Abstract:The warm ice at the bottom of polar ice sheet has small brittleness, high viscoelasticity, high temperature and pressure, and poor drillability. The cutting heat generated during rotary drilling can easily cause the ice chips to be in melting or semi-melting state; as a result, the ice chips will gather together and even freeze again locally over the drilling tool, resulting in frequent accidents in the hole. In order to understand the temperature change law of cutting tools during ice rotary drilling, theoretical study is conducted on the mechanical characteristics and heat transfer law of cutting tools, and then the theoretical model for cutting tool temperature calculation under drilling fluid circulation is established. The result shows that rotation speed of the drilling bit, cutting depth, friction coefficient, cutting edge angle and ice shearing strength et al. are all have important impact on cutting temperature. Although the low-temperature drilling fluid has good cooling and cooling performance, it can still make the cutting tool temperature rise by 2 to 5℃, adversely affecting warm ice drilling. In-depth optimization should also be made for the combination of drilling parameter.

Abstract:The ice core in Polar regions contains precious ancient climate and environment information, records the ancient atmospheric composition, and have characteristics of higher resolution, long time scale and amount of information and so on. It is very important to obtain ancient deep ice core to reconstruction the earth evolution and to predict the global climate changing. Therefore, the scientists in world are looking for ancient ice core and planning to carry out new deep ice core drilling projects. However, there are lots of problems when drilling in warm ice since the ice having lower melting point and higher temperature such as the slowly drilling speed, the lower core recovery and more sticking accidents and so on. So the warm ice drilling practices in Polar Regions are reviewed in this paper. And the technology problems drilling in warm ice are analyzed. At the same time, the influences of the cutting heat generated in the rotary drilling on drilling process are discussed. Based on these analyses, the research directions in future and the technical countermeasures for warm ice drilling are also put forward in this study, which may be provide some reference for our coming deep ice core drilling project and the subglacial bedrock core drilling project in Antarctica.

Abstract:Cutting heat generated during rotary drilling is extremely easy to melt ice located in warm ice layer of deep ice cap because the high temperature is almost close to or even reach ice pressure melting point, which results in low penetration rate, poor core recovery and frequent sticking accidents. So it is necessary to design a device to test the cutting heat which is influenced by WOB, rotation speed and the structure of cutting tool; the test results would provide the theoretical basis for the design of cutting tool structure and optimization of drilling parameters. With the XY-1 core drilling system as the platform, using the wireless signal transmission principle, the test stand for testing cutting heat generated during rotational drilling in ice layer is designed. Preliminary test results show that by this experimental device, the parameters of WOB, torque and cutting temperature can be accurately measured, which can also be used for the related experimental study.