Don Field Decommissioning Programme (pdf, 7.8MB) null - BP

Don Field Decommissioning ProgrammeDON-BP-001 Grout formwork Residual Drill CuttingsA detailed description of the items to be left is discussed in Paragraphs 5.2 to 5.4.5.2 Pipelines and Umbilicals between the Don Field and ThistleShortlisted options for the pipelines and umbilicals between the Don Field and Thistlewere each subject to a comparative assessment. The options were: Leave in situ Leave in situ with selective recovery Full recoveryThe recommended option is selective recovery for both pipelines and umbilicals. This isprimarily due to the imposed safety risk to divers involved in the removal activities. Fullrecovery is more technically complex and costly due to the challenges of recoveringaged pipelines and umbilicals through the trench soil, as discussed in the IndependentReview of BP Don Pipeline Decommissioning Options [2.9].5.3 Protection FeaturesGrout FormworkThe grout formwork (contained within approximately 9m x 2m x 0.4m canvas sacksweighing in excess of 20 tonnes) will remain in situ because it has no lifting strength dueto being grouted in situ with no reinforcement.The grout formwork is fully supported on the seabed, but would not support its ownweight during any lifting operation. There are no lifting points and any lift would requireto be configured in such a way as to fully support the concrete. The concrete groutwould fail under tension loads and may crumble in compression.The existing grout formwork is over-trawlable and this can be confirmed by trawlingtrials. For these reasons, it is proposed that the best option is to leave the groutformwork in situ and confirm over-trawlability by trawl trials.During the lifetime of the oil production pipeline, remedial work was performed atseveral locations that involved installation of grout formwork due to upheaval bucklingthat could potentially compromise the depth of burial of the pipelines. Grout formworkhas also been installed on the water injection pipeline.Since installation, the grout formwork has remained stable, maintained the depth ofburial of the pipelines and prevented any fishing interaction with the pipelines.The locations where the grout formworks are decommissioned in situ will be included inthe future monitoring campaign as part of BP’s commitment to monitor the pipelines foras long as necessary. If found that the grout formwork potentially poses a risk, thenaction will be taken to manage the risk.Executive SummaryMay 2011 2-7