Hole fluids for deep ice core drilling: a review

The contemporary stage of ice core drilling began about 1950. The first experience of deep drilling showed the significant hole closure in an open hole. The deepest "dry" bore-holes were 411 m (Site 2, Greenland, 1957) and 952 m (Vostok Station, Central Antarctica, 1972). For drilling at larger depths it is necessary to prevent the hole closure by filling of the bore-hole with a fluid. Fluids used at rock drilling are not suitable for ice drilling. Only spe- cial low-temperature fluids are fit.

For the first time the drilling in ice with fluid was made by USA CRREL at Camp Century in 1966 and then at Byrd Station in 1967-1968. The lower part of the bore-holes was filled by the aqueous ethylene glycol solution and the upper part was filled by the mixture of diesel fuel of arctic blend DF-A with the densifier (trichlorethylene).

During thirty years after this event not much deep bore-holes in ice were drilled (Table 1). The unfortunate choice of the type and the parameters of the fluid often caused sticking of the drill. Therefore, the choice of the fluid for the concrete drilling conditions is considered to be one of the most important parts of ice drilling technology (Gundestrup, 1989).

The main parameters of fluids used for ice deep drilling are:
1) density and fluid top;
2) viscosity;
3) frost-resistance;
4) stability;
5) compatibility with polymers and metals;
6) volatility;
7) flammability;
8) ice and water solubility;
9) toxicological and environmental characteristics;
10) cost.

This review of hole fluids for deep ice core drilling includes the necessary theses, equations, examples and properties data for the optimal choice of the hole fluid for the concrete drilling site.