Numerical Solver for Hydrate Plug Removal through One-Sided Depressurization Operations in Gas-Condensate Pipelines

One-sided depressurization is often employed in hydrate plug removal processes and has inherent risks associated with the high velocities that the plug achieves due to the pressure differential. In critical conditions, events such as pipeline ruptures may occur. Therefore, the need for detailed numerical studies to help reduce the risk of such operations is paramount. The present work devises a numerical methodology to predict the dynamics of plugs in transient two-phase flow conditions, coupled with a compositional model to determine the formation of the gas condensate. Different scenarios were examined to evaluate the impact on the plug displacement and flow variables due to the accumulation of a liquid slug at the plug head, as well as several operational conditions with different plug sizes, initial plug positions, and pressure differences. The effect of including an energy storage model in the insulating layers is also discussed. Results showed a negligible impact of the liquid formed at the plug's head. However, a significant impact on the temperature distribution due to the energy stored at the insulating layers was observed without affecting the pressure and plug variables. It was also shown that for all cases a fast transient occurs at the beginning of the plug displacement when it reaches very high velocities, followed by a slower transient. Depending on the operational scenario, the plug stops before reaching the pipeline exit or can reach the exit with high velocity, indicating the need to explore different scenarios to design this type of operation.