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 9.875-in LWD hole up to 17.5 in before installing the ACORK. We began by making up the BHA, which included a 9.875-in bit sub with float valve, a 17.5-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 retrieving the VIT camera, the drill string was lowered into the casing to 4926 mbrf (123.49 mbsf).
We then drilled with the hole opener to a total depth of 5537 mbrf (735.10 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 10.75-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 10.75-in casing. From 0230 hr on 2 June to 1730 hr on 3 June, we assembled 54 joints of 10.75-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 ~90,000 lb. During this operation, the umbilical cable, casing centralizers, and strapping (tie-wraps and banding material) were attached to the casing in the moonpool. A 0.25-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 10.75-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 9.875-in pilot bit, bit sub with float valve, 17-in underreamer, crossover sub, mud motor, crossover sub, six 8.25-in drill collars, crossover sub, 23 stands of 5.5-in drill pipe, one short (5 ft) joint of drill pipe, crossover sub, ACORK stinger, motor-driven core barrel latch sub, and the casing running tool. The total length of the drilling BHA was 737.83 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 2144.49 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 3708.41 mbrf, the VIT camera was deployed. Once the drill string was at 4790.03 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 (7 June). After 35.5 hr of drilling, the ACORK was landed, and we reached the total depth of 732.71 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 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 9.875-in bit, six crossover subs, a 17-in underreamer, a mud motor, eight 8.25-in drill collars, 81 joints of 5.5-in drill pipe, one 5.5-in drill pipe pup joint, an ACORK stinger sub, a motor-driven core barrel (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 10.875-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 5.5-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 (UGH) was removed, the VIT camera was deployed, and the UGH was reinstalled. At 1945 hr we resumed lowering the drill string to 4780.03 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.
Problems arose at 2330 hr when the RCB coring BHA encountered a tight spot in the casing at 4608 mbrf (4.14 mbsf). The BHA finally passed through the tight spot at 0145 hr on 11 June. The trip continued to 5327 mbrf (575 mbsf), where we began to retrieve the VIT camera; it was back on board at 0515 hr.
The trip continued to 5500 mbrf (699.00 mbsf), 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. Drilling Core 196-1173B-1R lasted from 0900 to 1300 hr and cored the interval from 5539 mbrf (737.1 mbsf) to 5548 mbrf (746.8 mbsf). 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 on 11 June.
Core 196-1173B-2R took 7.25 hr to cut from 5548.7 mbrf (746.8 mbsf) to 5553.60 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 (751.70 mbsf) to 5558.5 mbrf (756.60 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 mbrf (756 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 10.75-in casing. The bridge plug (Weatherford model 53PBP.1001; 10.75-in, 40.5-lb mechanical set cast-iron bridge plug) and 10.75-in mechanical setting tool (model 53MST.1002 with a crossover to 4.5-in American Petroleum Institute regular threads) were assembled to two drill collars, one tapered drill collar, and six joints of 5.5-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 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 470.95 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: bridge plug running tool, bit sub, two 8.25-in drill collars, one tapered drill collar, six joints of 5.5-in drill pipe, three crossover subs, and 40 joints of 5-in drill pipe. The forty-first joint of drill pipe above the BHA parted due to 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.