Study on Pigging Process Analyses and Control Methods for Moisture Gathering Lines: Study in Puguang Gas Field, China

The moisture gathering line of the Puguang Gas Field in China renders it prone to accumulating liquid at certain points due to topographic differences. Under operational conditions of pigging, liquid slug volumes, end drainage rates, and production separator surge volumes increase. Multiphase flow transient simulation software is used to study the P102 gas gathering station pigging process. The purging gas volume was measured to be $650\times {10}^4{\mathrm{m}}^3/\mathrm{day}$ and the purging duration to be $30\min$. The pigging liquid slug has been effectively controlled. When the spherical pig pushing volume reaches $190\times {10}^4{\mathrm{m}}^3/\mathrm{day}$, the terminal liquid slug flow peak has been declined from 2,264 to $\mathrm{1,634}{\mathrm{m}}^3/\mathrm{day}$, and the separator surge volume has been decreased from 49 to $38{\mathrm{m}}^3$. When a proportion integration differentiation (PID) controller is used rather than applying manual control, the emergent drainage time is reduced from 12 to $7\min$. The bypass pigging system has been designed and improved, and the peak of terminal liquid slug flow has been reduced from 1,375 to $637{\mathrm{m}}^3/\mathrm{day}$. The optimal bypass rate ranges from 6% to 8% to guide onsite pigging operations of the moisture gathering line of the Puguang Gas Field.