Rheology of Methane-Hydrate-Slurry Flow in 100% Water Cut System and Influence of Turbulent–Laminar Transition

Natural gas hydrates have attracted interest as a potential future energy resource. Hydrate plugging in production lines is one of the key issues for future gas hydrate production, but the mechanism leading to the plugging in a water-dominant system is not well understood. In this study, we conducted a series of flowloop experiments to investigate a change in the pressure drop (friction loss) of water-dominant flow of methane hydrate slurries with an increase in the hydrate volume fraction (≈0–35 vol %) with measurements of the viscosity and yield stress (with a Bingham plastic model) and visual observations using a video camera. While the pressure drop was almost constant below about 14 vol % of hydrate, it started to increase above the point coinciding with the turbulent–laminar transition and the increase became steeper at the higher hydrate volume fractions. These suggest an influence of the turbulent–laminar transition on the increase in the pressure drop, as the transition should result in the disappearance of turbulent eddies breaking hydrate aggregates. A Bingham plastic fluid model represented the rheological behavior of the slurries well below about 19 vol %, although above this limit, slip at the wall may limit its efficacy. In addition, the application of a Bingham plastic fluid model led to good predictions of the turbulent–laminar transition and estimation of the fractal dimension of hydrate aggregates. In the video images, the hydrate particles occupied the entire pipe space at only 3.7 vol % due to the diffuse nature of aggregates, suggesting differences as compared to suspensions consisting of noncohesive particles. Overall, this study provides new insights into the rheology of the hydrate slurries in water-dominant systems.