Abstract
The evaluation of the theoretical geothermal potential of identified unexploited hydrothermal reservoirs within the Vicano–Cimino and Sabatini volcanic districts (Latium region, Italy) has been made on the basis of a revised version of the classical volume method. This method is based on the distribution of the partial pressure of CO2 (pCO2) in shallow and deep aquifers to delimit areas of geothermal interest, according to the hypothesis that zones of high CO2 flux, either from soil degassing and dissolved into aquifers, are spatially related to deep hydrothermal reservoirs. On the whole, 664 fluid discharges (cold waters, thermal waters, and bubbling pools) have been collected from shallow and deep aquifers in the Vicano–Cimino Volcanic District and the Sabatini Volcanic District for chemical and isotopic composition, in an area of approximately 2800 km2. From this large hydro-geochemical dataset the pCO2 values have been computed and then processed to obtain a contour map of its spatial distribution by using geostatistical techniques (kriging). The map of pCO2 has been used to draw up the boundaries of potentially exploitable geothermal systems within the two volcanic districts, corresponding to the areas where endogenous CO2 raise up to the surface from the deep hydrothermal reservoirs. The overall estimated potential productivities and theoretical minimum and maximum thermal power of the two volcanic districts are of about 45 × 103 t/h and 3681–5594 MWt, respectively. This makes the Vicano–Cimino Volcanic District and the Sabatini Volcanic District very suitable for both direct and indirect exploitation of the geothermal resources, in view of the target to reduce electricity generation from conventional and poorly sustainable energy sources.
Highlights
In recent decades, the worldwide demand for energy has increased far beyond a critical threshold, with an associated rise in CO2 emissions being observed
The map of pressure of CO2 (pCO2) has been used to draw up the boundaries of potentially exploitable geothermal systems within the two volcanic districts, corresponding to the areas where endogenous
Based on a large and very detailed geochemical dataset, the aim of this study is to identify potential areas for high-to-low temperature resource exploitation and refine the estimation of the theoretical geothermal potential
Summary
The worldwide demand for energy has increased far beyond a critical threshold, with an associated rise in CO2 emissions being observed. Despite the significant potential highlighted by these preliminary explorations, the geothermal resources of Latium remain so far unexploited The reasons for this failure have mostly been related to the low permeability of the reservoirs [11], resulting in dry and unproductive boreholes for almost half of the deep wells drilled in the whole region, whereas potentially productive wells have regularly suffered the presence of hot brines (up to 350 g/L at Cesano; [5]) and/or corrosive gases (H2 S), so that operations always stopped at the preliminary phases. Notwithstanding these negative attempts, Italy is experiencing a renewed interest in geothermal energy favored by recent technological advances in exploration and exploitation, which have extended the potential of geothermal reservoirs to lower temperatures and greater depths, and encouraged by the growth of energy demand [1]
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