Wellhead Fatigue Analysis
Subsea Wellhead systems are subjected to fatigue damage from connected riser operations. Cyclic loading is induced through wave action or current driven vortex induced vibration (VIV). Each wellhead system has an allowable fatigue damage which is used up throughout the life of the well.
Current 5th and 6th generation drilling vessels have large subsea BOP’s which often have a natural frequency of between 4 to 6 seconds. This natural frequency often coincides with the wave frequency, resulting in wave driven resonance of the subsea BOP mounted on the wellhead. Resonance of the subsea BOP can induce in a high number of cycles, often consuming a large portion of the allowable fatigue damage during drilling of the well.
Older subsea wellheads which were drilled and worked over with 2nd to 4th generation vessels have lower subsea BOP stacks. The challenge with older wells is that they were not designed to be used with the modern day large BOP stacks. This often leaves a situation where the remaining fatigue damage is marginal, preventing future workover and abandonment operations.
AS Mosley has over 24 years of experience in managing wellhead fatigue, ensuring that a full life of well approach is adopted. The detailed analysis performed by our engineers provides operators with a prediction of the fatigue damage expected from planned operations. Our experience with challenging wells drilled several decades ago is unique, providing us with valuable lessons learned which allow us to support operations by minimising fatigue damage on critical subsea wellhead and conductor systems.
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