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Physical Properties of Thermal Water under In-situ-Conditions

PETher is a research project funded by the German Federal Ministry for Economic Affairs and Energy (BMWi, reference number: 0325761). The project partners are KIT (Karlsruhe Institute of Technology; technical project coordination), GeoT (GeoThermal Engineering GmbH, Karlsruhe; geoscientific project coordination), gec-co (Global Engineering and Consulting GmbH, Augsburg) and as subcontractor GTN (Geothermie Neubrandenburg GmbH).

The objective of PETher is to determine thermophysical properties (specific isobaric heat capacity, kinematic viscosity, density and thermal conductivity) of geothermal water under conditions that reflect the original conditions to be found in geothermal applications (pressure, temperature, chemical composition including gas content of the brine). The knowledge of these thermophysical properties is crucial in order to estimate the thermal output and therefore the economic viability as well as to optimize the plant or heating station design during the development and operation of a geothermal project. Up to now, only a limited number of measurements of selected physical properties have been made, usually under laboratory conditions as well as for individual geothermal plants. Currently available mathematical formulae describing the thermo-physical properties are typically not valid for the conditions to be found in geothermal applications and do not consider the substantial influence of the chemical composition of the thermal water. Also, actual geothermal waters have not been subject of detailed measurements systematically performed under operational conditions on a large-scale basis.

In this project, the thermophysical properties of geothermal water are measured under in-situ-conditions as functions of pressure, temperature, and salinity. The measurements are taking place directly at several geothermal applications located in Germany’s hydrogeothermal key regions. In order to do this, a mobile testing unit was developed and refined with instruments specifically designed in-house to meet any geothermal reservoir conditions to be found in Germany. The obtained results will be compared with standard analytical methods as well as used to calibrate laboratory measurements that simulate the encountered in-situ conditions. A series of tests will be performed in order to create a data base and to model the thermal water’s thermophysical characteristics as a basis for future designs of geothermal applications.

Fig. 1. Process and instrumentation diagram of the mobile testing unit. The thermal water flows from left to right. The measurement devices are partly built-in in series, partly parallel, but they are operated separately while measuring.