Geothermal
sites distribution and installed capacity by administrative regions (1998)
The
country is rich in low enthalpy geothermal energy. Conductive heat flow data vary
within the interval 30-80 mW/m2, while in the hydrothermal zones it reaches 140
mW/m2 (Sofia depression) and 200 mW/m2 in the Erma reka region (Petrov and Bojadgieva,1993).
The geological structure of Northern and Southern Bulgaria
is variegated and contrasting. The hydrothermal systems were formed mainly during
the Alpine tectonic activity in the Balkan region. Natural thermal springs are
not found in the region of Northern Bulgaria. Two artesian basins are located
in it - the Moesian and Varna basin. Thermal water was discovered only in deep
wells.
The southern part of the country has abundant springs which provide
drainage of nonstratified mountain systems. The springs are developed mainly in
granite and granitoid intrusions and ancient siliceous and metamorphic complexes.
The
hydrothermal data comes from prospecting carried out in hundreds of exploratory
and production wells, springs, ore pits and tunnels. In the ex-socialist countries,
geological exploration had extensive budgets enabling the identification of geothermal
reservoirs, proven by wells. The depth of the hydrothermal exploratory wells ranges
from 100 to 5000 m in Northern Bulgaria and from 100 to 1500 m in Southern Bulgaria.
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