BDTD - Biblioteca Digital de Teses e Dissertações

URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2289

Biblioteca Digital de Teses e Dissertações da UFPA (BDTD). Sistema Eletrônico de Teses e Dissertações (TEDE). Projeto BDTD/UFPA e Instituto Brasileiro de Informação em Ciência e Tecnologia (IBICT).

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Agora exibindo 1 - 20 de 29

Acesso aberto (Open Access)
Análise das aproximações RPP e RSP para meios isotrópicos
(Universidade Federal do Pará, 2002-08-16) SANTOS, Darcicléa Ferreira; PROTÁZIO, João dos Santos; http://lattes.cnpq.br/4210442535067685
This work presents linear and quadratic approximations of the Zoeppritz equations for the derivation of reflection and transmission coefficients from P-P and P-S events as a function of incidence angles and angular average, as well as the linear inversion analysis, AVO, in respect to the disassociated and combined P-P and P-S reflection events. The use of the so-called pseudoquadratic approximations was applied for the derivation of quadratic approximations only for PPevents, around the average contrasts of compressional and shear waves velocities and Vs/Vp ratio. The results of approximations derived in this work show that quadratic approximations were more precise than the linear ones in the two angular versions. The comparisons between these approximations in terms incidence angle and angular average show that the quadratic approximations are equivalent within the angular limit of [0º to 30º]. In the other hand, the linear approximations as a function of incidence angle are more precise than the linear approximations as a function of the angular average. In the linear inversion, sensitivity and ambiguity analyses were carried out and one could see that in the case of disassociated reflection P-P and P-S events, just a parameter can be estimated and the combination of these events can stabilize the inversion permitting the estimation of two physical parameters for the media (impedance, P-wave velocity and shear bulk module contrasts).
Acesso aberto (Open Access)
Análise de sensibilidade para estereotomografia em meios elípticos e anelípticos
(Universidade Federal do Pará, 2005-12) BARBOSA, Brenda Silvana de Souza; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739
Stereotomography is extended to general anisotropic models and implemented for elliptical and anelliptical anisotropy. The elliptical and anelliptical models present only three parameters. This makes them less sensitive to the ambiguity due to limited coverage of surface seismic experiments than transversaly isotropic or orthorhombic models. The corresponding approximations of the slowness surface restrict the validity of the present approach to qP events and mild anisotropy. Numerical experiments show the potential and the limitations of stereotomography in estimating macro-velocity models suitable for imaging in the presence of anisotropy as well as the importance of transmission events from multiple-offset VSP experiments for the success of the approach.
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 modelos de substituição de fluido em rochas sedimentares oriundas do nordeste brasileiro
(Universidade Federal do Pará, 2015-06-06) TROVÃO, Ana Alzira Fayal; FIGUEIREDO, José Jadsom Sampaio de; http://lattes.cnpq.br/1610827269025210
Carbonates reservoirs corresponds on about 50% of the hydrocarbon reservoir in the planet . This type of lithology presents different forms of heterogeneity, which are the main causes of errors in its characterization. This misunderstanding, can induces erroneous estimative elastic modules of rocks in saturated state. The main goal of this work is to perform a comparative analysis of fluid substitution models in unconventional carbonate reservoir. Specifically, fluid substitution processes analyzed in outcrops from Brazilian Northeast, under controlled laboratory conditions (temperature, pressure and degree of saturation) and under perspectives of the petrophysical and ultrasonic features by conventional theories (Gassmann, Biot) and unconventional (Brown and Korringa, Muller and Sahay). In this research, we analyzed six samples of carbonate rock and one sample of sandstone rock. The input data our analysis were: permeability, porosity, rock and grain density, elastic measures of compressional (Vp) and shear (Vs1 and Vs2) velocities. The measure of velocities was performed in cases of 100% gas (dry rock) and then replaced by water (100 % saturated by water). Our results show, that predictions performed by conventional fluid substitution models best fit in experimental measurements of sample considered homogenous. However, predictions performed by unconventional models (e. g., Muller and Sahay) shown best fit with most carbonates types, including tufa and limestanes.
Acesso aberto (Open Access)
Atenuação de múltiplas pelo método WHLP-CRS
(Universidade Federal do Pará, 2003-01-28) ALVES, Fábio José da Costa; LEITE, Lourenildo Williame Barbosa; http://lattes.cnpq.br/8588738536047617
In the sedimentary basins of the Amazon region, the generation and accumulation of hydrocarbons is related to the presence of diabase sills. These rocks present a great impedance contrast to the host rocks what turns to cause the generation of internal and external multiples with similar amplitudes the primary events. These multiples can predominate over the information originated at the deeper interfaces, making more difficult the processing, interpretation and imaging of the seismic section. In the present research work, we conducted de multiple attenuation in synthetic commonsource (CS) seismic sections by combining the Wiener-Hopf-Levinson for prediction (WHLP) and the common-reflection-surface-stack (CRS) methods. We denominated this new combination under the name and label of WHLP-CRS method. The deconvolution operator is calculated from the real amplitudes of the seismic section trace-by-trace, and this strategy represents efficiency in the process of multiples attenuation. Multiples identification is carried out in the zero-offset (ZO) section simulated by the CRS-stack applying the periodicity criteria between the primary and its repeated multiples. The wavefront attributes, obtained by the CRS-stack, are employed to move the shifting windows in the timespace domain, and these windows are used to calculate the WHLP-CRS operator for the multiple attenuation carried out in the CS sections. The development of the present research had several intentions as: (first) avoid the inconveniencies of the processed ZO section; (second) design and apply operators in the CS configuration; (third) extend the WHL method to curved interface; (fourth) use the good results obtained in the new CRS-stack technology whose application extends to migration, tomography, inversion and AVO.
Acesso aberto (Open Access)
Caracterização de reservatórios fraturados através de dados de ondas qP em levantamentos VSP Walkaway
(Universidade Federal do Pará, 2008) SILVA, Saulo da Costa e; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660
This dissertation presents a method to estimate the orientation of the axis of symmetry of a medium assuming it behaves effectively as a transversely isotropic medium (TI). The fracture orientation is then achieved from the estimation of the axis of symmetry of a TI medium. This estimative is done with the slowness and polarization vectors from qP waves, measured in VSP Walkaway experiments. The inversion process is based on linearized equations of the slowness and polarization vectors from qP waves and the weakly anisotropic parameters of the medium. Numerical tests are presented, on which the sensibility to factors like the strength of anisotropy, survey geometry, type of wave utilized and noise level are analyzed. Test results for a set of real data are also shown.
Acesso aberto (Open Access)
Datação pelo método de traços de fissão em apatita da região da estrutura dômica de Monte Alegre, Bacia do Amazonas (PA)
(Universidade Federal do Pará, 2011-04-05) NEGRÃO, Sílvia Cristina Barroso; LELARGE, Maria Lidia Vignol; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
In the northern portion of the Amazonas Sedimentary Basin, south of the Monte Alegre city (PA), a semi-elliptical structure defined by a group of small hills occurs, which is known as the Monte Alegre Dome. In the central portion of the dome, Devonian rocks of the Ererê Formation crop out, while toward the edge of the structure the Neodevonian to Mesocarboniferous successions, represented by the Barreirinha, Curiri, Oriximiná, Faro and Monte Alegre formations, are exposed. Diabase dykes and sills of about 200 Ma (Penatecaua Magmatism) cut this set of rocks. The formation of this dome structure has been related to the emplacement of dykes and sills of diabase. However, the contribution of Tertiary tectonism, present throughout the Amazon Basin, cannot be ruled out for the formation of the dome, since in the eastern and southern portions of this structure the Cretaceous to Tertiary rocks of the Alter do Chão formation are in faulting contact with rocks of the Ererê formation. In this study we applied the apatite fission track thermochronology in the diabase of the Penatecaua Magmatism in order to determine the age of formation of the dome structure, and to investigate the role of the Tertiary tectonics in the development of this structure. The apatite fission track method (AFT) is applied to study the thermotectonic evolution of a region, since the quantification of the fission tracks present in the mineral permits to estimate the age at which the rock passed through a given temperature (blocking temperature), which may be related to a tectonic event (uplift / subsidence) that occurred in the area. The mafic rocks studied in the region of Monte Alegre provided ATF apparent average ages between 53.2 and 43.6 Ma. These ages are interpreted as representing major tectonic events that occurred in the Tertiary (Early to Middle Eocene) that uplifted to shallower crustal levels and the diabases and the country rocks. The thermal histories obtained after modeling the AFT data allowed the recognition of four events of cooling, which occurred at 140-110 Ma, 110-100 Ma, 55-45 Ma and 30 Ma-recent. Just one sample (TFMA-12), located outside of the dome structure, did not record the Eocene tectonic event. The ATF data modeling also permitted to estimate cooling rates ranging from 0.4ºC / Ma for slower events, up to 2.82°C / Ma for faster events. Based on these cooling rates it is suggested that 3 to 3.35 km of rocks section was removed due to the reactivation of faults at different moments during the geologic evolution of the region, mainly along the Cenozoic. The apparent ATF ages between 43.6 and 53.2 Ma, as well as the significant cooling thermal event recorded in the Eocene by the data modeling revealed the important role that the Tertiary (Eocene) tectonic in the formation of dome structure of Monte Alegre. It is believed that the apparent ages of fission tracks (43.6 and 53.2 Ma) would place limits on the age of this Tertiary tectonics.
Acesso aberto (Open Access)
Deconvolução de perfis de poço através de rede neural recorrente
(Universidade Federal do Pará, 2006-03-05) RUÉLA, Aldenize de Lima; ANDRADE, André José Neves; http://lattes.cnpq.br/8388930487104926
For oil industry, the logs analysis is the main information source about the presence and quantification of hydrocarbon in subsurface. However, in two situations the new logging technologies are not economically viable and conventional logging tools must be used: The reevaluation of mature oil fields and evaluation of marginal oil fields. In conventional logs its data acquisition procedure may blur the value of physical property and the vertical limits of a rock layer. We are talking about an old problem in well logging – The paradox between vertical resolution and depth of investigation of a logging tool. Nowadays it is well handling by the high technology of new tools, but this problem persists in conventional old tools, e.g. natural gamma ray log (GR). Here, we present a method to smooth this kind of linear distortion in well logs by an integration of classical well log convolution model with recurrent neural networks. We assume that a well log can be well represented by an in depth convolution operation between the variation of rock physical property (ideal log) and a function that causes the distortion, called as vertical tool response. Thus, we develop an iterative data processing, which acts as a deconvolution operation, composed by three recurrent neural networks. The first one seeks to estimate the vertical tool response; the second one search for the vertical limits definition of each rock layer and the last one is constructed to estimate the actual physical property. To start this process we supply an appropriated first guess of ideal log and vertical tool response. Finally, we show the improvements in vertical resolution and in the physical property evaluation produced by this methodology in synthetic logs and actual well log data from Lagunillas formation, Maracaibo basin, Venezuela.
Acesso aberto (Open Access)
Empilhamento sísmico por superfície de reflexão comum: um novo algoritmo usando otimização global e local
(Universidade Federal do Pará, 2001-10-25) GARABITO CALLAPINO, German; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023; HUBRAL, Peter; http://lattes.cnpq.br/7703430139551941
By using an arbitrary source-receiver configuration and without knowledge of the velocity model the recently introduced seismic data stacking method called Common Reflection Surface (CRS) simulates a zero-offset (ZO) section from multi-coverage seismic reflection data. For 2-D acquisition, as by-products provides three normal ray parameters: 1) the emergence angle (β0); 2) the radius of curvature of the Normal Incidence Point Wave (RNIP); and 3) the radius of curvature of the Normal Wave (RN). The CRS stack is based on the hyperbolic traveltime paraxial approximation depending on β0, RNIP and RN. In this thesis is presented a new algorithm of the CRS stack based on two-parameters and one-parameter search strategy combining global and local optimization methods for determine the three parameters that define the stacking surface (or operator). This is performed in three steps: 1) two-parameters search by applying global optimization to determine β0 and RNIP; 2) one-parameter search by applying global optimization to determine RN; and 3) three-parameters search by applying local optimization to determine three parameters, using as initial approximations the parameter triple of the earlier two steps. In the first two steps is used the Simulated Annealing (SA) algorithm and the Variable Metric algorithm is used in the third step. To simulate the conflicting dip events, for each ZO sample where there are interference of intersecting events is determined an additional parameter triple corresponding to a local minimum. The stacking along the respective operator for each particular event allows to simulate their interference in the simulated ZO section by means of their superposition. This new CRS stack algoritm was applied to synthetic data sets providing high-quality simulated ZO sections and high precision determination of the stack parameters in comparison with the forward modeling. Using the hyperbolic traveltime approximation for identical radii of curvature RNIP = RN, an algorithm called Common Diffraction Surface (CDS) stack was developed to simulate ZO sections for diffracted waves. In a similar way to the CRS stack procedure, this new algorithm also uses the SA and VM optimization methods to determine the optimal parameter couple (β0, RNIP) that define the best CDS operator. The main features of the algorithm are the data normalization, common-offset data, large aperture of the CDS operator and positive search space for RNIP. The application of the CDS stack algorithm in a synthetic dataset containing reflected and diffracted wavefields provides as main result a simulated ZO section containing diffracted events clearly defined. The post-stack depth migration of the ZO section locates correctly the discontinuities of the second interface.
Acesso aberto (Open Access)
Inversão de dados eletromagnéticos com o regularizador Variação Total e o uso da matriz de sensibilidade aproximada
(Universidade Federal do Pará, 2012-12-20) LUZ, Edelson da Cruz; RÉGIS, Cícero Roberto Teixeira; http://lattes.cnpq.br/7340569532034401
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/7294174204296739
Iterative 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.
Acesso aberto (Open Access)
Migração em profundidade pré-empilhamento utilizando os atributos cinemáticos do empilhamento por superfície de reflexão comum
(Universidade Federal do Pará, 2007-11-12) LUZ, Samuel Levi Freitas da; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023
The Common-Reflection-Surface (CRS) stack is a new seismic processing method for simulating zero-offset (ZO) and common-offset (CO) sections. It is based on a second-order hyperbolic paraxial approximation of reflection traveltimes in the vicinity of a central ray. For ZO section simulation the central ray is a normal ray, while for CO section simulation the central ray is a finite-offset ray. In addition to the ZO section, the CRS stack method also provides estimates of wavefield kinematic attributes useful for solving interval velocity inversion, geometrical spreading calculation, Fresnel zone estimate, and also diffraction events simulation. In this work, Its proposed a new strategy to do a pre-stack depth migration by using the CRS derived wavefield kinematic attributes, so-called CRS based pre-stack depth migration (CRS-PSDM) method. The CRS-PSDM method uses the CRS results (ZO section and kinematic attributes) to construct an optimized stack traveltime surface along which the amplitudes of the multi-coverage seismic data are to be summed and the result is put in a point of the migration target zone in depth. In the same sense as in Kirchhoff type pre-stack depth migration (K-PSDM), the CRSPSDM method needs a migration velocity model. Unlike the K-PSDM method, the CRS-PSDM needs only to calculate the zero-offset traveltimes, i.e, along only ray conecting the considered point in depth to a given coincident position of source-receptor at surface. The final result is a zero-offset time-to-depth converted seismic image of reflectors from pre-stack seismic data.
Acesso aberto (Open Access)
Migração em profundidade usando a solução numérica da equação da eiconal
(Universidade Federal do Pará, 2001-06-12) LUZ, Samuel Levi Freitas da; CRUZ, João Carlos Ribeiro; http://lattes.cnpq.br/8498743497664023
In the last years we have seen an increasing interest in seismic imaging algorithms in order to obtain better informations about the earth interior. The Kirchhoff migration method is very useful for determining the position of seismic reflectors, if is known the seismic wave velocity model and the traveltimes are well determined through the earth model. The traveltime calculation is a necessary step for stacking the seismic data by means of the Kirchhoff migration operator. In this work the traveltimes are obtained by solving the eiconal equation of the ray theory. At first, the theory of Kirchhoff migration is reviewed, by considering depth migration in heterogeneous media with arbitrary curved reflectors. Secondly, the numerical solution of the eiconal equation is presented for transmited, diffracted and head waves. There offer, the depth migration algorithm is presented, must makes use of traveltimes obtained by the eiconal equation. Finally, the developed migration algorithm is applied to synthetic models, providing a very good image resolution in comparison with the conventional ray tracing migration methods, even in the presence of random or coherent (multiple reflections) noise.
Acesso aberto (Open Access)
Modelagem computacional de dados magnetotelúricos marinhos 2-D
(Universidade Federal do Pará, 2009) SAITO, Kymie Karina Silva; SILVA, Marcos Welby Correa; http://lattes.cnpq.br/3213216758254128
This study aims to investigate the scattering of plane waves caused by lateral variation of the physical properties of rocks. This is one of the most important to the success of exploration geophysics. The geophysical method used in this dissertation was magnetotelluric method (MT) and Marine Magnetotelluric (MMT). The tool used here was the finite element method, which is efficient to solve numerically the differential equations for electromagnetic fields of the geological structures with complex geometries. The computational procedures were used in the development and implementation of algorithms of numerical modeling of electromagnetic data. These algorithms were developed and implemented in several models of different geoelectrical parameters.
Acesso aberto (Open Access)
Modelagem eletromagnética 2.5-D de dados geofísicos através do método de diferenças finitas com malhas não-estruturadas
(Universidade Federal do Pará, 2014-10-23) MIRANDA, Diego da Costa; RÉGIS, Cícero Roberto Teixeira; http://lattes.cnpq.br/7340569532034401; HOWARD JUNIOR, Allen Quentin; http://lattes.cnpq.br/6447166738854045
We present a 2.5D electromagnetic formulation for modelling of the marine controlledsource electromagnetic (mCSEM) using a Finite Diference frequency domain (FDFD) method. The formulation is in terms of secondary fields thus removing the source point singularities. The components of the electromagnetic field are derived from the solution of the magnetic vector potential and electric scalar potential, evaluated in the entire problem domain that must be completely discretized for the use of the FDFD. Finite difference methods result in large sparse matrix equations that are efficiently solved by sparse matrix algebra preconditioned iterative methods. To overcome limitations imposed by structured grids in the traditional FDFD method, the new method is based upon unstructured grids allowing a better delineation of the geometries. These meshes are completely adaptable to the models we work with, promoting a smooth design of their structures, and may only be refined locally in regions of interest. We also present the development of RBF-DQ method, (radial basis function differential quadrature) which makes use of the technique of functions approximation by linear combinations of radial basis functions (RBF) and the technique of differential quadrature (DQ) for approximation of the derivatives. Our results show that the FDFD method with unstructured grids when applied to geophysical modeling problems, yield improved quality of modeled data in comparison with the results obtained by traditional techniques of FDFD method.
Acesso aberto (Open Access)
Modelagem numérica de dados MCSEM 3D usando computação paralela
(Universidade Federal do Pará, 2007) SOUZA, Victor Cezar Tocantins de; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
We developed the numerical modeling of Marine Controlled Source Electromagnetic (MCSEM) synthetic data used in hydrocarbon exploration for three-dimensional models using parallel computation. The models are formed of two strati ed layers: the sea and the host with a thin three-dimensional embedded reservoir overlapped by the air half-space. In this work we present a three-dimensional nite elements technique of MCSEM modeling using the primary and secondary decomposition of the magnetic and electric coupled potentials. The electromagnetic elds are calculated by numerical di erentiation of the scattered potentials. We explore the parallelism of the MCSEM 3D data in a multitransmitter survey, where as for each transmitter position we have the same forward model but with di erent data. For this, we use Message Passing Interface library (MPI) and the client server approach, where the server processor sends the input data to client processors to perform the calculation. The input data are formed by the parameters of the nite element mesh, together with informations about the transmitters and the geoeletric model of hydrocarbon reservoir with prismatic geometry. We observe that when the horizontal width and the length of the reservoir have the same order of magnitude, the in-line responses are very similar and the consequently the three-dimensional e ect is not detectable. On the other hand, when the di erence in the sizes of the horizontal width and the length of the reservoir is very large, the e ect 3D is easily detected in in-line along the biggest dimension of the reservoir. For measures done along the lesser dimension this e ect is not detectable, therefore, the model 3D approaches to a bidimensional model. The parallelism of multiple data has fast implementation and processing, and its time of execution is of the same order of the serial problem, with the addition of the latency time in the data transmission among the cluster nodes, which justifying this methodology in modeling and interpretation MCSEM data. Only simple 3D models were computed because of the reduced memory (2 Gbytes in each node) of the cluster of UFPA Departament of Geophysics.
Acesso aberto (Open Access)
Modelamento e correção de descentralização das imagens de tempo de trânsito
(Universidade Federal do Pará, 2003) FISCHETTI, Anna Carmela; ANDRADE, André José Neves; http://lattes.cnpq.br/8388930487104926
The imaging tools used to borehole wall features identification have been largely utilized by geologist and oil engineers to identify geological events in a open hole and inspect the casing tube. The acoustic borehole imaging tools generate a transit time image and an acoustic amplitude image that are used to this proposes. However those logs may have a non-realist interpretation, since some tools effect can negatively influence in the images appearance. This paper presents a transit time image model starting from the application of the Coulomb’s approach to the borehole wall rupture submitted to a plane state of tensions which will supply the borehole section that is the geometric form that will be mapped by the acoustic borehole imaging toll. The tool up displacement and the borehole wall imperfections are usually the responsible for the transducer displacement in relation to the borehole axis. This effect may have important responsibility in the acoustic images imperfections. Thus, a computational process of transducer repositioning in the borehole axis position obtains the correction of those images, called decentralization correction. A method of tool decentralization effect correction is presented too based on this model which is proposed based on the plane analytic geometry and in the ray method to the definition of the transit time of the acoustic pulse, with the objective of reconstruct the transit time images achieved by the decentralized tool, that is to say, correct these images becoming as they were achieved by the centralized tool in relation to the borehole axis.
Acesso aberto (Open Access)
Morfologia e sedimentologia da praia de macromaré de Ajuruteua, Pará: um estudo para definição de índices de sensibilidade ambiental ao derramamento de óleo
(Universidade Federal do Pará, 2007-10-28) BRAGA, Francisca de Paula da Silva; SOUZA FILHO, Pedro Walfir Martins e
The Ajuruteua macrotidal beach located in Northern Brazil is subject to oil pollution in response to the routes of tanker ships. Hence, it is very important to know the environmental characteristics to establish contingency plans. The aim of this work is to investigate the spatial and seasonal changes in grain size and morphologic properties along the intertidal zone (IZ) to define environmental sensitivity index (ESI) to oil spill in this beach zone. During this research it was carried out 23 beach profiles from foredunes to 1 m in deep in the subtidal zone under low spring tide condition. Along this profiles, sedimentary samples were collected in June, September and December 2005 (solsticious) and March 2006 (equinoctials). Sedimentary samples were analyzed in laser granulometer (Malvern Mastersize 2000) in 1/8φ interval. Topographical data were collected by TOPCON total station and processed using TOPOGRAPH 98SE and GOLDEN SOFTWARE (SUFER 8.0). The results show seasonal variations in the grain size and morphologic distribution in the IZ. On June and December the IZ is flat, while on March and September we observe the occurrence of a ridge and runnel system. On June and December, the upper IZ sediments are fine, well sorted, with positive skewness, tending to be coarser in direction to lower IZ, where the sediments are moderately to poorly sorted, with negative skewness. On September and March, it was observed heterogeneity on IZ sediment distribution; the grain size changes from fine to medium, from well to poorly sorted, with negative skewness. In the runnel, the sediments tend to be coarser with negative skewness and moderately sorting. To Ajuruteua beach ESI map elaboration we classified the index 3A as less sensible and the index 3E as more sensible. On June and December the lower IZ is more sensible (index 3D) to oil spill than upper IZ (index 3A). On March and September, the sensibility is higher, mainly along the runnel (3E), that work out as a trap, difficulting the oil cleaning.
Acesso aberto (Open Access)
Paleoambiente dos calcários e folhelhos betuminosos da Formação Guia, Neoproterozóico, Sudoeste do estado do Mato Grosso
(Universidade Federal do Pará, 2012-05-02) BRELAZ, Luciana Castro; LOPES, Renata Lourenço; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The establishment of large carbonate platforms worldwide linked to the sudden increase in global temperature after the last Cryogenian glaciation (~ 635 Ma) was concomitant with the ice-melting and transgressive events. In Brazil, one of the best examples of these post-glacial transgressive Ediacaran deposits is the Guia Formation, the calcareous unit of Araras Group, exposed for hundreds of kilometers in the North Paraguay Belt and Southern Amazon Craton. The Guia Formation consists predominantly of limestone and bituminous shale, more than 400 m thick. It was investigated in open pits of quarries in the Cáceres, Nobres and Cuiabá region, southwestern of the State of Mato Grosso, Brazil. The facies and stratigraphic analysis of the Guia Formation allowed recognizing of three facies associations (FA) representative of a retrogradational platform succession: FA1- lower shoreface influenced by storms, FA2- proximal offshore and FA3- distal offshore with slope facies. The association FA1 up to ~ 150 m thick, and includes marl and grey terrigenous-rich fine-grained limestone with megaripple bedding, wavy bedding and hummocky cross-stratification, produced by oscillatory and combined flow related to fairweather and storms wave in the shoreface zone. The association FA2 corresponds to the thickest deposits of the Guia Formation, reaching almost 200 m in thickness and consists of grey to black organic-rich ribbon limestone interbedded with shale. The remarkable lateral monotonous continuity of these deposits, extensive by hundreds of kilometers, suggests low energy conditions, below the storm wave base, related to the offshore zone. The large amount of organic material accumulated in these deposits associated with pyrite crystals implies stagnant and anoxic deep waters. Palynomorphs in these facies include a few species of leiosphaerids, indeterminate sphaeromorph acritarchs and probable algae fragments. The brown colour of amorphous organic material and acritarchs indicates moderate degree of maturation. The rarity of preserved organic forms and the large amount of amorphous organic matter indicate moderate degree of degradation. The association AF3 has 70 m thick and consists of limestone breccias with tabular clasts and slump features interbedded with fine-grained limestone. The intraformational breccias were formed by gravity flows generated during instability of carbonates in the distal offshore zone. These episodic gravity flows alternated with cyclic hemipelagic sedimentation (forming lime and terrigenous mud). Three aspects were considered to define the morphology of the platform: 1) the transition from shallow to deep deposits without an abrupt facies change; 2) the absence of brittle sinsedimentary deformation; and 3) the lateral continuity of these deposits over hundreds of kilometers, suggesting sedimentation in a homocline ramp. The existence of a wide carbonate ramp in the margin at the Amazon Craton during the Ediacaran, site of organic matter-rich lime mud deposition, opens perspectives for prospection of source rocks of a probable Neoproterozoic petroliferous system developed in the Central Brazil region.
Acesso aberto (Open Access)
Paleoambiente e proveniência da formação cabeças da bacia do Parnaíba: evidências da glaciação famenniana e implicações na potencialidade do reservatório
(Universidade Federal do Pará, 2014-06-10) BARBOSA, Roberto César de Mendonça; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The hydrocarbon prospection history of the Paleozoic Parnaíba Basin, northeastern Brazil, has been unfavorable when compared to the putatively large reservoirs of the Pré-Sal of the Coastal basins and the onshore Solimões Basin. However, the discovery of natural gas in the Devonian-Eocarboniferous siliciclastic deposits of the Canindé Group which include Pimenteiras, Cabeças and Longá formations, has motivated new research to improve the paleoenvironmental and paleogeographic interpretations to understand the petroliferous system, the possible plays and the potenciality of the Upper Devonian Cabeças reservoir. Based-outcrop facies and stratigraphic analysis combined with detrital zircon geochronology allowed to interpret the paleoenvironment and the sedimentary provenance from Cabeças reservoir. Six facies association grouped in the succession with up to 60m thick, records the evolution of deltaic system influenced by glacial processes mainly in the top of the unit: 1) distal deltaic front, composed of massive mudstone and conglomerate, sandstone with massive bedding, even parallel lamination and sigmoidal cross-bedding; 2) proximal deltaic front, represented by sandstone with massive bedding, even parallel lamination and sigmoidal cross-bedding sandstone and massive conglomerate; 3) deltaic plain, consisting laminated mudstone, massive conglomerate, sandstone with massive bedding and trough cross-bedding; 4) glacial shoreface, composed by sandstone with rippled bedded and hummocky crossbedding; 5) subglacial deposits, which include massive diamictite, diamictite with sandstone pods and intraformational breccia; and 6) melt-out deltaic front, consisting of sandstone with massive bedding, even parallel lamination, climbing ripple-cross lamination and sigmoidal cross-bedding sandstone, as well as, deformed sandstone. In the Fammenian (374-359 Ma), a fluvial dominated deltaic front prograding to the NW (eastern border of the basin) and to the NE (western border of the basin) on a storm influenced platform (Pimenteiras Formation). In the eastern border of the basin, the paleocurrent pattern and the U-Pb zircon ages spectrum indicate that the Cabeças delta was fed by source lands located in the southeastern of the basin, probably in the Borborema Province. Mesoproterozoic (~ 1.039-1.009 Ma) and Neoproterozoic zircon ages are the most populous, differently of the grains with Archean (~ 2.508-2.678 Ma) and Paleoproterozoic (~ 2.054-1.992 Ma) ages. The youngest concordant zircon grain yielded a 206Pb/238age of 501.20 ± 6.35 Ma (95% concordant) indicating Cambrian source areas. The main sediments source of the Cabeças delta in the eastern border were provide of the Transversal Zone Domain and the Brasilian plutons of the crystalline basement found in the southeast of the Parnaíba Basin. Small contribution of sediments was derived from the Central Ceará and of the Western Rio Grande do Norte domains. In the Famennian, the migration of the Gondwana Supercontinent to the South Pole resulted in the implantation of the glacial conditions concomitant with the sea-level fall and exposure of the coastal region. The advance of the glaciers upon the basement crystalline rocks and deltaic deposits generated erosion, deposition of diamicton with exotic and faceted clasts, as well as, glaciotectonic strucutures such as foliation, boudins, folds, duplex, faults and fractures reflecting a brittle-ductile tangential shear. The unconsolidated and water saturated substrate had temperature slightly below to the melting point of ice (warm permafrost). Sporadic conglomerate lenses (dump structure) in shoreface deposits suggest an ice-rafted process due to icebergs during glacier retreat phase. The increase of the temperature in the Late Famennian reflects the dextral rotation of the Gondwana and South Pole migration from western portion of the South America and to the West Africa. The new paleogeographic configuration positioned the basin in subtropical latitudes initiating the glacier retreat and increase the influence of the isostatic rebound. The structures formed during pressure decrease were clastic sills and dykes, ball-and-pillow structures, beds disruption and intraformational breccia. Thrust faults associated with foliated diamictites in the western border of the basin suggest glaciers migrating to the N-NE. The continuity of the sea-level rise propitiates the implantation of melt-out deltaic system and, afterwards, a transgressive platform (Longá Formation). Diamictites interbedded with deltaic front deposits in the Upper Cabeças Formation correspond intervals with low pore volume and can represent secondary stratigraphic traps in the reservoir. The subglacial primary anisotropies were found in the both borders of the Parnaiba Basin, extend the glacial influence and opens a new perspective about the heterogeneity and effective potentiality of the Cabeças reservoir from the Mesodevonian- Eocarboniferous petroliferous system.