Previous   |    Next

doi:10.2204/iodp.proc.344.106.2013

Operations

Transit to Site U1380

After an 11.4 nmi transit from Site U1381, the vessel stabilized over Site U1380 at 1715 h on 27 October 2012. The initial position was at the coordinates of Hole U1380A (8°35.9976′N, 84°4.4032′W), which was drilled during Expedition 334 in 2011 (proposed Site CRIS-10A). The vessel was then repositioned 20 m east of those coordinates. The position reference used for dynamic positioning was a combination of GPS signals and an acoustic positioning beacon, which was deployed at 1730 h on 27 October and recovered at 2310 h on 13 November.

Hole U1380B

Hole U1380B was established to conduct a jet-in test to determine the length of 16 inch casing that could be jetted into the formation with a reentry cone. Upon arrival, the jet-in bottom-hole assembly (BHA) was assembled with a 14¾ inch bit and lowered to 312.8 meters below rig floor (mbrf). The subsea camera was deployed, and the seafloor was tagged with the drill string to verify the water depth. Hole U1380B was spudded at 0118 h on 28 October 2012 (8°35.9952′N, 84°4.3908′W; 502.7 m water depth). After 11.25 h, the 14¾ inch bit had been jetted into the formation 50 m. The BHA was then pulled out of the hole, and the bit cleared the seafloor at 1310 h on 28 October, ending Hole U1380B.

Hole U1380C

The reentry cone was moved to the center of the moonpool, and a 48 m long string of 16 inch casing was assembled. The casing string was then picked up with the Dril-Quip running tool and lowered and latched into the reentry cone centered in the moonpool. Once the reentry system and casing were assembled (Fig. F3), the stinger that is run below the casing running tool was assembled and run inside the casing. The Dril-Quip running tool was made up and inserted into the casing hanger, and the assembly was lowered to the seafloor. The top drive was picked up, and the 16 inch casing string was jetted into the formation. Hole U1380C was spudded at 1145 h on 29 October 2012 (8°35.9879′N, 84°4.3918′W; 502.7 m water depth). After 9.5 h of jetting operations, the reentry cone landed on the seafloor. The subsea camera system was run to bottom, and the running tool was released and lifted clear of the reentry cone. The bit was pulled out of the hole, clearing the rig floor at 0155 h on 30 October. The next step was to drill a hole for the 10¾ inch casing, so a 14¾ inch drilling assembly was made up and run into the hole. The subsea camera system was deployed, the top drive was picked up, and after 20 min of positioning the vessel, Hole U1380C was reentered at 0550 h on 30 October.

Drilling began at 48 meters below seafloor (mbsf) and continued over the next 22.8 h to a total depth of 438 mbsf. Two high-viscosity mud sweeps were pumped, and the hole was checked for fill. After finding 3 m of fill, the hole was washed back to bottom and another high viscosity mud sweep was pumped. After cleaning the hole as much as practical, a wiper trip was performed. The bit was pulled back with the top drive to 260 mbsf. Excessive overpull and high torque were experienced while the bit was between 338 and 396 mbsf. The top drive was then set back, and the bit was pulled back to just above the casing shoe. The bit was then lowered back into the open hole section, and a hard tag (weight loss) was experienced at 289 mbsf. The drill string was pulled back 20 m, and the top drive was picked up. The hole was then washed and reamed back to bottom, where 3 m of fill was encountered.

After reaching total depth, two 50 bbl mud sweeps were pumped. Given the hole problems experienced on the first wiper trip, we conducted another wiper trip. The top drive was left in place, and the bit was pulled back to 289 mbsf. Overpull of 10,000–15,000 lb was experienced in the same interval as before. After reaching 289 mbsf, the top drive was set back and the bit was pulled back to just above the casing shoe. While running back to bottom, the first hard tag was experienced at 337 mbsf. The drill string was pulled back, and the top drive was picked up. The hole was then reamed back to bottom (438 mbsf), where 25 m of hard fill was encountered. The fill could not be washed through and had to be drilled and circulated out. Another two high-viscosity mud sweeps were pumped, and another wiper trip was performed. The same tight hole conditions were experienced between ~395 and 340 mbsf. The top drive was set back, and the pipe was tripped back to just above the 16 inch casing shoe. Running back into the hole with the bit, a hard tag was experienced again at 347 mbsf. The top drive was again picked up, and an attempt was made to jet into the hole without rotation. At 366 mbsf, 40,000 lb of overpull and 500 A of torque were experienced. We continued to run back in the hole with and without rotation to 425 mbsf. At that point, we decided to attempt to stabilize the formation with cement from 396 mbsf to ~50 m higher. Sixty-five barrels of cement were mixed, pumped, and displaced at 2045 h on 1 November. After pumping the cement, the drill string was pulled up above the theoretical top of the cement and 2.5 times the volume of the drill sting was pumped with seawater to flush any remaining cement from the drill string. The pipe was then pulled all the way back to just above the casing shoe and circulated again, this time with three times the volume of the drill string at 100 spm.

After waiting on the cement to cure for 9.8 h, we attempted to run back into the hole with the bit. Tight hole conditions were noted at 153–163 and 175 mbsf. At 175 mbsf, the top drive was picked up and we washed and reamed back to 347 mbsf, where we encountered the top of the cement plug. The cement plug was drilled out from 347 to 395 mbsf, and the rest of the hole was reamed back to 438 mbsf. Two high-viscosity mud sweeps were pumped at the bottom of the hole, and the drill string was pulled back to 328 mbsf with no pump and no rotation. We then washed down with no rotation from 328 to 406 mbsf. The maximum weight on bit experienced was 10,000–15,000 lb. At 406 mbsf, we began washing and rotating back to bottom. Two 50 bbl high-viscosity mud sweeps were pumped to clean up the hole, and the hole was displaced with 225 bbl of heavy (10.5 ppg) mud. We then pulled out of the hole with the top drive, and the drill string was pulled clear to surface to run casing. The 14¾ inch bit was laid out, and the Dril-Quip casing running tool was made up to the casing hanger and one stand and set back in the derrick. The drill floor was rigged up for running casing, and a short safety meeting with the crew took place. The 10¾ inch casing length that was selected was 406 m. This was made up of 29 joints of 10¾ inch casing, one shoe joint, and one pup joint on the 10¾ inch casing hanger. The 10¾ inch casing string was landed on the moonpool doors and secured, and the running tool was released. The casing stinger was then made up and spaced out. The running tool and the remainder of the casing BHA were made up, and the casing was run to just above the seafloor. The subsea camera was run down the casing string.

After positioning the vessel for reentry, Hole U1380C was reentered at 0745 h on 4 November. The subsea camera was recovered, and the casing was run into the hole to 179.3 mbsf, where tight hole conditions were experienced. The casing was pulled back to 150.3 mbsf, and the top drive was picked up and installed. Over the next 14 h, the casing was slowly worked into the open hole by applying weight while pumping with the top drive. The final depth of the casing shoe was within 18 m of the landing depth when the casing refused to advance any further. The casing eventually became stuck, and it required ~120,000 lb of overpull to free the casing from the formation. The casing was then pulled back to the surface, clearing the top of the reentry cone at 0035 h on 5 November. Using the casing elevator, the casing was landed on the moonpool doors at 0110 h. The running tool was released from the casing, and we made a decision to try to reenter the hole with a 9⅞ inch tricone bit and an underreamer assembly to clean out the hole. The idea was to not disassemble the casing while the hole was being prepared, which would allow us to run the casing quickly after the hole was cleaned to depth. The 9⅞ inch bit and the underreamer were picked up and deployed through the casing string in the moonpool. The casing was picked up with the running tool to deploy the subsea camera. The camera was then run to bottom, and the vessel was positioned for reentry. Hole U1380C was quickly reentered, and the bit was run to just below the bottom of the 16 inch casing. The top drive was picked up and reaming began from 51.4 mbsf.

At 216.7 mbsf, at 0045 h on 6 November, the driller experienced erratic drilling torque and then observed the loss of that erratic torque while adjusting his drilling parameters. A later review of the rig instrumentation data clearly showed not only erratic torque but an increase of weight in the hook load of ~40,000 lb. The driller reacted by changing his drilling parameters to try to find the cause of the erratic torque. After shutting the pumps down completely, the erratic torque vanished, as did the additional hook load weight. Restarting the pumps again with rotation resulted in not even the reaming torque that was present before the event. At that time, the tool pusher and the driller assumed that the underreamer had stopped functioning. The decision was made to pull out of the hole and inspect the drilling assembly. The bit cleared the reentry cone at 0229 h and was pulled to the rig floor at 0440 h. The bit and the underreamer appeared intact, with no obvious signs of damage. A test of the underreamer failed to energize the arms, and we made a decision to pick up a second underreamer and go back to reaming the hole to bottom.

The drilling BHA with the new underreamer was picked up and run to 371.2 mbrf. At that time, the casing hanger was picked up with the running tool to deploy the subsea camera. As the tool pusher began running the camera to bottom, he discovered that the casing string had parted just below the vessel. We realized that the erratic drilling parameters observed earlier in the day had been caused by the casing string parting and free falling into the hole. The casing reentered the reentry cone, made its way down the drill string, and landed on the rotating underreamer arms at 216.7 mbsf. The additional weight of the casing string caused the erratic torque when the casing shoe landed on the rotating underreamer arms. When the driller shut down the mud pumps, the underreamer arms closed and the casing continued its downhole trip. The subsea camera was run down the drill pipe to survey the possible damage to the reentry system and casing. The expectation was that the casing would have come to a stop with a portion of the casing extending out from the reentry cone. The initial underwater survey indicated that the casing had continued its downward journey and that the entire casing string was inside the existing hole.

After discussions on board, we decided to reenter the hole and determine if the hole was salvageable. The vessel was positioned for reentry, and Hole U1380C was reentered at 1357 h on 6 November. The camera was pulled to the surface, and careful observation near the surface indicated that only one complete joint plus the casing hanger (15.2 m total length) remained hanging below the ship. By subtracting that from the full length of the casing string we determined that 390.6 m of casing had landed inside the hole. The only question remaining was the condition of the casing. It was quickly determined that the top of the 10¾ inch casing string was very likely inside the 16 inch casing string. The drill bit was lowered without any significant resistance from inside the 16 inch casing to 336 mbsf. At that point, we applied 30,000–40,000 lb of weight, but no downward progress resulted from our efforts. After discussions with drilling and science staff, we decided to pull out of the hole and pick up a coring BHA with a rotary core barrel (RCB) bit. The subsea camera was deployed, and the hole was reentered at 0900 h on 7 November. The bit encountered a possible tag at ~8 mbsf, which we interpreted to be the top of the casing. If confirmed, the bottom of the casing should be found at ~398 mbsf; if so, the casing would be covering the problematic zone in the hole. The bit was lowered to 336 mbsf, and drilling proceeded carefully from 336 to 438 mbsf without problems. The hole was then circulated clean, the wash core barrel was pulled, and an RCB core barrel was dropped. RCB coring commenced at 1745 h on 7 November and continued without interruption until 2400 h on 10 November, reaching a total depth of 800 mbsf. Nonmagnetic RCB core barrels were used starting with Core 344-U1380C-11R. In an effort to improve recovery, we started cutting and pulling half cores with Core 25R. This dramatically improved core recovery, and coring by half cores continued. The total cored interval in Hole U1380C was 362.0 m with 202.4 m recovered for an overall recovery of 56% (Table T1). At the conclusion of coring, the hole was swept clean with a 40 bbl sweep of high-viscosity mud.

In preparation for logging, the drill string was pulled out of the hole to a depth just above the seafloor, clearing the reentry cone at 0720 h on 11 November. The subsea camera was deployed, and the bit was successfully released on the seafloor at 0855 h. Hole U1380C was reentered at 1005 h, the subsea camera was recovered, and the end of the drill pipe was placed at 336 mbsf. After holding a safety meeting on the rig floor, the triple combination (triple combo)–Ultrasonic Borehole Imager (UBI) logging string was rigged up and run into the hole at 1530 h. However, the logging tools were unable to advance past 398 mbsf, which coincided with the estimated depth of the casing shoe. The tools were pulled from the hole, and the drill pipe was advanced to 467 mbsf without difficulty. The drill pipe was then pulled back to 394 mbsf, and a reconfigured triple combo string without the UBI was picked up and run into the hole at 2310 h. This time the logging tools made it to 458 mbsf before encountering an obstruction. A review of the logs showed that the casing might have slipped down inside the hole (Fig. F4). The logging tools were pulled back to the surface, and the hole was checked to 496 mbsf with the end of the pipe, where an obstruction was encountered. The pipe was pulled back to 457 mbsf with 20,000 lb of overpull. In order to better clean the hole for logging, the drill string was pulled all the way out of the hole, reaching the rig floor at 0725 h on 12 November. A BHA with a used RCB bit was deployed. The subsea camera was deployed, and Hole U1380C was reentered at 1015 h. The drill pipe was advanced to 65 mbsf, where it encountered a slight obstruction. This depth was recorded as the new possible top of the 10¾ inch casing string, which would place the casing shoe at 455 mbsf. The pipe was eventually run in the hole to 496 mbsf, and the hole was washed down from 496 to 781 mbsf in 15.75 h. The hole was swept clean with a 40 bbl sweep of high-viscosity mud, and a second sweep of 20 bbl was pumped. The RCB bit was released in the hole at 768 mbsf, and the hole was again displaced with 230 bbl of heavy mud. In preparation for logging, the end of the drill string was placed at 443 mbsf. The triple combo logging tool string was rigged up for the third time and run into the hole at 1310 h on 13 November. However, the logging tools encountered a similar obstruction as before at 462 mbsf. After several attempts to get the tools to reenter the open hole, the tools were pulled back to the surface and rigged down. The drill pipe was lowered into the hole for one last depth check but encountered an obstruction at 438 mbsf. At that point all attempts to log Hole U1380C were abandoned, and the hole was plugged with a 10 bbl cement plug. The drill string was pulled from the hole, clearing the rig floor at 0055 h on 14 November. The rig floor was secured for transit, ending Hole U1380C and Site U1380.

Top of page   |    Previous   |    Next