Defining the Shallow Geothermal Heat-Exchange Potential for a Lower Fluvial Plain of the Central Apennines: The Metauro Valley (Marche Region, Italy)

Abstract

In this work we assessed the shallow geothermal heat-exchange potential of a fluvial plain of the Central Apennines, the lower Metauro Valley, where about 90,000 people live. Publicly available geognostic drilling data from the Italian Seismic Microzonation studies have been exploited together with hydrogeological and thermophysical properties of the main geological formations of the area. These data have been averaged over the firsts 100 m of subsoil to define the thermal conductivity, the specific heat extraction rates of the ground and to establish the geothermal potential of the area (expressed in MWh y−1). The investigation revealed that the heat-exchange potential is mainly controlled by the bedrock lithotypes and the saturated conditions of the sedimentary infill. A general increase in thermal conductivity, specific heat extraction and geothermal potential have been mapped moving from the coast, where higher sedimentary infill thicknesses have been found, towards the inland where the carbonate bedrock approaches the surface. The geothermal potential of the investigated lower Metauro Valley is mostly between ~9.0 and ~10 MWh y−1 and the average depth to be drilled to supply a standard domestic power demand of 4.0 kW is ~96 m (ranging from 82 to 125 m all over the valley). This investigation emphasizes that the Seismic Microzonation studies represent a huge database to be exploited for the best assessment of the shallow geothermal potential throughout the Italian regions, which can be addressed by the implementation of heating and cooling through vertical closed-loop borehole heat exchanger systems coupled with geothermal heat pumps.

Shallow Geothermal Potential of the Sant’Eufemia Plain (South Italy) for Heating and Cooling Systems: An Effective Renewable Solution in a Climate-Changing Society

“…The main aims are to map the variability and areal distribution of the ground heat-exchange potential throughout the study area, provide tools that might guide new investments in this air conditioning system and define the economic conditions and environmental benefits of exploiting such potential, reducing the CO 2 emissions at the local level. Our results highlight the medium-high shallow geothermal potential of the studied area compared to other similar studies in Italy and Europe [12,15,[24][25][26], suggesting that these systems might play a key role in the green energy transition of the Calabria region.…”

“…Considering that the first 100 m of the subsoil is usually interested in thermal exchanges using vertical closed-loop BHEs [9,15,24,55,56], each borehole was virtually extended, considering homogenous lithostratigraphic features or shortened up to this depth. This depth was also selected to elaborate the geothermal thematic maps.…”

“…The lithological information of each borehole was inserted into the database. The lithological units were classified following the modified "Unified Soil Classification System" [57], also used for the Italian Seismic Microzonation studies [58], and according to work [24]. This classification, which distinguishes 16 types of soil [58], is based on the dominant lithology and the hydraulic conditions and was simplified by subdividing soil units into gravel, sand and silt/clay in dry or wet conditions.…”

“…This empirical method permits the definition of the mean thermal load that can be extracted or injected in the subsoil, characterised by specific conditions during the year, avoiding major variations of the heat transfer fluid during the operational life of the geothermal system. This method, which is essentially based on the temperature difference between the ground and the heat carrier fluid, has been widely used in several studies [24,26,55,56,67,68] and relies on different variables. These latter are linked to the thermal properties of the ground (i.e., λ, SVC and undisturbed ground temperature) and of the borehole (depth, radius, thermal resistance), and the operational and design parameters of the low-temperature geothermal plant (minimum or maximum temperature reached by the fluid, clime, operational life).…”

A Review of Groundwater Heat Pump Systems in the Italian Framework: Technological Potential and Environmental Limits

“…Ref. [33] proposed a study of the geological, hydrogeological, and thermophysical properties of the subsoil in the lower Metauro sedimentary valley to highlight the area's thermal exchange potential; the study was carried out using only publicly available data. Four main zones were identified based on geothermal potential, which is mainly controlled by the bedrock lithotype and the saturated conditions of the sedimentary infill.…”