OPERATIONS

Leg 205 was originally scheduled to begin in San Diego, California, on 6 September 2002. Because of the threat of a dockworker strike in the western United States, the port call was changed to Victoria, Canada. As a result, the start of the Victoria port call changed to 2 September.

Leg 205 officially began with the first line ashore at 0900 hr 2 September. A number of changes resulted from the short time between the decision to change the port call and the start of the port call: (1) the Ocean Drilling Program (ODP) technical staff crossover occurred on 4 September; (2) the Transocean staff crossover took place on 6 September; and (3) the Leg 205 science party boarded the ship on 17 September in Acapulco, Mexico, during the transit from Victoria to proposed Site 1039R-A.

Prior to the loading of the Leg 205 supplies, a substantial amount of equipment used to support the Leg 204 gas hydrate objectives had to be taken off the ship. Pressurized gas hydrate samples, gas hydrate samples immersed in liquid nitrogen, and 340 boxes of core samples were off-loaded. A 20-ft refrigerated van used for processing and storing the gas hydrate samples on board was also removed from the ship. A number of special coring tools and special laboratory equipment for gas hydrate research also were off-loaded.

Immediately upon arrival in Victoria, 1095 metric tons of marine gas oil was taken on board and we started to load 60 metric tons of barite and 80 metric tons of sepiolite. After the food for Leg 205 was loaded, the following equipment was loaded: (1) seven joints of 16-in casing, (2) 30 joints of 10-in casing, (3) 139 joints of 4-in casing, (4) a new spool of core winch wire, (5) four standard reentry cones, (6) four CORK-II wellheads and associated instruments, (7) four 16-in casing hangers, (8) two 10-in casing hangers, (9) a new bicentered hole opener, and (10) other miscellaneous hardware.

An essential element of the long-term geochemical observatories to be installed during the leg was the downhole water, gas, pressure, and temperature sampling/monitoring equipment. During the port call, six downhole OsmoSamplers were assembled and stored in a water bath in the downhole measurements laboratory so that they would be completely prepared for deployment later in the leg. During assembly, temperature sensors were placed inside the OsmoSamplers. The pressure meters and data logger units were checked out and programmed in preparation for deployment.

At the request of the port authority, starting on 4 September, loading operations had to be suspended at 1700 hr each day for noise abatement. The ship left Victoria at 0754 hr on 7 September and began the transit to Acapulco to pick up the Leg 205 science party.

Because of Leg 204 operations continuing to the last possible minute and a very short (39 hr) transit to Victoria, Leg 204 personnel had only minimal time for the routine end-of-leg maintenance of the drilling equipment; much of this activity took place during the transit. In addition, the new core winch wireline was installed and some minor plumbing runs associated with the CORK-II wellheads were made during the transit.

Calm seas were encountered during the initial portion of the transit. On 15 September, however, the vessel began passing through the edge of a tropical depression (36- to 42-nmi/hr winds and 20-ft seas) which reduced the ship's speed. The weather moderated during the day of 16 September, and moderate seas were encountered for the rest of the transit to Acapulco.

The transit ended with the first line ashore at 1030 hr on 17 September in Acapulco. The total transit was 2636 nmi and took 239.4 hr at an average speed of 11.0 nmi/hr.

The primary objective of the brief Acapulco port call was to board the Leg 205 scientists and load a few pieces of equipment that were essential for Leg 205 operations but did not make the Victoria port call. This included two 10-in casing hangers and the 32-in vibration-isolated television (VIT) camera guide sleeve.

Because the weather forecast for the transit to Site 1253 (proposed Site 1039R-A) did not look favorable for using the cranes while under way, we decided to assemble the Site 1253 reentry cone while in port. Work on the reentry cone began at 1200 hr. By 1700 hr the reentry cone had been bolted together and tack welded enough to make it secure for the transit, and a pilot was requested for departure. During this time, a required safety briefing on the vessel's survival gear was given to the science party. In addition, we also took advantage of the fact that the vessel was moored with the starboard side to the dock and lowered lifeboats 2 and 4 to the water and started their engines. With all tasks completed in Acapulco, the last line was released at 1738 hr on 17 September and we began the transit to Site 1253.

The final welding of the reentry cone was completed (at 0600 hr on 18 September; all times given are local ship time which was Universal Time Coordinated [UTC] - 5 hr) during the transit to Site 1253. We also held additional safety meetings, introduced key Transocean personnel and the ODP operations manger to the science party, and gave science party members tours of the ship to familiarize them with the vessel.

At 1053 hr on 19 September, we changed course toward shore to disembark one of the ship's stewards because of a family emergency. At 1830 hr on 19 September, the vessel was positioned just off the south breakwater at Puerto Madero, Mexico. A small fishing boat arrived from Puerto Madero and took the steward to shore. At 1845 hr, the vessel resumed the transit to Site 1253.

At 1400 hr on 21 September, the vessel arrived at Site 1253.

The thrusters were lowered and the vessel was placed in dynamic-positioning mode at 1431 hr on September 21, and we deployed a seafloor positioning beacon at 1620 hr. The upper guide horn was then laid out and the reentry cone moved to the center of the moonpool doors. Drill collars were picked up for the bottom-hole assembly (BHA), assembled, and stored in the derrick. Three joints of 16-in casing (42.5 m) were assembled, and a 16-in casing hanger was made up to the casing string. The casing running tool was then attached to the casing string, and the casing string was lowered into the reentry cone until the casing hanger latched into the reentry cone. The weight of the reentry cone was picked up to verify it had latched properly. We then released the casing running tool and pulled out of the reentry cone. A visual inspection confirmed that the casing hanger latch ring was properly seated in the reentry cone landing ring latch ring groove.

The next step was to attach a 14-in tricone bit to the stinger below the casing running tool. The rest of the BHA was then made up and lowered into the reentry cone until the running tool landed. The running tool was latched into the 16-in casing hanger, and the entire assembly (16-in casing, reentry cone, and BHA) was picked up off the moonpool doors. The moonpool doors were opened, and at 2100 hr on 21 September, the reentry cone was lowered below the keel. The moonpool doors were then closed, and the pipe trip to the seafloor began.

At 0745 hr on 22 September, with the 16-in casing shoe and bit near the seafloor, the jetting-in process began, initiating Hole 1253A. At 0945 hr, the reentry cone mud skirt landed on the seafloor and the running tool was released. This was verified using the VIT camera system. The seafloor depth was determined to be 4387.1 meters below rig floor (mbrf) (4376.3 meters below sea level [mbsl]), and the bottom of the 16-in casing shoe was at 43.82 mbsf. We then retrieved the drill string in preparation to assemble an RCB BHA.

After installing the reentry cone and 16-in casing, we assembled an RCB BHA with a 9-in bit and bit release. The bit was lowered to the seafloor, and Hole 1253A was reentered at 0555 hr 23 September. We then drilled ahead without coring from 4431.0 to 4444.0 mbrf (43.8 to 56.8 mbsf), where a DVTPP measurement was taken. The temperature and pressure data appeared to indicate that the tool moved while in the formation.

When the DVTPP was recovered, the colletted delivery system (CDS) was jammed with rust and sediment. This created a seal inside the upper barrel above the collets, trapping pressure inside the barrel. A vent hole was drilled in the upper barrel to prevent this from recurring, and the CDS was cleaned up and redressed with a new set of collets. After stroking the tool to verify performance, the CDS was set aside for use at a later time.

We continued to drill ahead without coring from 4444.0 to 4537.2 mbrf (56.8 to 150 mbsf) when the DVTPP was deployed a second time. Unfortunately, this run of the DVTPP also experienced tool movement while in the formation, resulting in poor data. A review of the tool and deployment procedures is under way.

We then drilled ahead without coring to 4757.1 mbrf (369.9 mbsf), where we started RCB coring. Cores 205-1253A-1R through 4R, consisting of nannofossil chalk and claystone, were taken from 4757.1 to 4787.6 mbrf (369.9 to 400.5 mbsf). The rate of penetration (ROP) in the sediments was 23 m/hr, and we had a core recovery of 73%.

Cores 205-1253A-5R through 9R were cut from 4787.6 to 4817.0 mbrf (400.5 to 429.9 mbsf) in a very dense and hard gabbro sill. The ROP in the gabbro was 1.7 m/hr, and core recovery was 70.3%. Another change in the drilling occurred when we encountered sediments in Cores 205-1253A-10R through 13R. The ROP was 18.2 m/hr, and core recovery dropped to 17%.

We encountered more gabbro in Cores 205-1253A-14R through 28R from 4817.0 to 4916.0 mbrf (429.9 to 528.9 mbsf). A few thin sediment layers were present in the gabbro, but these were only minimally recovered. The ROP dropped to 1.4 m/hr, and core recovery rate was 50%. At the end of cutting Core 205-1253A-25R, a small amount of erratic torque in the drill string was observed. With 53.2 total rotating hours on the bit, 45.2 hr of which was in hard rock, the decision was made to trip the drill string for a bit change. The bit cleared the seafloor at 1950 hr on 27 September. During the trip out of the hole, tight spots were noted at 4816, 4734, and 4647 mbrf. The bit cleared the rig floor at 0245 hr on 28 September. The used drill bit was in good condition but was slightly reduced in gauge.

A new 9-in RCB bit was made up to the BHA. Because of the length of time drilling in hard rock, the mechanical bit released was also replaced. The BHA was spaced out for the RCB and lowered to the seafloor.

Hole 1253A was reentered at 1108 hr on 28 September. The bit was lowered into the hole to 4816 mbrf (429 mbsf), where excessive drag was encountered. We picked up the top drive and washed/reamed from there to the bottom of the hole at 4903.1 mbrf (516 mbsf). Once the 32 m of fill in the bottom of the hole was cleaned out, we resumed RCB coring.

After the bit change, we continued RCB coring from 4903.1 to a total depth of 4987.1 mbrf (515.9 to 600.0 mbsf) and recovered 59.6 m (71%). The penetration rate through this hard gabbro section was only 1 m/hr. The lowermost 6 m of the hole appeared to have numerous ledges and may be deviated. Because of the slow penetration rate and no clear indication that we were close to the bottom of the gabbro, we decided to stop coring.

Next, we circulated 30 barrels of sepiolite to clean out the hole and made a wiper trip in preparation for logging. While the pipe was lowered back to bottom during the wiper trip, an obstruction was encountered at 4920 mbsf (533 mbsf). The top drive was picked back up and used to rotate and wash to the bottom of the hole. Several ledges were reamed on the way back to total depth. Torque in the bottom 6 m of the hole led us to speculate that this section may be deviated. As this section is so close to the bottom of the hole, there was no way to confirm this with a survey.

After 2 m of fill in the hole was washed out, 30 barrels of sepiolite was circulated to ensure that all the debris was washed out of the hole. Then, in preparation for logging, the entire borehole volume was displaced with 185 barrels of sepiolite. The bit was pulled out of the hole, and the ship was offset 50 m north to drop the bit on the seafloor. At 2308 hr on 2 October, the pipe reentered Hole 1253A and the end of the pipe was positioned at the 16-in casing shoe at 4431 mbrf (44 mbsf).

The logging equipment was rigged up, and the triple combo tool string was lowered into the hole. The tools would not penetrate past a bridge at 4537 mbrf (150 mbsf). Because the upper sediment section had been logged previously during ODP Leg 170 and our primary logging objective was the deeper part of the section, we decided to postpone logging until after we set the 10-in casing into the top of the first sill.

We retrieved the drill string, and the bottom of the BHA was back on the rig floor at 1615 hr on 3 October. To prepare for the installation of the 10-in casing, we needed to widen the 9-in hole to 14 in. We attached a 14-in reaming bit to the BHA, lowered it to the seafloor, and reentered Hole 1253A at 0044 hr on 4 October. We then drilled (without coring) from the 16-in casing shoe (4431 mbrf; 44 mbsf) to 23 m into the top of the upper gabbro (4810 mbrf; 422.8 mbsf). To make sure the hole was in the best condition possible to install the 10-in casing, the entire borehole volume was circulated two times, a wiper trip was made (without any significant hole problems), the borehole volume was circulated again, and then the hole was filled with sepiolite. The 14-in reaming bit was then pulled out of the hole; it reached the rig floor at 1345 hr on 5 October.

After assembling 30 joints of 10-in casing (411 m) and a cementing shoe, we lowered it to the seafloor and reentered Hole 1253A at 0210 hr on 6 October. We picked up the top drive with a cementing manifold and landed the 10-in casing hanger in the reentry cone at 0445 hr on 6 October. The casing was cemented in place with 40 barrels of cement (15.8 lb/gal). The cementing was completed at 0650 hr, the casing running tool was released, the cementing manifold was laid out, the top drive was racked back, and the drill string was pulled out of the hole. The camera system was recovered while the pipe was pulled out of the hole, and the drill string was back on the rig floor at 1530 hr on 6 October.

Our next step was to drill out the cement plug at the bottom of the casing as well as clean out the hole to total depth (600 mbsf) in preparation for logging and installing the CORK-II. We assembled the BHA with a tricone bit (Reed HP21 9-in mill tooth), ran it down to the seafloor, and reentered the hole at 0011 hr on 7 October. The top of the cement was encountered at 4795 mbrf (407.8 mbsf), which is ~5 m above the bottom of the 10-in casing shoe.

The cementing plug and cement inside the casing were drilled out in 45 min, and then the hole was cleaned to 4987.1 mbrf (600.0 mbsf). The hole was swept clean with 30 barrels of sepiolite, and we started a wiper trip by raising the bit up to the 10-in shoe. On the way back down to 600 mbsf, 20,000 lb of weight was taken at 4976 mbrf (588.8 mbsf), so we rotated and washed the hole from there to total depth. We found 7 m of fill in the bottom of the hole. The hole was swept again with 50 barrels of sepiolite and then displaced with 60 barrels of sepiolite in preparation for logging.

Before we could log, we had to drop the bit on the seafloor. The bit was pulled clear of the reentry cone at 1630 hr on 7 October, and the vessel was offset 50 m north. The rotary shifting tool (RST) was deployed on wireline to release the bit. The mechanical bit release (MBR) shifted smoothly; however, the bit did not drop off. The RST was picked up and then dropped on top of the MBR support bearing, knocking the bit free at 1840 hr.

We reentered Hole 1253 (at 2027 hr), positioned the bottom of the pipe near the 10-in casing shoe at 4798 mbrf (410.8 mbsf), racked back the top drive, and started to rig up for logging. After assembling the triple combo tool string and lowering it into the hole to 4917 mbrf (530 mbsf), we lost communication with the tool and it had to be pulled out of the hole. The Hostile Environment Litho-Density Sonde was leaking oil; it was replaced with the Hostile Environment Litho-Density Tool. The reconfigured triple combo tool string was lowered down the drill string until it landed on a bridge at 4917 mbrf (530 mbsf). The tools could not be worked past the bridge, so the hole was logged from that point up to the seafloor and then pulled out of the hole.

The FMS-sonic velocity tool string was assembled and lowered into the hole until it landed on a bridge at 4917 mbrf (530 mbsf). The tools would not pass the bridge, and we logged from there up to the 10-in casing shoe (4798 mbrf; 411 mbsf). The FMS was lowered for a second pass, and this time it passed through the bridge at 4917 mbrf, coming to rest on another bridge at 4951 mbrf (564 mbsf). We logged from that point up to the 10-in casing shoe and then pulled the tools out of the hole. Once we had disassembled the logging tools, we pulled the drill string out of the hole, clearing the reentry cone at 2215 hr on 8 October. After the bottom of the pipe was back on the rig floor (0515 hr on 9 October), the drill line was slipped and cut.

The next operational step at Hole 1253A was to deploy the CORK-II observatory. After preparing the rig floor and all the tools required, the 4-in casing screen was picked up and hung off at the rotary table. A latch nipple for landing/latching the OsmoSampler inside the casing was attached to the screen. To the top of the screen, we attached one full joint of 4-in casing, one 2-m-long piece of 4-in casing, and one 3-m-long piece of 4-in casing. The screen was lowered into the moonpool, where the flat umbilical was connected to the two -in pressure monitoring hydraulic lines extending from the top of the screen. The screen was then lowered through the moonpool as the umbilical was strapped to the 4-in casing.

A CORK-II inflatable packer was picked up next and attached to the top of the 4-in casing. The packer was lowered into the moonpool, where the umbilical was severed and connected to the two -in pressure monitoring hydraulic pass-through lines extending from the bottom of the packer. The packer was then lowered through the moonpool, and the umbilical was connected to the two -in pressure monitoring hydraulic pass-through lines extending from the top of the packer.

We then attached 33 joints of 4-in casing, one 2-m-long piece of 4-in casing, and one 3-m-long piece of 4-in casing (467.44 m total length) to the top of the packer. The umbilical was strapped to the 4-in casing and centralizers attached to the casing as the screen/packer subassembly was lowered through the moonpool.

During deployment of the 4-in casing string and umbilical, at ~16 m above the packer, one of the three umbilical -in hydraulic lines was severed and split out of the umbilical. A -in pressure monitoring line termination screen was connected to the split-out umbilical hydraulic line. The termination screen will be used to monitor the pressure above the packer and below the 10-in casing shoe. The termination screen was banded to the 4-in casing, and centralizers were positioned at the top and bottom of the termination screen to protect it.

The CORK-II running tool was latched onto the CORK-II wellhead. The wellhead was then picked up and made up to the top of the 4-in casing string. The wellhead was lowered into the moonpool where the umbilical was severed and connected to the bottom of the wellhead. The packer setting hose was made up between the CORK-II running tool and the top of the wellhead, completing the assembly.

All of the sampling valves and bleed valves on the wellhead were opened, and the wellhead was lowered into the water to purge the hydraulic lines of air. The -in hydraulic lines connecting the pressure meter control valves to the pressure meters were filled with water before the wellhead was picked up. The wellhead was raised back to the moonpool level, where all valves were closed. Large rubber bands were then attached to the individual valve handles such that they would hold the valves in the closed position during the deployment. This was done to prevent the valves from partially opening during the deployment as happened with the ACORK valves deployed during Leg 196. With all hydraulic lines purged, all valves closed, and a last-minute inspection of the wellhead completed, the CORK-II assembly was lowered to the seafloor.

Hole 1253A was reentered at 0320 hr on 10 October. The 4-in casing screen shoe was lowered to 4874 mbrf (487 mbsf), where we picked up the top drive and lowered the wireline sinker bar assembly into the hole for a sounding run. The wireline sinker bar assembly reached 4915 mbrf (527.8 mbsf), which was 7 m below the OsmoSampler sinker bar's final position.

The lower weak link (900 lb) was made up to the top of the OsmoSampler sinker bar. This subassembly was then picked up and landed in the top of the drill string. The upper OsmoSampler was attached to the latch/running tool subassembly with 4.88 m of -in braided nylon rope. The upper weak link (1500 lb) was attached to the bottom of the upper OsmoSampler followed by 13.4 m of -in braided nylon rope. The lower OsmoSampler was then attached to the rope.

The Hole 1253A OsmoSampler subassembly (23.61 m overall length) was picked up, and the bottom of the lower OsmoSampler was connected to the lower weak link on top of the sinker bar that hung off in the drill pipe. The entire assembly (27.31 m overall length) was then lowered down the drill string until the latch/running tool subassembly landed on the drill string. The wireline sinker bar assembly was made up to the latch/running tool subassembly, and then the entire assembly was slowly lowered down the drill string in steps to prevent differential pressure from damaging the osmotic pumps.

The OsmoSampler assembly was lowered until the latch/running tool subassembly landed in the latch nipple on top of the 4-in casing screen. The latch/running tool was jarred down on to set and lock the latch (lock mandrel) in the latch nipple. A 3000 lb overpull with the wireline confirmed that the latch was locked in place. The latch/running tool was then jarred up on, shearing the running tool release pin and releasing the running tool from the latch at 1110 hr on 10 October. The running tool and wireline were then pulled out of the hole.

The packer setting go-devil was then dropped down the inside of the drill string. The CORK-II wellhead was then lowered into the hole until it landed and latched into the reentry cone. A 5000 lb overpull with the drill string confirmed that the wellhead was latched into the reentry cone.

The drill string was pressured up to 800 psi and held for 30 min to set the packer. While the drill string was being pressurized, the pressure gauge fluctuated once as if there was a sudden small change in volume. Also, occasionally while holding the 800-psi pressure, the pump had to be engaged at 2-3 strokes per minute to maintain the pressure. After 30 min, the drill string pressure was increased to 1800 psi and held for 10 min to activate the spool valves (to connect the pressure sensors in the wellhead to the downhole screens). Finally, all of the drill string pressure was bled off through the rig floor standpipe manifold relief valve.

The final step was to install the remotely operated vehicle platform around the wellhead on top of the reentry cone. The landing platform and deployment bridle were assembled in the moonpool and then lowered down the drill string to the reentry cone on the logging line. After landing the platform on top of the reentry cone, the deployment bridle acoustic releases were activated at 2245 hr on 10 October. The logging line was raised, and the weight indicator showed a reduction in weight of 800 lb, confirming that the platform had been released. The logging line and platform deployment bridle were then pulled out of the hole.

We then deployed the camera system to visually inspect the installation. No problems were observed during the visual inspection, so the CORK-II running tool was released from the wellhead at 0050 hr on 11 October.

The wireline sinker bar assembly was deployed to recover the packer setting go-devil to prevent having to retrieve the drill string when it was full of water. However, the go-devil was encountered at 400 mbrf instead of down near the seafloor at the CORK-II running tool, where it should have been. It took 1.5 hr and jarring with 8000 lb of overpull to recover the go-devil. When it was recovered, the go-devil seals were missing. The top drive was racked back, and the drill string and camera system were pulled out of the hole. The CORK-II running tool cleared the rig floor at 0945 hr on 11 October (Table T1).

While the drill string was being retrieved, the ship moved in dynamic-positioning mode to Site 1254 (1.1 nmi). The beacon from Site 1253 was recovered at 0430 hr on 11 October and redeployed at 0945 hr on 11 October in Hole 1254A.

The Site 1253 CORK-II was visited by Alvin ~1 month following installation. This visit confirmed that despite the failure of the go-devil, the CORK-II installation had been successful and was property functioning. For details of the Alvin dive and videos of the CORK-II, see "Postcruise Alvin Submersible Visit to Site 1253 and 1255 CORK-IIs" in the "Leg 205 Summary" chapter.