Fractured Geothermal Reservoirs: the Cases of Chile and Italy

Chile and Italy have a great geothermal potential since they are respectively located along the Andean volcanic arc and belong to the volcanic districts spreading the Tyrrhenian border. In both geological context an aspect that should not be neglected is the structural control role which modifies the properties of rocks, fluid flow and the general functioning of the system. Understanding the redistribution of heat and geochemistry due to hydrogeological processes can help to better assess the role played by faults and structures on the aquifers and geothermal systems.

A proper conceptual model for analyzing fractured reservoirs is a crucial step for any kind of modeling exercise, since fracturation greatly affects rock permeability and this is strongly scale dependent. Two different geological settings- Pocuro Fault Zone (Central Chile) and Ischia island (South Italy)- are been modeled using data from previous projects and new ones collected during 2017 at both areas.

We use Reactive Transport Model (RTM) using data to assess thermal water geochemical behavior at both site considering the local geology and hydrogeochemical data.

Results indicate that the Pocuro Fault Zone controlled the past fluid flow migration and permeability of a geothermal field were fluid flow temperature reached more than 230ºC as indicated by mineral association (waikerite, clorithe) observed. Modern thermal water with low salinity and temperature between 25ºC and 30ºC are not able to reproduce the observed mineralogy. Different scenario were implemented and it is necessary to improve pressure to reproduce the outcropping mineralogy. While at Ischia island, thermal ground and fresh water have been collected after 2017 Casamicciola earthquake to assess the RTM.