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4.8 Outcome 203
development and to target the deviated wells into the rim of the stimulated zone.
A downhole seismic network of six stations registers the microseismic events
occurring during stimulation in Soultz, while a surface seismic network is also
available and well adapted for the microseismic event magnitude determination.
The strength of those microseismic events was up to ML = 2.9 for the stimulation
of GPK3. In order to prevent the development of strong microseismicity, the
stimulation strategy was adopted to lower flow rates and shorter duration (compare
Table 4.1).

4.8.1.2 Hydraulic Stimulation Groß Sch¨ onebeck
In the Groß Sch¨ onebeck wells, three stimulation treatments were performed in
the wells EGrSk3/90 and GtGrSk4/05, respectively. Table 4.3 summarizes the
productivity improvement of each stimulation. In the well EGrSk3/90, the first
stimulation was carried out in the sandstone section, the other two stimulations
included the underlying volvanic rocks as well.
The three hydraulic stimulations in the well GtGrSk4/05 were carried out
separately in two sandstone sections and the volcanic rocks. To determine
the improvement factor a production test was carried out for all sections
together. Individual contribution of each section was determined by a profiling
flowmeter.
Microseismic monitoring was performed during the last treatment in EGrSk3/90
from subsurface, but no events could be registered. During the first two treatments
in GtGrSk4/05 microseismicity was monitored in the well EGrSk3/90 at 3800 m
depth. Observation of the microseismic events reveals a very low seismicity during
and after stimulation (80 events).

Table 4.3 Summary of the stimulation treatments in the
wells EGrk3/90 and GtGrSk4/05 in Groß Sch¨onebeck.

Well Duration Volume Flow rate Productivity Improvement Located
3
−1
–1
(days) (m ) (l s ) (l s −1 bar ) factor of microseismic
productivity events
EGrSk3/90 0.51 167 3.75 0.027 Initial PI Not measured
EGrSk3/90 0.58 307 6.22 0.059 2.2 Not measured
EGrSk3/90 0.24 338 16.4 0.112 1.9 Not measured
EGrSk3/90 1.0 859 4.3–14.7 0.207 1.9 No events
GtGrSk4/05 volcanics 0.06 4.4 0.83 0.004 Initial PI –
GtGrSk4/05 volcanics 0.5 356 8.2 0.0849 22 78
GtGrSk4/05 sandstones1 0.3 250 9.5 0.028 Initial PI –
GtGrSk4/05 sandstones1 0.5 356 8.2 0.142 5 2
GtGrSk4/05 sandstones2 0.2 170 10.3 0.034 Initial PI –
GtGrSk4/05 sandstones2 0.5 356 8.2 0.057 1.67 Not measured