IODP Expedition 306:
North Atlantic Climate 2
Week 7 Report
PDF file is available for download.
April 25, 2005
Operations
CORK/Thermistor Deployment at Site U1315, Hole U1315A (continued):
Hole 1315A was drilled to a depth of 179.07 mbsf and cased
with 10-3/4" casing. The base of the casing was cemented and the casing string
was displaced with bentonite mud. In preparations for deploying the CORK, Hole
1315A was reentered for the 3rd and final time at 04:48 hr April 19.
Space out was tight given the short length of the CORK stinger (20.85 m). For
the thermistor string deployment, the CORK head was left 9.0 m shy of landing
out in the 16" casing hanger. This left ~12.3 m of stinger in the hole and
allowed the pipe to be hung off at the rotary table for breaking the drill pipe
connection and deployment of the thermistor string.
The
thermistor string, specially designed for long term monitoring of the upper 150
mbsf of the sediment column, was assembled and deployed via wire line at 10:30
hr April 19 and latched in. The drill string was lowered the remaining 9.0 m
and the CORK head landed out at the correct pipe depth. After verifying that
the CORK head was properly latched, the CORK was successfully released.
Installation of the Hole U1315A CORK was officially completed as of 12:37 hr
April 19.
Hole 642E: The Hole 642E reentry cone was found using sonar and the
underwater VIT system 548 m south of Holes 642A/B on a bearing of 173° at
067°13.1850' N latitude by 002° 55.7789' E longitude. According to the
documentation the cone should have been located 450 m to the southeast (a
bearing of 135°). Hole 642E was reentered at 13:05 hr 19 April; a total of
16-1/4 hours after the search was initiated. Hole 642E was drilled to a total
depth of 1229.4 mbsf on ODP Leg 104. It was left cased 62.5 m into basement
placing the casing shoe at 371.5 mbsf. To minimize disturbance in the hole the
end of the pipe was placed only 15.3 m below seafloor.
A
downhole record of temperature was obtained using the Lamont Temperature,
Acceleration, and Pressure (TAP) tool in combination with the Triple Combo to a
total depth of 588 mbsf, where an impassable obstruction was reached. In
addition, the Formation Micro Scanner (FMS)-Sonic tool was deployed. The drill
string was retrieved and the bit cleared the sea floor/reentry cone at 10:05 hr
and by 13:10 hr all drill pipe had been recovered aboard ship. The rig floor
was secured, all thrusters/hydrophones raised, and the drill ship was underway
for Dublin, Ireland at 13:15 hr on April 21.
Under
favorable weather and calm seas, the 977 nmi transit south to the Dublin pilot
station was completed at an average speed of 10.3 kt at 9:00 hr on April 25, a
full 19 hours ahead of schedule. The transit to our assigned berth in Dublin
was short and at 13:00 hr April 25, 2005 we put our first line ashore
officially ending IODP Expedition 306.
Science Update
The
primary objective at Site U1315 is to document bottom water temperature
variations and monitor its subbottom diffusion over a 5-year period. Bottom
water temperature and salinity variations are monitored with instrumentation
that sits in the water column via an elevated reentry cone. Diffusion of the
thermal wave through the subsurface is monitored with a 150 m thermistor string
deployed in a cased and CORKed borehole.
To assess current background thermal conditions in the region, a downhole record of
temperature from nearby Hole 642E was obtained. Results from the TAP tool
indicate a bottom water temperature at the seafloor of ~0.2°C. The upper 10 m
of the borehole has a very steep gradient (~2500°C/km). Below this depth, the borehole has a relative low gradient of ~22°C/km. At a depth of ~500 mbsf, a
strong positive temperature excursion to ~42°C may indicate inflow. FMS imaging
of the hole yielded good results and will allow the correlation to existing
core data and filling in the gaps (~60% of the formation). In combination with
detailed FMS resistivity measurements and imaging, and sonic data, it will be
possible to get reliable permeability estimates. Understanding the permeability
will allow better understanding of fluid flow and temperature gradients
observed in the borehole.
Technical Support and HSE Activities
Laboratory report: The laboratories and instruments are basically in
stand-by mode while the hole prepared for the thermistor string was finished
and the logging program at Site 642 was concluded. Cleaning is in progress for
port call in Dublin. Shipping papers for the cores and a small off going
shipment are being prepared. The cleaned labs are being used by the science
staff, working on their final reports.
HSE: Fire
and Boat Drill included monitoring and verification of the alarm bells,
including those in the lab stack. The lifeboats were lowered to the embarkation
level, doors opened and engines started. Information on the EPIRBS, lifeboat
emergency locator beacons, and radar reflectors was provided. The beacon
transmits to satellites that relay the position to rescue resources. The radar
reflector aids planes in locating the lifeboat from high search pattern.
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