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

Abstract

Increasing demand for energy is driving the need to explore the deeper oceans and the far north. While higher temperature, pressure and longer tie-backs are challenges going deep, highly sensitive environment is an issue exploring far north. The discovery of large reserves in the far north has brought the challenges of exploration, production, and transportation in the cold regions like Prudhoe Bay, the Mackenzie Delta, and the Arctic Islands into focus. To transport hydrocarbons to market, pipelines used in the Arctic have unique challenges and stringent design conditions that must be met to ensure reliable operations in such remote and sensitive environments. To avoid flow assurance risks, the adage “the hotter the better” is in stark contrast to the sensitive nature of the Arctic environment to temperature changes, and where “the colder the better” is more appropriate. Permafrost, and its potential disturbance, is the most important factor to be considered for pipeline thermal design. High temperatures can disturb the in-situ state of the permafrost, causing settlement and instability 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 internal fluid temperatures 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, the conventional idea of a high value insulation like pipe-in-pipe with a vacuum annulus to avoid heat loss to the sensitive Arctic surroundings may seem to be a good solution, but it may not be the optimal solution. This paper discusses a hypothetical scenario (based on field cases) of a multiphase pipeline design and highlights the associated flow assurance/operational risks.