Technology of drilling in permanently frozen rock

When drilling in frozen rock,the temperature in borehole is one of the main factors influencing drilling technology.The rule and characteristic of the defrosting zone's development around the borehole at different temperature levels are depicted.Characteristics of technology of starting a hole are analyzed from the drilling fluid's components,temperature and flow regime,and from drilling time and rate as well.According to the relation between the temperature and the ratio of the diameter of the defrosting zone to that of the drilling bit,the volume of washing fluid is optimized.The permissible temperature of casing is determined by the diameters of casing and drilling bit and the temperature of washing fluid.Suggestions on improving the quality of cementing in frozen rock are brought forward.