Modeling the impact of temperature on the saturation state and behavior of minerals in the Soultz-sous-Forêts geothermal system

The approach used in the present study is based on calculation of the saturation indices of a large number of minerals in a given aqueous geothermal fluid from the activities of the aqueous species as a function of temperature. Our model accounted for a wide range of different mineral groups in order to make sure a large freedom for the numerical calculations. The modeling results showed that when the temperature of the geothermal reservoir cools, minerals like calcite, illites, quartz, clinochlore, K-feldspar, pyrite, galena, and barite show a tendency towards equilibrium state, which indicates that they may be precipitated. In contrast, other minerals initially present in the fresh granite including anorthite, K-muscovite, and annite remained unsaturated and may be dissolved. These mineral behaviors were further illustrated with mineral stability diagrams. The modeling results confirm that special attention should be paid to these minerals when studying changes in porosity and permeability of the geothermal reservoir. Future effort for extending the kinetic database for minerals should first concern these mineral phases.