Controllability analysis of severe slugging in well-pipeline-riser systems

Jahanshahi, Esmaeil; Skogestad, Sigurd; Helgesen, Anette Hoel

doi:10.3182/20120531-2-no-4020.00014

Cited by 17 publications

(18 citation statements)

References 11 publications

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“…We were able to stabilize the system up to Z = 20% by using nonlinear observers. However, as the valve opening increases, control becomes more difficult [14].…”

Section: A Measuring Top-side Pressurementioning

confidence: 99%

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Anti-slug control experiments using nonlinear observers

Jahanshahi

Skogestad

Grøtli

2013

2013 American Control Conference

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Abstract-To prevent slug-flow on offshore oil production units, controlling a subsea pressure is the recommended solution. However, the subsea pressure is not often available as a measurement. The top-side pressure is usually measured but it is difficult to use for stabilizing control, because of its Right Half-Plane zero dynamics combined with nonlinearity. We have used the top-side pressure as measurement for different observers to estimate state variables of the system, and then used the estimated states for control. This scheme was tested in experiments using three types of observers. A simple Luenberger observer with a large gain was found to be more robust than the standard Unscented Kalman Filter (UKF). We modified the UKF to a Fast UKF for time-scale separation of the closed-loop system. The resulting observer was robust, also less sensitive to measurement noise compared to the simple Luenberger observer when measuring the top-side pressure. Surprisingly, the nonlinear observers were not able to work in closed-loop when the subsea pressure was used as the measurement. On the other hand, a linear observer worked very well for this case with a larger operating range compared to that of the top-side pressure.

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“…We were able to stabilize the system up to Z = 20% by using nonlinear observers. However, as the valve opening increases, control becomes more difficult [14].…”

Section: A Measuring Top-side Pressurementioning

confidence: 99%

“…Based on a controllability analysis in [3] [14], it is much easier to stabilize the system by using the subsea pressure compared to the top-side pressure. The system could be stabilized up to 40% valve opening by controlling the subsea pressure with a simple PI controller (Fig.…”

Section: B Measuring Subsea Pressurementioning

confidence: 99%

Anti-slug control experiments using nonlinear observers

Jahanshahi

Skogestad

Grøtli

2013

2013 American Control Conference

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“…Here t is the right normalized eigenvector associated with the unstable RHP pole (p) such that At = pt. For these system models (two dominant conjugated RHP poles) the pole vector can be used as an indication of the input's influence to the output [13]. Tables 3-6 show the values for all the estimated lower controllability boundaries for linearizations at Z = 30%, Z = 45%, Z = 60% and Z = 75%.…”

Section: Lower Boundsmentioning

confidence: 99%

“…However at this point it is uncertain which of these measurements are preferable for control purpose. A comparison carried out in [6,13] concluded that P b is the best controlled variable for single-input-single-output (SISO) control, where w o is preferred if only considering topside measurements, while P t gave the worst results. However in [20] a pressure control comparison was made where it was concluded that P b and P t did equally well as a SISO controlled variable, where P t actually performed best.…”

Section: System Analysismentioning

confidence: 99%

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Comparison of Model-Based Control Solutions for Severe Riser-Induced Slugs

et al. 2017

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Control solutions for eliminating severe riser-induced slugs in offshore oil & gas pipeline installations are key topics in offshore Exploration and Production (E&P) processes. This study describes the identification, analysis and control of a low-dimensional control-oriented model of a lab-scaled slug testing facility. The model is analyzed and used for anti-slug control development for both lowpoint and topside transmitter solutions. For the controlled variables' comparison it is concluded that the topside pressure transmitter (P t ) is the most difficult output to apply directly for anti-slug control due to the inverse response. However, as P t often is the only accessible measurement on offshore platforms this study focuses on the controller development for both P t and the lowpoint pressure transmitter (P b ). All the control solutions are based on linear control schemes and the performance of the controllers are evaluated from simulations with both the non-linear MATLAB and OLGA models. Furthermore, the controllers are studied with input disturbances and parametric variations to evaluate their robustness. For both pressure transmitters the H ∞ loop-shaping controller gives the best performance as it is relatively robust to disturbances and has a fast convergence rate. However, P t does not increase the closed-loop bifurcation point significantly and is also sensitive to disturbances. Thus the study concludes that the best option for single-input-single-output (SISO) systems is to control P b with a H ∞ loop-shaping controller. It is suggested that for cases where only topside transmitters are available a cascaded combination of the outlet mass flow and P t could be considered to improve the performance.

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