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Renewable energy

Hot Dry Rock 01: Validation of hot dry rock resources in the Hunter Valley, New South Wales

Renewable Energy Commercialisation in Australia, Australian Greenhouse Office, 2003
NOTE: The status of these projects will have changed since the time of publication, and project contacts may also have changed.

The Australian National University and Pacific Power/ Geodynamics are exploring geothermal resources for conversion into green energy base-load power.

Since an international conference in Canberra in 1993 described huge energy resources locked up in hot granite bodies in Australia, there has been increasing interest in how we can tap these resources and where the best sites reside in terms of connection to national electricity markets. The best sites from a geological point of view have been delineated at remote localities during oil and gas exploration, but the hunt is on for a site where a pilot plant could be connected directly to the national grid.

One possible site lies in the Hunter Valley south of Muswellbrook, where the first tenement in Australia for the right to extract heat from 'hot dry rock' (HDR) was granted to Pacific Power in February 1999. Pacific Power and researchers at the Department of Geology, Australian National University, teamed up to investigate the Muswellbrook geothermal anomaly. With the help of $790,000 in funding under the Renewable Energy Commercialisation Program, the project has determined the areal extent of the geothermal anomaly, and the temperatures and rock properties at a depth of around two kilometres in the core of the anomaly.

A series of shallow (300 metre to 920 metre deep) boreholes were drilled over the anomaly and temperature measurements were made in each borehole. A larger 1946 metre deep hole was then drilled in the central region of the anomaly and more than 1km of continuous core samples were taken to identify the rocks present and their physical properties. Temperature logs were also run and these demonstrated that the temperature is at least 900C at the bottom of the borehole. This temperature is much higher than is normally expected in Australia at such depths, which confirms that this area in the Hunter Valley is highly prospective for geothermal energy.

A 19km long seismic reflection survey was then carried out along an east-west track over the anomaly. Analysis of the seismic results and those from a micro-gravity study along the same track suggested that a buried granite probably exists at a depth of at least 5km. The geothermal anomaly is apparently due to radiogenic heat production in this buried granite, which means that the granite represents a substantial source of energy. The results of the project stimulated commercial interest in Australia's hot dry rock resources to such an extent that a new company, Geodynamics Limited, was successfully floated on the Australian Stock Exchange in 2002. This company has now acquired the Hunter Valley geothermal tenement from Pacific Power in addition to an adjoining site and two sites in the Cooper Basin in north-east South Australia. Geodynamics has raised capital of $11.7 million from its initial public offering and has commenced an ambitious development program near Innamincka, South Australia that will see the drilling of the hottest borehole ever drilled in Australia. Temperatures of over 2700C are anticipated at a depth of 4.9km.

Successful development of the Cooper Basin and Hunter Valley resources would constitute a major source of green energy base-load power for Australia. At an average temperature of 2500C, approximately 180 petajoules of usable heat for electricity production is available per cubic kilometre of rock. The combination of Australia's predominant crustal shortening stress conditions and buried granite hot rocks opens the way for low-cost engineered geothermal reservoirs based on only one injection well and two production wells. Economic modelling, performed by the Energy Laboratory at Massachusetts Institute of Technology, USA as part of the International Energy Agency's Geothermal Implementing Agreement, suggests that such a system has very favourable economics and could surpass most other renewable energy options. Moreover, the huge scale of Australia's geothermal resources, particularly those beneath the Great Artesian Basin, could provide economies of scale to rival those of base-load generation from coal.

For more information please contact

Dr Prame Chopra
Reader in Geophysics
Department of Geology
Australian National University
ACT 0200
Tel (02) 6249 3224
Fax (02) 6249 5544

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