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10th International Congress of the Brazilian Geophysical Society
- Conference date: 19 Nov 2007 - 23 Nov 2007
- Location: Rio de Janeiro, Brazil
- Published: 19 November 2007
151 - 200 of 484 results
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Investigação de Aqüíferos Fissurais utilizando o método eletrorresistividade: Região de Serrote Preto, Itapiúna/CE – Resultados Preliminares
More LessA garantia de desenvolvimento de uma região está intimamente ligada à existência de água. A certeza do desenvolvimento, no entanto, está ligada a vários fatores, entre eles, a utilização racional desse bem tão precioso. Como aproximadamente 75% da superfície do Ceará encontra-se numa área de fraca vocação hídrica para o armazenamento (o Embasamento Cristalino), a extração nesse tipo de terreno torna-se uma atividade não muito simples onde a geofísica tem um papel fundamental. A extração de água propriamente dita é precedida por uma atividade chamada, comumente, de “locação de poço”. Esta, por sua vez, é composta por atividades de interpretação de imagens de satélites e fotografias aéreas, cujo produto direciona os trabalhos geofísicos. A
segunda parte dos trabalhos de locação de poço é o levantamento geofísico de campo propriamente dito e, a terceira, a interpretação dos resultados. Vale acrescentar que a água utilizada pelos habitantes locais ou advém diretamente da chuva (onde é armazenada em cisternas) ou de pequenos açudes que se formam por ocasião do período chuvoso ou de poços tubulares profundos (60 metros ou mais). Como não são raras as notícias de insucesso na extração de água nesse tipo de terreno a partir de poços tubulares, procuramos otimizar esse processo de locação de poço, indicando uma metodologia adequada o que constitui o principal objetivo de um projeto intitulado Levantamento Geofísico Integrado para Exploração de Água Subterrânea no Cristalino – Projeto tapiúna/CE (CNPq/FUNCEME). Este trabalho, no entanto, tem como objetivo principal a apresentação dos resultados preliminares da primeira etapa de campo do projeto supracitado.
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Prospecção Geofísica de Água Subterrânea em Xinguara/PA Aplicação do Método HLEM em Meio Cristalino
Authors Karina Palheta Gomes and José Geraldo das Virgens AlvesElectromagnetic methods have been successful when applied for ground water survey in metamorphic and igneous terrains, especially if perfectly combined with information of structural components. During the research done in Xinguara, in the Southeast of Para, Brazil, HLEM profiles were run in the transversal direction of both the fractures and the foliation. Even though the fractures didn’t seem to be opened, the high foliation dips must have deepened the intemperism, creating vertical bodies with promising permo-porosity for water infiltration and aquifers formation.
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Arquitetura sedimentar do sistema turbidítico pliocênico do Golfo de Lion, Mediterrâneo Ocidental
Authors E. Ferreira, A.T. Reis, R. Perovano, C. Gorini, W. Weibul and M. MepenThe Gulf of Lion located in the Western Mediterranean has in its basin important deep water turbidity complexes, like the Rhône Deep-Sea Fan. During the Pliocene, the feeder system of this fan would have been constituted by multiple canyons; while in the Quaternary, the feeder system would have converged for a single canyon - the Petit-Rhône Canyon. However, the analysis of an isopac map of the Pliocene suggested that the pliocene sequence converges for two principal canyons - the Marti and the Petit-Rhône Canyon.
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Estruturação tectônica da porção sul da Bacia de Cumuruxatiba e sua influência nos sistemas petrolíferos
The Cumuruxatiba Basin is located at the Southeast of the Bahia State. The total area of the Basin is calculated in around 20.500 km ². The geological context suggested that the basin is located on the contact between two differents geotectonic provinces: the San Francisco Craton and the Orogenic belt of Araçuaí. Although important reserves haven't been proven until today, the Basin shows some geologic characteristics that can transform it in an important producer hydrocarbon region. This basin has two recognized petroleum systems: Cricaré-Cricaré(!), that show subcomercial oil accumulation; and Regency-Urucutuca(!), that show comercial oil accumulation (Arraia Field). The geologic evolution of the Cumuruxatiba Basin, as well as other basins of the eastern Brazilian coast, it was controlled for tectonics events associates with the drifting of continents, this evolution include the opening of the Atlantic Ocean. In this context, lacustrine sediments of the phase rift are covered by evaporitics rocks of the Aptian and by the rocks of the passive margin. The expressive occurrence of basaltic-volcanic rocks (From Upper Cretaceous to Paleogene-Neogene) are distinguished by the constitution of highs volcanics of Royal Charlotte and Abrolhos.
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Processamento de dados sísmicos da Bacia de Campos utilizando deconvolução multicanal para a supressão de múltiplas
Authors Fábio da Cunha Novaes and Milton J. PorsaniThis work demonstrates the processing of 2D seismic data from the Campos Basin, using multi-channel predictive deconvolution as a tool in the filtering of multiple events generated from the reverberation of the seismic energy in the water bed. The processing of the data was divided in stages: conversion of format, geometry, edition, spiking deconvolution, corrections of amplitude, NMO correction, multi-channel predictive deconvolution, velocity analysis, radon filtering, stacking and migration. Each stage was explained, with respect to their relevance. The results for the multi-channel predictive deconvolution were satisfactory demonstrating to be a good tool in the multiple attenuation. The Radon filtering had a good performance in the internal multiple attenuation in the data. The performance in sets of filtering addes to the efforts made in the other stages of processing, mainly in the velocity analysis were responsible for the good final results.
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Acquisition and Processing of Multi Azimuth Towed Streamer
Authors E. Fromyr, C. Page, R.V. Borselen, J. Keggin, W. Rietveld and T. ManningThe streamer Multi Azimuth technique is an extension of conventional marine towed-streamer acquisition method. It is an attempt to overcome the lack of uniform illumination of the target due to irregular and complex target geology or a complex overburden. While this technique has not been in general use, an increase in the past few years has led to some impressive comparisons (see Kravik et al). As a result of increased use, several key aspects have been adopted for success and are discussed here. In addition, a few data examples are included to demonstrate benefits of this technique.
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Crystal – A Wide Azimuth Towed Streamer Program
By E. Fromyrremained a challenge for the seismic industry over the last two decades. In the marine environment depth migration of long offset (in-line) data has been considered to be the best option. Recent modeling has shown (see Regone) that increased cross-line offset offers a better alternative. It improves illumination, but in addition gives improved attenuation of multiple energy (see Regone and Keggin et.al), in difficult sub-salt imaging environments. It is well known that stationary receiver systems like vertical cables or OBC offer an acquisition solution adequate for solving the above mentioned challenges. However, due to the efficiency and cost effectiveness of the streamer method it is most welcomed that we can now achieve the same surveys objectives with conventional streamer alternatives. This new Towed Streamer Wide Azimuth method represents however, new challenges in terms of survey design, acquisition methodology and operation. In this paper we discuss these aspects in the context of a large scale wide azimuth exploration program in the Gulf of Mexico.
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Análise da atenuação de ondas compressionais em sedimentos marinhos
More LessThe main purpose of this research is to investigate the relationship between acoustic property of marine sediments (attenuation) and sedimentological parameters, including grain-size.
In laboratory, an ultrasonic system of 2.25 MHz was constructed to measure compressional wave propagation in marine sediments. Nine (9) piston-cores were collected at Rio de Janeiro continental shelf, offshore Arraial do Cabo. Before splitting the cores, approximately 2.550 measurements were taken. After this, cores were split in two halves and described. Grain-size measurements were taken.
The 3D attenuation diagram in frequency domain displayed good information of spectral attenuation. The medium sands have values of attenuation varying from 1,110 to 1,300 dB/m. The fine sands have the smallest values acquired in this research varying from 400 to 700 dB/m. The propagation in muddy sands recorded values from 1,250 to 1,750 dB/m, constituting the largest values in this research. The sandy mud has values from 1,150 to 1,550 dB/m, considered high when compared to other sediments. The consolidated mud has values varied from 850 to 1,150 dB/m. The attenuation results in fluid mud were very low varying between 500 a 600 dB/m.
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Wide Azimuth Tow Streamer Acquisition: From Field Development to Exploration Applications, and Back Again
Authors Damian Hite and Philip M. FontanaMarine 3D wide-azimuth towed streamer acquisition methods have provided signifiant improvments in seismic imaging of deep water sub-salt reservoirs in the Gulf of Mexico. The intial surveys were designed to provide very dense trace sampling. Subsequent to these successful field specific surveys, wide-azimuth acquisition designs have been developed to allow cost effective use of the technique over large areas for exploration objectives. This paper will describe a “sparse” acquisition configuration that has been derived from the source / receiver geometry used on the Mad Dog survey for BP. This design allows a full suite of data densities from the initial first pass for the exploration objectives to successively appended additional data acquired through the appraisal and management phases of field development.
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Modelling, Stack and Imaging: Marine Seismics
This paper summarizes practical aspects of seismic modelling of a marine geological ambient of petroleum exploration of passive sedimentary basins along the Brazilian coast. The results of a consistent attention to stack and imaging demonstrate the basics and the potential of the combined SU/WIT processing systems. The central attention is grounded on the data driven CRS (Common Reflection Surface) stack, as we also look at to establish a workflow for seismic reevaluation of sedimentary basins. The CRS stack is atractive because it is a velocity independent method, and is founded on recovered wave front attributes. Using these attributes, a post-stack Kirchhoff type time migration is automatically carried out.
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Sistemas sedimentares progradacionais da plataforma continental ao largo do Estado do Rio de Janeiro, Bacia de Santos, Brasil: resultados preliminares
Authors R.C.M. Maia, A.T. Reis, E.C. Alves and C. GoriniThis work focus on the sedimentary architecture of the continental shelf and shelf edge of Santos basin, in order to identify and to map the main sedimentary systems between Cabo Frio High and São Sebastião Islands, identified on the available data set. This study is based on seismic analysis of monocanal seismic lines from GEOMAR XX and XVI surveys, presenting seismic penetration of about 400 ms. The Santos basin comprises a prograding continental shelf, whose depositional pattern is the result of an intense sedimentary input regime that took place since Eoceno time. However, the Neogene sedimentary architecture of the continental shelf/slope was not until now the object of regional studies. Our results show that the sedimentary systems can be devided up into two main sets of seismic facies: set I comprises diverging seismic reflectors indicating deposition under dominate subsidence; set II comprises clinoforms and tabular sedimentary units reflecting deposition mainly under the influence of eustatic oscillations.
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Multiple factors influence deep-water coral mound morphology and distribution in the Straits of Florida: Insights from Autonomous Underwater Vehicle (AUV) surveys
Authors B.S. Thiago, Mark Grasmueck, Gregor P. Eberli and David A. ViggianoIn 2005, an Autonomous Underwater Vehicle (AUV)was used for the first time to map five deep-water coral mound fields in the Strait of Florida. The AUV cruises 40m above seafloor and is equipped with a suite of geophysical and oceanographic sensors that
produce fine-scale maps, including 3m highresolution multi-beam and 0.5m side-scan sonar images. A series of human-occupied submersible dives were used to groundtruth the AUV sites, via sample collection and video transects. When compiled, these datasets indicate that deep-water coral ecosystems in the Straits of Florida are complex, with an unexpected morphological variability and abundance of deep-water coral mounds. The tallest and largest mounds are found in the western side of Great Bahama Bank, whereas corals are less dense and form smaller ridges in the middle of the Strait and in the Miami Terrace. The observed differences in mound distribution and development throughout the Straits are likely to result from multiple factors, including hydrodynamic conditions and antecedent topography.
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Empilhamento CRS de dados marinhos reais, da quebra do talude da Bacia do Jequitinhonha
Authors Izaias M. Júnior and Marco A.B. BotelhoBecause the oil and gas reservoirs usually happens in portions of sedimentary basins that present a complex geological structure, the search for more accurate imaging methods has been of great interest of the petroleum industry. The CRS (Common Reflection Surface) technique,created in the begin of this century, is a new seismic data processing technique that does the stacking of the seismic data to simulate zero-offset sections and has the advantage over the traditional techniques that it does not depend on the macro velocity model. In this work we present the CRS stacks of the real marine data acquired over the talude of the Jequitinhonha Basin and we do the comparison of this results with the traditional stacking technique CMP (Common Midpoint). We also present phase shift time migrationof the stacked data, obtained from the CMP and CRS methods. We conclude that the CRS stacking, when compared to the CMP stacking, presents a better image quality and emphasizes more efficiently the coherent events
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A New Starting point for the history of South and Equatorial Atlantic Oceans
Authors Maryline Moulin, Daniel Aslanian, Jean Louis Olivet and Patrick UnternehrThe attempts to obtain the pre-opening fit (and to evaluate its age) and the early evolution of an ocean are strongly dependent to the hypothesis made for the location of the first typical oceanic crust and often require an assessment of the rigidity of the surrounding plates (for the South Atlantic Ocean, see Pindley & Dewey, 1982; Curie, 1984; Unternehr et al. 1988; Nürnberg & Müller, 1991; Lawver et al., 1999; Macdonald et al., 2003, for the Central Atlantic – Olivet, 1984, Olivet et al., 1996, Sahabi et al., 2004, etc.). Moreover, as in South Atlantic Ocean, this work could be complicated by the lack of well-defined magnetic anomalies that could mark the early history. Nevertheless, the consequences induced by a pre-break-up kinematic reconstruction are tremendous on the genesis of the continental passives margins that marked the breakup area (age, timing, constraints on movements) and on the timing of the first evolution of the ocean (Sahabi et al., 2004).
Several authors have already addressed the problem of the pre-opening reconstruction in the South Atlantic Ocean, in the past. Nevertheless, the more recent entire reconstructions of the break-up history (Nürnberg & Müller, 1991; Eagles, 2006) present numerous unexplained misfits (gaps, overlaps and misalignments) that invalidated the fit. We present here a new reconstruction based on magnetic data, satellite altimetry and oceanic and continental geological constraints. This reconstruction is the canvas in which the problem of the continental margins genesis should be addressed.
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Estruturas halocinéticas indicativas de deformação dúctil: exemplo do Golfo de Lion - Mediterrâneo Ocidental
Authors R.J. Perovano, A.T. Reis, E.S.A. Ferreira, C. Gorini, W.W. Weibul and M. MepenThe marine sedimentary sequence of the Gulf of Lions (Miocene-Holocene) contains an evaporitic level of Messinian age (5,6-5,3 Ma), whose gravitational gliding is the motor for the salt tectonics that affects the area. Plio-Quaternary salt tectonic deformations developed characteristic structural zonations: an extensive proximal domain characterized by lystric normal faults, and a distal contractional zone dominated by diapirs, connected by rigid gliding domain – the so-called Rigid Gliding Province. This province is relatively little deformed in relation to both the extensive and the contractional domains. However, we observe the presence of saltcored anticlines forming zones of buckle folds which affect Plio-Quaternary sequences. In the present work we undertake a seismic analysis in order to investigate the nature and mechanisms of deformation involved. Our results show the occurrence of buckle folds along the socalled Rigid Gliding Province. These deformations are concentrated in large area of the southwestern region of the Gulf of Lion, covering the whole area between the upslope extensional faults and the distal diapirs, while to the East, they are limited to a narrow zone close to the distal salt diapirs. The seismic analysis shows as well that the buckle folds are late deformational structures dating from middle Pliocene to Early Quaternary. The formation of salt-cored anticlines is probably due to a late mechanism of ductile layer-parallel shortening. On the other hand, the concentration of buckle folds in the southwestern region of the Gulf is probably due to the concave morphology of the sub-salt relief in the area, which seems to have induced a pattern of convergent radial gliding of both the salt layer and the sedimentary cover. As a result, the area and the mechanical role of the intermediate
translational province have changed with time, evolving from a real Rigid Gliding Province (between Early to Middle Pliocene) to a deformation zone that accomodates part of the upslope extension (between Upper Pliocene to Early Quaternary).
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Sismo-estratigrafia do Holoceno na porção Noroeste da Baía de Guanabara, Rio de Janeiro - Brasil
Authors Marcello Carnevale, Marcelo Sperle and Isadora Timbóde Janeiro City, Brazil. The bay is surounded by a number of small cities and its sedimentation rate has been increasing since the fifty´s. In order to evaluate its sedimentary thickness and stratigraphy we have selected an impacted area behind Ilha do Governador for a seismic research. We have used a high resolution seismic system (CHIRP) for mapping the stratigraphy and basement morphology in this area. In order to constrain the seismic data we have collected long-cores and made sedimentological analisys. The sismo-stratigraphic analysis revealed six sedimentary layers composed by muds and sands with different geoaccoustical patterns (some of them with gas). The mean sedimentary thickness is about ten meters. The deepest layer, just above the basement, is composed by holocenic marine transgressive sands and not by pleistocenic regressive fluvial sands as previous suggested by other works.
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On the mapping of fluid muds in coastal areas: Cassino Beach Experiment - Rio Grande, South Brazil
Authors Marcelo Sperle, Suzana Vinzon, Lauro Calliari and Izabella de FreitasThe present study was carried out during the project Wave Attenuation on Muddy Bottoms – A Multidisciplinary Field Study offshore Cassino’s Beach, Southern Brazil (March/2005-February 2007). Although little documented, the fluid mud identification is very important to reduce costs with maintenance of harbors. In this research we have used a DGPS satellite system for positioning the high resolution seismics (CHIRP/2-16 kHz) and the high precision echosounder (33-210 kHz). Despite of the exact thickness mapped in the present study we found that the high frequency echosounder (210 kHz) was the best way for mapping the fluid mud body. By using signal processing techniques and proper calibration it’s capable to estimate the top and base of the fluid mud deposit. However the analysis of in situ rheological parameters, combined with the acoustical measurements, is the best way for determining the fluid mud thickness.
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Brazilian and Angolan Passive Margins: the kinematic constraints
The thinning of continental passive margins is usually explained by models using stretching or simple shear. Nevertheless, those models imply hypothetical extensional structures and large horizontal movements between the two homologous margins (more than 250 km for the Brazilian andAngolan Margins). Zaiango refraction/reflection data together with the new closest pre-opening fit given by Moulin et al. (submitted) show that vertical motions prevail compared to horizontal motions in the formation on the huge thinned Angolan-Brazilian basin.
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Deconvolução preditiva multicanal de reflexões múltiplas na região do talude continental
Multiple attenuation represents one of the most important and difficult problem in seismic data processing. It is even more difficult when the seismic data was acquired along the continental slope area. The slope of the sea floor and the complexity of the geology, interfere seriously in the quality of the final seismic stacked section. In the present paper we illustrate the application of a direct multichannel predictive deconvolution method in the attenuation of multiples, associated with the ocean bottom, in a seismic line of the Jequitinhonha basin. The results show that the filtered stacked section is practically free of the multiples allowing for a better definition of the primary reflections.
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A tectônica gravitacional no Cone Submarino do Amazonas: resultados preliminares
Authors A.T. Reis, C.G. Silva, V. Oliveira, B.C. Vendeville, C. Gorini, L. Loncke, R. Mourgues, J. Mattioda and N. CaldasIn this work we integrated structural analysis of about 9000 km of multichannel 2D seismic data with an isopach map of the sedimentary cover to evaluate how gravity tectonics has operated in the Amazon Cone. The interplay between sedimentary loading and bathymetric slope seems to have been the main mechanisms responsible for the development of two quite different structural compartments mapped in the area: the larger and structurally complex Northwestern Compartment, and the shorter and structurally more incipient Southeastern Compartment.
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The crustal structure of the Moroccan continental margin from wide-angle and reflection seismic data
The Atlantic margins of Morocco with its neighbouring Jurassic oceanic crust is one of the oldest on earth (Sahabi et al., 2004). It is conjugate to the Nova Scotia Margin of North America. Combined wide-angle and reflection seismic data have been acquired on this margin during two cruises. The SISMAR marine seismic survey acquired seismic profiles on the NW, in the Seine Basin, and the DAKHLA survey on the southern Moroccan margin, in front of the Reguibat Ridge. Both cruises followed a similar acquisition planning resulting in two data sets which are ideally suited for comparison of the margin structure in the north and in the south.
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Cicatriz de remoção no talude da região norte da Bacia de Pelotas
More LessThe detailed morphology of the continental slope in the North of the Pelotas Basin was obtained using multibeam data, which allowed the identification of seafloor small features. Larger features and its regional context were obtained using singlebeam data.
A digital terrain model was calculated and with this model, integrated with 3,5kHz profiles, important information regarding features, morphogenesis and sedimentary processes in the continental slope was obtained. It was observed that slump and slide regions described by Mello et al. (1992), and regions with scarps and faults described by Lima (2004), seem to be part of a huge region of sedimentary removal in the upper and intermediate slope, if inserted in a regional context. This region remains as a removal scar with related slump/slide lobes that generated a slope retreat. Scarps and ridges were identified in shallow waters. They individualize steps and small channels where the removal process was probably initiated. The sediment removal by gravitational and mass flows sculpted the scarps and channels. In deeper waters two huge channels were observed. Those channels must have been the pathway to deeper water of the sediments removed from shallow waters, helping to develop the huge removal scar.
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Interaction of drift and gravitational depositional processes on the sedimentary architecture of the southern Brazilian continental margin
Authors Michelle Mepen, Cleverson Guizan Silva and Antonio Tadeu dos ReisBased on seismic facies analysis of about 8.000 km of multichannel seismic lines (LEPLAC IV), we interpreted that gravitational and drift processes have had an important role on the sedimentary construction and evolution of the Brazilian South Margin. Until the Eocene, progradational sedimentary processes were essentially gravitational in nature. In some places, such as the northeast sector of the margin, deposition was conditioned by basement features that acted as obstacles for sediment dispersal. However, after the Upper Eocene, the margin experienced the prevalence of contour currents influence, whose deposition shifted mostly to northeast, seawards and backwards Drift deposits exhibit different shapes and seismic facies, which indicate a variety of depositional environments in the study area.
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A determinação da base do talude na região do cone do Amazonas
The Amazon Fan, like other deep sea fans, represents an individualized morphologic and morphodynamic unity of a continental margin. Therefore it can not be compared to a normal continental slope and rise in accordance with geological processes and
physiography and also can not be compared to a portion of the margin outside of it. These features have their own peculiarities and cannot be entirely compared among themselves in a common basis, with respect to gradients and major physiographic divisions and morphogenetic processes. The typical bathymetric profile of the Amazon Fan does not show a noticeable regional break in the gradient. This is demonstrated by the presence the channel-levee system that has widespread distribution on the surface and on the subsurface of the fan. This system was established only when a transition of bathymetric gradients reached such a value that made it possible to the meandering channel-levee systems be installed. With the purpose of identifying the base of the continental slope and further the FOS this work will look into the Amazon Deep Sea Fan as a unique physiographic feature associated with a complex geology.
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The Brazilian Northern Continental Margin and its Continental Shelf Outer Limit
The Brazilian Northern Continental Margin presents the most extensive geological continental shelf reaching around 400km from the coastline. Another relevant aspect is the presence of the Amazon Submarine Fan which had an important role in the sedimentation of the margin. The Brazilian Government delivered its Continental Shelf Outer Limit Submission to the United Nations General Secretary on 17 May 2004 in accordance with Article 76 of the United Nation Convention on the Law of the Sea (UNCLOS). Since then, five meetings between Brazilian Representatives and members of the Commission on the Limits of the Continental Shelf have been held. As consequence of the exchange of ideas and better knowledge of the issues concerning implementation of article 76 some modifications were performed in the draw of the Continental Shelf Outer Limit in this region. These modifications were conducted as resulting of improvement in the methodology for the establishment of Continental Shelf Outer Limit and the availability of further seismic and bathymetric data carried out. The outer limit was calculated employing the Caris LOTS software. In order to consolidate all the modifications implemented in the draw of the outer limit, it was delivered to the United Nations General Secretary in the late February 2005 an Addendum to the Brazilian Submission. The changes performed in the draw of the outer limits are supported by technical and legal arguments and contribute both to a better understanding of the Brazilian Northern Margin as to a better entitlement of the region within the UNCLOS requirements, and did not represent a substantial gain of area for the Braziliant.
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Aplicação de Perfilagem Geofísica em Furos de Sondagem na Mina de Córrego do Feijão e Depósito Dois Irmãos - Cia Vale do Rio Doce – Minas Gerais
During the evaluation of iron deposits, it is important to determine bulk density of geological formations at various depths. To put this issue in a practical way, we present the results of the application of wireline logging in Córrego do Feijão Mine and Dois Irmãos deposit, Minas Gerais-Brasil. The aim of this study is to investigate the possibility of recording the in-situ densities of subsurface iron ore bodies. The measurement system is constituted of a gamma-ray source and three detectors mounted in the instrument which is lowered into a borehole and the backscattered gamma-rays are counted. In the following, this gamma-ray counting rate is transformed into density supposing the calibration curve is a true exponential function and the densities come from core data. By comparing densities determined in laboratory and through the logs we have found differences below 15% supposing the borehole diameters are nearly constant. Some tests done into cased holes have also shown prominent results.
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Caracterização do Campo Térmico Atual e Evolução Térmica da Plataforma Continental do Estado do Rio de Janeiro
Authors Roberta A. Cardoso and Valiya M. HamzaThe emphasis of the present paper is focused on the characterization of the present temperature field and evaluation of the thermal history of the crust on the continental platform in southeast Brazil and your implications on the thermal maturation. The characterization of the present temperature field was realized from the determination of geothermal parameters like bottom water temperature, bottom hole temperature, thermal gradient, thermal condutivity of the geological formations and heat flow. Beyond the temperatures of deeper layers of the crust like top of basement and bottom of the crust and lithosphere. The values of thermal gradient and heat flow obtained are found in the range of 24 to 41 °C/km and de 53 to 66 mW/m2, respectively. To evaluate the thermal evolution were obtained the paleotemperatures of the sedimentary layers from studies of the tectonic evolution of the platform. The subsidence models sugested that geologic evolution of the Campos basin took place in two distinct stages: an initial stage of 130 to 68Ma, followed by a second stage lasting from 68 to the present and provided information on paleothermal conditions for the earlier periods of basin evolution. Thus the results point to a systematic decrease in heat flow since the early rifting episode. The paleo heat flow values are in excess of 100mW/m2 for the early periods, with duration of less than 20Ma. Such conditions are believed to be typical of periods immediately following the rifting episode. Heat flow is found to be relatively moderate (in the range of 60 to 90mW/m2) during the intermediate phase, with duration of 40 Ma. For the remaining periods, with duration of 60Ma, the heat flow values are found to be comparable to the present day values. The time-temperature indices calculated on the basis of Lopatin method indicate that thermal maturation stage compatible with oil and gas generation was reached only during the last 45 Ma.
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Gradiente e Fluxo Geotérmico nas Regiões Norte e Noroeste da Bacia do Paraná
Authors Antonio Jorge de Lima Gomes and Valiya M. HamzaComo parte de um projeto de avaliação de recursos geotermais da Bacia do Paraná e com o objetivo de interpretar o campo térmico regional da porção Norte e Noroeste da Bacia, foram utilizados 199 dados geotérmicos, distribuídos em quatro países da América do Sul, sobretudo para um melhor entendimento geotérmico desta porção da Bacia. A distribuição destes dados compreendeu quatro Estados do Brasil (Mato Grosso, Mato Grosso do Sul, Goiás e Bahia), e ainda, outros três Países da América do Sul (Bolívia, Paraguai e Argentina). Foram realizadas novas compilações de levantamentos realizados a partir da década de 1950, muitos já disponíveis em publicações e outros de relatórios técnicos institucionais, incluindo também dados de poços de petróleo com temperatura de fundo de poço BHT. A maior parte dos dados geotérmicos estudados e analisados faz parte integrante da Base de Dados do Laboratório de Geotermia do Observatório Nacional/MCT. Devido à baixa densidade de dados dos Estados do Mato Grosso, Mato Grosso do Sul e Goiás (totalizando 49 locais no território brasileiro) utilizamos também resultados de levantamentos de três países vizinhos, sendo 52 dados da Bolívia, 35 do Paraguai e 63 da Argentina. A elaboração de mapas geotermais permitiu avaliações do gradiente térmico e do fluxo geotérmico em escala regional. Também foram utilizados os dados de condutividade térmica disponíveis na literatura. Os resultados obtidos indicam que esta região é caracterizada por gradientes geotérmicos situados num intervalo de 10 a 640C/km e fluxo térmico compreendido entre 32 e 180 mW/m2. Constata-se a existência de uma possível faixa anômala na direção Norte-Noroeste da Bacia do Paraná, apresentando valores de gradientes geotérmicos superiores a 20 0C/km e fluxo térmico maior que 70 mW/m2. Esta região de alto gradiente e fluxo térmico apresenta aspectos coincidentes com uma região de alta sismicidade.
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Estrutura Termal da Litosfera nos segmentos cratônicos de Salvador e São Francisco
Authors Carlos H. Alexandrino and Valiya M. HamzaRegional variations in geothermal gradients and heat flow across the São Francisco craton and the neighboring metamorphic fold belts are examined on the basis of geothermal data from the highland areas of eastern Brazil. The database employed include results of geothermal measurements in 63 localities. The results indicate that the northeastern segment of cratonic area and the adjacent metamorphic fold belts are characterized by mean geothermal gradients in the range of 12 to 18oC/km. The estimated heat flow values are found to fall in the range of 35 to 55mW/m2, with the cratonic area having low values relative to those in the fold belts. On the other hand, the southwestern segment of this craton and the São Francisco sedimentary basin are characterized by higher gradient values, in the range of 20 to 24ºC/km, and the corresponding heat flow values are in excess of 60mW/m2. Crustal thermal models have been developed to examine the implications of the observed intra-cratonic variations in heat flow. These models take into consideration variation of thermal conductivity with temperature as well as change of radiogenic heat generation with depth. Vertical distributions of seismic velocities were used in obtaining estimates of radiogenic heat production in crustal layers. Crustal temperatures are calculated based on a procedure that makes simultaneous use of the Kirchoff and Generalized Integral Transforms, providing thereby analytical solutions in 2D and 3D geometry. The results point to temperature variations of up to 250oC at the Moho depth, between the northern and southern segments of the craton. There are indications that such differences are responsible for the contrasting styles of deformation patterns in the adjacent metamorphic fold belts.
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Estrutura termal da crosta sob a bacia de Taubaté
Authors Iran F. Rodrigues and Valiya M. HamzaApresenta-se neste trabalho a primeira avaliação da estrutura termal da crosta sob a bacia de Taubaté, com base nos estudos geotérmicos das décadas de 1970, 1980 e outros mais recentes. A base dados geotérmicos utilizados inclui resultados obtidos em 62 locais distribuídos em 16 municípios. Os gradientes térmicos encontrados estão no intervalo de 8 a 57 ºC/km, sendo que os maiores valores estão na parte central desta bacia. Os valores correspondentes de fluxo geotérmico estão na faixa de 50 a 120 mW/m2. Os resultados de mapeamento apontam para a existência de pelo menos duas anomalias geotérmicas, nos municípios de Taubaté e Pindamonhangaba. Com base nesses dados foram determinadas temperaturas, tanto na base do pacote sedimentar como na crosta inferior, permitindo desta forma avaliações quantitativas da estrutura termal da litosfera local.
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Prospecção de Manganês com Radar de Penetração no Solo (GPR) no Oeste da Bahia
More LessGround-penetrating radar (GPR) surveys were undertaken in three areas placed near old manganese deposits on the western part of Bahia State. The type of manganese ore identified in the areas is the eluvial-coluvial manganese crust ore. Most of these lithologic units are overlain by sandy and silty sediments of tertiary and quaternary ages. Radar data were acquired using a constant-offset configuration following parallel stright lines over the areas to detect manganese deposits. The radargrams were acquired with 80, 200 and 400 MHz antennas and display reflections from the upper and lower boundaries of the deposits revealling not only the position of the ore body but also if it is concentrated or scattered.
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Métodos magnético e cintilométrico aplicados ao salvamento arqueológico do sítio Jaburu do Rio Paru
More LessMagnetic and scintillometric methods were applied in a site to help the rescue of archaeological remains. Magnetic measurements were taken to indicate places for excavation, while the objective of the scintillometry was to find a relation between the gamma ray counting and the thickness of the TPA layer that in the Amazon Region shelters archaeological remains. The magnetometry lead to the discovery of a well preserved human skeleton and several ceramic fragments. The scintillometry showed a good correlation between gamma ray counts and the TPA thickness.
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Investigação geofísica no sítio arqueológico Engenho Murutucu, Belém-PA
Geophysical methodology was applied to help an archaeological survey in finding remains of ancient occupation and foundations in the Engenho Murutucu, a sugar mill dated of the eighteenth century. Starting from a magnetic map constructed from measurements taken in a previous survey, 26 GPR profiles were carried out with a 400 MHz antenna. The Depth of investigation in the GPR profiling was around 2m. GPR results were correlated to the magnetic data giving indications for archaeological intervention in the area.
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Emprego da sísmica de reflexão com a técnica Mini-sosie na área urbana da cidade de São Paulo
Authors Dante Pires de Souza, Renato Luiz Prado and Oleg BhokonokShallow seismic reflection studies were performed in the urban area of Sao Paulo City, Brazil. The purpose was to image structural discontinuities of the bedrock of the Sao Paulo Sedimentary Basin. This work also aimed to use the Mini-Sosie technique in this noisy area. This paper discusses some aspects and results of this employment. The combined interpretation of the stacking seismic section of this campaign and the seismic section previously obtained by Bokhonok (2005) suggests that the discontinuities are related to the NE structures present in the study area.
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Levantamentos magnéticos para estudos de geofísica rasa: Uma experiência de campo no Sítio Controlado de Geofísica Rasa (SCGR) do IAG/USP
More LessHigh resolution ground magnetics has shown proved utility in characterizing environmental hazardous sites in industrial and urban contexts. To experiment geophysical methods over previously known targets, a test site was constructed at the University of São
Paulo (Sítio Controlado de Geofísica Rasa - SCGR) by burying at known positions a variety of representative objects. Here, we present results from magnetic surveys performed at this site, by using three different equipments: a proton precession magnetometer, a fluxgate gradiometer, and an optical pumping gradiometer. Each device enables specific sampling density, and thus different resolution for the anomalies generated by the buried sources (drums, pipes, tubes, concrete structures, stones, among others). Our results illustrate common responses from such targets, which may help the interpretation of real data sets from near-surface applications.
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Construção de um sistema automático para monitoração geotermal rasa
A prototype of an automatic equipment based in PIC microcontroller with high performance was develloped for application in shallow geothermal studies. To study of thermal structures of soil and subsoil affected by incident solar radiation on solid surface of the Earth are buried temperature sensors as thermistors until 5 meters depth. These sensors allow measurements with uncertainty of 0,01o C using a 16 bits AD converter. This equipment has autonomy of one year in power consumption and EEPROM memory capacity.
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Espessura da camada de basalto e profundidade do embasamento na Bacia do Paraná (Bebedouro - SP), com função do receptor e dispersão de ondas superficiais
Authors Luiz Souza, Josimar A. Silva, Marcelo Assumpção and José Roberto BarbosaFrom January 2004, earth tremors started to occur at Northwest of São Paulo because of drilling of wells. IAG/USP installed a seismographic net in the region to study the intense seismic activity, but besides the local events, distant earthquakes from Andean region were also recorded and were used to study the upper crustal layer through the receiver function method. Surface waves started to be recorded with the migration of the local earthquakes to the west, allowing its dispersion study. The structural model obtained from receiver function was used as input to generate the surface wave dispersion curve, which showed a good coherence with the measured data (velocity and period). This result shows that the two methods are imaging the same structures, and that it is possible to do a joint inversion in the future.
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Uma aplicação de sísmica de reflexão rasa multicomponente (3C) em área urbana
Authors Oleg Bokhonok, Liliana Alcazar Diogo and Renato Luiz PradoWe present the results of three component seismic reflection experiment designed to evaluate the potentiality of the multicomponent shallow seismic reflection method for the geological and geotechnical investigation in noisy urban environments. The field test was made on the Sedimentary Basin of São Paulo, in the urban area of the city of São Paulo. It were employed 96 channels for the acquisition, equally distributed among the vertical, radial and transversal components (32 for each one).The vertical geophones were 40 Hz and the horizontal one 28 Hz. A sledgehammer-plate system was used as seismic source. The preliminary results indicated that the multicomponent shallow seismic reflection method is an effective tool that can be used to the proposed problem, allowing a better data interpretation. By using polarization filter it was possible to improve the S/N ratio.
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Hydraulic Fracture Mapping From Treated Well. Channelized Reservoirs Development Optimization In Mexico
Hydraulic fracturing is of prime interest for waterflooding and Enhanced Oil Recovery (EOR), and the orientation of the fractures is a key factor for the selection of optimum well locations. The microseismic monitoring of hydraulic fracturing treatment is now recognized as an helpful tool to map fractures. This paper highlights the advantage of monitoring fractures from the treatment well itself and as an illustration presents the results obtained by PEMEX in channelized Chicontepec reservoirs (Mexico), where extensive fracturing jobs are largely carried out to stimulate the oil recovery of the turbidites reservoir complexes. The specificity of the presented monitoring surveys stands in the deployment of tools in the treatment well itself. The microseismicity recorded yields to provide consistent orientation of fractures. These results confirm the great potential of this unique approach, as it leads PEMEX to review the stimulation scheme for a cost-effective reservoir stimulation.
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Prospect generation in frontier areas using electromagnetic scanning
Authors Dave Ridyard, Jan-Erik Lie, Bjorn Petter Lindhom and Carl HutchinsElectromagnetic scanning is a new application of proven seabed logging technology. Sparse spatial sampling and wide azimuth geometry permits the rapid identification of buried resistive anomalies potentially indicative of hydrocarbon accumulations. In this paper, we evaluate the costs and benefits of various geometries applied to prospects in the Campos basin.
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Uma proposta para detecção e localização de explosões usando arranjo de geofones
Authors Alexandre Horstmann and Marcílio Castro de MatosThis work proposes a low cost seismic acquisition system for seismic events detection caused by explosions, ballistic impacts and the ones generated by heavy armament, for the Brazilian Army. The proposed system was divided in three parts: seismic data acquisition, seismic wave detection and locating the epicenter of the seismic event. The acquisition of the seismic data was done using conventional geofones and microcomputers with data acquisition boards. The detection of the seismic waves was implemented by filtering in the time-frequency domain using the S transform. The location algorithm includes the solution of a nonlinear system, whose variables are the vertical velocity of the seismic wave and the coordinates of the target, using the least square method. The results showed that the efficacy in detection of the seismic event was fundamental for a good precision in locating the target.
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Considerations of observed spectral anomalies over hydrocarbon reservoirs generated by microtremors
Authors E.H. Saenger, B. Steiner, S.M. Schmalholz, M. Lambert, Y.Y. Podladchikov, B. Quintal and M. FrehnerNarrow-band, low-frequency (1.5-4 Hz) tremor signals on the surface over hydrocarbon reservoirs (oil, gas and water multiphase fluid systems in porous media) has been observed worldwide. These ‘hydrocarbon tremors’ possess remarkably similar spectral and
signal structure characteristics, pointing to a common source mechanism, even though the depth (some hundreds to several thousands of meters), specific fluid content (oil, gas, gas condensate of different compositions and combinations) and reservoir rock type (such as sandstone, carbonates, etc.) for each of those sites are quite different. However, the physical mechanisms underlying these observations are presently not fully understood. We propose a scientific strategy for better understanding those phenomena. Using well-known rock physical relationships we have identified on macro-, mesoand microscale different mechanisms which can induce anomalies in the low-frequency band. Using different numerical approaches we are able to compare these mechanisms with observations in the field.
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Low frequency spectral modifications of seismic background noise due to interaction with oscillating fluids entrapped in porous rocks
Authors Marcel Frehner, Stefan M. Schmalholz and Yuri PodladchikovIn recent years a new method for direct hydrocarbon indication was developed. Studies of passive seismic data in the frequency range below 20Hz have shown that the frequency content of the ever-present geoseismic background noise changes above hydrocarbon reservoirs. Different explanations for this observation have been proposed. In this study, the effect of oscillating pore fluids on the background noise is investigated. A non-wetting fluid drop entrapped in a pore can oscillate with a characteristic eigenfrequency. Capillary forces act as the restoring force driving the oscillations. A 1D wave equation is coupled with a linear oscillator equation, which represents these pore fluid oscillations. The resulting linear system of equations is solved numerically with
explicit finite differences. The most energetic part of the seismic background noise, i.e frequencies around 0.1- 0.3Hz are used as the external source. This part is presumably related to seismic surface waves generated by ocean waves. It is shown that the resulting elastic wave initiates oscillation of the pore fluid The oscillatory energy of the fluid drops is transferred continuously to the elastic rock matrix. In consequence the elastic matrix carries a second frequency, the eigenfrequency of the pore fluid oscillation on top of the applied external frequency. The presented model is considered as a possible explanation for the observed spectral modifications above hydrocarbon reservoirs. Time evolution of the pore fluid oscillation seems to be related to the thickness of the hydrocarbon reservoir.
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Aplicação do Método de Decomposição Empírica (EMD) à análise de dados geofísicos aplicados à prospeção
Authors André Lopes Ferreira and Eder MolinaThe aim of this work is to study and to apply the Empirical Mode Decomposition, a relative new method for the analysis of nonlinear and nonstationary signals applied to the geophysical prospection data. A new software was developed in order to implement this method and to allow one to process geophysical signals. The results obtained so far with the processing of a set of synthetic data show the efficiency of the developed algorithm and it lead to a good perspective in the processing of geophysical signals.
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Numerical modeling by finite difference of the seismoelectric waves propagation in porous saturated media
Authors Francisco J. A. Vanzeler and Viatcheslav PriimenkoIn this work we have used the equations of the coupled poroelastic-electromagnetic phenomena to simulate by finite-difference methods the seismoelectric responses of poroelastic reservoir 2D models, using sources with frequencies in the seismic range, and receivers located in the well. This data will be used to define the maximum investigation range from the well, and also the elastic and electrical-chemical conditions for the detection of the amplitude of the conversion of seismic energy into electromagnetic energy, providing a quantitative base for planning seismoelectric acquisition jointly with VSP tools. The high resolution of seismoeletric information generated in the elastic and electrical-chemical interfaces can be used as complementary information to the VSP data for the interpretation and characterization of reservoirs microstructures, the fluid content and their interfaces, and the fluid physical-chemical properties. This work will contribute with quantitative measurement of the seismoelectric signals strength generated in siliciclastic petroleum reservoir and to evaluate the use of this data to detect permeability barriers, microfractures and fluid contact.
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Integrated Application of Passive Seismic Technology For Trapped Oil Detection in Mature Fields and Hydrocarbon Discoveries in Adjacent Compartments
Authors Serdar Kaya, Ernst D. Rode and Karim AkrawiIn the oil/gas industry, one of the main objectives for the geophysicist, geologists and geoscientists is to fully understand the geological structure by spending tremendous effort. Yet, hydrocarbon pool areas are still source of major uncertainties. Success rates in drilling productive wells are still rather low even with the advanced technologies used today. Hence the growing interest for the application of a direct hydrocarbon indicator using low frequency passive seismic technology, which has started to gain momentum in exploration and field development. The scope of this study is to better understand two mature fields in the Caspian region by using passive seismic results integrated with all other available field data. The results and the methodology applied are discussed in this paper.
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Análise de imagens de sistema poroso de rochas-reservatório
Authors Bruno Luís Gonçalves Dilly and Alexandre Campane VidalThe goal of this work is to study and to develop a software that estimates petrophysics proprieties of reservoir rocks by analysing bidimensional petrographic images. These proprieties are some of the factors that condition fluid flow inside reservoir rocks, and the knowledge of their behavior can be fundamental for the comprehension of the sedimentaries structures and of the diagenetics processes, over reservoir flow. To achive our objectives, we have implemented the following functions in MATLAB: image segmentation, histogram equalization, porosity measurement and pore labelling.
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Determinação de Parâmetros Petrofísicos com Programas interativos que usam Perfis Geofísicos de Poços
Authors Anderson Nogueira Mendes and Geraldo Girão NeryTurbiditic sandstones, the main hydrocarbon reservoirs in the northwest portion of the Namorado Field, are characterized by some petrophysical parameters such as: thickness, density, clay content, water saturation, elastic constants, among others, in order to make possible such application in the evaluation of “Mature Fields” at present stage of exploration of the oil industry. The Namorado Field is located in the central part of the Campos Basin – RJ, Brazil, approximately 70km off coast and between 150-250m bathymetric depths. It is one of the most producing oil field of the brazilian continental margin. This study was accomplished by the Schlumberger methodology introduced in a program named Interactive PetrophysicsTM 3.2.24, using acquisition data logs Gamma Ray (GR), Sonic (DT), Resistivity (ILD), Density (RHOB) and Neutron (NPHI) for the determination of those petrophysics parameters
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Quantificação experimental do efeito da argilosidade sobre propriedades petrofísicas de sedimentos siliciclásticos
Experimental quantification of clay content effect on petrophysical properties of sand-shaly sediments is explored here through the use of a synthetic standard composed of glass micro spheres and caulinite clay. Mean diameter of micro spheres is 0.7 mm,
representative of mean graded sand, and the clay is passant in a 200 mesh screen. The synthetic standard is used here because its admittance for whole possible sand-clay mixture. Seven centimeters long samples are used based on a sensitivity analysis to sample length. Furthermore, P-wave velocities are measured on natural unconsolidated sediments. Results show that permeability decays under an exponential function with clay content while porosity decays as a parabolic function. Meanwhile, sample density holds a linear inverse relationship with clay content. Estimative of specific surface area through Kozeny-Carman equation shows that this property keeps a directly linear dependency with clay content. Experimental measurements of P-wave velocities of dry
natural unconsolidated sediments generate fitting functions which may be used to predict their velocities under any effective pressure condition.
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Simulação do Perfil Sônico em Intervalos de poços perfilados apenas com os Perfis de Raios Gama e Resistividade
More LessThe sonic log is used by petroleum engineers to calculate the mechanical parameters of the rocks, in order to construct the drilling strategy of the wells. However, in many correlation boreholes the sonic log is not available. Thus, in this work, it was shown that, to overcome this problem, the sonic log was simulated using only of gamma ray and resistivity logs jointly with algorithm FCM (Fuzzy C-Means), which uses concepts of the Fuzzy logic. To make this, it was utilized log data from Namorado Oil Field in Campos Basin, Southeast Brazil. This methodology was successful, because it was obtained small mean errors and standard deviations (less than 4%), verifying, at the same time, that the best relation between the sonic log is linear regarding gamma ray log and logarithmic regarding resistivity log.
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