Analysis of deep carbonate platform for the identification of geothermal potential structures in the Valle Latina (Internal Central Apennine)

Geothermal energy is a significant resource, and effectively harnessing it requires identifying deep geothermal systems, which include the heat source, reservoir, and transport medium—typically water in its various phases, depending on temperature and pressure. Italy possesses favorable geological conditions for the exploitation of geothermal energy, a process that dates back to the early 1900s. Regions along the central Apennines, particularly the Tuscany district and the overall Tyrrhenian and peri-Tyrrhenian coasts, exhibit high heat flux and geothermal gradients. These areas are home to several potential reservoirs, creating suitable conditions for geothermal energy stored within the carbonate platform structures that lie beneath the surface. This work focuses on the geothermal potential of the southern Latium region, that has been relatively underexplored in the past for the geothermal energy. In recent decades, studies have focused on defining the buried carbonate structures and their structural trends, particularly in the Valle Latina area to characterise potential reservoir, having a main secondary porosity due to their extensive network of fractures. The Valle Latina is a significant geological depression located in central Italy, nestled between the Monti Ernici to the east and the Monti Lepini to the west. It is part of the central Apennine range and is characterized by a combination of sedimentary, volcanic, and tectonic processes. The target of this project is: i) to describe the structural model of the deep carbonate platform reservoir in the Valle Latina by reconstructing its 3D geological model and; ii) to assess its geothermal potential. These objectives were pursued using subsurface data provided by the Videpi project of the previous Ministry of Economic Development (today MASE, Ministry of Environment and Energy Security), the published data on hydrocarbon fields, and the temperature at depth estimated from the Italian National Geothermal Database and especially confidential subsurface geophysical data made available by two oil and gas companies. A dataset of one hundred 2D seismic profiles was interpreted and integrated with the publicly available isochrone maps across the Valle Latina to define the main structural picture at a regional scale. 2D seismic interpretation, depth conversion and the construction of geological cross-sections were performed with the software Kingdom (S&P Global). 3D modeling was completed using both Kingdom, and Surfer (Golden Software). The top of a Miocene-Cretaceous carbonate platform was identified as the main regional seismic reflector, a key element for interpreting the carbonate reservoir. The outcomes suggest a possible hybrid tectonic style for the Valle Latina, indicating a transition from the dominant thrust tectonics (active for most of the structuring of the orogen) to an extensional deformation (limited to the last 3-2Ma). During the Tortonian period, pelagic deposits were compressed and pushed on top of a carbonate platform domain (Frosinone Formation). Subsurface data revealed multiple stacked thrust sheets inside the flysch deposits initially involved in a sequence of forward movement towards the east-northeast, synchronous with the late Tortonian foredeep to wedge-top sedimentation. From the Pliocene to the present, the area has been uplifted and subsequently deformed by normal faults that cut across the accretionary wedge. The current study employs a multidisciplinary approach to assess the selected area's geothermal potential by defining the carbonate reservoir's structural setting and its temperature at depth. Some of the most promising carbonate structures have been selected, and the volume method has been applied to assess their geothermal potential. Then, a probabilistic approach has been adopted for the prospect with the most interesting evaluation to obtain not a single value but a distribution of values of the technical potential. The results show that one of the chosen structures has a significant amount of heat available, both for low- to mid-enthalpy and for high-enthalpy. It's important to assess the production capabilities of other structures and the surrounding areas to better understand how the existing wasted heat can be utilized.