Jökull - 01.12.1987, Page 16

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Fig. 2. Tectonic map of the Krafla area, showing the
caldera, the active fissure swarm and the location of the
Krafla power plant. — Mynd 2. A myndinni er sýnd
stciðsetning Kröfluöskjunnar, jarðhitasvœðisins og orku-
versins innan spriingukerfisins.
1970, and the first wells were drilled in 1974. The pur-
pose of the exploration program was collection of in-
formation on structure, extent, subsurface temper-
atures, chemistry, production characteristics and capac-
ity of the reservoir. Before the completion of this
program the decision to build a 60 MW electric power
plant at Krafla was made, its construction being concur-
rent with drilling for steam. The plant was completed in
1977 but drilling has continued. When the plant was
started in 1978 the available steam was sufficient for the
production of 7 MWe, but presently 30 MWe are gener-
ated. Thus the first installed unit is fully utilized.
Three fields within the Krafla area have been drilled
into: the Leirbotnar, Suðurhlíðar and Hvíthólar fields
(Fig. 3). Recovery of steam from the Krafla reservoir
has been relatively poor, the main cause being the mag-
matic activity in the area. The activity started in 1975
shortly after the production drilling began. The first
wells were in the Leirbotnar field and these were ad-
versely affected. Magmatic gases intruded the reservoir
and contaminated its fluids (Ármannson et al., 1982).
The Suðurhlíðar and Hvíthólar fields have not suffered
similarily, but their generating capacities proved limit-
ed. The subsurface characteristics of the three fields are
very different. The Leirbotnar field is divided into an
upper, water saturated, zone with a mean temperature
of 205°C down to about 1000 m depth and a lower,
boiling, zone with temperatures from 300-350°C. The
Suðurhlíðar field is a boiling system, and the Hvíthólar
field exhibits boiling characteristics down to 700 m depth
with a cooler regime below.
Early investigations in the area have been described in
review articles by Stefánsson (1980, 1981). Since then
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Fig. 3. The three well fields at Krafla. — Mynd 3. Bor-
svœðin við Kröfluvirkjun.
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