Reliable and Repeatable Evaluation of Kinetic Hydrate Inhibitors Using a Method Based on Crystal Growth Inhibition

Low dosage hydrate inhibitors (LDHIs)—antiagglomerants (AAs) and kinetic hydrate inhibitors (KHIs)—are increasingly used as an alternative to the traditional thermodynamic hydrate inhibitors for controlling gas hydrate problems in the petroleum industry. As nucleation inhibitors, KHIs induce an extended induction time ( t i ) at particular subcoolings before nucleation of hydrate can proceed to growth. However, due to the stochastic nature of nucleation, gaining repeatable and transferrable induction time results can be very challenging and time-consuming. To overcome this problem, study on KHI crystal growth inhibition (CGI) has yielded a KHI evaluation technique which is considerably simpler than induction time measurements. Moreover, this study shows that KHIs create a number of well-defined hydrate CGI regions as a function of subcooling which are completely repeatable and transferrable between different setups. These regions range from complete inhibition (CIR), to slow growth region (SGR), and ultimately to rapid growth region (RGR) as subcooling increases, making KHI assessment more rapid and reliable. Furthermore, results revealed that a true induction time can only be measured for a relatively short-range of subcooling within the SGR and RGR. Likewise, hydrate nucleation induction time is impossible to measure in the CIR, supporting CGI studies which show that hydrate growth is completely/indefinitely inhibited in this subcooling range.