Produção Científica



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

Interpreta√ß√£o de se√ß√Ķes de resistividade e cargabilidade aparente.
Eduardo Menezes de Souza Amarante. Interpreta√ß√£o de se√ß√Ķes de resistividade e cargabilidade aparente. 2014. TCC de gradua√ß√£o em Geof√≠sica, Universidade Federal da Bahia. Orientador: Milton Jos√© 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

Atenua√ß√£o de reflex√Ķes m√ļltiplas de curto per√≠odo utilizando deconvolu√ß√£o 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. An√°lise Tempo-Frequ√™ncia do Sinal S√≠smico Utilizando a Distribui√ß√£o Wigner-Ville e o M√©todo de M√°xima Entropia: Aplica√ß√Ķes para Estimativa do Fator Q e de Atributos.
Zoukaneri Ibrahim Moumouni. An√°lise Tempo-Frequ√™ncia do Sinal S√≠smico Utilizando a Distribui√ß√£o Wigner-Ville e o M√©todo de M√°xima Entropia: Aplica√ß√Ķes para Estimativa do Fator Q e de Atributos. 2014. Tese (Doutorado em Geof√≠sica) - Universidade Federal da Bahia. Orientador: Milton Jos√© 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 (An√°lise P√≥s-imageamento Voltado √† Predi√ß√£o de Press√£o em Bacias Sedimentares Produtoras de √ďleo e G√°s). 2015. Tese (Doutorado em P√≥s Gradua√ß√£o Em Geof√≠sica) - Universidade Federal do Par√°, Coordena√ß√£o de Aperfei√ßoamento de Pessoal de N√≠vel Superior. Orientador: Lourenildo Williame Barbosa Leite.
Tese de Doutorado
03/11/2015

Silvia Lorena Bejarano Berm√ļdez. Crit√©rios para Avalia√ß√£o de Solu√ß√Ķes em Problemas Inversos Lineares e Linearizados: Gravimetria e Tomografia de Tempo de Tr√Ęnsito.
Silvia Lorena Bejarano Berm√ļdez. Crit√©rios para Avalia√ß√£o de Solu√ß√Ķes em Problemas Inversos Lineares e Linearizados: Gravimetria e Tomografia de Tempo de Tr√Ęnsito. 2015. Tese (Doutorado em Geof√≠sica) - Universidade Federal da Bahia, Conselho Nacional de Desenvolvimento Cient√≠fico e Tecnol√≥gico. Orientador: Amin Bassrei.
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