Modeling and Control Solutions for Riser Slugging in Offshore Oil Fields

A highly transient flow regime called riser slugging can develop in pipelines from wellheads to separation tanks which introduces severe oscillations of pressure and flow rates in off-shore processes. Mitigation of the intensity of riser slugging may be achieved via anticipative control actions on valves positioned at the entrance and at gas/oil exits of the separators. In Phase 1, this work is concerned with the development of a simplified phenomenological model for the producing system, including a set of wells performing gas-lift, their corresponding risers, entrance manifold and a gas-oil separator. The input variables to this integrated model are the percentage of opening of choke and exit valves on the separator. The corresponding output variables are its internal pressure and liquid level in the separator. The oscillating slugging in the pipelines arises naturally as a consequence of the values chosen for specific model parameters like down-hole pressures, gas injection flow rates, fluid properties and geometry of wells and lines. In Phase 2, this work is involved with the mitigation of slugging consequences via determination of optimum adaptive decentralized control strategies actuating on the choke and exit valves on the gas-liquid separator. Finally, in Phase 3, we approach the identification of a stochastic predictor for the entire system (risers + tanks) adopting an ARX MIMO structure, periodically tuned to the real process by using recorded time series of inputs and outputs. With a tuned ARX predictor, optimum anti-slugging control strategies can be periodically established for the real process..