Hydrate slurry flow characteristics influenced by formation, agglomeration and deposition in a fully visual flow loop

摘要

Gas hydrates pose impeded flow risks and serious safety hazards in oil and gas transportation pipelines. This makes it imperative to look for appropriate hydrate control strategies. In this study, the hydrate slurry flow characteristics were investigated under multiphase flow conditions using a high-pressure fully visual flow loop. At different liquid loadings and mixture velocities, pressure drop variations were monitored from the initial hydrate formation to deposition and bedding, and the flow patterns were observed throughout the experiments. It was found that the hydrate slurry flow may involve four stages of hydrate formation, agglomeration, deposition and bedding prior to pipeline blockage. The effective volume and water conversion fractions were also obtained at different stages. The results showed that the lower liquid loading causes quicker and more severe hydrate blockage problem mainly due to more mass transfer of gas into water hence higher water conversion rate. Moreover, lower mixture velocity resulted in a higher hydrate bedding tendency. The results also confirmed further formation and deposition of gas hydrates due to a drastic temperature drop immediately after the liquid flow stopped in the system. In addition, the flow characteristics in sloped pipe sections (both upslope and downslope) were studied to investigate the effect of driving forces on the hydrate deposition. Slug flow was observed in the upslope while stratified flow in the downslope. Furthermore, hydrate accumulation tends to occur in the transition position between the horizontal pipes and the sloped pipes due to the effect of gravity.