Following the announcement of the Australian Government's Onshore Energy Security Initiative in August 2006, Geoscience Australia has established a geothermal energy project. The project aims to improve the existing knowledge about the type and location of geothermal resources in Australia on a national scale. It also aims to encourage investment, exploration and exploitation of this energy source through provision of pre-competitive geoscience datasets relevant to geothermal energy.
To achieve these objectives, the geothermal project aims to:
Figure 1
Distribution of drill holes
© Geoscience Australia
Current understanding of Australia's geothermal resources is based on limited data such as temperature measurements taken in 5722 petroleum and mineral boreholes across the country (Figure 1) which were used to generate a map of estimated crustal temperatures at a depth of five kilometres (Figure 2; Chopra & Holgate, 2005).
Heat flow data, which is the product of geothermal gradient and thermal conductivity, are rarer, with the most recently published compilation containing less than 200 heat flow data-points for Australia (Figure 3). These temperature and heat flow measurements are unevenly distributed and, where no temperature or heat flow data exist, the available information has been interpolated over large areas to generate national-scale maps.
Compilations of other national-scale datasets relevant to exploration for geothermal energy are incomplete, non-existent or not publicly accessible. Datasets such as the 3D distribution of high-heat producing granites overlain by insulating low thermal conductivity sediments will be useful for identifying locations with potential for high temperatures. Geothermal energy is an emerging industry in Australia and access to targeted geoscience information will lower the risk to explorers and investors as well as facilitate the exploitation of this low-emission energy source.
Figure 2
Estimated Crustal Temperature
at 5km Depth
© Geoscience Australia
Measuring heat flow is a two-step process which requires both field-based and laboratory-based measurements. Wireline logging equipment is used to measure temperature profiles down a borehole or the geothermal gradient and a thermal conductivity meter is used to measure the thermal conductivities of rock samples collected from the same borehole. Use of the temperature measurements in conjunction with measured conductivity will enable Geoscience Australia to estimate the heat flow at each site and provide an insight into the potential of the geothermal resource.
The geothermal energy project has been granted the funds needed to purchase the required field and laboratory equipment and expects to have an operational heat flow capability by the end of 2007.
For the duration of the Onshore Energy Security Program, new heat flow data will be collected from existing drillholes across Australia which meet certain criteria, specifically that they are deeper than 300 metres, have core samples available and are accessible. The drillholes need to be sufficiently deep to avoid climate-related seasonal, annual and decadal temperature variations, which can propagate down to about 100 metres, and thermal disturbances caused by the circulation of shallow groundwaters. Three hundred metres is considered to be deep enough to account for these disturbances and enable the depth-dependent, regional geothermal gradient to be established (Barbier, 2002). Drillholes included in the compilation incorporate mineral, petroleum, coal, stratigraphic and water bores. Depending on data coverage and geothermal prospectivity, there may be new drill-holes in some locations.
New heat flow data will be collected in collaboration with State and Territory Geological Surveys under the existing National Geoscience Agreement.
Figure 3
Surface heat flow map for Australia
© Geoscience Australia
In the Geothermal for Cities sub-project, the geothermal resources beneath selected capital cities and/or major population or industrial centres across Australia will be assessed and quantified. This will be done by measuring geothermal gradients and rock thermal conductivities in existing drillholes near these centres and generating estimates of heat flow.
Current knowledge of Australia's geothermal resource distribution is focused almost exclusively on the high temperature (>150°C) hot rock resources, which given appropriate geological conditions and technological expertise, can be used to generate electricity. To date, far less attention has been given to mapping the distribution of lower temperature (<100°C) geothermal resources, which have significant potential for direct-use applications when located near populated areas. The purpose of Geothermal for Cities is to provide information on such resources.
Direct-use refers to the immediate use of the heat energy rather than converting it to some other form of energy such as electrical energy. It is more efficient to use geothermal energy directly, rather than for electricity generation: cycle conversion efficiency for geothermal power generation is around 10-20 per cent, meaning that up to 90 per cent of the extracted geothermal energy is lost as heat (Tester et al., 2005). There is an extensive range of direct-use applications including agricultural (eg: greenhouse heating), industrial (eg: evaporation, drying, sterilisation, chemical extraction), space heating, bathing, aquaculture and water desalination (see Figure 4, Lindal (1973)). In May 2005, worldwide direct-use of geothermal energy was approximately 273 372 TJ/yr (75 943 GWh/yr), equivalent to annual savings of 25.4 million tonnes of oil and 24 million tonnes of carbon emissions to the atmosphere (Lund et al., 2005).
Figure 4
Potential direct-use applications
of geothermal energy
© Geoscience Australia
The essential components of the hot rock model in the Australian context are buried, high-heat producing granites which are insulated by a three to five kilometre thick overlying package of low thermal-conductivity sediments. This map includes information about volumes of buried granites using 3D modelling of seismic, gravity and magnetic data, their heat-generation capacity and geochemical composition, as well as the composition, conductivity and thickness of overlying sediment packages.
There are several national-scale datasets, including groundwater temperatures, and locations of paleo-volcanic activity, thermal-IR anomalies and infrastructure which will assist the geothermal industry. Throughout the geothermal project, these datasets will be compiled and made available to industry and the public through Geoscience Australia's information portal.
To enable effective storage, capture and distribution of existing and new geothermal data collected by Geoscience Australia, a geothermal information system will be developed. Ultimately it will include data such as temperature, heat flow, thermal conductivity and other rock properties which will be accessible via the internet.
For the duration of the Onshore Energy Security Program, the geothermal project will work towards providing a national scale estimate of Australia's geothermal resource. In conjunction with this process, and in collaboration with other geothermal stakeholders, Geoscience Australia will be involved in the development of a geothermal reserves definition scheme similar to the minerals-based JORC code and petroleum-based SPEE scheme. Establishing such a scheme is critical to large-scale development of the geothermal industry. It would allow Australian geothermal exploration companies to define their resources to an agreed standard and attract development funding in the same way as mineral and petroleum exploration.
The Geothermal Project is creating a series of factsheets which detail various aspects of geothermal energy use in Australia. The first two in the series can be accessed below in either low or high resolution.
| Title | Authors |
|---|---|
| Geoscience Australia Record 2009/015: The Cooper Basin Region 3D Map Version 1: A Search for Hot Buried Granites. |
AJ Meixner and F Holgate |
| Geoscience Australia Record 2008/018: Proceedings of the Sir Mark Oliphant International Frontiers of Science and Technology Australian Geothermal Energy Conference. |
H Gurgenci and AR Budd |
| Title | Authors & Where Presented |
|---|---|
| Mapping Heat Across the Australian Continent | Anthony Budd Presented at the 3rd Hot Rock Energy Conference in Adelaide, August 2007 |
| Geothermal Resource in Australia - Status and Research Needs [PDF 1.8MB] | James Johnson Presented at the Geothermal Energy Industry Roundtable at Parliament House, March 2007. |
Geothermal Energy project email: geothermal@ga.gov.au