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doi:10.2204/iodp.proc.338.104.2014

Operations

Site C0012

Hole C0012H

The D/V Chikyu arrived at Site C0012 at 1045 h on 2 December 2012; the remotely operated vehicle (ROV) was prepared with four transponders and dove at 1230 h. The ROV dropped the transponders by 2100 h, after which it was recovered to the surface and the vessel moved to the planned Hole C0012H well center by 2200 h. Dynamic positioning calibration was completed by 2345 h, and the LWD assembly, including the sonicVISION tool, was made up for running into the hole. The LWD bottom-hole assembly (BHA) began running into the hole at 0430 h on 3 December. After passing a series of mid-water tests, the LWD tools reached the seafloor when the real-time data signal was lost. After spending some time on troubleshooting operations, the tool was pulled out of the hole to the rig floor for examination and possible replacement, reaching the deck at 0245 h on 4 December. Although a jamming alert from the TeleScope was received and visual inspection found no issues with the tool, a spare TeleScope was swapped into the BHA and run back at 0645 h on 4 December. A series of tests were again run as the BHA was lowered down to the seafloor, and once all had been completed successfully, the LWD BHA was ready to spud in. Using the LWD tools to determine the mudline, the seafloor was set at 3538 m drilling depth below rig floor (DRF) (3509.5 meters below sea level), and drilling ahead resumed at 1730 h. The Schlumberger logging engineers were concerned that the sonicVISION configuration should be changed by downlink because in their estimation the real-time sonic velocity was not reliable. After close consultations with the Co-Chief Scientists, it was decided to leave the sonicVISION configuration as is and continue drilling from 3686 m DRF at 2315 h on 4 December. At 0430 h on 6 December, the planned total depth (TD) of 4238 m DRF (700 mbsf) was reached, after which an additional 10 m was drilled ahead to allow the sonicVISION tool to record an interval where resistivity was seen to increase. The final TD in Hole C0012H of 4248 m DRF (710 mbsf) was reached at 0515 h. Inclination and azimuth surveys took place during circulation, and then a spot of kill mud was set before pulling out of the hole to 1994 m DRF began, ending at 1145 h. The BHA reached the surface at 2300 h, after which the tools were laid down and preparation for coring at Site C0002 began. Transponders were released from the seafloor and all were recovered by the watch-boat Hakuryu Maru by 1500 h on 7 December. The vessel then began to move to Site C0002.

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