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doi:10.2204/iodp.proc.345.110.2014 Hole U1415J1K.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 U1415J was sited in close proximity to Hole U1415I (see F8 in the “Expedition 345 summary” chapter [Gillis et al., 2014b]) because of the scientific significance of the layered series recovered at the bottom of Hole U1415I. From the beginning, Hole U1415J was established as a reentry hole in a nested free-fall funnel (FFF) configuration with casing (Fig. F1). Hole operations are summarized in Table T1 and outlined below. All times are ship local time (UTC – 7 h). Drilling operationsAfter our last operation in Hole U1415I, a failed attempt to reenter the hole with a 14¾ inch tri-cone bit, we offset the ship 10 m north, verified that the seafloor was free of any boulders, and observed the bit tag the seafloor at 4850.0 meters below rig floor (mbrf). After we recovered the camera system, Hole U1415J was spudded at 1855 h on 31 December 2012 using a 14¾ inch tri-cone bit. Drilling proceeded at ~1.2 m/h from 0 to 7 meters below seafloor (mbsf) and then slowed to ~0.6 m/h until total depth of 4865 mbrf (15 mbsf). After three wiper trips to clean the hole, we assembled a FFF around the drill string in the moonpool. The base of the FFF had an opening of 16 inches, and we did not attach a casing stinger below the FFF. We dropped the FFF, and the drill string began taking weight soon after the FFF was deployed. We then spent 11.25 h washing and reaming the bottom 10 m of the hole. After one last wiper trip, the drill string and the 14¾ inch bit were recovered to the rig floor at 1400 h on 2 January 2013. A 15 m string of 10¾ inch casing was made up and hung off the moonpool doors for free-fall deployment. A new 9⅞ inch rotary core barrel (RCB) bottom-hole assembly (BHA) was made up and lowered through the casing to the seafloor for reentry. The 16 inch FFF was found buried upright in the cuttings pile of Hole U1415J; only the upper parts of the rim and deployment shackles were visible. The FFF was reentered at 0420 h on 3 January and the camera system was retrieved. The drill string began taking weight at 9 mbsf and was easily washed down one more meter to 10 mbsf. The cone of a FFF was assembled around the drill string in the moonpool and connected to the cut-off joint of the 10¾ inch casing that had been previously hung off in the moonpool. The total length of the casing was 15.0 m from the cone base to the end of the casing shoe. The assembly was free-fall deployed at 0730 h on 3 January. The hole was washed and reamed to total depth (15 mbsf) and circulated clean with two 25 bbl mud sweeps. Ghost Core 345-U1415J-2G, containing 0.2 m of rock fragments and two buckets-full of coarse sand interpreted to be drill cuttings was recovered from the cleaned interval at 1045 h on 3 January. We resumed RCB coring and Cores 3R through 5R were retrieved from 15.0 to 34.9 mbsf. Hole problems required washing and reaming at ~32 and 34.9 mbsf, during which ghost Cores 6G and 7G were recovered by 0200 h on 5 January. Another fresh core barrel was dropped, and on this attempt the bit made it easily to total depth (34.9 mbsf), and RCB coring resumed. The hole drilled smoothly, and Core 8R was recovered from 34.9 to 45.2 mbsf at 0805 h. During retrieval, the area between 4878 and 4882 mbrf (28 and 32 mbsf) remained problematic and was once again reamed and conditioned multiple times. RCB coring resumed at 0900 h, and Core 9R was cut from 45.2 to 55.3 mbsf and arrived on deck at 1355 h on 5 January. Coring continued through Core 13R, which extended the hole to 79.4 mbsf. A wiper trip was conducted, and the bit was raised to 6.5 mbsf without encountering any problems. The bit was then lowered back into the hole and took weight at ~37 mbsf. The driller was able to wash and ream to 45 mbsf. The bit was lowered and encountered weight again at 57 mbsf. The driller washed and reamed the hole to total depth at 79.4 mbsf. The bit was raised off the bottom of the hole and became stuck at 72 mbsf with high circulation pressure, no rotation, and no ability to move the bit up or down. The pipe was worked for 2.5 h before it was pulled free with 100 klb overpull. The bit was pulled up to 6 mbsf inside the 10¾ inch casing. The core barrel that was in place during this wiper trip was recovered (Core 14G), and a new core barrel was dropped. We decided to use cement to help stabilize the hole. However, we had not yet observed the nested FFFs and therefore did not know how far the 15 m of casing attached to the FFF extended down and into the borehole. We raised the bit back up into the 10¾ inch casing and deployed the camera system to constrain the height of the FFF above seafloor. The top of the second, “upper” funnel appeared to be ~2 m above the rim of the first, leaving the casing shoe at ~13 mbsf. After retrieving the camera system, we wanted to get the bit as deep as possible before cementing. After passing a tight spot at 38 mbsf, we were able to wash and ream to 57 mbsf. However, we could not get past this depth and stopped trying at 0800 h on 7 January. At this time, the core barrel that was in place during this washing and reaming was retrieved (Core 15G). We deployed a new core barrel, washed and reamed back down to 57 mbsf, and pumped 25 bbl of cement that contained 0.25 lb/sack of lost-circulation material. After the cement was in place, we raised the bit up to 15 mbsf and the 10¾ inch casing was flushed to remove any cement from this area. The bit was then pulled out of the hole, and the drill string was flushed to clear out any remaining cement residue. We slipped and cut 115 ft of drill line and then retrieved the drill string. The bit was back on the rig floor at 2315 h on 7 January. We then assembled a new BHA with a 9⅞ inch tri-cone bit for drilling out the cement. This bit does not recover core but has a more robust cutting structure for reaming and clearing operations. The drill string was lowered to the seafloor, and we reentered Hole U1415J at 1130 h on 8 January. After recovering the camera system, the bit was run to 57 mbsf before encountering fill, without any evidence of cement. The hole was reamed once again to 77 mbsf and swept with high-viscosity mud. The bit was pulled up to 14 mbsf for a wiper trip and then lowered back down to 76 mbsf. The bit was then positioned at 63 mbsf, and a second remedial cement job was performed using 35 bbl of cement. During the cement job, the bit was lowered to 71 mbsf. After the cement was pumped, the bit was raised up to the casing shoe, and the 10¾ inch casing was flushed to ensure that no cement remained in this interval. The bit was pulled clear of the seafloor, and the drill string was circulated to flush any remaining cement from the pipe. Because we wanted to drill out the cement with the same bit, we had to wait for the cement to harden. While waiting for this to happen, we conducted a near-bottom camera and 3.5 kHz pinger survey of two other potential drill sites (see the “Bench site survey” chapter [Gillis et al., 2014a]). At the completion of the survey, we reentered Hole U1415J at 2215 h on 9 January. We felt that the cement still needed a little more time to harden, so we kept the bit in the 10¾ inch casing until 0630 h. On lowering the bit into the hole, we encountered the same obstruction at ~35 mbsf, but it was easily passed. This time, the bit encountered cement at 63 mbsf, which we drilled out to 73 mbsf. Several hours were required to drill back down to the total depth of the hole (79.4 mbsf). Little advancement could be made until we significantly reduced the pump strokes to ~30 strokes/min, which allowed the bit to advance to the bottom of the hole. Each time a mud sweep was pumped, clear pump pressure changes were observed, suggesting that the cuttings might now be getting circulated out of the hole. We then drilled 5 m of new hole (to 84.4 mbsf) without coring in an unsuccessful attempt to reach a more competent formation. At this point, we decided to retrieve the drill string to switch back to an RCB coring BHA. The bit was back on the rig floor at 0600 h on 11 January. We assembled a new BHA with a 9⅞ inch RCB coring bit, lowered it to the seafloor, and reentered Hole U1415J at 1700 h on 11 January. The bit began to take weight at the normal 35 mbsf but was able to pass through quickly. The hole was then washed and reamed, reaching the bottom of the hole (84.4 mbsf) at 0130 h on 12 January. The core barrel used during this reaming (Core 17G) was recovered and on deck at 0230 h on 12 January. We dropped a new core barrel and resumed RCB coring. Core 18R advanced from 84.4 to 89.1 mbsf. All drilling parameters appeared stable and good. Initial indications were that the two remedial cement jobs were successful and that the cuttings were now being expelled from the hole. New fill on bottom between cores appeared to be from the immediate formation being drilled into and not from uphole. Core 19R was advanced from 89.1 to 94.1 mbsf. Coring parameters remained reasonably constant and the penetration rate was initially 2.5 m/h but jumped to 5.0 m/h midway through cutting Core 19R. After recovering Core 19R, we encountered challenges getting back to the bottom of the hole. Once we did, however, Cores 20R and 21R were cut from 94.1 to 101.8 mbsf and recovered 1.58 m (21%). Hole conditions continued to be problematic, and we conducted a wiper trip up to 74 mbsf that encountered tight spots at 82 and 86 mbsf. Core 22G was recovered from this reamed interval (between 82 and 101.8 mbsf). After eventually getting back to bottom, Core 23R extended 2 m into new formation (101.8–103.8 mbsf). Once again, we had challenges washing and reaming back to the bottom of the hole (103.8 mbsf). In the end, we were unable to get completely back to bottom and our pump pressures remained abnormally high, leading us to suspect that one or more bit nozzles were plugged. We decided to attempt cementing the lower 20 m of the hole (our third cement job in this hole) and then retrieve the drill string to replace the bit while the cement hardened. Before pumping the cement, we retrieved Core 24G. After positioning the bit at 96 mbsf, we pumped 12.5 bbl of cement. The bit was raised to 76 mbsf while pumping the cement. The bit was then pulled to 15 mbsf so that any cement remaining in the casing/FFF could be circulated out. We pulled the bit out of the hole at 1605 h on 13 January. The drill string was then flushed of any remaining cement, and the bit was back on the rig floor at 0135 h on 14 January. A new RCB (C-7) bit with a mechanical bit release (MBR) was assembled to the bottom of the BHA. We also added a fourth stand of drill collars to the BHA. After tripping to the seafloor, operations were put on hold while a slip and cut of the drill line was completed. We reentered Hole U1415J at 1542 h on 14 January. Once the camera system was back on board, the driller commenced lowering the pipe into the hole. The drill string took weight at 36 mbsf but was able to pass this interval relatively easily. The bit encountered cement at 78 mbsf and was drilled out to 99 mbsf (3 m below the bit depth when cementing). We washed and reamed the rest of the way back down to the bottom of the hole (103.8 mbsf). After we retrieved the core barrel that was in place while washing and reaming from 99.0 to 103.8 mbsf (Core 25G; 0.48 m recovered), we resumed RCB coring. While cutting Core 26R (103.8–111.8 mbsf), the first 4.2 m drilled at a slow 1.3 m/h, but the last 3.8 m was penetrated in <3 min. Core 26R was recovered on deck at 0830 h on 15 January. While retrieving the core, the drill pipe became stuck. We tried to free the drill string for >1 h before deciding to release the bit as the next step in freeing the drill string. When lowering the MBR shifting tool with the sinker bars to release the bit, we attached the core orientation (FlexIT) tool so we could determine the hole inclination. We had to offset the ship ~260 m (~5% of water depth) to lower a tool joint down nearly 8 m to the rig floor so that the core barrels could be removed and the shifting/FlexIT tools deployed. Our attempt to shift the MBR sleeve and release the bit was unsuccessful, so we retrieved the shifting tool. Data from the FlexIT tool indicated the hole was ±3° from vertical. This put to rest one proposed theory that we had been tracking down a high-angle fault and might never drill out of the fractured material. On our second attempt to release the bit, we added a core barrel to the shifting tool and pumped it down to the bit at 70 strokes/min. The sinker bars were then run into the hole to retrieve the shifting tool and release the bit. However, before the sinker bars reached the core barrel, the drill string worked itself free. The sinker bars were recovered, leaving the core barrel and shifting tool in place. If we had recovered the core barrel, the sleeve would have shifted, leaving the bit and MBR in the hole. Once the pipe was free, we were able to pull the drill string, and the bit was back on the rig floor at 0130 h on 16 January. Because of the continually problematic and deteriorating hole conditions and the diminishing return on recovering core samples for science, the decision was made to abandon Hole U1415J and move to a different location. |
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