Just drill a little deeper to unlock earth's heat, geothermal expert says

Now here's an interesting idea. Instead of decommissioning hundreds of North Sea oil and gas wells, why not “recommission” them as sources of lucrative, carbon-free geothermal energy?

By Sam Phipps

This entirely new industry could support thousands of jobs and deliver a clean, affordable alternative to nuclear, whose future in the UK is in doubt anyway.

That was the suggestion of George E. Lockett, promoter of geothermal energy development in the North Sea, at DecomWorld's 9th Annual North Sea Decommissioning Conference, held in November in Aberdeen.

Most of the technology is already available, Lockett said, and the UK continental shelf has a relatively thin crust, about 10km thick compared with 40km to 70km on land, giving the wells there high bottom-hole temperatures. He appealed to oil and gas operators to log depths and temperatures so that hotspots could be mapped, and said geothermal technology could supply more than 100,000MW of electricity within 50 years.

“The main cost of geothermal is drilling the wells,” Lockett said. “But there are already about 450 structures in the North Sea made of concrete, with a life span of 300 years or so. Why decommission them? Why not find an alternative use?”

He added: “The reason it has not been developed in the UK to date is that supposedly you have to drill far down. But in the North Sea we find there are very high temperatures that can be tapped easily,” Lockett said.

Instead of decommissioning redundant platforms, Lockett said the industry should drill multiple horizontal wells off each rig to depths of up to 10,000m. Lamprell’s LeTourneau Super 116E jackup rig, scheduled for completion in 2014, will be able to drill that far down, and other structures of similar specification are also on the horizon.

Geothermal gradients of 35°C per kilometre have been recorded in the continental shelf crust, Lockett said. That's rate at which heat goes up the farther down you go. Geothermal energy can be harnessed in three ways: high wellhead pressure spis a turbine; gas from oil-brine is separated and burned; and hot water flowing through heat exchangers boils an organic fluid to spin a turbine.

With the total cost of UK decommissioning estimated at between £30bn and £45bn, Lockett questioned why some of that sum could not be spent on developing geothermal, which could potentially be a more efficient resource than nuclear.

Scotland has ruled out building any new nuclear power stations, and in March 2012 E.ON UK and RWE npower announced they would be pulling out of developing new plants, putting the future of nuclear in the whole UK in doubt.

Centrica is widely expected to withdraw from the EDF-led consortium to build nuclear reactors at Hinkley Point in Somerset, western England, because of spiralling costs. The plant is estimated to cost £14bn and doubts have arisen about possible returns for investors.

“If I had a £14bn budget for geothermal in the North Sea, I am sure we could build an equivalent power station,” Lockett said.