<p align="left" class="Abstract" style="margin-top: 0in; margin-right: 0in; margin-bottom: 6.0pt; margin-left: 0in; text-align: left; line-height: 150%">The proper understanding of cooling temperature and cooldown time for the shut-in operation of a subsea production system transporting waxy hydrocarbons from the reservoir to the host facility is one of the important flow assurance issues for managing heat retention and insulation requirement in the production system due to wax deposition. In recent years, there has been a common practice to utilize transient multiphase flow simulators in determining cooldown time and corresponding thermal insulation requirement for retaining sufficient heat before the wax can precipitate and deposit in the subsea production system and block the flow. Though, such software can predict the cooldown time and corresponding insulation requirement reasonably well for the assumed pipeline configurations and reservoir fluid properties, they are nevertheless expensive, complex in operations, time consuming. They need detail analysis of the subsea production system and require special technical expertise to operate.&nbsp;</p><p>The purpose of this paper is to develop an analytical transient thermal model for determining the cooling temperature and cooldown time for shut-in operation of a subsea pipe-in-pipe production system, transporting waxy crude oil from the reservoir to the host facility. Here, the cooldown time is defined as the time when the cooling temperature approaches the wax appearance temperature during any shut-in operations. Also, the cooling temperature may help restart the warm well earlier, well before the system arrives to the cooldown time temperature for the short duration of shutin operations. The analytical model builds upon the inhomogeneous transient model incorporating internal temperature gradient. The model results are benchmarked against the commercial OLGA simulation results for a selected subsea pipe-in-pipe flowline configuration typical to the Gulf of Mexico, for which field data are available. The model predictions resemble well with OLGA results over a range of conditions. The model could also optimize the dry insulation and cooldown time requirements with limited flowline configurations and fluid properties efficiently and economically under any subsea environments.</p>

A New Transient Thermal Model for Predicting Cooling Temperature and Cooldown Time of a Subsea Pipe-in-Pipe Flowline System Transporting Waxy Hydrocarbons

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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