Old oil wells not suited for geothermal use

A recent announcement of $1.7 billion in federal funding to help remediate oil wells has resurrected an old question: Do those old oil wells on the back 40 have any potential for new life in geothermal energy production?

“The typical oil well isn’t set up for the flow rates needed for geothermal power and retrofitting probably isn’t possible,” said Grant Ferguson, an associate professor in the University of Saskatchewan’s College of Engineering.

Ferguson, who specializes in groundwater and hydrogeology, explained that oil wells typically deliver a few litres per minute, while geothermal applications require hundreds of litres per minute.

It’s a limitation Kirsten Marcia knows well.

“I get asked that a lot and you always hope (oil wells) can be used for something like geothermal, but they’re not designed the same way,” she said. Marcia is chief executive officer of Deep Energy, a geothermal power development company near Estevan.

Marcia said that geothermal facilities like Deep’s use a process called binary organic rankine cycle. This involves bringing hot, saline water — in this case, about eight times as salty as the ocean — to the surface. There, heat from the 125 C water vaporizes butane, which is used to spin turbines and generate electricity. The butane cools back to liquid and the saline water is then pumped back underground via return wells to be re-heated.

To make it work, the flow must be about 10 times that of a typical oil well, driven by big, down-well submersible pumps.

“You’re dealing with at best a seven-inch well in the oilfield, whereas what we need to use is closer to 10 inch,” Marcia said. “An oil well is too skinny of a straw.”

Deep’s pilot plant is expected to provide five megawatts of power, or about enough for 5,000 homes, when it comes online in late 2021.

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