Multicomponent solute geothermometry of balneologic thermal waters by help of PHREEQC | Geothermometrische Modellierung der Lagerstättentemperatur balneologisch genutzter Thermalwässer mit Hilfe von PHREEQC
2019
Kersten, Michael
Modeling of the reservoir temperature of thermal waters is possible with hydrogeochemical speciation model software. However, certain conditions have to be met, if using PHREEQC for such an integrated multicomponent solute geothermometry approach. Above all, the formation water has to have preserved its chemistry during its ascent which would thus represent the original thermodynamic equilibrium with its mineral paragenesis at the reservoir depth. For carbonate minerals, the thermodynamic database should be critically evaluated and must contain five-parameter polynomials for the temperature dependence of the mineral solubility. Instead of the classic phreeqc.dat thermodynamic database, the new carbfix.dat set was used. In addition, incongruent solubility of aluminosilicates and equilibrium with Al hydroxides (gibbsite, boehmite) have to be considered, which results in a more reliable estimation compared to estimates based on Al concentrations. As a result of this modeling, a normal reservoir geothermal depth gradient of 3 °C per 100 m was calculated for the thermal springs of Wiesbaden city center.
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