Results tagged “geothermal energy” from Journal Live - Blog Central
We successfully concluded the installation of a casing (basically, a continuous steel tube in the borehole) to a depth of 245m. We had to be sure and achieve the very best "grouting" (i.e. installation of cement) between the casing and the rock wall of the borehole.
In view of the fractures at 161m, this actually meant filling the borehole back to that level with grout, which we then had to drill out. We completed all of that by Thursday 24th March, so the first drilling rig was then able to leave site.
Then on Monday 28th, we had a red letter day - the Minister for Energy and Climate Change, the Rt Hon Chris Huhne MP, came to visit the borehole project. As Minister Huhne's Department are one of the main funders of the project, we were delighted he was able to visit us.
What an irony, though, after all the frantic activity, that his visit happened to fall in the only time in 6 weeks that there hasn't been a drilling rig on site! However, the Minister was very understanding, and indulged in the time-honoured practice of looking at the concrete cover and imagining the rocks and pipework down below.
Well, we've done it: successfully traversed the potential perils of the Coal Measures - that's to say the 235m of strata which might have contained old mine workings. I was up at the site on Friday afternoon (March 11th) as the drill bit was approaching a depth of 234m, which was the depth at which we anticipated encountering the Brockwell Seam.
Apart from a few wee spots where the slightly deeper Marshall Green and Victoria seams were worked (e.g. around Widdrington and Sacriston respectively), the Brockwell Seam is the deepest (and oldest) coal seam to have been routinely worked in the Great Northern Coalfield.
Bang on cue, the drill bit suddenly speeded up, and the rig cut through the Brockwell Seam like a knife through butter. That was great, because if it had cut like a knife through thin air, we'd have had even greater problems maintaining flushing of the borehole with water.
Thanks a million to all who have left questions and comments, and apologies for not responding sooner - it's been a bit busy! I've prepared a few answers below. I DID try to do this via the comments function myself, but I got bombed out, so at least I've paid in sweat and tears for my delay in responding to you all!
Q: "Tim Marlton said: Sounds like a very exciting project. If heat is removed from the earth's core, the core will cool down a little faster than its normal rate - are there thought to be any side effects of this?"
A: Good question. Actually it's not heat conducted from the Earth's core (or mantle) we're seeking here, but heat generated high up in the Earth's crust be slow, natural, harmless, radioactivity. Although it is possible to "overdraw" this locally, most boreholes will function well for several decades before they need to be "rested". In the meantime, replacement boreholes can be drilled nearby in good time. The original boreholes can be brought back on line later.
The wisdom of using the specialist services of Drilcorp to get us through the potential zones of old workings has now been thoroughly vindicated. Having sailed through the horizons of the High Main and Hutton coal seams - both of which might well have delayed us with lots of open voids - the next potential hurdle was the Harvey Seam (sometimes called the Beaumont Seam hereabouts) at about 168m.
Now if you believe the old records, the Harvey wasn't actually accessed from the North Elswick Colliery shaft nearby. However, as accurate mine plans were only kept routinely after about 1875, you can't be sure that you won't hit old workings, especially if the seam is thicker than about one metre. (Even 0.5m seams were sometimes worked - spare a thought for the poor lads that had to do that!).
We needn't have worried about the Hutton coal seam at all - albeit this is the seam worked most widely in the northern half of the Durham Coalfield and this adjoining block north of the Tyne. We caught the Hutton in an unworked spot! The drill bit entered the seam at 108m below ground, and swiftly proved 1.3 m of pristine coal. So that fracture at 92m depth certainly wasn't a bed separation feature, just a natural fracture in the sandstone.
We've now had no bother from either of the first two seams we feared might hinder our progress - the High Main and the Hutton - and we've to drill another 60m before the next possible zone of workings is reached, at 168m below ground in the Harvey Seam.
I'm beginning to think we are drilling through an old "shaft pillar" - that is, a zone without any workings other than the roadways connecting the main bodies of workings to the shaft itself. Shaft pillars were always left around mine shafts to ensure the stability of this vital link to surface. It looks like our geothermal drilling might well be benefiting from the shaft pillar associated with the North Elswick Colliery shaft nearby.