Experimental Investigation on the Gas Phase Behaviour and Inhibition for Hydrates with CO2-Rich Gas in an Oil–Water System

During deepwater oil and gas production and shut-in operations, the high-pressure and low-temperature environment readily induces hydrate formation of CO2-rich associated gas in oil–water systems, thereby posing serious flow assurance risks. This study systematically investigated the nucleation, growth, and morphological evolution of hydrates in oil–water systems under different gas-phase states using fully visualized high-pressure apparatus, along with the effects of temperature, pressure, CO2 concentration, and inhibitors on hydrate formation behavior. The results showed that gas phase transition significantly altered the hydrate induction time, gas consumption, and growth time. However, once the gas was liquefied, mass transfer became hindered, and the growth process exhibited pronounced dynamic fluctuations. Phase transitions caused by variations in CO2 concentration also exerted a significant influence on hydrate growth, among which the terminal subcooling had the most pronounced effect on the integrated growth index. Compared with monoethylene glycol (MEG), methanol lowered the peak value during the rapid hydrate formation stage, markedly reduced the hydrate growth rate, and led to a prolonged period during which the pressure remained above its initial value. These findings revealed the hydrate formation characteristics in oil–water systems and mechanism of thermodynamic inhibitors, providing a theoretical basis for ensuring flow safety in CO2-rich oil and gas wellbores and pipelines.