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12th International Congress of the Brazilian Geophysical Society
- Conference date: 15 Aug 2011 - 18 Aug 2011
- Location: Rio de Janeiro, Brazil
- Published: 15 August 2011
1 - 100 of 465 results
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Landslide Interpretation and Magnitude-Frequency Statistics Analysis in The Lushan Basin, Taiwan
Authors Chien-Yuan Chen and Ho-Wen ChenThe Lushan Hot Spring area in Nantou County, Taiwan, suffered serious sediment disasters after typhoons Sinlaku and Jangmi in 2008, and following Typhoon Morakot in 2009. The basin’s landsldies after the typhoons brought rain was examined using the frequency-area statistics distribution. The critical state indices attributed to landslide frequency-area distribution are discussed and the marginally unstable characteristics of the study area indicated. The landslides were interpreted from Spot 5 images before and after disastrous events. The results of the analysis show that the power-law landslide frequency-area curves in the basin for different rainfall events-induced tend to coincide with a line. The temporal trend of the rainfall-induced landslide frequency-area distribution shows 1/f noise and scale invariance. The landslide frequency-area distribution could be estimated in advance by three-parameter inverse-gamma distribution with a critical slope of 1.0.
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Prestack 2D Parsimonious Kirchhoff Depth Migration of Elastic Seismic Data
Authors Robert Sun and George A. McMechanWe extend prestack parsimonious Kirchhoff depth migration (Hua and McMechan 2003) (which is a fast migration), to two-dimensional (2D), two-component (2C), reflected elastic seismic data, from a P-wave source. The P-to-P reflected (PP) waves and P-to-S converted (PS) waves in an elastic common-source gather recorded at the earth’s surface are first separated into PP- and PS-wave seismograms. Source and receiver apparent slownesses (p values) are estimated for the peaks and troughs in both separated PP and PS waves. For each PP and PS reflection, a source ray is traced, in the P- (or the S-) velocity model, in the direction of the emitted ray angle (determined by the source p value), and a receiver ray is traced, in the P- or S-velocity model, back in the direction of the emergent PP (or the PS) wave ray angle (determined by the PP or PS wave receiver p value), respectively. The image point is adjusted from the intersection of the source and receiver rays to the point where the sum of the source and receiver times equals the observed two-way reflection traveltime. The orientation of the reflector surface is determined to satisfy Snell’s law at the ray intersection point. The amplitude of a P-wave (or an S-wave) is distributed over the first Fresnel zone along the reflector surface in the P (or S) image. Stacking over all the single-source P- and S-images separately gives the stacked P- and S- images, respectively. The quality of prestack parsimonious elastic Kirchhoff migration is not as good as that of full prestack Kirchhoff, or reverse-time, migration, but the computing time is reduced by orders of magnitude because the amount of ray tracing is significantly reduced. Thus, parsimonious elastic migration is most useful, when reducing computing time is more important than migration quality, such as in migration velocity analysis, which iterates migration many times.
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Low-Frequency Extension of The Backus Averaging Method
Authors A. Stovas and Y. RoganovThe standard Backus (1962) averaging method is widely used for upscaling of the well-log data to seismic frequency range. In many cases, with strong heterogeneity within the upscaling unit, the Backus averaging is not accurate enough. We propose to extend the Backus averaging method for the low-frequency case and introduce the dispersive Backus model using the Baker-Campbell-Hausdorff (BCH) series (Serre, 1965). We derive the first- and second-order terms of this series, and extend this technique to the medium with arbitrary number of layers in a period. That results in the correction term for velocity dispersion at low frequencies. We show that the phase velocity in such media is the even function of frequency.
The accurate description of velocity dispersion for effective medium is very important in seismic modelling and inversion of seismic data into effective reservoir properties.
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Areal Surface Characterization of Acid Fractures in Carbonate Rocks
More LessFracture surface characteristics have significant effect on fracture hydraulic conductivity. The available acid-fracture conductivity correlations do not consider surface characteristics or make an incipient use of it. A proper description of the acid-fracture surfaces is the initial step towards the right consideration of surface roughness in hydraulic conductivity. This paper presents an areal (3D) surface evaluation of acid-etched fractures, simulated in samples taken from whole cores of an oil producer limestone. The topography of acid-fractured surfaces was assessed using a laser profilometer. The surfaces were evaluated with a set of 3D surface parameters. The results showed that the main features of acid-etched surfaces are large roughness, negative skewness, high kurtosis, and intermediate isotropy, mostly random but with some spatial orientation. The acid-fractured surfaces can be represented by the rms height, which showed great linear correlation with most of the surface parameters. The parameters texture aspect ratio, bearing index, valley retention index, and density of summits showed low correlation with rms height. A method to calculate fracture width from surface topography was developed. An attempt to explain abnormal behavior in initial conductivity tests revealed the potential use of surface characterization for fines management in oil and gas reservoirs. Improved acid fracture correlation may be achieved using surface characterization parameters.
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Determinação da Estrutura Vertical de Latossolos Usando Sondagens Elétricas Verticais
More LessThe purpose of this work is to present a procedure for survey of soils, based on DC electrical resistivity. The study area has 5 km2 and is located at Distrito Federal, in the central region of Brazil. Results showed that clay rich soils are less resistive than sandy soils, and vertical electrical soundings (VES) permitted to identify the underground variation of resistivity. The sandy soils have 22200 Ohm.m, and a conductive-resistive-conductive structure, where the upper layer has 1.3 meters of thickness. The clay rich soils have 6200 Ohm.m and a resistive-conductive-resistive structure, where the upper layer has 4 meters of thickness.
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Shale Gas Exploration and Production
By S. SunjayShale gas is natural gas from shale formations which acts as both the source and the reservoir for the natural gas. Each Shale gas reservoir has unique characteristics. Shale has low matrix permeability, so gas production in commercial quantities requires fractures to provide permeability . For a given matrix permeability and pressure, gas production are determined by the number and complexity of fractures created, their effective conductivity, and the ability to effectively reduce the pressure throughout the fracture network to initiate gas production. Understanding the relationship between fracture complexity, fracture conductivity, matrix permeability, and gas recovery is a fundamental challenge of shale-gas development. Shale gas reservoirs almost always have two different storage volumes(dual porosity) for hydrocarbons, the rock matrix and the natural fractures .Because of the plastic nature of shale formations, these natural fractures are generally closed due to the pressure of the overburden rock. Consequently, their very low, matrix permeability, usually on the order of hundreds of nanoDarcies (nD), makes unstimulated, conventional production impossible. Almost every well in a shale gas reservoir must be hydraulically stimulated (fractured) to achieve economical production. These hydraulic fracture treatments are believed to reactivate and reconnect the natural fracture matrix .
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A Model-Based Approach to the Common-Diffraction-Surface Stack Method – A Synthetic Case Study
Authors Hashem Shahsavani, Jürgen Mann, Iradj Piruz and and Peter HubralThe Common-Reflection-Surface (CRS) stack method parameterizes and stacks seismic reflection events in a generalized stacking velocity analysis. It considers a discrete number of events contributing to a given stack sample such that conflicting dip situations can be handled. The reliable detection of such situations is difficult and missed contributions to the stacked section cause artifacts in a subsequent poststack migration. This is deleterious for complex data where prestack migration is no viable
option due to its demands on velocity model accuracy, such that we might have to rely on poststack migration. As an alternative, the conflicting dip problem has been addressed by explicitly considering a virtually continuous range of dips with a simplified stacking operator in a process termed Common-Diffraction-Surface (CDS) stack. In analogy to the CRS stack, the CDS stack has been implemented and successfully applied in a data-driven manner based on coherence analysis in the prestack data. In view of the computational costs, we present a more efficient model-based approach to the CDS stack designed to generate stack sections optimized to image discontinuities by poststack migration. This approach only requires a smooth macro-velocity model of minor accuracy. We present our results for the synthetic Sigsbee 2A data and compare them to the results of CRS stack and datadriven CDS stack.
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3D-Vsp from Interpreter’S Perspective
Authors M.C. Schinelli, E.A. Thedy, R.C. Sansonowski, O.F. Keller and P.R.S. JohannThe point of view of interpreters working with 3D-VSPs interpretation is seldom explored. We report here their experience during the interpretation of a marine and two land 3D-VSP projects.
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Comparação do Desempenho das Técnicas Análise Por Principais Componentes E Fator De Máxima Autocorrelação Para Processamento de Dados Aerogeofísicos: Investigação Teste Num Prospecto da Província Mineral do Tapajós
The MAF (Maximum Autocorrelation Factor) technique, more precisely the kernel version, was applied to an airborne geophysics dataset for the assessment of the geologic information in the area of the Maués Prospect (Brazilian Amazon). This method is characterized as another approach of the well known Principal Component Analysis technique that also was utilized in this case study. Based on the visual and statistical analysis, the results were compared for the determination of the main lithologies in this portion of the Tapajós Mineral Province. This case study shows that the use of the (Kernel) MAF has a great potential for applications in multivariategeologic data.
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O Papel da Aerogamaespectrometria, da Aeromagnetometria e do Sensoriamento Remoto na Caracterização de Terrenos Greenfield do Cráton Amazônico: Resultados e Desafios na Discriminação de Alvos Exploratórios na Província Mineral do Tapajós
The investigation of greenfield terrains through the airborne geophysics dataset provides valuable information about the geologic context and, mainly, the metalogenetic understand. Almost exclusively, there are available regional (low resolution) airborne geophysical data, like gamma-ray spectrometry and magnetic data, and, in this context, some information about the geology can be interpreted. But, the use of high resolution data, like the gradiometer magnetometry, and remote sensing images increases the potential of applications for the characterization of these terrains, like the vast area of the Amazon craton. The Tapajós Mineral Province, located in the states of Amazonas and Pará (Brazil), was selected as a case study in this paper for the recognition of the potential targets for mineral exploration.
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Por Que a Avaliação da Acurácia de Mapas Previsionais é Importante na Pesquisa Mineral? Uma Análise Baseada em Métodos de Estatística Multivariada Discreta no Prospecto 12 de Outubro, Província Mineral do Tapajós
The accuracy assessment of predictivity maps used in the mineral research comprises the goal of this paper that analyses methods for investigation of this nature. One case study aiming the determination of gold potential areas in the Tapajós Mineral Province is showing through the comparison of the performance of two neural network techniques in relation to truth ground points available by MAPEX Company.
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A Expressão Dos Diques Máficos do Setor Oeste da Província Mineral do Tapajós Visualizada em Dados Aeromagnetométricos de Baixa E Alta Resolução: Novas Interpretações Geológicas
Mafic dykes’ swarms of the Tapajós Mineral Province western portion were investigated by use of airborne geophysical data characterized by different resolutions. Additionally, geochemistry data related to amount of gold in soil and in rock were integrated with geophysical images and interpretations were done. Specifically, the relationship of gold anomalies with the approximation of mafic dykes was observed, like in Rosa de Maio, Bandeirante and Maués prospects, besides the deformations of this mafic geologic unit, which give new insights for interpretations for this area.
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Orthorhombic Migrations for Imaging Fractured Reservoirs
Authors Jaime A. Stein and Robert WojslawThe combined effects of horizontal layering and vertical fracturing in the reservoir produce orthorhombic anisotropy. In order to properly image these kinds of reservoirs, we need to abandon the simple assumption of VTI and HTI as independent effects, used in current migration algorithms, and adopt new simultaneous accountings of both effects in the form of an orthorhombic time migration. In this paper we will describe the theoretical underpinning of orthorhombic symmetry, how we use it in migration and then show some results on real data. A discussion about the challenges associated with doing velocity updating will be briefly discussed at the end of the article
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3D P-Wave Anisotropy Analysis Technique to Fracture Detection in a Colombian Limestone Reservoir
Authors Deying Zhong, Yan Li, Jun Li, Jinding Huang, Mark Mo, Nelson Rojas and Claudio RinconFracture detection technique based on 3-D P-wave seismic dataset has been a powerful tool for fractured reservoir characterization in recent years. However, as the most economical method of fracture detection, the accuracy and resolution of this method has been doubted sometimes. The major aspect of this paper is to prove the effectivity of this method. Traditionally, fracture information comes from well data, in particular image log and core. The purpose of this article is to prove that P-wave azimuthal anisotropy technique not only can describe the fracture character in thin limestone reservoir to regions between the wells but also can get result with good accuracy and resolution. The results indicated that the final fracture orientation and intensity got from 3D P-wave azimuthal anisotropy are extremely consistent with FMI/CMI data from drilled wells.
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Geoelectricals Surveying in Aluvional Sediments of Madeira River (Porto Velho/Ro)
The construction of two hydroelectric dams in Madeira River, near to Porto Velho city, will force the dredges, which explore residual gold in the stream bed, to change the location. The purpose of this work was to identify the auriferous conglomerate from Mucururu Formation using geophysical studies. Vertical electrical soundings (VES) and continuous vertical electrical sounding (CVES) were done in pre-determined places by geologists. In total were done 52 VES and 9 lines of CVES.
After an integration of geophysical data and geological observation were determined the most propitious places to have this auriferous conglomerate. A borehole with lithological description is suggested in some points to a better calibration of the model.
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Non-Hyperbolic Term Estimation for VTI Inversion from Walkaway VSP and Surface Seismic Data
By Emil BliasWalkaway VSP data provides information for interval anisotropic parameter estimates for transverse isotropy with vertical symmetry axis (VTI). For any depth tomographic/migration velocity analysis, we need an adequate initial depth velocity model. Dix-type approach provides us with explicit inversion formulas for velocity model estimation. To estimate these interval parameters, using Dix-type inversion approach, we need to estimate non-hyperbolic term of NMO function. In walkaway VSP data, NMO function can be obtained from first breaks, while in surface seismic it is estimated through non-hyperbolic semblance analysis. In both cases, determination of non-hyperbolic term is the most unstable procedure in interval VTI inversion. Because exact explicit formula for reflected time in a layered (even isotropic) media is unknown, we have to use some approximation. Different approximations have different accuracy in different geology. Here we investigate accuracy of different approximations on four models with weak and strong anisotropy and modest and large vertical velocity changes.
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An Easy Procedure to Estimate the Preliminary Shape of a Complex Magnetic Anomaly Through Inversion Software
More LessThe inversion of magnetic data is a difficult task when remanent magnetization is present. The available softwares do not take into account the remanence component in order to simplify the involved mathematics and reduce the time consuming processing.
Here, we examine and compare two different approaches to invert a magnetic complex anomaly set with induced and remanent magnetization, using transformations of the total magnetic field. The first method uses the analytic signal of the vertical integral of the TMI data. The second method uses the amplitude of the magnetic anomaly field. Both methods simulates the anomaly responses as they were just induced under a vertical magnetic field. The University of British Columbia’s Geophysical Inversion Facility (UBC-GIF, mag3d and grav3d programs) were used to invert the data. The susceptibility models resultant from both methods were compared with gravity inversion over the same anomaly. The outcome models show a certain difference in the result parameters, however, the overall result can be used for a preliminary estimation of the anomaly and instigate the further pass of research.
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Combining Geophysical, Geochemical and Geostatistical Methods to Detect Contamination Anomalies in a Controlled Dump in Oporto, N Portugal
More LessThe characterization and environmental monitoring of Municipal Solid Waste (MSW) deposits are an increasing area, in terms of the interdisciplinary studies involved. Whatever the solution adopted for the MSW treatment, its final containment on landfill is not the end of the problem. Rather, the need for continuous monitoring, tracking the evolution of the waste mass in all its surroundings, will contribute to evaluate the environmental consequences of the existence of a deposit of MSW. The assessment of contaminants dispersion in Controlled Dumps (CD) of MSW is possible through the combination of geophysical, geochemical and geostatistical methods as described in this paper. The methodology applied in this study will contribute to evaluate the environmental consequences of the Matosinhos CD (N Portugal), which is set in a granitic crystalline geological context with a permeability controlled by differential weathering associated with fracturing. The statistical methods here described (Lepeltier, 1969; Matschullat et al. 2000), more commonly applied to geochemical data, were adapted to be used with our set of 2D resistivity profiles in order to relate them and thus delineate the contamination anomalies in the CD surroundings. Groundwater samples were collected in piezometers, upstream and downstream of the CD, with the aim of directly confirming the presence of contaminants indirectly detected by the geophysical and geostatistical methods. The combination of these different approaches allows an approach towards the detection and delineation of contaminant plumes from these deposits.
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Improved Imaging and Reservoir Characterization with Dual Sensor Streamer
Authors Eivind Fromyr and Cyrille ReiserThe use of collocated pressure and motion sensors allows the separation of the up- and down-going waves and thereby removal of the receiver ghost. Having access to the up- and down-going wavefields yields significant benefits for seismic data processing and imaging, and ultimately quantitative reservoir interpretation. The resulting increase in seismic bandwidth, high and low, yields improved resolution of the geological layers as well as improved accuracy in extraction of elastic attributes.
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Interpretação Qualitativa de Dados Aerogeofísicos na Escala de Semi-Detalhe da Folha Rio Pardo De Minas, Minas Gerais, Brasil: Sd-23-Z-D-V-4
More LessThe geophysical methods are usually used as auxiliary tool in geological mapping. In the Rio Pardo de Minas sheet, located in the northern state of Minas Gerais, was used to detail mapping to 1:50.000 the magnetometry and gamma-spectrometry. The maps of Analytic Signal and Vertical Derivative were used to determine guidelines and bodies of the region, maps of K, Th, U and their composi-tions are used to dertermine a lito-geophysics regions. This work has aims to aid the geological mapping of the region.
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Magnetotelluric Response Estimates under the Equatorial Electrojet in Brazil
Authors E.U. Ulugergerli, S.L. Fontes, R.M Carvalho, C.R. Germano and A. CarrasquillaMagnetotelluric responses of soundings under the equatorial electrojet in Brazil have been estimated for four distinct locations at the north and south of the Magnetic Equator. It has been observed that the effect of the concentrated ionospheric currents (electrojet) in equatorial zones is added to the electromagnetic data and act as source. The difference between daytime and nighttime data indicates that source boosted by the electrojet, mainly observed at daytime, provides better estimation of the earth response functions even for lower frequencies (<0.01Hz).
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Aerogammaspectrometry for Lode-Au Deposits Exploration in Western Pampean Ranges-Argentine
Authors Gerardo Fanton, Patricia M. Martinez and Mario E. GimenezGiven the importance and economic potential of the region was held data processing geophysics obtained gammaspectrometrics maps relationship Th / K, Kd (potassium anomalous) and parameter F. Finally a ternary map data gammaspectrometrics where anomalous potassium integrate data, parameter F and K / Th. From the interpretation of these maps could define hydrothermal alteration zones associated with the presence of gold mineralization.
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Analysis of Atmospheric Variables Influence on the Surface Global Solar Irradiation
The current national energy scenery indicates the need of clean and renewable energy sources applications. Then, it is necessary to study the renewable energy resources and their variability. Therefore, the article aims at studying the influence of atmospheric aerosols and precipitable water in the global solar irradiation at the surface. Stochastic models were developed to compar the ratio betweenthe global solar irradiation at the surface and at the top of the atmosphere (Kt) with the atmospheric variables by using data acquired at the Southern Space Observatory, located in the Brazilian Southern region. Only clear sky days were used. After data validation, it was observed that the developed models have presented low statistical deviations, however, there was significant improvement in the estimates provided by the one that used as input variables the transmittances associated with atmospheric aerosols and Rayleigh scattering, and vapor water absorptivity.
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Efeito de Diferentes Sistemas de Manejo na Resistividade Elétrica de Latossolos
More LessIn this work, DC electrical resistivity measurements were used for to evaluate agricultural areas where no-tillage and conventional management systems have been established for 20 years. The study area is located at Distrito Federal, in the central region of Brazil. It was observed that conventional system area is less resistive than no-tillage system area. This result can be related to the fact that management systems influenced soil micro and macro aggregates distribution, what is related with permeability. Conventional system causes disruption of soil macro aggregates, increasing soil porosity and water retention and decreasing permeability and resistivity.
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Combining Wavelet Transform and Neural Network to Differentiate the Stratigraphy from Logs of Namorado Oilfield in Campos Basin
More LessOn well logging, there is a great interest to improve the vertical resolution of the logs, aiming the identification of different layers or geological formations along the borehole and the construction of a reservoir model. Generally, the identification of hydrocarbon formation lithology from geophysical logs employs several approaches as lithology crossplots (such as ‘‘M–N lithology plot’’ which requires a sonic log, density log, and neutron log) or the combination gamma-ray neutron-density log method. Also, numerous
mathematical approaches have been proposed to perform this task computationally, between them, artificial intelligence techniques. In this sense, the purpose of this study was to identify the formation interfaces from geophysical well logs using a combination of wavelet transform and neural network methods. The first technique was applied to smooth the logs, while the second was utilized to fit them to a selected lithological model. The input variables were gamma-ray, resistivity, density, neutron porosity and
sonic logs from Namorado Oilfield in Campos Basin. This method is easy to implement in a computer with MATLAB platform and it showed a good performance in the discrimination of main layers.
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2011-Inctet Progress Report on Magnetotelluric and Geomagnetic Depth Soundings in the Borborema Province and Adjacent Terrains, Ne Brazil
In order to enhance our knowledge about the tectonic processes responsible for the geological evolution of the Borborema Province and adjacent regions, the National Institute of Space Research (INPE) and the National Observatory (ON) are conducting
Electromagnetic Induction studies in northeastern Brazil, which are being supported by the National Institute of Science & Technology for Tectonic Studies (INCTET) project during the past three years. Such studies contemplate the deep geophysical
probing of this region with Magnetotelluric surveys (MT) and Transient Electromagnetic soundings (TEM) along several geoelectric transects and an array of Geomagnetic Depth Soundings (GDS), which complement other geophysical methods. The focus of
this study is directed to the identification of geoelectric variations in electric conductivity at distinct lithospheric depths and associations of geoelectric strikes and anisotropy with structural grain and stress patterns, particularly in the long ubiquitous structural features that cross the province and that constitute major geoelectric heterogeneities, at the near surface crust and also in the lower crust and upper mantle. The preliminary results indicate a lithosphere with a very variable electrical resistivity. The upper-mid crust shows up as a very resistive layer, overlying a less resistive lower crust and upper mantle. In some areas the mantle is very resistive, characteristic of a cratonic origin. Exceptions to a resistive crust are found under the Seridó belt, Jatobá rift basin and the Araripe intracratonic basin, marked by an underlying conductive crust. Laterally, the deeper portion of the crust and upper mantle is highly segmented in blocks with alternating juxtaposed higher and lower resistivities. This pattern is suggestive of highly deformed regions by transform dominated tectonic regimes, with the presence of contrasting mechanically strong cratonic-like keels against weaker zones likely subjected to delamination processes that might have produced magmatic related lithospheric re-fertilization by metasomatism.
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Geoelectric Dimensionality of a Magnetotelluric (MT) Survey in Parecis
Authors Jean Marie Flexor and Hans Schmidt SantosA survey of eighty-eight broadband (0001-1000s) magnetotelluric (MT) sounding stations was deployed in a transect from Parecis Basin, Brazil, in a direction al-most perpendicular to the dominant structural lineament. An image of the subsurface conductivity distribution was obtained from the 2-D inversion of MT data, linked to well logging resistivity data. In a first time, we assumed previ-ously a 2-D dimensionality for the inversion procedure, using as geoelectric "strike" an angle of 1400 (± 15 0) clockwise with respect to the geographic north. This is the direction of the dominant regional structural lineaments shown by the elongated geometry of the basin and by the lineaments revealed in the aeromagnetic data. In a second time, we went to check the consistency between the direction previously adopted for the 2D inversion and the intrinsic directionality deduced from rotational properties of the tensor impedance through a procedure of decomposition (McNeice and Jones, 2001), where we retrieve the geoelectric regional direction for a set of 36 MT soundings in the profile. The results show that the distribution of angles is not uniform as it would be expected but that the direction previously assumed is perfectly compatible with the trend of the mean directions calculated for the "strike. " This result shows that in the presence of indications of the directions of structural lineaments, it is not necessary to proceed the decomposition of tensor impedance.
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Aplicações da Filtragem Svd na Análise de Velocidades e no Empilhamento Cmp
Authors Oscar F. Mojica, Milton J. Porsani and e Michelangelo G. da SilvaNo presente trabalho aplicamos o m´etodo de filtragem adaptativa baseada no m´etodo SVD (Singular Value Decomposition) para a melhoria da an´ alise de velocidades e do empilhamento CMP. Antes da aplicac¸ ˜ao do m´etodo ´e feita a correc¸ ˜ao
normal moveout (NMO) dos sismogramas, tendo como finalidade deixar as reflex˜oes de interesse aproximadamente horizontais. A filtragem SVD trabalha na forma multicanal e pode ser aplicada seguindo um procedimento padr˜ao que consiste na
selec¸ ˜ao de um conjunto de trac¸os vizinhos tomados ao redor do trac¸o alvo da filtragem. Desta forma trac¸os de diferentes tiros podem ser utilizados na filtragem SVD. A coleta de trac¸os pertencentes a diferentes tiros, no mapa de cobertura, pode ser representada por um operador espacial. No presente trabalho utilizamos um operador de cinco pontos que denominamos operador em cruz que opera sobre todos os trac¸os do mapa de cobertura do levantamento s´ısmico. A cada posic¸ ˜ao do operador, o trac¸o filtrado (centro do operador) ´e obtido tomando-se a primeira ou somando-se a(s) primeira(s) autoimagem(ns) do painel de 5 trac¸os selecionados. Desta forma reforc¸amos a coerˆencia correspondente `as reflex ˜oes prim´ arias, em detrimento do sinal restante (ground-roll, m´ ultiplas e demais eventos n˜ao correlacionados), localizado nas demais autoimagens. A filtragem SVD pode ser vista como um m´etodo de filtragem adaptativa multicanal onde cada trac¸o filtrado guarda certo grau de coerˆencia
com os trac¸os imediatamente vizinhos. O m´etodo foi testado sobre uma linha s´ısmica terrestre da Bacia do Tacutu. Os resultados obtidos mostram espectros de velocidades com melhor definic¸ ˜ao, como tamb´em sec¸ ˜oes empilhadas exibindo melhor continuidade das reflex˜oes e menor ru´ıdo ground-roll, comparado com os resultados do processamento bruto (sem a filtragem SVD).
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Inversão de Impedância Acústica Usando Regularização Mista
More LessA inversão sísmica de impedância acústica é uma etapa fundamental para caracterização de reservatório, pois além de fornecer informação quantitativa permite que o dado seja interpretado em termos de propriedades intervalares. Para se atingir um bom resultado, esta inversão tem que caracterizar bem as camadas, ou seja, marcar e posicionar bem as interfaces que as separam e recuperar o valor correto de suas impedâncias. No entanto diferentes modelos de impedância podem atender igualmente bem aos dados. Para solucionar este problema, neste trabalho é proposta o uso simultâneo de dois critérios para regularizar a inversão sísmica de impedância acústica: a minimização da norma L2 do vetor de diferença entre o modelo invertido e o modelo de referência e a minimização da variação total do vetor de parâmetros.
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Aplicação do Método de Polarização Induzida em Área De Disposição de Resíduos Sólidos no Município de Caçapava do Sul - Rs
Authors Mônica Teixeira de Oliveira and César Augusto MoreiraThe geophysics is an effective method for investigation of contaminated areas for the most several types of pollutants, mainly in areas of disposition of residues solid, used in the characterization of contrasts of physical properties in the presence of pollutant substances. This work applies the Polarization Induced method in waste landfill, located in Caçapava do Sul city (RS). The landfill this seated on fractured metamorphic rocks, belonging to the Vacacaí Metamorphic Complex (Neoproterozoic). Were accomplished 8 lines of electric profiling, with spacing of 5m between electrodes and 10 investigation levels. Were also accomplished 83 measures of strike and dip fractures. The geophysical result allows characterize the layer of residues for low cargabilidade
values. Vertical anomalies below the layer of residues are interpreted as fracture zones with possible leachate accumulation, characterized by low cargabilidade values.
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Interferometric Microseism Localization for Multistage Fracture Monitoring
Authors Oleg V. Poliannikov and Alison MalcolmWe show how interferometric methods can be used to improve the location of microseismic events when those events come from several different fractures and are observed from a single well. This is the standard setup for a multi-stage hydraulic fracturing
experiment. Traditionally, in such experiments each event is located separately. Here, we adapt the interferometric approach to the problem of locating events relative to one another and show that this reduces the uncertainty in location estimates. To
completely recover the Green’s function between two events with interferometry requires a 2D array of receivers. When only a single observation well is available, we do not attempt to recover the full Green’s function, but instead perform a partial redatuming of
the data allowing us to reduce the uncertainty in two of the three components of the event location.
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2D Acoustic Full Waveform Tomography of Marine Streamer Data – Data Preparation and Choice of Inversion Strategies
Authors Anna Przebindowska and Andre Kurzmann and Thomas BohlenIn recent years, many synthetic studies have shown the great resolution potential of full waveform tomography. Nevertheless, application to field data is not a common standard yet. This study discusses some of the problems related to the inversion of conventional single sensor marine streamer data in the 2D acoustic approximation. To reconstruct realistic velocity models from the field data additional effort is required to overcome the problem of the local minima and to improve the convergence of the waveform inversion. This mainly concerns the field data preprocessing and the choice of adequate inversion strategies. For a marine field data set we experienced that the application of a 3D-2D correction, a data denoising algorithm, and amplitude corrections are essential preprocessing steps. Furthermore, we investigate synthetic case studies which mimic real acquisition geometries and source signals to evaluate the benefits of different preconditioning approaches and model assumptions.
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Métodos Geoelétricos no Estudo da Contaminação Subterrânea na Área do Cemitério Municipal de Rio Claro - Sp
Authors Walter Malagutti Filho and César Augusto MoreiraThis paper presents and discusses the applying results of electrical resistivity method, using the techniques of vertical electric sounding (VES) and 2D electrical profiling (EP), in the groundwater contamination surveying in the municipal cemetery in Rio Claro - SP, by the necrochorume. This effluent can cause soil and groundwater contamination due to the presence of elements such as nitrate, dissolved metals, viruses and bacteria, with inherent risks to human health. Such contaminant presence in the geological environment has often resulted in lower resistivity values when compared to a non-impacted area. The given characteristic allowed the application of the geophysical techniques proposed for the area, whose results allow the definition of three bands which could be seen in the resistivity profiling sections, leading to the identification of uncontaminated areas - high resistivity - areas with residual contamination - intermediate values - and probably contaminated areas - low resistivity. The groundwater flow direction definition through VES has demonstrated the concomitant migration (necrochorume) to E / NE. The geophysical result has shown correlation with the spatial and temporal cemetery occupation evolution throughout its history, once the low and high resistivity values have been respectively associated to the most ancient and most recent built regions in the cemetery area.
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Hierarchical Strategy for Full Waveform Inversion in the Frequency Domain
Authors R. Brossier, C. Castellanos, B. Dupuy, V. Etienne, Y. Gholami, G. Hu, S. Operto, D. Pageot, V. Prieux, A. Ribodetti and A. Roques and J. VirieuxFull waveform inversion (FWI) of seismic traces recorded at the free surface allows the reconstruction of the physical parameters structure on the underlying medium. Our two main objectives are the reconstruction of multiple classes of parameters on one side and the formulation of both the acoustic and elastic FWI for 3D geometries. A quasi-Newtonian method with a preconditioned L-BFGS algorithm provides scaled gradients of the misfit function for each class of parameter. For onshore applications where body waves and surface waves are jointly inverted, P- and S-wave velocities (VP and VS) must be reconstructed simultaneously using a hierarchical inversion algorithm with two nested levels of data preconditioning. The first one concerns the frequency sampling from low to high frequencies during the inversion procedure. The second one performs a data preconditioning by an exponential decay after the first arrival time. Simultaneous inversion of multiple frequencies rather than successive inversions of single frequencies significantly increases the S/N ratio of the models. For offshore applications where VS can have a minor footprint in the data, a hierarchical approach which first reconstructs VP in the acoustic approximation from the hydrophone component followed by the joint reconstruction of VP and VS from the geophone components can be the approach of choice. Among all the possible minimization criteria, we found that the L1 norm provides the most robust and easy-to-tune criterion as expected for this norm. In particular, successfull reconstruction of VP and VS on a realistic synthetic offshore case study is possible when white noise with outliers has been added to the data. The feasibility of 3D FWI is highly dependent on the efficiency of the seismic modelling. Frequency domain modelling based on direct solver allows one to tackle small-scale problems involving few millions of unknowns at low frequencies. If the seismic modelling engine embeds expensive sourcedependent tasks, source encoding can be used to mitigate the computational burden of multiple-source modelling. However, the source encoding is very sensitive to noise in the framework of efficient frequency-domain FWI where a limited number of frequencies is inverted sequentially. Time-domain modelling for the estimation of harmonic components of the solution is an alternative of choice even for 3D frequency-domain FWI because it allows one to extract an arbitrary number of frequencies at a minimum extra cost, a procedure useful when multiple frequencies are inverted together.
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Mapping the Depths Uncertainty by Comparison Between Multibeam Regular and Crosscheck Lines
Authors Adriano Vieira de Souza and Cláudia Pereira KruegerMaps and graphics are useful to approach the total vertical uncertainty and to evaluate the quality of the hydrographic survey. They are created supported by the Standards for Hydrographic Surveys, from International Hydrographic Organization (2008), and according to the analysis of comparison between multibeam regular and crosscheck lines. Complementary, one will be able to identify some biases that were not removed during the sensors’ calibration. The methodology is based on the results of the analysis of two distinct
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Effective Utilization of a Priori Information in Waveform Decomposition
Authors Georgy Mitrofanov and Viatcheslav PriimenkoWe propose an effective algorithm of using a priori information in the problems of decomposition of seismic signals. The algorithm is realized in two steps. In the first stage there is defined a solution using pseudo a priori information, ensuring stability and uniqueness of the decomposition problem solution. In the second step we define a minimum quantity of available a priori information, which allows obtaining the exact solution of the corresponding problem. The latter is one of the principle moments for the waveform inversion using the real seismic signals.
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O Conceito de Profundidade Efetiva Para a Propagação Acústica em Águas Rasas
More LessIn this work we deal with the problem of the sound propagation in shallow ocean waters. More precisely, we show that the classical ocean acoustic sound propagation models, namely, the Ideal and the Pekeris wave guide models have many similar features. This analysis can be developed if we take in to account the fundamental effect of the evanescent waves propagation into the seabed. The present analogy between the two models is based on the concept of the ocean effective depth related to excitation of the
resonant sound propagation modes in these media.
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How to Resolve Hti Effects from Marine Narrow-Azimuth Data?
More LessMedia exhibiting horizontal transverse isotropy (HTI) are usually associated with an oriented stress field or open fractures. Seismic reflection traveltimes beneath such media vary with the source-receiver azimuth. Firstly, we present a P-wave seismic processing method which simultaneously scans for three characteristic HTI parameters to optimize the moveout correction of narrow azimuth (NAZ) CMP gathers, where multi-azimuth (MAZ) techniques like sectoring are unsuitable. Secondly, we extend the method to detect the fracture direction and to run the automatic analysis on 3D super-gathers. Finally, we apply to a marine multi-source/streamer NAZ data demonstrates the effectiveness of this method.
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Inversion of Marine Controlled Source Electromagnetic Data Using a “Structure”-Based Approach
More LessWe present a fast “structure”-based inversion workflow for interpreting marine Controlled Source Electromagnetic (mCSEM) data, which reconstructs the resistivities and shapes of regions of interest using an inversion algorithm where the model is parameterized using both open and closed “structures”. These a priori information may come from independent measurements (e.g., seismic) or from the results of an image-based inversion workflow. We show that the “structure”-based inversion is capable of quantitatively reconstruct the resistivities and shapes of the regions of interest such as prospective reservoirs to obtain models that are consistent with both the mCSEM and the seismic data and that considerable improvement in resolution is achieved compared to the current state-of-the-art. We illustrate the advantages and drawbacks of the “structure” inversion using both synthetic and real data acquired in the Santos Basin, offshore Brazil.
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Efeito da Amostragem Sobre a Distribuição Espacial de Contaminantes no Solo
Authors Adriana Lemos Porto and José Agnelo SoaresThis work aims a sampling mesh optimization to detect a possible contamination by volatile organic compounds (VOCs) in an area of storage of petroleum products, of around 20 hectares, where 2.361 soil samples were collected, 0.5 m, 1.0 m and 1.5 m deep, at each sampling point. The technique used was the ordinary kriging. The soil samples were analyzed by PID technique (Photon Ionization Detection). The strategy adopted was the analysis of krigged maps obtained from sampling with increasing reduction in the number of samples. Random and sequential sampling were adopted. Krigged maps were constructed with 100%, 75%, 50% and 25% of all available data, at each depth level. Mesh optimization was judged from three parameters: 1) the variography of each krigged map; 2) the RMS difference (Root Mean Square) between each krigged map with data reduction and its corresponding krigged map with 100% of data and; 3) the impacted area, according to each krigged map, considering each contaminated point as that with VOCs concentrations greater than 20 ppm. The sampling reduction tends to increase the RMS difference while the impacted area almost do not alters, being this effect higher for the 1,5 m depth level. Considering that the averaged range, the RMS difference and the impacted area do not change substantially with the reduction in the number of samples, until the limit of 50%, it can be recommended, for economic reasons, the reduction in the number of samples up to this limit.
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A Gravimetric Study of Heterogeneities in Intermediate Crust Beneath the General Levalle Basin- Córdoba Province– Argentina
We present the results of a gravimetric study carried out in the region of the General Levalle sedimentary basin, Cordoba province, Argentina. We obtained the geometry of the basement roof for the region where the basin is located and the surface of the crust-mantle interface. The latter resulted in a surface of mild slope that deepens to the west. The fact that the interface crust-mantle is rather plane indicate that the sedimentary column has no antiroot that isostatically balances it. Also, the gravimetric effect of the sediments was evaluated and subtracted from the Bouguer anomalies. In the basin area, a positive gravimetric effect was identified, which may be linked to inhomogeneities located in the intermediate crust.
On the basis of the gravimetric results, their comparison with stratigraphic analysis and of basin studies of the region, we propose possible alternatives that consider the presence of thick masses in the intermediate crust: 1)Emplacement of alkaline magmas during the Cretaceous extension, 2) An anomaly in the geometry of the crust, whether by the effect of a thinned crust associated to Cretaceous rifting or to Cenozoic extension or 3) Due to the flexion of the upper crustal layer during the Andean compression.
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Condição Meteorológica Troposférica Durante a Ocorrência do Evento de Efeito Secundário do Buraco de Ozônio Antártico Sobre o Sul do Brasil do dia 28/09/2008
Durante o período de primavera do Hemisfério Sul, massas de ar pobre em ozônio se desprendem do buraco de ozônio antártico e atingem as latitudes médias em um fenômeno conhecido como “Efeito Secundário do Buraco de Ozônio Antártico” que ocorre no período da primavera do Hemisfério Sul. Para comprovar a ocorrência do fenômeno, foram utilizadas medidas da coluna total de ozônio, obtidas pelo Espectrofotômetro Brewer instalado no Observatório Espacial do Sul (29,42°S; 53,87°O) em São Martinho da Serra, RS, bem como medidas da coluna total de ozônio e imagens coletadas pelo satélite OMI da NASA e foram realizadas análises de mapas de vorticidade potencial sobre superfícies isentrópicas geradas através do software GrADS (Grid Analysis and
Display System) com dados do NCEP e trajetórias retroativas de massas de ar usando o modelo HYSPLIT da NOAA. No dia 28 de setembro de 2008, foi comprovada a ocorrência de “Efeito Secundário do Buraco de Ozônio Antártico” sobre o Sul do Brasil e foi feita uma análise das condições meteorológicas atuantes na troposfera utilizando mapas de altura geopotencial e vorticidade em 500 hPa, vento em 250 hPa e pressão ao nível do mar e espessura entre 500 e 1000 hPa, gerados através do software GrADS, além de imagens de satélite do GOESS 10 do vapor d’água. Observou-se que este evento de queda na coluna total de ozônio ocorreu durante a passagem de uma massa estável e sem nebulosidade sobre o Sul do Brasil do dia 27 para 28 de setembro de 2008, respectivamente o dia anterior e o dia em que o valor da coluna total de ozônio obteve o valor baixo, e no dia 29 de setembro de 2008, dia em que a coluna total de ozônio começou a se restabelecer, condições meteorológicas favoráveis ocasionaram a
formação de uma intensa área de nebulosidade sobre o Sul do Brasil.
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Caracterização Geoelétrica em Ocorrênica de Sulfetos de Cobre, Porção Norte da Bacia do Camaquãa, Caçapava do Sul (Rs)
Authors Syngra Lopes and César Augusto MoreiraThe set of procedures and steps taken for the incorporation of reserves is called mineral exploration. The mineral exploration can be done in two basic forms: through direct and indirect techniques. The direct techniques are represented by geological mapping, trenches, wells, borehole and chemical analysis of soil and rocks samples. The indirect techniques consist basically of the use of remote sensing and geophysical methods. The study area consists in copper mineral occurrence previously studied by boreholes and trenches, located in the rural municipality of Caçapava do Sul city (RS). This paper proposes the utilization of the electrical resistivity and induced polarization geophysical methods, through by electrical profiling technique. This study is the intersection of geological and geophysical data in an attempt to assess accuracy of geophysics in the recognition of mineralized levels. The geophysical data appear for anomalies high chargeability for the lapillitics tuffs domain, close to the crossing of two fault systems that suggests a deposit mineral structurally controlled. The radial disposition of the lines in surface made possible the generation of 3D models, that they allow the integrated analysis of the physical parameter, besides the space understanding of the ore body.
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Diurnal Patterns of Volatile Organic Compounds in the Atmosphere of Sao Jose Dos Campos
The study of the concentration of volatile organic compounds in the atmosphere is of fundamental importance because it contributes to environmental pollution like photochemical smog as well as its toxic effects on health. The city of Sao Jose dos Campos, Sao Paulo, Brazil, in recent years has shown strong growth and increasing in the industrial economy, leading to an intense development of the urban area. In addition, the city is geographically located near the capital Sao Paulo, Brazil, and is surrounded by roads that have heavy flow of vehicles, which characterizes this region as potential for the emission of VOCs. This paper aims to characterize the daily cicle of emission of light VOCs (C1-C6) in Sao Jose dos Campos, being collected and analyzed air samples from Univap region 7.5 km from the city center, away from roads and main avenues, located in the neighborhood Urbanova. The most abundant organic species found were: n-butane, n-pentane, 1-butene, trans-2-butene, cis-2-butene, 1-pentene and isoprene.
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Resistividade Elétrica em Área Contígua a Aterro Sanitário
In two places, called P2 and P3, located in an urban area near to the landfill from the city of Manaus (AM), geophysical survey was carried out using the geoelectrical method, having as its principal aim the finding of influence in the subsurface, the landfill leachate arises from this, and consequently contribute to better knowledge about the delimitation of the extent and geometry of the plume of contamination correspondent.
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Aquisição Contínua de Dados de Resistividade Elétrica em Ambiente de Água Doce
Authors Andresa Oliva and Chang Hung KiangNesse trabalho é descrita a técnica de aquisição contínua de dados de resistividade em ambiente aquático. Essa técnica, conhecida como CRP (Continuous Resistivity Profiling), amostra continuamente os valores de resistividade por meio de um cabo multieletrodo, utilizando arranjo dipolo-dipolo com 8 níveis de investigação, o que possibilita a aquisição de uma linha com mais de 30 km por dia. Esse sistema foi instalado a bordo de uma embarcação de porte médio e a aquisição foi realizada em um curto espaço de tempo. O posicionamento das aquisições foi obtido por meio de um GPS marítimo acoplado a um sonar. Os dados de posicionamento e da batimetria foram gravados automaticamente no resistivímetro. Em um pré- processamento, os dados de resistividade foram integrados às posições obtidas com o GPS. O passo final para a obtenção de imagens de alta resolução foi a inversão dos dados utilizando o 2D smooth model. A profundidade de investigação máxima obtida com o espaçamento de 10 m entre os dipolos foi de 24 m. Os ensaios foram executados na represa Salto Grande, localizada no município de Americana-SP.
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Petrophysical Characterization of Carbonates
Authors Dayse Daltro de Castro and Paula Ferrucio da RochaBrazilian carbonate fields have been developed based on seismic data interpretation, and static and dynamic reservoir models. An appropriate inversion seismic data depends on the knowledge of the relationship between depositional geometries, facies, rock fabric and the seismic and petrophysical properties. Based on the premise that the seismic properties are functions of saturation and differential pressure (confining pressure minus pore pressure), we conducted analysis of laboratory velocity measurements (compressional-Vp and shear-wave-Vs) dry and brine-saturated of approximately 35 rock samples of carbonates, and correlated them to porosity for a better understanding of seismic signatures.
The rock samples, covering a wide range of depositional environments, were analyzed qualitatively and quantitatively. A crucial step was the establishment of a relationship between measured compressional (VP) and shear-wave (VS) velocities dry and brine-saturated with bulk porosities. Saturation of the pore space caused an increase and decrease in compressional and shear-wave velocities as well as changes in the bulk and shear modulus. The Vp/Vs ratio also shows changes in brine-saturated samples. An increase in the Vp/Vs ratio was verified in most of samples but in a few no changes was observed.
This data analysis was applied to establish, in the future work, the rock – seismic signature relationship to develop an up scaling tool to improve seismic inversion data in order to reduce uncertainty in the seismic interpretation in Brazilian carbonates fields.
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Utilização da Tomografia Elétrica Para Detecção de Dutos Enterrados em Zonas Submarinas
A geo-electric survey can be conducted for monitoring the position of pipeline in the sea floor. In this method an electric current is driven through the ground and the resulting potential differences are measured at the surface. Anomalous conditions or inhomogeneities within the sub-surface, such as electric better or poorer conducting materials, are inferred from the fact that they deflect the current and distort the normal potentials. Pipelines, despite their steel content, give resistive anomalies. This is caused by the concrete coating of the pipeline and the presence of gas and / or oil within the pipeline.
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Comparative Winds’ Statistical Distributions Study for the Central Southern Region of Brazil
The industrial and social development of a country requires large amounts of energy, particularly electricity. To follow the development with an efficient power grid, the human society has sought alternative energy sources that are economically and ecologically viable. The wind energy is one of such alternatives. However, the deployment of wind farms requires a previous study of the winds’ statistical profile in the region of interest. With this in mind, this work performs an analysis of three different statistical distributions to see which best fits the wind profile in the Central Region of the South of Brazil. The Weibull, Log Normal and Rayleigh statistical distribution were studied and compared with the values of wind speed collected at 50 meters from the SONDA site operating in São Martinho da Serra, RS in the Southern Space Observatory - OES/CRS/CCR/INPE–MCT. The analysis was performed between 2005 and 2009 showed that among the three distributions, the Weibull presents the best correlation and the smaller errors, MBE and RMSE.
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Modelagem Numérica Tridimensional da Resposta do Perfil de Indução na Presença de Diferentes Geometrias da Zona de Invasão
Authors Alfredo Carrasco and Abel CarrasquillaA perfilagem de indução eletromagnética é uma das técnicas geofísicas de poço mais utilizadas na avaliação da resistividade da zona virgem de reservatórios que contem hidrocarbonetos, devido à sua boa profundidade de investigação. Entretanto, a resistividade dessa zona virgem medida por esse perfil pode resultar mascarada pelo filtrado da lama que invade a formação, o que ocorre durante a perfuração dos poços. Assim, o objetivo do presente trabalho é simular a resposta do perfil de indução na presença de diferentes geometrias tridimensionais das zonas invadidas, utilizando para tal um algoritmo que usa o método das equações integrais. A ferramenta de indução usada na simulação foi a clássica 6FF40 da SCHLUMBERGER, cujos resultados mostram que a existência de uma zona de invasão sempre altera as respostas do perfil, tanto para os modelos de rampa, como do slope, e, de maneira mais significativa, no caso da presença do annulus.
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Data Management System for Multidirectional Muon Detector
This article describes the development and implementation of a data management system that is used for information storage and retrieval, generated by a Multidirectional Muon Detector. This instrument is in operation at the Southern Space Observatory (SSO), National Institute for Space Research (INPE), located in São Martinho da Serra, Brazil. The result of this work has enabled past and present data to be accessed in a dynamic and interactive way, through an easy-of-use Web-based data query system.
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Interpretação Magnética-Estrutural de Modelos Sintéticos e na Região do Rio Tapajós, Estado do Pará - Brasil
More LessThe aim of this work is to evaluate a reduction-to-the-pole filter for magnetic data at low latitudes and its implications for structural interpretation. For this purpose we have analyzed the anomalies generated by several methods of data enhancement with and without reduction-to-the-pole. These methods have been applied to synthetic prisms located at low magnetic latitudes and the resulting anomalies have been compared with those calculated at the magnetic pole. The synthetic models have been generated from a program that calculates the anomalies from prisms with arbitrary dimensions, susceptibilities and depths. The method has also been applied to the magnetic data of the Amazon Basin and the Amazon Craton, (Northern Brazil). For synthetic data, the reduction-to-the-pole algorithm used in this work improved the performance of the enhancement methods, since after its application the maximal amplitude of the transformed the anomalies were positioned over the edges of the sources, facilitating the magnetic-structural interpretation. For real data, the good correlation between magnetic lineaments - particularly those inferred by the method of tilt derivative of the total horizontal gradient, recently proposed - and the interpreted geological structures indicate that the reduction-to-the-pole may be applicable even when the data located in low magnetic latitudes.
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Comparação da Radiação Ultravioleta Quando da Ocorrência dos Eventos de Efeitos Secundários do Buraco de Ozônio Antártico Sobre o Sul do Brasil Dos Dias 16/10/2003 E 28/09/2008
A análise da radiação ultravioleta nos dias em que ocorreram eventos dos efeitos secundários do Buraco de Ozônio Antártico sobre o Sul do Brasil é o objetivo do trabalho. O estudo de caso foi realizado para os dias 16 de outubro de 2003 e 28 de setembro de 2008. Verificaram-se os dias em que houve a ocorrência de eventos dos efeitos secundários do buraco de ozônio Antártico na região central do Rio Grande do Sul, escolhendo-se dois dias nos quais inexistia a incidência de nuvens. Realizou-se a análise da integral diária da radiação ultravioleta para os dias selecionados a fim de se comprovar o aumento da radiação ultravioleta com a chegada de massas de ar pobre em ozônio vindas da Antártica. Para avaliar os efeitos secundários do Buraco de Ozônio Antártico foram usados dados coletados do Espectrofotômetro Brewer, instalado no Observatório Espacial do Sul – OES/CRS/CCR/INPE – MCT, em São Martinho da Serra/RS (29,42ºS, 53,87ºO). Realizou-se análise de Vorticidade Potencial (VP), usando GrADS (Grid Analysis and Display System) com dados reprocessados do NCEP (National Centers for Environmental Prediction), e trajetórias retroativas de massas de ar, usando o modelo HYSPLIT da NOAA. Sendo que para a análise da radiação ultravioleta foram utilizados os dados do Espectrofotômetro Brewer. Da correlação da radiação ultravioleta com os eventos dos efeitos secundários do Buraco de Ozônio Antártico percebe-se que a incidência de radiação ultravioleta é inversamente proporcional a coluna total de ozônio.
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The Growth of Airborne Gravity Gradiometry – And Challenges for the Future
Authors Daniel DiFrancesco and Lockheed MartinIn recent years there has been a continuing and growing interest in airborne gravity and gravity gradiometer capabilities. This attention implies both that significant achievements have been realized and that we have not yet arrived at the optimal capability – and that the process continues to find even better solutions. Advances in sensor systems, operational efficiency, data processing, and interpretation have all contributed to improved offerings to the market. Acceptance and interest by industry is evidenced by the numerous focused workshops, publications, and investment over the past decade. The prospect for greater usage is tempered a bit by the lack of definitive success stories and relatively high cost. The future for airborne gravity is also clouded by a number of questions: How much does airborne gravity help achieve the ultimate objective of finding more resources? What is the value of information (VOI) to the commercial market? What is lacking in order for airborne gravity to achieve full potential? With a view towards the future, it is also instructive to ask, “Where will airborne gravity be in five or ten years?”
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Joint Inversion of Multimode Rayleigh Waves for Geotechnical Characterization of Soils at a Test Site in Ubatuba/Sp Using the Masw Method.
Authors Sérgio Bezerra Lima Júnior and Renato Luiz PradoThis paper discusses the use of MASW method (multichannel analysis of surface waves) using the join inversion of fundamental mode with the first mode of dispersion data of surface waves, based on results from a survey in area of erosion and landslide in Ubatuba city, state of São Paulo. Here we also discuss aspects related to the acquisition, processing and data inversion. The approach of using fundamental and first mode brought greater stability in the inversion process, compared with the results using only the fundamental mode. Moreover, the method was less sensitive to the superficial layers (up to 10 meters) compared to GPR and refraction methods. The multimode inversion of Rayleigh waves was able to map deeper interfaces where the layers have distinct elastic properties (i.e. different shear waves velocities).
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Can we Correct for Azimuth Dependant Variations of Residual Move-Out in Land Waz Context, Using Depth Non-Linear Slope Tomography? An Imaging Case History
High-density wide azimuth (WAZ) land surface acquisitions have demonstrated superior imaging capabilities. Apart from the traditional poor signal-to-noise ratio of land data we face a new challenge: the necessity of reconciling the kinematics of the various azimuths. In this paper, we present an imaging case history involving WAZ non-linear slope tomography. Using surface information (kinematic invariants), velocity model updates are performed both in depth and time. We chose to start from an initial pre-stack time migrated (PreSTM) dataset. After applying a structurally consistent filtering to improve the S/N ratio on stacked data, we used a dense automated tool for dip picking. In parallel residual move-out (RMO) was computed on all azimuths simultaneously. Our case study demonstrates that WAZ non-linear slope tomography in the depth domain greatly improves the imaging of the structures when compared to the initial PreSTM result. We observe that even if tomography in the time domain significantly enhances imaging, it cannot successfully honor the kinematics of the various azimuths within the constraints of time imaging assumptions. On the contrary, WAZ non-linear slope tomography in the depth domain offers an efficient way to reconcile these kinematics, thus promoting the use of depth imaging when processing high-density WAZ data, even in the context of mild geological complexity.
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Basement Geometry, From Magnetic and Gravity Data in Gastre Trough, Chubut, Argentina
More LessA gravimetric and magnetometric study at Gastre Trough, province of Chubut, allowed to reveal its basement geometry. Maps of anomalies show a fractured basement with high and sunk blocks inside the Trough. The minimum anomalous are associated to graben-like depocenters possibly inverted during the Tertiary, while the maximum are linked to basement blocks. Some of these blocks outcropping at the edges of the trough and some others covered by sediments inside. A 3D analytical signal and a gravity horizontal gradient were applied in order to make an appropriate interpretation, associating the maximum magnetic susceptibility changes and density to contacts between different lithologies. Finally, outcropping density values as well as seismic density values allowed to make 2D density models across to the Trough, which showed the presence of a high basement as central Gastre Trough.
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Anomalias de Fator Metal Associada à Ocorrência de Cobre Sulfetado Estruturalmente Controlado
More LessThis paper presents the results of the Electrical Resistivity and Induced Polarization geophysical methods applied in mineral occurrence area of copper sulphites. They were measured the parameters electric resistivity and chargeability, through the technique of electric profiling, with willing lines in surface of the azimutal form. The area is located in the rural zone of the Caçapava do Sul city (RS), inserted in the Camaquã sedimentary basin, formed by sedimentary and vulcanogenics stratigraphycs units, locally characterized by medium to coarse arkosic sandstone, intensely cimented and recrystallizeds, with azurite and malachite presents in fractures. Structural measures were accomplished in fractures that resulted in the definition of two assemblages (N18o and N112o). The line N6° crosses the N112° fractures assemblage and it presents anomaly of high intensity in depth, in contrast with N96° line that crosses the N18° assemblage and it describes the presence of anomaly of very high intensity in depth. The field acquisition in azimutal format made possible the elaboration of 3D model and that elucidates clearly form, anomalous areas associated the carbonates presence in surface and sulfhides in depth. The crossing between the geophysical result and structural measures allowed determine the mineralization directions principals.
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Análise, Modelagem E Interpretação de Dados Gravimétricos no Lineamento Guapiara – Região Sudeste do Estado de São Paulo
The geophysics, particularly the gravimetry, has been used to support the understanding of subsurface structures, contributing to the elucidation of arrangement, relations and partitioning between crustal masses. In the present work, the use of gravimetry helped in the characterization of the structural framework in the region of Guapiara Lineament, where there is a swarm of mesozoic basic dykes subparallel to the directions N40-50W. The dykes cross the precambrian lands and the basement of the Ribeira Belt, and penetrate in the Parana Basin to the height of the Parana River. The confection of maps of the Bouguer Anomaly revealed a accentuated high gravimetric guided by NW-SE which corresponds to the trend of highest concentration of dykes, correlated to the Guapiara Lineament. crustal models were made based on Bouguer anomaly values that characterize the high gravimetric gradient highlighted in the beam area of dykes, to recognize the influence of the mantle. It was found that occurs in the region a significant thinning of the crust, due to the rise in the mantle, reflecting the epirogenética activity which represents the spread of efforts occurred at the edge of plate tectonics related to the divergent within the plate in the Cretaceous.
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Installation of a Broadband Seismological Station in the Faixa Paraguai
Authors J.A.C. Vieira, R.C. Dantas and G.S. FrançaThis project is a just the beginning of the study of the seismicity and tectonics at the Faixa Paraguai, located at Mato Grosso and Mato Grosso do Sul (states from the middle-west of Brazil). The region is well known for the geological faults and folds and has a peculiar structure compared to the Craton Amazonico. To better study the structure, there is the demand to install a seismological station and then to speculate on receptor function, seismic tomography and other things. The data analysis will be responsability of the Seismological Observatory of The Brasiília University (SIS/UnB) such as this whole project. The first travel will be done by the first week of June of 2011 and the installation will be concluded by 2 days. Until the date of the congress, we expect that the station works fine and show some results about the seismicity in the area.
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Parametrização de Campo Bidimensional de Velocidades Sísmicas Usando Ondaletas
Authors Helcio Moreira Perin and Wilson Mouzer FigueiróThe aim of this work is the representation (parameterization) of compressional seismic velocity field model of two dimensional geological structure by means of orthogonal functions known as wavelets more specifically, those so-called Haar wavelet. Some
comparative numerical experiments are performed among wavelet series with and without the use of scale function. The velocity field approximation, obtained by such technique, depends on the indices values used in the series, these have influence on the quality of the model representation. It is observed that the proposed parameterization offers a good accuracy for representation of the used field, however it is just advantageous the use of the scale function in the wavelet series with lower indices values.
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Pillargrid Conversion for Seismic Modeling
Authors Charles Cote and Michael Prange and Hugues DjikpessePillargrid and unstructured mesh models describe geometry and properties in different ways that are optimized for distinct types of simulation. For instance, finite-element simulators typically require unstructured, watertight and piecewise-polynomial descriptions of geometry and properties, while industry-standard fluid-flow simulators often use a pillargrid description of "connected bricks" in which the hexahedral cells may have voids between them when converted into a piecewise-linear description of the surface geometries, and the properties within each cell are constant. A conversion method is described to extract the geometry and properties from a pillargrid to build a watertight, piecewise linear model. The algorithm comprises partitioning the pillargrid into subvolumes within which properties are smoothly varying, building triangulated bounding surfaces for each of the subvolumes, and generating a mesh of property nodes for each of the subvolumes. Such conversion is useful for instance to simulate geophysical and geomechanical wave fields inside high-resolution reservoir models that are consistent with fluid-flow simulation models. The proposed algorithm has been validated on both synthetic and field examples.
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Eagle Ford Shale Prospecting with 3D Seismic and Microseismic Data
Authors Galen Treadgold and Bill McLain and Steven SinclairThe Eagle Ford Shale in South Texas (Figure 1) is one of the more exciting shale plays in the United States at the current time. Recently published reports of well tests describe gas well rates exceeding 17 mmcf/d and oil well rates commonly in excess of 1500 bopd with numerous 2000+ bopd tests. Acreage lease rates continue to climb as more positive results come from drilling within the trend. A key issue for the exploration companies is finding where to focus acreage acquisition and optimize drilling plans for optimal gas and oil recovery. Our paper will first consider the geologic context of the Eagle Ford and then look at the geologic drivers for locating a productive well. With improved understanding of local rock properties, focus shifts to geophysical techniques, in particular, comparing and contrasting the value of seismic and microseismic data in building a successful exploration plan.
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Regional and Local Anomaly Separation in the Almada Basin (Bahia State), Using Gravity Data from the Grace Satellite
Authors A.C. Gordon and C.F. Valeria and U. WebsterWe have detected in the Almada Basin, northeast Brasil, a high correlation between the regional gravity effects produced by the crust-mantle interface obtained from 2D forward modeling and the gravity data from the GRACE satellite. The altitude of the satellite mission of about 500 km works naturally as an upward continuation filter, allowing the use of this kind of data as an independent estimator of the regional component of the gravity field in the Almada Basin.
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Wave Form Inversion Migration (WFIM) Method
We represent a 3D time variant of the Wave Form Inversion Migration (WFIM) method. The method is based on the exact solution of an inverse problem for the wave equation considered in the Born approximation. The formulae obtained are tested on the synthetic and real field data.
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4D Monitoring: Example of 4D Interpretation in Lower Flanks Systems, Dália - Angola
More LessSome field of Lower Congo Basin deep offshore are composed of heterogeneous turbidites channels of Miocene age located in Angola at water depth that range between 700 – 1500 meters. The Dalia field, located in Block 17, is characterized by four main sedimentary complexes, called Upper Main Channel, Lower Main Channel, Lower Flanks and Camelia. This area is characterized by high resolution seismic data (10 m) that is used for fine reservoir characterization and monitoring.
After one year and half of production, a first 4D seismic survey was acquired. This 4D seismic monitor bring more accurately interpretation on facies distribution and a better understanding of reservoir communications. The 4D effects seen on Dalia are large since time shifts associated to production were used to interpret 4D signals and upscale them inside the reservoir model.
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Aplicação de Gpr Para Avaliação de Via Permanente em Estrada Férrea no Brasil
Authors Debora S. Carvalho and Roberto OkabeThis paper presents the application of GPR on a Brazilian railway mapping, for evaluation and management of the railroad. GPR antennas were installed in a vehicle used in daily inspections of the track. The qualitative parameters mapped were moisture, contamination and thickness of ballast and intermediate layers and the results were validated with the excavation of a trench at a selected spot on the road, categorized as a priority number one for maintenance. The use of GPR is presented as a tool for decision making in the management process of railway maintenance, through the fast and continuous detection and identification of formations of endemic degradation’s processes on the track railway, even incipient and not visible from the surface, with no traffic interruption, and ranking and prioritization in a rational manner and using a systematic way for the problems according to the seriousness of its occurrences.
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Preliminary Study of Atmospheric Methane Emissions in a Lentic Systems
More LessThe decaying organic matter releases, among other gases, methane (CH4), composed of semi-opaque to infrared radiation has an important role in the greenhouse. The knowledge of how the lentic systems emit gases from the anaerobic decomposition of non
lignified material, primarily composed of herbaceous plants and areas of peeling macrophytes has been highlighted in several studies. This paper presents the results of a preliminary test to work on the emission of greenhouse gases in reservoirs on the methane produced in one of the ponds for water supply INPE - National Institute for Space Research, Cachoeira Paulista / SP. To determine the flow of methane was carried out a campaign in December 2010 and the gas flow determined using the static chamber technique. The environmental parameters measured were the temperature of air and water, pH, redox potential, conductivity, dissolved oxygen and total dissolved solids. The overall average of valid flows was 59.1 ± 91.98 mgCH4/m2/dia and analysis of
the environmental parameters indicates that the methane concentration was high in environments with a pH lower than 4 and lower levels of dissolved oxygen in water.
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Ocean Bottom Node Processing in Deep Offshore Environment for Reservoir Monitoring
More LessTo complement a 3D High Resolution streamer survey, Total E&P operated in 2008-2009 a large 3D Ocean Bottom Node (OBN) acquisition to monitor a hydrocarbon reservoir in deep offshore Angola (Ceragioli et al, 2010). Mirror node imaging has already proved to be more appropriate for 4D imaging and reconciliation with streamer data. However positioning and timing issues as well as azimuthal coherent stacking of data need to be precisely tackled for better preserving their high frequency content. In this paper we show the importance of estimating accurate time statics for nodes deployed in a deep offshore environment. Secondly we demonstrate that the concept of Offset Vector Binning using hexagonal tiles is applicable to this node data acquisition. Mirrored data migration in Common Offset Vector domain provides Common Image Gathers with preserved offset and azimuthal information, which enables azimuthal residual velocity analysis for a better stacking of information at all offsets and azimuths.
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Monitoramento Temporal De Contaminação Por Chorume Usando Métodos Geoelétricos
Authors José Ricardo Melges Bortolin and Walter Malagutti FilhoThis work describes a temporal monitoring of the contamination plume from the controlled landfill of Rio Claro (SP), through the resistivity method, comparing 2D Electrical Profiling dipole - dipole results, carried out in 1999 and 2008. The leachates produced on the landfill diminish the electrical resistivity of the natural ambient, characterizing the contamination. Thus, zones of low resistivity, with values smaller or same a 50 ohm.m, had been associates to the contamination for landfill wastewater. The joint interpretation of the sections of apparent resistivity allowed to identify alterations of the dimensions of the contamination plume in elapsing of the years. Governed by the main and secondary flows, the contamination plume advanced in direction to the limits west and soul of controlled landfill. Complementarily, Vertical Electrical Soundings had allowed verifying the depth and the direction of the underground water flow, and to characterize geo-electrically the lithology on which is seated the controlled landfill: predominantly sandy and silty sediments.
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Multibeam Echosounders Capability to Detect Fluid-Mud Layers in the Water Column
More LessDuring extreme rain events occurred in Itajaí, SC, Brazil in November 2008, the high water flow in the Itajaí-Açú River caused intense sediment transportation, which destroyed harbor facilities. Several objects, as ship containers, were carried through the channel, forcing maritime authorities to close the harbor in order to guarantee the navigation security. An expeditionary bathymetric survey has been requested, with the main purpose to quickly map hazards and depth variations within the main navigation channel. The Brazilian Navy Directorate of Hydrography and Navigation (DHN) provided a small team, which has been moved from Laguna-SC to Itajaí-SC, to perform a bathymetric survey using an EM3000 multibeam echosounder. Also, a small boat, termed LB Betelgeuse, had to be moved from Florianópolis-SC to Itajaí-SC. In 2 days, a total of 19 Km distance of channel has been surveyed, from its entrance at seashore until inside the Itajaí-Açú River. A full-coverage seafloor map was built enabling the harbor authorities to safely proceed with further operations in the area. During this survey, some intriguing echo-character features were detected close to the channel entrance, which has been investigated by divers, proving to be correlated with the presence of fluid-mud sediments. This echosounder has no water column imagery available, so original depth telegram was used. Water column low-density features were unexpected to be detected by the survey team, as they should be filtered out by the bottom tracking algorithms used to calculate the depths. But, this echosounder model demonstrated to be very useful to reliably detect the fluid-mud layers in the water column. This work presents the fluid-mud echo-character features detected by a multibeam echosounder, so it can be better recognized in the future surveys.
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Fibre Optic Permanent Reservoir Monitoring Breakthrough
Authors Hilde Nakstad and Jan Langhammer and Morten EriksrudThe largest ever offshore fibre optic permanent reservoir monitoring installation was successfully finished in October 2010 at a producing oil field in the North Sea. All the channels are working and recording seismic traces (i.e. channel status is 100%), which is a great achievement for such large seismic spread in the marine environment. The decision to install an optical sensing system was mainly due to the design life expectancy of the fibre optic system. The installation of the seismic system is expected to contribute to enhancing the remaining production, which will extend the life of the field and ensure optimal location of future production wells.
We advocate optical sensing technology as an important part of the toolbox for maximizing field production in a cost efficient way. The “optical oil field” may represent the next significant step in technology for reservoir monitoring and improved hydrocarbon recovery.
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4D Gravity Modeling: Integrating Seismic Data With Highly Constrained Gravity Inversions for Effective Reservoir Monitoring
Authors Richard A. Krahenbuhl and Yaoguo LiWe demonstrate a robust workflow for time-lapse gravity modeling in reservoir sequestration/production monitoring applications. This systematic approach outlines a reliable methodology to understanding the value and limitations of 4D gravity at a particular site, for both pre-acquisition decision making, and as a guide for post-data acquisition interpretation. To demonstrate, we present a multifaceted feasibility study for monitoring CO2 injection into a reservoir at various injection times using 4D micro-gravity method. The simulations are performed for a currently active CO2-EOR site, the Louisiana Delhi Field in the United State. We construct an accurate representation of the field directly from current seismic data, followed by application of binary inversion technology adapted to the time-lapse gravity problem and tailored to the specific site. Finally, we illustrate a method of resolution analysis to demonstrate the decreased recoverability of fluid movement at the site in the presence of varying data noise.
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Observações de Ondas de Gravidade de Méedia Escala na Região Equatorial do Brasil
Authors I. Paulino, H. Takahashi, A. F. Medeiros, R. A. Buriti, C. M. Wrasse and D. GobbiUsing images of the OHNIR airglow emission over S˜ao Jo˜ao do Cariri (7:4oS; 36:5oW) during the second Spread-F Experiment (SpreadFEx), from September to November 2009, 26 medium-scale gravity waves (MSGW) were observed, and their observed parameters were estimated. Simultaneous measurements of the mesospheric winds and temperature [obtained by a meteor radar and an OH(6,2) photometer, respectively] were used to calculate the intrinsic parameters of these waves. The characteristics of these waves, in general, are similar to it was observed during the first campaign. Most waves presented wavelengths between 50 and 150 km, periods from 20 to 100 min, and phase between 20 m/s and 80 m/s, propagating eastward. The intrinsic parameters revel that the wind may reduce the phase speeds. Most waves had vertical wavelength smaller than 20 km. Furthermore, two MSGWs presented an unusual intrinsic phase speed, i.e, they were faster than 85 m/s. These two waves have a potential to reach altitudes higher than 150 km, and, consequently, they may be more powerful in seeding equatorial spread F.
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A General Framework for 3D Interpretation of Magnetic Data Affected by Remanence and Self-Demagnetization
Authors Yaoguo Li and Richard A. Krahenbuhl3D inversion of magnetic data has been successfully used in many aspects of geophysical exploration over the last decade. In a majority of cases, one can assume that the direction of magnetization is the same as the current inducing field direction, and generalized magnetic inversions requiring this information typically perform well in recovering susceptibility distributions. However, the sometimes unknown direction of total magnetization, caused either by the presence of high magnetic susceptibility or remanent magnetization, has limited the use of this technique. We present a general framework for solving these problems by examining the three classes of magnetization and formulate a suite of methods of practical utility in any magnetic environment. The first class performs inversion for the case of induced magnetization with weak magnetic susceptibility, where the magnetization direction is the same as the Earth’s inducing field. The second class focuses on the estimation of total magnetization direction when the field is not purely induced, and then incorporates the resultant direction into an inversion algorithm that assumes a known direction. The final class focuses on the direct inversion of the amplitude of magnetic anomaly vector, a quantity that depends weakly upon magnetization direction. With these new developments, we show that it is now feasible to invert any magnetic exploration data set, regardless of whether it is purely induced, or affected by strong remanence or self-demagnetization.
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Prospecção de Água Subterrânea no Município de Piçarra–Pa Usando Vlf e Resistividade
Authors Gilvana Bezerra de Sousa and José Gouvêa LuizThis research was carried through in the city of Piçarra, Located in the southwest of the state of Pará. The study was done to map lineaments associated to fractures in basement rocks and to investigate the nature of the subsoil through geophysics, using the electromagnetic VLF and resistivity methods . The integrated analysis of the geophysical data allowed to recognize in the area two hydrogeologic dominions: Fractures zones in basement and sediments. The results guided the location of wells for ground-water exploitation.
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Reducing Exploration Cycle Time in the Campos Basin: Integrating Seismic Data Acquisition and Processing
Authors Kerly Sanchez and Alex Cooke and Franck LeDiagonThis paper presents the integrated approach to seismic data acquisition and processing currently being used in the Campos basin. An advanced onboard data processing workflow is described that was designed to provide high-quality data directly from the seismic vessel, enabling earlier reservoir and exploration decisions.
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Large-Scale TTI Imaging in Areas of Limited to No Well Control
Authors Olga Zdraveva, Michael Cogan, Saeeda Hydal and Rafik DerbalaDepth imaging with anisotropic models has been shown to deliver more geologically plausible and accurate images. Derivation of accurate parameters describing anisotropic properties of the medium requires incorporating well information. However, there are vast exploration areas around the world with very limited to no well control that do require high-quality anisotropic imaging to allow adequate interpretation of deeper targets. We use a simple workflow that allows building of tilted transversely isotropic (TTI) models in areas of very limited well control. We present a case study from the Kwanza basin offshore Angola where we built a detailed TTI model over an area of more than 8000 km2. We incorporate general knowledge of the area and analysis of data anellepticity in the process, derive Thomsen’s δ in wells from a neighboring area, and use spatially variable ε and δ fields, honoring the variation of the anellipticity and the geometry of the provided horizon interpretation. The results are compared against images produced with both an isotropic model and a much simpler regional TTI model. The results illustrate that accounting for TTI in complex media is a prerequisite for producing geologically plausible and interpretable images, and that adding interpretation driven complexity in the TTI models could further improve the interpretability of pre-salt targets.
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High Resolution Imaging for Subtle Geological Features in the Llanos Basin
Authors Michael Smith and Paul Cunningham and David BehrmanWe demonstrate in a seismic processing project from the Llanos basin in Colombia that increasing bandwidth prior to migration can improve the spatial (lateral and vertical) resolution and the subsequent velocity analysis can produce a more detailed velocity profile which in turn improves image quality. The increase in bandwidth prior to migration reduces both vertical and lateral wavelet widths and, thus, increases spatial resolution. The improved spatial resolution in turn permits a more detailed velocity field to be defined both laterally and vertically. This approach, bandwidth expansion prior to migration, can be applied to both time and depth migration flows.
We apply the high resolution imaging technique to the relatively thin Oligocene to Early Miocene Carbonera sandstones from the Llanos basin. Traps are typically three-way structural closures bounded by faults with relatively small throws. Using the high-resolution imaging, the thin sands, their lateral pinchouts and the fault locations can be more accurately mapped reducing exploration risk.
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Estimativas da Umidade de Solos Com Gpr: Revisão e Resultados
Authors Marcelo Jorge Luz Mesquita and José Gouvêa LuizA summary on the application of GPR as a tool to estimate soil humidity is presented. Several relations that allow estimating humidity from dielectric constant obtained from the GPR wave velocity are discussed, as well as the methodology for the GPR data acquisition. Results from experiments are also presented to show the viability and limitations of this GPR application.
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Japanese Tsumani 2011 Effects on the Geomagnetic Field: Preliminary Results
More LessThe vertical component of the geomagnetic field observed by ground-based observatories of the INTERMAGNET network has been used to analyze the effects of the Japanese tsumani, 2011. The purpose of this work is to observe the geomagnetic variations induced by a tsunami resulting from the strong earthquake on 11 February 2011. We choose four stations that were influenced or more direct affected by the tsumani. The stations considered in this analysis were: Kanoya (KNY), Memambetsu (MMB), Guam (GUA) and Charters Towers (CTA). To detect these disturbances in the geomagnetic data, the discrete wavelet technique have been used in three levels of decomposition. We were able to detect the localized behavior of the geomagnetic variations induced by the movement of electrically conducting sea-water through the geomagnetic field, i. e., the identification of transients related to the tsunamis. As well, using the minutely magnetogram data, it was able to localize the inicial phase and time of the tsunami maximum height. The first interpretation of the results suggests that discrete wavelet transform can be used to characterize the tsumanis effects on the geomagnetic field, but need further study.
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Building Anisotropic Models for Depth Imaging: Comparing Different Approaches
More LessSeismic images are only as good as the velocity models used to produce them. As we move from “easy oil” to “difficult oil”, targets in subsalt, sub-basalt, and deep complex areas, we can no longer build the simple isotropic models of the past. To fully leverage the potential of new data types (e.g., wide azimuth and long offsets), we have to move to anisotropic imaging (VTI or TTI) in all geological provinces. Incorporating anisotropy increases our ability both to focus the seismic data and to accurately position our seismic images for drilling decisions. While these goals are achievable with anisotropic models, they are only met when geology and data from boreholes are intimately incorporated into velocity model building from the very start. We discuss several different approaches for anisotropic model parameter estimation and we illustrate some of the possible strategies for model building with case studies from the Gulf of Mexico and West Africa.
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Application of 3D Interbed Multiple Attenuation in the Santos Basin, Brazil
More LessImaging of pre-salt reservoirs in the Santos Basin can be significantly affected by the presence of strong interbed multiples in the data. These multiples can be predicted using a data-driven, true azimuth convolution method similar to surface-related multiple elimination (SRME), and removed using a suitably constrained subtraction technique. We discuss the application of this method to Santos Basin data, and present results on 2D synthetic data and 3D real data.
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Estudo Geofísico de Vazamento de Combustíveis em Posto de Abastecimento
Authors Aline Muriel da Cunha Menezes and César Augusto MoreiraThis paper presents the results of applying the Electrical Resistivity method by electrical profiling technique to investigate the fuel presence in soil and groundwater proceeding in station gas, located in an urban area Caçapava do Sul (RS), on soil in situ, from modification of Caçapava granite. The results suggest an association between low resistivity anomalies zones with potentially degraded from underground tanks storage in free phase form, now represented as residual phase. The electrical resistivity method proved to be an important tool for assessment and environmental monitoring in conjunction with direct methods of investigation.
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Ensaios Sísmicos (Refração Utilizando Ondas P E S E Ensaio Com Ondas Superficiais) Na Caracterização Geotécnica de Um Aterro.
More LessThis paper presents the results of a seismic refraction survey (using shear and P waves) and Multi Channel Analysis of Surface Waves (MASW) carried out a landfill. P-waves and shear waves velocities has allowed to get dynamic properties (Poisson´s ratio) of the landfill. The MASW survey has identified an inversion of shear wave velocity that can be related to the interface between the compacted landfill and the natural terrain situated below this.
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Normalized Reflectivity in Reverse Time Migration
Authors André Bulcão, Gustavo Catão Alves and Djalma Manoel Soares FilhoReverse Time Migration has recently gained much attention as a viable and accurate technique for imaging reflectors, especially in complex geologies. However, reflection amplitudes in RTM are problematic and limit its applications when correct reflectivity is necessary. In this work, normalized reflectivity amplitudes for reflectors in Reverse Time Migration are achieved when the amplitude matrix used for the excitation time image condition is applied as a normalization factor to the migrated image. The amplitude matrix acts as a weighing factor that takes into account the illumination of the target reflector, giving more accurate results for the reflection coefficient. Results are shown for a simple 2D horizontal model and for 2D horizontal model with a diving reflector. In both cases, a reflection coefficient is obtained that closely matches the theoretical trend. A wave separation technique applied for increasing the amplitude accuracy is also discussed (Bulcão et al 2007), despite the marginal gains.
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VSP Survey Assists in the Reservoir Characterization of Deep-Water Turbiditic Reservoir Offshore Brazil
More LessIn this case study we review the main results from a rig-source VSP survey, acquired in a deep-water deviated well drilled offshore Brazil. The primary goal for the VSP was to illuminate the lateral variation of thin sand and shale bodies, with higher resolution than available with surface seismic data. This was achieved initially by 2D migration of the VSP data and later, through acoustic impedance inversion of the VSP data.
New surface seismic data is being acquired in the area and the VSP results will be used to quantitatively assess the data processing and the well tie quality. Seismic parameters such as phase, true amplitude and anelastic attenuation are readily available from the VSP measurements. The anelastic attenuation is quite important in this area as the overburden is dominated by highly cyclic siliciclastic deposition, which results in strong attenuation of the seismic data.
Finally, we present some advanced VSP data processing techniques, such as migration of surface related multiples and far field signature estimation for Q-factor computations, which added value to the VSP results.
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The Multicomponent Seismic Paradigm: Conservative Principles
Authors Carlfred Bautista and Luis Antonio Castillo LópezThis article pretends to show the basic concept inherent to the processing of converted waves (P mode to S mode), concepts specifically related to the correction required for the location of the seismic converted wave.
A formal geometric deduction is made of the equation that governs the correction to the coordinates of common midpoint. It is solved by MatLab algorithm, considering straight ray path in an homogeneous and isotropic medium. This correction distinguishes the converted wave processing compared to conventional P-wave processing.
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Electrical Resistivity Tomography to Follow up an Airborne Em Rock Slide Mapping Survey – Linking Rock Quality With Resistivity
More LessWe investigate an active rock slide in Western Norway with ground- and airborne resistivity mapping to ultimately find weakness zones & sliding planes embedded in crystalline bedrock. The study area comprises phyllite, a low grade metamorphic rock type that tends to be reworked to clay in disturbed zones. Mapping these electrically conductive clay zones was the aim of the survey. GPS measurements over the last 5 years indicate that precipitation drives rock slide movements. The role of ground water is thus a crucial factor to investigate for risk assessment in the area. Based on a successful airborne electromagnetic (AEM) demonstration survey, we conducted a total of 1.600 profile meters of ground resistivity measurements to confirm AEM anomalies, to gain precise 2D geometries and to link conductivity anomalies with geology. All resistivity results confirm AEM anomalies and refine their lateral extent. In the East we find consistency between a strong conductor, dipping sub horizontal SW with an outcropping thrust fault, separating phyllite and gneiss. In the West a conductor dipping steeply NNW seems to be fed by surface water and may represent a formerly unknown sliding plane. Detailed geotechnical follow up is pending (drilling and instrumentation).
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Aerogeofísica (Magnetometria e Gamaespectrometria) Como Suporte Ao Mapeamento Geológico da Folha Baturité, Norte do Estado do Ceará
This work refers to the results from the processing and interpretation of airborne geophysical data (magnetic and gamaespectrometry) with the goal of give support to the geological mapping of the Baturité sheet (1:100.000), located in the north of Ceará state, northeast of Brazil and developed by the Geological Survey of Brazil (CPRM). The geophysical processing products together with the geologic mapping were able to determine the mains lithoestratigrafic domains and the structural framework of the study area.
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Geostatistical Reservoir Modeling Issues, How Seismic Can Help: A Typical Case Study
More Less3D earth modeling is a key issue for Reservoir Characterization. Fluid flow simulations based on a reliable model of reservoir heterogeneities will provide better prediction of hydrocarbon production. Moreover the uncertainty on the reservoir structure, the rock properties and the contacts may be assessed by means of simulations that preserve the geological features of the reservoir. This paper deals with a geostatistical workflow of a 3D reservoir modeling applied to real data of a siltstone reservoir. The first key issue is the optimal use of the available data: the wells with information on markers of key horizons, lithofacies and porosity and an acoustic impedance cube that brings relevant information for constraining the porosity model and facies proportions. The second point is related to the comparison of different geostatistical methods. The main steps of the workflow are: - Surfaces simulations delimiting the top and bottom of the reservoir, using the information from wells. - Facies simulations (Sequential Indicator Simulation, Truncated Plurigaussian Simulation). It requires the building of a flat stratigraphic grid (Flattening) within which variograms calculations and simulations are performed. After the flattening, the 3D vertical proportions curves (VPC) are computed. A 2D proportion constrained by a seismic attribute is used to constrain the 3D VPC. These proportions are used for the facies simulation. - 3D porosity simulations are achieved independently for each facies, then a cookie cutting procedure constrained by the facies simulations provide the final porosity simulations. - Finally, simulations are transferred from the stratigraphic space to the real space. Several types of simulations are used (Surfaces simulations, SIS, TPGS, 2D porosity simulations, 3D porosity simulations, contact). To evaluate the different available models, volumetric calculations based on simulations of the different parameters provide stochastic distributions of volumes.
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Diffraction Separation Using the Crs Technique: A Field Data Application
Authors Endrias G. Asgedom and Leiv -J. Gelius and Martin TygelDiffracted waves are often associated with geological structures like faults, pinchouts, wedgeouts or a sudden change in facies (Kanasewich and Phadke, 1988). Identification of such structures in a seismic or ground penetrating radar (GPR) image is highly
dependent on our ability to utilize the diffracted energy. Unfortunately, diffractions often manifest themselves on seismic (or GPR) data with a much weaker signal strength compared to reflections and they often fall within the noise level. As a consequence, classical signal processing methods treat diffractions as noise and imaging is carried out in favor of reflections. Recently, however, different approaches have been proposed to separate diffractions from reflections so that additional high-resolution information can be obtained from direct imaging of the diffracted energy. In this paper, we propose to perform diffraction and reflection separation based on the Common Reflection Surface (CRS) concept. Within this formulation, suppression (or attenuation) of reflections is carried out by selecting the appropriate stacking surface for diffractions based on a coherency measure. Here we tested both Semblance and MUltiple SIgnal Classification (MUSIC) as a coherency measure for the CRS parameter estimation. The potential application of the technique has been demonstrated employing a multi-offset GPR dataset.
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Levantamento Magnetométrico em Aterro de Resíduos Sólidos – Rincão Dos Bitencourt, Município de Caçapava do Sul – Rs
More LessGeophysical investigations in several environmental studies are common. The aim objective of this study is to detect contaminations in different levels of investigation (shallow and depth) in a non-invasive form. The main objectiv is to evaluate and detect the lateral and deep limits from a waste landfill site located in Bitencourt farm near Caçapava do Sul city, Rio Grande do Sul State- Brazil. The area served as landfill and received an amount of 28.000 ton. during 14 years of different wast types without any environmental criteria worldwide stablished. In 1994 the area has to be recuperated and started a recovering plan determined by the environmental agency (FEPAM). The results indicate that may have accured a significant material deposition due the presence of faults and fractures in the rocks that act as substract for the waste landfill. Total magnetic field map and processment techniques allows to detect anomalies in shallow and in depth levels and also its geometry and depth recognization. The geophysical modeling in the A – B profile permits the better understanding, analysis and visualization from the studied area. The waste were deposited in the landfill area in a regular manner (depth and in area) and a 12 meters limit and 1 meter minimum were stablished for the landfill. The magnetometric method in landfill waste sites is unusual but in this case was effective by the fact that the area have low noise presence (powerlines, antennas, vehicles, etc). The method is a valuable tool and recomended to contaminated áreas where the magnetic fiel is undisturbed.
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Autonomous Nodes – The Future of Marine Seismic Data Acquisition?
Authors Chris Walker and Steve McIntoshWhilst autonomous or “cable free” seismic recording is not a new technology, having been originally developed by Amoco in the 1970s with the Seismic Group Recorder, its application offshore has been relatively recent.
A number of surveys have been undertaken in the Gulf of Mexico, UKCS and offshore West Africa in deep water where the nodes, as the autonomous recording units are now referred to, are deployed and recovered using Remotely Operated Vehicles (ROVs).
Recently FairfieldNodal have introduced a node based marine system which does not require the use of ROVs for node deployment and recovery.
In this paper we will review both deep water and this new “shallow” water technology and show the improved productivity and enhanced operational performance that autonomous nodes can provide.
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A Proposal of New Method for Estimating Depth of Curie Surface
The power density spectrum of magnetic anomaly based on radial average is a procedure commonly used to estimate the depth of the Curie surface. Many applications are found in the literature, for different geological contexts. Despite this, some methodological and operational difficulties are present: (1) radial average, assuming a priori that the medium is isotropic and that there is a single point to start the Fourier transform; (2) difficulty and ambiguity in determining the segment containing the points of similar inclination: (3) the need for manual procedure on examination of the spectrum. An alternative method is investigated and presented in this work. The first is the decomposition of oscillatory series by analysis of variance instead of Fourier analysis; the second is to use variogram to determine the wavelengths and the third is the use covariance spectrum as function of wavelength as a power spectrum. The method was tested on an area east of the Paraná basin, where determinations of Curie depth and heat flux from temperatures in oil wells are found of in the literature.
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Application of Digital Rock Physics for Geophysical Rock Properties
Authors Naum Derzhi and Carl Sisk and Zubair KalamTraditionally,the values of reservoir rock properties have been acquired from log data or direct measurement in a physical laboratory. Recent advances in imaging and image processing, together with improved availability of high performance computing, gave rise to digital techniques for investigating the properties of rock samples. These techniques are based on high-resolution imaging of the rock’s pore space, segmentation of the images into pores and various minerals and simulation of the physical processes controlled by the desired rock properties. These techniques form the novel discipline of digital rock physics (DRP). The goal of the current work is to validate the results of DRP measurements of geophysical parameters by comparing them with the results obtained in traditional physical laboratories.
This study includes eight core plugs from a Cretaceous formation, representing four reservoir rock types. Multiple sub-samples of each core plug were taken and analyzed using the digital rock physics technique.
Our DRP computations are compared with the results of physical measurements of the geophysical properties on samples from Cretaceous formations. The latter measurements were conducted on regular core plugs, several cm in size, much larger than the digital rock samples used in this study. Although some of the physical data represent samples from wells different from where the digital samples used here were extracted, these physical samples cover the rock types included in the study. The geophysical property values obtained in the digital rock physics laboratory closely match the results of physical measurements.
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Estudo Geoelétrico em Sequência Ultramáfica Mineralizada em Cromo, Municipio de São Sepe - Rs
More LessThis paper presents the results of Electrical Resistivity method applied in characterization of metamorphosed ultramafic body in chrome mineralization, located in the São Sepé city (RS). The study area occur rocks of Vacacaí Metamorphic Complex and Basic-ultrabasic Metamorphic Complex. These complexes bring together a wide range of lithotypes, predominantly ultrabasic terms in the form of magnesian serpentinites and schists, with subordinate terms metabasic. The method of the Electrical Resistivity allowed to relate the results of pseudosseções with ultramafic bodies in depth, it was possible to visualize the intervals of the rocks due to the contrast in physical properties between the host rock and the mineralized bodies in chrome. The inversion models were masked by smoothing, not allowing a clear understanding of the format as the resistive zones pseudosections.
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Challenges and Solutions in Wide Azimuth Seismic Data Processing and Imaging for Geologically Complex Areas
Authors Ruben D. Martinez and Jon Burren and Ernesto LemosOver the last years, wide azimuth (WAZ) seismic data collection techniques have shown to provide improved seismic resolution and subsurface illumination than conventional narrow azimuth (NAZ) surveys. However, WAZ geometries pose processing challenges. Proper WAZ compliant pre-processing is required to prepare the 3D seismic data for depth velocity model building and migration in order to produce useful seismic depth images for structural interpretation and prospect generation. WAZ 3D tomography should be used to provide accurate velocity models accounting for velocity anisotropy. The estimation of anisotropic parameters is vital to tie the wells and it is still a challenge and the subject for significant research efforts. During the model building stage, WAZ Beam PSDM (prestack depth migration) is preferred; it is efficient and accurate. Implemented in an interactive environment, anisotropic depth models can be delivered in a short time allowing the interpreter to have more time for the geologic interpretation. After several iterations, WAZ compliant hi-end imaging algorithms, such as anisotropic prestack one-way wave equation migration or reverse time migration are employed to produce the final seismic image. In this presentation, we will review and illustrate challenges and solutions in WAZ seismic processing and imaging using data sets from complex geology areas.
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A 3-D Azimuth-Rich Survey on the Sedimentary Cover in Santa Catarina Island
Authors Saulo S. Martins and Jandyr M. TravassosIt is well known that a 3-D survey can provide the best visualization of the subsurface. But the common practice in 3-D GPR is very poor in comparison with the corresponding for the land 3-D seismic. The usual deployment of closed-spaced fixed-offset profiles have limited azimuthal information and restricts processing to post-stack. In this paper we use another field deployment that is richer in azimuth and thus produces a much better image of the subsurface. We compare our methodology with the usual deployment to illustrate the differences in rendered cubes and in time-slices.
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Project of an Earth Station for the Brazilian Scientific Nanosatellite (Nanosatc-Br)
The Mission NANOSATC-BR aims to get scientific data of the regions at South Atlantic Magnetic Anomaly (AMAS) and at the Equatorial Ionosphere Electrojet on the Brazilian Territory (Schuch, 2008), employing a nanosatellite, which is characterized by its small size, form of a cube, weighting about 1 kg and edges with 10 cm (pattern CubeSat). An Earth Station has been studied to communicate with nanosatellite. Two solutions were evaluated for implementation: The first is to acquire a complete station with a specialized company; the second option is the construction of an Earth Station in the laboratory, applying equipment used by radio amateurs. In this paper is discussed the process used to develop the second solution, with emphasis on the construction and/or
use of antennas Yagi-Uda, mainly because it is cheaper and easy to implement. Moreover, the second solution allows the application of knowledge acquired in academy. The main objective is to determine the best antenna, evaluating the angle of half power, gain, impedance and costs.
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