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doi:10.2204/iodp.proc.333.103.2012

Operations

After recovering transponders by remotely operated vehicle, the D/V Chikyu left IODP Hole C0002G at 0300 h on 10 December 2010. After 8 nmi of transit at an average speed of 4 kt, the Chikyu arrived at the first transponder location for Site C0018 at 0500 h. Deployment of four transponders and calibration finished at 2045 h, and we began preparation for HPCS/EPCS/ESCS coring. The 11 inch HPCS/EPCS/ESCS bottom-hole assembly (BHA) was run into Hole C0018A at 1445 h on 11 December. Coring began at 0115 h on 12 December and continued to the 36th core, and we decided to finish at 314.15 mbsf at 2103 h on 16 December (Table T1). Operational problems were few and minor during the course of 4 days of coring. Those included damage to a seal in the inner barrel, failures on shooting, and a broken lower part of the sinker bar assembly. After recovering the inner barrel and sinker bar assembly, we spotted kill mud, displaced the hole with seawater, and pulled out of the hole. The bit was back on the rig floor at 0500 h on 17 December.

Core recovery was excellent for piston coring with the HPCS to 153.85 m drilling depth below seafloor (DSF) (Core 333-C0018A-17H), but core liner collapse or expansion in the core barrel caused problems for several cores (Cores 333-C0018A-9H and 16H were damaged). After experiencing repeated incomplete penetration and reaching the estimated MTD bottom, the coring system was shifted to the EPCS at 190.65 m DSF (Core 333-C0018A-24T). EPCS recovery was variable, ranging from 90.7% to 0% with an average recovery of 47.2%, as attempts to adjust the penetration of the EPCS cutting shoe ahead of the drill bit were met with mixed success. We switched to the ESCS after the seventh core. ESCS core recovery was surprisingly better than expected, with good recovery ranging from 70.8% to 114.9% and an average recovery of 87.35%.

Both the EPCS and the ESCS were used below the MTD (EPCS from 190.65 m DSF and ESCS from 257.15 m DSF), and core quality assessment from X-ray computed tomography (CT) scans showed no major difference between EPCS and ESCS cores. Both systems formed fractured biscuits 2–4 cm thick. However, ESCS cores appear to contain more slurry. Once split, degradation between EPCS and ESCS cores is obvious as the thickness of shear zones between biscuits and core liner increases. Some cores, including HPCS cores, were also strongly affected by gas expansion, resulting in voids and bubbly slurry intervals.

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