Gas/condensate flow with low liquid loading is a multiphase flow phenomenon commonly encountered in raw gas transportation. This paper discusses the effects of different insulation scenarios on the transient behaviors after shut-in of a deepwater pipeline/riser system that carries low-liquid-loading multiphase flow.

The investigated pipeline/riser system is located in the Gulf of Mexico at 5,000-ft water depth. The system consists of a 15-mile long subsea pipeline tieback and a 7,940-ft long steel catenary product export riser. The thermal insulation scenarios studied are: (1) the subsea pipeline is in a pipe-in-pipe configuration with insulation between the flowline and casing; the production riser is an 8-inch single pipe with external insulation coating; (2) both the subsea pipeline and production riser are in pipe-in-pipe configurations. For each scenario, two product flowrates with two gas-liquid ratios were investigated.

Numerical transient analyses were conducted by simulating the system shut-in conditions. The temperature and liquid holdup responses are presented. The effects of insulations on the responses are discussed based on fundamental heat transfer and multiphase flow principles. The results of this study will improve the understanding of transient behavior of low-liquid-loading multiphase flow after shut-in of insulated deepwater pipeline/riser systems, and provide beneficial information for deepwater field development.

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