Influence Analysis of the Vibration Frequency to the Dynamic Response of Deepwater Drilling Casing String

The dynamic response of the casing string under the mud line is concerned by engineer when deepwater drilling operating. Considering with the nonlinear characteristics of seabed soil, a dynamic differential equation of the casing string below mud line was established. Then the Newmark method was adapted to solving this equation by time step. Results illustrate that, the deformation and internal force of the casing string in low frequency region have little difference with the static situation. The amplitude of the string displacement increases gradually at the natural frequency. And the hysteretic phenomenon more and more obviously at this point also. In general, there are almost no influences to the dynamic lateral bearing of the casing string when not considering the wellhead vertical force. Use a static method to analyses the wellhead stability and the string bearing capacity can meet the project requirement. The dynamic analysis of casing string coupled with the marine riser is very necessary to future work.