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doi:10.2204/iodp.proc.347.107.2015

Operations

Transit to Hole M0063A

The vessel began the transit to Site M0063 (proposed Site BSB-9) at 1945 h on 6 October 2013 when the pilot boarded the Greatship Manisha. The vessel arrived on station over Hole M0063A at 0225 h on 8 October and began preparations for coring (Table T1).

Hole M0063A

During preparations for coring in Hole M0063A, a discrepancy in the depths submitted by the two transponders deployed on the seabed template was noted. Therefore, additional caution was exercised when tagging the seafloor and taking the first core. A 1 m push sample was conducted to gauge the true mudline depth. Following this, seven piston cores were recovered before a problem with a spline from the overshot messenger ceased coring operations. Fishing attempts were unsuccessful, so the pipe was tripped back to the point at which the spline and core barrel were lodged. During the early hours of 9 October 2013, the partial pipe trip successfully recovered the core barrel and intact core and pipe was run back down to the previously cored depth. Two further piston cores were successfully recovered to deck, but the third again became stuck as the overshot release sleeve became jammed in the pipe. On this occasion, the fishing attempt was successful, and the pipe did not have to be tripped. Modifications were made to the overshot release system, and coring continued successfully for the remainder of 9 October and into 10 October, with a further 19 cores being recovered to deck.

Following recovery of Core 29H, a change in lithology meant the next piston core took three attempts and flushing of the hole to free it from the bottom-hole assembly (BHA). The following two piston cores had good recovery. Because of encountering a till lithology, it was decided to change to the extended nose system. However, from this point onward and despite trying different coring systems, recovery and penetration continued to be low. After discussion with the Co-Chief Scientists, it was decided to open hole sections with spot sampling to try to progress through the till unit. This continued until midnight.

At midnight on 10 October, a coarse gravel lithology was encountered. After 10 m, a hammer sample was taken, which returned 1 cm³ of material. At 0150 h, it was decided that the hole was no longer viable because of the risk of caving and stuck pipe. Preparations then began for downhole logging. Pipe was brought up to 18 meters below seafloor (mbsf), and logging sheaves were set up.

Logging preparations commenced at 0150 h, with the drill string being tripped to 18.5 mbsf. The first tool string consisted of the compact gamma ray and compact induction tools. The tool string was run down the hole at 0322 h and downward logging began at 0340 h. The first uplog commenced at 0349 h from 108.5 mbsf and ended at 0404 h, with the tool recovered on deck at 0440 h. The second run included the compact gamma ray, compact spectral gamma, and compact sonic tools and commenced at 0451 h when the tool was run into the hole. The tool string also reached a maximum depth of 108.5 mbsf. The third run included the compact gamma ray and compact microimager tools. This tool string was run into the hole at 0628 h, and the maximum depth of 108.5 mbsf was again reached. The uplog began at 0701 h and ended at 0727 h. Rig down was complete by 0830 h, and the vessel prepared to move to Hole M0063B.

A total of 38 cores were recovered in Hole M0063A, with three open-hole sections, reaching a maximum depth of 115.81 mbsf. Hole recovery was 92.89% when the open-hole sections were discounted.

Hole M0063B

Cores from Hole M0063A expanded significantly upon reaching the deck, and there was a resultant loss of core material upon removal of the piston. The coring strategy for Hole M0063B was therefore modified to maximize the amount of sediment recovered. The new strategy involved penetrating 2 m into the sediment for each 3.3 m run to allow room in the liner for expansion of the sediments without incurring sediment loss. This involved pulling back 1.3 m from the base of each washed-out interval before firing the piston corer system (PCS). Following each PCS sample run, the BHA was advanced by 2 m. Although this reduced the production rate, it proved very successful in collecting higher quality cores with no loss of sediment. This process continued successfully for 14 piston coring runs before the hole was terminated and preparations were made for transit to the midterm port call.

A total of 14 cores were recovered in Hole M0063B, reaching 29.0 mbsf. Hole recovery was 99.28%.

Following completion of Hole M0063B, the drill floor and containers were secured for transit and the Greatship Manisha sailed for the port of Nynäshamn, arriving at 0730 h on 12 October 2013. Once alongside, provisions, drilling mud, and spares were brought on board and frozen microbiology samples were offloaded to World Courier. The vessel departed Nynäshamn at 1730 h, sailing back to Site M0063.

Hole M0063C

The vessel arrived on station at 2115 h on 12 October 2013. By 0215 h on 13 October, the drill string, collars, and BHA were run to just above the seabed. Coring then commenced, with 22 successful piston core runs on 13 October. To maximize the recovery of the expanding sediments, the same strategy used in Hole M0063B was again adopted, whereby the PCS was pulled back 1.3 m from the base of each washed-out interval before firing the PCS. Following each PCS sample run, the BHA was advanced by 2 m. This procedure continued to provide the most complete sequence within this expanding sediment package.

Coring with the PCS continued smoothly on 14 October. At 93.3 mbsf, till was encountered that prevented a full 3.3 m piston stroke being achieved. It was decided to open hole 3 m and take a hammer sample. This confirmed that coring had progressed into a diamicton, and the decision was made to terminate the hole at 1720 h on 14 October. Preparations were then made to bump over to Hole M0063D to establish a new hole.

A total of 40 cores were recovered from Hole M0063C, with one open-hole section, reaching a maximum depth of 96.40 mbsf. Hole recovery was 99.29% when the open-hole section was discounted.

Hole M0063D

Operations began in Hole M0063D at 1830 h on 14 October 2013. The first piston core was fired from 1.8 m above the seabed, creating an offset in core run depths between Holes M0063C and M0063D to aid stratigraphic correlation.

Coring continued successfully for the remainder of 14 October and throughout 15 October. Again, the sediments recovered were highly gaseous and expanded significantly. PCS operations continued the morning of 16 October until Run 41 became stuck in the BHA at 86.8 mbsf and attempts to free it proved unsuccessful, with the wireline string parting.

After discussion, as the hole was within 9 m of the expected depth for the clay to till transition, it was decided to terminate Hole M0063D at this point. The drill string was tripped, and the BHA was brought up to the slips. The core barrel was released, and the core was recovered for curation.

Problems with torquing the top subs resulted in the BHA being exchanged with a spare. The vessel then bumped across to the microbiology hole (M0063E), and preparations were made for coring, with running of pipe.

A total of 40 coring attempts were conducted in Hole M0063D, with one open-hole section, reaching a maximum depth of 86.8 mbsf. Hole recovery was 98.59% when the open-hole section was discounted.

Hole M0063E

The vessel bumped across to the microbiology hole (M0063E), and preparations were made for coring, with running of pipe commencing at 2020 h on 16 October 2013.

On 17 October, piston coring continued well throughout the day, with 21 cores recovered to deck. Initially, the coring rate was adjusted to enable microbiological sampling to keep pace, but the rate returned to normal after the first six cores as the intensive sampling scheme reduced with depth.

Coring continued well throughout the morning of 18 October with eight piston cores recovered to deck. However, by 0900 h, winds and sea swell had built to such an extent that tool handling on the drill floor became unsafe. Operations were therefore suspended, waiting on weather until 1645 h, when coring operations recommenced, with a further eight piston cores recovered to deck by midnight.

The hole ended at 92.8 mbsf at 0610 h on 19 October following the recovery of a till lithology. A total of 43 cores were recovered, with one open-hole section. Hole recovery was 99.69% when the open-hole section was discounted.

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