In Milos island, Cyclades Greece, geothermal exploration includes geological
mapping, mapping thermal manifestations, mapping temperature gradients by
temperature measurements within shallow wells, DC-Schlumberger resistivity
soundings, geochemical surveys, gravity mapping, SP and magnetic surveys, MT and
AAMT soundings, and drilling of the 5 deep wells. The geology of the island
includes from top to bottom lavas, alluvia deposits, volcanic products (tuffs,
hydrothermally altered tuffs, lahars and breccias), neogene sediments and the
metamorphic basement (schists). The gravity survey indicated that the top of the
basement is located deeper at depths 600-800m around the bay of Milos. The thermal
manifestations, as well as geochemical and passive microseismic surveys indicate
the presence of an active deep hydrothermal system beneath the east and the south-
central-east parts of the island. Geothermal gradients and earlier DC soundings
pointed at Zefyria plain, the south-central-east part of Milos and Adamas as the
most promising areas for production drilling, area which was further broadened by
MT and AAMT soundings. Passive seismic surveys indicated that the hydrothermal
system extends down to 5km through a system of active faults and fracture zones.
The magnetic survey, hydrothermal alterations and some geochemical data indicate
that the west part of the island is also of geothermal interest, but no deep wells
have been drilled there yet. Drilling with many shallow and five deep wells proved
the existence of the following three main types of fluids for geothermal
exploration: (a) low enthalpy (up to 100°C) shallow water table in areas of high
temperature gradient, (b) 100-250°C water within the neogene sediments in places
where it is present at sufficient depth and has enough thickness, and (c) high
enthalpy pressurized water of 300-325°C temperature within the faults and fracture
zones of the basement at depths between 1-5 km.
|