Prospective Medium Enthalpy Geothermal Resources in Sedimentary Basins of Northern Greece

Abstract

In Northern Greece there is a large number of low enthalpy geothermal fields with water temperatures of 30-100oC. These fields are located at very shallow depths (30-500 m) in the post-orogenic basins of the area (e.g. basins of Strymon, Nestos Delta, Xanthi-Komotini, Evros) and in the island of Samothrace. The geological and tectonic conditions are favorable for the presence of medium enthalpy (T=100-150oC) geothermal fields at greater but exploitable depths (up to 2000 m) not excluding the high enthalpy ones. For example, the temperature of 122oC was determined at depth of 1377 m in a geothermal exploration borehole in the Nestos Delta basin. The active and extensional tectonics, the crustal thinning and the magmatic intrusions (Tertiary plutonic and volcanic rocks) increase the regional heat flow and they are responsible for the positive geothermal anomaly in many places of the basins. The significant thickness of the Tertiary and Quaternary sediments (permeable strata alternating with impermeable ones) creates some interesting and exploitable supplementary uppermost reservoirs. Sometimes the large and open faults, which affect the metamorphosed basement, create horsts covered by the overlying sedimentary sequences. The tectonically fractured metamorphic substratum often made up of carbonate rocks (Mesozoic- Paleozoic limestones and marbles) permits the formation of important deep pressure reservoirs with very good permeability. The medium enthalpy geothermal fluids can be used for power generation by the utilization of the binary (Rankine or Kalina) cycle systems with good financial results due to the expected high temperatures of the fluids and the important flow rates. The increased need for electric energy in Northeastern Greece and the legally fixed price per KWhe make this enterprise attractive.