Geothermal energy resources:
Above - A 10 meter high lava fountain - an unlimited amount of power and energy.
There are four types of geothermal resources:
- Hydrothermal resources.
- Geopressured resources.
- Hot dry rock (HDR).
- Magma.
Of the four types, only hydrothermal resources are currently commercially viable.
Hydrothermal resources
are created when hot water and/or steam is formed in fractured or porous rock. These rocks are located at shallow to moderate depths - between 100 metres to 4.5 kilometres - underneath the earth’s surface. The hydrothermal resources come in the form of either steam or hot water, depending on the temperatures and pressures involved. Some hydrothermal resources are heated by hot molten rock to temperatures between 180 degrees Celsius and 350 degrees Celsius.
There are three basic components of hydrothermal resources – a heat source (such as the hot molten rock), an aquifer containing accessible water and above this, an impermeable rock that “seals” the aquifer. We can capture geothermal energy from this resource by drilling into the aquifer and extracting the hot water or steam. High-grade hydrothermal resources are usually used for electricity generation, while low-grade resources are used in direct heating applications.
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Geopressured resources
consist of hot brine saturated with methane deep inside the earth’s interior. They are found in large, deep aquifers under high pressure. The water and methane are trapped in sedimentary formations at a depth of about 3km-6km. The temperature of the water is in the range of 90 degrees Celsius to 200 degrees Celsius. The major region of geopressured reservoirs discovered to date is in the northern Gulf of Mexico.
Hot dry rock (HDR)
is a heated geological formation that does not contain any water. This resource is virtually limitless and it is more accessible than other geothermal resources. There is a large potential for hot dry rock technologies to be used for energy production in the eastern states of Australia.
Magma
Magma or molten rock is the largest geothermal resource. .However, magma is not an easily accessible resource because it is found at depths of 3km-10km and deeper under the earth’s surface. It has a temperature which ranges from 700 to 1,200 degrees Celsius. The resource has not been well explored to date.
For more information go to the “Geothermal resources” section at:
 http://www.rise.org.au/info/Res/geothermal/index.html
 Next Section >> The advantages of geothermal energy.
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