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IODP Expedition 327:
Juan de Fuca Ridge-Flank Hydrogeology
Week 6 Report (9-15 August 2010)
PDF file is available for download.
16 August 2010
Operations
Hole U1362A Drilling and Conditioning
Further wiper trips were
abandoned in favor of deepening the hole by ~30 m to provide a deeper ÒratÓ
hole for the L-CORK deployment. The rotary core barrel (RCB) assembly was
switched to a 9-7/8 inch tri-cone drilling assembly. The tri-cone bit is
equipped with bigger cutters and bearings better suited to handling rough
drilling conditions and is also capable of handling the higher flow rates
necessary for effective hole cleaning. At 0700 hr on 9 August, the pipe round
trip began and at 1935 hr that same evening Hole U1362A was reentered for the
ninth time. The bit was run to a depth of 476 m below seafloor (mbsf) without
rotation or circulation. The hole was washed and reamed through 20 m of soft
fill to total depth and a 50-barrel high-viscosity mud sweep was circulated.
Another 17 hr were required to deepen the hole by 32 m to a final total depth of
528 mbsf. Two 75-barrel high-viscosity mud sweeps were pumped and at 1800 hr on
10 August a series of three wiper trips were initiated to clean up and
condition the hole. This required 11 hr to complete including the requisite mud
sweeps. After the third wiper trip the pipe was lowered without rotation or
circulation to 515 mbsf. After some resistance at that depth, the pipe broke
through the plug easily and the hole was clean to total depth. At 0500 hr on 11
August the pipe was tripped back to the casing shoe and 3-1/2 hr were spent on
stand-by, waiting for the hole to equilibrate and to allow any remaining
cuttings to fall to the bottom. During that time, general rig maintenance was
conducted as well as a pressure test of the rig circulation system in preparation
for the packer flow test. At 0930 hr on 11 August the drill string was lowered
into the hole without rotation or circulation, reaching a depth of 512 mbsf. A
75-barrel high-viscosity mud sweep was circulated and the drill string was
recovered back to the surface.
Hole U1362A Wireline Logging and Packer Flow Testing
The wireline logging/packer
bottom-hole assembly (BHA) was assembled, the drill string was tripped to the
seafloor once again, and at 0211 hr on 12 August Hole U1362A was reentered for
the tenth time. The pipe was spaced out to a depth of 264 mbsf (still inside
10-3/4 inch casing) and preparations began for wireline logging. At 0545 hr on
12 August a single suite of logging tools was run in the hole (see Science
Results for tool details). The logging string reached a depth of 507 mbsf
without any resistance and this was considered deep enough for logging
purposes. Two full passes were made from 508 mbsf to the casing shoe at 308
mbsf. A third partial pass was made from 508 to 373 mbsf across the area of
interest for the lower packer setting. Wireline logging was completed and the
tools were rigged down by 1615 hr on 12 August.
The drill string was then
lowered to 519 mbsf without rotation or circulation for another depth check.
The end of the pipe was raised to 436 mbsf, positioning the TAM packer assembly
at the desired depth of 424.5 mbsf. After some difficulty in setting the packer
in open hole, which was attributed to the >2 m of vessel heave, the first
flow test was completed by 0430 hr on 13 August. The drill string was raised up
into the 10-3/4 inch casing for the second and final flow test. This test was
cancelled when after repeated attempts the packer failed to lock in pressure.
The packer would set and pressure up but the pressure could not be locked in.
At 1000 hr on 13 August the drill string was tripped to the surface and the end
of the pipe cleared the rotary table at 1800 hr. Upon recovery, inspection of
the packer showed evidence of damage and water was seen leaking from a bad
gouge near the lower end, making it apparent why the packer failed to hold
pressure.
Hole U1362A L-CORK Head Assembly and Deployment
Assembly of the L-CORK began
at 1845 hr on 13 August. The CORK running tool was made-up to a 2 m drill
collar joint and laid out on the rig floor for later use. The bull nose was
then made up with three perforated and coated 8-1/4 inch drill collars. A
single joint of perforated and coated 5-1/2 inch casing along with the required
crossover subs was then made up and lowered into the moonpool area. A
microbiology miniscreen was installed on the lower end of the 5-1/2 inch casing
joint and its umbilical was attached. A chemistry miniscreen was attached in
the upper third of the 5-1/2 inch casing joint along with its umbilical. At
2130 hr the first inflatable packer was installed, followed by a landing collar
and the first swellable packer assembly. A pressure miniscreen was installed on
the 4-1/2 inch casing mandrel below the inflatable packer along with the
umbilical connection. It was at this point that concerns were raised about the
swellable packer diameter because the swellable element was >9-3/4 inches in
places. This packer was designed with four separate packer halves that had
molded channels on the inside to accommodate the umbilical lines. The halves
can be bolted together over the umbilicals and the design is such that the
packer will swell into and heal any remaining gaps over time. This process is
supposed to take on the order of several weeks to complete once the element is
submerged in sea water. Because there were concerns over getting a 9-3/4 inch
plus diameter into the open hole it was decided that the packer elements should
be machined down to 8-1/2 inches. While time consuming (~8 hr for each pair of
packer halves) this was considered the more prudent approach. The first pair of
swellable packer elements was ready for installation at 1100 hr on 14 August,
allowing work to proceed in the moonpool with umbilical connections and
miniscreen installations. Installation of the second swellable packer pair
began at 1830 hr that evening. By 2200 hr, eight additional joints of 4-1/2
inch casing were run and then the second set of inflatable and swellable
packers were installed. This also included additional chemistry and pressure
miniscreens. Another 22 joints of 4-1/2 inch casing were run by 0845 hr on 15
August. At that point, the L-CORK head was picked up, the CORK running tool was
made-up to the L-CORK head, and the head was made up to the top 4-1/2 inch
casing joint, all within 30 min. The final umbilical terminations were made
including all strapping and securing. Only a few casing centralizers were
installed on the CORK stinger to minimize the potential for getting stuck in
the open hole during deployment. A single 5-1/2 inch centralizer was used to
protect the lowermost chemistry miniscreen. A 4-1/2 inch centralizer was used
next to the lowermost pressure screen, above the first swellable packer, and
below the second inflatable packer. This was followed by a pair of 4-1/2 inch
centralizers installed on all 4-1/2 inch casing joints that would remain inside
the 10-3/4 inch casing. The packer inflation hose was installed between the
running tool and the L-CORK head, the valves were opened, and after picking up
a single stand of drill collars, the L-CORK was lowered into the water. The
L-CORK was then pulled back up to close the valves and secure the valve handles
with rubber bands. One final operation was to test fit the VIT/subsea TV frame
over the L-CORK head. The pipe trip to the seafloor with the L-CORK assembly
was initiated at 1300 hr on 15 August.
Hole U1362A L-CORK Instrument String Assembly and Deployment
At 1630 hr on 15
August the drill string was positioned just above the seafloor and preparations
began for deployment of the instrument string. A 250 lb sinker bar was
assembled with six discrete osmotic sampler sections. With the osmosamplers
suspended in the pipe the deployment of the Spectra rope and temperature
loggers began. The deployment proceeded faster than in the past because the
string had lifting eyes pre-spliced into the Spectra rope at 25 m increments.
It is estimated that this new technique saved hours of rig time in the
deployment of the 464 m instrument string. The instrument string was slowly lowered
to the bottom at 1815 hr and by 1945 hr the string had landed and latch-in had
been verified with 400 lbs of overpull. Within minutes the weakened shear pin
was sheared off and the wireline was recovered. By 2230 hr the drill string was
spaced out for reentry and the VIT/subsea TV arrived at the end of the
pipe. The attempted reentry was
suspended at this point when it became apparent that the instrument string was
protruding beyond the end of the CORK bull nose by a significant amount. The
wireline sinker bar and first osmosampler section were visible beyond the CORK
stinger. It was not considered advisable to attempt reentry and deployment in
the open hole as this would most likely result in damage to the instrument
string and possibly loss of the hole. The remainder of the evening was spent
discussing options and developing a mitigation plan.
Science Results
Core description, shipboard
sampling, and laboratory measurements continued
throughout the week. A science meeting was held to discuss preliminary
data from Site U1362, followed by a sampling party for postcruise analyses.
All Hole U1362A cores have
now been described for igneous petrology. Vein logging is complete for Sections
2R-1 to 7R-1. After reviewing all cores, it was decided that adjacent units
with similar flow morphology would be combined into a single unit with subunits
used to identify minor differences. Eight units are now used to define the
stratigraphy in Hole U1362A. Units 1, 3, and 5 have been classified as pillow
lavas based on their igneous texture and abundant chilled margins that are
often curved. Units 2 and 7 have been designated as thin flows or sheet flows.
Units 4, 6 and 8 are classified as sheet flows that are meters thick with
occasional chilled margins. Overall pillow lavas represent approximately half
of the cored interval. Breccias are limited in this hole and are predominantly
only present on a millimeter to centimeter scale along chilled margins. One
example of a 50 mm hydrothermal breccia vein is present in Core 9R. The basalt
throughout Hole U1362A is sparsely to moderately phyric with a range of
secondary minerals including saponite, carbonate, Fe-oxides, celadonite and
sulphides. Hydrothermal veins vary from microns to several millimeters in width
and display a wide variety of compositions and orientations. Shipboard XRD
results record the presence of clay, zeolites, and carbonate in veins. ICP-AES
results are being analyzed. Thin section descriptions of each unit and
alteration style are ongoing. Structural measurements are complete for Sections
2R-1 to 18R-5.
Whole round physical properties analyses have been
completed for all remaining cores from Hole U1362A. Gamma ray attenuation
density data continue to produce consistent peak bulk density values of ~2.5 g/cm3,
with slightly higher values in massive, high recovery sections. Magnetic
susceptibility values are similar to previous results (1000 x 105 SI
to 3000 x 105 SI).
Total counts from the natural gamma ray logger were low (between 1 and 5
counts per second) for all cores. No further thermal conductivity measurements
were taken, giving a total of three measurements in Hole U1362A, all in the
upper sections.
P-wave
velocity measurements of saturated samples have been completed with a
verification step of using an acrylic standard every four measurements.
Furthermore, since the estimated P-wave
velocities are not stable, we measured the velocities four times for each axis
of the cubic-shaped samples and obtained average values. Because P-wave velocities were still not satisfactory to us, we
measured velocities of dry samples. P-wave
velocities in saturated samples range from 4.7 to 6.3 km/s. In the next step,
we are going to saturate all samples again, calculate P-wave velocities by manual picking and check the reliability of the estimated velocities. Bulk density and porosity analyses have been completed as well. Bulk densities range from 2.57 to 2.89 g/cm3.
The microbiology group assembled two colonization
experiments for the Hole U1362A CORK instrument string and assisted with the
deployment of the microbiology umbilical.
Remanent magnetization measurements were completed for Hole U1362A and
the data are being analyzed.
Hole U1362A was logged with a single wireline toolstring composed of a cablehead
with a pseudo-SP (spontaneous potential) sensor, the HNGS gamma ray sonde, the
HLDS density sonde, the LDEO MTT temperature tool, the GPIT orientation tool,
and the UBI acoustic imaging tool. Both the HLDS mechanical caliper and UBI
ultrasonic caliper provided the operations and science groups with the data
needed to accurately place packers in the borehole, which was the primary
objective of the logging program. Three passes of the toolstring indicated that
acceptable packer seats exist at 419 and 450 mbsf.
Formation pressure data were recovered successfully from the packer
flow test conducted at 424.5 mbsf.
Engineers, CORK
specialists, and Transocean staff met to discuss safe working practices on the
moonpool in preparation for the CORK deployment. Three umbilical reels were
loaded onto stands and moved to the moon pool. Banana sheaves used to support
the umbilicals were hung in the moonpool. The chemistry, microbiology, and
pressure screens were prepared for deployment on the CORK. During the CORK
deployment, staff assisted with securing the umbilicals to the casing,
attaching screens, and the making the necessary umbilical terminations. Pressure testing and troubleshooting of the electronic RS (ERS) tool continued according to Stress Engineering's directions.
Outreach
Videoconferences were
conducted with a science camp at the University of Southern California and
students in Nouméa (New Caledonia). Other activities included a microbe
culturing activity, a talk on seafloor and ocean crust bacteria, and deployment
of the ROVs at night to test their lights. Individual projects are continuing
on curriculum materials and experiments to be used in schools, art, and
computer animation.
Technical Support and HSE Activities
HSE activities
Weekly fire and boat drills were held on Monday and Sunday.
Laboratory activities
Processing of hard rock cores
continues. Staff continues to provide support for various science, education
and engineering projects. Laboratory projects in progress include the
following: section half multisensor logger software upgrade completed and data
validation testing in progress, whole core multisensor logger software upgrade
in user testing, moisture and density/pycnometer software upgrade, and
laboratory documentation updates. Minor updates were released for several LIMS
applications.
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