Ice-core drilling problems and solutions

Drilling problems include any difficulties encountered while drilling a borehole. Even during carefully planned projects different problems can occur while drilling in ice. The common drilling technology in ice sheets and glaciers differs from conventional rock drilling and that is why the causes of drilling accidents and the ways they can be eliminated are also different. The most commonly encountered ice-core drilling problems are the following: lost objects in the borehole, sticking drills, disorder cable spooling, cable damages, breakdown of surface and downhole equipment, casing leaking, and inability for penetration. This paper addresses possible solutions and, in certain cases, preventive measures for solving of these problems. Fishing with magnetic tool or conical drill head are proven methods of retrieving relatively small details from the borehole. Problems with cable behavior can be solved by orthocyclic spooling method and careful cable pre-tension. To prevent leaking in the casing shoe, a special thermal head is proposed. Problems associated with borehole closure can be solved by the limitation of the drilling depth in dry holes and the limitation of the closure rate in wet holes. Series of proven and unproven measures were suggested to improve drilling performance in the warm ice but still now the ultimate decision is not found. Using the technique of dropping frozen glycol, it is possible to free a drill stuck in a deep hole at temperatures down to ~ − 30-40 °C. If all attempts to recover the sticking drill are unsuccessful, the next step of accident elimination should be focused on removing of the cable from the hole. The simplest way is to use rotary wireline cutter. Then the hole can be deviated using gravity features of cable-suspended drilling technology and drilling can be continued to the target depth.