This eleventh entry was published originally by JSHarris on the 15th August 2013 and received 1,197 views on the closed forum
Just a short entry this time, as we had a quiet week last week. The brickie that was scheduled to stick up a Bradstone boundary wall on top of our retaining wall (which is the boundary with the neighbour) first delayed a couple of times, then earlier this week cried off altogether, as he’d had an offer of a 6 week job elsewhere. This left us in the lurch a bit, as that boundary only has a bit of temporary fence on top of a 2.5m drop. I think I’ve found another brickie and labourer team who can start in a week or so, though, so we should get the wall done, albeit later than we wanted.
This week’s excitement got off to a good start when the drill rig turned up on site, with all the usual hassle involved when we block the lane for ages while unloading heavy plant. We have one very friendly local chap who always stops for a chat when walking past with his dog (I think he’s one of those people who just likes to chat for hours). When the rig was setting up he was chatting away, full of questions, and I was busy trying to get on with checking dimensions around the site, making sure the rig was in the right place and a dozen other jobs, so, in a moment of impatient mischievousness I told him that I was just about to put the Cuadrilla signs up on the gate as we were drilling and fracking for shale oil. Within half an hour I had a visit from another prominent local, full of indignation that there was going to be an oil well drilled in the village. Took me longer to explain that it was just a water borehole we were drilling, and that my comment about fracking was just a joke, than it would if I’d spent half an hour earlier just chatting to the bloke with the dog…………….
Here’s a picture of the drill rig:
And a boring one (awful pun intended) I took looking straight down the hole:
The drill rig sill be on site for another day or two, fingers crossed that they find water…………………
ProDave 15 Aug 2013 10:08 PM :
Telling your locals you are fracking, was probably on a par with joking with airport security “What do you think is in my bag, a bomb?”
jsharris 16 Aug 2013 08:23 AM
You’re absolutely right, but at the time I was in a bit of a rush trying to make sure the drillers weren’t going to get held up by me doing last minute check measurements, and this chap (nice as he is) does like to chat away non-stop for hours if you let him. With hindsight I should have guessed that my weak attempt at humour would backfire, but all’s well now. Last night I had a couple of neighbours come up to me and joke about when we thought we’d hit oil, and talking to the drillers they’ve had more of the same from passers by.
The blue/black gault that they’re drilling through at the moment seems full of fossils, some quite nice. There’s also some odd-shaped hard lumps of lighter looking fossil coming up, so I did a search on what was likely to be found in Cretaceous gault. According to Wikipedia:
“Gault often contains numerous phosphatic nodules,some thought to be coprolites and may also contain sand as well as small grains of the mineral glauconite. Crystals of the mineral selenite are fairly common in places, as are nodules of pyrite.
Gault yields abundant marine fossils, including ammonites (such as Hoplites, Hamites, Euhoplites, Anahoplites, and Dimorphoplites), belemnites (such as Neohibolites), bivalves (such as Birostrina and Pectinucula), gastropods (such as Anchura), solitary corals, fish remains (including shark teeth), scattered crinoid remains, and crustaceans (such as the crab Notopocorystes). Occasional fragments of fossil wood may also be found.”
The odd-shaped lumps seem to me to be what’s described above as “phospatic nodules”, so I looked up “coprolites”. Rather unpleasantly these seem to be fossilised animal poo, maybe from dinosaurs (the stuff we’re drilling through was laid down around 100 to 146 million years ago). In the hope it might be good for the garden after all these millions of years I’m piling it up in a corner…………….
joiner 16 Aug 2013 11:20 AM
jsharris 16 Aug 2013 11:51 AM :
It seems that using 100 million year old dinosaur poo as fertiliser is now the least of my problems. I was called over to the site first thing by the drillers, as they’d hit a problem. They’re drilling with compressed air to blow the cuttings out of the hole, and when they hit a depth of around 20m yesterday afternoon they were made aware that there were bubbles coming up in the stream and a pond further up the valley.
It seems the hole has hit a fault and compressed air is making its way deep underground (presumably via some of the springs that abound around the area) and into the stream. The director of the borehole company drove up this morning to look at the problem and they are now trying to add more casing to try and seal up around the hole and stop the air getting out. The air won’t cause any problem, but they are worried that it will blow some of the gault clay that they’re drilling through into the springs, which will then turn the stream black. Although this wouldn’t be harmful to the environment (it’s only ancient mud and the stream is too small at this point to have much in the way of fish in it) the fact that it is highly visible in what is a crystal clear chalk stream is bound to get the Environment Agency wound up within hours, and the last thing we need is them on our backs.
We’re keeping our fingers crossed that the extra casing does the job. They’ve put in as much casing as the small rig they have on site can handle, so if this doesn’t fix it then they’ll need to swap rigs for a bigger one, which will add a three week delay.
ProDave 16 Aug 2013 02:56 PM
Ah, so you ARE fracking after all ! (I’ll get my coat)
jsharris 16 Aug 2013 05:08 PM:
Actually, it’s a damned good illustration of the risks that fracking presents. We were blowing air up in the bottom of a stream around 50 to 60m away from where we’re drilling, and across the other side of a lane. Our drill obviously hit an unforeseen crack in the heavy gault clay, something the the hydrogeologist didn’t even think was possible. I’ve just come back from the site and the extra casing down the hole seems to have done the job for now, as they’re back drilling again, with no sign of anything coming up in the stream.
One unpleasant consequence of this is that overnight the water from the stream flowed back though this fault and filled the borehole, turning the clay cuttings into thick, black porridge, that the drillers are trying hard to drill out. As you can imagine, this is an unbelievably messy job. This black and slimy porridge of clay is being blown out of the 8″ hole by a 600 cfm compressor. It looks for all the world as if we’ve hit a gusher of oil, with this black stuff shooting into the air and raining down everywhere. I think I’m going to have to look at getting a minidigger in to dig a ditch for the stuff, as at the moment it’s around ankle height all over that end of the site.
How deep have you gone? and how deep do you expect to go before you reach decent water that you can drink?
jsharris 16 Aug 2013 09:10 PM
So far we’re only at around 25m, target depth is 55m. The hydrogeologists report reckons that we should have to go through around 35 to 45m of this nasty gault clay (which is normally considered to be an aquitard, a waterproof sealing layer) and then we should hit a thin (around 6 to 8m thick) bed of running greensand, which is water bearing. The water down in this greensand is ancient, hundreds, perhaps thousands, of years old, as it’s trapped underneath the thick layer of gault clay. The prognosis is that the borehole should be able to deliver 4 to 6 cubic metres an hour, far more than we’ll ever need (we probably don’t ever need more than 1/2 cubic metre per day). It also suggests that the water quality will be high, and that we probably won’t need to do any treatment on it (although we’ve budgeted for a filter and UV treatment unit).
So far the hydrogeologist has been reasonably accurate in terms of the strata and the probability of their being hydraulic continuity between the stream and the borehole location, but he’s seriously confused by the fact that we blew compressed air through an apparent fault at around the 15m depth point, as there’s no indication that this could happen (it’s the thing that worries me about fracking, do the geologists REALLY know what the risks of groundwater contamination are?).
At a push we could just use the stream water and treat it. It comes from several springs just a few hundred yards up the valley, and is a typical chalk downland stream, sparklingly clean. We seem to have a connection from the stream to the borehole at around the 15m depth point (perhaps because we’ve intercepted an underground feeder spring), so the fall back would be to just line the bore and add a filter pack.
If we get to target depth, then we will seal and line the hole down to the lower greensand (to keep out the water from the higher levels) and just stick a glass media filter pack at the bottom to keep the sand out and give us a pretty clean source of water.
joiner 21 Aug 2013 07:59 PM :
All of this confirms people’s fears over fracking.
As you say, J, no one can tell with total accuracy what’s down there and given the pressures that fracking exerts, far in excess of anything you’re putting down there, then a fault a many times the size of yours (especially when deliberately enlarged to release the trapped deposits) has the potential to cause irreversible damage.
jsharris 22 Aug 2013 09:02 AM :
From what I can gather, the statistics from the US seem to put the risk of ground water contamination or significant disturbance (i.e. reducing the height of the water table) from fracking at around 7%. That’s largely due, perhaps, to the cavalier approach to this in the US, but there are some real horror stories out there connected with recent fracking activity. The pro-frackers argue that the process has been used since the 1930’s, but they neglect to point out that horizontal drilling and fracking is a new process, and one that seems to have a much higher risk of disturbance to deep geology. I think the other major issue is that the UK is far more densely populated than the US and has a much greater reliance on underground aquifers for its water supply. For example, if fracking polluted the chalk aquifer that supplies much of the water for the south and south east of England,then alternative water supplies would have to be found for many millions of homes. This makes the UK a far riskier place to use this technology than the US, where the impact might be just a single large town losing its water supply (as happened at Barnhart, Texas, recently).