Evaluation of Multiphase Flow Assurance Challenges in Subsea Tieback Systems Connecting OML 119 to the Bonga FPSO, Offshore Rivers State

Subsea tieback systems experience complex multiphase flow assurance challenges including hydrate formation, wax deposition, and severe slugging, and these challenges are particularly acute in long-distance tiebacks where temperature loss over the flowline length elevates risks of thermodynamic instability. This study evaluates the flow assurance challenges in the subsea tieback system connecting OML 119 satellite wells to the Bonga Floating Production Storage and Offloading vessel, offshore Rivers State, South South Nigeria. Steady-state and transient multiphase flow simulations were performed using OLGA software, incorporating fluid PVT data from recombined wellstream samples, pipeline geometry, and seabed temperature profiles derived from oceanographic surveys. Hydrate formation envelopes were constructed using a Cubic-Plus-Association equation of state. Wax appearance temperature measurements from pour point and cross-polarised light microscopy experiments were incorporated to define wax deposition onset conditions. Simulation results indicate that under normal operating conditions the system operates within acceptable hydrate-free and wax-deposition-free margins, but that extended shutdown scenarios of more than 18 hours create hydrate formation risk in three sections of the tieback flowline. Methanol injection volumes and pigging frequency recommendations are derived from the simulation results to address these risk scenarios. Keywords: flow assurance, hydrate, wax deposition, subsea tieback, Bonga FPSO.