Programa de Pós-Graduação em Geofísica - CPGF/IG

URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2355

O Programa de Pós-Graduação em Geofísica da UFPA (CPGF) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA). Foi o segundo no Brasil a formar recursos humanos em Geofísica em nível de pós-graduação stricto sensu. Criado em 1972, funcionou até 1992 junto com os Cursos de Pós-Graduação em Geoquímica e Geologia.

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Agora exibindo 1 - 8 de 8

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)
Experimental verification of Hudson and Eshelby-Chen’s effective crack theory
(Universidade Federal do Pará, 2015-12-04) HENRIQUES, Jéssica Pena; FIGUEIREDO, José Jadsom Sampaio de; http://lattes.cnpq.br/1610827269025210
Physical modeling of cracked / fractured media in downscaled laboratory experiments has served as a great alternative for understanding the anisotropic media behavior. In this work, it was performed ultrasonic measurements on samples with low crack densities and different aspect ratios. The main goal was to investigate the experimental behavior of elastic parameters, such as: waves velocities and Thomsen parameters ε and 𝛾 and elastic stiffness coefficients for transverse isotropic media. Comparison of the results with the predictions made by the effective models of Hudson (1981) and Eshelby-Cheng (1993), it was also investigated in this work. Twelve samples were prepared with two types of cracks density, 5 and 8%. The cracks that have three different aspect ratios (0.133, 0.1778 and 0.2667) were formed by rubber inclusions in a homogeneous isotropic matrix resin. Moreover, an isotropic matrix sample was constructed by only epoxy resin. Among all samples, six (three for each density) have only one aspect ratio type (samples with single crack), while another six (three for each density) have three types of different aspect ratio (mixed samples). Among the predictions of the models, the Eshelby-Cheng (1993) shows a better fit in relation to the experimental results for samples with single crack (for the two densities of inclusions). However, none of the models predicts accurately with minimal tendency for the mixed samples.
Acesso aberto (Open Access)
High resolution GPR applied to the “Capela Pombo”
(Universidade Federal do Pará, 2016-02-29) ESPEJO ZEBALLOS, Manuel Alejandro Junior; SILVA, Marcos Welby Correa; http://lattes.cnpq.br/3213216758254128
In this work was applied electromagnetic method (GPR), to identify surface layers in a speci c urban environment. The measurements were performed to map the surface layers and artifacts that make up the study area "Capela de Nosso Senhor dos Passos - a Capela Pombo" in the Barrio of Campina-Bel em. This chapel has a previous work that rescues the importance y architectural features that it has, together with the evidence recollected by the author Dominic Savio de Castro Oliveira, who noted the historical importance that has not only to be the last private chapel in the city of Belém, this author also acknowledges her design as an Italian architect's work possible Guissepi Jos e Antonio Landi. The pro les obtained after corresponding processing procedure, show that this probably presences of structures, rest of the previous building structure, which previously was in this space. The study aimed to identify anomalies. The study aimed to identify structural abnormalities, as well as possible characteristic burials of the time when it was actively used. The results of the GPR measurements were encouraging, since the method presented response of approximately 1.80 meters deep, one can identify anomalies control for the reasons as presented Chapel, and present possible anomalies related to structural foreign bodies.
Acesso aberto (Open Access)
Inversão da forma de onda orientada ao alvo
(Universidade Federal do Pará, 2016-09-16) COSTA, Carlos Alexandre Nascimento da; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739
We propose a new target-oriented waveform inversion to estimate the physical parameters from a specific target in the subsurface from observed data from deviated-VSP acquisition or surface seismic data. Furthermore, we investigate a strategy to estimate the impulse responses from a local target in the subsurface from deviated-VSP acquisition or surface seismic data as an iterative sparse inversion approach, where the main feature of this strategy is that all multiple scattering in the data is used to enhance the illumination at target level. In these approaches we fit the upgoing wavefields observed at a specific level near the local target with the upgoing wavefields estimated at same depth level through convolution-type representation for the Green’s function. The main feature of the target-oriented waveform inversion is that we just need to know the up- and downgoing wavefields at the depth level above the target area to estimate the physical parameters for the area of interest. We show through numerical tests that the iterative sparse inversion approach does not require dense sources sampling to estimate the impulse responses from a target below a complex overburden, because of all the extra illumination via multiples. The physical parameters above the target area is not necessary to know if we use the data from deviated-VSP geometry of acquisition, but for surface seismic data we need to know a smooth physical parameter above the target area to estimate the up- and downgoing wavefields at depth level nearby the local target. For surface seismic data we used Joint Migration Inversion to estimate the up- and downgoing wavefields at depth level near the target area.
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/1610827269025210
Diffracted 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.
Acesso aberto (Open Access)
Modelagem 1D e 2,5D de dados do método CSEM marinho em meios com anisotropia transversal inclinada
(Universidade Federal do Pará, 2014-02-28) SANTOS, Walleson Gomes dos; RÉGIS, Cícero Roberto Teixeira; http://lattes.cnpq.br/7340569532034401
In this work I present the solution to the electromagnetic field generated by a horizontal electric dipole in transversally isotropic media with vertical (TIV) as well as inclined (TII) symmetry axis. In one-dimensional models the electromagnetic field was obtained with two distinct methods: (1) For the TIV case, I have written a semi-analytical solution to the Maxwell’s equations, by using a vector potential formulation; (2) For the TII case, the field was represented as the composition of primary and secondary fields, where primary fields are those found in an underlying isotropic layered medium, and the secondary field is calculated numerically via the finite element method in the spatial Fourier transform domain (kx, ky, z). This last methodology was also used to calculate the fields in two-dimensional structures, including inclined anisotropy in any region of the models. In this 2,5D case, I have applied the finite element method in the (x, ky, z) do main. Here I have used unstructured meshes to discretise the media, and parallel programming to solve the linear systems of equations. The responses were used to study the effects of electrical anisotropy in marine CSEM data.
Acesso aberto (Open Access)
Modelagem 2,5D dos campos usados no Método Eletromagnético a Multi-Frequência - EMMF
(Universidade Federal do Pará, 2012-12-19) SILVA, Valdelírio da Silva e; DIAS, Carlos Alberto; http://lattes.cnpq.br/9204009150155131; RÉGIS, Cícero Roberto Teixeira; http://lattes.cnpq.br/7340569532034401
This thesis shows the 2.5D calculation of synthetic data from the Multifrequency Electromagnetic Method (EMMF, from the portuguese name). The work is presented in two main parts: the first one presents the details of the numerical methods used in the calculation of the fields generated by the Horizontal Loop of Current, placed on the surface of bi-dimensional earth models; the second part uses the achieved results to simulate EMMF method data, which are the real and imaginary parts of the radial magnetic field from the loop. In the second part, we observe the computed fields from several different models, including variations in their physical properties as well as in the geometry of their features. We aim at estimating the sensibility of these fields to the structures that can be found in a sedimentary basin. With this modeling, we are able to study the characteristics of the data and to find how the two components of the radial field, real and the imaginary, contribute with separate and complimentary information about the structures in the models. The results show that the radial magnetic field presents very good lateral resolution, for a measure taken from a fixed source. The observed capability of these data to resolve target structures will be extremely important for the future work with the inversion of such data, as well as for the building of apparent resistivity sections.
Acesso aberto (Open Access)
Rock physics attributes analysis for identification and characterization of fluid content at hydrocarbon reservoirs - revisiting the Viking Graben basin dataset
(Universidade Federal do Pará, 2015-04-17) TERUYA MONROE, Jorge Antonio; FIGUEIREDO, José Jadsom Sampaio de; http://lattes.cnpq.br/1610827269025210
In the characterization of hydrocarbon reservoir, most of methodologies used in rock physics or seismic reflection are based on the physical properties analysis of rocks which are associated to anomalous effects in seismic sections. These anomalies are, many often, associated to indicators of fluids (oil, gas and/or water) in the hydrocarbon reservoir. In this work, we perform a study in order to characterize a hydrocarbon reservoir at north Viking Graben region, in the North Sea. In addition to the seismic data, well-logs from two locations (wells A e B) were also used in our analysis. However, in our data set analysis, beyond to perform AVO analysis, Vp/Vs versus impedance (Ip) and Vp/Vs - Φ we applied the trend angle methodology and well-logs data set analysis as well as Gassmann fluid substitution. Through AVO analysis in the re-processing of Viking Graben seismic data set, where found three anomalous zones with a high potential for the presence of fluids (gas/oil). Thus using templates of rock-physics and the analysis by attributes (trend angle) to classifying the fluids and determinate the possibility of gas-sand that are present at wells A and B.

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