Australian Geothermal Styles

The known Geothermal Resources in Australia lack areas of recent volcanic activity, but do have large volumes of identified high heat producing granites within 3 to 5 kilometres from the surface. This is potentially a vast resource of energy that can be tapped by Engineered Geothermal System (“EGS”) technology. Extensive exploration is underway to explore for shallow geothermal resources in the Eromanga Basin in south-west Queensland and parts of far north South Australia. Interest is also being shown in geothermal energy sources along the Queensland coast closer to existing electricity transmission lines through the Government’s Coastal Geothermal Energy Initiative. Research is currently being undertaken to investigate the potential of tapping hot saline, geothermal aquifers so called Hot Sedimentary Aquifer ("HSA"), that lie between 2–4 kilometres underground in many parts of Australia as a new geothermal energy resource for base-load electricity generation.

Source Geodynamics Ltd

HSA- Hot Sedimentary Aquifer

Geothermal reservoirs in sedimentary basins are referred to as the Hot Sedimentary Aquifer (“HSA”) model. In recent years, the geothermal industry has realised that some sedimentary basins contain attractive geothermal resources - zones which have medium temperatures (120oC to 160oC) and are permeable resulting in good fluid flow rates for geothermal energy production (80 kilogram per second (kg/s) to over 200 kg/s per well).

The best known examples of attempts to commercialise HSA in Australia are:

• The Great Artesian Basin, Australia. This is one of the world’s largest sedimentary basins and the source for Australia’s only geothermal power plant to date (at Birdsville) with gross generation capacity of 120 kilowatt electricity (kWe). The plant uses water at 98 degrees Celsius that is produced from a 1,280 metre deep bore in an aquifer in the Eromanga Basin, one of the basins comprising the Great Artesian Basin.
• Areas within the Adelaide Geosyncline, such as where Earth Heat's tenements are, have been considered prospective by a number of companies including Torrens Energy Ltd, Planet Gas Ltd and Petratherm Ltd. Ongoing studies continue to suggest that deeper HSA targets are present and could be considered for development.
• The Otway Basinin Victoria. Panax Geothermal Limited has produced the first steam in early 2010 from Salamander-1 well in the Otway Basin near Penola in South Australia. This is the first geothermal well in Australia to test a HSA.

Hot Sedimentary Aquifer (HSA)

Conventional Geothermal System (CGS)

Source: Hot Rock Ltd presentation 14-7-10

Enhanced Geothermal Systems

This type of geothermal resource refers to a man-made geothermal system, which is different from sedimentary and volcanic geothermal systems in that there is no natural fluid circulation path. These systems are targeting impermeable buried granite bodies where water does not flow through at reasonable rates.

Therefore, EGS developers artificially create a flow path with suitable permeability using a process known as “hydraulic stimulation”. This type of geothermal resource has huge potential as a longer term source of clean energy. EGS sources are usually radiogenic granites at depths of 4,500 m to 5,000m. The granites can produce higher than average geothermal gradient owing to the release of heat from the decay of the minor amounts of radioactive elements present. One cubic kilometre of hot granite at 250°C has the stored energy equivalent of 40 million barrels of oil.

Australia is estimated to have 22,000 EJ or 5,000 times its annual energy consumption stored in EGS resources (Burns et al, 2000). The EGS is already being targeted for development in Australia and, according to an estimate by Electricity Suppliers Association of Australia, may provide up to 5 GWe or 10% of present Australian electricity generation by 2030. The Cooper and Eromanga basins region in Queensland and the neighbouring state of South Australia are prospective for EGS geothermal resources that could potentially generate 4,000MWe of base-load electricity by 2030 (Queensland Geothermal Energy Centre of Excellence).

In the standard EGS, a primary fluid, typically brine, is circulated through the geothermal reservoir in a continuous loop. The brine brings the heat to the surface, and transfers it to a secondary fluid with lower boiling point, typically isopentane, through circulation in a heat exchanger. This secondary fluid is then expanded through a turbine-generator to produce electricity. The brine and isopentane are both captured for the cycle to be repeated to maintain the electricity generation. The best known example of attempt to commercialise EGS in Australia is in the Cooper Basin in central Australia. This is a sedimentary basin, but the EGS geothermal project is focussed on the underlying basement rocks which are granites. The Australian company Geodynamics Limited is currently testing its man-made reservoir system where to date, the company has drilled five wells - Habanero 1 (4,421 m), Habanero 2 (4,357 m), Habanero 3 (4,221 m), Jolokia 1 (4,911 m) and Savina 1 (3,871 m). The company plans to commission a 1 MWe pilot plant by early 2012 followed by a 25 MWe commercial demonstration plant in following years. Worldwide researchers have been progressively developing demonstration EGS systems since 1987 with good results at the Upper Rhine Graben on the France-Germany border and Soultz-sous-Fort’s in France.

Companies such as Torrens Energy Ltd and Geothermal Resources Ltd have reported high prospectivities for this type of development, and their tenement holdings are in the same geological region as those of Earth Heat.

Hot Fractured Rocks (HFR)

Enhanced Geothermal Systems (EGS)

Source Hot Rocks Ltd presentation 14-7-10

Burns, K L , Weber, C , Perry, J, Harrington, H J, 2000. Status of the Geothermal Industry in Australia.
Proc. World Geothermal Congress 2000, Kyushu-Tohoku, Japan.

Queensland Geothermal Energy Centre of Excellence website: http://www.uq.edu.au/geothermal/the challenge