Technology for the utilization of deep geothermal reservoirs in Germany

The Geothermal Technology Program at GFZ identify suitable geological structures and horizons for extracting energy and develop new methods to increase the productivity of deep geothermal reservoirs. In this context, the former gas exploration well Gross Schoenebeck EGrSk3/90 (50 km northeast of Berlin) was reopened and deepened to the 4309 m depth to serve as a geothermal in situ laboratory for testing stimulation concepts. The objective of these stimulation operations was to create secondary flow paths and to improve the inflow performance of the well. In addition, Gross Schoenebeck is the only test site of the EU-project I-GET (Integrated Geophysical Exploration Technologies for deep fractured geothermal systems), where new, cost-effective and reliable geothermal exploration techniques are developed to increase the success rate of drilling. Based on the data of deep neighbouring wells and the industry seismic measurements, a model was generated to visualise the geological setting and to plan the course of the second well. The well encounters a typical sequence of various geological formations, known in the North German Basin. A series of 2370 m of Quaternary to Triassic sediments is underlain by 1492 m of Zechstein salts, and the following section of this well, which was foreseen for testing, comprises 400 m of Rotliegend formation (siltstones, sandstones, conglomerates and 60 m of underlying volcanic rocks) down to the final depth of 4309 m. The well Gross Schoenebeck makes the deep sedimentary Rotliegend reservoir accessible, which is characterized by water bearing porous and fractured rocks. The Rotliegend reservoir consists of a sequence of sandstones, conglomerates, and volcanic rocks with formation fluids of 150 grad C at porosities of up to 10 %. Experiments in this in-situ geothermal laboratory should lead to a reliable technology for a sufficient production of deep fluids in such reservoirs. (authors)