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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
1 - 20 of 484 results
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An AVO Indicator Based on the Impedance Concept
Authors V. Grosfeld and L. Tunes SantosIn the last two decades, many approximations for the PP reflection coefficient have been proposed in the literature. Basically, all of them are derived from the classical approximation of Aki & Richards, using additional assumptions on the medium parameters. The aim of constructing such approximations is to establish reliable attributes that can be capable to indicate the presence of oil or gas. In this work we review some well known approximations and their respective attributes. We also introduce a new indicator
based on a impedance-type of approximation for the reflection coefficient. Numerical examples are also provided.
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Reservoir characterization using lithology cube on a Cretaceous field offshore Brazil
Combining AVO inversion results with rock physics on lithology and fluid information from well data in a Cretaceous field in Campos basin enables the use of statistical techniques to discriminate two types of igneous rocks in the area: low impedance and high impedance basalts, and the evaluation of the probability of the fluid content on a regional scale.
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A FORTRAN Facility to Compute Physical Parameters for Multigroup Gamma Ray-based Logs
More LessEfficient numerical solutions of gamma ray transport equations in geological media normally require an additional process that includes a scheme of diffusion for multiple coupled energy groups. To predict adequately the values of the experimental and theoretical parameters in a such scheme it is necessary a new look that takes into account the wide variation of nuclear parameters with gamma ray energies. Unfortunately, many of these parameters cannot be determined directly from the tabulated data. To overcome this problem it is introduced FORTRAN algorithms to include these groups coupling and can at the same time be applied to a wide variety of lithologies with 1 ≤ Zeff ≤ 20. To perform this approach, many FORTRAN subroutines and functions are developed to compute diffusion coefficient and total and scattering cross-sections for a large number of discrete energy groups. It is found that any intervals of energy below 5 MeV can be simply implemented and have successful applications on the computation of these parameters in addition to the elements of a transition matrix that couples energy groups. As a help an useful and simple scheme for group selection is also proposed, which has improved the accuracy of the FORTRAN algorithms.
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Comparison of VSP and sonic-log data in non-vertical wells in a hetereogeneous structure
Authors Petr Bulant and Ludĕk KlimešIn order to compare the results of sonic-log measurements and of vertical seismic profiling (VSP), the sonic-log velocities are used to estimate the corresponding travel time in the geological structure, which is then compared with the VSP travel time. In this paper we show how to calculate the sonic-log travel time in the geological structure from the sonic-log velocities while taking into account the effects of the non-vertical propagation of seismic waves due to the source offset and due to the heterogeneous velocity in the structure, together with the effects of well trajectory differing from strictly vertical. We also estimate the errors due to the commonly used assumption of vertical propagation.
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Calibração do perfil sônico a partir do perfil VSP
Authors Roseane M. Misságia and Marcos V. Barbosa MachadoIn this work, it was carried out a synthetic sonic log analysis made from a model simulating a reservoir between two low permeability beds. This analysis related on the log correction with check shot data and the application of the new data to VSP modeling. The procedure showed efficient to calibration of the different scales involves in the log and in the wellbore seismic.
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Coplanar coil array in laminated formations with linear transition zones
More LessThe one-dimensional profiles obtained by one coplanar coil array show polarization horns in front of horizontal bed interfaces, caused by accumulation of electric charges on those boundaries. This polarization effect allows a good positioning of thinly laminated reservoirs. Such horns are smoothed out when there is a gradational transition between the beds. In this work, we study the response of a coplanar coil array in a thinly laminated reservoir. We also study the behavior of the polarization horns in linear transition zones between beds. We build the transition zone with a sequence of thin homogeneous layers whose resistivities varies linearly.
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Investigações geofísicas em áreas submersas rasas: qual o melhor método?
The objective of this article is to discuss and assess the applicability of geophysical methods by focusing on seismic methods in studies conducted in shallow waters. Criteria to help to select the most appropriate geophysical method to solve geological or eotechnical issues must be established to minimize problems, particularly environmental ones. The focus on shallow waters was driven by the lack of systematic data and the demand for geological and geotechnical knowledge in these areas, due to the concentration, in these sectors, of the main economic activities of our current society like projects of ports, moles, ducts, marinas, bridges, tunnels, fishing activities, beach regeneration, mineral prospecting, waterways, dredging and reservoirs. In any of these
topics, basic geological knowledge of the bottom and sub bottom of water-covered areas is essential to ensure the success of the project. Considering this, geophysical methods, particularly seismic ones, are investigation tools that effectively contribute to generate new information, and are the only set of tools available to quickly and objectively provide enough data to improve the geological understanding of the area under investigation.
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Estimativas de teores de umidade de solos empregando o método GPR em área de escorregamentos em Ubatuba/SP
Authors Renato Luiz Prado, Rodolfo Moreda Mendes and Fernando A. M. MarinhoGround penetrating radar (GPR) reflection and direct travel time data were used to estimate soil water content in two unstable hillside areas in the city of Ubatuba, state of São Paulo, Brazil. Data were collected during five different campaigns over a period of one year using multioffset geometry with 100 MHz and 200 MHz antennas. The moisture content data obtained by the reflection travel time data allowed to construct 1D profile up to 10 meters depth, but did not show a significant seasonal variations. However, it was observed for the surface horizon by the exam of the direct travel time.
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Influência do dossel da floresta de Caxiuanã nos fluxos de calor entre o solo e a atmosfera
Air temperatures at 8, 30 and 52 m above ground and vertical fluxes of latent heat and sensible heat at 54 m height, were measured during one month of the dry season (August, 2005) and another month (April, 2005) of the rainy season at Caxiuanã’s forest micrometeorological tower. The average temperature profiles for daylight and night periods, as well as, the sensible and latent heat fluxes estimated and measured, showed significantly different and frequently opposite behavior of these quantities, within two layers defined between 8 and 30 m, below the forest canopy, and 30 to 52 m, above the canopy. The canopy seems to act as a heat source during the daylight hours and a sink of heat at night. Overall, the sum of the sensible and latent heat fluxes may reach 90% of the short wave net radiation, over this site. The results suggest that more attention should be given to the air layer below the canopy, if one seeks to understand the heat and water vapor exchanges between the soils surface and the atmosphere, above the canopy of such type of forest.
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“Risk, Reward & Regulatory Compliance – New Challenges for Geophysical Information Systems?”
More LessGeophysics was traditionally a specialist’s province, a tool to help locate, quantify and produce hydrocarbons. But with public interest in the energy sector growing exponentially and topics such as climate change, corporate accountability and energy politics appearing in seemingly every news bulletin, many other groups are starting to demand geophysical information. Additionally, geophysicists are demanding access to a wider range of data types and data sources than ever before. This is revolutionizing the way we manage seismic and other types of E&P data. With the assistance of recent case studies, this paper will examine the new tools at our disposal and make suggestions for a real-time, integrated and above all holistic approach.
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Localização de Tubulações Metálicas Instaladas no Sitio Controlado de Geofísica Rasa do IAG-USP através dos Métodos Eletromagnético Indutivo e GPR
Authors Vinícius Rafael Neris dos Santos and Jorge Luís PorsaniThis research shows some results obtained with Inductive Electromagnetic (EM38 equipment), and GPR-Ground Penetrating Radar methods applied for detect steel pipes buried at test site of the IAG/USP. Steel pipes until 1.5 meters deep were detected by Inductive Electromagnetic method. 200MHz GPR profiles permit to detect the steel pipes and the depth slices were important for characterize the pipes extension. The results obtained by two different geophysical methods present good agreement, and can be used to mapping interferences buried in subsoil.
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Long Offset Transient Electromagnetic (LOTEM) for monitoring fluid injection in petroleum reservoirs – Preliminar results of Fazenda Alvorada Field (Brazil)
More LessThis work presents the preliminary results obtained using LOTEM (“Long Offset Transient Electromagnetic”) method in a producing petroleum field in Northeast Region of Brazil (Bahia State). The main goal of the study is to produce subsurface images for monitoring fluid injection after EOR (Enhanced Oil Recovery) operations. Five stations were selected, and, a careful processing was applied in all of them to remove noisy data. A preliminary one-dimensional (1D) interpretation was done using forward models, where it was possible to observe oil/injected water contacts.
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Resistividade elétrica utilizada no imageamento da contaminação proveniente da disposição de resíduos de óleos lubrificantes
Geophysics has been showing to be effective in identifying areas contaminated by waste disposal, contributing to the soundings programs aiming direct sampling and monitoring well installation to become more efficient. In this context, the purpose of this work was to evaluate the potential of the resistivity method in characterizing the contamination of the lubricant oil residues disposal area in Ribeirão Preto - SP. The geophysical methods used enabled the geophysical anomalies identification, which characterized the contamination produced by the leachate migration originated in the cells filled with the lubricant oil waste.
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Aplicação da técnica CDI de imageamento para o sistema GEOTEM
More LessThe objective of subsurface imaging is to transform responses measured by ATDEM methods in an image of the electrical conductivity versus depth (CDI) and with this, to get information on target geometry and conductivity (geoele ctrical model). This work presents a methodology to get CDIs over the measurement profile (2-D) used subsequently to visualize the geoelectrical model in 3-D, which would help to integrate and to understand the local geology. To accomplish this, a layered geoelectrical model is used (1-D) together with the depth attained by the maximum electrical induced current concept. The conductivity and the layer characterization are based on a simplified modeling algorithm (late asymptote approximations). Resultant software was adapted processes GEOTEM data.
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Processamento de dado AEM: CDI e inversão para o sistema GEOTEM
More LessThe aim of this paper is to carry out a comparison between two types of 2D electromagnetic modeled sections. They are normally used on AEM (Airborne EletroMagnetic) quantitative interpretation, especially on those obtained from ATDEM measurements (ATDEM). One is derived from fast modeling of the asymptotic secondary magnetic flux decay and is one of the most common quantitative interpretation tool. The other is based on the wave equation and is of more restrict usage as 1D inversion techniques, both parametric and structural. The two approaches were applied to airborne GEOTEMTM system real data, collected on a survey at San Pedro Valley (Southeast Arizona) in 1997. The available data from this survey was made available by the USGS and was used in this quantitative analysis. As such, 2D sections from 1D model inversion were obtained. The geoelectrical model from these sections were further 3D (volumetric) interpolated (voxels), allowing a 3D representation form off the region spatial conductivity distribution.
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Constrained inversion of 3-D electromagnetic HMD and VMD data
Authors Frayzer L. Almeida and Luiz RijoThis work presents an algorithm for 3-D inversion of electromagnetic data associated with inductive sources: HMD (horizontal magnetic dipole) and VMD (vertical magnetic dipole). The proposed inversion algorithm is based on the method of Marquardt subsidized by a scheme of normalization of the objective function using the amplitude and phase of the vertical component of the observed magnetic field combined with the absolute constrain of the body’s depth and the conductivity of a region around the body. The forward problem was solved by the finite element method using the three components of the magnetic vector potential plus the electric scalar potential and the Coulomb gauge. The results of the experiments with the three models show that the proposed inversion algorithm, with the imposed constrains, is able to delineate clearly 3-D conductive simple bodies hosted in resistive media.
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Estudo comparativo das técnicas de Elementos Finitos e Equação Integral na modelagem eletromagnética bidimensional
More LessThe Finite Element Method and the Integral Equation Method are used extensively in the electromagnetic modeling in Geophysics. In this work we compare the processing times in both methods to calculate the fields generated by an infinite line of current over a 2D earth, in several different models. We find that the Finite Element Method is generally faster in our modeling.
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Ausência de Reflexão Interna Total em Meios Condutores
Authors Luiz G. Guimarães and Edson SampaioBaseados nas equações de Maxwell e Lei de Ohm, mostaremos neste trabalho que em meios condutores a propagação de ondas planas depende de vários fatores tais como, estado de polarização, freqüência temporal bem como das relações constitutivas do meio. Como conseqüência direta destes fatos, mostraremos que a lei de Snell em meios condutores é bem distinta daquela usual em meios dielétricos. Uma das grandes diferenças é ausência de reflexão interna total na propagação de ondas entre meios condutores. Além disso, também mostraremos que tais meios se comportam como “filtros de polarização”. Analisaremos este problema para o caso em que uma onda eletromagnética gerada no mar penetra em uma rocha sobreposta a um reservatório contendo hidrocarbonetos.
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Forward modeling of self-potential fields in mineral exploration
More LessNatural self-potential (SP) fields observed in the vicinity of conductive ore bodies can be explained in terms of electrochemical reactions the conductor participates. Battery-like models assume that a buried conductor creates an anode-cathode pair by conveying to oxidizing areas in the near surface a flow of electrons from reducing areas at depth. For conductors with invariant composition (inert electrode model) a quantitative formulation is already available. This paper employs numerical Green’s functions to optimize the evaluation of SP fields from inert electrode models and simulates their response from common conditions found in mineral exploration.
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Estrutura geoelétrica da Bacia do Iguatu, Ceará, Brasil
Authors Jean M. Flexor, Giovanni C. Stael, Carlos R. Germano and Sergio L. FontesA set of forty five broadband (001-1000sec) magnetotelluric (MT) soundings have been made along two profiles (SW-NE) and (NW-SE ) crossing the Iguatu Basin, Ceará, Brazil, a Brazilian intra cratonic basin. The shape of the basin is almost elliptic and these two profiles correspond to the two semi axes. The static shift galvanic effects which distorts the TE mode of MT data were removed using time domain transient electromagnetic measurements (TDEM) at each sounding station. 2-D inversions of MT profiles gives an estimate of the geoelectric structure in subsurface. In the SW-NE profile, the depth of basement reaches a maximum of about 1800 m with a depocenter displaced in the NE direction. In the NW-SE profile, almost perpendicular to the regional geological trend, the maximum depth is about 1200 m. These depths and shapes are compared with 3-D inversion gravity models.
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