Produção Científica
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. |
Apresentação
| Deconvolution and correlation-based interferometric redatuming by wavefield inversion Seismic interferometry is a method to retrieve Green's functions for sources (or receivers) where there are only receivers (or sources, respectively). This can be done by correlation-or deconvolution-based methods. In this work we present a new approach to reposition the seismic array from the earth's surface to an arbitrary datum at depth using the one-way reciprocity theorems of convolution and correlation type. The redatuming process is done in three steps: (a) retrieving the downward Green's function for sources at the earth's surface and receivers at the datum, (b) retrieving the corresponding upward Green's function, and (c) retrieving the reflected upward wavefield for sources and receivers at the datum. Input for steps (a) and (b) are the surface data and wavefields simulated in a velocity model of the datum overburden. Step (c) uses the responses of steps (a) and (b) as input data in the convolution-based interferometric equation. The method accounts for inhomogeneities in the overburden medium, thus reducing anticausal events and artefacts as compared to a purely correlation-based procedure. |
Apresentação
| Comparação entre o algoritmo ε de Wynn e o ∆2 de Aitken no cálculo de componentes eletromagnéticas de fontes geofÃsicas dipolares. Este trabalho apresenta os procedimentos utilizados na determinação de componentes de campo de algumas fontes geofÃsicas em modelos geoelétricos unidimensionais por meio de quadratura com extrapolação (QWE - Quadrature With Extrapolation). Os resultados com QWE foram determinados a partir de duas técnicas de aceleração de convergência: o algoritmo \epsilon de Wynn e o processo \Delta^2 de Aitken. Com análises no emprego ao Dipolo Elétrico Horizontal na direção x (DEHx), o Dipolo Magnético Vertical (DMV) e o Dipolo Magnético Horizontal na direção x (DMHx) quando possuem solução analÃtica, demonstra-se que o algortimo Delta^2 de Aitken também pode ser utilizado na modelagem de dipolos, tendo erro relativo na mesma ordem do algoritmo \epsilon, mas em geral maior número de avaliações. |
Apresentação
| Full-waveform inversion using an efficient preconditioning method for the gradient vector Full-waveform inversion (FWI) is a efficient method and it has been used successfully to invert subsurface parameters. It consists basically on the minimization of the difference between the predicted and observed data. However, its application using finite-difference schemes is limited to low frequency content and the increase of the range of higher frequency will demand a high computational cost of the wavefield propagation procedure and also the whole inversion scheme. To overcome this problem, we apply the rapid expansionmethod (REM) for numerical wavefield extrapolation inside the FWI workflow thus increasing the frequency content of the inversion process. Besides that, an efficient preconditioningmethod using source-receiver illumination (PSRI) for computing the gradient vector in order to increase resolution of the models and better convergence of the objective function has also been proposed. Beyond that, we compared the performance of the preconditioning method with relation to conventional gradient method for two types of source signature. To test the efficiency of our proposed FWI approach, we apply it using a frequency multiscale scheme for a synthetic data set with a complex velocity model. The inversion results show satisfactory inverted velocity models which can be used to produce depth imaging of high quality. Thus we demonstrate the effectiveness and applicability of our FWI scheme using REM combined with a multiscale approach. |
Apresentação
| Multichannel Predictive Deconvolution and Parabolic Radon Transform for Multiple Reflection's Filtering on Land Seismic Data From Solimões Basin The Solimôes basin became the target of oil exploration campaigns after the discovery of the Juruá field in the 1970s. Its geological evolution is marked by magmatic spills represented by the diabolic sills, which, in addition to preventing seismic energy, generate Multiple reflections, creating problems in processing. This work proposes the application of multichannel predictive deconvolution for the attenuation of multiple reflections after ground-roll filtration. The results showed that although the periodicity of these events was not totally perfect, the method was effective in terrestrial data, attenuating multiple reflections and preserving the primary reflections. |
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