Transient Multiphase Flow Analysis of Fluid Displacement Operations for Hydrate Management in Deepwater Satellite Oil Wells

In deep offshore brownfield oil wells, hydrate formation can readily occur within flowlines following an unplanned production shutdown. To mitigate this risk, a widely adopted industry practice involves depressurizing the production and gas lift flowlines and displacing residual production fluids using inert liquids. This operation must be executed promptly after the interruption when the shutdown time exceeds the no-touch time. While dead oils are commonly used for this purpose, diesel is often employed due to its greater availability, low viscosity, and minimal potential to exacerbate flow assurance issues. This study presents a systematic, simulation-based comparison of the flow assurance performance of displacement operations using diesel and two distinct dead oils in two mature deep-water Brazilian wells. The fluids, wells, and subsea layouts were modeled using commercial software packages. Additionally, the fluids were tuned based on rheological and chemical properties obtained through laboratory characterization. Key operational parameters such as injection temperature, flow rate, and the effectiveness of the displacement liquids were analyzed. The findings reveal that the maximum pressures observed within the lines during displacement varied significantly between the fluids. The magnitude of this parameter can be further reduced by increasing the temperature and reducing the flow rate of the displacement liquid, making some fluids a safer option under certain conditions. The volume fractions of residual fluids remaining after the displacement also highlighted the effectiveness of the displacement liquids, with higher viscosities generally improving displacement efficiency. Specifically, diesel showed residual fractions of up to 27% for gas and 4% for water, while the dead oils demonstrated better effectiveness based on their viscosities and operational parameters. These results underscore the importance of selecting appropriate displacement fluids to optimize flow assurance and mitigate hydrate formation risks in deep-water wells.