Subsea Production Two-Phase Flow Modeling and Control of Pipeline and Manifold Assemblies

Developed in this paper is a new approach to subsea production two-phase flow modeling and control of pipeline and manifold assemblies. For that purpose, a reduced-order model is developed for transient two-phase gas-liquid flow in pipelines. First, a mechanistic model is used to calculate the steady-state pressure drop and liquid holdup. From this model, effective fluid properties are calculated and used as arguments to the dissipative distributed parameter model. A modal approximation technique is then used to render the model into a rational polynomial form appropriate for time-domain analysis and controller design. A new low-frequency magnitude correction is applied to the approximated transfer functions providing an improved matching for the steady-state gain without affecting the dynamics of the system. The resulting low-dimensional two-phase flow model is then used to coordinate the arriving pressures at the manifold for different GVF levels through electro-hydraulic valves located at the wellheads.