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Hotter than hoped!

Testing and analysis at the boreholeWe finally got round to starting what will be a lengthy process of testing and analysis of what exactly lurks down the borehole – and the main thing to report so far is that the temperature down there is even higher than we’d dared to hope.

A bit of jargon for you: the rate at which the temperature increases with depth into the Earth’s interior is called the ‘geothermal gradient’. To get a number for this in nice round figures (without resorting to lots of zeroes), I normally express the geothermal gradient in degrees C per hundred metres (deg. C/100m). In most of the UK, the background geothermal gradient is on the order of 2.2 to 2.5 deg. C/100m.

In the work we did a few years ago in Weardale, where we drilled right into the buried granite up there – which naturally produces heat to add to that conducted upwards from the semi-molten mantle of the Earth (more than a dozen tens of kilometres below) – we found a geothermal gradient of about 3.8 deg. C/100m.

Four men working at the boreholeNow, our theory about Tyneside is that the main hope of geothermal resources right here relates to the same granite, although that is not thought to lie closer to the city centre than the Winlaton area. Thus any heat coming from the granite is likely to be moving towards Newcastle along a large system of faults and deeply buried beds of sandstone. Well, we definitely drilled into the right sandstones, from 1500 to 1800m below the city. But given the distance to the granite, I still thought we’d be doing well if the geothermal gradient exceeded 3 deg. C/100m. It was hard to tell exactly what geothermal gradient we were getting during drilling, when the drilling fluid is sloshing up and down the hole, cooling in the air at surface and so on. The indications were positive, but quite how good would it be once it had had a chance to settle?

To our delight the answer is 3.9 deg. C/100m – even higher than we found in Weardale! This is a phenomenal result, and it suggests that the bottom hole temperature at 1821m will be closer to 80 deg. C than the 70s we were previously hoping for. That’s great news. Frustratingly though, we now need to mobilise some different gear to clear a small blockage in the borehole at 969m, where some shale beds have tipped across the hole since we flushed the mud out. It’ll take us a bit of planning before we can do that, but with a fantastic geothermal gradient like this we have every encouragement to get back in there as soon as possible and take the next steps towards harnessing this increasingly exciting resource.

6 Responses to “Hotter than hoped!”

  1. Tom Fletcher says:

    This technology and way of creating/harnessing energy is something that will grow over time. It would be interesting to know the cost viability of these projects as energy under ground would be more appealing to the masses than energy creation above ground with the likes of land based wind turbines.

  2. John Martin says:

    That really is impressive I am by no means an expert on this technology but understand its importance, what are the hopes for the project, what type of capacity (heat output) is possible here and assuming this has both commercial and domestic potential what from a domestic perspective is the likely model/size/scope of a district heating scheme?

  3. Paul Steverson says:

    This great news, so the Weardale granite is hot and Newcastle is too.

    What are the chances that other granites are hot too?

    Underlying Derbyshire we have granite too (as evidenced by high Radon levels) but this is deep and maybe dry? Any plans to test anywhere else anytime soon?

    • Paul Younger says:

      Most of the granites in northern England that have been accessed (several are deeply buried) have proved to be good heat producers. The Wensleydale Granite, and the Lake District granites are all comparable to the Weardale Granite. As far as I’m aware, nobody’s definitively proved a granite beneath the Peak District yet, but there’s plenty of circumstantial evidence that there may well be one there, similar to the North Pennine ones, as the overlying mineralisation is rather similar. I’d love to drill deep in Derbyshire too – and one of these days, somebody will get the cash together to try it!

  4. Paul Younger says:

    Thanks for your interest John. Not many folk want to know all the technical details. Here’s a summary for your delectation:

    Phase 1
    • Drilled by Drilcorp (specialists in drilling through mined Coal Measures) using a Beretta T151S rig, which is a multi-functional top-drive rig with a pull-back of 20 tonnes.
    • Manual installation of a 23½” conductor pipe to 1.5m
    • Drilling (using rock-rollers) commenced at 23” diameter, leading to installation of an 18” casing to 20m
    • A temporary 133/8”casing installed, to maintain upflow velocities, and drilling continued at 12¼” to 245.5m
    • Borehole completed some 10.5m below the floor of the deepest productive seam (the Brockwell)
    • Geophysically logged, then 95/8” casing installed and grouted, and successfully pressure-tested at 1300 – 1500 psi

    Phase 2

    • Drilled by Geometric-COFOR with a HH102 Hydraulic Hoist rig, with 102 tonne pullback
    • Drilled with BOP rated to 3000 psi
    • Drilled with rock-roller at 8½” to ~1000m
    • Installed and grouted casing to 954m, and pressure-tested to 3,000 psi
    • Continued drilling at 6” to t.d. (1,821m)
    • Interval 954 – 1,821m left unlined
    • Geophysical logging late October 2011

    As for the shale spalling, we anticipated that something like this might well happen, not so much because of loss of mud weight as because of the adjustment of the shales to the initially lower salinity of the water (just town water) that we replaced the drilling mud with. I don’t regret replacing it, as we really do need to access groundwater in the end, and don’t want to leave the mud to clog the precious bottom reaches of the borehole if avoidable. The conductivity shows the water in the borehole has now equilibrated with the natural groundwater, so if we can clear the blockage it might well settle down now. The caliper log shows the amount of shale that has spalled is pretty minor, but still enough to prevent access by a delicate logging sonde. We are currently planning a cable tool solution to that problem.

  5. John Midgley says:


    Is there anywhere I can see the well profile? hole sizes, casing size and type, shoes and what kind of drilling rig was used?

    Since you’ve flushed the mud out, what fluid type have you replaced it with? And is it a mud weight problem that let the shales fracture to bridge the hole?

    I know… questions, questions…



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