INTERACTION BETWEEN DRILLSTRING AND ICE-PROTECTION PIPE WHILE DRILLING DEEPWATER WELLS IN WATER BASINS WITH ICE SHEETS

摘要

While drilling deepwater stratigraphic wells in the water basins with ice sheets, drillers usually encounter the problem of a drillstring protecting from ice loads. One of the methods of the drillstring protection from ice impact provides for clearance installation of an ice pipe in the drilling vessel unit moonpool with the pipe bottom several meters below the keel. The paper suggests the numerical-analytical method of the stress-deformated state calculation for the drillstring and the ice-protection pipe with allowance for contact interaction between the drillstring, the ice protection pipe and the moonpool wall. The ice load value is determined based on the condition of equality between the kinetic energy of a moved ice floe and the elastic energy of the "drillstring - ice-protection pipe" system. The principle of the minimum potential elastic energy is used for calculating the system equilibrium configuration, with account to constraints of the system element displacement. The method of coordinate-by-coordinate descent is used to find a solution for the conditional minimization problem. The developed method is employed to evaluate the efficiency of the ice pipe design to be used while drilling deepwater stratigraphic wells from the Botnica multi-function icebreaker in the Arctic region under the International Ocean Drilling Program (IODP). The study showed that the suggested ice pipe design was capable of withstanding impacts of ice floes moving at 1.5 m/sec with thickness of 1 m and with diameter up to 3.5 m.