In a flowline/riser system large liquid slugs and surges can be formed by operational changes or due to the flow conditions and physical characteristics of the flowline. These liquid slugs and gas surges may result in large oil and gas production losses when they arrive at a production platform. Slugging may cause high-level trips in separators and lead to unstable operation of topside facilities. The S3® Slug Suppression System provides a reliable solution to the slugging problem.

In 2002 Dril-Quip (Europe) Ltd delivered the first two commercial S3 units to Shell UK Exploration and Production (Shell Expro). The first unit was designed for the Otter development (TotalFinaElf) in the North Sea and installed on the North Cormorant platform (13 km flowline, 12" riser diameter, 18 bara separator pressure). In October 2002 the unit was successfully commissioned and is presently operating. The second system has been installed on the Brent Charlie platform in the North Sea, and is used for the Penguins development (64 km flowline, 14" riser diameter, 35 bara separator pressure). The unit was commissioned in January 2003. The commissioning results prove that the S3 can control liquid slugs and gas surges. The operational data shows that the control strategy is robust, flexible and capable of operating within all flow regimes encountered in the flowline.

The S3 system consists of a small separator with dynamically controlled valves at the gas and liquid outlets. The system is placed just upstream of the production separator. Shell Global Solutions developed the system with advanced control algorithms over the past years. The new technology was successfully tested at a test rig in Amsterdam and during field trials at the Shell Expro Gannet Alpha platform [1]. Operation of the S3 system was also extensively simulated with the dynamic numerical tools Traflow and Olga2000 and compared to other slug mitigation methods. An exclusive license was granted to Dril-Quip (Europe) Ltd to manufacture and supply the S3. Based on the field experience with the system, the S3 has proven to control/mitigate slugging.

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