Luhan Xu

Choking is a common method for controlling severe slugging in offshore oil and gas pipeline–riser systems. By combining experimental data with OLGA simulation, the influence of the installation position of the choke valve on control performance is analyzed. The results indicate that installing the valve near the riser top enables the elimination of slug flow at a larger valve opening, and can mitigate the pressure rise in the pipeline and facilitate valve selection for the slug control system, thus improving the safety and stability of the oil and gas transportation system. The mechanism analysis concludes that the principle for optimizing the valve installation position is to suppress liquid accumulation and liquid slug formation in the pipe section on an FPSO unit and to promote gas outflow. In a practical offshore pipeline case, the results under low-liquid-production-rate conditions are consistent with the simulated trends of the laboratory pipeline. However, in the case of the biggest production rate, the control performance at different installation positions tends to converge. The findings of this study can provide a reference for designing slug control strategies on offshore oil and gas production platforms.

When using topside choking to eliminate severe slugging in offshore pipeline–riser systems, the resulting stability and effectiveness depend critically on the choice of variables in the associated control model. In this study, both potential process variables and manipulated variables are investigated via manual choking experiments. Monotonicity and linearity are adopted as principles for selecting the optimal variables, and the availability of signals in an offshore field is also considered. Both amplitude-domain and time-domain variables are studied, of which five are recommended as the process variable, while the resistance factor of the choking valve is the optimal manipulated variable; other variables may act as auxiliary variables in the control model. How to determine the set value of the process variable is also discussed. Validation experiments with automatic control show that the optimized variables enable faster stabilization. This study offers a reference for the design of slugging control for offshore fields.