Hot rocks

New studies by an Australian company have shown how the cost and risk of producing geothermal energy – the production of electricity from steam generated through circulating water through hot rocks kilometres underground – could be reduced.

The company, Petratherm, has shown that the water can readily be heated and returned to surface in less dense rock strata above target hot granites. Current hot rock energy projects in Australia focus on establishing the “heat exchange” process within the heat producing granite itself, rather than the covering strata immediately above them.

Petratherm says the news has improved the prospects for its Paralana-1B well, 130 kilometres east of Leigh Creek in South Australia, which will become the Company’s first commercial hot rocks energy producer.

“Our subsurface engineering studies suggest that a significant lowering of the technical risk associated with the development of an underground heat exchanger (the fluid circulation system) at Paralana may occur by developing the fluid cell in the overlying cover strata rather than in the underlying granite,” said Petratherm’s Chief Executive Officer, Peter Reid.

At the Paralana test site, Petratherm has developed a model that shows that the depth to the top of the high heat producing granite is 4.5 kilometres. However, target temperatures, in the order of 200 degrees Celsius, as required for the economic production of electricity, would appear to occur within the overlying insulating cover at a depth of just 3.5 kilometres.