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 between 25 and 50°C for every kilometre of depth due to heat from the Earth's core. But as much as half the cost of geothermal power plants comes from drilling into the Earth.
Old oil and gas wells often plunge several kilometres deep to reach reserves. Refitting their shafts to circulate water could provide an easy way to extract this energy, says Xianbiao Bu and colleagues from the Chinese Academy of Sciences in Guangzho.
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 (Renewable Energy, DOI: 10.1016/j.renene.2011.10.009).
Xianbiao believes that a typical well could produce around 54 kilowatts of electricity - not much compared to a full-sized power plant running on coal, gas or nuclear energy. But with an estimated 2.5 million abandoned oil and gas wells in the US alone, huge stores of energy could be going untapped.