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 - 12 de 12

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Anomalias eletromagnéticas de corpos tubulares inclinados em contato com o manto de intemperismo usando diferentes arranjos de bobinas-modelamento analógico
(Universidade Federal do Pará, 1997-03-16) SILVA, Roberto Cesar Alves; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
Electromagnetic methods are mainly applied in the prospection of massive sulphide deposits. These deposits are frequently long in extension and thin, therefore the interpretation can be carried out considering a half-plane model in a resistive ambient. However, in Amazon region or in semi-arid and tropical regions where a partialy conductive to conductive overburden is encountered, interpretations using a resistive ambient model give erroneous results. The objective of this work is to study the influence of the conducting overburden on electromagnetic anomalies of inclined sheet-like bodies in ohmic contact with the overburden, using coil configurations - horizontal coplanar (HCP), vertical coplanar (VCP), vertical coaxial (VCA) and minium couple system (PERP). These studies are realized with the aid of analog modelling where the ore-body is simulated by a graphite sheet and the conducting overburden by ammonium choride solution. Generally, the diferente coil systems studied here show the similar characteristics of the overburden effects, reserving some peculiar effects of each coil system. The effects of a conductive overburden in ohmic contact with the orebody could be briefly described as follows: (i) There is an anti-clockwise phase rotation initially with the increase in the overburden induction number, but with further increase the phase rotates clockwise; (ii) The form of the quadrature anomaly profile is altered due to the appearence of an extra peak on the down-dip side of the ore-body, and (iii) The peak to peak quadrature anomaly on the up-dip side increases uniformly with increase in the overburden induction number. Highest anomalies are obtained with the horizontal coplanar system and lowest with vertical coplanar. No extra-peak in the quadrature profile is observed with the vertical coaxial system in this study. Also, the overbuden effects are more prominent in the horizontal coplanar system compared to vertical coil systems, and in the anomalies of the less inclined half-planes and at lesser depths.
Acesso aberto (Open Access)
Aplicação 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)
Avaliação geofísica e geológica de um porção de quebra de talude da Bacia do Jequitinhonha
(Universidade Federal do Pará, 2013) SANTOS, Renata Vieira dos; SARGES, Roseane Ribeiro; http://lattes.cnpq.br/9737447758598999; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660
The seismic reflection methods use at the exploration and development hydrocarbon reservoirs is due to its vast and dense sampling in both area and depth, combined with techniques refinement to processing seismic reflection data, from these data, are generated seismic sections, which after applying appropriate treatment, are used in the interpretation of the strata and/or the subsurface geologic structures. At this paper have made one Geophysics Geological analysis at two real marine seismic lines 2D of break portion embankment Jequitinhonha Basin. Therefore, we performed a set of seismic processing in order to mitigate the multiple reflections common marine data, moreover, were estimated velocity models in depth, used to determine the depth migrated seismic sections. At these were identified reflective surfaces. Through analysis at these surfaces markings of sismofacies. have made based on the initial concepts seismic stratigraphy in order to evaluate the product quality derived from the seismic processing used at this study for seismic stratigraphic interpretation, which is based on the analysis termination patterns of reflectors and internal standard of sismofacies.
Acesso aberto (Open Access)
Deconvolução de perfis de poços através do ajuste de energia
(Universidade Federal do Pará, 1994-04-14) GUERRA, Carlos Eduardo; LOVELL, Michael Anthony
Resistivity measurements are of fundamental importance for the calculation of oil saturation in potentially producing reservoirs. The combined measurement of shallow and deep resistivities enables the determination of the parameters Rt, Rxo and di. But in complex reservoirs we have difficulty in obtaining a confident reading of Rt, due to the low vertical resolution of deep reading tools. In laminated reservoirs, for example, the deep induction reading ILD can be interpreted erroneously with the belief that the measurement refers to one bed. This may be true for extreme case of thick beds, but more often is not. This problem can be partly resolved by enhancement of the vertical resolution of the deep reading log through comparison with the high resolution (shallow resistivity) log. One approach is to use a high resolution log where there is good correlation with the deep reading log. This correlation can be better evaluated if we apply a filter to the high resolution log such that theoretically the resultant log has the same vertical resolution as the low resolution log. However, this assumes that the vertical response of the high and low resolution tools are available, and in practice this is often not the case. In this study we attempt to demonstrate an alternative approach where the filter can be obtained from consideration of the frequency domain. The technique compares the spectral energy of the high and low resolution logs. It is shown that the vertical resolution depends fundamentally on the spectral energy of the actual log based on Parseval Theorem. Next a linear regression is applied to the filtered high resolution and low resolution logs and for each depth a minimisation routine is applied to determine the best correlation interval between the logs. Finally a correction factor is applied to each point on the low resolution log. This factor is considered by the correlation coefficients over the interval minimised for each point. The results obtained with induction logs are promising and the metodology shoud be aplyed on diferent logs techniques.
Acesso aberto (Open Access)
Efeitos do manto de intemperismo sobre anomalias “VLF” dos corpos tabulares inclinados
(Universidade Federal do Pará, 1997-03-16) ROZAL, Edilberto Oliveira; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
Application of eletromagnetic methods for mineral exploration in tropical regions is complicated due to a presence of a conducting overburden encountered in these regions. In the Amazon region, overburden is well developed and conductive; while in semi-arid regions there may be a fine layer containing salts. Consequently, considerable error is introduced in the interpretation of EM data if the presence of the conducting overburden is ignored. In order to study the overburden effects, on VLF anomalies due inclined tabular bodies in contact with the former (Ohmic - overburden), a number of analog model experiments were conducted for varying response parameters of the overburden and the ore body. Overburden is simulated by an amonium chloride solution (NH4Cl) and the ore body by inclined grafite sheets of different thicknesses. Three overburdens of varying conductance were used to simulate diverse geological situations. Both, tilt-angle and elipsity anomalies decrease in amplitude with the increase in depth of the ore body and the position of the peak in the profile is removed further away from the crossover irrespective of the presence of the overburden or not. There is some increase and tilt-angle anomaly profiles. Eliptisity anomaly increases with the increase in the condutance of the overburden while tilt-angle anomaly decreases a little bit. However, at higher overburden condutances both of then are attenuated. Phase angle are rotated anti-clockwise with the overburden. This rotation is more intense at higher induction number of the conductor. In the presence of the ohmic-overburden and at moderate values of their condutance, the conductor appears (i) at lower depth than the real, due to the increase in the anomaly amplitude, and ii) less conducting due to the anti-clockwise rotation of the Argand diagram.
Acesso aberto (Open Access)
Eletroresistividade aplicada à caracterização hidrogeológica para o abastecimento da cidade de São Domingos do Araguaia-Pará
(Universidade Federal do Pará, 1996-02-13) SILVA, Arnaldo de Queiroz da; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
The use of geophysical methods (electrical, eletromagnetics and well logging) for groundwater exploration in many areas in the State of Pará has been possible due to a program of cooperation between the Fundação Nacional de Saúde and the Universidade Federal do Pará, in which the Department of Geophysics and the Graduate Programe in Geophysics are respossible for the research and techinical work. This thesis has been conducted under such program. Our objective in this work is to find geoelectrical criterious for caracterization of the subsurface geology for hydrogeological exploration, based on apparent resistivity, data observed in cristaline rock environment. First, we analysed the influence of some 2D structures on resistivity data using vertical electrical sounding with Schlumberger array. This study was carried out with the computer program SEV2D, developed in the Departament of Geophysics, based on the finites elements technique. The results show clearly the ambiguities which are obtained when 1D interpretation is used for two-dimentional geological environment. The pratical aspect of the thesis is concerned with the processing and interpretation of resistivity data obtained in São Domingos do Araguaia in the southeset of the State of Pará. The Schlumberger array was used in the vertical electrical sounding survey. By correlating the geophysical results with geological informations it was possible to define the best zones for groundwater exploration in the prospected area.
Acesso aberto (Open Access)
Eletroresistividade na prospecção hidrogeológica no município de Ourilândia do Norte-PA
(Universidade Federal do Pará, 1996-05-22) SOUSA, José Antonio Ferreira de; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
Geophysical prospecting for groundwater in crystalline regions is a difficult task due to the presence of faults, fractures and lateral variations of resistivity in the overburden. To analyze the influence of bidimensional (2D) variation of resistivity on Schlumberger vertical electrical soundings several layer models were studied containing 2D vertical and dipping structures. These 2D structures are located in the alteration mantle at varying distances from the sounding position. The numerical modeling was done employing the finite element method using an algorithm developed for this purpose (EGSLIB/SEV2D). The results of simulation show that the Sclumberger vertical electrical sounding technique over bidimensional media is not very effective as in sedimentry and alluvial regions due to the phenomenon of ambiguity which complicates the interpretation of the curves. Among the geophysical methods used for hydrogeological investigation, electroresistivity is simplest, economical and efficient. 32 Schlumberger vertical electrical soundings and several kms of dipole-dipole profiling were realized in the Ourilândia do Norte town in order to help locate sites for tube-wells. The apparent resistivity curves were treated and processed considering an isotropic, homogeneous, horizontal layers model, using algorithm EGSLIB/SEV1D and EGSLIB/SEV1DINV program. This permitted to establish approximate geoelectrical models for the subsurface geology of the town. Two distinct geological zones could be recognized based on interpreted geoelectric sections and available geological information. One of the zones is formed by soil/embankment followed by a soil horizon containing sandy sediments over a sandyclay layer and finally the bedrock. This geological sequence predominated in the town. The other zone is formed by soil/embankment overlying a sandyclay bed which is underlain by granitoids type Rio Maria. This second zone is limited in the central part of the town. The sand and sandyclay stratum posses good potential for water storing.
Acesso aberto (Open Access)
Estimativas da condutividade térmica dos minerais e rochas e influência de parâmetros térmicos e petrofísicos na resistividade aparente da formação
(Universidade Federal do Pará, 1995-08-09) COZZOLINO, Klaus; HOWARD JUNIOR, Allen Quentin; http://lattes.cnpq.br/6447166738854045
The present study carries out estimates of thermal conductivity in the principal rock-forming minerals, as well as estimates of the average conductivity of the solid phase of five common lithologies (sandstones, dolomites, limestones, anhydrites, clay lithologies). Several thermal models were compared, permitting the verification of one as the most appropriate to represent the aggregate of minerals and fluids of which rocks are composed. The results of this study can be applied to a wide variety of thermal models. The chosen methodology is based on a non-linear regression algorithm denominated Random Search. The algorithm's behaviour is evaluated with sinthetic data before being applied to real data. The geometric mean model is used in the regression to obtain the values of thermal conductivity in these rock-forming minerals. The regression method used in each lithological sub-group gave the following values for average thermal conductivity in the solid phase: sandstones 5.9 ± 1.33 W/mK, limestones 3.1 ± 0.12 W/mK, dolomites 4.7 ± 0.56 W/mK anhydrites 6.3 ± 0.27 W/mK and for argillceous lithologies 3.4 ± 0.48 W/mK. In the sequence the fundaments for the study of heat diffusion are presented in cylindrical coordinates. The effects of invasion of mud filtrate into the formation are considered using an adaption of simulation of well injection techniques originating in theories developed in reservoir engineering. Assuming the original temperature of the formation as a reference, the relative errors in apparent resistivity can be estimated. In this phase of the work the finite differences method is used to measure distribution of the well-formation temperature. Simulation of the invasion is carried out in cylindrical coordenates via an adaptation of the Buckley-Leverett equation into carthesian coordenates. Effects such as the appearance of mudcakes in the borehole, gravity and capilliary pressure are not taken into consideration. The radial distribution of resistivity is obtained via the distribution of saturation and temperature, and is convolved with the radial geometrical factor of the induction tool (transmissor-receiver), resulting in the apparent resistivity of the formation. Admitting as reference the original temperature of the formation, the relative errors in apparent resistivity are obtained at each time. Through variation of certain parameters, it becomes clear that the porosity and original saturation of the formation can be responsible for serious errors in the measurement of resistivity, especially if such readings are taken immediately after drilling (MWD). The difference in temperature between well and formation is the principal cause of such errors. In situations where this difference is large, therefore, profiles with- induction tools should only be carried out between 24 and 48 hours after the well has been drilled.
Acesso aberto (Open Access)
Estudo da resposta de perfilagem de indução de camadas finas com diferentes arranjos de bobinas: modelamento analógico
(Universidade Federal do Pará, 1993-12-16) CARVALHO, Paulo Roberto de; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
Analog model studies were carried out comparing the eletromagnetic responses of various two-coil systems in a borehole, in order to improve the vertical resolution of the indution tools. For this purpose geoeletric models, simulating well-logging situations in the stratified beds of varying thicknesses, with or without fluid invasion, were constructed at a reduced scale of 20. The sensitivity of the system to measure relative fields (secondary/primary) is of the order of 0.01 %. Following conclusions were drawn after analysing the response profiles obtained for a coaxial and a coplanar coil systems: • In case of thin conducting beds placed in relatively resistive beds, such as shale beds in sandstones containing hydrocarbons, the coaxial system shows a better resolution than coplanar system both in determination and estimating the thickness of thin beds; • On the other hand, in the presence of thin resistive beds placed in relatively conductive zone, such as sandstone containing hydrocarbons lying in a shale, the coplanar coil system gives a better vertical resolution than the coaxial system; • "Shoulder effect" is much more pronounced in the coaxial system than the coplanar coils; • In case of thick beds, bed-boundaries are well defined in the coplanar coil system response. However, when the thickness is reduced the small oscillating signal indicating the interfaces disappears.
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Formulação e implementação de um pacote para interpretar mapas magnéticos utilizando os polinômios de Walsh
(Universidade Federal do Pará, 1992-12-30) RAMOS, Alexandre José Santos; O'BRIEN, Douglas Patrick
In this work we develop a method for the automatic interpretation of magnetic field data. This methodology determines the boundaries and magnetizations of geologic units. The often of abrupt variations of the magnetization of geological units are modeled in this methodology. These abrupt lateral variations will be represented by discontinuous polynomials known as Walsh polynomials. Several new concepts were developed in order to apply Walsh polynomials to solve aeromagnetic data inversion problems. Among these new concepts we can list. (i) - An optimum algorithm to generate a set of "quasi-orthogonal" polynomials using a Walsh magnetization distribution. (ii) - The use of the damped least squares method to stabilize the inverse solution. (iii) An investigation of positional invariance problems, which are inherent in the Walsh polynomials. (iv) - The choice of the order of the polynomials taking into account the limitations of resolution and the behaviour of the eigenvalues. Using these features of magnetized bodies it is possible to formulate the direct problem, i.e, the bodies magnetization obeys Walsh distribution. It is also possible to formulate the inverse problem, in which the magnetization that generates the observed field obeys the Walsh series. Prior to applying the method it is necessary to estimate the depths to the magnetic sources. We have chosen a method developed by LOURES (1991), which is based on the Euler homogenous equation which requires the knowledge of the magnetic field and its derivatives. We tested the method with real data from a region in the Alto Amazonas sedimentary basin. The aeromagnetic data were provided by PETROBRÁS.
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Modelagem de perfis de indução no domínio do tempo por diferenças finitas
(Universidade Federal do Pará, 1997-01-07) BESERRA, Antonio Adelmo Freire; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
A new approach of modeling the response of the induction tool in a borehole in the time domain is presented. Here I have solved electromagnetic field diffusion equation in a horizontally stractified medium by finite difference method. The transmitter loop is excited by the step function current. The receiver loop is positioned coaxially in the borehole above the transmitter at a fixed distance. The solution of the difusion equation takes into account the primary and secondary fields. The primary field is obtained analytically and the secondary is calculated by the Alternating Direction Implicit method. The resulting tri-diagonal system is solved by the recursive algorithm proposed by Claerbout. Finally, the electric field in the receiver is computed at different positions of the tool in a borehole and these values are plotted against the depth of measurement. The results obtained show that measuring electric field in the time domain is very eficient to detect the bed boundaries, even if the beds are very thin.

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