The bit was pulled from Hole 1173A, clearing the seafloor at 1930 hr on 6 June. After the positioning beacon was released and recovered at 2100 hr, the vessel started moving to proposed Site ENT-03A (Site 1174) in dynamic positioning (DP) mode. The drill string was recovered during the transit and the bit cleared the rotary table at 0445 hr on 7 June, officially ending Hole 1173A. A positioning beacon was dropped at 0700 hr on 7 June, establishing Site 1174.
The precision depth recorder indicated a water depth of 4754.4 meters below rig floor (mbrf). An eight-drill collar advanced hydraulic piston corer/extended core barrel (APC/XCB) bottom-hole assembly (BHA) was made up with an 11.4375-in roller cone bit, a lockable float valve, a seal bore drill collar, landing saver sub, top sub, head sub, nonmagnetic drill collar, five 8.25-in drill collars, one tapered drill collar, six joints of 5.5-in drill pipe, and a crossover sub to 5-in drill pipe. The drill string was tripped to the seafloor, the bit was positioned at 4741.1 meters below sea level (mbsl) (4752.4 mbrf), and core was taken but did not recover any sediment. The bit was repositioned at 4746.1 mbsl (4757.4 mbrf) and Hole 1174A was successfully spudded at 1735 hr on 7 June. Core 1H recovered 4.4 m of sediment, establishing the drilling depth as 4751.2 mbsl (4762.5 mbrf).
Cores 1H to 8H were cored from 0 to 64.4 mbsf and recovered 47.04 m (73%) (Tables T1, T2). Fine-grained sand and silts likely caused the somewhat low core recovery. The force required to pull the APC barrel out of the formation increased until it reached 70,000 lb on Core 7H. Core 8H resulted in a partial stroke with only 3 m of penetration, so the coring system was changed over to the XCB.
Core 9X was cut from 64.4 to 74.1 mbsf. When we tried to retrieve the core barrel, it could not be pulled free from the BHA. A 50-bbl sepiolite pill was pumped past the core barrel in an effort to clean out any sands/silts that might be causing it to jam, but this did not help, and the entire drill string had to be recovered. The bit cleared the rotary table at 0130 hr on 9 June, officially ending Hole 1174A.
When the BHA reached the rig floor, it was discovered that the core barrel was stuck inside the nonmagnetic outer drill collar. After the core barrel was finally dislodged, one of the XCB latching mechanisms (dogs) was found to have failed. A 1.5-in-long piece was missing from the middle of the latch dog. One of the remaining ends of the latch was still locked inside the XCB body and had rotated outward, pinning the core barrel in place. This is the first known occurrence of this type of failure, and the cause is as yet unknown.
The decision was made to set a drill-in-casing (DIC) system in Hole 1174B to case off the loose sands near the seafloor in preparation for an 1150-m-deep penetration through the protothrust and décollement zones. Eleven joints of 11.75-in casing (142.2 m) were made up with a new 14.75-in sawtooth casing bit welded on the end and hung off on the moonpool doors. A 9.875-in tri-cone bit was made up to the drilling assembly and was spaced out ~1 m ahead of the casing bit. Once the drilling assembly was attached to the casing assembly, a DIC reentry funnel was attached to the DIC drive bushing. The completed DIC assembly was then lowered to the seafloor.
While we assembled the DIC system, it was necessary to allow the ship to drift with the current. After the DIC assembly had reached the seafloor, another hour of maneuvering in DP mode was required to move the vessel back on location. Hole 1174B was spudded at 0943 hr on 10 June.
The DIC was first jetted into ~50 mbsf with maximum jetting parameters of 45 strokes per minute (spm), 400 psi, and 5000-10,000 lbs weight on bit (WOB). Then the DIC was drilled into 143.67 mbsf (4906.17 mbrf) with maximum drilling parameters of 80 spm, 1050 psi, 8000-10,000 lbs WOB, 10 rpm, and 6000-9000 ft-lb of torque. Total time for emplacement was ~7.25 hr, and no problems were encountered.
The rotary shifting tool (RST) was then deployed on the wireline to unlatch the DIC. The weight of the DIC casing, ~22,000 lb, was slacked off in preparation for unlatching. The RST had to be worked through the DIC three times before a definite indication of the release sleeve shifting was observed. The drill string was then picked up, and the weight of the DIC system was lost, indicating that it had released properly.
We intended to have Hole 1174B penetrate a relatively thick section that might be unstable; therefore, the decision was made to round trip the drill string to remove the DIC drive sub and then reenter with a standard rotary core barrel (RCB) BHA. Thus, the drill string was recovered.
The DIC BHA was broken out, and an RCB BHA was made up. The RCB was tripped to the seafloor and the vibration-isolated television (VIT) camera frame was lowered to the seafloor in preparation for reentry. The search for the DIC reentry funnel began at 1830 hr on 11 June, and the funnel was first sighted visually at ~2315 hr. At 2347 hr on 11 June, Hole 1174B was reentered and the VIT was recovered. The bit was lowered into the hole with moderate drag until the bit had reached 52.5 mbsf, where some resistance was encountered. The top drive was picked up, and the bit had to be worked down all the way through the cased section.
Hole 1174B was then cored from 143.7 to 265.8 mbsf (4906.2 to 5028.3 mbrf) with high erratic torque. At this depth the bit became stuck. The drill string was worked for 1 hr, and 120,000 lb of overpull was required to free the bit. The bit was raised up inside the casing with drag and high erratic torque all the way. The bit was eventually raised to 50 mbsf (4852 mbrf), where the high erratic torque finally disappeared.
The bit was lowered once again, encountering an obstruction at 52.5 mbsf (4854.5 mbrf). The bit was worked through this problem area inside the casing several times until it was thought that the obstruction was no longer a threat to the coring operations. The bit was then lowered back down into the open hole, encountering fill at 172.5 mbsf (4935 mbrf). After the hole was washed and reamed to bottom, coring resumed.
Some further insight into the mysterious high erratic torque previously observed while coring in Hole 1174B appeared in the top of Core 20R. A piece of chewed-up metal ~3 in long, 1.5 in wide, and 0.25 in thick was recovered. Additional pieces of metal were found in other succeeding cores. Unfortunately, the origin of the metal is still not clear.
While retrieving Core 40R from 524.3 mbsf (5286.8 mbrf), the forward core winch wireline parted at the crown with the core barrel at 3664 mbrf. The frayed end of the wireline caught in the oil saver on top of the swivel and T-bar clamps were used to pull the parted wireline up through the top drive. Preparations were then made to string the parted wireline back over the crown sheave and reattach it to the coring winch. However, when the derrick man reached the crown, he discovered that the outboard wireline crown sheave had failed.
Approximately one-third of the sheave rim on the outboard side had separated from the sheave body. A used sheave was located on board and was installed to replace the failed sheave.
The parted wireline was strung over the replacement sheave and reattached to the core winch with cable clamps. The parted wireline was recovered along with the core barrel, which contained 9.21 m of core. The forward core winch was secured, and the aft core winch, which had 9600 m of new wireline on it, was placed into service. A total of 8.25 hr of down time was incurred as a result of the parted wireline and failed sheave.
Although rotation and circulation were maintained while we recovered the parted wireline and replaced the failed sheave, a wiper trip was carried out before we resumed coring operations. The bit was pulled to 128.43 mbsf (4890.93 mbrf) inside the DIC casing shoe. Once the bit was back inside the casing, an overdue maintenance of the drill line (slip and cut) was carried out. The bit was then lowered to 459.86 mbsf (5222.36 mbrf), where slight drag was encountered. The top drive was picked up and the hole was washed and reamed to 524.3 mbsf. Approximately 7 m of soft fill was encountered in the bottom of the hole. RCB coring then resumed, and Cores 41R to 102R were recovered from 533.9 to 1119.8 mbsf (5882.3 mbrf). After the DIC was drilled in to 143.7 mbsf, Hole 1174B was continuously cored through 976.1 m of section. Recovery was 577.57 m (60%).
Because some gas was detected in the formation, the hole was displaced with 280 bbl of heavy mud. After the hole was displaced, the pipe was pulled out of the hole with no rotation or circulation. When the bit reached 398.2 mbsf (5160.3 mbrf), a tight spot was encountered and the pipe was worked without picking up the top drive. A 60,000-lb overpull was being applied to the drill string when the pipe came free. However, the drill string weight was ~70,000 lb lighter, indicating that the drill string had parted, and the pipe trip continued. The drill string had parted 467 m above the seafloor.
Once the drill pipe was clear of the seafloor, the two seafloor positioning beacons were given release commands. The primary beacon released and was recovered. However, the backup beacon failed to release and was not recovered. Once the beacon was on board and the end of the pipe was near the rig floor, the thrusters and hydrophones were raised and the vessel began the 2-hr transit to proposed Site ENT-05A (Site 1175).
The end of the drill pipe cleared the rig floor at 2230 hr on 22 June. The pin connection on the bottom of drill pipe stand number 26 had failed. Lost in the hole were a 9.875-in RCB bit, a mechanical bit release, an outer core barrel, a top sub, a head sub, seven 8.25-in drill collars, a transition drill collar, six joints of 5.5-in drill pipe, a crossover sub, and 75 joints of 5-in drill pipe.