Mitigation of Slug Formation in Pipeline-Riser Systems Using Bypass Lines: A Simulation-Based Approach

Slug formation in pipeline-riser systems has constituted a serious flow challenge that requires frequent evaluation to eliminate where possible. This work evaluates the volume flow at the riser top, fluid pressure at the outlet, accumulated and surge liquid volume flow, and riser base pressure for different bypass line sizes to attenuate slugging. A simulation-based approach was adopted, and a pipeline-riser model was developed, with a fluid characterization and property generation tool utilized for the fluid properties. A base case pipeline-riser model was created with a self-lift bypass line of internal diameter 6 inches for the pipeline to transport gas to the riser at a location above the riser base, connected to the start point at 2141.8186 ft. The bypass line transmits the pipeline gas to the riser at approximately 1/3 (90 ft) of the riser's total height from the base. A phase splitter node (start-up point) was placed at a distance of 2141.8186 ft along the pipeline between an internal node and a separator network. The phase splitter node was configured to allow only gas to pass through the “bypass line” and liquid through the “Subsea Tieback.” Results show a stable liquid production of approximately 2861.35 bbl/day at the top side when an auxiliary bypass line of size 4 inches was used as a gas re-injection line into the riser column, whereas for the 2-inch, 6-inch, and 8-inch bypass lines, the total liquid flow was changing with time. There was a pressure build-up at the riser base, causing severe slugs to form and accumulate at the riser base, reaching the highest for the 2-inch bypass line size and the lowest for the 4-inch bypass line. An auxiliary self-lift bypass line of 4-inch size was the most effective in mitigating slugging in the pipeline system for the line sizes evaluated.