Jökull - 01.12.1987, Side 19

Leirbotnar became contaminated with magmatic gases
causing deposition and corrosion in wells with a concom-
itant decline in their productivity. Extensive studies of
the chemistry of fumarole steam in the area performed
in 1978 and 1979 resulted in the definition of three major
upflow zones in the Krafla caldera (Gíslason et al. 1978,
Armannsson & Hauksson 1980). The Leirbotnar and
Leirhnjúkur upflows were found to be contaminated by
magmatic gas, but the Suðurhlíðar upflow in the south-
ern flanks of Mt Krafla unaffected. In 1980, drilling
continued with two production wells in the Leirbotnar
field and one exploration well in Suðurhlíðar. The ex-
ploration well showed that the reservoir in Suðurhlíðar
was not affected by the magmatic activity. This was in an
agreement with the fumarole studies. Five wells were
drilled in the Suðurhlíðar field in 1981 and 1982. These
draw sufficient steam for the production of 15 MWe. As
reservoir modeling studies suggest this to be close to the
maximum capacity of the field drilling was stopped in
Suðurhlíðar. In June 1980 a small field of surface alter-
ation near the southern rim of the caldera, the Hvíthólar
field, was observed steaming. Chemical analysis of the
85.07. 0884
Fig. 6. Gas concentrations of fumarole fluids in the
Krafla geothermal area. 1979-1986 (adapted from Ár-
mannsson and Benjamínsson 1986). — Mynd 6. Gas-
breytingar í gufuaugum á árunum 1979-1986.
Fig. 7. Typical temperature profiles for the three well
fields at Krafla. — Mynd 7. Einkennandi hitaferlar fyrir
borsvæði Kröfluvirkjunar.
steam revealed that a reservoir temperature of 260-
270°C could be expected and that the fluids were not
contaminated by magmatic gases. In 1982 and 1983 three
wells were drilled in this field one of which is a good
producer. The Hvíthólar field is however small and of
limited producing capacity.
The future drilling strategy in Krafla is yet to be
decided. Additional fields could still be found and uti-
lized. However the results of studies of well fluids and
fumarole steam have shown a large decline in the mag-
matic gas component of the reservoir fluids in the affect-
ed fields as Fig. 6 shows (Benjamínsson, 1985; Ármanns-
son & and Benjamínsson 1986). So the most interesting
prospect in the near future is apparently drilling in the
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