Heat transfer modelling of thermal anti-freezing method for ice hot-point drilling

Abstract

The melting water produced from ice during hot-point drilling can easily freeze and cause the hot-point drill to stick. Two different thermal anti-freezing methods exist to prevent water-filled boreholes from refreezing: the heating cable method and lateral heating method. However, the required power density and ice temperature distribution when using these two methods have not been fully discussed. In this study, heat transfer models of the two thermal anti-freezing methods were first developed based on a simplified heat conduction equation by considering the downward movement of the hot-point drill. Subsequently, case studies were conducted to determine the characteristics of the heat transfer during hot-point drilling. Finally, the variations in the power density, power consumption, borehole closure time, borehole closure length, and thermal layer thickness for both thermal anti-freezing methods were evaluated. We recommend that the heating cable method should be used to drill boreholes with shallow depths or small diameters in temperate ice, whereas the lateral heating method can be applied to a wide range of ice temperatures, borehole diameters, and borehole depths. Generally, the paper presents useful guidance for designing the heating cable and lateral heater and reducing the risk of borehole freezing.