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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Item 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/4210442535067685This 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).Item 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/7294174204296739Stereotomography 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.Item 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/3148365912720676In 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.Item 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/1610827269025210Carbonates 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.Item Acesso aberto (Open Access) Caracterização de reservatórios fraturados através de dados de ondas qP em levantamentos VSP Walkaway(Universidade Federal do Pará, 2008) SILVA, Saulo da Costa e; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660This dissertation presents a method to estimate the orientation of the axis of symmetry of a medium assuming it behaves effectively as a transversely isotropic medium (TI). The fracture orientation is then achieved from the estimation of the axis of symmetry of a TI medium. This estimative is done with the slowness and polarization vectors from qP waves, measured in VSP Walkaway experiments. The inversion process is based on linearized equations of the slowness and polarization vectors from qP waves and the weakly anisotropic parameters of the medium. Numerical tests are presented, on which the sensibility to factors like the strength of anisotropy, survey geometry, type of wave utilized and noise level are analyzed. Test results for a set of real data are also shown.Item Acesso aberto (Open Access) Deconvolução de perfis de poço através de rede neural recorrente(Universidade Federal do Pará, 2006-03-05) RUÉLA, Aldenize de Lima; ANDRADE, André José Neves; http://lattes.cnpq.br/8388930487104926For oil industry, the logs analysis is the main information source about the presence and quantification of hydrocarbon in subsurface. However, in two situations the new logging technologies are not economically viable and conventional logging tools must be used: The reevaluation of mature oil fields and evaluation of marginal oil fields. In conventional logs its data acquisition procedure may blur the value of physical property and the vertical limits of a rock layer. We are talking about an old problem in well logging – The paradox between vertical resolution and depth of investigation of a logging tool. Nowadays it is well handling by the high technology of new tools, but this problem persists in conventional old tools, e.g. natural gamma ray log (GR). Here, we present a method to smooth this kind of linear distortion in well logs by an integration of classical well log convolution model with recurrent neural networks. We assume that a well log can be well represented by an in depth convolution operation between the variation of rock physical property (ideal log) and a function that causes the distortion, called as vertical tool response. Thus, we develop an iterative data processing, which acts as a deconvolution operation, composed by three recurrent neural networks. The first one seeks to estimate the vertical tool response; the second one search for the vertical limits definition of each rock layer and the last one is constructed to estimate the actual physical property. To start this process we supply an appropriated first guess of ideal log and vertical tool response. Finally, we show the improvements in vertical resolution and in the physical property evaluation produced by this methodology in synthetic logs and actual well log data from Lagunillas formation, Maracaibo basin, Venezuela.Item Acesso aberto (Open Access) Medidas de coerência para análise de velocidade na migração em tempo(Universidade Federal do Pará, 2011) MACIEL, Jonathas da Silva; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739Iterative methods for migration velocity analysis depend on objective functions to measure the flatness of reflection events in common image gathers (CIG). Time migration is a simple imaging method to evaluate these objective functions. Using time migration we studied the influence of objective functions on the results of migration velocity analysis. We propose two new objective functions for migration velocity analysis: Extended Differential Semblance and the product of Classical Semblance times the Extended Differential Semblance. Numerical experiments using the Marmousoft data show the effectiveness of the new objective functions to estimate velocity models producing at events in common image gathers.Item Acesso aberto (Open Access) Migração em profundidade usando a solução numérica da equação da eiconal(Universidade Federal do Pará, 2001-06-12) LUZ, Samuel Levi Freitas da; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023In the last years we have seen an increasing interest in seismic imaging algorithms in order to obtain better informations about the earth interior. The Kirchhoff migration method is very useful for determining the position of seismic reflectors, if is known the seismic wave velocity model and the traveltimes are well determined through the earth model. The traveltime calculation is a necessary step for stacking the seismic data by means of the Kirchhoff migration operator. In this work the traveltimes are obtained by solving the eiconal equation of the ray theory. At first, the theory of Kirchhoff migration is reviewed, by considering depth migration in heterogeneous media with arbitrary curved reflectors. Secondly, the numerical solution of the eiconal equation is presented for transmited, diffracted and head waves. There offer, the depth migration algorithm is presented, must makes use of traveltimes obtained by the eiconal equation. Finally, the developed migration algorithm is applied to synthetic models, providing a very good image resolution in comparison with the conventional ray tracing migration methods, even in the presence of random or coherent (multiple reflections) noise.Item Acesso aberto (Open Access) Modelagem computacional de dados magnetotelúricos marinhos 2-D(Universidade Federal do Pará, 2009) SAITO, Kymie Karina Silva; SILVA, Marcos Welby Correa; http://lattes.cnpq.br/3213216758254128This study aims to investigate the scattering of plane waves caused by lateral variation of the physical properties of rocks. This is one of the most important to the success of exploration geophysics. The geophysical method used in this dissertation was magnetotelluric method (MT) and Marine Magnetotelluric (MMT). The tool used here was the finite element method, which is efficient to solve numerically the differential equations for electromagnetic fields of the geological structures with complex geometries. The computational procedures were used in the development and implementation of algorithms of numerical modeling of electromagnetic data. These algorithms were developed and implemented in several models of different geoelectrical parameters.Item Acesso aberto (Open Access) Modelamento e correção de descentralização das imagens de tempo de trânsito(Universidade Federal do Pará, 2003) FISCHETTI, Anna Carmela; ANDRADE, André José Neves; http://lattes.cnpq.br/8388930487104926The imaging tools used to borehole wall features identification have been largely utilized by geologist and oil engineers to identify geological events in a open hole and inspect the casing tube. The acoustic borehole imaging tools generate a transit time image and an acoustic amplitude image that are used to this proposes. However those logs may have a non-realist interpretation, since some tools effect can negatively influence in the images appearance. This paper presents a transit time image model starting from the application of the Coulomb’s approach to the borehole wall rupture submitted to a plane state of tensions which will supply the borehole section that is the geometric form that will be mapped by the acoustic borehole imaging toll. The tool up displacement and the borehole wall imperfections are usually the responsible for the transducer displacement in relation to the borehole axis. This effect may have important responsibility in the acoustic images imperfections. Thus, a computational process of transducer repositioning in the borehole axis position obtains the correction of those images, called decentralization correction. A method of tool decentralization effect correction is presented too based on this model which is proposed based on the plane analytic geometry and in the ray method to the definition of the transit time of the acoustic pulse, with the objective of reconstruct the transit time images achieved by the decentralized tool, that is to say, correct these images becoming as they were achieved by the centralized tool in relation to the borehole axis.Item Acesso aberto (Open Access) Processamento e imageamento NMO/CRS de dados sísmicos marinhos(Universidade Federal do Pará, 2010) NUNES, Fernando Sales Martins; LEITE, Lourenildo Williame Barbosa; http://lattes.cnpq.br/8588738536047617This work is devoted to processing and imaging of marine seismic reflection data selected from the Jequitinhonha Basin, Bahia, where two stack methods were used, the NMO-based and the CRS-based. It was also applied the CRS-partial prestack data enhancement for the densification of CMPs. Several tests were performed with these methods to optimize parameters of the stacking operators, and to improve the processing strategies. One of the efforts during processing was the attenuation of the surface-related multiple, what was attacked by applying the Radon and SRME techniques. It was also applied the densification of the data to improve the signal/noise ratio. As a conclusion, a strategy was chosen based on the comparative results of better visual and higher coherence values, having the CRS method presented superior results to the results with the NMO method, based on the visualization of reflection events that were not noticed in other sections.Item Acesso aberto (Open Access) Reconhecimento de fáceis em perfis geofísicos de poços com rede neural competitiva(Universidade Federal do Pará, 2015-02-27) COSTA, Jéssica Lia Santos da; ANDRADE, André José Neves; http://lattes.cnpq.br/8388930487104926The description of a depositional system based on the recognition of sedimentary facies is critical to the oil industry to characterize the petroleum system. In the absence of these facies description by cores or outcrop, we present a methodology based on intelligent algorithm able to identify facies of interest in wireline logs. This methodology uses a competitive neural network to extract geological information from the physical properties mapped in the M-N plot. The competition among neurons identifies the facies of interest, which have been previously identified in a cored borehole in other non-cored boreholes in the same oil field. The purpose of this methodology is to encode and transmit the geological information gained in cored boreholes to non-cored wells and thus achieve the geological interpretation of the facies of interest in an oil field. This methodology has been evaluated with synthetic data and actual wireline logs from two cored boreholes drilled in the Namorado oil field, Campos Basin, Brazil.Item Acesso aberto (Open Access) Regularização em estereotomografia(Universidade Federal do Pará, 2009) MELO, Luiz André Veloso; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739Obtaining an accurate velocity model is an essential part of imaging complex structures. In complex environments, conventional methods do not produce satisfactory results. Slope tomography is an effective tool for improving the velocity estimate. This method uses the slowness components and traveltimes of picked reection or difraction events for velocity model building. On the other hand, the unavoidable data incompleteness requires additional information to assure stability of inversion. One natural constraint for raybased tomography is a smooth velocity model. This study proposes to evaluate smoothness regularizations to slope tomography that require the evaluation of partial derivatives of the velocity model with respect to the spatial coordinates. One of evaluated regularizations is a new kind of smoothness constraint based on the reection angle. I evaluate results measuring data mist, velocity model results and scattering points recovered after inversion on synthetic data. In numerical tests the new constraint leads to geologically consistent models.Item Acesso aberto (Open Access) Verificação experimental do modelo efetivo de Hudson-Crampin para meios anisotrópicos fissurados cujo o meio de fundo apresenta isotropia transversal(Universidade Federal do Pará, 2017-03-17) CHIBA, Bruce Fabini Franco; FIGUEIREDO, José Jadsom Sampaio de; http://lattes.cnpq.br/1610827269025210The physical modeling of cracked media, using scaled laboratory experiments, has been used as an alternative for understanding the effect of anisotropy on the characterization of the cracked hydrocarbon reservoir. The main objective of this work was to verify experimentally the predictions of Hudson-Crampin’s effective model to cracked media. For this purpose, ultrasonic and petrophysical measurements were performed on sixteen synthetic anisotropic samples with different crack densities distributed in four groups with distincts aspect ratios (0.08, 0.20, 0.32 and 0.52). Beside theses, one sample no cracks and weak VTI ansisotropy were used as reference sample. The cracks were simulated by void spaces in the form of discs in an matrix (made with sand and cement). Related to the estimatives of velocity performed by the theoretical models, Hudson-Crampin’s model presents a better adjustment for VP and VS propagating perpendicular to the plane of cracks for the dry and saturated conditions. These estimatives became more evident in the case where the crack density and aspect ratios are low. In addition to the velocity values, our comparison was also performed in terms of Thomsen’s parameters ε, γ and δ.