Simmering rocks found several kilometres beneath the earth's surface hold the potential to meet our power needs
WITH the fossil fuels
depleting fast, hot dry
rock (HDR) found several
kin under the earth's
surface promises an ecofriendly, economically
viable and virtually inexhaustible energy source.
The Australian Geological Survey Corporation
(AGs()) predicts that one cubic km of
rock at 25(Y'C can produce the energy
equivalent of 40 million barrels of oil
(Prospects, Vol 2, No 2).
By 2010, it is estimated that Asia
would be responsible for nearly 50 per
cent of the world's global greenhouse
gases. In such a scenario, 11DR technology could provide a clean, emission-less
source of energy that, in some cases,
would be sufficient to meet an entire
nation's demands. Besides
Australia, scientists in
Japan and the us are also
working on the HDR technology which is especially
suitable for countries like
India, where the geological
pattern favours easy
exploitation of this source.
Tapping the subterranean fount of energy involves drilling
holes several ken deep into tile earth
where the temperature of rocks ranges
from 200-250'c. Water is pumped into
these bore holes and allowed to circulate
through the source rock's fracture network, which may have fissures barely a
few millimetres wide. This water is then
ejected under pressure From a second
hole in the form of steam. The steam is
used to power turbines for electricity
generation, after which it is condensed
back to water that can be re-used.
The cost of drilling a bore hole to
reach the hot rocks is about the sanie as
for drilling an oil well.
The HDR technology is different
from the conventional geothermal
exploration. Whereas the former
involves injection of water into the bore
holes and uses the heat of the rocks for
deriving energy, the latter requires
searching for permeable 7ones where
water is already flowing at high temperstores and which can Lit tapped and
brought to the surface.
Says Donut Wyborn, AGSO'S pi incipal research scientist, "Many countries
are interested in ibis technology but not
all have the source rocks which are suitable." For example, in countries like
Indonesia and the Philippines, where
the hot volcanic rocks are close to the
surface, the iii)t@ technology does not
hold good. Stress lines in the rocks produce compitcated fractures which
inakes the HDR method unsuitable. On
the other hand, geothermal energy is
widely tapped in Indonesia and the Philippines.
The poiential of ADR was first tested
in the Los Alamos National Laboratory,
Arizona in the '70s. Currently, 2
Japanese organisations, the New
Lnergy and Industrial Technology
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