The Castel Giorgio-Torre Alfina (CG-TA, central Italy) is a geothermal
reservoir whose fluids are hosted in a carbonate formation at temperatures
ranging between 120°C and 210°C. Data from deep wells suggest the existence of
convective flow. We present the 3D numerical model of the CG-TA to simulate
the undisturbed natural geothermal field and investigate the impacts of the
exploitation process. The open source finite-element code OpenGeoSys is
applied to solve the coupled systems of partial differential equations. The
commercial software FEFLOW® is also used as additional numerical constraint.
Calculated pressure and temperature have been calibrated against data from
geothermal wells. The flow field displays multicellular convective patterns
that cover the entire geothermal reservoir. The resulting thermal plumes
protrude vertically over 3 km at Darcy velocity of about m/s. The analysis of
the exploitation process demonstrated the sustainability of a geothermal
doublet for the development of a 5 MW pilot plant. The buoyant circulation
within the geothermal system allows the reservoir to sustain a 50-year
production at a flow rate of 1050 t/h. The distance of 2 km, between the
production and reinjection wells, is sufficient to prevent any thermal
breakthrough within the estimated operational lifetime. OGS and FELFOW results
are qualitatively very similar with differences in peak velocities and
temperatures. The case study provides valuable guidelines for future
exploitation of the CG-TA deep geothermal reservoir
