Novel Active Slug Control in Angola - Development & Field Results

Slug flow in multiphase flowlines can cause operational instabilities which, when severe, lead to mechanical damage or even shutdown of processing facilities. While a number of control schemes to handle slugging have been published, many of them require subsea instrumentation or make use of calculated "pseudo-variables" for control, values which have no real physical meaning. Hydrodynamic slugging was anticipated during design of a new facility in Angola, and a simulation study demonstrated that a control scheme from the published literature could be applied effectively to control the slugging. However, that solution was rejected because of the use of a pseudo-variable as the principal control point. Therefore, a novel control scheme was developed and tested on simulation for both hydrodynamic slugging and severe riser-induced slugging and later patented.(1,2) The project implemented the novel active slugging control using a topsides control valve and topsides instrumentation. While a pseudo-variable, a pseudo-flow controller, was employed, it was part of a cascade scheme such that the principal control variable was a real topside pressure measurement. Upon commissioning, slugging at the facility was found to be more severe than anticipated during design, but the novel active slug control scheme was effective in controlling incoming slugs.