Navegando por Assunto "Eletrorresistividade"

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Acesso aberto (Open Access)
Eletroresistividade aplicada ao estudo de água subterrânea no município de Salvaterra-Marajó-Pará
(Universidade Federal do Pará, 1979-08-14) BEZERRA, Cesar Augusto Campos de Alencar; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
A pilot area of 200 Km2 in Salvaterra county along the east edge of Marajo island was selected to make a study of groundwater using electrical resistivity methods. Sixty-five Schlumberger vertical electric soundings and six horizontal Wenner resistivity profiles were made. The sounding data were first interpreted individually with the auxiliary point method, and later reinterpreted in groups using an iterative curve-calculating routine. The results show the range of resistivities in this area vary between 5 and 40000 ohm-m. The aquifer appears to be defined by a sequence of layers with resistivities between 500 and 4000 ohm-m. In this pilot area three favorable sub-areas were delimited, covering about 40% of the area, where the interpreted aquifer thickness is in excess of 20 m and sometimes as great as 80 m. The depht to the top of this aquifer zone varies between 1.3 and 6.6 m in the three sub-areas. The geophysical interpretations were verified by four shallow drill holes (to 20 m). Two of these, located within the favorable sub-areas, showed dominantly sand sediments and the other two, drilled outside the favorable areas, showed much more clay and organic material, but limited amounts of fine sand. Analyses of water samples from many existing wells and of the new drill holes show that, in general, there are no problems with the quality of these shallow groundwaters. The only exceptions are several wells withing 100 m of Marajo Bay which show considerable increases in salinity during the height of the dry season, when the Bay waters also have maximum salinity. The ages and origin of the long oval belts of sand are not known with certaint, but they could be channel sands deposited by an ancient river or distributary of this deltaic region. The results of this research have outlined three large zones of good groundwater potential which will be very important for the agricultural and industrial development of this region.
Acesso aberto (Open Access)
Estudos hidrogeoquímicos e geofísicos na região da Braquidobra de Monte Alegre-PA
(Universidade Federal do Pará, 2005-04-11) LOPES, Elem Cristina dos Santos; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Monte Alegre brachyanticline is located in the central-western Pará and is one of the most striking structures of the Paleozoic Amazon sedimentary basin. The dome outcropping surface is elliptical with axes of 30 and 20 km trending NESW and NW-SE, respectively. At the present erosion level, rocks of the Ererê, Barreirinha, Curiri, Oriximiná, Faro, Monte Alegre, Itaituba and Alter do Chão formations, as well as the Penatecaua diabase are exposed. Thermal springs with temperatures from 29 to 37ºC issue out of the Ererê Formation. The present study focuses on the physico-chemical characterization of surface and groundwater that occur within the dome and on the interaction with their mineral environment. In addition, the thermal waters are also characterized isotopically and their subsurface temperatures estimated with basis on the silica and Na-Ca-K geothermometers. Gravimetric and resistivity methods were applied aiming at detecting potential sources that could account for the heating of the thermal waters. The Piper diagrams show a wide chemical variation for both the surface and groundwater which spread over the bicarbonate, calc-sulfate and sodic-chloride fields. The thermal waters are chemically more homogeneous and fall on the bicarbonate and sodic-chloride fields. This variability reflects the composition of the rocks through which the waters migrate, whose components result mainly from hydrolysis and redox reactions involving pyrite and sulfate minerals. Most water samples are in equilibrium with kaolinite as deduced from activity diagrams constructed at 25ºC, 1 atm and at quartz saturation. The thermal water samples cluster near the boundary kaolinite-sericite, whereas a few samples of surface waters that drain the Itaituba Formation plot near the line separating the kaolinite and leonhardite stability fields. The samples of the Menino Deus thermal spring collected in October/2002 reached equilibrium with sericite but failed to equilibrate with paragonite despite their Na/K ratios being higher than unity. Furthermore, most water samples are saturated with quartz. During the dry season, sample FT-27 and those from the Menino Deus thermal spring presented higher silica contents causing them to equilibrate with pyrophyllite. Isotopic data show that the Monte Alegre thermal waters have a meteoric origin with δ18O and δD values coincident with the global meteoric water line, although slightly enriched in deuterium. The excess of deuterium varies seasonally, being recorded values of 11,8-14,8 ‰ in the dry season and 4-9,5 ‰ in the wet season. Sub-surface temperatures for the thermal waters estimated with the silica geothermometer yield mean values of 71°C (wet season) and 83°C (dry season). Average water circulation depths ranging from 1560 m (wet season) to 1900 m (dry season) were calculated assuming a geothermal gradient of 30°/km and using the estimated sub-surface temperatures. After infiltrating into the ground, these meteoric waters are heated and rise back to the surface through a channel way network, particularly NE-SW and N-S-trending faults which truncate the brachyanticline flanks. Gravimetric surveys allowed to infer the presence of a lacolith-like body at a depth of about 1.3 km. This body is thicker close to the central portion of the brachyanticline. Contact relationships between sedimentary units and the laccolith could also be defined. Likewise, fractures and faults could be mapped at depth whose traces are visible on SRTM radar images. Resistivity profiles did not identify any thermal anomaly in the area, but they confirm the lithological diversity of the geological units as well as faults that may have served as conduits to the fluids.
Acesso aberto (Open Access)
Implantação do campo de testes da UFPA para medidas geofísicas
(Universidade Federal do Pará, 2013) ALVES, Jerry Williamis Lima; LUIZ, José Gouvêa; http://lattes.cnpq.br/8676530374310847
We describe the results obtained during the implementation of the Federal University of Pará test site for geophysical measurements. The work was done in three stages. In the first stage, preliminary studies were accomplished to know the physical background of the area. In the second, artifacts were buried to simulate geophysical anomalies in the measurements. In the third one, new measures were performed to detect anomalies caused by the buried artifacts. Only a part of the artifacts that are scheduled for burial was buried in the site. The buried artifacts are metal pipes, metal drums, and plastic drums. The measures implemented in the first and third stages involved the methods of Electrical Resistivity, Ground Penetrating Radar (GPR), Electromagnetic and Magnetic. The measurements performed in the third stage showed the presence of artifacts in the actual position where they were buried, which turns the area suitable to serve as a training site for geophysical experimental practices.
Acesso aberto (Open Access)
Investigação geofísica da contaminação por derivados de hidrocarbonetos nas redondezas do Posto Cristal (Belém-Pa)
(Universidade Federal do Pará, 2013) SILVA, Márcio Antonio dos Santos; SILVA, Lúcia Maria da Costa e; http://lattes.cnpq.br/8612431024609774
Acesso aberto (Open Access)
Métodos geofísicos aplicados a prospecção de água subterrânea no município de Ponta de Pedras - Ilha de Marajó - Pará
(Universidade Federal do Pará, 1979-02-22) KOBAYASHI, Carmelina Nobuko; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
This work was perfomed in an area of 25 km2 in Ponta de Pedras, Marajó Island. The purpose of this work was to study the geometry of the aquifers and to select favorable zones for development of ground water. Two geophysical methods were used: seismic refraction and electroresistivity. The first one was used experimentally intending to find out the possibility of its application in the area. The seismic results obtained confirm the original expectance of the existence of shallow geologic horizon at the subsurface, not able to be distinguished by the seismic method. Vertical electrical soundings and horizontal perfil resistivity were done with the electrical resistivity method. The results of the interpretation point out favorable areas in the central part of the study area and in a zone extending to the north of the prospected area. The thickness of the shallow aquifer varies between 0 and 50 m.
Acesso aberto (Open Access)
Métodos geofísicos aplicados a prospecção mineral na região do Igarapé Chega Tudo, Maranhão - Brasil
(Universidade Federal do Pará, 1982-12-29) ORTEGA GONZALEZ, Moisés; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
This work of geophysical prospecting was carried out on a NW-SE geological lineament zone from Chatão - on the right side of Gurupi river up to 5 km beyond Chega Tudo in the State of Maranhão. The field work with the application of magnetic (total field), radiometric, electroresistivity (Schlumberger, Wenner and Half-Schlumbergere) and EM (Sligram) methods was carried out in two stages: a) reconnaissance survey of a 22 km2 area with magnetic and radiometric methods, and b) detailed survey of a 3.5 km2 area with electroresistivity and EM methods. The objectives were to study the main geoelectrical structures associated with mineralized zones, and to select among the used geophysical techniques the one with greater resolution to locate sub-surface quartz veins with gold mineralization. The magnetic method shows a large anomaly in the NE region of the area of reconnaissance, whereas the radiometric method indicates only the background value everywhere. Therefore the latter will be not discussed. The electroresistivity and EM surveys indicate many important anomalies on the detailed area. The electroresistivity and magnetic interpretation were carried out by computacional techniques whereas the EM data were interpreted by phase diagrams. The results show a good correlation between the magnetic and electroresistivity anomalies and the mineralized zone. The EM method was not found effective because it could not discriminate the anomalies inside and outside the mineralized zone. All anomalies were tested with well logs. Since the studied area has the same degree of difficulties for geological prospecting as any other similar area in the Amazon region, the results presented here show that the magnetic and electroresistivity methods, which turned out to be very effective as exploration tools for prospecting gold at Chega Tudo region, could be applied to any other environment with similar geological characteristics.
Acesso aberto (Open Access)
Métodos geofísicos aplicados ao mapeamento geológico numa área da Região Bragantina-Pará
(Universidade Federal do Pará, 1979-12-13) FERREIRA, João Batista; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
The following research is about the aplication of geophysical methods in a pilot area in the Bragantina region, NE of Pará, as an auxiliary to geologic mapping. The area is covered with thick tertiary sediments and presents occurrences of industrial rocks such as limestone and granite, representing an outcrop surface smaller than 5% of area. Studies carried out by Goulart (1978) revealed that it is impossible to determine parent rock of the superficial material, of the A horizon. This makes difficult the surface geologic mapping and can lead to exaggerated extrapolation of the contacts, such as that which took place in the preliminary mapping. The geophysical methods applied in the area are: Electroresistivity and Magnetometry. Some mechanical sounding was carried out also. The results obtained contributed to a better understanding of the structural features mapped, and also made it possible to discover other important features. Two areas were defined for future detail study, with the objective to distinguish between the limestones of better and poorer quality. In reference to the granite region a new mapping of that area is suggested.
Acesso aberto (Open Access)
Modelagem de eletrorresistividade 2-D a partir do potencial elétrico secundário
(Universidade Federal do Pará, 2013-02-07) CASTRO, Wagner Ormanes Palheta; SILVA, Marcos Welby Correa; http://lattes.cnpq.br/3213216758254128
One of the traditional methods of exploration geophysics is the Eletrical Resistivity Method, established about a century ago by the Schlumberger Brothers and sincethen widely used in mineral exploration, hydrogeology and environmental studies and research from geothermal sources. The method involves injection of electrical current in the subsurface and measurement of the resultant potential. The locations of sources and receivers will be determined by the arrangement chosen for the survey. After processing, we can obtain pseudo-sections of apparent resistivity that indicates the distribution of the conductivity in subsurface. Due to the simplicity of the physical basis of its formulation, the method presentes easy computational implementation when compared to the other controlled source electromagnetic methods. In literature there are numerous computational modeling jobs, which computes the answer to problems 2D and 3D. In these previous works, the results are obtained from the total electric potential. In this work, we present the modeling of electrical response of 2D media with the dipole-dIpole array, obtained from the secondary electric potential. The solution is calculated using the finite element method with unstructured mesh. To validate our results, we compare them with 2D response obtained fron total potential.
Acesso aberto (Open Access)
Modelagem direta de dados de eletrorresistividade 3-D
(Universidade Federal do Pará, 2014-02-14) CARVALHO, Maria Rosilda Lopes de; SILVA, Marcos Welby Correa; http://lattes.cnpq.br/3213216758254128
The Electrical Resistivity is one of the most traditional method in applied geophysics. Over 80 years its development has been taken beside the advances in numerical modelling and processing. Recently, the three-dimensional modeling and inversion has become part of the workflow of the geophysicists. We present in this work a 3-D finite element technique applied to the resistivity method by using the secondary electric potential. For the development of the methodology, we silulate surveys of the resistivity method with dipole-dipole and Schlumberger arrays, in order to measure the lateral and vertical variations of apparent resistivity. These arrays consist of the injection of electric current in the earth surface and measurement of electrical potential. In this work, the sounding curves and pseudo-sections of apparent resistivity, are obtained through modeling of 3-D resistivity, using regular finite element mesh. For purposes of validation, the results are compared with the responses available in the literature and have been shown satisfactory. We can thus consider it a reliable and robust algorithm.
Acesso aberto (Open Access)
Prospecção de água subterrânea no município de Piçarra-PA usando VLF e resistividade
(Universidade Federal do Pará, 2011) SOUSA, Gilvana Bezerra de; LUIZ, José Gouvêa; http://lattes.cnpq.br/8676530374310847
This research was carried through in Piçarra city, located in the southeast of Pará state. The study had as main focus the mapping of lineaments associated with the basement fractures and the subsoil nature through geophysics, using the Very Low Frequency (VLF) electromagnetic and resistivity methods. The integrated analysis of geophysical data allowed the recognition of two hydrogeological domains in the area: Fractured zones and sediment thickness above the basement rocks, aiming to guide the location of groundwater captation wells. The study provided indications of the most promising locations for groundwater captation and the best sites to build water wells for the city supply.