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

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DON-BP-001Don Field Decommissioning Programme5.4 Present Condition5.4.1 GeneralThe Don oil production and water injection pipelines have been out of service since2003. Both pipelines have been cleaned by pigging and flooded with seawater prior tobeing disconnected.The last intelligent pig run was performed in 1996 and the results indicated that the oilproduction pipeline was fit for purpose. However, the results indicated channelling in thewater injection pipeline. Modelling used at the time predicted through wall thicknessfailure of the water injection pipeline in 2000, however this never occurred.The internal inventory of the pipelines has not been displaced since the productionceased, ie oil production and the water injection pipeline contain produced fluids andde-aerated seawater respectively. The pipelines were made hydrocarbon freeduring 2009.5.4.2 Length and Location of Exposures and Spans8in Oil Production Pipeline (PL598)The last inspection of the 8in oil production pipeline in 2009 reported that the pipelinewas almost entirely (98.5% of the total length) buried with only 267m of exposure. Ofthis length, 223.9m is associated with the Thistle and Don manifold spoolpieces and10m with their transition zones.Only one anomalous span was found by the most recent inspection of the 8in oilproduction pipeline in 2009. This 11.2m long x 0.15m high span is associated with ashallow, unprotected buckle, close to the Thistle Installation at KP 0.6266. No spans willremain on the 8in production pipeline once the primary scope is carried out.8in Water Injection Pipeline (PL599)The last inspection of the 8in water injection pipeline in 2009 reported that the pipelinewas almost entirely (98.3%) buried with only 296m of exposure. Of this length, 221.7mis associated with the Thistle and Don manifold spoolpieces.Only one anomalous span was found by the most recent inspection of the 8in waterinjection pipeline in 2009. This 22.1m long x 0.25m high span, is at the pipeline exit fromthe bridge at the Thistle Installation at KP 0.0984. This span will remain in situ until theThistle decommissioning.5.4.3 Present Burial DepthBurial depth information is available when a GVI is performed. Although performed lessfrequently than sidescan sonar survey, GVIs demonstrated consistent burial depths forboth pipelines.The most recent GVI on the full length of the pipelines was performed in 2009.Pipelines10-22 May 2011
Don Field Decommissioning ProgrammeDON-BP-001Excluding pipeline sections designed not to be buried and exposures (as listed inParagraph 5.4.2), the typical depth of burial is 0.30m to 0.50m for the 8in oil productionpipeline and 0.24m to 0.52m for the 8in water injection pipeline as shown in Figures10.21 and 10.22 respectively. The small 3.4m long area at KP 12.292 on the productionpipeline, shown as an exposure in Figure 10.21, is a rock dumped area (rock has beendisplaced over the crown of the pipeline) but is still considered satisfactory. The area atKP 14.847 on the oil production and water injection pipelines, shown as an exposure inFigures 10.21 and 10.22, is the NLGP crossing which is mattressed.Due to the low seabed currents and stiff clay soil in the area, these conditions willcontinue in future.Figure 10.21 8in Production Pipeline (PL598) Burial DepthFigure 10.22 8in Water Injection Pipeline (PL599) Burial DepthPipelinesMay 2011 10-23
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Executive SummaryMay 2011 2-5Table
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Descriptions of Items to be Decommi
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Don Field Decommissioning Programme (pdf, 7.8MB) null - BP

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