## 1 Introduction  
Energy production using affordable, sustainable and reliable resources has become one of the central topics of European development policy vision while concerns over climate change and energy independence have given increasing importance to the implementation of non-fossil fuels in the national energy mix. Advances in technological capabilities and substantial cost reductions in renewables are needed to facilitate the integration of these energy sources in end-use applications for the scaled transformation of existing energy systems. Of the available environmentally friendly energy resources, geothermal energy can be used directly for heating and cooling buildings as well as to produce electricity. Moreover, depending on the specific geological, hydrogeological and thermo-physical conditions such as temperature, flow rate and geothermal water mineralisation grades, prevailing in an area to be analysed, there are several possibilities for the industrial and economic utilisation of heat energy potentially accumulated. Direct use technologies are currently growing in applications including district heating, space heating with the use of heat pumps, agricultural purposes (e.g., greenhouses), fish farming, milk pasteurization and other purposes. By cascading exploitations of available heat, realising a multi-variant and comprehensive use of the resource is possible according to the corresponding temperature demand [1]. In [2], the authors presented a review of worldwide applications of geothermal energy for direct utilization, updating the previous survey carried out in 2015 and comparing data from the previous versions. The total installed capacity, reported at the end of 2019, for geothermal direct utilization worldwide turns out to be equal to 107,727 MWt, with a percentage increase of 52% over 2015. The total annual energy use is 1,020,887 TJ (283,580 GWh), indicating a 72.3% increase and a compound annual growth rate of about 11.5%. According to the information available in [2], in Italy there are 37 direct-use geothermal sites, 5 of which are for district heating, 5 for individual space heating, 1 was an industrial process site, 6 for fish farming, 4 for greenhouse heating and 16 for swimming and bathing. At the end of 2017, the total installed capacity exceeds 1400 MWh, with a corresponding heat utilization of 10,915 TJ/yr. The main share of geothermal direct use is held by the space heating sector (42% of the total energy, 52% of the overall installed capacity), followed by thermal balneology (32% for both values) and fish farming (18% and 9% respectively). Agricultural applications, industrial processes and other minor uses together account for around 8% of total geothermal use. Despite the great potential for development in Italy, the available geothermal energy resources for direct use are not fully developed, and the national current urban and regional energy paradigms rely heavily on fossil fuels. The share of geothermal heat production in Italy, excluding geothermal heat pumps, in the total thermal production from Renewable Energy Sources (RES) is limited to a percentage of 1.3% [3]. Over time, a variety of hydrocarbon reservoirs has been identified, and Italian sedimentary basins have been explored for both oil and gas extraction purposes. Since 1985, 7246 wells have been drilled for hydrocarbon extraction in Italy, 898 of which are located onshore with varying operational statuses [4]. Additionally, geological and geophysical exploration campaigns into the deepest regions of such geological contexts have ascertained the coexistence of hydrocarbons and low-temperature to medium-temperature geothermal energy resources [5; 6]. Recent investigations have attempted to assess geothermal potentials, exploring deep geothermal resources in different regions and reconstructing heat flow maps at different depths [7; 8; 9]. Since they are stored in subsurface geological formations and associated with hydrocarbons, geothermal resources need to be extracted before use.