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Active control of the production choke valve is the recommended solution to prevent severe slugging flow conditions at offshore oilfields. The focus of this work is to find the structure of a simple, yet robust anti-slug control system. In order to find suitable control variables for stabilization, a controllability analysis of the system with different available measurements or different combinations of them was performed. Moreover, for including robustness and performance requirements at the same time, the controllability analysis was extended to a mixed sensitivity H ∞ optimization problem. Two case studies were considered; first, the controllability analysis was performed on a pipeline-rise system using a 4-state model for comparing the results to the previous works. Next, using a 6-state model, the results were extended to a more general well-pipeline-riser system. The controllability results were in accordance with the practical experience in anti-slug control.

A anti-slug control requires operation around an open-loop unstable operating point. One solution is to design a robust controller based on a mechanistic model. An alternative and more robust approach is to identify an unstable model of the system based on input-output data. We used a closed-loop step test to identify an unstable linear model. From this, we obtained a second order IMC (Internal Model Control) controller that can be implemented as a PIDF controller. From the asymptotes of the proposed IMC controller, we also derive a simple tuning for PI-controller. Next, we considered two types of robust H ∞ controller (mixed-sensitivity and loop-shaping). The proposed model identification and control solutions were verified experimentally on two different test rigs. We found that the robustness and performance of the IMC (PIDF) controller is comparable with the H ∞ controllers. However, the prosed IMC (PIDF) controller is easier to tune compared to H ∞ control.