Hotbeds of energy

Simmering rocks found several kilometres beneath the earth's surface hold the potential to meet our power needs

Published: Monday 31 July 1995

-- 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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