Theory calculation and testing of air injection parameters in ice core drilling with air reverse circulation

Drilling with air reverse circulation is considered one of the most promising technologies in ice core drilling, especially in firn-ice drilling, as it has many advantages in preventing air circulation loss, improving stability of the borehole, and promoting penetration rate. The effectiveness of this technology depends on whether or not the ice chips and cores can be conveyed to the surface through the central channel of the drill tool. In order to determine the adequate volume flow rate of the gas needed to satisfy the demand for continuous return of the ice cores and chips, a mathematical model to evaluate the injection pressure was studied. A series of experiments were carried out to test the actual air velocity required to move ice cores and ice chips with different sizes and clearances between the ice cores and the inner wall of the pipe. Based on the calculation and testing results, the minimum air volume requirements with different borehole depths in ice core drilling with air reverse circulation were confirmed. For a borehole with depth of 1000 m and diameter of 134 mm, the volume flow rate and pressure of air under standard atmosphere condition are at least 6.27 m³/min and 0.70 MPa to transport ice chips and ice cores with diameter of 60 mm and length of 250 mm.