OPERATIONS

After the drill string was pulled out of Hole 1253A, the ship moved in dynamic-positioning mode to Site 1254 (1.1 nmi) while the drill string was being retrieved. The beacon from Site 1253 was recovered at 0430 hr on 11 October 2002 and redeployed at 0945 hr on 11 October at Site 1254A (all times reported are local ship time, which is Universal Time Coordinated [UTC] - 5 hr).

Hole 1254A

The first operation at Site 1254 was to install a reentry cone and 16-in surface casing. Two joints (29.37 m) of 16-in casing were made up to a casing hanger and latched into a standard reentry cone. The reentry cone was lowered to the seafloor, and Hole 1254A was initiated at 2225 hr on 11 October. The seafloor was determined to be 4194 meters below rig floor (mbrf).

The sediments proved to be quite consolidated near the seafloor, and 10 hr was required to jet in the 16-in casing. The casing running tool was released at 0850 hr on 12 October, and the drill string was pulled out of the hole, clearing the reentry cone at 0900 hr. The camera system was recovered, and the casing running tool cleared the rotary table at 1645 hr 12 October.

After installing the reentry cone and 16-in casing, we assembled an RCB bottom-hole assembly (BHA) and lowered it to the seafloor. Hole 1254A was reentered at 0110 hr on 13 October, and we drilled without coring from the 16-in casing shoe at 4223 mbrf (29 mbsf) to 4244 mbrf (50 mbsf). A DVTPP measurement was made at 50 mbsf, but the data were not usable. Hole 1254A was then drilled from 4244 to 4344 mbrf (50 to 150 mbsf), where a second DVTPP deployment was made; the data were once again not usable. Hole conditions through this part of Hole 1254A were stable, and the rate of penetration was 9.3 m/hr.

RCB Cores 205-1254A-1R through 6R were cut from 4344 to 4397.8 mbrf (150-203.8 mbsf). A third DVTPP measurement was made at 203.8 mbsf, and for the first time during this leg, good temperature data were recorded. The pressure data, however, were not good. RCB Cores 205-1254A-7R and 8R were taken from 4397.8 to 4417 mbrf (203.8-223.0 mbsf). Cores 205-1254-A-1R through 8R penetrated 73 m, and we recovered 66.59 m (91%) (Table T1); the overall penetration rate was 10.8 m/hr. No hole problems were encountered, and the hole remained stable while this interval was cored.

Hole 1254A was then drilled without coring from 4417 to 4494 mbrf (223-300 mbsf) in 8.5 hr (9 m/hr). The hole remained stable throughout this drilled interval, requiring only periodic circulation of sepiolite mud to keep the hole clean.

To determine the upper and lower boundaries of the décollement, Hole 1254A was cored from 4494 to 4561.7 mbrf (300-367.5 mbsf). Cores 205-1254A-9R through 16R had a recovery of 58.41 m (87%) (Table T1), and the penetration rate through this interval was 10 m/hr.

Sepiolite mud was circulated periodically over this cored interval to maintain hole stability; however, none of the anticipated hole problems associated with drilling through a décollement occurred. The hole was displaced with 111 barrels of sepiolite, and the RCB bit was pulled out of the hole. The RCB bit cleared the reentry cone at 0530 hr on 16 October and reached the rig floor at 1230 hr.

A BHA was assembled with a 14-in bit for opening the hole in preparation for installing the 10-in casing string. We reentered Hole 1254A at 2135 hr on 16 October and rotated and washed from the 16-in casing shoe at 4223 mbrf (29 mbsf) to 4527 mbrf (333 mbsf). Fifty barrels of sepiolite mud were then circulated to clean out the hole, and twice the borehole volume was then circulated. We then conducted a wiper trip that encountered a tight spot at 4395 mbrf (201 mbsf). The bit was washed and reamed through the tight spot and lowered back down to the total depth of the 14-in hole at 4527 mbrf (333 mbsf); 2 m of fill at the bottom of the 14-in section of hole had to be washed out.

We circulated another 50 barrels of sepiolite and twice the hole volume with seawater. A second wiper trip was undertaken back to the 16-in casing shoe and encountered tight spots at 4482, 4420, and 4386 mbrf (288, 226, and 192 mbsf). During the wiper trip back down, the bit encountered a bridge at 4386 mbrf (192 mbsf), which supported ~20,000 lb of drill string weight. We washed and reamed through this tight spot and back down to 4527 mbrf (333 mbsf).

Once again, we swept the hole with 60 barrels of sepiolite and twice the hole volume with seawater. The hole was then displaced with 255 barrels of sepiolite to help stabilize the hole while we prepared to assemble and install the 10-in casing string. The drill string encountered no significant drag while it was pulled out of the hole. The bit cleared the reentry cone at 2215 hr on 17 October and reached the rig floor at 0500 hr on 18 October.

Twenty-eight joints (324 m) of 10-in casing were made up and attached to a 10-in casing hanger. The cementing tools were assembled and attached to the casing running tool, which in turn was made up to the 10-in casing string. The 10-in casing string was then lowered to the seafloor, and Hole 1254A was reentered at 1738 hr on 18 October.

The 10-in casing shoe was lowered to 4426 mbrf (232 mbsf) when it suddenly appeared to hang up, as identified by a reduction in string weight of 20,000 lb. The drill string was immediately picked up to the hanging weight of the string. The casing was lowered again and took weight at the same depth.

A stand of drill pipe had just been picked up, and there was not much traveling space in the rig available to work the casing up and down. The casing was worked within these traveling limits without being able to pass the tight spot.

The space-out was such that the drill string could not be picked up without activating the Crown-O-Matic (the stand of drill pipe was too close to the top of the derrick) and could not be lowered and secured on the rig floor without putting the casing in compression. Thus, the ship was offset far enough to allow the drill string to be landed on the drilling elevator stool without putting the casing in compression. A stand of drill pipe was laid out, and the ship was moved back over the hole. When we raised the drill string so that we could remove a single joint of drill and attach the top drive, the reentry cone was pulled up off the seafloor along with the 10-in casing string.

The 10-in casing string and reentry cone were worked in an unsuccessful attempt to free the reentry cone from the casing string. The vibration-isolated television (VIT) camera system was lowered to the reentry cone for a visual inspection. It appeared that a joint of 10-in casing had collapsed inside the reentry cone. With all options for freeing the reentry cone from the 10-in casing string exhausted, the 10-in casing string with the reentry cone and 16-in casing attached was pulled out of the hole.

Once the casing string with the stuck reentry cone was clear of the seafloor, we offset the ship 0.5 nmi perpendicular to the seismic line on which Site 1254 is located. If the reentry cone or other hardware fell off during recovery, we didn't want it to fall in the area where the scientists wanted to attempt another CORK-II installation. The reentry cone was pulled into the moonpool at 0845 hr on 19 October. While laying out the 10-in casing string, we found four joints that were bent. This bending likely occurred during attempts to break off the casing inside the reentry cone at the seafloor. Approximately 3 m of a collapsed joint of 10-in casing was found protruding out of the top of the reentry cone.

It was deemed unsafe and too costly in time to attempt to salvage the reentry cone and casing. Thus, preparations were made for jettisoning the reentry cone. The connection between joints 7 and 8 was partially loosened. The reentry cone was then lowered below the keel of the ship and hung off near the top of joint 9 in slips at the rotary table. Although the casing was hung off in the slips, the elevator was left attached to the casing and positioned just beneath the collar. A padeye was then welded to the casing just below the elevator to prevent the joint from jumping upward when the reentry cone was released. With all personnel cleared from the rig floor and the moonpool area, the rotary table was engaged to finish unscrewing the loosened connection, and at 0920 hr on 19 October the reentry cone was jettisoned, ending Hole 1254A.

Hole 1254B

The scientific party decided to make a second attempt at installing a CORK-II at Site 1254. The ship was then moved to ~48 m at N36°E from Hole 1254A. After the 10-in casing handling equipment was rigged down, the 16-in casing handling equipment was rigged up. A reentry cone, which had been previously assembled for our next site, was moved into the well center on top of the moonpool doors. Two joints of 16-in casing (20 m) plus a 16-in casing cementing shoe were then made up to a 16-in casing hanger, and the assembly was latched into the reentry cone. The jetting BHA was then made up and latched into the 16-in casing hanger. The reentry cone was then picked up off the moonpool doors, and the reentry cone was then lowered to the seafloor. We started washing in the 16-in casing at 2550 hr on 19 October, beginning with Hole 1254B. After it was washed into the seafloor to 20.42 mbsf in 6.5 hr, the casing running tool was released and the drill string was retrieved. Our next step was to drill a 14-in hole into which we could install the 10-in casing. We assembled a drilling BHA with a 14-in bit, lowered it to the seafloor, and reentered Hole 1254B at 2134 hr on 20 October.

The 14-in hole was advanced to 4418 mbrf (231 mbsf) when the upper fault zone was penetrated. As we advanced through the fault, increased fill and torque were encountered. The fault zone had to be reamed and swept clean by circulating sepiolite before the bit could penetrate deeper.

When the bit reached 4452 mbrf (265 mbsf), the hole began to pack off around the drill string. The bit was raised 20 m and then washed and reamed back down to 265 mbsf. We drilled to 4465 mbrf (278 mbsf) when the pipe became stuck. After 3 hr of working the pipe with overpull up to 200,000 lb, the pipe was raised again.

Because of the poor drilling conditions, we decided to conduct a wiper trip. The bit was pulled up to 4289 mbrf (102 mbsf), encountering 80,000 lb of drag from 4453 to 4415 mbrf (266-228 mbsf). It took 6.75 hr to wash and ream back to the bottom of the hole at 4465 mbrf (278 mbsf); 40 m of fill in the bottom of the hole had to be drilled and washed out. With hole conditions deteriorating and no hope of setting casing to the décollement, we decided to install a CORK-II to monitor the upper fault zone.

The bit was pulled up to the 16-in casing shoe at 4210 mbrf (23 mbsf), and then the pipe was lowered back down. The bit encountered resistance (took weight) at 4397 mbrf (210 mbsf) and was washed and reamed from there to 4424 mbrf (237 mbsf). With the bit at the bottom of the hole, we circulated from the bottom up in preparation for setting 10-in casing. Because the 14-in hole extended through the zone of interest, the hole was left full of seawater and no sepiolite mud was used. The bit was pulled out of the hole and was back on the rig floor at 0830 hr on 23 October.

Seventeen joints (197 m) of 10-in casing were then assembled, and a casing hanger was attached to the top. The cementing and casing running tools were latched into the casing hanger, and the entire assembly was lowered to the seafloor. At 1822 hr on 23 October, Hole 1254B was reentered with the 10-in casing string. It appeared that the hole was producing fluid as we observed, as evidenced by a billowing cloud within the reentry cone and water flowing out of the drill pipe at the rig floor between connections.

The casing was lowered to 4360 mbrf (173 mbsf) when it encountered some resistance and began to take weight. At this point, we picked up the top drive to wash the casing in. The cementing manifold was picked up, and the casing was landed at 2045 hr on 23 October. We confirmed that it was latched in and cemented it in place with 20 barrels of 15.8-lb/gal cement. The 10-in casing shoe was at 198.88 mbsf. The casing running tool was released and was back on the rig floor at 0915 hr on 24 October.

Our next operation was to drill out the cement plug and clean out a rathole for the CORK. We assembled a drilling BHA with a 9-in tricone bit, lowered it to the seafloor, and reentered Hole 1254B at 1716 hr on 24 October. After lowering the bit to the casing shoe, it took 1.5 hr to drill through the shoe. The hole was then cleaned to 4424 mbrf (237 mbsf) in preparation for deploying the CORK-II. The hole was then circulated from the bottom up and left with only seawater in it. The drill bit was pulled out of the hole and was back on the rig floor at 0445 hr on 25 October.

After some routine preventative maintenance (slipping and cutting the drill line), we started assembling the CORK-II. A screen, packer, 15 joints of 4-in casing (230 m), umbilical, centralizers, and the wellhead made up the complete CORK-II. The wellhead was lowered to the moonpool doors, where the pressure data logger was tested; it was then lowered into the water to purge the hydraulic lines. At 1445 hr on 25 October, the CORK-II assembly was lowered to the seafloor and Hole 1254B was reentered with the CORK-II at 2050 hr. The 4-in casing was lowered to 4366 mbrf (179 mbsf) when it encountered some resistance and began to take weight. The top drive was picked up so that we could jet the 4-in casing in. The jetting process was hampered as a result of having to maintain the drill string pressure below 400 psi to prevent inflation of the packer.

After ~8 hr of attempting to jet the 4-in casing in with the active heave compensator on at 0745 hr on 26 October, the top joint pin of the 4-in casing failed through the last engaged thread. With the CORK-II wellhead still attached to the running tool, the vessel was offset to observe the reentry cone. At the time of the failure, the end of the pipe was ~10 m above the reentry cone. The broken end of the 4-in casing was extending out of the reentry cone, but otherwise the reentry cone did not appear to have any observable problems. The CORK-II wellhead was retrieved and was back on the rig floor at 1645 hr on 26 October, ending Hole 1254B. The scientists decided to abandon efforts to deploy a borehole installation at this site and decided to move to Site 1255 (proposed Site 1043R).

The Site 1254 beacon was released at 1106 hr and was back on deck at 1221 hr on 26 October. The ship moved the ~1.1 nmi to Site 1255 in dynamic-positioning mode while the CORK-II wellhead was being recovered.

Return to Hole 1254B

After finishing operations at Site 1255, we moved back to Hole 1254B in dynamic-positioning mode to attempt to fish the screen, packer, and 4-in casing that was left in Hole 1254B.

The vessel was positioned over Hole 1254B at 1721 hr on 2 November. A fishing BHA was assembled, consisting of a choker loop formed from wire rope slings, a rig-fabricated jet sub, five 8-in drill collars, one tapered drill collar, and the usual two stands of 5-in drill pipe and a crossover sub.

The fishing tool was lowered to 4157 mbrf, and at 2343 hr on 2 November the 4-in casing was snared. We applied 20,000 lb of overpull to the fish (4-in casing), and it suddenly dropped off. When the snare was set, the end of the wire rope slings was too far below the end of the BHA for us to visually confirm if the fish was still there. Also, the total weight of the casing string being fished was too small to be distinguished on the weight indicator. The vessel was offset 0.5 nmi as the BHA was pulled out of the hole so that if the fish dropped off, it would not land back on the reentry cone. When the fishing BHA was back on the rig floor, the snare was empty and the casing was not recovered. When the ship was positioned back over the hole so that we could inspect the reentry cone with the VIT camera, we observed that the casing was still sticking out of the reentry cone. After the camera was back on deck and all equipment secured we began the transit to Balboa, Panama, at 1600 hr on 3 November. Leg 205 ended with the last line ashore at 1030 hr on 6 November.