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PSWestern Australia’s Geothermal Resources*
Western Australia commenced a new era in the search of energy from geothermal resources to broaden State’s energy base by the first acreage release for geothermal exploration in the Perth Basin on 22 January 2008 (Figure 1). Coincidently, the first Australian geothermal production well reached its target depth of 4221 m in Geodynamics Habanero 3 (Figure 2). The geothermal acreage release followed the amendments to the State’s Petroleum Act 1967 that was proclaimed in January 2008, Petroleum and Geothermal Resources Act 1967.
South Australia was the first State to develop legislation for geothermal exploration and granted the first Australian Geothermal Exploration Licence (GEL) in 2001. Since then about 12 geothermal wells have been drilled in South Australia by the following companies: Geodynamics, Petratherm, Green Rock Energy, Scopenergy, and Geothermal Resources (Figure 2). There is an increasing trend with exponential increase in interest, companies, and investment for exploring and developing geothermal energy. The investment totalling $686 million has been proposed for five-year work program by 27 companies in 166 licences.
The majority of current and forecast investment to
explore for, and demonstrate the 
potential
of, geothermal energy in Australia
focused on hot rock enhanced geothermal systems (EGS). The most promising
Australian basins include: Cooper Basin in the south-west corner of Queensland
and South Australia, the Hunter Valley, New South Wale, and the Perth Basin,
Western Australia.
For this century, energy outlook indicates that
there will be significant energy supply from geothermal, solar, wind, and hydro
resources. Of these, geothermal energy from hot rocks shows the greatest
potential for long-term, continuous electricity supply and Australia leading way
in EGS technology. The trend in EGS technological advances indicate, within
decades, the cost for electricity generation from EGS will be competitive with
conventional energy generation from coal and natural gas, and lower than any
other form of renewable energy (solar, wind, wave, tidal).
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Geothermal energy includes thermal or
electrical power produced from the heat contained in the Earth. There
are two basic types of energy that can be sourced from Earth’s heat —
that from hydrothermal systems (hot geofluids) and from hot rocks (hot
dry rocks, HDR). Geothermal energy from hot rocks differs from the
conventional hydrothermal energy process that produces power
commercially in geologically active areas. Since 1970 research has
been undertaken worldwide aimed at commercial utilization of the
Earth’s heat from hot rocks, using technology referred to as EGS
(enhanced geothermal systems) that is applied to HDR sources so that
energy can be extracted. To utilize hot dry rocks, EGS technology is
For electricity generation, suitable
temperatures for hot water and steam range from 120 to 370°C. In
contrast, shallower reservoirs of lower temperature (21-149°C) can be
Direct use of low-temperature hydrothermal resources (~50°C) in Australia include swimming pool heating at Perth’s Challenge Stadium, Victoria’s spa developments at Mornington Peninsula and Mataranka, New South Wales’s artesian baths at Moore, Lighting Ridge, and Pilliga. For heating and cooling, heat source pump are in use at the Canberra’s Geoscience Australia building, Hobart’s Integrated Energy Management Centre, Antarctic Centre, and the Aquatic Centre as well as at the Perth’s Melville Aquatic Centre.
Medium-temperature hydrothermal resources
(50-100°C) are in use in many places in the world, including
Birdsville in Queensland. These hydrothermal resources are in use for
both direct heating and cooling and electricity production, with a
Conversion of geothermal energy into power is economically feasible only when three factors can be satisfied: 1) the resource is located at shallow depths, usually less than 3 km, but possibly as deep as 7 km; 2) porosity and fracture permeability are sufficient to produce large quantities of thermal water, either naturally or by enhanced geothermal system technologies; and 3) the hot geothermal fluids can be efficiently transported (typically less than a few tens of kilometres) to a power-generating facility.
Geological, hydrogeological, electrical,
magnetic, geochemical, and seismic data are
Australia is tectonically stable and does
not have geologically active areas characterized by volcanism, crustal
rifting, and recent mountain building that typically host
high-temperature hydrothermal provinces. However, there is
At present, the only geothermal energy
being
Australian and Western Australian geothermal resources have been discussed by: Sass (1964), Sass et al. (1976), Cull (1977, 1979, and 1982), Cull and Denham (1978), Narayan et al. (1998b), Chopra (2005), Chopra and Holgate (2007), and Ghori (2007 and 2008).
First study, specifically to evaluate
geothermal energy, for Western Australia, was initiated in the 1980s
from hydrothermal resources and recognised low temperature reservoirs
(65-85oC) at greater depths (2-3.5 km), with the best
economic The first study by Bestow (1982), mainly focused on low-temperature geothermal reservoirs up to 100oC, applying the available data on heat flow, geothermal gradient, and hydrogeology to the geological framework of the Yilgarn Craton, and the Eucla, Officer, Canning, Carnarvon, and Perth basins. The study was more qualitative than quantitative and concluded that geothermal and hydrogeological conditions for developing a geothermal resource for both direct use and power generation are present in Western Australia.
The second study by Chopra and Holgate
(2007) was on high-temperature geothermal reservoirs up to 200oC.
The aim of the study was to map and identify the most suitable areas
within the Canning, Carnarvon, and Perth basins that may have
The Chopra and Holgate (2007) study has
evaluated the quality and quantity of available subsurface temperature
data from 273 petroleum exploration wells in the Canning (100),
Carnarvon (90), and Perth basins (83), and extracted temperature data
from more than 580 wells yet to be evaluated. The purpose was to
calculate reliable true formation temperatures, to estimate the
equilibrium geothermal gradient for each well. Higher than normal
geothermal gradients recorded in many wells provided the first
indication of high heat flow (Figure 3). In Australian basins, the
high crustal temperatures are usually associated with local high-heat
production under rocks of low thermal conductivity. At present,
detailed geochemical information on the basement in the studied wells
is not available. The estimates of equilibrium geothermal gradient and
depth to basement have been The most prospective basin for geothermal energy appears to be the Carnarvon Basin, followed by the Canning and Perth basins. This is based on the present-day geothermal gradient for wells where the estimated depth to 200°C is less than 5 km (Figures 4 and 5). Geochemical analyses of basement rocks are required to assess the heat-generation capacity of rocks, as small differences in the concentrations of thorium and uranium can have quite significant impacts on heat-generation capacity, whereas large variations in potassium concentration have only a second order effect on the heat-generation capacity. The stress conditions are best known for the Perth Basin where the predominant orientation of the maximum horizontal stress is east-west, with similar conditions inferred for the Canning and Carnarvon basins. Given that this stress orientation is compatible with both strike-slip and overthrust failure, an understanding of relative stress magnitudes is also required for assessing the uncertainty in the application of EGS technology. The extent and economic feasibility of hydrothermal and hot rock geothermal resources are presently unknown because studies were qualitative, rather than quantitative, and based on limited datasets. Data gathering, validating, and interpretation of greater than 900 wells is underway for a quantitative assessment that requires systematic geological, hydrogeological, geophysical, and geochemical evaluation to further delineate and prove these resources.
This north-south elongated trough in the southwest of Western Australia (Figure 1) contains mostly a Permian to Lower Cretaceous succession under a thin cover of Tertiary. The eastern boundary is the Darling Fault and the basin extends offshore to the continental-oceanic boundary. The Perth Basin has been studied since the early 1900s for geological mapping and evaluation of coal, water, mineral, and petroleum resources. The published and unpublished data of these studies are archived in the GSWA Library; they provide detail background on geology of the Perth Basin. This evaluation, as a first look, is mainly based on GSWA publications including those on geothermal resources — Bestow (1982), Chopra and Holgate (2007), Ghori (2007 and 2008); for hydrogeology — Thorpe and Davidson (1991), Davidson (1995), those on petroleum geology — Crostella (1995), Mory and Iasky (1996), Crostella and Backhouse (2000), Owad-Jones and Ellis (2000) and unpublished company reports submitted to GSWA. Most of the data archived in GSWA Library were the basis of the studies consulted for this study.
Figure 6 shows generalised stratigraphy of
the Perth Basin and distribution of water aquifers, petroleum
reservoirs, and The salinity of the groundwater in the youngest Quaternary-Neogene aquifers ranges from about 130 to 12,000 mg/L TDS (total dissolve solids), temperature at the water table ranges from 19 to 24oC, averaging about 21oC (Davidson 1995), and the age of water ranges from present to about 2000 years at the base (Thorpe and Davidson, 1991). Within the Cretaceous Leederville aquifer, the salinity ranges from 176 to 2511 mg/L TDS, and temperature from 20 to 39oC. The average geothermal gradient is about 25oC/km. The oldest Yarragadee aquifer is a major confined aquifer underlying the entire Perth region and extending to the north and south within the Perth Basin. It is a multi-layer aquifer, more than 2 km thick. The salinity of groundwater ranges from 140 to more than 10,000 mg/L TDS, and temperature ranges from 28 to 45oC and averages about 39oC. The geothermal gradient is about 25oC/km. The maximum depth to the base of the aquifer is about 3 km; this indicates temperature of 90oC (using 20oC at the water table). This is comparable to the finding of Bestow (1982): low temperature reservoir ranging from 65oC to 85oC at a depth range of 2 to 3.5 km. The highest temperature groundwater lies beneath the Kings Park Formation in the central Perth region (Davidson, 1995).
Figure 7 shows the distribution of:
geothermal gradients, and Figure 8 shows the temperature versus depth.
These figures are based on data available from 145 artesian monitoring
bores. Of these, 47 were Petroleum wells (242) provide temperature distribution for a larger area and a greater depth (850 m) than the Perth region water bores. Of these, 83 wells have been studied by Chopra and Holgate (2007) for geothermal gradients and the remaining are under study. Figure 9 shows the Perth Basin subsurface temperatures as a function of depth: a) recorded BHTs (540) in 242 petroleum wells; b) Jurien 1; c) Woodada Gas Field. These plots show that the recorded temperatures and depths are up to 150oC and 4.5 km, respectively. The corrected estimated equilibrium temperatures are expected to be higher than these recorded temperatures, which are generally 10 to 20% higher. For the Perth Basin, the estimated geothermal gradients in 83 wells by Chopra and Holgate (2007) indicate the presence of wells with very high to normal gradients, ranging from 90oC/km to 20oC/km (Figure 3). Gradients in wells deeper than 2 km are considered more reliable and representative for hot dry rock resources. Conceptual models for petroleum and geothermal resources have been developed for the Beagle Ridge (Figure 10a) and the Cadda Terrace (Figure 10b) of the Perth Basin, because high geothermal gradients are observed in Jurien 1 (55oC/km) on the Beagle Ridge and Woodada 02 (40oC/km) within the Cadda Terrace. Jurien 1 was drilled to a total depth of 1026 m and intersected granitic basement at 967 m. The extrapolated recorded temperatures indicate that 200oC is expected to reach between 2.5 km and 3 km (Figure 9b). It is an economical depth for developing geothermal resources, if other factors for developing EGS are found favourable. Figure 9c shows the subsurface temperatures as a function of depth in 17 wells of the Woodada Gas Field. The extrapolated temperatures indicate that 200oC is expected to reach between 4 and 5 km; these are suitable depths for developing geothermal resources with EGS favourable conditions. The reservoir temperature of the Woodada Gas Field is 120oC at depth range from 2125 m to 2496 m (Owad-Jones and Ellis, 2000). For the Perth region as a whole, stress data collected in situ are available from 43 locations at different depths and from different sources, but for the Perth Basin portion, the data are exclusively from borehole breakouts recorded in 20 petroleum exploration wells. The recorded maximum horizontal stress orientations are E-W across the Perth region (Reynolds and Hillis, 2000); these observations are highly relevant for assessing the HDR prospectivity of the basin, because maximum horizontal stress is favourable (Chopra and Holgate, 2007). First acreage release in Western Australia is the beginning of a major expansion in exploration for hot dry rock geothermal resources. Amendments to the Petroleum Act 1967 to grant rights for geothermal energy exploration and development have facilitated the growth of a new industry in Western Australia. Pre-competitive geoscience information relevant to hot rock geothermal exploration largely comes from petroleum exploration wells. These are generally in clusters, sparsely distributed at basin scale. Whereas temperature measurements from petroleum well logs are reasonably reliable, in-situ stress measurements, required for applicable EGS technology are uncertain. Much more reliable geoscience information is required to assist private sector exploration for geothermal resources in Western Australia, most of which will be focused near energy-demand centres or near existing major power-transmission routes (Ghori, 2008).
Bestow,
T.T, 1982, The
Chopra, P.N, 2005, Status of the geothermal industry in Australia, 2000-2005: Proceedings, World Geothermal Congress 2005, Antalya, Turkey, 24-29 April 2005.
Chopra, P.N, and F. Holgate, 2005, A GIS analysis of temperature in the Australian crust: Proceedings, World Geothermal Congress 2005, Antalya, Turkey, 24-29 April 2005.
Chopra,
P.N, and F. Holgate, 2007, Geothermal energy
Cull, J.P, 1977, Geothermal energy prospects in Australia: Search, v. 8, no. 4, p. 117-121.
Cull, J.P, 1979, Regional variations in Australian heat flow: Australia BMR, Journal of Australian Geology and Geophysics, v. 4, no. 1, p. 1-13.
Cull, J.P, 1982, An appraisal of Australian heat flow data: Australia BMR, Journal of Australian Geology and Geophysics, v. 7, p. 11-21.
Cull, J. P, and D. Denham, 1978, A case for research and development on geothermal energy in Australia: Australia Bureau of Mineral Resources, Record 1978/58, p. 7.
Crostella,
A., 1995, An evaluation of the hydrocarbon
Crostella, A., and J. Backhouse, Geology and petroleum exploration of the central and southern Perth Basin, Western Australia: Western Australian Geological Survey, Report 57, 85 p.
Davidson, W.A., 1995, Hydrogeology and groundwater resources of the Perth Region, Western Australia: Western Australia Geological Survey, Bulletin 142, 257p.
Ghori, K.A.R., 2007, Search for energy from geothermal resources in Western Australia: September 2007 Petroleum in Western Australia, Western Australia’s Digest of Petroleum Exploration, Development and Production, Department of Industry and Resources, Perth, p. 36-39.
Ghori, K.A.R, 2008, The search for Western Australia’s geothermal resources: Geological Survey of Western Australia Annual Review 2006-07, p. 25-31.
Hillis, R. R., and S. D. Reynolds, 2000, The Australian Stress Map: Journal of the Geological Society, London, v. 157, p. 915-921.
Mory, A.J., and R.P. Iasky, 1996, Stratigraphy and structure of the onshore northern Perth Basin, Western Australian Geological Survey, Report 436, 102 p.
Narayan, S.P., D. Naseby, Z. Yang, and S.S. Rahman, 1998a, Petroleum and hot dry rock: two of the energy sharing commonalities: APPEA Journal 1998, p. 830-847.
Narayan, S.P., D. Naseby, Z. Yang, and S.S. Rahman, 1998b, Creation of HDR reservoirs under Australian in-situ stress conditions, in Proceedings of Twenty-third Workshop on Geothermal Reservoir Engineering: Stanford University, Stanford, California, USA, January 1998, p. 322-329.
Owad-Jones, D., and G. Ellis, 2000, Western Australia atlas of petroleum fields, Onshore Perth Basin: Petroleum Division, Department of Mineral and Energy Western Australia, Volume 1, 114 p.
Regenauer-Lieb, K., and F. Horowitz, 2007, The Perth Basin geothermal opportunity: September 2007 Petroleum in Western Australia, Western Australia’s Digest of Petroleum Exploration, Development and Production, Department of Industry and Resources, Perth, p. 42-44.
Reinecker, J., O. Heidbach, M. Tingay, B. Sperner, and B. Müller, 2005, The release of the 2005 World Stress Map: World Stress Map Project, Geophysical Institute, Karlsruhe University (http://www.world-stress-map.org).
Sass, J.H, 1964, Heat-flow values from the Precambrian of Western Australia: Journal of Geophysical Research, v. 69, no. 2, p. 299-308.
Sass, J.H., J.C. Jaeger, and R.J. Munroe, 1976, Heat flow and near-surface radioactivity in the Australian continental crust: United States Geological Survey, Open-File Report 76-250, 91p.
Somerville, M., D. Wyborn, P. Chopra, S. Rahman, D. Estrella, and V.D.M. Theo, 1994, Hot dry rock feasibility study, a report compiled for the Energy Research and Development Corporation: Canberra, Australia, Energy Research and Development Corporation, ERDC 94/243, 133p.
Thorpe, P.M., and W.A. Davidson, 1991, Groundwater age and hydrodynamics of the confined aquifers, Perth, Western Australia, in Proceedings of the International Conference on Groundwater in Large Sedimentary Basins, Perth, Western Australia, 1990: Australian Water Resources Council Series, no. 20, p. 420-436. |
