geophysicist to achieve the difficult task of recommending an Wall things considered 3D design.
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Development and Testing of Mathematical Algorithms for Source and Streamer Positioning during Marine Seismic Exploration
Authors V. Gikas, P.A. Cross and A. Asiama-AkuamoaIn order to analyse 3D offshore seismic data and utilise the final geophysical product it is necessary to know the position of each gun and hydrophone in the spread for each shot. In recent years the problem has become extremely complex, mainly due to an expansion of the type and quantity of survey data collected. Moreover it has become increasingly common for clients to require proof (often in real time) that the survey 'quality' specifications are being met. Hence there is today a real need to develop a completely general (for flexibility purposes), rigorous and integrated (for error propagation, and therefore QA/QC purposes) approach to the positioning of guns and hydrophones during seismic exploration and this paper is an attempt to address that need. It describes the mathematical basis and implementation of a Kalman filter that can, in principle, handle any number of vessels, streamers and guns and any set of observations to produce either realtime or post-processed positions and quality (precision and reliability) measures - a filter that can also be used prior to data collection to test the suitability of a proposed set of measurements to meet the positioning quality specifications. The paper also describes tests that were conducted using a real set of marine seismic positioning data.
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The Question of Azimuths
More LessOver the last two decades, 3D recording and processing of seismic data has seen a very significant increase in usage. Data acquisition systems today have at least an order of magnitude more channels than they did when the earliest 3D surveys were recorded. In many of the surveys recorded today, systems with more than 1000 channels are being used, and an increasing number of onshore surveys are being acquired with the number of live recording channels in excess of 2500. Data processing algorithms have changed from being mere extensions of two dimensional processes to being truly three dimensional in nature. Most of the criteria (such as offset ranges, spatial sampling, etc.) used to determine the optimum recording geometries are well understood, and industry is, in general, in agreement on these issues. There is one aspect of 3D recording, however, on which general industry agreement has not been reached, and that is the question of the range of azimuths over which the data should be acquired. This paper will review the relationships between using a wide or narrow range of azimuths, survey orientation, their impact on the use of different processing algorithms, and the resultant cost of the survey.
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Designing Full Range Land 3-D Seismic Surveys
By H.K. RigdonThe introduction of land 3-D seismic imaging in the mid 1980's also introduced numerous two-dimensional recording spread geometries. These designs include the traditional swath or wide lime profiling. the checkerboard or buttoo/patch design and the loop that became popular for areas of limited access. These static or limited rollalong spread designs were imposed by the limitations of available cable dependent recording systems. Each spread design has numerous pros and cons associated with its unique spread geometry, but a major disadvantage has been the limited cross-line information that can be recorded by most of these designs. This limitation often results in data sets that do not accurately image the geological objectives. This is due to the heavy trace weighting in the inline direction that can results in amplitude striations or elongations on time slices yielded from the processed data sets. These striations will occur in the inline direction and are unrelated to the subsurface geology. A solution to this problem is the recording of full range or wide azimuth 3-D data volumes that yield a wide range of source-receiver azimuths for each subsurface bin trace population.
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Fluid Migration Associated with Allochthonous Salt in the Northern Gulf of Mexico: An Analysis Using 3D Depth Migrated Seismic Data
Authors W.M. House and J.A. PritchettThe emplacement of allochthonous salt bodies in the Northern Gulf of Mexico, and their subsequent deformation to form secondary salt features involves the upward movement of salt along discrete feeder conduits. The detachment of allochthonous salt from a deeper source results in the collapse of these conduits. Structural disruption associated with this collapse creates a permeability pathway to allow enhanced fluid migration from depth into shallower section. Some of the high pressure fluids migrating upward along these permeability conduits will impinge on a permeability barrier created by the horizontal to sub-horizontal base of allochthonous salt sheets. Additional high pressure fluids associated with shale compaction and dewatering will also move upward to the base of salt permeability barrier. The constant influx of high pressure fluids into the zone immediately below salt prevents the shale in this zone from undergoing normal compaction, resulting in the formation of a lithologically distinct "gumbo zone". This gumbo zone has been encountered in many of the subsalt wells drilled in the Gulf of Mexico. Abnormally high pore pressures are often associated with this gumbo zone beneath the salt sheets covering the southern shelf area, offshore Louisiana. Fonnation pressure gradients within this zone can be as much as 0.04 psilft (0.8 ppg) above the regional pressure gradient.
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Solutions for Effective Land 3·D Seismic Imaging
By H.K. RigdonSuccessful application of three-dimensional seismic imaging during the past several years has resulted in land 3-D surveys becoming large (50 to 100 square miles) and complex due to irregular shapes, traversing congested areas and encountering major obstructions and physical barriers. These characteristics often result in poor subsurface coverage and increased acquisition costs. A solution for reducing acquisition costs and improving subsurface coverage is the utilization of radio-frequency (R-F) telemetry recording systems. The absence of telemetry cables allows the noncable system to traverse all terrains with reduced cost while providing continuous coverage. Also, the system reduces safety hazards associated with difficult and populated areas. The software driven features of the R-F telemetry system allows easy deployment of receiver spreads which yield uniform trace offset and azimuth distributions that are often necessary for improved processing and confident interpretation of stratigraphic anomalies. As demand for increased channel count (2000+) becomes a reality, the increased equipment volume and weight associated with kilo-channel systems also becomes an economical limiting factor. R-F systems can reduce the overall equipment volume compared to cable telemetry systems by as much as fifty-percent. This volume reduction significantly increases production rates which in turn translates into significantly reduced acquisition costs. An R-F telemetry system results in reduced field activities which has a savings effect on the environment. This trait of R-F telemetry allows seismic activities where otherwise would be a limiting effect for cable systems. The R-F system improves safety of a seismic field crew due to the elimination for the need to cross highways, waterways, reduced activities in mountainous and other hazard terrain.
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Atenuaçăo de Ruidos de Alta Freqüęncia Utilizando Arranjo de Fonte
More LessA utilizaçăo de arranjos geométricos é uma alternativa possivel, durante a aquisiçăo de dados sísmicos, para a atenuaçăo de ruidos superficiais. Aproveitando-se esta propriedade, foi realizado um levantamento experimental em área com qualidade deficiente devido ŕ presença de fortes reverberaçőes, causadas por lâmina de água inferior a 20m e fundo oceânico carbonatico. Adquiriram-se duas Iinhas coincidentes, uma com fonte convencional e outra com fonte defasada em tempo para simular um arranjo longo. A utilizaçăo desta ultima objetivou a atenuaçăo das altas freqüęncias, que săo as componentes principais das reverberaçőes. Os resultados obtidos mostram que a fonte defasada foi efetiva no cancelamento deste ruído, fornecendo maior continuidade nos refletores profundos (principal objetivo exploratório na área analisada), onde ocorre predomínio de baixas freqüęncias. Os resultados corroboram que, em algumas situaçőes, levantamentos recentes (com arranjos menores) tęm qualidade inferior a levantamentos antigos devido ao registro de ruidos de altas freqüęcias. As mudanças de arranjo aqui apresentadas năo devem ser executadas no caso de objetivos exploratórios do tipo estratigráfico, devido ŕ diminuiçăo na resoluçăo vertical.
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Projeto 4D - Aquisiçăo de Alta Resoluçăo com Cela Fracionária
Authors N. Brasil Ferreira and M. do Amaral de AlmeidaO Projeto 4D no Campo de Fazenda Alvorada, Bacia do Recôncavo, Bahia, tem caráter pioneiro no Brasil. O planejamento, coordenaçăo e execuçăo estăo sendo feitos de forma integrada e envolvem setores de pesquisa, produçăo, desenvolvimento e exploraçăo da Petrobras. O objetivo básico do Projeto e o monitoramento do avanço da frente de vapor, através da comparaçăo de sucessivos dados de sísmica de reflexăo 3D de alta resoluçăo, obtidos ao longo do tempo, durante o processo de injeçăo (Schwedersky, 1994). O presente trabalho trata dos parâmetres de aquisiçăo propostos e do experimental feito na area. O dispositivo de registro sugerido utiliza, de forma inédita em levantamentos 3D terrestres no Brasil, cela fracionária extremamente reduzida, com 6,25 m2. A multiplicidade nominal é homogęnea em toda a área de interesse geológico e igual a 10. O número de pontos de tiro e o custo do levantamento săo equivalentes aos de um dispositivo com cela 5 m x 5 m (25 m2) e multiplicidade 40. De acordo com os resultados do experimental, foi definida a profundidade de 6 m para colocaçăo de fontes e receptores.
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Aquisiçăo Sísmica 3D Terrestre na Bacia do Recôncavo, Bahia
More LessDesde dezembro de 1990, sete levantamentos tridimensionais terrestres foram realizados na Bacia do Recôncavo, Bahia, Brasil. O estágio avançado de exploraçăo e a forte estruturaçăo da bacia justificam a necessidade de projetos 3D. Do total de projetos, quatro săo exploratórios, dois explotatórios e um misto. A qualidade sísmica das áreas, com base nas linhas 2D pré-existentes, é via-de-regra regular a deficiente, afetada pelas rochas aflorantes e variaçőes topográficas. O objetivo deste trabalho e mostrar a evoluçăo dos parâmetres de campo, no sentido do uso de número crescente de canais, lanços bipartidos simétricos, dispositivos com forte concentraçăo azimutal, multiplicidade nominal elevada e hornogęnea na área de interesse geológico e amostragem uniforme de afastamentos dentro de cada cela e entre celas, obtida com a diagonalizaçăo das linhas de tiro em relaçăo ŕs linhas de receptor. A principal dificuldade no planejamento 3D é compatibilizar boa amostragem temporal e espacial, e cobertura adequada, com custos năo proibitivos. A maior parte dos dados está em fase preliminar de interpretaçăo, mas é clara a contribuiçăo da sísmica 3D para a definiçăo das feiçőes estruturais e o mapeamento dos horizontes objetivo. Alguns exemplos de time slices e de seçăo sísmica săo mostrados no final do trabalho.
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Planeamiento / Adquisicion de un Programa de 3D Inofensivo al Medio Ambiente en la Sur de la Argentina
Authors E. Trinchero, C.J. Verret and G.J. CarstensLa Patagonia Argentina es una zona semidesértica ubicada en el extremo sur del país, que ha sido permanentemente agredida por las actividades de exploración y explotación de petróleo, produciendo en muchos casos dańos en el ecosistema prácticamente irreversibles. La necesidad de registrar sismica 3D en un yacimiento de mas de 2.500 m'/dia de producción, con mas de 800 pozos, baterías de tanques, oleoductos, oficinas y otra serie de obstáculos en superficie, en un área prácticamente devastada por ańos de explotación irracional planteo en problema de difícil solución. El detallado análisis de diversas alternativas, la utilización de la gran cantidad de caminos existentes para ubicar las fuentes, la decisión de ampliar substancialmente el numero de canales a utilizar y una serie de consideraciones adicionales finalmente permitieron reducir los 402 km. de lineas a cortar que consideraba el proyecto original a tan solo 57 km. Estas consideraciones también permitieron eliminar el uso de explosivos como fuente, utilizándose únicamente vibradores. Todos estas alternativas no afectaron los atributos del diseńo, dado que se requería un fold alto y una muy buena distribución de ángulos y de distancias.
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O Processamento de Campo no Controle da Qualidade de Dados Sísmicos na Amazônia
Authors A. Tanaka, N.T. Zago, J.A. Rosseto and A. Cândido BezerraA utilizaçăo de sistemas de processamento de dados sísmicos em equipes heliportáteis na Amazônia foi iniciada em 1993 com o objetivo de executar o controle de qualidade dos dados antes do envio ao centro de processamento de grande porte. Em 1994, o processo obteve um avanço tecnológico importante com a introduçăo de estaçőes de trabalho que propiciaram maior velocidade ao processamento e ampliaram as possibilidades de análise do dado sísmico. Devido a localizaçăo das áreas de pesquisa em áreas de floresta amazónica, distante dos centros de processamento de dados, o tempo necesáario para se obter uma seçăo sismica pode consumir algunas semanas. O processamento de campo cumpre entăo o papel de avaliar a confiabilidade dos dados levantados, assim como disponibilizar uma sevăoo sísmica preIiminar em 48 horas após o último registro da linha sísmica.
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Modelamento Preliminar para Monitoramento do Avanço da Frente de Vapor
Devido ŕ melhora progressiva da qualidade sísmica, principalmente com levantamentos 3D de alta resoluçăo, tem sido possivel a detecçăo das alteraçőes petrofisicas introduzidas nos reservatórios por alguns processos térmicos de recuperaçăo secundária e terciária. O monitoramento de tais processos é de extrema importância para o sucesso de projetos desta natureza e o método sísmico pode-se constituir em uma eficiente ferramenta para este tim. Neste trabalho discute-se as possibilidades de monitoramento da evoluçăo da injeçăo contínua de vapor que será realizada em um reservatório fluvio-eólico através de sucessivos levantamentos sismicos 3D de alta resoluçăo. A partir dos dados obtidos por simulaçăo de fluxo, estimou-se as variaçőes de velocidade sísmica em funçăo da temperatura através de mediçőes em Iaboratório. Estas variaçőes foram introduzidas no modelo geológico da área e a resposta sísmica foi avaliada através de modelamento sísmico numérico (traçado de raio), podendo-se concluir que há possibilidade de se mapear o avanço da frente de vapor.
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Coexistence; Exploration and the Environment - Seismic Operating with Care in Rain Forests and Wetlands
Authors P.S. Cunningham, J.L. Kreamer, J.G. Winston, L.M. Chenault and G.L. WattOne of the major challenges in our industry today is successfullymeeting two needs of the planet that often appear to be conflicting: • Meeting the economic needs of nations through sustainable development of natural resources while • Preserving the integrity and diversity of our environment. Nowhere is this more critical than in the world's wetlands and rain forests. This presentation demonstrates the principles and practices that have fostered coexistence of environmental protection and sustainable development projects in tropical forests and wetlands in the Americas. Excerpts from two projects are shown, one in the rain forests and savannahs of Bolivia, and one in a national wildlife refuge in the Louisiana marshland.
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Wide Aperture Reflection Profiling (WARP) in Environmentally Sensitive Rain Forest Areas
Authors H. Mack, P.S. Cunningham, N.J. House-Finch, J. Makris and M. Le VotWide Aperture Reflection Profiling (WARP) is emerging as a viable and cost-effective method for seismic reconnaissance. It can provide an initial evaluation of the extent, depth and structure of a sedimentary basin, including a measurement of seismic velocities. It is a less costly method than conventional seismic methods which makes it extremely useful in reducing the area in which to focus a standard frontier area exploration program. And without doubt, it has a much smaller impact on the environment than other seismic methods.
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Levantamento de Refraçăo Sísmica no Aterro Sanitário de Brasília
Authors H. de Araújo Franco and J.W. Corręa RosaEste trabalho apresenta os dados de sismica de refraçăo utilizado no intuito de determinar a profundidade do nível freático, a espessura do solo e do Iixo soterrado no Aterro Sanitário de Brasilia - DF. Foi realizado um total de 5 perfis sísmicos, sendo 2 com arranjo longo e 3 com arranjo mais curto de geofones. Os dois primeiros visavam determinar a profundidade do nível freático e espessura do solo e, os últimos, distinguir a camada de detritos soterrada. Os perfis de arranjo longo definiram duas camadas com diferentes velocidade de propagaçăo de ondas P, de 400 m/s e 2000 m/s. Através do processo de inversio baseado no processamento SIPT, pode-se definir a variaçăo lateral da interface detectada nos dois perfis; os quais săo consistentes com a profundidade do nível freático local. Os perfis mais curtos năo evidenciaram diferenças de velocidade de propagaçăo de ondas P no meio amostrado. Possivelmente devido a camada de Iixo ser de pouca espessura ou porque tal camada constitui um nível de velocidade mais baixa que o nível de solo compactado superior.
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BARENTS SEA CARBONATE PLATFORMS AND RELATED PETROLEUM POTENTIAL
By N.M. IanovaBy geophysical investigations such as reflection seismic survey, gravimetric and magnetometric measurements, the Barents Shelf (BS) has been found to consist of stable areas with relatively thick crust and more mobile zones of Late Paleozoic- Mesozoic activity with thin crust. The mobile zones are rift related. First of all they are the South-Barents and North- Barents Basins. To the west, deep grabens are present (the Nordkapp and Tiddly Basins,Bjornoya, Hammerfest), where mainly Mesozoic terrigenous deposits of a considerable thickness (up to 14-17 km) form the sedimentary cover. Carbonate Platforms with relatively reduced thickness of Permian-Mesozoic clastic sediments are characteristic of stable areas. As a rule some part of Mesozoic deposits is eroded. As a result, a top of Upper Devonian-Permian mainly carbonate complex lies on the average depth 3-5 km. Carbonate platforms are developed widely within the.Barents Shelf (BS): the Pechora Platform, Bjarmeland, Finnmark Platforms, platforms within the Kola-Kanin Monocline, isometric highs mainly in the central part of the BS (the Fedihskiy High, Central Bank High, Persey High,Demidovskaya Saddle), also a platform within the eastern part of the Svalbard Archipelago. Besides, carbonate formations are developed on the eastern peripheral part of the BS, including such large.
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Estudo Geofísico e Geoquímico da Contaminaçăo de Agua por Aterro Sanitário
Authors H. de Araújo Franco and A.C.B. PiresEste trabalho apresenta dados preliminares do estudo da contaminaçăo de águas superficiais e subterrineas provocada pelo deposito de resídueo sólidos de Brasilia - DF, utilizando-se de técnicas geofisicas e de química aguatica. O aterro está ascentado sobre ardósias, com raras intercalaçőes de quartzitos, pertencentes ao Grupo Paranoá. Dados de 86 sondagens elétricas verticais, dispositivo de Shlumberger, exibem um mesmo padrăo, definindo 5 camadas geoelétricas: (1) solo seco, (2) solo úmido ou saturado, (3) nível laterítico, (4) saprolito saturado e (5) rocha să. Mapas de isoresistividade aparente com AB/2 contante, evidencia um trend de baixos valores na direçăo do Parque Nacional de Brasilia, evidenciando uma possível pluma de contaminaçăo. Esta possível pluma é também evidenciada nos dados de quimica aquática.
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