Production Potential of Severe Slugging Control Systems

Abstract

AbstractThe application of riser top valve choking in severe slugging control has shown that feedback control stabilises slug flow with a valve opening larger than manual choking, resulting in an increased oil production. However, the reason and ultimate potential for an active slug control system to increase oil production, as well as how to achieve this potential are still unclear. A systematic method based on the pressure bifurcation map of a riser system is proposed in this work to analyse the production and pressure loss relationship at the different operating points resulting from the various slug control strategies. It is shown that for a given unstable riser production system with known inlet and outlet boundary conditions, production loss or gain due to operation in stable or unstable operating conditions could be predicted by using a pressure dependent dimensionless variable known as production gain index (PGI). This gives a clear indication of the ultimate potential to increase oil production through feedback control. This analysis has been successfully applied to an industrial riser system modeled in the commercial multiphase flow simulator, OLGA. Production predicted by using the PGI agrees with actual simulated production. The analysis is based on the understanding that the closed-loop stable operating point must match the corresponding open loop unstable equilibrium point. This result is very significant in planning and implementing suitable control strategy for stabilizing unstable riser-pipeline production systems with the aim of achieving stability and ensuring increased productivity, especially for brown fields.