The mechanisms of phase re-distribution and of gas/condensate flow in a deepwater lazy-wave riser after system shutdown are studied numerically and theoretically. This is the second of three papers in series. The investigated system consists of a 15-mile long subsea pipeline tieback to a floating structure, via a 9,800-ft long lazy-wave production riser. The subsea well is located at 6,350 ft of water in the Gulf of Mexico. The system transports a gas-condensate mixture with gas-oil ratio of 1000 scf/stb. This study revealed that besides pressure, the external and internal heat transfer during system cool-down are main factors for the phase re-distribution between gas and liquid and along the system. The liquid holdup variations are caused by the interfacial mass transfer between gas-liquid interface and phase re-allocation due to the combined effects of gravitational and buoyancy forces. The phenomena are discussed based on fundamental heat transfer and multiphase flow principles. Gas/condensate flow is a multiphase flow phenomenon commonly encountered in raw gas transportation. The results of this study will improve the fundamental understanding of multiphase flow transient behavior in deepwater pipeline/riser systems, and provide beneficial information for production system design.

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