Phase 2 of the RAID project entails construction, assembly and testing of the RAID drilling platform, including staging in Antarctica for future scientific operation on the East Antarctic ice cap. To prepare for future readiness, field trials with the RAID system were completed in austral summer field seasons between 2016 and 2020. Having tested what we could in North America in our synthetic ice column, we conducted the Antarctic Field Trials (AFT) in thick firn and ice in order to test individual components, validate our operational plan, evaluate full integration of the drilling system in a deep-ice setting, and learn from drilling operations in order to prepare for science drilling as an autonomous, traverse-capable system. Antarctica is the only place to effectively integrate the entire drilling system under real-world conditions and evaluate the capability of components designed for operation in the thick firn and ice expected on the polar ice cap.
To prove the operational capacity of the mobile RAID system, our field trials included traversing over snow, site set-up, augering of firn and installation of casing, drilling through thick ice, retrieving ice and rock cores, rigging down, stabilizing the borehole, and redeploying to a base station. Specific technical goals are outlined below.
Our field trials took place near McMurdo Station to take advantage of the established USAP transport and logistics system, thereby reducing risk, cost, and footprint in Antarctica. The RAID equipment was shipped to Antarctica in late 2015 and off-loaded at McMurdo Station in January 2016. After wintering over, the first field trials (AFT1) began in late 2016 after the RAID equipment was moved from winter storage to the nearby ice shelf, loaded onto ski platforms, and traversed to a drilling site near Minna Bluff (see figure). After each field trial, the equipment was winterized on snow berms at Williams Field to be readied for future testing or traversing to South Pole. The RAID field trials were conducted autonomously from McMurdo and other Antarctic services to provide a realistic exercise of future science operations, but the close proximity to McMurdo provided a backup of mechanical, field, and medical services if needed.
The primary criteria for selecting a site to conduct RAID field trials are simple — thick, grounded ice. Ideally, a suitable location is accessible for multiple ski-module deployment, within relatively short traverse range, and be fairly flat with no steep slopes. The small plateaus of grounded ice on the south side of Minna Bluff provide the best location for full-scale field trials of the RAID drilling system in the McMurdo operating area. At Minna Bluff the ice has a thickness of about 600 m, is easily accessible by traversing across the Ross Ice Shelf along the established South Pole traverse (SPoT) route, and rises gently above the ice shelf at two small piedmont glaciers, all within a traverse distance of <200 km.
The region near McMurdo Station is primarily underlain by rocks of the McMurdo Volcanic Group, chiefly alkaline basalts exemplified by the eruptive units on Ross Island, Mt. Erebus and Mt. Discovery. Minna Bluff is a narrow, 45 km-long ridge extending southeast from Mt. Discovery, a Miocene alkaline stratovolcano. The main rock types are basanite and phonolite containing large (up to 5 cm) kaersutite and feldspar megacrysts, abundant comagmatic inclusions (kaersutite-rich), and rare mantle xenoliths. Since the late Miocene, Minna Bluff has been a terminal pinning point for the Ross Ice Shelf and is a local topographic barrier helping to block the Ross Ice Shelf from flowing into McMurdo Sound. Eruptions of alkaline basalt occurred between about 8-12 Ma, during which time lavas partly interacted with ephemeral glacial ice. Minna Bluff is surrounded by thick, relatively stable ice of the Ross Ice Shelf, which extends to McMurdo Station.
Airborne ice-penetrating radar (IPR) was flown across this area by the University of Texas-Austin to image the edge of the Ross Ice Shelf in the vicinity of Minna Bluff, White Island and Black Island. A representative radargram is shown (see figure), which transects the eastern of the two small piedmont glaciers and the eastern flank of Black Island. On the southern end, this record shows the transition between thick ice overlying water in the Ross Sea and bedrock of Minna Bluff. A grounding line is visible at about –45 km (at the surface break in slope). The very intense, flat reflector at about –400 m depth is the base of floating ice over seawater and shows strong multiples (reflected radar waves) below. The rougher reflector toward Minna Bluff is the grounded ice interface. Internal reflectors within grounded ice show a continuous record of ice accumulation banked against bedrock. AFT sites for the drilling trials were chosen because they have greatest thickness (≥600 m) and lie farthest from subglacial water of the Ross Sea.
The primary goal of the Antarctic field trials is to probe the RAID system’s ability to operate successfully as an integrated whole instrument in a realistic, thick-ice environment. RAID is a complex system whose components have been individually tested, but experience shows that a successful system is much more than the sum of its parts. For this reason, whole-system testing is crucial. Personnel are also very much a part of this system, and Antarctic field trials give us an opportunity to assess field team integration.
For practical reasons, the lack of deep ice in North America precluded a realistic test of the deep-borehole fluid circulation and other unique facets of RAID. Although completion of a North American Test in Utah in early 2015 required successful integration of key RAID components, the test facility simply could not reproduce Antarctic deep-ice conditions. Computational fluid dynamics modeling indicated no fluid pressure problems during deep ice drilling, but the future success of RAID depends on real-world field trials. Notably, the speed of penetration and other RAID operational steps must be measured for overall RAID planning purposes and ultimate success in the deep field, and this is only possible in a realistic setting. At the same time, trials are best done in a low-marginal-cost and low-risk environment, rather than directly on the Polar Plateau.
Taking into consideration all these factors, we chose the location at Minna Bluff near McMurdo as the best compromise between realism, cost, and risk. Antarctic field trials also provided an invaluable opportunity for drillers to learn in the harsh environment of Antarctica. The Minna Bluff site is legendary for its sudden storms (“Herbie Alley”), yet it is relatively close to McMurdo in the event of a true emergency. Safety is the number one priority of RAID operations, and the field trials provided an excellent chance to flag potential safety concerns and implement mitigation of safety issues.
The RAID concept fundamentally embodies speed, with a design ultimately intended to produce multiple holes to bedrock per season. This translates to a design goal of about 40 hours to drill through 3000 m of ice. Therefore, one important objective of the Antarctic field trials is to measure how fast RAID can penetrate thick ice, including all the pipe handling and fluid recirculation processes. With only 600 m of ice at Minna Bluff, the comparable duration at this speed would be 8 hours. Because the ice thickness is slightly more than 600 m, a small increment of ice at the bottom of the borehole can be used for further tests of the ice coring systems.
A multitude of other small tasks must be performed in a nimble fashion if RAID is to ultimately succeed and deliver scientific discovery at a high rate. We defined a full list of criteria that will be evaluated for determining success of the field trials, including many speed-related benchmarks. These are provided in section 6 of the original AFT Field Plan [download PDF].
FIELD TRIAL RESULTS
RAID deployed to the field for its first Antarctic Field Trials (AFT1) in October, 2016. An initial deployment of drillers from DOSECC Exploration Services (DES) to Antarctica in mid-October began the process of unpacking the RAID modules from winter storage, preparing all equipment for the field, and mounting the RAID modules on ISO ski units in preparation for traversing to the test site at Minna Bluff.
The RAID traverse left McMurdo Station on November 23, arriving at Minna Bluff on the 26th. The remaining team of drillers flew to the newly established field camp on November 30, and the RAID PI’s and project manager were transported on December 2.
Drilling operations commenced on December 1 and continued until December 26. An initial large-diameter borehole was made by auger at the first hole (A.1.1) to a depth of 49 m. Unable to make a pressure seal with the borehole packer, the hole was deepened by extending the auger length with the addition of small-OD drilling rods. On December 3, the augers became stuck in the borehole above a cut depth of 52 m after attempting to evacuate firn cuttings. Upon attempting to remove the augers from the borehole, one of the connecting pins sheared off, leaving 19 sections of auger in the hole. Various attempts were made to free the augers, but no mechanical process was successful. After receiving approval from the NSF, direct application of an antifreeze (glycol) helped to free the augers and the entire string was removed on December 8.
Attempts were made to deepen hole A.1.1 by a combination of augering short distances and bailing out cuttings, coupled with periodic pressure tests with the packer unit. After attempting a pressure test at 67 m depth, the augers became packed in with cuttings again on December 14. As before, glycol was applied to the stuck augers after receiving approval for this release from the NSF, and the augers were freed by December 19. At this point, hole A.1.1 was abandoned with no positive pressure test achieved.
The RAID drill and rod modules were moved to a new site (A.1.2) on December 20 and set up to begin a new auger borehole on December 21. A supplementary set of augers was purchased and delivered from a New Zealand supplier, which arrived from McMurdo on December 20. Firn augering commenced at A.1.2 on December 21 and quickly reached a cut depth of 78 m in a few hours, after which all augers were removed. A subsequent pressure test failed to reach an effective seal at a depth of 72 m. After extensive efforts to remove all cuttings from the borehole (without the use of augers), the hole was cleared to a depth of 78 m for pressure tests beginning on December 24. Several attempts to achieve a positive pressure test were made, but no combination of equipment, pressurization, or hole conditioning was successful. Following a decision from the NSF on December 27, hole A.1.2 was also abandoned and the project started preparations for demobilization back to McMurdo.
In summary, two boreholes were attempted at Minna Bluff and neither one resulted in reaching below the firn zone to create a successful seal against non-permeable ice. Many of the tangible first-order drilling goals for the AFT were not achieved, including deep ice drilling by use of fluid circulation, taking deep ice cores, and taking cores of subglacial rock. Despite the challenges and limited results, however, the AFT provided many positive outcomes and lessons learned.
In AFT1, we learned to avoid getting augers stuck in the firn by decreasing the rotation rate so as not to induce melting and refreezing of cuttings, and to bring extra auger flights to the field in the anticipation of encountering firn layer thickness greater than expected. Progress was also limited by not fully anticipating equipment needs. On the positive side, AFT1 demon- strated the soundness of mounting modules on skis, capability of traverse vehicles, functioning of the power module temperature control system and rig set-up and take-down. AFT1 also showed that it is possible to auger quickly through firn (3 h) to 79 m depth, with no issues of excessive torque, which had been a concern.
AFT2 (2017-18). The RAID project conducted its second Antarctic Field Trials (AFT2) during the month from December 5, 2017 to January 10, 2018. Over these field trials we successfully established a camp by traverse; set up the RAID system in a field setting; augered multiple boreholes through firn to record depths (maximum 131 m); set a packer and maintained a pressure seal; established fluid circulation between the drill and fluid-recirculation system; and advanced the ice drill in reverse-circulation (RC) mode.
Challenges and delays were the result of several factors. Weather delays were significant this year, resulting in an eight-day delay of our first crew getting to McMurdo. Next a hydraulic issue with the drill caused a nine-day delay to troubleshoot and assess. Next, an improperly redesigned auger bit resulted in a too-narrow hole; this resulted in auger sticking, excess chips in the hole, and difficulty positioning the packer at the firn-ice transition. A field decision was made to use the drill to force the packer down the borehole, which may have contributed to later hydrofracturing.
Luckily, adequate units of the older auger bit design were on-hand to auger the proper diameter hole. However, using the older design resulted in excess chips (part of the reason for the redesign). Successful augering rates and over-drilling of the hole (to 130 m) mitigated the chip problems and led to a successful packer placement. Fluid drilling was initiated but was delayed by ice blockage and valve failure in the Fluid Recirculation System (FRS) that may have been caused by improper shut-down and storage the previous season. After repairs were made the fluid drilling had problems due to clogging of the ice-cutting bits when advancing through the fluid-ice slurry (perhaps due to excess ice chips in the hole due to the old auger cutting bit design). In addition, hydrofracturing of ice occurred at significantly lower pressure than was experienced in prior seasons tests (perhaps a result of pushing the packer down the first borehole and stressing the ice). Together, these resulted in delays that ultimately caused us to miss our major goals of drilling a deep ice borehole and coring either ice or bedrock.
Three boreholes were augered to depths of 97, 105 and 131 m, respectively. The first hole (Dec 17) was made with an improperly redesigned cutting head (the cutting head lagged the auger flights by 60°) that also was too small relative to the packer diameter. The second (Dec 23) and third (Dec 26) holes were made with the older, wider cutting head reconfigured with a new cutter geometry. Each hole presented challenges with proportion of ice cuttings, installing the packer, and making a packer seal, resulting in slow progress and numerous changes in anticipation of RC drilling. Based on observations made at the time, the team took an approach of experimentation, testing, and information-gathering over a goal of advancing the drill. Findings from these experiences were captured in valuable lessons learned.
An important problem concerns the ability and risk of ice to hydrofracture. This is a common problem in any kind of fluid-assisted drilling, and there is virtually no prior experience with this while drilling ice in Antarctica, other than the RAID packer test at Castle Rock in 2015-16. At that test, ice was found to hydrofracture at 150 psig, whereas it fractured at 105 psig at Minna Bluff this year. It is possible that the prior fracturing of the ice due to forcing the packer down in Hole #1 (located 10 feet away horizontally from subsequent holes) created weaknesses that enabled the hydrofracturing.
Lessons from AFT2 included recognition that improper auger cutting head geometry (in particular, misalignment or ‘clocking’ of the cutters with respect to the openings onto the auger flights) causes clogging of the bit with ice and contributes to the risk of getting the auger string stuck. A crucial lesson was that hydraulic fracturing of the ice due to fluid overpressure is an inherent risk that must be carefully managed going forward. Here, over-pressure means the excess borehole fluid pressure required to induce fracture in ice, which we define simply as the total fluid pressure minus the ice pressure or, more explicitly, the surface fluid pressure measured at the pump plus the fluid hydrostatic pressure in the borehole column minus the ice hydrostatic (or overburden) pressure. Overpressure in this context is the fluid pressure required to hydraulically fracture ice at depth in a borehole. At AFT2, the ice hydrofractured at an overpressure of only 0.7 MPa, or 105 psig, even though the drill design calls for overpressures as high as 1 MPa, or 150 psig, in order to circulate the fluid during deep drilling. It was also demonstrated that too close a proximity of boreholes in AFT2 (<100 m separation) might have contributed to hydrofracture by weakening the ice, particularly under the warm conditions at Minna Bluff. Hydrofracture problems and risks are discussed in an internal report here.
AFT3 (2019-20). We completed a successful third round of Antarctic Field Trials (AFT3) with RAID at Minna Bluff during the 2019-20 austral season. Major goals identified for AFT3 were achieved, despite several both inherent and unexpected challenges. As a result, the Antarctic Field Trials have demonstrated that as a working prototype RAID has the capability for which it was designed.
Between November 2019 and February 2020, RAID completed 4 boreholes at three drill sites. We demonstrated routine firn augering and setting a packer seal, establishing fluid circulation for ice drilling, fast cutting of a borehole in ice, switching to wireline bottom-hole coring, retrieving cores of subglacial materials, and logging holes with an optical dust logger.
Highlights of major outcomes include the following:
- fast augering of three firn boreholes to accommodate a packer at depths of 85-107 m, now established as a reliable method for making holes in firn
- successful testing of a new borehole ‘bailer’, designed and built by IDP to remove firn cuttings and ready the borehole for deployment of a packer
- demonstrated first use of a conventional ice-core drill with modified cutters to make a microcrack-free packer seal, and to recover several meter-long ice cores for density verification
- found via testing that 350 psi is a safe and effective pressure for packer inflation to seal off the permeable firn with casing
- collection of core samples from firn-ice transition for H2 measurement
- rapid deep ice drilling using a non-coring rotary ice-cutting bit with fluid circulation (penetration up to about 680 m, a new Antarctic record)
- first successful use of a new pressure relief valve to prevent accidental hydrofracture of ice by fluid overpressure
- measurement of temperature (-10 °C) at the bottom of a borehole reaching the glacier bed, demonstrating a cold-based glacier and validating heat model prediction of -10.3 ˚C
- successful penetration into a mixed zone of glacial ice, mud, and glacial debris, all while maintaining fluid circulation
- cored 1 m of near-basal ice for gas, age, and isotopic analysis using wireline coring inserts
- cored basal glacial till and 3 m of bedrock from just below ice-rock transition
- obtained borehole logs using the ‘slim’ Bay-type laser dust logger made for RAID boreholes
- obtained borehole video logs using an optical televiewer
- development of a new method to evacuate drilling fluid from boreholes
- down-rigging, packing, moving, and re-rigging the RAID system between drill sites in less than 1.5 days
- demonstrated ability to drill ice quickly, equivalent to 2000 ft in 8 hours, in 3rd hole
- discovered that the risk of hydrofracture does not increase with depth, as predicted
- blog posts during the field season, providing a real-time picture of life in the field and RAID drilling progress to the public.