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doi:10.2204/iodp.pr.336.2012

Operations

Port call and transit to North Pond

Prior to Expedition 336, the JOIDES Resolution was berthed in Curaçao. Although Expedition 336 officially did not begin until 15 September 2011 in Barbados, all of the subseafloor borehole observatory (CORK) hardware and experiments were sent to Curaçao in advance of the expedition. In addition, a few scientists and engineers boarded the ship in Curaçao and used the 2-day transit to Barbados to start preparing the CORK observatories and a new in situ tool for detecting microbial life in ocean floor boreholes—the Deep Exploration Biosphere Investigative tool (DEBI-t).

Expedition 336 officially began with the first line ashore in Bridgetown, Barbados, at 0948 h on 15 September. Other than personnel transfers, only minor port call activities were planned; these began immediately after the early arrival of the ship. On Day 2 of the port call, the remaining scientists, engineers, technical staff, and crew boarded the ship in Barbados on 16 September. The vessel was then secured for sea and departed Bridgetown, Barbados, at 0742 h on 17 September. The pilot departed the vessel at 0812 h, and the vessel started the 986 nmi transit to Hole 395A. Times are presented in ship local time, which is Universal Time Coordinated (UTC) – 3 h for all drilling operations during this expedition. We arrived over Hole 395A at 2330 h on 20 September, having averaged 11.4 nmi/h. At 0012 h on 21 September, the vessel was placed in dynamic positioning mode over Hole 395A and operations began. All operational tasks, along with task start and end times, are listed in Table T1.

Hole 395A

Operations for Hole 395A began by picking up the CORK pulling tool for the Hole 395A CORK and making it up to a pony drill collar. The rest of the bottom-hole assembly (BHA) was attached and the drill string was tripped to just above the seabed. At 2166 meters below rig floor (mbrf), tripping operations were temporarily halted to install the vibration-isolated television (VIT) camera system to begin running the subsea camera. It quickly became apparent that there was a problem with the sonar system on the camera system, and it had to be retrieved for repair. Tripping continued to 2824 mbrf, where operations were again suspended to install the camera system. Tripping operations resumed as the camera system was carefully lowered toward the seafloor. Periodically, the camera system winch was stopped and the hoisting function was engaged. At ~3700 mbrf, it became clear that the winch did not have sufficient power to retrieve the camera system. Drill pipe tripping operations continued while mechanics and engineers diagnosed the winch problem. When tripping operations were complete, the top drive was installed. However, from 1630 h on 21 September until 1630 h on 22 September, diagnostics and repair were performed on the camera system winch. After both the hydraulic motor and the hydraulic pump were changed, the winch was restored to working condition. The camera system was deployed and lowered carefully to the seafloor. The Hole 395A reentry cone and CORK were located, and the pulling tool was lowered over the CORK and latched on. The CORK was then picked up ~7 m, and the core line was deployed to retrieve the data logger, which was attached to a 600 m long thermistor string. After running an overshot three times and attempting to jar onto the top of the data logger, attempts to pull the thermistor string were suspended and the CORK was pulled to the surface along with the data logger/thermistor string. After the CORK was landed and secured in the moonpool, the recess where the top of the data logger was located was cleaned and the overshot was installed. The data logger was then jarred loose and all 600 m of the thermistor string, including 10 thermistors and the sinker bar, was removed at the rig floor. The thermistors were cut out of the string, and portions of the string were sampled for microbiological analysis. A lifting sub was installed on top of the CORK, and it was pulled through the rig floor and then moved to the starboard aft main deck for sampling. Next, the stinger, made up of three joints of 5.5 inch drill pipe, was broken down and laid out for additional microbiological sampling. After the rig floor was cleared of CORK pulling tools, the logging bit and BHA were made up and the drill string was tripped back to seafloor. There was a break in tripping operations after running Stand 70 to deploy the camera system, which was lowered to the bottom, following the bit. Hole 395A was reentered after 19 min of maneuvering. After rigging up to log with the DEBI-t microbiology string (DEBI-t, natural spectral gamma ray, and temperature), the tool string was run into the hole to log Hole 395A. After a 45 min interval to repair the logging winch, the tools were run down into the hole. The logging tool was unable to pass a section of the hole at 4670 mbrf (~186 mbsf), and after repeated attempts the logging string was pulled back to the surface and rigged down. On the basis of previous logs, we inferred that the tool string could not pass this section because it was hanging up on a ledge. After the logging bit was lowered ~21 m below the ledge, we were able to make two runs with the microbiology logging string all the way to the depth objective of 600 mbsf. The logging string was not lowered farther to keep it from landing on the bottom of the hole and causing potential damage to the tools.

After logging was concluded, the drill bit was also lowered to 600 mbsf to check for obstructions and make sure the hole was ready for the new CORK to be installed. When no obstructions were encountered, the string was pulled out of the hole and tripped back to the surface. After the drill line was slipped and cut, assembly of the new Hole 395A lateral CORK (L-CORK) commenced. Around midnight on 26 September, all casing, packers, umbilicals, and the CORK were assembled from the bottom to the top. Although the perforated casing was coated with epoxy to minimize the amount of exposed steel, the coated steel casing was washed with 10% ethanol and painted with an underwater curable epoxy paint. The deepest umbilical screens were deployed at the transition between the drill collars and 5.5 inch perforated casing. Umbilicals were secured with stabilizers (two per joint, with additional stabilizers near packers and screens) and sturdy plastic zip ties. Duct tape was used near packers to secure fittings. The CORK included a combination of steel and fiberglass casing.

The CORK was then lowered ~10 mbrf to purge the pressure lines of air. The CORK was then raised to the moonpool and all of the purge valves were closed. All but one of the valves in the microbiology and geochemistry bays were closed. The open valve was attached to a fast-flow OsmoSampler with both standard and microbiology OsmoSamplers.

Next, we lowered the CORK ~100 mbrf to ensure the camera system sleeve would pass freely over the CORK head. The OsmoSampler instrument string was then assembled and lowered inside the CORK. An attempt to land and latch the top plug was made, but the top plug could not be latched. The CORK was pulled back and landed in the moonpool, and an attempt was made to latch the top plug at the rig floor level. After numerous attempts with two different top plugs, it was finally decided to run the top plug without the latch being engaged; however, the top plug will still work as a gravity seal given the underpressured hydrologic system. When the CORK was pulled to the surface to check the top plug, it was apparent that the lateral valve and flow meter interface had broken off the lateral port on the CORK body. The port was then sealed with a 4 inch cap. It is unclear how the breakage occurred, and this type of valve was deployed successfully on two CORKs during IODP Expedition 327, on the CORK at ODP Site 1200, and on four cement deep-sea delivery vehicles.

Finally, we started lowering the CORK to the seafloor. The camera system was installed during the deployment and lowered to the bottom following the CORK. When the casing string stinger was just above the seabed, the drill string was spaced out for reentry and Hole 395A was reentered at 2003 h. The casing was carefully lowered into Hole 395A while observing the weight and carefully watching the string at known critical depths in the borehole (based on previous logging data). We then installed the top drive, and the drill string was spaced out to land the CORK. The CORK was apparently landed and over the next 2 h the packers were inflated to 1400 psi according to the inflation procedure and appeared to be holding pressure; however, there was no slight decrease in pressure, typical of the packers inflating. Simultaneously, the camera system was pulled to the surface, and we began putting together the remotely operated vehicle (ROV) platform. At 0800 h the ROV platform had reached the CORK head and released. The release was not smooth, with one side of the platform releasing before the other side. Eventually, the platform completely released and appeared to settle into position. An initial attempt was made to release the running tool from the CORK. After ~45 min of attempting to release the running tool, the camera was retrieved to remove the ROV platform release mechanism and slings in order to allow the camera to get a closer view of the CORK running tool. While the camera was being pulled to the surface, the driller lost the 10,000 lb of overpull that was being maintained on the CORK. At the time, we assumed that the running tool had released. However, when the camera system was lowered back to the seafloor to make a visual check of the CORK installation, we observed that the CORK head was no longer inside the reentry cone but was still attached to the running tool, offset from the reentry cone, and had broken off from the CORK casing below. We retrieved the camera system and drill string. Once the CORK head was back at the moonpool, we began to survey the damage. The CORK head was then raised up to the rig floor, the running tool was removed, and the CORK head was laid down.

The CORK head experienced forces that bent the body through the lower part of the instrument bays. Also, the welded connection between the cup packer subassembly and the L-CORK mandrel had failed ~4 m below the top of the reentry cone. This part of the assembly was a slip fitting that was not welded completely, and little of the connection was welded. When the 5 inch pipe was severed, the Spectra rope and umbilicals were also cut, leaving the downhole tool string in place. On the basis of recovered pieces of casing and the upper end of the remaining 5 inch diameter cup packer subassembly, the 5 inch pipe mandrel near the seafloor is not completely rounded but might not be closed enough to restrict the recovery of the downhole samplers, sensors, and experiments. Several stainless steel tubes likely extend above the cup packers and the top of the 5 inch casing. These tubes may impede recovery of the downhole instrument string.

After the 10.75 inch casing in Hole U1382A was released, a camera survey was made of the Hole 395A reentry system to provide initial data for formulating a plan to recover the downhole instrument string in 4 y with an ROV. The ROV platform was slightly offset from the center of the reentry cone, which made it nearly impossible to see down into the casing where the remainder of the CORK must be located. One of the three sonar reflectors appears to be missing, and some views of the ROV platform, which rests on the cone and is not latched, are suggestive of possible damage to the platform.

The CORK pressure logging system was recovered along with the broken-off wellhead. The recorded data do not definitively resolve whether or not the downhole CORK packers actually inflated. The seafloor gauge and three formation gauges show very similar slight increases in pressures after the time of attempted inflation, but the similarity to the seafloor gauge could be consistent with a tidal influence without inflation of the downhole packers. However, there may be no evidence that the packers did not inflate based on analysis of the overall volume of the system, inflated packers, packer setting line, drill string, and standpipe in relation to the pressure change observed. The inflated packer volume represents only ~0.1% of the total system volume. Thus, if the overall system is truly closed (i.e., there are no leaks), then no additional pumping would be required to inflate the packers after shutting in the inflation pressure. Also, the pressure change observed during the packer inflation process indicates, assuming a closed system, a volume change equal to ~25 times that of the total volume of the inflated packers. Some of this volume change is most likely leakage in the system. Thus, based on onboard data and initial analyses, we cannot say whether or not the packers are inflated; however, we have no reason to believe that they are not inflated.

Our next objective was to install a CORK in Hole U1382A (50 m west of Hole 395A) to monitor the uppermost basaltic crust. However, this plan was put on hold when we had to leave the area because of Tropical Storm Philippe. After the ship was secured for transit at 0215 h (29 September), we departed Hole 395A and headed to the northeast to avoid the approaching storm.

Engineering summary

The first North Pond objective, pulling the old CORK and thermistor string in Hole 395A, was successfully completed.

The new Hole 395A L-CORK, a design modified to fit DSDP reentry hardware, failed during the final stages of installation in the borehole. Preliminary analysis suggests that the bottom ~0.6 m of the L-CORK became hung up, indicated by damage to the leading edge of the lowermost stabilizer fins. This exposed the L-CORK—designed to be much longer and narrower than usual to fit the DSDP-style cone while still accommodating broader science objectives (i.e., extended height for the bays in which the scientific experiments are placed)—to much higher bending loads than anticipated. It is believed the system cracked at a weld just above the landing seat, which led to even higher loads and bending of the wellhead itself and then eventual failure at the weld. A final report will be prepared once the L-CORK, video evidence, and instrumentation data are further reviewed. However, examination of the recovered old Hole 395A CORK revealed damage to its stabilizer fins in the same area as the new Hole 395A L-CORK that failed. We also observed a noticeable lack of corrosion to its landing ring. Combine this with the inability of the old CORK to be latched-in during Leg 174B and one might assume it also landed high. The old CORK was shorter and more robust, especially in the area just above the landing ring, so it was exposed to much lower stress. As for why the CORKs landed high, we have very little information. One theory is that the interior diameter of the reentry cone’s 24 inch transition pipe, through which the stabilizer fins must pass, is narrower than indicated on DSDP engineering diagrams. A final engineering report of this failure will be produced either during or shortly after the expedition, so these initial findings may be revised.

Site U1382

The primary objective for Hole U1382A was to install a CORK to perform long-term coupled microbiological, biogeochemical, and hydrological experiments in uppermost basaltic crust. We installed a reentry cone with 53 m of 16 inch casing, installed 102 m of 10.75 inch casing and cemented it a few meters into the basaltic basement, cored 100 m of basalt below the casing, conducted downhole logging and hydrologic (packer) experiments, and installed a CORK that extends to 188.7 mbsf.

After operations in Hole 395A, we intended to go directly to Hole U1382A (50 m west of Hole 395A). However, we had to leave the area because of Tropical Storm Philippe. After the ship was secured for transit at 0215 h on 29 September, we headed to the northeast to avoid the approaching storm. After Tropical Storm Philippe crossed over the North Pond drilling area, we returned to Hole U1382A at 1224 h on 1 October.

We assembled a reentry cone and 52.98 m of 16 inch casing and lowered it to the seafloor. The trip was temporarily suspended to install the camera system, which was lowered as the pipe trip continued to just above the seafloor. When the casing shoe was just above the seafloor, the top drive was picked up and the drill string was spaced out to start Hole U1382A. We started jetting in the reentry system at 0745 h on 2 October. After 2.75 h the reentry cone mud skirt was landed on the seafloor, verified with the camera system, and the casing running tool was released from the casing. The camera system was then pulled to the surface as the drill string and running tool were pulled back to the rig floor. The BHA was set back, and the running tool was de-torqued at the rig floor. The BHA for drilling the 14.75 inch hole was assembled, and the drill string was tripped to just above the reentry system. During the pipe trip the camera system was installed and lowered as the drill string was tripped to bottom. After the drill string was spaced out for reentry, the bit reentered Hole U1382A at 0348 h on 3 October. The top drive was then picked up, and the drill string was run to the casing shoe and spaced out for drilling. The sediment section was drilled without coring from 4547 to 4584 mbrf (53–90 mbsf), at which point basement was contacted. Drilling parameters indicated a fairly hard formation from 90 to 93 mbsf, but drilling proceeded fairly quickly from 93 to 99 mbsf. From 99 to 110 mbsf, drilling parameters again were slow and consistent, indicating a hard formation. We decided to terminate the hole at 110 mbsf to allow 8 m of rathole below 10.75 inch casing that would extend to 102 mbsf. After the hole was conditioned, the bit was tripped above the casing shoe, the top drive was removed, and the drill string was tripped back to the rig floor. Before we could begin rigging up for running casing, we had to slip and cut 115 ft of drill line. We assembled 101.86 m of 10.75 inch casing that included a 14.75 inch outside diameter swellable packer one joint from the top and a casing hanger with a seal ring. We attached the casing running tool, lowered the entire casing string to the seafloor, and reentered Hole U1382A at 1355 h on 4 October. The casing was lowered smoothly into the hole until the last couple of meters, when we had to circulate to help clear the way so it could fully land. After the casing string was fully landed and latched, we cemented it in place with 20 bbl of cement blended with lost-circulation material (Cello-Flake). The cement displacement calculation was made to leave ~15 m of cement inside the casing above the casing shoe. Once we released the casing running tool from the casing hanger (1712 h on 4 October), we pumped seawater through the drill string to clean it of any remaining cement. Before we retrieved the casing running tool, we performed a 30 min survey of the Hole 395A reentry system (50 m to the west). The casing running tool arrived back on the rig floor at 0200 h on 5 October.

Our next step was rotary core barrel (RCB) coring, so we assembled a new C-7 RCB bit (with center bit) with a three-stand BHA and lowered it to the seafloor. A break in tripping pipe occurred around 1030 h to install the camera system, but the system was quickly retrieved when the subsea camera did not work. The pipe trip continued for another hour and was halted again to install the repaired camera system. At 1330 h the drill string was spaced out for reentry, and Hole U1382A was quickly reentered at 1337 h. The bit was carefully run into the hole, and cement was encountered 14 m above the casing shoe (1 m below the expected 15 m). The top drive was then picked up, and the cement was drilled from 88 mbsf to just below the casing shoe that had been positioned at 102 mbsf. We circulated mud to clean the hole, recovered the center bit by wireline, dropped an RCB core barrel, and RCB coring began. The first core on deck, Core 336-U1382A-2R, arrived at 2245 h on 5 October. Coring continued through Core 336-U1382A-12R, which was on board at 2320 h on 7 October. We cored 100 m of section from 110 to 210 mbsf and recovered 31.8 m (32%). After coring was completed, five wiper trips were made from total depth to the casing shoe and back to total depth. The first three trips revealed tight spots and circulation problems. The fourth and fifth trips were made with no evidence of drag or circulation problems, and no fill was found at the bottom of the hole. After hole cleaning and conditioning were completed, the drill string was tripped from the hole, clearing the seafloor at 0729 h on 8 October.

After the bit was back on the rig floor and before logging began, we assembled a stand of 6.75 inch perforated and coated drill collars for the lowermost portion of the CORK installation. We wanted to make up the drill collars before assembling the CORK to make it easier and more efficient to paint with epoxy prior to being deployed. Next, we assembled a logging BHA with a logging bit and the drill string packer, lowered it 64 m into Hole U1382A, and began deploying the logging tools. Logging proceeded with a modified triple combination tool string, with the DEBI-t on the bottom of the string. Log data were collected while the string was lowered to the bottom of the hole. However, while logging upward, the power failed ~20 m below the casing. The tool string was pulled to the surface, and the problem was found to be in the cable head. The cable head was re-terminated, and we decided to run the Formation MicroScanner (FMS)-sonic tool string next. After two successful passes, the lower portion of the FMS (calipers) would not enter the logging bit. After 2 h of working the string up and down, opening and closing the calipers, and pumping seawater, the entire tool string was able to pass through the logging bit; when it was recovered, one of the caliper arms had been damaged. We then spaced out the drill string for the hydrologic (packer) flow test and began attempting to inflate the packer. We made four attempts to set the packer inside the 10.75 inch casing; however, each time, high vessel heave (3 m) caused the packer to deflate, so the experiment was terminated. Before pulling out of the hole and installing the CORK, we lowered the entire BHA (including the deflated packer) until the logging bit reached the bottom of the hole to check that the hole was still open to full depth. We did not encounter any problem intervals and found only ~1.5 m of fill. The drill string was recovered, and the bit was back on board at 1328 h on 10 October. Before we could begin our next operation, we had to slip and cut 115 ft of drill line. We started assembling the CORK at 1500 h on 10 October.

The preassembled 6.75 inch coated, painted, and perforated drill collar stand was picked up and run through the rotary table. Epoxy paint was used to touch up rust marks, and 10% ethanol was used to wipe grease from all exposed steel between the bottom of the casing and the top of the combination packer. After a crossover was installed, we attached 15.35 m of 5.5 inch coated and perforated casing. Miniscreens were attached to the outside of the lowermost perforated 5.5 inch casing joint. The lowermost four miniscreens included one titanium microbiology screen (connected to a Tefzel umbilical) and three stainless steel miniscreens for chemistry (two connected to 0.125 inch stainless umbilicals and one attached to a 0.25 inch umbilical). The next set of four miniscreens, including a second titanium microbiology screen (connected to a Tefzel umbilical) and three stainless steel miniscreens for chemistry (one connected to a 0.125 inch stainless umbilical and two attached to 0.25 inch umbilicals) was placed just above the first set of miniscreens. The stainless steel miniscreen for pressure (connected to a 0.25 inch stainless umbilical) was strapped to the casing immediately above the second set of miniscreens. Crossovers to the 4.5 inch fiberglass casing were installed, and then 44.25 m of 4.5 inch fiberglass casing was made up. Umbilicals from the miniscreens and plastic Kwik-zip centralizers were installed on the outside of the casing as it was run. Next to be installed was a crossover from the fiberglass casing to the landing seat for the instrument string, followed by the joint with the swellable and inflatable packers. Umbilicals were terminated and connected to the bottom and top of the combination packer. Above the packers, ~91.01 m of uncoated and unperforated 4.5 inch steel casing was run, followed by the CORK head. All pressure and sampling lines were connected to the bottom of the CORK. It took us 10 h to complete assembly, and the bottom of the CORK string extends to 188.7 mbsf.

Our next step was to assemble and install the OsmoSampler string into the CORK at the rig floor. Modifications were made before and during installation (thicker springs were installed, and parts were ground off of the latching mechanisms so they would stick out further) so that it would latch into the CORK head; however, these modifications did not work. The CORK head was submerged for 10 min to clear the pressure line of air, and then the CORK head was raised through the moonpool. A fast-flow OsmoSampler system was attached, and all of the unused valves were closed. The used valves include one pressure valve and a 0.125 inch chemistry line attached to the fast-flow OsmoSampler. The CORK was then lowered to ~100 m. The camera system was then test fit over the CORK, and at 0630 h on 11 October, we began lowering the CORK package to the seafloor. The camera system was installed, and Hole U1382A was reentered for the last time at 1630 h on 11 October.

After carefully lowering the CORK into the hole, we landed the CORK at 1820 h on 11 October. The packer was inflated (to 1400 psi, which then bled off to ~1280–1300 psi), and the camera was pulled to the surface. Next, the ROV platform was assembled and rigged up with the ROV deployment tool attached below the camera system and then lowered back to the seafloor. The platform was released over the CORK at 0055 h on 12 October. The camera system was retrieved and after the ROV deployment system was removed, the camera was lowered back to the bottom to observe the final step of installing the Hole U1382A CORK—releasing the running tool from the CORK. This was successfully released at 0425 h on 12 October. The drill string with the CORK running tool was recovered back on board at 1145 h, ending Hole U1382A.

Site U1383

Our objective at Site U1383 was to install a multilevel CORK observatory to perform long-term coupled microbiological, biogeochemical, and hydrological experiments in deeper portions of the oceanic crust. Our first step was to use an 18.5 inch tricone drill bit to perform a jet-in test to determine the length of 20 inch casing to install with the reentry cone. While we assembled the BHA and lowered to the seafloor, we retrieved the seafloor beacon used for Hole 395A and transited ~5.8 km to Site U1383 in dynamic positioning mode. After arriving at Site U1383, we dropped a positioning beacon at 1812 h on 12 October. The jet-in test in Hole U1383A began at 2240 h on 12 October and reached 36 mbsf at 0200 h on 13 October. The penetration rate during the last 2 m was very slow. The 18.5 inch bit was back on board at 0930 h, ending Hole U1383A.

On the basis of the jet-in test, we deployed 34.84 m of 20 inch casing for Hole U1383B. The casing and reentry cone were run to the bottom, but our initial attempt jetted in the casing to only 29 mbsf. After trying to advance the casing for over 3 h with no progress, we pulled the string out of the seafloor and moved 50 m to the northeast. Our second attempt to start Hole U1383B began at 0810 h on 14 October. This time, we were able to fully land the reentry system and casing at 1015 h. We released the running tool at 1035 h and retrieved the drill string, with the bit arriving on the rig floor at 1915 h.

Our next job was to drill an 18.5 inch hole into uppermost basement for the 16 inch casing. After both drill collar pup joints and the casing running tool were laid out, the 18.5 inch bit was removed, the nozzles were changed, and the BHA was made up and run back to the bottom. During the trip into the hole we had to pause to slip and cut 115 ft of drill line and to start lowering the camera system for reentry. We reentered Hole U1383B at 0518 h on 15 October, began drilling at 0704 h, and encountered basement at 0723 h at 53 mbsf. Drilling continued to 68 mbsf at a penetration rate of ~2 m/h. We drilled to this depth to allow ~9 m of rathole for the 16 inch casing. Once 68 mbsf was reached, the hole was reamed and conditioned and the bit was retrieved.

After the bit was back on the rig floor at 0450 h on 16 October, the casing running tool was picked up and made up to the BHA and set back in the derrick. A total of 58.82 m of 16 inch casing, including the casing hanger, was assembled. The running tool was made up to the casing, and the casing was then run to the bottom, pausing only to deploy the camera system. Hole U1383B was reentered at 1524 h after ~20 min of maneuvering. The casing was then lowered into the open hole until the casing shoe contacted the sediment/basement interface. The casing shoe would not pass the interface after 1 h of attempts, even with rotation. The ship was offset, and repeated attempts were made until the shoe passed the basement contact. Unfortunately, the casing was unable to advance enough to successfully land the casing hanger in the reentry cone. The final position of the casing shoe was ~3 m short of landing. The 16 inch casing was retrieved at 1945 h on 16 October, arriving back on the rig floor at 0315 h on 17 October. The top two joints of casing were removed, and the length of the casing shoe joint was shortened by 5 m. A new casing shoe was welded onto the shoe joint, and at 0800 h the casing was lowered back into the hole. The running tool was reattached, and the casing was once again run back to the bottom. The camera system was installed 70 stands into the trip to the bottom. At 1537 h Hole U1383B was reentered with the 16 inch casing for the second time. The casing was successfully landed at 1630 h and cemented into place with 20 bbl of cement with lost-circulation material (Cello-Flake). The casing running tool was released at 1745 h, and the drill string was circulated out to remove any excess cement from the string. At 1845 h on 17 October the drill string was pulled back to the surface, stopping only so that the camera system could be removed. The running tool cleared the rotary table at 0130 h on 18 October and then was de-torqued and laid out.

The next stage of operations was to drill ~100 m of basement to install 10.75 inch casing. A new bit was made up to the BHA, and the drill string was tripped to the bottom. At 90 stands into the trip, the camera system was installed and run to the bottom behind the bit. The trip was suspended just above the seafloor to slip and cut 115 ft of drilling line from the drawworks winch. Hole U1383B was reentered at 1210 h on 18 October after 15 min of maneuvering. The bit was tripped to near the bottom, the top drive was picked up, and cement was tagged at 49 mbsf (5 m above the casing shoe). After 45 min of drilling, the bit reached the bottom of the cement at 57 mbsf (3 m below the casing shoe). From 1500 h on 18 October through 0515 h on 19 October, drilling proceeded to 89.8 mbsf. At this depth torque increased, RPM became erratic, and penetration rates dropped to zero. A wiper trip was performed from 89.8 mbsf to the 16 inch casing shoe at 54 mbsf and back to the bottom. Attempts to resume drilling were unsuccessful. At 1000 h, we decided to pull the bit and inspect it at the surface. The top drive was set back, and the drill string was pulled from the hole. The bit cleared the rotary table at 1750 h on 19 October. Inspection of the bit revealed that two of the three rotary cones and both shanks, including bearings and nozzles, had broken off the body of the bit. Only one cone remained on the bit, and it too had all the inserts broken off. After discussions with all of the operations staff on board, we decided that we would have a greater chance of achieving the expedition objectives by starting a new hole rather than trying to salvage Hole U1383B.

At 1830 h construction began on a reentry cone for Hole U1383C. Because of several factors, we decided to start the new reentry system with 16 inch casing jetted in to a depth of 34.58 m at the same location as the original jet-in test in Hole U1383A. Assembly of the Hole U1383C reentry cone was completed at 0630 h on 20 October. The reentry cone was moved to the moonpool and positioned on the moonpool doors, and then 35 m of 16 inch casing was picked up, landed, and latched into the reentry cone. The running tool was then released, and the stand was set back in the derrick. The stand with the 14.75 inch drill bit was then picked up, followed by another 5 m of 8.25 inch drill collar pup joints to space the bit out to the 16 inch casing shoe. The drill collar stand with the casing running tool was picked up and made up to the BHA and lowered and latched into the 16 inch casing hanger. The remainder of the BHA was assembled, and the reentry system and casing were lowered to just above the seafloor, stopping every 30 stands to fill the drill string. The camera system was installed 90 stands in and run to just above the reentry system. Hole U1383C was spudded at 1900 h on 20 October. The reentry system was jetted in ~35 m, and the casing running tool was released at 2130 h. The camera system and drill string were then pulled back to the surface, and the 14.75 inch bit cleared the rotary table at 0545 h on 21 October. After the nozzles on the bit were changed, the drilling BHA was assembled and run back to the bottom. The camera system was installed at Stand 70 and run to the bottom, following the bit to the seafloor. At 1130 h the vessel began maneuvering, and Hole U1383C was reentered at 1444 h. After the top drive was picked up, drilling began at 1635 h on 21 October. Contact was made with basement at 38 mbsf, just 3 m below the 16 inch casing shoe, after only 10 min of drilling. Basement drilling continued with slow penetration rates (0.5–2.5 m/h), reaching a total depth of 69.5 mbsf at 1840 h on 22 October.

We assembled 60.41 m of 10.75 inch casing with a swellable packer just below the casing hanger and lowered it to just above the seafloor, pausing about halfway to deploy the camera system. After ~30 min of maneuvering, we reentered Hole U1383C at 1626 h on 23 October. The casing string was landed at 1720 h, and we confirmed it was latched in with a 20,000 lb overpull. The casing was secured in place by pumping 25 bbl of cement with lost-circulation material (Cello-Flake). The casing running tool was released at 1940 h, the drill string was flushed clear of any remaining cement, and we started pulling out of the hole. With the casing running tool at 2336 mbrf, the trip was halted so we could slip and cut 115 ft of drill line. We also spent 2 h replacing a spool valve and repairing a hydraulic line on the 5 inch pipe racker. We then continued retrieving the casing running tool, which was back on board at 0825 h on 24 October.

We assembled an RCB bit and BHA, verified the core barrel space out, and lowered it to the seafloor. About halfway down, we paused to deploy the camera system. This reentry took us only ~10 min of maneuvering. After we retrieved the camera system, installed the top drive, and spaced out for drilling, we tagged the top of the cement at 43.8 mbsf (~16.6 m above the casing shoe). Once we drilled out the cement and cleaned out the rathole, we recovered the center bit. We dropped an RCB core barrel and started coring at 0000 h on 25 October. We cut Cores 336-U1383C-2R through 18R from 69.5 to 211.6 mbsf. After Core 15R had been cut, we performed a wiper trip back up to the casing shoe and encountered 20 m of fill while getting back to the bottom of the hole. Hole cleaning remained a priority, with mud sweeps being performed on average twice during each cored interval. A total of 142.1 m was cored, and 28.55 m was recovered (20%). Just as Core 18R began to be cut (with 45.8 h on the bit), the vessel began experiencing high heave. This heave made it almost impossible to keep sufficient weight on the bit to keep it on the bottom, so we circulated cuttings out of the hole with a final mud sweep and pulled the bit out of the hole. The RCB bit was back on board at 1720 h on 28 October. It was fortunate that we did not continue coring with this bit because it had experienced bearing failures on all four roller cones.

We conducted routine rig maintenance while we assembled a new C-7 RCB bit and inspected the float valve and support bearing assemblies. This maintenance identified a faulty air cylinder for the locking pin on the motion compensator that had to be repaired, which resulted in 9.25 h of rig downtime. During the repair we assembled the previous BHA and added three more drill collars. We installed a center bit so that the float valve would remain open during the trip, allowing the drill string to fill with seawater. At 0630 on 29 October we started tripping the BHA to the seafloor. The reentry cone was visible as soon as the camera system reached the seafloor, and the bit was almost directly over the cone. We reentered Hole U1383C in several minutes at 1231 h on 29 October. We retrieved the camera system and the center bit and lowered the bit to the bottom of the hole to check for tight spots and to circulate out any fill at the bottom before changing bits.

We assembled a second RCB bit to continue coring in Hole U1383C. After the bit was lowered to the bottom of the hole, it was circulated clean. An RCB core barrel was dropped, and coring resumed with Core 336-U1383C-19R. We decided to core with drilling knobbies because of high vessel motion and operating in deep water. RCB coring continued through Core 336-U1383C-23R, at which point we made a short wiper trip to both clean a short section of hole and to replace three drilling knobbies with a stand of 5.5 inch drill pipe. Once the bit was back on the bottom, we circulated a mud sweep and resumed coring. Two 20 bbl sweeps were pumped on every core to keep the hole clean. We decided to stop RCB coring at 4756.7 mbrf (331.5 mbsf) because of accumulating bit hours, minimal time left in the expedition, and because a sufficient depth was reached to achieve the CORK objectives. Thirty-one cores recovered 50.31 m of rocks from a 262.0 m interval. Overall recovery was 19%, varying from 8% to a maximum of 43%.

We conducted three wiper trips to prepare the hole for downhole logging, packer experiments, and CORK installation. At 1400 h on 1 November, the first wiper trip began, and hole cleaning continued until the following day. Three wiper trips were made from total depth to the 10.75 inch casing shoe and back. Tight spots were recorded at 4692, 4703, 4708, 4716, 4724, 4743, 4751, and 4752 mbrf (266.8, 277.8, 282.8, 290.8, 298.8, 317.8, 325.8, and 326.8 mbsf). These spots were reamed and rechecked during the first wiper trip. At the end of the first wiper trip, 4 m of fill was found on the bottom and cleaned out. We circulated a 70 bbl sweep of high-viscosity mud, and then the hole was displaced with salt water. The subsequent two wiper trips did not detect tight spots or fill on the bottom. At 0545 h on 2 November we started to pull the string out of Hole U1383C, and it cleared the seafloor at 0625 h. The RCB bit was back on the rig floor at 1315 h.

Before we started assembling the logging/packer BHA, we picked up and assembled six 6.75 inch perforated drill collars into a stand. The exterior of the stand was then completely coated with an epoxy paint and set back in the derrick to cure. This stand is the lowermost portion of the CORK completion string.

The logging and drill string packer BHA was then assembled and lowered to the seafloor. After ~3 min of maneuvering, we reentered Hole U1383C at 2342 h on 2 November. The logging bit was then positioned ~5 m from the base of the 10.75 inch casing shoe.

The logging equipment was rigged up to run the adapted microbiology combination II (AMC II) tool string, which included the DEBI-t deep UV-induced fluorescence, density/caliper (Hostile Environment Litho-Density Sonde [HLDS]), and spectral gamma ray (Hostile Environment Natural Gamma Ray Sonde [HNGS]) tools. During assembly the resistivity tool failed and had to be removed from the string. The tool string was run into the hole, and two full passes were conducted, tagging bottom and confirming drill pipe depth and lack of fill in the hole. After this first tool string was back on board, the FMS-sonic tool string was rigged up. This tool string included the spectral natural gamma ray, Dipole Shear Sonic Imager (DSI), and FMS tools. This second string also completed two successful passes; it was pulled out of the hole and rigged down at 2315 h on 3 November. Following logging, we picked up the top drive and prepared for the first of three scheduled packer tests. We were unable to set the packer in the casing, and the test at this level was abandoned. The packer was then moved to 4566 mbrf (140.8 mbsf) in open hole. The packer was inflated, and flow tests were completed as scheduled. The packer was then moved to the final position but was unable to hold pressure. The packer experiment was concluded, the top drive was set back, and the drill string was pulled out of the hole to just above the seafloor.

Before beginning CORK installation in Hole U1383C, we decided to deploy an ROV platform in Hole U1383B to facilitate a future borehole observatory installation by ROV. We moved to Hole U1383B, deployed the camera system, and reentered the hole at 1350 h on 4 November. We retrieved the camera system, assembled a modified ROV platform around the drill pipe, and let it free fall down onto the reentry cone at the seafloor. The platform had been modified to self-center on the reentry cone because there was no CORK wellhead to help it center as designed. The camera was deployed, and the platform was observed to be sitting in the cone—although perhaps just slightly off-center. The bit was pulled out of the hole at 1818 h. After pulling the bit well above the seafloor, we paused operations to slip and cut the drill line. At 2015 h the trip out of the hole resumed, and the logging bit arrived back on the rig floor at 0300 h on 5 November. We observed that the drill string packer element had experienced a blowout. After we had the drill collars stored in the derrick, we began assembling the Hole U1383C CORK.

The observatory assembly started with lowering the preassembled 6.75 inch perforated drill collar stand below the rig floor. We picked up, assembled, and painted with epoxy four additional 15 ft long perforated drill collars, which we added to the top of the first stand to provide additional weight to the bottom of the CORK to hopefully ease the string past a ledge encountered during hole cleaning. We then started assembling the various pieces of the CORK, including (1) external umbilicals terminated at screens, (2) coated and perforated steel and slotted fiberglass tubing, (3) landing seats, (4) packers, and (5) a variety of required crossovers. Five external umbilicals allow access to these three zones for microbiological, geochemical, and pressure sampling. The CORK tubing (coated steel and fiberglass) extends to 247.6 mbsf and includes perforated and slotted intervals (67.4–129.4, 154.8–181.1, and 203.7–246.6 mbsf) that provide access to the three isolated intervals but leave the bottom portion of the hole open for future logging and access (247.6–331.5 mbsf). An internal OsmoSampler string extends the full length of the CORK and includes seals isolating the three zones and microbiological, geochemical, and temperature experiments.

At just after 1700 h on 5 November, we finished assembling the 247.6 m long CORK observatory and picked up the CORK head and attached it to the casing string. The last umbilical connections were made to the bottom of the CORK head. The CORK was then lowered to the moonpool and landed on the moonpool doors. The CORK running tool was then removed, and the OsmoSampler instrument string was assembled and lowered inside the CORK and casing. The CORK running tool was then reinstalled, and the packer inflation line was connected. The CORK was then lowered below the keel to flood the umbilicals to remove air from the pressure lines. The CORK was then raised to the moonpool, and the seafloor fast-flow OsmoSampler was installed. All valves except the geochemistry bay upper Zone 2 valve (which was connected to the seafloor fast-flow OsmoSampler) were closed and secured. The CORK was lowered to ~100 mbsl, and the camera frame was test fit over the CORK head. At 0000 h on 6 November 2011, after ~21 h of assembly, we started lowering the CORK assembly to the seafloor. During the trip in the hole, the drill pipe was filled with seawater every six stands, which lengthened the trip to a total of 8.25 h. At 0915 h the vessel began maneuvering to reenter Hole U1383C. The hole was reentered at 0941 h. After reentry, the CORK was slowly lowered into the hole while drill string weight was carefully monitored and the procedure was observed with the camera. Approximately 35 m above the landing point, the top drive was picked up, and the CORK was fully landed at 1127 h on 6 November. Afterward, the mud pumps were brought online to pump up the packers. We applied pressure to the packers for 30 min but were unable to get them to hold a sustained pressure. It was evident there was a small leak somewhere in the system between the standpipe on the rig floor and the bottom packer. We were unable to detect where the leak might be, and there are many possibilities or combinations depending on where the leak is—from all packers pressurized and sealing to only the top swellable packer sealing. After the camera was recovered, the ROV platform was assembled and hung from the camera frame and run to the bottom. The platform was released at 1630 h without incident. The camera was then pulled back to the surface, the slings and releasing tool were removed, and the camera was lowered back to the bottom to monitor the release of the running tool from the CORK head. The running tool was released at 2015 h on 6 November, ending the Hole U1383C CORK deployment. When the CORK running tool was released, the CORK wellhead also appeared to rotate. Several possibilities could account for this action, but it is likely the result of tightening the upper casing in excess of the manual tightening on the rig floor. A similar occurrence was noted with the Juan de Fuca CORKs. The camera and drill string were retrieved, with the CORK running tool arriving back on the rig floor at 0315 h on 7 November, ending Hole U1383C.

Sediment and basement contact coring (Holes U1383D, U1383E, U1382B, and U1384A)

The final operations of the expedition were focused on APC/XCB coring of the sediment above basement and the sediment/basement contact in four holes.

Hole U1383D

The advanced piston corer (APC)/XCB BHA was made up with a new APC/XCB bit and lowered to 4 m above seafloor. The vessel was positioned halfway between Holes U1383B and U1383C, offset 5 m to the northwest, and Hole U1383D was spudded at 1426 h on 7 November. Six APC cores were taken from 0 to 43.3 mbsf (Cores 336-U1383D-1H through 6H) and recovered 47.89 m of sediment. Core 6H only penetrated 0.2 m before hitting basement, so the majority of the recovery was sucked in when pulling the barrel out of the formation. After hitting basement with the last APC core, we penetrated 1 m with Core 336-U1383D-7X and recovered 0.76 m. Hole U1383D ended at 2350 h on 7 November when the bit cleared the seafloor.

Hole U1383E

The vessel was then offset 10 m to the southeast, and Hole U1383E was spudded at 0038 h on 8 November. APC Cores 336-U1383E-1H through 6H extended to 43.2 mbsf and recovered 50.38 m of sediment. Core 6H only penetrated 2.3 m before encountering basement, so the remaining 6.22 m of sediment recovered was likely sucked in when the barrel was pulled out of the formation. After the last piston core hit basement, the XCB core barrel was dropped, and the sediment/basement interface was cored for ~1 h to a depth of 44.2 mbsf. Core 336-U1383E-7X recovered 0.3 m. Hole U1383E ended at 1000 h on 8 November, when the bit cleared the seafloor.

Hole U1382B

After pulling out of Hole U1383E and raising the bit well above seafloor (4300 mbrf), we moved in dynamic positioning mode to Site U1382. After the 3.28 nmi transit was completed at 1445 h, the bit was lowered to just above the seafloor, and the top drive was picked up and spaced out for spudding. Hole U1382B was spudded at 1700 h on 8 November. APC Cores 336-U1382B-1H through 10H extended to 90.0 mbsf and recovered 83.70 m of sediment. Core 10H, the last APC core, encountered basement after penetrating ~8.5 m, so the lowermost portion of sediment recovered in this core is likely flow-in. Temperature measurements with the advanced piston corer temperature tool (APCT-3) were attempted on Cores 3H through 5H. The measurements were not good as a result of tool movement, and they were discontinued because they were thought to be disturbing the sediment cores. Subsequent splitting of the cores seemed to indicate that the disturbed cores could have been caused by the lithology of the cores—coarse sediments as large as pebble-size were found inside the cores. After basement was hit with the last piston core, the XCB core barrel was dropped, and the sediment/basement interface was cored. After a few minutes of XCB coring, the formation changed, and the XCB quickly advanced to the remainder of the kelly length (4.7 m). After Core 336-U1382B-11X was pulled, another core barrel was dropped, and XCB coring continued until hard formation was encountered around 98.8 mbsf. After 30 min of coring with no advance, Core 336-U1382B-12X was pulled. The XCB cutting shoe had lost all of its carbide teeth, and only 18 cm of core was recovered. Cores 336-U1382B-11X and 12X recovered a total of 0.58 m over an 8.8 m interval. Hole U1382B ended at 1315 h on 9 November when the bit cleared the seafloor.

Hole U1384A

After raising the bit above the seafloor (4400 mbrf), we moved in dynamic positioning mode to Site U1384. The 3.38 nmi transit was completed at 1815 h. We lowered the bit to just above the seafloor, picked up the top drive, and spaced out for spudding. Hole U1384A was spudded at 2130 h on 9 November. APC Cores 336-U1384A-1H through 11H extended to 94.7 mbsf and recovered 93.51 m of sediment. Core 11H was only a partial stroke, likely because basement was encountered. XCB Core 336-U1384A-12X advanced 1.5 m in ~40 min, where penetration stopped. When Core 12X was retrieved, 0.58 m of core had been recovered and the XCB cutting shoe had lost all of its carbide teeth. Hole U1384A ended at 0042 h on 11 November.

After the drill string was back on board, the BHA was disassembled and the drill floor was secured for transit. The transit to Ponta Delgada began at 0042 h on 11 November. The planned arrival time in Ponta Delgado is 0730 h on 17 November.

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