Golf charlie
I think that the bedrock below London is several hundred metres below the surface. Most tunnels are through clay, but I could be wrong.

I've often wondered what the potential for geothermal exploitation is in the Auvergne is. I don't if you've ever been but the extinct/dormant volcanoes make a dramatic change from the surrounding area. When going full tilt must have been quite a place.

Supertroll

I did what I usually do, reduce the problem to basic thermodynamics to get a basic BOE calculation.

Can you do a more detailed analysis or link me to one?

How many useless wind turbines can you see from your 'ringside seat' EM?

@GC: Re Wytch Farm: "Approval is subject to a number of conditions, including the prevention of fracking for shale gas."

I bet if the fracking was about sequestering CO2 the Council would have no objections.

IDAU: "Take a look at the size of the bull on the 1,000 yard range at Bisley, and scale up..."

I do like a man who can call on experience of Bisley for a metaphor. I have memories of shooting there (nothing other than squadron competitiveness). That bull does look small!

No Fracking at Wytch Farm anyway. It is a Green Herring.

●Wytch Farm oil production extended in Dorset. 6 September 2013●

"Future development at Wytch Farm, Kimmeridge and Wareham oilfields includes drilling new wells
Oil production is to be extended for a further 21 years at western Europe's biggest onshore oilfield, in Dorset.

Dorset County Council granted permission for Perenco UK Ltd to extend the operational life of Wytch Farm, in Poole Harbour, from 2016.

Wytch Farm currently produces 20,000 barrels per day. The remaining reserves are estimated to be 43m barrels.

Approval is subject to a number of conditions, including the prevention of fracking for shale gas.

The council's planning committee approved a total of 39 applications, including extensions at Wareham and Kimmeridge oilfields which are also operated by Perenco UK Limited."

https://www.bbc.co.uk/news/uk-england-dorset-23961621

TinyCO2

For six years I have had a ringside seat as Tamboran Resources tried to get permission to prospect for shale gas in Fermanagh.They have failed to convince the Assembly, the Council, the farmers, the fishermen, the tourist industry or the local population.

Futures prices for natural gas are currently between $6 and $9.45/mbtu.

https://www.cmegroup.com/trading/energy/natural-gas/uk-nbp-natural-gas-usd-mmbtu-icis-heren-front-month.html

The only estimated price I could find for UK shale gas was that it was uneconomic if the price was below $9.68/mbtu. Unless gas prices surge, there is no economic case for shale gas.

Yes Ross, this photo of a wnd farm looks a lot like Jonah Field only there's the added 'bonus' of dead birds.

https://s27836.pcdn.co/wp-content/uploads/2016/05/mars-wind-PA.jpg

EM

A few fracking terminals, after the initial process, are far less of a blight on the landscape than all those expletive wind turbines, they can be easily camouflaged by tree etc. Wind turbines are a REAL blot on the landscape; expensive and inefficient to boot.

EM. You don't understand geothermal energy. You don't deplete a specific 100 metre cube of its usuable heat, and then (potentially) move to the next block. The low transmissivity of rock means that only the heat stored near to fractures has time to migrate and raise the temperature of the circulating fluid. When that has been withdrawn the heat further away is still migrating towards the fracture and cannot raise its temperature sufficiently to be useful. Even with a efficient fracking job, most of the granite in your 100 cubic metre block will be too far away from a fracture to be useful. So in order to supply sufficient heat a significantly larger volume of granite must be fractured and heat-drained. If only 5% of the granite's heat can be drained, then a volume 20 times that you have contemplated will be needed.

A further problem is that after an estimated 25 years, and the shutting down of the geothermal plant, most of the original heat within the exploited granite will still be in place. Consequently heat transport toward the depleted site will be extremely slow. It may be possible to seal the fractures and then re-frack, creating new fractures that are adjacent to more heat, but that doesn't appear to be be contemplated.