Produção Científica

**Apresentação**

Signal analysis and time-frequency representation using SSA and adaptive AR methodsWe apply the Singular Spectral Analysis (SSA) method in an iterative and recursive way to estimate individual components of the signal. Following we apply the short time autoregressive method to obtain a time-frequency representation of the signal. For the computing of the instantaneous frequency we provide a new equation which depend on a single autoregressive coefficient. The effectiveness of the new approach is demonstrated in a synthetic data example and in the removal of ground-roll noise from land seismic data. |

**Apresentação**

Combining tilt derivative filters: new approaches to enhance magnetic anomaliesWe extend the concept of two earlier enhancement techniques based on the local phase of the magnetic anomaly, namely the vertical (TDR) and horizontal (TDX) tilt angles, which are defined by the inverse tangent of ratios involving the total horizontal gradient and the vertical derivative. These filters are useful to locate both shallow and deep sources, because they equalize the signal amplitudes. The proposed approach is based on the addition and subtraction of TDR and TDX. The TDR+TDX filter produces constant values over the causative bodies, while TDR-TDX generates peaks over the center of bodies and is constant out of them. By applying the proposed techniques to synthetic and aeromagnetic data we show that they locate more clearly the centers and edges of the sources in comparison to TDR and TDX, respectively. The combined filters have essentially the same computational cost as TDR and TDX and can replace them as auxiliary interpretation tools.Keywords: Qualitative Methods, Local Phase Filters, Aeromagnetic Data.RESUMO. Estendemos o conceito de duas tÃ©cnicas de realce baseadas na fase local da anomalia magnÃ©tica: as inclinaÃ§Ãµes do sinal analÃtico (TDR) e do gradiente horizontal total (TDX), definidos pelo arco tangente de razÃµes envolvendo o gradiente horizontal total e a derivada vertical. Estes filtros sÃ£o Ãºteis para localizar tanto fontes rasas quanto profundas. O mÃ©todo proposto baseia-se na adiÃ§Ã£o e subtraÃ§Ã£o dos filtros TDR e TDX. O filtro TDR+TDX produz valores constantes sobre as fontes causadoras, enquanto que o TDR-TDX produz picos sobre o centro dos corpos e Ã© constante onde fontes causadoras nÃ£o sÃ£o verificadas. Aplicando as tÃ©cnicas propostas aos dados sintÃ©ticos e reais mostra-se que elas localizam mais claramente os centros e as bordas dos corpos em comparaÃ§Ã£o com o TDR e o TDX, respectivamente. Os filtros combinados tÃªm essencialmente o mesmo custo computacional dos filtros originais, TDR e TDX, e podem substituÃ-los como ferramentas de interpretaÃ§Ã£o.Palavras-chave: MÃ©todos Qualitativos, Filtros de Fase Local, Dados AeromagnÃ©ticos. Federal |

**Apresentação**

2D Poststack Seismic Data Inversion with Curvelet Denoising PreconditioningSeismic inversion methods are highly sensitive to the noise present in the data set. The need to enhance the signal-to-noise ratio (SNR) motivates the researchers do develop increasingly sophisticated denoising methods and combine them into other techniques. While some methodologies operate on a single scale, the curvelet transform established itself as multi-scale transform useful to decompose the seismic signals into multi-resolution elements. In this study, we evaluate the benefits of curvelet denoising as a preconditioning method to poststack seismic data in an 2D acoustic inversion processing using a Bayesian framework. Our tests on a synthetic data set modelled from the Marmousi model and the real data set from the Brazilian offshore Campos Basin have shown that the curvelet thresholding method can be successfully applied for random noise elimination. Even the use of a hard global threshold might allow improvements in the deepest parts. Future work will have to show whether alternatives that ensure a more robust way of selecting the coefficients can take into account the wavelength change with depth variation. |

**Apresentação**

Sequence Stratigraphy of Rift Successions - A Conceptual ModelDue to the basins asymmetry and the subsidence controlled by one major fault zone, the accommodation space within a rift basin is variable, and the popular passive-margin-based sequence stratigraphic scheme, where depositional systems tracts develop following a predictable order during a complete cycle of base-level change, is not applicable. For a practical and useful stratigraphic analysis of rift basins, conceptual and methodological adaptations are required. The present paper discusses and exemplifies these adaptations, proposing an integrative sequence stratigraphic conceptual model with two different scenarios (gradual and punctuated subsidence) and defining three tectono-stratigraphic phases: (1) the rift initiation phase, which is characterized by isolated and restricted faults which create incipient half-grabens, infilled with fluvial and deltaic facies; (2) the rift development phase, during which the initial rift faults tend to link and to form a larger and deeper depositional area, recording lacustrine facies with an overall retrogradational trend, and; (3) rift termination phase, when the accommodation decreases, the sedimentation regime is progradational, and the rift basin is filled with fluvio-deltaic and eolian facies. The model is illustrated with examples from two adjacent rift basins from the northeastern region of Brazil, the RecÃ”ncavo and Camamu basins. |

**Apresentação**

Seismic Attributes and Time-Frequency analysis by using Wigner-Ville distribution combined with the Maximum Entropy MethodThe growing need for more defined images of seismic attributes for analysis and description of reservoirs encourages the development of new methods that are capable of displaying high resolution images of seismic attributes. Therewith, we propose the use of the method called Maximum Entropy of Wigner-Ville (MEM-WV), that combines the distribution of Wigner-Ville with the Burg's Maximum Entropy method, in order to get the high resolution power spectrum of the seismic signal. In this method, the power spectrum is obtained by doing Fourier Transform (FT) of each Kernel term of Wigner-Ville, and then by estimating and extending each Kernel sequence. In order to better describe hydrocarbon reservoirs, this work will favor the achievement of structural, stratigraphic and geomorphological attributes with higher resolution. |

**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. |

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