## 2 Materials and Methods  
### Test Site: The Villafortuna-Trecate Oilfield  
A variety of petroleum systems has been identified in Italy as a result of complex geological and sedimentary history. According to [26], Italian hydrocarbon occurrences can be classified as associated with three main tectono-stratigraphic systems: the carbonate Mesozoic substratum of the foredeep/foreland area and the external thrust belts, thrusted terrigenous Oligo-Miocene foredeep wedges (Southern Alps, Northern Apennines, Calabria and Sicily) and terrigenous Pliocene-Pleistocene successions of the late foredeep basins of the Apennines, in both the Central and Northern Adriatic Sea and the Po Plain.  
In this study, attention is focused on an analysis of the geothermal resources potentially associated with a disused hydrocarbon well named Trecate4, which is located within the Villafortuna-Trecate oilfield (Figure 1).  
The Villafortuna-Trecate system represents one of the largest oil accumulations of the Italian Middle Triassic carbonate petroleum system. It involves dolomitized platform units of Late Triassic-Early Jurassic that were charged by Middle Triassic carbonate source rocks deposited in the confined basins created by rifting. Due to its depth, it can be pursued only in the outer sector of the foredeep and in the foreland regions (the Piedmont area) [27]. The main reservoir associated with the Villafortuna-Trecate field was identified at a depth between 5800 m and 6100 m [28].  
The selection of the proposed case study was guided by the preliminary results presented in [29], which identified the wells located within the Villafortuna-Trecate oilfield as the most suitable to be converted into geothermal ones and also in function of their deep and constructional features. Considering the related thermophysical parameters, the amount of thermal energy that they would allow recovering turned out to be larger in comparison with the wells located in comparable Italian sedimentary contexts.  
Detailed litho-stratigraphic information and temperature data visualisation related to the Trecate4 hydrocarbon well have been found on the Italian National Geothermal Database (BDNG), the largest collection of Italian geothermal data [8]. Moreover, information regarding productive and dismissed oil and gas wells in Italy was also provided by the National Mining Office of the Italian Ministry for Economic Development (MISE) and by the website VIGOR promoted by MISE-DGRME (Direzione Generale Risorse Minerarie ed Energetiche) and the Italian Geological Society and the Ascomineraria Association.  
For properly defining thermophysical parameters, values reported in [31; 32] were used. Notably, in [31], by measuring its value in both dry and wet conditions, the authors investigated and defined the thermal conductivity of 200 rock samples collected from four different regions of Southern Italy (Calabria, Campania, Apulia and Sicily). Moreover, in [32], the framework of the MIUR 2008 project \"Geothermal resources of the Mesozoic basement of the Po Basin: groundwater flow and heat transport\" was utilized in order to accurately estimate the thermophysical properties of a wide variety of sedimentary and intrasedimentary volcanic rocks from the Po Basin.  
As demonstrated by information related to the litho-stratigraphic units reported in Table 1, the stratigraphic succession associated with the Trecate4 well is mainly composed of carbonate platform rocks, with the exception of a surface unit consisting of terrigenous deposits. The analysed well has a maximum depth of 6282 m and bottom-hole temperatures reaching 168 \({}^{\circ}\)C (Figure 2).  
Figure 1: Simplified stratigraphic and geographic location of the Italian petroleum systems (Modified from [30]. Copyright Geological Society of London, 2018).