Michelângelo G. da Silva

SVD filtering applied to ground-roll attenuation

We present a singular value decomposition (SVD) filtering method for attenuation of the ground roll. Before the SVD computation, normal move-out (NMO) correction is applied to the seismograms, with the purpose of flattening the reflections. SVD is performed on a small number of traces in a sliding window. The output trace is the central trace of the first few eigenimages. These contain mostly horizontally aligned signals, and other noise in the data will be suppressed. By performing this action with the sliding window moving in steps of one trace, the number of output traces is equal to the number of input traces. The new method preserves the character and frequency content of the horizontal reflections and attenuates all other type of events. We illustrate the method using land seismic data of the Tacutu basin, located in the northeast part of Brazil. The results show that the proposed method is effective and is able to reveal reflections masked by the ground roll. The new SVD filtering approach provides the results of better quality, when compared with the results obtained from the conventional f-k filtering method.

An Adaptive Local-slope SVD Filtering Approach to Enhance Events On Seismic Sections

We present an adaptive singular value decomposition (SVD) filtering method for enhancement of the spacial coherence of the reflections and for the attenuation of the uncorrelated noise. The SVD filtering is performed on a small number of traces and a small number of samples collected around each data component. The method uses the local slope of the reflections to re-sample the data set surrounding each data component and the SVD filtering is locally applied to compute the filtered data. The filtered data component is obtained by stacking the components of the first K eigenimages along the slope. The method is applied in two steps: (i) before the SVD computation, the normal move-out (NMO) correction is applied to the seismograms, with the purpose of flattening the reflections. We use the local slopes equal to 90◦ to preserve the horizontal coherence of the primary reflections and (ii) for the second step the SVD filtering uses as input the filtered data of step-1 and the method is applied in the common-offset domain. Now the local slopes of the reflections are used in order to drive the SVD filtering. We illustrate the method using land seismic data of the Tacutu basin, located in the Northeast of Brazil. The results show that the proposed method is effective and is able to reveal reflections masked by the ground-roll.

Filtragem SVD aplicada à melhoria do rastreamento de horizontes sísmicos

We present an application of a singular value decomposition (SVD) filtering approach to the automatic detection of seismic horizons. The SVD filtering approach may be seen as a multichannel filtering method where each filtered seismic trace retains the coherence of the neighbouring seismic traces. The SVD filtering preserves the amplitude and phase relations and reinforces the spacial correlation between seismic events, and at the same time it reduces the incoherent noise in data, which normally is associated to the last eigenvalues. The SVD decomposition is performed on each subset of traces around each trace of the original 2D or 3D seismic data. The filtered trace is obtained from the most important eigenvalues and eigenvectors. We illustrate the application of the new approach on 3D post-stack land seismic data. The improvement of the resultant coherence in the seismic reflected events allows for greater autotracking robustness during the automatic interpretation of the seismic horizons. The SVD filtering approach is computationally efficient and improves significantly the coherence, the consistency and the spacial continuity of the seismic events making easier the automatic detection of the commercial software in the search for patterns along the autotracking process.

Processing of large offset data: experimental seismic line from Tenerife Field, Colombia

Manuscript ID: 20170072. Received on: 05/21/2017. Approved on: 11/13/2017. ABSTRACT: Exploration seismology provides the main source of information about the Earth’s subsurface, which in many cases can be presented as a simple model of horizontal or near-horizontal layers. After the seismic acquisition step, conventional seismic processing of reflection data provides an image of the subsurface by using information about the reflections of these layers. The traveltime from a source to different receivers is adjusted using a hyperbolic function. This expression is used in the case involving an isotropic medium, which is a simplification of nature, whereas geologically complex media are generally anisotropic. A subsurface model that more closely resembles reality is the vertical transverse isotropy, which defines two parameters that are required to correct the traveltimes: the NMO velocity and the anellipticity parameter. In this paper, we reviewed the literature and methodology for velocity analysis of seismic data acquired from anisotropic media. A model with horizontal layers and anisotropic behavior was developed and evaluated. The anisotropic velocity was compared to the isotropic velocity, and the results were analyzed. Finally, the methodology was applied to real seismic data, i.e. an experimental landline from Tenerife Field, Colombia. The results show the importance of the anellipticity parameter in models with anisotropic layers.

Aplicação de balanceamento espectral e DMO no processamento sísmico da Bacia do Tacutu

Na decada de 80 a PETROBRAS realizou uma campanha exploratoria de hidrocarbonetos na Bacia sedimentar do Tacutu, que compreendeu a aquisicao de varias linhas sismicas alem da perfuracao de dois pocos pioneiros. A aquisicao foi conduzida com baixa multiplicidade sismica CMP (12). Adicionalmente, a qualidade dos dados sismicos e ruim devido a forte presenca do groundroll. A baixa razao sinal/ruido e a baixa multiplicidade comprometem seriamente a qualidade das imagens de subsuperficie, geradas como resultado final do processamento sismico. No presente trabalho investigamos o desempenho de varias tecnicas de filtragem para melhorar a qualidade das imagens sismicas. O fluxograma de processamento convencional utilizado seguiu os passos basicos: geometria, correcao de amplitude, analise de velocidades, correcao de NMO e DMO, e empilhamento. Com o objetivo de atenuar o groundroll utilizamos a tecnica de balanceamento espectral, que se mostrou bastante eficaz, comparada com o metodo tradicional FK. Os resultados obtidos sobre a linha sismica 50-RL-90, nos permitem sugerir um procedimento para melhorar a qualidade das secoes sismicas empilhadas, associadas a dados de baixa qualidade e pequena cobertura sismica.