Once the gas hydrate is formed, immeasurable damage will be imposedon pipelines especially for long-distance, high-pressure, deep-watersubsea wet gas pipeline. Therefore, the normal solution is strict controland precaution the hydrate’s formation. The thermodynamic inhibitors,such as ethylene glycol (MEG), methyl alcohol (MeOH) always beinjected into wet-gas pipeline. Injection suitable dosage inhibitor helpsto lower down hydrate formation temperature to prevent hydrate’sformation in the stage of commissioning and continuous production.However, there is hardly any reports on hydrate’s precaution when inshut-in. In this paper how to economically and safely avoid theformation of hydrate in the phase of shutdown is studied. Based on asubsea wet gas pipeline ZB which lying in the Bohai bay of China, andwith the help of dynamic multiphase flow simulator OLGA, keyparameters along the pipeline are computed, which show that hydratewill be formed after several hours’ shutdown. For a safe operation,measures should be taken to both the planned and emergence shutdown:To the planned shut-in of the ZB, the regular practice of elevatingdosage of MEG doesn’t work as to the topography. To the emergenceshut-down, method of venting and burning is chosen against thehydrate’s formation, which can be also used in planned shutdown whenothers method is failure. In order to cut down the venting gas amount tothe greatest extent, the law between venting rates and the total amountof burned gas is depicted and analyzed. Finally, an optimal venting rateof 2000 Sm3/d is achieved for pressure relieving after shutdown. Theresults and the analytical approach adopted in the paper provide sometechnical support for the similar offshore wet gas pipeline and othermulti-fluctuate onshore wet-gas pipeline.
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