Professor Paul Younger, Director of the Newcastle Institute for Research on Sustainability based at Newcastle University, knows a thing or two about digging holes.
As a geologist and environmental engineer, drilling boreholes is what he has spent a large part of his career doing.
The first were drilled during the 1990s when Paul worked on securing the water supply that Berwick-upon-Tweed currently benefits from, but since 2004 he has been drilling deeper in the hunt for the ultimate lowcarbon energy source – geothermal. ‘As renewable energies go, geothermal is one of the most appealing’, Paul says. ‘Unlike wind turbines there’s almost no visual intrusion after installation and unlike wind, solar or tidal, geothermal is available at all times, whatever the weather, because deep geothermal energy arises from incessant, natural, heat-generating processes taking place deep in the Earth’s crust and mantle.’
The North East is thought to be more active than most when it comes to these geothermal processes with miners in some of the region’s last working collieries reporting warm salty waters at the foot of the mines which, on closer inspection, showed signs of having risen up from much hotter zones located far below. Central Newcastle is no different and when the opportunity arose at the 24 acre development site, home to Scottish & Newcastle Brewery until 2004, the teams at Newcastle and Durham Universities recognised the potential to provide some, if not all of the energy requirements for Science City, the next phase in Newcastle’s reinvention. In 2005 the city was identified as one of six UK ‘Science Cities’ in recognition of the world-class research being undertaken by its universities and the potential of its science industry base. The aim of the development is to ensure Newcastle becomes synonymous with scientific excellence in areas such as ageing, health, stem cells and regenerative medicine. Science City also aims to be renowned in the field of sustainability, and by harnessing the power of a geothermal borehole on site and producing fuel-free heat, the partnership is setting the perfect example.
The hope is that the borehole will provide enough energy to heat Science City and potentially neighbouring Eldon Square which is why the government’s Department of Energy and Climate Change has invested £400,000 towards the project. The Science City Partnership have funded the rest of the exploration which will cost in the region of £1.2 million. If that sounds like a lot of money for a hole in the ground that may or may not yield what they’re searching for, Professor Paul has a proven track record when it comes to sniffing out geothermal energy. ‘Our very first geothermal borehole in 2004 was at Eastgate in Weardale and it provided the largest geothermal resource yet found in the UK. In the deepest parts of this new borehole in Newcastle, we’ve been expecting to find some of the same sandstones I drilled up at Berwick 20 years ago. It’ll be great to see them again, especially if, as expected, they yield lots of hot water!’
Drilling began in earnest on 23rd February this year with the engineers predicting it would take six months to make it down to the intended 2,000 metre depth. Before any real drilling began a large diameter ‘surface casing’ was installed to a depth of 20 metres to keep out any unconsolidated soil and loose ground affected by shallow mining long ago.
The drilling process was carefully planned in advance and took place in phases with local firm Drilcorp contracted to carry out the most difficult first section through possible old mine-workings. A special drill bit fitted with teeth smashed up the different types of stone it encountered at the rock face as the borehole deepened; these small particles were then pumped back up the borehole by special drilling mud which passed into tanks at ground level, where the rocks were separated. The mud was recycled back down the hole to help keep it open before special steel casing tubes were cemented in place to keep the hole open long term. Engineers had anticipated running into a series of medieval coal mine workings during the first 300 metres of drilling and the fear was that the old workings might swallow the circulating drilling mud in a single gulp. At just 13 metres the drill bit entered the High Main coal seam, the level of coal that made Newcastle rich in the first place, but fortunately no voids were hit.
At 98 metres below ground level the drill entered the Brass Thrill coal seam. ‘This coal was clearly unmined, which we expected.’says Professor Paul, ‘The old colliery shaft nearby recorded the seam as only being 0.4 metres thick, which shows how coal seam thicknesses vary in this region. The Brass Thrill seam was mined most recently in Ellington Colliery on the Northumberland coast, where it was usually approaching two metres in thickness.’
The name Brass Thrill harks back to mining dialect, ‘Brass’ being the nickname for the yellowy iron pyrites or ‘fool’s gold’ while ‘Thill’ is coal-mining dialect for seat-earth. Everything was going to plan until 161 metres when the first void was hit. ‘As it was above the recorded level of the seam roof it must have been a “migrated void.”’ explains Paul. ‘Basically that’s where one bed of rock after another has clattered down when a mine void collapses. The intersection of this void by the borehole had a dramatic effect on the standing water levels, they had been around six metres below ground up to that point, but shot down to 60.5 metres when we hit the void. If you put your ear to the borehole you could hear water cascading down to the water line.’ At this point Paul had to call upon the skills and experience of the engineers who were drilling. They injected a special concrete into the bottom of the borehole to close off the connection, with modest results, so a CCTV camera was sent down for a closer inspection. The decision was made to inject bentonite, a type of clay that swells to ten times its size when wet. This raised the water level in the borehole by 20 metres and allowed for drilling to recommence. ‘The hope is that the borehole will provide enough energy to heat Science City and potentially neighbouring Eldon Square’
By 11th March the borehole had bypassed the potential perils of old coal workings and was at a depth of 234 metres. The next hurdle for the team was the Brockwell Seam, the deepest and oldest level of coal to have been mined in the Great Northern Coalfield which, fortunately, the drill bit cut through like a hot knife through butter. At 245 metres the drilling tools were withdrawn and specialist contractors visited the site to run equipment down the borehole that would confirm the geological sequence so far and test the temperature gradient in the hope it was creeping towards the 80C (176F) which is the maximum the engineers might hope to find at 2,000 metres. The first set of steel casing was grouted into place ahead of the arrival of ‘the big rig’ on site which would continue drilling towards the target depth.
As the first section of the borehole was completed ahead of schedule it left more time to finalise contractual arrangements with the specialist subcontractors, Geometric COFOR, who were tasked with drilling the remaining 1,750 metres. ‘This turned out to be a lot more challenging than we’d bargained for,’ admits Paul ‘at the best of times there are relatively few large onshore drilling rigs in the UK and with the price of oil being so high lately, those rigs have been in heavy demand. For the likes of us, with only one borehole to drill and a strict budget, it’s difficult to interest a company that might have an offer to drill a series of deep boreholes for major oil and gas companies.’
In the end, much to Paul’s relief, he was able to book his first choice rig. ‘It was the one I’d most fancied all along, having seen it in action up in Scotland about three years ago. To a hydrogeologist like me it’s a sight to behold. It has a mast standing 18 metres high and a hydraulic hoisting capacity of more than 100 tonnes – enough to lift 50 cars at once!’ Paul is quick to point out that the rig is only part of the package and even more important is the skilled, dedicated crew that operate it; they arrived on site on 31st May and quickly entered into the spirit of the Science City venture.
By mid-June progress was progress was continuing briskly at a rate of over 100 metres a day and at 460 metres the borehole even hit some more coal. ‘We weren’t really expecting a substantial coal seam at this point in the geological succession, so it was a pleasant surprise. I fancied calling it ‘The Younger Seam’ if no one objected!’!’ laughs Paul. At 650 metres depth the drill was cutting through a Carboniferous limestone series when Paul’s colleague Laura Armstrong, from Durham University, who was logging and analysing the rock cuttings, noticed some flecks of classic light grey limestone known as Corbridge Limestone which notably rises to the surface in the Tynedale town. The next challenge for the project was the dreaded Great Whin Sill rock Paul had predicted.
‘Whin Sill is the rock on which Hadrian’s Wall stands, it’s the rock over which High Force falls in Teesdale and on which Bamburgh Castle stands, it also forms the Farne Islands.’ A true North East icon and hard as bell metal, Whin Sill is the reason many of the region’s historic landscapes are still around to behold. Unfortunately this is not good news for the drill bit and was identified as a major challenge before ground had even been broken in February. Paul anticipated as much as 60 metres of slow progress as the team made their way through this layer of igneous rock. ‘It’s exceptionally hard, hence the name “Whin” which is an old North Country word for “hard.” Old-time miners who encountered it in the lead mines of the North Pennines always knew they were in for a struggle, with much drilling and blasting needed to make headway through it.’
Before doing battle with the Whin Sill a brand new drill bit was fitted, specially selected to cope with the tougher rock. At this stage the borehole was at 717 metres and made brisk progress until around 800 metres when drilling dropped from six metres an hour to just 0.6 metres – confirmation that the engineers had struck Whin Sill. ‘To drill in such hard rock it’s a good idea to reduce the drill’s rotation rate and increase the weight on it. With this strategy and plenty of patience and perseverance we finally cleared the base of the Whin Sill after 60 metres of very tough drilling.’ At this stage the drill was carving up rock at a depth of 3,000 feet. To offer some perspective, that is as deep as the loftiest peaks in the Lake District are high. If the borehole was to reach its desired depth it would finish twice as deep as this. Progress slowed again just short of 950 metres, which was unusual as the drill wasn’t due to hit another shelf of Whin Sill until the 1,200 metre mark. The decision was made to bring the drill bit back to the surface 50 metres ahead of schedule and when it arrived back at ground level the teeth were completely worn away. ‘It was a sight to behold,’ says Paul, ‘not only were the teeth badly worn or absent, but the outer casing had been worn away altogether. The lads on the rig said they’d never seen a bit so badly damaged. It seems that the punishment it took in the Whin Sill left it vulnerable when it met further resistance deeper down.’ With the tools out of the borehole, a team from the British Geological Survey moved in to perform some temperature tests. At 949 metres the temperature was a balmy 40ºC, about 50 percent above the UK average; if the gradient continued at that rate the bottom temperature could be around 73ºC which would represent an excellent result for Paul and the team.
By now it was mid June and Laura had identified more cuttings of Whin Sill coming up at 1,060 metres. ‘It was a mixed blessing for us,’ admits Paul. ‘The Whin Sill has a very low ability to conduct heat, so it can act as a duvet, trapping useful heat deeper below ground which in the long run is great, but in the short term it’s a right pain to drill!’ As well as being central to so many iconic landscape features in the region the Whin Sill is also fascinating from a geological perspective, as Paul explains. ‘It solidified about 280 million years ago from what amounted to an underground flood of molten rock. While volcanic lava is magma that spills out at the surface, Whin Sill, which is essentially the same stuff, prised open adjacent beds of sedimentary rock and squeezed into the gaps.’ The various limestones at this depth are full of fossils and many corals which are a reminder that the North East was once a shallow tropical sea that experienced temperatures and conditions similar to what the Bahamas enjoy today – a thought to keep you warm on the cold winter nights ahead.
Towards the end of June everything was going to plan with steady progress being made but, unbeknownst to Paul and the crew, disaster was just around the corner, or down below to be precise. ‘At 1,100 metres the rods wouldn’t proceed any further. We later discovered this was because, inexplicably, the new drill bit had detached itself.’ At over a kilometre below ground level this presented a massive challenge for the team who quickly embarked on an extreme fishing challenge in a bid to retrieve an item six inches in diameter from a six-inch diameter hole, over a kilometre below ground level. The team did manage to pick it up on the drill rods only for it to fall to the bottom again before it reached the surface. Special tools were brought in, including a giant thread-cutting tool known in the industry as a spear, designed to bore into a metal object and grip it. The spear failed to bite and when a giant magnet also failed to land the prize the decision was taken to bury the dislocated bit and drill past it. ‘We plugged the bottom 100 metres of the borehole with cement, then after it had set, re-entered with our drilling tools, set up to deviate slightly away from the present line. We drilled through the wall of the original borehole, by passed the section where the bit will be forever entombed, and continued on down towards our target depth.’
After delicately sidestepping the lost drill bit the team had motored on to 1,675 metres by early July, passing the one mile mark along the way. The drill was cutting through rocks over 350 million years old which turned out to be an unusual red sandstone – normally at this depth they are grey. ‘It’s strange to find a sandstone one mile below the surface that is obstinately red. What does it mean? Well, it might mean that this sandstone was not accumulated in a river or a swamp, as most of the shallower ones were, but on land, as blown sand in a desert landscape.’
Paul can’t be sure just now but is hopeful an analysis will reveal more later in the year. By now it was mid August and the borehole was 1,800 metres deep when the rock changed again. It was an unusual layer that Paul predicted was some of the oldest beds from the Carboniferous period and proved extremely tough to penetrate. ‘Once it was clear we weren’t going to hit the red sandstone again anytime soon, we decided to declare an end to deepening the borehole. The depth was 1,821 metres – the deepest borehole ever drilled on Tyneside and the deepest direct heat geothermal borehole in the UK.’ Before tools were removed the borehole was flushed out to remove the dense drilling mud and, after cooling down, the water level settled just a few centimetres from ground level. It was covered and left to rest to allow the water to mix with the native groundwater, so that when Paul and the team return for testing this month it will give representative measurements of the all-important temperature.
‘We remain optimistic that we have a very good chance of developing deep geothermal energy on the site, but we’ll have to wait until our test work is complete before we can say quite how much heat the borehole will yield in the long term.’
