| Abstract |
The collection and use of geothermal information to draw a heat flow density (HFD) map and determine the geothermal regime of the crust for mainland Portugal began at the end of the seventies. The data have been collected from all the available scientific publications and internal reports of Portuguese institutions that have been working in the geothermal field. Recent data have also been obtained by the authors to make studies on crustal geothermal modeling and palaeoclimatology. Due to the existence of large granitic regions in northern Portugal, with long faults in several directions, surface heat flow density estimations for that area are difficult to obtain. Furthermore, most of the wells drilled there are shallower than 120 m. However, many of the Portuguese thermal springs are located in that region. On the other hand, intensive mining in southern Portugal has created a large and reliable HFD data set for the region. In most Portuguese sedimentary basins, geothermal data come from deep oil prospecting wells. All the geothermal information collected up to now in mining, water and oil wells that were considered appropriate to calculate surface heat flow density are shown as an updated HFD map of mainland Portugal. It also includes surface HFD values obtained using geothermometry techniques applied to thermal waters with deep circulation. The updated surface HFD map is compared with the Portuguese geological map. Based on those data, a map with different HFD zones is presented. This map could be used for geothermal exploitation purposes at national scale. In general terms the HFD values for mainland Portugal range from 40 mW/m2 to 115 mW/m2, with an average value of about 75 mW/m2. |