The GeneSys- and Prometheus-Projects are linked by an ambitious goal; while
HDRresearch efforts have until recently been limited to settings where crystalline
rocks prevail, these projects now tackle the challenge to transfer major ideas and
concepts to sedimentary rocks. This is an important step to make, since for a
substantial fraction of potential sites sedimentary rocks will be found at the target
depth for geothermal energy extraction.
For both projects porosity and permeability of the rocks at target depth are low, and
hydrothermal use is consequently not feasible. Also direct use of geothermal energy
is the common objective of both projects. Still, the projects do not just duplicate
ideas, instead they follow different concepts.
The Prometheus-Project of the Bochum Ruhr-University daughter company “rubitec” is
aiming to install a two well HDR-system at a depth of approximately 4km. Anticipated
operation figures are a production flow rate of 30l/s and well head temperatures of
at least 110°C to deliver a thermal power output of 7MW. So far, a detailed
feasibility study has been carried out. Knowledge of the geological situation to a
depth of approx. 2km is very good as a consequence of coal mining. As no deep wells
are present in the vicinity a deep exploration well is mandatory for further planning
of the underground heat exchanger. Due to the geological situation the production and
injection well will have to be drilled as deviated wells into the Upper Carbonian
sandstones/quartzites. The concept and detailed planning of the stimulation of the
underground heat exchanger will be based on the results of drilling, logging
and hydraulic testing within the exploration well. Drilling and testing is
anticipated to start in 2006.
In contrast to the classical HDR-systems, one-well concepts, where one well is
simultaneously used for the production of hot water and reinjection of the cooled
water, are in the focus of the GeneSys-project. These concepts will in particular be
attractive for sites where a thermal power in the range of few MW is required. The
GeneSys project started in 2003 as a joint project of the ‘German Federal Institute
for Natural Resources and Geosciences’ (BGR) and the 'Leibniz Institute for
Geosciences’, both located in Hannover, Germany. The project aims to finally provide
geothermal energy for space heating of the building complex of the institutes. In
preparation of the project at the Hannover site, an extensive test program has been
carried out in the abandoned gas exploration well Horstberg Z1 (final depth: 4,100m)
which is operated as a research well by BGR. It was
shown that in sedimentary rocks large hydraulic fractures can be propagated by
waterfrac technique and, that a residual hydraulic transmissivity of the fracture is
kept even if no proppants are added. Also the feasibility of three different
innovative one-well concepts were successfully tested. Encouraged by the positive
results the realisation of the project at the Hannover site started in 2005.
Currently the drilling of a 3,800m well is prepared. Beyond, concepts and methods
will be further developed by hydraulic tests at the Horstberg site.