Geothermics Greater Munich Area
The Malm of the Southern German Molasse Basin, known as fissure-karst-aquifer, is regarded as a significant reservoir of geothermal energy in central Europe with respect to production of heat as well as electrical power. Existing exploration results from various projects provided reliable parameters for long-term modelling of economical aspects at regional scale for the first time. The aim of the present project is to investigate the sum total capacity of this reservoir and the width of the area of mutual influence of several adjacent geothermal plants by numerical modelling.
A geothermal power plant in Unterhaching, south of Munich, generates heat for a municipal network and, additionally, 3.36 MW of electrical power. Two boreholes (doublet with injection well and production well) penetrated the top of the Malm at a depth of approx. 3000 m. Carbonate sediments of the Malm (Upper Jurassic) build the bottom of the entire Bavarian/Austrian Molasse basin from north (Danube River) to south (Alps) and are characterized as a high-productive aquifer with increasing depths and temperatures towards the Alps (south) due to their cracks and their degree of karstification. Geological faults within the Malm are particularly prominent in this respect because of their increased density of cracks and hence their increased permeability of fluids. Therefore, for determination of the geothermal potential the exploration of the geological structure and the degree of karstification of the Malm is essential.
2-D seismic profiles, originally carried out in the framework of hydrocarbon exploration in the 1970ties and 1980ties, were reprocessed and reinterpreted by the Leibniz Institute for Applied Geophysics (LIAG, Hannover, formerly known as GGA Institute) with kind permission of the company RWE Dea AG (Hamburg). The most prospective areas are those where seismic diffractions (hyperbolic arrivals in traveltime section caused by point scatters) occur together with decreased seismic velocities. These features indicate differences in facies of the Malm, geological faults, degree of karstification and possible fluid inclusions. Location and the deviation of the boreholes Unterhaching Gt 1 and Gt 2, about 4 km apart, were defined from these 2D seismic profiles. Both boreholes were successful and supplied at least 118 l/s water of temperatures of 130,5 oC. Supplementary vertical seismic profiling (VSP) and moving source VSP-measurements were carried out in the production well Unterhaching Gt 1 for a more detailed investigation of its vicinity.
In order to explore the sum total geothermal capacity of the Malm in the Munich area, the following subprojects are scheduled by an integrated programme of the LIAG and the Bayerisches Landesamt für Umwelt (BayLfU, Munich):
1) A high-resolution 4 x 5 km 3-D seismic reflection survey to explore facies and geological structures around the injection well Unterhaching Gt 2 with target depths to 4000 m;
2) regional geological 3-D modelling of structures aided by additional existing 2-D seismic profiles;
3) hydrological modelling and
4) numerical modelling of ground water currents.
Economical usage of the geothermal energy obtained from karst aquifers will be based at larger scale on results of the present study. Sustainable usage of geothermal energy can be improved and the operational risk will be reduced. The numerical model will be made available by administrative authorities as a tool for assessment of projected geothermal usage of the Malm reservoir.
Dr. Rüdiger Schulz
- Dr. Ewald Lüschen
- Dr. Michael Dussel
01.05.2008 - 31.12.2011