New Concepts for Extracting Geothermal Energy from One Well: The GeneSys-Project

In Germany, doublet-systems that consist of one production and well one injection well are usually installed to recover geothermal energy from great depths. However, the “GeneSys” project aims to develop a single well concept for direct use of geothermal energy. In this concept, the production and injection wells are realized within the same well. The 4000 m deep Horstberg well is located in the Northern German Basin and serves as a geothermal test well. A large hydraulic fracture was created there in a low permeabilty formation (Middle Bunter) by applying performing a massive hydraulic fracturing operation. The good hydraulic properties of the fracture and the hydraulic link formed between two layers of the Middle Bunter are the basis for two different schemes: a circulation scheme between the two layers and a huff-puff scheme. The huff-puff operation mode is the cyclic injection of cold water into the fracture and production of the heated water after a certain recovery time. Both concepts have been tested successfully at Horstberg. The thermal output was higher than 1 MWth, which is sufficient to supply large office buildings with geothermal heat. In June 2009, the drilling operation for a deep well was initiated in Hannover. It is intended to supply the buildings of the Geozentrum Hannover with heat using one of the tested single well concepts.