Wellhead and Conductor Assessments
Wellhead and conductor systems are subject to loading from connected riser operations.
Wellhead loading can come from the following sources:
- Static and dynamic loads imparted through vessel motions
- Environmental wave loading induced through the riser
- Environmental current induced loading
- Static and dynamic axial tension loads
- Accidental events such as a single mooring line failure or dynamic positioning drift off/drive off scenario
Operating envelopes for connected riser operations and a calculated fatigue life are typical outputs of a wellhead and conductor assessment.
Loading on subsea wellhead and conductors has increased significantly in the past few years due to 5th and 6th generation drilling vessels. The large subsea BOP’s often have a natural frequency of between 3 to 6 seconds, which often coincides with the wave frequency. This results in BOP dynamics which can induce a high number of cycles, often consuming a large portion of the allowable fatigue damage during drilling of the well. The structural strength and fatigue resistance of a wellhead and conductor system is required to be certified before operations can be safely performed.
It is also prudent during the well planning stage that the potential for a cement shortfall is considered. Analysis is performed by AS Mosley to investigate the effect of either an external cement shortfall and/or a shortfall between the surface casing and conductor. Figure 1 provides an example of an external cement shortfall which can occur during well construction where cement returns to mudline are not achieved.
Figure 1 – External Cement Shortfall Example
AS Mosley has over 22 years of experience in managing wellhead and conductor assessments, ensuring that operating limits are maximised and fatigue damage minimised. The detailed analysis performed by our engineers provides operators with a prediction of the structural loading and fatigue damage expected from planned operations. Our experience with challenging North Sea wells drilled several decades ago is unique, providing us with valuable lessons learned which allow us to support operations.
For more information on Wellhead & Conductor analysis contact us directly.