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Victoria University Antarctic Research Expedition Science and Logistics Reports 1998-99: VUWAE 43

CRP-2 Site completion

CRP-2 Site completion.

The drilling plan called for coring to cease on November 23, allowing for 2 days of logging, 5.5 days for returning the drilling system to Cape Roberts, and 7 days for breaking down the camp and storing on Cape Roberts. This presumed a normal ice year in which heavy plant could move safely on the sea ice until the first week in December. In 1998 down-hole progress was much slower than expected early in the season. With the hole 200 m short of the target depth on November 21 and down-hole progress at 30 m/day, it was decided that drilling could be continued a little beyond the schedule date.

The timing of the cessation of drilling was decided by the on-site project management after a new projected time scale was developed primarily by the Science Support Manager and Drilling Manager. Several factors were taken into account:
  • Down hole logging requirements
  • Sea ice conditions at the drill-site including observations of surface ice conditions.
  • Horizontal Sea Ice Offset
  • Sea ice conditions on the supply route and the transition onto Cape Roberts
  • Time required to complete the Camp Recovery and storage on Cape Roberts
  • Aircraft availability for all returning CRP personnel to Christchurch

By the time the drill site was abandoned significant surface melt had occurred in the immediate vicinity of the Drill Rig and Mud Huts primarily due to the reflection of sunlight of the buildings. After the removal of the drill rig it also became apparent that the ice platform immediately under the drill rig was in very poor condition and had been strongly corroded by accumulated minor spills of salt rich drill fluid. We took extreme care in the operation of the heavy plant close to the drill site area during site abandonment. The surface prediction of the timing of surface melting is extremely difficult but can occur within a period of 2-3 days during warm temperatures and bright sunlight. We also hope to reduce the quantity of spilt drill fluid that accumulates around the drill rig in the future with better capture proceedures.. Sea ice offset was evident from the angle of the sea riser at the surface by 18 November, when a chain hoist was fitted to the top of the riser (Annular Diverter) to reduce the angle at the entry point of the NQ drill string. At this time horizontal ice offset from spud-in was 9 m. By the time coring finished on November 25 the offset was at least 11 m and some difficulty with rotation was evident during high current flow. This offset is about 6% of water depth and corresponds well with the latest engineering study and this can now be used to predict part of the system's operational constraints.

The transition route onto Cape Roberts had become flooded with sea water in the tide crack zone by 22 November. Other less suitable routes were available but these crossed more highly fractured ice in the 30-m-wide tide crack zone. The nature of the sea ice and ice foot transition at Cape Roberts varies from season to season which can influence the timing of flooding, melting and cracking and it's safe use.