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12th International Congress of the Brazilian Geophysical Society
- Conference date: 15 Aug 2011 - 18 Aug 2011
- Location: Rio de Janeiro, Brazil
- Published: 15 August 2011
81 - 100 of 465 results
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Japanese Tsumani 2011 Effects on the Geomagnetic Field: Preliminary Results
More LessThe vertical component of the geomagnetic field observed by ground-based observatories of the INTERMAGNET network has been used to analyze the effects of the Japanese tsumani, 2011. The purpose of this work is to observe the geomagnetic variations induced by a tsunami resulting from the strong earthquake on 11 February 2011. We choose four stations that were influenced or more direct affected by the tsumani. The stations considered in this analysis were: Kanoya (KNY), Memambetsu (MMB), Guam (GUA) and Charters Towers (CTA). To detect these disturbances in the geomagnetic data, the discrete wavelet technique have been used in three levels of decomposition. We were able to detect the localized behavior of the geomagnetic variations induced by the movement of electrically conducting sea-water through the geomagnetic field, i. e., the identification of transients related to the tsunamis. As well, using the minutely magnetogram data, it was able to localize the inicial phase and time of the tsunami maximum height. The first interpretation of the results suggests that discrete wavelet transform can be used to characterize the tsumanis effects on the geomagnetic field, but need further study.
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Building Anisotropic Models for Depth Imaging: Comparing Different Approaches
More LessSeismic images are only as good as the velocity models used to produce them. As we move from “easy oil” to “difficult oil”, targets in subsalt, sub-basalt, and deep complex areas, we can no longer build the simple isotropic models of the past. To fully leverage the potential of new data types (e.g., wide azimuth and long offsets), we have to move to anisotropic imaging (VTI or TTI) in all geological provinces. Incorporating anisotropy increases our ability both to focus the seismic data and to accurately position our seismic images for drilling decisions. While these goals are achievable with anisotropic models, they are only met when geology and data from boreholes are intimately incorporated into velocity model building from the very start. We discuss several different approaches for anisotropic model parameter estimation and we illustrate some of the possible strategies for model building with case studies from the Gulf of Mexico and West Africa.
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Application of 3D Interbed Multiple Attenuation in the Santos Basin, Brazil
More LessImaging of pre-salt reservoirs in the Santos Basin can be significantly affected by the presence of strong interbed multiples in the data. These multiples can be predicted using a data-driven, true azimuth convolution method similar to surface-related multiple elimination (SRME), and removed using a suitably constrained subtraction technique. We discuss the application of this method to Santos Basin data, and present results on 2D synthetic data and 3D real data.
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Estudo Geofísico de Vazamento de Combustíveis em Posto de Abastecimento
Authors Aline Muriel da Cunha Menezes and César Augusto MoreiraThis paper presents the results of applying the Electrical Resistivity method by electrical profiling technique to investigate the fuel presence in soil and groundwater proceeding in station gas, located in an urban area Caçapava do Sul (RS), on soil in situ, from modification of Caçapava granite. The results suggest an association between low resistivity anomalies zones with potentially degraded from underground tanks storage in free phase form, now represented as residual phase. The electrical resistivity method proved to be an important tool for assessment and environmental monitoring in conjunction with direct methods of investigation.
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Ensaios Sísmicos (Refração Utilizando Ondas P E S E Ensaio Com Ondas Superficiais) Na Caracterização Geotécnica de Um Aterro.
More LessThis paper presents the results of a seismic refraction survey (using shear and P waves) and Multi Channel Analysis of Surface Waves (MASW) carried out a landfill. P-waves and shear waves velocities has allowed to get dynamic properties (Poisson´s ratio) of the landfill. The MASW survey has identified an inversion of shear wave velocity that can be related to the interface between the compacted landfill and the natural terrain situated below this.
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Normalized Reflectivity in Reverse Time Migration
Authors André Bulcão, Gustavo Catão Alves and Djalma Manoel Soares FilhoReverse Time Migration has recently gained much attention as a viable and accurate technique for imaging reflectors, especially in complex geologies. However, reflection amplitudes in RTM are problematic and limit its applications when correct reflectivity is necessary. In this work, normalized reflectivity amplitudes for reflectors in Reverse Time Migration are achieved when the amplitude matrix used for the excitation time image condition is applied as a normalization factor to the migrated image. The amplitude matrix acts as a weighing factor that takes into account the illumination of the target reflector, giving more accurate results for the reflection coefficient. Results are shown for a simple 2D horizontal model and for 2D horizontal model with a diving reflector. In both cases, a reflection coefficient is obtained that closely matches the theoretical trend. A wave separation technique applied for increasing the amplitude accuracy is also discussed (Bulcão et al 2007), despite the marginal gains.
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VSP Survey Assists in the Reservoir Characterization of Deep-Water Turbiditic Reservoir Offshore Brazil
More LessIn this case study we review the main results from a rig-source VSP survey, acquired in a deep-water deviated well drilled offshore Brazil. The primary goal for the VSP was to illuminate the lateral variation of thin sand and shale bodies, with higher resolution than available with surface seismic data. This was achieved initially by 2D migration of the VSP data and later, through acoustic impedance inversion of the VSP data.
New surface seismic data is being acquired in the area and the VSP results will be used to quantitatively assess the data processing and the well tie quality. Seismic parameters such as phase, true amplitude and anelastic attenuation are readily available from the VSP measurements. The anelastic attenuation is quite important in this area as the overburden is dominated by highly cyclic siliciclastic deposition, which results in strong attenuation of the seismic data.
Finally, we present some advanced VSP data processing techniques, such as migration of surface related multiples and far field signature estimation for Q-factor computations, which added value to the VSP results.
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The Multicomponent Seismic Paradigm: Conservative Principles
Authors Carlfred Bautista and Luis Antonio Castillo LópezThis article pretends to show the basic concept inherent to the processing of converted waves (P mode to S mode), concepts specifically related to the correction required for the location of the seismic converted wave.
A formal geometric deduction is made of the equation that governs the correction to the coordinates of common midpoint. It is solved by MatLab algorithm, considering straight ray path in an homogeneous and isotropic medium. This correction distinguishes the converted wave processing compared to conventional P-wave processing.
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Electrical Resistivity Tomography to Follow up an Airborne Em Rock Slide Mapping Survey – Linking Rock Quality With Resistivity
More LessWe investigate an active rock slide in Western Norway with ground- and airborne resistivity mapping to ultimately find weakness zones & sliding planes embedded in crystalline bedrock. The study area comprises phyllite, a low grade metamorphic rock type that tends to be reworked to clay in disturbed zones. Mapping these electrically conductive clay zones was the aim of the survey. GPS measurements over the last 5 years indicate that precipitation drives rock slide movements. The role of ground water is thus a crucial factor to investigate for risk assessment in the area. Based on a successful airborne electromagnetic (AEM) demonstration survey, we conducted a total of 1.600 profile meters of ground resistivity measurements to confirm AEM anomalies, to gain precise 2D geometries and to link conductivity anomalies with geology. All resistivity results confirm AEM anomalies and refine their lateral extent. In the East we find consistency between a strong conductor, dipping sub horizontal SW with an outcropping thrust fault, separating phyllite and gneiss. In the West a conductor dipping steeply NNW seems to be fed by surface water and may represent a formerly unknown sliding plane. Detailed geotechnical follow up is pending (drilling and instrumentation).
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Aerogeofísica (Magnetometria e Gamaespectrometria) Como Suporte Ao Mapeamento Geológico da Folha Baturité, Norte do Estado do Ceará
This work refers to the results from the processing and interpretation of airborne geophysical data (magnetic and gamaespectrometry) with the goal of give support to the geological mapping of the Baturité sheet (1:100.000), located in the north of Ceará state, northeast of Brazil and developed by the Geological Survey of Brazil (CPRM). The geophysical processing products together with the geologic mapping were able to determine the mains lithoestratigrafic domains and the structural framework of the study area.
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Geostatistical Reservoir Modeling Issues, How Seismic Can Help: A Typical Case Study
More Less3D earth modeling is a key issue for Reservoir Characterization. Fluid flow simulations based on a reliable model of reservoir heterogeneities will provide better prediction of hydrocarbon production. Moreover the uncertainty on the reservoir structure, the rock properties and the contacts may be assessed by means of simulations that preserve the geological features of the reservoir. This paper deals with a geostatistical workflow of a 3D reservoir modeling applied to real data of a siltstone reservoir. The first key issue is the optimal use of the available data: the wells with information on markers of key horizons, lithofacies and porosity and an acoustic impedance cube that brings relevant information for constraining the porosity model and facies proportions. The second point is related to the comparison of different geostatistical methods. The main steps of the workflow are: - Surfaces simulations delimiting the top and bottom of the reservoir, using the information from wells. - Facies simulations (Sequential Indicator Simulation, Truncated Plurigaussian Simulation). It requires the building of a flat stratigraphic grid (Flattening) within which variograms calculations and simulations are performed. After the flattening, the 3D vertical proportions curves (VPC) are computed. A 2D proportion constrained by a seismic attribute is used to constrain the 3D VPC. These proportions are used for the facies simulation. - 3D porosity simulations are achieved independently for each facies, then a cookie cutting procedure constrained by the facies simulations provide the final porosity simulations. - Finally, simulations are transferred from the stratigraphic space to the real space. Several types of simulations are used (Surfaces simulations, SIS, TPGS, 2D porosity simulations, 3D porosity simulations, contact). To evaluate the different available models, volumetric calculations based on simulations of the different parameters provide stochastic distributions of volumes.
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Diffraction Separation Using the Crs Technique: A Field Data Application
Authors Endrias G. Asgedom and Leiv -J. Gelius and Martin TygelDiffracted waves are often associated with geological structures like faults, pinchouts, wedgeouts or a sudden change in facies (Kanasewich and Phadke, 1988). Identification of such structures in a seismic or ground penetrating radar (GPR) image is highly
dependent on our ability to utilize the diffracted energy. Unfortunately, diffractions often manifest themselves on seismic (or GPR) data with a much weaker signal strength compared to reflections and they often fall within the noise level. As a consequence, classical signal processing methods treat diffractions as noise and imaging is carried out in favor of reflections. Recently, however, different approaches have been proposed to separate diffractions from reflections so that additional high-resolution information can be obtained from direct imaging of the diffracted energy. In this paper, we propose to perform diffraction and reflection separation based on the Common Reflection Surface (CRS) concept. Within this formulation, suppression (or attenuation) of reflections is carried out by selecting the appropriate stacking surface for diffractions based on a coherency measure. Here we tested both Semblance and MUltiple SIgnal Classification (MUSIC) as a coherency measure for the CRS parameter estimation. The potential application of the technique has been demonstrated employing a multi-offset GPR dataset.
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Levantamento Magnetométrico em Aterro de Resíduos Sólidos – Rincão Dos Bitencourt, Município de Caçapava do Sul – Rs
More LessGeophysical investigations in several environmental studies are common. The aim objective of this study is to detect contaminations in different levels of investigation (shallow and depth) in a non-invasive form. The main objectiv is to evaluate and detect the lateral and deep limits from a waste landfill site located in Bitencourt farm near Caçapava do Sul city, Rio Grande do Sul State- Brazil. The area served as landfill and received an amount of 28.000 ton. during 14 years of different wast types without any environmental criteria worldwide stablished. In 1994 the area has to be recuperated and started a recovering plan determined by the environmental agency (FEPAM). The results indicate that may have accured a significant material deposition due the presence of faults and fractures in the rocks that act as substract for the waste landfill. Total magnetic field map and processment techniques allows to detect anomalies in shallow and in depth levels and also its geometry and depth recognization. The geophysical modeling in the A – B profile permits the better understanding, analysis and visualization from the studied area. The waste were deposited in the landfill area in a regular manner (depth and in area) and a 12 meters limit and 1 meter minimum were stablished for the landfill. The magnetometric method in landfill waste sites is unusual but in this case was effective by the fact that the area have low noise presence (powerlines, antennas, vehicles, etc). The method is a valuable tool and recomended to contaminated áreas where the magnetic fiel is undisturbed.
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Autonomous Nodes – The Future of Marine Seismic Data Acquisition?
Authors Chris Walker and Steve McIntoshWhilst autonomous or “cable free” seismic recording is not a new technology, having been originally developed by Amoco in the 1970s with the Seismic Group Recorder, its application offshore has been relatively recent.
A number of surveys have been undertaken in the Gulf of Mexico, UKCS and offshore West Africa in deep water where the nodes, as the autonomous recording units are now referred to, are deployed and recovered using Remotely Operated Vehicles (ROVs).
Recently FairfieldNodal have introduced a node based marine system which does not require the use of ROVs for node deployment and recovery.
In this paper we will review both deep water and this new “shallow” water technology and show the improved productivity and enhanced operational performance that autonomous nodes can provide.
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A Proposal of New Method for Estimating Depth of Curie Surface
The power density spectrum of magnetic anomaly based on radial average is a procedure commonly used to estimate the depth of the Curie surface. Many applications are found in the literature, for different geological contexts. Despite this, some methodological and operational difficulties are present: (1) radial average, assuming a priori that the medium is isotropic and that there is a single point to start the Fourier transform; (2) difficulty and ambiguity in determining the segment containing the points of similar inclination: (3) the need for manual procedure on examination of the spectrum. An alternative method is investigated and presented in this work. The first is the decomposition of oscillatory series by analysis of variance instead of Fourier analysis; the second is to use variogram to determine the wavelengths and the third is the use covariance spectrum as function of wavelength as a power spectrum. The method was tested on an area east of the Paraná basin, where determinations of Curie depth and heat flux from temperatures in oil wells are found of in the literature.
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Application of Digital Rock Physics for Geophysical Rock Properties
Authors Naum Derzhi and Carl Sisk and Zubair KalamTraditionally,the values of reservoir rock properties have been acquired from log data or direct measurement in a physical laboratory. Recent advances in imaging and image processing, together with improved availability of high performance computing, gave rise to digital techniques for investigating the properties of rock samples. These techniques are based on high-resolution imaging of the rock’s pore space, segmentation of the images into pores and various minerals and simulation of the physical processes controlled by the desired rock properties. These techniques form the novel discipline of digital rock physics (DRP). The goal of the current work is to validate the results of DRP measurements of geophysical parameters by comparing them with the results obtained in traditional physical laboratories.
This study includes eight core plugs from a Cretaceous formation, representing four reservoir rock types. Multiple sub-samples of each core plug were taken and analyzed using the digital rock physics technique.
Our DRP computations are compared with the results of physical measurements of the geophysical properties on samples from Cretaceous formations. The latter measurements were conducted on regular core plugs, several cm in size, much larger than the digital rock samples used in this study. Although some of the physical data represent samples from wells different from where the digital samples used here were extracted, these physical samples cover the rock types included in the study. The geophysical property values obtained in the digital rock physics laboratory closely match the results of physical measurements.
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Estudo Geoelétrico em Sequência Ultramáfica Mineralizada em Cromo, Municipio de São Sepe - Rs
More LessThis paper presents the results of Electrical Resistivity method applied in characterization of metamorphosed ultramafic body in chrome mineralization, located in the São Sepé city (RS). The study area occur rocks of Vacacaí Metamorphic Complex and Basic-ultrabasic Metamorphic Complex. These complexes bring together a wide range of lithotypes, predominantly ultrabasic terms in the form of magnesian serpentinites and schists, with subordinate terms metabasic. The method of the Electrical Resistivity allowed to relate the results of pseudosseções with ultramafic bodies in depth, it was possible to visualize the intervals of the rocks due to the contrast in physical properties between the host rock and the mineralized bodies in chrome. The inversion models were masked by smoothing, not allowing a clear understanding of the format as the resistive zones pseudosections.
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Challenges and Solutions in Wide Azimuth Seismic Data Processing and Imaging for Geologically Complex Areas
Authors Ruben D. Martinez and Jon Burren and Ernesto LemosOver the last years, wide azimuth (WAZ) seismic data collection techniques have shown to provide improved seismic resolution and subsurface illumination than conventional narrow azimuth (NAZ) surveys. However, WAZ geometries pose processing challenges. Proper WAZ compliant pre-processing is required to prepare the 3D seismic data for depth velocity model building and migration in order to produce useful seismic depth images for structural interpretation and prospect generation. WAZ 3D tomography should be used to provide accurate velocity models accounting for velocity anisotropy. The estimation of anisotropic parameters is vital to tie the wells and it is still a challenge and the subject for significant research efforts. During the model building stage, WAZ Beam PSDM (prestack depth migration) is preferred; it is efficient and accurate. Implemented in an interactive environment, anisotropic depth models can be delivered in a short time allowing the interpreter to have more time for the geologic interpretation. After several iterations, WAZ compliant hi-end imaging algorithms, such as anisotropic prestack one-way wave equation migration or reverse time migration are employed to produce the final seismic image. In this presentation, we will review and illustrate challenges and solutions in WAZ seismic processing and imaging using data sets from complex geology areas.
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A 3-D Azimuth-Rich Survey on the Sedimentary Cover in Santa Catarina Island
Authors Saulo S. Martins and Jandyr M. TravassosIt is well known that a 3-D survey can provide the best visualization of the subsurface. But the common practice in 3-D GPR is very poor in comparison with the corresponding for the land 3-D seismic. The usual deployment of closed-spaced fixed-offset profiles have limited azimuthal information and restricts processing to post-stack. In this paper we use another field deployment that is richer in azimuth and thus produces a much better image of the subsurface. We compare our methodology with the usual deployment to illustrate the differences in rendered cubes and in time-slices.
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Project of an Earth Station for the Brazilian Scientific Nanosatellite (Nanosatc-Br)
The Mission NANOSATC-BR aims to get scientific data of the regions at South Atlantic Magnetic Anomaly (AMAS) and at the Equatorial Ionosphere Electrojet on the Brazilian Territory (Schuch, 2008), employing a nanosatellite, which is characterized by its small size, form of a cube, weighting about 1 kg and edges with 10 cm (pattern CubeSat). An Earth Station has been studied to communicate with nanosatellite. Two solutions were evaluated for implementation: The first is to acquire a complete station with a specialized company; the second option is the construction of an Earth Station in the laboratory, applying equipment used by radio amateurs. In this paper is discussed the process used to develop the second solution, with emphasis on the construction and/or
use of antennas Yagi-Uda, mainly because it is cheaper and easy to implement. Moreover, the second solution allows the application of knowledge acquired in academy. The main objective is to determine the best antenna, evaluating the angle of half power, gain, impedance and costs.
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