Development of a Crystal Growth Inhibition Based Method for the Evaluation of Kinetic Hydrate Inhibitors

Ross Anderson*, Houra Mozaffar, Bahman Tohidi Kalorazi

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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Abstract

Over the past decade, low dosage hydrate inhibitors (LDHIs) - which include anti-agglomerants (AAs) and kinetic hydrate inhibitors (KHIs) - have seen increasing use as a cost effective technology for gas hydrate control in the oil and gas industry, offering significant CAPEX/OPEX advantages when compared with traditional thermodynamic inhibitors (e.g. methanol, glycols). While AAs prevent agglomeration/plugging, KHIs are primarily understood to be nucleation inhibitors, inducing an extended ‘induction time’ at a specific subcooled condition before hydrate nucleation can proceed to growth. The best known KHIs are water soluble poly-n-vinylamides such as poly-n-vinylcaprolactam (PVCap), poly-n-vinylpyrrolidone (PVP) and related polymers. As KHIs are seen primarily as ‘nucleation delayers’, evaluation is typically undertaken through measurement of induction times as a function of various parameters at the conditions of interest. However, as nucleation is stochastic by nature, obtaining repeatable/transferrable data is often highly problematic and time-consuming, making robust evaluation difficult. Here, we demonstrate that less well investigated aspect of KHI polymers - their ability to inhibit crystal growth - is considerably simpler to quantify than nucleation inhibition. Beginning at low aqueous concentrations (e.g. > 0.1 mass% aqueous), PVCap and other KHI polymers induce a number of highly repeatable, well-defined hydrate crystal growth inhibition (CGI) regions as a function of subcooling. Discernible by step changes in relative growth rates − commonly by an order of magnitude − CGI regions range from complete inhibition (even hydrate dissociation), through severely to moderately reduced growth rates, ultimately to final rapid/catastrophic growth as subcooling increases. Closely related to induction time data, CGI regions are readily measurable using conventional hydrate laboratory equipment, with subcooling extents − which it is speculated are polymer crystal surface absorption related phenomena − providing a means to assess KHIs more rapidly and reliably, while giving an increased confidence in performance under worst case scenario (hydrate present) field conditions.
Original languageEnglish
Title of host publicationProceedings of the 7th International Conference on Gas Hydrates (ICGH 2011)
PublisherHydrafact Ltd.
Pages2161-2174
Number of pages14
Volume3
ISBN (Electronic)9781510815094
Publication statusPublished - 2011
Event7th International Conference on Gas Hydrates 2011 - Edinburgh, United Kingdom
Duration: 17 Jul 201121 Jul 2011

Conference

Conference7th International Conference on Gas Hydrates 2011
Country/TerritoryUnited Kingdom
CityEdinburgh
Period17/07/1121/07/11

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