Application of the Revised Volume Method for the Evaluation of the Geothermal Potential in the Vicano-Cimino Hydrothermal Reservoir (Central Italy)

Abstract

The revised Volume Method is used here to evaluate the geothermal potential of the practically exploited Vicano-Cimino hydrothermal reservoir. This method is based on the distribution of pCO2 (partial pressure of CO2) in shallow and deep-originated waters to define areas of geothermal interest, according to the hypothesis that anomalous degassing zones of endogenous CO2, from either soil degassing and spring and well waters, are spatially related to deep fluids raising up from underlying hydrothermal reservoirs. On the whole, 333 fluid discharges (cold waters, thermal waters and bubbling pools) were collected within the Vicano-Cimino Volcanic District (VCVD) for chemical and isotopic compositions, in an area of approximately 1,400 km2. From this large hydro-geochemical dataset the pCO2 values were computed and then processed to obtain a map of its distribution by using geostatistical techniques (kriging). The resulting thematic map was then used to draw up the boundaries of high pCO2 areas within the VCVD, potentially corresponding to the exploitable sectors of the deep hydrothermal reservoir. The estimated potential productivity and the total extractable thermal power of the VCVD are approximately of 10×103 t/h and 517-979 MW, respectively. This makes the VCVD suitable both for direct and indirect exploitation of the geothermal resources, in view of the target to reduce electricity generation from conventional and poorly sustainable energy sources.