OPERATIONS

An operations summary of Leg 196 Site 1173 is presented in Table T1. Previous Leg 190 operations at Site 1173 are reported in Moore, Taira, Klaus, et al. (2001).

Leg 196 began with the first line ashore to Berth 4-E East Wharf, Keelung, Taiwan, at 0904 hr on 2 May 2001. Public relations tours were held each day with members of the press. VIP tours (including Chinese Taipei's vice president) were conducted on 4 May, and the bulk of the visitors were on board on 5 and 6 May. Major port call activities consisted of removing geochemical radioactive sources from the ship and loading a considerable amount of equipment, including ACORK casing (260 joints) and hardware, the Anadrill LWD/MWD tools, and 120 tons of sepiolite.

Immigration formalities were completed on 2 May, and the loading of 700 metric tons of fuel from 100-metric ton barges was finished at 2050 hr. Divers inspected the thrusters and main propulsion system to ensure they were not fouled by fishing lines during Leg 195. Additional inspection dives were conducted on the afternoon of 3 May.

On 3 May the vessel was shifted 40 ft astern to make room for other ships berthing at the dock; the incoming air freight and food were loaded. We then unloaded surface freight containers, placed the freight onto the dock, and began loading it onto the ship. The Anadrill MWD/LWD tools were unloaded onto the dock, and the Anadrill engineers began dockside assembly and testing. The loading of the bulk sepiolite began, with a pneumatic truck used to transfer it onto the ship; 56 tons was loaded. Liquid helium was received, and the cryogenic magnetometer was filled.

After considerable efforts to coordinate logistics and obtain permits, the two radioactive sources for the geochemical logging tool were taken off the drillship on 4 May. Then we were allowed to load the sources for the LWD/MWD logging tools onto the ship. On 4 May the Anadrill engineers continued unloading and testing the LWD/MWD tools, and the remaining 64 short tons of bulk sepiolite was loaded. The trucks carrying the 10-in and 20-in casing began arriving, and we started to unload and stage it on the dock; during this process each joint was measured and labeled.

On 5 May, assembly and testing of the LWD/MWD tools continued, the casing handling and loading continued, and the off-going freight was taken off the ship. By 0830 hr on 6 May, all casing had been loaded. A total of 226 joints of 10-in casing was stored in the riser hold, and 36 joints of 20-in casing was stored in the riser hold, as well as on top of the riser hold hatch, as the riser hold was full. The LWD/MWD tool testing was completed, the tools were loaded, and the crew began securing the ship for departure.

The last line away from Keelung was at 0900 hr on 7 May. The transit to Site 1173 began at 0930 hr, when the harbor pilot disembarked. After a transit of 784 nmi we arrived at the Global Positioning System (GPS) coordinates of Site 1173 (32°14.6634´N, 135°1.5085´E) at 0645 hr on 10 May.

During the transit, the rig crew assembled the first reentry cone; it was moved into position on the moonpool doors in preparation for deployment. Repairs were made to the underreamer used during Leg 195 (seal replacements, 22-in cutter sets changed, and jet function verified). The rig crew performed preventive rig maintenance and repairs.

The ship experienced a power interruption during the transit (at 2347 hr on 8 May) caused by a shutdown of main engine 2 due to high crankcase pressure. This resulted in a slight reduction in speed that lasted 15 min. Repairs to the piston pin and insert carrier on cylinder 7 were made, and complete preventive maintenance was performed on this engine.

In preparation for operations at Site 1173, we attached a used 18-in tricone mill-tooth bit (Hughes X44) to the 22-in underreamer. This, in turn, was made up to an 8-in positive displacement mud motor (Baker-Hughes Drilex model D825MSHF), and the assembly was tested. The pressure drop at a flow rate of 275 gallons per minute (gpm) was low (75 psi) and leakage high, so we changed to a backup mud motor that had a 125-psi pressure drop at 275 gpm. The Dril-Quip cam-actuated drill-ahead (DQ CADA) casing running tool was made up to the 20-in casing hanger and a short (pup) joint of casing.

Hole 1173B

At 0645 hr on 10 May, we arrived on location, lowered the thrusters and hydrophones, and started making up five stands of drill collars. A positioning beacon was not immediately deployed because the scientists requested an offset of 50 m at 314° from the position of Hole 1173A, which was cored during Leg 190; the ship maintained station by using GPS. The ship was over the desired position of Hole 1173B at 0810 hr on 10 May, and a seafloor positioning beacon (Datasonics SN2031; 14.0 kHz; 214 dB) was deployed at 0835 hr.

Reentry Cone and Casing Operations

At 1200 hr on 10 May, we began rigging up to run 20-in casing by welding a casing guide shoe to the bottom joint and then adding nine more joints of casing. This casing was then added to the short (pup) joint of 20-in casing attached to the bottom of the casing hanger that was already latched to the casing running tool; the total length of this assembly was 120.6 m. This assembly was then landed and latched into the reentry cone at 1845 hr; the running tool was unlatched so that the BHA could be run into the casing.

Next, we began assembling and running the drilling BHA into the casing. The BHA consisted of the 18-in bit, 22-in underreamer, bit sub with float, mud motor, and four stands of 8-in drill collars for a total length of 123.5 m. The casing running tool was attached to the top of the BHA; the BHA was lowered into and latched to the casing and reentry cone. The reentry cone, BHA, and casing were lowered through the moonpool at 2100 hr.

By 0800 hr on 11 May, we had lowered 4781.8 m of drill string and deployed the vibration-isolated television (VIT) camera in preparation for spudding Hole 1173B. A backup seafloor positioning beacon (Datasonics SN2029; 15.0 kHz; 214 dB) was deployed at 0635 hr. When the VIT camera reached the casing running tool at 1030 hr, we observed that the reentry cone was missing but that the running tool and casing hanger were still attached to the drill string. We began assembling the second reentry cone.

The VIT camera was recovered; we changed the VIT camera drill pipe guide sleeve with the larger casing guide sleeve so that we could lower the camera over the casing to inspect it. At 1515 hr, the camera was lowered over the running tool, and we began inspecting the casing. The entire casing string, bit, and underreamer appeared to be intact. We continued to the seafloor with the drill string and camera to see if we could locate the lost reentry cone. We were unable to locate the reentry cone; the search was abandoned at 1930 hr; we began tripping out of the hole so we could rig up the second reentry cone.

On 12 May, we had raised the drill pipe, secured the casing in the moonpool, removed the casing running tool, racked the drill collars in the derrick, and laid down the mud motor, underreamer, and bit. At this time we had to perform the routine slipping and cutting of the drill line, which was completed at 1100 hr. The casing was taken apart at the first collar, and the second reentry cone was moved into position over the casing collar. The top piece of casing was reattached through the reentry cone; the casing was lowered and latched into the second reentry cone. This time we welded the casing hanger to the reentry cone to prevent it from detaching. We tripped the drilling BHA back into the casing and latched the running tool; the entire assembly with the second reentry cone was lowered through the moonpool at 1830 hr.

On 13 May at 0445 hr, we experienced a VIT camera problem but continued tripping drill pipe while the camera was changed out. The drill pipe was lowered to 4781.8 meters below rig floor (mbrf), the VIT camera was deployed again at 0600 hr, and we picked up the top drive and spaced out in preparation to spud. Hole 1173B was spudded at 0717 hr. We drilled in the 20-in casing with the underreamer and mud motor to 4926.1 mbrf (124.2 mbsf). With the 20-in casing shoe depth at 4922.5 mbrf (120.6 mbsf), we released the casing running tool at 1110 hr; we started tripping out of the hole with the drill pipe and VIT camera. The bit cleared the seafloor at 1225 hr and the rig floor at 2315 hr.

A summary of Leg 196 Site 1173 operations is presented in Table T1. Previous coring operations at Hole 1173A conducted during Leg 190 are reported in Moore, Taira, Klaus, et al. (2001).

Logging while Drilling

As soon as the tools were laid down, we started assembling the LWD/MWD BHA at 0030 hr on 14 May. The Anadrill engineers loaded the radioactive logging sources at 0515 hr. We then picked up the top drive and tested MWD tools at 300 gpm (60 strokes per minute [spm]) and 800-psi standpipe pressure. By 0600 hr we had assembled and tested the 9-in bit, LWD bit sub with float, LWD RAB tool, MWD tool, LWD ISONIC tool, LWD azimuthal neutron and density tool, and the LWD crossover sub. We added five drill collars, a tapered drill collar, and six joints of 5-in transition drill pipe, for a total length of 139.9 m. We removed the top drive and calibrated the Anadrill drawworks encoder. At 0700 hr on 14 May, we started tripping the drill string down to the seafloor. Unfortunately, we had to stop at 0930 hr (at 1406.8 mbrf) because of an approaching tropical storm (Cimaron). We tripped out of the hole and secured for transit by 1615 hr on 14 May to avoid the approaching storm.

We continued the transit to evade Tropical Storm Cimaron until 0030 hr on 15 May, when the captain felt it was safe to return to the site. The ship arrived back on site at 1100 hr on 15 May. The total transit was 185 nmi and lasted just over 18 hr.

Once we were back on location, the LWD/MWD BHA was assembled, the radioactive sources were loaded, and the tools were tested. We began lowering the LWD/MWD tools to the seafloor at 1330 hr on 15 May. When the drill string reached 3876.1 mbrf, the VIT camera was deployed. However, the camera signal was lost when it reached 102 mbrf. The camera was retrieved, and we found that the camera cable had been damaged in the upper guide horn. Approximately 110 m of cable was cut off, and the cable was reterminated. While this was being done, the drill string was tripped to 4769.6 mbrf. The repaired VIT camera was deployed at 0330 hr on 16 May. While the camera was being lowered to the seafloor, the drill crew assembled extra drill collar stands in preparation for the next site.

The VIT camera reached the top stabilizer/sensor pad on the LWD tool at 0830 hr but could not be lowered past it. The installed VIT guide sleeve (the same one used for the drilling tools) had an internal diameter of 9 in, and the external diameter of the stabilizer pad was 9 in. The camera was retrieved, the guide sleeve was changed to the casing guide sleeve (internal diameter of 27 in), and the camera was redeployed at 0830 hr on 16 May. The reentry cone came into view at 1002 hr and was reentered in 1.5 hr. The drill string was lowered into the casing while the VIT was retrieved.

The drill string was spaced out in preparation for drilling and the Anadrill LWD/MWD tools were tested. Drilling/logging operations began at 1500 hr on 16 May at 4922.5 mbrf (120.5 mbsf). The drillers attempted to maintain a 50 m/hr rate of penetration (ROP), as the scientists had requested. The effective ROP was lower than this due to the time required to make pipe connections. The average surface drilling parameters were a weight on bit (WOB) of 4-7 klb at 60 revolutions per minute (rpm), a torque of 150-175 A, and a flow rate of 327 gpm (67 spm) with a standpipe pressure of 1250 psi.

LWD/MWD operations continued until 1545 hr on 17 May, when Hole 1173B reached a total depth of 5539.0 mbrf (737.1 mbsf). The top drive was disconnected from the drill string and racked back in preparation to pull out of the hole. Because of deteriorating hole conditions, however, the top drive had to be reattached to provide rotation and allow circulation. The maximum overpull was 30 klb. The top drive was removed at 5346.6 mbrf. During the trip out of the hole, the LWD tools were recording the entire interval and the speed was controlled at 70 m/hr from 5221.9 to 5171.9 mbrf (420.0-370.0 mbsf) to evaluate LWD ISONIC velocity data quality. The drill bit cleared the seafloor at 2135 hr on 17 May.

Heave Compensation Experiments

Two experiments were conducted during the drilling of the hole to assess the efficacy of the shipboard active heave compensation (AHC) system. We used the MWD tool to measure downhole drilling parameters, including downhole WOB, torque, and bit bounce. These measurements are made using paired strain gauges near the base of the MWD collar, are transmitted to the surface for recording, and are not in downhole memory. Strong MWD pressure signals were recovered at the surface using MWD pulse rates of 3 bits/s at up to 5500 mbrf depth in Hole 1173B. Surface data from the rig instrumentation system (RIS), including surface rotations per minute, torque, WOB, ship heave, pitch, and roll, were recorded synchronously. Sea states up to 2 m and heave to 1.5-2 m were recorded during drilling at Site 1173.

For the first experiment six intervals were drilled with the AHC off (4955.7-4974.7, 5080-5099.3, 5224.2-5243.3, 5387.7-5406.9, 5464.6-5493.9, and 5527-5532 mbrf). During these intervals, drilling proceeded using the passive heave compensation system that was used for most ODP drilling prior to Leg 189. The approximate depths (in mbrf and mbsf), stand length, and times for each AHC-off interval are listed in Table T2. The second experiment consisted of drilling four intervals with the AHC preloaded, which allows the driller to set the surface weight prior to putting the bit in the bottom of the hole (5329-5358, 5406-5435, 5435-5464, and 5522-5527 mbrf). Whether or not this practice is effective in controlling penetration rates is debatable. The approximate depths (in mbrf and mbsf), stand length, and times for each AHC-preloaded interval are listed in Table T3.

Real-time shipboard observations suggest that the AHC damps high-frequency variations in uphole rotations per minute and torque, as well as the high-frequency variation in downhole WOB. The comparison of downhole MWD parameters with the surface information will be analyzed postcruise to evaluate the shipboard heave compensation system and drilling practices.

Hole 1173C

Logging while Drilling

Hole 1173C was designed to obtain LWD/MWD logs from the uppermost section that was cased off in Hole 1173B. The ship was offset 50 m to the northwest of Hole 1173B, and Hole 1173C was spudded at 2320 hr on 17 May. The LWD/MWD drilling/logging operations were conducted from the seafloor (4801.9 mbrf) to a total depth of 4976.9 mbrf (175.0 mbsf), which was reached at 0500 hr on 18 May. The ROP was controlled at 60 m/hr, and the effective ROP (including the time required to make pipe connections, etc.) was 30.9 m/hr. The average surface drilling parameters were a WOB of 4 klb at 60 rpm, a torque of 150 A, and a flow rate of 327 gpm (67 spm) with a standpipe pressure of 1250 psi.

The drill string cleared the seafloor at 0650 hr on 18 May; the LWD/MWD BHA reached the rig floor at 1430 hr. The LWD/MWD tools were disassembled, and the drill bit cleared the rotary table at 1655 hr on 18 May. One of the two seafloor positioning beacons was retrieved, and the other was turned off and left on the seafloor for use later in the leg when we would conduct ACORK operations. The drilling equipment was then secured for the transit to the next site.

Following Site 808 LWD/MWD operations and the short port call in Kochi, we returned to Hole 1173B. The Kochi harbor pilot boarded the ship at 0742 hr, and the last line away was at 0800 hr on 29 May. After the pilot departed, we began the transit back to Site 1173 at 0812 hr. After traveling 104 nmi in 9.3 hr, we arrived at Hole 1173B at 1730 hr on 29 May, started lowering the thrusters, and turned the seafloor positioning beacon on.

Our first objective was to reenter Hole 1173B and open the 9-in LWD hole up to 17 in before installing the ACORK. We began by making up the BHA, which included a 9-in bit sub with float valve, a 17-in hole opener, crossover subs, and drill collars. At 1910 hr, the ship was in position over Hole 1173B. The bit was lowered to 3534.3 mbrf, where the VIT camera was deployed at 0345 hr on 30 May. The bit was lowered to 4794 mbrf, and we began to search for the reentry cone at 0645 hr. Hole 1173B was reentered at 0832 hr. While we retrieved the VIT camera, the drill string was lowered into the casing to 4926 mbrf (123.5 mbsf).

We then drilled with the hole opener to a total depth of 5537 mbrf (735.1 mbsf). The AHC was turned off because of ship heaves of 2.8-3.3 m while we drilled the interval from 5133 to 5181 mbrf. Twenty-barrel sepiolite mud sweeps were pumped to maintain good hole conditions at 177, 235, 292, 350, 388, 446, 504, 552, 590, 648, and 735 mbsf. The drill string was worked through tight spots at 379-389 and 542-552 mbsf. The average drilling parameters were a WOB of 5-10 klb, top drive rotation of 60 rpm, top drive torque of 200-400 A (maximum of 600 A), and pump pressures of 1350-1800 psi at 120-140 spm.

Before pulling out of the hole, we circulated two 60-bbl sepiolite mud sweeps while the bit was at 735.1 mbsf. The trip out of the hole started at 0800 hr on 1 June. Tight spots at 670, 650, 590, and 495.1 mbsf required rotation and circulation. After the bit cleared the seafloor at 1420 hr on 1 June, from 1515 to 1645 hr, the drill line was slipped and cut. The bit reached the rig floor at 0230 hr on 2 June, the drill collars were racked back in the derrick, and the bit and hole opener were laid out.

While opening the hole, the moonpool area was prepared for assembling ACORK screens, packers, and casing. A working surface across the moonpool doors was created with I-beams and floor gratings. Tools and supplies were staged in the moonpool area, including the 10-in casing centralizers, steel banding, tie wraps, and so forth. The pneumatic umbilical cable reel was set forward of the moonpool area by the drill collar racks; jack stands were welded to I-beams to support the umbilical reel.

The ship was offset ~5 nmi west of Hole 1173B in preparation for assembling the ACORK screens, packers, and 10-in casing. From 0230 hr on 2 June to 1730 hr on 3 June, we assembled 54 joints of 10-in casing, five screen joints, and four external casing packers. The total length of the ACORK from the casing shoe to the landing joint was 727.77 m, and the weight was ~90 klb. During this operation, the umbilical cable, casing centralizers, and strapping (tie-wraps and banding material) were attached to the casing in the moonpool. A -in outer diameter stainless steel tube was joined between the lowermost screen and packer. Above this the umbilical was hydraulically connected to the bottom and top of each of the screens and packers.

The casing handling equipment was removed from the rig floor by 1800 hr on 4 June. We then moved the ACORK head, ported sub assembly, and 10-in casing landing joint from the main deck to the drill floor. After this was attached to the ACORK casing string, the complete assembly was lowered to and hung off the moonpool doors. The casing running tool was released at 2055 hr on 3 June, and we started assembling the drilling BHA. The BHA included a 9-in pilot bit, bit sub with float valve, 17-in underreamer, crossover sub, mud motor, crossover sub, six 8-in drill collars, crossover sub, 23 stands of 5-in drill pipe, one short (5 ft) joint of drill pipe, crossover sub, ACORK stinger, motor-driven core barrel (MDCB) latch sub, and the casing running tool. The total length of the drilling BHA was 737.8 m. Assembly of the drilling BHA was completed at 0500 hr on 4 June.

Once the drilling BHA and ACORK assembly was completed, the final connections of the umbilical to the ACORK head were made. Lowering the ACORK assembly into water in the moonpool purged the air from the stainless steel tubing. From 0800 to 0900 hr on 4 June, the complete assembly was lowered to 1143.3 mbrf. We then deployed the VIT camera to confirm the spacing of the drill bit/underreamer in relation to the bottom of the casing and to verify the proper functioning of the underreamer and mud motor. Once the VIT camera was recovered, the drill string was lowered to 2144.5 mbrf in preparation for the transit back to Hole 1173B. Two 30-ft joints and one 20-ft joint of knobby drill pipe were included at the top of the drill string to provide additional strength to withstand the stress while returning to the site. The transit in dynamic positioning (DP) mode began at 1430 hr on 4 June.

We had begun assembling the ACORK ~5 nmi west of Hole 1173B at 0230 hr on 2 June. Because of the current, we had to allow the ship to drift while we made up the casing. By the time we had finished assembling the ACORK and had lowered it to 2144 mbrf, the ship had drifted 26 nmi east of Hole 1173B at 1430 hr on 4 June. During the transit back to Hole 1173B, we averaged 0.5 nmi/hr and were back on location at 0035 hr on 7 June.

When the drill string had been lowered to 3708.4 mbrf, the VIT camera was deployed. Once the drill string was at 4790.0 mbrf (0630 hr on 7 June), we began the search for Hole 1173B. At 0840 hr, we reentered Hole 1173B and lowered the drill string to the bottom of the casing. We attached the top drive and began to drill in the ACORK. We continued to observe the operations with the VIT camera until it stopped working at 1320 hr on 7 June. After 35.5 hr of drilling, the ACORK was landed, and we reached the total depth of 732.7 mbsf at 1855 hr on 8 June. The lowermost 86 m drilled very slowly, taking ~19 hr to penetrate. The drilling parameters increased with depth, with drag increasing to 20-40 klb, and pump strokes per minute increasing from 70 to 130 spm as the standpipe pressure increased from 700 to 2800 psi. The WOB was 15-20 klb.

At 1900 hr on 9 June, the go-devil shifting tool was deployed to divert the flow path so we could inflate the packers. An increase in pressure at 2030 hr indicated that the ported sub assembly had been shifted. By 2200 hr, the packers had been inflated and the spool valves shifted.

Our next step was to release the casing running tool so that the drilling BHA could be removed, leaving the ACORK assembly installed. At 2030 hr on 9 June, we attempted to release the casing running tool, but unfortunately, it would not release. At 2200 hr, the VIT camera was deployed to observe the running tool. We maneuvered the ship in a 40-m circle as the drill string was worked up and down with torque to release the running tool. After 7.5 hr, the running tool finally released, and the drilling BHA was raised one joint to confirm this.

After the VIT camera was retrieved by 0715 hr on 9 June, we began assembling the remotely operated vehicle (ROV) platform on the moonpool doors. The deployment bridle and dual acoustic release mechanism were connected to the logging wireline; the entire assembly was lowered into the moonpool at 0915 hr on 9 June. The ROV platform had landed on the ACORK and was released at 1355 hr.

Once the logging wireline had been retrieved, we began tripping the drilling BHA back up to the rig floor. The bit cleared the seafloor and ACORK head at 2125 hr. When the bit was at 908 mbrf (0445 hr on 10 June), a 5-ft drill pipe joint failed at a pin connection, and the entire drilling BHA was lost. This occurred when the failed pin connection was in the lower guide horn one joint below the rig floor. The following equipment was lost: a 9-in bit, six crossover subs, a 17-in underreamer, a mud motor, eight 8-in drill collars, 81 joints of 5-in drill pipe, one 5-in drill pipe pup joint, an ACORK stinger sub, an MDCB latch sub, the casing/ACORK running tool, one tapered drill collar, and nine joints of 5-in drill pipe.

The next operational step was to drill out below the end of the 10-in casing to allow fluid/pressure communication between basement and the deepest ACORK monitoring zone. We decided to use the RCB coring system. Eight drill collars had to be picked up from the drill collar rack, measured, and made up to replace those we had just lost. The top sub and head sub were added, and the RCB core barrel space out was checked. The remaining drill collars that were racked in the derrick were added to the RCB BHA. We started lowering the bit to the seafloor at 0545 hr on 10 June. When the bit was at 3280 mbrf, tripping of the pipe was stopped to allow the drill line to be slipped and cut. We also used this time to replenish the drill pipe available in the racker. Twenty-one joints of 5-in drill pipe were taken from the riser hold, made into stands, and placed in the pipe racker.

At 1900 hr on 10 June, the upper guide horn was removed, the VIT camera was deployed, and the upper guide horn was reinstalled. At 1945 hr we resumed lowering the drill string to 4780.0 mbrf, where it was spaced out for reentry. The search for the reentry cone began at 2230 hr. The 30-in-diameter ACORK head was reentered at 2328 hr (see Fig. F34).

Problems arose at 2330 hr when the RCB coring BHA encountered a tight spot in the upper part of the casing. The BHA finally passed through the tight spot at 0145 hr on 11 June. The trip continued to 5327 mbrf, where we began to retrieve the VIT camera; it was back on board at 0515 hr.

The trip continued to 5500 mbrf, where the top drive was picked up. The hole was washed and reamed to 5539 mbrf (737.1 mbsf). The drill string was spaced out, and RCB coring began (Table T4). Drilling Core 196-1173B-1R lasted from 0900 to 1300 hr on 11 June and cored the interval from 5539 mbrf to 5548 mbrf. A problem was identified with the coring wireline and the oil saver sub that required a slip and cut of the wireline. This delayed the retrieval of Core 196-1173B-1R until 1545 hr.

Core 196-1173B-2R took 7.25 hr to cut from 5548.7 mbrf (746.8 mbsf) to 5553.6 mbrf (751.7 mbsf). Slow penetration rates and increased pump pressure suggestive of core jamming led us to pull this core before it had penetrated the full length. The core was on deck at 0030 hr on 12 June. Core 196-1173B-3R was taken from 5553.6 mbrf (751.7 mbsf) to 5558.5 mbrf (756.6 mbsf). Coring operations were stopped at 756 mbsf on 12 June at 0500 hr, as the time allotted for coring had expired. Hole 1173B reached a total depth of 5558.5 mbrf (756.6 mbsf). The top drive was used to pull out from 5558.5 mbrf (756 mbsf) to 5500 mbrf (699 mbsf); the top drive was then racked back, and the trip out of the hole continued. The bit cleared the seafloor at 0745 hr and the rig floor at 1615 hr on 12 June.

The final step in completing the Hole 1173B ACORK was to set a bridge plug at 722 mbsf inside the 10-in casing. The bridge plug (Weatherford model 53PBP.1001; 10-in, 40.5-lb/ft mechanical set cast-iron bridge plug) and 10-in mechanical setting tool (model 53MST.1002 with a crossover to 4-in American Petroleum Institute regular threads) were assembled to two drill collars, one tapered drill collar, and six joints of 5-in drill pipe. This bridge plug BHA was lowered to 3275 mbrf, where the VIT camera was deployed. The drill pipe was lowered to 4778 mbrf, where the top drive was picked up for drill string space out and reentry. The search for the reentry cone began at 0415 hr on 13 June. The 30-in-diameter ACORK head was reentered at 0610 hr.

The bridge plug was run in the hole to 5268 mbrf (466.3 mbsf). The VIT was retrieved at 0900 hr. The trip continued to 5498 mbrf (696 mbsf). The top drive was picked up, and the drill string was spaced out to set the bridge plug at 722 mbsf. The bridge plug requires 10 revolutions of right-hand rotation to set the upper slips. When right-hand rotation was applied to the drill string, the torque built to ~600 A in only eight revolutions. Numerous unsuccessful attempts were made from 1030 to 1200 hr to achieve the required 10 revolutions. While holding torque in the string, the crew worked the string up and down 15 m with no drag or overpull.

We then started pulling the pipe up the hole while trying to set the bridge plug at every stand; it was a wet trip. When the bridge plug reached 466.3 mbsf and the connection was made, the drill pipe at the rig floor had no water in it. Immediately upon pulling up on the next stand, overpull was observed, and then the sequence of actions to set the packer was initiated. Forty thousand pounds of overpull was held for 5 min to set the packer. Then 5 klb of weight was set down on the packer. A second overpull of 40 klb was applied and then bled off to neutral weight. The drill string was rotated to the right to release the running tool from the bridge plug. The torque climbed to 250 A with three rotations and then fell to 150 A, indicating that the bridge plug was set.

The drill string was then raised to 437 mbsf. After removing the top drive, tripping operations continued. The driller observed that the drill string weight appeared to be ~30 klb too low. The trip continued until the bottom of the pipe should have been at 471.0 mbrf when a failed 5-ft drill pipe joint cleared the rotary table at 2400 hr. Five joints of 5-in drill pipe were removed from service: four had been bent and one had parted in the tube body. The following equipment was lost: a bridge plug running tool, a bit sub, two 8-in drill collars, one tapered drill collar, six joints of 5-in drill pipe, three crossover subs, and 40 joints of 5-in drill pipe. The 41^st joint of drill pipe above the BHA parted as a result of compression bending ~8.4 m from the tool joint shoulder. Analysis of the drilling data suggests that the bridge plug had set at 466 mbsf. The 471-m length of lost equipment suggests that the parted drill pipe is at the top of the ACORK head assembly. Since the bridge plug had set, we determined there was nothing more that could be done at Hole 1173B and began the transit to Hole 808I at 0000 hr on 14 June. We were unable to recover the seafloor positioning beacon once it reached the surface.

After finishing operations at Site 808, we returned to Hole 1173B to conduct a camera survey of the Hole 1173B ACORK. After a 9.25-hr DP transit, the ship arrived at Hole 1173B at 0420 hr on 29 June. The drill string was lowered to 4795 mbrf, and the seafloor search for the reentry cone and ACORK began at 0600 hr. The reentry cone was located at 0618 hr and was observed until 0630 hr (see Fig. F35). The parted end of the drill pipe was inside the ACORK minicone and did not appear to stick out above it. Other than the fact that the inner bore of the ACORK is unusable, the Hole 1173B ACORK installation appeared to be intact. We began recovering the drill string and the VIT camera at 0630 hr on 29 June. The VIT camera was retrieved at 1200 hr. When the bit cleared the rig floor (2215 hr), we observed that the underreamer arms had broken off the underreamer that was used at Site 808. This may have been one of the problems contributing to our inability to penetrate to the total depth while installing the ACORK in Hole 808I. The BHA containing the underreamer used to install the ACORK in Hole 1173B was lost after installation as described above. It is conceivable that similar problems with those underreamers contributed to the difficulties in completing the final 100 m of ACORK penetration in Hole 1173B. The transit to Yokohama began at 2215 hr. Leg 196 ended with the first line ashore at 0830 hr on 1 July 2001 in Yokohama.