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Renewable energy

Hot Dry Rock 02: Hot Dry Rock Geothermal Reservoir Development

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 hot dry rock program aims to generate carbon-free electricity by circulating water through subsurface granites that can reach 2500C.

Under certain conditions, subsurface granites can reach 2500C and higher at depths of 3 to 5 kilometers. These granites are hot for a number of reasons. They are relatively high in decaying radioactive elements, and heat is conducted from very hot sources below. In most cases (and preferably), the granites are buried beneath thick insulating sedimentary rocks.

The aim of a hot dry rock (HDR) program is to harness the energy in these granites by injecting water into a borehole and circulating it through a permeable reservoir created by hydraulically fracturing pre-existing, minute cracks in the rock. Success primarily depends on the presence of these natural fractures. The injected water is superheated as it passes through the hot rocks and returned to the surface via adjacent boreholes, where it is converted to carbon-free generated electricity using conventional steam turbine technology. Extending the reservoirs and adding more boreholes (injection and production) can increase power output.

The University of New South Wales (UNSW) is highly regarded, both domestically and internationally, in the field of hot rock energy (HRE) and its exploitation as a viable resource. It began its work on HRE in 1993, and its intensive research and studies, particularly in respect to HRE geothermal reservoir behaviour, have continued unabated ever since.

A study funded by the Australian Government's Energy Research and Development Corporation and completed in 1994 concluded that Australia is probably the only country that has extensive HDR resources with the potential to generate electricity many times its current total annual electric power needs. A significant proportion of this resource resides in the Cooper Basin. The university has determined that the granites in the Cooper Basin have the most favourable characteristics for HDR development.

The university has an exclusive arrangement with Scopenergy Limited, which was recently granted a geothermal exploration licence to exploit HDR energy sources from Block HDR-2000C in the Nappamerri Trough Region of the Cooper Basin. Block HDR-2000C covers an area of approximately 500km2, which has an estimated geothermal potential of about 102,000PJ (equivalent to 17 billion barrels of oil). This is sufficient to produce 500MWe over 25 years.

With the support of a $1 million grant under the Renewable Energy Commercialisation Program and additional funding from industry, UNSW will evaluate the HRE reservoir potential of the granite at the base of Big Lake #60 in block HDR-2000C. This was drilled and suspended as a possible future gas producer in 1997. This well reached a total depth (TD) of 9,800 feet, and granite is expected to be encountered within approximately 100 feet of this depth. The project aims to develop assessment methodology and criteria, invaluable tools for characterising HDR resources and determining the most appropriate reservoir development process. Very significant greenhouse gas reductions will result from the widespread exploitation of these HDR resources.

Although overseas HDR programs have not been successful to date, it is considered that geological and related conditions in Australia are infinitely more favourable than those encountered in HDR projects in the USA, Europe and Japan.

For more information please contact

Assoc. Prof. Sheik S. Rahman
School of Petroleum Engineering
University of New South Wales
Sydney NSW 2052
Tel (02) 9385 5659
Fax (02) 9385 5182

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