Directional drilling

Directional Drilling (DD) technology can be used in deep glacier boreholes to obtain additional ice cores from any depth and create supplemental boreholes for geophysical research on glacier ice properties under natural conditions. Experimental directional drilling was done using an antifreeze thermal electrical drill (ATED) in a PICO test well. A special device called a whipstock was used for the deflection of the ATED in previously-drilled borehole. The test demonstrated that a whipstock deployed in the main borehole permits directional drilling to obtain extra ice core. The experimental whipstock was placed 25cm above the bottom of the 4.5m deep borehole. The ATED was inclined in previously-prepared cavity to an angle of up to 3°. When the second borehole reached a depth of about 6m from the whipstock it had no inclination. The distance between axes of the main and secondary boreholes was about 0.3m. The whipstock was frozen into the main borehole during directional drilling experiment and afterwards, it was heated electrically and removed from the hole

Ice core drilling complications

A common fear for all ice drillers is a stuck drill. A less severe but important concern is a foreign object in a borehole, deflected borehole or slush formation in a borehole filled with an ethanol-water solution (EWS). Prevention is the most efficient way to avoid troublesome situations. However, should these problems arise it is important to be equipped with safe and efficient tools. A stuck drill occurs rather frequently but it is rarely serious. Electro-mechanical (EM) drills usually become stuck due to inefficient chip removal from the kerf. When the drill gets stuck there are several possible actions. The simplest initial approach should be sharp jerks with a reverse rotating core barrel. Many times the Byrd Polar Research Center (BPRC) dry hole EM drill has been successfully recover using this technique. When this technique fails, another solution to the problem is to pour a few liters of auto-antifreeze into the hole using a rubber hose to bypass the upper firn. This usually frees the drill in less than one hour. In 1999 the cable on the BPRC EM drill broke, but we successfully recovered the drill from 110m depth using \u27fishing tool\u27. Ethanol thermal drills also experience complications. In order to free a thermal drill when the main heating element has failed, a second heating element can be turned-on by switching the polarity of the power. There are a number of reasons why slush can form and clog a borehole. This paper presents a field proven technique for the EWS concentration correction at any depth in the borehole. Directional drilling (DD) techniques can be used to resume drilling if the drill or foreign object cannot be removed from the borehole. This paper discusses how to recover a drill with a broken cable and describes techniques that may be used to prevent cable suspended drills similar to the BPRC dry hole EM drill from becoming stuck. The paper discusses how to maintain the correct EWS concentration and general drill design safety options

Controller for portable intermediate depth ice core drilling system

The primary objective of ice core drilling is to obtain the highest quality core while minimizing the effort needed. This requires a control system with precision control and convenient operation. An intermediate-depth portable ice core drilling system designed and constructed at the Byrd Polar Research Center (BPRC) has been tested during four expeditions under different working conditions. Several design options were tested to both control and monitor performance of the winch, thermal and electro-mechanic drills. An attempt has been made to develop a universal controller that can be used with either thermal or electro-mechanical drills and with various power sources, ranging from a conventional alternating current (AC) portable generator, custom high voltage direct current (DC) generator or an array of solar panels. Currently, controller system built in two configurations : (1) to operate a 500m winch, dry hole electro-mechanical (EM) drill and fluid electro-thermal (ET) drill at low (1kW) power, and (2) to operate a 500m winch, EM and ET drills at high power (400Vdc and 6.0kW). To allow the use of different power sources and different drills a modular design was chosen. The control system includes three modules : (1) for measuring and indicating drill depth, drill rate, and cable tension, (2) for driving reversible winch and drill motors at the same time (225Vdc, 2.25kW), and (3) for driving a high power (400Vdc, 20kW) drill or winch motor. The controllers are built around industrial servo-amplifiers (SA) for DC brush motors and have over-voltage and over-current protection. This design permits convenient positioning of each module on the winch frame. This paper describes the details of the design and functional options of an ice drill control system

Performance of intermediate depth portable ice core drilling system on polar and temperate glaciers

A portable ice core drilling system was developed at the Byrd Polar Research Center (BPRC) and tested during four field seasons on both polar and temperate ice fields. The prime features of the new drilling system include its low power requirement, light weight, depth capability of 500m, quick setup, easy ice core handling, and high ice core production rate (ICPR). Since 1997,more than 1200m of ice cores has been recovered with the BPRC dry hole electro-mechanical (EM) drill. After modifications described in this paper, the drill achieved the following performance characteristics : (1) drilling from the surface to 15m in one hour in cold firn; (2) drilling to 30m within 2.5 hours and (3) drilling to 100m within 14 hours, with an average ICPR of 7.15m/h. Six boreholes in the temperate ice on the summit of Mt. Kilimanjaro (5985m a. s. l.) totaling 200m were drilled to bedrock. The deepest hole was drilled down to 51m. High concentrations of dust and thick layers of volcanic ash were common features in the Mt. Kilimanjaro ice, where the average ICPR was 8-10m/h. A new version of the antifreeze-thermal-electric drill (ATED) has been developed and laboratory tested. The paper presents a comprehensive examination of the EM and ATED drill performances based on quantitative data regarding drill design and conditions at drilling sites. The optimal protocol for coring in polar and temperate ice at air temperatures above the melting point is examined

Intermediate depth ice core drilling support systems: power generators and shelters

Arctic and high altitude ice coring operations require lightweight and efficient equipment. Power sources, fuel and shelters in some cases compose up to 50% of the cargo delivered to a drilling site. Solar panels, two-stroke gasoline and air-cooled portable diesel generators have been used in Arctic and high altitude glaciers to power the drilling setup. On the summit of Mt. Kilimanjaro (5895m above sea level) a portable air cooled diesel generator provided 1kW of electricity for electro-mechanical drilling. The average fuel consumption was 0.66liters of fuel per hour. More than 150m of ice cores in three locations were drilled with this power source. For 150m shallow ice coring a diesel generator and fuel was found to be 40% of the weight than 1.5kW array of solar panels. Assembly and disassembly of diesel generator takes one tenth of the time necessary to assemble/disassemble the array of solar panels. However, solar power is environmentally friendly. The purpose of the shelter is to protect personnel and equipment from the wind and blowing snow. At high altitude drilling sites the shelter provides a shadow to keep the drill and an ice core at temperatures below freezing. A set of lightweight shelters allowed flexible and weather independent ice coring operations in the Arctic and high altitude glaciers. Custom-built and commercially available lightweight geodesic domes have a 12man/h setup time and provide comfortable working conditions during stormy days in Greenland and on the summit of Mt. Kilimanjaro. An additional reflective cover maintains the air temperature inside of the dome below the freezing point at 1200-1300W/m^2 solar radiation. A portable, fast setup and commercially available shelter for the power generator was tested and demonstrated durableness during stormy days in Greenland. This paper describes field-tested, lightweight, reliable and fuel-efficient power generators and lightweight shelters