An Innovative Gas-Dominated Hydrate Flow Loop and Its Application for Evaluation of Kinetic Hydrate Inhibitor in Multiphase Flowing State

Hydrate blockage in pipelines severely affects the safe and efficient production and transportation in the oil and gas field, while kinetic hydrate inhibitor (KHI) is a promising technology to prevent hydrate blockage. The equipment used for hydrate flow assurance studies is mainly for liquid-dominated systems, and there is limited equipment and study available for gas-dominated systems. This study introduced an innovative gas-dominated hydrate flow loop for hydrate blockage prevention research, which can achieve the gas–liquid–hydrate multiphase circulation flow in the pipe through operation of a high-pressure fan under a high gas–liquid ratio (40:1). By adjustment of the crucial experimental conditions such as fluid composition, flow rates, and experimental temperatures, the hydrate formation kinetics and visualized morphology can be investigated with high reliability. Furthermore, the inhibitory performance of KHI at different concentrations was systematically investigated using the gas-dominated flow loop. The results demonstrated that the inhibitory effect of KHI on hydrate nucleation monotonically increased with an increase of concentration. Meanwhile, the inhibitory effect of KHI on hydrate growth varied nonmonotonically with its concentration, where an obvious drop of inhibition performance was recognized in the intermediate concentration zone, and different hydrate growth patterns were also observed through the visible pipe with different KHI concentrations. This is the “concentration effect” of KHI, and we confirm it for the first time under flow state in the flow loop. This study highlighted the characteristics of the innovative gas-dominated flow loop for the hydrate flow assurance study, and experimental results of KHI can be an important reference for the selection of inhibitor concentration.