WORKING GROUP 9 
MARCHESINI, PISTOLESI, BOLOGNINI 
527 
energy is assumed to be represented by a cooling body of rocks (batholite or 
one of its apophyses) underlying the region. The main reason for this assump 
tion is the strong thermic positive anomaly observed, shown by near surface 
temperature and by high gradient in drilled wells. Other reasons are repre 
sented by direct surface shows of steam and by a whole series of mineralisations 
reservoir 
Fig. 3. The structural style (schematic) (Courtesy of Larderello S.p.A. Pisa - Italy) 
scattered in the area. Volcanic activity took place in surrounding areas during 
early Quarternary. 
The carrier of the thermic energy to the wells is essentially represented by 
the water, whose efficiency is largely dependent upon the intensity of circula 
tion and, therefore, the value and type of the reservoir permeability. 
The structure plays an important role, even if quite different from the role 
played by structure in oil and gas fields. In the case of steam, the restriction 
imposed by the necessity of closure does not exist, and it is replaced by condi 
tions favoring the access and circulation at depth. Obviously, large positive 
structures may contribute to the raising of the isotherms toward the surface. 
Furthermore, positive structure has a definite economic value in reducing