Dissertações em Geofísica (Mestrado) - CPGF/IG

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/4993

O Mestrado Acadêmico pertente a o Programa de Pós-Graduação em Geofísica (CPGF) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA).

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Acesso aberto (Open Access)
Adaptação do método de Bott para contraste de densidade variando com a profundidade
(Universidade Federal do Pará, 2013-08-23) GOMES, Karina Palheta; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491; SANTOS, Darcicléa Ferreira; http://lattes.cnpq.br/5813659873067927
We present a new method to estimate the basement relief of a sedimentary basin through the analytic extension of the expression of the slab Bouguer for the case of a density contrast between the basement and the sediments decreasing monotonically with depth according to a hyperbolic law. The method requires that the noise in data have a standard deviation smaller than 0.01 mGal. The basement relief estimates are obtained at positions located directly below each observation. The methodology was applied on synthetic data from a simulated sedimentary basin presenting smooth basement relief. The method produced estimated basement topographies close to simulated basement topographies. The method was also applied to three sets of real Bouguer anomalies: Recôncavo Basin (Brazil), Büyük Menderes Graben (Turkey) and San Jacinto Graben (United States). The solutions produced by the proposed method attained maximum basement depth estimates in accordance with the available geological information: 6 km to Reconcavo Basin, 1.6 km to Büyük Menderes Valley, and 2.2 km to San Jacinto Graben.
Acesso aberto (Open Access)
Análise comparativa de três métodos de inversão aplicados a dados gravimétricos e magnéticos em perfil
(Universidade Federal do Pará, 1985-10-07) CUTRIM, Alteredo Oliveira; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491
Nonlinear inversion of potential field data has been traditionally accomplished by the least squares method. As far as the anomalous field is corrupted by Gaussian random noise. Least squares inversion has a good performance. However, when the data are contaminated by non Gaussian noise, which is the case of most geological noise, the least squares method presents an extremely poor performance. As a result, alternative methods must be employed in this case in order to produce realistic and meaningful interpretations. This paper presents a comparison among the least squares method, the minimum absolute error and M-fitting applied to non linear inversion of potential field data. The analysis is performed using theoretical data generated by synthetic models simulating several geological settings. The results show that in the presence of geological noise represented either by small shallow bodies above the main body, or by large interfering bodies adjacent to the main body, M-fitting presents a much batter performance as compared with the least squares or the minimun absolute error methods. In the presence of Gaussian random noise, however M-fitting has a poor performance. Since a Gaussian noise is a white noise, a law pass filter applied to the observed data would remove part of the Gaussian noise with a minimum loss of the low wavenumber signal. On the other hand, most geological noise have important low wavenumber spectral components so that this noise cannot be eliminated without a significant loss of signal. Therefore, the M-fitting method may become an important interpretation tool when applied to complex areas (where anomalies are usually contaminated by geological noise) provided the data have been previously filtered by a suitable law pass filter. All three methods analysed in the paper are applied to a real magnetic anomaly due to a dike of diabasic rock intruded in sandstones and shales from the Piauí Formation, in Parnaíba Basin, Brazil. All three methods yielded similar interpretations which are consistent with the available a priori geological information. The fact that all methods produced similar results indicates a low level of geological and Gaussian random noise in the data.
Acesso aberto (Open Access)
Análise da resolução do modelo de Hughes em sondagens magnetotelúricas
(Universidade Federal do Pará, 1996-02-13) SANTOS, Elinei Pinto dos; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
In most geophysical exploration methods, the interpretation is carried out assuming an uniformily stratified Earth model. Due to the lack of uniqueness in the inversion of eletromagnetic data, all of the methods require theoretical modeling techniques to aid interpretation. In the literature data has usually been interpreted in terms of a one-dimensional conductivity structure; commoly the Earth is assumed to be horizontally uniform so that the conductivity is a function of depth only. In this work a new technique was developed to model a generic two-layer Earth in which the interface separating the layers can be represented by a Fourier series. The technique involves a pertubation method to find the effects of a sinusoidal boundary with small ondulations. Because the first-order pertubation solution is a linear one, we can use the overlap principle and combine solutions for several different sinusoids to form the solution for any two-layer in which the boundary is represented by a Fourier series. Comparison with the finite elements technique, the following conclusions can be drawing: • For one model of a flat, two-layer Earth, the layers separated by an interface whose depth varies sinusoidal in one diretion, the eletromagnetic response are more strong when the first layer tickness is of the order of skin depth of the eletromagnetic wave in the medium; • On the other hand, the aparent resistivity for this model is not affected by the change in the spatial frequency (v) of the boundary; • In case of using the general solution for any two layer Earth that can be developed in Fourier series, this technique produced good results when compared to finite elements technique. The lineralization restrict the application of the technique to small structure, nevertheless, a lot of structure can be model in simple way and the computational time is very fast; • When the dimension of the first layer has the same order of magnitude of the structure, this technique is not recommended because for some particular sounding position, the apparent resistivity curves obtained show a small shift when compared to the curves obtained by finite elements.
Acesso aberto (Open Access)
Análise das aproximações RPP e RSP para meios isotrópicos
(Universidade Federal do Pará, 2002-08-16) SANTOS, Darcicléa Ferreira; PROTÁZIO, João dos Santos; http://lattes.cnpq.br/4210442535067685
This work presents linear and quadratic approximations of the Zoeppritz equations for the derivation of reflection and transmission coefficients from P-P and P-S events as a function of incidence angles and angular average, as well as the linear inversion analysis, AVO, in respect to the disassociated and combined P-P and P-S reflection events. The use of the so-called pseudoquadratic approximations was applied for the derivation of quadratic approximations only for PPevents, around the average contrasts of compressional and shear waves velocities and Vs/Vp ratio. The results of approximations derived in this work show that quadratic approximations were more precise than the linear ones in the two angular versions. The comparisons between these approximations in terms incidence angle and angular average show that the quadratic approximations are equivalent within the angular limit of [0º to 30º]. In the other hand, the linear approximations as a function of incidence angle are more precise than the linear approximations as a function of the angular average. In the linear inversion, sensitivity and ambiguity analyses were carried out and one could see that in the case of disassociated reflection P-P and P-S events, just a parameter can be estimated and the combination of these events can stabilize the inversion permitting the estimation of two physical parameters for the media (impedance, P-wave velocity and shear bulk module contrasts).
Acesso aberto (Open Access)
Análise de ambiguidade em métodos de campo potenciais através de análise fatorial, Q-Modal
(Universidade Federal do Pará, 1989-07-18) LOPES, Simone da Graça Fraiha; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491
A method is presented to analyze ambiguity in geophysical interpretation. Initially, alternative solutions are obtained which are assumed to be representative of the region in parameter space where ambiguity is more pronounced. In a second stage, these solutions are grouped and ordered using Q-mode factor analysis. The method was applied to synthetic potential field data where some important causes of ambiguity are simulated, such as discretizing and truncation of the anomaly, and the presence of random and geologic noise. A single prism is employed as an interpretation model and in both gravity and magnetic cases the prism depth extent stands out as the main cause of ambiguity. The second cause is either the depth to the top when the anomaly presents a strong signal, or the width when the anomaly presents a weak signal. The presence of random noise is not an important factor leading to ambiguity. On the other hand, the presence of interfering sources is a strong fator in both gravity and magnetic interpretation. The application of the method to real anomalies illustrates its importance in defining alternative solutions, and the importance of the a priori information in the establishment of the causes of ambiguity. The presented method may be applied at any stage of an exploration project. At each stage it provides relevant information which may be useful in planning the next stage. Compared with other methods usually employed in ambiguity analysis such as confidence regions, for exemple, the proposed method has the advantage of requiring no statistical assumptions about the error distribuition.
Acesso aberto (Open Access)
Análise de feições geológicas na região de Tartarugalzinho, Amapá, através de métodos geofísicos
(Universidade Federal do Pará, 2009) MARTINS, Saulo Siqueira; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734; LUIZ, José Gouvêa; http://lattes.cnpq.br/8676530374310847
Two geophysical methods were applied to detect geologic structures on the oriental edge of the Guianas Shield. The gravimetric method was applied mainly to find faulting on the basement, associated to shear belts that have orientation NW-SE. It was found faulting on the basement as well as an indication that the crust suffered a thinning in some region of the edge. The GPR electromagnetic method was applied to find geologic discontinuities on the sediments and to check if they are reflex of structural faults on the basement and/or reactivation of some of them. The GPR showed places where discontinues and some paleostructures can be observed. The study was also applied to understand how the basement discontinuities can influence on the formation of Tertiary sedimentary basins and on the formation of shallow paleostructures.
Acesso aberto (Open Access)
Uma análise de métodos de supressão de múltiplas de superfície livre aplicados a um dado real
(Universidade Federal do Pará, 2011-10-14) OLIVEIRA, Andrei Gomes de; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660
The seismic record in 2D linear events are common features in the seismograms. These events are overlap with interesting reflections (early reflections) complicating the stages of seismic processing and identification of possible subsurface geological horizons. It possible highlight multiple surface that distinguished from others by a low frequency, high amplitude and low velocity of propagation. The identification and removal of multiple reflflections in seismic data is a real step of great importance in seismic processing, because the attenuation can prevent many of these errors in the interpretation of geological images seismic. This study is the determination of a processing flow for multiple attenuation free surface. Methods of elimination of multiple surface (SRME, Radon filtering, predictive deconvolution domain τ - p and fk filltering) applied to a real data 2D were used in different combinations. These are analyzed and presented the results are the best combinations.
Acesso aberto (Open Access)
Análise de parâmetros da função característica de Hamilton
(Universidade Federal do Pará, 1998) TAVARES, Isabel Cristina; SÖLLNER, Walter Franz
The velocity analysis is a fundamental process in reflexion seismic, where the stacking velocity as well the zero offset traveltime are sufficient for determining the geological model for media with flat layers. On the other hand the Hamilton formalism uses the same parameters (velocity and zero offset traveltime) for determining the characteristic function for that kind of model. For a three-dimensional heterogeneous geological model with arbitrarily curved surfaces, the characteristic function is defined by nine parameters. This thesis aims at determining the characteristic function through the analysis of parameters using times slices in traveltime function, both in the CMP and zero offset ensemble. This analysis is done by the observation the behavior of each parameters during the fitting between the calculated characteristic function and the traveltime function obtained from the data survey.
Acesso aberto (Open Access)
Análise de resolução em tomografia interpoços em 3-D
(Universidade Federal do Pará, 2000-12-15) SOUZA, Syme Regina de Deus; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739
The joint inversion of multiple crosswell surveys traveltime data allows the reconstruction of high resolution 3-D slowness models suitable for monitoring enhanced oil recovery processes and detailed reservoir characterization. However, the non-uniform volumetric ray coverage unavoidable in crosswell surveys requires additional information to the tomographic system in order to obtain stable solutions. The 3-D tomographic problem is analyzed discretizing the models in 3-D prismatic meshes and using the singular value decomposition. The projection angle of target models in the subspace orthogonal to the effective null space of the tomographic matrix is an useful criteria for designing mesh and data acquisition geometry in order to better conditioning the tomographic reconstruction. The approach can also be used during the linear iterations to redefine the mesh or evaluate the requirement of additional prior information to the tomographic system.
Acesso aberto (Open Access)
Análise de sensibilidade para estereotomografia em meios elípticos e anelípticos
(Universidade Federal do Pará, 2005-12) BARBOSA, Brenda Silvana de Souza; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739
Stereotomography is extended to general anisotropic models and implemented for elliptical and anelliptical anisotropy. The elliptical and anelliptical models present only three parameters. This makes them less sensitive to the ambiguity due to limited coverage of surface seismic experiments than transversaly isotropic or orthorhombic models. The corresponding approximations of the slowness surface restrict the validity of the present approach to qP events and mild anisotropy. Numerical experiments show the potential and the limitations of stereotomography in estimating macro-velocity models suitable for imaging in the presence of anisotropy as well as the importance of transmission events from multiple-offset VSP experiments for the success of the approach.
Acesso aberto (Open Access)
Análise de um esquema de inversão para estimativa de anisotropia local a partir de dados de VSP
(Universidade Federal do Pará, 2012-05-18) BARRETO, Adriano César Rodrigues; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660
Inversion scheme for the determination of arbitrary in a vicinity of a receiver situated inside a borehole from the data obtained during a multi-offset multi-azimuthal VSP experiment is studied. The data consist of vertical components of the slowness vector and all components of the polarization vector of P waves direct and reected. The inversion is made from a first order approximation around an reference arbitrary isotropic medium, that does the relation between the data of slowness and polarization of P waves parameters and the weakly anisotropic medium (WA parameters). This inversion scheme applies to arbitrary anisotropy medium, provided that the anisotropy is weak and independent of downhole type (vertical, horizontal or inclined). The results show that reversing is sensitive to the number and orientation of the proles of sources that are distributed on the surface. An analysis of the design of an experiment and discussion about the choice of parameters of the reference isotropic medium are presented. Within the realistic assumptions about the level of noise is possible to estimate the phase velocity for a limited angular aperture around the well.
Acesso aberto (Open Access)
Análise de um esquema linear para estimativa de anisotropia local a partir de dados de onda P em experimentos de VSP multiazimutal
(Universidade Federal do Pará, 2013-08-08) MACAMBIRA, Raiza de Nazaré Assunção; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660
This study presents an analysis of the linear inversion scheme for estimating anisotropy in the neighborhood of a receiver placed in a well using the vertical components of the slowness and polarization vectors of P-waves measured in multi-azimuth walkaway vertical seismic profile (VSP) surveys. Independently of the medium above the geophone (homogeneous or heterogeneous) and the shape of the well (directional or curved, vertical or sloped), an inversion is performed from a first-order approximation around a reference isotropic medium. The analysis of the inversion scheme considers factors such as the noise level of the data, the type of P-wave, the degree of the anisotropy of the medium, the choice of parameters in the reference isotropic medium and the degree of heterogeneity of the medium.
Acesso aberto (Open Access)
Análise de velocidade por otimização do semblance na reflexão sísmica
(Universidade Federal do Pará, 2010) VIEIRA, Wildney Wallacy da Silva; LEITE, Lourenildo Williame Barbosa; http://lattes.cnpq.br/8588738536047617
This work had as a general aim to develop a systematic methodology for the inversion of seismic reflection data organized in common-midpoint gathers (CMP), starting from 1D vertical variation of velocity and thickness that allows to obtain interval velocity, vint,n, in time, the correspondent interval thickness, zn, and the correspondent mean-square velocity, vRMS,n in individualized CMP gathers. A direct consequence of this work the transformation of these values from time to depth. Two methods were developed to attack the problem defined as velocity analysis based on the estimation of interval velocity. The first method was based on manual picking of reflection events on CMP gathers, and inversion by curve fitting in the least-square sense. The second method was based on the otimization of the semblance function to obtain an automatic picking. The methodology combined two types of optimization: a Global Method (Price or Simplex), and Local Method (second order gradient or cojugate), subject to a priori information and constraints. The picking of events in time-distance section is of fundamental importance in the process of inversion, and the picked points are the input data along with a priori information of the model to be adjusted. The picking must, in principle, avoid events that represent multiples, diffractions and intersections, and in a section over 50 pickings can be made, while in a semblance map not more than 10 events could usually be picked by eye. The application of this work is focused on seismic data of marine sedimentary basins to obtain a distribution of velocities for the subsurface, where a plane-horizontal model is applied for individual CMP sections, and that the solution can be used as an initial model in subsequent processes. The real data used in this study were collected by Petrobras in 1985, and the selected seismic line was of number L5519 of the Camamu Basin, and the CMP presented is of number 237. The line consists of 1098 shot points with right-lateral arrangement. The sampling interval is 4 ms. The spacing between the geophones is 13.34 m with the first geophone located at 300 m from the source. The spacing between the sources is 26.68 m. As a general conclusion, the method for estimating interval velocity in this work stands as an alternative support to velocity analysis, where it is necessary a control over the sequential inversion of CMP gathers along the seismic line such that the solution can be used as an initial model for imaging, and further tomographic inversion. As future work, we can be propose studies directely and specifically related to seismic velocity analysis by extending the 2D semblance optimization method to 3D, and extending the present studies to the method based on the image ray, aiming at producing a continuous velocity map for the entire section in an automatic way.
Acesso aberto (Open Access)
Análise do efeito da discretização do modelo de velocidades nas migrações Kirchhoff e Kirchhoff-Gaussian- Beam 2D pré-empilhamento em profundidade
(Universidade Federal do Pará, 2014-02-28) PAIXÃO, Marcelo Tavares; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023
The Gaussian Beam (GB) is an asymptotic solution of the elastodynamic equation in the paraxial vicinity of a central ray, which approaches better the wave field than the standard zero-order ray theory. The GB regularity in the description of the wave field, as well as its high accuracy in some singular regions of the propagation medium, provide a strong alternative to solve seismic modeling and imaging problems. In this dissertation , I present a new procedure for pre-stack depth migration with true-amplitude, combining the flexibility and robustness of Kirchhoff migration type using superposition of Gaussian beams to represent the wave field. The proposed migration algorithm comprises in two stacking process: the first is the beam stack applied to subsets of seismic data multiplied by a weight function defined such that stack operator has the same formulation of the integral of the Gaussian beams superposition; the second is a weighted diffraction stack by means of the Kirchhoff type integral having as input the stacked data. For these reasons it is called Kirchhoff-Gaussian-Beam (KGB) migration. In order to compare the Kirchhoff and KGB methods with respect to the sensibility on relation to the discretization length, we apply them to the well-know 2D Marmousi dataset using four velocity grids, i.e. 60 m, 80 m, 100 m e 150 m. As result we have that both methods present a much better image for smaller discretization interval of the velocity grid. The amplitude spectrum of the migrated sections provide us with the spatial frequency contents of the obtained image sections.
Acesso aberto (Open Access)
Análise teórica do problema de Weaver da falha infinita, modo TE magnetotelúrico
(Universidade Federal do Pará, 2003-02-14) GUIMARÃES, Raimundo Nonato Menezes; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
In this work it is shown an analytic solution for the Magnetotelluric TE mode infinite fault, taking in consideration the presence of the air. The solution following the hybrid solution, partially analytic and partially numeric, proposed in 1985 by Sampaio. In his solution he applied eight boundary conditions. We found that four of them are mathematically inconsistent and had to be modified. The modification of them took us to the analytic solution discussed here. This solution is compared with those obtained by Weaver and by Sampaio and with finite element method, using resistivity contrast equal to 2, 10 and 50 between the two sides of the fault. As a result, the analytic solution obtained here for the normalized electric field shows a better fit with the finite element solution then those proposed by either Weaver or Sampaio. This is a very difficult problem and it is still open to a definitive analytic solution. The one shown here is just one big step toward this goal.
Acesso aberto (Open Access)
Anomalias eletromagnéticas de corpos tubulares inclinados em contato com o manto de intemperismo usando diferentes arranjos de bobinas-modelamento analógico
(Universidade Federal do Pará, 1997-03-16) SILVA, Roberto Cesar Alves; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
Electromagnetic methods are mainly applied in the prospection of massive sulphide deposits. These deposits are frequently long in extension and thin, therefore the interpretation can be carried out considering a half-plane model in a resistive ambient. However, in Amazon region or in semi-arid and tropical regions where a partialy conductive to conductive overburden is encountered, interpretations using a resistive ambient model give erroneous results. The objective of this work is to study the influence of the conducting overburden on electromagnetic anomalies of inclined sheet-like bodies in ohmic contact with the overburden, using coil configurations - horizontal coplanar (HCP), vertical coplanar (VCP), vertical coaxial (VCA) and minium couple system (PERP). These studies are realized with the aid of analog modelling where the ore-body is simulated by a graphite sheet and the conducting overburden by ammonium choride solution. Generally, the diferente coil systems studied here show the similar characteristics of the overburden effects, reserving some peculiar effects of each coil system. The effects of a conductive overburden in ohmic contact with the orebody could be briefly described as follows: (i) There is an anti-clockwise phase rotation initially with the increase in the overburden induction number, but with further increase the phase rotates clockwise; (ii) The form of the quadrature anomaly profile is altered due to the appearence of an extra peak on the down-dip side of the ore-body, and (iii) The peak to peak quadrature anomaly on the up-dip side increases uniformly with increase in the overburden induction number. Highest anomalies are obtained with the horizontal coplanar system and lowest with vertical coplanar. No extra-peak in the quadrature profile is observed with the vertical coaxial system in this study. Also, the overbuden effects are more prominent in the horizontal coplanar system compared to vertical coil systems, and in the anomalies of the less inclined half-planes and at lesser depths.
Acesso aberto (Open Access)
Aplicação de análise de séries temporais em perfis de poço
(Universidade Federal do Pará, 1993-08-17) SILVA, Hamilton Pereira da; LOVELL, Michael Anthony
This thesis describes the application of time seris analysis to wireline logs. Through this technique it is possible to evaluate both their repeatability and vertical resolution, and determine the optimum sampling interval and acquisition speed for different logs. A comparison between three wells is also made, based on the same type of log. The sequence used, is to obtain data, in the same domain, for which the number of samples (N) does not exceed 2048. For these data the mean sample value and the algebraic polynomial are determined. The following were then applied, in order: cosine taper, high pass filter, Hanning window, the calculation of the coherence function, the phase spectra, and the signal to noise ratio of the power spectra for both the signal and the noise. For the coherence function, it was necessary to calculate the level of confidence for 50 necessary to determine the vertical resolution of some logs. The others were calculated to provide information concerning the position of the levels of coherence calculated. In relation to the phase spectra, its calculation suggests it is necessary to obtain additional information in respect of the processed logs, or in other words knowledge of any relative depth shifts made between the principal and repeat sections. The signal to noise ratio was calculated to investigate the possibility of evaluating the different types of logs by making a comparison with the coherence and the calculated power spectra. The power spectra of the signal and the noise were calculated to provide one additional parameter to evaluate the repeat section. In theory the power spectra of the signal and the noise of the repeat section should be equal to their respective spectra for the principal sections. The data used in this work were provided by PETROBRAS and originated in four boles of the Potiguar Basin. These are referred to as Holes A, B, C, and D. The evaluation of the repeatability between different types of logs indicates that, for Hole A, the microspherical log (MSFL) has better repeatability than the porosity log (CNL), and that this repeats better than the gamma ray log (GR). For the logs run in Hole D, a decrease in the speed at which the logs are run, from 550 m/hr to 275 m/hr, is advantageous only for the neutron porosity log. The velocity of 920 m/hr used in Hole C is totally inadequate for the resistivity logs (MSFL, ILD, and ILM). A decrease in the sampling interval from 0.2m to 0.0508m, for the gamma ray and neutron porosity logs, and to 0.0254m for the density log, gives good results when applied to Hole D. The calculation of vertical resolution indicates, that the neutron porosity is of superior quality when compared with the natural gamma ray in Hole A. In hole C the microspherical log (MSFL) has a vertical resolution of the same order as the natural gamma ray log (GR) in Hole B. This confirms the inappropriate speed for the logs acquired in Hole C. For Hole D, the calculation of vertical resolution indicates a superior quality for the high resolution density log when compared with the high resolution gamma ray log. The comparison between Holes A, B and D, uses the respective neutron porosity logs, confirming that the presence of noise, in general, is directly linked with the porosity of the formation - a higher porosity indicates more noise and consequently, a lower quality log is obtained. Analysis of phase spectra of each log indicates a depth shift exists between the principal and repeat sections for all the logs of Hole C. This could be confirmed through superposition of the sections.
Acesso aberto (Open Access)
Aplicação de deconvolução homomórfica a dados sísmicos
(Universidade Federal do Pará, 1998) GOMES, Maria de Valdivia Costa Norat; LEITE, Lourenildo Williame Barbosa; http://lattes.cnpq.br/8588738536047617
A seismic record is often represented as the convolution of a wavelet with the impulse response relative to the reflection path. The process of separating these two components of the convolution is termed deconvolution. There are a number of approaches for carrying out a deconvolution. One of the most common is the use of linear inverse filtering, that is, processing the composite signal through a linear filter, whose frequency response is the reciprocal of the Fourier transform of one of the signal components. Obviously, in order to use inverse filtering, such components must be known or estimated. In this work, we deal with the application to seismic signals, of a nonlinear deconvolution technique, proposed by Oppenheim (1965), which uses the theory of a class of nonlinear systems, that satisfy a generalized principle of superposition, which are termed homomorphic systems. Such systems are particularly useful in separating signals which have been combined through the convolution operation. The homomorphic deconvolution algorithm transforms the convolutional process into an additive superposition of its components, with the result that the single parts can be separated more easily. This class of filtering techniques represent a generalization of linear filtering problems. This method offers the considerable advantage that no prior assumption about the nature of the seismic wavelet or the impulse response of the reflection path need be made, that is, it does not require the usual assumptions of a minimum-phase wavelet and a random distribution of impulses, although the quality of the results obtained by the homomorphic analysis is very sensible to the signal/noise ratio, as demonstrated.
Acesso aberto (Open Access)
Aplicação de métodos hidroacústicos para estudo e dragagem na região portuária de Cabedelo - PB, Brasil
(Universidade Federal do Pará, 2014-11-17) LOPES, Victor Hugo Rocha; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660
This paper presents the use of hydroacoustic methods used for mapping and detection of subsurface stratigraphic features to support a project of dredging and demolishing of the left edge of the navigation channel of the Paraíba do Norte's River to expand the port zone of Cabedelo/PB. High-resolution seismic data and bathymetric data are used to map two main objectives: top of the Acoustic Rocky Basement (TARB) and the superimposed sedimentary package. This information is important to support the volume calculation of the material to be dredged and/or demolished along the navigation channel. The data analysis indicates that the expansion of the Cabedelo's Port firstly suggested by the Docas do Paraíba Company to be in the Forte Velho's locality becomes expensive due to the large volume of sedimentary and rocky material to be dredged. Thus, the Lucena region is presented as an alternative to the port expansion since presents lower volume of material to be dredged that reduces substantially the costs and time of execution of the work.
Acesso aberto (Open Access)
Aplicação de modelos de substituição de fluido em rochas sedimentares oriundas do nordeste brasileiro
(Universidade Federal do Pará, 2015-06-06) TROVÃO, Ana Alzira Fayal; FIGUEIREDO, José Jadsom Sampaio de; http://lattes.cnpq.br/1610827269025210
Carbonates reservoirs corresponds on about 50% of the hydrocarbon reservoir in the planet . This type of lithology presents different forms of heterogeneity, which are the main causes of errors in its characterization. This misunderstanding, can induces erroneous estimative elastic modules of rocks in saturated state. The main goal of this work is to perform a comparative analysis of fluid substitution models in unconventional carbonate reservoir. Specifically, fluid substitution processes analyzed in outcrops from Brazilian Northeast, under controlled laboratory conditions (temperature, pressure and degree of saturation) and under perspectives of the petrophysical and ultrasonic features by conventional theories (Gassmann, Biot) and unconventional (Brown and Korringa, Muller and Sahay). In this research, we analyzed six samples of carbonate rock and one sample of sandstone rock. The input data our analysis were: permeability, porosity, rock and grain density, elastic measures of compressional (Vp) and shear (Vs1 and Vs2) velocities. The measure of velocities was performed in cases of 100% gas (dry rock) and then replaced by water (100 % saturated by water). Our results show, that predictions performed by conventional fluid substitution models best fit in experimental measurements of sample considered homogenous. However, predictions performed by unconventional models (e. g., Muller and Sahay) shown best fit with most carbonates types, including tufa and limestanes.