3D geological, thermo-physical and rheological modelling for geothermal exploration: the case study of Ischia Island, Southern Italy

In the frame of the "Geothermal Atlas for Southern Italy" Project, a detailed 3D geological, thermal and rheological model of Ischia Island was built by integrating geological, geophysical and geochemical data. A critical review of publicly available data allowed us to organize a complete dataset in Petrel (Schlumberger) environment for the 3D geological modelling. The geological maps, well data and several geophysical data were used to constrain the shallow region of the model from the youngest deposits to the tuff rocks of the St. Nicola Synthem and the deposits of Ancient Ischia (for detail on stratigraphy see, Ispra web site 2015). Seismic data were used to constrain the deeper level of the Ischia Island up to the Meso-Cenozoic Carbonate rocks (Finetti & Morelli, 1974). Moreover, in order to implement the thermal and rheological analysis, we modeled the deeper surfaces of crystalline basement and Mohorovi?i? discontinuity based on previous studies in literature. In the second step, we performed a 3D numerical modelling of thermal field by using the a priori geological and geophysical information and by consideration of thermo-hydraulic properties including internal heat production and mechanical heterogeneities of the crust beneath the volcanic island. We solved, in a numerical context, the heat and fluid transport equation in a conductive/convective steady-state regime. We simulated the effects on the thermal field of a laccolith intrusion at shallow level in the crust (Paoletti et al., 2009). Subsequently, a parameters optimization procedure was applied to minimize the difference between the computed and measured temperature data. Finally, the thermal model was used as a priori information to image the 3D rheological stratification of the shallow crust beneath the volcanic Island of Ischia in order to understand the mechanical behavior of the crust in this area. As result of our study, we proposed the 3D geometry of the Brittle/Ductile transition, calculated numerically, for the active volcano of Ischia Island. The thermal field in the geothermal reservoir has also been figured out.