Objective In order to investigate the characteristics of hydrate deposition in gas-dominated deadlegs, a series of experiments on hydrate deposition were conducted in a specially designed gas-dominated deadleg setup.
Methods During the experiments, natural convection happened on and the gas in the deadleg under the action of density difference, further induced the transportation of the high-temperature vapour inside the deadleg and the condensation of the vapour on the cold pipe wall. As a result, the condensed water eventually reacted with the gas and formed hydrate deposits on the pipe wall.
Results In experiments, there existed a dangerous position in the deadleg where the hydrate deposits grew fastest, had the largest thickness and was most likely to form blockage. Moreover, the thickness and apparent volume of the hydrate deposits gradually decreased in the late stage of the experiments. According to the different mass and heat transfer conditions during the formation of hydrates, there existed six different hydrate deposit morphologies in the deadleg from top to bottom.
Conclusions During the experiment, the growth rate of the hydrate deposits gradually decreased, which was mainly caused by the "insulation effect" of the hydrate deposits. The conclusions of this work can provide a guidance for the development of hydrate management strategy in deepwater deadlegs.
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