To picture real geothermal reservoir conditions temperature and pressure depending parameters must be considered. Therefore it is possible to calculate these values for water saturated rocks under real reservoir pressure and temperature conditions for relevant depths. Those parameters can be validated by a Thermo-Triax-Cell. This Thermo-Triax-Cell is able to simulate the existing temperature and pressure conditions in the target horizon of a geothermal reservoir and furthermore induce a pore pressure on the rock sample. This device offers the opportunity to determine permeabilities from outrop samples under realistic reservoir conditions. The adjacent figure illustrates the principle of the Thermo-Triax-Cell.
The test device is a custom-designed thermal triaxial test cell, which was planned in cooperation with WILLE Geotechnik GmbH since 2008. The apparatus allows shear tests and permeability measurements under reservoir conditions. Experiments can be conducted at reservoir temperature and pressure conditions, hence simulating a high enthalpy reservoir regime under percolation of hydrothermal model fluids.
For this purpose, APS GmbH (Wille Geotechnik) and the Department of Geothermal Science and Technology of the TU Darmstadt developed a test facility. Further information can be found here in the poster (german).
The unique design allows experiments with tempered rocks and fluids up to ~200 °C. Built of V4A premium steel, the cell can be operated with highly aggressive (corrosive) fluids. Both fluid and rock can be individually tempered, thus allowing a wide range of testing setups to simulate real reservoir conditions. Shear tests can be done on dry and saturated samples. Additionally, fluids can be pumped through the sample during shear tests, thus allowing permeability measurements and monitoring under reservoir conditions. Tests are envisaged to be run over several weeks to monitor changes in the host rocks mineralogy and stability. Test fluids can be mixed, and can be sampled during the test runs.
The goal is to perform shear tests on typical reservoir rocks under reservoir conditions, and determine their compressibility, while changes in permeability are monitored. This will lead to a better understanding of the physical processes in the true reservoir.