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9th International Congress of the Brazilian Geophysical Society
- Conference date: 11 Sep 2005 - 14 Sep 2005
- Location: Salvador, Bahia, Brazil
- Published: 11 September 2005
201 - 300 of 462 results
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An application example of shallow seismic reflection technique for geologicalgeotechnical mapping in the urban area of the city of São Paulo, Brazil
Authors Oleg Bokhonok, Renato Luiz Prado and Liliana Alcazar DiogoWe evaluate the potential of shallow seismic reflection for a geological and geotechnical research in noisy urban environments with a paved surface. The field tests were made at the Sedimentary Basin of São Paulo, in the urban area of the city of São Paulo. It was verified that a sledgehammer and 100 Hz geophones provide the most suitable equipment. An interpretation of the CMP section, interpolated by the well information, demonstrated a high potential for mapping geological structures with numerous details and good continuity. The information obtained from the final seismic section revealed various sediment strata of the São Paulo Basin and several bedrock structures. The results characterize the shallow seismic reflection method as a flexible tool that can be adapted to the objectives of the proposed research. The latter can be accomplished by defining appropriate acquisition parameters as well as through perceptive processing.
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Modelo geométrico estrutural a partir de interpretações em seções sísmicas de alta resolução
Outline the 3D geometry of the structural model from high resolution seismic faults interpretation was the main objective of this work. The analysis of a seismic array of lines, acquired transversally to the predominant structural trend, resulted in interpretation of various fault segments. After coherence tracking of this alone segments along the seismic sections, some fault planes came out. Those planes were converted to pillars in order to interpolate surfaces for constructing the structural model skeleton. The resulted 3D grid was stuffed with faults heterogeneity preserving the interpretation and preparing the model for horizons insertions and 3D integration.
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LEVANTAMENTO GEOFÍSICO EM CORDÕES ARENOSOS, ZONA COSTEIRA DA BAÍA DE SEPETIBA, ITAGUAÍ – R J: RESULTADOS PRELIMINARES
It is presented in this paper the results of a geophysical research based on electrical resistivity applied to Holocene deposits, located at the inner part of the Sepetiba bay, at the Itaguaí county, state of Rio de Janeiro. Interpretation of the data showed results that nicely match with the conventional models of such architectural depositional element, that will be integrated to the geological model of a wider area that is under investigation. The results of this investigation has also served to test the resistivity equipment that is being developed by the Geophysical Laboratory of the Federal University of Rio de Janeiro.
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Processamento sísmico de reflexão rasa em rochas fraturadas do Grupo Itararé
Authors R. Brunetta, M.K. Bartoszeck, M. K., J.N. Lonardelli, J. N., A. Rigoti, S.P. Rostirolla, S. P., C.J. Appi and C. J. BolsistaHigh resolution seismic was used to study rocks of the Itararé Group for fracturing reservoir caracterization. The area of the studies is next to Ponta Grossa city (PR), where are exposed rocks like sandstones, basal shales, diamictic and conglomerates. The seismic processing has become a great challenge because there is no good evident reflector in shot window. In the attempt of identifying these reflectors, traditional techniques of seismic processing, like Predictive Deconvolution that comes to be used with relative success at the area in studies, even not be usually applied in shallow seismic.
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Aplicação de tomografia elétrica na detecção de tambores plásticos na área do Sítio Controlado de Geofísica Rasa do IAG/USP
O resumo mostra resultados de tomografia elétrica 2D realizada sobre tambores plásticos enterrados na área do Sítio Controlado de Geofísica Rasa do IAG/USP. A metodologia aplicada teve como objetivo identificar o padrão das anomalias elétricas dos tambores plásticos utilizando o arranjo dipolo-dipolo com espaçamento entre os dipolos de 1 metro. Os resultados mostraram que os parâmetros de campo utilizados permitiram somente identificar a posição horizontal dos tambores. Os alvos apresentaram anomalias de alta resistividade e baixo valor de cargabilidade.
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Prospecção arqueológica por métodos geofísicos no Sudeste do Pará: O caso do Sítio Domingos, Canaã dos Carajás
More LessMagnetic, resistivity, and ground penetrating radar (GPR) measurements were carried out on an archaeological site under investigation to find remains buried by ancient people that could have lived in the area. Archaeological excavation on places indicated by magnetic anomalies revealed concentration of ceramic fragments and intact pottery. The correlation between resistivity measurements and the soil profile described in the area suggest the 1810 to 2560 Ohm.m range as the most representative for the archaeological occupation layer. GPR images showed anomalous features correlating to several magnetic anomalies. Those features, however, are not very conclusive to represent the searched remains. Because of that, GPR is not recommended to be the main tool for archaeological prospecting in the area.
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Caracterização do Solo para Uso em Agricultura de Precisão através de Métodos Elétricos e Eletromagnéticos (GPR): Resultados Preliminares
More LessIn this work, the Ground Penetrating Radar-GPR and Continuous electric profile-VERIS methods had been used to characterize the structures of the soil for use in precision agriculture. The studies were carried out in a pilot area closed for soy plantation located in Farroupilha farm, Mato Grosso state, Brazil. GPR Profiles allowed characterizing the subsurface until 12 m depth. The main images structures were: the soil thickness, a lateritic layer with iron oxide and the water table top. The electric conductivity mapping obtained with VERIS profiles showed that the conductivity varies laterally and it is heterogeneous for all the pilot area until 1 m of depth. The results had shown a good correlation between the reflections zones from GPR profiles and the electric conductivity anomalies zones. In regions where the conductivity is highest, there is absence of GPR reflections. On the other hand, where the conductivity is lowest occur good penetration of the radar and the reflectors are stronger.
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Utilização de Metodologias Geofísicas na Identificação de Manilhas de Concreto Instaladas no Sítio Controlado de Geofísica Rasa do IAG/USP
Authors Welitom Rodrigues Borges and Jorge Luís PorsaniThis work presents some results obtained with the Ground Penetrating Radar (GPR), electric, and inductive electromagnetic (EM38) methods applied to identify concrete tubes installed in Shallow Geophysical Test Site SCGR – IAG/USP. The results showed that the GPR is the most effective method for concrete tubes identification, and that objects buried in soils with electric resistivity lower than 200 ohm.m were not identified by other methods.
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Metodologia geofísica aplicada ao salvamento arqueológico de área adjacente a mineroduto no nordeste do Pará
More LessMagnetic, total count gamma cintilometry, and ground penetrating radar measurements were carried out on two archaeological sites located adjacent to the place where a miner duct will be buried. The aim of the measurements was to indicate the optimal areas for archaeological excavation to find subsurface remains related to ancient communities that lived in the sites. Magnetic measurements showed anomalies that lead to the discovery of a large amount of ceramic fragments and
other remains. Cintilometry allowed discriminating argillaceous from sandy soil, an important result since sandy soil can be correlated to the archaeological layer, where remains are normally found.
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Seismic Inversion by Principal Components Analysis and Neural Networks
Authors Oswaldo Ludwig Júnior and Wilson M. FigueiróThis paper describes how Artificial Neural Networks can be employed to solve seismic inverse problems. The main objective is to obtain one-dimensional Earth velocity models from seismic waveform data. Precedent works are discussed and a new approach is suggested. It means, the Principal Component Analysis is adopted to avoid redundant information that is originated due to the Common Middle Point gather. A secondary objective is to reduce the total number of network parameters and increase the generalization skill on the neural network.
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Aplicação do WTdecon - deconvolução colorida implementada por Transformada Wavelet
Authors Evaldo C Mundim, Heron A. Schots, João M. de Araújo and Deilson M. TavaresThis paper presents the application of WTdecon, a new seismic deconvolution technique applied to deep water seismic data in Campos Basin, Brazil. WTdecon deconvolution doesn’t rely on the white reflectivity hypothesis, instead associates the reflectivity series to major fluctuations on the trace amplitude spectrum. The seismic wavelet is the smoothest component being obtained by Wavelet Transform decomposition of the seismic amplitude spectrum. Given that, the deconvolution is implemented in a deterministic way.
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Direct hydrocarbon detection experiment in Potiguar Basin
From March to May 2004 PETROBRAS performed an experimental geophysical survey in Potiguar basin, Brazil. For the first time, in a Brazilian sedimentary basin, the technology named “Hydrocarbon Micro-Tremor Analysis” (+\0$6
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Aplicação da decomposição espectral em campo cretáceo da bacia de campos, análise e comparação de metodologias
The Spectral decomposition has been used widely in a on seismic interpretation. Because of this, many companies developed themselves algorithms for application of the spectral decomposition technique. This work shows the applications and results of four metodologies based on spectral decomposition, that is the technique proposed initially by Partyka et al. (1999) . These metodologies were applied on oilfield placed in the continental margin of the Campos basin, offshore Brazil.
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PROCESSAMENTO E INTERPRETAÇÃO DE DADOS AEROGEOFÍSICOS DA PORÇÃO CENTRO-OESTE DO DOMÍNIO CEARÁ CENTRAL, NW PROVÍNCIA BORBOREMA
This paper reports the processing and interpretation of the airborne geophysical data (MAGNETIC and GAMAESPECTROMETRY) from the Itatira Project (1977). The aerogeophysical themes can be used on the characterization of the tectonic framework of the Ceará central region. The data processing was able to distinguish the inner differentiation of the Santa Quitéria migmatitic complex and the distinct nappe systems in the Ceará supracrustal sequence. Granites bodies and faults are well recognized in the airborne products.
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Estimación de espesores reales de las principales unidades tectono-estratigráficas Mesozoicas-Cenozoicas en la Plataforma Deltana, Cuenca Oriental de Venezuela
Authors R. Karla and M.I. JácomeSix tectono-stratigraphic units have been regionally defined in an area of 12.321 Km2 located towards the marine extension of the eastern Venezuelan basin (i.e. the Deltaic Platform of the Orinoco River). The tectono-stratigraphic units studied are: 1) Cretaceous-Paleogene; 2) Lower Miocene; 3) Middle Miocene; 4) Upper Miocene and 5) Pliocene. Decompacted isopach maps have been generated to determine the original thickness and regional 3D distribution of these tectono-stratigraphic units in the area, and to relate these units to tectonism and sediment supply. The descompacted isopach maps have been produced using thirteen regional 2D seismic reflection profiles previously interpreted and published. The seismic profiles are more than 1500 km long and have been digitised and converted to depth.
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Development of a digital proton magnetometer: an efficient algorithm model to determine the Larmor precession frequency
Authors André Wiermann and Luiz C. C. BenyosefThis paper presents results from a algorithm model proposed to estimate the central value for small measurement data sets. The algorithm was derived to achievea computationally efficient method to estimate the Larmor precession magnetometer that is being developed at the Observatorio Nacional (Wiermann & Benyosef, 2004). An additional comparison is shown between the proposed algorithm and a technique called meadian that combines mean and median procedures and it is based on statistical bootstrapping.
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Simulação sísmica entre poços e tratamento tomográfico dos dados visando a caracterização geológica – geotécnica rasa
More LessA tomografia sísmica é uma ferramenta muito importante para imagear diferenças de propriedades físicas em subsuperfície. Uma boa distribuição dos raios é um fator muito importante para o sucesso dessa inversão. Um dos algoritmos mais conhecidos em tomografia é o SIRT.
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AEROGEOFÍSICA APLICADA COMO FERRAMENTA DE SUPORTE AO MAPEAMENTO GEOLÓGICO NA REGIÃO DE NOVA XAVANTINA – MT, BRASIL CENTRAL
The present paper aim shows the processing of the aerogeophysical data from the Barreiro Project (1976), generating themes than can be used as a tool to suporte geologic mapping in the region of Nova Xavantina-MT, Central Brazil. They include K, U and Th channels images, and a color composition RGB (K:Th:U). Also, anomalous magnetic field transformed products, as the analytical signal amplitude and inclination (zero order), and total horizontal gradient amplitude (first order). Magnetic themes reflect the main structural trends (E-W e NE-SW) in the area. We found a good correlation between the known geologic units and gamma ray spectrometry products. But, more detailed domains were identified in the processed data that need to be checked in a future the fieldwork.
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PROCESSAMENTO E INTERPRETAÇÃO DE DADOS AEROGEOFÍSICOS DA REGIÃO DE PORANGATU – GO, BRASIL CENTRAL
This paper aim shows the processing and interpretation of the aerogeophysical data from the PGBC (1975/1976), generating themes than can be used as a tool to suporte geologic mapping in the region of Porangatu (GO), Central Brazil. They include K, U and Th channels images, and a color composition RGB (K:Th:U). Also, anomalous magnetic field transformed products, as the analytical signal amplitude and inclination (zero order). The aerogeophysical themes can be used on the characterization of the tectonic framework and litologic differentiation.
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Condutividade térmica a partir de perfilagem geofísica de poço
More LessIn this paper, using self-similar mixture laws, we developed a set of analytical expressions to derive, explicitly, the thermal conductivity of granular sedimentary rocks, from measurements of the true electrical conductivity and porosity obtained from geophysical well logging. The developed equations were tested with well log data from oil fields in Reconcavo basin, and the averaged results are comparable to sample laboratory measurements made by Carvalho (1981).
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Tomografia ultrasônica em testemunhos: simulação de inclusões e interlaminados
Authors Michelli Silva de Oliveira and José Agnelo SoaresThis work presents a simulation study for ultrasonic tomography in cores. More specifically, the capacity of this technique to image inclusions and interlaminated units is investigated. Tomograms representing internal P wave velocities of virtual cores are obtained. These virtual cores are defined in terms of initial velocity models that have zones of high or low wave velocity. The ultrasonic tomography technique is based on ray tracing through an arbitrary grid of cells with constant velocities. Tomograms are obtained as a result of a data inversion algorithm that, in this work, uses alternatively, the algebraic reconstruction technique (ART) or the piecewise polynomial truncated singular values decomposition (PP-TSVD) one. Five different initial models, representing reasonable geological cores, were tested. All results were considered acceptable, but for strong contrasts of velocity the inversion algorithms do not work so perfectly, what is believed due to the using of straight ray paths.
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Análise Petrofísica do “Arenito Namorado” na Porção Sudeste do Campo de Namorado - Bacia de Campos, Brasil
More LessBrazil fossil energy requirements are increasing along last years, and Brazil’s reserves are going to decrease after 2006, in order to have a minimum impact over Brazil’s fossil energy consumes, it will necessary found new reservoirs or re-explorer ancients reservoirs with new technologies.
Namorado´s field is a re-exploration area, but it’s difficult for university’s researches found data like petrophysics characteristics in the field, for this motive this study calculated shale volume, total sand, net to gross o the petroliferous sand, porosity, water saturation, over seven reservoirs identified in a stratigraphic cross-section.
This project was development with a software “Geographix” (Prizm) of Landmark Graphics, and it was used wire log like as Gamma Ray, Density, Neutron and Induction dual laterolog.
The reservoir level was denominated as “Arenito de Namorado”, this level represents a turbidite reservoir and dated as Cretaceous, with a poor lateral continuity. Between the seven levels reservoir here interpreted, the superior level (F) and de inferior level (A) show the most interest for re-exploration with a low percentage of shale volume (less than 15%).
Water saturation was calculated in 3.5% for the deeper reservoir (A)_less than their maximum value calculate in 16%, and over 16% for the rest of reservoirs; for the porosity is observe a minimum value of 10% and the calculus for the different reservoirs are over 15%, this facts let us to thing that the “Arenito de Namorado” deeper level (level A) has conditions for re-exploration.
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Um fluxo de trabalho para modelagem de eletrofácies com entrelaçamento de técnicas de classificação supervisionada e não-supervisionada
More LessThis paper presents a workflow to build logfacies models which is based on the interlaced application of non-supervised and supervised statistical techniques. The workflow allows answering, in an interactive manner, some basic issues which appear in any logfacies modeling program: How many facies may be recognized? Which is the best log suite to be used in? How the generated logfacies correlate with the original lithofacies? Due to the interactive process between supervised and non-supervised techniques, the proposed workflow is biased to produce a fewer number of logfacies than the number of original lithofacies, but those logfacies tend to correspond to, in a physical properties sense, those most representative lithofacies. A main feature of this workflow is the adoption of the logfacies column provided by a non-supervised classification algorithm as the input column of facies for a supervised classification procedure. This feature warrants that the recognized logfacies suite is the best possible, in terms of log physical properties and lithofacies reproduction. Finally, it is shown a real case were this workflow was applied successfully.
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Projeto e construção de um tomógrafo ultrasônico para testemunhos
More LessThis paper presents the development of a novel petrophysical equipment, the ultrasonic tomograph for well cores, which may be used for several petrophysical analysis, as inhomogeneous composition, patch saturation or internal distribution of stress in rock samples. Initially, a brief introduction to seismic transmission tomography is done in order to drive the understanding of this imaging technique as a whole. Some particularities about well core tomography are discussed, as the number of piezoelectric transducers to be distributed around the core section, the grid of cells used for velocity determination, the algorithm used for data inversion, and the simplification of considering straight ray tracing. Details about the project of this equipment, which at the moment of writing of this paper was yet under construction, are presented. Finally, the effect of stresses on rock velocities is investigated and the results indicate the ultrasonic tomography of orientated cores as a very promising technique for determination of direction and magnitude of in situ stress.
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Quantificação da anisotropia sísmica de folhelhos antes, durante e após a geração de hidrocarbonetos
More LessShales represent an important parameter in the discovery of oil accumulation. They are however a lithological type not often studied in terms of the relationships between the petrophysical properties and the velocity of seismic waves. The main objective of this work is to understand the influence of the hydrocarbon generation process in the seismic velocities (shale anisotropy). The elastic velocities have been measured in samples plugged in directions parallel and perpendicular to the bedding and, whenever possible, 45 degrees to the bedding. The anisotropy simulation of hydrocarbon generation process was made using the combination of Thomsen’s petrophysical model and the effective media theory. The combined analysis of anisotropy and mineral composition indicates a more significant contribution of the expansive clay minerals in the anisotropy values. The simulation of the presence of gas inside of organic matter affects in a substantial way the spread of the P wave, which has its velocity reduced when going through organic matter with gas. Therefore, although anisotropies observed in the shales samples studied are not strongly related with the contents of organic matter in the low and high degrees of thermal maturity samples, the simulation of the hydrocarbon generation process indicates that, during the generation process, the contribution of organic matter is as relevant as the presence of oriented clay minerals.
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Computing Resistivity Anisotropy and Structural Dip Using Multi-component Induction Data
Authors Berthold Kriegshäuser, Bill Corley, Michael Rabinovich and Lev TabarovskyA multi-component induction tool like the 3DEXSM provides all the data necessary to derive formationresistivity parallel and perpendicular to bedding. It hasbeen shown in the past that the resistivity perpendicularto bedding can be extremely important to detect andquantify hydrocarbons in so-called low-resistivity pay zones. However, in order to accurately derive formation resistivities at any relative dip from the 3DEX data, the formation dip and azimuth needs to be known. Until recently, this information needed to be provided as a priori information, either from surface seismic data, and/or derived from borehole imaging analysis. In this paper we discuss a new method that utilizes all 3DEX data to derive not only formation resistivities parallel and perpendicular to bedding but also formation dip and azimuth. The 3DEX tool is comprised of three mutually orthogonal transmitter-receiver pairs that allow measurement of the full magnetic field matrix at multiple frequencies. Using a rapid two-step least-square optimization scheme we first derive at every logging depth formation dip and azimuth; then we compute formation resistivities parallel and perpendicular to bedding. We first validated our algorithm with synthetic examples, and then, we applied this enhanced processing to many field data sets, for example, to data acquired offshore Brazil. The generally good agreement between the computed formation dips and azimuths from 3DEX data and those obtained from borehole imaging data confirm the strength and efficacy of this new processing algorithm.
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Simulação do perfil sônico para poços do campo de Namorado utilizando lógica fuzzy
More LessNowadays the offshore industry depends on deepwater exploration that represents costs around thousand million dollars. New techniques of optimization are very welcome to save time and money for petroleum companies.
In this work we will show a new technique using fuzzy systems with real data from an offshore Brazilian field, called Namorado field.
Using this new technique we may simulate the sonic log in wells where we don´t have these data. For this purpose we need other types of log data, like resistivity, gamma ray and sonic log from neighborhood wells.
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Intervalos de variação da velocidade cisalhante no arenito Namorado a partir de um modelo para meios efetivos
More LessIn this paper, shear-wave velocity (VS) intervals were estimated for 32 Namorado sandstone’s samples using Hashin & Shtrikman’s (HS) bounds. In order to achieve this purpose, we assumed the Namorado sandstone as a rock composite with 40% quartz, 25% feldspar, 20% oil, 10% clay and 5% brine. The upper and lower HS bounds resulted from this hypothesis remained in the following intervals: 22.15 and 6.26 GPa for bulk modulus (K), and 17.82 and 2.66 GPa for shear modulus (μ). Moreover, distinct values for the Possion coefficient (ν) were assumed (0.30, 0.25, 0.20, 0.15 and 0.10). The availability of P-wave sonic (DT) and density (RHOB) logs allowed calibration of K and μ for each assumed value of ν, as a function of compressional velocity (VP) and bulk density (ρ). Therefore, a linear relationship between K and μ could be calculated for each ν used, as well as constant VP/VS values (1.8709 for ν = 0.30, 1.7319 for ν = 0.25, 1.6329 for ν = 0.20, 1.5584 for ν = 0.15 and 1.4999 for ν = 0.10). As a result, an interval containing probable VS values could be estimated for each value observed of VP.
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The use of well logs in logfacies modeling – example in the Namorado Field, Campos Basin, Brazil
Authors Camila Faria de Albuquerque, José Agnelo Soares and Claudio BettiniOne of the most important stages for oilfield development is the reservoir modeling, which can be performed in many ways. In this study, we decided to use facies modeling based on well logs, owing to their availability in the petroleum industry. We have used the statistical software Enterprise Guide 2.0, with a specific tool developed for logfacies modeling. The logfacies modeling used here includes a sequence of stages: calibration, validation and application of a discriminant function, which can be linear or quadratic. The data were previously treated with discriminant and cluster analyzes. This study describes an example of the application of this technique to the Namorado Field, Campos Basin, Brazil, showing the modeling stages and the results for two wells.
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PROCINT_LOG: “Software” Acadêmico para Processamento e Análise de Perfis Convencionais de Poço
More LessPROCINT_LOG is a free GUI academic software that runs under MATLAB and is useful for simplified conventional oil and gas well logs analysis. It works through two distinct modes: (1) direct petrophysical parameters inclusion from both field copies and digital
files and (2) by reading digital file and performing the calculations along chosen intervals. The software load ASCII and LAS format files and identifies the logs available, supplying both a header file with additional information about the well and a matrix with the depth in the first column and logs in the remain columns. The last can be loaded by PROCINT_LOG and checked out for unusual highly noisy and/or spurious data, allowing an efficient data control. Furthermore, each one of the proposed processing modes fits well to any chosen processing sequence, allowing the log interpreter to drive your own perspectives into log analysis. To provide a little of perspective, fundamental well-logging principles are stressed by informative icons that can be searched at any time the interpreter need. Calculations such as invasioncorrected resistivity, shale volume, and Archie, Dual Water and Simandoux methods for water saturation computations and three types of water resistivity computations are viable. One complete example is performed on both synthetic and real data and results are checked against visual analysis to show the usefulness, rapidness and accuracy of PROCINT_LOG in performing accurate logs analysis.
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Projeto RADAM-D - conversão e disponibilização em meio digital das imagens originais geradas pelos projetos RADAM e RADAMBRASIL
The RADAM Project (for Radar Amazon), organized in October 1970, was a Brazilian government decision to undertake a reconnaissance survey of the Amazon region and the adjacent Brazilian Northeast. The major objective was to collect information on mineral resources, soils, vegetation and land use. In June 1971, the first flights took place. In July 1975, the program was expanded to the hole country and had its name changed to RADAMBRASIL. The remote-sensing platform was a twin-jet Caravelle flying at an altitude of 12 km with a speed of approximately 690 km/h. On board was the side-looking radar Goodyear Mapping System 1000 (GEMS). The generated data are stored at CPRM-Geological Survey of Brazil. This RADAM-D Project deals with the preservation of original SLAR image negatives and diafilms through data scanning and digitization. The project works with the inventary of available material, organization of radar strips, high resolution image scanning, composition of final images and its publication.
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Variações da metodologia de micronivelamento de Minty em dados aerogeofísicos no domínio do espaço
Authors Mariana V. Maziviero, Rodrigo S. Portugal and Adalene M. SilvaO método de Minty (1991) vem sendo utilizado extensivamente para micronivelamento de dados aerogeofísicos no domínio do espaço, 1-D. No entanto, este método possui algumas limitações, que motivou a remodelagem desta rotina utilizando diferentes filtros. Estes filtros foram testado exaustivamente em um levantamento aerogeofísico a fim de verificar as características dos resultados finais (dado micronivelado) e possibilitando uma comparação entre eles.
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O efeito de adjacência em imagens de satélite numa atmosfera Rayleigh: uma aplicação no estado da Paraíba
More LessThe analysis of the influence of atmospheric effects in remote sensing are based on the principle that the imaged surface is uniform. This assumption has been a great problem in the case of low reflectance surfaces such as water surfaces (water reservoirs, lakes), for which the background influence is very important. The atmospheric correction method used here is based on the optical properties of the atmosphere. A background function is used to evaluate the percentage of the background contribution. In order to evaluate the adjacency effect on Landsat-5 images, several areas of different sizes were selected over the water reservoir of São Gonçalo, located in the interior region of Paraíba state. The adjacency effect is clearly seen in the selected areas.
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CAMPO DE ANOMALÍAS CORTICALES DEL SATÉLITE MAGSAT OBTENIDO POR CALIBRACIÓN CON DATOS DE SUPERFICIE CON APLICACIONES AL CAMPO DE ANOMALÍAS DE LA RED GEOMAGNÉTICA DEL BRASIL
Authors Jaime R, Añazco P and Luiz Muniz Barreto y Ronaldo M. De CarvalhoIn this work a crustal anomaly field of total intensity (F) at Earth’s surface level for the Brazilian territory is derived. The starting point was the crustal anomaly field obtained from Magsat data, to the average height of the satellite (350 km), by a calibration process, with surface profile anomalies and done by bands. This calibration is an alternative to the continuation methods. The anomaly field of the geomagnetic network, analyzed according to this calibrated field, displays an intense spurious negative
anomaly of approximately 150 nT, in the southern region of the country, that covers the states of São Paulo and Paraná. It has an orientation almost NE and a length of 7 degrees approximately. This effect seems to be produced by the insufficient removal of South Atlantic Magnetic Anomaly (SAMA), when the main field of the data is removed with the reference model IGRF of order and degree equal to 10. This problem should be present in every geomagnetic database, for this area, where the main field was removed with that reference model.
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Controle da Escala na Estacionaridade de Perfis de Poço (Scale dependence of well log stationarity)
Authors Adalberto da Silva and Armando Zaupa RemacreUpscaling (or downscaling) is a fundamental procedure to reservoir management in order to integrate scattered and linear high vertical resolution well logging data with volumetrically widespread but low vertical resolution seismic data. Analysis of the log signal behaviour must precede the interpreter’s decision on filtering denoising and scale transference methods. As a rule, well logging data is assumed as a stochastic, non-stationary realization and this assumption conditions the filtering method choice. In this paper, we analyse a set of four curves from seven vertical wells at Namorado Field, Campos Basin, Brazil using Fourier, wavelet filtering and variogram analysis to investigate the scale dependence of the geophysical signal, exploring the different filter responses to stationary and non-stationary signals. Using a 10 meter cutting wavelength that corresponds to the parasequence scale of the Namorado field turbidite system, the Fourier filtered signal preserves much more the variance than its wavelet filtered analogue. This indicates a strong stationary content of the geophysical signal at this scale level and suggests a decoupling of the signal in components at reservoir level: a medium to high energy / large scale stationary component and its fine scale non-stationary counterpart. This result poses some important constraints on the well logging data filtering strategy choice and its use in scale transference.
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Results from new technology and workflows for fast track reservoir characterisation of a Palaeocene deep marine turbidite field
Authors Martyn Millwood Hargrave, Rod Christiansen and Henry MorrisThe Brenda field in UK North Sea Block 15/25b (see Figure 1) has undergone very rapid exploration and appraisal in 2004 and is now poised to move into development and production phases over the next 18 months.
Over 12 “cluster” penetrations of the Palaeocene Upper Balmoral reservoir have been drilled and a substantial amount of reservoir data has been collected. The objective of the project required fast assimilation and integration into operations to ensure that each well was targeted and optimally drilled with the benefit of the enhanced understanding of the previous data collected.
We describe the combination of rock physics driven seismic interpretation of attributes, and new technology for “inversion of inversion” for reservoir characterisation used to fast track the Brenda field previously considered non economic.
The Brenda net oil reservoir varies from 15m- 30m in thickness trapped by a combination of structural and stratigraphic elements and our understanding of the relative importance of the two major controls and modifiers such as hydrostatic gradients is still evolving.
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Construction and validation of an integrated 3D geomodel for reservoir characterization – case study, offshore Angola
Authors Antonio Kaschaka and Idima PimentaWM field, offshore Angola produces significant quantities of oil from sandstones of the Upper Cretaceous Vermelha Formation. This sequence of mixed carbonate and interbedded siliciclastic sediments was deposited as a transgressive-regressive barrier island system. Approximately 97,5 m of conventional whole core was examined in order to define depositional facies and understand their relationships. Three principal facies were recognized: (1) inner shelf to shoreface sediments characterized by bioturbated, argillaceous, dolomitic siltstones, very fine-grained sandstones, and silty/sandy dolowackestones; (2) beach/barrier bar complex ranging from well-sorted, very fine-to fine-grained to poorly sorted, very fine-to very coarse-grained subarkoses and arkoses commonly containing planar cross-lamination; and (3) lagoon and tidal-flat sediments composed primarily of argillaceous dolomudstones and wackestones punctuated by dolomitic sandstones.
This integrated study used geophysical, geologic, and engineering data simultaneously to guarantee the accuracy in the models to be used for simulation purposes on a well by well basis, for matching the past dynamic performance, and to investigate the future reservoir management strategies such as remaining hydrocarbon reserves estimates, better understanding of water conformance, and to minimize the risks on implementing new production wells.
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Incorporating Seismic Constraints into High-Resolution Geologic Models
More LessWell data alone cannot accurately recover the requested property variations, because of their sparse lateral distribution and their large spacing, compared to the size of the lateral heterogeneities to be modeled. On the opposite and despite its poor vertical resolution, seismic data provide valuable information to overcome such a limitation as it benefits from the highest lateral density of information. Accurate descriptions of the lateral variation of reservoir heterogeneities is a critical issue when generating reservoir models dedicated to history matching and sub-sequent production forecasts.
This paper describes one of the workflow that has been successfully applied on a turbidite field in Angola, which allows (1) extracting reliable constraints from post-stack seismic amplitudes and (2) incorporating them into high-resolution geological models.
Relevant constraints are generated using seismic reservoir characterization techniques, based on seismic inversion followed by seismic facies analysis and generation of net-to-gross maps. Then, for geological modeling, we chose a pluri-gaussian modeling technique, which provides the requested level of flexibility for mixing the obtained map with well data and thus solving the downscaling issues.
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Saturating pore fluid Bayes Indicator for reservoir mapping
More LessA seismic-based reservoir properties estimation is implemented and tested in this work. The main goal in this work is to map oil saturated sands based on a sandshale oil field system. We consider petrophysical measurements as source of information to construct a conditional probability density function (PDF) for water saturated sand and a conditional PDF for oil saturated sand. Using these PDFs’ and seismic attributes from a reservoir cell, we compute the probability for water saturation given the attributes and the probability for oil saturation given the attributes. From these probabilities and following a Bayesian criterion we create an indicator for saturating fluid to this cell and the associated Bayes error. We analyze each reservoir cell to create a map for oil saturated indicator, water saturated indicator and the associated uncertainty. Several seismic attributes are analyzed in this work and using the maximum entropy measured from these PDFs’ we decide the most informative attributes and attribute pair to reduce uncertainty. In the current time, the methodology was successful tested in well log data. Our next step is to test the methodology with seismic attributes and apply the methodology in a real situation.
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Reservoir characterization using high frequency seismic data in Roncador, Campos Basin
Based on a detailed mapping of surfaces and faults (accomplished with high resolution seismic) and the use of seismic attributes, geological models are constantly updated, to better estimate reservoirs spatial distribution and their petrophysical properties at Roncador (Campos Basin). Such models are used in fluid flow simulations. The results present significant improvements on detailing the characteristics and properties of reservoirs compared to conventional seismic data. Also, a brief discussion about resolution and detection is included.
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A Bayesian approach for lithofacies identification and classification
Authors Igor L. S. Braga and Luiz Geraldo LouresThis work introduces a methodology for lithofacies identification and classification following the probabilistic theory of pattern recognition. This methodology applies the Expectation Maximization algorithm to identify lithofacies in the learning stage. This unsupervised learning process is applied to well log data to identify lithofacies. Uncertainty analysis is performed to predict the classification success and the Bayesian decision theory is applied to classify new incoming data. This methodology was tested in well log data. The results achieved are interesting enough to extend the methodology to seismic resolution to classify lithofacies in the inter-well zone using seismic attributes.
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Vertical Seismic Facies Detection Through Unsupervised 3D Voxel Based Seismic Facies Classification Applied to a Turbidite Field in Campos Basin, Brazil
Authors Marcílio C. Matos, Paulo L.M. Osório and Paulo R.S. JohannWe propose to use the 3D voxel based unsupervised seismic facies classification to identify vertical facies variations within a turbidite reservoir. The technique was applied to a real data from a deep water field in the Campos basin, Brazil, and the results were compared with other classical facies analysis method, with similar results.
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Sensitivity Analysis in Various Inversion Schemes for evaluating Saturation and Pressure changes in the Context of 4D seismic studies
More LessHere, a sensitivity analysis on saturation (ΔS) and pressure (ΔP) variations due to uncertainties in the input parameters of several inversion schemes is presented. In this sense, input parameters can be classified with respect to how their uncertainties impact the value of estimated inverted parameters, all of which depend on reservoir thickness, or stage of production, and the particular inversion scheme considered. In this sense, the possibility of diminishing uncertainties in the predicted values of ΔS and ΔP is tied to the feasibility for discrimination of the critical input parameters, as sources of uncertainty for the inverted indicators (ΔS and ΔP). This way, it would be possible to concentrate efforts in obtaining reliably the important inputs for inversion.
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INTEGRATION OF TECHNOLOGIES FOR IMPROVED RESERVOIR RECOVERY
More LessThere are several options in the industry today when considering the technologies to be used in a seismic program. Consideration must be made when designing the survey, the acquisition technique to be used and what technologies to apply that ultimately result in improved recovery from the objective(s). These technologies include not only the traditional towed streamer arrays, ocean bottom cable systems and ocean bottom autonomous nodes, but also as to what type of seismic source, sensors, source/receiver positioning techniques, quality control processes and methodologies and even the personnel assisting with the survey operations. Attention to these details must start in the initial planning stages and be implemented during the survey acquisition and data processing, through product deliveries. These processes will involve several disciplines within and outside the geophysical community. Integrated discussions are ongoing, which will in due course, improve probabilities for improved recovery.
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Interpretação Inteligente de Perfis de Produção
More LessProduction Logging can be interpreted in intermittent wells using the intelligent analysis program presents in this work, called PAINTWELL, which permits to use of same string configuration than a conventional Production Loggging. This program can be performed in layered reservoir, determining the flowrate and type of the fluid for each production zone. The use of Artificial Neural Network as integrated part of this analysis program, provides a powerful tool to describe how downhole logging and advances in computer processing and interpretation data could spearhead the transformation that can take place in production logging with use of this new technique. This methodology should aid the production and reservoir engineering to solve recovery problems during the well life. The results of the production log using the PAINTWELL method is very similar to measurements using test separator in production facilities for each single perforated interval. This program was applied successfully for an typical intermittent well on Maracaibo Lake basin, in Venezuela, which produces oil with high water cut using a gas-lift completion system.
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High resolution 4D-friendly analysis: application to gas-oil contact monitoring at Troll West
Authors Alexandre Bertrand, Sean McQuaid, Roman Bobolecki, Sture Leiknes and Hans Egil RoA new workflow automatically providing high-resolution 4D-friendly attributes is applied to the Troll West Gas Province datasets (offshore Norway) to monitor the movement of the gas-oil contact. It consists in generating attributes of velocity and amplitude changes using enhanced resolution imaging and morphing. Morphing is used to remove velocity or noise-induced traveltime differences between the vintages, resulting in a 4Dfriendly difference which reflects more genuine changes of amplitude. These attributes are used to train a neural network scheme for estimation of gas-saturation changes and quantification of the gas-oil contact movement. The analysis shows coning along the tracks of a number of multilateral wells and identifies undrained volumes for infill drilling.
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Steam injection monitoring with high resolution time lapse seismic
Authors Marco Schinelli, Selma Sacramento and Odilon KellerThe challenge to produce parafinic oil from shallow sandstone reservoir in the Fazenda Alvorada onshore field, located Northeast of Reconcavo Basin, led to the option of using steam injection as a secondary recovery process. In 1994, a project was designed to introduce the 4D seismic technology in Petrobras and at the same time to evaluate the efficiency of that recovery process. Petrobras opted by monitor the injection using for the first time high resolution time lapse seismic. Geophones with 60 Hz resonance were used instead of conventional 10 Hz in the sucessive acquisitions. Circumstantial reasons led to almost 5 years interval between the successive surveys what increased the difficulties to the project. This work will focus on some aspects related with acquisition, processing and interpretation of that 4D project.
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Improving 4D Seismic Data Interpretation using Geostatistical Filtering
More Less4D Seismic is becoming a conventional tool for hydrocarbon reservoirs monitoring and management, especially for heavy oil bearing fields (Calvert, 2005). In this case, 4D, or time-lapse seismic, can be used to detect important reservoir properties variations imposed by thermal enhanced oil recovery processes. This work aims at identifying remaining noise, invariant common features and time-dependent variations in oil reservoirs from post-stack amplitude time-lapse data. It involves a geostatistical multivariate technique called factorial co-kriging, an extension of the factorial kriging (FK) technique proposed by Matheron (1982). It is based on the decomposition of spatial correlations to identify redundant structures at various scales. Three seismic surveys, with different acquisition parameters, were acquired at the same site in different calendar times to monitor the progress of injected steam fronts into a heavy-oil reservoir. These seismic volumes were then carefully processed to minimize their discrepancies. Factorial co kriging revealed possible common geological structures, 4D effects and remaining noise, and it seems to be an efficient method for extracting common regional trends from several repeated seismic datasets.
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Time-Lapse Feasibility Analysis for a Brazilian Offshore Field: Target on Saturation and Pressure Changes Interpretation
Time-lapse feasibility study is not only the first step to validate a 4D campaign; it is also an essential tool for the interpretation of the acquired seismic volumes. In this paper we present a practical example of feasibility study for a Brazilian offshore reservoir to illustrate the main issues and benefits of feasibility analysis. Our goal is to emphasize which information may be accessed with the feasibility analysis, as well as the uncertainties and nonuniqueness in time-lapse feasibility and interpretation.
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ATUM Field: 4D QUALIFICATION OF 2 SEISMIC VINTAGES USING GEOSTATISTICS
Authors L. Sandjivy, C. Magneron, C. Formento and Odilon Keller4D spatial diagnostic and geostatistical filtering (factorial kriging) were applied to the 1987 and 2003 seismic vintages acquired on the PETROBRAS RN Atum field. The goal was to evaluate the suitability of these seismic data to highlight 4D production effects. A spatial analysis (controlled by frequency power spectrum) and factorial kriging were used to quantify and suppress the noises and acquisition artefacts in both data sets in order to improve the 4D repeatability. After spatial filtering, the measured coherency (both vertically and spatially) between the two cubes was largely improved but major amplitudes differences still remained due to the different acquisition parameters: streamer in 1987 and ocean bottom cable conventional in 2003. Consequently, the data were not qualified as such for a further 4D study: Instead, dedicated spatial filters controlled by geophysical frequency spectrum were derived to enable comparison and further amplitude equalization of the data sets. The filtered results are currently being used to increase the confidence level on structural interpretation of both seismic data sets.
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Repeatability issues of time-lapse marine seismic data
By Ola EikenRepeatability is a key issue in seismic monitoring, as it defines the noise threshold which a time-lapse change needs to exceed. Good measures of repeatability are non-trivial to define, and while NRMS (Normalized Root Mean Square) is widely used today, more than one parameter is needed to describe various aspects of the data. The background noise level and horizontal positioning variations are basic causes of non-repeatability which need to be controlled in data acquisition. Source- and receiver positions may be controlled by towing many streamers in parallel and having overlapping swaths, by keeping the source on a pre-defined line, and by laterally steerable streamers. Timing variations, caused by water layer variations, may be corrected for by data dependent matching, provided the position variations are not too large. Optimizing the choice of sampling parameters, as streamer separation, number of streamers, amount of swath overlap, cable steering or not, may be guided by repeatability modeling. A simplified scheme taking the statistical distribution of position variations into account is suggested.
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Estimativa de porosidade e saturação a partir de dados sísmicos 4D
More LessWe present a methodology for porosity and saturation estimation from a 4D P wave impedance data using bayesian probability theory. The proposed methodology is tested on synthetic data, considering two different states of knowledge about the reservoir at legacy data (pre production). We first assume that the initial saturation (Swi) of reservoir is well known. In this case we can infer the porosity values from the legacy data and water saturation from the monitor data, assuming that porosity is not changed due to production. In the second case, we assume that exists some degree of uncertainty about the initial saturation. For this case, we introduce an attribute called “porosity perturbation”, exploring the strong coupling which exists between porosity and saturation. Porosity perturbations can be computed using any reasonable reference state of initial saturation to yield an indirect measure of saturation changes over the reservoir. This approach is applicable to situations where both porosity and pressure do not vary significantly.
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Contextualizando a importância da repetibilidade na sísmica 4D
More LessPetrobras is beginning its 4D seismic investments in Brazil. As this is yet a non-disseminated technology in our company, common sense leads us to study and try to reproduce the successful experiences of other oil companies worldwide. North Sea is the oil province where are the major 4D seismic investments in the whole world, with very high incomes. As everybody knows, Statoil (Norway) has continuously contracted 4D seismic acquisitions for many oil fields. Its success is due, mainly, to the high repeatability level in successive acquisitions for a certain field, what was essential in obtaining a high quality 4D response. When learning with this experience, it’s important to have in mind the geological and geophysical characteristics of that basin, as well as sea conditions during the North Sea acquisition season. The objective of this paper is to relate the importance of repeatability in 4D seismic to the peculiarities of oil fields to be imaged, in order to point the differences between North Sea (Norway) and Campos Basin (Brazil) and to suggest a strategy adapted to the reality of this brazilian basin. For optimization of investments in seismic acquisition, the suggestion is to perform feasibility studies that take into account petrophysical and seismic aspects as well as operational limitations and costs related to obtaining a high repeatability level.
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Inferência Bayesiana da saturação
Authors Raquel G. Teixeira and Luiz Geraldo LouresThis methodology was developed following the Bayesian methodology of inferece and seeks for an fluid indicator for the pore fluid and an associated quality meassurement. The sources of information are well log data and seismic attribut data. This article presents the theorectical background and results from tests using a set of well log data.
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Assessment of rock quality classification based on Principal Coordinates Analysis of conventional petrophysical and NMR data
More LessThis paper shows how principal coordinates analysis, PCO, can contribute to asses the correspondence between porosity, permeability and the ratio of moveable fluid over bound fluid volumes data and the rock quality classification of water saturated core plug samples. The rock quality characterization of the samples from El Furrial field in eastern Venezuela is based on the determination of the Winland-Pittman equation of the port size. This characterization, taken from the literature, is based on NMR measurements of water saturated core plugs samples. The results show that a plot of the first and second PCO yields a characteristic horse shoe curve (2D), or a more accurate spiral curve (3D) by taking also the third PCO (3D) into account. The trajectory of these curves follows a continuous variation in the rock quality of the samples, from Megaporosity down to Nanoporosity. This procedure represents an easy, non-destructive way to obtain a rock quality classification based on conventional and NMR derived petrophysical variables and PCO.
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Dry Rock Elastic Moduli Behavior with Pressure
More LessThe knowledge of the pressure dependence of dry rock bulk and shear moduli is essential in time-lapse seismic studies, both on the feasibility and on the interpretation of 4D results. This behavior is accessed only through experimental determination, and there are many different regression laws proposed on the literature to represent it. We had compared the effectiveness of a set of different laws on large data sets of dry rock velocities measured on the lab. In this paper we focus our attention in three of these laws that are widely used on time-lapse and also seems more reasonable than other relations often applied.
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Saturation and pressure inference from velocities and density
Authors Fernando Moraes and Colin MacBethWe present a Bayesian formulation for the inference of saturation and pressure from seismic attributes, using Gassmann’s equations in connection with a dry frame pressure sensitivity law. Laboratory data is analyzed for the most representative pressure sensitivity parameters. A 1D inversion example on synthetic data illustrates how the methodology works.
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Effective design for full-wave three-dimensional land and marine seismic surveys
More LessWhile many of the same basic principles apply, designing full-wave 3D seismic surveys is considerably more complicated than designing conventional P-wave 3Ds or even pure S-wave 3Ds. With faster down-going (P-wave) energy and slower up-going (S-wave) reflections, common midpoint analysis fails for converted wave data. These data must be analyzed in the common conversion point (CCP) domain. Since Vp/Vs ratios vary with depth and lithology, estimating converted wave fold coverage depends strongly on knowledge of the subsurface geology. Because of the asymmetry of converted wave ray paths, a survey design that acquires uniform P-wave (or S-wave) fold coverage will result in non-uniform converted wave fold coverage. Filling gaps and reducing variability in the CCP fold coverage can be a complex exercise. Several land and marine (OBC/OBS) survey design types (wide and narrow azimuth, orthogonal and parallel, slant and variable line spacing) are examined using different bulk Vp/Vs ratios for estimating converted wave fold coverage for targets at different depths. Additional comparisons are conducted using converted wave ray tracing through a layered model with variable Vp/Vs ratios. Due to offset mutes, shallow fold coverage is more difficult to acquire in all 3D survey design problems and requires denser source and receiver line spacings. Because of the asymmetry of ray paths for converted wave data and the typically high Vp/Vs ratios encountered in shallow sedimentary sequences, this shallow imaging problem is even more dificult for converted wave data, requiring even higher density receiver line spacings on the surface. Slanted shot lines and variable receiver and source line intervals will help to reduce CCP fold variations. Wide-azimuth survey designs will allow more subsurface overlap and will improve the cross-line fold coverage of converted wave surveys. For the purposes of this paper, full-wave 3D survey design will focus on P-wave and converted-wave (PSwave) acquisition. The main design factors involved in including the pure S-wave ray paths would be the addition of shear wave sources in orthogonal polarizations.
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Desafios, técnicas e equipamentos utilizados em levantamentos sísmicos terrestres recentes na bacia do Espírito Santo
More LessIn the Espirito Santo basin, the seismic data shows very good response, mainly when compared with another Brazilian land basins. In spite of this, many times the stacked data presents a characteristic low quality aspect, because the seismic parameters used in acquisition or the physiographic features that restrict the work in the surface (lakes and swampy areas). Considering the requirement for better seismic data, including that unavailable data like in lakes, the land seismic acquisition activities in the Espirito Santo has incorporated the technologies from the transition zone acquisition crews and used different planning and designs. In the last year (2004), a new seismic acquisition took place in the BT-ES-22 block, where was chosen a new field layout different from the normal one used by Petrobras (the swath field layout is normally applied). In this way, a non-orthogonal field layout was used – with receiver lines in a forty-five degrees angle from the shot lines – and with parameters defining a 20x20 meters square bin. And taking advantage of hydrophones, air guns and transition zone tools, it was possible to accomplish the acquisition in all over the area of BT-ES-22, including lakes and swampy areas. The seismic data displays a better quality than the ones acquired in previous projects, mainly considering the high frequency content, azimuthal distribution, nominal fold and bin shape and size.
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Get to the Point – Seismic Data Acquisition for Full-wave Imaging
Authors Paul Brettwood, Marty Williams and Cara KigerSince the earliest use of seismic data in hydrocarbon exploration, geophysicists have primarily concerned themselves with the apparent direction and speed with which the waves travelled through the earth. They effectively focused on the P-waves and treated the shear and near-surface waves as noise that need to be removed.
Full-wave imaging questions this conventional approach, as geophysicists now realise that a rock particle’s behaviour when a seismic wave passes it reveals new information about the subsurface. This is in part due to the fact that the rock particles do not necessarily appear to move neither in the same direction nor with the same velocity as the passing wave.
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Optimized AVO analysis by using an optimal linear approximation
Authors M. Riede, E. Causse, A.J. van Wijngaarden, A. Buland, J.F. Dutzer and R. FillonWe propose a method, namely OptAVO to build enhanced linear AVO approximations. The basis functions of the approximation are orthogonal and their coefficients represent a new set of AVO attributes. These attributes can directly be used for AVO classification or to obtain better estimates of the usual coefficients (e.g., intercept, gradient). The method will be illustrated for class I reflectors using large reflection angles. A real data example shows the applicability of the proposed approach.
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Diagnosis of “fizz-gas” and gas reservoirs in deep-water environment
Authors De-hua Han and Michael Batzle“Fizz-water” or “Fizz-gas” is a rather ill-defined and misused concept. For some, it refers to gas in solution with brine; for others, it is defined as small amounts of free gas phase. This small, uneconomic gas content then gives rise to seismic bright-spots or other Direct Hydrocarbon Indicators (DHIs). Unfortunately, it is often the culprit of choice when no other reason can be found. However, progress has been made in assessing the problem. We have systematically examined physical properties of fluid and rock, and fluid interaction with rock to examine gas saturation effect on acoustic velocities, especially in deep-water sands of the Gulf Mexico . Furthermore, we have reviewed the current AVO and Rock physics interpretation techniques to propose optimum DHIs. Several promising techniques of seismic evaluation of gas saturation are in development.
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On the Inversion of Seismic Amplitudes for Lithology, Fluid and Pressure Analysis
By N. C. DuttaReservoir description using seismic data has two major components: inversion of seismic data to extract attributes such as P- and S-wave velocities and bulk densities, and relate those parameters to reservoir properties, such as rock and fluid types, fluid saturation, porosity and pore pressure through fundamentals of rock physics. Implicit in the process are two key as-sumptions: the seismic data quality must be good enough for inversion, and the inversion algorithm must be robust and fast enough to yield reliable and consistent results economically with acceptable non-uniqueness. We have seen much progress in both areas. In seismic acquisition, we have seen considerable advancement that contributed to the quality of the seismic data, especially in the prestack domain. These are: single sensor recording (a large number of channels/offset), accurate and cali-brated source and receivers and their positions, digital group forming, and towing cables at shallow water depths to minimize swell noise. All of these enable us to access surface seismic data with high S/N and fidelity that often rivals the fidelity of the Vertical Seismic Profiles (VSP). Seismic inversion algorithms also reached new heights. The advent of high-speed digital data processors and cluster technology impacted significantly the performance of various inversion algorithms; we are now inverting routinely seismic data in the full offset domain and just not restricting ourselves to the stacked data.
In this paper we discuss the advances in seismic inversion technology that utilizes the amplitude information along with data consistent velocity analyses. First, we briefly review the basic assumptions behind the AVO, EI and full waveform inversion techniques in the prestack domain. While the users of the AVO and EI technology have focused on carrying out inversions using “large angle” assumption- presumably for extracting bulk density information, we show that this may not be feasible due to the neglect of various physical effects, such as interbed multiples, mode conversions and reflection and transmission losses which are omnipresent.
Full waveform prestack inversion (FWPI) is currently the highest level of inversion technology in the industry. Unlike prestack inversion methods such as AVO, the FWPI technique uses a finite-difference elastic model to compute the entire seismic waveform. This provides an advantage over AVO methods in capturing thin-bed effects in data and increasing the potential resolution of the process. The process is computationally intensive and discussed in detail by Mallick (1999). Rock physics-based constraints are applied to speed convergence as well as to reduce ambiguities. Nonetheless, results from this as well as any non-linear inversion process tend to be sensitive to the quality of the a-priori model. However, given a good rock physics model and a-priori information, the output resolution exceeds that produced by other inversion techniques. We have also found that the ambiguities associated with the inversion process can be further reduced if the prestack data has high S/N.
The FWPI technique is computer intensive. Currently this is used in the 1D mode to create pseudo-logs of Vp, Vs and density at selected points in a 3D data volume. These pseudo-logs are then used in the hybrid inversion technique (Mallick (1999) to propagate the benefits of FWPI inversion over 3D volumes. In its current form, hybrid inversion involves computation of pseudologs from full-offset seismic data at selected pilot points in the 3D volume using the FWPI technique, as well as AVO p-intercept and pseudo-shear data over the entire volume. Shear-wave output from FWPI pilot points are used to calibrate the AVO pseudo-shear data. Then both p-wave and pseudo-shear data are independently inverted using a poststack algorithm. Poisson's ratio and other elastic attributes for lithology discrimination are computed from the poststack inversion results. The hybrid inversion process requires input of a 3D a-priori model and a geologically consistent rock physics model, calibration of 3D attribute volumes, and interactive 3D visualization.
We illustrate the entire procedure with examples from several basins.
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Current status and future trends in seismic lithology and fluid prediction
More LessWe present cutting edge techniques for lithology and pore fluid prediction from pre-stack seismic amplitudes, by combining statistical techniques, geological constraints and rock physics models. A promising tool for early exploration detection of reservoir lithologies and hydrocarbons is to do AVO classification constrained by depth trends. We show a blind-test from an offshore Brazil discovery where the method successfully predict the presence of oil.
Another rock physics tool for seismic reservoir prediction, useful for late stage exploration and production stage oil fields, is the rock physics template (RPT) technology. This technique can be used to classify elastic seismic inversion results.
Finally, we summerize what we foresee as the future trends in rock phyisics and seismic lithology and fluid prediction. There is a clear trend of more sophisticated inversion routines (3-term AVO and full-waveform inversions) as the computer intensivity increases. Also, there is a trend of more integration of disciplines like geology, statistics and physics both in modelling and interpretation. Attenuation and frequency attributes will be increasingly important especially in gas fields.
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Kirchhoff modeling and migration in weakly anisotropic medium using the pWFC (perturbed WaveFront Construction method)
Authors Alcides Aggio and Rodrigo Portugal and Eduardo FilpoThe presence of velocity anisotropy in the layers or in the overburden leads to mispositioning of reflector structures and degradation the image quality, when an isotropic migration processing is performed on seismic data. These distortions occur even for weakly anisotropic layers, which are the most common type of rocks in geologic models for seismic applications. In this paper we present a method where a first-order perturbation is applied to the wavefront construction algorithm which generates a traveltime table that fits the traveltime of a weakly anisotropic medium with arbitrary of symmetry. We call this method the perturbed WaveFront Construction (pWFC). These traveltime tables are used in traditional Kirchhoff modeling and migration algorithm. The pWFC allows an approximated computation of traveltime tables for weakly anisotropic medium efficiently, avoiding a more intensive computation by a full anisotropic ray-tracing algorithm. To illustrate the difference when considering or not weak anisotropy in the seismic processing, two common-offset (100m and 1100m) data were modeled using WFC isotropic and using pWFC method. The 1100m dataset was migrated twice using a Kirchhoff algorithm once using an isotropic traveltime tables and the other a traveltime tables computed by the pWFC method.
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Variações da metodologia de micronivelamento de Minty em dados aerogeofísicos no domínio do espaço
Authors Mariana V. Maziviero, Rodrigo S. Portugal and Adalene M. SilvaO método de Minty (1991) vem sendo utilizado extensivamente para micronivelamento de dados aerogeofísicos no domínio do espaço, 1-D. No entanto, este método possui algumas limitações, que motivou a remodelagem desta rotina utilizando diferentes filtros. Estes filtros foram testado exaustivamente em um levantamento aerogeofísico a fim de verificar as características dos resultados finais (dado micronivelado) e possibilitando uma comparação entre eles.
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Estimativa de parâmetros elásticos anisotrópicos efetivos a partir de perfis geofísicos de poços: Aplicação ao reservatório Namorado, Bacia de Campos
More LessThe sedimentary package associated to the Namorado reservoir, in Campos Basin, can be represented by a layer-induced anisotropic interval. In this contribuition, we determined, for the corresponding reservoir, the elastic matrix associated to a transversely isotropic medium with vertical axis of symmetry. We used the so-called Backus averaging to calculate the density-normalized stiffnesses from bulk density and shear and compressional sonic well logs. To assess the strength of anisotropy in the Namorado sedimentary interval, we also calculated Thomsen’s parameters ε, γ and δ. The calculation of these measures of anisotropy confirm the expected values for sedimentary rocks to which weak anisotropy is associated.
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Propagação de ondas SH em meios monoclínicos
A monoclinic media, inside of the limits of the linear elasticity, has a specular plan of symmetry. The propagation in this plan is the case most general of propagation of elastic wave in an anisotropic media for which, a purely cisalhante deformation and normal to the plane of propagation can occur in all the directions. When this plan is vertical, these purely cisalhantes waves are waves SH and so that its propagation is possible, the media must have a vertical plan of specular symmetry and the propagation must be given in this plan. This work investigates the effect of the anisotropy on scale SH waves and that information on the anisotropy can be extracted of these effect. The analysis made here, for more general anisotropic environment where these waves exist, is sufficiently simple and produces some results surprising.
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Amplitudes e padrões de polarização do espalhamento de pulsos em meios anisotrópicos
More LessTo extract lithological information from subsurface by means of a survey of seismic data has become a great challenging in relation to a seismic research because of the lack of insufficient hypotheses of stratification made by isotropic layers, which should represent through surveys the behavior of elastic field with great offset between source and receiver, geophones multicomponent data, measures of three-dimensional vertical seismic profile (VSP) and so forth. For this reason, a pattern of subsurface has been demanded in order to be adequated to this new reality. As a result, the seismic prospecting starts considering the presence of anisotropy, so the anisotropic pattern of subsurface is the one which is closer in of supra named surveys. In special, for the seismic survey in relation to the reservoirs characterization, the anisotropy that is induced by fractures is the one that is more similar to the needs and it is widely referred in the literature. This paper aims at showing formalism to modeling the scattered of pulses from incident plane waves occurred in horizontal plain interface which separates anisotropic layers. This scatter is obtained through clear formulation of traction deformation fields as function of propagator, polarization and impedance matrixes of media, this formalism will be later used to obtain the of transmission and reflection coefficients matrixes through a horizontal plain interface and, finally, it is generalized to a scattering through multiple layers. Doing that, it is possible to calculate the pulse scattering through layers after we insert the amplitude of analytical pulse to an incident wavefield.
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Aumentando o limite de visibilidade de dados sísmicos 3D em reservatórios de águas profundas com detalhes estruturais e estratigráficos
Authors Rogério de A. Santos, Márcio Spínola and Ricardo R. P. AlvesThis work attempts to show some aspects of 3D-seismic reservoir characterization using seismic attributes in a presence of channel-lobes turbidite play located in Brazilian passive Margin. Some attributes were selected and combined to extract qualitative information on subtle faults and its relationship with stratigraphic and depositional systems. Some latest industrial algorithms for attribute calculation, 3D image processing and detection of subtle structural features were applied. Recommendations on workflows and selection of 3Dseismic attributes during a seismic reservoir characterization study were suggested, which the choice of the kind of seismic attribute to be used will intrinsically depend on the quality of the data, initial seismic processing to recover the signal quality , the geological knowledge of the particular area, the kind of geological features and associated geometry as well as the knowledge of the attribute itself to be used for enhancement and detection. All these aspects have impact on the economic
uncertainty for field development because it can produce deviation on the predicted production curves and NPV of some deep water exploitation projects.
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APLICAÇÃO DE TÉCNICAS DE TEMPO FREQÜÊNCIA PARA A DETECÇÃO DE CAMADAS DELGADAS
More LessA new alternative method to characterize thin beds is presented here. We propose to use the ridges of the joint time-frequency analysis, as a new way to detect the instantaneous frequencies and their associated amplitudes, in each trace, and then to use them as a tool to detect thin beds. The technique was applied to a synthesized wedge model and also to a thin bed offshore turbidite reservoir in Campos Basin, Brazil.
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Using Seismic Attributes in Facies Distribution for Reservoir Models
More LessWe describe a workflow that was successfully applied on two case studies in the Campos basin, southeast Brazil, to allow (1) the extraction of reliable geological information from multivariate seismic data, and (2) to incorporate this information as a constraint into highresolution geological models. This paper focuses on the first part of this workflow (extraction of a meaningfull seismic constraint).
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Application of S Transform in the Spectral Decomposition of Seismic Data
Authors Mauren Paola Ruthner and Adelson S. de Oliveiraidentification of stratigraphic features, especially in the characterization of thin reservoir. However, Spectral Decomposition is based on the windowed Discrete Fourier Transform, which provides a less optimized time-frequency analysis.
The S Transform differs from the windowed Fourier Transform in the adoption of a window model whose width is adjusted to the frequency that is analyzed. This confers the S Transform properties similar to those of wavelets Transforms in terms of time-frequency resolution.
This paper presents results of the application of the S Transform to the spectral decomposition of synthetic and real seismic data.
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Automatic Fault Extraction Using Ant Tracking Algorithm in the Marlim South Field, Campos Basin
More LessThe main objective of this paper is to present a comparison between manually interpreted faults and automatically generated fault surfaces using an innovative workflow recently introduced in the geophysical community. The manual fault interpretation performed in an area of Marlim South Field at Campos Basin, located offshore the southeastern Brazilian coast, took 10 days of work, during which a geophysicist delineated the main regional faults. On the other hand, the automated fault extraction approach allowed the interpreter to perform the same task in 3 days. The results showed a good match between the manually and the automatically interpreted faults. The Ant Tracking attribute was significantly helpful for the identification of the fault framework and the extraction of the fault surfaces for later editing, analysis and filtering.
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Princípio da SismoCamada Elementar e sua aplicação à Técnica Volume de Amplitudes (tecVA)
Authors Élvio M. Bulhões and Wander Nogueira de AmorimA SismoCamada Elementar (SCE) ou camada de rocha de menor espessura que o dado sísmico consegue resolver é aqui definida como o elemento chave de ponderação para o cálculo e obtenção do dado sísmico com a técnica Volume de Amplitudes (tecVA), com processamento sísmico pós empilhamento, com e sem rotação de fase.
Sendo assim, apesar da robustez dessa técnica, quanto maior for o grau de fidelidade na tomada dos valores dessa SCE para determinado dado sísmico, maior será a resposta geológica, litológica e estrutural, advinda do dado sísmico tratado.
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Análise de sensibilidade das aproximações parabólica e hiperbólica do tempo de trânsito do método de reflexão sísmica
Authors C. C. C. and C.C.C. LimaIn this paper we present a sensitivity analysis of the parabolic and hyperbolic double traveltime surfaces for a model formed by homogeneous and isotropic layers with curved interfaces. The model is described by the paraxial ray theory, where the normal ray is taken as the zerooffset trajectory. The sensitivity analysis is performed on first order derivatives of the parabolic and hyperbolic traveltimes with respect to each one of the wavefront parameters: (1) the emergence angle of the normal ray (b0); (2) the radius of curvature of the normal-incidencepoint wave (NIP wave) (RNIP); and (3) the radius of curvature of the N wave (RN). In this analysis we look for to indicate a relationship between linear and non-linear parts of the optimization, the relative participation of the close-in to the distant data in the inversion problem, as well as to show that to reach the semblance minimal (or maximal) needs few iterations in the optimization process.
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Combined seismic attributes to recognize the architecture and evolution of turbidities- Marlim Sul field, Campos Basin, Brazil
More LessThis method was employed on studies of reservoirs in Marlim Sul field located in Campos Basin, Brazil. It takes account two simple seismic attributes, minimum amplitude of one surface and acoustic impedance of one time interval between two surfaces. However, both attributes are combined to allow volumetric visualization of sand bodies and recognize the geometries e genetic relationships besides the evolution of reservoir system of turbidities .
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Identificação de reflexões múltiplas utilizando os parâmetros das frentes de onda PIN e Normal
Authors João Carlos R. Cruz, Pedro Chira-Oliva and Francisco J. M. de SouzaThe multiple reflections included in the seismograms hide informations important about the reflectors in subsurface and can become completely invisible. Especially in marine data acquisition, the water layer often behaves as a wave trap and the waves are repeatedly reflected at the sea surface and sea bottom without significant amplitude loss. In order to identify and locate a target reflectors, these multiple must be eliminated or, at least, attenuated. In this work, the interbed symmetric multiple reflections were identified in synthetic datasets. We compare the parameters of hypothetical wavefronts Normal-Incidence- Point (NIP) and Normal (N) obtained by forward modeling and Kirchhoff migration. This comparison was extended to consider the Normal-Moveout (NMO) velocity. These comparisons let us to identify and differentiate between multiple and primary reflections.
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Using band-tridiagonal preconditioners for 1D seismic waveform inversion
Authors Milton J. Porsani and Saulo Pomponet de OliveiraGeophysical inversion is quite a challenge. Many different methods and strategies have been developed in the past decades. Global methods like simulated annealing and genetic algorithms do not depend on an initial model, although they may be time consuming using a huge number of fitness evaluations. Local methods such Gauss-Newton require a ’good’ start model and may be not convergent to the global minimum of the objective function. In this paper we evaluate the use a band-tridiagonal preconditioner in the multiple reweighted least square inversion method (MRLS) to the seismic waveform inversion. The MRLS inversion method is a type-gradient method that generates many candidate models for each sensitivity matrix, exploring the model space in a very effective way. A numeric example shows that the inverted model has better fitness and may be obtained with less computational CPU time, when compared to the results given by the Gauss-Newton approach.
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Deconvoluçao de volume sısmico 3D utilizando norma Lp
Authors Paulo E. M. de Melo and Milton J. PorsaniWe present some results obtained with a new method of iteractive deconvolution applied to 3D seismic volumes. A sub-set of seismic traces of the original volume is deconvolved with the iteractive method and the result is used in the estimation of a non-causal filter which is applied to the whole remaining volume. This procedure was applied to a maritime 3D pos-stacking seismic volume (demo VoxelGeo PARADIGM) and it showed itself to be quite effective and efficient in computational terms. Events associated to the deconvolved 3D volume translate the increase in temporal resolution of the XT panels.
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Determination of reservoir features by using the Prony filtration and Log-parameter ratios
The Prony filtration method provides a high resolution in study of frequency variations for media response. It allows us to analyze the production horizons features for short time intervals. The analysis is based on the general dynamics Prony parameters, which characterize the frequency variations for each of the time intervals. The parameters can be used for the determination of wells the parameters when a ratio between these parameters and Log-data is available. We discuss two examples of application of the dynamics Prony parameters for prediction of target horizons features. The obtained results show high potential of this technique for the analysis of thin layer objects.
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Calibração do Fluxo de Processamento: Um Enfoque na Análise Espectral
More LessHaving in mind the increasing claim for high-resolution images from subsurface and knowing that new methods and algorithms are being developed to get around this problem, we present and discuss in this paper a processing flow created by the free package data processing. By this processing flow, which is addressed to the application of pos-stack migration and the method Wave Analogue of The Common Depth Point (WCDP), comparisons were made about the images from subsurface obtained, coming to conclusions about the application of the processing flow to the quality of the results obtained. Besides that, it has been trying to provide a processing routine that can relieve futures researches, especially in scientific community, where the application of the seismic processing tool is needed.
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Noise attenuation for Common Hydrophone Gathers
Authors Gary C. Aldunate and Flor A. VivasThis work shows how the noise present in 2-D prestack marine data sorted in Common Hydrophone Gathers (CHG) can be attenuated via FX deconvolution. Three ways to solve the Hermitian Toeplitz matrix in the FX deconvolution codes were tested and compared as well. The unitary complex prediction Wiener filter FX, is calculated directly from LU decomposition and iteratively by Levinson and Gradient Conjugated recursion, in frequencyspace domain. FX filtering in the CHG domain can avoid the muting of noisy traces in the edition process.
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Empilhamento SRC-2D: Comparação entre as estratégias de busca SRC pragmáticaextendida e global-local
Authors Paschoal Jr, W. G. and G. GarabitoThe seismic imaging method called Common-Reflection- Surface (CRS) stack simulates a zero-offset (ZO) section from multi-coverage seismic data. For the 2-D case, the hyperbolic traveltime approximation used by the CRS stack depends on three kinematics attributes, which defines a stacking surface for each sampling point in the ZO section to be simulated. The main task of CRS stack method is the estimation of these three optimal attributes by means of automatic search strategies, based on coherence analysis evaluated in the pre-stack data. Currently, based on two different parameter search strategies, called extended-pragmatic CRS search strategy and localglobal CRS search strategy, there are two CRS stack implementations, which were validated by simulating ZO sections from synthetic and real data sets. Their results had been compared to other similar results, obtained by the conventional NMO/DMO stack method. In this paper, we present a short description of these two CRS strategies and compare both implementations in their application to the wellknown Marmousi data set.
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Uniform Resampling Using the Sinc Function
Authors Ana Carolina Camargo and Lúcio Tunes SantosIt is common to nd problems in handling data that falls on a nonequally spaced grid. Then, we say that is necessary making an uniform resampling, i.e., interpolating the nonuniform samples of a sign in a set of equally spaced points.
In this work, it is rst shown that the resampling problem can be formulated as a problem of solving a set of linear equations Ax = b, where x and b are vectors of the uniform and nonuniformsamples, respectively, and A is a matrix of the sinc interpolation coef cients [Rosenfeld (1998)]. The solution for this system is given by the pseudoinverse matrix which is computed using singular value decomposition (SVD) in a process that is called Uniform ReSampling (URS). In large problems, the computation of the pseudoinverse is impractical. Using the fact that the contribution of the b(i)'s in the computation of the x(j)'s, when they are distant, is very small, Rosenfeld created an algorithm that was called Block Uniform ReSampling (BURS). Such algorithm uses only a limited number of points around t(j), point of the uniform grid, to calculate each uniform sample x(j), decomposing thus the problem into solving a small set of linear equations for each uniform grid point. These equations are a subset of the original equations Ax = b and are once again solved using SVD. The nal result is both optimal and computationally ef cient. A result is presented to illustrate.
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Phase spectrum applied to pinch out zones analysis
More LessWe are going to discuss the possibility of using the phase spectrum of seismic signals for analysis of pinch out zones in thin layer reservoirs. The results presented show by analysis of the phase spectrums help to determine more accurately the pinch out point, reducing the domain of uncertainty. These results were obtained by using synthetic and real data. The synthetic data was obtained for signals having frequencies similar to real ones.
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Noise suppression in seismic data with sparse coding
Authors Sam T. Kaplan and Tadeusz J. UlrychIndependent and principal component analysis are used to find a series representation of data. Principal component analysis finds a compact representation of the data, while independent component analysis finds a sparse representation. The data are corrupted with additive random noise, and the coefficients in the series expansion are filtered, removing the portion of the series that is more indicative of noise than signal. For the series representation of the data found using principal component analysis, the filter consists of a simple truncation of the series. For independent component analysis, a Bayesian filter is applied to the coefficients of the series expansion; thus, allowing for prior knowledge to be applied to the distribution of the coefficients.
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Compensation for Q-losses revisited - A more stable approach using SVD
More LessThis paper discusses an improved approach for Qcompensation. The approach is based on a singular value decomposition of a matrix that represents earth’s attenuation and dispersion processes according to Futterman’s model. It is shown that the proposed approach may provide a much broader frequency band recover of signals under severe attenuation than methods supported by usual stabilizing techniques. It also briefly discusses a very common misleading thought of timevarying processes as a succession of stationary filters. Synthetic and real data examples are shown.
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Supressão do ground roll utilizando o m´etodo do balanceamento espectral
More LessGround roll is a coherent noise of high amplitude and low frequency that appears in land seismograms. This type of seismic event overlap primary reflexions creating difficulties in the processing and interpretation of the seismic data. In the past years many different filtering techniques has been proposed to attenuate these noise. In this paper, we test a new approach which is based on spectral decomposition of the seismograms coupled with the use of automatic gain control (AGC) applied on each decomposed panel associated to each band of frequency used in the decomposition. A similar approach is used into the software FOCUS (Paradigm). These approach was tested on synthetic and real seismograms. The numerical examples demonstrates that the ground roll may be considerably attenuated suggesting the use of the new approach as a efficient tool useful to increase the ratio signal to noise in land seismograms.
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Amplitude Preserving Kirchhoff Pre-stack Time Migration for Time Lapse Processing on Troll West
Authors David Bannister, Momotchil Roussanov and Charles JonesA method of applying weighted scalars in preserved amplitude pre-stack depth migration (Jousset, 1999) has been adapted for time processing and included in a time lapse (4D) processing scheme incorporating Kirchhoff pre-stack time migration. The method, known as ADA (Acquisition Dependent Amplitude) compensation removes the requirement for a pre-migration regularization stage, honours the true source and receiver locations of the data and reduces the acquisition footprint. The method is applicable to 3D acquisition and is particularly well suited to 4D studies, where removal of acquisition effects to improve repeatability is a key requirement. The application of ADA on multiple vintages of 3D data acquired over the same area provides a testing ground to demonstrate the effectiveness of this technique. Presented in this case study is an example of the application of the ADA method to time lapse processing of data from the Troll West gas province.
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Correçao dip moveout em dados s´ısmicos da Bacia sedimentar do Tacutu
Authors Michelângelo G. da Silva and Milton J. PorsaniWe present the results obtained in the processing of reflection seismic data of the Basin Sedimentary of the Tacutu applying the method dip moveout (DMO) in common shot gather using the logarithmic transformation of both the time and the space coordinates. The main objective was obtain a velocity field and to generate the zero-offset stacked section. The processing flowchart involved the residual velocity analysis of the seismic data. We obtain estimation the velocity field of the subsurface most real and to increase the reason signal-noise of the stacked section with the correction dip moveout.
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A practical approach to OBC summation and geophone calibration in areas of shallow water and hard seafloor
Authors Greg Beresford and Gaël JanexA methodology for processing two-component (2C) ocean bottom cable (OBC) seismic data based on the principle of cross-ghosting (Soubaras, 1996) is applicable to some of the most difficult field situations where water depths are in the 20m to 60m range and where there may be a hard variable seafloor giving rise to strong guided waves and geophone coupling “resonances”. Effective summation of hydrophone(H) and geophone(G) components depends on geophone calibration to compensate for this seafloor coupling. The methodology breaks naturally into three steps: data analysis and pre-filtering of common receiver records; LS estimation of calibration filters from pre-filtered data; and finally summation. Pre-filtering to attenuate guided and other horizontally propagating waves is a critical step because such waves “in-fill” the ghost notches especially on the geophone records and reduce the effectiveness of cross-ghosting. The analysis of common receiver records is also critical in order that the best data window can be found which contains primarily reflected P-waves.
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Interpolação e regularização de dados sísmicos usando a transformada de Radon linear (τ-p) 2D e 3D
More LessSeismic surveys are designed on the purpose that all samples collected during the seismic experiment fall on a specific regular grid. Nevertheless, this data regularity is almost impossible to achieve due to different constrains during seismic acquisition. A very important non-cultural irregularity which occurs during marine seismic surveys is hydrophone cable drift caused by ocean currents (cable feathering).
These irregularities must be treated in the first steps of seismic data processing and data regularization can be the right tool to be used. Regularization may improve the overall performance of important steps in seismic processing like velocity analysis and migration.
Data interpolation and regularization are performed using the τ-p transform, with slant stack 2D and 3D algorithms. We discuss different issues in 2D and 3D data regularization using τ-p transforms, such as ideal parameterization to avoid artifacts and the 2D experiments related to interpolation and regularization of gaps in seismic information and cable feathering.
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Pesquisa e desenvolvimento em geof´ısica atrav´es do reprocessamento de dados sísmicos: A experiência do Laboratório de Geofísica Computacional da Unicamp
Desde a significativa mudança do cenário exploratório de petróleo e gás com a criaçöo em 1997 da Agência Nacional de Petróleo (ANP), foram estabelecidas no Brasil especiais condiçöes e oportunidades de pesquisa, desenvolvimento, formaçäo de recursos humanos e prestaçäo de serviços em variadas áreas do setor. Se adequadamente exploradas, estas oportunidades devem promover o estabelecimento de conteúdo local às diferentes atividades, conteúdo este imprescindíıvel para a independência científica e tecnológica do País. O importante acervo de dados s´ısmicos existente no Banco de Dados de Exploraçäo e Produçäo (BDEP), também vinculado à ANP, oferece oportunidades importantes para as atividades de processamento sísmico, sobretudo no reprocessamento de dados mais antigos com a utilizaçäo de m´etodos e tecnologias mais atualizadas. É nesse pano de fundo que se insere o projeto “Aplicaçäo de técnicas especiais em reprocessamento sísmico” celebrado entre a ANP e o Laboratório de Geof´ısica Computacional (LGC) da Universidade Estadual de Campinas (Unicamp) e desenvolvido no período de janeiro de 2002 a julho de 2005. No per´ıodo foram processadas e reprocessadas linhas sísmicas representativas de muitas das bacias sedimentares brasileiras, com resultados importantes de melhoria de imageamento. Os resultados obtidos confirmam o valor do reprocessamento sísmico, mesmo adquiridos com tecnologias antigas e de baixa qualidade, no sentido de extraçäo de conhecimento e informaçäo em várias áreas e localidades, muitas vezes inacessíveis hoje a novos levantamentos.
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Estudo do impacto do uso de geofones com ressonância de 10 Hz e 60 Hz na aquisição 3D de alta resolução
Authors Selma S. Sacramento and Marco C. SchinelliPara monitoramento da injeção de vapor no campo de Fazenda Alvorada, na Bacia do Recôncavo foi projetada uma aquisição 4D de alta resolução, com o uso de geofones de 60 Hz, cargas e geofones enterrados e cela de 2,5 x 2,5 metros, dentre outros parâmetros não convencionais, com o objetivo de maximizar a resolução sísmica ao nível dos reservatórios a serem monitorados. Simultaneamente, para estudar o impacto do uso dos geofones de 60 Hz, foram usados redes convencionais de geofones de 10 Hz agrupados, cujo resultado serviria para avaliar a possibilidade de em novas campanhas de monitoramento, serem usados geofones convencionais no lugar dos de alta freqüência. O resultado do experimental mostrou que os geofones de 60 Hz não foram determinantes para o resultado obtido pois este também foi alcançado com o uso dos geofones convencionais. Serão descritos neste trabalho os resultados obtidos com o uso dos geofones de 60hz e 10hz no mesmo levantamento 3D, avaliando alguns aspectos operacionais da aquisição e o procedimento usado para processamento, alem das diferenças entre cada conjunto de dados.
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Aplicação dos Métodos PMC e SRC em Dados Sísmicos Sintéticos de um Modelo Representativo da Bacia do Solimões, Região Amazônica, Brasil
Among the several difficulties found in the exploration for oil and gas in the Amazon area, the existence of diabase sills, although of its importance to the process of maturation of organic matter in all Brazilian Paleozoic basins, difficults the seismic exploration, since the diabase disturbs the seismic signal, generating multiple reflections and spherical divergence. With the purpose of understanding the seismic wave propagation and, principally, the difficulties found by the seismic imaging methods in these complex geological settings, in this paper we present the first results of acoustic seismic modeling in a synthetic model of the Solimões Basin- Brazil, using finite-differences techniques, as well as the seismic processing of this data set by the Common Midpoint (CMP) and Common Reflection Surface (CRS) stacking methods.
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Segmentation of well-log data
More LessIn this paper we present a method to automatically detect stationary segments in well-log data sequences. This process is carried out by searching for change points which correspond to abrupt changes in the statistical nature of the underlying process. For this purpose the we analyze the behavior of the probability density functions (pdf) of two adjacent sub-samples as they move along the original data sequence. A statistical test is used to set a significance level of the probability that the two distributions are the same, thus providing a means to decide how many segments comprise the data by keeping those change points that yield low probabilities. Examples using simulated and real well–log data show that the results are in good correspondence with what seems to be a reasonable segmentation.
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Processamento CRS de dados deconvolvidos usando o metodo de Wiener-Levinson
Authors Rosangela Maciel and Milton J. PorsaniThe removal or attenuation of multiple reflections represents a problem for seismic data processing. Such multiple reflections interfere with the primary ones and may generate large difficulties to the interpreter and to the seismic migration methods. The Wiener-Levinson (WL) predictive deconvolution is a technique which has been in use for quite some time in the attenuation of multiples, having its application limited to a periodical occurrence of the event. This work shows some partial results related to the use of the
WL multichannel predictive deconvolution, combined with the method of zero-offset generation section through the stacking of the commom reflection surface (CRS). The CRS method is very recent and it shows itself as a good alternative when compared to the traditional stacking methods (DMO/NMO). It does not require prior information on the velocity model. In the present stage of the work we are introducing NMO correction by using the stacking velocity calculated in function of the parameters trio obtained through the CRS method with the objective of generating common off-set sections to apply the filter. The obtained results were statisfactory and quite promising.
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Imageamento WCDP 2D em profundidade: uma versão para meios lateralmente homogêneos
More LessThis paper presents some results of implementation of a pre-stack migration procedure based on the Wave Analogue of the Common Depth Point (WCDP) method. The method is based on the exact solution of an inverse acoustic scattering problem, considered in the Born approximation. We analyze the performance of the WCDP migration considering a depth variant of the algorithm.
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True-amplitude CRS-based Kirchhoff time migration for AVO analysis
Authors Miriam Spinner and Jürgen MannThe achievable image quality and the reliability of amplitudes in Kirchhoff migration strongly depend on the selection of the migration aperture. Too small an aperture leads to underestimated amplitudes and the loss of steep events. On the other hand, too large apertures tend to cause operator aliasing and include unnecessary noise and contributions from unwanted events. Our aim is to use CRS-based minimum apertures in Kirchhoff prestack time migration to obtain the best possible input for AVO/AVA analyses.
The basic idea is demonstrated for a synthetic data set which contains events from a common sequence of gas/water/oil contacts. We discuss the determination and extrapolation of stationary points and projected Fresnel zones based on CRS wavefield attributes, as well as a simple and efficient way to set up a migration velocity model. The first results show a significant reduction of amplitude dispersion in common-image gathers as well as in the zerooffset section, thus providing superior input to AVO/AVA analyses.
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