Spatial and temporal reconstruction of the temperature distribution to assess the water circulation in the Euganean Geothermal Field (NE Italy)

The Euganean Geothermal Field (EGF) represents one of the biggest thermal areas of Europe extending on a plain band of 25 km2 in Veneto region (NE Italy). Approximately 14x106 m3 of water with temperature from 65 to 86\ub0C were exploited in 2014 from fractured layers located in Mesozoic to Oligocene formations. The hydrogeological setting of the 300-600 m deep aqui fer is elucidated through transmissivity and temperature maps, while the 800-1000 m deep aqui fer is less exploited and investigated. The exploitation influences the natural regime of the aqui fers causing seasonal fluctuations of the level related to the variation of the extraction. In 2014 -15, five surveys were conducted to measure the potentiomet ric level and the water temperature in approximately 130 wells (depth up to 1064 m) during periods of high and low exploitation. The data are used to perform temperature maps of both aqui fers outlining the spatial and temporal variations of the temperature. The maps of the shallow aquifer evidence two areas with temperature higher than 84\ub0C and an outward decrease. The higher temperature is comparable with the 100\ub0C reservoir temperature calculated with geothermometers suggesting a quick ascent of deep fluids through open fractures with a small loss of heat, while a longer path causes the decrease. The maps of the deep aquifer show higher temperature than the shallow one, but the few available data do not allow a detailed analysis. Small variations of temperature among the surveys are depicted, but the distributions are slightly comparable. In addition, the temperature collected during 30 vertical thermal logs are examined evidencing a correspondence with the maps, although the logs are performed in inactive wells. Therefore, the correlation of the areal variations depicted with different methods suggests that the geological setting controls the temperature distribution in the EGF. In conclusion, the performed spatial and temporal reconstruction improves the knowledge of the hydrogeological setting of the thermal area providing useful data for the management of such resource