In the course of the research project MinTherm the technical feasibility of a deep geothermal power plant, based on two different Austrian underground projects, is investigated. This thesis explores the potential to use energy in existing underground infrastructures. The aim is to register the necessary infrastructure, the necessary safety requirements and collecting the necessary operating and process parameters for two Austrian underground projects. The basic idea is the use of a superior geothermal depth level, which increases with the depth. These underground energy reservoirs have been developed by existing tunnel- and gallery entrances. Those circumstances replace unnecessary meters of drilling and the connected costs. Two possible locations are investigated. The first location (hereinafter project study A) is in the area of the underground mining Breitenau in Styria. The second location (hereinafter project study B) is situated in the project area of the Gleinalmtunnel nearby St. Michael also in Styria. The rock overburden in both project studies is around one thousand meters. The existing tunnels allow to start drilling in a superior geothermal area than it would be the case with a drilling start at the surface. This results in an elimination of the whole drilling work and drilling costs up to this depth. In this master thesis the focus is on petrothermal systems. The reason therefor is to avoid a geographically limitation cause of geological conditions. At the beginning of the main part for both projects the general technical requirements for a project realization is carried out. Especially the geological and geothermal conditions to run a petrothermal system are important. The geomechanical conditions were especially in the area of the planned cavern creation investigated. In the cavern it is also being considered to construct the drilling rig. For a project realization logistic is an essential factor and can be a major challenge. Especially if there is a running mining operation like in project study B. The critical factors therefor are transport, dimensions, achievable depth and the necessary operation resources. Also the consequences of a geothermal project concerning safety and environment were part of this thesis. Furthermore, the arrangements for feeding the grid were investigated. The project related relevant parameters and properties were identified and evaluated. After an extensive research, less insightful exploration material for depths above two thousand meters depth has been found. In both project studies, crystalline bedrock is expected at about six kilometers depth. This crystalline rock was tested for geothermal relevant parameters. This makes a statement possible, if the ground is suitable as "heat exchanger" for a deep geothermal power plant and which technical steps are required to realize a project. In the closing part of this thesis the parameters of both project studies are assessed and project-related risks and opportunities identified. The summary forms a potential assessment of both projects. The fundamentals of this assessment are geological, geothermal and infrastructural conditions.