Annals of Glaciology 47 2007 73 Drilling comparison in ‘warm ice’ and drill design comparison L. AUGUSTIN,1* H. MOTOYAMA,2 F. WILHELMS,3 S. JOHNSEN,4 S.B. HANSEN,4 P. TALALAY,5 N. VASILIEV5 1 Laboratoire de Glaciologie et Géophysique de l’Environnement du CNRS (associé à l’Université Joseph Fourier – Grenoble I), 54 rue Molière, BP 96, 38402 Saint-Martin-d’Hères Cedex, France E-mail: [email protected] 2 National Institute of Polar Research, Kaga 1-9-10, Itabashi-Ku, Tokyo 173-8515, Japan 3 Alfred-Wegener-Institut für Polar- und Meersforschung, Am Handelshafen 12, D-27570 Bremerhaven, Germany 4 Department of Geophysics, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark 5 St Petersburg State Mining Institute, Line 21, 2, 199106 St Petersburg, Russia ABSTRACT. For the deep ice-core drilling community, the 2005/06 Antarctic season was an exciting and fruitful one. In three different Antarctic locations, Dome Fuji, EPICA DML and Vostok, deep drillings approached bedrock (the ice–water interface in the case of Vostok), emulating what had previously been achieved at NorthGRIP, Greenland, (summer 2003 and 2004) and at EPICA Dome C2, Antarctica (season 2004/05). For the first time in ice-core drilling history, three different types of drill (KEMS, JARE and EPICA) simultaneously reached the depth of ‘warm ice’ under high pressure. After excellent progress at each site, the drilling rate dropped and the drilling teams had to deal with refrozen ice on cutters and drill heads. Drills have different limits and perform differently. In this comparative study, we examine depth, pressure, temperature, pump flow and cutting speed. Finally, we compare a few parameters of ten different deep drills. 1. INTRODUCTION In the years 2003–06, European, Japanese and Russian drilling teams at different sites in Antarctica and Greenland had the experience of drilling ice under high pressure, close to the pressure-melting point. It was a unique field experiment and an opportunity to test the performance of different drills in such conditions, which cannot be reproduced in a laboratory without tremendous technical effort and financial cost. ‘Warm ice’ (unpublished data from the ‘International Partnership in the Ice Core Sciences’ Workshop, 2004) under high pressure (P > 25 000 kPa) seems to be problematic for electromechanical drills. Several shallow drillings in temperate glaciers have been conducted successfully without any special difficulty (personal communications from B. Koci and H. Rufli, 2006). The environments in dry holes and in fluidfilled holes differ from each other, having different pressure and ice temperature gradients. In deep holes, close to the pressure-melting point, the main issue is that the water produced by the heat of the cutting process refreezes. Each drill performs differently in warm ice. Several parameters, including cutter angle, cutting speed, pump flow, amount of chips transported and drilling fluid, are important. All the data presented in this paper are drillers’ data. Some of them are approximate. Depths are drillers’ depths, which can include uncertainty coming from depth-meter error, cable elasticity, hole inclination and temperature gradient. For Vostok, Antarctica, depths are derived from ice-core measurement. 2. THE FIVE DRILLING SITES One drilling site, the North Greenland Icecore Project (NorthGRIP) site, is located in the Northern Hemisphere, *Visiting engineer at Ice Core Drilling Services, University of Wisconsin– Madison, 1225 West Dayton Street, Madison, WI 53706-1490, USA. and the other four are located in the Southern Hemisphere (Table 1). NorthGRIP The drill used at NorthGRIP is an EPICA (European Project for Ice Coring in Antarctica) drill with the motor section and the anti-torque section of the ISTUK drill used in the 1990s at GRIP (Gundestrup and others, 1984). The drilling twice reached bedrock. In July 2003, basal water rose 45 m into the hole due to drilling-fluid pressure imbalance. The 45 m of refrozen water were drilled out in July 2004. The final depth was 3091 m. EPICA DC The drill used at Dome C, Antarctica, is also an EPICA drill, with a motor and electronic section developed in Brasimone, Italy, by Ente per le Nuove tecnologie, l’Energia e l’Ambiente (ENEA; S. Panichi and others, unpublished information). The anti-torque is from the ISTUK drill. The final depth was 3270 m, 16 m above bedrock (Augustin and others, 2007). EPICA DML The drill used in Dronning Maud Land, Antarctica, was the same as at NorthGRIP. The drilling ended in January 2006, reaching bedrock. The depth was 2774 m; basal water rose several meters. Dome Fuji The JARE (Japanese Antarctic Research Expedition) drill was used at Dome Fuji, Antarctica (Tanaka and others, 1994; Fujii and others, 2002). The drilling reached 3029 m depth in January 2006, and 3035 m in January 2007. Vostok The drill used was the KEMS-132 (core electromechanical drill; Kudryashov and others, 1994, 2002). Drilling reached 3650 m depth in January 2006 and continued in 2006/07. 74 Augustin and others: Drilling comparison in ‘warm ice’ Table 1. Drilling-site characteristics Location Latitude Longitude Elevation (m) Ice thickness (m) Accumulation (kg m–2 a–1) Mean annual surface temperature (8C) NorthGRIP EPICA DC EPICA DML Dome Fuji Vostok Greenland 758 N 428 W 2917 3090 175 –31 Antarctica 758 S 1248 E 3250 3280 25 –55 Antarctica 758 S 08 E 2892 2755 64 –44 Antarctica 778 S 408 E 3810 3035+ 27 –54 Antarctica 788 S 1068 E 3488 3753 21 –56 Table 2. First difficulties at the drilling sites Depth (m) Temperature (8C) Pressure (kPa) T (8C) NorthGRIP EPICA DC EPICA DML Dome Fuji Vostok 2931 –7.1 26 200 5 3119 –5.8 28 100 3.6 2670 –5 24 300 3.1 3000 –2.8 27 000 0.8 3500 –7.9 31 900 5.4 3. DRILLING PERFORMANCES IN WARM ICE For each drilling site we compare depth, temperature, pressure and temperature difference from pressure-melting point (T). We also look at drill characteristics. ‘First difficulties’ What we call ‘first difficulties’ is the first remarkable penetration rate change approaching warm ice (Table 2). One of the first signs is ice chips frozen onto shoes and cutters’ cutting edges. The JARE drill encountered first difficulties much later than the other drills, progressing normally until T ¼ 1.18C. EPICA drills performed differently at the three different sites. The drill versions were slightly different and were operated by different driller crews at each drilling site, which probably explains the variation in T from 3.18C to 58C. The KEMS-132 drill seems to have encountered drilling difficulties earlier, at T ¼ 5.48C. At most sites, drillers can use change parameters like cutter head rotation speed, cutting angles and fluid circulation to deal with the first difficulties encountered when drilling warm ice. First use of ethanol/water solution At three of the sites (NorthGRIP, EPICA DC and EPICA DML), ethanol/water solution (EWS; Zagorodnov and others, 1994) was used to facilitate drilling (Table 3) by being poured into the hole at the start of each run (Augustin and others, 2007). With the EPICA drill it was used within the very short range Table 3. First EWS use at drilling sites Depth (m) Temperature (8C) Pressure (kPa) T (8C) NorthGRIP EPICA DC EPICA DML 3002 –4.9 27 000 2.8 3150 –5.2 28 400 3 2700 –4.3 24 200 2.6 2.68C < T < 38C, showing the limitations of the EPICA drill’s capability to penetrate ‘warm ice’. Last drilling depth So far, drilling operations have been concluded at only two sites, NorthGRIP and EPICA DC. At EPICA DML, refrozen water may be drilled in the near future. At Dome Fuji, the temperature is very close to pressure-melting point (T ¼ 0.38C), and there are 15 m left before bedrock. With some difficulty, our Japanese colleagues are still able to drill without using EWS. At Vostok, the situation is affected by the presence of the subglacial lake, the distance to which is estimated at 105 m. Water should refreeze at the interface (Salamatin and others, 1998). In the 2005/06 season, KEMS132 was able to penetrate into ‘warm ice’ with some difficulty (Table 4). The data in Tables 2–4 are also displayed in Figure 1. Drill characteristics We compare the flow, fluid velocity, density and cutting speed of the four drills operated at the five sites (Fig. 2). The JARE drill has the smallest pump flow (8.5 L min–1), and the KEMS drill the highest (27.5 L min–1). KEMS has the highest cutting speed (0.76 m s–1), and JARE and NorthGRIP the lowest (0.3 m s–1). These preliminary data from field experiments show that flow and fluid velocity are not the only determinant factors for drills to behave better in ‘warm ice’. The JARE drill had excellent results with the smallest pump flow. It also has a great capacity to store ice chips. The mechanical action of the boosters inside the chips chamber provides an excellent chip density (0.49), much higher than that of the other drills. It will be interesting to follow the KEMS-132 drill performance, to see how close to the pressure-melting point the drill can go. EPICA drills have limited capability in ‘warm ice’, as shown by the use of EWS to overcome this problem. Two different types of drilling fluid were used at the five different sites. NorthGRIP, EPICA (DC and DML) and Vostok used a two-component drilling fluid (D30 or D60 mixed with Augustin and others: Drilling comparison in ‘warm ice’ 75 Fig. 1. Drilling comparison: first difficulties, EWS first use, and last drilling depth. 141B), while at Dome Fuji a single drilling-fluid component, n-butyl acetate, is used (Talalay, 2002). These two drilling fluids have different effects on the cutting process close to the pressure-melting point. Another example of a deep ice-core drill that used n-butyl acetate and reached warm ice is the PICO 132 mm drill used at Siple Dome, Antarctica, in 1999. Data are not complete, but the drill reached bedrock close to the pressure-melting point (T ¼ 1.748C). No problems were encountered (Bentley and Koci, 2007). 4. DRILL DESIGN COMPARISON Ten different deep drills, or more if we include all the different versions, have been manufactured since deep ice coring began. The first one, the CRREL (US Army Cold Regions Research and Engineering Laboratory) electromechanical drill, was used at Byrd Station, Antarctica, in 1968 (Ueda and Garfield, 1969). Unfortunately, few data are available for this drill, so it is not listed with the others in Table 5. The Italian drill IDRA is still under development at the time of writing. It is scheduled to be used for the Talos drilling operation during the 2007/08 Antarctic season. The Berkner drill is a short version of the EPICA drill, with a different motor section. The ISTUK drill (Gundestrup and others, 1984) and the PICO (Polar Ice Coring Office) drill (Wumkes, 1994a, b) were used in the 1990s. The Deep Ice Sheet Coring (DISC) drill, developed by Ice Core Drilling Services (ICDS), Madison, Wisconsin, USA, tested in Greenland in summer 2006 in pure Isopar K. The very low density value of Isopar K (0.761 g cm–3) may have significantly affected the performance of the DISC drill. EPICA, JARE and KEMS have already been mentioned. Drill length, core length, ice-chip concentration and ice-chip density are shown in Figure 3. Table 4. Last drilling depth in February 2006 Depth (m) Temperature (8C) Pressure (kPa) T (8C) NorthGRIP EPICA DC EPICA DML Dome Fuji Vostok 3091 –2.1 27 600 0 3270 –2.6 29 500 0.3 2774 –2 24 800 0 3029 –2.3 27 300 0.3 3650 -4.9 32 600 2.4 76 Augustin and others: Drilling comparison in ‘warm ice’ Fig. 2. Drill comparison: pump flow, fluid speeds, ice-chip density and linear cutting speed. Table 5. Drill specifications Berkner1 DISC 20062 Drill length No. 1 (m) Drill weight in air (kg) Drill weight in fluid (kg) Drill descent speed (m s–1) Drill ascent speed (m s–1) Rotation speed (rpm) Hole diameter (mm) Core diameter (mm) Cutters o.d. (mm) Cutters i.d. (mm) Cutting angle (8) Clearance angle (8) Drill head body o.d. (mm) Outer tube o.d. (mm) Outer tube i.d. (mm) Core barrel tube o.d. (mm) Core barrel tube i.d. (mm) Core length maximum (m) Chips chamber tube o.d. (mm) Chips chamber tube i.d. (mm) Chips chamber filter (mm) Drive shaft o.d. (mm) Drive shaft i.d. (mm) Screen diameter o.d. (mm) Screen diameter i.d. (mm) Screen length (mm) Screen No. Chips chamber length (m) Pump flow (L min–1) Motor section diameter (mm) Electronic section diameter (mm) Anti-torque body diameter (mm) Average length of run (m) 6.5 160 ? 0.7 0.7 50 129.6 98 129.6 98 45 10 118 118 113 104 100 2.138 114.3 110.3 N/A 30.5 20 N/A N/A N/A N/A 3.213 18 ? ? ? 2 14.48 404 335 1.2 2.5 80 170 121.5 170 121.5 50 15 166 N/A N/A 157 137 4.29 151.5 128 N/A 0 0 119.8 108 760.9 8 6.09 114 127 133 127 2.49 EPICA3 JARE4 KEMS1325 ISTUK6 IDRA7 11 160 ? 1.4 1.4 57 129.6 98 129.6 98 45 10 118 118 113 104 100 3.75 114.3 110.3 N/A 30.5 20 N/A N/A N/A N/A 4.02 18 110 110 110 2.8 12.3 187 146 0.55 0.8 55 135 94 135 94 35/40 15 132 123 114 101.6 97.6 3.84 123 114 N/A 27.2 16.2 N/A N/A N/A N/A 5.510 8.50 102 102 118 3.67 13 240 ? ? ? 120 135 107 135 107 45 5 127 N/A N/A 127 117 3 ? 113 N/A 32 ? N/A N/A N/A N/A 4.5 27.5 ? ? ? 2.57 11.5 180 ? 1 1 50 129.6 102.5 129.6 102.5 45 12 112 Channels Channels 110 104 2.75 110 100 N/A 15 N/A N/A N/A N/A N/A 3.3 3.36 ? ? 110 ? ? ? ? ? ? ? 129.6 98 129.6 98 ? ? ? ? ? ? ? 3 88.9 84.9 83 0 0 N/A N/A N/A N/A 4.1 ? ? ? ? ? NorthGRIP8 PICO1329 11 150 ? 1 1 50 129.6 98 129.6 98 45 10 118 118 113 104 100 3.75 114.3 110.3 N/A 30.5 20 N/A N/A N/A N/A 4.02 18 ? ? 110 ? 25 625 ? ? ? 100 181 132 ? ? 45 15 ? ? ? ? ? 6 ? ? ? ? ? ? ? ? ? ? 105 ? ? ? ? Notes: o.d.: outer diameter; i.d.: inner diameter. Question marks indicate uncollected or unknown data. N/A: not applicable. Data sources: 1Personal communication from O. Alemany (2006). 2ICDS. 3Augustin (unpublished information). 4Tanaka and others (1994); Fujii and others (2002); Motoyama (unpublished information). 5Kudryashov and others (1994, 2002); Talalay (unpublished information). 6Gundestrup and others (1984); Hansen (unpublished information). 7Personal communication from S. Panichi (2006). 8Hansen (unpublished information). 9Wumkes (1994a, b). Augustin and others: Drilling comparison in ‘warm ice’ 77 Fig. 3. Drill design comparison: drill length, core length, concentration and ice-chip density. It is interesting to look at two drill parameters, Rd (Rd = core barrel length/drill length) and Rda (Rda = average core length drilled/drill length). Rd varies from 0.24 (PICO) to 0.34 (EPICA), while Rda varies from 0.16 (DISC) to 0.31 (Berkner). The ratio Rd is one of the most difficult parameters to determine in drill design, as one cannot know in advance how dense the ice chips inside the ice-chips chamber will be. Another interesting parameter is the concentration of ice cuttings, c (percentage of the ratio of the ice volume cut by the volume of the chips chamber), inside the chips chamber, as defined by Talalay (2006). For the nine drills, c varies from 73% (IDRA) to 38% (KEMS). KEMS’ designers were very careful, designing a long chips chamber giving a 38% concentration for their drill, while IDRA’s designers have been very optimistic, as the concentration cannot exceed 63% (Gardner, 1994, cited in Talalay, 2006). The ice-chip density inside the chips chamber can be checked during the drilling operation. If we call the design density Dd, calculated from the ice cut weight for the maximum possible core length, and the average density Da, calculated from the ice cut weight for the average core length obtained in the drilling operation, Dd varies from 0.39 (Berkner) to 0.67 (IDRA) and Da varies from 0.30 (DISC) to 0.49 (JARE). The Da obtained by the JARE drill is a maximum that can be reached inside a chips chamber. The density of ice chips inside a chip chamber depends on several factors such as chip size and chip shape, which themselves depend on cutting angle, cutting speed and ice structure. Studies of ice-chip structure would be very useful. The density of ice chips inside the chips chamber also depends on the ability of the fluid circulation and filtering systems to compact chips inside the chips chamber. Therefore it is not possible to calculate, at the time of the drill design, the ice-chip density that will be reached inside the chips chamber. The real ice-chip density value is known after the production of the first cores. History shows that very often designers are too optimistic and expect longer cores than the drill (ice-chips chamber capacity) allows. How densely the drill is able to pack the chips inside the chips chamber is an important issue. 5. CONCLUSION Data collection is incomplete, but we have some good information and possible tracks for drill design. The amount of ice chips produced, ice-chip transportation and storage are important factors in drill design. These factors directly affect the length of the drill, and therefore the speed of descent of the drill, which will have a direct impact on the duration of the whole drilling operation. The JARE drill is the most efficient in terms of ice-chip density; the mechanical action of an Archimedes screw located at the lower part of the chips chamber seems to be more efficient than the greater pump flow of the KEMS drill. Some uncertainties remain about how to overcome the problem of drilling warm ice, concerning the importance of pump flow and drillingfluid type. For most drillers, a large pump flow is a positive thing for pushing forward the limit of an electromechanical drill in warm ice, especially if cutting speed and pump flow can be driven independently, as permitted by the DISC drill. Nobody yet knows how far the limit of electromechanical drills in warm ice can be pushed. Experiments in natural temperature, fluid and pressure conditions can only be carried out on site, so it may take the drilling community a few more years to answer this question. Funding agencies, principal investigators and project partners should be aware of the difficulty of the task. This issue, arising at the very end of the project, should be resolved while drillers are still producing cores. This leaves very little room for tests and experiments, especially when, as tends to be the case, projects are running out of time and funding and the drilling teams are tired. 78 ACKNOWLEDGEMENTS We thank all the institutions and funding agencies of the different projects who have given this generation of drillers the unique opportunity of having all these deep-drilling projects take place within a few years. We warmly thank all the participants in the different drilling projects who have enabled these data to be collected and made this comparative study possible. This work is a contribution to the European Project for Ice Coring in Antarctica (EPICA), a joint European Science Foundation/European Commission scientific programme, funded by the European Union and by national contributions from Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Sweden, Switzerland and the United Kingdom. The main logistic support was provided by Institut Polaire Français–Emile Victor (IPEV) and Programma Nazionale di Ricerche in Antartide (PNRA) (at Dome C) and the Alfred-Wegener-Institut (at Dronning Maud Land). This is EPICA publication no. 203. Additional funding support was provided by the FP6 STREP EPICA-MIS. REFERENCES Augustin, L., S. Panichi and F. Frascati. 2007. EPICA Dome C 2 drilling operations: performance, difficulties, results. Ann. Glaciol., 47. Bentley, C.R. and B. Koci. 2007. Drilling to the beds of the Greenland and Antarctic ice sheets: a review. Ann. Glaciol., 47. Fujii, Y. and 25 others. 2002. Deep ice core drilling to 2503 m depth at Dome Fuji, Antarctica. Mem., Natl. Inst. Polar Res. 56, Special Issue, 103–116. Augustin and others: Drilling comparison in ‘warm ice’ Gardner, M. 1994. Matematischeskic golovolmki i razvlecheniya [Mathematical puzzles and dimensions]. Moscow, Onyx. [In Russian.] Gundestrup, N.S., S.J. Johnsen and N. Reeh. 1984. ISTUK: a deep ice core drill system. CRREL Spec. Rep. 84-34, 7–19. Kudryashov, B.B., N.I. Vasiliev and P.G. Talalay. 1994. KEMS-112 electromechanical ice core drill. Mem., Natl. Inst. Polar Res. 49, Special Issue, 138–152. Kudryashov, B.B. and 9 others. 2002. Deep ice coring at Vostok Station (East Antarctica) by an electromechanical drill. Mem., Natl. Inst. Polar Res. 56, Special Issue, 91–102. Salamatin, A.N., R.N. Vostretsov, J.R. Petit, V.Y. Lipenkov and N.I. Barkov. 1998. Geophysical and palaeoclimatic implications of the stacked temperature profile from the deep borehole at Vostok station, Antarctica. Mater. Glyatsiol. Issled./Data Glaciol Stud. 85, 233–240. Talalay, P.G. 2006. Removal of cuttings in deep ice electromechanical drills. Cold Reg. Sci. Technol., 44(2), 87–98. Talalay, P.G. and N.S. Gundestrup. 2002. Hole fluids for deep ice core drilling. Mem., Natl. Inst. Polar Res. 56, Special Issue, 148–170. Tanaka, Y. and 6 others. 1994. Development of a JARE deep ice core drill system. Mem., Natl. Inst. Polar Res. 49, Special Issue, 113–123. Ueda, H. and D.E. Garfield. 1969. Core drilling through the Antarctic ice sheet. CRREL Tech. Rep. 231. Wumkes, M.A. 1994a. Development of the U.S. deep coring ice drill. Mem., Natl. Inst. Polar Res. 49, Special Issue, 41–51. Wumkes, M.A. 1994b. Operational considerations of the U.S. deep coring ice drill. Mem., Natl. Inst. Polar Res. 49, Special Issue, 52–56. Zagorodnov, V.S., J.J. Kelley and O.V. Nagornov. 1994. Drilling of glacier boreholes with a hydrophilic liquid. Mem., Natl. Inst. Polar Res. 49, Special Issue, 153–164.
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