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

Don Field Decommissioning ProgrammeDON-BP-0013.3 8in Water Injection Pipeline (PL599)The 8in water injection pipeline between Thistle and the Don manifold, as shown inFigure 10.9, is 17.4km long and was designed to be trenched and buried. A tie-intee-piece and protection frame are located 13.1km from Thistle.Stabilisation features include flexiweight mattresses, grout formworks, grout bagsand supports.The pipeline is corroded with significant channelling through its entire length. It currentlycontains inhibited seawater at ambient pressure and is isolated at the Thistle topsides.The pipeline forms the return loop from Don to Thistle for the production pipelinecleaning programme, so the pipeline has been pigged and flushed as per the 8inproduction pipeline.The pipeline has remained trenched and is presently buried over 98.3% of its length.There are no spanning issues and no FishSafe spans have been found since installationin 1988. The secure soil and low seabed currents provide a stable environment in whichexposure or span development is not expected. Further details on the integrity of thepipeline are given in Paragraph 5.4.3.4 3in Chemical Injection Umbilical (PL600)The 3in chemical injection umbilical, as shown in Figure 10.10, is approximately 17.7kmlong, and was designed to be trenched and buried. The umbilical contains six chemicalinjection hoses.Stabilisation features include flexiweight mattresses, grout bags, rock dumpand supports.The umbilical has not been functional since it became blocked and then ruptured in1995. It presently contains scale inhibitor, corrosion inhibitor and methanol.The chemical injection umbilical has remained consistently trenched and is presentlyburied over 98.7% of its length. There is one span, located at the Thistle tie-in, theremoval of which will be deferred until the Thistle platform is decommissioned. Thetrenched condition is expected to continue due to the secure soil and low seabedcurrents associated with the area.3.5 4in Control UmbilicalThe 4in control umbilical, as shown in Figure 10.10, is approximately 17.7km long, andwas designed to be trenched and buried. The umbilical is used to carry electrical power,two-way electrical signals and hydraulic fluid for control and monitoring of the wells.Stabilisation features include flexiweight mattresses, grout bags, rock dumpand supports.The umbilical is not presently functional due to loss of electrical continuity.The umbilical has experienced a consistent burial profile throughout its operational lifeand is presently 99.8% buried. Due to the low seabed currents and stiff clay soil in thearea, it is likely that these conditions will continue.PipelinesMay 2011 10-9