An underinhibited system is defined as a system where an insufficient amount of thermodynamic inhibitor
is present to prevent hydrate formation. Underinhibition might occur due to malfunctioning of equipment,
temporary limitations in the inhibitor supplies or operational limitations or errors. Understanding the
plugging risk of such systems is important in order to take the correct precautions to avoid blocked
flowlines. In this paper we summarize the experimental efforts for the last decade within StatoilHydro on
the hydrate plugging risk in underinhibited systems. The flow simulator has been used as the main
experimental equipment. The overall results for systems underinhibited with ethylene glycol or methanol
show that the plugging potential increases up to a maximum at concentrations around 10-15 wt%. At higher
concentrations the plugging potential reduces compared to the uninhibited system. The results can be
explained as follows: As water is converted to hydrates in a system containing a thermodynamic inhibitor,
the inhibitor concentration will increase until the remaining aqueous phase is inhibited. This self-inhibited
aqueous phase will wet the hydrate particles, giving raise to the characteristic term of “sticky” hydrate
particles. The aqueous layer surrounding the hydrate particles will form liquid bridges, by capillary
attractive forces, upon contact with other hydrate particles or the pipe wall. During the hydrate formation
period, there is also a possibility that some of the liquid bridges are converted to solid ones, strengthening
the agglomerates. Depending on the oil-water interfacial tension, the phase ratio between the aqueous phase
and the solid hydrates and the conversion of liquid bridges to solid ones, this leads to increased plugging
risk at lower concentrations of inhibitor (< 20 wt%) and reduced risk at higher concentrations as compared
to the uninhibited system.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/1422 |
| Date | 07 1900 |
| Creators | Hemmingsen, Pål V., Li, Xiaoyun, Kinnari, Keijo |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Rights | Hemmingsen, Pål V.; Li, Xiaoyun; Kinnari, Keijo |
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