## 4 Conclusions  
Over time, the petroleum systems in Italian sedimentary basins have been explored for oil and gas extraction. Since 1985, 7246 wells have been drilled for hydrocarbon extraction. Of these, 898 wells are located onshore with various operational statuses. Geological and geophysical exploration campaigns have ascertained the coexistence of low- to medium-temperature geothermal energy resources in the deepest regions of such geological contexts. As such, energy production based on the exploitation of available low- to medium-temperature geothermal resources associated with disused deep oil and gas wells in Italian oilfields could represent a considerable source of renewable energy.  
This study used information on Italian hydrocarbon wells and on-field temperatures to apply a simplified coaxial WBHE model to three hydrocarbon wells. The main purpose was to analyse heat exchange mechanisms in three different Italian oil and gas fields (the Villafortuna-Trecate, Val d'Agri and Gela fields), emphasizing differences in the quantity of extracted thermal energy and considering different geological and depositional contexts.  
All calculations considered the detailed stratigraphic data and related thermophysical parameters (e.g., thermal conductivity, volumetric heat capacity and rock density) of each case study. The results indicate a substantial difference in the potential amount of extracted thermal energy between analysed sites, located in different Italian sedimentary contexts. With a fixed inlet working fluid flow rate of 3 kg/s and a fixed temperature of 50 \({}^{\circ}\)C, thermal power values were evaluated at 627.9 KW for Villafortuna 1, 75.3 KW for the Tempa Rossa 1D well and 100.5 KW for the Gela 38 hydrocarbon well. The Villafortuna 1 WBHE recorded a maximum extracted fluid temperature of 100 \({}^{\circ}\)C, which allows us to hypothesize a cascading exploitation mode of the heat accumulated. Unlike Villafortuna 1, Tempa Rossa and Gela fields had thermal load values that would be of no practical use. As such, the implementation of a coaxial borehole heat exchanger in a such hydrocarbon well may not be energetically or economically worthwhile.  
Improving the accuracy of the proposed models by means of future analysis is required: the basic assumption related to the constancy of the properties of the water as working fluid must be overcome by properly analysing the possibility of having phase change (evaporation) in the well, which would change the proposed models. The role in heat transfer and performance of extracting heat from abandoned wells of intraformational flows also needs to be properly considered.  
Despite the above considerations, the analysis approach with the associated simplified model proposed in this paper could represent a useful simplified methodological tool to allow the preliminary definition of the possibility of a selected Italian hydrocarbon well to be converted into a geothermal one by means of a coaxial-WBHE technology.  
After a preliminary analysis about the presence of industries and agricultural districts, it will be useful to produce a detailed evaluation of the industrial plants available in the area near the Villafortuna 1 well: a technical feasibility and cost-benefit analysis of the selected configuration in this proposed case study could represent the subject of future research work.  
All the authors conceived the research work aim; all the authors contributed in finding materials and analysis tools. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Information related to Italian hydrocarbon wells and temperature data are available at the web page of the National Mining Office of the Italian Ministry for Economic Development (MISE) and the Italian National Geothermal Database.  
The authors declare no conflict of interest.