Drill fluid selection for the SUBGLACIOR probe: a review of silicone oil as a drill fluid

As part of the ICE&LASER/SUBGLACIOR projects, an innovative probe called SUBGLACIOR is developed with the aim of perforating the ice sheet down to depths of 3500 m in a single season and continuously measuring in situ the isotopic composition of the meltwater and the methane concentration in trapped gases. Ice chips generated by the electromechanical drilling will be removed from the borehole by circulating a drill fluid. The selection of this drill fluid is important as it will have a major impact on the performance and the environmental evaluation. A literature review of drilling liquids is carried out to select potential fluids for further detailed testing. The selected fluids are varying grades of silicone oils, known as linear polydimethylsiloxanes, and ESTISOL™ 140, an aliphatic ester. The requirements for this project are similar to those for other deep ice-core drilling projects but, due to the embedded analytical system and the speed of drilling, there are some specific considerations. Following extensive testing, we conclude that a silicone fluid with a kinematic viscosity of 3 mm2 s−1 (3 cSt) is ideally suitable and affordable. This evaluation provides new insights into the use of silicone oils as a drill fluid that are of use to the wider ice-core drilling community.