Page 247 - Geothermal Energy Systems Exploration, Development, and Utilization

4.10 Case Studies 223

3000

140
3500 130
GPK 2 GPK 4
120
GPK 3 110
4000 100
Depth (m) 90

80
4500 70
60
50
5000 40
30
20
10
5500
500 0 −500 −1000 −1500 −2000
Northing (m)
Figure 4.20 Color contour plot of the event density in
50 × 50 m cells in the plane of the graph. Perpendicular
to this plane the cells are unlimited. All events localized
during the stimulations 2000, 2003, 2004, and 2005 were
included. (Please find a color version of this figure on the
color plates.)

derived from flowlogs. In terms of the life duration of an EGS-reservoir, the
stimulation of single structures may be critical. In further projects the application
of a multifrac concept should therefore be an issue to achieve a more volumetric
stimulation.
The concept of massive water injections may have the disadvantage of triggering
larger seismic events (Baisch et al., 2006). A few events above the threshold for
human detection have occurred during the massive stimulation of GPK2 and GPK3
(5 km). The biggest induced seismic event (M ≈ 2.9) in Soultz was recorded in 2003
during the shut-in period of the GPK3 stimulation. Although this event caused no
structural damage or any casualties, it triggered serious concerns of the population,
so that the succeeding stimulation of GPK4 was performed with significant smaller
water volume.

4.10.2.2 Chemical Stimulation
The operations of chemical stimulation in the geothermal wells of
Soultz-sous-Forˆ ets are relatively recent because they have started in 2003
in the GPK-2 well. Moreover, few operations were carried out and the chemical
treatments were limited in terms of time, volume, and concentration. The main
operations occurred in GPK-4 and GPK-3 wells between 2006 and 2007.