The Rotliegend of the North German basin is the target reservoir of an interdisciplinary investigation program to develop a technology for the generation of geothermal electricity from low-enthalpy reservoirs. An in-situ downhole laboratory was established in the 4,3 km deep well Groß Schönebeck with the purpose of developing appropriate stimulation methods to increase permeability of deep aquifers by enhancing or creating econdary porosity and flow paths. The goal is to learn how to enhance the inflow performance of a well from a variety of rock types in low permeable geothermal reservoirs. In the moment, we drill a new well to create a doublette at place and to establish a thermal water loop in the near future. A series of stimulation experiments with different fracturing concepts were carried out. In a first attempt open hole hydraulic proppant-gel fracturing treatments were conducted in two pre-selected sedimentary reservoir zones in Rotliegend sandstones in about 4 km depth. They proved to be on the one hand technically demanding and on the other hand less successful than expected due to a suboptimal design. Nevertheless, the main inflow zones could be clearly identified. In a second step the concept of zonal selection and proppant application was abandoned and massive waterfrac treatments were applied over the entire open hole interval of the well below 3874 m to the final depth at 4294 m. Evidence of the creation and properties of vertical fractures were retrieved from pressure response analyses and demonstrated a bilinear flow regime in the reservoir. Therefore, the stimulation effect in terms of a productivity increase can be determined for the described concepts and improvements can be recommended for similar field experiments.