Severe slug mitigation in an S-shape pipeline-riser system by an injectable venturi

Abstract

Severe slugging is a cyclic flow regime that causes pressure, flow and temperature oscillations which leads to an intermittent delivery of liquid (oil and water) and gas to processing facilities during hydrocarbon extraction and transportation. These oscillations can cause separator flooding, production reduction, platform trips and plant shutdown. This paper presents a novel method for severe slug mitigation in a pipeline-riser system which use an injectable venturi coupled to the pipeline-riser system upstream of the topside test separator for severe slug mitigation. Injectable venturi is a venturi tube that has an opening at its throat and a pipe inclined at 45° is inserted into this opening. Gas is injected through the pipe counter to the flow coming from upstream of the injectable venturi to choke the working fluid passing through the throat of the injectable venturi. Flow regimes maps, stability maps, severe slug envelopes and Hopf bifurcation maps were generated and used to demonstrate the performance of the injectable venturi in mitigating severe slugging in a pipeline-riser system. A similar experiment was conducted with the injectable venturi with no gas injection and the plain riser (without the injectable venturi coupled). The results from the experiment show that with the injectable venturi coupled to the pipeline-riser system, severe slugging was mitigated, the severity of severe slugging was reduced, the operating region of severe slugging (severe slug envelop) was reduced and stability was achieved at a larger valve opening. Practically, these results imply that oil and gas production can proceed more smoothly, thus, enhancing flow assurance. The injectable venturi with gas injection gave a better performance than with no gas injection. Thus, the effectiveness of the injectable venturi is not due to the venturi itself, but due to gas injection at the throat of the venturi.