Wednesday, November 12, 2014

DFDP-2 @ 489 m: Calamity! Again!

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



Fresh snow in Whataroa. Drill site is up the valley on right of photo.
12/11/14. Photo R. Sutherland.
Misfortune struck in the early hours of Wednesday morning. Drilling progress had slowed the previous day, and then it totally stopped. We had reached 489.5 m depth.

The drill was removed from the hole and we got a surprise: the drill bit was missing. So was the bottom 7.5 m of the bottom-hole-assembly (BHA).

Steps to recover the lost BHA piece are in motion. We know how to fish it out from our last experience.

Crossover (left) with stripped thread and a broken fragment inside.
It should look like the male thread on the right.
Note the stabiliser just above it.
12/11/14. Photo R. Sutherland.

Worn stabiliser. 12/11/14. Photo R. Sutherland.
Close-up of stripped thread and broken fragment still engaged.
12/11/14 Photo R. Sutherland
 The loss was caused by equipment failure: a broken thread. It is the same section of drill collar that bore the full impact when the BHA was previously dropped to the bottom of the hole, so it may have had a weakened thread. However, there are also signs that drill bit failure contributed to this incident.

The science team noted anomalies in the hours before the incident. Steel shavings were collected (damage to stabiliser and bit?) and traces of hydrocarbons detected (grease from the threads?). The bottom stabiliser is badly worn at its base, suggesting the hole was not in gauge (it was too narrow). It seems that the drill bit may have started to fail at least 8 m before BHA separation occurred.

Wireline logging is underway. It will help us understand the state of the hole and what happened.
We hope to be drilling again in a few days.

These little fellas really didn't care about our woes. They are always happy to see us.
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.

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