Air–Water Pigging Scheme for BoZi Pipeline Commissioning

This study focuses on the effect of isolation pig launch timing on the “oil injection after water isolation section” commissioning method for the BoZi natural-gas condensate pipeline, simulated using the OLGA dynamic multiphase flow simulator. We designed 18 sets of launch schemes for air–water isolation balls. Our analysis focused on changes in oil, water, and air distribution along the pipeline, flow regime at the crossing-over point, pressure at the first station, pressure along the pipeline, and liquid holding rate under different launch schemes. We also assessed the fluctuation amplitude of isolation ball velocity, change in air content at the end of the ball, and duration of ball reversal in certain uphill pipe sections. The key results indicate that using the strategy of “launch pig with a lagging water head” contributes to the safe commissioning of the pipeline. This method effectively prevents pressure reduction caused by excessive oil speed in downhill sections and void spaces formation in the tube, and reduces air–oil mixture. In the optimized scheme, the isolation pig’s movement was stable, and ensured safety of pipeline commissioning. Field application of the optimized scheme demonstrated excellent performance and practical effectiveness. In BoZi gas condensate pipeline commissioning, a suitable air–water isolation ball launch scheme requires a water filling length of over 47 km, with the lagging water head launch scheme extending to 58 km to prevent oil product gasification and to ensure commissioning safety. Increasing the length of water flow before the air–water isolation ball launch reduces slug flow duration at the crossing-over point. To use of numerical simulation saves about 95.3–96.2% of the time for each program, which greatly improves the efficiency of the study. The findings offer valuable guidance for pipeline engineers in selecting isolation pig launching schemes tailored to long downhill pipelines with complex elevation profiles, enhancing both operational stability and commissioning safety.