Jökull - 01.12.1961, Blaðsíða 41

U. N. CONFERENCE ON NEW SOURCES OF ENERGY, ROME 1961
Exploration of Subsurface Temperature in Iceland
BY
G. BODVARSSOM and G. PALMASON
STATE ELECTRICITY AUTHORITY, REYKJAVIK, ICELAND
SUMMARY.
A considerable amount of data on borehole
temperatures has been collected in Iceland. Tliis
luork has been carried out for three purposes.
Firstly, as a rneans of prospecting, secondly, in
order lo obtain data on the physical conditions
in thermal areas and, third, in order to obtain
a comparison betiueen thermal and non-thermal
regions. The results have furnished data on the
temperature of the water circulating in the ther-
mal regions ancl on the average outward con-
duction flow of heat in non-thermal regions.
The main part of the data has been collected
on the basis of temperature measurements in
boreholes. The boreholes are of various depths,
the maximum depth being 2,200 meters. Tem-
perature gauges consist of maximum mercury
thermometers, electric resistance thermometers
and vapour pressure thermometers. The applica-
bility of the various types is descussed.
In general boreholes are cooled by the drilling
fluid. Instationary temperature conditions are,
therefore, encountered and the correct evalu-
ation of this effect is of great importance. The-
oretical studies have been carried out and the
results are presented.
There appear to be possibilities of estimating
the base temperature of hydrothermal systems
on the basis of the chemical constituents in the
thermal zuater. Mainly the amount of silica dis-
solved in the water appsars to depend on the
temperature conditions. This phenomenon is
discussed briefly.
Results from thermal areas in Iceland are giv-
en in the final section of the paper zuhere, also,
the main implications of the results are discussed.
The maximum temperature sofar measured in
thermal regions in Icelancl is approximately 230
°C. The temperature gradient in nonthermal
regions has been found lo vary betzueen 0.033
and 0.163 °C/m.
I. INTRODUCTION.
The subsurface temperature field constitutes
the rnost important set of physical data to be
assessed in any exploration of natural heat
phenomena. The temperature studies are carried
out for three purposes. First, as a method of pro-
specting. Second, for the purpose of obtaing im-
portant quantitative data on the physical condi-
tions in thermal areas under exploitation.
Third, in order to obtain observational data on
regional temperature conditions and the ther-
mal mechanism generating thermal areas.
Temperature data can be obtained directly by
measurements in boreholes, or indirectly, on the
basis of geochemical inference. The latter met-
hocl is based on the fact that the equilibrium con-
ditions of certain geochemical reactions depend
substantially on the reaction temperature. Geo-
chemical data can thereforc in some cases be
indicative of reaction temperatures.
The purpose of the present paper is to give
a brief review of the thermal methods applied in
Iceland and report results frorn a few thermal
areas. The background of the paper is based on
observational material from a great nurnber of
boreholes in Iceland with an integrated depth
of 70,000 meters. The maximum depth drilled
is 2,200 meters. Moreover, extensive analytical
material on thermal waters and gases has been
available for the purpose of thermochemical in-
ference.
For general information on the physical con-
dition in thermal areas in Icelancl the reader is
referred to papers by Einarsson (1942) and Bod-
varsson (1961). l’he latter paper contains furth-
39