Gas-liquid guest mixed hydrates in oil-water systems: Multi-method analysis of formation and inhibition behaviors

Condensate gas, a key constituent of global natural gas reserves, plays an indispensable role in energy security and carbon neutrality, while its pipeline transport is threatened by gas hydrates formation. However, impact of oil phase on gas hydrates formation and kinetic hydrate inhibitor (KHI) application remains insufficiently explored. This study systematically evaluates the influence of oil phase large guest molecule substances (LGMS) such as cyclohexane and methylcyclopentane, on gas hydrates formation and kinetic inhibition by representative KHIs. The conventional pressure-based kinetic analysis method was proved insufficient in systems involving LGMS. Therefore, a multi-method approach was employed, combining routine gas consumption calculations, thermodynamic analysis, rheological tests for nucleation detection, Raman spectroscopy to reveal hydrate structure composition variation, and controlled dissociation to separate the mixed hydrates. Using this novel approach, results demonstrated that (i) LGMS altered gas hydrate phase equilibria, increasing formation driving force and accelerating hydrate nucleation. (ii) sI-sII or sI-sH mixed hydrates were observed in LGMS systems. In cyclohexane systems, the proportion of sII hydrates initially decreased and then increased, whereas in methylcyclopentane systems, the proportion of sH hydrates steadily increased throughout the formation process. (iii) LGMS promoted hydrates formation in water systems and reduced the inhibition efficiency of KHI. The effect of cyclohexane was particularly pronounced, while Inhibex 501 showed minimal sensitivity to the presence of LGMS. This study provides new insights into the kinetics of gas hydrate formation and inhibition in gas-liquid guest systems, contributing to improved KHI application strategies for gas hydrate control.