Dual effect of model condensate oil on how kinetic hydrate inhibitors (KHIs) inhibit methane hydrate formation

Natural gas is clean energy for carbon neutrality, while its transportation is threatened by gas hydrate blockage in pipelines. As a vital component of global gas reserve, the development of gas condensate fields is accompanied by condensate oil, however, how condensate oil affects hydrate formation and the performance of kinetic hydrate inhibitors (KHIs) remains unclear. This study experimentally investigated the impact of model condensate oil (n-hexane) on hydrate formation kinetics in both pure water and KHI systems (PVP, Luvicap-EG, and Inhibex-501). Results demonstrated that n-hexane promoted methane hydrate formation in pure water, but displayed the dual effect in KHI systems, which was related to KHI's type and subcooling: (i) n-hexane enhanced the performance of Luvicap-EG and Inhibex-501 at low subcooling, but weakened PVP, (ii) the role of n-hexane on Luvicap-EG and Inhibex-501 shifted from enhancement to weakening when increasing subcooling. Furthermore, combined with hydrate morphology analysis, a mechanism hypothesis was proposed that the dual effect originated from the various characters of n-hexane at gas-liquid-solid interface and bulk water phase, corresponding to different modes of hydrate formation. This study elucidates the complex influence of condensate oil on hydrate formation and inhibition, facilitating successful application of KHIs in gas condensate fields.