Geothermal

How do I Assess a Potential Geothermal Resource?

I live near a geothermal hot spring. Does that mean that there are geothermal power resources underground? How do I go about finding out? — John from Moscow, Idaho

Hi John. Thanks for your inquiry. I wish I could take a look at the spring. I came across one on a mesa just off a bike trail in the desert in New Mexico, and it was quite a beautiful sight. There was boiling water on the surface and all kinds of mineral deposits in and around the spring with patches of different colors.

The best answer I can give you to the first part of your question is a definite maybe. I would say that the chances are pretty good that you live near a geothermal resource. However, whether or not it is a resource that could be used for electrical power would require further exploration.

For a geothermal power resource you really need three things: 1. Hot water (do you happen to know the temperature of the spring?) 2. Permeability in the rock, and 3. Both of these attributes at a depth that is economically reachable.

To find out if your spring sits atop a resource with those attributes, there are a number of places you can look. Websites such as www.navdat.org, www.earthchem.org, www.inl.gov/geosciences/seismicnetwork.shtml, http://earth.google.com/, and http://landsat.gsfc.nasa.gov/, list public data or images regarding the chemistry of rocks, temperatures at the bottom of numerous drill holes, seismicity, or changes in surface geology. There is almost certainly data available for your area. However, even with all this great information, you still might not know if your spring sits upon an exploitable resource.

I’d recommend contacting your state geologist or state energy office to see if they can help you find out more about geothermal resources in your area. Or, you can look for help at the GEA website or the Geothermal Resources Council website. You might find a company or consultant that operates in Idaho, and ask them if they’ve looked in your area.

Regarding your second question, I’ll try to answer from the perspective of a geothermal developer. A company would assemble a team of in-house experts or contract with independent consultants to explore an area, such as yours, that contains geothermal surface features. You shouldn’t think that if there is a good resource at your site, someone has already developed it. Many areas in the West have hidden geothermal resources and the US Geological Survey estimates that even in geothermal resource-rich areas like Idaho, 80% or more of the resource base has yet to be discovered!

Once a team is assembled, they would review all of the available data on local geology and geothermal activity, including satellite photos, and go out into the field to look closer at potential indicators. If this goes well and the site looks promising, the company will then usually drill some preliminary “temperature gradient” holes to see if the temperature gets hotter faster than normal as you drill deeper. They could also use several geophysical tools to try to get a better picture of the subsurface.

Even after all of this preliminary work using the array of tools and methods currently available, there is no way of being 100% certain there is a marketable resource without actually drilling a deep well. Since drilling wells is quite costly, the goal of the aforementioned exploration activities is to try to decrease the risk of drilling a dry or otherwise uneconomical well.

Various ideas have been proposed for better and more effective exploration tools, but they are expensive to develop and test. Plus, the Department of Energy Geothermal Research Program has been targeted for termination (see my last Ask the Experts Column for more information). We hope that if Congress restores the DOE Geothermal Research Program, high priority will be given to developing advanced exploration technology. The high cost and risk associated with answering a fairly straight-forward question like yours is one of the biggest obstacles to the greater use of geothermal resources.  

I hope this helps, and good luck in your exploration!