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doi:10.2204/iodp.proc.345.113.2014 Hole U1415P1K.M. Gillis, J.E. Snow, A. Klaus, G. Guerin, N. Abe, N. Akizawa, G. Ceuleneer, M.J. Cheadle, Á. Adrião, K. Faak, T.J. Falloon, S.A. Friedman, M.M. Godard, Y. Harigane, A.J. Horst, T. Hoshide, B. Ildefonse, M.M. Jean, B.E. John, J.H. Koepke, S. Machi, J. Maeda, N.E. Marks, A.M. McCaig, R. Meyer, A. Morris, T. Nozaka, M. Python, A. Saha, and R.P. Wintsch2OperationsIntegrated Ocean Drilling Program (IODP) Hole U1415P was sited on the southern margin of a small promontory between Holes U1415G and U1415O (see Fig. F8 in the “Expedition 345 summary” chapter [Gillis et al., 2014b]). From the outset, Hole U1415P was established as a reentry hole and was intended to be a nested free-fall funnel (FFF) configuration with casing similar to that in Hole U1415J. However, after deployment the initial FFF cone tipped over and could not be used. Instead, we were able to successfully reenter the bare hole and installed a FFF with 12.5 m of 10¾ inch casing. The primary accomplishment in Hole U1415P was rotary core barrel (RCB) coring that extended from 12.5 to 107.9 meters below seafloor (mbsf) and recovered 30.57 m of gabbroic rock (32% recovery). In addition, material was recovered in five ghost cores obtained during hole cleaning operations in previously drilled portions of the hole. Hole operations are summarized in Table T1 and outlined below. All times are ship local time (UTC – 7 h). Drilling operationsAfter conducting a visual survey and selecting the position for Hole U1415P, we recovered the camera system, installed the top drive, spaced out the drill string, and started Hole U1415P at 1255 h on 26 January 2013. The 14¾ inch bit was washed without rotating to 2.0 mbsf (4866.0 meters below rig floor [mbrf]), and drilling proceeded to 11.0 mbsf (4875.0 mbrf). We then assembled a hard rock recovery system–style FFF cone. The 26 inch interior diameter of this cone was reduced to 16 inches by attaching portions of a CORK fishing tool funnel. In contrast to our previous FFF cone deployments, this time we attached a base plate to the bottom of the FFF. After the FFF cone was deployed to the seafloor, we continued drilling the hole to 12.5 mbsf. The camera was deployed to observe the orientation of the FFF cone and the bit pulling out of it. However, the FFF was very difficult to see through clouds of sediment. Eventually, we decided not to wait and pulled the bit out of the hole and through the FFF cone at 1545 h on 27 January. The bit appeared to heave down on the cone at least twice in the process. The bit was back on the rig floor at 0105 h on 28 January. We assembled 12.5 m of 10¾ inch casing and hung it off on the moonpool doors. Next, we assembled a RCB bottom-hole assembly (BHA) and lowered it through the casing in the moonpool to the seafloor. The camera system was also deployed to the seafloor. Before we prepared to locate and reenter Hole U1415P, we had to slip and cut the drill line for the fourth time during this expedition. After installing the top drive and spacing out for reentry, it was immediately apparent that the FFF cone was not sitting upright. Some camera perspectives looked as if the FFF cone was leaning to one side, whereas in other perspectives it appeared to be lying fully on its side. At the base of the FFF cone was a dark spot that appeared to be the top of the hole. Discussions alternated between attempting to reenter the cone or the hole. Eventually the pipe was maneuvered close enough to take a stab at cone reentry. The cone was indeed lying on its side at too high an angle for reentry, and this attempt failed. We then moved the bit over the dark area at the base of the FFF cone and successfully reentered Hole U1415P at 1450 h on 28 January. The total time expended after starting to search for the FFF cone was 2.6 h. The reentry of the bit into the open 14¾ inch hole with >4800 m (3.0 miles) of drill string deployed was quite an impressive feat achieved by the dynamic positioning system and drilling staff. The camera system was recovered, and the hole was redrilled from 8.0 to 12.5 mbsf and swept with high-viscosity mud. The core barrel used during washing and reaming this interval (Core 345-U1415P-2G) was recovered with 2.36 m of rubble. Our next step was to assemble a FFF cone to the 12.5 m of 10¾ inch casing hung off in the moonpool. We free-fall deployed the 10¾ inch casing with the attached FFF and dropped a core barrel to start coring ahead. The driller could not identify the normal pressure spike that occurs when the core barrel has landed at the bottom of the BHA. When the pump pressure was increased to confirm the core barrel had landed properly, the rotary hose that supplies drilling fluid to the top drive suddenly burst. The hose failed on the top drive connection at 2400 psi even though the hose is rated to 5000 psi working pressure. After we installed a new hose, we reached the bottom of the hole (12.5 mbsf) at 0500 h on 29 January. We started RCB coring, and Core 3R (12.5–18.1 mbsf) arrived on deck at 1225 h. We had some difficulty getting the bit through the depth where the hole diameter changed from 14¾ inch to 9⅞ inch, but we were able to drill out this area (Core 4G; 12.5–16.5 mbsf). RCB coring resumed, and Cores 5R–10R extended the hole from 18.1 to 45.6 mbsf and recovered 12.19 m (44% recovery) of nicely cored pieces of gabbro. Core 11R was cut in only 45 min of rotating time. RCB coring continued to Core 18R, extending to 82.3 mbsf and recovered on deck at 0920 on 1 February. As the hole was deepened, we experienced faster coring rates through a formation inferred to be more fractured, leading to increasingly difficult hole cleaning. Eventually, we decided to pull out of the hole for a bit change because of increasing bit hours, decreasing recovery, and extended periods of washing/reaming back to bottom after recovering core barrels. We pulled the bit out of the hole, and the bit was back on the rig floor at 1845 h on 1 February. After assembling a new C-7 RCB bit, we lowered the drill string, deployed the camera system, installed the top drive, and spaced out the drill string for reentry by 0530 h on 2 February. We reentered Hole U1415P at 0553 h on 2 February. During reentry, we confirmed the top of the FFF cone was at 4862.5 mbrf. The height of the FFF from base plate to rim is 1.2 m, placing the base of the FFF at 4863.7 mbrf. The seafloor tag depth was determined to be 4864.0 mbrf on 26 January at slack tide. The FFF depth was established on 2 February when the tide tables indicated a high tide of 0.2 m. Therefore, the FFF appears to be installed right at the seafloor (4863.9 m versus 4864.0 m). We washed and reamed to the bottom of the hole (82.3 mbsf) slowly to clean out the hole in small increments as opposed to loading up the annulus with large amounts of fill/cuttings and then having to wash these out all at once. After we finished washing and reaming to the bottom of the hole (82.3 mbsf), we recovered the core barrel used during this hole cleaning (Core 19G; 0.6 m recovered) at 1920 h. We resumed RCB coring, and Core 20R was cut from 82.3 to 89.4 mbsf. Before retrieving Core 20R, the hole had to be washed and cleaned enough to attempt making a connection. At the time, several bit nozzles also appeared to be plugged. At 0030 h on 3 February, we were able to remove a drilling knobby so that Core 20R could be recovered (0130 h) with 2.42 m of nicely cored gabbro. A new core barrel was deployed, and the drillers were able to partially unplug the bit nozzles. Before coring could resume, the hole had to be washed and reamed from 79.0 to 89.4 mbsf. At 0900 h, the core barrel deployed during this reaming was retrieved (Core 21G). We had to wash and ream back to the bottom of the hole again but then continued coring from there. Cores 22R and 23R were recovered from 89.4 to 107.9 mbsf and recovered 4.87 m (26% recovery). After retrieving Core 23R, hole conditions began deteriorating, with the hole packing off and the bit taking weight ~9 m above the bottom of the hole. As we had just added a joint of pipe and the bit was unable to pass below this depth, we had to offset the ship 100 m to reach a connection so that the driller could pull up and lay out the same piece of pipe. At this point, we raised the bit to 76.0 mbsf, resumed hole cleaning, reamed back to the bottom of the hole (107.9 mbsf), and recovered the core barrel used during the reaming (Core 24G). Once again, the hole packed off and circulation and rotation were lost while making the connection after laying out the barrel, so we offset the ship 100 m (2% of water depth) to reach a connection in order to remove more drill pipe. We raised the bit to 79.0 mbsf and started to work the bit back down. However, after making another connection the bit could not be advanced further because of high torque, packing-off, and plugged nozzles. Ultimately, we decided to stop trying to core and to conduct a wiper trip to prepare the hole for logging. To prepare for logging, we raised the bit to 11.9 mbsf (inside the 10¾ inch casing) and then lowered it back down the hole. Problems were encountered at 41, 55–60, and 84–90 mbsf that had to be drilled through. We elected not to attempt to clean out the ~18 m of hard fill in the bottom of the hole. At 1215 h on 4 February, the bit was back up to 11.9 mbsf (inside the casing). We deployed the camera and pulled the bit clear of the hole at 1434 h. At 1449 h on 4 February, we observed the bit successfully release from the BHA. The end of pipe reentered Hole U1415P at 1550 h after only 15 min of maneuvering. We recovered the camera, placed the end of pipe at 10 mbsf, and lowered the first logging string into the hole (caliper and Dipole Sonic Imager). We had decided to deploy a very short logging string because of the poor hole conditions and risk of the tools getting stuck. The logging tool string could not pass 24 mbsf (11.5 m below the 10¾ inch casing shoe). The logging tools were retrieved so that the end of pipe could be lowered past the trouble area. However, the end of the drill pipe could not be lowered past 20 mbsf (7.5 m below the casing shoe), so we terminated our logging. We pulled the bit out of the hole at 0315 h on 5 February. RCB coring in Hole U1415P extended from 12.5 to 107.9 mbsf and recovered 30.57 m (32% recovery) of gabbroic rock. In addition, five cores were recovered from previously drilled portions of the hole during the hole cleaning operations. Because there was not sufficient time remaining to conduct any further drilling operations, as we had dropped the bit for logging, we deployed the camera and 3.5 kHz pinger to conduct a final seafloor survey across Hole U1415P (see Table T1 and Fig. F3 in the “Bench site survey” chapter [Gillis et al., 2014a]). The survey was completed at 0845 h on 5 February. Although the drill string was back on board at 1745 h, the beacon retrieved at 1838 h, and the hydrophones raised by 1900 h on 5 February, we delayed our departure until 2000 h on 5 February so that inductively coupled plasma–atomic emission spectroscopy geochemical analyses that are sensitive to ship motion could be completed. After we raised the thrusters, we started our transit to Balboa, Panama, at 2048 h, about a half day ahead of the scheduled departure time. During the transit, ship local time was shifted ahead 1 h on 7 February (to UTC – 6) and 1 h on 9 February (to UTC – 5). The ~1467 nmi transit from Hess Deep to Balboa took 6.5 days at 9.3 nmi/h. Expedition 345 ended with the first line ashore at 1151 h on 12 February 2013. |
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