Since you’ve already drilled the hole . . .

Old oil and gas wells might soon be reborn as environmentally friendly geothermal power generators.

Geothermal energy holds promise as a low-carbon source of electricity because of its ubiquity: Rock temperatures increase by 25 to 50 degrees Celsius for every kilometer of depth due to heat from the Earth’s core. And as much as half the cost of geothermal power plants comes from drilling into the Earth.

Old oil and gas wells often plunge miles deep. Refitting their shafts to circulate water could provide an easy way to extract energy, say Xianbiao Bu and colleagues from the Chinese Academy of Sciences in Guangzho. Their article was published online last month in the journal Renewable Energy.

The team proposes a pipe-within-a-pipe design. Water would flow down one pipe to the bottom of the well, heat up and then be pumped up an inner pipe to the surface, where it would drive a turbine.

Xianbiao believes that a typical well could produce around 54 kilowatts of electricity. That’s not much compared with a full-size power plant running on coal, gas or nuclear energy. But with an estimated 2.5 million abandoned oil and gas wells in the United States alone, huge stores of energy may be going untapped.

New Scientist