Electromechanical drilling of a 300-m core in a dry hole at Summit, Greenland

During the EUROCORE project in 1989 at Summit, Central Greenland, a 304.8-m long ice core of 105mm diameter was retrieved with an electromechanical drill. A dry drilling technique was used in order to minimise contamination of the ice. A special drill head with a small chipping depth was designed to assure minimal fracturing of the core. The quality was excellent to the depth of 180m, but then deteriorated due to increasing brittleness of the ice. Down to 280m we were able to maintain the mean length of unbroken core pieces above 0.1m by reducing the pitch from 7 to 2mm. The sticking of the consequently finer chips to the drill barrels was reduced by treating the barrels repeatedly with a silicone-based wax solution. Hole enlargement cutters near the upper end of the drill head prevented the drill from becoming stuck due to borehole closure.