Produção Científica



Artigo em Revista
09/12/2013

DECONVOLUTION OF SEISMIC DATA USING PHASE CHANGE OPERATORS
Apresentamos uma nova abordagem para deconvolução do pulso sísmico. Investigamos o uso de operadores de mudança de fase para obtenção de filtros de fase mista a partir de filtros de fase mínima. Os operadores de mudança de fase são construídos a partir das raízes associadas aos filtros de Wiener-Levinson. Escolhendo subconjuntos daquelas raízes é possível gerar um conjunto de filtros inversos de fase mista. A escolha do filtro ótimo é realizada através do método de otimização conhecido com algoritmo genético. Para tanto utilizamos a norma varimax para medida da simplicidade do traço deconvolvido. O método foi testado utilizando
dados sísmicos sintéticos e reais.
Artigo em Revista
05/07/2013

Using NARX model with wavelet network to inferring the polished rod position.
Although several studies have been conducted on the sucker-rod pumping system, even today, the acquisition of the polished rod position is carried out by using position transducers. In this paper, we present experimental results showing that the dynamic position of the polished rod can be inferred from the torque current of a three-phase induction motor (which is given by sensorless vector AC-drive) using nonlinear autoregressive model with exogenous input (NARX) with wavelet network (wavenet). The results obtained in the validation stage show that, on the basis of the experimental set used in this work, the best estimated model is suitable to represent the dynamic behavior of the polished-rod of the pumping unit.
Artigo em Revista
05/07/2013

High-resolution gathers by inverse filtering in the wavelet domain.
We have developed and applied an inverse Q filter formulation using the continuous wavelet transform (CWT), which provides a natural domain for time-variant operations, such as compensation for propagation in attenuating and dispersive media. The well-known linear attenuation model, given as a function of time and frequency, was applied very efficiently over wavelet coefficients in the time-frequency domain to correct for amplitude and phase distortions, as necessary. The inverse CWT yields the recovered trace with a broader bandwidth. The process works on a trace-by-trace basis, making no distinction if the data is pre- or poststack. Our motivation was to develop gather conditioning tools to enhance prestack interpretation techniques such as amplitude variation with offset (AVO) analysis and inversion — a technique that is often compromised by tuning and other propagation related issues that degrade seismic resolution. Thus, we investigated the AVO fidelity of our filter and the sensitivity of the results to incorrect values of Q, using real and synthetic data. Our synthetic data experiments clearly showed that AVO anomalies are recovered and preserved in a stable manner, even with values of Q off by 50% of its correct value. The application in time-migrated gathers shows a very natural increase in the vertical definition of the events, especially due to the partial elimination of the tuning effect. The benefits for imaging are also evidenced by comparing stacked sections before and after inverse Q filtering. The higher resolution of seismic sections leads to a better definition of smaller scale stratigraphic and structural features.

Artigo em Revista
05/07/2013

Review of active faults in the Borborema Province, Intraplate South America Integration of seismological and paleoseismological data.
In this paper, we provide a review of the properties and behavior of active faults in the Borborema Province, northeastern Brazil, using instrumental, historical and paleoseismological records. The Borborema Province is one of the most seismically active parts of the South American stable continental region (the South American Platform). The Province encompasses an area ~ 900 km long and ~ 600 km wide. It is composed of a branching system of Neoproterozoic orogens, encompassing Archean and Proterozoic inliers deformed during the Brasiliano orogeny at ~ 750–500 Ma. Active faults reactivate shear zones or regional foliation and quartz veins or cut across the preexisting fabric. Active faults are usually strike–slip and generate events ≤ 5.2 mb, which we interpret as the lower limit for maximum possible earthquakes. Seismicity is concentrated in the upper crust down to a depth of 12 km. Earthquake sequences illuminated naturally occurring faults up to 40 km long and segments in the order of 0.5–2.6 km in faults related to induced seismicity. Earthquakes have a recurrence interval of ~ 15 years for Ms = 4. Paleoseismological data indicate that although earthquakes associated with surface ruptures have not occurred in the last 200 years, they struck the region in the last ~ 100 ka. Paleoearthquakes have a recurrence interval of ~ 15.8 ka for magnitudes of ~ 5.5 Mw in individual faults. Moreover, earthquake-induced soft-sediment deformation caused by events of at least 5.5–6.0 Ms have occurred at least six times in the last 400–10 ka in one alluvial valley. Seismically defined faults are concentrated along the continental margin at the border of sedimentary basins as far as 250–300 km inland in areas of extended crust; faults in the paleoseismic record are also found in rift basins along this margin. Both records also reveal that active faults tend to be hydraulically conductive.
Artigo em Revista
05/07/2013

Entropic Regularization to Assist a Geologist in Producing a Geologic Map. Entropy
The gravity and magnetic data measured on the Earth’s surface or above it (collected from an aircraft flying at low altitude) can be used to assist in geologic mapping by estimating the spatial density and magnetization distributions, respectively, presumably confined to the interior of a horizontal slab with known depths to the top and bottom. To estimate density or magnetization distributions we assume a piecewise constant function defined on a user-specified grid of cells and invert the gravity or magnetic data by using the entropic regularization as a stabilizing function that allows estimating abrupt changes in the physical-property distribution. The entropic regularization combines the minimization of the first-order entropy measure with the maximization of the zeroth-order entropy measure of the solution vector. The aim of this approach is to detect sharp-bounded geologic units through the discontinuities in the estimated density or magnetization distributions. Tests conducted with synthetic data show that the entropic regularization can delineate discontinuous geologic units, allowing a better mapping of sharp-bounded (but buried) geologic bodies. We demonstrate the potential of the entropic regularization to assist a geologist in obtaining a geologic map by analyzing the estimated magnetization distributions from field magnetic data over a magnetic skarn in Butte Valley, Nevada, U.S.A. We show that it is an exoskarn where the ion exchange between the intrusive and the host rock occurs along a limited portion of the southern intrusive border.
Artigo em Revista
05/07/2013

Reconstruction of geologic bodies in depth associated with a sedimentary basin using gravity and magnetic data
We present a comprehensive review of the most common gravity and magnetic interpretation methods to in depth retrieval of the geometry of two types of geologic bodies associated with a sedimentary basin: 1) sedimentary basement relief; and 2) salt bodies. In reconstructing a basement topography we identify three groups of methods: the automatic, the spectral and the nonspectral methods. The reconstruction of salt bodies geometries from gravity data usually uses the interactive forward
modeling, but recently gravity inversion methods have been developed to interpret this kind of geological environment.
Artigo em Revista
05/07/2013

Seismic Coherency Measures in Case of Interfering Events: A Focus on the Most Promising Candidates of Higher-Resolution Algorithms.
In this article, the use of coherency measures in seismic signal processing is reviewed, along with the introduction of higher-resolution parameter estimation methods. The actual problem analyzed is that of separating diffractions from reflections and utilizing them to perform higher-resolution imaging of small-scale subsurface structures. The main idea is that diffracted waves can be described by a modified moveout equation normally employed by the common reflection surface (CRS) technique. A number of coherency measures have been proposed to assess how well a moveout (defined by some trial parameters) approximates a target signal. Traditional methods using semblance often fail in cases of interfering events. This fact has motivated the investigation of alternative coherency measures based on higher-resolution techniques like multiple signal classification (MUSIC), eigenvector (EV), and minimum variance (MV). Here, the various algorithms are tested employing controlled seismic data from the Marmousi model as well as field data acquired by a ground-penetrating radar (GPR). It is found that the MUSIC algorithm provides the best result slightly ahead of EV and with MV falling somewhere between these two techniques with the more standard approach based on semblance and time migration.
Artigo em Revista
05/07/2013

Features of phase spectrum and its calculation in seismic data processing.
Using simple examples we show the main features of the phase spectra, which have to be taken into account in seismic data processing. In this case the peculiarities of phase spectra processing in terms of probabilistic and statistical characteristics are considered. Based on previous theoretical results and using the results of the analysis of the spectra calculated for the real seismic signals, there are formulated simple criteria to ensure high performance and stability of the statistical procedures for the phase spectra processing. It allowed us to construct a simple procedure for continuous extension of the phase spectra of signals observed on real traces, and thereby ensure the uniqueness of their determination. The uniqueness is important for the joint processing and analysis of large sets of phase spectra,
calculated from the observed seismic signals. Such obtained spectra can be effectively used in various practical problems. Thus, based on the analysis of synthetic and real data, we show that using the phase spectrum can reduce the zone of uncertainty in determining the pinch-out points of a horizon.
Artigo em Revista
05/07/2013

Filtragem de Prony de dados sísmicos: base teórica.
Neste artigo estamos discutindo um método novo para o processamento de dados sísmicos e sua utilização em vários problemas geológicos e geofísicos. O m´etodo é baseado na decomposição de Prony e seleção de componentes desta decomposição a fim de obter dados sísmicos correspondentes a uma faixa estreita de frequências. Portanto, o método pode ser chamado de filtragem de Prony. Seu melhor análogo é um filtro passa-faixa. No entanto, o método da filtragem de Prony oferece maior resolução de imagem de sinal em relação à variável temporal. Além disso, o método permite a obtenção de um parâmetro de atenuação correspondente à frequência de filtragem. Isto torna possível investigar mudanças no parâmetro de atenuação em função da frequência. Uma atenção especial é dada às dificuldades principais que podemos encontrar em processamento de dados sísmicos: (i) fundamentos teóricos da decomposição de Prony para obter estimativas estáveis do espectro de Prony para sinais semelhantes a sinais sísmicos; (ii) utilização do espectro de Prony no processamento de filtragem de sinais, ou seja, a construção de algoritmos da filtragem de Prony; e (iii) descrição da tecnologia de filtragem de Prony e exemplos que demonstram as suas capacidades na prática. Usando exemplos simples, apresentamos ideias básicas da tecnologia, ilustrando os principais pontos que são importantes para a aplicação deste método no processamento de dados
sísmicos reais. Os resultados obtidos mostram uma boa estabilidade do algoritmo para diferentes formas de onda e na presença de outros sinais e de ruído. Esperamos que esta abordagem chame a atenção de especialistas para o método não-linear de filtragem de Prony, bem como para aspectos de sua implementação em análise espectral de geofísica.
Artigo em Revista
05/07/2013

Utilização efetiva da informação a priori na inversão da forma de sinal sísmico.
Neste artigo considera-se uma abordagem geral sobre a utilização da informação a priori na decomposição do sinal sísmico observado, essencial à solução de problemas inversos da sísmica. Através disto é possível propor um algoritmo efetivo, com potencial para reduzir consideravelmente o volume da informação a priori , necessária durante a preparação dos dados para a solução do problema de inversão da forma do sinal, e, também, no processamento de dados reais. O algoritmo está baseado na análise de componentes multivalorados e permite determinar a quantidade e estrutura da informação a priori , necessária para a solução do problema de decomposição. O algoritmo é realizado em duas etapas. Na primeira, através da construção da solução do problema e utilizando uma informação pseudo a priori , é garantida a unicidade e estabilidade da solução. Na segunda etapa, determina-se a quantidade mínima de informação disponível a priori permitindo, assim, obter a solução verdadeira do problema.
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