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Ice core drilling complications
Authors: Zagorodnov VS, Thompson LG, Mosley-Thompson E and Kelley JJ
Year: 2002
Keywords: directional, replicate, deviation
Periodical/Journal: Memoirs of National Institute of Polar Research, Special Issue No. 56
Page Range: 196-205
Abstract: 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 'fishing tool'. 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.
ISSN/ISBN: 0386-0744
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