| Pigging is an important work to ensure multiphase transmission pipelines from QK18-2platform to QK18-1platform under safe and stable operation. So, it is necessary to study the many aspects involved in the implementation of pigging. Meanwhile, the research and practical operation experience can be used to provide technical support for other submarine pipelines in Boxi oilfield when deciding and implementing pigging program, and gradually realize pigging work for all pipes within the oilfield, achieving the goal of safety management of submarine pipelines in Tianjin Ltd., CNOOC finally.Firstly, according to QK18-2platform multiphase medium, a judgment is made that it will not form hydrates in this multiphase transmission pipeline at low flow, normal flow and restart condition. Slug flow during normal transportation and pigging is analyzed, as well as the temperature drop characteristics after shutdown. Secondly, applying OLGA software to establish a specific model for this multiphase submarine pipeline from Boxi QK18-2platform to QK18-1platform, such significative parameters as pressure, temperature along the pipe, pigging velocity, liquid holdup in pipe and the accumulated amount of liquid in terminal during pigging are studied. Combined with the practical facilities, this section of pipe reaches all the pigging qualifications.Finally, the mixed transmission pipeline is pigged successfully by using same diameter pig, shrink pig, brash pig and gauging pig in turn. The final result of the pigging operation indicates that the pipeline has certain corrosion. However, the main ingredients are the serious scale in the downhole and submarine pipe. The smooth implementation of these four pigs indicates that the pig material can meet the requirements. And the time of collecting the pigs is accord with the simulation results. |
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