Physicochemical properties of potential low-temperature drilling fluids for deep ice core drilling

•The electrical conductivities of all tested liquids are very small (< 0.003 μS/cm).•The thermal conductivities of all tested liquids are far less than that of water.•The potential drilling fluids have absolutely no influence on PTFE O-rings.

Drilling fluids are added to deep ice boreholes to facilitate control pressure and remove chips. The drilling fluids currently in use are not intelligent choices for the future from safety, environmental, and technological standpoints. Two potential fluid types, namely, low-molecular weight dimethylsiloxane oils (DSOs) and low-molecular-weight fatty-acid esters (FAEs), were suggested to replace the drilling fluids currently in use. For this study, six types of liquids (DSO-3,0cs, KF96-2,0cs, ethyl butyrate, n-propyl propionate, n-butyl butyrate, and n-amyl butyrate) were selected because of their appropriate density-viscosity properties. These liquids were tested for properties such as electrical conductivity, thermal conductivity, and compatibility with plastics. The results indicated that the electrical conductivities of all the liquids were very small (< 0.003 μS/cm), and an electric field applied in the electromechanical drills was not sufficient to ionize the liquid. The thermal conductivities of all the tested liquids were considerably less than that of water. However, n-propyl propionate indicated the best performance in terms of the cooling ability at subzero temperatures. The effect of FAEs on O-rings swelling was stronger than that of the DSOs. The potential drilling fluids had absolutely no influence on polytetrafluoroethylene (PTFE) O-rings; hence, they could be considered as the ideal sealing material. Tests indicated that low-molecular-weight DSOs and FAEs were both applicable as drilling fluids for deep ice core drilling. It is suggested that the final decision should be confirmed by field-based and practical experiments in test boreholes.