Validation of Hydrochemical Analyses and Gas Concentrations of Deep Geothermal Aquifers

Abstract

Data collected in previous projects indicates that the hydrochemical parameters recorded at surface level are not necessarily a good approximation of the water under reservoir conditions. With increasing temperature and gas loading the pH value is significantly effected by degassing. Thus geochemical calculations based on the measured values at surface level and without taking the individual degassing procedures into account are likely to give false predictions. This restriction partly also applies to depth samples. Here, degassing and changes of the hydrochemical parameters have to be taken into account as soon as the sample is opened in the laboratory to insert e. g. the pH probe. The techniques presented in this study present a reliable and reproducible way to calculate the hydrochemical composition and the gas loading under reservoir conditions. Within the scope of this study, it was also evident, that no geothermal water in the Malm Aquifer in the Bavarian Molasse Basin contained excess CO2. Although all gas analyses contained CO2, this CO2 was stripped from the aqueous solution. The amount stripped from the water depends on the concentration of other gases with lower solubility.