Produção Científica
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. |
Apresentação
| Iterative SSA method to filtering of the land seismic data Normally the singular value decomposition (SVD) filtering is applied in the time × distance domain, exploring the spatial correlation between a set of seismic traces. In the present work we explore the Singular Spectrum Analysis (SSA) method in the time direction using a iterative algorithm. The SSA method extract the correlation between reflected events along the time variable and decompose seismic traces in the low (first eigenimage only) and high frequency parts (sum the rest of the eigenimages). We illustrate the effectiveness of this new approach to the prediction and subtraction of the ground roll and improve velocity analisys and stacking of the seismic data. |
Apresentação
| Stabilized unidimensional deconvolution-based imaging conditions in Marchenko imaging Multiple reflections are typically not accounted for in seismic migration processes, which can lead to the emergence of artifacts. In Marchenko imaging, we retrieve the complete up- and downgoing wavefields in the subsurface to construct an image without such artifacts. The quality of this image depends on the type of imaging condition that is applied. In this work, we introduce an imaging condition that is based on stabilized unidimensional deconvolution (SUD). Two specific approaches are considered. In the first approach, we use the full up- and downgoing wavefields for deconvolution. Although this leads to balanced and relatively accurate amplitudes, the crosstalk is not completely removed. The second one is to incorporate the initial focusing function in the deconvolution process, in such a way that the retrieval of crosstalk is avoided. We compare images with the results of the classical cross-correlation imaging condition, which we apply to reverse-time migrated wavefields and to the up- and downgoing wavefields that are retrieved by the Marchenko method. |
Apresentação
| Conventional seismic processing flow analysis: 2D line of the Rio Grande Chain region Southeastern Brazil Seismic reflection is one of the most important tools for the oil and gas industry, both in the exploratory and in the production phase. It is divided into three components: acquisition, processing and interpretation. This work is inserted in the context of seismic data processing. For this, the processing of a real 2-D line acquired in 1979, located in the region of the Rio Grande Chain, southeast of Brazil, was made using the software ProMAX/SeisSpace. In order to generate a representative image of the geological framework of the area, a conventional processing flow that includes two different procedures was applied: procedure 1 and procedure 2, which are respectively related to the application of post and pre-stack migrations. The steps of the processing flow were submitted to different parameterizations, and the inputs and outputs were compared aiming to evaluate how they work to improve the seismic data. Based on the processing flow used, the best result obtained for the final seismic section was the one corresponding to the Kirchhoff pre-stack time migration, due to its better seismic aspect. |
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