Geomechanical Investigations in the North Alpine Foreland Basin, SE Germany

In Germany, deep geothermal energy is playing an increasingly important role in achieving Germany's climate targets. Progressing this form of renewable energy requires reliable prediction of the potential of deep hydro- and petrothermal systems in carbonate reservoirs. Consequently, the Geothermal-Alliance Bavaria, a federally funded geothermal research collaboration, establishes geothermal energy as a reliable source of domestic energy. To accomplish these goals, Upper Jurassic carbonates (once described as Malm), which are main targets in the North Alpine Foreland Basin, SE Germany for hydrothermal geothermal energy, are subject to extensive geomechanical investigation. Due to the heterogeneous structure of this carbonate aquifer, the rock properties cannot be predicted with sufficient accuracy. However, these geotechnical parameters are significant for the realisation of geothermal projects, as they control the well stability and fracture initiation and propagation, as well as its stimulation potential. Hence, an extensive rock mechanic laboratory programme was carried out on carbonate rocks from scarcely obtainable drill cores from hydrocarbon/research wells and equivalent rocks, so-called analogue samples, from quarries. Non-destructive and destructive testing methods allowed the determination of elasticity, strength, and fracture toughness parameters. The mode II fracture toughness experiment was accompanied by a high-speed camera. Numerical simulation programmes are essential for evaluating the initiation and propagation of hydraulic conductive cracks in geothermal reservoirs. These codes dynamically simulate elastic and plastic deformation, allowing the simulation of fracture initiation and propagation within the rock mass. This geomechanical reservoir characterisation enables a better insight into the Malm aquifer in order to contribute to a higher efficient utilisation of this energy source in Germany in the future.