Experimental Investigations on the Thermophysical Properties of Synthetic Geothermal Fluids

Abstract

Due to their often very high salt content, the thermophysical properties of geothermal fluids may differ significantly from those of pure water. Therefore, it is of crucial importance for the sustainable design of geothermal power plants to know these properties as exactly as possible. Based on fluids of the North German Basin which are dominated by sodium chloride and calcium chloride, an integrated laboratory study is conducted at GFZ-Potsdam. This study ultimately aims at closing existing data gaps by means of systematic measurements at relevant p-T-conditions. Additionally, suitable site-independent mixing rules are to be found to predict the thermophysical behaviour of a site-specific saline fluid by composition only. Sodium chloride and calcium chloride solutions and mixtures of both serve as a synthetic analogue for this type of geothermal fluid. For this geothermal setting, the thermophysical parameters density, viscosity, electrical and thermal conductivity as well as specific heat and sonic velocity have to be determined systematically in the range between 0 mol∙kg-1 to saturation, up to 150°C and 450 bars with respect to different mixing ratios of the salts. We will present the measurements of individual parameters and resulting conclusions regarding the thermophysical parameter predictions with the help of existing mixing rules.