Field Decommissioning

• Successful flushing across 8 trees and their associated riser systems to clean the returns to below 30mg/l hydrocarbon in water content

• Propelled cleaning pigs from Buchan Alpha to Forties Charlie within strict limits set by onshore processing facility

Challenge

To flush all of the risers and subsea pipework from Buchan Alpha topsides. Systems were looped and each system flushed to a hydrocarbon in water content of below 30mg/l. The export pipeline pigging operations had to be managed to ensure that the onshore facilities fluid receipt capabilities were not compromised. This resulted in a stop/start pigging programme from pig launch to receipt.

Solution

Due to platform processing rate limitations for the ‘inter-field’ flushing operations on the Buchan Alpha, different pumps with varying flushing rates and pressures were supplied to fulfil the scopes of work on the platform. Preservation chemicals were injected into the appropriate systems to aid in maintaining the integrity of the pipelines before final decommissioning / disposal.

results

All lines were successfully cleaned to the required specification as verified by platform personnel. The Buchan Alpha disconnected from all flowlines and was towed to Shetland for decommissioning / scrappage works to be carried out.