Sustainable energy production from geothermal reservoirs requires an exact knowledge
of the hydrological aquifer rock properties as well as the processes that could
potentially alter its productivity. The latter comprise both mechanical (e. g. fines
migration) and chemical (fluid-rock interactions) effects.
To perform controlled long-term investigations on the evolution of sedimentary rock
transport properties at conditions pertinent to deep geothermal reservoirs two new
permeameters have been set up at the GFZ-Potsdam.
The apparatuses allow for a variety of continuous petrophysical measurements at a
maximum temperature, lithostatic- and pore pressure of 200 °C, 140 and 50 MPa,
respectively. The permeability, ultra-sonic p- and s-wave velocities and the specific
electric conductivity of the rock can be determined. In particular, the use of
corrosion-resistant parts allows for experiments with highly saline formation pore
fluids that can be sampled under pressure for further chemical analysis. The typical
duration of an individual test is four to twelve weeks.
Experiments are comparatively performed on two types of sandstones: a Lower Permian
(Rotliegend) reservoir rock from Eberswalde, Germany and a pure Quartzite from
Fontainebleau, France. In addition, two kinds of pore fluids are used: a low salinity
brine (0.1 mol NaCl) and a synthetic Ca-Na-Cl formation fluid with a TDS-content of
In a first series the former fluid was used to petrophysically characterize both
rocks as a function of temperature and effective pressure within the relevant range
of up to 150 °C and 75 MPa, respectively. I addition, in a continuous flow experiment
the permeability and the specific electric conductivity of the reservoir sandstone
were monitored as a function of time during six weeks at constant p-T-conditions. In
an ongoing series similar continuous flow experiments are performed using the second,
highly saline reservoir fluid. These tests are also complemented by pH and redox
potential measurements of the pore fluid that is sampled in regular time intervals.