Monday, February 7, 2011
Wireline logging took several days because of borehole instability issues and yet more technical obstacles. We did not get clear runs through the whole borehole on some of the tools, but we have collected a very nice dataset with a wide range of tools: natural gamma, calliper, electrical resistivity, spontaneous potential, density,
porosity, full waveform sonic, dipmeter, and induction flow meter.
Installation of observatory equipment in borehole DFDP-1B is still under way. We successfully installed a 2 Hz seismometer at the base of the borehole. We have 4 piezometers in place to monitor pore fluid pressure, and will install a fifth tomorrow. Twenty five sensors monitor the average temperature gradient in the borehole and detailed thermal structure immediately above the fault. We will continue with observatory installation and testing tomorrow.
First photo: Full waveform sonic tool and wireline logging truck
Right: Observatory installation team: Jennifer Eccles, Mike Hasting, Simon Cox, myself (kneeling), Alex, John
Townend, and Jeremy Cole-Baker.
An initial observation that I found interesting was confirmation that fault gouge is an effective hydraulic seal. A preliminary estimate of pore pressure difference across the fault in DFDP-1B is equivalent to 33 m of water head. This partly explains borehole instability when the hole was left open: there was a “waterfall” within the borehole trying to wash fractured rocks above the fault into and down the borehole. When trying to clear the borehole in DFDP-1A, to grout a cement-bentonite seal into the fault, we punctured a temporary breach with a long plastic pipe.
There was the most extraordinary slurping noise as water was sucked out of the drill string into the lower pressure gravel aquifer beneath.
Egor lowers casing with a shoe bit and casing advancer inside
Over the next few days we will wind up field operations, demobilise equipment, and secure the permanent observatory. It is gratifying to know that, despite substantial challenges, our long hours, good planning, and excellent contractors have led to success for all of our main technical objectives. We collected lovely cores across the fault, ran a full suite of wireline logs, and installed a fault zone observatory. I specially thank the students involved and our visitors from Liverpool University. Everyone worked long hours and behaved in a very professional and collegial way.
The whole operation was very slick. You really would not have known what a steep learning curve we
had actually all been on. Finally, I give massive thanks to Egor our “senior” driller. He worked hard and long hours, never had a day off, solved the many technical challenges we created for him, and mostly kept a smile on his face too (though he didn’t like torrential rain).
This is Rupert signing out for now. Over following months the massive quantity of samples and data we collected will need to be carefully analysed and written up, so it may take some time before I poke my head up above water again. The next phase, DFDP-2 (>1 km), already has advanced plans, but we will certainly want to improve them now that we have had this practical experience and learnt so much about what we might find at greater depth.
Egor and Alan
Finally, in case you haven't seen it, here is a short introduction to the Alpine Fault Drilling project:
Tuesday, February 1, 2011
|A sample of cemented cataclasite is carefully extracted from the core catcher|
Coring progressed smoothly this time, even though one of our drillers walked out on us for no apparent reason. For the last two days I have been working as a drillers offsider, trying to keep us on track with the project, but it has been tough to balance every demand.A sample of cemented cataclasite is carefully extracted from the core catcher.
Drama continued again last night when a sudden storm passed through at 2-4 a.m., flattening our core processing and logging facility. Fortunately, nothing catastrophic was lost or damaged.We rebuilt better and were ready to drill again by 7 a.m.
|Cores of the Alpine Fault footwall emerge for the first time|
At about 7 p.m. we collected the first core from beneath the problem zone (thanks to the skill of our driller on the levers, “Egor”). This core and the subsequent two confirmed that we had just crossed the principal slip surface of the Alpine Fault at a depth of 128 m. Fantastic!
Both of our boreholes have obtained high-quality cores across the fault, including the precious fault gouge of the primary fault surface. There is a clear sense of excitement and achievement, and a big group has decided to work through the night to see what is going to appear.The rock cores currently emerging are really interesting, because the rock types immediately beneath the fault are not well known, in comparison to the well exposed and studied sequence above.
|A beautiful core of the Alpine Fault from 128 m|
It is premature for me to say what the rocks are that we cored, but brilliant white and green shades indicated that we had crossed the fault. We decided to keep going for another shift, and over the next 24 hours a preliminary geological description will be constructed.
If all goes to plan, we will have finished our main phase of drilling tomorrow. We will move onto
wireline logging and geophysical observatory installation. I personally now need a few hours
sleep after the drama of the previous two nights.
|John Townend, Richard Norris, Rupert Sutherland, and Virginia Toy consider achievement so far|
Friday, January 28, 2011
Thursday, January 27, 2011
Tuesday, January 25, 2011
Egor, the driller, and some of the DFDP-1A team happily show off a perfect core of the principal slip surface of the Alpine Fault.
After we cleaned those cores and carefully logged them, we came to realise that we had not crossed the Alpine Fault, we were just getting the most beautiful cores. Maybe it was just the effect of increased confining pressure that resulted in better cohesion and recovery of the cataclasite. Our lab work, wireline logs and the DFDP-1B results should help to provide a scientific explanation for this change.
After 20 m of near perfect core recovery, we definitely did hit the principal slip surface. We were at 90 m depth. It was obviously the fault because there was Quaternary gravel lying beneath the thick sequence of cataclasite. The driller, “Egor”, was more excited than anyone – a perfect core across the critical zone. Fantastic!
The precious fault gouge core is now in a very secure box in a secret location and is marked “Beware of Virginia”. After reaching a depth of 96 m, we were having difficulty advancing further and for various reasons we decided to halt
drilling and then withdraw the drill string.
The project so far has been frantic, but efficient and very successful. There we were holding the first core of the Alpine Fault on Sunday evening and we were not even scheduled to start coring until the following Monday morning. We were at least 3 days ahead of schedule and it dawned on me, as project manager, that none of the other contractors were even here yet and some instruments had not even arrived from the USA. Elation started to turn into a mild panic. There was a lot of work to do and plans to change.
The revised plan and workforce has now started to fall into place, and the TV, radio, and newspapers have been on the phone all day. We reached a consensus decision today on where to site the DFDP-1B borehole and the percussion air-hammer crew has now showed up to start installing a surface casing at the new site. The current intention is to knock a 6” casing down to nearly 70 m, to try and avoid the difficult materials found in shallow parts of the DFDP-1A borehole. We are hoping to reach a total depth of around 200 m in our next borehole, if we hit solid rock beneath the fault. We start tomorrow morning.
Monday, January 24, 2011
Horizon Drilling diamond coring rig at DFDP-1A drill site, Gaunt Creek. Core processing and logging is in tents behind the white container. Alex Pyne (Scientific Drilling Office, Victoria University of Wellington, NZ) is helping and training us with regard to core processing, and Brett Carpenter (Penn. State, USA) brings practical SAFOD experience. They are both helping NZ students learn the art of cleaning and then piecing cores and fragments back together. We drilled at a rate of 1.5 m/hr and obtained 56% core recovery over our first 30 m, but this will hopefully improve as our drillers hone their technique. The rock is shattered and altered to clay by the fault, so it is difficult material to collect.
Brett Carpenter (Penn. State, USA) and Carolyn Boulton (Canterbury, NZ) process a core. They remove it from the metal split that comes out of the core barrel, clean it, record operational data and preliminary notes, and then deliver it to the logging geologists for a detailed description.
The team of logging geologists has been coordinated by Virginia Toy (Otago, NZ), and is made up of David Prior (Otago, NZ), Dan Faulkner (Liverpool, UK) and Elisabetta Mariani. The cores are described in detail, sampled in key places, and then shrink-wrapped in plastic and boxed for later analysis. The whole team has to work together to communicate what we are learning about the geology back to the drillers, so that they can predict how to better drill the next core and maximise our core recovery. This is a tough job, because nobody has ever drilled into the Alpine Fault before, and it is particularly poorly known what lies beneath the fault.
And in breaking news…
Just as I am about to post this, I am seeing some spectacular cores from near 70 m depth. I think we may have just crossed the principal slip surface of the Alpine Fault and passed into rocks that are very poorly known, but seem to produce great looking cores. I will post a further update after the cores have been cleaned, logged, and the science team have discussed them.
Our video that describes the project is here
Friday, January 21, 2011
In the photo, Virginia Toy and John Butt are looking pleased to have made such great progress. The Alpine Fault is exposed in the cliff face just above their heads, 150 m behind them.
In addition to the start of drilling activities, a team of people led by Rob Langridge (GNS Science) and Greg de Pascale (Canterbury Uni.) have confirmed Alpine Fault location to the north of our drill site and found basement rock exposed at the surface; and a seismic reflection survey led by Andrew Gorman (Otago Uni.) is almost complete at the drill site, which will help to tie geophysical properties of the fault zone with drilling results.
This is a really great start, thanks to the big team of people that have already helped.
Thursday, January 20, 2011
For an overview and brief introduction to this project see Julian's Blog or check out the video below.
After several days of road improvements to access our drill site, Jimmy Arnold’s efforts were put to the test yesterday with the arrival of the trucks. The first truck weighed 42 tonnes and had difficulty getting round a few corners, but the road performed well and everything got to the drill site before lunch.
Three large trucks, at least half a dozen smaller vehicles, and a digger established our site. By
the time we stopped for dinner we had already hammered down 24 m of steel casing using a
Concentrix rotary air hammer system operated by John Butt.
Despite not expecting to start sampling for a few more days, we jumped into action and logged
cuttings and drilling progress. At the base of 9 m of bouldery gravel we hit water-charged sand and then passed into cuttings of homogeneous mylonite with abundant clay. The easy penetration and high saturation of water and clay indicated that, although we had reached the target of basement rock, it was unlikely to core easily or leave a stable borehole wall. We continued to knock down casing. Conditions improved below 19 m depth, with much less water and a moderate but stable drilling rate.
This morning we added one additional 6 m casing. From 20-30 m depth we had observed a stable drilling penetration rate through relatively dry (impermeable) fractured rock and there was a consensus between myself, Virginia Toy (Otago University), and the drillers John Butt (Butt drilling), Ken Mears (Westmere Drilling) and Brent Herrick (Horizon Drilling) that we now had a stable base to start coring operations from.
Here is the video that outlines the purpose of the project