Hot Rock Cafe EarthCache
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Power without carbon. No emissions.
A vast hot fractured rock resource exists beneath the Innamincka area of Central Australia. About 320-million years ago, molten granite with abundant radioactive elements rose up from the depths of the earth's core. 20-million years later, after it had cooled, the granite was unroofed by erosion, and its surface sculpted by glaciers. During the unroofing, natural cooling fractures expanded and filled with water. The granite was then blanketed by river and lake deposits of shale, coal and sandstone that now contain the natural gas of the Cooper Basin. Later still, the region was covered again by river deposits that now form part of the Great Artesian Basin. Nature has brought together in one place a huge body of hot fractured granite with its insulator of gas-and water-bearing sedimentary rocks at a depth within reach of current drilling technology. Granites generate about 10 microWatts of heat per cubic metre continuously for hundreds of millions of years. If hindered from escaping by an insulator, the heat accumulates such that can be exploited for generating electricity. In the hottest part of the Cooper Basin, the thermal gradient is 60 degrees per kilometre or almost 300-degrees at a depth of 5 kilometres.
At Innamincka, the resource will utilised after opening natural horizontal cracks or fractures by pumping high-pressure water into the granite. The natural horizontal shearing stress in the crust then shifts the roof of every crack sideways so that it slips a few millimetres when the water pressure is released. The minute sideways slippage increases the permeability along the fracture systems by a thousandfold. That means that water can now circulate through an engineered plumbing system to make an effective heat exchanger. The network of water-filled cracks becomes the heat reservoir. Recirclated water is used to generate electricity in the power station on the surface.
To log this Earth Cache you must email me the answers to the following questions. Please do not post your answers in your log, which would ruin the sense of discovery for others! UPDATE 2017. The information sign has been removed. The answers are available on the interwebs. Google is your friend.
1. What is the depth of the bores?
2. In megawatts what is the size of the power station?
3. As a final requirement, post a photograph of yourself with your GPS showing the power station in the background.
I then recommend that you drive a distance equivalent to the depth of the bores. Compare this horizontal distance with the vertical distance of the bore. Consider the engineering required to drill a hole this distance. You are encouraged to comment on what you enjoyed or found interesting at the location when logging your visit.
Additional Hints
(Decrypt)
Vg'f abg obevat.