A transient simulation model to predict hydrate formation rate in both oil- and water-dominated systems in pipelines

摘要

The high pressure and low temperature operational conditions of deepwater subsea facilities often result in the formation of gas hydrates, which is one of the most challenging flow assurance issues. The variant water cuts and flowline geometries could result in complicated flow patterns leading to different hydrate formation mechanisms. In previous work, we have developed hydrate formation models both for oil- and water-dominated systems. The model for oil-dominated systems considers the water phase being dispersed as droplets in an oil continuous layer, and uses either a kinetics or a transport model to calculate hydrate formation at the interface of water droplets. On the other hand, water-dominated systems contain small amounts of oil, and a mass transfer-based hydrate growth model is used. This paper presents a new transient hydrate formation model that predicts hydrate growth and transportability in oil- and water-dominated environments, which might be present simultaneously in oil and gas pipelines due to changes in fluid distribution in complex multiphase flow systems. Simulations of high-pressure pilot-scale flowloop experiments at different water cuts are used to verify this modeling approach. Furthermore, the proposed hydrate simulation tool is applied to analyze the flow dynamics of a subsea tieback involving hydrate formation at varying water cuts after flowloop verification. This simulation model is targeted to be widely used to simulate oil-dominated pipelines, as well as high water cut systems leading to phase inversions, and represents a step further towards the development of more comprehensive hydrate formation models.