Severe or riser slugging
At the ultimate lowpoint (i.e. the riser base), terrain slugging can often be so dramatic that it is also known as severe or riser slugging. Severe slugging occurs when liquid accumulates at the riser base for an extended period of time under certain flow conditions, particularly if there is a downward slope in the line at the riser base and the flowrate is low. Severe slugging is a significant problem particularly in deepwater production systems, and hence has received an enormous amount of attention, both from an analytical viewpoint and also with respect to proposed solutions.
Source: API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, Fourth Edition, Reaffirmed 2011. Global Standards