Application of selected geothermometers to exploration of low-enthalpy thermal water: the Sudetic Geothermal Region in Poland

The most important intakes of thermal waters within the Sudetic Geothermal Region occur in three separate hydrogeothermal systems: (1) Lądek, (2) Duszniki and (3) Cieplice. All these waters are of meteoric origin and circulate in crystalline rocks to different depths. Their outflow temperatures are between less than 20°C and to about 87°C. To evaluate the geothermal fields in the light of their prospectiveness, to further exploration of thermal energy resources, we took an effort to apply selected isotopic and chemical geothermometers to assess the maximum possible temperatures, which may be found in the reservoirs. The only chemical geothermometers which give a reliable range of reservoir temperatures are SiO₂ (chalcedony), Na–Ka–Ca and partly Na–K ones. The oxygen isotopic geothermometer in the SO₄–H₂O system gives a real range of estimated reservoir temperatures only for deeply circulating waters in the Cieplice area. On the other hand, in the case of CO₂ rich waters in the Duszniki area, where outflow temperatures do not exceed 30°C, application of chemical or isotopic temperature indicators always leads to erroneous results due to the lack of equilibrium in the thermodynamic system of water–rock interaction.