Methods for Measuring the Density and Viscosity of Saline Geothermal Fluids Under Reservoir Conditions

Abstract

For the sustainable operation of a geothermal system, it is important to know the flow characteristics of the geothermal fluid as exactly as possible. Therefore, viscosity and density are important thermophysical parameters. In sedimentary basins, as prominent targets for geothermal energy exploitation, fluids are mostly highly saline and mainly consist of sodium chloride and calcium chloride. To obtain systematic knowledge about the viscosity and density of sodium chloride and calcium chloride solutions and mixtures of both salts, a laboratory study was conducted. For geothermal applications, salt solutions with different concentrations need to be measured at pressure and temperature conditions up to 200°C and 500 bar. For the viscosity measurement, a flow-through apparatus originally designed for rock-physical measurements was converted into a capillary viscometer. So far, measurements up to 125 bar and 90°C were conducted. Viscosity data of the salt solutions were obtained relative as deviation from pure water, used as the calibration agent for each temperature and pressure step. In this contribution, the general concept and the modifications of this apparatus will be outlined. Density measurements are obtained by using an oscillating u-tube densitometer (DMA HP from Anton Paar). The results obtained so far will be presented and compared to existing literature values, whenever available.