Determining the critical time points for hydrate formation in the presence of kinetic hydrate inhibitors: A rheological and kinetic study

[Display omitted] •Kinetics and rheology were both studied for hydrate formation with KHIs’ presence.•The concept of ‘critical time’ was proposed to distinguish hydrate formation stages.•Hydrate kinetics and rheology has various sensitivity to determine the critical time.•One new KHI was proposed which has good inhibition performance on hydrate. Kinetic hydrate inhibitors have the characteristics of delaying hydrate nucleation and reducing hydrate growth rate. The utilized of kinetic hydrate inhibitors for hydrate blockage risk management is a promising technology for hydrate prevention in oil and gas industry. In this study, the rheological and kinetic properties of gas–water systems contained pure water, polyvinyl pyrrolidone and newly-synthesized inhibitor during hydrate formation at different subcooling degrees were in situ characterized using a high-pressure rheometer. By analyzing the experimental results, the concept of ‘critical time’ have been proposed to divide the time-varying process of hydrate formation into multiple stages. The three critical times indicated distinct trends in viscosity and pressure changes, as well as varying risks of hydrate blockage in hydrate prevention. The results further compared the differences in determining critical time through pressure and viscosity. The critical time of hydrate nucleation determined by viscosity was earlier than pressure due to the hypothesis of lag in gas consumption. The critical time of rapid hydrate growth determined by viscosity was later than gas consumption, which may be due to that the sharp increase in viscosity requires the aggregation of hydrates. According to the inhibition effect evaluation results determined by three critical times, it was found that the newly-synthesized inhibitor was more effective than polyvinyl pyrrolidone in inhibiting nucleation, delaying rapid hydrate growth time and reaching high viscosity time. This study can provide a comprehensive evaluation method for assessing the performance of kinetic hydrate inhibitors from both kinetic and rheological perspectives.