Data Gaps in Thermophysical Fluid Data for Geothermal Applications

Abstract

An integrated development and use of a geothermal site for sustainable energy provision requires the thermophysical fluid properties to be known in detail. Due to often highly complex fluid compositions, e.g. high salinity and mineralization of the brines, their properties generally depart significantly from those of pure water and are often unknown. To close this gap a new laboratory has been installed at the GFZ German Research Centre for Geosciences that enables measurements of the most important thermophysical fluid properties at conditions relevant for deep geothermal reservoirs and the related technical installations at the surface. The principal parameters addressed are: density, viscosity, speed of sound, specific heat, thermal conductivity, and electrical conductivity. Off-the-shelf solutions are complemented with in-house constructions where the former are not available, particularly for high pressure and temperature measurements. Special attention was given to materials selection issues in connection with the high corrosion potential of geothermal brines. We subdivided the experimental p-T space into three fields: (1) ambient pressure and T less than 80°C, (2) p less than 20 MPa and T less than 150°C, and (3) p less than 50 MPa and T less than 200°C. For geothermal applications this covers all reservoirs to accessible depths of 5 km having a normal geothermal gradient. In our contribution we conduct a comprehensive evaluation of literature data identifying a need for further measurements. Also, the laboratory installations will be presented highlighting technical in-house developments for viscosity, speed of sound, and electrical conductivity measurements at elevated pressures and temperatures.