The discovery of large reserves has brought Arctic Circle and the challenges of exploration, production, and transportation in the cold regions like Prudhoe Bay, the Mackenzie Delta, and the Arctic Islands into focus. Unlike pipelines in other regions, pipelines in Arctic region have their unique challenge of narrow design limit.The hotter the better to avoid flow assurance risks but given the sensitive nature of the environment to temperature in the Arctic, lower temperatures are desired. Permafrost is the most important factor to be considered for pipeline thermal design. Thermal impact of the pipeline on the permafrost is the governing factor for design in many cases. High temperatures can disturb the soil settlement and stability in the permafrost zone. Also, high pipeline temperatures demand deep trenches to avoid melting the surface ice challenging installation and increasing CAPEX.Designing the pipeline to maintain high fluid temperatures inside the pipeline to reduce flow assurance risks and lower pipeline outer temperatures to minimize the impact on the environment is the best solution. To maintain high fluid temperatures and reduce heat loss to the environment, conventional idea of perfect insulation like pipe-in-pipe with vacuum annulus to avoid heat loss to the cold and sensitive Arctic surroundings may seem to be a solution, but may not be the best solution. The paper discusses a hypothetical scenario (based on field cases) of such a pipeline design and highlights the associated flow assurance/ operational risks.Results, Observations and Conclusions:Study with different PIP annulus fluid properties is performed to understand the behavior during various operational scenarios and through the life of field. To cover the range of annulus fluid properties, Nitrogen at different pressures from atmospheric pressure to low vacuum levels is considered in the pipe-in-pipe annulus for the study. To investigate on how the PIP properties affect the insulation performance, temperature profiles of the fluid, PIP annulus fluid, soil surrounding the pipe, and the ambient were analyzed during normal operation and shutdown.&nbsp;Pipe-in-pipe annulus with N2 at 0.29 psia (20 mbar)/150 °F has an Overall Heat Transfer Coefficient (OHTC) of 0.17 BTU/hr-ft2-°F compared to pipe-in-pipe annulus with N2 at 15 psia/150 °F case at 0.30 BTU/hr-ft2-°F. The pipeline configuration with lower U-value loses less heat to the surroundings, maintaining the desire higher fluid temperatures and minimal thermal foot print on the surroundings and is thus the lower U-Value pipe-in-pipe configuration is attractive to serve the purpose. But, looking at the big picture highlights the operational risks associated with the lower U-value pipe-in-pipe configuration.&nbsp;The pipe-in-pipe configuration with lower U-Value has relatively minimal impact on the environment but the same advantage (lower surrounding soil temperature i.e. higher dT between the fluid and the outside soil) turns into operational risk during shutdown. The cooldown time for the pipe-in-pipe with lower U-value (i.e. with higher dT between the fluid and the surrounding soil) is shorter compared to the pipe-in-pipe with higher U-value. Similar trend but with much big difference in the cool down times is observed during late life with high water cut production.&nbsp;The study indicates that for the buried pipe-in-pipe, the higher the temperature difference between the fluid and the surrounding soil, the shorter is the cooldown time (i.e., the higher the PIP vacuum level the shorter is the pipeline cooldown time). It is recommended to evaluate the pipe-in-pipe configuration behavior during various operating scenarios and optimize to serve dual purpose of minimizing the impact on the environment and reducing the operational risks while minimizing the OPEX.

Thermal Design of Pipelines – a Challenge for Flow Assurance in the Arctic

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

OMAE 2021

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.