Produção Científica

**Apresentação**

Iterative solution of a class of nonlinear Fredholm integral equationsWe 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**

AquisiÃ§Ã£o automÃ¡tica de formas de ondas (P e S) em amostras de rochas reais/sintÃ©ticas com formatos cilÃndrico e quadrÃ¡ticoEste trabalho propÃµe o desenvolvimento de sistema automÃ¡tico de baixo custo para medidas ultrassÃ´nicas em amostras de rocha sintÃ©ticas anisotrÃ³picas fissuradas com formatos de cubos ou plugs cilÃndricos. A partir dessas mediÃ§Ãµes automÃ¡ticas foi possÃvel obter sismogramas de formas de onda P e S. Nesses dados os sismogramas no tempo variam com o Ã¢ngulo, 0 â€“ 180Â° (onda S) e 0 â€“ 90Â° (onda P). Para testar a viabilidade da nossas instrumentaÃ§Ã£o, medidas ultrassÃ´nicas foram realizadas em amostras anisotrÃ³picas (em estado seco) com formatos cÃºbicos e cilÃndricos. O tempo estimado para obtenÃ§Ã£o dos dados de onda S foi de 00:17:30 minutos (para amostras cÃºbicas) 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 specimensSeismic 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**

PropagaÃ§Ã£o de ondas ultrassÃ´nicas elÃ¡sticas em modelos sintÃ©ticos com heterogeneidades esfÃ©ricasThe 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 MediaWe 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**

InterpretaÃ§Ã£o sÃsmica 2D de estruturas tectÃ´nicas na bacia Sergipe-AlagoasSedimentary 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 databaseWe 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 inversionSeismic 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**

ComparaÃ§Ã£o entre o algoritmo ε de Wynn e o ∆2 de Aitken no cÃ¡lculo de componentes eletromagnÃ©ticas de fontes geofÃsicas dipolares.Este trabalho apresenta os procedimentos utilizados na determinaÃ§Ã£o de componentes de campo de algumas fontes geofÃsicas em modelos geoelÃ©tricos unidimensionais por meio de quadratura com extrapolaÃ§Ã£o (QWE - Quadrature With Extrapolation). Os resultados com QWE foram determinados a partir de duas tÃ©cnicas de aceleraÃ§Ã£o de convergÃªncia: o algoritmo \epsilon de Wynn e o processo \Delta^2 de Aitken. Com anÃ¡lises no emprego ao Dipolo ElÃ©trico Horizontal na direÃ§Ã£o x (DEHx), o Dipolo MagnÃ©tico Vertical (DMV) e o Dipolo MagnÃ©tico Horizontal na direÃ§Ã£o x (DMHx) quando possuem soluÃ§Ã£o analÃtica, demonstra-se que o algortimo Delta^2 de Aitken tambÃ©m pode ser utilizado na modelagem de dipolos, tendo erro relativo na mesma ordem do algoritmo \epsilon, mas em geral maior nÃºmero de avaliaÃ§Ãµes. |

**Apresentação**

Full-waveform inversion using an efficient preconditioning method for the gradient vectorFull-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. |

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