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doi:10.2204/iodp.proc.342.104.2014 OperationsAll times shown are local ship time (UTC – 2.5 h). See Table T1 for coring summary. Hole U1403A summary
Hole U1403B summary
DescriptionAfter a 946 nmi transit from Site U1402 at a speed averaging 12.6 kt, the vessel arrived at Site U1403, the first site of the Paleogene Newfoundland sediment drifts project. The local vessel time was advanced 0.5 h during the transit, placing the vessel in the timezone for Newfoundland. The original plan for this site called for drilling three holes to a depth of ~250 m DSF, but the science decision was ultimately to complete operations with two holes: Hole U1403A to 253.3 m DSF and Hole U1403B to 265.1 m DSF. The decision was made to log Hole U1403B; however, the logging attempt failed because the tool became stuck and part of it broke off. Attempts to recover the tool also failed, resulting in loss of time. Hole U1403A coringThe vessel stabilized over Site U1403 at 1708 h on 11 June 2012. The drill pipe was prepared and run to the seafloor. The precision depth recorder–calculated depth for the site was 4957.7 mbsl, and after some consideration, 4952 m drilling depth below rig floor (DRF) was selected as the shoot depth for the first core. Hole U1403A was spudded at 1020 h on 12 June. The mudline core recovered 5.85 m of sediment, and seafloor depth was established at 4955.7 m DRF (4944.3 mbsl). This seafloor depth was later suspected to be ~4 m too high, based on the seafloor depth for Hole U1403B and correlative features found in Hole U1403B. The advanced piston corer (APC) recovered Cores 342-U1403A-1H through 17H, where a hard layer was encountered at ~148 m DSF. Nonmagnetic core barrels were used for APC coring, and orientation was performed on all APC cores with the FlexIT tool. The extended core barrel (XCB) was deployed from Cores 18X through 29X to a final depth of 253.3 m DSF. The seafloor was cleared at 1240 h on 14 June, ending Hole U1403A. Overall core recovery for Hole U1403A was 231.82 m for the 253.3 m interval cored (92% recovery). Hole U1403B coringThe vessel was offset 20 m east, and Hole U1403B was spudded at 1730 h on 14 June. The 3.9 m long mudline core established seafloor depth at 4960.1 m DRF (4948.7 mbsl), which is 4.4 m deeper than recorded in Hole U1403A. This finding, along with other indicators, called into question the accuracy of the mudline core depth calculation in Hole U1403A. Cores 342-U1403B-1H through 16H were recovered using nonmagnetic core barrels, and orientation was performed with the FlexIT tool. The chert layer identified in Hole U1403B was found to be exactly at the depth expected from Hole U1403A data, confirming the initial error in water depth for Hole U1403A. The XCB was deployed for Cores 17X through 18X, until we broke through the chert layers at 150.4 m DSF. The APC coring system was again deployed for Cores 19H through 22H to 175.9 m DSF. After a partial stroke core with a 2.97 m recovery, the XCB was again deployed for Cores 23X through 32X to a final depth of 265.1 m DSF. Overall, core recovery for Hole U1403B was 229.81 m for the 265.1 m cored interval (87% recovery). At the conclusion of coring at 2200 h on 16 June, the hole was swept clean with 30 bbl of high-viscosity mud, and the drill string was pulled from the hole to 78.43 m DSF for logging with the triple combination (triple combo) and Formation MicroScanner-sonic tool strings. At 2215 h, the Schlumberger Engineer began rigging up the logging equipment. The first logging run reached the bottom-hole assembly (BHA) but was unable to exit the BHA. The tools were returned to surface and examined to determine cause, and after making some corrections to the wireline tools, they were again deployed at 0710 h on 17 June. The tool string was run back to the BHA and again failed to pass through. This time the tools became firmly stuck inside the BHA with ~17 m of the tool string extending out from the bit. After working the tools for several hours with no progress, the Kinley crimp was set on the wireline above the tool to prevent the tool from falling out, and the logging line was severed at 1830 h on 17 June using the Kinley cutter. The wireline was retrieved and spooled back onto the winch drum. The drill string was pulled from the hole with a carefully calculated space out, which should have resulted in the bottom of the Schlumberger tool string being at least 5 m above seafloor when the pipe was set down on the dual elevator stool. At 0630 h on 18 June, with ~117 m of the BHA remaining below the rig floor, the end of the Schlumberger wireline was found. The tool string was freed from the BHA and rigged down on the drill floor. It was discovered that the triple combo tool string had parted at the lower (MC) centralizer. This left ~17 m of tools missing from the bottom of the tool string, including the nuclear sources for the density and porosity tools. When the bit cleared the rig floor, inspection revealed manganese nodules lodged between the roller bit cones, along with other typical seafloor sediments. Manganese nodules and surface sediments were also found in the broken end of the MC centralizer on the triple combo. A close examination of the tool failure supports the speculation that when the BHA cleared the rig floor, the high bottom current that we had been experiencing since first coming onto site had caused the BHA to shift with the current while the logging tool string remained in the hole. At this point all parties involved contacted their respective shore counterparts and informed them of the loss of the nuclear sources. Shipboard personnel outlined the limited actions that could be taken toward identifying the location and condition of the sources. The plan included a seafloor camera survey using a 100 m × 100 m search grid centered over Hole U1403B. While the drill string was being tripped toward the seafloor, the subsea camera system and vibration isolation transport (VIT) were readied for deployment. A grapple was attached to the underside of the camera frame, which would have been able to grab the “fish” while the winch, in combination with the drill string, was used to lift the tools toward the surface. The VIT frame is designed not to slide over the bit on the end of the drill string. After tripping the drill string to 3499 m DRF, the rig was secured at 1645 h on 18 June. Installation of the VIT system around the drill pipe in the moonpool, which routinely takes 30 min, proved complicated because of the ocean current pushing the pipe all the way to the side of the lower guide horn, which could therefore not be opened. The ship was eventually powered up, and using a combination of drift and powering down current, we were able to centralize the drill pipe in the moonpool, which allowed us to open the doors. After the VIT was deployed to 100 m DRF, the doors were closed and the upper guide horn was replaced. It took almost 2.5 h to accomplish this task. The camera was run to the bottom while the drill string was tripped to bottom. During the entire camera run, the camera was shaking, vibrating, and rotating around the pipe at different depths. At 2145 h, with the bit ~30 m from seafloor, the signal from the subsea camera was lost. The Mesotech sonar, which is also mounted on the VIT frame, failed as well. While pulling the camera to surface, the winch operator noticed that the effort required to pull the camera frame up was much less than normal for the water depth. Our suspicion that the coaxial cable supporting the camera system had failed was confirmed when the camera cable arrived at the rig floor. At that point there was no option other than to pull the drill string from just above the seafloor and to recover the VIT frame with subsea camera and sonar. Preliminary estimates for the time to repair the camera system were 24–48 h. Siem Offshore and IODP personnel determined that another attempt at a survey, if the camera could be repaired, would very likely result in another failure of the VIT subsea camera system. The impact of the ocean currents on the VIT frame resulted in two failures of the camera and sonar during the first deployment and nearly resulted in the loss of the only reentry system that IODP has available to continue the program. Further attempts could have resulted in the complete loss of our mission-critical reentry system. The decision not to deploy the camera system again at this site also meant that we were unable to locate the lost logging tool or Hole U1403B, which compromised our ability to follow the abandonment guidelines of an irretrievable well-logging source given to us by the onsite Schlumberger engineer. The requirement to immobilize and seal the sources into place with a cement plug was impossible to accomplish because it was impossible to find either the tool string or the hole. The drill string with the damaged VIT was recovered at ~1400 h on 19 June. A total of 2.7 days was spent for the attempt to log. The drill floor was secured at 1415 h, ending Site U1403 and Hole U1403B. The vessel then proceeded under way to Site U1404. |
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inch APC/XCB bit with 136.00 m BHA