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doi:10.2204/iodp.proc.331.101.2011

Operations strategy

All drilling from the D/V Chikyu is continuously monitored at the seafloor using a video camera mounted on an ROV operated by Oceaneering, Inc. This device was invaluable for observing drilling induced hydrothermal flow. We used heavy triangular, gimbaled guide bases at three holes, one each at Sites C0013, C0014, and C0016, to allow reentry for deep drilling and for postdrilling operations, including casing and capping. The casing in each of these holes was hung from the guide base, a valved wellhead corrosion cap was fit over the hole, and a steel mesh platform with valve controls was installed on its top. Holes C0013E and C0014G were cased to total depth, using perforated screened casing in depth intervals where flow was thought to occur. Hole C0016B was not cased, but it was capped, with a 3 m piece of pipe welded beneath it as a substitute for full casing of the 45 m deep hole. The research group of Co-Chief Scientist Ken Takai has recently developed an in situ cased-hole fluid sampler (DEEP-SAMPLER) and a microbial colonization device (BIO-SAMPLER). These sampling tools will enable them to retrieve indigenous subseafloor fluids and microbes at the seafloor through these cased holes using an ROV. Development of these types of third-party tools greatly extends the usefulness of IODP drill holes, provides research opportunities for investigating subseafloor fluid flow and microbial communities, and permits long-term monitoring of drilling-induced disturbance of seafloor and subseafloor environments.

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