Hydrogeochemical Modeling of Deep Formation Water Applied to Geothermal Energy Production

The extraction of formation water for geothermal energy production in the North German Basin is affected by the precipitation of certain minerals, e.g. Ba sulfates. These scalings often disturb the continuous production of geother- mal energy. PHREEQC modeling is used to predict such scalings, as well as the hydrogeochemical and technically induced processes occurring in geothermal energy production systems. To reproduce hydrogeochemical compositions of the formation water the modeling starts with the equilibration in pure water of defined mineral assemblages representing the rock matrix of deep formations, and potentially co-existing fixed-pressure gas phases. To simulate corrosion and sampling effects on the hydrochemical composition, the solutions are subsequently exposed to Fe(0), temperature and pressure decreases, and finally to a gas exchange with the atmosphere. The modeled results agree with observed scalings and hydrogeochemical data measured at five geothermal wells in the North German Basin.