Abstract
Prior to a planned transition in producing zones, an 18,000′ single well subsea tieback flowline to a deepwater Gulf of Mexico production facility experienced a restricted flowline ID and partial blockages due to paraffin deposition. Efforts were coordinated to provide support in the design, product selection, and determination of success for the flowline remediation. Transient multiphase flow simulations were created and tuned/validated with historical slugging data to estimate initial effective ID of the subsea flowline. The models were then applied to the planned clean-out procedure to develop performance indicators during and after flushing operations. A two-step remediation consisting of a 24 hour hydrocarbon solvent/dispersant mixture soak, followed by a 4,000 bbl seawater and waterbased paraffin dispersant flush at increasing rates utilizing solvency, dispersancy, and shear was used to remove deposition and increase cross-sectional flow area of the pipeline by 85% (initial effective ID ~2.5 in., final effective ID ~3.4 in.). The procedures were created to minimize risk of packing solids following initial disaggregation, while maximizing effectiveness of the flowline clean-out within the economic constraints of a depressed oil market.
