The chemistry of deep geothermal fluids is essentially controlled by the reservoir rock, i.e. by the solubility of its minerals and by fluid inclusions. The reservoir fluid is usually in geochemical equilibrium with the surrounding rock. Above-ground heat extraction and pressure relief during production disturb the system and alter the physical, hydrochemical and thermodynamic parameters of the geothermal water. Subsequent reactions can be mineral precipitations and/or solutions. Furthermore, the typically highly saline geothermal fluids are highly corrosive to the materials used in drilling and production.
The aim of our research is to obtain a better understanding of the chemical changes in the geothermal system during circulation throughout the entire cycle. Geochemical water-rock interactions can cause a change in rock permeability and consequently influence the injectivity of the well and damage parts of the geothermal system such as pipe systems or pumps. Laboratory experiments are used to address these issues. The boundary conditions of these experiments are taken from real conditions in the reservoir and the surface installations of existing geothermal power plants. Complementary numerical modelling with THMC codes is performed to understand and quantify the thermal-hydraulic processes, chemical interactions and mass transport. The modeling codes used are TOUGHREACT, PhreeqC and Elmer.
For a long-term and viable exploitation of a geothermal reservoir, it is necessary to consider in detail the chemical interactions between the injection fluid and the mineral phases of the rock. For a continuous operation of a geothermal plant, it is also necessary to be able to predict and reduce the corrosive processes in the above-ground technical plant components.