corrosive species and scaling in wells at olkaria ... - Orkustofnun

geothermal reservoir for production
of water and steam, extensive field
investigations were carried out in
the period between 1968 and 1970.
This effort revealed a hightemperature
geothermal resource.
The reservoir temperatures are
between 250˚ and 320°C. The
stratigraphic succession of the
Reykjanes geothermal field,
revealed by drilling, consists of four
main units, namely an upper strata
(< 120 m) characterised by pillow
basalt and on top by subaerial basalt
flows of postglacial age. A more
dominant sedimentary tuff
formation above 1000 m and more
crystallized basalt formations at
greater depths have been identified
(Tómasson, 1971). Thick
hyaloclastite tuff formations have
also been identified at depth.
FIGURE 3: A simplified geological map with the
locations of high-temperature geothermal fields in Iceland
The wells drilled produced high
pressure brine and steam. The
development of the Reykjanes
geothermal area was based on an
interest in producing common salt
from brine. A salt production plant
was set up in the early 1970’s with
a 0.5 MWe power plant. More
recent surface resistivity studies
(Karlsdόttir, 1997) delineate an area
with an extent of ~ 10 km 2 for the
Reykjanes geothermal system,
whereas surface manifestations only
cover about 1 km 2 . Accelerated
drilling was undertaken in
Reykjanes during the period 2002 to
2005 and a total of 24 wells have
been drilled for electricity
production. A 100 MWe power
plant was commissioned at
Reykjanes in May 2006. The
locations of wells drilled into the
Reykjanes geothermal field are shown in Figure 4.
FIGURE 4: Location of wells in the
Reykjanes geothermal field
The Svartsengi geothermal field (Figure 5) is located about 15 km to the east of the Reykjanes
geothermal field. Stratigraphically it consists of basaltic formations down to ~300 m depth, followed
by about 300 m thick hyaloclastite series, and this is the cap rock of the reservoir. Underneath the
hyaloclastites there are flood basalts. At 1000-1300 m depth intrusions become dominant (Franzson,
1983; 1995). A fissure swarm crosses the reservoir in the eastern part of the well field. Surface
manifestations are limited and mostly confined to fumaroles in a post-glacial lava field. Discharges to
the surface are in the form of steaming fumaroles. Reservoir temperatures are uniform between 235
and 240°C (Björnsson, 1999). The field supports a geothermal combined heat and power plant with ~
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