A new leak-tight borehole casing at Dome Concordia station, Antarctica, for the SUBGLACIOR project

Romain Duphil,Philippe Possenti,Luc Piard

doi:10.3189/2014aog68a022

Abstract

AbstractIn the frame of the SUBGLACIOR project, a new type of casing has been installed for testing during the 2013/14 austral summer season at Dome Concordia station, Antarctica. The SUBGLACIOR probe requires a full fluid column up to the surface, in order to circulate fluid for ice-chips recovery. This makes it essential that the casing is leak-tight through the porous firn column. We have evaluated existing solutions before opting to test a new method. This new system is made of polyethylene pipes which are welded together at the surface while the casing pipes are lowered into the reamed borehole. It is simple and lightweight and allows the casing to be installed quickly with optimum chance of being leak-tight. The installed casing has been tested both with compressed air and drilling fluids and has proven to work.

Highlights

Most ice-core intermediate or deep drilling projects require use of a drilling fluid to prevent borehole closure due to ice pressure
The fluid is dropped into the borehole from the surface using a basic pumping system
To prevent leakage through the porous firn layer the borehole needs to be cased throughout the first 60–120 m until the pore close-off depth of the ice is reached

Summary

INTRODUCTION

Most ice-core intermediate or deep drilling projects require use of a drilling fluid to prevent borehole closure due to ice pressure. They were lowered into the borehole with three 1.5 mm diameter stainless-steel wires (attached on a stainless-steel cap which is placed at the tip of the first section) using small manual winches This casing was very light ( 2.5 kg m–1), but was not tight. When polyethylene tubes are connected using heat fusion welding, shoulders are built up on the inner and outer pipe walls These inner shoulders should be removed mechanically by the head of the SUBGLACIOR probe, specially designed for reaming. The tubes are lowered down the borehole with three 1.5 mm diameter stainless-steel wires (attached on a stainless-steel cable which is placed at the tip of the first section) using the three small manual winches synchronously. Each cable is rated to a total weight of 600 kg

OPERATIONAL PROCEDURE DURING THE TEST SEASON

CONCLUSION