A number of old fossil fuel wells in northern England that were being lined up for fracking could now set a template for the future of the UK's geothermal industry.
The wells, located in North Yorkshire, had produced gas for years until they were eventually depleted.
The operator, Third Energy, was keen to repurpose the wells for fracking in a bid to source more gas from the rocks below.
That was until fracking came to a halt in the UK when it was banned by the government in 2019.
Now, the operator — since acquired by renewables group CeraPhi Energy in 2024 — hopes to use the site to tap geothermal energy.
The deepest well at the site, known as KM8, is located at Kirby Misperton, and descends for 3km.
Unlike fracking, there is no forcing of fluid into the adjacent rock, said Russell Hoare, Managing Director at Third Energy.
“You're not touching the geology at all," he was quoted as saying in an interview with the BBC. “You’re just putting a small tube on the inside of the well.”
The Third Energy project was profiled in detail in an article in the BBC’s Future Planet series.
The company’s approach to the development, known as closed-loop geothermal, involves a sealed, water-filled loop sunk deep inside the well to absorb the naturally occurring heat at the bases.
The warmed water in the loop then returns to the surface, returning heat that can then be passed onto to nearby buildings and consumers.
In tests, the BBC reported, the temperature at the well's base was hotter than the company expected – around 115C (240F), rather than the anticipated 90C (190F).
Early indications suggest that the system could maintain a steady temperature of around 42C (108F) at the surface.
Heat pumps could boost this supply further, if necessary, before passing it on to customers.
“That well, if it was configured properly, could probably provide enough heat for 100 homes,” said Hoare.
He added that Third Energy has 12 wells in total in Yorkshire that could be used for geothermal energy, three at Kirby Misperton.
“What this gives me is potentially another 25-plus years’ life out of those wells,” he added.
Potentially, the network of geothermal boreholes could also be expanded in the future.
Last year, CeraPhi Energy was awarded a contract to study the prospect of developing geothermal heat networks that could decarbonise heating for three schools and a fitness centre in the Yorkshire town of Pickering.
But the process isn't cheap, the BBC report added: for a well half the depth of KM8, the cost could reach up to £1mn (US$1.3mn) to drill and fit with the water loop equipment.
The long-term pay-off is that the wells gain a new lease of life, providing heat for years to come, whilst keeping any fossil fuels in the ground.
Potentially, the idea could provide a template for the repurposing of other oil and gas wells for geothermal energy — although it is not without its sceptics.
The BBC cited various experts questioning the idea’s feasibility, both from a technical and economic perspective, however some were optimistic.
“It certainly sounds ambitious, but it doesn't sound impossible,” said Fleur Loveridge at the University of Leeds, who specialises in underground energy systems.
She added that there are already examples of closed-loop borehole heat exchangers that have produced significant amounts of heat, including one in Germany.