Abstract
Hot-water drilling in ice with near-bottom circulation is more advantageous than traditional hot-water drilling with all-over borehole circulation in terms of power consumption and weight. However, the drilling performance of this type of drill has been poorly studied. Initial experiments showed that drilling with single-orifice nozzles did not proceed smoothly. To achieve the best drilling performance, nozzles with different orifice numbers and structures are evaluated in the present study. The testing results show that a single-orifice nozzle with a 3 mm nozzle diameter and a nine-jet nozzle with a forward angle of 35° had the highest rate of penetration (1.7–1.8 m h−1) with 5.6–6.0 kW heating power. However, the nozzles with backward holes ensured a smoother drilling process and a larger borehole, although the rate of penetration was approximately 13% slower. A comparison of the hollow and solid thermal tips showed that under the same experimental conditions, the hollow drill tip had a lower flow rate, higher outlet temperature, and higher rate of penetration. This study provides a prominent reference for drilling performance prediction and drilling technology development of hot-water drilling in ice with near-bottom circulation.
Highlights
Hot-water drill systems are effectively used to provide access holes for the observation of ice shelf anisotropy, the recovery of sub-ice seabed samples, the investigation of interior ice structures, video imaging, temperature logging, estimations of distortion inside the ice, assurance of basal sliding speed, clean access to subglacial lakes, and numerous other scientific goals [1,2,3]
The hot water required is usually heated at the surface through large boilers, which are pumped at high pressure through borehole hoses into nozzles to melt the ice
A total of 60 tests were conducted in the laboratory of the Polar Research Center in Changchun (Figure 7)
Summary
Hot-water drill systems are effectively used to provide access holes for the observation of ice shelf anisotropy, the recovery of sub-ice seabed samples, the investigation of interior ice structures, video imaging, temperature logging, estimations of distortion inside the ice, assurance of basal sliding speed, clean access to subglacial lakes, and numerous other scientific goals [1,2,3] In these systems, the hot water required is usually heated at the surface through large boilers, which are pumped at high pressure through borehole hoses into nozzles to melt the ice. In most cases, an additional pump is installed to pump water from the borehole to the surface tank for recycling. Heat losses in the hot water flow are avoided before they reach the lowest part of the hole
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