A series of stimulation experiments were carried out at the well Groß Schönebeck, a
geothermal research well in the north-eastern part of Germany. The aim was the
development of concepts for the productivity enhancement of geothermal wells in that
region. In a first attempt hydraulic proppant-gel fracturing treatments were
conducted in two sedimentary reservoir zones with high permeability at about 4 km
depth. These treatments were performed under challenging conditions in the open hole
section at a temperature of about 150°C. They proved to be on the one hand
technically demanding and on the other hand less successful than expected due to a
suboptimal design. Most likely, the small injection volumes combined with a low
proppant density did limit the success of these operations. Nevertheless, the
productivity of the well could be increased by a factor of two. The characterisation
of the inflow zones after the proppant fracs and derived values for the minimal
horizontal stress led to a completely different frac concept. Massive waterfrac
treatments were now applied over the entire open hole interval of the well below 3874
m to the final depth at 4294 m. Again, a significant increase of productivity was
achieved, demonstrating that waterfracs can be a successful and effective stimulation
concept for the geological situation. Evidence of the creation and properties of a
very long vertical fracture were retrieved from pressure response analyses
demonstrating a bilinear flow regime. The stimulation effect in terms of a
productivity increase was determined for the described concepts and improvements are
derived for similar field experiments.
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