Page 292 - Geothermal Energy Systems Exploration, Development, and Utilization

268 5 Geothermal Reservoir Simulation
a continuous decrease in temperature can be observed at observation point 2. After
seven years of production, the cold water reaches the second production fracture
(first gel/proppant frac) and after an additional five years, the waterfrac is also
affected by the cold water front, leading to a further reduction of temperature.
◦
Consequently, a production temperature of 132 C was simulated after 30 years
production.

5.5.5
Conclusions

By means of the well-known reservoir geometry, structure geology, hydrothermal
conditions, and the occurring coupled processes, we simulated the change of the
geothermal reservoir conditions at the Groß Sch¨ onebeck site. This delivers an
improved understanding of the reservoir behavior and leads to an interpretation
of the long-term reservoir characteristics during geothermal power production.
For a better prediction of the long-term reservoir behavior it becomes essential
to integrate mechanical properties and chemical interaction. These requirements
cannot be captured by FEFLOW simulation software. Therefore, the presented
results are a basis for further investigations by numerical simulations with a
coupled THMC simulator.

5.6
Bad Urach

The case study for the application of the stochastic THM model is based on a
large data set for the Urach Spa geothermal site compiled in several research
projects (Haenel, 1982; Tenzer et al., 2000). The idea of the application case study
is to demonstrate the methodology for an uncertainty analysis of THM-coupled
processes in a typical geothermal reservoir in crystalline rock. A basic assumption
of the conceptual model for the Urach Spa site is that due to dense fracturing,
the geothermal reservoir can be represented as a heterogeneous porous medium.
There is no database available in order to construct DFN models.

5.6.1
The Influence of Parameter Uncertainty on Reservoir Evolution

5.6.1.1 Conceptual Model
Urach Spa location was originally designed as a scientific geothermal pilot project.
The proposed boreholes (U3 and U4) dipole flow circulation system (i.e., a
‘‘doublet’’) are located 400 m apart. On the basis of the large amount of scientific data
available on the Urach Spa reservoir, we developed a three-dimensional model of
the reservoir system. Parameters relevant to reservoir fluid flow and heat transport
that were used in the model were based on the results of previous studies. The
hydraulically active areas allowing the reservoir to be represented geometrically as a