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doi:10.2204/iodp.proc.338.106.2014

Operations

Hole C0021A

The D/V Chikyu shifted from Hole C0018B, where LWD operations were just completed, and we prepared to run the LWD bottom-hole assembly (BHA) into the hole from 2200 h on 26 December 2012. The seabed was tagged (water depth = 2940.5 meters below sea level [mbsl]) at 2330 h, and washing down to 40 mbsf in Hole C0021A commenced. From 40 mbsf, drilling ahead began at 0100 h on 27 December, and rotation speed gradually increased until reaching total depth (TD) (294.0 mbsf): 15 rpm × 1.8–2.5 kNm (40–45 mbsf), 30 rpm × 0–5.0 kNm (45–50 mbsf), 45 rpm × 0–5.0 kNm (50–60 mbsf), 60 rpm × 0–5.0 kNm (60–103 mbsf), and 80 rpm × 1.6–8.3 kNm (103–294 mbsf). TD was reached at 1100 h, and the hole was spotted with kill mud. While the LWD BHA was pulled out of the hole to the surface, overpull (80 kN) was observed from 88 to 101 mbsf; no other overpull was observed. The drill string was broken and racked back to the derrick while the vessel moved to the next site by 2030 h in preparation for LWD at IODP Site C0022.

Hole C0021B

After coring operations were completed in Hole C0022B, preparations began for testing the small-diameter rotary core barrel (SD-RCB) system at 1515 h on 6 January 2013; however, during make-up of the SD-RCB BHA, it was found that the head sub would not fit the other SD-RCB parts, so the test was cancelled at 1900 h. From that time, making up the hydraulic piston coring system (HPCS) BHA and running into the hole began for coring at Site C0021. By 0300 h on 7 January, the BHA reached 2930.7 m drilling depth below rig floor (DRF) while drifting to Site C0021 (the well center was reached by 0145 h). From 0330 h, troubleshooting the crown-mounted heave compensator began, during which operations continued in stand-by while the main Hydralift Power Swivel line was also cut and slipped. Upon completion at 1030 h, the coring BHA continued to be run into the hole to 2964 m DRF. The coring BHA was set to capture the first core while still above the seafloor. At 1145 h, while the BHA was at 2969 m DRF, the HPCS inner barrel was shot, penetrating 5.9 m. The seafloor was then determined as being 2972.5 m DRF (2944.0 mbsl). After the first core was taken, the BHA was washed down to 80 mbsf before coring resumed at 1515 h. There was a short pause in coring from 1845 to 2045 h while the wireline blowout preventer hydraulic hose leak was fixed. Coring resumed with Core 338-C0021B-5H at 108.5 mbsf from 2100 h and ended at Core 12H. Cores 10H, 11H, and 12H became stuck in the inner core barrel; therefore, coring continued with the extended punch coring system (EPCS) for the last two cores. Efforts to recover the stuck core liners continued on the rig floor until 9 January as coring continued. EPCS Core 13T was cut at 1730 h from 175.5 mbsf, and coring finished with EPCS Core 14T to a final TD of 194.5 mbsf at 2100 h on 8 December. Kill mud was spotted at 2230 h, and the EPCS BHA was pulled out of the hole to the surface, finishing at 0130 h on 10 January and ending operations related to Site C0021.

The ship began transit to Shimizu port, Japan, reaching port on the morning of 11 January. The scientists disembarked, and the expedition officially ended on 13 January.