Drilling consortium – University of Copenhagen

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NEEM > Science consortia > Drilling consortium

Drilling consortium

Names and contact details for chairs:

Sigfus Johnsen (sigfus@gfy.ku.dk)
Olivier Alemany (alemany@lgge.obs.ujf-grenoble.fr)
Frank Wilhelms (fwilhelm@awi-bremerhaven.de)

Point of contact and procedure for joining the consortium mailing list

Please go to http://mailman.nbi.ku.dk/listinfo to sign up for the NEEM-drilling mailing list. The list is managed by the consortium chairs.

A brief description of the work of the consortium

Activities of the drilling consortium

Several meetings have been held between members of the consortium in order to address the problems connected with developing and producing drill parts for the coming seasons. The task has been shared among the group members involving the mechanical workshops in Bern, Grenoble and Copenhagen.

Drilling issues

The NEEM drilling consortium has access to several types of mechanical rotary drills that are suitable for various drilling projects.

  Drill Type Core diam. Core length Max depth
1
Hand auger
dry 3'' 0.7 m
30 m
2 Shallow dry 3'' 1.0 m
350 m
3 Hans Tausen
dry 4'' 1.5 m
350 m
4 Hans Tausen
wet 4'' 1.5 m
1500 m
5 NGRIP/EPICA wet
4'' 3.5 m
3500

 

All these drills are equipped with cutters that cut away the ice around the core. In the NGRIP/EPICA deep drill the cuttings are stored in a 4 m long chips chamber above the core which is stored in a rotating 4 m long core barrel with a drill head and cutters mounted at the lower end. Above the chip chamber we have a motor section and an electronic section that is mainly used for the wet drillings.

When the drill is full we pull in the cable and special spring loaded knives (core dogs) dig into the core and help break the core free from the bottom of the hole. After each drilling run the drill, filled with the core and cuttings inside, is pulled by the winch to the 6 m deep drill trench. The core is then retrieved and the drill cleaned for cuttings. Working with the drill in the trench is made easy by tilting the tower and drill in a horizontal working height position.
Wet drilling means that the hole is filled with liquid that matches the density of the ice. Thus the hole is stable and does not collapse as can happen when drilling in dry holes to greater depths. In wet drilling operations we need to install a casing in the porous firn in order to be able to keep the liquid level as close to surface as needed. Installing the 27 cm diameter casing tubes is done in a 3 stage operation. First we drill a dry hole down to 110 m where the ice is not porous any more. With the shallow drill the hole is only 11 cm wide, much too narrow for the tubes. Hence the second stage is to ream the hole up to 27 cm diameter using 5 reamers with increasing width. Finally the 5.5 m long casing tubes are connected one by one and lowered into the hole using a chain hoist. The lowest casing tube is modified to ensure a liquid tight connection between the casing and the ice.

The NEEM drilling operation

Preparations for the 2500 m deep NEEM drilling started already in 2006. A new drilling liquid had to be located since Freon type liquids are no more allowed in Greenland. The new liquid is about 20 times more viscous than the liquid we used in previous deep drillings in Greenland and Antarctica. This requires several modifications of the drill design in order to ensure fast movement of the drill in the liquid filled hole.

In the summer of 2008 the field team made initial preparations for the drilling operation. Firstly a 6 m deep, 5 m wide and 30 m long drill trench was dug out and provided with a wooden roof. This ensures that we can drill in almost any weather condition. The drill tower was installed and an 8 m deep inclined trench for the lower half of the tower and the drill was dug using chain saws. The winch was placed on strong beams connected with the tower base. A warm workshop was built and equipped with most tools needed for repairing and maintaining the drill. Several structures including grated floor, operators cabin, working tables, liquid mixing station and ventilation were built and installed. When the winch was connected to the winch controller we discovered a malfunction that could not be repaired. This mishap made it impossible to test the new drill as we had planned for during this summer. The early part of the 2009 drilling season will thus be used for testing the drill and make it ready for routine drilling. If our critical modifications of the drill are working well we expect to drill through the brittle zone, or pass 1300 m, before the end of the 2009 season.