Studies on pneumatic transport of ice cores in reverse circulation air drilling

Reverse circulation air drilling is considered one of the most promising technologies in ice core drilling because it can provide many benefits such as avoiding air circulation loss in snow-firn zones, promoting penetration rate, and shortening the time required for ice core recovery. The key of this technology is using a pneumatic conveying system to transport ice cores and ice chips from the bottom of the borehole to the surface. Therefore, analysis of air injection parameters is important for improved understanding of drilling ice cores with reverse circulation to enhance air drilling operations. To determine the adequate volume flow rate of the gas required to satisfy the demand for pneumatic conveying of ice cores and chips, a general theoretical model was developed in this study. A series of experiments were carried out to test the actual velocity and the pressure drop required to convey ice cores and ice chips. The experimental results exhibit reasonable agreement with the calculation data, and the maximum and the minimum errors between the calculated and experimental results are about 12.55% and 0.60%, respectively. Based on the theoretical models, the air volume flow rate profiles along the borehole depth were estimated. For a borehole depth of 500 m, to convey an ice core with diameter of 90 mm and a length of 500 mm, the minimum volume flow rate and the injection pressure of air under standard atmospheric conditions is about 5.25 m³/min and 1.06 MPa, respectively, if the clearance between the ice core and the wall of the inner drill pipes is set at 4 mm.