Optimizing the Take-Off Valve Opening of a Self-Lift By-Pass Conduit: A Novel Approach to Severe Slugging Mitigation in Offshore Pipeline-Riser Systems

Abstract

Abstract Previous numerical simulation studies, suggests that active optimization of the take-off valve on a by-pass pipe connected to a pipeline-riser system, is critical to the effective deployment of the self-lift severe slugging mitigation technique. Hence, there are recommendations for further experimental studies on the effective deployment of the self-lift severe slugging mitigation approach. Generally, severe slugging has adverse effect on multiphase flow transportation along the pipeline-riser system, with a potential 50% drop in production. Industry mostly relies on gas-lift, topsides choking and aggregation of high pressure wells as a means to manage severe slugging for typical deepwater oil fields. However, these methods have key disadvantages such as high volume of gas required for compression to mitigate severe slugging via gas-lift and the drop in production associated with topsides choking as a result of topsides choking being mainly effective at low valve opening. This study investigated the deployment of self-lift severe slugging mitigation technique via a 4 feet × 7 feet pipeline-riser section, consisting of a 2 inches by-pass pipe diameter, with the take-off valve designed to operate in such a manner as to tap-off associated gas via the valve and injected via the injection valve until it is able to break liquid slugs within the riser column. The results obtained from this experimental study indicated that severe slugging was better mitigated at between 50% - 70% valve opening of the take-off valve, while the injection valve was set at 50% valve opening, to compress air flowing as part of associated gas increased by 20%. Mitigation of severe slugging was observed with flow stabilization of the intermittent fluctuation at the outlet nozzle at the topsides of the riser section, which was set at about 30% opening. The results further revealed that self-lift could be adapted to mitigate slugging in a pipeline-riser section and also possibly deployed offshore.