Hydrothermal Alteration and Fluid Inclusion Studies in the Vulcano Geothermal Wells (Italy)

Abstract

the Aeolian Archipelago in the Tyrrhenian Sea, north of Sicily (Fig. "La Fossa" is the active crater on the island. Deep geothermal exploratory drilling commenced in the "La Fossa" caldera in the after the encouraging shallow exploratory well drilled in the 50s Sommaruga, 1984). Well was a producing well, located on the northern part of the caldera. The maximum temperature encountered in this well is about 200?C at a depth of 200 m. The two deep wells were drilled on the northern (VP-I) and southern (IV-1) parts of the "La Fossa" caldera and reached maximum depths of 1000 m and 2050 m respectively. Directional drilling was also performed in both wells. The maximum temperatures encountered are about in VP-1 and in IV-1. It is interesting to note that the down-hole measured temperature in well VP-1 cannot be taken as representative of stable subsurface thermal conditions, since temperatures were recorded shortly before and after an injection test (AGIP 1987). No exploitable fluids were found during drilling. Numerous studies of the compositions of gases from the fumaroles (Carapezza et al., 1981; Mazor et al., 1988; Martini, 1989) and studies of stable isotopes of volcanic rocks and fumarole fluids (Cortecci et. al, 1993) in the "La Fossa" area suggest that the hydrothermal fluids result from both magmatic fluid and sea water. The object of the present study is: (a) to unravel the water-rock interaction processes; (b) to gain information on the nature and origin of fluids that circulated through the rocks; and (c) to determine the thermal history of the system.