A new, modified version of the cable-suspended Ice and Bedrock Electromechanical Drill (IBED) was designed for drilling in firn, ice, debris-rich ice and rock. The upper part of the drill is almost the same for all drill variants and comprises four sections: cable termination, a slip-ring section, an antitorque system and an electronic pressure chamber. The lower part of the IBED comprises an auger core barrel, reamers, a core barrel for ice/debris-ice drilling and a conventional geological single-tube core barrel or custom-made double-tube core barrel. First, the short and full-scale field versions of the IBED were tested at an outdoor testing stand and a testing facility with a 12.5 m-deep ice well. Then, in the 2018–2019 summer season, the IBED was tested in the field at a site ~12 km south of Zhongshan Station, East Antarctica, and a ~6 cm bedrock core was recovered from a 198 m-deep borehole. A total of 18 d was required to penetrate the ice sheet. The retrieved core samples of blue ice, basal ice and bedrock provided valuable information regarding the Earth's paleo-environment.
A new type of drill bit designed with an annular slit was developed to enhance the reverse circulation effect of the down-the-hole hammer drilling technology. A computational fluid dynamics code, Fluent, was used to simulate the flow phenomena inside the drill bit. The simulation results show that the air flowing through the annular slit moves upward along the wall of the central passage of the annular drill bit and that there is no interference phenomenon similar to the normal drill bit, which is beneficial for the formation of reverse circulation. Meanwhile, the new drill bit with the annular slit was produced and tested in the laboratory. The results show that for the annular drill bit with the flushing nozzles closed, the mass flow rate of the sucked air is approximately 63.78 g/s, which is 1.76 times that of the normal drill bit, while it is about 2.46 times if the flushing nozzles are opened. In addition, many factors can affect the reverse circulation effect of the annular drill bit, including the slit width, the distance between the annular slit and the working surface of the drill bit, and the flow direction of the gas ejected from the annular slit.
A challenge for future deep-ice coring in central Antarctica is to identify an appropriate inert drilling fluid with no undesirable physical or chemical characteristics. The drilling fluids currently in use (kerosene-based fluids with density-increasing additives, ethanol and n-butyl acetate) are not intelligent choices for the future from safety, environmental and some technological standpoints. Recently proposed drilling fluids based upon ESTISOL TM have high viscosity at low temperatures, which severely limits their application in cold environments. This paper presents our research into the application of low-molecular-weight, fatty-acid esters (FAEs), substances commonly used in the fragrance and flavoring industries. According to available data, selected FAEs are not hazardous to human health. Considering density requirements alone, ethyl butyrate and n-propyl propionate best meet our present needs. The viscosities of these two chemicals are also the lowest among studied FAEs, not exceeding 4 mPa s at temperatures down to -60°C. Both compounds are highly volatile, and insoluble in water. Such properties are attractive, but the applicability of FAEs to deep, cold, ice drilling can be evaluated only after field-based, practical experiments in test boreholes. KEYWORD: ice coring
Debris-rich ice is often encountered when drilling into basal ice and rock glaciers. The standard steel bits used for ice core drilling are not suitable because the cutters are very easily broken by rock particles because their hardness and abrasiveness are higher than that of the ice. The tool steel and tungsten carbide inserts are easily damaged in intermixed ice-rock formations. To obtain high-quality core samples in debris-rich ice, it is necessary to find drill bits that can drill ice-rock mixtures with minimal load and acceptable penetration rate and torque. A special testing stand has been designed and constructed to study both standard and custom-made carbide and polycrystalline diamond compact (PDC) drill bits. The results show that both the carbide and the PDC drill bits can drill with high penetration rates in debris-rich ice containing very hard and abrasive granite particles at low drill loads of 500-1200 N. When the rock volume content is 30%, the penetration rates are 4.68 m/h, 5.9 m/h and 11.12 m/h for the standard six-tooth carbide drill bit, a PDC bit with a round compact and a PDC bit with a semi-round compact, respectively, under a drill load of 500 N with a rotation speed of 100 rpm. Within the range of drill loads of 500 to 1200 N and rotation speeds of 50 to 200 rpm, the maximum torque is no more than 45 Nm, and the power consumption is less than 0.8 kW. In addition, the temperature changes of the bit cutters caused by their cutting action were also measured. Results of the preliminary tests show that temperature variations increase from 3.67 to 5.96 ˚C when the drill load increases from 450 to 1200 N and from 4.17 to 6.21 ˚C when the rotation speed increases from 50 to 200 rpm.
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