Produção Científica



Artigo em Revista
22/07/2016

Relief Geometric Effects on Frequency-Domain Eletromagnetic Data
A perpendicular transmiter-receiver coils arrangement used in the frequency-domain eletromagnetic survey can have deviations in relation to its standard geometric definition due to the relief geometry of the surveyed area when combined with large transmitter-receiver distance and large transmitter loop. This happens because the local relief characteristics along the equivalent magnetic moment axis from the vertical, and receiver positions at different elevations. A study about that is carried on here substituting the rugged relief by an inclined plane. We have developed a new formulation for the n-layered model that allowed us to investigate the relief geometry effects on FDEM data but restricting the analysis to the two-layer earth model, considering three cases of transmitter-receiver situations controlled by the relief model. Such procedures resulted to be very useful to demonstrate their behavior departing from those curves obtained for an inclined and a horizontal ground. These results show that small deviations in the verticality of the transmitter loop axis or in the horizontality of the surficial plane causes significant deviations, even for angles as small as 1º
Artigo em Revista
25/05/2016

How much averaging is necessary to cancel out cross-terms in noise correlation studies?
We present an analytical approach to jointly estimate the correlation window length and number of correlograms to stack in ambient noise correlation studies to statistically ensure that noise cross-terms cancel out to within a chosen threshold. These estimates provide the minimum amount of data necessary to extract coherent signals in ambient noise studies using
noise sequences filtered in a given frequency bandwidth. The inputs for the estimation process are (1) the variance of the cross-correlation energy density calculated over an elementary time length equal to the largest period present in the filtered data and (2) the threshold below which the noise cross-terms will be in the final stacked correlograms. The presented theory explains how to adjust the required correlation window length and number of stacks when changing from one frequency bandwidth to another. In addition, this theory provides a simple way to monitor stationarity in the noise. The validity of the deduced expressions have been confirmed with numerical cross-correlation tests using both synthetic and field data.

Key words: Time-series analysis; Interferometry.
Artigo em Revista
23/03/2016

Automatic data extrapolation to zero offset along local slope
Velocity-independent seismic data processing requires information about the local slope in the data. From estimates of local time and space derivatives of the data, a total least-squares algorithm gives an estimate of the local slope at each data point. Total least squares minimizes the orthogonal distance from the data points (the local time and space derivatives) to the fitted straight line defining the local slope. This gives a more consistent estimate of the local slope than standard least squares because it takes into account uncertainty in the temporal and spatial derivatives. The total least-squares slope estimate is the same as the one obtained from using the structure tensor with a rectangular window function. The estimate of the local slope field is used to extrapolate all
traces in a seismic gather to the smallest recorded offset without using velocity information. Extrapolation to zero offset is done using a hyperbolic traveltime function in which slope information replaces the knowledge of the normal moveout (NMO) velocity. The new data processing method requires no velocity analysis and there is little stretch effect. All major reflections and diffractions that are present at zero offset will be reproduced in the output zero-offset section. Therefore, if multiple reflections are undesired in the output, they should be removed before data extrapolation to zero offset. The automatic method is sensitive to noise, so for poor signal-to-noise ratios, standard NMO velocities
for primary reflections can be used to compute the slope field. Synthetic and field data examples indicate that compared with standard seismic data processing (velocity analysis, mute, NMO correction, and stack), our method provides an improved zero-offset section in complex data areas.
Artigo em Revista
03/12/2015

Parallel Scalability of a Fine-Grain Prestack Reverse Time Migration Algorithm
Seismic imaging has evolved significantly due to the high demand from the oil/gas industry for hardware technological advancements, boosting the development of more sophisticated algorithms. In order to deliver the quality and accuracy required, the execution of these algorithms may lead to time infeasible solutions. Aiming at performance improvement, this work conducted the parallelization of the core of a reverse time migration (RTM) algorithm. Furthermore, analysis such as speedup and efficiency was performed in order to assess the scalability of the proposed method. While the many parallelization efforts so far deal with coarse-grain approaches, this letter tackles the intrashot fine-grain parallelization of prestack RTM, which increases the overall concurrency degree of the algorithm. Results using 2-D synthetic data show that the proposed approach is scalable, which means that an increase in hardware resources and/or in problem size will lead to a proportional increase in speed and/or accuracy.
Trabalho de Graduação
03/11/2015

Interpretação de seções de resistividade e cargabilidade aparente.
Eduardo Menezes de Souza Amarante. Interpretação de seções de resistividade e cargabilidade aparente. 2014. TCC de graduação em Geofísica, Universidade Federal da Bahia. Orientador: Milton José Porsani.

Trabalho de Graduação
03/11/2015

Atenuação do ground-roll utilizando a deconvolução no domínio da frequência.
André Luis Emanuel Góes Dantas. 2014. TCC de graduação em Geofísica, Universidade Federal da Bahia. Orientador: Milton José Porsani.
Trabalho de Graduação
03/11/2015

Atenuação de reflexões múltiplas de curto período utilizando deconvolução preditiva adaptativa.
Deize Almeida dos Santos. 2015. TCC de Graduação em Geofísica. Universidade Federal da Bahia. Orientador: Milton José Porsani.
Dissertação de Mestrado
03/11/2015

Lucas José de Almeida. Atenuação de ruídos coerentes e interpolação de dados sísmicos utilizando a análise de multirresolução.
Lucas José de Almeida. Atenuação de ruídos coerentes e interpolação de dados sísmicos utilizando a análise de multirresolução. 2015. Dissertação (Mestrado em Geofísica) - Universidade Federal da Bahia. Orientador: Milton José Porsani.
Tese de Doutorado
03/11/2015

Zoukaneri Ibrahim Moumouni. Análise Tempo-Frequência do Sinal Sísmico Utilizando a Distribuição Wigner-Ville e o Método de Máxima Entropia: Aplicações para Estimativa do Fator Q e de Atributos.
Zoukaneri Ibrahim Moumouni. Análise Tempo-Frequência do Sinal Sísmico Utilizando a Distribuição Wigner-Ville e o Método de Máxima Entropia: Aplicações para Estimativa do Fator Q e de Atributos. 2014. Tese (Doutorado em Geofísica) - Universidade Federal da Bahia. Orientador: Milton José Porsani.
Tese de Doutorado
03/11/2015

Wildney Wallacy da Silva Vieira. Post-imaging Analysis of Pressure Prediction in Productive Sedimentary Basins for Oil and Gas Exploration (Análise Pós-imageamento Voltado à Predição de Pressão em Bac
Wildney Wallacy da Silva Vieira. Post-imaging Analysis of Pressure Prediction in Productive Sedimentary Basins for Oil and Gas Exploration (Análise Pós-imageamento Voltado à Predição de Pressão em Bacias Sedimentares Produtoras de Óleo e Gás). 2015. Tese (Doutorado em Pós Graduação Em Geofísica) - Universidade Federal do Pará, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior. Orientador: Lourenildo Williame Barbosa Leite.
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