In preparing for and carrying out the decommissioning activities offshore, there are a number of elements that we felt were good practice and others that with the benefit of hindsight we felt were not so good. The lessons we have learned from these aspects of the project will be carried forward to future projects.

This work was carried out as part of a wider campaign with Stamford well abandonment and decommissioning works led to cost efficiencies and savings;
• Onshore cutting trials: We felt there were benefits in carrying out onshore trials to validate different cuttings techniques that could be used for the WHPS;
• Xmas tree cleaning: Be cognisant that the quantity and density of marine growth might not be as expected, requiring extra time for cleaning operations;
• Xmas tree valve testing: We found it useful to prepare contingency plans to allow us to deal with passing valves;
• Pipeline pressure: We have found it useful to leave the pipeline at seabed ambient pressure prior to conducting underwater operations as this made it easier to implement contingency plans in the event that pipeline valves were found to be passing;
• Concrete mattresses: We found it beneficial to carry out trial lifts of the concrete mattresses in the field to facilitate an understanding of the condition of the mattresses and to ensure that it would be possible to recover the mattresses safely;
• Pipeline and umbilical cutting: We found it effective to use hydraulic shears for cutting the pipeline, pipespools and umbilical rather than using diamond wire cutters;
• Grout bag recovery: We found it effective to use a hydraulic grab for removing grout bags.