Helium leads to geothermal energy resources
When we think about alternative sources of energy, we often forget the potential of geothermal energy resources. In fact, it has been estimated that accessible geothermal energy in the U.S. represents 90 quadrillion kilowatt-hours or 3,000 times the country's total annual energy consumption. So far, it has been difficult and expensive to locate good sources of geothermal energy. But now, two U.S. researchers have found a new method which doesn't require drilling. They are using the ratio of helium isotopes in surface waters to point to the best sources of geothermal energy. But read more...
You can see above a photo of one of the researchers, Matthijs van Soest, from Arizona State University (ASU), sampling surface water in the northern Basin and Range, which includes parts of California, Nevada, Oregon, Idaho, and Utah. "The sample is collected without direct exposure to air and stored in the copper tube, foreground left, which will be sealed by crimping." (Credit: Berkeley Lab)
This new tool for identifying potential geothermal energy resources has been discovered by geochemists Mack Kennedy of the DOE's Berkeley Lab (LBL) Earth Sciences Division and Matthijs van Soest, an associate research professional at the ASU School of Earth and Space Exploration.
I'm sure you all want to know why helium isotopes found in surface waters can lead to sources of geothermal energy. Here is an explanation taken from the ASU news release. "Earth’s crust contains a variety of noble gases, one of those being helium. Natural helium occurs as two isotopes, helium-4 (4He) and helium-3 (3He.) Typically, helium-4 is more abundant in Earth’s crust, whereas helium-3 is more abundant in the mantle below. Thus, the helium-3/helium-4 ratio of the gas found in groundwater can provide an indication of the extent to which the water has interacted with volcanic rocks derived from the mantle."
So Kennedy and van Soest "made their discovery by comparing the ratios of helium isotopes in samples gathered from wells, surface springs, and vents across the northern Basin and Range," as reports a LBL news release, "Helium Isotopes Point to New Sources of Geothermal Energy". "Helium-three, whose nucleus has just one neutron, is made only in stars, and Earth's mantle retains a high proportion of primordial helium-three (compared to the minuscule amount found in air) left over from the formation of the solar system. Earth's crust, on the other hand, is rich in radioactive elements like uranium and thorium that decay by emitting alpha particles, which are helium-four nuclei. Thus a high ratio of helium-three to helium-four in a fluid sample indicates that much of the fluid came from the mantle."
The researchers think they found a new way to locate potential geothermal energy resources. "'A good geothermal energy source has three basic requirements: a high thermal gradient -- which means accessible hot rock -- plus a rechargeable reservoir fluid, usually water, and finally, deep permeable pathways for the fluid to circulate through the hot rock,' says Kennedy. 'We believe we have found a way to map and quantify zones of permeability deep in the lower crust that result not from volcanic activity but from tectonic activity, the movement of pieces of the Earth's crust.'"
For more information, this research work has been published in Science under the title "Flow of Mantle Fluids Through the Ductile Lower Crust: Helium Isotope Trends" (Volume 318, Number 5855, Pages 1433-1436, November 30, 2007). Here is a link to the abstract.
Even if the researchers' thesis looks convincing, it remains to be seen if the energy utilities will use it.
Sources: Arizona State University news release, November 30, 2007; and various websites
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