Enabling safe and reliable operations of subsea wellheads has a high priority in the global oil and gas industry. The objective of the current paper is to provide a novel method for bending moment estimates at the wellhead based on indirect moment measurements; this moment, together with fatigue properties are then used for fatigue damage estimation. Indirect bending moments are based on inclinations and accelerations measured by motion reference units (MRU) attached to blowout preventer (BOP), lower marine riser package (LMRP) and lower riser joint (LRJ) immediately above the lower flexible joint (LFJ). Also, required is the tension time history in the same period at the LRJ. The proposed methodology here can be implemented and integrated into a portal for data acquisition and visualisation.
In order to validate the proposed method for indirect bending moment estimation, strain gages have been attached to a BOP and marine riser during drilling operations offshore Norway. Strain gage readings are transformed to bending moment which is used as reference (the so-called direct moment). The proposed method is used to calculate the moment indirectly, the so-called indirect moment. The resulting indirect moments agree very well with the direct moments.