526 
SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
ing carried out so far indicates that the present boundaries are not final, and 
that some of the minor centers may connect with each other. 
The producing beds are exploited by wells at depths between 220 m and 
1000 m. These wells are drilled with techniques closely related with those of 
oil exploration. 
Approximately 175 wells are producing, out of a total of approximately 240 
wells drilled. The main reservoir is represented by Triassic dolomitic lime 
stone (fig. 2), highly brecciated, pertaining to an extensive evaporitic forma 
tion. It has undergone, at places, intense fracturing and solution processes. 
It overlies directly an impervious group of metamorphic schists and quartz 
ites (basement). Additional reservoirs are occasionally afforded by other 
carbonate rocks of the 600 m thick (average) Liassic to Lower Cretaceous 
sequence, when intensely fractured. This last group of beds may, or may not, 
at different places, be present between the Triassic evaporitic formation and 
the overlying cap-rock. 
The cap-rock is afforded by shaly sediments, often in chaotic setting, which 
include various formational elements, ranging in age from Cretaceous to 
Eocene. 
The temperature, measured from steam at the well-head on first eruption, 
varies between +130° and +230° centigrades. The source of the thermic 
1*48’ 1*18' 
Fig. 2. Geological map (schematic): Q = Quaternary (elastics); Tp — sandstone; Tm = 
conglomerates, shale, marl; To = sandstone; MeTe = Eocene to Upper Cretaceous shale, 
sandstone, limestone in chaotic setting (cap rock); Mj = Jurassic-Cretaceous limestone 
(occasional reservoir); T = dolomitic limestone, evaporites (main reservoir); PT = meta- 
morphics; eo = ophiolites; H = major mineralisations (metals); /\ steam outerop; f\ = 
steam producing area.