Groundwater Might ID Geothermal Energy Sources

Scientists might have discovered a way to find underground sources of geothermal energy that doesn't require difficult and costly drilling, according to news from Arizona State University (ASU).

The continental U.S. is believed to have enough heat energy deep within the Earth to power the nation at current levels for about 3,000 years. However, geothermal energy hasn't yet become a major resource because sources are difficult to locate.

"Since many geothermal resources are hidden, that is, they do not show any clear indications of their presence at the surface, locating them by just using observations made at the surface is difficult," said ASU researcher Matthijs van Soest. "Often when people thought there might be a geothermal resource below the surface the only way to determine if their assumption was correct was drilling and drilling is extremely expensive."

However, van Soest and B. Mack Kennedy, a scientist at Lawrence Berkeley National Laboratory, might now have found another, easier way to pinpoint sources of geothermal energy without drilling.

Their finding is based on a normally occurring difference in the types of helium found near the surface in the Earth's crust and in deeper regions of the mantle below. These two isotopes -- atoms of the same element that have different weights because of a different number of neutrons in their nuclei -- are helium-4 and helium-3.

Helium-4 is more common close to the Earth's surface, while helium-3 is more abundant in the mantle layer below the crust. While groundwater normally has a low ratio of helium-3 to helium-4, van Soest and Kennedy have found that water close to geothermal energy sources have much higher ratios.

The two researchers found unusually high ratios of helium-3 to helium-4 in water from some hot springs near Nevada's Dixie Valley geothermal power plant. They then sampled more than 60 hot springs and shallow wells in other regions, and found similarly high helium-3 to helium-4 ratios, indicating those areas could be potential sources of geothermal energy.

"When we found the elevated ratios, we knew that the only way these waters could be enriched with helium-3 was if they had interacted with fluids from the Earth's mantle," said van Soest. "Areas where we can sample fluids near the surface provide a way of getting a relatively cheap and easy indication of what's happening deep down. Applying what we know about the helium ratios makes the exploration for geothermal resources cheaper and faster."

Arizona State University/Eurekalert, "Helium Isotopes Point to the Best Sources of Geothermal Energy." URL: (http://www.eurekalert.org/pub_releases/2007-11/asu-hip113007.php)