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doi:10.2204/iodp.sp.302.2004


CORING STRATEGY

The coring vessel is ‘Vidar Viking’, an AHTS vessel with a polar ice class, full DP and a 2 m-diameter moonpool with under-hull ice protection via a retractable ‘skirt’. The depth of protection requirement has been decided from data acquired from ice-stream modelling of the vessel hull during the design phase.

SeaCore, an offshore drilling contractor has been contracted to provide drilling services. A SeaCore modular drilling rig (R100 Model) structurally modified and equipped to operate in up to –20 degrees centigrade temperatures with top drive of sufficient lifting capacity installed for coring operations. Drilling tubulars are API standard with up to date thread and crack inspections and comprise 7” OD drillcollars and 5” API Range 2 drillpipe, both with 5 1/2” FH connections and a minimum 4” ID. The rig comes complete with pipe rack, pipe handling, power packs, mud tanks and all accessories and spares. Naturally degrading polymer mud will be used while drilling.

Coring tools

BGS will supply a multi-function wireline suite of interchangeable coring tools for the expedition. Because these tools are new developments, ESO will additionally carry a proven suite of wireline coring tools (Appendix III). A variety of core bits will also be carried to allow coring in all anticipated formations including roller-cone core bits, PDC and natural diamond bits, and pilot bits with specially designed diamond crowns for hard-rock core recovery.

All inner barrels operate within the same outer core barrel. Thus it will be possible to sample soft to firm sediments and competent rock without tripping the drillstring, provided the main core bit lasts for the entire borehole length.

A modification of the ODP piston corer will be the main tool of use in soft to stiff formations. Due to derrick restrictions this is limited to a 4.5 m core length. Apart from the length of this tool all other dimensions are the same as the existing ODP APC. There are additional inner-barrel tools should difficult or sandy formations be encountered. These include a push corer that can be rotated if required and can collect up to 4.5 m core length. For more competent formations an inner barrel system equivalent to the ODP XCB and RCB is used and can be variably adjusted to project or be part of the main drill bit. All of these systems are equipped with a non-return valve that seals overpressure borehole fluids from travelling up the drillstring ID and onto the drillfloor while the inner barrel is latched.

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