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Drilling set to start on UK’s deepest onshore borehole

Work to drill boreholes for the UK’s first deep geothermal electricity plant is set to get underway in Cornwall today and will set a new record for the deepest onshore borehole ever drilled in the country.

Two J-shaped boreholes – one 2.5km deep and another 4.5km deep – are expected to generate up to 3MW of electricity from early 2020 at the site on United Downs Industrial Estate near Redruth.

The deepest onshore borehole ever drilled in the UK is currently believed to extend to 3.5km so the deeper of the two new wells will set a new UK record when completed next year.

The 216mm diameter boreholes will be drilled by contractor Marriott using a Herrenknecht Innova TI418 rig to extend 800m through metamorphic mudstone and into very hard granite.

“Both holes will be used for water circulation through the hot rocks,” said Ryan Law who is CEO with project promoted Geothermal Engineering. “The 2.5km well will be used for injection, while the 4.5km will be used for production.

“The rig we are using is proven technology as it has just come from a project in Helsinki, Finalnd where is completed a 6.5km deep bore. Here the challenges are that we are undertaking a directional drill into a hard faulted zone of rock and it will be interesting to see how the drilling responds.”

Law expects the shallower bore to be completed by the end of the year and the deeper bore by spring. “If they perform well and we get the flow rates we are anticipating then the site could be producing electricity by early 2020.”

The project has received approximately £18M in funding, including £10.6M from the European Regional Development Fund, £2.4M from Cornwall Council and £5M in crowd funding through Abundance Capital. The project is being developed by Geothermal Engineering and Arup, which has supported the project, has signed an agreement to purchase renewable energy guarantee certificates to secure zero carbon electricity from the plant.

Law says that the drilling work will help prove the concept of exploiting a natural, pre-existing fault with high permeability for geothermal energy. “There are potential for projects elsewhere in the UK where the geothermal gradient is high enough.”

Representatives from 40 universities from all over Europe are expected to visit the site next week. “There is substantial research potential here,” said Law. “Geothermal is seen as part of the energy solution and it is very important.”

Geothermal Engineering has said that it is hoping to raise a further £150M on the success of this scheme to fund further larger geothermal plants across Cornwall and Devon.


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