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10th International Congress of the Brazilian Geophysical Society
- Conference date: 19 Nov 2007 - 23 Nov 2007
- Location: Rio de Janeiro, Brazil
- Published: 19 November 2007
201 - 300 of 484 results
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Aplicação da perfilagem geofísica em projetos de perfuração de poços de petróleo
Authors Marcos Leite, Abel Carrasquilla, Jadir Silva, Luiz Lobo, Rafael Curtinhas and Sandro BatistaAn oil well drilling project is a multidisciplinary task that involves knowledge derived from several technologi-cal areas such as geology, geophysics and petroleum engineering. So, it is considered of outstanding impor-tance for works involving the interfaces of the above men-tioned disciplines. Summing up, it helps us to see how the interaction between them can provide an interdisciplinary vision of the phenomenology involved in the process. In the present work, it was shown how the application of gamma rays, sonic and density logs can help in the selec-tion of bits and drilling parameters using Gulf of Mexico geophysical well logging data. As an example of the re-sults obtained in this work a perforation strategy is con-structed.
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Compressional-wave velocity variation in the upper Macaé formation: A well-log regression analysis study
Authors Fabrício O.A. Augusto, Jorge Leonardo Martins and Jadir C. da SilvaIn this contribution, a regression analysis methodology allows prediction of P-wave velocities in locations where sonic logs are for some reason unavailable. The proposed methodology uses fundamental geophysical well logs (i.e., nuclear and resistivity logs)
for least-squares estimation of regression coefficients. Fractional effective porosity and clay volume as well as bulk density form the set of assumed independent variables in the corresponding regression models. Considering P-wave velocities varying according
to linear, parabolic and multivariate linear models, the calibration process confirms previous results showing porosity as the most important dependence parameter in the regressions. When calibration is extended to a well far away from the original location, it reveals that combinations of certain obtained regressions can predict P-wave velocities in the formation under study with reasonable accuracy.
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Identificação de Fácies em Perfis através de Lógica Fuzzy
Authors Helaine Moraes and André AndradeThe actual reservoir characterization problems, seek for a better integration among geological information and well logging. We introduce here a new method based in fuzzy inference, which is able to map facies description in well log data by a convenient
representation of log readings in a ladder diagram to produce a fuzzy representation of facies in a cored well. The behavior of this method is evaluated with actual well log data from boreholes in Namorado oil field, Campos’ Basin, Brazil.
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Interpretação do Gráfico de Hingle Através de Rede Neural Competitiva
Authors Carolina Barros and André AndradeThe water saturation is a petrophysical property important for formation evaluation and reservoir qualification and defines the final well destination. For clean formations, the water saturation is estimated from logs by Archie’s equation involving the rock porosity and the true formation resistivity. The Archie’s equation solution needs the value of formation water resistivity, which may be acquired by Hingle plot. In despite of well logging technological development, the log analyst still handles with visual interpretation of Hingle plot, subject of human errors. The objective here is to build a new architecture of competitive neural network to produces a Hingle plot interpretation, providing a first approach of water saturation, based on angular pattern recognition. The evaluation of this methodology is accomplished on synthetic and actual well logging data.
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Imageamento de modelos artificiais de testemunhos através de tomografia ultra-sônica
Authors José Agnelo Soares and Maira da Costa de Oliveira LimaA new ultrasonic tomography equipment was developded to be used in rock core internal imaging. In order to analyze the equipment performance, nine artificial core samples were produced and imaged on this apparatus. These artificial cores were done using an involving mass of either mortar or pure Portland cement with rock inclusions of several types, sizes and shapes. Tomograms of transmitted P wave velocities were obtained for each core model and they are discussed here in terms of model reproduction and image quality. In general, the ultrasonic tomography equipment proved to be a very useful tool to image the interior of rocks samples. The data inversion procedure used in this work do not consider intrinsic rock anisotropy nor ray bending, what cause imaging failure in case of rocks with strong anisotropy or intense velocity contrast between inclusions and wrapping mass. In these cases, the final image quality may be enhanced if these rock features are incorporated to the data inversion algorithm. This tecnique may be expanded to a wide spectra of uses like integrity tests of structures or historical buildings, rock blocks QC, crosswell tomography between sounding holes of urban or mine galeries, an so on.
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Integrac¸ ˜ao dos parˆametros el ´etricos com RMN para caracterizac¸ ˜ao de testemunhos
More LessThe petrophysical characterization, in lab scale, of drill cores, was obtained using electrical measurements perfomed in the samples saturated with solutions of NaCl for six different salinities. These petrophysical data have been compared to Nuclear Magnetic Resonance NMR measurements. In this way the petrophysical caracterization of these rock bodies, using electrical and NMR parameter, resulted in the qualitative and quantitative estimate of the acquired petrophysical parameters.
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Pore throat size classification from Nuclear Magnetic Resonance measurements in rocks
Authors Jesús P. Salazar and Briseida MorilloThe pore throat size is an important quantity to be determined in special analysis of core rock samples because reservoirs can be classified from this measurement. This classification is normally called Petrofacies. A new methodology to obtain Petrofacies
from transversal relaxation times is shown in this work for a case study. This methodology is based not only in the relationship that exists between capillary pressure and pore throat size but also in the relationship that exists between the transversal relaxation time (T2) and the pore size.
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Estudos geofísicos para mapeamento de contaminaçãoe utilização como instrumento de conscientização sócio-ambiental
Authors Juliano das Flores Bahia and Vagner Roberto ElisThe high populational density in urban areas, had caused environmental problems related to the genesis and, mainly, the deposal of residuals generated by these inhabitants, which in many situations, the final destiny is the ground. The present work has the propose of evaluating the contamination caused by the “in situ” deposition of domestic residuals and sewerage, using geophysics methods to build an efficient methodology on evaluation and characterization of environmental problems with these characteristics. Subsequently the research is applied in environmental education in schools near the investigated area and the guests that comes to the park.
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Laboratory Petrophysics with Quality: The transformation process of a research and development laboratory towards quality
Authors Beatriz Santiago, Pedro Romero and Olivar Lima de LimaIn the context of this work, the transformation process towards quality of the petrophysics laboratory of the Center of Research in Geology and Geophysics (CPGG) of the Federal University of Bahia (UFBA), located in Salvador, Bahia (BA), Brazil, is presented.
The quality system implemented in this laboratory was based on the norm ISO/IEC/EN 17025 (General Requirements for the Competence of Testing and Calibration Laboratories), which constituted a fundamental tool for the implementation. However, during the
implementation process, some problems were encountered. This was going to be reflected in an excessive investment of time and money. It was possible to identify the causes that generate additional costs and delay the implementation process of the quality system ISO/IEC/EN 17025 in the petrophysics laboratory. This was done by using two of the basic quality control tools: the Cause-Effect diagram (Ishikawa or Bone fish) and the Pareto diagram. With the Cause-Effect diagram, the common and special causes of variation (six in total) were detected. As a result of the analysis with the Pareto diagram the relationships between problems and causes were found.
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Shale Characterization by Intelligent Algorithms
More LessIn formation evaluation, the matrix of a reservoir rock is characterized by a set of physical constants, mostly obtained from laboratory measures in cores. The variability in shale composition produces a great variation of its physical properties and a set of log readings may be used as physical constants to characterize the shale. This set is refereed as shale parameters and is used to perform the shale correction, when porosity values are calculated using well log data. The shale parameters may be obtained from log readings in front of a shale layer by visual log interpretation, which may be strongly affected by noise measurements or log misinterpretation caused by geological ambiguity (radioactive sands) or drilling parameters (mud resistivity). We present a method to produce the shale zonation and extract shale parameters from well log data, which may mitigate the log misinterpretation by an intelligent algorithm that merges artificial neural network with genetic algorithm, emulating the interpretation of a z-plot composed by the M-N plot and the natural gamma ray log in the third axis. The behavior and evaluation of this method is shown with actual well log data from one borehole in Namorado oil field, Campos’s basin, Brazil.
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Comportamento aerogeofísico de kimberlitos e corpos associados
Authors Leandro G. da Silva and Augusto César Bittencourt PiresThe Coromandel region is worldwide known for its large diamond exploration. Several ultramafic alkaline intrusions belonging to the Alto Parnaíba Igneous Province (APIP) are also found there. Magnetic and gamma-ray anomalies due to ultramafic intrusions were identified from 250m line-spaced airborne geophysical data and three-dimensional image analisys were created to visualize it. Images from magnetometry shows dipolar anomalies generated by the kimbelitic bodies and some outcropping ones may be observed by gamma-ray products, such like eTh and eU images. Using radiometric data lead us to find new similar anomalies that may be interpreted as intrusive bodies of kimberlite or kamafugite signatures. Field checking, geochemical analysis and petrographical studies are needed to confirm the relationship between anomalies and new bodies.
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Topographic beach profiling with differential global positioning system (DGPS) - Peró beach, Cabo Frio, Rio de Janeiro State, Brazil
More LessTopographic beach profiles have significant utility in coastal environments. An environmental high-energy condition provides some uncertainly in results from traditional methodologies for beach profiling. The employment of differential global positioning system
(DGPS) method has advantages in comparison with other ones. The results are well definite beach profiles with 0.001-meter precision in some cases, depending on positioning concepts. It provides better studies of seasonal beach variations. The method
proposed was applied at Peró Beach, Cabo Frio, Rio de Janeiro State, Brazil on 2007 summer. Profiles are connected to Brazilian Geodesic System (Instituto Brasileiro de Geografia e Estatística - IBGE).
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Implementação de filtros gamaespectrométricos utilizando as técnicas NASVD e MNF no ambiente do Software Oasis Montaj
After applying conventional processing in the airborne gamma-ray spectrometric method, there is still noise in the spectra. Several approaches are suggested to remove this remaining noise. These methods include noise-adjusted singular value decomposition (NASVD), and maximum noise fraction (MNF). The methods are applied to raw spectra data prior to integrating counts in the K, U and Th windows and conventional processing. The two methods are applied to a survey data set for comparison. The methods presented were able to reduce noise in the original data set.
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The effect of inaccuracy in cloud cover data on solar estimates provided by radiative transfer model
More LessCloud cover index (CCI) obtained from satellite images contains information on cloud amount and their optical thickness. It is the chief climate data to get reliable assessment of solar energy resources using radiative transfer models like the model BRASIL-SR. The wide range of climate environments in Brazil turns CCI determination into a complex task and a great scientific effort has been employed to get reliable and confident CCI values from satellite images (Ceballos at al., 2004, Martins et al., 2004). This work illustrates the influence of CCI determination method on estimates of surface solar irradiance provided by model BRASIL-SR by comparing deviations among ground measurements and model results. Two techniques using visible and thermal infrared images of GOES-EAST and another on using only visible images were employed to feed model BRASIL-SR. The ground data was measured in Caicó/PE where solarimetric station is operating since 2002 as part of project SWERA. It was noted that bi-spectral techniques have reduced mean bias error up to 66% and root mean square error up to 50%.
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Workflow for characterization of subsurface lithofacies and saturation fluid
More LessThe main goal of Bayesian inference is to update the probability that a hypothesis may be true based on evidence or observations. Therefore, this methodology makes possible to infer subsurface parameters through the seismic responses, quantifying the uncertainties inherent in the data. However, to calibrate the model, the method uses the prior available information, such as well logs, core samples, geological and petrophysical knowledge, etc. This methodology was applied on a data volume from an offshore Brazilian field to generate, as a final product, a lithofacies model and a fluid indicator for this field.
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Fracture network seismic facies analysis in Campos Basin, Brazil
More LessStratigraphic inversion and seismic facies analysis (non supervised K-means approach) has been performed in fractured carbonates reservoir in deep-waters Campos Basin. The facies analysis has shown that 5 from 12 facies could be interpreted as fractured facies, which has been interpreted in term of fracture occurrence probability. A Principal Component Analysis, as a cut-off on the amount of unvertainty have demonstrated the robustness of the main lineament forms. The result is a seismic facies map that could be used as a map of fracturation intensity in the top of reservoir, with intensity values comprised in the range [0;1]. This map was used as a seismic constraint for a reservoir modeling.
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Methodology for Characterization of a Clastic Reservoir Based on Correlations between Electrofacies, NMR and Image Logs. A Case Study from the Gulf of San Jorge Basin
This work presents a methodology for characterization of clastic reservoirs. It has been developed with data from the Bajo Barreal formation in the Golf of San Jorge Basin. The methodology is based basically on the definition of Electrofacies and their correlations with conventional open hole logs, resistivity image and NMR logs (T2 distributions and Diffusivity maps); in addition, these data have been associated with information from neighbor wells and 3D seismic. The electrofacies analysis has allowed us to
interpret sedimentary deposits in a continental environment. Furthermore, it yielded information on structural dip of the area and the directions of paleoflows of the reservoirs, which has been found to be in agreement with the seismic interpretation and outcrops observations at the surface. As a result of this study, a reservoir classification could be established, supported by criteria related to sedimentary genesis, petrophysical characteristics and fluid typing, for which NMR log analysis has added a very significant value. This methodology for reservoir characterization will find future implementations in the generation of geological models, especially in areas with enough amounts of data at disposal. These areas are of particular interest for purposes of validation and
testing the new generated models, towards reducing the uncertainty in the selection of future well locations.
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Métodos Baseados em Núcleos e Máquinas de Suporte Vetorial em Aplicações de Geofísica de Petróleo
Authors Geovan Tavares, Hélio Lopes, Alex Laier, Rener Castro, Rogério Santos and Amin MuradKernel based methods and support vector machines are recognized today as important methods in areas such as artificial intelligence and bioinformatics, among others. Increasingly in the last years applications to geophysics is becoming widespread, emphasis made to the oil industry. In this paper we propose a new method to distinguish between reservoir and non reservoir characteristics in a seismic sample. Volumetric multiatribute seismic and well data are used in the training process.
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Reconstrução Topológica Tridimensional de Objetos Geológicos em Bacias Marítimas Usando Dados Sísmicos 2D ou 3D: uma Ferramenta Exploratória e Explotatória de Hidrocarbonetos
Authors Thomas Lewiner, Hélio Lopes, Geovan Tavares, Alex Bordignon, Rener Castro and Rogério SantosThe interplay between geophysics and geology is today one of the main challenges in reservoir characterization. In this paper we expose the ideia that by careful mathematical formulation and computer graphics tools it is possible to reconstruct 3D geological forms starting with seismic parameters. We reconstruct all the topological components of isosurfaces in subvoxel resolution starting with seismic parameters. Each isosurface component represents the boundary of a geobody. This type of reconstruction helps the modeler to understanding better the seismic information, the geobody spatial characteristics and make quantitative estimations such as reservoir volume.
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Mineração Visual de Multiatributos Sísmicos para Classificação de Multifácies
Authors Hélio Lopes, Alex Bordignon, Rener de Castro, Thomas Lewiner, Geovan Tavares, Rogério Santos and Amin MuradThe understanding of large data clustering is a relevant problem in several areas of science and engineering. Seismic signal are in general represented by large data sets. For petroleum geophysicists the choice of areas of interest is a demanding task. In this paper we introduce data mining visualizationtechniques, stellar coordinates and transfer functions, which easy the task of dealing visually with data clustering in an interactive and intuitive way allowing the user to make meaningful choices of 3D regions of interest to work with.
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Characterization of turbidites from the Urucutuca Formation of the Almada Basin, Bahia – Brazil, using seismic and petrophysical well log data
Authors Klédson Tomaso, P. Lima and Carlos Alberto DiasFifty 2D-seismic lines and 17 well logs were used to characterize the reservoirs of the Urucutuca Fm palaeo-canyon of the Almada Basin (Bahia – Brazil). A 3D geological model based on this interpretation allowed an evaluation of the Urucutuca Fm and its turbidite canyons as potential petroleum reservoirs. The log analyses indicate great variation of effective porosity, which reach a maximum value of 25%. The clay content of the sandstones also presented substantial variation, from 10% to 60%. The information obtained from the seismic lines indicates a strong tectonic influence on the geometry of the Almada Canyon, this resulting in two canyons which connect in the offshore portion of the basin. The connection of the canyons has been observed from the continent to 27 km offshore. The results indicate that the Urucutuca Fm is an important horizon for future oil exploration, with favorable genetic and petrophysical characteristics.
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Novos Desafios Para Caracterização Sísmica em Bacia Madura
Authors Jaciara Barreto and Marco SchinelliSeismic activities in Reconcavo basin started in the fourties, and since then has challenged geophysics for the improvement in seismic quality in an adverse environment with a wide range of near surface conditions and complex geology. The results of high resolution 3Ds, using more than 1.2 x 106 traces/Km2, orthogonal patterns or time lapse surveys has proven that there are technological solutions for the seismic response and level of resolution needed for reservoir characterization activities. Besides modern technologies another focus now is on how to overcome challenges of working on transition or urban areas, where missed shotpoints due to obstacles can severly impact quality response in many of our fields. In this work we are going to show historical results, the most successful tecnologies and discuss solutions to overcome seismic acquisition difficulties.
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Controls of the antecedent topography on Holocene shoal morphology, Bahamas: results from high-resolution sub-bottom profiling
Authors F. Eduardo G. Cruz, Gregor P. Eberli and Arthur AyresHigh-resolution sub-bottom profiling reveals an unexpected shallow Pleistocene topography and the internal geometry of Holocene shoals around Ocean Cay on the western margin of Great Bahama Bank. The continuous sand belt north of Ocean Cay is anchored on a Pleistocene high, while south of Ocean Cay discontinuous tidal deltas are situated on shallower Pleistocene bedrock. Here we report on the investigation of the antecedent topography in these two areas by interpreting approximately 120 km of
shallow, high-resolution seismic data acquired using a full spectrum digital sub-bottom profiler. Preliminary results from this interpretation indicate that the laterally continuous sand belt north of Ocean Cay developed behind a subtidal to exposed rock ridge that is located seaward of the active sand belt. This ridge acts as anchor for the Cat Cay Shoal and probably prevented vigorous sediment transport. Unexpectedly, the top of Pleistocene underlying the shoal complex is deeper north of Ocean Cay compared to the southern area. This irregular Pleistocene topography played an important role during initial stages of bank margin flooding controlling sediment accumulation and result in contrasting thicknesses of the Holocene deposits; it is thicker than 5 meters in the north but usually less than 5 meters in the south.
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Lógica fuzzy aplicada à determinação de eletrofácies ao longo de um poço e interpretação de perfis geofísicos
In recent years, techniques of artificial intelligence have been applied in some studies of reservoir characterization, mainly in the electrofacies determination. Among them, the fuzzy logic can be mentioned, which uses linguistic variables and a set of rules to determine electrofacies from well-log data. In this paper the boundary-value of each electrofacies was determined from the well-logs and cores interpretation as well as the application of logic fuzzy for the distinction of electrofacies in the well NA7. The boundary-values had been used for the parameters definition of input variables in fuzzy logic application. For the result validation, a comparison with core data of the well NA7 was done. Due to variation of the results of the first stage and the great amount of available information, the use of fuzzy logic reduced the time of data analysis and the interpretation inaccuracy. The comparison between the results of this technique and core data showed similarities in the electrofacies determination throughout the well.
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INFERÊNCIA DE SATURAÇÃO E PRESSÃO ATRAVÉS DE ANÁLISE INTEGRADA DE ATRIBUTOS ELÁSTICOS E DADOS DE PRODUÇÃO
Authors Renzo Francia Mimbela and Fernando MoraesWe present a bayesian formulation for the inference of saturation and pressure from 4 D seismic attributes, using a simple linear model, as suggested by Floricich, et al., (2005). The linear model provides a direct link between time-lapse signatures and pressure and saturation changes in the reservoir. Time-lapse signatures are represented by differences of seismic attributes, such as velocities and density. A calibration procedure provides the values for the model coefficients. This requires production data at the wells that we evaluate by a material balance formula. The methodology is tested on synthetic data generated, first, by reservoir simulation, which yields true saturation and pressure distributions. Saturation and pressure are then used to obtain the attributes and their corresponding time-lapse signatures by conventional petroelastic modeling using Gassmann and a pressure sensitivity model. The results demonstrate that the proposed inversion is able to recover the original saturation and pressure changes and the associated uncertainties.
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Dedução e análise dos campos elétrico e magnético gerados por transmissor quadrado de um sistema geofísico eletromagnético a multi-freqüência
Authors Marcos V. Barbosa Machado and Carlos A. DiasThe multi-frequency EM method is being tested successfully for oil exploration and reservoir fluid monitoring at on-shore environments. The inversion procedures presently used for obtaining the electrical parameters of the underground from the data registered
at the receiver assumes that the finite-size sourcetransmitter (a current square loop on the ground) is a point-source vertical magnetic dipole. This approximation implies limitation on the transmitter-receiver separation minimum distance to be at least 6 times the side of the loop. In this paper the fields are deduced for finite source, of square and circular shapes, and compared to each other and to point dipole-source fields, as well. New graphics have been constructed for showing the inversion function of the measured data, for a finite source square loop, and compared to the dipole-source. It is shown that when using, for instance, T-R separation 1.5 times the side of square loop, that approximation is not valid at all.
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Bases Petrofísicas Para Emprego de Métodos Elétricos e Eletromagnéticos na Exploração Direta de Petróleo
More LessIn this paper we discuss the petrophysical basis for employing electric and electromagnetic methods in the direct detection of oil in underground reservoirs. From the volumetric conductivity approach proposed by Lima and Sharma (1992) we present physical simulations that satisfactorily show that the simultaneous measurements of resistivity and induced polarization parameters can be used to distinguish the presence of hydrocarbon even in reservoirs containing very fresh waters. Field results using inductive multifrequence EM measurements attest the feasibility of the results.
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50 years odyssey of an academic life : an overview at the 70th birthday celebration
More LessAn outline of my auto-biography is delineated. The presentation of the specific topics and times follows a chronological sequence and the facts are presented in their historical, social and philosophical contexts. Five academic institutions and a scientific association have here their genesis traced.
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Cooperação Universidade – Indústria: O caso do método marine Controlled Source Electromagenetic (CSEM) na exploração de hidrocarbonetos
By L. RijoThe new geophysical method marine Controlled-Source Electromagnetic is creating in the petroleum industry an expectation as a innovative tool for exploration of petroleum in deepwater. This method is the result of three decades of intensive research in marine geophysics done by many American and European universities. In virtue of new favorable conditions (deepwater exploration, high price of petroleum) the petroleum industry begins to invest seriously in this technology. As a consequence the progress of the method CSEM has been accelerated and now is the universities that have to catch up. The Petrobras one of the world leader company in petroleum exploration in deepwater is accompanying closely the evolution of this new technology. In collaboration with our
university, the only one carrying research on CSEM method, Petrobras is supporting to train geophysicists in this new technology, following to the trail left behind by Prof. Carlos Dias.
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Integração preliminar de dados MT, TDEM, GRAV e MAG na delimitação dos Domínios Crustais Jaguaribeano e Ceará Central, Província Borborema (NE do Ceará)
This paper presents the interpretation of magnetotelluric (MT) and transient (TDEM) soundings and gravimetric/magnetic data carried out along a 100 km long section between Beberibe and Icapui cities, located in the eastern coast of the Ceará (NE Brazil). The horizontal fields were sampled in the N-S and E-W directions at four frequency bands. The static-shift was corrected using TDEM soundings. The ocean effect was investigated using three-dimensional numerical modelling. The interpretation was based on a 2-D model obtained from the inversion of the MT data (TE and TM-modes). These EM data were interpreted with both gravimetric and magnetic data. The obtained model allows, for the first time, the characterisation of: 1) the uppermost structures correlated to the Meso-Cenozoic sedimentary formations and groundwater reservoirs, 2) the underlying structures associated to Central Ceará and Jaguaribeano domains of the Northern Segment of the Borborema Province and 3) the structures associated with the Senador Pompeu, Orós and Jaguaribe shear fault systems (Neoproterozoic).
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Inversão de dados eletromagnéticos na exploração de óleo e gás
Authors Moacyr S. Bezerra and Hédison K SatoThis paper presents part of a research involving fre-quency domain electromagnetic data collected in a petro-leum field. Using the mutual impedance EM formulation for HCP (horizontal coplanar loop) arrangement over a horizontally stratified earth, the field data are inverted using the VFSA (Very Fast Simulated Annealing) method. The layer conductivities are considered complex to repre-sent the electrical polarization phenomena. The data and the theoretical response for two transmitter-receiver sepa-ration are presented and discussed.
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Hydrocarbon detection and reservoir imaging during enhanced oil recovery using an inductive EM multi-frequency method
Authors Carlos. A. Dias, Olivar. A.L. de Lima, Hédison. K. Sato and José. A.C. MoraesWe discuss the results of an experimental study performed with a multi-frequency electromagnetic method over a mature oil field in Recôncavo basin, Bahia-Brazil. Five 1.8 km transects 200 m apart and extending over a block of the oil reservoir were surveyed. The processed EM data are represented as cross-sections and maps of apparent resistivity and induced polarization parameter, using a consistent plotting procedure. All the sections, controlled by well logging data, allow to recognize the following geological features: (i) the oil sandstone horizons and their trapping shales; (ii) the oil-water interface and some zones of water invasion; and (iii) lateral electric contrasts representing fault zones. These results suggest the real possibility of the use of the spectral EM method in the direct detection of hydrocarbons, as well as for monitoring the efficiency of the artificial fluid injection used for secondary recovery. Also, this experiment brings about a further development in the inductive measurement of IP and introduces, for the first time, the use of this property in oil reservoir exploration and characterization.
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3D electromagnetic holographic imaging in offshore petroleum exploration
Authors Michael S. Zhdanov and Takumi UedaMarine controlled-source electromagnetic (MCSEM) surveys become widely used in off-shore petroleum exploration. However, the interpretation of the MCSEM data is a very challenging problem because of the enormous amount of computations required in the case of the multi-transmitter and multi-receiver data acquisition systems used in these surveys. In this paper we present a new approach to the solution of this problem based on the method of electromagnetic migration and holographic imaging.
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Monitoramento Sismográfico com Sensores de Fundo Oceânico em Águas Profundas e Ultra-Profundas: Resolução da Imagem Sísmica de Fraturamento Hidráulico
Authors Afonso E.V. Lopes, Jesus Berrocal and Luciana Cabral NunesHydraulic fracturing is often used in oil industry to increase the productivity of hydrocarbon reservoirs, which suffer hydrocarbon pressure and permeability of gas/oil-bearing sediments. The generated hydraulic fracture is accompanied by shear cracks, which microseismic events usually with magnitude below -0.5 (Mw). These microseismic events can be monitored with OBS (Ocean Bottom Seismograph) in deep-ocean. We present in this work a numerical simulation of hypocentral errors and seismic image resolution of small fractures.
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Evolução Espaço Temporal da Sismicidade de Nova Ponte/MG
Authors C.N. Chimpliganond, K.T. Sousa, D. Caixeta, L V. Barros and G.S. FrancaNova Ponte Reservoir is located at Minas Gerais State, SE of Brazil, on the Araguari river. The impoundment started in October 1993 creating a lake with volume of 12.8km3 and maximum depth of 132m. The pre-impoundment monitoring was made with one station for 8 years, and no local event had been detected. Two months after the lake start to be filling, the occurrence of some events felt by the local population lead to the deployment of a five vertical analog stations network. In 1995 this network was replaced by a digital one, which is operating until now. In this study, we present preliminary results for this activity that will be investigated as a probably result of spatio-temporal evolution of reservoir-triggered seismicity.
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Time-lapse seismic under low repeatability – A Campos Basin real case
More LessCampos Basin, as the main and more developed oil-prone offshore basin in Brazil, has a multitude of production facilities that make any surface seismic survey over the fields a challenge. Towing streamers among production platforms, FPSO units, drilling rigs, drilling ships, buoys and other types of surface obstacles is a difficult job, but inevitable when working there. If this complexity is already a concern in obtaining reliable 3D images, it´s potentially more harmful for time-lapse projects. Besides the big endeavour for mimicking the baseline acquisition geometry under strong marine currents that cause wide cable feathering, the presence of different obstacles at the time of the monitor survey implies a different undershooting configuration. These two factors, in conjunction, make impossible to achieve a high level of repeatability in 4D projects involving towed streamers in this basin. Nevertheless, one can get a reasonable 4D response under this situation when geological framework, seismic quality and reservoir petrophysical characteristics are so propitious that prevail over the adverse operational environment. The results obtained in the first brazilian offshore time-lapse seismic project, at Marlim Field, were promising. A very good seismic quality at this portion of the basin, the existence of a high-porosity tertiary unconsolidated sandy reservoir and a significant saturation change after eight years of production allowed that the seismic expression of fluid substitution were good enough for a qualitative 4D interpretation.
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Effective Pressure Coefficients of Some Brazilian Rocks
Authors Guilherme Vasquez, Eurípedes Vargas, Marcos Leão, Cleide Bacelar, Júlio Justen and Irapoan AlvesThere are enumerous efforts to obtain information about saturation and pressure changes due to reservoir production from time-lapse seismic data. In spite of some good examples existing on the literature, there are a lot of approximations behind those studies. Generally, it is assumed that the seismic properties are functions of saturation and differential pressure Pd (overburden minus fluid pressure). Actually, the stress that governs the seismic behavior is the effective stress Pef , which is not exactly equal toPd . In fact it is equal to the overburden stress minus n times the fluid pressure. Such coefficient (n) is known as the effective stress coefficient. Sometimes depending on the cirscunstances, it might be identified as the Biot-Willis coefficient taking into consideration the bulk modulus of the porous media. In this paper it will be presented laboratory results in a tentative to quantify the n values for Brazilian limestones and tight sands. It is important to point out, that is the first effort to perform this sort of measurements on Brazilian rocks. The results have shown that the mentioned approximations can introduce errors on pressure estimations from time lapsed data even for high porosity rocks.
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Live and Let Gassmann Work
Authors Guilherme Vasquez, Júlio Justen, Cleide Bacelar and Cassiane NunesThe Gassmann’s equations are one of the most powerful tools for seismic and log interpretation guided by rock physics. They make possible different scenario simulations based on known situations for exploration of new plays, delimitation wells location, reservoir development studies, infill drilling, and for time-lapse seismic feasibility and interpretation studies. Although, occasionally, the geoscientists make few abuses on applying the Gassmann’s equations, it’s well known that it has some limitations. On the other hand, there are some sceptics that claim it is an unproved theory or that it has more limitations than applications. Statements like “Gassmann does not work for carbonate rocks”, “It works only for seismic frequencies”, etc., constitute paradigms, and are not necessarily the ground truth. We had some experience through the years on applying Gassmann’s equations to laboratory and log data and also integrating these results to seismic responses. In this paper we discuss the Gassmann’s equations, in terms of their applicability and limitations. We use numerous examples where it works even under adverse conditions, and discuss some other cases where they fails. This paper is not addressed to rock physicist experts, but it is aiming both to defend the Grassmann’s equations and advise those beginners on fluid substitution simulations.
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Beyond a regional pore pressure model: Geology, clay diagenesis, and limits on VES-based modeling
More LessWe develop and test interval velocity-effective stress models for the deepwater Gulf of Mexico using 10 wells. In this calibration data, we observe deep data offset from the regional trend that can lead to a misinterpretation of the velocity-effective stress relationships in the area. We examine the potential causes for the offset data including unloading due to late pressure generation and lithologic effects. We are able to circumstantially relate the outlier data to clay diagenesis, but we cannot distinguish between a late geopressure and a lithologic effect. Removal of the deep offset data from our dataset allows us to approximately duplicate a regional model for pressure prediction in the Gulf of Mexico, but the local calibration does not provide any insights for refining our pore pressure predictions.
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O poço na inversão sísmica: Testes e simulações
The seismic inversion, acoustic or elastic, has been widely applied in the oil industry. Excellent results on reservoir characterization and fluid and litology discrimination contribute to this tendency. However, as all methodology, it is based on some assumptions, from which the most related to this study are: The wells used on the inversion process must be corrected and calibrated for the same situation observed on the seismic. It is well known that the borehole is subjected to the effects of some
phenomena that invalidate this assumption, for instance the mud filtrate invasion on the formation or borehole wall washouts. The aim of this paper is to investigate the influence of well logs in the seismic inversion. To achieve it, it is verified the effect of mud filtrate invasion, as well as the simulation of different saturation scenarios, in the stage of wavelet estimation and definition. The effect of well logs on the a priori model creation, that inserts the low frequencies absent in the seismic data, is also verified as well.
Another important stage is the well to seismic calibration with the final inverted seismic volumes, that is, the comparison and interpretation of the impedance(s) and density volumes with the data observed at the wells. The simulation with different merging frequencies for the a priori model and seismic help us to understand that there is no “magic numbers”, but the need for each analysis to be done along with a calibration study.
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Estudos de petrofísica em carbonatos da margem leste brasileira
More LessThe seismic inversion requires detailed understandig of the relationship between the seismic and the petrophysical properties of the reservoir. The aim of this paper is to contribute to the knowledge of the Brazilian carbonate rock properties using laboratory measurements and well logs. Empirical functions relating velocity, porosity and permeability were fit by regression analysis and the obtained equations were compared to the published ones. It is well known that velocity and permeability in carbonates are controlled by the combination of porosity and pore type. But the analysis of our dataset showed that this relation between velocity and pore type is not so clear. We also applied the velocity deviation log of Anselmetti e Eberli (1999) to our data.
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Rights of Access and Permitting for Onshore Seismic Acquisition in Brazil
Authors Daniel C. Pedroso and Marco A.E. GeorgAmong all activities performed for onshore petroleum exploration, 3D seismic acquisition is the operation in which the industry is more directly involved with local communities. Dealing with all aspects related to this relation – technical, legal and social – is a challenge that sometimes needs to be faced months in advance of the beginning of the seismic activities. This paper discusses the peculiar aspects of Brazil and the role of the seismic permitting crew, covering from negotiation methods to legal procedures that will be necessary to guarantee the success of the project.
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Evaluating a high-channel-count point-receiver acquisition system in South America
Authors German Ocampo, Roberto Parrado and Peter WattersonIn 2006, WesternGeco recorded three cross-spread and noise tests in the main productive basins of Argentina and Chile (Neuquen and San Jorge basins in Argentina and Magallanes basin in Chile). Our clients require higherresolution 3D seismic data to map stacks of thin reservoir layers in clastic braided stream reservoirs. The tests demonstrate that the enhanced frequency bandwidth provided by use of a high-channel-count integrated pointreceiver acquisition and processing system can solve these resolution problems. WesternGeco has named this acquisition system the QLand system. The process of noise removal and signal preservation is called digital group forming (DGF). The critical obstacle associated with conventional seismic data is surface wave noise such as ground roll, substantial noise from the oilfield infrastructure, and strong wind noise. The data were acquired using conventional I/O System II and Sercel 408 equipment simulating single-sensor and single-source points. The results from DGF tests reveal that the dense sampling of the coherent noise and point-receiver-based noise attenuation could be critical to achieve client goals. The clients involved in these three proof-of-concept tests were Pan American Energy (BP) and Repsol in Argentina and Empresa Nacional del Petróleo (ENAP) in Chile.
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Can anisotropy parameters derived by seismic velocity analysis improve PSDM image?
Authors Ray Gedaly and Qingbo LiaoA synthetic 2D Earth Model is used to investigate the ability to accurately estimate Anisotropy parameters Delta and Epsilon from Residual Moveout in Depth Gathers and whether such seismic-derived parameters can yield a better Depth image.
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Theory and laboratory experiment on anisotropy of attenuation and velocity in fractured medium. Part II* – Attenuation anisotropy
Authors T. Chichinina, V. Sabinin, G. Ronquillo-Jarillo, I. Obolentseva, L. Gik and B. BobrovThe aim of this work consists in studying of anisotropy of attenuation linked to the velocity anisotropy in fractured media which are transversely isotropic (TI) due to aligned fractures. We develop a theory that predicts certain relationship between anisotropies of P-, SH- and SV-wave attenuation and velocity. Taking into account the interplay of velocities and attenuations, we develop the effective TI model of attenuative fractured medium fitted to the experimental data. In the first part*, we consider anisotropy of velocity, and in the second part, which is this paper, - anisotropy of attenuation. We perform joint inversion of the data on attenuation and velocity of P, SV-, and SH-waves taking into account their interrelationship due to the mutual dependence on the complex weaknesses – the normal and the tangential ones. We try to verify the proposed theoretical model by means of comparing it with the experimental data. We found out that Thomsen-style attenuation parameter is independent of attenuation associated with cracks; it is a simple function of -ratio in model material. The attenuation parameter QεSPVV/Qδ may be meaningful for fracture characterization because it is defined by the -ratio.
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Theory and laboratory experiment on anisotropy of attenuation and velocity in fractured medium. Part I* – Velocity anisotropy
Authors G. Ronquillo-Jarillo, T. Chichinina, V. Sabinin, I. Obolentseva, L. Gik and B. BobrovWe have performed an ultrasonic experiment on anisotropy of wave propagation in the model constructed from plexiglas plates, with oil saturation and without any saturation. We have determined the directional dependencies of P- and S-wave velocities and have estimated from them Thomsen’s anisotropy parameters of the effective transversely isotropic (TI) medium ε, δ, γ and P-, S-wave symmetry-axis velocities and . The problem of estimating of the anisotropy parameters was complicated because of lack of the experimental data at the symmetry axis and in its vicinity (because of the special acquisition system of the experiment). Nevertheless, we have resolved the problem and estimated the crack weaknesses and , that enabled us to determine the fractured-medium characteristics such as crack density, for example. The experiment confirmed the theory, following which depends on the type of crack-fill fluid (liquid or gas), and ⊥PV⊥SVTΔNΔNΔTΔ is not dependent of it but is defined by the crack-density value. Besides, we found out that the sign of δ (plus or minus) can serve to distinguish dry cracks from saturated. The values of the crack weaknesses and estimated in this paper will be used in the second part* of the paper for the construction of the effective TI model of attenuative fractured medium fitted to the experimental data.
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The low and high frequency limits for anisotropic parameters in a layered medium
Authors Mercia Betania Costa e Silva and Alexey StovasThe aim of this work is to investigate the relationship between the layer-induced anisotropic parameters å and ä from two layer isotropic medium when calculated in the low frequency limit (by Backus averaging) and in the high frequency limit (from the PP ans SS traveltime parameters). It shown that the effective medium from both PP and SS traveltime parameters computed from a two layer isotropic medium is not exactly a VTI medium. Nevertheless, the approximate solution can be used. The comparison between the low frequency limit and both PP and SS high frequency limits is discussed on synthetic and real data examples.
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Análise de AVA multi azimutal em meios elásticos fraturados
More LessNessse trabalho foi estudado o efeito da presença de um sistema de fraturas paralelas entre si e a um dos eixos coordenados horizontais, sobre o campo de coeficientes de reflexão calculados em função das variações de angulo de inclinação e azimute. Foram tomadas duas camadas homogêneas e anisotrópicas separadas por uma interface plana horizontal. A camada superior possuia simetria VTI. Para a camada inferior foram construídos três modelos distintos fazendo-se variar o tipo de preenchimento (fraturas secas ou preenchidas por fluido) e orientação das fraturas (perpendiculares ao eixo x e y, gerando assim, camadas HTIx e HTIy respectivamente. Foram então construídos estereogramas residuais para os coeficientes de reflexão das ondas qP, qS1 e qS2 em função dos ângulos de inclinação e azimute. O objetivo foi averiguar a influência da presença de fraturas diferentemente caracterizadas, sobre os coeficientes de reflexão, através da detecção de eventuais padrões de variação em algumas dessas superfícies que pudessem indicar características específicas dos meios fraturados.
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Ray tracing and inhomogeneous dynamic ray tracing for anisotropy specified in curvilinear coordinates
Authors Einar Iversen and Ivan PšenčíkRay tracing has recently been expressed for anisotropy specified in a local Cartesian coordinate system, which may continuously vary in a model. It takes advantage of the fact that anisotropy has often a simpler nature locally (and is thus specified by a less number of elastic parameters) and that the orientation of its symmetry elements may vary. We extend this approach by replacing the local Cartesian coordinate system with a curvilinear one of global extent and by applying the approach to ray tracing and inhomogeneous dynamic ray tracing. Our formulation has several advantages compared to standard ray tracing and inhomogeneous dynamic ray tracing for anisotropy specified in global Cartesian coordinates. Among these are improved efficiency, lower consumption of computer memory, and conservation of anisotropic symmetry throughout the model.
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Modelagem Sísmica 3D em Meios Anisotrópicos com Simetria Polar Local
More LessIn this work we introduce a method for 3D elastic modeling to cope with seismic simulations on locally transverse isotropic (LTI) media. In order to make elastic modeling on complex media composed of thick tectonic deformed shale layers more realistic, we eneralize the finite differences scheme proposed in (Kelly, 1974) to handle seismic simulations for polar anisotropic media, where the direction of the symmetry axis varies continuously along the model. In our method, we define eight parameters at each grid point: density, P and SV phase velocities along the polar symmetry axis, Thomsen parameters (Thomsen, 1986) and the local direction of the polar symmetry axis itself, defined by its elevation and azimuth angles. In a simple illustration we show wave field reflections and propapagation as a result of variations of axis symmetry.
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Estimativa de Orientac¸ ˜ao do Eixo de Simetria Atrav´es de Dados de VSP Walkaway de Ondas qP
More LessAn attempt is made to estimate orientation of the axis of symmetry of a transversely isotropic (TI) medium from qP wave slowness and polarization vectors measured within a walkaway VSP experiment in a receiver situated in the borehole. The inversion scheme is based on linearized equations expressing qP-wave slowness and polarization vectors in terms of weak anisotropy (WA) parameters. The TI symmetry of the medium is assumed to be formed by a system of parallel thin layers. Formula for the determination of the angle of the axis of symmetry of the TI medium is introduced and tested on several numerical tests.
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Feições Texturais Sísmicas em Ambientes Deposicionais Marinhos: Caminhos para a Sismo-Aloestratigrafia
More LessSeismic textures are revisited looking for a more detailed qualitative analysis of seismic data involving lithological and petrophysical factors using some marine examples. Concepts for new aspects of stratigraphy derived from seismic data are introduced. Named as Seismic-Allostratigraphy it has the primary goals of offering tools for better description of seismic internal features from mapped layers and the seismic response for sedimentary facies understanding.
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Distribuicåo de Fluido e Resposta Sismica: Relevåncia no Monitoramento do Reservatorio
Authors Olga C.C. García and Sergio A.B. Da FontouraA avaliação da dinâmica do reservatório através da interpretação time-lapse tem adquirido uma importância relevante na indústria do petróleo. Vários desafios precisam ser vencidos nessa tarefa. Em princípio, descobrir a contribuição de cada efeito decorrente das mudanças no reservatório nos dados sísmicos se torna fundamental. Os atributos sísmicos são afetados de maneira complexa por vários fatores. A saturação é um dos mais importantes, pois influencia no módulo elástico da rocha e sua resposta sísmica e também gera uma dependência da velocidade da freqüência utilizada. Este fenômeno é conhecido como dispersão da velocidade. Além disso, a transição de fluido homogêneo efetivo para fluido com distribuição heterogênea estabelece um mecanismo de dispersão presente para freqüências sísmicas in situ. Neste trabalho, é explorado o comportamento da velocidade em função do tipo de fluido e sua distribuição. Dois tipos de modelos de distribuição de fluido são utilizados: efetivo uniforme e heterogêneo. Resultados mostram que, para o mesmo valor de saturação, distribuições heterogêneas de fluido multifásico apresentam maiores valores de velocidade compressional respeito a distribuições uniformes de fluido. A análise é realizada para diferentes tipos de rocha e fluidos com o intuito de avaliar a sensibilidade de cada modelo a parâmetros do reservatório tais como temperatura, pressão, porosidade e parâmetros elásticos da rocha. É discutida a relevância da consideração de cada modelo na modelagem da resposta sísmica para cenários de injeção de água e injeção de gás.
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Modelos lineares como ferramenta de seleção de atributos na criação de “meta-atributos” sísmicos
More LessA integração de dados de sísmica com perfis de poços é uma busca constante dos geoscientistas. A hipótese testada foi se o traço sísmico e o registro de poço podem ser tratados como séries temporais. Assim, o sinal dinâmico da sísmica pôde se correlacionar com o sinal discreto do registro de poço e o modelo dinâmico para regressão pôde ser aplicado. Para poços direcionais deve-se considerar uma média dos valores dos traços sísmicos para correlacionar com os dados de profundidade ao longo do poço. Existe um grande número de atributos sísmicos e, para muitos, sem significado físico não está bem compreendido. Com auxílio do OpendTect foram calculados treze atributos instantâneos e através de uma busca exaustiva encontrou-se o melhor “metra-atributo” para cálculo da porosidade. Além disto, foi simulada uma busca progressiva. Após o detalhamento do modelo de espaço de estados concluimos que a busca progressiva permite uma escolha de um conjuto de atributos a um menor custo omputacional sem sacrifício da acuracidade do modelo.
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Energia Teager-Kaiser associada à transformada wavelet na geração de atributos sísmicos
More LessA new method to estimate the instantaneous seismic traces energy is presented here. We propose to use the Teager-Kaiser energy associated with wavelet transform to generate a joint time-frequency representation, which can be used as a nonlinear energy tracking of the seismic waves. The method was applied to detect important geological marks and reservoir zones on synthetic seismic traces from well logs. It was also applied to real seismic data and has shown effective to reveal important geological features.
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Hydrocarbon Prospecting in Deep Water Trinidad using AVO and Spectral Decomposition.
Authors Carlos Moreno, Maria A. Perez, Jeff Meyer, Alan Huffman, Mohamad Etemadi and Laszlo BenkovicsAmplitude versus offset (AVO) and spectral decomposition (SD) techniques were used for direct hydrocarbon identification (DHI) in the Plio-pleistocene section in Deep Water Trinidad & Tobago to help to quantify better the risk during hydrocarbon prospecting. In order to understand and predict the seismic response for different fluid types and lithologies, AVO and SD modeling based on existing well log information close to the study area were performed. The controlled synthetic models simulated the seismic response for wet sands, commercially saturated gas sands, and partially saturated gas sands, as well as variations due to lithology. After modeling and validation of the technique with real pre-stack and post-stack seismic data on calibration well locations, seismic analysis supported with AVO and SD technologies was performed to evaluate prospects located in Deep Water in Trinidad & Tobago. Very subtle differences in the AVO and SD responses were the only way to discriminate between hydrocarbon and lithology. Very subtle variations during AVO and SD analysis suggest that the lithology factor can produce false DHI in the area.
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Processing solutions for Wide Azimuth data: Outcome from a WATS field experiment in deep water Gulf of Mexico
Authors M. Magesan, JC. Ferran, S. Kaculini and J. FaulknerWide Azimuth Towed Streamer (WATS) acquisition has already proved to be a key technique in improving seismic imaging, especially in complex areas such as sub-salt plays. In 2006, a WATS field experiment was conducted in a deep water area of the Gulf of Mexico. The purpose was to challenge recently developed 3D processing algorithms and find the most suitable processing strategy for a wide azimuth dataset. The results indicate that a 3D shot based processing sequence is an effective solution that accommodates the effects related to the multi-pass acquisition method and realizes the full benefit of the recorded 3D wide azimuth wave field.
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Qualidade do Imageamento Sísmico através do Reprocessamento de Dados – Bacia do Solimões
Authors Marcela Pellizzon, Marisa Makler and Ronan ÁvilaSeveral researches have been made during the last twenty years about the diabase sills in Solimoes basin and the effect of these in seismic data processing. These rocks strongly influence the exploratory activities in a basin, because the diabase disturbs the sign and generates multiple and spherical divergence, increasing the exploratory risk in these areas. In the present work a method of 2D seismic reprocessing will be presented using Prestack Kirchhoff Time Migration in an older seismic data of Solimoes basin. The objective of this paper is to show the main sequence flow of the process. As a result we have an increase of the quality of imaging under the basalt layers. The 2D lines processed give relevant improvement of the quality of signal, showing better the faults zones and preserving the geological structures than the older data.
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Seismic wavelets and earth’s impulse response amplitude and phase recovery using second order statistics or deterministic methods
Authors Pedro L. Tavares, Paulo S.R. Diniz and Eduardo A.B. da SilvaIn this paper we approach the problem of recovering the earth’s impulse response and the seismic wavelets used to probe the earth by the use of techniques inspired in blind equalization methods developed for digital communication systems. We present
a recently proposed class of algorithms to recover, by seismogram observation only, both amplitude and phase of the seismic wavelets and the earth’s impulse response, assuming a single-input multipleoutput (SIMO) finite impulse response (FIR) model.
In this class of algorithms no assumptions regarding minimum phase of the seismic wavelets are necessary and the earth’s impulse response can be assumed both white or colored (using second order statistics) or even deterministic (using deterministic methods). The only assumption on the seismic wavelets used is that there should be no common zeros on their Ztransforms. With just this assumption we have shown that the recovery of both amplitude and phase of the earth’s impulse response and the seismic wavelets themselves can be accomplished using only second order statistics or direct algebraic manipulations of the seismograms. The only minor drawback is a mild scalar ambiguity intrinsic to the problem. Tests are presented confirming the validity of these algorithms. The results obtained are promising, indicating that this class of algorithms has the potential of opening avenues for a large number of new applications.
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Vertical and Lateral Resolution in the CRS Method: A Practical Study
Authors Fernando Gamboa, Armando Lopes, Lucas Freitas and Martin TygelIn this paper, we discuss the gain in vertical resolution and, maybe, loss of lateral resolution due to the application of the Common Reflection Surface (CRS) method. The CRS method strongly reduces the random noise, allows a better range of frequencies to
recovery by, for example, a spectralwhitening process. It is because CRS uses a larger number of traces than the CMP method to simulate the same ZO trace. But this larger sum, especially the lateral sum, maybe cause loss of lateral resolution. Using the EG 3D model, CREWES 3C-3D Seismic Data Set, were done some tests applying the CRS method with different apertures and studied its effect in the Signal/Noise (S/N) ratio, and also in a synthetic trace was done a test to evaluate the capacity of CRS to recover a trace.
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Interpreting 4D differences with complex trace analysis
Authors H. Hoeber, S. Campbell, M. Dyce, D. Whitcombe and R.C. SkeeneWe show how complex trace analysis can be used to phase and amplitude match seismic data. This technique can be used to deterministically split a 4D difference into two components representing the common amplitude and the common phase. We compare our method to statistical common cube methods, such as singular value and geostatistical decompositions.
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Inteligência artificial identificando modelos deposicionais e de reservatórios de hidrocarbonetos usando sísmica 2D e 3D
Authors Ernesto Marchioni Fleck and Rogerio de Araujo SantosThis work suggests the use of a new method of seismic data clustering that can aid in the visualization of seismic maps. Seismic data are primarily made of signal and noise and, due to their dual composition, have asymmetric distributions. Seismic data are traditionally classified by methods that lead the proposed groups’ references to their mean values. The mean value is, however, sensitive to noise and outliers and the classification methods that make use of this estimator are, consequently, subject to generating distorted results. Although other works have suggested the use of the median in cases where the distributions are asymmetric – due to the fact that this estimator is robust with respect to noise and outliers – none have proposed a method that would lead the groups’ references to the median value while treating seismic data. The method proposed in this work includes, therefore, an algorithm that leads the groups’ references to their medians. The iterative treatment of seismic data through the use of a non-linear function that is adequate for the gradient descent generates results with mean-square errors inferior to those generated by the use of the mean value. The algorithm’s nonlinearity constant determines how seismic data are led from the mean value towards the median. Convergence can be achieved with little iteration in the proposed method. It can, therefore, be used as a tool in the sizing of petroleum reservoirs and can also be used to determine the differences between similar geological structures.
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O reprocessamento sísmico, com ênfase na sua contribuição para o conhecimento das bacias brasileiras
More LessThanks to Petrobras and to ANP Brazil has a very well preserved seismic legacy data. Most of them were registered applying technologies that today make it possible to increase value during their reprocessing. Some of this information was obtained in areas that became critical due logistic or environmental issues and probably represents the only possible version for ever. This article will present results and gains obtained during the last two years when extent areas of some important Brazilian’s basins were reprocessed using the state of the art of processing technologies.
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Multi-dimensional data regularization for modern acquisition
Authors Gordon Poole, Philippe Herrmann and Henning HoeberData regularization is critical for the suppression of Kirchhoff migration noise and the production of a clean migration image. Techniques that perform data regularization simultaneously along two axes provide a solution where multiple passes of a 1D approach fail. We introduce a versatile two-dimensional Fourier reconstruction algorithm that regularizes the input data as well as filling gaps in the coverage. We validate the algorithm on a synthetic cross-spread gather example as well as demonstrating the technology on a real offset volume dataset. The results show an improved continuity of the data and preservation of the data character even where we observe conflicting dips. Our one-pass approach can handle empty and overfold bins thus making use of all recorded traces and simplify the pre-stack processing flow.
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Seismic horizon mapping across faults with Growing Neural Gas
Authors Aurélio M. Figueiredo, Marcelo Gattass and Flavio SzenbergManual horizon mapping from 3D seismic data is a very time-consuming task. Most automated or semiautomated methods have undesired limitations, like the inability to find correlated horizon portions separated by interruptions, particularly seismic
faults. We present a clusterization-based method to extract horizons that uses the Growing Neural Gas (GNG) algorithm. The sample representing each voxel is replaced by its local behavior in the vertical direction. Lateral similarity measures are implicitly
stored in the sample distribution over the created clusters. The method was applied to real seismic data to extract horizons and performed well even when the surface was completely separated by seismic faults on volume data.
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Atenuação do ground roll utilizando filtros anti-simétricos tipo Wiener-Levinson
More LessGround roll or superficial rolling noise occurs in land seismic data dominating some portions of the seismograms masking the seismic reflections of interest.. The attenuation of this kind of noise represents a serious obstacle to the processing of land seismic data. This paper presents a new filtering approach based on the welll known Wiener-Levinson deconvolution method. The causal and anti-causal Wiener-Levinson filters are combined to form an anti-symmetric non-causal filter. The method was tested on seismic data of the Tacutu basin and the results demonstrate that the new approach is very effective, showing a stacked seismic image with an improved time resolution and better lateral continuity of the reflections, when compared to the conventional results of the f-k method.
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Processamento CMP e SRC de dados sísmicos elásticos 2-D gerados a partir de um Modelo Representativo da Bacia do Solimões, Região Amazônica, Brasil.
More LessAmong 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 elastic 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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Reprocessamento de dados sísmicos da Bacia do Solimões - Migração Prestack x Poststack
Authors Bruno M. Silva, Leo R. Nascimento, Ronan Ávila and Roberto R. BaldanzaDuring the restart of the seismic exploration in the Solimões Basin, in 1976, a large distribution of surveys was constructed in the central zone of the basin. It was also the beginning of the use of the CDP method and digital record methods. The migration of these data, done during the first processing, was developed at that time by the method considered the state of the art: the Poststack Kirchhoff Migration. Nowadays, the reprocessing of old seismic data using modern methods has been very common around the world (Ritchie et al, 2005 e Chopra et al, 2004). New prospects have been obtained based on new and more powerful methods of signal/noise enhancements, multiple attenuation and mainly migration. The present work exposes some lines of the seismic data reprocessing project from the Solimões Basin. The first processing produced sections with reasonable quality until the zone of 1,5 seconds, but with signal/noise ratio very low below this level. Besides, the excess of coherency filters in the prestack data
hidden geologic faults that at the present time are clearer in the reprocessing sections. The differences between the sections produced with Post and Prestack Migration will be presented revealing that Prestack Migration of these data acquired during the 70’s and 80’s showed results of excellent quality referring to the fault zones and the structures below the three large diabase sealer that cover the basin, mainly below 1,5 seconds.
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2-D CRS Stack : one-step versus multi-step strategies
Authors G. Garabito, João C.R. Cruz and Peter HubralThe Common Reflection Surface Stack (CRS) method simulates zero-offset (ZO) sections by means of summing the amplitudes of seismic events in the multicoverage data by using a stacking surface. For 2-D media, this stacking surface depends on three
kinematics attributes of two hypothetical waves at the point of emergency of the normal incidence central ray, namely, the emergency angle of the normal ray, the radius of curvature of the Normal Incidence Point Wave and the radius of curvature of the Normal Wave. The optimization problem in the CRS method consists in determining, from the multicoverage seismic data, the three CRS parameters associated to each sample point of ZO section to be simulated. The simultaneous determination of these parameters can be made by means of multidimensional global search process (or global optimization), using as objective function some coherence criterion. In this work we present a new one-step strategy (i.e. the three CRS parameters are obtained simultaneously) to implement the 2-D CRS stack method. To test the one-step CRS strategy, we apply it to the Marmousi synthetic dataset and the results show a better continuity of the seismic events in comparison with the results of the multi-step CRS stacking strategy.
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Atenuação de reflexões múltiplas com deconvolução multicanal no domínio afastamento comum versus ponto-médio comum
Authors Rosangela Corrêa Maciel and Milton José PorsaniThe multi-channel Wiener-Levinson predictive deconvolution is a filtering technique, which has been successfully used for the attenuation of multiple reflections of marine seismic data. Normally the filtering is done through the use of traces corrected from the normal move out, and organized in panels of common-offset (CO) or common midpoint (CMP) gathers. Recently this method has been combined with the common reflection surface (CRS) stacking method. In the present paper we apply the direct multichannel
predictive deconvolution method (Porsani and Ursin, 2007) using traces collected from the CO and CMP domains, and located at the neighborhood of each target trace. Numerical results using data from the Gulf of Mexico demonstrate the effectiveness of the new approach for the attenuation of the multiple associated to with the sea bottom.
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Filtered and Enhanced Resolution in Spectral Signal Seismic Processing
Authors Dorian Caraballo Ledesma and Yezid Torres MorenoTime-frequency representations are showed in this work for analysis of the seismic data in applications with spectral resolution and filtering. The first is the Gabor transform and the second one is the Fractional order Fourier transform. Both provide to the seismic data a affective tool for the spectral treatment. Simulations have been made with synthetic data where the main goal is improve the signal processing.
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Local Angle Domain in Seismic Imaging
Authors Zvi Koren, Igor Ravve, Allon Bartana and Dan KosloffImaging systems involve interaction of two wave-fields at the image points (elements): incident and reflected/diffracted. Each wave-field can be decomposed into local plane-waves (or rays) indicating the direction of propagation. The direction of the incident and the reflected/diffracted rays can be conventionally described by two polar angles, respectively. Each polar angle includes two components: dip and azimuth. Therefore, a set of four scalar angles is required to define an angle domain imaging system at a given image point. Ray-based and wave-equation angle-domain migrations deal with systems in which at each image point both the incident and the reflected wave-field are composed of a wide range of directions. The imaging stage involves combination of ray pairs (or pairs of local plane waves) indicating the incident and reflected/diffracted rays. Each ray pair maps seismic data, recorded on the free surface, into the four-dimensional Local Angle Domain (LAD) space. In our notation, these angles are dip and azimuth of the ray-pair normal, opening angle and opening azimuth. We establish relationships between the directions of the ray pairs and the LAD angles. We consider a general case of transverse isotropy with tilted axis of symmetry (TTI) and waves or converted waves.
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Subsalt Imaging – The wide azimuth experience
Authors S. Kapoor, Michael O’briain, Dawit Desta, Ilgar Atakishiyev and Michiru TomidaNew acquisition techniques such as wide azimuth (WAZ) and rich azimuth (RAZ), together with more accurate velocity models and migration algorithms, are being developed to meet the demand to provide accurate images in Gulf of Mexico subsalt exploration
areas. In this paper, we will share experiences gained and real data examples from processing several such surveys.
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Imaging Ultra Deep Geologic Structures using Wave Equation Migration and Illumination
Authors Alexander Mihai Popovici, Sean Crawley, Yining Li, Cristian Lupascu and Sergey FomelWe present a novel technology, designed to enhance seismic resolution and imaging of ultra-deep complex geologic structures by using (1) wave-equation depth migration and (2) wave-equation velocity model building technology for deeper data penetration and recovery, steeper dip and ultra-deep structure imaging, and accurate velocity estimation for imaging and pore pressure prediction, and (3) accurate illumination and amplitude processing for extending the AVO prediction window. Ultra-deep wave-equation imaging provides much greater resolution and accuracy than what can be accomplished with standard imaging technology. The advanced imaging methodology may improve the success rate and cost effectiveness for new deep-field discoveries, and also has applications in increasing recovery efficiency for the development of existing fields.
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Explicit high-order reverse time pre-stack depth migration
Authors Matthew H. Karazincir and Clive M. GerrardReverse time pre-stack depth migration, which uses the two-way acoustic wave equation, is not a new concept. Conventionally the method has been very computationally intensive and, therefore, has been considered impractical for production 3D depth imaging projects. Here we describe an efficient algorithm that can be used on large scale 3D seismic data. To make it practical and efficient we employ explicit 2nd order in time and high order in space domain finite differences, and use domain decomposition methods to split the image cube amongst multiple CPU’s, when necessary. Only a few finite differencing layers are communicated between related CPU’s, by message passing. High order spatial finite differences handle numerical dispersion and allow larger time steps than those possible with the, more conventional, pseudo-spectral method. We will show an overview of the method along with 2D and 3D synthetic and real data examples.
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Evaluation of wave equation angle domain common image gathers
Authors Dan Kosloff, Igor Ravve, Zvi Koren and Allon BartanaAngle domain common image gathers are an important analysis tool for the correctness of the velocity used in seismic migration. These gathers also form a useful input for amplitude versus angle (AVA) studies. This study examines two alternative procedures for generating angle domain common image gathers in wave equation migration. The first procedure, developed in Xie and Wu (2002), is based on a harmonic decomposition of the downward continued wave fields. The second approach, developed in Sava and Fomel (2003), is based on performing a slant stack on local offset gathers. The later approach is much easier to implement and computationally faster compared to the first approach. Examination of the two methods by means of a simple synthetic example shows that the procedure of Xie and Wu produces the same residual moveout curves as Kirchhoff depth migration. Conversely, the procedure of Sava and Fomel produces moveout curves that deviate from the curves obtained by ray based migration. We therefore conclude that in spite of the extra complication and cost, the procedure of Xie and Wu should be preferred for velocity updating methods which are based on the shape of the residual moveout curves.
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Vertical image waves in elliptically anisotropic media
Authors J. Schleicher, A. Novais and J. CostaBy reparameterization of the kinematic expressions for remigration in elliptically anisotropic media using a new ellipticity parameter, we derive a new image-wave equation in elliptically anisotropic media, which describes the reflector position as a function of the medium ellipticity. This imagewave equation, which is a kind of medium-dependent oneway wave equation, can be used for automatically stretching a migrated image in depth until wells are tied or other geologic criteria are met. In this way, it is possible to find an estimate of the vertical velocity, which cannot be detected from time processing only. A simple numerical example confirms the validity of the theory.
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A Comparison of Imaging Conditions for Wave-Equation Shot-Profile Migration
Authors J. Schleicher, J. Costa and A. NovaisThe application of an imaging condition in wave equation shot profile migration is important to provide illumination compensation and amplitude recovery. Particularly for true-amplitude wave-equation migration algorithms, a stable imaging condition is essential to successfully recover the medium reflectivity. We study a set of image conditions with illumination compensation. The imaging conditions are evaluated by the quality of the output amplitudes and the artifacts produced. In numerical experiments using a vertically inhomogeneous velocity model, the most stable of the tested imaging condition divides the up- and downgoing wavefields after inverse Fourier transform.
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Surface wave group velocity tomography of the southeastern Brazilian Continental Margin
Authors Ricardo Thomas Beck and Jorge Luis de SouzaA large quantity of Rayleigh wave dispersion curves were used to image the southeastern Brazilian continental margin. Several important geological features were detected in those images. According to the images, the São Paulo plateau has a cylindrical form throughout the major part of the lithosphere of the region and it spreads over a wider region at the base. This behavior suggests a hotspot formation.
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Basin reevaluation by CRS-stack-based seismic reflection imaging
Authors Björn Z. Heilmann, Lourenildo W.B. Leite and Anderson B. GomesIn this case study we are giving attention to the seismic processing of a challenging land data set from the Takutu Basin, North Brazil. The presented results were produced in the framework of an binational research project which aims at developing a new seismic reflection imaging workflow well suited for reprocessing seismic data and reevaluation of exploration prospects. In this specific case, the data was acquired under difficult conditions many years ago. Thus, the main problem encountered was the poor quality of the data, especially with respect to coverage and signal-to-noise ratio. The data suffered from top-surface topography, a strongly varying weathering layer, and complex near-surface geology. Due to the fact that the spatial CRS stacking operator fits the actual reflection events
much better than conventional stacking operators and involves many neighboring CMP gathers into the stacking
process, a strong improvement of the signal-to-noise ratio can be expected. Furthermore, the large fold of the CRS
operator provides a significantly increased statistical basis for residual static correction compared to conventional approaches, which also makes this approach particularly suited for reprocessing data sets such as the one at hand.
In view of these complex conditions the conducted imaging workflow, i.e. stack, residual static correction, redatuming, tomographic inversion, and pre- and poststack depth migration, led to a significant improvement in resolution, signal-to-noise ratio, and reflector continuity.
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Uma estratégia de migracão RTM para aquisições bi e tri-dimensionais
In this work we introduce a scheme of reverse time migration specially designed for offshore data acquired with a single boat pulling one or two air-guns and some streamers of receivers. 2-D and 3-D depth migrations are performed using the concept of areal shot record, as it was introduced in (Berkhout, 1992). In our scheme, an areal shot record is computed through the sum of convolutions between the seismograms registered along a sail line and a synthesis operator, which is designed in order to form a specific wave front just above the target zone (controlled illumination). All extrapolations are performed solving the acoustic two-way wave equation without any assumption in relation to the macro-velocity field. We illustrate the method with an application on the 3-D SEG-EAGE Overthrust model and 2-D Marmousi model. Except for some small artifacts, less than forty areal shot records were enough to image the main interfaces. The execution time was considerably lesser than the one required to reserve time migrate all seismograms independently.
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Redatumação por Famílias CFP de dados influenciados pela presença de canyons no assoalho marinho
In this paper, we introduce a new formulation for data recorded redatuming on surface that are influenced by canyons present in marine floor, using the concept of Common Focus Point (CFP) Gather, with wavefield extrapolations without asymptotic approximations. This new formulation proposes to eliminate the effects of the floor marine topography (Filgueiras, 2007). It is based on the concepts of CFP technology introduced by Berkhout (1997a. and 1997b.) and the virtual source method, introduced by Bakulin and Calvert (2004). The CFP technology, a particular case of Areal Shot Record, uses the concept of synthesis operator, which was generated on reference datum, and it was registered on surface of the velocity macro model. The algorithm applied here, for this methodology, was developed by the finite differences technique, with fourth order approximation for spatial derivatives and second order approximations for time derivatives. Synthesis operator CFP, or summation of them, is extrapolated in time and registered on the surface, generating a new seismogram, which is the CFP gather (for the case of the commom shot gather) or CFP gathers (for the case of areal shot record – Berkhout, 1992). The next step of the redatuming is the CFP gather by wave equation extrapolation for reference datum. This procedure implies a new datum a final seismogram redatuming, capable to show the reflections with no canyons influence of the most all reflectors that are under the reference datum. From cinematic point at view, the results from synthetic data were satisfied.
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True-amplitude diffraction-stack redatuming
Authors Matheus F. Pila, Jörg Schleicher and Amélia NovaisThe purpose of redatuming is to transform seismic data acquired at a certain measurement surface to simulated data as if acquired at a different measurement surface. Based on the chaining of diffraction-stack migration and isochron-stack demigration, we derive a true-amplitude diffractionstack-type redatuming operator for zero-offset data. It consists of performing a single weighted stack along adequately chosen stacking lines. For simple types of media, we derive analytic expressions for the stacking lines and weight functions and demonstrate its functionality with numerical examples.
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Estudo de formas implementacionais da equação da onda imagem para remigraço na profundidade
Authors Fernando Perin Munerato, Jörg Schleicher and Amélia NovaisIn this work we study different implementational forms of the image-wave equation for depth remigration. This is a partial second-order differential equation similar to the acoustic wave equation. We determine, additionally to consistency and stability, the conditions for dispersion and dissipation of six finite-difference schemes for this equation in different forms, obtained by change of variables. These conditions cannot be simultaneously satisfied, i.e., a precise result is not easily obtained. Numerical tests confirm the theoretical stability results for three of the investigated schemes but fail for the others.
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Subsalt illumination studies through longitudinal and transversal wave propagation
Authors Riaz Alai, Jan Thorbecke and Eric VerschuurIn this paper, propagation and illumination studies have been performed for acoustic and elastic wave field propagation through a realistic model representing a typical Gulf of Mexico salt structure. Strong wave conversions may occur at the interfaces of sediments and adjacent salt bodies. These wave conversions occur because of the high velocity contrasts and inhomogeneities, and in general (longitudinal) P-waves get scattered, refracted and converted due the stronger wave distortion effects of (longitudinal) P-waves at these strong velocity contrasts, yielding large shadow zones. On the other hand, the converted (transversal) S-waves, propagate in general in the salt bodies with less wave front distortion because of their lower propagation velocity and, therefore smaller contrasts with the surrounding sediment P-wave velocities.
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Time and depth remigration in elliptically anisotropic media using image-wave propagation
Authors R. Aleixo and J. SchleicherIn this work, we derive image-wave equations, that is partial differential equations that describe the dislocation of a reflector image as a function of the velocity model, for time and depth remigration in elliptically anisotropic media, under variation of migration velocity and medium ellipticity. A simple numerical example demonstrates the validity of the theory.
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Velocity analysis of marine seismic data using Reverse Time Migration
Authors Marco A. Barsottelli Botelho and Antônio V. Moura LimaIt is proposed a scheme using finite-difference Reverse Time Migration (RTM) and two or more common shot gathers which is able to perform as a velocity indicator. The procedure was tested on synthetic and real marine data and allow to define a good velocity model with erros of approximately 5%. The procedure presented here can be used on any data aquired over complex geology. It constitutes a advantage over the conventional seismic processing velocity analysis, based on normal move out equation, which is based on the assumption of flat and horizontal reflectors.
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Obliquity correction for reverse time migration
More LessThe quality of seismic images obtained by reverse time migration strongly depends on the employed image condition. We propose a new imaging condition, which is motivated by stationary phase analysis of the classical crosscorrelation imaging condition. Its implementation requires the Poynting vector of the source and receiver wavefields at the imaging point. An obliquity correction is added to compensate for the reflector dip effect on amplitudes of reverse time migration. Numerical experiments show that using an imaging condition with obliquity
compensation improves reverse time migration by reducing backscattering artifacts.
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Migração de turning waves através das equações da onda unidirecionais: Implementação da migração PSPI para turning waves
Authors Jeferson A.C. de Andrade, Flor A. Vivas and Reynam da C. PestanaThe one-way wave equations (OWWE) can modeling and migrate wave fields in high accurate until near horizontal
propagation. Wave fields which overturned in vertical gradient of velocity model and reflected after or before of the turning points – also called reflected turning waves, are not taking in account in the conventional imaging process. Recently a new strategy to imaging turning waves has been proposed. First the downward extrapolation is applied with the conventional imaging condition. Then the upward extrapolation of the wave fields with three new imaging conditions are applied to consider the turning waves. In this work we give a geometrical interpretation of each imaging condition, discuss the fundaments of the cited turning wave, the migration strategy applied and show the results obtained with the PSPI migration method on a salt dome data without and with turning waves image conditions.
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Regularized Diffraction Tomography for Trigonal Meshes Applied to Reservoir Monitoring
More LessDiffraction tomography is an inversion technique that allows the reconstruction of subsurface velocity field from scattered acoustic field data. A higher resolution imaging conventionally requires estimation of a larger number of parameters. A trigonal mesh was applied, in order to strongly reduce the number of parameters. Thus, instead of estimate velocity for each cell in a regular grid, it was estimated only at triangle vertexes, which act as control points to the interpolation of velocity field within each triangle. Regularization was required to avoid sharp artifacts due to trigonal elements. A synthetic model was adopted to test the feasibility of the proposed method
for reservoir monitoring.
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Metodologias de extração de parâmetro ótimo de regularização a partir da curva L: aplicação em tomografia de tempos de trânsito
Authors Felipe A. Terra, Amin Bassrei and Eduardo T.F. SantosInverse problems in geophysics are usually ill-posed, in such a way that regularization is one possibility to have more stable solutions. The quality of the regularized solution however depends on the appropriate selection of the regularization parameter λ. One now popular tool for the selection of λ is the so-called L-curve, reintroduced in the literature of inverse problems by Hansen in the 1990’s. L-curve may sometimes provide a non-optimal λ for imaging, so that in the present work we compare three methodologies for the selection ofλ. The first one is the λ provided by the Hansen’s toolbox. The second is the visual inspection of the L-curve built by us, and the third one is the critical point of the L-curve first derivative, which is, in general, equivalent to the inflection point, or the L-curve’s knee. This point is the appropriate compensation between the x axis which is the data parameter error, and the y axis, which represents the amount of regularization. Extensive simulations with synthetic data in traveltime tomography leaded us to the conclusion that all three methodologies are feasible, although we noticed that for the zero order regularization, with noisy data, visual inspection and first derivative methodologies provided the best results.
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Elastic inversion for thin-layer models in the spectral domain using the Laplace transform
Authors Georgy Mitrofanov, Viatcheslav Priimenko, Roseane Missagia and Luís H. AmaralSolution of the inverse problem for thin-layered elastic models is built by the methods of nonlinear optimization using an effective solution of the direct problem in the spectral domain. We obtain the solution with an explosion source for the two-component seismograms. Special attention is given to investigation of the behavior of the residual functional in the spectral domain in dependence on various parameters of the inverse problem because the residual functional may have the local minima and maxima. At that the parameter of the Laplace transform can play the key rule. Our research allowed us to formulate a strategy for the minimization of the residual functional and to find the global minimum point. Realization of the strategy allowed us to estimate the parameters in the spectral domain for thin-layered objects, which are similar to real media.
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Seismic ray tomography using function norm
Authors Vânia G. de Brito dos Santos and Wilson M. FigueiróThe high computer processing time consumption is a problem usually related to the seismic ray tomography methods. This occurs because, in each step of the iterative inversion process defined by the tomographic method, the two-point ray-tracing problem must be solved for each pair source-receiver. In order to solve such kind of trouble, the vector norm, commonly used as an error function to be minimized in inversion procedures, is substituted by an integral function norm, which allows us to estimate model parameters by means of the minimization of the area between observed and calculated traveltime curves that are interpolated or adjusted to the data points. Relatively simple mathematical developments and numerical experiments with seismic velocity field models show that integral
function norm permits us to save a lot of processing time without an important loss of accuracy. Sometimes,
parameters of the model can be better estimated using function norm than the vector norm traditionally used in
seismic inversion tomography.
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Modeling, Migration and Inversion with Gaussian Beams, Revisited
More LessGaussian beams have been shown in some cases to provide smoother leading order asymptotic expansions of the solution of wave equations than classical ray theory provides. They do this through complex-valued traveltime functions that describe the propagating wave in a tube around some central ray. Quadratic exponential decay orthogonal to the central ray arising from the imaginary part of the traveltime provides a "skin depth" to the ray tube.
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Kirchhoff-Gaussian-Beam prestack depth migration – application to complex data
Authors Carlos A.S. Ferreira and Samuel H. GrayIn this work we successfully apply the Kirchhoff-Gaussian-Beam prestack depth migration (KGB-PSDM) process on a finite-difference modeled, 2D synthetic seismic dataset representative of the Urucu River oilfield (Solimões Basin, Brazil). In these examples, the traveltimes are computed using a simple solution of the eikonal equation and weights are applied to correct amplitudes from spherical divergence effects. The results are then compared to true amplitude Kirchhoff depth migration.
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The Advantages of Plane-Wave Reverse Time Migration
Authors Denes Vigh, E. William Starr and Carlos Eiffel Arbex BelemAfter exhausting the Kirchhoff summation and one-wave equation techniques, especially in subsalt imaging, the industry turned to two-way wave equation implementations or in other words Reverse Time Migration (RTM). This algorithm allows steep dip imaging, any lateral velocity variation and correct amplitude and phase information at the same time. The only hurdle is an acceptable turnaround time. The first and most obvious implementation is the shot domain version which is the most time consuming. Another possibility is the plane-wave approximation where we gain speed and may keep the quality at the same level as the RTM shot domain implementation.
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Zero-offset seismic amplitude decomposition and migration
Authors Bjørn Ursin and Martin TygelIn an anisotropic medium, a normal-incidence wave is multiply transmitted and reflected down to a reflector where the phase velocity vector is parallel to the interface normal. The ray code of the up-going wave is equal to the ray code of the down-going wave in reverse order. The geometrical spreading, KMAH index and transmission and reflection coefficients of the normal-incidence ray can be simply expressed in terms of products or sums of the corresponding
quantities of the one-way normal and NIP waves. Here we show that the amplitude of the ray-theoretic Green’s function for the reflected wave also follow a similar decomposition in terms of the amplitude of the Green’s function of the NIP wave and the normal wave. We use this property to propose three schemes for trueamplitude post-stack depth migration in anisotropic media where the image represents an estimate of the zero-offset reflection coefficient. The first is a map migration procedure in which selected primary zero-offset reflections are converted into depth with
attached true amplitudes. The second is a raybased, Kirchhoff type full migration. Finally, a wave equation continuation algorithm can be used to reverse-propagate the recorded wavefield in a halfvelocity model with half the elastic constants and double the density. The image is formed by taking the reverse-propagated wavefield at time equal zero followed by a geometrical spreading correction.
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Wide Angle FD and FFD Migration using Complex Padé Approximations
Authors D. Amazonas, J. Costa, J. Schleicher and R. PestanaSeismic Migration by downward continuation using the one-way wave equation approximations has two shortcomings: imaging steep dip reflectors and handling evanescent waves. Complex Pad´e approximations allow a better treatment
of evanescent modes, stabilizing finite-difference migration without requiring special treatment for the migration domain boundaries. Imaging steep dip reflectors can be improved using several terms in the Padé expansion. We discuss the implementation and evaluation of wideangle complex Pad´e approximations for finite-difference and Fourier finite-difference migration methods. The dispersion relation and the impulsive response of the migration
operator provide criteria to select the number of terms and coefficients in the Padé expansion. This assures stability for a prescribed maximum propagation direction. The implementations are validated on the Marmousi model dataset and SEG/EAGE salt model data.
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Migração Pré-empilhamento dos Dados Sísmicos BP 2004
Authors Nei D. Figueiredo, Enock F. Alves, Reynam Pestana and Gary AldunateIn this work we applied three pre-stack migration techniques on the BP 2004 dataset. It was migrated with the Kirchhoff migration method, using the Seismic Unix package (SU), the phase-shift plus-interpolation (PSPI) migration method and also the plane wave (OP) migration method. These two last methods were implementing in parallel and incorporated to our SU version. The results with the Kirchhoff method using a smoothing velocity field were not quite good. Using PSPI and OW, the results were satisfactory and show the top and base of the salt body well imaged. But the salt´s flankes didn’t have a good image. This dataset is still a challenge for migration methods.
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3D Modeling and Migration of a Wide-Azimuth Towed Streamer Survey
Authors A. Guitton, B. Kaelin, F. Ortigosa, D. Bevc, C.A. Fernandez, J. Higginbotham, B. Fontecha and J.M. CelaA 3D synthetic wide-azimuth towed-streamer (WATS) dataset is modeled and migrated. The modeling was performed on MareNostrum at the Barcelona Supercomputer Center using a maximum of 2000 cpus. This dataset is then migrated with three imaging techniques suited for complex overburden. First, a wave-equation method based on a one-way propagator is used. Second, a two-way method that utilizes one-way propagators for the wavefield extrapolation downward and upward is tested. Finally, a method based on the solution of the two-way acoustic wave equation, also known as Reverse Time Migration (RTM) is selected.
We compare the migration results in 2D and 3D and show that the best results are obtained when more information is incorporated in the imaging process, e.g., turning and/or prismatic waves. In practice, the selection of a migration algorithm is based on computational and geophysical considerations. For instance, the complexity of the subsurface indicates if turning waves are needed or not. Our ability to estimate an accurate velocity model influences which method will produce the best results. Finally, computing resources could present challenges when large datasets need to be migrated, especially for advanced imaging techniques such as RTM. Here, our ability to use MareNostrum, the 5th largest computer in the world, proved extremely valuable.
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