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

Abstract

As part of the ICE&LASER/SUBGLACIOR projects, an innovative probe called SUB-GLACIOR 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 mm 2 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.

The SUBGLACIOR drilling probe: concept and design

“…In addition, this fluid is environmentally friendly. Our tests in the laboratory have shown that it does not interfere with the OF-CEAS spectrum in case of contamination of the water (Triest and others, 2014). Furthermore, our tests in a cold room at −10°C, where we dropped ice chips into 3 L of silicone oil and let the mixture sit for >6 weeks, showed no cluster formation.…”

“…After evaluating several types of fluid, we finally chose silicone oil 3 cSt (3 mm 2 s −1 ) (Triest and Alemany, 2014). The density of this fluid can balance the ice pressure (930 kg m –3 at 0°C and 970 kg m –3 at –40°C); its freezing point is around −120°C; and its kinetic viscosity is reasonably low (3 mm 2 s −1 at 25°C) even though this value rapidly increases below −30°C (12mm 2 s −1 at –55°C, which is three times greater than with the usual mixture of kerosene D40 with hydrochlorofluorocarbon HCFC-141b).…”

“…To determine the optimal hydraulic working point, the regular head loss was determined for different flow rates on a flowline going from the surface to the probe and then back to the surface (Alemany and others, 2014). The calculation takes into account the ice-chip production by the probe head, the drilling-fluid viscosity, the hosepipe and borehole geometry, and the temperature: first, for pure drilling fluid being injected between the hosepipe at the surface (point 1 in Fig.…”

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

“…The density-viscosity tests (Talalay, 2007;Triest and Alemany, 2014;Xu et al, 2014) demonstrated that only a small number of DSOs and FAEs meet the ice-drilling requirements. Furthermore, some of the physicochemical properties of these liquids were unknown and require further clarification before conducting practical experiments in the test boreholes.…”

“…Although there are several DSOs, the low-viscosity grades (b 5 mm 2 s −1 ) of silicones (e.g., KF96-1,5cs and KF96-2,0cs) are the closest match to the requirements for a drilling fluid (Triest and Alemany, 2014). Some of DSOs, namely PMX200 from Dow Xiameter, have exposure limits; however, most of DSOs have no specifications on the air contamination levels.…”