TALDICE PROJECT

Drilling was performed with electro-mechanical drilling equipment, using a drilling fluid to balance the overburden of pressure and to prevent ice flow closure of the borehole.
 
During the 2004-2005 season, a 4 m deep trench was dug using vehicle (PB330), and an initial pilot hole and reaming were drilled using the James Ross drilling system available at LGGE (drilling capacity of 400 m) to a depth of approx 128 m. The first 96 m was lined with a fibre reinforced plastic casing to prevent the borehole from collapsing in on itself and to prevent the drilling fluids from seeping out of the bore hole. At the end of drilling operations, 10 metres of casing (including up to 5 m above the surface) were added to the original casing to allow access to the hole later on. The hole can thus be used for decade for temperature or ice dynamics studies.
 
During the 2005-06, 2006-07 and 2007-08 austral summer seasons, the initial pilot hole was filled with drilling fluid, and drilling continued down to 1620 m using a Berkner drill system provided by LGGE and BAS. An Italian IDRA drill system was tested during the 2007-08 season, but only over a few runs. This drill tries to combine the "Russian pumping system" and the more classical lower part of the EPICA drill. The chip compaction in the chip chamber did not work properly, which did not allow the drill to produce a long enough core.
 
The electro-mechanical drilling equipment (Berkner drill system) draws heavily on the design of the EPICA drill and earlier Hans Tausen drill (Mulvaney et al, 2007). The drill system was hung by a cable consisting of 7 conductors surrounded by 40 piano wires. The drill was lowered into the borehole, coring was performed, the drill was brought back to the ground surface, and the core was removed. The borehole was 130 mm in diameter, and the extracted ice core was 98 mm in diameter. Each drilling operation extracted a 2 m long ice core segment along with ice chips produced during the drilling operation. On the ground, the ice core segment was taken out of the core barrel, and the ice chips containing borehole liquid were removed from the chip chamber of the drill. The detailed design and manufacture of the winch-system was subcontracted to the Italian company. It was designed and built specifically for this project in collaboration with ENEA Brasimone in order to fit into a Twin Otter and to meet the technical specifications for ice drilling. The motor, the gear-reducer, and the mast and mast tilt mechanism could easily be dismounted from the main frame to help with handling in the field.
 
The use of fluid is vital for deep drilling operations, and special attention was given to its selection and use. Depending on the properties of the ice, dry drilling is possible to depths of approximately 200 m to a maximum of 350 m. Greater core depths require the use of a stabilising fluid to compensate for the hydrostatic pressure of the surrounding ice, thus preventing the plastic deformation of the borehole and constriction of its diameter. Based upon extensive experience in the framework of European deep ice core projects (GRIP, EPICA DC, EPICA-DML, Berkner Island), the most appropriate drill fluid for use at Talos Dome was identified as a mixture of 68% of Exxsol D40 with 32% Solkane 141b densifying agent; a total of 25,920 litres (D40: 17,640 litre, Solkane 141b: 8,280 litre) was used.