Jökull - 01.12.1987, Page 15

Exploration and development of the
Krafla geothermal area
HALLDÓR ÁRMANNSSON, ÁSGRÍMUR GUÐMUNDSSON
AND BENEDIKT S. STEINGRÍMSSON
Orkustofnun, National Energy Authority
Grensásvegur 9, 108 Reykjavik, lceland
ABSTRACT
The Krafla high temperature geothermal area is situ-
ated within the neovolcanic zone in Northeastern Iceland.
The geology ofthe area is dominated by an active central
volcano, with a caldera and an active fissure swarm. The
volcanic activity at Krafla is episodic, occurring every
250-1000years, and each episode lasting 10-20 years. The
latest eruptiveperiod started inl975. The geothermal area
is within the Krafla caldera. Surface manifestations like
steaming fumaroles and altered ground cover an area of
aboutl5 km2. In the uppermost 700 meters the geothermal
reservoir is characterized by a large resistivity low in the
central part of the caldera and two smaller ones at the
caldera rim. The major anomaly is underlain by a higher
resistivity body, coinciding with a change in the lithology
from hyaloclastites to basaltic lavaformations, increased
frequency of intrusive rocks and high temperature hy-
drothermal alteration. Three separate upflow channels
within the main geothermal area have been identified by
geochemical studies. The Krafla area is under exploita-
tion and 24 deep wells have been drilled to provide ge-
othermal steam for the Krafla electric power plant, com-
missioned just before the present volcanic activity started.
The wells are sited in three different fields which differ
considerably in size and production characteristics. Parts
of the reservoir are liquid saturated but the bulk of it is
boiling. Temperatures of35(PC have been encountered at
2 km depth. The permeability is 1-4 millidarcy and the
average wellflow is relatively low. Numerical simulation
studies of the present wellfields indicate that they can
sustain 55 MW electric production for at least 30 years.
The developement of the Krafla geothermal area has
been performed in the shadow of the volcanic activity.
Magmatic gases have intruded the geothermal reservoir
and contaminated two of the three major upflow zones
causing deposition and corrosion in production wells.
The magmatic influence has been on the wane for the
last few years.
INTRODUCTION
The Krafla geothermal area is located in the Neovol-
canic zone in northeastern Iceland (Fig. 1), about 10 km
northeast of Lake Mývatn (Fig 2). It is located within the
Krafla caldera, which was formed about 100 thousand
years ago (Sæmundsson, 1983). Volcanic activity in the
Krafla region is extensive and there have been several
eruptive periods during the last few thousand years. The
most recent one started late in 1975 and nine eruptions
have already taken place in Krafla during this period,
the last one in September 1984 (Björnsson, 1985).
An exploration program for the area was initiated in
Fig. 1. The central volcanoes and fissure swarms within
the Northeast Volcanic zone in Iceland, (Björnsson
1985). — Mynd 1. Einfölduð mynd af gos- og sprungu-
kerfum á Norðausturlandi.
JÖKULL
No. 37,1987