Staßfurt: fluid transport in rock salt - spatial distribution and dynamics
This scientific joint venture revolves around the massive damages caused by flooded salt mines under the city of Staßfurt (Saxony-Anhalt). Salt mining is conducted extensively at Staßfurt since the middle of the 19th century. Due to the lack of geotechnical experience at that time meanwhile all salt mines are lost by massiv influx of water. The uncontrolled outwash of salt in the underground by intensive inflow of groundwater persists till this day. As a consequence the downtown area has sagged partially up to 7 meters, sink holes occured and wide areas of the town had to be teared down and turned partially into a lake. Further severe damages are anticipated.
This joint venture consists of several research institutions, universities and companies examining broadly the current situation to estimate the ongoing processes in the area. Staßfurt shall gain some planning reliability for the future on this way.
Our contribution is to examine the dynamics and mass transport of groundwater inside drilling cores taken from the salt rock and to visualise and quantify flow patterns and mass transport at the milli- and microscale. For this purpose we conduct flow through experiments with radioactive tracered water which we image by means of positron-emission-tomography (PET).
Positron emission tomography in geosciences
PET is mainly for financial reasons rarely applied in geosciences. Accordingly only few work was done on this topic so far.
The Reactive Transport Division of the Institute of Radiochemistry of the HZDR is examining the possibilities this technology offers for geosciences now for many years. For this purpose a commercial MiniPET scanner is available. Drilling cores and sediment columns up to 10 cm in diameter can be scanned with a spatial resolution of 1.15 mm and a time resolution of 60 s. A couple of isotopes are available as PET nuclides that can be used as inert tracer compounds accordingly to the posed problem. Radio tracer concentrations of 10-8g/l can be easily detected.
The Institute of Geosciences of the University of Mainz generates high resolution CT-data sets of the inner structures of these drilling cores in order to match the measured flow patterns with the structure. Additionally particle tracking simulations of the flow patterns are conducted that base on the Lattice-Boltzmann method. The alignment of simulations with PET measurements shall lead to a wider understanding of the ongoing processes as well as to possible strategies for upscaling to the kilometer scale.
project executing organisation: Karlsruher Institute of Technology (KIT)
coordination: Bundesanstalt für Geowissenschaften und Rohstoffe (BGR)
Dr. Johannes Kulenkampff (HZDR)
|a) "Leaning tower of Staßfurt". The tower of the St. Johannis church was teared down in 1964 when it reached an inclination of 4,60m due to the sagging of the underground.
b) Depression sink hole near Staßfurt in 1998. Uncontrolled flooding with fresh water causes instabilities in the saline underground.
c) New downtown of Staßfurt. Within the scope of the "Internationale Bauausstellung 2010 (IBA)" new designed towntown. The historic city center had to be replaced by a lake.
|Application of PET in geosciences. A tracer impulse is injected into a continuous fluid current and its flow patterns are imaged in three dimenions.
|Picture: Martin Wolf
|PET: Propagation of the tracer throug a drilling core. The time frames after tracer injection are given.
LBM: Simulated particle tracking of a tracer impulse inside a driling core based on a lattice-Boltzmann model (LBM). The LBM in turn is based on high resolution CT images of fractures and cleavages inside the drilling core. CT and LBM is provided by JGU Mainz.
|Pictures: Martin Wolf