Reuse of old deep wells in Brandenburg, North German Basin – potential and challenges (Transgeo Project)

The ongoing structural transformation from the hydrocarbon industry to sustainable green energy is one of Europe's current challenges. In Germany, there are about 15,000 boreholes with depths ≥ 400 m (deep wells). Transgeo, a transnational project (EU Interreg program), aims at identifying the potential of such boreholes for geothermal energy production in Germany (+4 other countries). A central aspect of the project is the collection of data from deep wells. This data is then entered into databases and fed into a web-based IT-tool to demonstrate the potential of deep wells for geothermal energy production to future investors. The reuse of old wells, especially former oil or gas wells, is particularly attractive as it can reduce the costs of otherwise very expensive geothermal drilling while utilizing existing infrastructure. The deep wells in the eastern part of the North German Basin are mostly several decades old. As the former GDR was seeking economic independence, considerable effort was put into exploring and mapping national raw material deposits. Therefore, numerous comprehensive studies and data collections are still available in the archives. Analyses of samples taken, measured parameters, etc., are invaluable. The important parameters are not only temperature, porosity, and permeability in identified pay zones within formations of interest, but also technical data on well construction. Once abandoned, detailed information on the location of cement bridges and geological background information or technical problems during or after the drilling process becomes important when considering reuse or planning a new drilling.