Shallow geothermal properties maps of the Italian underground soil: a lithological approach

The shallow geothermal resources are used worldwide to produce thermal energy in support of the decarbonization process. To fully exploit geothermal resources on a national scale, appropriate tools need to be developed, such as mapping of ground thermal properties, which enables identification of the shallow geothermal potential of large areas. Using the ISPRA (Italian Institute for Environmental Protection and Research) public database, we classified more than 28000 Italian perforation sites resulting from hydrological research studies, surveys, or civil engineering works. The ISPRA database provides generic and non-uniform lithological descriptions for each site. The lithological descriptions have been harmonized to obtain 28 classes that summarize the lithological variation in Italian shallow underground soils. Geological maps, additional well data, and further geological information have been used to interpret those lithological descriptions that were unclear or not fully-explained. Based on the lithological classification, we estimated the vertical trend of thermal conductivity within the perforation sites and the related geothermal potential concerning closed-loop geothermal probes. The obtained trends have been used to compute the mean thermal conductivity of the subsurface at shallow depth and the mean geothermal potential. We finally produced online-available national-scale maps that can be used to highlight the shallow geothermal potential of specific regions and to identify areas in the Italian territory that might be suitable for low enthalpy geothermal purposes.