Drill heads of the deep ice electromechanical drills

Electromechanical drilling with near-bottom fluid circulation is widely used for recovering deep ice cores in Antarctica and Greenland. At least 7 different electromechanical drills have been designed: CRREL (USA), ISTUK (Denmark), KEMS (Russia), PICO-5.2″ (USA), JARE (Japan), Hans Tausen (Denmark, France, Germany, Switzerland), and DISC (USA). Choosing an optimal drill head design is one of the most important challenges for the development of ice drilling technology because it affects not only the efficiency of the ice cutting action, but also other important drilling parameters: rate of penetration, core quality, length of the run, borehole trajectory, etc. Typically a drill head consists of the body, cutters mounted to the bottom side, shoes, and core catchers. Drill head sizes and performances differ from drill to drill. At this time, current drill head design and drilling modes are successful for coring in 'cold' ice. The primary remaining problem is improving performance of drill heads in 'warm' ice close to its pressure melting point where drilling becomes complicated by icing of the cutters and drill head, packing of drill clearances, and a decrease in penetration rate. Focusing on these problems, different schemes of ice-core drill heads are reviewed, and recommendations for designing are given.