Observer design for multiphase flow in vertical pipes with gas-lift-theory and experiments

• Published in: Modeling, identification and control Vol. 26; no. 2; pp. 65 - 80
• Main Authors: AAMO, O. M, EIKREM, G. O, SIAHAAN, H. B, FOSS, B. A
• Format: Journal Article
• Language: English
• Published: Oslo Research Council of Norway 01.04.2005; Norsk Forening for Automatisering (NFA); Norwegian Society of Automatic Control
• Subjects: Applied sciences; Characteristics of producing layers. Reservoir geology. In situ fluids; Computer science; control theory; systems; Control theory. Systems; Crude oil, natural gas and petroleum products; Crude oil, natural gas, oil shales producing equipements and methods; Energy; Exact sciences and technology; Fluid dynamics; Fuels; Fundamental areas of phenomenology (including applications); Modelling and identification; Multiphase flow; Nonhomogeneous flows; Nonlinear observer design; Physics; Prospecting and production of crude oil, natural gas, oil shales and tar sands; Integral proportional control; Pipe flow; Feedback regulation; Gas injection; Linear control; Modeling; Nonlinear observer design; Internal flow; Active system; Robustness; System identification; Riser; State estimation; Input output model; Petroleum technology; Multiphase flow; Vertical pipe; Gas piping; Pressure control; Experimental study; Petroleum; Closed feedback; Reservoir engineering; Production platform; Non linear observer
• ISSN: 0332-7353; 1890-1328
• DOI: 10.4173/mic.2005.2.1

Unstable regimes occurring for multiphase flow in vertical risers have successfully been stabilized using conventional linear control techniques. However, these control systems rely on downhole measurements which are at best unreliable, if at available. In this paper, we design a nonlinear observer for the states of the multiphase flow that relies on topside measurements only, and apply it to estimate downhole pressure for feedback control. A key feature of the design is that it exploits the structure of the model to obtain robustness with respect to the internal flows in the system. Combining the nonlinear observer with conventional PI control of the downhole pressure, we demonstrate in laboratory experiments the potential for increasing production from gas-lift wells by stabilizing the multiphase flow.