The aim of the project is to investigate the possibility of expanding electricity production from medium and low enthalpy geothermal sources, identifying the most suitable geological areas and using binary cycle production plants.
The research focused on purely geological problems, the development of refined modeling analyses to verify the sustainability of the exploitation of the geothermal resource over time, the study of seismicity and the use of binary systems of the OCR – Organic Rankine Cycle type. These systems allow the exploitation of geothermal fluids at lower temperatures than those of high enthalpy.
To achieve the objectives, the geological studies focused on two potential geothermal systems in central Italy, where the reservoir is located in the Mesozoic limestones of the Tuscany series. The analysis of the geological data, together with the borehole data, allowed the creation of fairly refined 3D geological models. For the Torre Alfina-Castel Giorgio geothermal field, located in northern Lazio on the border with Umbria, fluid-dynamic simulations were carried out, which allowed the generation of the undisturbed natural system of the field and the convective circulation of the fluids, with excellent feedback between the calculated temperature and pressure parameters and those measured experimentally in the borehole.
Various scenarios were then developed to simulate the extraction of fluids and their total reinjection from multiple boreholes with a total flow rate of 1050 t/h, reasonably compared to a binary plant with a nominal power of 5 MWe and the temperature of the geothermal resource (~140-150°C). The simulations carried out show the sustainability of electricity production for a period of 50 years, with modest overpressure values in the geothermal reservoir, which remain within 3.3% of the pre-existing value.
The second geothermal field studied is located in the Lucignano area in Tuscany and has higher temperature values (~180°C) than the Torre Alfina – Castel Giorgio field. An accurate 3D geological model has been developed.
The above numerical simulations were carried out using the GeoSIAM v.1.1 modeling suite, which is specifically designed for geothermal energy and allows fluid dynamic, geomechanical and geochemical simulations.
With regard to seismicity, the results of the ICHESE Commission – International Commission on Hydrocarbon Exploration and Seismicity in Emilia Romagna – and subsequent in-depth studies, which studied the influence of human activities on the devastating earthquakes that struck the Emilia Romagna region in May 2012, were accurately analyzed. The analyses carried out excluded any cause-effect relationship between the seismic phenomenology and the Casaglia geothermal field and the Cavone hydrocarbon field.
From a plant engineering point of view, the state of the art of ORC cycles was evaluated, which, thanks to special working fluids, are able to exploit significantly lower temperatures compared to traditional water-steam cycles. These systems are a reliable technology already used in various sectors, such as biomass and heat recovery, but must be adapted to the specific characteristics of each geothermal system in order to optimize its performance. Activities focused on applications with medium enthalpy geothermal sources and temperatures in the order of 120-180°C, in line with the two geothermal sites analyzed.