Q. What are geothermal energy resources?

Heat is a form of energy and geothermal energy is literally the heat contained within the Earth. There are two types of geothermal energy resource trapped underground depending on the water source. Geothermal energy is produced from hot geothermal water already in the ground or water which becomes hot after it is pumped underground. The first type occurs where water has naturally percolated, become heated by the earth’s heat and become trapped underground in reservoir rocks which hold the geothermal water in natural voids, cavities or fractures in the rocks which are permeable. Permeable means the ability of water to flow through the natural or engineered cavities or fractures in the rocks. The other type of geothermal resource is where underground rocks themselves are very hot but are dry either because of lack of natural voids, cavities or fractures in the rocks which can hold water or lack of water (“Hot Dry Rocks”) in the rocks. The permeability has to be engineered and water pumped through the hot dry rocks to collect the heat.

Q. What is conventional geothermal energy?

Heat is a form of energy and geothermal energy is literally the heat contained within the Earth. Conventional geothermal energy is extracted from water that has seeped over time into fractured, or porous, hot rocks. The rocks are usually hot because they are in regions of the earth that are geologically active, such as active volcanic areas. The hot water and/or steam is forced to the surface under its own pressure and fed directly to a turbine in a power plant to produce electricity.

Q. What is the heat source for HDR energy?

The natural heat contained in dry rocks below the earth’s surface, trapped in the dry rock by an overlying insulating layer of sedimentary rocks.

Q. How is HDR energy extracted?

Holes are drilled deep into the hot rocks, and water is forced down at high pressure, opening a network of natural fractures creating a permeable reservoir through which water can flow. Water is pumped through the hot fractured reservoir rocks and becomes very hot as it extracts heat from the rocks. The superheated water is returned to the surface via production wells, passed through a heat exchanger thereby heating and vaporizing a separate fluid circulating through the power plant which drives turbines in the plant to produce electricity. The water is returned to the first well and continually recycled.

Q. What does Enhanced Geothermal System (“EGS”) mean?

An Enhanced Geothermal System is where the hot rocks which contain the geothermal energy do not have a naturally water saturated permeable reservoir. In an EGS the permeable reservoir has to be engineered. This is done either by: (1) hydraulic fracture stimulation to open up natural fractures or zones of weakness in the rock via injection of water under high pressure into the rocks or (ii) injection of acid in the rock to dissolve minerals to enhance the rock permeability along existing fracture zones having acid soluble minerals. Water then can flow or be pumped through these fractures and zones to collect the heat from the hot rocks.

An EGS system is sometimes known as Hot Fractured Rocks (“HFR”). This is sometimes used where hydraulic fracture stimulation is used to enhance the permeability in hot dry rocks with no open fractures or in rocks which have open fractures which are water saturated.

Q. Is HDR experimental technology?

No. The technologies to drill the deep wells and engineer a permeable reservoir in the hot rocks, the two principal keys to success, are not new. Power plants used in conventional geothermal projects are reliable and commercially available and used extensively around the world. While there are no large scale commercial HDR projects in operation various projects are being pursued in Europe (Czech Republic, France, Germany, Switzerland) and in the USA. Australia has outstanding potential resources, which have been estimated at 7,500 times its total current annual energy consumption. Green Rock Energy is a leader in bringing HDR technology on stream in Australia.

Q. What are the benefits of HDR energy?

HDR energy produces no greenhouse gases or other pollutants, production plants have a very small “footprint” and, unlike natural energy from wind, wave and solar sources, where production fluctuates, HDR energy is generated on a 24/7 basis. This continuous generation is known as “base load” electricity. Geothermal energy is classified as renewable energy and accordingly obtains the benefit of carbon credits.

Q. Is energy produced from HDR a “renewable resource”?

The answer depends on the time scale used. While the temperature of the reservoir rocks will decline as heat is extracted from them over periods calculated to be around 15 to 20 years, the heat will be replenished after production ceases by heat conducted from the surrounding hot rocks. Current modeling suggests that HDR-driven generators in Australia will still be producing electricity at full load when the world’s known oil resources have been exhausted. This can be accomplished by drilling new wells, or sidetracking from, or deepening, existing wells into the adjacent hot rocks.

Q. Is HDR produced electricity price competitive?

Our modeling of a 400MWe power plant at Olympic Dam indicates it would be competitive with alternative electricity power sources.