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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Navegando Dissertações em Geofísica (Mestrado) - CPGF/IG por CNPq "CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOFISICA::SISMOLOGIA"
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Item 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/8498743497664023The 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.Item Acesso aberto (Open Access) Estudo do método de inversão tomográfica 2D baseada nos atributos cinemáticos da onda NIP e construção de interface gráfica para o processo de picking(Universidade Federal do Pará, 2007) OLIVEIRA, Iran Gadelha de; CALLAPINO, German Garabito; http://lattes.cnpq.br/6064981270181319In this work, a new tomographic reflection inversion method is studied, with the objective of determining smooth and isotropic velocity models for real and synthetic seismic data. The velocity model is obtained by the program NIPTOMO, which is an implementation of a tomographic inversion method of the kinematic attributes of the hypothetical waves NIP (normal incidence point). The input data for the tomographic inversion, e. g., traveltime tables and NIP attributes (wavefront curvature radius and emergence angle) are obtained through a set of picked points on a simulated zero-offset (ZO) section, previously obtained by the common-reflection surface (CRS) method. The choice of picked points in a ZO section is normally made using automatic picking programs that identify locally coherent events in a seismic section, based in user-defined parameters. The picking process is one of the most critical steps in this new method, since the choice of non primary reflection events, such as diffractions and multiples, may lead to errors in the velocity model obtained by the tomographic inversion. This work has as main objective develop an interative picking program to give to the user the control of the choice of primary reflection points that are used as input for the tomographic inversion. The present picking program was tested on the synthetic Marmousi dataset and on a real data from the Tacutu Basin, Brazil (seismic line 50-RL-90). The results obtained show that the interative picking process for the choice of primary reflection events points favors the determination of a precise velocity model.Item Acesso aberto (Open Access) Inversão quadrática de dados de AVO usando algoritmo de Marquardt(Universidade Federal do Pará, 2004-11-12) MENDES, Ana Cristina Marques; PROTÁZIO, João dos Santos; http://lattes.cnpq.br/4210442535067685In this work, the exact and quadratic approach expression of Knott-Zöeprtiz are presented, as well as its coefficients, amplitudes, Rpp and Rsp, respectively, all of them as a function of the relative contrast, as well as the inversion of quadratic parameters of AVO data. In this inversion of the quadratic parameters, we have used the non-linear Levenberg-Marquadt algorithm, considering only converted and reflected events, either in the non-combined form. In the study of the physical parameters impedance contrast, shear modulus and P wave velocity, we have werified which of those parameters can be effectively inverted. The results have shown that the impedance contrast (δz) is very well solved when it is related with the P wave velocity contrast (δα) or with the shear contrast (δμ), considering reflected events in the case of high, moderate and low model contrasts. On the other hand, when the impedance constrast is fixed and the two other parameters in consideration are related, the results show that these parameters are bad solved, e.g., the ambiguity region becomes large and the parameters become ambiguous and unstable. In the case of a converted event and in the combination of converted and reflected events, considering low and moderate contrast models (δz) is well solved, which is not the case when we consider a high contrast model.Item Acesso aberto (Open Access) Joining diffraction filter and residual diffraction moveout to constructo a velocity model in the depth and time domains: application to a Viking Graben data set(Universidade Federal do Pará, 2014-08-14) COLLAZOS GONZALEZ, Jaime Andres; FIGUEIREDO, José Jadsom Sampaio de; http://lattes.cnpq.br/1610827269025210Diffracted seismic waves are generated by unsmooth structures in the subsurface with a size on the order of seismic wavelengths. Because the incident wave field can be significantly affected by these discontinuities, many important properties of the seismic events can be used to improve the velocity model building. In this thesis, we propose a practical approach to construct velocity models in the time and depth domains using diffractions. This methodology applies the plane wave destruction (PWD) filter jointly with the residual diffraction moveout (RDM) method to construct velocity models in time and depth domains. Our method does not depend on any requirements except for identifiable diffractions filtered from reflection events and an arbitrary initial velocity model as input. The post-stack migrated images (in the time and depth domains) are compared with the mi- grated images derived from conventional seismic processing steps. In both cases, we used post-stack Kirchhoff Migration. Beyond the to the need to identify and select the diffraction events in the post-stack migrated sections in the depth domain, the method has a very low computational cost of processing time. To reach an acceptable velocity model was less compared with conventional processing. The applicability of our methodology was verified using a real Viking Graben seismic dataset.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) Métodos de otimização global aplicados na busca dos parâmetros SRC(Universidade Federal do Pará, 2004-06-21) CARMO, Klaus Mairan Laurido do; GARABITO CALLAPINO, German; http://lattes.cnpq.br/6064981270181319The Common Reflection Surface Stack (CRS) method provides the simulation of zerooffset (ZO) sections by means of the summing seismic events of the multicoverage data contained in the stacking surface. This method does not depend on the velocity macro-model of medium; it only requires a priori knowledge of the near-surface velocity. The simulation of ZO sections for this stacking method uses a hyperbolic second-order traveltime approximation of the paraxial rays to define the CRS stacking surface or CRS stack operator. For 2D media, this operator depends on three kinematic attributes of two hypothetical waves (NIP and N waves), observed in the point of emergency of the central ray with normal incidence, namely, the angle of emergency of the central ZO ray (β0), the radius of curvature of the Normal Incidence Point Wave (RNIP) and the radius of curvature of the Normal Wave (RN). Therefore, the optimization problem in the CRS method consists in the determination, from the seismic data, of the three optimal parameters (β0, RNIP, RN) associated to each sample point of ZO section to be simulated. The simultaneous determination of these parameters can be made by means of multidimensional global search process (or global optimization), using as objective function some coherence criterion. The optimization problem in CRS method is very important for the good performance with respect to quality of the results and mainly to computational cost, compared with the methods traditionally used in the seismic industry. There are several search strategies to determine these parameters, based on systematic searches and using optimization algorithms, where only one parameter at each time can be estimated, or the two or three parameters simultaneously. Taking in to account the search strategy by means of the application of global optimization, these three parameters can be estimated through of procedures: in the first case the three parameters can be simultaneously estimated and in second case initially two parameters can be determined simultaneously (β0, RNIP), and subsequently the third parameter (RN), using the values of the two parameters already known. In this work it is presented the application and comparison of four algorithms of global optimization to find the CRS optimal parameters: Simulated Annealing (SA), Very Fast Simulated Annealing (VFSA), Differential Evolution (DE) and Controlled Random Search – 2 (CRS2). As importants results of the application of each optimization method, as well as between the methods regarding the effectiveness, efficiency and reliability to determine the best CRS parameters are presented. Subsequently, applying the global search strategies for the determination of these parameters, by means of the optimization method VFSA that presented the best performance, the CRS stacking was applied to the Marmousi dataset, one stacking using two parameters (β0, RNIP), estimated by global search, and another CRS stacking using the three parameters (β0, RNIP, RN), also estimated by global search.Item Acesso aberto (Open Access) Migração 3D no tempo usando a teoria dos raios paraxiais(Universidade Federal do Pará, 1998-09) QUEIROZ, Norcirio Pantoja; SÖLLNER, Walter FranzThis presentation aims at the 3-D time migration of zero offset data, in true amplitude. This method is based on paraxial ray theory and uses a diffraction time function which is directly and correctly determined by the measurement of pre-stack seismic data. It is not necessary to know a macro velocity model in order to apply the time migration. In order to obtain a true amplitude time migration the migration result must be multiplied by a scaling factor and convolved with a known function. Together with a scaling factor, a filter was applied in order to recover the signal phase altered during the migration process. Due to the computational limitation synthetic dada in 2-D was used aims to test the program efficiency. The result was satisfactory, showing the efficiency and robustness of process.Item Acesso aberto (Open Access) Migração com amplitude verdadeira em meios bidimensionais (2-D) e introdução ao caso 2,5-D(Universidade Federal do Pará, 1999) URBAN, Jaime Antonio; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023In the recent past years we have seen through various published papers an increasing interest in true amplitude migration methods, in order to obtain more informations about the reflectivity properties of the earth subsurface. The most part of these works has treated of this thema either based on Born approximation as given by Beistein (1987) and Bleistein et al. (1987), or on ray theoretical wavefield approximation as given by Hubral et al. (1991), Schleicher et al. (1993) and Martins et al. (1997). By considering arbitrary source-receiver configurations the compressional primary reflections can be imaged into time or depth-migrated reflections so that the migrated wavefield amplitudes are a measure of angle-dependent reflection coeffients. In order to do this various migration algorithms were proposed in the recent past years based on Born or Kirchhoff approach. Both of them treats of a weighted diffraction stack integral operator that is applied to the input seismic data. As result we have a migrated seismic section where at each reflector point there is the source wavelet with the amplitude proportinal to the reflection coefficient at that point. Based on Kirchhoff approach, in this thesis we derive the weight function and the diffraction stack integral operator for the two dimensional (2-D) and for the two and one half (2.5-D) seismic model and apply it to a set of synthetic seismic data in noise environment. The result shows the accuracy and stability of the 2-D and 2.5-D migration methods as a tool for obtaining important information about the reflectivity properties of the earth subsurface, which is of great interest for the amplitude versus offset (angle) analysis. In summary, we present an expressions for the 2-D and 2.5-D weights as a function of parameters along each ray branch of the in-plane trajectory. Moreover, we show examples of application of the true-amplitude depth migration algorithm to synthetic seismic data obtained by ray theory seismic modeling using the Seis88 package (Cervený e Psencík, 1988), in order to make a numerical analysis and to verify the stability and accuracy of the algorithm. The results confirmed the removal of the geometrical spreading from migrated data, even in presence of noise. Additional tests were performed for pulse distortion analysis in depth rnigrated sections (Tygel et al., 1994) and to obtain reflection points attributes by multiple diffraction stack (Tygel et al., 1993).Item Acesso aberto (Open Access) Migração FD 3D em profundidade usando aproximação de Padé complexa(Universidade Federal do Pará, 2011-06-21) COSTA, Carlos Alexandre Nascimento da; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739Conventional implementations of 3D finite-difference (FD) migration use splitting techniques to accelerate performace and save computational cost. However, such techniques are plagued with numerical anisotropy that jeopardizes correct positioning of dipping reflectors in the directions not used for the splitted operators. We implement 3D downward continuation migration without splitting in the space coordinates using a complex Padé approximation and implicit finite differences. In this way, the numerical anisotropy is eliminated at the expense of a computationally more intensive solution of a large banded linear system. We compare the performance of the iterative stabilized biconjugate gradient (Bi-CGSTAB) and the multifrontal massively parallel direct solver (MUMPS). It turns out that the use of the complex Padé approximation provides an effective preconditioner for the Bi-CGSTAB, reducing the number of iterations relative to the real Padé expansion of the FD operator. As a consequence, the iterative Bi-CGSTABmethod ismore efficient than the directMUMPSmethodwhen solving for a single termin the Padé expansion. Forwide angle approximations direct methods are required. These algorithms are validated and the properties evaluated computing themigration impulse response in the SEG/EAGE salt model.Item Acesso aberto (Open Access) Migração FFD 3D em profundidade usando aproximação de Padé complexa(Universidade Federal do Pará, 2011) CAMPOS, Itamara do Socorro da Silveira; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739Fourier finite-difference (FFD) migration implementations use splitting techniques to accelerate performace and save computational cost. However, such techniques introduce numerical anisotropy which leads to mispositioning of dipping reflectors along directions not used for splitting the migration operator. We implement 3D FFD continuation migration without splitting in the frequency-space domain using the complex Padé approximation and implicit finite differences. This approach eliminates numerical anisotropy at the expense of a computationally more intensive solution of a large banded linear system. Numerical experiments in homogeneous and heterogeneous models show that splitting techniques produce noticiable positioning erros for models with strong lateral velocity variation. We compare the performance of the iterative stabilized biconjugate gradient (BICGSTAB) and the multifrontal massively parallel direct solver (MUMPS). It turns out that the use of the complex Padé approximation provides an effective preconditioner for the BICGSTAB, reducing the number of iterations relative to the real Padé expansion. The iterative BICGSTAB method is more efficient than the direct MUMPS method when solving for a single term in the Padé expansion. For wide angle approximations more terms are required to represent the migration operator, in this case direct methods are required. The algorithm is validated and the properties evaluated computing the migration impulse response in the SEG/EAGE salt model.Item Acesso aberto (Open Access) Modelagem acústica por diferenças finitas e elementos finitos em 2-D e 2,5-D(Universidade Federal do Pará, 2004-10-26) SILVA NETO, Francisco de Assis; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739Acoustic modeling provides useful synthetic data for evaluating seismic processing and imaging in complex geological settings. High order finite difference (FD) and finite elements (FE) was implemented and evaluated in homogeneous and inhomogeneous model. The FD algorithm are estended to 2,5-D for variable density models. Seismic modeling of oil reservoirs targets somewhat similar to those occuring at Paleozoic Basins in the Amazon are presented. Long period multiples produced between the free-surface and the Cretaceous- Paleozoic interface, the low resolution of the seismic waves near the reservoir and the week reflections at the interface between the reservoir rocks and the cap rock are the main features of the synthetics which presents a challenge to seismic imaging.Item Acesso aberto (Open Access) Modelagem sísmica por diferenças finitas em meios bidimensionais com difratores(Universidade Federal do Pará, 2000-09-14) FERNANDES, Lindemberg Lima; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023The subject of this work is the seismic modeling in medium with strong discontinuities in physical properties with enphasis in diffractions events. This research intend to contribute for a better comprehension and control of seismic modeling in complex medium. According to various authors, the Amazon Basin is formed by sedimentary rocks deposited since the Ordovician to the present, reaching depth up to 5 Km. The bodies of basalt between the paleozoic sediments are arranged as basaltic layers reaching thickness of hundred meters, which add to 90,000 km3. The ocurrence of these structures is responsible for the existence of multiple reflections during the propagation of the seismic waves, which makes impossible a better imaging of horizons located bellow the basaltic layers An accoustic velocity model was used to demonstrate this geological situation. The seismograms were calculated with a program of finite-difference with a fourth order aproximation of the acoustic wave equation in space and time. The aplication of the finite-difference method for modeling the propagation of the seismic waves has improved the understanding of the wave propagation in significant heterogeneous medium and achieves a good resolution in the interpretation of seismic reflection events in areas of interest As a result of numerical experiments accomplished in a complex geological medium a significant influence due to multiple reflection observed in a high velocity layer causing an increase in a loss of energy that made the data more dificult to analise. Because of this problem I advise the integration of the data from both surface and wells, to achieve a better imaging below the basaltic layer.Item Acesso aberto (Open Access) Um novo algorítimo para implementação do método de empilhamento SRC 3-D e modelagem sísmica da Bacia do Amazonas(Universidade Federal do Pará, 2006-05-23) LIMA, Charles Cristiano de Assis; CALLAPINO, German Garabito; http://lattes.cnpq.br/6064981270181319The Common Reflection Surface Stack (CRS) is a seismic reflection imaging technique that is independent of velocity model to simulate Zero-Offset (ZO) seismic section or volume. This technique have been used, alternatively, in seismic reflection processing and many works have been demonstrate that the CRS method shows results with better signal to noise rate and lateral resolution in comparison with conventional methods, e. g., NMO/DMO stack. The CRS stack provides some attributes or wavefield parameters that could be used in many applications, e.g., velocity models estimation, AVO and AVA analysis, geometric spread factor estimation, projected Fresnel zone, and others. The CRS technique has a second order hyperbolic traveltimes approximation in central ray vicinity. In the 3-D case, for a normal central ray or ZO, the CRS operator depends on eight parameters, estimating by coherency analysis from seismic data. In this work, the 3-D ZO CRS operator is analyzed for both reflection and diffraction events with respect the traveltimes obtained from straight modeling. I present a new CRS stack algorithm to simulate ZO sections or volume. I still present, in this work, a 3-D seismic modeling of the sedimentary Amazon Basin with SW3D consortium packages. The geologic model was based in true geologic and geophysics data.Item Acesso aberto (Open Access) Processamento de dados sísmicos da bacia do Camamu(Universidade Federal do Pará, 2009) MATOS, Ligia Naia de; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660Seismic Imagining is one of the manners to visualize on subsurface. To get at a reliable seismic imagining, a long way must be covered. The first stage is the seismic acquisition, its the planned evil its carries serious troubles. After the seismic acquisition we need to processes the data. Seismic data processing is alteration of seismic data to suppress noise, enhance signal and migrate seismic events to the appropriate location in space. Processing steps typically include analysis of velocities and frequencies, static corrections, deconvolution, normal moveout, dip moveout, stacking, and migration, which can be performed before or after stacking. In this work, our objective is a seismic migration from a Camamu basin 2D acquisition line. In this line we have many the dificulties arise from the factors free surface multiples e peg-lags. We are going to use as seismic processing methodology the common median point stack and the pos-stack migration by ProMax (Landmark Inc) software. To attenuate multiples we have used predictive deconvolution, radon filter and f - k filter techniques . The results are satisfactory when we compare to results without theses techniques.Item Acesso aberto (Open Access) Processamento, inversão e imageamento de dados sísmicos marinhos(Universidade Federal do Pará, 2012) SILVA, Douglas Augusto Barbosa da; LEITE, Lourenildo Williame Barbosa; http://lattes.cnpq.br/8588738536047617This work was there on the study and processing, inversion and imaging in time and in depthof Marmousi seismic data, and of the real Jequitinhonha obtained in the Bahia state Brazilian atlantic oriental continental platform. Were applied the NMO and CRS stack methods andthe niptomographic inversion technique of the cinematic attributes of the wave field. Withthe NMO stack was obtained a velocity distribution map throughout the velocity analysis onthe semblance coherence map and straight afterward the stacked and migrated sections in thedomain of the time and depth. The stack method of the common reflection surface (CRS)was applied with the crsstack-511 program to obtain the stacked and migrated sections inthe time domain and to extract the field wave parameters throughout the coherence analysis and of the redundancy obtained on the seismic data of multi-device. The niptomographicinversion phenomena of reflection took place throughout the aplication of the niptomo program,which is an implementation of the inversion method of the cinematic attributes ofthe NIP hypothetic wave, extracted straight from the CRS stack, to obtain an smoothedvelocity model, and subsequently, a migrated section in depth. The migrated sections areof the Kirchhoff kind. The techniques used follow a pre-determined and realized flowchartfollowing a file “makefile”, that works as an stage organizer. These stages were realized in theLinux desktop and in the Seismic Uni*x system of the Center for Wave Phenomena (CWP)of Colorado School of Mines. The results of the three techniques were compared with theaim of illustrating the evolution of the visual quality of the reluctant sections throughout theevents continuity trace-by-trace and the signal/noise relation, to analyze differences and improvementsin the migrated sections expecting a better geologic interpretation and organizebetter terms of processing and imaging, trying to aid possible well succeed drillings.