Friday, October 31, 2014

DFDP-2 @ 396 m: Calamity! Dropped bottom-hole-assembly (BHA)

Rupert Sutherland, GNS Science and Victoria University of Wellington
John Townend, Victoria University of Wellington
Virginia Toy, University of Otago

Drill site 22/10/2014  Photo J. Thomson
We removed the drill from the hole last Thursday (23/10/2014) at a depth of 396 m, so that we could survey the hole and reconfigure the drill. The wireline logging survey went smoothly. It is about 56 degrees Celsius near the bottom of the hole.

Wireline logging tool. Photo: J. Thomson.
The drill bit was found to be worn and the hole had reached 12° off vertical. The deviation was caused by mechanical interaction between the drill and the dipping rock fabric. At least it was heading in the right direction (northwest, towards the fault).

Worn PDC drill bit. Photo: R. Sutherland
 Tricone bit, collars, and stabilisers. 
24/10/2014 Photo: R. Sutherland.

The drilling team reconfigured the drill pipe and switched to a new drill bit. This time we used a tri-cone type of bit. The bit is attached to heavy, rigid ‘collars’, and wider pieces of pipe called ‘stabilisers’ that centralize them in the hole. The entire ‘bottom-hole assembly’ (BHA) weighs 7400 kg in mud and is 72 m long. It is connected to the surface with steel drill pipes.

Fishing tool and fragment of
recovered wire rope. 
Photo: R. Sutherland.

Calamity struck at 13:09 last Friday afternoon (24/10/2014), just before the Labour Day long weekend. A wire rope snapped and the entire BHA dropped down the hole. We are very relieved that nobody was hurt. An independent technical investigation is being conducted by an engineer and we await his findings.

Our immediate strategy is to try and retrieve the BHA from the hole. This process is known as ‘fishing’. The BHA weighs 7.4 tons, so the first step in fishing is to extricate anything preventing a good grip. The drillers were successful in fishing out of the hole some broken fragments of wire rope and some of the top fixings. They are now working to establish whether they can lower a socket over the top of the BHA. If that is possible, they will use a special tool used in the oil drilling world to lock onto the BHA and lift it back to the surface. This tool is being transported from New Plymouth.

Fishing tool 30/10/2014  
Photo: J. Townend.

What does this mean for the project? It is certainly going to delay progress, but everyone is working hard to recover and continue. While fishing operations are underway, we have been analysing the data collected so far and documenting our preliminary findings.

If the BHA cannot be retrieved, we will cement it in place and side-track (deviate) the hole above it. This will mean re-drilling about 100 m of hole, but we can re-use most of the steel casing already installed.
We had expected delays of some sort from the outset, so we have contingency built into our scheduling. The delays so far mean that the project will continue into December, and we are very much hoping to get back on track so that we can finish before Christmas.

Nobody said it would be easy!

Check out our new video that shows you what a bottom-hole-assembly actually looks like before it is assembled and put in the hole...

Check out our video that describes the purpose of the DFDP project...

Some comedians did a parody of the safety of our project last week, but is it safe? We think it is, but don't take our word for it. See the video made by the Chairman of our independent Safety Panel...

See also:
The DFDP-2 wiki pages

Primary funders of the DFDP-2 project are: the International Continental Scientific Drilling Program (ICDP), the Marsden Fund of the Royal Society of New Zealand, GNS Science, Victoria University of Wellington, and the University of Otago.

Wednesday, October 22, 2014

DFDP-2 @ 360 m: solid rock since 240 m

Rupert Sutherland, GNS Science
John Townend, Victoria University of Wellington
Virginia Toy, University of Otago

A lot has happened since our last update. We have completely reorganised the site and positioned a new drill rig over the borehole. We’ve tidied up all the big steel pipes, and the Washington Drilling trucks, rig, and drillers, have left. We’ve hoisted the flags on our science facility and are getting down to some serious business in solid rock.

Onsite science facilities 22/10/14. Photo R. Sutherland.
The main phase of open-hole drilling began at 3 pm on Sunday 19 October, and we had reached 360 m depth by 7 am this morning. Our rate of progress varies between 1 and 4 metres per hour. We are now working in shifts around the clock.

The geology group is collecting rock cuttings made by the drill bit and transported to the surface entrained in the drilling mud. The mud travels down the centre of the drill pipe, out through the bit, and back up to the surface. It emerges at 25°C, but we know from downhole measurements that the temperature at the bottom already exceeds 50°C.

8.5” PDC drill bit. Photo: R. Sutherland.

We have three main science tasks at the moment. The first is to document drilling rates and mud characteristics. These measurements tell us about rock properties, fluid pressures and downhole temperatures. The second is to use wireline tools to survey the borehole during breaks in drilling. Finally, we are carefully analysing the rock cuttings to determine when to stop this phase of open-hole drilling and to start collecting rock cores.

Drill rig and mud pump 22/10/14. Photo R. Sutherland.

Primary funders of the DFDP-2 project are: the International Continental Scientific Drilling Program (ICDP), the Marsden Fund of the Royal Society of New Zealand, GNS Science, Victoria University of Wellington, and the University of Otago.

Saturday, October 11, 2014

DFDP-2 @ 236 m: hot water

Over the last few days we have been slowly progressing through sediments containing cobbles and boulders. The team looking at small fragments of rock cuttings have done a great job in being able to tell us that we are definitely not in bedrock yet.
A couple of days ago, we became frustrated by our slow progress and removed (tripped out) our drill string from the borehole, to put a sharper bit and heavier drill string back in. During this process, the mud in the hole became diluted with water from the bottom (the hole has 12” steel casing around it), and the well started to flow (artesian).
By the time the new drill string was in the hole we were producing hot water at 5 litres/second and 43°C. This was a great opportunity for the fluid and gas chemists, and for those of us who are interested in the thermal and fluid state of the fault.

Warm water at dawn 10/10/14. (photo D. Prior)

The flow was controlled by injection of new drilling mud and drilling recommenced, but it continued to be difficult to advance the casing. We are now at 236.6 m depth. A decision was made yesterday to start installation of a new 10” steel casing string. The basic idea is that each slightly-smaller casing is nested inside and protected by the previous one. We have to make progress through this difficult-to-drill zone, and this is our only option.

We are making slow but steady progress. The chemistry and gases of the hydrothermal fluids seem similar to those of nearby hot springs in bedrock, and the high fluid flow rates suggest a quite different hydrology to the silty sediments that we were drilling through up until now. We think it likely that we are close to a contact between sediments and bedrock.
Meanwhile, the ICDP training course in Franz Josef Glacier has ended and participants have returned to Whataroa to help on-site. Our scientific facilities are almost all fully completed and providing a comfortable and efficient workspace.

Geophysical tool assembly 8/10/14 (photo J. Townend)

Events of the last few days again confirm that scientific investigations can produce interesting and unexpected results — the power output of our geothermal production was about 0.7 megawatts.

Tuesday, October 7, 2014

DFDP-2 @ 202 m: drill sediments

Rupert Sutherland, GNS Science
John Townend, Victoria University of Wellington
Virginia Toy, University of Otago

Covered area being constructed at drill site 6/10/14.
We are now simultaneously drilling and advancing 12” casing (inside 16” casing) using a dual-rotary drilling method. We have reached 202 m. In fact, we have spent several hours drilling since we were at 201 m and there is an exciting possibility that we have finally hit solid rock*(see below). The cuttings and thin-section lab is up and functioning, and the rock type appears to be consistent with local basement rock. However, we will continue on until we are confident this is not just a locally-derived boulder.
Dual-rotary drilling and advancing 16” casing 28/9/14.
The site is really starting to take shape, but is noticeably less busy since the ICDP training course started yesterday. The centre-piece of the science facility is 7 containers housing: mud gas monitoring equipment; wireline logging tools; a rock preparation and thin-section lab; a core scanning lab; a clean(ish) lab for data entry and microscopes; an operations centre and site office from which earthquakes and drilling parameters can be; and a coffee room.
The wireline logging container should arrive tomorrow and the office and coffee room have just arrived and are being fitted out. The large outdoor covered area got tested by driving rain and strong winds that were strong enough to move several of the shipping containers. It is amazing that the cover could withstand such a battering.
John Townend arriving on site at dawn 4/10/14.

*It turns out that it wasn’t. We continue drilling.

Primary funders of the DFDP-2 project are: the International Continental Scientific Drilling Program (ICDP), the Marsden Fund of the Royal Society of New Zealand, GNS Science, Victoria University of Wellington, and the University of Otago.

Thursday, October 2, 2014

DFDP-2 drilling started

Rupert Sutherland, Principal Investigator, GNS Science
John Townend, Principal Investigator, Victoria University of Wellington
Virginia Toy, Principal Investigator, University of Otago
Simon Cox, Quaternary Team Leader, GNS Science

The start of DFDP-2 drilling activities in the Whataroa Valley 1/9/2014.

The aim of the DFDP-2 project is to examine a major fault before it ruptures in a large earthquake. What are the ambient conditions in the fault zone? What are the physical properties of the materials? What is the fault zone’s internal structure? Answers to these and many other questions will help us understand what happens when a fault ruptures in an earthquake and how slip accumulates to form a plate boundary. Have a look at our video for an introduction to the DFDP-2 project:

Our results will have implications for global earthquake science. This is why scientists from twelve countries have come together to gather information on fault geometry, temperature and pressure conditions, collect rock and fluid samples, and install long-term monitoring equipment. It is also why the international community, via the International Continental Scientific Drilling Program (ICDP) has funded more than half of the project, and why we have been successful in obtaining funding from the Marsden Fund.
The DFDP-2 project will have specific value to New Zealanders. It is surely important to understand the largest source of seismic hazard in South Island. What will happen during and after the next major earthquake? Does the hazard vary from day to day? Does anything unusual happen before an earthquake? Could we develop a warning system? Does the Alpine Fault offer benefits as well as hazards? For example, does the fault host a geothermal resource? Our project will help address these questions too.
DFDP-2A during coring of sediments 17/9/2014.
Phase 1 of DFDP-2 involves drilling and installation of casing though sediments in the Whataroa Valley. Drilling started on 29 August 2014 with installation of 12” casing using a dual-rotary-air method. The 12” casing was advanced to 29 m depth, and then 10” casing to 125 m. At this point, we opted to mobilise the coring rig earlier than originally planned, to sample the sediments and determine how to proceed. The sediment layers proved thicker than we had thought, and sediment cores could provide valuable information.

On 14 September, we started coring sediments. After moderate recovery between 125 and 160 m, we drilled open-hole with a stratopack bit and rapidly progressed to 206 m. On 17 September, we stopped coring glacial diamictites at 212 m depth.

Rupert Sutherland and Simon Cox inspect core.
The project has already produced results that have surprised many and will lead to a new understanding of activity on the fault and the mechanism by which glaciers cut and fill valleys.
The relatively young (<500 yr) cobbly river gravels are only a few metres thick. Below this, to a depth of about 50 m, there is a sequence of pebbly river gravels that are at least 12,000 yr old. Deposits from an ancient river delta are found between 50 and 77 m depth, and below this, we discovered a thick sequence of silts, likely deposited on the bed of an ancient lake that filled the space carved out by a glacier. Below 197 m, we find evidence for rocks that were rafted and dropped into a fairly deep lake from floating ice as the glacier retreated.
We infer that the lake-bed was at least 300 m below the sea level of the time, which itself was at least 100 m lower than today. We are examining samples to see if it was a marine fiord. We have recovered many wood samples suitable for radio-carbon dating the thick sequence of sediments.
The steepness of the valley wall is a surprise to every scientist involved. There are very few slopes >50 m in extent that dip >45° in the modern topography. How has the rock face stayed so steep? Does this have implications for the strength of shaking during Alpine Fault earthquakes? We are only 1 km from the surface trace of the fault.
The static water level in the upper gravel unit (29 m depth) is about 5 m below ground surface. Below 120 m, we encountered artesian pressures, as anticipated, but a shut-in pressure could not be determined. Low flow rates (<0.3 l/min) imply low permeability, consistent with high silt contents.
We measured the temperature at 120 m depth in DFDP-2A and calculated a geothermal gradient of 139°C/km. This result needs to be interpreted with caution. First, slight artesian flow of warm water from the open hole below 120 m depth may be significant. The corrected value may be closer to 80°C/km. Second, we anticipated an elevated geothermal gradient and artesian pressures based on hydrogeological modelling, and it may not persist to greater depth.
Scientific drilling often provides unexpected results. The new sediment thickness, temperature, and fluid pressure data are useful for planning deeper operations, but we also have to now re-examine models of landscape evolution, geothermal circulation, and ancient fault movements in the Southern Alps.

Operations continue and the project is ramping up to its main phase. The first hole, DFDP-2A, is now a monitoring hole that we had originally intended to drill later. On 24 September, we began pulling casing and then we started a new borehole, DFDP-2B, about 10 m closer to the valley wall. We have since installed 16” casing to 47 m using dual-rotary-air and are about to start dual-rotary-mud. This has caused about a week’s delay, but we may make up time if bedrock is not much below 220 m. Stay tuned!