Evaluation of three exploitation concepts for a deep geothermal system in the North German Basin

In this paper, we compare three exploitation strategies for the deep geothermal system of Groß Schönebeck in the North German Basin. Investigating optimum reservoir designs is one of the key issues for efficient and sustainable utilization of geothermal resource. With this objective we simulate the hydraulic-thermal coupled subsurface processes related to the provision of geothermal energy. The presented application, including visualization, mesh generation and numerical simulation, is based on open source software. The numerical investigations of the three exploitation concepts take into account all geological layers, major natural fault zones, hydraulic fractures, geothermal wells and related hydraulic-thermal coupled processes. In the current exploitation concept, the fluid flows through the rock matrix between the injection and the production well (matrix dominated). The related numerical model is compared and calibrated to available field data. Then, the model is used to investigate two alternative stimulation concepts. All three concepts were evaluated taking into account the evolution of the production temperature as well as the hydraulic conductivity between production and injection well. As an alternative to the current situation, a fracture dominated system is investigated where the fluid flows through hydraulically induced fractures between injection and production well. Compared to the reference model, a twofold increase in productivity could be observed together with a significantly reduced time before the onset of a thermal breakthrough. The second alternative is a hybrid concept combining both matrix and fracture-dominated flow paths between the production and the injection well. We show that this hybrid approach could significantly increase the reservoir productivity and prolongs the time before the onset of thermal breakthrough.