Stabilizing Slug Control Using Subsea Choke Valve

Abstract

This thesis study the possibility of riser slugging control in oshore oil productionusing a subsea choke valve. A 5-state simplied model of a well-pipelinerisersystem is introduced and tted to a reference model in the ow simulatorOLGA. The models have two inputs, a subsea valve at the wellhead and a topsidevalve at the top of the riser. The eect the valves have on the behavior ofthe simplied model are tted to simulation data from the OLGA-model usingbifurcation diagrams.An input-output controllability analysis of the simplied model show thatanti-slug control using a subsea valve at the wellhead is more dicult than theconventional solution, which is to use the topside choke valve. This is conrmedby simulations on the simplied model using Hinfinity-controllers.Stabilizing control of the OLGA-model using the subsea valve was unsuccessful,despite testing dierent measurement combinations and control structures.A more promising solution for controlling riser slugging using a subsea valve istested in OLGA, where a subsea valve located near the base of the riser can keepthe system stable at riser slugging conditions. This is also seen in an experimenton a small scale ow lab.