Abstract
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.
Highlights
In offshore oil & gas installations the pipelines transport a multi-phase mixture of liquids and gases.A typical offshore oil & gas pipeline system consists of three connected subsections: The production well, the subsea transport pipeline, and the vertical riser [1]
||KS||∞,min and ||SG ||∞,min are both larger for pressure transmitter (Pt) which indicate the system is sensitive to measurement noise and input disturbances
The linearized model analysis gave an indication of which controlled variables are preferable and it was concluded that the low-point measurements are preferable over the topside transmitters where the topside flow transmitter is the best alternative if only topside measurements are available
Summary
In offshore oil & gas installations the pipelines transport a multi-phase mixture of liquids and gases. The compressors often have limited capacity, and they cannot always track the required gas-injection setpoints required for eliminating the severe slugs [9] This solution requires extra facility installation, operation as well as maintenance, which can significantly expend the costs for production. Energies 2017, 10, 2014 the pressure and flow oscillations and correspondingly eliminate or mitigate the slugs, the production rate can be reduced For this reason several studies have focused on anti-slug control with large valve openings to both eliminate the severe slugs and optimize the production rate [10,11,12]. The objective is to find the best available controlled variable for existing offshore pipeline-riser installations and to compare the performance of linear controllers with realistic uncertain running conditions.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
