Jökull - 01.12.1966, Page 45

GUNNAR BODVARSSON1:
Some Considerations on the Optimum Production
and Use of Geothermal Energy
ABSTRACT
Various geological and geophysical pheno-
mena of interest in connection icith the pro-
duction of geothermal energy are described ancl
discussed. A lumpecl parameter model for the
hydrology of thermal areas is given. Some ele-
mentary optimization problems in the geo-
thermal industry are discussed.
(1) INTRODUCTION
The utilization of natural heat resources for
power generation and building heating is a
technology of a rather recent origin. The first
geothermal power plants were built in Italv
about half a century ago, and the first district
heating system was put into operation in
Reykjavík, Iceland, in 1930.The development has
been rather slow, and, as of now, geothermal
power plants in Italy, New Zealand, and the
U.S.A. generate a total of about 600 MW of
electric power. In Iceland some 75,000 people
live in houses heated by geothermal sources.
The future of the industry is somewhat un-
certain, but geothermal areas are known to
exist in a great number of locations, mainly
in the Circum-Pacific belt. Some of these areas
may possess considerable potential.
The geothermal industry has much in com-
mon with the petroleum industry. Geological
and geophysical exploration, well drilling, pip-
ing and/or power generation are the most
important steps in the development of geo-
thermal sources. In solving the various pro-
blems involved the geothermal industry has
1) Department of Oceanography, Oregon
State University, Corvallis, Oregon. U.S.A.
borrowed heavily frorn the older and more ad-
vancecl petroleum industry.
Some of the most difficult, and also the
most interesting, problems in both industries
are encountered in connection witlr the un-
certainties involved in the exploration and
production phases. Large scale exploration must
be carried out with rather small chances of
detecting workable sources, and, mainly in the
geothermal industry, large scale plants must.
be built on the basis of incomplete data on
the potential and useful life of the sources. On
the basis of meager information the geothermal
engineer altempts to work out the optimal de-
sign and operation of plants and sources.
From the more basic point of view, the pro-
blem of optimization in the geothermal in-
dustry has not received much attention, and
a discussion therefore appears to be useful.
The present paper is written for the modest
purpose of pointing out some of the main pro-
blems involved.
For the benefit of the unacquainted reader
it should be mentioned that geothermal areas
may produce hot water, wet steam, or dry
superheated steam. Steam pressure varies from
a few up to about 25 atmospheres. Depth of
producing wells is up to 1,000 meters in steam
areas, and up to 2,200 meters in water areas.
The diameters of producing wells varies from
150 to 400 mm.
(2) HYDROTHERMAL SYSTEMS
(2.1) General considerations. There is practi-
cally no doubt that the thermal water and
steam produced by hot springs ancl boreholes
is predominantly of meteoric origin. In other
words, it is ordinary ground water which has
been heated to elevated temperatures through
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