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IODP Expedition 335:
Superfast Spreading Rate Crust 4
Week 6 Report (15-22 May 2011)
PDF file is available for download.
Given the persistence of cobble-sized material near the
bottom of the hole, indicated by the contents of the reverse circulating junk
basket of bit run 14, a new Smith 7JS tricone bit was picked up and fitted with
3X15 nozzles and affixed to a 3-stand BHA with the goal of grinding up the
remaining loose rock. The drilling assembly reentered Hole 1256D at 0730 h on
15 May. Hard contact was made at a depth of 1518.8 mbsf. From 1415 h on 15 May
until 0615 on 16 May the hole was washed and reamed from 1518.5 to 1521.1 mbsf
and flushed with 460 bbl. of high viscosity mud sweeps. The bit was tripped to
surface after 14.5 rotating hours to ascertain the condition of the bit and
assess the progress. The bit cleared the seafloor at 1015 h and the rotary at
1545 h on 16 May.
The cones exhibited virtually no wear except for a chipped
insert on the gauge cutter. The bearings were tight with some apparent
shirttail wear and minor junk damage present on the big body. These were
characteristics of a bit that had done very little actual drilling. When the
bit diameter was measured it was found to be under gauge by 7/16". Apparently
the bit had been literally squeezed into a smaller diameter hole (< 10" in
diameter). The conclusion was that the bottom ~3 m of the hole were considerably
undersized and would have to be reamed to full gauge before fishing could
A tricone was located in the bit inventory that contained
the desired hard-facing and leg reinforcement. The sixth tricone bit used
during the expedition was selected based less upon cutting structure and more
upon the amount of armor on the legs since that would be the area that would
receive most of the wear during reaming. A Smith FH3VPS 9 7/8" tricone was made
up to a 3-stand BHA without external junk baskets. The bit reentered Hole 1256D
for the 16th time of the expedition at 0245 h on 17 May. By 0815 h, washing and
reaming operations began. The under-gage section of the hole ranging from
1516.5 to 1519.7 mbsf was reamed for 15 rotating hours and flushed with a total
of 260 barrels of high viscosity sepiolite sweeps.
The bit was pulled clear of the seafloor at 0340 h on 18 May
and recovered at 0900 h. The tricone bit was found to be in gage. Although the
tricone was missing six teeth on the middle row of one cone it was in
reasonably good condition. The missing teeth indicated that that cone contact
had been made with the debris at the bottom of the hole. During the reaming care was taken to
avoid penetrating below 1520 mbsf to prevent metal to metal contact with the
RCB bit wreckage and avoid potentially leaving more junk in the hole.
Once the reaming was concluded, a flat-bottomed 9 5/8" mill
was made up to the 3-stand BHA with an external junk basket (EXJB) and
deployed. The mill entered Hole 1256D at 1850 h on 18 May and initiated milling
at 0130 h on 19 May. Shortly after reentering the cone for the 17th time during
the expedition, the total length of drill pipe tripped during the cruise passed
100 miles. This milestone was acknowledged by a message of thanks to the
Transocean teams from the Shipboard Science Party. Milling progressed without
incident until 1330 h. The driller frequently picked up the tool a little off
bottom and decreased the pump pressure to let cuttings settle and be captured
in the EXJB. This is referred to as "working the junk baskets." A total of 300
barrels of mud was circulated to flush the hole during milling.
The mill cleared the seafloor at 1920 h on 19 May and was
recovered by 0315 h the next morning. The trip out of the hole was suspended
for 1.5 hours for the 6th slipping and cutting of the drilling line. The
abrasive hard surface on the face of the mill was completely worn away and the
diameter of the tool under-gage by 0.5".
The second milling tool run was made with a 9" flat-bottom
mill, which reentered the hole at 1415 h on 20 May. From 1945 h until 0145 h on
21 May the bottom of the hole was milled and the junk baskets worked. Based on
the excessive wear to the first milling tool, the rotating time for the second
mill run was scaled back from 12 hours to 6 hours. A total of 320 barrels of
sepiolite mud were circulated to keep the hole clean. The drill string was
pulled free of the seafloor at 0645 h and the second milling tool was secured
on deck at 1225 h on 21 May. The milling surface was abraded clean and some
minor junk damage was noted on the side of the mill. There was also a 3"
200-degree circumferential grove cut into the crossover sub located just above
the mill. The EXJB was unloaded and found to contain the usual small cuttings
and gravel with some small fresh cuttings of metal. This was the first
suggestion that we had finally started to mill bit debris.
The next fishing attempt was made with the third deployment
of the RCJB and three EXJBs. This assembly reentered Hole 1256D at 2230 h, on
run #19 of the expedition. The tool was run to ~3 m off bottom and the junk
baskets worked for ~10 min with the pump strokes as high as 150 spm and
standpipe pressure reaching 1850 psi. Following a 100 barrel mud flush, the RCJB was worked to the bottom (~1521 mbsf) with minimum rotation and very light weight on bit. We are presently recovering the drill string.
The fishing tools used this week for hole remediation
operations continued to recover significant rock material ranging from
fine-grained cuttings to large cobbles (up to ~5 kg). Encouragingly reentries
were smooth with no difficulties over the last runs, and the fishing tools tagged
remaining hard fill at the bottom of the hole without encountering any
obstructions on the way down. The hole is now clear of the very large amount of
sand-like cuttings that were retrieved last week during several successive
fishing runs. On re-entry the entire re-cone is now clearly visible with
obvious signs of borehole cuttings deposited on surrounding sediment blanket,
indicating much more effective cleaning and pumping of material from the bottom
of the hole.
The science party has been occupied describing and analyzing
last week's recovered rock material. Because of the large size of some of the
samples recovered, contact and textural relationships are being documented that
are rarely observed in the usual ~6 cm-wide cores. Overall, they depict a
section of metamorphosed sheeted dikes, intruded by a series of small-scale
evolved plutonic rocks and minor gabbro. Most rocks are fine grained with
granoblastic contact metamorphic textures, and are slightly altered to
amphibole and minor albite, epidote, titanite, and chlorite. Samples are cut by
veins of amphibole and minor chlorite, epidote, and quartz. Coarser grained
intrusive material is more highly altered to amphibole, albite and titanite.
Crosscutting relationships between veins with different compositions, observed
both in hand samples and thin sections, have been described in detail. The
reduction of the first set of geochemical data is underway.
Education and Outreach
A live ship-to-shore broadcast with several members of the
IODP Expedition 335 science party was the highlight of an event at the NSF on
Wednesday, organized by Deep Earth Academy staff and former School of Rock
participants for 85 kindergarten through 6th grade teachers. The teachers were
recipients of the prestigious 2010 Presidential Award for Excellence in Mathematics
and Science Teaching (PAEMST). Nine additional broadcasts from the ship to
schools in China, France, England, Australia, and the US, are scheduled before
the end of the expedition.
Technical Support and HSE Activities
Technical staff provided support for coring operations on
Hole 1256D and assisted scientist with special experiments. Other technical
activities included support for the DESClogik project, continued work on the
science pallet storage reorganization project, chemistry lab facility upgrades (planning), and completion of a thin section training video.
The weekly fire and abandon ship drill was held as scheduled. No incidents to report.