IKU Stratigraphic Drilling Projects 1982 - 1993
Drilling ships with dynamic positioning systems were employed together with marine Piggyback or CCS drilling equipment in nearly all cruises. Heatflow measurements were also done from these ships.
Various fishing, supply and survey vessels were used in the early-mid 1980s to obtain short bedrock cores using a small deployable electric drill and overburden material using a vibro-corer.
M/V Pholas, used in 1982 and 1984 while operated by Coe Metcalf Shipping. The vessel, later named "Norskald", was scrapped in 2002.
Photo: Patrick Hill, from www.quaysides.freeuk.com/favourites/pholas.htm
M/V Bucentaur, used in all cruises between 1985 and 1993 while operated by Farmand Survey / DSND. The ship is now operated by Fugro.
Photo from a Farmand Survey brochure
Maximum penetration is 5.5 m with possible extension to 8.5 m. Core diameter is 25 mm.
The BIO-Drill can be operated from any vessel that has a winch system capable of handling the equipment at the given water depth.
Marine piggyback diamond coringMost of the cores were drilled using the "Piggyback" coring method which uses two drill strings, each having its separate power swivel.
An outer drill string (modified API 5" = 127 mm outer diameter, 4" = 101.6 mm inner diameter), guided through a 15 t heavy seabed re-entry frame (seabed template), is used to drill through the (poorly consolidated) overburden, using e.g. a roller bit. When the bit has reached the top of the (hard) bedrock, the string is fixed by hydraulic clamps in the seabed template. As the drillstring is heave-compensated, its top has now a fixed height above seabed, while the ship still can move up and down.
As the piggyback coring machine always has a constant distance to the bedrock, the diamond coring can be carried out with the same precision as on land.
When the core barrel (3.05 m long) is full (indicated by increased mud pressure), it is retrieved from the hole using a wire, and a new barrel is dropped into the hole.
Maximum core length is 3 m, core diameter is 54 mm.
Core recovery obtained with the piggyback sys-tem is typically 97 - 99 %.
Principle of the Piggyback coring method.
Drill bit (roller bit) for Quaternary overburden, inner drill string with diamond bit for bedrock coring, 54 mm diameter bedrock core (all upside-down).
The water depth of about 1500 m at the Vøring Plateau prevented the use of the Piggyback method, as the double drill string would by far exceed the maximum allowable dynamic load (40 tons) of the derrick of M/S Bucentaur.
A coring system of Russian construction was therefore employed. It uses a single 5 3/4" drillstring of aluminium (O.D. 197 mm, I.D. 146 mm) and a suite of wireline-operated downhole tools for drilling, coring and reaming, e.g. various coring tubes, a retractable bit and a mud-driven downhole turbine.
All coring/sampling tools and all drill bits except the casing show (reaming bit) of the main drill string can be operated and exchanged without pulling the drill string.
Maximum core length is 4.5 m, core diameters are 97 mm and 67 mm. Core recovery was significantly poorer than that typically obtained with the Piggyback system.
CCS: Modes of operation (grey = modules that generate or transmit power).
Published February 28, 2008