Smith predictor for slug control with large valve stroke time

Abstract

Abstract Active control has been recognised as one of the most promising methods to mitigate slugging by several researchers. However, choke valves used in offshore oil and gas production systems are often in a large size with a very large stroke time (time for a valve traveling from fully open to fully close or vice versa). This leads to not only a significant but also variable input time delay because the actual time delay also depends on the input increment value at each sampling point. In many practical offshore slug control systems, the large valve stroke time has been a major factor impacting significantly on the slug control performance. In this work, a modified Smith predictor is proposed to resolve this problem. Firstly, the traditional Smith predictor, which was mainly designed for fixed measurement time delay, is specially modified for variable input time delay using measureable delayed signal (actual valve position). Then, a linear model is adopted to present the slugging system without a time delay. Finally, the modified Smith predictor is implemented and tested using OLGA simulation software coupled with Matlab through OPC. Results show that the modified Smith predictor can significantly improve slug control performance when the choke valve has a large stroke time. With the Smith predictor, the system can operate at a larger valve opening, hence increase oil production.