DP Hunter - drillship of the Tahiti Sea Level Expedition (310)
After an exhaustive search for a suitable vessel, the DP Hunter was chosen as the appropriate vessel to be the mission-specific platform for the Tahiti Sea Level Expedition. The ship had been mainly used for diving support operations, however she had all of the requirements that allowed the ship to be successfully converted for drilling. The ship was already equipped with a large moonpool (7.6 x 6.1m), a hollow shaft open at the deck and hull, watertight to the sides and ideally situated on its deck for installation of a mobile drilling rig. The ship also has a large open rear deck which was able to accommodate the laboratory equipment. Equally as important was that the DP Hunter has a high specification dynamic positioning system (DPS) allowing safe operation close to coral reefs. In addition, the ship was well equipped with both berth and office space suitable for the operation.
MOBILISATION AND DRILLING EQUIPMENT:
The DP Hunter came on charter in late August 2005 in Tampa, Florida (USA) where the drilling equipment was installed. The rig used was the R100, the same one used successfully by the drilling contractors SeaCore for the IODP Arctic Coring Expedition during summer 2004. With the requirement for very high recovery rates in porous coral, a mining-type wireline coring system was employed. This system is commonly termed ‘piggy-back’ coring because a mining coring rig is installed on top of the conventional API rig which deploys drill pipe as conductor pipe to the sea bed, so that all coring is carried out in compensated mode.
The conductor pipe is a heavyweight drill pipe or casing with an ID of approximately 100 mm and a casing shoe to set it approximately 1 m into the seabed. A sea-bed template (1.5 m diameter and weighing 10 to 12 tonnes) deployed at the end of the conductor pipe made re-entry to the same drillhole possible.
After mobilisation in Tampa, the DP Hunter departed for Tahiti via the Panama canal, to begin drilling operations on October 6 2005.
