Anderson, Ross

Glénat, Phillipe

Mozaffar, Houra

Tohidi Kalorazi, Bahman

Low dosage 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 over traditional thermodynamic inhibitors (e.g. methanol, glycols). As KHIs are traditionally considered ‘nucleation inhibitors’ - i.e. they extend the induction (or ‘hold’) time, ti, at a specific subcooling before hydrate nucleation proceeds to growth - evaluation is typically undertaken by measurement ti 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. Likewise, the focus on nucleation, and associated belief that the appearance of hydrate crystals in a KHI inhibited system means the inhibitor has failed, lowers confidence in field use. Here, we discuss the application of a new crystal growth inhibition (CGI) based approach to evaluate a number of commercial formulations for a gas condensate system. As reported for simple gas−water−polymer systems in a companion paper, commercial KHI formulations similarly induce a number of highly repeatable, well-defined hydrate crystal growth inhibition regions as a function of subcooling, ranging from complete inhibition (even hydrate dissociation), through severely to moderately reduced growth rates, ultimately to final rapid/catastrophic growth as subcooling increases. Delineation of these regions provides a much more reliable and rapid means to evaluate the relative performance of KHIs under simulated worst case scenario conditions; i.e. hydrate already present. Furthermore, the ability of KHIs to completely or severely inhibit hydrate growth even when modest fractions of hydrate (e.g. 0.5% of water converted) are present gives greatly increased confidence in terms of real-world application. Significantly, while recommended by vendors for the systems under study, tested KHIs varied greatly in their ability to inhibit crystal growth, demonstrating the limitations of traditional ti based test methods in providing a suitably robust evaluation protocol

Application of a New Crystal Growth Inhibition Based KHI Evaluation Method to Commercial Formulation Assessment

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