Investigation of Slug Suppression System in Deepwater Scenario

In pipeline-riser systems, pressure fluctuations which result from the formation of large liquid slugs and gas surges due to operational changes or low mass flow rate from production wells and the profile of pipeline-riser systems often lead to trips at the inlet of the separator; and thereby, the problem causes a a loss of the production.
In this study, on a sample deep-water oil field off the coast of West Africa is focused. The field lies in water depths greater than 1000 m. Moreover, the wells are connected via a pipeline-riser system to the topside. The slug suppression system (S3) was changed as a control structure on the field case study.
S3 comprises of a mini separator coupled with dynamically controlled valves at the liquid and gas outlets. This control structure was modeled on OLGA, a one-dimensional, and two-fluid equations based commercial multiphase flow simulation tool. In implementing the S3, it was transformed into a parallel configuration of two proportional-integral (PI) controllers (the separator level and pressure controllers) which controls the total volumetric flow and liquid flow respectively by subsequent opening of the valves at the outlets while stabilizing the riser base pressure. In addition, separator sizing was based on the volume of multiphase fluid at the riser-top. Also, controller-tuning parameters were obtained from parametric studies with pressure and liquid level set point at 20.5 bar and 0.5 m.
Finally, it is found out that S3 is able to stabilize the riser base pressure and flow rate at the outlet of the mini-separator. Moreover, the comparison of production rates before and after the implementation of the control structure indicated an increase of 12.5% in the production rate.