Produção Científica

**Apresentação**

Nova abordagem iterativa e multifrequÃªncia em tomografia geofÃsica de difraÃ§Ã£oSeismic tomography is used in reservoir geophysics as an important method for high resolution imaging. The classic Born approach, used in monochromatic diffraction tomography in the condition of weak scattering, has as a limitation the need for prior knowledge of the background velocity. In this work we propose several iterative approaches of tomographic inversion, where the background velocity field is updated at each iteration, but the knowledge true background is not required. In addition to the iterative process, one can choose to use a single frequency or several frequencies at each inversion. In the first approach, a single frequency is used, which is kept constant. In the second, at each iteration, several frequencies are used simultaneously, which are also kept constant. In the third, in addition to the background velocity, the working frequency is also updated. Finally, in the last approach, the multiple frequencies used simultaneously, are updated iteration to iteration. The proposed approaches were tested in a synthetic model containing a dipping layer and a paleochannel with well to well acquisition geometry. The data were contaminated with Gaussian noise. The iterative process, together with the use of multiple frequencies, generated good results with small velocity and model parameter errors. |

**Apresentação**

Deâ€“Primary TTIâ€“RTM Using the Pâ€“Pure Analytical WavefieldBased 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 pureâ€“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 pseudoâ€“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 pseudoâ€“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 downâ€“ and upâ€“going components for each time step in an explicit way. This allows us to employ the causal imaging condition for TTIâ€“RTM practical applications. Moreover, the deâ€“primary migration result shows that it successfully remove the lowâ€“wavenumber artifacts typical from conventional RTM. |

**Apresentação**

Comparison of Time-Frequency Localization Methods and Spectral EvolutionThe 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 âˆ’ 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 â€œwellâ€ localization in time and frequency. |

**Apresentação**

Pore pressure estimation by using a modified boundary element methodThis 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 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. |

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