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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 - 250 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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