Artigos Científicos - FAGEOF/IG
URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2545
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Item Acesso aberto (Open Access) Guaruman: a natural amazonian fiber with potential for polymer composite reinforcement(Associação Brasileira de Metalurgia e Materiais, 2019-08) GOMES, Laercio Gouvêa; SILVA, Alisson Clay Rios da; CÂNDIDO, Verônica Scarpini; REIS, Raphael Henrique Morais; SERGIO, Neves Monteiro; PINHEIRO, Miriane AlexandrinoThe Amazonian region of South America is known for its diversified number of plants from which food, medicine, wood and fibers have, since long time, been produced by local natives. A typical example is the guarumã (“guaruman”as suggested English spelling) scientifically identified as Ischinosiphon koem, an abundant plant found in the low lands alongside rivers of the state of Para in Brazil. Fibers extracted from the stem of the guaruman are used in ropes and baskets owing to their strength. In the present work, the possibility of applying guaruman fibers as reinforcement of polymer matrix composites is, for the first time, investigated. Amounts up to 30 vol% of continuous and aligned fibers were incorporates into epoxy matrix composites. Density measurements disclosed the guaruman to be one of the lightest natural fibers. Tensile tests indicate that the guaruman fiber addition was able to improve the composite elastic modulus. However, no significant change was found in the ultimate strength, total strain and resilience. On the other hand, a cost-effective analysis revealed a substantial reduction of ~29% in the epoxy composite price due to the incorporation of fibers. Preliminary ballistic evaluation disclosed a potential for application of guaruman epoxy composites in multilayered armor.Item Acesso aberto (Open Access) Resistividade e polarização induzida (IP): modelagem analógica(2006-03) GALLAS, José Domingos Faraco; VERMA, Om PrakashThe aim of this study is to develop an analogical modeling methodology for IP and resistivity. Simple geometrical cylindrical and tabular shapes were built using standard cement, quartzitic sand and graphite. The experiment was carried out with various amounts of graphite in order to measure the IP response for different model geometries. The results are discussed in terms of IP response as a function of geometry, graphite content, depth and strike of the models.Item Acesso aberto (Open Access) Deconvolução de processo sísmico não-estacionário(2000-03) LEITE, Lourenildo Williame Barbosa; ROCHA, Marcus Pinto da Costa daThe present paper treats the application of the Kalman-Bucy filter (KBF), organized as a deconvolution (KBDF), for the extraction of the reflectivity function from seismic data. This means that the process is described as non-stationary, and corresponds to a generalization of the Wiener-Kolmogorov theory. The mathematical description of the KBF preserves its relationship to the Wiener-Hopf filter (WHF) that deals with the counterpart stationary stochastic process. The strategy to solve the problem is structured in parts: (a) The optimization criterion; (b) The a priori knowledge; (c) The algorithm; and (d) The quality. The a priori knowledge includes the convolutional model, and establishes statistics to its components (effective source wavelet, reflectivity function, and geological and local noises). To demonstrate the versatility, applicability and limitations of the method, we performed systematic deconvolution experiments under several situations of additive noise levels and effective source wavelet. First, we demonstrate the necessity of equalizer filters, and second that the spectral coherence factor is a good measure of the quality of the process. We also justify the present study for its application in real data, as exemplified.Item Acesso aberto (Open Access) Treatment of geophysical data as a non-stationary process(2003) ROCHA, Marcus Pinto da Costa da; LEITE, Lourenildo Williame BarbosaThe Kalman-Bucy method is here analized and applied to the solution of a specific filtering problem to increase the signal message/noise ratio. The method is a time domain treatment of a geophysical process classified as stochastic non-stationary. The derivation of the estimator is based on the relationship between the Kalman-Bucy and Wiener approaches for linear systems. In the present work we emphasize the criterion used, the model with apriori information, the algorithm, and the quality as related to the results. The examples are for the ideal well-log response, and the results indicate that this method can be used on a variety of geophysical data treatments, and its study clearly offers a proper insight into modeling and processing of geophysical problems.Item Acesso aberto (Open Access) CRS seismic data imaging system: a case study for basib reevaluation(2007-09) LEITE, Lourenildo Williame Barbosa; HEILMANN, Björn Zeno; GOMES, Anderson BatistaThis paper summarizes practical results of a consistent attention to the seismic processing and interpretation of some land data lines from a set of the Tacutu graben (Brazil), where was applied the fundamental steps of the WIT imaging system grounded on the data-driven CRS (Common Reflection Surface) stack.As a major result, we expect to establish a work-flow for seismic reevaluation of sedimentary basins. Founded on the recovered wave front attributes of the CRS stack, a smooth macro-velocity model was obtained via tomographic inversion. Using this macro-model, pre- and post-stack depth migration was carried out. Besides that, other CRS-stack based processing techniques were performed in parallel as residual static correction and limited-aperture migration based on estimated projected Fresnel zone. A geological interpretation was attempted on the stacked and migrated sections. From visual details of the panels, we could interpret discontinuities, thinning, a principal faulted anticline where plays of horsts, grabens and rollovers are present. Also, part of the selected line needs more detailed processing to make better evident any present structures in the subsurface.Item Acesso aberto (Open Access) Filtros ótimos: efeitos de janelas e de tipo de fase(2003-06) LEITE, Lourenildo Williame Barbosa; ALVES, Fábio José da CostaThe central objective under investigation in this paper is the performance of WHL deconvolution operators for the compression of the seismic source-pulse under the conditions of non-minimum phase and density of events on the trace, as is the case supported for the real data and batch deconvolution. The method of attack to the constructed problems is centered on the information content of the autocorrelation function submitted to different conditions of: (a) the truncation and taper windows; (b) the characteristics of the operator phase (if minimum or non-minimum phase); (c) the measure of quality; (d) the whitening level; (e) the noise present and equalization; (f) the balancing of the trace; (g) the physical principles of wave propagation as expressed and limited by the convolutional model. Results can only be obtained numerically, and they are shown in the form of albums with increasing difficulties, and they demonstrate how the time windows on the autocorrelation serve to diagnostic and to improve the performance of the operators. We conclude that many questions still arise when deconvolution techniques are applied to seismic reflection data from sedimentary basins, and that the Goupillaud model is convenient for simulations through its simple and complete mathematical description.Item Acesso aberto (Open Access) Caracterização geoelétrica de área de curtume localizada no distrito industrial de Icoaraci, Bélem-Pará(2006-12) NUNES, Lana Patrícia Martins; LUIZ, José GouvêaA study covering the shallow subsurface was performed in order to investigate the possibility of underground contamination by liquids used in the industrial processing of dead animal skin to produce tanned hide. The study was carried out inside the area of the Couro do Norte industry, located in the Icoaraci Industrial District (Belém-PA). The used geophysical methodology was: resistivity (imaging and vertical electric soundings), spontaneous potential, electromagnetic (slingram) and ground penetrating radar (GPR). The integrated geophysical interpretation of data indicated the underground flow direction and a shallow plume of contamination, caused probably by the disposal of effluents by the Couro do Norte industry.Item Acesso aberto (Open Access) Metodologia geofísica aplicada ao estudo arqueológico dos sítios Bittencourt e Jambuaçu, Estado do Pará(2010-06) ARAGÃO, Rigler da Costa; LUIZ, José Gouvêa; LOPES, Paulo Roberto do CantoMagnetic, total count gamma radiation, and Ground Penetrating Radar (GPR) measurements were carried out on two archaeological sites located adjacent to the place where a miner duct will be buried. The aim of the measurements was to indicate the optimal áreas for archaeological excavation to find subsurface remains related to ancient communities that lived in the sites. Magnetic measurements showed anomalies that lead to the discovery of a large amount of ceramic fragments and other remains. Gamma radiation allowed discriminating argillaceous from sandy soil, an important result since sandy soil can be correlated to the archaeological layer, where remains are normally found. Ground penetrating radar confirmed the magnetic anomalies and showed several other anomalous features not related to the archaeological remains.Item Acesso aberto (Open Access) 3D raytracing through homogeneous anisotropic media with smooth interfaces(2002-12) COSTA, Jessé Carvalho; SCHOENBERG, Michael; URBAN, Jaime AntonioTwo-point raytracing problem is solved for events in a piecewise homogeneous and laterally varying 3D anisotropic media by continuation techniques. In conjunction with the shooting method the algorithm can be used for computation of qP, qS1, and qS2 events. The algorithm has the same performance and robustness as previous implementations of the continuation method for tracing rays in isotropic models. Routines based on our algorithm have several useful applications. First, an efficient forward problem solver for traveltime inversion of elastic parameters in the presence of anisotropy. Second, Newton-Raphson iterations during two-point raytracing produce wavefront attributes, slowness and wavefront curvature. These attributes allows the computation of geometrical spreading and second order approximations for traveltimes. Therefore it can be used to investigate the effects of anisotropy on CRS, in simple velocity models.Item Acesso aberto (Open Access) Linearização dos coeficientes de reflexão de ondas qP em meios anisotrópicos(2001-04) GOMES, Ellen de Nazaré Souza; PROTÁZIO, João dos Santos; COSTA, Jessé Carvalho; SIMOES FILHO, Ivan A.The reflection coefficients at a planar interface separating two anisotropic media have a nonlinear dependence on the elastic parameters and densities of both media. Linear approximations on the elastic parameters for the qP wave reflectivity are more convenient for AVO/AVD analysis. We present the solution of the Zoeppritz equations in terms of impedance and polarization matrices. Using this approach and assuming weak impedance contrast and weak anisotropy, a simple derivation of linearized approximations for qP the reflectivity is presented for general anisotropy. The linear approximations of reflection coefficients, qP and converted waves, for qP incidence are very close to the exact results for incidence angles up to 30 degrees considering moderate impedance contrast and anisotropy.Item Acesso aberto (Open Access) Wave equation depth migration using complex Padé approximation(2009-03) PESTANA, Reynam da Cruz; LUCAS, Jacira Cristina de Freitas; COSTA, Jessé CarvalhoWe propose a new method of depth migration based on a constant density variable velocity wave equation in the space-frequency domain. A complex Padé approximation of the wave equation evolution operator is used for wavefield extrapolation. This method mitigates the inaccuracies and instabilities due to evanescent waves and produces images with fewer numerical artifacts than those obtained with a real Padé approximation of the exponential operator, mainly in media with strong velocity variations. Tests on zero-offset data from the SEG/EAGE salt model and the 2D Marmousi prestack dataset show that the proposed migration method can handle strong lateral variations and also has a good steep dip response. We compare the results of the proposed method with those obtained using split-step Fourier (SSF), phase shift plus interpolation (PSPI) and Fourier finite-difference (FFD) methods.Item Acesso aberto (Open Access) 2-D ZO CRS stack by considering an acquisition line with smooth topography(2005-03) OLIVA, Pedro Andrés Chira; CRUZ, João Carlos Ribeiro; CALLAPINO, German Garabito; HUBRAL, Peter; TYGEL, MartinThe land seismic data suffers from effects due to the near surface irregularities and the existence of topography. For obtaining a high resolution seismic image, these effects should be corrected by using seismic processing techniques, e.g. field and residual static corrections. The Common-Reflection-Surface (CRS) stack method is a new processing technique to simulate zero-offset (ZO) seismic sections from multi-coverage seismic data. It is based on a second-order hyperbolic paraxial traveltime approximation referred to a central normal ray. By considering a planar measurement surface, the CRS stacking operator is defined by means of three parameters, namely the emergence angle of the normal ray, the curvature of the normal incidence point (NIP) wave, and the curvature of the normal (N) wave. In this paper the 2-D ZO CRS stack method is modified in order to consider effects due to the smooth topography. By means of this new CRS formalism, we obtain a high resolution ZO seismic section, without applying static corrections. As by-products the 2-D ZO CRS stack method we estimate at each point of the ZO seismic section the three relevant parameters associated to the CRS stack process.Item Acesso aberto (Open Access) A quick review of 2D topographic traveltimes(2005-03) CALLAPINO, German Garabito; OLIVA, Pedro Andrés Chira; TYGEL, Martin; SANTOS, Lúcio TunesThe Common-Reflection-Surface (CRS) stacking method was originally introduced as a data-driven method to simulate zero-offset sections from 2-D reflection pre-stack data acquired along a straight line. This approach is based on a second-order hiperbolic traveltime approximation parameterized with three kinematic wavefield attributes. In land data, topographic effects play an important role in seismic data processing and imaging. Thus, this feature has been recently considered by the CRS method. In this work we review the CRS traveltime approximations that consider the smooth and rugged topography. In addition, we also review the Multifocusing traveltime for a rugged topography. By means of a simple synthetic example, we finally provide first comparisons between the various traveltime expressions.Item Acesso aberto (Open Access) Migração (2,5-D) com amplitudes verdadeiras em meios com gradiente constante de velocidade(2002-04) CASTILLO, Luis Antonio Lopes; CRUZ, João Carlos Ribeiro; CALLAPINO, German Garabito; URBAN, Jaime AntonioThe true-amplitude seismic migration, in time or depth, provides a measurement of the reflection coefficients of primary reflection events. These are constituted by P-P reflection of longitudinal waves at smooth reflectors. One of the mostly used method is the Kirchhoff migration, by which the seismic image is obtained by stacking the seismic wavefield using a diffraction surface, also called Huygens Surface. In order to obtain true amplitude migration, i.e. the removal of geometrical spreading, it is introduced a weight function in the migration operator. The weight function is determined by the asymptotic solution of the migration integral at stationary points. The ray tracing is a fundamental tool for determining the weight function and the traveltime, that increases the computational costs of the migration process in heterogeneous media. In this work it is presented a true-amplitude migration algorithm tailored for two-and-one-half dimensional model, i.e. when the velocity field varies only with two coordinates of the three dimensional Cartesian system. It is emphasized the special case of constant gradient velocity. As a second topic, this work concerns about recovering seismic attributes from pre-stack seismic data by applying the double diffraction stack inversion. The estimated parameter is the incidence angle at the reflector. Combining the estimated reflection coefficient and the incidence angle, it is possible to perform the so-called Amplitude versus Angle Analysis (AVA) on the interested reflector.