Update Heat Flow Density Map for Portugal

New thermal conductivity, heat production and temperature data obtained in Portugal were used to produce a new heat flow density map. Heat flow density values in Portugal vary between 42 and 115 mW/m2 and allow the extrapolation of temperatures to depths not yet reached by existing boreholes. Additionally, temperature maps at 500 and 1000 m depths and a two-dimensional model constructed along a north-south profile in the area where there is more geothermal information are given

Fault activity studies in the Lower Tagus valley and Lisbon region using geophysical data

he Metropolitan Area of Lisbon and the Lower Tagus Valley (LTV) region are located in central Portugal and inhabited by nearly 4 million people. The region has suffered throughout its history the effect of destructive earthquakes caused by hidden faults, possibly related to the plate boundary, which is sited approximately 400 km south of the region (Figure 1). In spite of low slip-rates and big recurrence times that have been estimated for these local, regional faults, they can produce moderate-to-large earthquakes that cause large damage and loss of life, as in 1344, 1531, or 1909 (e.g. Justo and Salwa, 1998; Cabral et al., 2003; 2013). The shorter occurrence time of the earthquakes might be owing to the existence of multiple active faults and/or time clustering owing to stress drop caused by proximal faults (e.g. Carvalho et al., 2006). Therefore, the seismic hazard and risk evaluation of the region has long been a reason of concern. Geological outcrop and geomorphologic mapping identified several regional faults in the LTV region that could be the source the historical earthquakes, but some of them do not affect. Quaternary sediments and lacked the proofs that they were active faults. On the other side, in the vast quaternary alluvial plains that cover the region, it was difficult to identify active faults, as the sedimentation/erosion rates erase any possible surface rupture caused by the low slip-rate faults (<0,35 mm/y). By the late-20th century, seismic reflection data that had been acquired for the oil-industry till the beginning of the 1980s began to be used to identify the major hidden fault zones (e.g. Cabral et al., 2003; Vilanova and Fonseca, 2004; Carvalho et al., 2006). Potential field data was also used to locate active faults in the areas where no seismic data is available (Carvalho et al., 2008; 2011). Though a few more active faults have been proposed, the vast majority of authors agree that the following active faults threaten the region: Nazaré-Caldas da Rainha, Lower Tagus Valley, Ota, Azambuja, Vila Franca de Xira (VFX), Pinhal Novo and Porto Alto faults (Garcia-Mayordomo et al., 2012; Vilanova et al., 2014). In this work, we discuss the acquisition, processing and interpretation of near surface geophysical works carried out over three of these faults — the VFX, Porto Alto and Azambuja faults — in order to confirm they have had activity during the Holoceneera. Their location is shown in Figure 2. We further estimate some of its fault parameters (vertical displacement, slip-rate, length, etc.) and respective implications in terms of seismic hazard

As águas de Alfama : a riqueza esquecida da cidade de Lisboa

A existência de várias nascentes em Alfama, relatada desde pelo menos os tempos árabes, conheceu vários tipos de utilização ao longo dos séculos, fazendo parte da história da cidade de Lisboa. Esta importância histórica revela-se nos vários aspectos relativos à utilização diversificada das águas, como o abastecimento dos barcos durante a época dos descobrimentos, ou ainda através da dinâmica própria que imprimiam à zona, traduzida pela utilização das águas pelas lavadeiras da cidade. Algumas destas nascentes tinham temperatura de emergência superior a 20ºC e, de acordo com relatos de época, eram possuidoras de virtudes terapêuticas que as fizeram, além disso, ser amplamente procuradas e utilizadas pela população de Lisboa, fundamentalmente de parcos recursos. As águas destas nascentes, entretanto totalmente seladas e abandonadas há mais de 25 anos, chegaram a ser qualificadas de "minero-medicinais" pela então Inspecção de Águas, tendo sido assim aproveitadas em vários "balneários públicos" nos finais do século XIX. Estes "balneários públicos" serviram durante décadas a população de Lisboa e arredores, tendo igualmente sido significativamente influentes na vida da cidade. O aparecimento da Fonte das Ratas, na década de 60 do século XX, contribuiu para manter viva actualmente a memória das águas de Alfama. Este trabalho aborda, de uma forma simplificada, a localização geográfica das nascentes baseada na documentação histórica, bem como as características geológicas e hidrogeológicas da zona e o modo como estas águas foram exploradas durante vários séculos. São igualmente feitas algumas considerações respeitantes a possíveis usos que estas águas poderão ter, a verificar-se manterem na actualidade as características que as tornaram famosas

Heat Flow Density Estimations in the Portuguese Northern Hercynian Massif using Silica Geothermometry

Surface heat flow density (HFD) estimates in the Portuguese northern Hercynian Massif are difficult to obtain using the usual Fourier method. As a matter of fact, this zone is mostly composed by granitoid and metamorphic rocks, and most wells drilled there are too shallow for reliable HFD calculations; furthermore, HFD estimates are scarce and their geographical distribution is still very irregular. All these conditions imply that a HFD map for this region must be obtained using alternative methods, such as the silica geothermometry method. Under certain conditions, the use of silica geothermometers to estimate HFD in mineral waters has proved to be an effective way to understand and establish the thermal regime in areas with scarce conventional HFD determinations. Because temperatures obtained with silica geothermometry are related to deep thermal conditions in the crust and to water-rock equilibrium, a regional HFD analysis may be carried out using those temperatures. The silica geothermometer, developed by Truesdell in 1976 (Truesdell, 1976), give good results for low SiO2 concentrations, which is the case for the Portuguese northern Hercynian Massif, and is applied to more than 30 samples of mineral water occurrences reported for the zone. This number of samples, even though small, is considerably higher and more evenly distributed than conventional HFD estimates for the same area. Application of silica geothermometry to northern Hercynian Massif waters shows a discrete reservoir temperature zoning, ranging from about 45 ºC, in its southwest limit, to more than 120 ºC, towards its northeast limit. Using temperatures obtained by silica geothermometry and heat flow density values calculated through the conventional method in an area of 1º x 1º in the study zone, an empirical linear relationship between HFD and temperatures obtained by silica geothermometry is obtained and used to construct a HFD map for the Portuguese northern Hercynian Massif. The resulting HFD map is compared with the general geological and structural framework, and an attempt to a geothermal characterisation of the Portuguese northern Hercynian Massif is made

As águas de Alfama como património hidrogeológico de Lisboa = Alfama Springs as an hydrogeological heritage of Lisbon

O património hidrogeológico das Águas de Alfama, em Lisboa, é aqui abordado de forma muito sucinta, através do modo como as suas águas foram utilizadas ao longo de vários séculos. Faz-se igualmente uma descrição geológica da zona e uma caracterização hidroquímica muito genérica das águas, baseadas em registos históricos. Por fim perspectivam-se novas utilizações para a água, passíveis de integrar a recuperação urbanística e social deste bairro histórico de Lisboa

Combined study of mineral deposits and deep geothermal for energy production or urban heating – Comparison between the Portuguese (Neves-Corvo) and the Hungarian (Recsk) case studies

Energy and metals are essential resources in the 21st century and with the economic and technical development are more and more required. The fulfilling of these requirements leads to the need to produce both more ore and energy. Considering these goals, the project CHPM2030 (“Combined Heat, Power and Metal extraction”) was launched in January 2016, focused on the characterization of European mining regions that can be linked to both metal extraction and renewable energy production. The aim of this project is to convert ultra-deep metallic mineral formations into an “orebody-enhanced geothermal system” to co-produce energy and metals. This study will focus on two mining areas (Recsk in Hungary and Neves-Corvo in Portugal), considered CHPM2030 case studies, comparing them regarding mineral (ore) and geothermal potential in terms of heat-flow density values and their implication in temperatures in depth estimations. Especially, when it concerns geothermal energy, the surface demand is an important factor to consider, so wider studies are required

Sondagens mecânicas e prospecção geofísica na caracterização de fluidos

Doutoramento em GeociênciasEsta dissertação aborda a utilização de métodos geofísicos de superfície e de profundidade na caracterização de fluidos, compreendendo várias abordagens distintas, consoante o tipo de temática em análise. Assim, o assunto proposto para a presente dissertação relaciona-se com a utilização conjunta de sondagens mecânicas e prospecção geofísica na caracterização de fluidos através da exploração de três temáticas distintas, designadamente a Hidrogeologia, a Geotermia e o Ambiente. O presente trabalho de dissertação baseado na experiência profissional da autora, é feito de acordo com o estabelecimento de uma linha condutora, fundamentada e estruturada, para uma visão global do modo como a interpretação integrada das sondagens mecânicas e dos métodos geofísicos dá um forte contributo para a melhoria do conhecimento de uma região, seja ele geológico, hidrogeológico ou ambiental. Os temas a abordar foram seleccionados não só pela sua indiscutível importância, devido ao interesse estratégico que actualmente suscitam, como também pelos diferentes modos de processar e interpretar a informação geofísica adquirida consoante os objectivos da mesma, de forma a salientar particularidades na respectiva interpretação e integração de dados.This work discusses the use of geophysical methods in the characterization of fluids. It comprises several different approaches, depending on the type of the analyzed thematic. Thus, the issue proposed for this thesis is related with the combined use of geophysical surveys and boreholes to characterize fluids, through the approach of three distinct subjects, namely Hydrogeology, Geothermics and Environment. This dissertation is based on the professional experience of the author and follows a structured conductive line for an overview of how the integrated interpretation of borehole and geophysical methods information gives a strong contribution to improve the geological, hydrogeological or environmental knowledge of a region. The subjects for discussion were selected not only for their unquestionable importance, due to the strategic interest that they currently generate, but also because of the different ways of processing and interpreting geophysical data acquired according to the same objectives, in order to highlight peculiarities in their interpretation and data integration

3D electrical structure definition of aquifer systems in the Kalahari basin in Southern Angola based on legacy data reprocessing

ABSTRACT: The Kalahari-Ohangwena transboundary aquifer system, recently identified in Northern Namibia, comprises 3 major aquifers with very different characteristics. The shallowest is discontinuous and with limited reserves, but it has local importance in water supply for the population, since it is easy to reach, and often presents good hydrochemical quality. An intermediate deeper aquifer is characterized by high salinity while the deepest aquifer, also mostly saline, can present zones with fresh water. However, the latter is located at considerable depths and is shaped by the bottom of the basin basement. There hasn't been a systematic hydrogeological data acquisition for decades in this area of Angola, but legacy electrical resistivity data reprocessing from geophysical surveys conducted >50 years ago in the Cunene Province allowed the construction of a quasi-3D geoelectrical model for the Angolan side of KOH aquifer system in the Cuvelai-Etosha basin. This model is based on 482 vertical electrical soundings carried out in 1966-67, using the Schlumberger array, that contribute to confirming the presence of the Kalahari-Ohangwena aquifer system in Angola. The obtained quasi-3D model highlights the geoelectrical features of hard bedrock and is validated with other hydrogeological and geophysical information. The quasi-3D electrical resistivity data is interpreted using selected boreholes and two time-domain electro-magnetics transects carried out in Namibia, in the 2000s. Although both geophysical data acquisitions were >40 years apart, the results show a very good correlation between the deeper aquifer and the aquitard separating the intermediate aquifer from the deeper aquifer either with the results from Namibia or the borehole data. This is a direct result of the lack of alteration in the hydraulic conditions over these decades, without significant anthropogenic activity and negligible extraction from deep wells. Based on this analysis, the original dataset was considered a reliable source and this quasi-3D model was validated. Furthermore, the model can be considered in the future as an important tool for groundwater resources management, as well as a good starting point for further hydrogeological research in the province of Cunene.info:eu-repo/semantics/publishedVersio