Environmental Engineering Reference
In-Depth Information
Fig. 6.13
Upstream hydraulic stimulation
Furthermore, it has been demonstrated that the predicted thermal drawdown com-
pared well with the field data from a 1-year circulation test conducted at the
Hijiori site.
6.6
Reinjection for Enhancement of Existing
Hydrothermal Reservoirs
One remaining area of research is the serious global issue of declining heat pro-
duction from existing geothermal reservoirs. At the same time, geothermal energy
facilities are faced with the challenge of disposing of extractive water after its heat
has been used for electricity generation or local heating. Such water can be con-
taminated with various minerals making their discharge to surface waters an en-
vironmental issue. For this reason many administrations have required by law that
an injection well must be produced to provide a return path for extracted water, as
illustrated in Fig.
6.13
.
However there are concerns about the potential cooling effects of re-injected
water on the reservoir, since discharged water is generally after passage through
the power plant cooling tower, and therefore quite low temperature. For this reason,
many geothermal facilities inject the extracted water
downstream
of the reservoir.
This avoids the danger of too much cooling in the reservoir but this may lead to
inadequate water flows. We thus briefly consider this issue.
The reservoir system with reinjection shown in Fig.
6.13
can be considered as
analogous to the artificial water circulation system illustrated in Fig.
6.6
. For exist-
ing hydrothermal systems, it is thus proposed to utilize the reinjection in order to
