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This paper is based on the data published in research report of P. G. Talalay and N. S. Gundestrup; Hole fluids for deep ice core drilling : A review. Copenhagen University, Copenhagen, 1999,120p. In the practice of deep ice core drilling only three types of bore-hole fluids have been used : 1) petroleum oil products (fuels or solvents) containing densifier, 2) aqueous ethylene glycol or ethanol solutions, 3) n-butyl acetate. The main parameters of drilling fluids 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. The main properties of bore-hole fluids which have been used in practice for deep ice drilling as well as potential bore-hole fluids are described. The analyzing of the property's data showed that there are no ideal drilling fluids. All types of used and potential drilling fluids have their own advantages and disadvantages. Probably one of the most promising types of drilling fluid is low-temperature silicone oil. It is non-aggressive, inert, and non-toxic. The main problem of silicone oil use is the relatively high viscosity at negative temperatures that have influence on the travel time of the drill string and finally on the total time drilling. The final choice of the drilling fluid depends on the possibilities and the ways of solving of indicating problems and depends on the rational correlation between the cost of drilling fluid and other properties of the fluid.

The drilling of deep bore-holes in ice requires that the hole is filled by a liquid to compensate the ice-overburden pressure. Moreover, the hydrostatic pressure of the fluid should be exactly known in order to estimate the hole closure. The estimation of the hydrostatic pressure in the bore-hole can be made in two different ways. The first is the in situ measurements using pressure sensor, and the second is calculation of the pressure using the sampling of drilling fluid from different depths. The second method can be used also for prognosis of the hydrostatic pressure when the necessary density of the hole liquid is chosen. The paper includes the necessary equations for the calculation of hydrostatic pressure for one and two-compound liquids based on the pressure and temperature in the bore-hole. The measured and calculated densities are compared for the GISP2 bore-hole at Summit, Greenland, and it shows a high correlation. The difference between measured pressure and calculated pressure along most of the hole length doesn't exceed 0.12%.