Throughout drilling, completion and workover activities risers are subject to environmental loading from currents, waves and vessel offset, these dynamics could cause fatigue in the riser structure. Due to their smaller diameter, completion and workover risers (CWORs) are especially susceptible to Vortex Induced Vibration (VIV) during open water operations.
An operator began development drilling on a field offshore Indonesia using a jackup rig in around 95m water depth. A 7-5/8” completion riser was used to complete the wells with a surface blowout preventer (BOP). Due to the nature of the application and the severity of the environmental loading conditions, VIV was observed during completion of the first well. Although riser analysis showed that currents over 1.5 knots were fatigue critical for the completion riser, two uncertainties remained in the model:
The through depth current loading;
Effectiveness of the riser vortex suppression.
Because of these unknowns and in order to demonstrate fitness-for-purpose of the completion riser during the well completion operations, a VIV monitoring system was installed. Providing the utmost simplicity, this monitoring system consisted of a single dynamic curvature sensor installed at the top of the riser, 3.5m below the drill floor. This sensor was connected to a central control unit via a topside cable. The strain data was captured and calibrated on board using proprietary software, with the bending stress data calculated at 8 points around the riser circumference.
This paper provides details on the monitoring system provided. On top of this, the paper will analyse the data collected throughout these completion operations and share the key conclusions from this monitoring campaign.