Research On Melting Process And Ice Hot-water Drilling System

Hot-water drilling is one of the fastest methods to drill boreholes in glaciers and nowadays it is actively used for the observation of ocean cavities under ice shelves,the retrieval of sub-ice seabed samples,the study of internal ice structures,video imaging,temperature logging,measurements of deformation within ice,the determination of basal sliding velocity,clean accessing to subglacial lakes,and many other scientific objectives.The main aim of the research is to develop theoretical basis of the hot-water ice drilling systems and establish relationship between the key drilling parameters(flow rate,delivery pressure and temperature of the delivered water),controlled outcome variables(diameter of the drilled borehole,rate of penetration,power and oil consumption for ice melting and refreezing rate of the borehole)and independent variables(current/target depth and temperature of ice).The paper summarized the research significance and current development of hot water drilling technology at home and abroad in high-mountain glaciers and polar ice drilling,recognized the serious lack of theoretical research of hot water drilling technology in China,and tried to solve the problems of insufficient theoretical research on hot water drilling and ice melting process.Numerical modeling of hot-water drill was made and a shallow hot-water drilling system was developed.The main conclusions of the paper are:(1)Theoretical estimations of hot-water drilling parameters showed that higher flowrate and water temperature could achieve bigger rate of penetration(ROP)and borehole diameter.In most cases of intermediate or deep hot-water drilling,the friction pressure losses play critical roles in the required delivery pressure of hot water flow,and mostly depend on the length of the hose,hose diameter,and flow rate,while the local pressure losses may be much more important for shallow drills to provide a strong contact upon bottom ice.The length of time that a borehole remains sufficiently open depends on the surrounding ice temperatures and initial borehole radius.(2)The author used effective heat capacity method to make simulation modeling of hot-water ice-melting process.For short-time simulation,flowrate and water temperature have obvious effect on ROP but fewer influence on borehole diameter.The results of modeling simulation of refreezing rate are similar with the calculation results.For 0.3 m borehole diameter,if ice temperature was-30?,the borehole would totally get frozen after 12 h;if ice temperature was-10?,the borehole would keep open even after 72 h.(3)A portable shallow hot-water drill system has been designed and tested in an ice drilling test facility that allows the testing of numerous ice drills throughout the year.The shallow hot-water drill system is composed of 4 sub-systems: water heating system,consists of a high pressure washer,that could deliver water at a temperature in the range of 80–155?C,a flow of 4–10 L/min and a pressure as high as 14 MPa;water delivery system,mainly consists of winch and high-pressure hose,valves;drilling system,consists of mast,dead weight and nozzle;control and measuring system,consists of control box,encoder,temperature sensors,water pressure gauge,flow meter,inner dimeter gauge etc..(4)In general,the shallow hot water ice drilling system worked adequately.The nozzles with a 1.8-mm,2-mm,and 2.5-mm orifice diameter fit best with the system,and a large orifice diameter(3 mm)created a large-diameter borehole with a proportionate decrease in the ROP.Under the hot water flowrate of 10 L/min with a temperature of 60 °C,the 1.8-mm and 2-mm nozzles created 98–114 mm diameter boreholes at a penetration rate of 34–37 m/h,while the 2.5-mm nozzle produced a 146–156 mm borehole at a rate of approximately 25 m/h.The highest efficiency(relation of power used for ice melting to input power from fuel energy)of 83% was achieved in the Run 17 because ROP was as high as 29.5 m/h and drilling depth was quite shallow(only 3 m)resulting rather small heat losses in surrounding ice.While in the other runs the efficiency was smaller in the range of 67-76%.The heat losses were attributed mainly due to the unproductive heat conducted into ice or air and energy loss in burner.(5)Results of the theoretical estimations were evaluated through comparison with the main drilling parameters obtained through laboratory tests.Most of the deviation between the experiments and theoretical estimations did not exceed 7%(in most cases the experiment data were smaller than the theoretical lines).However,several experimental points had a deviation as high as 21%,which could be explained by the observational errors and system malfunctions during the tests.In general,the theoretical data and model seems to be accurate and can be used for estimations of the main parameters of hot-water drilling systems.