Client: Confidential
Location: North Sea


The oil producing well is located in the North Sea in around 330 meters of water and is equipped with a vertical X-mas tree.

The production wing valve (PWV) failed to close or closed very slowly, when the well was warm and flowing.


The objectives of the study were to;

  • Evaluate the effect the known failure in the X-mas tree will have on the risk
  • Evaluate the effect of identified risk reducing measures
  • Provide recommendations concerning future status/operation of the well based on evaluation of the effect of risk reducing measures


The study resulted in  several recommendations related to the X-mas tree in question;

  1. X-mas tree test frequencies
  2. Contingency plans should another failure occur
  3. Investigate if identical X-mas trees may have the same problem.
  4. Change logics of PSD and EDS to ensure that the X-mas tree has a proper shut down sequence
  5. Evaluate the testing requirements for the main bore valves in subsea X-mas trees in general. The main intention of a test should be to observe FTC failures during flowing conditions.