ABSTRACT

This paper presents a new method for severe slugging mitigation in pipeline-riser systems. It describes the use of an injectable venturi coupled to the pipeline-riser system upstream of the choke valve before the topside test separator for severe slug attenuation and system stability. An injectable venturi is a venturi tube that has an opening at its throat and a pipe inclined at 45° is inserted into this opening. Thus, gas is injected counter to the flow coming from upstream of the injectable venturi to choke the working fluid passing through the throat of the venturi.

Experiments were carried out in a 2" pipeline-riser system which comprises of a 40 m long horizontal pipe connected to an 11.75 m high S-shape riser followed by a 5.2 m horizontal topside section. The results of stability study showed that with an injectable venturi applied the system achieves stability quicker than without the injectable venturi. In addition, combining the injectable venturi with the choke valve to choke the pipeline-riser (bifurcation study) stabilised the system at higher valve opening and lower pressure compared to choking the pipeline-riser with the choke valve only. For the case studied (Vsl = 0.25 m/s and Vsg = 3.1 m/s), the critical valve opening (bifurcation point) for injectable venturi is 27% while that of pipeline-riser is 21% and their riser base pressures were 2.3 barg and 2.7 barg respectively. The low loss of energy due to the gradual change in geometry of the venturi may account for its ability to achieve stability at a lower riser base pressure. Thus, there was a 29% increase in valve opening and a 15% reduction in the riser base pressure. These practically imply an increase in oil production.

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