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

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, t_i, at a specific subcooling before hydrate nucleation proceeds to growth - evaluation is typically undertaken by measurement t_i 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 t_i based test methods in providing a suitably robust evaluation protocol.