Hydrate crystals start to form in oil and gas production lines at high pressure and low temperature and this mechanism can lead to the blockage of the flow line. Solutions to prevent hydrate formation in pipelines are becoming an important issue with the development of deep and ultra deep offshore production systems, where the thermodynamic conditions of hydrate formation are found. The conventional approach is to avoid hydrates by injection of thermodynamic inhibitors like methanol or glycol. But with the increase of water depth, volume of inhibitors needed become too large. Today, Oil Companies are focussing on Anti- Agglomerate Low Dosage Additives (AA-LDA) allowing hydrate particles to form but with a finite size. Then production fluid becomes a slurry with effective transport properties. Measurements conducted in a flow loop indicate that for light oil, settling effects are important and must be taken into account. This paper presents a transient transport numerical code based on a two-layer model framework: a bed of packed particles at the bottom of the pipe and above it, a mixture of solid hydrate dispersed in oil phase. Moreover, exchanges are possible between these layers because of sedimentation at low velocities or remixing in higher velocities. Thus, pressure drop, volumetric fractions and velocities are computed in transient conditions for typical pipe topography, and comparisons with experimental measurements show good agreements.
Stratified and dispersed flow of gas hydrates in offshore production
Schicht- und disperse Strömung von Gashydraten in Offshore-Produktionsanlagen
2004
15 Seiten, 10 Bilder, 7 Quellen
Aufsatz (Konferenz)
Englisch
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