Updated Geothermal Assessment of Lower Cretaceous Aquifer in Lisbon Region, Portugal

The region of Lisbon is an urban area with the highest population density and energy demand in Portugal. It also presents very favorable geological environments for geothermal purposes. The historical and/or current existence of warm springs and deep sedimentary aquifers in Cretaceous and Jurassic formations, identified by hydrocarbon exploration surveys since the mid-fifties, as well as geothermal gradient and heat flux density studies, suggest a considerable geothermal potential (50oC at 1500 m depth). This study presents an updated geothermal potential assessment of the Lower Cretaceous formations in the Lisbon region, based on the volumetric deterministic method and definitions formulated by Muffler and Cataldi (1978). Accurate data for this geothermal assessment have been obtained through multidisciplinary approaches, involving geology, hydrogeology, temperature and water flow measurements from groundwater wells and other boreholes, integrating new information from recent geophysical studies providing essential geological information on the structure and geometry (delineating isobaths and isopachs and possible boundaries) of the sedimentary sequence. The results identified the eastern sector of the city of Lisbon and the south bank of the Tagus River as the most promising areas for geothermal purposes (direct uses of heat or even electricity production). A geothermal potential (Heat in Place) of 3.8 GJ/m 2 , higher than the previously estimated 1.7 GJ/m 2 for the same reservoir in the Atlas of Geothermal Resources in Europe (Hunter and Haenel, 2002) has been obtained, highlighting the capabilities of the Lower Cretaceous formations for future geothermal