Geothermal Lab

Thermo Triaxial Cell

The investigation of thermal aquifers and determination of important rock parameters is one of the main topics in the research area of the Geothermal Energy Group. As the most thermal energy storages are located in aquifers deep below the earth’s surface, the different pressure and temperature conditions should be taken into account for the measurement of rock parameters. Therefore, the Geothermal Energy Group has established a new laboratory to carry out investigations on aquifer and rock parameters under “in situ” conditions.

The centerpiece of the new Geothermal Lab is a thermo-hydro-mechanical triaxial cell (Figure 1) invented by APS GmbH (Wille Geotechnik) that especially is designed for abovementioned research issues.

The thermo triaxial cell can simulate true conditions prevailing in the target formation of an aquifer and thus offers the possibility to determine the permeability of the rock under realistic overburden and pore water pressure conditions. The alignment of strain, pore pressure and temperature is continuously variable and allows the implementation of almost any reservoir condition.

The design of the triaxial cell (Figure 2, Left) allows mounting of consolidated and hard rock in the form of core samples. An impermeable and temperature resistant membrane encloses the sample throughout the measurement process while the sample is burdened by triaxial pressure and circulated by pore fluids. Additionally, a hydraulic gradient is generated by differences in pore pressure so that the flow rate and permeability can be measured (Figure 2, right).


Due to the variable use of fluids of different chemical composition (up to highly aggressive fluids), complex physico-chemical reactions in reservoirs can be simulated. The hydraulic and chemical changes caused by solution, transport and precipitation of various mineral phases can thus be studied more precisely than under normal p/T conditions at the surface.

Technical Data:

  • triaxial cell made of stainless V4A (CrNiMo-) steel with high pressure and temperature resistance (up to 30 MPa and 180 °C)

  • sample container for Ø 50 mm and Ø 72 mm plugs

  • axial pressure up to 1000 kN load by single-acting plunger (100 mm piston stroke) and measurement of sample deformation by displacement transducers

  • triaxial pressure up to 30 MPa

  • two high pressure controls for pore pressure up to 30 MPa and flow rate of max. 200 ccm/run of tempered and aggressive pore fluid

  • adjustment of required hydraulic gradient and measurement of rock permeability ranging from tight (~10-9 m/s) to high permeable (~10-2 m/s)

  • continuously variable heating sleeve for temperatures up to 180 °C