Geothermal gradient and heat flow in the state of Rio de Janeiro

Abstract

ABSTRACT.Results of geothermal studies carried out at 72 localities have been used in evaluation of temperature gradient and heat flow values of the upper crust in the state of Rio de Janeiro. The investigations included temperature logs in boreholes and wells, calculation of geothermal gradients, measurements of thermal conductivity and determination of heat flow density. In addition, estimates of temperature gradients and heat flow were also made for areas of thermo-mineral springs, based on the so-called geochemical methods. Analysis of these data sets, after incorporation of appropriate corrections (for the perturbing effects of drilling operations, topography and climate changes) has allowed for the first time a better understanding of the regional distribution of thermal gradients and heat flow within the study area. RESUMO.Resultados de estudos geotérmicos efetuados em 72 localidades foram utilizados na avaliação de gradientes de temperatura e o fluxo geotérmico da crosta superior no Estado do Rio de Janeiro. As investigações incluíram a realização de perfilagens térmicas em furos e poços, determinação dos gradientes térmicos, medições de condutividades térmicas e estimativas da densidade do fluxo geotérmico. Como complementos, também foram estimados gradientes e fluxo geotérmico dasáreas de ocorrências de fontes termo-minerais, utilizando métodos geoquímicos. Análises desses dados após a incorporação das correções apropriadas (efeitos de perfuração, topografia e variações climáticas recentes) tornaram possível pela primeira vez um melhor entendimento da distribuição regional de gradientes térmicos e do fluxo de calor naárea de estudo. Os resultados obtidos indicam que os gradientes térmicos variam entre 14 e 26 • C/km nas regiões metamórficas Pré-Cambrianas e de 19 a 33 • C/km nasáreas de bacias sedimentares Fanerozóicas. Muitas das formações rochosas apresentaram condutividade térmica compreendida entre 2,2 e 3,6 Wm -1 K -1 . Conseqüentemente, os valores médios encontrados para o fluxo geotérmico regional situam-se no intervalo de 40 a 70 mW/m 2 . Mapas de contorno, preparado a fim de examinar as variações regionais, revelam que o gradiente e o fluxo térmico são sistematicamente mais elevados na parte oeste daárea de estudo, em comparação com aquelas encontradas na parte leste. Existem indicações de que a anomalia geotérmica na parte oeste está provavelmente associada com a faixa das intrusivas alcalinas Terciárias situadas entre a região de Itatiaia e Cabo Frio. O calor residual das intrusões magmático do período Terciário superior configura-se como um dos possíveis mecanismos responsáveis por esta anomalia térmica.

Evaluation of geothermal gradient and heat flow distribution in Delta State, Nigeria

“…The study shows that the geothermal gradient for the area ranges from 25.47 to 31.16 0 C/km. These values fall within the range interval typical of the gradients commonly encountered in tectonically inactive areas [9]. This result conforms to earlier work carried out in the Niger Delta area by Akpabio and Ejedawe [6] which shows that the thermal gradient ranges from 26.2 to 29.5 0 C/km.…”

“…In this study, the measured temperature was plotted against the corresponding depth interval for all the wells and a linear least square fitted to the set of data [9,12]. The gradient of the fitting corresponds to the geothermal gradient.…”

“…Four different methods are employed in determining thermal gradients, depending on the characteristics of primary data. These are designated as the conventional (CVL), conventional bottom temperature (CBT), aquifer temperature (AQT) and geochemical (GCL) methods [9]. Temperature distribution is one of the major factors controlling hydrocarbon generation, sediment digenesis and migration of hydrocarbons including other pore fluids [10].…”

Climate Changes of the Recent Past in the South American Continent: Inferences Based on Analysis of Borehole Temperature Profiles

“…The details of the experimental techniques employed for temperature and thermal conductivity measurements have been discussed in academic theses (e.g. Vitorello, 1978;Araújo, 1978; and in publications dealing with heat flow measurements (Hamza et al, 1987;Hamza and Muñoz, 1996;Gomes and Hamza, 2005). A direct evaluation of the quality of data acquired in the earlier works is a difficult task since the experimental techniques used for temperature and thermal conductivity measurements have undergone substantial changes over the last few decades.…”

“…The sources of conventional data sets employed in the present work may be considered as falling into five main groups: -New data acquired in ten different localities in the Amazon region, during the period of 2006 to 2008 (Hamza, 2006;Hamza, 2007); -Results of recent geothermal measurements in the cordilleran region of Colombia Alfaro et al, 2009). -Data acquired during the period of 2000 -2005, as part of geothermal projects for mapping heat flow variations in the coastal area of southeast Brazil (Gomes, 2003;Gomes and Hamza, 2005;Hamza et al, 2005). Some of these have been employed in studies of climate change the state of Rio de Janeiro Hamza et al, 2003); -Data acquired during the decade of 1980, mainly in the state of São Paulo, as parts of hydrocarbon and geothermal energy exploration programs.…”