Navegando por Assunto "Teoria paraxial do raio"

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Acesso aberto (Open Access)
Migração Kirchhoff pré-empilhamento em profundidade usando aproximação paraxial do tempo de trânsito
(Universidade Federal do Pará, 2014-08-28) CUNHA, Antonio Rizimar de Andrade; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023
In order to get an accurate image of the subsurface we need efficient techniques for evaluating the wave field. In literature we find several geophysical methods based on the numerical solution of the seismic wave equation. Among the various techniques of seismic imaging, Kirchhoff prestack depth migration remains widely used because of its flexibility in processing data through several geometries of acquisition, and its practicality in solving problems related to imaging. Assuming this view, we seek to create more efficient alternatives for the accurate calculation of the parameters involved in migration processes. We consider the efficient calculation of the traveltimes as a critical factor, focusing on the fundamental amplitude in their respective points in depth using the Paraxial Ray Theory through the Runge-Kutta method of fourth order. The paraxial extrapolation of the traveltimes belongs to the class of dynamic ray tracing, where it is possible to determine information in complex geological environment on regions influenced by shadow zones. The application of this technical demands amounts previously arranged in a central reference beam that is obtained from the kinematic ray tracing, furthermore a macro velocity model of the medium is necessary for the traveltimes calculation. For comparison, we consider two different ways to calculate the traveltimes tables: The first was performed by routine RAYT2D from SEISMIC UNIX (SU) package, which is considered a robust method of evaluation; the second is based on Paraxial05 method. The depth migration required the seismic data input and the traveltimes. The images were obtained from an algorithm written in SHELL and a third image is obtained through the difference between the two initial results.
Acesso aberto (Open Access)
Um novo algorítimo para implementação do método de empilhamento SRC 3-D e modelagem sísmica da Bacia do Amazonas
(Universidade Federal do Pará, 2006-05-23) LIMA, Charles Cristiano de Assis; CALLAPINO, German Garabito; http://lattes.cnpq.br/6064981270181319
The Common Reflection Surface Stack (CRS) is a seismic reflection imaging technique that is independent of velocity model to simulate Zero-Offset (ZO) seismic section or volume. This technique have been used, alternatively, in seismic reflection processing and many works have been demonstrate that the CRS method shows results with better signal to noise rate and lateral resolution in comparison with conventional methods, e. g., NMO/DMO stack. The CRS stack provides some attributes or wavefield parameters that could be used in many applications, e.g., velocity models estimation, AVO and AVA analysis, geometric spread factor estimation, projected Fresnel zone, and others. The CRS technique has a second order hyperbolic traveltimes approximation in central ray vicinity. In the 3-D case, for a normal central ray or ZO, the CRS operator depends on eight parameters, estimating by coherency analysis from seismic data. In this work, the 3-D ZO CRS operator is analyzed for both reflection and diffraction events with respect the traveltimes obtained from straight modeling. I present a new CRS stack algorithm to simulate ZO sections or volume. I still present, in this work, a 3-D seismic modeling of the sedimentary Amazon Basin with SW3D consortium packages. The geologic model was based in true geologic and geophysics data.