Movement characteristics of bypass pigs in natural gas condensate pipelines

In the middle and late production stages of natural gas condensate pipelines, the problems of increased liquid accumulation and friction usually occur in the pipelines. Therefore, regular pigging operations are essential to ensure the safety and efficiency of the oil and gas pipelines. However, the traditional pigs often go out of control as a result of their same velocity with the driving gas during the operation, which brings about a series of problems. Thereby, a new type of bypass pig was designed and developed, and a matching experimental system of horizontal-vertical pipelines was built to analyze the movement characteristics of the bypass pigs in different structures. Herein, air and water were used as the flow media, and the data of flow, pressure and terminal liquid level during pigging were collected by the LabView data collection system in real time. By changing the parameters such as the bypass rate, the driving gas velocity, the liquid velocity, etc., the movement characteristics of the bypass pig were explored, and the abnormal movement process of the pig and the internal mechanism of eliminating pig slug were analyzed. As shown in the results, the movement velocity of pigs can be slowed, the pressure fluctuation in the pipelines can be mitigated and the liquid holdup in the slugs before the pigs can be reduced with the bypass pigs for the purpose of effectively controlling the volume of slugs. The research results could provide references for in-depth understanding of mechanism of bypass pigging technology and promoting its engineering application.