Produção Científica



Artigo em Revista
04/07/2013

Offset continuation (OCO) ray tracing using OCO trajectories.
Offset continuation (OCO) is a seismic configuration transform designed to simulate a seismic section as if obtained with a certain source-receiver offset using the data measured with another offset. Since OCO is dependent on the velocity model used in the process, comparison of the simulated section to an acquired section allows for the extraction of velocity information. An algorithm for such a horizon-oriented velocity analysis is based on so-called OCO rays. These OCO rays describe the output point of an OCO as a function of the Root Mean Square (RMS) velocity. The intersection point of an OCO ray with the picked traveltime curve in the acquired data corresponding to the output half-offset defines the RMS velocity at that position. We theoretically relate the OCO rays to the kinematic properties of OCO image waves that describe the continuous transformation of the common-offset reflection event from one offset to another. By applying the method of characteristics to the OCO image-wave equation, we obtain a raytracing-like procedure that allows to construct OCO trajectories describing the position of the OCO output point under varying offset. The endpoints of these OCO trajectories for a single input point and different values of the RMS velocity form then the OCO rays. A numerical example demonstrates that the developed ray-tracing procedure leads to reliable OCO rays, which in turn provide high-quality RMS velocities. The proposed procedure can be carried out fully automatically, while conventional velocity analysis needs human intervention. Moreover, since velocities are extracted using offset sections, more redundancy is available or, alternatively, OCO velocities can be studied as a function of offset.
Artigo em Revista
04/07/2013

Exploring self-affine properties in seismograms
Self-affine properties have been observed in a large variety of rough profiles and time series from natural data sets. In this work, seismograms used for oil prospecting, which contain information of distinct subsurface features collected by seismic waves reflected or scattered at their interfaces, are taken into consideration. It is expected that any self-affine property, measured by the Hurst exponent H, depends on the depth. For each seismic trace, H is evaluated locally within a moving window, which is chosen narrow enough to reveal space dependency but also wide enough to display scale invariance. With the use of color code diagrams, it is possible to draw two-dimensional diagrams that show the local dependence of H for the analyzed seismogram. The reliability of the method is tested by the investigation of seismograms that contain ground roll components, as well as multiple reflections. The effect of different kinds of filter in the scaling properties is also investigated. In this case, comparisons are drawn among the diagrams obtained from original seismograms and those subjected to appropriate filter to eliminate spurious components.
Artigo em Revista
04/07/2013

Amplitudes e padrões de polarização de pulsos em meios anisotrópicos
Extrair informações litológicas da subsuperfície através de dados sísmicos constitui-se num grande desafio à prospecção sísmica, pois a hipótese de estratificações formadas por camadas isotrópicas se mostra insuficiente para representar o comportamento do campo elástico em levantamentos com grandes afastamentos entre fonte e receptor, geofones multicomponentes, medidas de VSP tridimensional, entre outros. Sob este panorama, a prospecção sísmica passa a considerar modelos anisotrópicos de subsuperfície para, por exemplo, caracterizar reservatórios. O objetivo deste texto é apresentar um formalismo para modelar o espalhamento de pulsos a partir de ondas planas incidentes em interfaces planas horizontais que separam meios anisotrópicos. Este espalhamento é obtido primeiramente, através da formulação explícita dos campos de deformação e tração como função das matrizes propagadoras, de polarização e de impedância do meio. Em seguida, este formalismo é usado para a obtenção das matrizes dos coeficientes de reflexão e transmissão através de uma interface plana horizontal para posteriormente, ser generalizado para o espalhamento através de múltiplas camadas. Finalmente, inserem-se ao campo da onda incidente as amplitudes de um pulso analítico para calcular o espalhamento do pulso através de estratificações.
Artigo em Revista
16/01/2013

Soluções de Problemas envolvendo Equações Diferenciais Sujeitas a Incertezas
Este trabalho objetiva analisar, através de alguns exemplos, a influência de se considerar aleatoriedades na solução de equações diferenciais com dados e/ou parâmetros aleatórios. Um comparativo das médias das soluções das equações estocásticas com as soluções das equações determinísticas simplificadas, nas quais substituímos os parâmetros aleatórios por suas médias, é apresentado. Estes
exemplos mostram que a média da solução, que normalmente é uma informação relevante em aplicações, pode ser qualitativamente diferente da aproximação obtida pela solução de uma equação diferencial determinística na qual substituímos os parâmetros aleatórios por suas médias.
Artigo em Revista
16/01/2013

A space–time multiscale method for computing statistical moments in strongly heterogeneous poroelastic media of evolving scales
A new multiscale procedure is proposed to compute flow in compressible heterogeneous porous media with geology characterized by power-law covariance structure. At the fine scale, the deformable medium is modeled by the partially coupled formulation of poroelasticity with Young’s modulus and permeability treated
as stationary random fields represented by their Karhunen–Loève decompositions. The framework underlying the multiscale procedure is based on mapping these random parameters to an auxiliary domain and
constructing a family of equivalent stochastic processes at different length scales characterized by the same ensemble mean and covariance function. The poromechanical variables inherit a space–time version of the scaling relations of the random input parameters which allows for constructing a set of multiscale solutions of the same governing equations posed at different space and time scales. A notable feature of the multiscale method proposed herein is the feasibility of solving both the poroelastic model and the Fredholm integral equation for the eigenpairs of the Karhunen–Loève expansion in an auxiliary domain with much lower computational effort and then derive the long term behavior at a coarser scale from a straightforward rescaling of the auxiliary solution. Within the framework of the finite element approximation, in conjunction with
the Monte Carlo algorithm, numerical simulations of fluid withdrawal and injection problems in a heterogeneous poroelastic reservoir are performed to illustrate the potential of the method in drastically reducing the computational burden in the computation of the statistical moments of the poromechanical unknowns in large-scale simulations.
Artigo em Revista
16/01/2013

A Numerical Comparison Between Quasi-MonteCarlo and Sparse Grid Stochastic Collocation Methods
Quasi-Monte Carlo methods and stochastic collocation methods based on sparse grids have become popular with solving stochastic partial differential equations.These methods use deterministic points for multi-dimensional integration or interpolation without suffering from the curse of dimensionality. It is not evident which method is best, specially on random models of physical phenomena. We numerically study the error of quasi-Monte Carlo and sparse gridmethods in the context of groundwater flow in heterogeneous media. In particular, we consider the dependence of the variance error on the stochastic dimension and the number of samples/collocation points for steady flow problems in which the hydraulic conductivity is a lognormal process. The suitability of each technique is identified in terms of computational cost and error tolerance.
Artigo em Revista
16/01/2013

Effect of Element Distortion on the Numerical Dispersion of Spectral Element Methods
Spectral element methods are well established in the field of wave propagation,in particular because they inherit the flexibility of finite element methods and have low numerical dispersion error. The latter is experimentally acknowledged, but has been theoretically shown only in limited cases, such as Cartesian meshes. It is well known that a finite element mesh can contain distorted elements that generate numerical errors for very large distortions. In the present work, we study the effect of element distortion on the numerical dispersion error and determine the distortion range in which an accurate solution is obtained for a given error tolerance. We also discuss a double-grid calculation of the spectral element matrices that preserves accuracy in deformed geometries.
Dissertação de Mestrado
10/01/2013

Filtragem adaptativa SVD de volumes sísmicos 3D para realçar refletores e estruturas geológicas.
Washington Oliveira Martins. Filtragem adaptativa SVD de volumes sísmicos 3D para realçar refletores e estruturas geológicas. 2012. Dissertação (Mestrado em Geofísica) - Universidade Federal da Bahia, . Orientador: Milton José Porsani.
Tese de Doutorado
10/01/2013

Dorian Caraballo Ledesma. Deconvolução de dados sísmicos de reflexão utilizando mudança de fase do filtro de Wiener-Levinson. 2011.
Dorian Caraballo Ledesma. Deconvolução de dados sísmicos de reflexão utilizando mudança de fase do filtro de Wiener-Levinson. 2011. Tese (Doutorado em Geofísica) - Universidade Federal da Bahia, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior. Orientador: Milton José Porsani.
Dissertação de Mestrado
10/01/2013

Processamento de Dados Sísmicos com Grandes Afastamentos: Dados Sintéticos e Linha Sísmica do Campo de Tenerife, Colômbia.
Francisco Ortega Gamboa. Processamento de Dados Sísmicos com Grandes Afastamentos: Dados Sintéticos e Linha Sísmica do Campo de Tenerife, Colômbia. 2012. Dissertação (Mestrado em Geofísica) - Universidade Federal da Bahia, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior. Orientador: Amin Bassrei.
<<  <   1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31   >  >>