| Title | Geothermal Energy Exploitation of Campi Flegrei Using a Deep Borehole Heat Exchanger: the Coupling of the Borehole Model with a SHEMAT Reservoir Model |
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| Authors | Claudio ALIMONTI, Gennaro SEPEDE, Elena SOLDO |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | geothermal energy, deep borehole heat exchanger, reservoir model, SHEMAT, Campi Flegrei |
| Abstract | Campi Flegrei area (Italy) is a caldera that hosts a hot and saline geothermal system with a geothermal gradient in the range 100 ÷170 °C/km. The area is famous since Roman times and between 1930 and 1973 the Italian energy companies carried out some exploration campaigns, demonstrating that fluids with high temperatures are present at relative shallow depths. Unfortunately, the industrial exploitation of the geothermal resources have never take off, because of the low cost of oil price in 80’s, and the lack of interest for renewable energies, but the scientific investigation on the area continued. The interest for the utilization of geothermal energy in the Flegrean area restarted after 2010, but the social concern for the effects of drilling and fluid extraction represents a barrier for the projects development. The possibility to produce geothermal energy without brine extraction, using a deep borehole heat exchanger, may be the key to achieve the social acceptance. The feasibility evaluation of the this closed geothermal plant should include the study of the heat transfer inside the formation and of the temperature decline in the surrounding of the device. This is true especially in the case of Campi Flegrei area, where the geological and hydrological structure of the reservoir produces an advective transport in the first 2 kilometers, which may produce a recovery action with respect to the heat extracted from the ground. In this paper we propose a coupled model of the geothermal reservoir and the deep borehole heat exchanger. The reservoir model has been built using the SHEMAT software, developed by Aachen University. The software is able to simulate the production of brines through wells but not the production of heat via heat exchangers. Therefore the conductive heat transfer in the deep borehole heat exchanger has been simulated using a numerical model based on the Fourier equation. The coupling between the two models has been made with an iterative approach, searching the convergence of the ground temperature in contact with wellbore walls and the wall temperature of the external casing of the borehole heat exchanger. |