Hydrate blockage observation and removal using depressurization in a fully visual flow loop

Hydrate blockages impose a serious flow assurance problem on gas transportation pipelines. Regular inspections for the formation of hydrate blockages are imperative along with the use of an effective blockage removal method. In this study, the processes of hydrate blockage formation and removal were investigated using a fully visual flow loop. Comprehensive analysis of the pressure drop was performed along with a discussion of the acquired visual images of the hydrates to describe the phenomena. Hydrate blockage first occurred in no through-flow zone of the pipeline, specifically in deadleg. The results showed that higher LL (liquid loading: the initial liquid volume fraction) caused a blockage in the inlet, while lower LL caused a faster and more widespread blockage. Moreover, shut-in and restart operations also caused blockages due to the temperature decrease and annealing of hydrate. The experiments showed that blockages formed more quickly as a result of lower LL during the shut-in operation. This necessitated the reduction of shut-in duration and maintenance of the temperature at phase equilibrium condition. In addition, the depressurization method was used to decompose bulk hydrate in order to remove the blockage. The results confirmed that stepwise depressurization could be applied to prevent hydrate reformation at a higher LL and water conversion rate, while a lower backpressure could be used at lower LL to efficiently remove blockages.

Automated summary

Hydrate blockages in gas transportation pipelines pose a serious flow assurance problem, and both the formation and removal processes require comprehensive analysis. The study revealed that LL plays a crucial role in the formation of blockages, with lower LL during shut-in operations leading to faster formation of blockages.