It takes more than 130 megawatts of coal-fired power to mine coal in the Powder River Basin, and oil and gas development is among the largest drivers for growing electrical demand in Wyoming.

In some cases, the cost of electricity can shrink margins below profitability for some operations. Now, operators of marginal oil fields - or stripper well operations - may have an opportunity to harness renewable geothermal power.

Reno, Nev.-based Ormat Technologies Inc. recently announced a successful test using hot water from a producing oil well to generate electricity. The 12-month test was performed in conjunction with the Rocky Mountain Oilfield Testing Center at the Naval Petroleum Reserve 3 at Teapot Dome north of Casper.

"It's using a waste resource to produce power," said Lyle Johnson, U.S. Department of Energy engineer.

The 250-kilowatt unit tested at Teapot Dome uses about 18,000 barrels of production water per day and can power about 12 percent to 18 percent of the entire oil field.

The production water at the site is about 190 degrees Fahrenheit. It heats up a secondary, organic fluid with a low boiling point that vaporizes and spins a turbine coupled to a generator. Then the production water can be reinjected or treated for surface discharge.

Johnson said wells in declining oil fields usually produce a large amount of water anyway. The Ormat process simply harnesses the heat from that water.

"The heat normally cools and is lost. Now, we're taking the heat out of the water and generating electricity," Johnson said.

Similar units have long been in use in Australia and Thailand, but with geothermal wells with temperatures well over 300 degrees Fahrenheit. Johnson said the aim of this process was to use lower-temperature water in order to create energy efficiency for low-producing oil fields, thus keep them operational for longer.

"The thing about it is this is not an off-the-shelf item. (Ormat) made modifications to make it work in this environment," Johnson said.

That includes two 40-foot air-cooling towers as opposed to water cooling units because of the lack of water resources here.

Johnson said the generator is most efficient with cool air temperatures in the winter. Warmer months require more volumes of production water - up to 40,000 barrels per day.

A large number of oil and gas wells in the United States produce hot water as well as hydrocarbon products, according to RMOTC. It's estimated that production fluids that are 220 degrees Fahrenheit and below are capable of generating up to 5,000 megawatts of power.

About 8,000 wells were identified in Texas for the technology by the U.S. Geothermal Research Project Office. Ormat is now assessing the feasibility of utilizing the wells to support on-site power generation.

Contact energy reporter Dustin Bleizeffer at (307) 577-6069 or dustin.bleizeffer@trib.com.