Replicate Coring System
Replicate coring begins by lowering equipment to a depth of special interest and shaving, or broaching, ice from one side of the borehole. All boreholes have a slight inclination (tilt) to them, and the ice is shaved off of only the higher side (the headwall) of the hole.
The broaching continues until about a 13-meter-tall wedge of ice has been removed from the side of the hole. The tip of the wedge points up the hole, and the penetration of the wedge into the side of the borehole increases to about 10 centimeters at the bottom of the wedge. Another piece of equipment cuts a flat shelf at the bottom of the wedge, which is the starting point for recovering “replicate” core that is parallel to the main core.
The wedge of removed ice provides space to tilt the coring drill out of the main borehole so the coring drill head can bore into the shelf. Replicate core will be recovered along paths that are from seven to 92 meters long depending on the science needs.
The drill uses arms that push against the side of the hole to tilt the drill in the borehole, allowing drilling operations to be directed at a specific side of the borehole. To perform the process requires a range of sensors that monitor azimuth, inclination, horizontal force, amount of extension of the arms, and cutting speed and torque, as well as good communications between the drill and engineers.
The deviation is made out of the higher side of the borehole so that borehole logging equipment can slide down the lower side of the borehole and not get trapped in the short hole created by the replicate coring system.