Produção Científica
Apresentação
| De–Primary TTI–RTM Using the P–Pure Analytical Wavefield Based on the relation between the real and imaginary components of the analytical wavefield, an im- proved scheme to construct its imaginary part by solving the TTI pure–P wave equation only once is proposed in this work. Our scheme requires the calculation of the first time derivative of the real wave- field and the application of the inverse of a pseudo–differential operator. For time extrapolation of the real wavefield and its first order time derivative, we employed the rapid expansion method, which is unconditionally stable and free of numerical noise. To apply the spatial and spectral terms of the inverse pseudo–differential operator in an explicit manner, the definition of the wavefront propagation direction is introduced. The proposed method can improve the computation of analytical wavefield, therefore, separate the wavefield into down– and up–going components for each time step in an explicit way. This allows us to employ the causal imaging condition for TTI–RTM practical applications. Moreover, the de–primary migration result shows that it successfully remove the low–wavenumber artifacts typical from conventional RTM. |
Apresentação
| Comparison of Time-Frequency Localization Methods and Spectral Evolution The main purpose in the present work is the comparison of some methods that can be applied for a time-frequency map distribution of seismic data, that is typically a multi-sensor technique. The generalized data attribute analysis is potentially a data-driven methodology to complement geological information for interpretation purpose. A seismic signal carries the information from the subsurface, and the goal is the oil and gas exploration in a porous and fractured medium. The propagating signal samples the geology by the transmission and reflection seismic fields, and the characteristics of the medium is present in the data under geometric and frequency properties. And the important principle underlying the t − f decomposition is that an arbitrary signal is caused by a linear superposition of elementary wavelets, but goes further to an atomic decomposition, in the sense that of “well†localization in time and frequency. |
Apresentação
| Pore pressure estimation by using a modified boundary element method This paper resumes a research for solving numerically a three-dimensional problem of elastic stationary oscillations, with a particular application to the case pore pressure in sedimentary rocks. The method can be used not only for applications in oil and gas exploration, but also for modeling buried structures and structural components such as foundations, tunnels, trenches, cavities, etc. The basis of this method is the construction of integral equations kernels as a response to an analogue Delta loading, or to its derivatives. The finiteness of the kernels gives the possibility to increase accuracy in many orders, and to solve the elastic problem in the case of discontinuity in the normal vector to the contouring S surface to the goal volume V. As an example, we show that the variation of the characteristics of the static stress state under the influence of pore pressure depends essentially on the contact geometry, and a little on the type of boundary condition at the contact. |
Apresentação
| Iterative solution of a class of nonlinear Fredholm integral equations We consider the numerical solution of functional integral equations, a particular class of nonlinear Fredholm integral equations, by the collocation method with piecewise linear basis functions. The nonlinear algebraic system arising from the spatial discretization is iteratively solved with a fixed-point algorithm. |
Apresentação
| Aquisição automática de formas de ondas (P e S) em amostras de rochas reais/sintéticas com formatos cilÃndrico e quadrático Este trabalho propõe o desenvolvimento de sistema automático de baixo custo para medidas ultrassônicas em amostras de rocha sintéticas anisotrópicas fissuradas com formatos de cubos ou plugs cilÃndricos. A partir dessas medições automáticas foi possÃvel obter sismogramas de formas de onda P e S. Nesses dados os sismogramas no tempo variam com o ângulo, 0 – 180° (onda S) e 0 – 90° (onda P). Para testar a viabilidade da nossas instrumentação, medidas ultrassônicas foram realizadas em amostras anisotrópicas (em estado seco) com formatos cúbicos e cilÃndricos. O tempo estimado para obtenção dos dados de onda S foi de 00:17:30 minutos (para amostras cúbicas) e para dados de onda-P foi de 00:10:00 minutos (para amostras cilÃndricas). |
Apresentação
| Rock physical properties controlling P-wave dispersion and attenuation in outcrop carbonate specimens Seismic waves propagation in dry and saturated elastic media gives insight into the rock physical properties. The poroelasticity Biot theory provides us with a theoretical basis for understanding the phenomena of low-frequency seismic waves dispersion and attenuation due to wave-induced fluid flow. One of the most accepted mechanisms to explain the phenomenon of wave attenuation in saturated porous media is the fluid flow induced by the wave on the mesoscopic scale, i.e., a scale larger than the pore size and much smaller than the wavelength. This work has the aim of investigating the influence of petrophysical and elastic properties of rock parameters in P-wave dispersion and attenuation in carbonate samples. It was performed through laboratory evaluation, using static and dynamic measures of the P-wave velocity under dry and saturated conditions. Therefore, here we applied Gassmann and Geertsma and Smith (1961) approaches, for estimate P-wave dispersion, Dvorkin and Mavko (2006) model to estimate the attenuation and determination of the characteristic frequency by interlayer flow White et al. (1975) model on the mesoscopic scale. |
Apresentação
| Propagação de ondas ultrassônicas elásticas em modelos sintéticos com heterogeneidades esféricas The manufacture of synthetic rocks samples has a great importance in the study of the elastic properties of the rocks based on the variation of heterogeneities. In this present work we constructed synthetic sandstones with different number of heterogeneities in the samples. In this work we constructed and analyzed (in dry condition and ambient conditions) eleven samples were constructed in this work. In total, ten heterogeneous samples and an isotropic sample for reference. The heterogeneous samples were divided in two groups (A abd B). Group A with heterogeneities of 3.75 mm diameter and group B with heterogeneities of 5.67 mm diameter. From P- and S-waveforms were measured Vp and Vs velocities as well as Vp/Vs ratio. As expected both velocities decrease with increasing of scatter in the sample. However, was noted a decreasing more pronounced for Vp velocities for both groups and VS for group B. |
Apresentação
| The CRS Method for Weakly Anisotropic VTI Media We describe an extension of the Common-Reflection-Surface (CRS) method for vertical tranversely isotropic (VTI) anisotropic media. The obtained second-order coefficients of the extended CRS traveltime explicitly depend on the Thomsen parameters that describe the VTI medium. Considering only the offset direction, the proposed CRS traveltime assumes a nonhyperbolic traveltime character which can be compared with VTI nonhyperbolic traveltimes that considers short-spread normal moveout velocities for plane horizontal reflectors. Numerical experiments showed that the proposed approach yields better traveltime approximations when an estimated stacking velocity is considered instead of short-spread normal moveout velocity. |
Apresentação
| Interpretação sÃsmica 2D de estruturas tectônicas na bacia Sergipe-Alagoas Sedimentary basins along the Brazilian continental margin present evidence of deformation long after the breakup of Pangea, from the rift to the post-rift period. Understanding faults propagation on the passive margin is important to the knowledge about reactivation of preexisting structures. Moreover, it is important to know how such faults influenced morphologically and structurally the basin during the post-rift period. The goal of this current work was to contribute to the knowledge of the tectonic-stratigraphic framework of the Sergipe-Alagoas basin, as well as to study the basin tectonic evolution through seismic interpretation of four seismic sections perpendicular to each other. This current work brought good results regarding the structural framework of the studied area. During the seismic interpretation, the main features were outlined on the sections. The seismic horizons were marked utilizing well data to correlate with the geological formation. Thus, it was possible identify tectonic deformations e how they affect rift and post-rift stratigraphic units. |
Apresentação
| On the influence of texture on ultrasonic velocities of carbonate rocks using a global petrophysical database We investigate the influence of textural parameters, such as grain size and pore aspect ratio distributions, in the relation between ultrasonic velocities (Vp and Vs) and porosity. The entire study is based on a petrophysical database created using software technology to scan published records of core sample measurements. We use the Differential Effective Medium (DEM) model and Keys-Xu approximation to describe the relationship between the velocities and porosity. Rock physics templates created from a set of Equivalent Pore Aspect Ratio (EPAR) values helps discriminating the effect of grain size and pore distribution. |
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