Fuel, Vol.252, 458-468, 2019
Hydrate formation management simulations with anti-agglomerants and thermodynamic inhibitors in a subsea tieback
The rapid formation of gas hydrates in subsea tiebacks is regarded as one of the most challenging problems in flow assurance. Due to economic reasons, the hydrate controlling strategy has moved from hydrate avoidance to hydrate management. Efficient design of hydrate management techniques requires a better understanding of hydrate formation kinetics, as well as a robust transient hydrate simulation tool. In this work, we use a transient hydrate simulation tool with the ability of predicting hydrate formation in oil- and water-dominated systems simultaneously to capture complicated multiphase flow scenarios expected in oil and gas flowlines. This modeling tool can be applied to estimate hydrate formation in flowlines exhibiting both water- and oil-dominated environments at different locations, which is especially useful in modeling transient shut-in/restart operations as well as high water cut scenarios. This simulation tool can track the concentration of multiple thermodynamic inhibitors and consider the injection of anti-agglomerants through the cohesive force change between hydrate particles. This paper presents modeling results of a real black oil subsea tieback system, considering its geometry, production data and fluid properties. The hydrate formation rates and plugging risks at different water cuts, gasoil ratios and liquid holdups were estimated both during steady state operation and shut-in/restart conditions. A hydrate blockage formed in the real field at 49 vol% water cut was successfully predicted using the transient hydrate prediction model. This simulation tool can be applied to predict the hydrate formation rate and amount under the complicated multiphase flow scenarios in oil/gas fields, and could be useful for the design and optimization of hydrate management approaches in flowlines.