The German Molasse Basin hosts a high geothermal potential particularly in its southernmost part where the well-known Upper Jurassic carbonate Malm aquifer lies in 4.6 – 5 km depth. While the Malm aquifer is already exploited in the Munich area, the knowledge for sustainable geothermal development and economic exploitation of the southernmost part is still limited.
The research project Dolomitkluft (i.e. dolomite fracture) addresses the geothermal development, testing and analysis of the first fracture dominated dolomitic aquifer in the deep Malm of the Bavarian Molasse Basin. The test site is located in the district Bad Tölz-Wolfratshausen, about 40 km south of Munich and east of the Lake Starnberg. Several research topics are dealt out among the partners of the joint project, Enex, LIAG, GEOS, GTN, and TUM. Enex is the license owner of the test side and coordinator of the joint research project. The scientific lead has the LIAG (Prof. Dr. I. Moeck).
Particularly, the project aims the geothermal exploitation of the 5000 m deep Malm formation close to Geretsried in the district Bad Tölz-Wolfrathausen, 40 km south of Munich. License owner is Enex Power Nord GmbH &Co KG. The first drilling operation started in 2013 with the longest geothermal well in Europe with a 6036 m long well path. However, the productivity was significantly lower than expected and turned out as beyond any economic level. The exploitation concept followed the so-called facies concept, where a particular porous carbonate facies type is expected from 3D seismic interpretation. The dry well GEN-1 was plugged in August 2013 and the negative results from this prominent project provoked a considerable draw-down in the whole geothermal market in Germany.
With Dolomitkluft a sidetrack will be drilled from the dry well GEN-1, targeting a graben type fault zone. Deep fault zones are hitherto scientifically understudied: the dimensions of damage zone, fault core, the permeability variability in these fault zones compared to intact rock are not well quantified. The interaction between fault kinematics, diagenetic processes and facies types affecting the reservoir quality criteria porosity and permeability in depth are not well known. Therefore, a 330 m long drill core is planned along the sidetrack covering intact reservoir rock, damage zone and fault core of the 5000 m deep fault. Structural geological, geomechanical, geohydraulic and seismic analysis will help to characterize the fault zone. The results will be crucial for future geothermal development in the Malm and fault controlled geothermal play types in general.
The following tasks shall be performed by LIAG to reach the project goals: (I) seismic velocity model representative for the Southern Molasse Basin for an optimal fault interpretation; (II) dimensioning of fault zones for a numeric TH reservoir model, extension of LIAGs existing regional TH model of the Munich area; (III) frac-simulation as proof for the EGS utilization potential of dolomites; (IV) planning/assignment/petrographic Analysis of 330 m drill core from the Reservoir drilled through a fault zone; (V) thin section analysis of cutting and core material, input of comprehensive data sets into GeoTIS; (VI) stress field analysis, kinematic fault analysis, quantification of fault reactivation potential; (VII) public relation through professional outreach (e.g. brochures), workshops for knowledge transfer.