Heat flow and deep temperatures in the Chaves geothermal system,Northern Portugal |
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| Affiliation: | 1. Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal;2. Laboratoire G-Time, DGES, Université Libre de Bruxelles, ULB, Av. Roosevelt, 50, CP, 160/02, 1050 Brussels, Belgium;3. Instituto Nacional de Meteorologia e Geofísica, Mindelo, Cape Verde;4. School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen''s Road, Bristol BS8 1RJ, UK;5. Lamont-Doherty Earth Observatory at Columbia University, Comer Geochemistry Building, 61 Route 9W, P.O. Box 1000, Palisades, NY 10964-8000, USA;6. Instituto Politécnico de Lisboa, ISEL/ADF, Lisboa, Portugal;7. Institute de Physique du Globe de Paris, France;8. Laboratório Nacional de Energia e Geologia, I.P., 2610-999 Amadora, Portugal;9. Cape Verde;1. Montana Tech, Department of Geophysical Engineering, Butte, MT 59701, United States of America;2. Montana Tech, Department of Geological Engineering, Butte, MT 59701, United States of America;3. Montana Tech, Department of Environmental Engineering, Butte, MT 59701, United States of America;4. Butte-Silver Bow country, Planning Department, Butte, MT 59701, United States of America |
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| Abstract: | The geological, geoelectrical, geochemical and temperature data related to the Chaves geothermal system have been integrated to obtain a better understanding of the Chaves basin. Geoelectrical surveys carried out in the basin reveal a low-resistivity zone (10 ohm m), associated with a shallow geothermal reservoir, in the central part of the graben, bounded by higher-resistivity rocks. The top of this zone varies between 400 and 200 m and its maximum thickness (1600 m) is located at the centre of the basin. Thermal models for the Chaves basin and for the region are presented using the structure obtained by geoelectrical methods and a mean heat flow value of 95 mW m-2 derived from borehole measurements. The heat transfer takes place mainly by conduction, except near the faults, where convective flow is important. The medium is considered dishomogeneous and there is a great thermal conductivity contrast between the sediments in the basin and the surrounding rocks. The results obtained for the Chaves basin show that the mean temperature value in the shallow geothermal reservoir is 62°C. The maximum temperature value predicted to the bottom of this reservoir is 95°C. A regional forced convective-circulation model is suggested based on geomorphological, geochemical, isotopic data and to rmal models. |
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