Within the GeneSys-Project, the BGR (Federal Institute for Geosciense and 
Resources) and GGA-Institute (Leibnitz Institute for Applied Geosciense) aim at 
the extraction of deep geothermal energy (3500-4000 m) from the tight 
sediments of the Northern German Basin. Therefore three new concepts for 
geothermal heat extraction using a single-well-concept have been developed, 
since drilling costs are a crucial point to the efficiency of geothermal plants.

All concepts have been developed for the use in low-permeable sediments to 
provide small to medium-sized consumers with geothermal heat in the order of 
2 MWth. Key technology to all concepts is the water-frac-technique, which is 
used to create large fractures in the sedimentary rocks.

- Deep circulation concept: Via a hydraulic fracture a highly permeable geologic 
fault is connected to the well. Hot water can be withdrawn from the formation.

- “Huff-Puff”-concept: A hydraulic fracture is created, which acts as a storage 
reservoir for injected cold water. The cold water heats-up and can be produced 
as necessary. The cycles of injection and production can be adapted to the 
needs of the consumer – e.g. injection during weekend and production during 
working days or injection in summer and production in winter.

- Two-strata concept: A hydraulic fracture connects two strata of sandstones. 
Both strata are connected to the well. A tubing passing a packer gives access 
to the lower stratum while the upper stratum is linked via the annulus of the 
same well. Water is injected into the lower sandstone, heats-up while migrating 
through the fracture and is produced from the upper sandstone layer. A 
persisting circulation is established.

The Huff-Puff and the Two-Strata concept have been successfully applied at the 
geothermal research well Horstberg Z1 in the Mittlere Buntsandstein formation. 
By the end of 2007 a 3800 m deep well will be drilled in the town of Hannover 
to supply office and laboratory buildings of the GEOZENRUM with geothermal 
heat by using a coast efficient single-well concept.

Grensasvegur 9
Reykjavik,
Iceland