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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Agora exibindo 1 - 20 de 108

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 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)
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 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 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)
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 Well-Tie no imageamento de uma área da bacia Tumbes-progresso
(Universidade Federal do Pará, 2014-08-29) CHAGAS, Tiago Paulo Câncio das; SILVA, Carolina Barros da; http://lattes.cnpq.br/5306784916926352; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660
Geological areas with large lateral velocity variations, such as in areas with faults and salt domes are complex areas, in general, seismic imaging time is limited. In these cases, the seismic imaging depth can provide better results. However, a velocity model is needed in depth with precision, which is not an easy task. An alternative to estimate the depth velocity model is provided by Well-tie technique. With the calibration of the synthetic trace data obtained from wells, seismic section with the depth map of velocity can be obtained through the time-depth curve. In this study, we used the Well-Tie to improve the model of RMS velocity obtained from the processing of seismic data. The updated velocity model was converted to depth and used to generate an in depth migrated seismic image of a region of Tumbes Basin-Progress.
Acesso aberto (Open Access)
Aplicação dos métodos elétrico e eletricomagnético para o estudo hidrogeológico no município de Altamira-Pará
(Universidade Federal do Pará, 1998-11-20) BAPTISTA, João Júnior; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
This work due application of the electroresistivity and electromagnetic geophysical methods in the municipal district of Altamira, in the central area of the State of Pará, with the purpose of mapping the thickness of the aquifer layers and occurrence of diabase intrusions for finding a groundwater wells. In this area are many outcrops of basement crystalline rocks covered with sediments of ages from the Paleozioc to Quaternary. The objective is to obtain water from the sediments of Inferior Devonian, more exactly in the Maecuru Formation. There were made thirty four vertical electric soundings using the Shlumberger arrangement, the AB/2 distance varying from 100 to 500 meters. Also there were made 108 transient electromagnetic soundings with "coincident loop" arrangement, using an square loop of 50 meters. Due to electronic problems and supraparamagnetic noises, the results of this electromagnetic soundings became very distorted, impossible to get from them important geologic information. Then, electromagnetic synthetic models were created to represent the geology of the area. The data were obtained from the field were presented as apparent resistivity curves. They were plotted using a log-log scale and interpreted using the EGSLIB/SEV1D first and then with the EGSLIB/SEV1DIN program. The models used were horizontal, isotropic and homogeneous layers. The interpretation results allowed to determine approximate geoelectrical models which reflects the underground geological situation. The interpretation results from the electric surveys were confronted with the results of the qualitative interpretation from the isogams map of the total magnetic field, allowing to delimit with more precision the zone of incidence of diabase sills, located at the north of the area. From the four distinguished geoeletric horizons, the third is essentially constituted by sands, therefore it is best for groundwater storage.
Acesso aberto (Open Access)
Aplicação dos métodos eletromagnéticos VLF e HLEM na prospecção hidrogeológica no município de São Domingos do Araguaia-PA
(Universidade Federal do Pará, 1996-04-25) FARIAS, Valcir João da Cunha; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
This work deals with the geological mapping using the electromagnetic methods VLF and HLEM to hidrogeological study of the county São Domingos do Araguaia in the southest of the State of Pará. It was carried out within the cooperation agreement between the Fundação Nacional de Saúde and the Universidade Federal do Pará, through the Geophysics Department and the Curso de Pós-Graduação em Geofísica. Also, we studied the quantitative performance of the VLF method, applied to ground water prospecting. First, we analysed the VLF response, by means of the parameters (tilt angle and ellipticity) of the ellipse of polarization of various geological situations likely to be found in the local under study, and for hidrogeological studies of other areal as well. Also, we evaluated the influence of different physical parameters of selected models using finite elements method. The quantitative analyse of the field data was carried out by trial and error using theoretical curves obtained by means of model simulation suggested by the qualitative interpretation using Fraser's filter and profiles of the HLEM method. The results showed the existence of structural features with trends N-S and NE-SW which correlated with the regional geology are normal and transference faults, respectivily. Based on these results, it was selected several sites for drilling of well with maximum probability of sucess.
Acesso aberto (Open Access)
Aplicação dos métodos gravimétrico e magnetométrico para a definição do comportamento estrutural da faixa de dobramentos Araguaia
(Universidade Federal do Pará, 1988-04-25) CARVALHO, João da Silva; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
Interpretation of gravimetric and aeromagnetometric informations of the northern region on the Araguaia Orogenic Belt covering an area of aproximately 129.000km2 is presented in this thesis. The area lies between is 47º50’W and 50º30’W longitudes and between 4º50’S and 9º00’S latitudes, over southeast Pará State, north-northwest of Goiás State and west of Maranhão State. The gravimetric and altimetric measurements were carried out along highways and roads in the region. The gravity data, after corrections and reductions are presented in the form of Bouguer anomalies map on scale 1:500.000. The gravimetric pattern of Araguaia Orogenic Belt shows features principally of longitudinal extension, with approximately meridional direction. These features are correlated with the known lithological and structural units in the area. In the central-meridional portion of the map, appears an extended zone of intensive negative anomaly (less than -100mgal). This zone suffers two inflexios, one in the northwest (NW) which correlates to Carajás Lineament, and the other along latitude 5°30’S. The higher gravimetric values, notably in the northwest portion (cratonic domain), are related to the influence of the metavulcanics Grão Pará Group, and those in the northeast portion are attribuited to the denser mass intruded in the crust. Notable, also a gravimetric peak on the eastern flank of the brachyanticlines. This peak could be linked to a denser mass placed under this region tectonially, creating elevations in crust base-level and consequently of the basement. Generally, the eastern flank of orogenic belt show a gradient more intensive than the western, due to principally the geometric configuration of structures. In the similar way there is a notable ascendent regional gradient from south to north. Through the analysis of magnetic intensity maps, of the Projeto Geofísico Brasil-Canadá (PGBC), diferent individual domains were identified. These domains correlate lithologically and structuraly with the geotectonics units that constitute the regional framework and their subunits. Analytical gravity and magnetic modelling were carried out for semi-quantitative interpretation with the objective to establish the basement geometric pattern of the Araguaia Orogenic Belt, and the vinculated structures. On the basis of gravimetric informations, we could verify a geometric higher pattern in the form of imbricated slices over the substratum. The higher negative anomaly in the center-meridional portion of the orogenic belt could be related with the deficiency of deeper mass (a depression in the crust bottom), or due to the presence of a low density mass in the supercrustal layers, in that zone. The gravity depression in the southwest of the area, between Guarai and Tupirama, could be attribuited to a depression in the basement, and in the similar way the negative anomaly associated with Carajás Lineament is related to a sinformal structure.
Acesso aberto (Open Access)
Aproximações não-hiperbólicas do tempo de trânsito utilizando aproximantes de Padé
(Universidade Federal do Pará, 2017-07-03) NEVES, Rodolfo André Cardoso; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023
Traveltime approximation is a fundamental tool of the stack and migration steps in seismic data processing. To increase the accuracy of these approximations, we propose new traveltime approximations based on Padé approximants, to CMP and CRS gathers. Hyperbolic approximations such as normal moveout (NMO) and comom reflection surface (CRS) are taylor series approximations of second order of the reflection traveltime. Padé approximants appear as an alternative to Taylor series, because they converge quickly to the desired function, and they have a major radius of convergence improving approximations acuracy. They can be obtained through the proper Taylor serie of the approximated function. This new approximation is obtained from the [2/2] Padé approximation of the generalized moveout equation; and from [2/2] Padé approximation of the Taylor series expansions of fourth order of the CRS surface. The acuracy of Padé approximation is superior when compared with other convencional approximations: normal moveout, shifted hyperbola and Transversal isotropic medium with vertical symetry axis (VTI). CMP gather Padé approximations depend just only one more parameter than normal moveout approximation and they keep the acuracy for long offsets. CRS gather non hyperbolic approximations, non hyperbolic CRS, fourth order CRS and Padé CRS, have major acuracy than hyperbolic CRS, increasing the convergence of the approximation for offset and CMP domain. The quadratic approximation of fourth order CRS is superior than non hyperbolic CRS approximation, producing less error in least square CRS parameter inversion.
Acesso aberto (Open Access)
Cálculo da porosidade: identificação do argilomineral
(Universidade Federal do Pará, 2017-04-20) ALMEIDA, Thales Luiz Pinheiro de; ANDRADE, André José Neves; http://lattes.cnpq.br/8388930487104926
In the daily practice of Formation Evaluation it is common the adoption of simplifying hypotheses or premises about the physical properties of the reservoir rock constituent materials to allow the porosity calculation. The knowledge of the physical properties of the clay in the reservoir rock is fundamental for porosity calculation. In this work it is argued that the physical properties of the clay mineral in the reservoir rock are different from the mean physical properties of the nearby shale layers. Geologically, the clay is one of the constituent materials of shale rock and to admit that the physical properties of the shale are equal to the physical properties of the clay in the reservoir rock means to disregard all the other constituents and to assume a sedimentary continuity that due to numerous postpositional processes may not occur. In this work, we apply the angular competitive neural network to the Density- Neutron Plot to show that if a reservoir rock and a shale present in the basin have the same clay, they have the same angular pattern. This methodology is presented with synthetic data and evaluated with actual well logs and core analysis from borehole drilled in the Namorado’s field, in the Campos Basin, Brazil.
Acesso aberto (Open Access)
Cálculo de porosidade com a rede neural competitiva
(Universidade Federal do Pará, 2015-10-26) ROSELLÓN GUZMAN, Laura Yesenia; ANDRADE, André José Neves; http://lattes.cnpq.br/8388930487104926
Porosity is the petrophysical property that quantifies the fluid volume in the reservoir rock under for subsurface original condition. However, its calculation by the densityneutron method is extremely difficult in non cored borehole by the lack of the knowledge about the matrix physical properties (density and neutron porosity). This work presents a method for enabling the use of density-neutron Method in non cored boreholes, showing a realistic estimate of the matrix physical properties for each reservoir layer, using a angular competitive neural network. For each layer, network training is performed in the density-neutron plot built with the points of this layer and the information about the grain density (matrix density), obtained in the core analysis. This method is presented with synthetic data, which satisfy the petrophysical model and real data from two cored wells in the Namorado field, Campos basin.
Acesso aberto (Open Access)
Caracterização de hidratos de gás a partir de dados geofísicos da região da Bacia Tumbes-Progresso (Peru)
(Universidade Federal do Pará, 2014-02-25) TEJADA SOTO, Zoraida Roxana; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660
Gas hydrate is known as a potential source of hydrocarbon energy. However, the detection of exploitation of this resource is still inexpressive. This is due to two factors: the diculty of detecting pro table areas of gas hydrates and due to the high risk involved in exploration. In this study, an analysis is presented to detect possible areas of gas hydrate ocurrence in a region of Tumbes-Progresso Basin, using geophysical data: magnetic, gravity, seismic and borehole (well data). It presents three approaches to demarcate the possible zones of hydrate: First, magnetic and gravity anomalies analyzed with respect to the geology and the study area that was chosen. It was subsequently made a seismic imaging the region of interest and the gas hydrates has been identied based on the presence identication of BSR (Bottom Simulating Refletor), This reflector correspond to a limit between gas hydrate and free gas zone. BSR potential was applied the AVO analysis (Amplitude Versus Oset). Finally, in the third approach, well data are evaluated, calculating the porosity and saturation of the rock in the gas hydrate stability zone. According to the analysis presented, It was veried the occurrence of gas hydrate in the study area.
Acesso aberto (Open Access)
Caracterização hidrodinâmica do Furo da Laura (Rio Guajará-mirim), Amazônia Oriental
(Universidade Federal do Pará, 2014-12-01) FERNANDES, Aldo Rafael Pascoal; ROLLNIC, Marcelo; http://lattes.cnpq.br/6585442266149471
Preserve our coastal and estuarine environments are of great importance to local and regional development, as these environments are located most cities and serve as a cradle for several specimens, despite these environments gather information and know their characteristic and seasonal patterns are important aspects. In this context, Laura hole (Rio Guajará-Mirim), transitional estuarine environment and important role in the economic and social framework for coastal communities, cities and surroundings, serves as one of the main routes of fishing inputs to the state. The Hole Laura is a water body adjacent to Marajó Bay, has two connections to the same and is under their direct influence, is located at coordinates UTM 22M, 796169-830035 W and S 9880864-9916228 through it were held three oceanographic, dry season (October 2013), the rainy season (February 2014) and dry (August 2014), this important stream with use of equipment for measurement of geophysical parameters in the region bathymetry, hydrodynamic, tide variation and salinity. There was in possession of these parameters the hydrodynamic behavior, classification and tidal range, phase difference between ebb and flood, salinity trend in the stream in response to the Marajó Bay, besides the identification of morphological features characteristics and seasonal analysis these changes in the collection of sections 1 and 2 pre-established, as well as mapping and preparation of a bathymetric map of the study area.
Acesso aberto (Open Access)
Comparação dos filtros de velocidade e do operador WHLP-CRS na atenuação de múltiplas
(Universidade Federal do Pará, 2004-04-20) CRUZ, Edson Costa; LEITE, Lourenildo Williame Barbosa; http://lattes.cnpq.br/8588738536047617
The geological motivation of this work is the imaging of sedimentary basin structures of the Amazon region, where the generation and accumulation of hydrocarbons is related to the existence of diabase sills. The seismic motivation is the fact that these intrusive rocks present a great impedance contrast with respect to the host rock, what gives rise to external and internal multiples, with primary-like amplitudes. The seismic signal of the multiples can predominate over the primary reflection signals from deeper interfaces, making difficult the processing, interpretation and imaging of seismic sections. In this work we study the attenuation of multiples in common shot (CS) sections by the comparison of two methods. The first one is the combination of the Wiener-Hopf-Levinson (WHLP) and the common reflection surface (CRS) stacking techniques, here called WHLPCRS, where the operator is exclusively designed in the space-time domain. The second method is a velocity filter (ω-k), applied after the CRS stacking, where the operator is exclusively designed in the frequency-wavenumber domain. The identification of the multiples is performed on the zero-offset (ZO) section simulated by the CRS stacking, using the periodicity between primaries and its multiples. The wavefront attributes, obtained through CRS stacking, are inserted on movable space-time windows, used to calculate the WHLP-CRS operator. The ω-k filter calculations are performed in the frequency-wavenumber domain, where the events of interest are selected for cutting or passage. The ω-k filter is classified as a cut-off filter, with amplitude alteration and preservation of phase, the limits of it are imposed by a space-time sampling. In practical aspects we conclude that for the case of multiples, separated events on the x-t domain are not necessarily separated on the ω-k domain, which raise difficulties in the designing of a ω-k operator with a similar performance when compared to the x-t operator.
Acesso aberto (Open Access)
Condutividade elétrica complexa de rochas
(Universidade Federal do Pará, 1979-08-14) ROCHA, Brígida Ramati Pereira da; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
Laboratory measurements of complex conductivity were made on 28 drill-core samples from area MM1-Prospect 1 of the Carajás Mining District. The objective of this research was to help interpret field geophysical survey of the area using Induced Polarization and AFMAG methods. The laboratory measurements of amplitude and phase of conductance were taken in the frequency interval of 10-3Hz to 104Hz. The method used was the direct measurement of impedance using a memory osciloscope, a signal generator, and two high input impedance differential preamplifiers. The electrode system chosen for the measurements was the 2 electrode platinized-platinum because its frequency response is flat in the frequency range used. AlI the measurements were made at a constant temperature of 24°C±1°C. A petrographic study of the samples was done, using thin sections, polished sections and X-ray diffraction. Copper content, in the form of sulfides, was determined using atomic absorption. As a result of the petrographic study, the samples were classified in five distinct groups: granite, biotite schist, amphibolite and magnetite quartzite-iron formation. The grade of Cu was variable in the five groups, ranging from 50 ppm to 6000 ppm. In the conductivity measurements it was observed that, among the five groups, the samples of iron formation gave the largest variations with frequency. The granite samples had spectra flatter than those of schist or amphibole. In conclusion, these measurements show that the field Induced Polarization and AFMAG anomalies near these three drill holes (F1, F2 and F3) are due primarily to the magnetic iron formation, and secondarily due to associated low-grade chalcopyrite mineralization.
Acesso aberto (Open Access)
Conversão tempo-profundidade de seções sísmicas empilhadas por raio imagem e raio normal
(Universidade Federal do Pará, 2014-06-24) REZENDE, Diogo Pena; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023
In general, the oil industry makes the time-to-depth conversion of seismic data by the image ray tracing method. This method takes time into the depth, point to point, the amplitudes of the time migrated seismic section. For each point of the migrated time section, it is necessary to trace a ray perpendicular to the surface. After this, the amplitude of the migrated point of the section takes place in depth. The seismic migration method pre- or post-stack consists of placing seismic events in the correct positions in time or depth sections. Seismic depth sections provide an image near of the subsurface, in order to facilitate the identification of possible oil accumulating geological structures. The conversion of sections from the time to the depth domain is an intermediate step in the construction of seismic images in depth. This work developed and tested a method of converting time to depth the zero-offset seismic sections. In this case, the construction of sections in depth uses normal ray tracing method. The proposed method makes use of the (slowness versus time of intersection) transformation on the zero-offset section. Each point in the domain provides initial conditions for the normal ray tracing: a start position of the initial rays and initial angles formed with the normal to the surface, i.e., the slowness initial parameter. Unlike ray image method, several rays use the same travel time and the same initial position, defining an isochronous curve. The amplitude of each point in the zero-offset section takes place to depth from the distribution of values along each isochronous curve in depth. The image ray based time-to-depth conversion has good recovery of the depths of reflectors as well as low computational cost, since it is necessary only one ray to convert each point of the section in time. However, the reflector continuity may be damaged in case of sharpened curvature. In turn, by normal ray the time-to-depth conversion correctly approximate the depth of the reflectors, since the same point in time assigns several times in depth. However, it has a higher computational cost, because it is necessary many rays to convert one point in time.