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doi:10.2204/iodp.sp.331.2010

Postdrilling strategy

Recently, an in situ cased-hole fluid sampler (DEEP-SAMPLER) and a microbial colonization device (BIO-SAMPLER), which were mentioned as possible third-party tools for postdrilling investigation in the IODP 601-Full3 proposal, have been developed by a research group for the principal proponent. These sampling tools have enabled us to retrieve indigenous subseafloor fluids and microbes from the seafloor through cased or cemented 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. In order to assure the applicability of these postdrilling sampling and monitoring tools, the protection of the hole and the preservation of subseafloor fluid flow are essential. Thus, full casing of the drilled holes using heat-resistant materials that are chemically tolerant to H₂S, CO₂, O₂, and Cl, together with the deployment of screens at appropriate depths corresponding to the subseafloor hydrothermal fluid paths, is planned during the expedition as follows (Fig. F8):

1. For proposed Site INH-1D, casing and cementing operations are impossible because of expected unstable seafloor and subseafloor conditions. But, for alternative Sites INH-1C, INH-2C, and INH-3C, steel casing and sealing by wellhead cap are possible.

2. For proposed Site INH-4D (and proposed Site INH-5D), drilling operations are expected to encounter fluid outflow due to the possible penetration of subseafloor hydrothermal fluid paths. Thus, cementing may be impossible, but casing and sealing by wellhead cap are possible.

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