Experimental Evaluation of Kinetic Hydrate Inhibitors and Mixed Formulations with Monoethylene Glycol for Hydrate Prevention in Pure Water and Brine-Oil Systems

Thermodynamic hydrate inhibitors (THIs) and kinetic hydrate inhibitors (KHIs) are widely studied and used in the oil & gas industry for hydrate prevention. In this experimental study, we applied an isothermal procedure and tested four different KHIs-poly(vinylpyrrolidone) (PVP), Inhibex 501, Luvicap EG, and VC-713-KHI-KHI mixtures, and KHI-MEG (monoethylene glycol) mixtures to evaluate their inhibitive performance on structure II methane-propane hydrate formation in stirred reactors. Two liquid systems (pure water and brine-oil-water), two cooling rates (6 and 4.5 K/h), and two subcooling levels (12.8 and 7.8 K) were examined. The results showed that, with single KHI dosing, Inhibex 501 has the best inhibitive effect in the pure water system, while Luvicap EG and VC-713 performed better in the brine-oil-water system. The performance of KHI-KHI mixtures was found to be similar to that of the single KHI composition of lower molecular weight. In experiments with KHI-MEG mixtures, MEG contributed to the combined inhibitive effect mostly for its thermodynamic effect on the system equilibrium; on the other hand, low concentration KHIs in the mixed formulations showed a synergistic effect that could not only reduce the dosage of MEG but also maintain the overall inhibitive effect on hydrate formation. The addition of NaCl and mineral oil may also prevent hydrate growth owing to water-salt ion interactions and interfacial barrier effects of the mineral oil.