| 摘要 |
An off-shore ice island structure for location over a submerged drill site in waters which normally freeze in winter. The structure includes a buoyant protective caisson which freezes in position over the drill site upon onset of winter. A barge floats on water kept unfrozen within the caisson, and is connected to the caisson so it can be swivelled generally about a vertical axis to adjust the circumferential location of the drilling axis of drilling apparatus carried on the barge. The drilling apparatus is movable relative to the barge to enable further adjustment of the drilling axis location. The arrangement enables the drilling axis to be maintained in substantial vertical alignment with the drill site despite movement of the caisson caused by the surrounding shelf ice. The caisson is part of an ice island structure whose mass is built up by successive flooding and freezing steps to ground it on the sea bed. The capability for fixing the location of the drilling axis despite shelf ice movement permits drilling operations to commence long prior to grounding of the ice island. Various arrangements are disclosed for moving the barge from within the caisson for reuse at another drill site.
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